CN111868973A

CN111868973A - Immobilized selenium in porous carbon in the presence of oxygen, and use in rechargeable batteries

Info

Publication number: CN111868973A
Application number: CN202080001976.4A
Authority: CN
Inventors: 徐文庆; 李晓明; 沙伊莱什·帕特卡; 埃尔金·E·艾斯勒; 安东尼奥·贝尼托·弗尔特斯·阿里亚斯; 玛尔塔·塞维利亚·索利斯
Original assignee: Consejo Superior de Investigaciones Cientificas CSIC; II VI Delaware Inc
Current assignee: (CSIC); Consejo Superior de Investigaciones Cientificas CSIC; II VI Delaware Inc
Priority date: 2019-02-08
Filing date: 2020-02-10
Publication date: 2020-10-30
Also published as: CN112105582A; DE112020000018T5; GB2617281A; DE112020000025T5; KR102647675B1; KR20200118465A; GB202307728D0; JP2023093466A; KR20230059844A; KR102528313B1; JP7253559B2; CN118299530A; JP2022501292A; GB202014022D0; GB202110880D0; CN112105582B; KR102528307B1; JP7536935B2; GB2617281B; GB2585578A

Abstract

In a method of preparing an immobilized selenium system or host, a selenium-carbon-oxygen mixture is formed. The mixture is then heated to a temperature above the melting temperature of selenium and the heated mixture is then cooled to ambient or room temperature, thereby forming an immobilized selenium system or body.

Description

Immobilized selenium in porous carbon in the presence of oxygen, and use in rechargeable batteries

Cross Reference to Related Applications

This application is a continuation-in-part application of U.S. patent application No. 15/434,655 filed on 16.2.2017 and also claims benefit of U.S. provisional patent application No. 62/802,929 filed on 8.2.2019. The disclosures of the above applications are incorporated herein by reference in their entirety.

Background

Technical Field

The present application relates to the field of high energy density lithium secondary batteries (batteries). More particularly, the present application relates to a method of preparing a carbon-selenium nanocomposite and applications thereof. The invention also relates to an immobilized selenium comprising selenium and carbon. The invention also relates to a preparation method and application of the immobilized selenium. One use of immobilized selenium is in rechargeable batteries. The present invention also relates to rechargeable batteries that are capable of discharge-charge cycling at a rapid rate (e.g., 10C-rate) with a minimum level of capacity fade, while being capable of substantially recovering their electrochemical performance (e.g., specific capacity) when charged at a low rate (e.g., 0.1C-rate).

Description of the Related Art

With the increasing demand for energy by humans, secondary batteries (e.g., lithium-sulfur batteries and lithium-selenium batteries) having high specific energy and high volumetric energy density have attracted extensive interest. Group 6A elements of the periodic table (e.g., sulfur and selenium) have shown a two electron reaction mechanism during electrochemical reaction with lithium. Although the theoretical specific mass capacity of selenium (675mAh/g) is lower than that of sulfur (1675mAh/g), the density of selenium (4.82 g/cm)³) Higher than sulfur density (2.07 g/cm)³). Thus, the theoretical volumetric energy density of selenium (3253 mAh/cm)³) Energy density near the theoretical volume of sulfur (3467 mAh/cm)³). At the same time, selenium is semiconducting and shows better conducting properties compared to sulphur close to electrically insulating materials. Thus, selenium may exhibit higher activity levels and better utilization efficiency even at higher loading levels, compared to sulfur, resulting in high energy and power density battery systems. In addition, the selenium-carbon composite may have further improved electrical conductivity relative to the sulfur-carbon composite to obtain a more active electrode material.

As described in patent publication No. CN104393304A, graphene oxide is reduced to graphene solvothermally while hydrogen selenide is oxidized to selenium by passing hydrogen selenide gas through the graphene dispersion. The selenium graphene electrode material prepared by the method is matched with an ether electrolyte system, namely 1.5M lithium bis-trifluoromethanesulfonylimide (LiTFSI)/1, 3-Dioxolane (DOL) + dimethyl ether (DME) (volume ratio is 1: 1); the charging specific capacity in the first circulation reaches 640mAh/g (close to the theoretical specific capacity of selenium). However, during charge-discharge, the polyselenide ions dissolve in the electrolyte, showing a significant amount of shuttling effect, which leads to subsequent capacity fade. Meanwhile, the preparation steps of the graphene oxide raw material used in the process are complex, and the method is not suitable for industrial production.

Patent CN104201389B discloses a lithium-selenium battery cathode material utilizing a nitrogen-containing layered porous carbon composite current collector composited with selenium. When the nitrogen-containing layered porous carbon composite current collector is prepared, firstly, a nitrogen-containing conductive polymer is deposited or grown on the surface of a piece of paper, and then alkali activation and high-temperature carbonization are carried out to obtain a self-supporting nitrogen-containing layered porous carbon composite current collector taking carbon fibers as a network structure; the nitrogen-containing layered porous carbon composite current collector is then further composited with selenium. The deposition method for preparing the conductive polymer is complicated and the process of film formation or growth is difficult to control. The preparation process is complicated, which is associated with an undesirably high cost.

Furthermore, there is an increasing demand for long-life, high energy density and high power density rechargeable batteries with the capability of charging and discharging at fast rates in electronics, electric/hybrid vehicles, aerospace/unmanned aerial vehicles, submarines and other industrial, military and consumer applications. Lithium ion batteries are an example of rechargeable batteries in the above applications. However, although the technology of lithium ion batteries has matured, lithium ion batteries do not meet the demand for better performance and cycling capability.

Atomic oxygen has an atomic weight of 16 and has the ability to transfer 2 electrons. For the purpose of preparing high energy density batteries, lithium-oxygen rechargeable batteries have been studied. The battery has the greatest stoichiometric energy density when it includes an oxygen cathode paired with lithium or sodium metal as the anode. However, most of the technical problems in Li// Na-oxygen batteries remain unsolved.

Elemental sulfur is also in the oxygen group and has the second highest energy density (after oxygen) when paired with a lithium or sodium metal anode. Lithium-sulfur or sodium-sulfur batteries have been widely studied. However, polysulfide ions (intermediates) formed during the Li-S or Na-S battery discharge process dissolve in the electrolyte and shuttle from the cathode to the anode. When reaching the anode, polysulfide anions react with lithium or sodium metal, resulting in a loss of energy density, which is undesirable for battery systems. In addition, sulfur is an insulator that requires a high loading level of carbon material to achieve a minimum level of conductivity. Due to the extremely low conductivity of sulfur, Li/Na-S rechargeable batteries are very difficult to discharge or charge at a fast rate.

Disclosure of Invention

Disclosed herein is a method of preparing a two-dimensional carbon nanomaterial having a high degree of graphitization. The two-dimensional carbon nanomaterial is composited with selenium to obtain a carbon-selenium composite material, which is used as a cathode material paired with a lithium-containing anode material to obtain a lithium-selenium battery pack with high energy density and stable electrochemical performance. A similar method may be used to further assemble a pouch-shaped cell (pouch cell), which also exhibits excellent electrochemical properties.

Also discloses a preparation method of the selenium-carbon composite material with easily obtained raw materials and simple preparation steps.

The selenium-carbon composite described herein may be obtained from a preparation method comprising the steps of:

(1) carbonizing an alkali metal organic salt or an alkaline earth metal organic salt at a high temperature, then washing with dilute hydrochloric acid or some other acid, and drying to obtain a two-dimensional carbon material;

(2) mixing the two-dimensional carbon material obtained in the step (1) with selenium in an organic solution, heating and evaporating the organic solvent, and then realizing the compounding of the selenium and the two-dimensional carbon material through a multi-stage heat insulating (soaking) step to obtain a carbon-selenium compound.

In step (1), the alkali metal organic salt may be selected from one or several of potassium citrate, potassium gluconate and sodium saccharate. The alkaline earth metal organic salt may be one or two selected from calcium gluconate and calcium saccharate. The high temperature carbonization may be carried out at 600-1000 deg.C, desirably at 700-900 deg.C; the carbonization time is 1 to 10 hours, desirably 3 to 5 hours.

In step (2), the organic solvent may be selected from one or several of ethanol, dimethyl sulfoxide (DMSO), toluene, acetonitrile, N-Dimethylformamide (DMF), carbon tetrachloride and diethyl ether or ethyl acetate; the multi-stage ramp-and-soak section may refer to ramping up to a temperature of 200 ℃ to 300 ℃, desirably 220 ℃ to 280 ℃, at a ramp rate of 2-10 ℃/min, desirably 5-8 ℃/min, followed by a soak at that temperature for 3-10 hours, desirably 3-4 hours; heating is then continued to 400-.

Also disclosed herein is a lithium-selenium secondary battery comprising the carbon-selenium composite. The lithium-selenium secondary battery may further include: a lithium-containing anode, a separator, and an electrolyte.

The lithium-containing anode can be one or several of lithium metal, a lithiated graphite anode, and a lithiated silicon-carbon anode material (by assembling graphite and silicon-carbon anode material and a lithium anode into a half-cell battery, discharging to make a lithiated graphite anode and a lithiated silicon-carbon anode material). The separator (membrane) may be a commercially available membrane such as, but not limited to, Celgard membrane, Whatman membrane, cellulose membrane, or polymer membrane. The electrolyte can be one or more of a carbonate electrolyte, an ether electrolyte and an ionic liquid.

The carbonate electrolyte can be selected from one or more of diethyl carbonate (DEC), dimethyl carbonate (DMC), Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and Propylene Carbonate (PC); and the solute may be selected from lithium hexafluorophosphate (LiPF)₆) Lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium perchlorate (LiClO)₄) And lithium bis (fluorosulfonyl) imide (LiFSI).

For ether electrolyte solutions, the solvent may be selected from one or several of 1, 3-Dioxolane (DOL), ethylene glycol dimethyl ether (DME) and triethylene glycol dimethyl ether (TEGDME); and the solute may be selected from lithium hexafluorophosphate (LiPF)₆) Lithium bis- (trifluoromethanesulfonyl) imide (LiTFSI), lithium perchlorate (LiClO)₄) And lithium bis-fluorosulfonylimide (LiFSI).

For ionic liquids, the ionic liquid may be one or more room temperature ionic liquids [ EMIm]NTf2 (1-ethyl-3-methylimidazolium bistrifluoromethanesulfonylimide salt), [ Py13]NTf2 (N-propyl-N-methylpyrrolidine bistrifluoromethanesulfonylimide salt), [ PP13]NTf2 (N-propyl-methylpiperidinoalkoxy-N-bistrifluoromethanesulfonylimide salt); and the solute may be selected from lithium hexafluorophosphate (LiPF)₆) Lithium bis (trifluoromethylsulfonyl) imide (LiTFSI), lithium perchlorate (LiClO)₄) And lithium bis (fluorosulfonyl) imide (C)LiFSI).

Also described herein are lithium-selenium pouch battery packs comprising the carbon selenium composites.

Compared to the prior art, regarding the preparation method of the selenium-carbon composite material disclosed herein, the two-dimensional carbon material has the following advantages: the raw materials are easily available at low cost, the preparation method is simple, high practicality and suitability for mass production, and the obtained selenium-carbon composite material shows excellent electrochemical properties.

Also disclosed herein is an immobilized selenium (immobilized selenium host) comprising selenium and a carbon backbone. The immobilized selenium comprises at least one of: (a) sufficient energy is required to enable the selenium particles to reach kinetic energy of more than or equal to 9.5kJ/mol, more than or equal to 9.7kJ/mol, more than or equal to 9.9kJ/mol, more than or equal to 10.1kJ/mol, more than or equal to 10.3kJ/mol or more than or equal to 10.5kJ/mol so as to escape the immobilized selenium system; (b) temperatures of 490 ℃ or higher, 500 ℃ or higher, 510 ℃ or higher, 520 ℃ or higher, 530 ℃ or higher, 540 ℃ or higher, 550 ℃ or higher or 560 ℃ or higher are required to allow the selenium particles to acquire enough energy to escape the immobilized selenium system; (c) the carbon skeleton has a thickness of 500m or more²/g、≥600m²/g、≥700m²/g、≥800m²/g、≥900m²/g or more than or equal to 1,000m²Surface area per gram (with pores less than 20 angstroms); (d) the carbon skeleton has a surface area of 20% or less, 15% or less, 10% or less, 5% or less, 3% or less, 2% or less, 1% or less of the total surface area (for pores of 20 angstroms to 1000 angstroms).

Also disclosed herein are cathodes or rechargeable batteries comprising immobilized selenium. The selenium may be doped with other elements, such as, but not limited to, sulfur.

Also disclosed herein are composites comprising selenium and carbon, the composites comprising a platelet morphology having an aspect ratio of ≥ 1, ≥ 2, ≥ 5, ≥ 10 or ≥ 20.

Also disclosed herein are cathodes comprising a composite comprising selenium and carbon and comprising a platelet morphology having an aspect ratio of ≧ 1, ≧ 2, ≧ 5, ≧ 10, or ≧ 20. Also disclosed herein are rechargeable batteries comprising a composite comprising selenium and carbon and including a platelet morphology having the aforementioned aspect ratio.

Also disclosed herein is a rechargeable battery comprising a cathode, an anode, a separator, and an electrolyte. Rechargeable batteries may be charged at 0.1C, 0.2C, 0.5C, 1C, 1.5C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C, or faster. The cathode may comprise at least one element of the chalcogen group (e.g., selenium, sulfur, tellurium, and oxygen). The anode may include at least one element of alkali metals, alkaline earth metals, and group IIIA metals. The separator may include an organic separator or an inorganic separator, and the surface thereof may be optionally modified. The electrolyte may include at least one element of alkali metals, alkaline earth metals, and group IIIA metals. The solvent in the electrolyte solution may include organic solvents, carbonates, ethers, or esters.

The rechargeable battery can have a specific capacity of 400mAh/g or more, 450mAh/g or more, 500mAh/g or more, 550mAh/g or more, or 600mAh/g or more. Rechargeable batteries can undergo electrochemical cycles of 50 cycles or more, 75 cycles or more, 100 cycles or more, 200 cycles or more, and so forth. After performing a high C-rate charge-discharge cycle (e.g., 5 cycles at 0.1C, 5 cycles at 0.2C, 5 cycles at 0.5C, 5 cycles at 1C, 5 cycles at 2C, 5 cycles at 5C, and 5 cycles at 10C), the rechargeable battery can maintain a specific battery capacity of greater than 30%, greater than 40%, greater than 50%, greater than 60%, greater than 70%, or greater than 80% of the second discharge specific capacity at a cycle rate of 0.1C. Rechargeable batteries may have a coulombic efficiency of greater than or equal to 50%, > 60%, > 70%, > 80%, or > 90%. Rechargeable batteries may be used in electronic devices, electric or hybrid vehicles, industrial applications, military applications such as drones, aerospace applications, marine applications, and the like.

Brief Description of Drawings

FIG. 1 is a 50,000X scanning electron micrograph of the carbon material of example 1;

fig. 2 is a 0.1C charge and discharge curve for the lithium selenium battery of example 1;

fig. 3 is a 0.1C charge and discharge curve for the lithium selenium battery of comparative example 2;

fig. 4 is an optical image of the pouch-shaped battery cell pack of example 1;

fig. 5 is a 0.05C charge and discharge curve of the pouch-shaped battery cell pack of example 1;

FIG. 6 is a flow chart of a method of preparing immobilized selenium;

fig. 7 is a scanning electron microscope image of a carbon skeleton prepared by the method of example 9;

FIG. 8 is an X-ray diffraction pattern of a carbon skeleton prepared by the method of example 9;

fig. 9 is a raman spectrum of a carbon skeleton prepared by the method of example 9;

FIG. 10A is a graph of cumulative (cumulative) and incremental (incremental) surface areas of a carbon skeleton prepared by the method of example 9;

FIG. 10B is a plot of cumulative pore volume and incremental pore volume for a carbon skeleton made by the method of example 9;

FIG. 11A is a graph of TGA analysis of immobilized selenium prepared by the method of example 10;

FIG. 11B is a graph of TGA analysis of a non-immobilized selenium sample prepared by the method of example 10 using Se-Super P-carbon and Se-graphite;

FIG. 11C is a graph of TGA analysis of non-immobilized selenium samples prepared using Se-Super P-carbon (FIG. 11B) under argon flow and at heating rates of 16 deg.C/min and 10 deg.C/min;

FIG. 11D is a plot of the rate constants for samples of non-immobilized selenium (Se-Super P complex-solid line) and 2 different immobilized seleniums (228-;

FIG. 12 is a plot of the Raman spectrum of immobilized selenium prepared by the method of example 10;

FIG. 13 is a graph of an X-ray diffraction pattern of immobilized selenium prepared by the method of example 10;

FIG. 14 is an SEM image of immobilized selenium prepared by the method of example 10;

fig. 15 is an exploded view of a coin cell battery comprising cathodes prepared according to the methods of example 11 or example 13;

fig. 16 is a graph of cycle test results for a first lithium-selenium button cell battery (0.1C) (fig. 16A-left) and a second lithium-selenium button cell battery (0.1C, then 1C) (fig. 16A-right) of the type shown in fig. 15 prepared by the method of example 12;

fig. 17 is a graph of cycle testing at different cycle rates for a lithium-selenium coin cell battery of the type shown in fig. 15 prepared by the method of example 12;

fig. 18 is a graph of 0.1C cycle test results for a lithium-sulfur doped selenium coin cell battery of the type shown in fig. 15 with a polymer separator made according to example 13;

fig. 19 is a graph of 1C cycle test results for a lithium-sulfur doped selenium coin cell battery of the type shown in fig. 15 with a polymer separator made according to example 13.

FIG. 20 is an SEM image of a three-dimensionally interconnected thin-walled porous carbon nanomaterial produced from glucose;

FIG. 21 is BET N of three-dimensionally interconnected thin-walled porous carbon nanomaterials produced from glucose₂Isotherms (a) and pore size distributions (c);

FIG. 22 is an SEM image of a three-dimensionally interconnected thin-walled porous carbon nanomaterial created from soy flour (soybean mills);

FIG. 23 is BET N of three-dimensionally interconnected thin-walled porous carbon nanomaterials produced from soy flour₂Isotherms (b) and pore size distributions (d).

Detailed Description

The present invention will be further described below with reference to specific examples. Unless otherwise indicated, the experimental procedures in the following examples are conventional; reagents and materials are available from commercial sources.

Example 1:

(A) preparation of selenium-carbon composite material

After grinding and milling, the appropriate amount of potassium citrate was calcined at 800 ℃ for 5 hours under an inert atmosphere and cooled to room temperature. Washing with dilute hydrochloric acid to neutral pH; filtering and drying to obtain two-dimensional carbon nano material (figure 1); weighing the two-dimensional carbon material and the selenium according to the mass ratio of 50:50, and then uniformly stirring and mixing the two-dimensional carbon material and the selenium with an ethanol solution of the selenium; after evaporation of the solvent, the mixture was dried in an oven; heating the dried mixture to 240 ℃ at 5 ℃/min and holding for 3 hours; then continuously heating to 450 ℃ at the speed of 5 ℃/min; preserving the heat for 20 hours; and cooling to room temperature to obtain the selenium-carbon composite material.

(B) Preparation of selenium-carbon composite cathode

The selenium-carbon composite prepared above is mixed with carbon black Super P (TIMCAL CL) and CMC/SBR (weight ratio 1:1) as binder, and water, and is pulped, coated, dried and other steps through a fixed formula to obtain the selenium-carbon composite cathode.

(C) Assembling a lithium-selenium battery

The selenium-carbon composite cathode prepared as above, lithium foil as an anode, Celgard separator as a separator, and 1M LiPF as an electrolyte₆The EC/DMC solution of (a) was assembled into a lithium selenium coin cell battery and a lithium selenium pouch cell battery (fig. 4).

(D) Lithium-selenium battery testing

The lithium-selenium button cell battery and the lithium-selenium pouch cell battery were subjected to constant current charge-discharge tests using charge-discharge equipment. The test voltage range was 1.0V to 3.0V and the test temperature was 25 ℃. Based on the mass of selenium, the specific discharge capacity and charge-discharge current level were calculated standardly. The charge-discharge current was 0.1C or 0.05C. The lithium selenium button charge and discharge curves are shown in fig. 2, and the specific test results are shown in table 1 below. The lithium selenium pouch battery test results are shown in fig. 5.

Example 2:

the conditions were the same as in example 1, but the raw material carbonized into two-dimensional carbon was sodium citrate. The battery test results are summarized in table 1 below.

Example 3:

the conditions were the same as in example 1, but the raw material carbonized into two-dimensional carbon was potassium gluconate. The battery test results are summarized in table 1 below.

Example 4:

the conditions were the same as in example 1, except that the high temperature carbonization temperature of the carbon material was 650 ℃. The battery test results are summarized in table 1 below.

Example 5:

the conditions were the same as in example 1, but the dried mixture was heated to 300 ℃ at 5 ℃/min and held at that temperature for 3 hours. The battery test results are summarized in table 1 below.

Example 6:

the conditions were the same as in example 1, but the dried mixture was heated to 240 ℃ at 5 ℃/min and held at that temperature for 3 hours, then the temperature was increased further to 600 ℃ and held at that constant temperature for 20 hours. The battery test results are summarized in table 1 below.

Example 7:

the conditions were the same as in example 1, except that the lithium-Se battery was equipped with a lithiated graphite anode, instead of a lithium anode sheet. The battery test results are summarized in table 1 below.

Example 8:

the conditions were the same as in example 1, except that the lithium-Se battery was equipped with a lithiated silicon carbon anode, instead of a lithium anode sheet. The battery test results are summarized in table 1 below.

Comparative example 1:

the conditions were the same as in example 1, but polyacrylonitrile was used as a raw material. The battery test results are summarized in table 1 below.

Comparative example 2:

the conditions were the same as in example 1; but a one-step compounding process is used to prepare the selenium and carbon composite. In this example, the dried selenocarbon mixture was heated to 500 ℃ at 5 ℃/min and held at that temperature for 23 hours to obtain a selenocarbon composite. The charge-discharge curve of the battery made from the selenium-carbon composite thus obtained is shown in fig. 3; the battery test results are summarized in table 1 below.

Battery test results summarized in table 1

Having thus described a method of preparing a selenium carbon composite, a method of preparing immobilized selenium and the use of immobilized selenium in, for example, a rechargeable battery, will be described.

Selenium is an element of the same group as oxygen and sulfur, i.e., group 6 of the periodic table. Selenium has a rather high electrical conductivity, superior to oxygen and sulphur. US 2012/0225352 discloses the manufacture of Li-selenium and Na-selenium rechargeable batteries with good capacity and cycling capability. However, some level of polyselenide anions shuttles between the cathode and anode of such batteries, creating additional electrochemical performance that needs to be greatly improved in practical use. Documents relevant to this field include the following:

"Electrode Materials for Rechargeable Batteries", Ali Aboultrane and Khalil Amine, US patent application 2012/0225352, 9/6/2012.

"Lithium-Selenium subcordary Batteries bathing non-FlammableElectrolysis", Hui He, Bor Z. Jang, Yanbo Wang and Arena Zhamu, U.S. patent application No. 2015/0064575, 3/5/2015.

"Electrolysis Solution and sulfured-based or Selenium-based bagging said Electrolysis Solution", Fan Dai, Mei Cai, Qiangfeng Xiao and Li Yang, US patent application 2016/0020491, 2016, 1/21.

"A New Class of Lithium and Sodium Rechargeable Batteries Based on Selenium and Selenium-Sulfur as a Positive Electrode", Ali Aboumerane, Damien Dambournet, Kerena W.Chapman, Peter J.Chupa, Wei Wang and Khalil Amine, J.Am.chem.Soc.2012,134, 4505-4508.

"A Free-Standing and ultra-long-life Lithium-segmented by 3D Mesoporous Carbon/Graphene Hierachiacal Architecture", Kai Han, ZHao Liu, Jingmei Shen, Yuyuan Lin, Fand Dai and Hongqi Ye, adv.Funct.Mater. 2015,25,455- "463.

"Micro-and Mesoporous Carbide-Derived Carbon-Selenium Cathodes for high-Performance Lithium Selenium Batteries", Jung Tai Lee, Hyea Kim, MarinOschatz, Dong-ChanLee, Feixiang Wu, Huang-Ting Lin, Bogdan ZDyrko, Wan Ilchao, Stefan Kaskel and Gleb Yushi, adv.

"High-Performance liquid silicon Battery with Se/Microporous carbon composite Cathodode and Carbonate-Based Electrolysis", Chao Wu, Lixia Yuan, Zhen Li, Ziqi Yi, Rui Zeng, Yanong Li and Yunhui Huang, Sci, China mater.2015,58, 91-97.

"Advanced Se-C Nanocomposites" a Bifunctional Electrode Material for born Li-Se and Li-ion Batteries ", Huang Ye, Ya-Xia Yin, Shuai-Feng Zhang and Yu-GuoGuo, J.Mater.chem.A., May 23,2014.

"Lithium ion as a conditioning Electrolyte Additive for Lithium-Sulfur Batteries: Mechanisms of Performance Enhancement", Feixiang Wu, Jung TaeLee, Naoki Nitta, Hyea Kim, Oleg Borodin and Gleb Yushi, adv. Mater.2015,27, 101-.

"A Se/C Composite as refractory Material for Rechargeable lithium batteries with Good Electrochemical Performance", Lili Li, Yuyang Hou, YaqiingYang, Minxia Li, Xiiaowei Wang and Yuping Wu, RSC adv, 2014,4, 9086-.

"electronic Selenium for Electrochemical Energy Storage", Chun-PengYang, Ya-Xia Yin and Yu-Guo Guo, J.Phys.chem.Lett.2015,6, 256-266.

"Selenium @ mesoporous Carbon Composite with Superior Lithoium and Sodium Storage Capacity", Chao Luo, Yunhua Xu, Yujie Zhu, Yihang Liu, Shiyouzhing, Ying Liu, Alex Langork and Chunsheng Wang, ACSNANO, Vol.7, No.9, 8003-.

Also disclosed herein is an immobilized selenium comprising selenium and carbon. The immobilized selenium may comprise selenium in elemental form or selenium in compound form. Selenium may be doped with other elements such as, but not limited to, sulfur. Immobilized selenium is capable of localizing elemental selenium atoms that function electrochemically properly without shuttling between the cathode and anode of the battery. The immobilization of selenium allows the elemental selenium atom to gain two electrons during the discharge process and form selenide anions at the locations where the selenium molecules/atoms are immobilized. The selenide anion can then lose two electrons during the charging process to form an elemental selenium atom. Thus, the immobilized selenium may be used as an electrochemically active agent for rechargeable batteries having a specific capacity that may be up to a stoichiometric level, may have a coulombic efficiency that may be 95% or more, 98% or more, or up to 100%, and may achieve a substantially improved sustainable cycling capability.

In batteries made with immobilized selenium, the electrochemical behavior of elemental selenium atoms and selenide anions during charging is a process that ideally functions properly. Having Sp²The carbon skeleton of the carbon-carbon bond has delocalized electrons distributed over conjugated six-membered ring aromatic pi-bonds spanning a G-band graphene-like local area network defined by D-band carbons. In the presence of an electrical potential, these delocalized electrons can flow across the carbon skeleton with little or no resistance. Selenium immobilization Sp of the carbon skeleton can also be compressed (compress)²Carbon-carbon bonds, which create stronger carbon-carbon bonds, may result in improved electronic conductivity within the carbon backbone network. At the same time, selenium immobilization may also result in compression of the selenium particles, resulting in stronger selenium-selenium chemical and physical interactions, possibly resulting in improved electrical conductivity between the immobilized selenium particles. In addition to the presence of the carbon backbone bindable stabilizing selenium moieties, carbon-selenium interactions are also enhanced by compression when both carbon-carbon bonds and Se-Se bonds are enhanced by selenium immobilization. This portion of selenium can be used as an interfacial layer of the carbon skeleton to successfully immobilize the stabilized selenium portion. Thus, electrons can flow between the carbon skeleton and the immobilized selenium with minimal resistance, and thus the electrochemical charge/discharge process can effectively function in a rechargeable battery. This in turn allows the rechargeable battery to maintain a near stoichiometric specific capacity and have the ability to cycle at almost any practical rate with a low level of impairment to the electrochemical performance of the battery.

The carbon skeleton may be porous and may be doped with other compositions. The pore size distribution of the carbon skeleton may be sub-angstrom to several microns, or to a pore size distributor by using nitrogen, argonGas, CO₂Or other absorbent agents as probe molecules to characterize the pore size. The porosity of the carbon skeleton may include a pore size distribution having peaks in at least one of the following ranges: sub-angstroms to 1000 angstroms, or 1 angstrom to 100 angstroms, or 1 angstrom to 50 angstroms, or 1 angstrom to 30 angstroms, and/or 1 angstrom to 20 angstroms. The porosity of the carbon skeleton may further include pores having a pore size distribution with more than one peak in the range described in the foregoing statement. Immobilized selenium may facilitate a carbon backbone with small pore sizes, where electrons can be rapidly delivered and collected with minimal resistance, which may allow selenium to function more electrochemically properly in a rechargeable battery. The small pore size may also provide more carbon skeleton surface area, wherein the first portion of selenium may form a first interface layer for selenium immobilization of the second portion. Furthermore, the presence in the carbon backbone with a fraction of medium size pores and a fraction of large size pores may also facilitate efficient delivery of solvent lithium ions from the bulk solvent medium to the small pore region, where the lithium ions may lose coordinated solvent molecules and be transported in the solid phase of lithium selenide.

The pore volume of the carbon framework can be as low as 0.01mL/g and can be as high as 5mL/g, or can be from 0.01mL/g to 3mL/g, or can be from 0.03mL/g to 2.5mL/g, or can be from 0.05mL/g to 2.0 mL/g. A pore volume having a pore diameter of less than 100 angstroms, or less than 50 angstroms, or less than 30 angstroms, or less than 20 angstroms, may be greater than 30%, or greater than 40%, or greater than 50%, or greater than 60%, or greater than 70%, or greater than 80% of the total measured pore volume that may be obtained by using a gas utilizing nitrogen, CO, or carbon monoxide₂Argon and other probe gas molecules. The carbon may have a surface area of greater than 400m as measured by BET²A/g, or more than 500m²Per g, or more than 600m²A/g, or more than 700m²Per g, or more than 800m²A/g, or more than 900m²Per g, or more than 1000m²/g。

The carbon may also be substantially amorphous, or it may be characterized by a very broad peak centered at a d-spacing of about 5 angstroms.

The carbon may comprise Sp²Carbon-carbon bond having D-band and G-Bands are characteristic raman peak shifts. In the examples, Sp of carbon²The carbon-carbon bond is characterized by being centered at 1364 + -100 cm in Raman spectrum^-1Has a height of about 296 + -50 cm^-1Has a D-band and a center of 1589 +/-100 cm^-1Has a diameter of about 96 + -50 cm^-1G-band at FWHM of (G-band). The area ratio of the D-band to the G-band may be 0.01 to 100, or 0.1 to 50, or 0.2 to 20.

The carbon may be in any form, i.e., for example, flakes, spheres, fibers, needles, tubes, irregular, interconnected, agglomerated, discrete, or any solid particles. Sheets, fibers, needles, tubes or some morphologies with a certain horizontal aspect ratio may be beneficial to achieve better inter-particle contact, resulting in better conductivity, possibly enhancing rechargeable battery performance.

The carbon may have any particle size, with a median particle size of from nanometers to several millimeters, or from several nanometers to less than 1000 micrometers, or from 20nm to 100 micrometers.

The properties of the carbon skeleton can affect selenium immobilization, and the interaction between the carbon skeleton surface and the selenium particles can affect the performance of the rechargeable battery. Sp²The position of carbon in the carbon skeleton may contribute to the realization of Se immobilization. Sp from small carbon skeleton pores²Carbon may be advantageous, which can be quantified by the NLDFT surface area method, as discussed in example 9 herein. The surface area of the carbon skeleton pores smaller than 20 angstroms may be 500m or more²/g、≥600m²/g、≥700m²/g、≥800m²/g、≥900m²/g or more than or equal to 1,000m²(ii) in terms of/g. The surface area of the carbon skeleton pores of 20 angstroms to 1000 angstroms may be 20% or less, 15% or less, 10% or less, 5% or less, 3% or less, 2% or less, or 1% or less of the total surface area of the carbon skeleton.

The immobilized selenium may comprise selenium that is vaporized at a temperature higher than elemental selenium, with reference to the following definition of selenium vaporization: elemental selenium in the Se-Super P composite loses 50% of its weight at a temperature of 480 ℃; elemental selenium in the Se/graphite composite lost 50% of the weight of selenium contained at a temperature of 471 ℃. The immobilized selenium loses 50% of its weight at a temperature higher than 480 ℃, for example at a temperature of 490 ℃ or higher, 500 ℃ or higher, 510 ℃ or higher, 520 ℃ or higher, 530 ℃ or higher, 540 ℃ or higher, 550 ℃ or higher, 560 ℃ or higher, 570 ℃ or higher, or 580 ℃ or higher. Selenium in the immobilized selenium may require kinetic energy of 9.5kJ/mol, 9.7kJ/mol, 9.9kJ/mol, 10.1kJ/mol, 10.3kJ/mol, or 10.5kJ/mol or more to overcome bonding and/or intermolecular forces in the immobilized selenium system and escape into the gas phase. In an example, the last portion of the vaporized immobilized selenium may require kinetic energy of 11,635J/mol (> 660 ℃ C.) or more to escape the carbon skeleton, may be critical for selenium immobilization, and may serve as an interface material between the carbon skeleton and the majority of the immobilized selenium molecules. Therefore, the portion of selenium that requires kinetic energy of 11,635J/mol or more is called interfacial selenium. The amount of interfacial selenium in the immobilized selenium may be equal to or greater than 1.5%, equal to or greater than 2.0%, equal to or greater than 2.5%, or 3.0% of the total immobilized selenium.

The immobilized selenium may comprise selenium having an activation energy higher than the activation energy to be overcome for conventional (non-immobilized) selenium, such that the selenium escapes from the immobilized Se-C complex system. The activation energy of the non-immobilized selenium (Se-Super P composite system) was determined to be about 92kJ/mol according to ASTM method E1641-16. The activation energy of selenium in the immobilized selenium comprising selenium and carbon is greater than or equal to 95kJ/mol, greater than or equal to 98kJ/mol, greater than or equal to 101kJ/mol, greater than or equal to 104kJ/mol, greater than or equal to 107kJ/mol or greater than or equal to 110 kJ/mol. The activation energy of selenium in the immobilized selenium containing selenium and carbon is more than or equal to 3 percent, more than or equal to 6 percent, more than or equal to 9 percent, more than or equal to 12 percent, more than or equal to 15 percent or more than or equal to 18 percent larger than the activation energy of selenium in the Se-Super P compound. Immobilized selenium may be more stable than non-immobilized selenium, which is why batteries comprising immobilized selenium may be better electrochemically cycled, possibly due to selenium being immobilized in a Se-C complex, resulting in minimized (or eliminated) selenium shuttling between the cathode and the anode.

The immobilised selenium may comprise selenium which may be Raman inactive or Raman active, typically within 255 + -25 cm^-1Or 255 +/-15 cm^-1Or 255 +/-10 cm^-1Has a raman peak. The Raman relative peak intensity is defined as being at 255cm^-1The raman peak area at (a) is relative to the D-band peak area of the carbon raman spectrum. The immobilized carbon may contain a Raman relative peak intensity of 0.1% or more,More than or equal to 0.5 percent, more than or equal to 1 percent, more than or equal to 3 percent and more than or equal to 5 percent of selenium. The immobilized selenium may contain more than or equal to 5% selenium, more than or equal to 10% selenium, more than or equal to 20% selenium, more than or equal to 30% selenium, more than or equal to 40% selenium, more than or equal to 50% selenium, more than or equal to 60% selenium, or more than or equal to 70% selenium.

The immobilized selenium may include selenium having a red-shift from the raman peak of pure selenium. The red-shift is defined by the positive difference between the raman peak position of the immobilized selenium and the raman peak position of pure selenium. Pure selenium is usually about 235cm^-1Has a raman peak. The immobilized selenium may include a Raman peak red shift of 4cm or more^-1、≥6cm^-1、≥8cm^-1、≥10cm^-1、≥12cm^-1、≥14cm^-1Or more than or equal to 16cm^-1The selenium of (1). A red shift of the raman peak indicates the presence of compression on the selenium particles.

The immobilized selenium may comprise carbon, possibly in a compressed state. In the compressed state, electrons can flow with minimal resistance, which helps to rapidly transfer electrons to selenium and form selenium anions for electrochemical processes during the discharge-charge process of the rechargeable battery. Sp for carbon skeleton comprising immobilized selenium²The D-band and/or G-band in the Raman spectrum of the carbon-carbon bond may show a red shift of 1cm or more^-1、≥2cm^-1、≥3cm^-1、≥4cm^-1Or more than or equal to 5cm^-1。

The immobilized selenium comprises selenium having a higher collision frequency than non-immobilized selenium. This high collision frequency may be due to selenium in the immobilized Se-C system in a compressed state. The collision frequency of selenium in non-immobilized selenium was determined to be about 2.27X 10 according to ATSM method E1641-16⁵. The collision frequency of selenium in the immobilized selenium containing selenium and carbon is more than or equal to 2.5 multiplied by 10⁵、≥3.0×10⁵、≥3.5×10⁵、≥4.0×10⁵、≥4.5×10⁵、≥5.0×10⁵、≥5.5×10⁵、≥6.0×10⁵Or more than or equal to 8.0 multiplied by 10⁵. The immobilized selenium may have a collision frequency that is more than or equal to 10%, more than or equal to 30%, more than or equal to 50%, more than or equal to 80%, more than or equal to 100%, more than or equal to 130%, more than or equal to 150%, more than or equal to 180%, or more than or equal to 200% higher than the collision frequency of the non-immobilized selenium in the Se-C complex. Due to more selenium substancesThis may lead to better electron conductivity in the immobilized selenium system. The immobilized selenium in the Se-C complex will also have a higher collision frequency against the walls of the carbon host (e.g., carbon backbone), which may result in better electron delivery or harvesting from the carbon backbone during electrochemical cycling, which may result in a battery (comprising immobilized selenium) with improved cycling performance, e.g., achieving more cycling and/or cycling at a much higher C-rate, which is highly desirable.

Immobilized selenium includes selenium having a lesser tendency to leave its host material (carbon), which has a kinetic rate constant of 1/5 or 1/10 or 1/50 or 1/100 or 1/500 or 1/1000 or less than that of non-immobilized/regular selenium. In our example, immobilized selenium includes selenium with less tendency to leave its host material (carbon), which has ≦ 1 × 10^-10、≤5×10^-11、≤1×10^-11、≤5×10^-12Or less than or equal to 5X 10^-13Kinetic rate constant (at 50 ℃).

The immobilized selenium may comprise selenium which may be amorphous as determined by X-ray diffraction measurements. diffraction peaks having a d-spacing of about 5.2 angstroms are relatively smaller or weaker than those of the carbon skeleton, e.g., 10% weaker, 20% weaker, 30% weaker, or 40% weaker.

Immobilized selenium can be prepared by physically mixing carbon and selenium, and then melting and homogenizing (or mixing or blending) the selenium molecules to achieve selenium immobilization. Physical mixing can be achieved by ball milling (dry and wet), mixing with a mortar and pestle (dry or wet), jet milling, horizontal milling, disk milling, high shear mixing in a slurry, conventional slurry mixing with blades, and the like. The physically mixed mixture of selenium and carbon may be heated at a temperature equal to or higher than the melting point of selenium and lower than the melting temperature of carbon. The heating may be performed in an inert gas environment, such as, but not limited to, argon, helium, nitrogen, and the like. The heated environment may include air or a reactive environment. Immobilization of selenium may be achieved by impregnating dissolved selenium into carbon, followed by evaporation of the solvent. The solvent for dissolving selenium may include alcohols, ethers, esters, ketones, hydrocarbons, halogenated hydrocarbons, nitrogen-containing compounds, phosphorus-containing compounds, sulfur-containing compounds, water, and the like.

Immobilizing selenium may be achieved by melting a substantial amount of selenium in the presence of carbon, and then removing excess non-immobilized selenium.

The immobilized selenium system or the host may comprise more than or equal to 30%, more than or equal to 40%, more than or equal to 50%, more than or equal to 60%, more than or equal to 70%, more than or equal to 80%, or more than or equal to 90% of the total amount of selenium in the system or the host. The non-immobilized selenium may be vaporized at a lower temperature than the immobilized selenium.

The immobilized selenium system or host may comprise immobilized selenium doped with one or more additional/other elements from group 6 of the periodic table, such as sulfur and/or tellurium. The dopant level may be as low as 100ppm by weight up to 85% by weight of the immobilized selenium system or host.

An exemplary method of preparing immobilized selenium is illustrated in fig. 6. In the method, selenium and carbon are mixed together under dry or wet conditions (S1). The mixture may be optionally dried into powder (S2), and then the dried powder may be optionally granulated (S3). The results of step S1 and optional steps S2 and S3 produce a carbon skeleton, which is the starting material for step S4. In step S4, selenium is melted into the carbon skeleton. The selenium melted into the carbon skeleton is dried, thereby producing the immobilized selenium of step S5. The preparation and characterization of immobilized selenium is described subsequently herein in connection with example 10.

The immobilized selenium may be used as a cathode material for a rechargeable battery. To make the cathode, the immobilized selenium may be dispersed in a liquid medium, such as, but not limited to, water or an organic solvent. The cathode comprising immobilized selenium may comprise a binder, optionally another binder, optionally a conductivity promoter, and a charge collector. The binder may be inorganic or organic. The organic binder may be a natural product (e.g., CMC) or a synthetic product (e.g., SBR rubber latex). The conductivity facilitating agent may be of the carbon type, such as graphite derived small particles, graphene, carbon nanotubes, carbon nanoplatelets, carbon black, and the like. The charge collector may be, for example, an aluminum foil, a copper foil, a carbon cloth, or other metal foil. The cathode may be prepared by coating the slurry (or slurries) containing the immobilized selenium onto a charge collector, followed by a typical drying process (air drying, oven drying, vacuum oven drying, etc.). The immobilized selenium slurry may be prepared by a high shear mixer, a conventional mixer, a planetary mixer, a double planetary mixer, a ball mill, a vertical attritor, a horizontal mill, or the like. The cathode comprising the immobilized selenium can be pressed or roll-milled (or calendered) before it is used in a battery assembly.

A rechargeable battery comprising immobilized selenium may include a cathode comprising immobilized selenium, an anode, a separator, and an electrolyte. The anode can include lithium, sodium, silicon, graphite, magnesium, tin, and/or suitable and/or desirable elements or combinations of elements from group IA, group IIA, group IIIA, etc. of the periodic table (periodic table) of elements. The separator may include an organic separator, an inorganic separator, or a solid electrolyte separator. The organic separator may comprise a polymer, such as polyethylene, polypropylene, polyester, halogenated polymer, polyether, polyketone, and the like. The inorganic separator may include glass or quartz fibers, a solid electrolyte separator. The electrolyte may include lithium, sodium or other salts, salts of group 1A of the periodic table, salts of group IIA of the periodic table, and organic solvents. The organic solvent may include organic carbonate compounds, ethers, alcohols, esters, hydrocarbons, halogenated hydrocarbons, lithium-containing solvents, and the like.

The immobilized selenium containing rechargeable battery pack may be used in electronics, electric or hybrid vehicles, industrial applications, military applications such as drones, aerospace applications, marine applications, and the like.

The rechargeable battery comprising immobilized selenium may have a specific capacity of 400mAh/g active amount of selenium or higher, 450mAh/g or higher, 500mAh/g or higher, 550mAh/g or higher, or 600mAh/g or higher. A rechargeable battery comprising immobilized selenium can undergo 50 cycles or more, 75 cycles or more, 100 cycles or more, 200 cycles or more, etc. of electrochemical cycling.

Rechargeable batteries comprising immobilized selenium can be charged at 0.1C, 0.2C, 0.5C, 1C, 1.5C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C, or faster. After a broad range of high C-rate charge-discharge cycles of 30 or more cycles (e.g., 5 cycles at 0.1C, 5 cycles at 0.2C, 5 cycles at 0.5C, 5 cycles at 1C, 5 cycles at 2C, 5 cycles at 5C, and 5 cycles at 10C), the rechargeable battery comprising immobilized selenium can maintain a specific battery capacity of > 30%, > 40%, > 50%, > 60%, > 70%, > 80% of the specific second discharge capacity at a cycle rate of 0.1C.

The following are several embodiments that illustrate the subject matter of the invention. However, these examples should not be construed in a limiting sense.

Examples

Characterization method

Scanning Electron Microscope (SEM) images were collected on a Tescan Vega scanning electron microscope equipped with an energy dispersive analysis X-ray (EDX) detector.

Raman spectra were collected by Renishaw inVia raman microscope (confocal). Laser raman spectroscopy is widely used as a standard to characterize carbon and diamond, and provides readily distinguishable characteristics of each of the different forms (allotropes) of carbon (e.g., diamond, graphite, buckyball, etc.). In conjunction with Photoluminescence (PL) technology, non-destructive methods are provided to study various properties of diamond, including phase purity, grain size and orientation, defect levels and structure, impurity types and concentrations, and stress and strain. In particular, the first-order diamond Raman peak is at 1332cm^-1Width of diamond peak and graphite peak (at 1350 cm)^-1D-band at 1600cm^-1G-band) is a direct indicator of the quality of diamond and other carbon materials. In addition, the stress and strain levels of diamond or other carbon particles and films can be estimated from the diamond raman peak shift. The diamond raman peak shift rate under hydrostatic stress is reported to be about 3.2cm^-1a/GPa, peak shifts to low wavenumbers under tensile stress and peak shifts to high wavenumbers under compressive stress. The raman spectra discussed herein were collected using a Renishaw inVia raman spectrometer with a 514nm excitation laser. More information on the use of raman spectroscopy to characterize diamond can also be found in reference (1) a.m. zaitsev, Optical proprties of Diamond,2001, Springer and (2) S.Prawer, R.J.Nemanich, Phil.Trans.R.Soc.Lond.A (2004)362, 2537-.

By nitrogen absorption and CO absorption with 3FLex (Mircoritics) equipped with Smart VacPrep for sample degassing preparation₂Absorption to measure the BET surface area and pore size distribution of the carbon sample. In measuring CO₂And N₂Prior to absorption, the sample is typically vacuum degassed at 250 ℃ for 2 hours in a Smart Vac-Prep. Nitrogen absorption was used to determine BET surface area. Nitrogen absorption data and CO₂The absorption data were combined to calculate the pore size distribution of the carbon sample. About N₂And CO₂The absorption data are combined to determine details of the pore size distribution of the carbon material, please refer to "Dual gas analysis of microporosity carbon dioxide generating 2D-NLDFT heterologous surface model and combined absorption data of N₂and CO₂", Jacek Jagilello, Conchi Ania, Jose B.Parra and Cameron Cook, Carbon 91,2015, page 330-337.

Thermogravimetric analysis (TGA) and TGA-Differential Scanning Calorimetry (DSC) data were measured for the immobilized selenium sample and the control sample by a Netzsch thermal analyzer. TGA analysis was performed at 16 deg.C/min, 10 deg.C/min, 5 deg.C/min, 2 deg.C/min, 1 deg.C/min heating rates, and other heating rates under an argon flow rate of-200 mL/min. For consistency purposes, a typical amount of immobilized selenium sample for TGA analysis is about 20 mg.

The activation energy and collision frequency of immobilized and non-immobilized selenium were determined by TGA according to the method described in ASTM method E1641-16.

The X-ray diffraction results of different carbon, Se-carbon samples and immobilized selenium were collected on a Philip diffractometer.

The battery cycling performance of rechargeable batteries containing immobilized selenium was tested on a Lanhe CT2001A battery cycling tester. The charge and discharge current of the rechargeable battery containing immobilized selenium is determined by the amount of selenium contained in the immobilized selenium and the cycle rate (0.1C, 0.5C, 1C, 2C, 3C, 4C, 5C, 10C, etc.).

Example 9: synthesis and characterization of the carbon skeleton.

To form a first residue, a charge of 260g of potassium citrate was added to the crucible, and the crucible was placed into a quartz tube within a tube furnace. A stream of argon gas was flowed into the furnace and the furnace was heated from room temperature (-20 ℃ to 22 ℃) to 600 ℃ at 5 ℃/min. The furnace was held at this temperature for 60 minutes, after which the furnace was shut down and the charge was removed from the crucible after cooling of the furnace, recovering 174.10 grams of processed residue. To form the second and third processed residues, the same process described for the first residue was repeated for charges of 420 and 974 grams of potassium citrate, respectively. The resulting second and third processed residues weighed 282.83 grams and 651.93 grams, respectively.

1108.9 grams from the three processed residues were combined together in a crucible, the crucible was placed in a quartz tube inside a tube furnace, and a stream of argon gas was flowed into the furnace. The furnace was heated to 800 ℃ at 5 ℃/min. The furnace was held at 800 ℃ for 1 hour. The furnace was allowed to cool, after which the crucible was removed from the quartz tube and 1085.74 grams of the first final residue were recovered.

Following the same procedure described in this example (800 ℃), a charge of 120 grams of potassium residue was charged to the furnace, resulting in about 77 grams of a second final residue (800 ℃).

The first and second final residues were combined to yield about 1,163 grams of a third final residue.

1,163 grams of the third final residue was then mixed with 400ml of water to form a slurry, which was divided approximately equally into four two-liter beakers. The pH of each slurry was measured to be greater than 13. Next, concentrated hydrochloric acid solution was added to each beaker, carbon dioxide evolved vigorously, and subsided at a pH of less than about 5. More hydrochloric acid solution was added to obtain a pH of about 1.9. The slurry was then filtered and washed into a filter cake, which was dried in an oven at 120 ℃ for about 12 hours followed by vacuum drying at 120 ℃ for 24 hours, yielding four samples of carbon skeleton, totaling about 61.07 grams.

These carbon skeleton samples were characterized by SEM, XRD, raman, BET/pore size distribution. Fig. 7 shows SEM results of one carbon skeleton. The surface morphology of typical carbon skeleton particles prepared in the method described in this example had a sheet-like morphology with sheet edges connected to each other, a sample thickness of 500nm to 100nm, and a sample width (or length) of 0.5 μm to 2 μm, and thus had an aspect ratio (defined as the ratio of the longest dimension of the sample width (or sheet length) to the sample thickness) of ≧ 1, for example, an aspect ratio ≧ 5 or more, or an aspect ratio ≧ 10.

The X-ray diffraction pattern for one of the carbon frameworks shown in fig. 8 shows that the carbon framework is substantially amorphous in phase. However, it does show a broad diffraction peak centered around 2 θ of about 17 °, indicating a d-spacing of about 5.21 angstroms.

The results of Raman scattering spectra of a carbon skeleton are shown in FIG. 9, showing Sp²The carbon has a height of about 1365cm^-1D-band at (curve 1) and a band width of about 1589cm^-1G-band at (curve 2), FWHM 296cm each^-1And 96cm^-1. Both the D-band and the G-band show a mixture of Gaussian and Lorentzian distributions; the D-band has a Gaussian distribution of about 33% and the G-band has a Gaussian distribution of about 61%. The ratio of the area of the D-band to the area of the G-band was about 3.5.

BET surface area of 1,205m, measured by nitrogen absorption, of a carbon skeleton²(ii) in terms of/g. By using the NLDFT method, the incremental pore surface area versus pore width is plotted in FIG. 10A, showing a cumulative pore surface area of 1,515m²(ii) in terms of/g. The difference between BET surface area and NLDFT surface area may result from the fact that: with nitrogen and CO₂The absorption data of the two are used for calculating NLDFT distribution; CO 2₂Molecules can enter pores that are smaller than those that nitrogen molecules can enter. NLDFT surface area of pore with peak at 3.48 Angstrom 443m²/g, NLDFT surface area of the pore at 5.33 angstroms of 859m²(iv)/g, and NLDFT surface area of pore at 11.86 angstroms (up to 20 angstroms) is 185m²(iv)/g, the NLDFT surface area for a pore of 20 angstroms or less amounting to 1,502m²/g, while the NLDFT surface area of the 20 to 1000 angstrom pores is only 7.5m²A/g, and a surface area of the pores of 20 angstroms or greater is only about 0.5% of the total surface area.

By nitrogen absorption and CO₂The pore size distribution of the carbon skeleton sample was measured by absorption. Combining nitrogen absorption and CO₂The absorption results of the absorption to produce the pore size distribution shown in fig. 10B. The relationship of incremental pore volume (mL/g) to pore width (angstroms) shows that there are three major peaks located at 3.66 angstroms, 5.33 angstroms, and 11.86 angstroms; cumulative pore volume (mL/g) versus pore width (angstroms) shows that there is about 0.080mL/g of pores at the 3.66 angstroms peak, about 0.240mL/g of pores at the 5.33 angstroms peak, about 0.108mL/g of pores at the 11.86 angstroms peak, 20 angstroms or less pores with 0.43mL/g, 20 angstroms to 100 angstroms pores with 0.042mL/g, and a total of 0.572mL/g of up to 1000 angstroms pores.

Example 10: preparation and characterization of immobilized selenium.

0.1206 grams of selenium (showing the bulk properties of selenium) were added to a set of agate mortar and pestle, and 0.1206 grams of the carbon skeleton prepared according to example 9 were added to the same agate mortar and pestle. The selenium and carbon skeleton mixture was hand milled for about 30 minutes and transferred to a stainless steel mold (10 mm diameter). The mixture was pressed in a mold to a pressure of about 10MPa to form pellets of the mixture. The pellets were then charged into a sealed container in the presence of an inert environment (argon) and the sealed container containing the pellets was placed in an oven. The oven comprising the sealed container containing the pellets is heated to 240 ℃ (above the melting temperature of selenium) for, e.g., 12 hours. However, it is contemplated that any combination of time and temperature (above the melting temperature of selenium) may be used sufficient to react (partially or fully) selenium and carbon and form an immobilized selenium having some or all of the features described herein. Subsequently, after the pellets were returned to room temperature, the pellets were discharged from the container. The pellet discharged was the immobilized selenium of this example 10.

The immobilized selenium of this example 10 was then characterized by TGA-DSC and TGA. TGA-DSC analysis of the immobilized selenium was collected at a heating rate of 10 ℃/min under a flow of argon of 200 ml/min. There is no observable endothermic DSC peak at temperatures near the melting point of selenium (about 230 ℃), indicating that the immobilized selenium of this example 10 is different from the bulk (bulk) form of selenium molecules/atoms (which should have a melting point of about 230 ℃, here should be the endothermic peak).

Studies have shown that TGA-DSC data may be unreliable when the heating temperature reaches the point where selenium molecules begin to escape from the TGA-DSC sample crucible (graphite or ceramic). To this end, the gas phase selenium molecules (from the sample crucible) enter the argon carrier gas stream and appear to react with the TGA-DSC platinum sample holder, which distorts the actual TGA-DSC thermo-chemical behavior. Selenium molecules released from the sample crucible reacted with the platinum sample holder, resulting in a lower weight loss in this temperature region. The selenium-platinum complex in the platinum sample holder is then released into the gas phase when the heating temperature reaches a point above 800 ℃. Complete selenium release can occur at 1000 ℃. The study used up most of the immobilized selenium sample of this example 10. Thus, a new sample of immobilized selenium (16 grams) was prepared using the same method as described in the previous section of this example 10.

The thermochemical behavior of this new sample of immobilized selenium was studied by TGA analysis using a ceramic sample holder covered with a very small thermocouple for TGA analysis. The TGA analysis result of this new immobilized selenium sample is shown in fig. 11A, and the TGA analysis result of the selenium-carbon composite (made with 50-50Se-Super P-carbon composite and Se-graphite (ground graphite)) prepared in the same method as the preparation of the immobilized selenium of this example 10 is shown in fig. 11B. SuperP is a commercial grade of carbon black that is widely used in the lithium ion battery industry. Milled graphite was prepared by milling Poco 2020 graphite. TGA analysis data is also summarized in table 2 below.

TABLE 2

The immobilized selenium may have an initial weight loss temperature starting at about 400 ℃ compared to 340 ℃ for the Se-Super P-carbon composite and the Se-graphitic carbon composite; the mid-point weight loss temperature of the immobilized selenium may be about 595 ℃, versus 480 ℃ for the Se-Super P complex and 471 ℃ for the Se-graphite complex; and the Se-Super P complex and Se-graphite complex complete the major weight loss at around 544 c, while the immobilized selenium completes the major weight loss at 660 c. The Se-Super P-carbon composite and Se-graphitic carbon composite showed less than 0.6% weight loss at 560 ℃ to 780 ℃, while the immobilized selenium showed a weight loss of about 2.5% from the bottom of the major weight loss (-660 ℃ to 1000 ℃). These results indicate that non-immobilized selenium (Se-Super P-carbon composites and Se-graphite composites) can escape less than or equal to 1.2% of the total selenium from the composite at temperatures greater than or equal to 560 ℃ and that immobilized selenium can escape about 5.0% of the total selenium from the carbon skeleton at temperatures greater than or equal to 660 ℃. The following details are provided to give examples, which provide an understanding of the thermochemical behavior. However, these details should not be construed in a limiting sense.

Using the TGA mid weight loss temperature data as an example of thermochemical behavior, as the heating temperature increases, the kinetic energy of the selenium molecules in the Se-Super P composite and Se-graphite composite increases to a level where these selenium molecules have sufficient energy to overcome intermolecular interactions between selenium molecules and escape from the liquid phase of selenium. In this context, kinetic energy is 3RT/2, wherein: r is the gas constant and T is the temperature in kelvin.

It was observed that the average kinetic energy of the selenium molecules of the Se-Super P complex was measured as 9,391J/mol when the selenium molecules escaped from the mixture of Se-Super P complexes. However, immobilizing selenium requires more energy to be available so that the selenium has an average kinetic energy of about 10,825J/mol to move the selenium away from the carbon skeleton into a vapor phase selenium molecule. It is believed that selenium in the immobilized selenium (in atomic form, in molecular form, or in any form) may chemically interact with the selenium and carbon backbone in addition to the intermolecular interactions of selenium. Further, a last portion of the selenium that escapes from the carbon skeleton at 660 ℃ to 1000 ℃ has an average kinetic energy of 11,635J/mol to 15,876J/mol or more. This indicates that selenium in the immobilized selenium is more stable than selenium in the conventional selenium-carbon composite. The stabilized selenium in the immobilized selenium of this example 10 enhances the ability of selenium, in atomic form, in molecular form, or in any form, to remain inside the carbon skeleton during electrochemical processes, for example during charge and discharge cycles of a rechargeable battery comprising the immobilized selenium. In an example, this last portion of selenium may require kinetic energy of 11,635J/mol (> 660 ℃ C.) or more to escape the carbon skeleton and may be critical for selenium immobilization and may serve as an interface material between the carbon skeleton and a majority of the immobilized selenium molecules. The portion of interfacial selenium in the immobilized selenium may be greater than or equal to 1.5%, greater than or equal to 2.0%, greater than or equal to 2.5%, or 3.0% of the total immobilized selenium.

Fig. 11A also shows a TGA study of immobilized selenium with a heating rate of 16 ℃/min containing selenium with a midpoint weight loss temperature of 628 ℃. As shown in fig. 11C, the median weight loss temperature of Se contained is 495 ℃ at a heating rate of 16 ℃/min for the Se-Super P composite. Activation energy and collision frequency can be determined and calculated using known methods, such as ASTM E1641-16 and E2958-14, with different heating rates (e.g., 16 deg.C/min, 10 deg.C/min, 5 deg.C/min, 2.5 deg.C/min, and 1 deg.C/min). The temperature at 15% weight loss was tabulated for different heating rates, as shown in table 3 below.

The activation energy of selenium (non-immobilized or conventional) in the Se-Super P complex was determined to be 92.3kJ/mol with a collision frequency of 2.27X 10⁵. The activation energy of selenium in immobilized selenium (above 228-110) was also determined to be 120.7kJ/mol, with a collision frequency of 12.4X 10⁵. Another sample of immobilized selenium (155-82-2 above) prepared in the same procedure as example 10 was also measured to have an activation energy of 120.0kJ/mol and 18.3X 10⁵The collision frequency of (1).

Calculation of kinetic Rate constants of selenium Using the Arrhenius equation

Where k is the rate constant, Ea is the activation energy, a is the collision frequency, R is the gas constant, and T is the temperature in kelvin.

Referring to FIG. 11D, activation energy and collision measured as aboveThe collision frequency, kinetic rate constants were calculated at different temperatures using the arrhenius equation. FIG. 11D shows that non-immobilized selenium (Se-Super P complex-solid line) has a much higher rate constant than immobilized selenium (228-110 (dotted line) and 115-82-2 (dashed line)), e.g., about 4 orders of magnitude higher at 35 ℃ and about 3 orders of magnitude higher at 100 ℃. In the examples, the rate constant of non-immobilized selenium (Super P) is 2.668X 10 at 50 deg.C^-10And the rate constant of the immobilized selenium is 7.26 x 10^-14(155-82-2) and 3.78X 10^-14(228-110). Selenium with a lower kinetic rate constant has less tendency to leave the host material (carbon), which may lead to better battery cycling performance.

FIG. 12 shows the spectrum of immobilized selenium having a wavelength at 1368cm^-1D-band at 1596cm^-1The ratio of the area of the D-band to the area of the G-band was 2.8. Selenium immobilization shifts both raman peaks to higher wavenumbers, about 3cm for the D-band, compared to the raman spectra of the carbon skeleton shown in fig. 9^-1Red-shifted and 7cm for the G-band^-1Red shift, which indicates Sp in the carbon skeleton²The bond strength of the carbon is enhanced, about 4cm for the D-band^-1Red-shifted and about 8cm for the G-band^-1And (4) red shifting. At the same time, the ratio of the area of the D-band to the area of the G-band also decreased from about 3.4 to 2.8, indicating that the D-band became relatively weak or the G-band became relatively strong. Stronger G-bands may be desirable because G-bands may relate to carbon types that allow the carbon backbone to conduct electrons more easily, which may be desirable for electrochemical performance when used in a rechargeable battery. Bulk or pure selenium is typically about 235cm^-1Showing a sharp raman shift peak. For immobilized selenium, the Raman spectrum in FIG. 12 shows at about 257cm^-1A broad Raman peak (area 12.7% G-band) and a peak at about 500cm^-1A new broad peak (about 3.0% G-band area). It is believed that selenium immobilization changes the raman properties of the carbon skeleton and selenium, and all raman peaks shift to higher wavenumbers, indicating the carbon-carbon Sp of the carbon skeleton²The bonds and the selenium-selenium bond of selenium are in a compressed state.

Selenium fixationCarbon-carbon Sp of compression-enhanced carbon skeleton caused by methylation²Bonds and the Se-Se bond of selenium, resulting in stronger selenium-selenium and carbon-selenium interactions. Thus, selenium requires more kinetic energy to overcome the stronger Se-Se bond and stronger carbon-selenium interaction, which explains the observations in TGA analysis of immobilized selenium versus Se-Super P complexes and Se-graphite complexes.

Furthermore, under compression, the carbon skeleton will have a better ability to conduct electrons at the level of bonding; and under compression, selenium atoms or molecules also have a better ability to conduct electrons.

Stabilized selenium for immobilizing selenium and enhanced electronic conductivity across the carbon backbone and selenium may be desirable during electrochemical processes, e.g., improved specific capacity for active materials with minimal shuttle levels, improved cycling capability due to immobilization, capability to charge and discharge at higher rates, etc. However, this should not be construed in a limiting sense.

The X-ray diffraction pattern for the immobilized selenium prepared according to example 10 shown in fig. 13 shows a reduction in the intensity of the broad diffraction peak of the carbon backbone with a d-spacing of about 5.21 angstroms to only about 1/3 of the intensity, indicating that the immobilized selenium further renders the carbon backbone more disordered or causes more disruption to the order state of the carbon backbone. In the examples, it is believed that this is due to the compressive force applied to the carbon-carbon Sp²On the key.

Fig. 14 shows an SEM image of immobilized selenium prepared according to example 10, showing a lamellar morphology, as does the image of the carbon skeleton in fig. 7. Despite the fixation of about 50% selenium in the carbon skeleton, no selenium particles were observable on the surface of the carbon skeleton, yielding many flat sheets with high aspect ratios, except that the inter-sheet connections had been broken. These platelet morphologies are highly desirable for forming oriented coatings aligned in the planar platelet direction, producing platelet surface-to-surface contact, resulting in improved platelet-to-platelet conductivity, which can result in excellent electrical performance, for example, in electrochemical processes in rechargeable batteries.

Example 11: se cathode preparation

56mg of immobilized selenium prepared according to example 10 was added to a mortar and pestle; 7.04mg of Super P; 182 μ L of carboxymethyl cellulose (CMC) solution (containing 1mg of dry CMC for every 52 μ L of CMC solution); 21.126 μ L of SBR latex dispersion (containing 1mg of dry SBR latex for each 6.036 μ L of SBR latex dispersion); and 200 μ L deionized water. The particles, binder and water were manually ground into a slurry for 30 minutes to produce a cathode slurry. The cathode slurry is then coated onto one side of a sheet of conductive substrate (e.g., foil) and air dried. In an example, the conductive substrate or foil may be an aluminum (Al) foil. However, this should not be construed in a limiting sense as the use of any suitable and/or desired shape or form of conductive material is contemplated. For purposes of description only, the use of aluminum foil to form a selenium cathode will be described herein. However, this should not be construed in a limiting sense.

The slurry coated Al foil was then placed in a drying oven and heated to a temperature of 55 ℃ for 12 hours, resulting in a selenium cathode consisting of a dried sheet of immobilized selenium on one side of the Al foil, while the other side of the Al foil was uncoated (i.e., bare aluminum).

The selenium cathode was then punched into cathode disks, each disk having a diameter of 10 mm. Some of these cathode disks are used as cathodes for rechargeable batteries.

Example 12: Li-Se rechargeable battery pack assembly and testing

A Li-Se rechargeable button cell battery was assembled using the cathode disks from example 11 in the manner described in the examples discussed below and shown in fig. 15. In this example, a 10mm diameter cathode disk 4 from example 11 was placed on the base 2 of a 2032 stainless steel coin cell can that was used as the positive casing of a coin cell ("positive casing" in fig. 15), with the immobilized selenium sheet 5 facing up, away from the base 2 of the positive casing, and the bare Al side facing and in contact with the base 2 of the positive casing. Next, a battery separator 6 (19 mm diameter and 25 microns thickness) was placed on top of the cathode disk 4 in contact with the immobilized selenium disk 5. In an example, the battery separator 6 may be an organic separator, or an inorganic separator, or a solid electrolyte separator. The organic separator may be a polymer, such as polyethylene, polypropylene, polyester, halogenated polymer, polyether, polyketone, and the like. The inorganic separator may be made of glass and/or quartz fibers.

Then, LiPF will be included₆240 μ L of electrolyte 7 of Ethylene Carbonate (EC) (1M) and dimethyl carbonate (DMC) solvent (50-50 by weight) was introduced into the positive casing 2, followed by a lithium foil disk 8 (15.6 mm in diameter and 250 μ M thick) placed on the side of the separator 6 opposite the cathode disk 4. Next, a Stainless Steel (SS) shim 10 is placed on the side of the lithium foil disk 8 opposite the separator 6, followed by one or more foam disks 12 made of, for example, nickel, on the side of the SS shim 10 opposite the lithium foil disk 8. The lithium foil 8, SS gasket 10, and/or foam disk 12 may be used as the anode. Finally, a case 14 made of 2032 stainless steel 14 to serve as the negative electrode of the coin cell ("negative case" in fig. 15) is placed on the side of the nickel foam disk 12 opposite the SS gasket 10, and on the edge of the positive case 2. The positive housing 2 and negative housing 14 are then sealed together at high pressure (e.g., 1,000 psi). Sealing the positive and negative electrode casings (2,14) at high pressure also has the effect of compressing the stack (from bottom to top in fig. 15) comprising the cathode disk 4, separator 6, lithium foil 8, SS gasket 10 and Ni foam disk 12 together. Over a dozen button cell batteries were assembled using the above-described battery separators and glass fiber separators. The assembled coin cell batteries were then tested under the following conditions.

Some assembled coin cell batteries were tested at charge-discharge rates of 0.1C and 1C by using a Lanhe battery tester CT 2001A. Each button cell battery was tested as follows: (1) standing for 1 hour; (2) discharging to 1V; (3) standing for 10 minutes; (4) charging to 3V; (5) standing for 10 minutes; repeating the steps (2) to (5) to repeat the cycle test.

Fig. 16A (left) shows cycling test results (313 cycles at 0.1C charge-discharge rate) for coin cells prepared according to example 12 using cathodes prepared according to example 11, showing excellent cycling stability with a specific capacity of 633.7mAh/g after 313 cycles, which is a 93.4% retention of the initial specific capacity. The first discharge specific capacity is higher than stoichiometric, which may be due to some side reactions on the cathode and anode surfaces. From the start of the second cycle, the specific capacity begins to decrease with the cycle; however, the specific capacity slowly increased from about 30 cycles to about 120 cycles, then remained stable to about 180 cycles, and then decreased. Fig. 16B (right) also shows the excellent cycling stability of another coin cell (100 cycles at 0.1C followed by 500 cycles at 1C) with a specific capacity of 462.5mAh/g at 600 cycles, which is 66.0% retention of the second cycle capacity at 0.1C or 80.3% retention of the 105 th cycle capacity at 1C. The coulombic efficiency can be 95% or more, 98% or more, or up to 100%, indicating that there is no detectable amount of selenium shuttling between the cathode and anode. This electrochemical performance is believed to be due to the immobilized selenium in the cathode, preventing selenium from dissolving from cathode 14 and shuttling to anode 2.

Fig. 17 shows the cycling test results for button cells assembled with the polymer separator described in example 12 at different discharge-charge cycling rates (0.1C-rate to 10C-rate). The test protocol was similar to the above test except for the cycling rates (0.1C, 0.2C, 0.5C, 1C, 2C, 5C, and 10C); 5 cycles of charging and discharging for each C-rate; the cycle rate was then returned to the 0.1C cycle. At 0.1C rate, the battery exhibited a specific capacity of about stoichiometry. Furthermore, the battery pack showed good stability during cycling for cycling rates of 0.2C, 0.5C, 1C, and 2C. The batteries also exhibited rapid charging and discharging capabilities, 56% of the stoichiometric capacity cycled at 10C-rate, although the capacity was shown to decrease with cycling rate. In other words, at 10C-rate, the battery took 3.3 minutes to charge and discharge to/from 56% of stoichiometric capacity. At such rapid cycling rates, conventional batteries are not expected to survive.

The specific capacity of the Li-Se battery containing immobilized selenium was recovered to 670mAh/g, 98% of its full capacity, when cycled at 0.1C-rate at the start of the test. It is believed that (1) stabilization of selenium in an immobilized selenium cathode avoids seleniumLeaving the carbon skeleton to avoid selenium shuttling between the cathode and anode during cycling, which results in a battery with improved cycling performance; (2) sp²The carbon-carbon bond and carbon backbone, selenium-selenium bond and carbon-selenium interaction can all be under compression, potentially leading to excellent electrical conductivity within the carbon backbone, within the selenium particles and between the carbon and selenium interface, which can help achieve the cycling performance observed at high C-rates.

An immobilized selenium host comprising selenium and carbon prepared according to the principles described herein may include one or more of the following features:

(a) the kinetic energy required for the selenium particles to escape from the immobilized selenium can be more than or equal to 9.5kJ/mol, more than or equal to 9.7kJ/mol, more than or equal to 9.9kJ/mol, more than or equal to 10.1kJ/mol, more than or equal to 10.3kJ/mol or more than or equal to 10.5 kJ/mol;

(b) the temperature required for the selenium particles to escape from the immobilized selenium can be more than or equal to 490 ℃, more than or equal to 500 ℃, more than or equal to 510 ℃, more than or equal to 520 ℃, more than or equal to 530 ℃, more than or equal to 540 ℃, more than or equal to 550 ℃ or more than or equal to 560 ℃;

(c) the carbon may have a value of 500m or more²/g、≥600m²/g、≥700m²/g、≥800m²/g、≥900m²/g or more than or equal to 1,000m²Surface area per gram (for pores less than 20 angstroms);

(d) the carbon can have a surface area of less than or equal to 20%, less than or equal to 15%, less than or equal to 10%, less than or equal to 5%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1% of the total surface area (for pores of 20 angstroms to 1000 angstroms);

(e) the carbon and/or selenium may be under compression. The benefits of immobilized selenium wherein carbon and/or selenium is under compression versus a carbon-selenium system wherein carbon and/or selenium is not under compression may include: improved electron flow, reduced electron flow resistance, or both, which can facilitate electron delivery to and from selenium anions during charge and discharge of a rechargeable battery having a cathode comprised of immobilized selenium;

(f) for selenium to escape from the immobilized Se-C complex system, the immobilized selenium may comprise selenium having an activation energy higher than that of conventional (non-immobilized) selenium. In the examples, the activation energy of non-immobilized selenium (Se-Super P complex system) was determined to be 92kJ/mol according to ASTM method E1641-16. In contrast, in examples, the activation energy of selenium in immobilized selenium comprising selenium and carbon may be 95kJ/mol or more, 98kJ/mol or more, 101kJ/mol or more, 104kJ/mol or more, 107kJ/mol or more, 110kJ/mol or more. In another example, the activation energy of selenium in immobilized selenium comprising selenium and carbon may be greater than or equal to 3%, > 6%, > 9%, > 12%, > 15% or > 18% of the activation energy of selenium in the Se-SuperP complex;

(g) the immobilized selenium may comprise selenium having a higher collision frequency than non-immobilized selenium. In the examples, the collision frequency of non-immobilized selenium was determined to be 2.27X 10 according to ATSM method E1641-16⁵. In contrast, in the example, the collision frequency of selenium in the immobilized selenium containing selenium and carbon may be ≧ 2.5X 10⁵、≥3.0×10⁵、≥3.5×10⁵、≥4.0×10⁵、≥4.5×10⁵、≥5.0×10⁵、≥5.5×10⁵、≥6.0×10⁵Or more than or equal to 8.0 multiplied by 10⁵. The collision frequency of the immobilized selenium can be more than or equal to 10 percent, more than or equal to 30 percent, more than or equal to 50 percent, more than or equal to 80 percent, more than or equal to 100 percent, more than or equal to 130 percent, more than or equal to 150 percent, more than or equal to 180 percent or more than or equal to 200 percent larger than the collision frequency of the non-immobilized selenium in the Se-C compound; and

(h) the immobilized selenium can include selenium having a kinetic rate constant of no greater than 1/5, no greater than 1/10, no greater than 1/50, no greater than 1/100, no greater than 1/500, or no greater than 1/1000 that is the non-immobilized/conventional selenium kinetic rate constant. In an example, the immobilized selenium can include a selenium having ≦ 1 × 10^-10、≤5×10^-11、≤1×10^-11、≤5×10^-12Or less than or equal to 5X 10^-13Selenium with kinetic rate constant (at 50 ℃).

Sp of carbon (or carbon skeleton defined by the carbon) of immobilized selenium in the case where the carbon and/or selenium of immobilized selenium is under compression²The D-band and/or G-band of the Raman spectrum of C-C bonds may show a red (positive) shift from the carbon starting material, e.g.. gtoreq.1 cm^-1、≥2cm^-1、≥3cm^-1、≥4cm^-1Or more than or equal to 5cm^-1。

In the case where the carbon and/or selenium of the immobilized selenium is under compression, the selenium may have a raman peak (235 cm) from pure selenium^-1) Red (positive) shift of, e.g., ≧ n4cm^-1、≥6cm^-1、≥8cm^-1、≥10cm^-1、≥12cm^-1、≥14cm^-1Or more than or equal to 16cm^-1The red-shift may indicate compression of the selenium particles.

The immobilized selenium may be elemental selenium and/or compound selenium.

The immobilized selenium comprising selenium and carbon may be further doped with one or more additional elements from group 6 of the periodic table (hereinafter "additional G6 element"), including for example, but not limited to, sulfur and/or tellurium. The dopant level can be as low as 100ppm (by weight) up to 85% of the total weight of the immobilized selenium. In an example, the immobilized selenium may comprise 15% to 70% carbon and 30% to 85% selenium, and optionally an additional G6 element. In an example, the immobilized selenium may comprise a mixture of (1) 15% to 70% carbon and (2) 30% to 85% selenium + an additional element of G6. In a mixture comprising selenium + additional G6 element, the additional G6 element may comprise 0.1% to 99% of the mixture, and the selenium may comprise 1% to 99.9% of the mixture. These ranges of selenium + additional element G6 should not be construed in a limiting sense, however.

The immobilized selenium may comprise greater than or equal to 5% selenium, greater than or equal to 10% selenium, greater than or equal to 20% selenium, greater than or equal to 30% selenium, greater than or equal to 40% selenium, greater than or equal to 50% selenium, greater than or equal to 60% selenium, or greater than or equal to 70% selenium or higher.

The immobilized selenium may optionally comprise another element, such as sulfur, tellurium, and the like.

The immobilized selenium may be raman inactive or raman active. If Raman active, the immobilized selenium may have a concentration of 255 + -25 cm^-1At 255 +/-15 cm^-1Or at 255 +/-10 cm^-1Relative peak intensity of raman.

The immobilized selenium may comprise selenium having a Raman relative peak intensity of 0.1% or more, 0.5% or more, 1% or more, 3% or more, or 5% or more, as defined herein at 255cm^-1The area of the raman peak at (a) is relative to the area of the D-band peak of the carbon raman spectrum.

The carbon containing immobilized selenium may serve as a carbon skeleton for selenium immobilization. The carbon skeleton may haveSp²A carbon-carbon bond, Raman D-band at 1365. + -. 100cm^-1The G-belt is positioned at 1589 +/-100 cm^-1At least one of (1) and (b); d-band is located at 1365 +/-70 cm^-1The G-belt is positioned at 1589 +/-70 cm^-1At least one of (1) and (b); d-band is located at 1365 +/-50 cm^-1The G-belt is positioned at 1589 +/-50 cm^-1At least one of (1) and (b); d-band is located at 1365 +/-30 cm^-1The G-belt is positioned at 1589 +/-30 cm^-1At least one of (1) and (b); or D-band at 1365 + -20 cm^-1The G-belt is positioned at 1589 +/-20 cm^-1To (3).

The selenium-immobilized carbon may comprise Sp²A carbon-carbon bond having a Raman peak characterized by a D-band and a G-band. The area ratio of the D-band to the G-band can be 0.01 to 100, 0.1 to 50, or 0.2 to 20.

The selenium-immobilized carbon may comprise Sp²A carbon-carbon bond having a Raman peak characterized by a D-band and a G-band. Each of the D-band and the G-band may have an orientation of ≧ 1cm^-1、≥2cm^-1Or a larger displacement of higher wave numbers.

The carbon of the immobilised selenium may be doped with one or more other elements of the periodic table.

The selenium-immobilized carbon may be porous. The pore size distribution of the carbon skeleton may be one angstrom to several micrometers. The pore size distribution can have at least one peak located between 1 angstrom and 1000 angstroms, between 1 angstrom and 100 angstroms, between 1 angstrom and 50 angstroms, between 1 angstrom and 30 angstroms, or between 1 angstrom and 20 angstroms. The porosity of the carbon skeleton may have a pore size distribution having more than one peak within the aforementioned range.

The selenium-immobilized carbon can comprise 0.01mL/g to 5 mL/g; 0.01mL/g to 3 mL/g; 0.03mL/g to 2.5 mL/g; or a pore volume of 0.05mL/g to 2.0 mL/g.

The selenium-immobilized carbon can include a pore volume that can be > 30%, > 40%, > 50%, > 60%, > 70%, or > 80% of the total measurable pore volume (which has a pore diameter <100 angstroms, <50 angstroms, <30 angstroms, or <20 angstroms).

The selenium-immobilized carbon may include>400m²/g、>500m²/g、>600m²/g、>700m²/g、>800m²/g、>900m²G or>1000m²Surface area in g.

The selenium-immobilized carbon may be amorphous and may have a broad peak centered at a d-spacing of about 5.2 angstroms.

The carbon of the immobilized selenium may be in any form, tablet, sphere, fiber, needle, tube, irregular, interconnected, agglomerated, discrete, or any solid particle. Sheets, fibers, needles, tubes, or some morphologies having a certain horizontal aspect ratio may be beneficial for achieving better inter-particle contact, resulting in enhanced conductivity (over immobilized selenium made from different aspect ratios), which may be beneficial for electrochemical cells, such as rechargeable batteries.

The selenium-immobilized carbon can have any particle size, with a median particle size of 1-9 nanometers to 2 millimeters, 1-9 nanometers to <1000 micrometers, or 20 nanometers to 100 micrometers.

The selenium of the immobilized selenium may be amorphous, for example as determined by X-ray diffraction. The diffraction peak of selenium of the immobilized selenium, which may have a d-spacing of about 5.2 angstroms, may be weaker than the diffraction peak of the carbon backbone, e.g., 10% weaker, 20% weaker, 30% weaker, or 40% weaker.

In an example, a method of preparing immobilized selenium may comprise:

(a) physically mixing carbon and selenium. Physical mixing can be by ball milling (dry and wet), mixing with a mortar and pestle (dry or wet), jet milling, horizontal milling, disk milling, high shear mixing in a slurry, conventional slurry mixing with blades, and the like;

(b) the physically mixed carbon and selenium of step (a) may be heated at or above the melting temperature of selenium. Heating of the carbon and selenium mixture may occur in the presence of an inert gas environment (such as, but not limited to, argon, helium, nitrogen, etc.), or in an air or reactive environment;

(c) optionally homogenizing or blending the heated carbon and selenium to achieve selenium immobilization; and

(d) cooling the immobilized selenium of step (c) to ambient or room temperature.

In another example, immobilized selenium may be prepared by dissolving selenium onto carbon, followed by evaporation. The solvent for dissolving selenium may be alcohol, ether, ester, ketone, hydrocarbon, halogenated hydrocarbon, nitrogen-containing compound, phosphorus-containing compound, sulfur-containing compound, water, etc.

In another example, immobilized selenium may be prepared by melting selenium onto carbon, followed by removal of additional or excess non-immobilized selenium.

In an example, a method of preparing immobilized selenium may comprise:

(a) mixing together selenium and carbon under dry or wet conditions;

(b) optionally drying the mixture of step (a) at elevated temperature;

(c) optionally granulating the dried mixture of step (b);

(d) selenium is melted into carbon to produce immobilized selenium.

The immobilized selenium may be used as a cathode material for a rechargeable battery. The cathode may comprise an inorganic or organic binder. The inorganic binder may be a natural product (e.g., CMC) or a synthetic product (e.g., SBR rubber latex). The cathode may comprise an optional conductivity promoter, such as graphite-derived small particles, graphene, carbon nanotubes, carbon nanoplatelets, carbon black, and the like. Finally, the cathode may comprise a charge collector, such as an aluminum foil, a copper foil, a carbon fabric, or other metal foil.

A method of making a cathode can include coating a slurry comprising immobilized selenium onto a charge collector and subsequently drying the slurry coated charge collector (e.g., air drying, oven drying, vacuum oven drying, etc.). The immobilized selenium may be dispersed into the slurry and may be prepared by a high shear mixer, a conventional mixer, a planetary mixer, a double planetary mixer, a ball mill, a vertical attritor, a horizontal mill, etc. The slurry can then be coated onto a charge collector and then dried in air or under vacuum. The coated cathode may then be pressed or roll milled (or calendered) prior to use in a rechargeable battery.

Rechargeable batteries can be made using the immobilized selenium described herein. A rechargeable battery may include a cathode containing immobilized selenium, an anode, and a separator separating the anode and the cathode. The anode, cathode and separator may be submerged in electrolysisIn liquids, e.g. LiPF₆. The anode may comprise lithium, sodium, silicon, graphite, magnesium, tin, and the like.

The separator may include an organic separator, an inorganic separator, or a solid electrolyte separator. The organic separator may include polymers such as polyethylene, polypropylene, polyesters, halogenated polymers, polyethers, polyketones, and the like. The inorganic separator may include glass or quartz fibers, or a solid electrolyte separator.

The electrolyte may include lithium, sodium or other salts from group IA, IIA and IIIA in an organic solvent. The organic solvent may include organic carbonate compounds, ethers, alcohols, esters, hydrocarbons, halogenated hydrocarbons, lithium-containing solvents, and the like.

Rechargeable batteries may be used in electronic devices, electric or hybrid vehicles, industrial applications, military applications such as drones, aerospace applications, marine applications, and the like.

The rechargeable battery may have an electrochemical capacity of greater than or equal to 400mAh/g active amount of selenium, greater than or equal to 450mAh/g active amount of selenium, greater than or equal to 500mAh/g active amount of selenium, greater than or equal to 550mAh/g active amount of selenium, or greater than or equal to 600mAh/g active amount of selenium.

Rechargeable batteries may experience electrochemical cycling of greater than or equal to 50 cycles, greater than or equal to 75 cycles, greater than or equal to 100 cycles, greater than or equal to 200 cycles, etc.

Rechargeable batteries may be charged and/or discharged at 0.1C, 0.2C, 0.5C, 1C, 1.5C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C, or faster.

After performing a high C-rate charge-discharge cycle (5 cycles at 0.1C, 5 cycles at 0.2C, 5 cycles at 0.5C, 5 cycles at 1C, 5 cycles at 2C, 5 cycles at 5C, and 5 cycles at 10C), the rechargeable battery can maintain a specific battery capacity of > 30%, > 40%, > 50%, > 60%, > 70%, or > 80% of the second specific discharge capacity at a cycle rate of 0.1C.

Rechargeable batteries may have a coulombic efficiency of greater than or equal to 50%, greater than or equal to 60%, greater than or equal to 70%, greater than or equal to 80%, greater than or equal to 90%, or up to about 100%.

The coulombic efficiency of the battery is defined as follows:

wherein eta_cIs coulomb efficiency (%)

Q_outIs the amount of charge that leaves the battery during the discharge cycle.

Q_inIs the amount of charge that enters the battery pack during the charging cycle.

Rechargeable batteries may be charged at 0.1C, 0.2C, 0.5C, 1C, 1.5C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C, or faster C-rates. The C-rate is a measure of the rate at which the battery is discharged relative to its maximum capacity. For example, a 1C rate means that the discharge current will discharge the entire battery within 1 hour. For example, for a battery having a capacity of 100 amp-hours, this corresponds to a discharge current of 100 amps. For the same battery, the 5C rate is 500 amps, while the 0.5C rate is 50 amps.

The cathode of the rechargeable battery may include one or more elements of the chalcogen group, such as selenium, sulfur, tellurium, and oxygen.

The anode of the rechargeable battery may include at least one element of an alkali metal, an alkaline earth metal, and a group IIIA metal.

The separator of the rechargeable battery may include an organic separator or an inorganic separator.

The electrolyte of the rechargeable battery may include at least one element of alkali metal, alkaline earth metal, and group IIIA metal; and the solvent of the electrolyte may include an organic solvent, carbonates, ethers, or esters.

The rechargeable battery pack may have a specific capacity of 400mAh/g or more, 450mAh/g or more, 500mAh/g or more, 550mAh/g or more, or 600mAh/g or more.

After performing a high C-rate charge-discharge cycle (5 cycles at 0.1C, 5 cycles at 0.2C, 5 cycles at 0.5C, 5 cycles at 1C, 5 cycles at 2C, 5 cycles at 5C, and 5 cycles at 10C), at a cycle rate of 0.1C, the rechargeable battery can have a specific capacity of > 30%, > 40%, > 50%, > 60%, > 70%, or > 80% of the second specific discharge capacity.

Rechargeable batteries may have a coulombic efficiency of greater than or equal to 50%, > 60%, > 70%, > 80%, or > 90%.

Also disclosed are composites comprising selenium and carbon, which may have a platelet morphology with an aspect ratio of ≥ 1, ≥ 2, ≥ 5, ≥ 10 or ≥ 20.

The selenium of the complex may be amorphous, for example as determined by X-ray diffraction. The diffraction peak of selenium may have a d-spacing of about 5.2 angstroms, which may be weaker than the d-spacing of the carbon backbone, e.g., 10% weaker, 20% weaker, 30% weaker, or 40% weaker than the carbon backbone.

In an example, a method of making a composite can include:

(b) the physically mixed carbon and selenium of step (a) may be heated to the melting temperature of selenium or above, and the heating may occur in the presence of an inert gas environment (e.g., argon, helium, nitrogen, etc.), or in an air or reactive environment; and

(c) the heated carbon and selenium of step (b) may be homogenized or blended as an aid to achieving selenium immobilization.

In another example, the composite may be prepared by dissolving selenium onto carbon, followed by evaporation. The solvent for dissolving selenium may include alcohols, ethers, esters, ketones, hydrocarbons, halogenated hydrocarbons, nitrogen-containing compounds, phosphorus-containing compounds, sulfur-containing compounds, water, and the like.

The composite may be prepared by melting selenium onto (or into) carbon, followed by removal of additional or excess non-immobilized selenium.

In an example, a method of making a composite can include:

(a) mixing together selenium and carbon under dry or wet conditions;

(b) optionally drying the mixture of step (a) at elevated temperature;

(c) optionally granulating the dried mixture of step (b);

(d) selenium is melted into carbon to produce immobilized selenium.

The composite may be used as a cathode material for a cathode of a rechargeable battery. The cathode may comprise an inorganic or organic binder. The inorganic binder may be a natural product (e.g., CMC) or a synthetic product (e.g., SBR rubber latex). The cathode may comprise an optional conductivity promoter, such as graphite-derived small particles, graphene, carbon nanotubes, carbon nanoplatelets, carbon black, and the like. Finally, the cathode may include a charge collector, such as an aluminum foil, a copper foil, a carbon fabric, or other metal foil.

A method of making a cathode can include coating a slurry comprising immobilized selenium onto a charge collector and then drying the slurry coated charge collector (e.g., air drying, oven drying, vacuum oven drying, etc.). The immobilized selenium may be dispersed into the slurry and may be prepared by a high shear mixer, a conventional mixer, a planetary mixer, a double planetary mixer, a ball mill, a vertical attritor, a horizontal mill, etc. The slurry may then be coated onto a charge collector and then dried in room air or vacuum. The coated cathode may then be pressed or roll milled (or calendered) prior to use in a rechargeable battery.

Rechargeable batteries can be made using the above-described composites. Rechargeable batteries may be charged at 0.1C, 0.2C, 0.5C, 1C, 1.5C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C, or faster.

Example 13: preparing the sulfur-doped immobilized selenium, the electrode and the battery thereof.

In accordance with the principles and procedures described in example 10, 5 atomic percent (at%) selenium, 20 at% selenium, 35 at% selenium, and 50 at% selenium were replaced with sulfur, respectively, in the synthesis of immobilized sulfur-doped selenium detailed in table 4 below. Samples of sulfur-doped immobilized selenium were synthesized with a carbon backbone prepared according to the principles and methods described in example 9.

TABLE 4

Sample ID	Se,at％	S,at％	Se,wt％	S,wt％
					Se95S5	95	5	97.9	2.1
Se80S20	80	20	90.8	9.2
					Se65S35	65	35	82.1	17.9
Se50S50	50	50	71.1	28.9

The sample of immobilized sulfur-doped selenium thus prepared was then used to prepare a plurality of cathodes 4 comprising immobilized sulfur-doped selenium according to the principles and procedures for immobilizing selenium described in example 11.

The cathode thus prepared in this example, comprising immobilized sulfur-doped selenium, was then used to prepare a coin cell battery according to the principles and procedures described in example 12.

The assembled coin cell batteries of this example were then tested in the battery tester described in example 12 at charge and discharge cycling rates of 0.1C and 1C, following the same test protocol also described in example 12.

Electrochemical cycling results at 0.1C for coin cell batteries including cathodes composed of immobilized sulfur-doped selenium cathodes made from the immobilized sulfur-doped selenium sample (Se 50S50 in table 4) with a second cycle discharge capacity of 821mAh/g (which is considered good) and a stable coulombic efficiency of 95% or more, typically 98% or more (which is also considered good) or up to 100% are shown in fig. 18.

If selenium is assumed to have a stoichiometric specific capacity of 675mAh/g at a 0.1C cycling rate, the sulfur specific capacity would be estimated to be about 1,178mAh/g (for sulfur, it is considered good). Coulombic efficiencies of 95% or more, 98% or more, or up to 100% indicate that there is no significant amount of sulfur shuttling between the cathode and anode. The sulfur species in the immobilized sulfur-doped selenium battery functioned well in the electrolyte containing the carbonate. Generally, sulfur is expected to not function well in Li-S batteries with carbonates as electrolytes; conventional Li-S batteries typically use ether electrolytes. Carbonate-based electrolytes are commonly used in lithium ion batteries of the present invention. The carbonate-based electrolyte is more economical and more widely available in the market than the ether-based electrolyte.

Electrochemical cycling results at 1C cycle rate for coin cell batteries including cathodes composed of immobilized sulfur-doped selenium cathodes made from the immobilized sulfur-doped selenium samples (Se 50S50 in table 4) with a second cycle discharge capacity of 724mAh/g and a stable coulombic efficiency of 95% or more, typically 98% or more up to 100% are shown in fig. 19.

If selenium is assumed to have a specific capacity of 625mAh/g at 1C cycling rate, the sulfur specific capacity would be estimated to be about 966mAh/g (which is also unexpected). Sulfur is an insulator and has very low electrical conductivity. In general, Li-S batteries do not cycle well at fast cycling rates (e.g., at 1C rates).

It can be seen that immobilized sulfur-doped selenium overcomes two fundamental problems with Li-S batteries, namely shuttle effect and low cycling rate, when used as a cathode material in rechargeable batteries. Both problems are solved and batteries comprising cathodes comprising immobilised sulfur doped selenium can have a high energy density and a high power density in practical applications.

As can be seen, in an example, an immobilized sulfur-doped selenium system or host can be formed by a method comprising: (a) mixing selenium, carbon and sulfur to form a selenium-carbon-sulfur mixture; (b) heating the mixture of step (a) to a temperature above the melting temperature of selenium; and (c) cooling the heated mixture of step (b) to ambient or room temperature, thereby forming an immobilized sulfur-doped selenium body.

The immobilized sulfur-doped selenium host of step (c) may comprise selenium and sulfur in a carbon backbone host.

Step (a) may occur under dry or wet conditions.

Step (b) may comprise homogenizing or blending the mixture.

Step (a) may comprise forming the selenium-carbon-sulfur mixture into a body. Step (b) may comprise heating the body to a temperature above the melting temperature of selenium. Step (c) may comprise causing or allowing the body to cool to ambient or room temperature.

Step (b) may comprise heating the mixture for a sufficient time to fully or partially react the selenium and the carbon and sulfur.

In another example, a method of making an immobilized sulfur-doped selenium system or host can comprise: (a) forming a carbon skeleton; and (b) melting selenium and sulfur into the carbon skeleton.

In another example, a method of forming an immobilized sulfur-doped selenium system or host can comprise: (a) mixing selenium with carbon and sulfur; and (b) after step (a), dissolving selenium and sulfur onto carbon, thereby forming an immobilized sulfur-doped selenium system or host.

The solvent for dissolving selenium and sulfur may be alcohol, ether, ester, ketone, hydrocarbon, halogenated hydrocarbon, nitrogen-containing compound, phosphorus-containing compound, sulfur-containing compound, or water. The solvent may be added to one or more of selenium, sulfur or carbon prior to step (a), during step (a) or during step (b).

The method may further comprise (c) removing excess non-immobilized selenium, non-immobilized sulfur, or both from the immobilized sulfur-doped selenium system or host.

Also disclosed is a rechargeable battery pack including: a cathode comprising immobilized sulfur-doped selenium disposed on a conductive substrate; a separator in direct contact with the conductive substrate and in contact with the immobilized sulfur-doped selenium; and an anode separated from the cathode by a separator.

The rechargeable battery may further include an anode separated from the separator by lithium. In an example, the lithium may be in the form of a lithium foil.

The rechargeable battery may further include a cathode, a separator, an anode, and lithium immersed in the electrolyte.

In a rechargeable battery, the immobilized sulfur-doped selenium may comprise a selenium-carbon-sulfur mixture in which selenium and sulfur have been melted into carbon.

In the rechargeable battery, the separator may be formed of an organic material, an inorganic material, or a solid electrolyte.

Rechargeable batteries can have a coulombic efficiency of 95% or more.

Thus, a method of preparing a selenium carbon composite, a method of preparing immobilized selenium and the use of immobilized selenium have been described, for example, in a rechargeable battery, a method of preparing immobilized selenium in porous carbon in the presence of a desired level of oxygen species and the use of immobilized selenium in a rechargeable battery will be described.

Note that selenium is one of chalcogen elements including sulfur, selenium, tellurium, and the like. The description in this disclosure in relation to selenium applies equally to the remaining elements of the chalcogen, such as sulfur and tellurium.

In the present invention, selenium atoms or molecules are immobilized as elements in their oxidized form (in the charged state in a rechargeable battery) or as selenides in their reduced form (in the discharged state in a rechargeable battery), the selenium atoms being located within the pores of porous carbon, allowing the electrochemical reactions of the rechargeable battery to be properly cycled during the discharge and charge processes. During the discharge process, the elemental selenium atom (neutral Se) at the cathode is reduced and two electrons are obtained to become selenide anions (Se)^2-) Usually as salts, lithium selenide, Li₂Se is present and still located at the cathode. The chemical energy of the discharge process is efficiently converted to electrical energy for the rechargeable battery, with minimal levels of conversion to heat due to the inherent internal resistance of the battery. During the charging process of a rechargeable battery due to Li at the cathode₂The selenide anion in the form of Se is oxidized and loses two electrons to form an elemental selenium atom that remains at the cathode, so electrical energy is also efficiently converted to chemical energy. If selenium is not immobilized in the porous carbon, during the electrochemical reduction/oxidation (redox) process, the intermediate selenium species (usually in the form of polyselenides, Se)_n ^2-) May be formed in the cathode and dissolved in the liquid electrolyte of the battery system. The dissolved intermediate polyselenide species is then transported in a liquid electrolyte from the cathode through the battery separator to the anode where metallic lithium is found, reacting with the metallic lithium atoms and forming a salt composed of lithium and selenium on the surface of the lithium anode. The chemical energy generated by the reaction of lithium and the intermediate selenium species at the anode is converted to heat, rather than electrical energy, which is highly undesirable. In addition, in yangThe selenium salt formed on the electrode can then be converted back to polyselenide anions, even partially, which are then dissolved in the electrolyte of the battery and transported back to the cathode where it consumes additional electrical energy by gaining electrons and is reduced back to elemental selenium. Even though rechargeable batteries may be cycled due to undesirably low cycling efficiency, the conversion of electrochemical energy of selenium to heat or the consumption of additional electrical energy is undesirable. Note that batteries with undesirably low cycling efficiency often do not operate properly for the desired number of cycles.

Thus, the present invention embodies the desirability of immobilizing selenium in a porous carbon skeleton to achieve proper cycling of a rechargeable battery comprising a lithium anode, a selenium cathode, a separator and an electrolyte. Selenium is immobilized in the porous carbon and has an activation energy which in the examples may be 95kJ/mol or more, 98kJ/mol or more, 101kJ/mol or more, 104kJ/mol or more, 107kJ/mol or more, 110kJ/mol or more. The interaction of selenium and carbon in immobilized selenium comprising selenium and porous carbon is often more frequent, having in examples ≥ 2.5X 10⁵、≥3.0×10⁵、≥3.5×10⁵、≥4.0×10⁵、≥4.5×10⁵、≥5.0×10⁵、≥5.5×10⁵、≥6.0×10⁵Or more than or equal to 8.0 multiplied by 10⁵The collision frequency of (1). The kinetic rate constant (at 50 ℃) of immobilized selenium comprising selenium and porous carbon is ≦ 1 × 10 in the examples^-10、≤5×10^-11、≤1×10^-11、≤5×10^-12Or less than or equal to 5X 10^-13. The carbon skeleton plays an important role in the proper immobilization of selenium. Carbon with a certain amount of micropores (pore size of 20 angstroms or less) is desirable to spatially confine selenium within the micropores of the carbon backbone in order to achieve immobilization of selenium with a desired level of activation energy, collision frequency, and kinetic rate constant. The presence of a certain amount of mesopores (pore diameters of 20 to 500 angstroms) and/or macropores (pore diameters greater than 500 angstroms) in the carbon backbone is also desirable for the successful transport of lithium ions into the cathode during the battery discharge process and out of the cathode during the battery charge process, although not critical for the immobilization of selenium. The amount of micropores, mesopores, or macropores is generally characterized by the amount of pore volume (mL) per weight unit (g) of the carbon framework. A high level of pore (including micro-, meso-, and macro-pore) content may be required to spatially confine the high levels of selenium in the porous carbon. The more selenium is loaded into the porous carbon skeleton (per gram basis), the more chemical and electrical energy can be interconverted during the cycling process of the rechargeable battery.

The amount of micropores of the porous carbon used for selenium immobilization may be 0.3mL/g or more, 0.4mL/g or 0.5mL/g or more. The total amount of pores including micropores, mesopores and macropores is not less than 0.4mL/g, not less than 0.5mL/g and not less than 0.6 mL/g. The percentage of micropores in the total pores including micropores, mesopores, and micropores is 50% to 99%, 55% to 97%, and 60% to 95%.

For lithium transport between most electrolytes and locations where selenium is immobilized in micropores, short paths are preferred, while the presence of mesopores and macropores may be important for successful transport of lithium ions in and out to access the selenium immobilized in micropores, allowing the electrochemical process to function properly during the discharge and charge processes of the rechargeable battery. One of the particle sizes of the porous carbon may preferably be small, possibly 5 μm or less, 2 μm or less, 1 μm or less, 0.5 μm or less or 0.2 μm or less; the carbon particles may be relatively large in size, have thin interconnected walls, or may be small relative to the particle as a whole. The size of the porous carbon can be characterized by scanning electron microscopy, transmission electron microscopy, optical microscopy, laser scattering particle size analyzer, and the like.

Selenium is immobilized in the space of micropores of porous carbon particles having pores including micropores, mesopores, and macropores. Selenium is immobilized by strong interactions between selenium and the carbon skeleton within the pores of the porous carbon. Porous carbon with high surface area can have more active sites where selenium interacts with the carbon backbone. The porous carbon preferably has a size of 600m or more²/g、≥800m²/g、≥1,000m²/g、≥1,200m²/g or more than or equal to 1,400m²BET surface area in g.

Selenium is effectively immobilized in porous carbon through chemical interaction of selenium species with the carbon backbone surface. Oxygen-related functional groups in porous carbon may be a key species confirming strong chemical interactions with selenium. This strong chemical interaction may result in efficient immobilization of selenium, leading to an increase in activation energy, a decrease in kinetic rate constants and/or an increase in collision frequency. In order to obtain a desired level of chemical interaction between the backbone carbon atoms and the selenium atoms or molecules, the amount of oxygen-related groups or species in the porous carbon that are the interface between carbon and selenium may need to be sufficiently high so that the immobilization of selenium is effective for a rechargeable battery that can function properly during electrochemical discharge and charge cycles. The amount of oxygen-related species or oxygen functional groups can be characterized by the amount of oxygen content in the porous carbon analyzed by an oxygen analyzer (e.g., a LECO oxygen analyzer). The oxygen content of the porous carbon can also be characterized by other instruments that function similarly to LECO instruments, such as, for example, temperature programmed desorption (or thermogravimetric analysis, or TGA) with gas detectors, such as, but not limited to, mass spectrometry detectors, thermal conductivity detectors, etc., with the option of a comprehensive cold trap mechanism.

The porous carbon for selenium immobilization preferably has an oxygen content of 2% or more, 3% or more, 5% or more, or more preferably 7% or more.

Oxygen species in porous carbon can be classified and characterized by Temperature Programmed Desorption (TPD), typically CO formation₂Oxygen species that form CO and oxygen species that form water. In a stream of an inert gas (e.g. helium, nitrogen or argon) as a carrier gas, a sample of porous carbon is temperature-programmed heated at a defined heating rate to a temperature which can be as high as 1,000 ℃. Oxygen species in the porous carbon sample are destroyed at different temperatures to form CO which is eluted by the carrier gas₂CO and/or water. For porous carbon for selenium immobilization, with CO₂The ratio of the amount of oxygen associated with formation to the amount of oxygen associated with CO formation may be from 0.05 to 0.95, from 0.15 to 0.85, or from 0.2 to 0.8; with CO₂The amount of oxygen forming the correlation may be greater than or equal to 2%, greater than or equal to 3%, greater than or equal to 5%, or more preferably greater than or equal to 7%; the amount of oxygen associated with CO formation may be greater than or equal to 2%, greater than or equal to 3%, greater than or equal to 5%, or more preferably greater than or equal to 7%(ii) a The amount of oxygen associated with water formation may be greater than or equal to 2%, greater than or equal to 3%, greater than or equal to 5%, or more preferably greater than or equal to 7%.

In another aspect, the density of oxygen species of the skeletal carbon (micromoles per square meter, or μmole/m)²) It may be critical to achieve a sufficient level of chemical interaction between the carbon surface and the selenium atoms, resulting in satisfactory immobilization of selenium for proper cycling of the rechargeable battery. The porous carbon for selenium immobilization preferably has the following amounts: not less than 0.8 mu mole/m²、≥1.0μmole/m²、≥1.2μmole/m²、≥1.4μmole/m²Or more preferably 1.6 mol/m or more²The oxygen content of (a); or more than or equal to 0.8 mu mole/m²、≥1.0μmole/m²、≥1.2μmole/m²、≥1.4μmole/m²Or more preferably 1.6 mol/m or more²With CO₂The amount of oxygen formed; or more than or equal to 0.8 mu mole/m²、≥1.0μmole/m²、≥1.2μmole/m²、≥1.4μmole/m²Or more preferably 1.6 mol/m or more²The amount of oxygen associated with CO formation.

The presence of a sufficient amount of oxygen species in the backbone carbon appears to play a key role in the oxidative stability of the Se-C complex. Under ambient conditions, Se-C complexes made from carbon backbones with a small amount of oxygen species appear to be susceptible to oxidation under ambient conditions; this fresh material of Se-C composite shows a temperature-weight behavior similar to Se-C composite with a carbon skeleton with a sufficient amount of oxygen species; however, it has been surprisingly found that Se-C composites prepared with small amounts of oxygen species aged at ambient conditions for about two years to three months show a major exothermic weight loss at temperatures of about 200 ℃ - > 250 ℃, wherein the total weight loss of the Se-C composite exceeds the amount of selenium loaded onto carbon when freshly prepared; in another example, the amount of weight loss at these temperatures appears to correlate well with the amount of carbon backbone in the Se-C complex: the higher the amount of carbon skeleton, the more exothermic weight loss at a temperature of 200 ℃ to 250 ℃; in another example, the oxygen content of an aged (27 month) Se-C composite made with a carbon skeleton with a small amount of oxygen species increases up toAbout 24%; in another example, it is also interesting to note a significant decrease in the density of aged Se-C complexes made from carbon backbones with a small amount of oxygen species. Without limiting the scope or spirit of the invention, exothermic weight loss may be associated with oxidation of carbon-selenium complexes by ambient oxygen species (ambient oxygen and/or moisture at ambient conditions) and/or ambient oxygen species-assisted oxidation of carbon by elemental selenium, both of which result in the formation of oxidized carbon species; oxidation of the Se-C complex may occur near the pore opening of the complex; the newly formed oxidized carbon species near the orifice may form closed pores; then, during density measurement, the probe molecules of helium are not able to access the closed pores, which will result in a decrease of the density of the aged Se-C composite sample made with a carbon skeleton with a small amount of oxygen species. The decomposition products of the oxidized carbon species may be associated with carbon, selenium and/or oxygen, such as carbon dioxide, carbon monoxide, carbon diselenide, carbon selenoxide and the like, at temperatures of 200 ℃ to 250 ℃ under an inert carrier gas (e.g., argon or nitrogen). Note also that the self-supporting carbon skeleton with a small amount of oxygen species is stable under ambient conditions. The carbon and/or selenium in Se-C composites made with a carbon backbone with a small amount of oxygen species appear to be vulnerable to attack by environmental oxygen species along with selenium. This oxidative instability may translate well into poor electrochemical cycling performance of rechargeable batteries of Li-Se; the carbon skeleton may be slowly oxidized by elemental selenium in an electrochemical cycling environment, as in the ambient environment. It is not desirable to form oxidized carbon species in the Se-C complex. Some amount of selenium in the oxidized carbon species may not participate in the electrochemical cycling of the rechargeable battery, resulting in a permanent loss of the specific capacity of the rechargeable battery; the carbon skeleton, in addition to carrying selenium for its immobilization, plays a key role in providing a conductive pathway for (1) transferring electrons from an external circuit to elemental selenium during a discharge process, and (2) transferring electrons from selenium anions (Se) during a charge process^2-) Harvesting to the external circuit. If a portion of the carbon is oxidized by elemental selenium to form oxidized carbon species, the resistivity of the carbon skeleton may increase significantly, thus imparting utility for electricity during each electrochemical cycleThe conductive paths of sub-transport and electron harvesting, ultimately reaching levels at which the rechargeable battery pack does not function properly, do not mention the loss of electrical and chemical energy to heat, which is truly undesirable for rechargeable battery packs in terms of (1) energy inefficiency and (2) thermal management.

In contrast, Se-C complexes made with a carbon backbone with a sufficient level of oxygen species do not show any change in thermo-gravimetric analysis (TGA) behavior between fresh samples and samples aged about two and a half years under ambient conditions; no exothermic weight loss at temperatures of about 200 ℃ and 250 ℃; total weight loss of TGA is similar to the level of selenium loading (by weight) when freshly prepared; the oxygen content did not increase; and the density is not reduced. Thus, Se-C complexes having a carbon backbone with a sufficient amount of oxygen species achieve in some way a satisfactory level of immobilization of selenium by exerting a strong chemical interaction between carbon and selenium with interfacial oxygen species, increasing the oxidative stability of the Se-C complex.

Efficient immobilization of selenium in the carbon backbone can be achieved by the presence of a sufficient amount of oxygen species in the Se-C complex, possibly as an interface species capable of strong chemical interaction between the carbon backbone and selenium (in any chemical form). The amount of oxygen species required in the immobilized selenium carbon composite may depend on the level of oxygen species in the carbon backbone source and the level of selenium loading (by weight) in the Se-C composite. For selenium loadings of 50% or less, the amount of oxygen species in the Se-C complex is greater than or equal to 0.63mmol/g, greater than or equal to 0.94mmol/g, greater than or equal to 1.56mmol/g, or greater than or equal to 2.19 mmol/g; for selenium loadings of 50% to 60% (including 60%), the amount of oxygen species in the Se-C complex is 0.5mmol/g or more, 0.75mmol/g or more, 1.25mmol/g or more, or 1.75mmol/g or more; for selenium loadings of 60% or more, the amount of oxygen species in the Se-C complex is 0.31mmol/g or more, 0.47mmol/g or more, 0.78mmol/g or more, or 1.09mmol/g or more.

Note that a sufficient amount of oxygen species in the Se-C complex is not related to oxygen species involved in the exothermic thermal weight loss at temperatures of 200 ℃ to 250 ℃. Oxygen associated with the exothermic weight loss at temperatures of 200 ℃ to 250 ℃ can be generated very well by post-oxidation of the Se-C complex under ambient conditions by oxygen species such as oxygen and/or moisture in air.

A certain amount of oxygen species in porous carbon is typically generated during the porous carbon manufacturing process, which typically comprises a carbonization process, wherein the precursor is typically converted to carbon at a temperature below 700 ℃, more preferably below 650 ℃, further preferably below 600 ℃, followed by an activation process, wherein the carbon is typically activated to porous carbon at a temperature above 700 ℃, more preferably above 750 ℃, possibly about 800 ℃ or higher. The amount of pores of the porous carbon depends on the degree of activation. With different activating chemicals, e.g. water vapour, CO, by activation temperature and activation time₂Bases (e.g., NaOH, KOH, etc.), salts (e.g., K)₂CO₃、Na₂CO₃、ZnCl₂Etc.) to control the degree of activation. The more severe the activation conditions, the more pores the porous carbon produces. Activation at higher temperatures (e.g., about 1,000 ℃) and/or for a period of time results in porous carbon having a higher level of pores, which is desirable. However, activation at higher temperatures and/or for longer periods of time causes a higher level of oxygen species loss from the porous carbon, resulting in a lower level of oxygen species in the porous carbon, which is undesirable. By activating the porous carbon at a relatively lower temperature and/or for a shorter period of time, higher levels of oxygen species may be retained for the porous carbon, which may result in lower porosity, which is undesirable. The present disclosure contemplates the subject matter of the invention, which relates to the total amount of both pores and the amount of oxygen species of the porous carbon used for selenium immobilization, where a desired high level of selenium loading has a desired high level of immobilization characterized by elevated activation energy, elevated collision frequency, or a reduced level of kinetic rate constant.

As described in the previous paragraph, activation at higher activation temperatures and/or for longer periods of time results in higher levels of oxygen species loss. One of the trade-offs (compositional) may be activated at a relatively low temperature (e.g., about 800 ℃ and lower) and for a relatively long period of time (e.g., 10 minutes or longer). The present invention also implements a post-treatment of the porous carbon having the desired high level of pores resulting from the vigorous activation process, which results in an increase in the amount of oxygen species in the porous carbon. Such oxygen species-enhanced porous carbon then has both the amount of pores and the amount of oxygen species at the desired level, as described in the previous paragraph.

The porous carbon may be post-treated with an oxidant. The oxidizing agent may be an oxygen-containing chemical. The aftertreatment of the porous carbon can be carried out in the liquid or gas phase. The liquid phase post-treatment of the porous carbon may be carried out in an aqueous environment. The liquid phase post-treatment of the porous carbon may also be carried out in an organic solvent which may be hydrophobic or hydrophilic in nature. The liquid phase post-treatment of the porous carbon may also be carried out under salt melting conditions.

The post-treatment of the porous carbon may be carried out at a relatively low temperature, for example in a liquid at the boiling point of the liquid medium or lower. At elevated pressures above atmospheric pressure, the post-treatment temperature may be greater than the atmospheric boiling point of the liquid medium. Under vacuum, the post-treatment temperature may need to be below the atmospheric boiling point of the liquid medium.

The oxidizing agent may be nitric acid, hydrogen peroxide, a persulfate (e.g., ammonium, sodium, or potassium persulfate), a manganese salt, a vanadium salt, a chromium salt, or other transition metal-related element having a high oxidation state that allows for reduction. The oxidizing agent may be oxygen, ozone or an organic peroxide.

The post-treatment of the porous carbon in an aqueous environment can be carried out under acidic conditions, pH neutral conditions or basic conditions.

The post-treated porous carbon can be washed and dried. The dried post-treated porous carbon can be further treated under static conditions (gas flow, more preferably inert gas) at elevated temperatures (e.g.. gtoreq.150 ℃,. gtoreq.200 ℃ or. gtoreq.250 ℃). This heat treatment can rebalance with CO₂Oxygen species associated with formation, oxygen species associated with CO formation and H₂O forms a distribution of oxygen species.

The post-treatment of the porous carbon can increase the amount of oxygen species by more than or equal to 30%, more than or equal to 50%, more than or equal to 100% or more than or equal to 150%.

It may be more desirable to perform selenium immobilization at temperatures that preserve oxygen species that can serve as key sites for enhancing the chemical interaction of selenium and carbon backbone. The temperature at which the selenium is melted into the pores of the porous carbon may be at or above the melting point of selenium. Doping with other elements such as S, Te or some other impurity may lower the melting point of selenium.

Selenium (with or without dopant) may be loaded onto the carbon skeleton by means of impregnation. Selenium may be dissolved in a solvent to form a selenium solution. The selenium solution is then impregnated onto the porous carbon, followed by removal of the solvent by evaporation, leaving the selenium within the porous carbon. This impregnation process may be repeated in order to obtain a sufficient amount of selenium loading. This method can also significantly reduce the temperature of selenium loading onto porous carbon to a level below the melting point of selenium.

The source of porous carbon to produce for selenium immobilization can be from renewable carbon sources such as, but not limited to, biomass such as sugar, glucose, starch, protein, soy flour, nuts, hulls (from nuts, rice, wheat, etc.), fiber and sawdust from trees, or any carbon source naturally associated with. The source that produces the porous carbon for selenium immobilization can be a carbon-containing salt, as described in the previous section. The source that produces the porous carbon for selenium immobilization can be an acid comprising carbon, such as citric acid, gluconic acid, tannic acid. The carbon source may also be derived from chemicals, such as polyols, or polymers (e.g., polyacrylonitrile or polyphenols).

Description of the carbon preparation Process

The carbon materials described herein may be obtained from a preparation process comprising the steps of:

(1) mixing the different components: an inert salt, an activator, and a carbon precursor. The mixing process may include a ball milling process or a freeze drying process of solutions of different ingredients; and

(2) the mixture was carbonized at high temperature under an inert atmosphere, then washed with hot water to remove inorganic salts, and dried to obtain a 3D porous material comprising interconnected curved thin carbon layers.

In step (1), the inert salt may be selected from potassium chloride, sodium chloride or sodium carbonate. The activator may be selected from potassium carbonate, potassium bicarbonate or potassium oxalate. The carbon precursor may be selected from the renewable carbon sources described above. In step (2), the high temperature carbonization may be carried out at 800-; the carbonization time is 1 to 8 hours, desirably 1 to 4 hours.

The invention implements two main processes of manufacturing thin-wall interconnected porous carbon, namely a self-template process and an external template process.

The self-templating process may include the use of salts that contain carbon and may be carbonized, such as potassium citrate, potassium gluconate, potassium tartrate, calcium citrate, sodium citrate, and the like. When the salt is heated, it first undergoes a melting process with decomposition, forming water, carbon dioxide, carbon monoxide, light hydrocarbons and some tar-like viscous and odorous oils that may have oxygenated hydrocarbons (oxygenated hydrocarbons); as the decomposition proceeds, the cations of the original salt may be in a soluble form with newly formed anions of carbonate and/or oxalate and/or other forms of the salt; as the decomposition process continues, supersaturated conditions for the newly formed carbonate, bicarbonate, oxalate and/or other anions begin to build up when the concentration of the newly formed carbonate, bicarbonate, oxalate and/or other anions reaches the saturation point of solubility; note that the supersaturation of the solubility of the salt is thermodynamically quasi-stable; when the point of supersaturation is reached at which no more (or no) kinetic stabilization occurs, it results in crystallization of the newly formed salts of carbonate, bicarbonate, oxalate and/or other anions. Organic carboxylic acid salts containing hydroxyl groups (e.g., potassium citrate, potassium gluconate, potassium tartrate, etc.) can be crystallization inhibitors; such crystallization inhibitors allow higher levels of supersaturation to be established, which typically results in large numbers of crystallites of smaller size. The particle size of the newly crystallized carbonate, bicarbonate or any other form can be very uniform. As the temperature increases and/or time progresses, the decomposition proceeds and the viscosity of the melt may become higher, which may uniformly coat the surface of newly formed crystallites of carbonate, bicarbonate, oxalate, and/or other forms of salt. The carbon then eventually solidifies on the surface of the newly formed crystallites. This carbon templating process is described in this disclosure as a self-templating process, a carbonization process. The temperature of the self-templating process may be less than 700 ℃. This self-templating process may be performed by heating at a constant rate or a varying heating rate. The self-templating process may also be performed by keeping the heating temperature constant (or referred to as incubation) at a temperature of less than 700 ℃ or less.

As the temperature increases, the newly formed, self-templated, three-dimensionally interconnected thin-walled carbon undergoes an activation process by way of the newly formed crystallites as an activating chemical. For example, the activation process may be substantially based on carbon and newly formed crystallites (e.g., K)₂CO₃(from potassium citrate as feedstock), K₂CO₃+C→K₂O +2CO), which occurs at about 700 ℃ or higher. Consumption of carbon can lead to the creation of pores (particularly micropores) in the carbon, leading to the formation of three-dimensional interconnected thin-walled porous carbon. The activation temperature may be as high as 1,100 ℃. The rate of temperature rise can range from less than 1 deg.C/min up to 100 deg.C/min. An inert carrier gas stream, such as nitrogen or argon, may be used in the porous carbon manufacturing process. Reactive gases (e.g. CO)₂And steam) may also be used alone or in combination during activation and activation.

There may be additional or secondary reactions of the pores that may contribute to the production of carbon. Some of these reaction processes may include: i) by CO generated during the carbonization and/or activation process₂Gasification of carbon, ii) reduction of metal oxides (e.g. K) by carbon₂O + C → CO +2K), iii) embedding certain newly formed metal species (e.g., K) into the carbon layer, or iv) cation-related catalytic effects, which are particularly relevant in the case of potassium. As a result of unreacted K slowly taking place at temperatures greater than 800-850 deg.C₂CO₃(K₂CO₃→K₂O+CO₂) CO produced by decomposition of₂As a result of (3), gasification of carbon (C + CO)₂2CO) is particularly relevant.

The foreign templating process can include the use of foreign particles, such as activators (e.g., salts of alkali metals and carbonates (e.g., K)₂CO₃) Alkali metal hydroxide (e.g., KOH)), optionally along with an inert salt (e.g., KCl, NaCl, etc.) to create a large number of pores from the carbon source. Can be used forThe foreign particles are mixed with the carbon source either before or after carbonization, more preferably before the carbonization step. Such mixing of the foreign particles and carbon source can be achieved by physical blending, optionally followed by mechanical milling, or by recrystallization of the carbon source from an aqueous solution, aqueous slurry, or counterpart using an organic liquid medium, along with the foreign particle's chemistry. The drying process for the recrystallization process may be performed by evaporation, air drying, oven drying, spray drying, or freeze drying.

When the mixture is heated in an external templating process, carbonization-activation of the carbon source occurs on the salt template particles, similar to that described in the previous paragraph regarding the self-templating process. During the carbonization process, as the temperature increases and time progresses, the carbon source may melt and undergo decomposition in some manner, forming by-products, such as CO₂CO, water, light hydrocarbons and some viscous and sticky heavy hydrocarbons. The melt viscosity may increase and the melt may eventually coat and solidify on the surface of the foreign particle, forming an interconnected thin-walled carbon coating on the surface of the foreign particle. As the temperature continues to rise, the activation process begins and pores are created, which may be based essentially on high temperature redox reactions, such as K₂CO₃+C→K₂O +2CO, which occurs at a temperature of about 700 ℃ or higher.

For example, when the foreign particle optionally comprises an inert salt (e.g., KCl), the chemical (e.g., K) is activated₂CO₃) From 891 ℃ to, for example, about 630 ℃. Due to the formation of KCl-K at a temperature of about 630 DEG C₂CO₃Liquid phase systems, activation of interconnected thin-walled carbon can be significantly accelerated, possibly due to K₂CO₃Enhanced reactivity with carbonized products (interconnected thin-walled carbon), possibly through activating chemicals (e.g. K)₂CO₃In this case) to the surface of the interconnecting thin-walled carbon. This may indicate that a foreign templating process with foreign particles comprising an activation chemical and optionally an inert salt may indeed be a more feasible strategy to achieve synthesis of three-dimensionally interconnected thin-walled porous carbon with sufficient amount of pores while retaining sufficient amount of poresThe amount of oxygen-containing species (activated under less severe conditions, i.e. at lower activation temperatures). Meanwhile, the surface of the carbon surface can be coated with molten KCl-K₂CO₃Liquid phase separation, by possibly limiting the CO formed₂Diffusion of gas molecules to the surface of solidified three-dimensionally interconnected thin-walled porous carbon to prevent formation of CO₂And the formation of the interconnected thin-walled porous carbon, which is desirable for obtaining higher yields of interconnected thin-walled porous carbon. In addition, "monolithic" fused KCl-K₂CO₃The liquid phase may also limit gas diffusion of out-gassing gases (e.g., carbon volatiles), which may lead to the possibility of their redeposition on the three-dimensional interconnected thin-walled porous carbon, and increase the yield of the interconnected thin-walled porous carbon, which is desirable.

Example 14. three-dimensional interconnected thin-walled porous carbon nanomaterials: preparation and characterization of carbon- -by external template ₂ ₃The process: aqueous mixtures of freeze-dried carbon sources (e.g., glucose), activating chemicals (e.g., KCO), and optionally inert salts (e.g., KCl) A compound (I) is provided.

Adding appropriate amount of KCl and K₂CO₃And glucose in distilled water, the solution was frozen with liquid nitrogen (-196 deg.C), then transferred to a freeze dryer and freeze dried at a temperature of-50 deg.C and a pressure of 0.06mbar to yield KCl, K₂CO₃And glucose. The solid mixture was then carbonized at 850 ℃ for 1 hour under an inert atmosphere and cooled to room temperature, followed by washing with hot distilled water, filtration and drying to give the three-dimensionally interconnected thin-walled porous carbon nanomaterial shown in fig. 20.

The surface area of the three-dimensional interconnected thin-walled porous carbon nanomaterial derived from glucose was measured to be 2,316m²(ii)/g, total pore volume 1.04cm³A volume of micropores of 0.90 cm/g³(ii) g, having about 86% of the pores described as microporous and about 14% of the pores described as mesoporous and macroporous. FIG. 21 shows N of three-dimensional interconnected thin-walled porous carbon nanomaterials₂Adsorption isotherms and pore size distributions.

In another example, soybeans are usedThe powder can be used to replace glucose. As can be seen in fig. 22, the macrostructure of the three-dimensionally interconnected thin-walled porous carbon nanomaterial derived from soy flour is similar to the macrostructure derived from glucose. However, this material has 2,613m²Surface area per g, 1.42cm³Pore volume per g and 1.0cm³Micropore volume, in g, has about 70% of the pores described as micropores and about 30% of the pores described as mesopores and macropores. N of this material₂The adsorption isotherms and pore size distributions are shown in figure 23. The amount of mesopores of this soy flour-derived material is higher than the amount of mesopores of the glucose-derived material.

TABLE 5

Table 5 above shows the results obtained by targeting the precursors; an activator/templating agent; precursor/activator/templating agent weight ratio; and a plurality of different examples of three-dimensional interconnected thin-walled porous carbon nanomaterials prepared from foreign templates of different combinations of carbonization ratios; different combinations leading to the indicated textural properties and chemical composition, where V_BETApparent surface area; v_pTotal pore volume; and V_microMicropore volume.

Example 15: three-dimensional interconnected thin-wall porous carbon nanomaterial: preparation and performance of the capacitor.

The three-dimensional interconnected thin-walled porous carbon nanomaterial of example 14 can be used as an electrode in an electrochemical capacitor. The electrode comprises an organic binder, which may be, for example, PTFE or PVDF. Alternatively, the electrode further comprises a conductivity promoter, such as carbon black, graphene, carbon nanotubes, and the like. In a typical example, a mixture of 85 wt% active material, 10 wt% binder, and 5% conductivity promoter is prepared.

The method of making the electrode may comprise preparing slurries of the different components or a dry mixture thereof in a mortar. The slurry may be coated on a current collector or may be formed into a self-supporting electrode, such as a disk electrode. The electrodes may then be pressed or roll-milled prior to their use in electrochemical capacitors.

Symmetric electrochemical capacitors can be assembled using the above-described electrodes. Two electrodes of the same mass and thickness may be used. The current collector may be made of gold, stainless steel, aluminum, nickel, etc., depending on the electrolyte used.

The electrolyte may be an acidic aqueous solution (e.g., sulfuric acid or chloric acid), an alkaline solution (e.g., sodium hydroxide or potassium hydroxide), a salt (e.g., lithium sulfate, sodium sulfate, potassium sulfate, etc.); the electrolyte may be an organic solution, such as an organic salt, for example, tetramethylammonium tetrafluoroborate, tetraethylammonium tetrafluoroborate, tetrabutylammonium tetrafluoroborate, and the like, or an organic solution, such as an ionic liquid, for example, 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide, 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl) imide, and the like, or a pure ionic liquid as mentioned above.

Electrochemical capacitors can be charged at 0.2A/g, 0.5A/g, 1A/g, 5A/g, 10A/g, 20A/g, 50A/g, or faster. The assembled electrochemical capacitors were tested by using a computer controlled potentiostat. The tests consisted of cyclic voltammetry experiments (CV), electrochemical impedance spectroscopy studies (EIS), and galvanostatic charge/discharge (CD) cycling tests. Cell voltages can be up to 1V in acid or alkaline solutions, up to 1.5V in saline solutions, and up to 3V in organic and ionic liquid electrolyte solutions.

In the example, 1M H was used₂SO₄The solution of (2) is used as an electrolyte. Three-dimensional interconnections derivatized with glucoseElectrochemical capacitors made with thin-walled porous carbon nanomaterials (referred to as glucose-based) had a cell capacity of 57F/g at 0.2A/g, and electrochemical capacitors made with three-dimensionally interconnected thin-walled porous carbon nanomaterials based on soy flour (referred to as soy flour-based) had a capacity of 60F/g. Under the condition of the super-large current density of 110A/g, the battery capacity is respectively 24F/g and 31F/g.

In another example, 1M H was used₂SO₄The solution of (2) is used as an electrolyte. The glucose-based electrochemical capacitor had a cell capacity of 37F/g at 0.2A/g and the soy flour-based electrochemical capacitor had a cell capacity of 39F/g. At a current density of 20A/g, the battery capacities were 25F/g and 29F/g, respectively.

In another example, a solution of EMImTFSI in acetonitrile (1: 1 wt%) was used as the electrolyte. The glucose-based electrochemical capacitor had a battery capacity of 36F/g at 0.2A/g and the soy flour-based electrochemical capacitor had a battery capacity of 39F/g. At a current density of 30A/g, the battery capacities were 28F/g and 30F/g, respectively.

The Ragone-like curves for electrochemical capacitors with different electrolytes are shown in the graph X8. The robustness of the electrochemical capacitor was tested by long-term cycling at 5-10A/g over 5,000 cycles.

Example 16 three-dimensional interconnected thin-walled porous carbon nanomaterials: by an extrinsic template process, mixing (optionally followed by grinding) ₂ ₃Mill) carbon source (e.g., sugar, glucose, soy flour or sawdust), activating chemical (e.g., KCO) and optionally inert salt (e.g., KCl) And (4) preparing carbon.

Weighing appropriate amount of carbon source (such as sugar, glucose, soybean flour, sawdust (such as pine sawdust, cherry sawdust or oak sawdust)), activating chemical (such as K)₂CO₃) And optionally an inert salt, into a vessel followed by physical mixing, which may include mechanical milling, followed by transfer into a crucible, which may be made of ceramic, steel, stainless steel, or the like. Heating the mixture, optionally to a holding temperature equal to or less than 700 ℃, at a ramp rate of less than 100 ℃/min, under a flow of inert gas (which is also optional)For a period of time for carbonization, or directly heated to an activation temperature equal to or greater than 700 ℃, and held at that temperature for a period of time for activation. In the whole temperature rising process, the carbon source is decomposed into CO and CO₂Water, light and heavy hydrocarbons and viscous oil hydrocarbons. During the activation process, CO formation can continue₂Water and carbon volatiles.

After activation, the mixture is mixed with water and optionally neutralized with an acid (e.g., hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc.). The carbon slurry is then filtered and washed with water to a level having a low level of conductivity, e.g., less than 5,000 μ S/cm, less than 3,000 μ S/cm, less than 1,000 μ S/cm, and optionally washed with deionized or distilled water to a conductivity of less than 300 μ S/cm, less than 100 μ S/cm, or even less than 50 μ S/cm. The filter cake can be dried in an oven to dry off the water.

Then oxygen content, SEM, XRD, Raman, TGA-DSC, N₂And CO₂The BET surface area and the pore size distribution characterize the obtained three-dimensional interconnected thin-wall porous carbon nano material.

Table 5 below shows elemental analyses of three-dimensionally interconnected thin-walled porous Carbon nanomaterials, e.g., 237-8 (self-templated Carbon synthesized from potassium citrate), 237-51A (self-templated Carbon synthesized from potassium citrate), SKK2 (exotic templated Carbon), comparative commercial carbons, e.g., Elite C available from Calgon Carbon of Pittsburgh, Pennsylvania, USA; YP-50 available from Kruray co.ltd of Osaka, Japan; ketjen carbon black available from Lion Specialty chemicals co. ltd. of Tokyo, Japan; maxsorb available from Kansai cook and Chemicals co.ltd.of hydroog, Japan.

TABLE 6

Table 6 above shows two sets of carbons, one set being three-dimensionally interconnected thin-walled porous carbon nanomaterials, such as 237-8 (self-templated carbon synthesized from potassium citrate), 237-51A (exogenous templated carbon from glucose), 237-. XRD studies showed that the carbon materials in the table above were all amorphous. Raman studies show that the carbon materials in the above table are also amorphous in nature, showing amorphous carbon characteristic raman scattering at both the D and G peaks.

And then the prepared interconnected thin-wall porous carbon is used for preparing selenium immobilization. As previously described, the immobilized selenium of the present invention is obtained by mixing together appropriate amounts of selenium and carbon, followed by melting the selenium into interconnected thin-walled porous carbon in the presence of elevated levels of oxygen species; please refer to the previous description of the method for preparing immobilized selenium in the present disclosure. The immobilized selenium is then characterized by oxygen content analysis, XRD, raman, SEM, TGA-DSC, and the like.

Analysis of the oxygen content of immobilized selenium in three-dimensional interconnected thin-walled porous carbon nanomaterials with greater than 1.5 wt.%, greater than 2.0 wt.%, greater than 3 wt.%, or greater than 4.0 wt.%, compared to immobilized carbon-selenium composites prepared with commercial carbons having an oxygen content of less than 1.5%, less than 2.0 wt.%, less than 3 wt.%, or less than 4.0 wt.%.

TABLE 7

Table 7 above shows two different groups of immobilized selenium, one group (referred to as group I, i.e., Ketjen 600JD, 237-8, 237-51A, 237-67, 237-101D and SKK-2) having an oxygen content of about half the oxygen content of the three-dimensionally interconnected thin-walled porous carbon nanomaterials of 1% to 10%, 1.5% to 9%, or 2% to 8%, and the other group (referred to as group II, i.e., Elite C and Maxsorb MSP20X) having an oxygen content of at least five times, or greater than 8%, greater than 9%, or greater than 10%, the oxygen content of the carbon. Note that Ketjun carbon is a non-porous carbon, the carbon-selenium complex of which is considered to be non-immobilized selenium; therefore, its oxygen content remains very low, less than 1%.

The oxygen species in group I immobilized selenium can play a key role in the immobilization of selenium as an interfacial chemical group, allowing for strong interactions between carbon and selenium, resulting in a tighter packing of selenium atoms or species within the pores of the three-dimensionally interconnected thin-walled porous carbon nanomaterials, as evidenced by the enhanced collision frequency shown in the examples of the present disclosure. This interaction between the carbon backbone and the selenium atom or selenium chemical may further demonstrate higher intrinsic density.

For example, samples of immobilized selenium prepared from three-dimensionally interconnected thin-walled porous carbon nanomaterials (e.g., self-templated carbon synthesized from potassium citrate) have a carbon to selenium weight ratio of 50-50 (by weight). Surprisingly, it was found that the density was 3.42g/cm³. Note that selenium has a density of 4.819g/cm³The density of (c). By using 4.819g/cm³The carbon density in the immobilized selenium composite was calculated to be about 2.8g/cm³. Note also that the diamond had a 3.5g/cm³(ii) a density of (d); the graphite has a density of about 2.3g/cm³(ii) a density of (d); and the amorphous carbon has about 2.0g/cm³Typical density of (a).

The immobilized selenium is then used to make the cathode of a rechargeable battery by mixing the appropriate amount of immobilized selenium, aqueous or organic medium, and at least one binder, as previously described, and then coated onto a charge collector (e.g., aluminum foil) to produce a cathode comprising immobilized selenium. Please refer to the previous description of the method for preparing a cathode comprising immobilized selenium in the present disclosure.

The resulting cathode comprising immobilized selenium is then used to assemble a rechargeable battery with an anode (e.g., lithium), separator, electrolyte. Please refer to the previous description of assembling a rechargeable battery comprising a cathode comprising immobilized selenium in the present disclosure.

The resulting carbon samples can be further used in the electrode manufacturing process for capacitors or rechargeable batteries.

The embodiments have been described with reference to the accompanying drawings. Modifications and alterations will occur to others upon reading and understanding the preceding embodiments. Therefore, the foregoing embodiments should not be construed as limiting the present disclosure.

Claims

1. A method of preparing an immobilized selenium host comprising:

(a) forming a mixture of selenium, carbon and oxygen;

(b) heating the mixture of step (a) to a temperature above the melting temperature of selenium; and

(c) cooling the heated mixture of step (b) to ambient or room temperature, thereby forming the immobilized selenium body.

2. The method of claim 1, wherein the carbon is one of self-templating carbon or extrinsic-templating carbon.

3. The method of claim 1, wherein the amount of oxygen in the mixture is 0.63 mmoles/g or more for 50% or less selenium loading in the carbon.

4. The method of claim 1, wherein the amount of oxygen in the mixture is 0.5mmol/g or more for a selenium loading in the carbon of 50% (excluded) to 60% (included) (i.e., 50% < selenium loading ≦ 60%).

5. The method of claim 1, wherein the amount of oxygen in the mixture is 0.31mmol/g or more for 60% or more selenium loading in the carbon.

6. The method of claim 1, further comprising, prior to step (a), activating the carbon to form pores in the carbon.

7. The method of claim 5, further comprising combining or mixing the activated carbon with an oxidant.

8. The method of claim 7, wherein the oxidizing agent comprises at least one of:

nitric acid;

hydrogen peroxide;

an organic peroxide;

oxygen; and/or

Ozone.

9. The method of claim 7, wherein the oxidizing agent comprises at least one of the following in an aqueous environment:

ammonium persulfate;

sodium persulfate;

potassium persulfate;

a manganese salt;

vanadium salts, and/or

A chromium salt.

10. The method of claim 1, wherein the self-templated carbon is prepared by a process comprising:

carbonizing a salt by melting until an anion in the melt is supersaturated to form a crystalline salt in the melt;

increasing the viscosity of the melt until the melt coats the surface of the crystallites of the crystalline salt; and

solidifying the carbon in the melt on the surface of the crystallites.

11. An immobilized selenium body comprising a mixture of:

selenium;

carbon; and

oxygen.