CN108899486B - Sulfur electrolyte-coated positive electrode active material and preparation method thereof, and all-solid-state lithium sulfur battery and preparation method thereof - Google Patents

Sulfur electrolyte-coated positive electrode active material and preparation method thereof, and all-solid-state lithium sulfur battery and preparation method thereof Download PDF

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CN108899486B
CN108899486B CN201810614217.XA CN201810614217A CN108899486B CN 108899486 B CN108899486 B CN 108899486B CN 201810614217 A CN201810614217 A CN 201810614217A CN 108899486 B CN108899486 B CN 108899486B
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solid
active material
electrolyte
positive electrode
sulfur
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CN108899486A (en
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韩喻
姜会泽
王珲
郭青鹏
郑春满
洪晓斌
李宇杰
谢凯
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National University of Defense Technology
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/581—Chalcogenides or intercalation compounds thereof
    • H01M4/5815—Sulfides
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention discloses a positive active material coated with a sulfur electrolyte, a preparation method thereof, an all-solid-state lithium sulfur battery and a preparation method thereof, wherein the positive active material comprises Li2S and coating with Li2Li of S surface3PS4Or Li10GeP2S12. The preparation method comprises the preparation of P2S5Powder, GeS2Powder; mixing these powders with Li2Mixing and ball-milling S powder; and (6) heat treatment. An all-solid-state lithium-sulfur battery includes a positive electrode layer made of a positive electrode active material coating a sulfur-based electrolyte and a conductive carbon material. The all-solid-state lithium-sulfur battery is manufactured by a cold isostatic pressing method. The positive active material coated with the chalcogenide electrolyte has the advantages of good electrochemical stability, high ionic conductivity, good interface contact property and the like, and is a promising positive active material. The all-solid-state lithium-sulfur battery has the advantages of high utilization rate of active substances, good cycling stability, high safety performance and the like, and is a novel all-solid-state lithium battery with extremely high use value.

Description

Sulfur electrolyte-coated positive electrode active material and preparation method thereof, and all-solid-state lithium sulfur battery and preparation method thereof
Technical Field
The invention belongs to the field of all-solid-state lithium sulfur batteries, and relates to a sulfur electrolyte-coated positive electrode active material and a preparation method thereof, and an all-solid-state lithium sulfur battery and a preparation method thereof.
Background
With the development of human society, the demand for energy is becoming more and more urgent. Most of the traditional energy sources used in production and life of people are non-renewable energy sources, and can cause adverse effects on the environment in use. Therefore, environmental and energy problems are two major hot problems that people face and are urgently to solve for the twenty-first century.
The lithium ion battery is used as a low-carbon green new energy, has been widely applied to portable equipment such as mobile phones, notebook computers and cameras by virtue of the characteristics of large energy density, no memory effect, long cycle life and the like, and has a huge application prospect in the fields of electric automobile power supplies, energy storage power grids and the like. Currently, the major share of the lithium ion battery market is occupied by lithium ion batteries based on organic liquid electrolytes, but potential safety issues restrict their wider application. The solid electrolyte is used to replace organic liquid electrolyte, so that the safety performance of the lithium battery can be greatly improved, and the lithium battery can be applied to wider fields. In the existing all-solid-state lithium-sulfur battery, the solid-state lithium-sulfur battery composite positive electrode is generally formed by mechanically mixing an active substance, a solid electrolyte and carbon, the utilization rate of the active substance is low, and interface separation is easily caused by the volume change of the active substance in the circulation process, so that the circulation performance of the battery is directly influenced.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provides a positive electrode active material coated with a chalcogenide electrolyte and having good electrochemical stability, high ionic conductivity and good interface contact and a preparation method thereof, and also provides an all-solid-state lithium-sulfur battery with high utilization rate of active substances, good cycling stability and high safety performance and a preparation method thereof.
In order to solve the technical problems, the invention adopts the following technical scheme:
the positive active material coated with the sulfur-based electrolyte comprises a positive active material, wherein the surface of the positive active material is coated with the sulfur-based solid electrolyte; the positive electrode active material is Li2S; the sulfur-based solid electrolyte is Li3PS4Or Li10GeP2S12。
In the positive electrode active material coated with the sulfur-based electrolyte, the mass ratio of the positive electrode active material to the sulfur-based solid electrolyte is further improved to be 0.55-4: 1.
As a general technical concept, the present invention also provides a method for preparing the above-described positive active material coated with the chalcogenide electrolyte, comprising the steps of:
s1, mixing P2S5、GeS2Ball milling is respectively carried out to obtain P2S5Powder, GeS2Powder;
s2, P obtained in step S12S5Powder or P2S5And GeS2Mixed powder of (2), with Li2Mixing S powder and performing ball milling;
and S3, carrying out heat treatment on the product subjected to ball milling in the step S2 to obtain the positive electrode active material coated with the sulfur electrolyte.
In the above method for preparing a positive electrode active material coated with a chalcogenide electrolyte, the ball milling is performed under the protection of argon atmosphere in step S1; the rotation speed of the ball mill is 380 rpm-510 rpm; the ball milling time is 3-5 h; and in the ball milling process, ball milling is carried out for 40min, and standing and cooling are carried out for 20 min.
In the above method for preparing a positive electrode active material coated with a chalcogenide electrolyte, the ball milling is performed under the protection of argon atmosphere in step S2; the rotation speed of the ball mill is 380 rpm-510 rpm; the ball milling time is 5-20 h; and in the ball milling process, ball milling is carried out for 40min, and standing and cooling are carried out for 20 min.
In the above preparation method of the positive electrode active material coated with the chalcogenide electrolyte, the temperature rise rate in the heat treatment process is further improved to 5 ℃/min to 10 ℃/min in the step S3; the temperature of the heat treatment is 240-280 ℃; the time of the heat treatment is 0.5 to 3 hours.
As a general technical concept, the present invention also provides an all-solid-state lithium sulfur battery, comprising a positive electrode layer, a solid electrolyte layer and a negative electrode layer, wherein the solid electrolyte layer is arranged between the positive electrode layer and the negative electrode layer, and the positive electrode layer comprises an all-solid-state lithium sulfur battery composite positive electrode material made of the above-mentioned chalcogenide electrolyte-coated positive electrode active material and a conductive carbon material.
In the all-solid-state lithium sulfur battery, the positive electrode layer is further improved, and the positive electrode layer comprises the following components in percentage by mass:
20 to 30 percent of conductive carbon material,
70-80% of positive active material coated with sulfur electrolyte.
In the all-solid-state lithium-sulfur battery, the conductive carbon material is at least one of acetylene black, superconducting carbon, graphene, carbon nanotubes, carbon nanofibers and activated carbon; the negative electrode layer contains a negative electrode active material; the negative active material is at least one of a metal lithium sheet and an indium lithium alloy sheet; the solid electrolyte layer is an all-solid-state sulfide electrolyte material; the all-solid-state sulfide electrolyte material is Li3PS4Or Li10GeP2S12。
In the all-solid-state lithium-sulfur battery, the thickness of the positive electrode layer is further improved to be 0.1-50 μm; the thickness of the solid electrolyte layer is 100-1000 μm.
As a general technical concept, the present invention also provides a method for preparing the above all-solid-state lithium-sulfur battery, comprising the steps of:
(1) cold press molding the all-solid-state sulfide electrolyte material to prepare a solid-state electrolyte layer;
(2) placing the composite positive electrode material of the all-solid-state lithium-sulfur battery on one side of the solid electrolyte layer obtained in the step (1) for cold press molding to obtain a positive electrode layer/solid electrolyte layer material;
(3) and (3) taking the solid electrolyte layer as an intermediate layer, and placing the negative electrode active material on the other side of the solid electrolyte layer in the positive electrode layer/solid electrolyte layer material obtained in the step (2) for cold press molding to obtain the all-solid-state lithium-sulfur battery.
In the above method for preparing an all-solid-state lithium-sulfur battery, the all-solid-state sulfide electrolyte material is prepared by the following steps in step (1): under the protection of argon atmosphere, adding P2S5Powder or P2S5And GeS2Mixed powder of (2) with Li2Mixing S powder, ball-milling for 5-20 h at the rotation speed of 380-510 rpm, ball-milling for 40min each time in the ball-milling process, and standing and cooling for 20 min; carrying out heat treatment on the product obtained after ball milling at 240-280 ℃ for 0.5-3 h to obtain an all-solid sulfide electrolyte material; the pressure in the cold press molding process is 191-637 MPa.
In the above method for preparing an all-solid-state lithium-sulfur battery, the step (2) is further improved, wherein the all-solid-state lithium-sulfur battery composite cathode material is prepared by the following method: mixing the positive electrode active material coated with the sulfur electrolyte and the conductive carbon material, and ball-milling for 1-5 h at the rotating speed of 380-510 rpm to obtain the all-solid-state lithium-sulfur battery composite positive electrode material; the pressure in the cold press molding process is 191-637 MPa.
In the above preparation method of the all-solid-state lithium-sulfur battery, the pressure in the cold press molding process in the step (3) is further improved to 128MPa to 255 MPa.
In the preparation method of the positive active material coated with the sulfur-based electrolyte, when the raw material is P2S5And GeS2When mixing the powders of (1), GeS2And P2S5The molar ratio of (A) is less than or equal to 1.
Compared with the prior art, the invention has the advantages that:
(1) the invention provides a positive active material coated with a chalcogenide electrolyte, which comprises a positive active material and a chalcogenide solid electrolyte coated on the surface of the positive active material, wherein the positive active material is Li2S, the sulfur-based solid electrolyte is Li3PS4Or Li10GeP2S12. According to the invention, the surface of the positive active material is coated with the sulfur-based solid electrolyte, so that the interface between the positive active material and the sulfur-based solid electrolyte is changed from a solid physical interface to a chemical interface, thereby improving the interface contact performance and solving the problem of interface separation caused by volume change of the active material in the circulation process; meanwhile, when the positive electrode active material coated with the sulfur electrolyte is used for preparing the all-solid-state lithium sulfur battery, the utilization rate and the cycle performance of the active material of the all-solid-state lithium sulfur battery can be improved. Therefore, the positive electrode active material coated with the chalcogenide electrolyte has the advantages of good electrochemical stability, high ionic conductivity, good contact property of an interface (the interface refers to the interface of the positive electrode active material and the coated chalcogenide electrolyte) and the like, and is a promising positive electrode active material.
(2) In the positive active material coated with the sulfur-based electrolyte, the mass ratio of the positive active material to the sulfur-based solid electrolyte is 0.55-4: 1, and the mass ratio of the positive active material to the sulfur-based solid electrolyte is optimized, so that the utilization rate of the active material in the charging and discharging process is improved, and the total energy density is improved.
(3) The invention also provides a preparation method of the cathode active material coated with the chalcogenide electrolyte, which is characterized in that the chalcogenide solid electrolyte and the cathode active material are used as raw materials, the chalcogenide solid electrolyte is coated on the surface of the cathode active material by ball milling, heat treatment and other methods, namely the chalcogenide solid electrolyte is generated on the surface of the cathode active material through in-situ chemical reaction, so that the cathode active material coated with the chalcogenide electrolyte, which has the advantages of good electrochemical stability, high ionic conductivity and good interface contact property, is prepared, has the advantages of simple process conditions, simple operation, low cost and the like, is suitable for large-scale preparation, and is beneficial to industrial production.
(4) The invention also provides an all-solid-state lithium-sulfur battery, which comprises a positive electrode layer, a solid electrolyte layer and a negative electrode layer, wherein the solid electrolyte layer is arranged between the positive electrode layer and the negative electrode layer, and the positive electrode layer comprises an all-solid-state lithium-sulfur battery composite positive electrode material which is prepared from a positive electrode active material coated with a chalcogenide electrolyte and a conductive carbon material. According to the invention, the all-solid-state lithium-sulfur battery is prepared on the basis of the positive active material coated with the sulfur-based electrolyte, and the sulfur-based solid-state electrolyte in the positive active material coated with the sulfur-based electrolyte is coated on the surface of the positive active material, so that an interface between the positive active material and the sulfur-based solid-state electrolyte is converted from a solid-solid physical interface into a chemical interface, the utilization rate of the positive active material can be effectively improved in the charging and discharging process, the energy density of the battery is improved, and meanwhile, the problem of interface separation caused by volume change of the active material in the circulating process can be improved in the circulating process, so that the circulating performance of the all-solid-state lithium-sulfur battery is improved. Therefore, the all-solid-state lithium sulfur battery based on the positive active material coated with the sulfur electrolyte can meet the requirements of the all-solid-state lithium sulfur battery on the conductivity and ion conduction of the positive material, can improve the utilization rate of the active substance and the problem of the interface between the active substance and the solid electrolyte in the composite positive material, has the advantages of high utilization rate of the active substance, good cycle stability, high safety performance and the like, and is a novel all-solid-state lithium battery with extremely high use value.
(5) The invention also provides a preparation method of the all-solid-state lithium-sulfur battery, the all-solid-state lithium-sulfur battery with high utilization rate of active substances, good cycle stability and high safety performance is prepared by adopting a cold isostatic pressing method, and the all-solid-state lithium-sulfur battery has the advantages of simple process conditions, simple operation, low cost and the like, is suitable for large-scale preparation, and is beneficial to industrial production.
Drawings
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention.
Fig. 1 is an SEM image of a sulfur-based electrolyte coated cathode active material (a 3) prepared in example 1 of the present invention.
Fig. 2 is an XRD spectrum of the sulfur electrolyte-coated positive active material (a 3) prepared in example 1 of the present invention.
Fig. 3 is an XRD spectrum of the positive electrode active material coated with a chalcogenide electrolyte prepared at different heat treatment temperatures in example 1 of the present invention.
Fig. 4 is a graph showing the change in conductivity with temperature of the sulfur-based electrolyte-coated positive electrode active material (a 2) prepared in example 1 of the present invention.
Fig. 5 is a graph showing ion conductivity spectra of the positive electrode active material coated with a chalcogenide electrolyte prepared at different heat treatment temperatures in example 1 of the present invention.
Fig. 6 is a voltage-specific capacity graph of the all solid-state lithium sulfur battery (a) prepared in example 2 of the present invention and the all solid-state lithium sulfur battery (b) prepared in comparative example 2.
Detailed Description
The invention is further described below with reference to the drawings and specific preferred embodiments of the description, without thereby limiting the scope of protection of the invention.
The materials and equipment used in the following examples are commercially available. The experimental methods in the examples, in which specific conditions are not specified, were selected according to the conventional methods and conditions, or according to the commercial instructions. Unless otherwise specified, the data obtained in the following examples are the average of three or more repeated experiments.
Example 1
The positive active material coated with the chalcogenide electrolyte comprises a positive active material and the chalcogenide solid electrolyte coated on the surface of the positive active material, wherein the positive active material is Li2S, the sulfur-based solid electrolyte is Li3PS4。
In this example, the mass ratio of the positive electrode active material to the sulfur-based solid electrolyte was 0.82: 1.
A method for producing the above-described positive electrode active material coated with a sulfur-based electrolyte in the present example, comprising the steps of:
(1) taking P under the protection of argon atmosphere2S5Adding into a high-energy ball milling tank, ball milling for 3h at the rotation speed of 450rpm, wherein ball milling is carried out for 40min every time in the ball milling process, standing and cooling for 20min to obtain P2S5And (3) powder.
(2) Under the protection of argon atmosphere, according to Li2S、P2S5In a molar ratio of 90.5: 9.5, Li is weighed separately2S powder and P obtained in step (1)2S5Powder; placing the materials in a high-energy ball milling tank for mixing, ball milling for 8h at the rotating speed of 510rpm, wherein ball milling is carried out for 40min every time in the ball milling process, standing and cooling for 20min, and obtaining mixed powder.
(3) Transferring the product (mixed powder) obtained after ball milling in the step (2) into a tube furnace, heating to 240 ℃, 250 ℃, 260 ℃, 270 ℃ and 280 ℃ respectively at a heating rate of 5 ℃/min under the protection of argon atmosphere, and carrying out heat treatment for 1h at different temperatures to obtain the positive electrode active materials coated with the chalcogenide electrolyte prepared at different temperatures, wherein the positive electrode active materials coated with the chalcogenide electrolyte, which are corresponding to the heat treatment temperatures of 240 ℃, 250 ℃, 260 ℃, 270 ℃ and 280 ℃, are respectively numbered as A1, A2, A3, A4 and A5.
Example 2
An all-solid-state lithium-sulfur battery is composed of a positive electrode layer, a solid electrolyte layer and a negative electrode layer. The positive electrode layer was a composite positive electrode material for an all-solid-state lithium-sulfur battery, and was prepared from the positive electrode active material (a 3) coated with a chalcogenide electrolyte prepared in example 1 and acetylene black, wherein the mass ratio of the positive electrode active material coated with a chalcogenide electrolyte to acetylene black was 75: 25, i.e., the mass content of acetylene black in the composite positive electrode material for an all-solid-state lithium-sulfur battery was 25%, and the mass content of the positive electrode active material coated with a chalcogenide electrolyte was 75%.
In this embodiment, the solid electrolyte layer is an all-solid-state sulfide electrolyte materialMaterial, in particular Li3PS4。
In this embodiment, the negative electrode layer is a negative active material, specifically a metal lithium sheet.
In this example, the thickness of the positive electrode layer was 20 μm; the thickness of the solid electrolyte layer was 680 μm.
A preparation method of the all-solid-state lithium-sulfur battery according to the embodiment of the invention includes the following steps:
(1) preparing an all-solid-state lithium-sulfur battery composite positive electrode material and an all-solid-state sulfide solid electrolyte:
the positive electrode active material coated with the chalcogenide electrolyte (a 3) prepared in example 1 and acetylene black were weighed according to a mass ratio of 75: 25, and placed in a ball mill jar, and ball milled at 380rpm for 3 hours to obtain a composite positive electrode material for an all-solid-state lithium-sulfur battery.
Under the protection of argon atmosphere, according to Li2S、P2S5In a molar ratio of 75: 25, P is weighed separately2S5Powder and Li2And (3) placing the S powder into a high-energy ball milling tank for mixing, ball milling for 8h at the rotating speed of 510rpm, wherein ball milling is carried out for 40min every time in the ball milling process, and standing and cooling are carried out for 20 min. And then transferring the product obtained after ball milling into a tubular furnace, heating to 250 ℃ under the protection of argon atmosphere for heat treatment for 1h, and grinding to obtain all-solid sulfide electrolyte powder.
(2) And (2) putting 100mg of the all-solid-state sulfide electrolyte powder prepared in the step (1) into a mould (PEEK, 10 mm), and carrying out cold press molding under the condition that the pressure is 446MPa to prepare the solid electrolyte layer.
(3) And (3) placing 4mg of the all-solid-state lithium-sulfur battery composite positive electrode material prepared in the step (1) on one side of the solid electrolyte layer prepared in the step (2), and performing cold press molding under the condition that the pressure is 446MPa to prepare a positive electrode layer/solid electrolyte layer material.
(4) And (3) taking the solid electrolyte layer as an intermediate layer, placing a metal lithium sheet on the other side of the solid electrolyte layer in the positive electrode layer/solid electrolyte layer material prepared in the step (3), and performing cold press molding under the condition that the pressure is 191MPa to prepare a positive electrode layer/solid electrolyte layer/negative electrode layer material, namely the all-solid-state lithium-sulfur battery.
Comparative example 1
An all solid-state lithium sulfur battery substantially the same as that of example 2 except that: the composite positive electrode material of the all-solid-state lithium-sulfur battery used in comparative example 1 was different.
The preparation method of the all-solid-state lithium-sulfur battery composite positive electrode material used in comparative example 1 comprises the following steps:
(1) under the protection of argon atmosphere, according to Li2S、P2S5In a molar ratio of 75: 25, Li is weighed separately2S powder and P2S5And placing the powder in a high-energy ball milling tank, ball milling for 8h at the rotating speed of 510rpm, wherein ball milling is carried out for 40min every time, and standing and cooling are carried out for 20 min. And then transferring the ball-milled product into a tube furnace, heating to 250 ℃ under the protection of argon atmosphere, and carrying out heat treatment for 1h to obtain the all-solid sulfide electrolyte.
(2) Under the protection of argon atmosphere, according to Li2S, the mass ratio of the all-solid sulfide electrolyte to the acetylene black is 34: 41: 25, and the all-solid sulfide electrolyte and Li in the step (1) are weighed respectively2And S and acetylene black are placed in a ball milling tank, and ball milling is carried out for 3h at the rotating speed of 380rpm, so as to obtain the all-solid-state lithium-sulfur battery composite positive electrode material.
The positive electrode active material coated with the sulfur-based electrolyte in example 1, the all solid-state lithium sulfur battery in example 2, and comparative example 1 were subjected to the following tests:
(1) scanning Electron Microscope (SEM) testing: and (3) after carrying out gold spraying treatment on a sample to be detected, characterizing the surface appearance of the positive active material coated with the chalcogenide solid electrolyte by using a field emission scanning electron microscope.
(2) Ionic conductivity: a simulated battery is assembled by using stainless steel as a blocking electrode, and electrochemical alternating current impedance spectroscopy (EIS) tests are carried out at different temperature points of 25-60 ℃ and pass the conditions that the temperature is sigma = d/(R)bS) calculating the ionic conductivity.
(3) Cyclic voltammetry: and assembling a non-blocking symmetrical electrode battery, wherein the scanning speed is 0.1mV/s, the voltage range is 1V-4.5V, and performing cyclic voltammetry CV test.
(4) Constant current charge and discharge performance: the all solid-state lithium sulfur batteries assembled in example 2 and comparative example 2 were subjected to cycle performance tests. The test voltage range is 1.5V-4.5V, and the test temperature is 60 ℃.
The above test methods all belong to standard test methods in the field, and the selection is carried out according to the routine operation in the field when the parameters which are not disclosed are related.
Fig. 1 is an SEM image of a sulfur-based electrolyte coated cathode active material (a 3) prepared in example 1 of the present invention. In FIG. 1, (a) is a sample before heat treatment, i.e., the mixed powder prepared in step (2); (b) the sample after heat treatment is the positive electrode active material (A3) coated with the sulfur-based electrolyte; (a) the magnification of (a) and (b) is 5000 times. As can be seen from FIG. 1, the morphology of the sample before and after the heat treatment did not change much. The sample has Li in spite of being subjected to heat treatment3PS4Crystals appear, but the formed chalcogenide electrolyte is a glass ceramic electrolyte, and the surface of the chalcogenide electrolyte still presents amorphous morphology.
Fig. 2 is an XRD spectrum of the sulfur electrolyte-coated positive active material (a 3) prepared in example 1 of the present invention. In FIG. 1, (a) is a sample before heat treatment, i.e., the mixed powder prepared in step (2); (b) the sample after heat treatment was a positive electrode active material (a 3) coated with a sulfur-based electrolyte. As can be seen from FIG. 2, the XRD spectrum (b) of the sample after heat treatment contains not only Li2The characteristic peak of S also exists corresponding to the characteristic peak of sulfur-based Solid Electrolyte (SE).
Fig. 3 is an XRD spectrum of the positive electrode active material coated with a chalcogenide electrolyte prepared at different heat treatment temperatures in example 1 of the present invention. As can be seen from fig. 3, when the heat treatment temperature is 250 ℃, a characteristic peak of the sulfur-based solid electrolyte begins to appear in the XRD spectrum, and the intensity of the characteristic peak of the sulfur-based solid electrolyte increases with further increase of the heat treatment temperature. In the invention, the main purpose of the heat treatment is to convert the chalcogenide solid electrolyte of the coating layer from a glass state to a glass ceramic state, and the process is a crystallization process, wherein the contents of generated high-conductivity phases are different due to heat treatment at different temperatures, and the heat treatment temperature is 240-280 ℃, so that the obtained material has better ionic conductivity.
Fig. 4 is a graph showing the change in conductivity with temperature of the sulfur-based electrolyte-coated positive electrode active material (a 2) prepared in example 1 of the present invention. As can be seen from fig. 4, the positive electrode active material (a 2) coated with a sulfur-based electrolyte prepared in example 1 of the present invention exhibited excellent ionic conductivity, which was 1.24 × 10 at room temperature-4 S·cm-1。
Fig. 5 is a graph showing ion conductivity spectra of the positive electrode active material coated with a chalcogenide electrolyte prepared at different heat treatment temperatures in example 1 of the present invention. As can be seen from FIG. 5, when the heat treatment temperature was 240 ℃ to 270 ℃, the ionic conductivity of the positive electrode active material coated with the chalcogenide electrolyte increased with the increase of the heat treatment temperature, and the ionic conductivity of the positive electrode active material coated with the chalcogenide electrolyte obtained by heat treatment at 270 ℃ for 1 hour reached 1.29X 10-4 S·cm-1. When the heat treatment temperature is increased to 280 ℃, the ion conductivity of the positive electrode active material coated with the sulfur-based electrolyte shows a significantly decreased tendency.
Fig. 6 is a voltage-specific capacity graph of the all solid-state lithium sulfur battery (a) prepared in example 2 of the present invention and the all solid-state lithium sulfur battery (b) prepared in comparative example 1. As can be seen from FIG. 6, the all-solid-state lithium-sulfur battery prepared in example 2 of the present invention was operated at 60 ℃ at 0.05mA cm-2The current is charged and discharged circularly, and the first discharge capacity of the battery is 512mAh g-1The discharge plateau was about 1.98V. The discharge capacity of the battery at the fifth, tenth and fifteenth cycles is 598.7 mAh g-1、533.0 mAh g-1And 500.0 mAh g-1. While the all-solid-state lithium-sulfur battery prepared in comparative example 1 was operated at 60 ℃ at 0.05mA cm-2The current is charged and discharged circularly, and the first discharge capacity of the battery is 321.8 mAh g-1The discharge plateau was about 1.96V. The discharge capacity of the battery at the fifth, tenth and fifteenth cycles is 295.7 mAh g-1、282.6 mAh g-1And 279.8 mAh g-1. It can be seen that the all solid-state lithium-sulfur battery in example 2 has higher discharge capacity and better cycle performance, and the root cause is the all solid-state lithium-sulfur battery of the present inventionThe cell adopts a positive active material which has good electrochemical stability, high ionic conductivity and good interface contact and is coated with the sulfur electrolyte.
Therefore, the positive active material coated with the chalcogenide electrolyte has the advantages of good electrochemical stability, high ionic conductivity, good interface contact with the chalcogenide solid electrolyte and the like, the charge-discharge capacity of the assembled all-solid-state lithium-sulfur battery is obviously improved, the utilization rate of the active material is higher, and the full-solid-state lithium-sulfur battery has better cycle performance.
In the present invention, the same or similar technical effects as in example 1 were obtained for the positive electrode active material coated with the sulfur-based electrolyte when the mass ratio of the positive electrode active material to the sulfur-based solid electrolyte was 0.55 to 4: 1. The all-solid-state lithium-sulfur battery prepared by the method can achieve the same or similar technical effects as the embodiment 2.
The above examples are merely preferred embodiments of the present invention, and the scope of the present invention is not limited to the above examples. All technical schemes belonging to the idea of the invention belong to the protection scope of the invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention, and such modifications and embellishments should also be considered as within the scope of the invention.

Claims (8)

1. A method for preparing a positive electrode active material coated with a sulfur-based electrolyte is characterized by comprising the following steps:
s1, mixing P2S5Ball milling to obtain P2S5Powder; the ball milling is carried out under the protection of argon atmosphere; the rotation speed of the ball mill is 380 rpm-510 rpm; the ball milling time is 3-5 h; performing ball milling for 40min in the ball milling process, and standing and cooling for 20 min;
s2, P obtained in step S12S5Powder with Li2Mixing S powder and performing ball milling; the ball milling is carried out under the protection of argon atmosphere; the rotation speed of the ball mill is 380 rpm-510 rpm; the ball milling time is 5-20 h; performing ball milling for 40min in the ball milling process, and standing and cooling for 20 min;
s3, heating the ball-milled product in the step S2 to 250-270 ℃ for heat treatment for 0.5-3 h to obtain the positive active material coated with the chalcogenide electrolyte; the heating rate in the heat treatment process is 5-10 ℃/min;
the positive active material coated with the chalcogenide electrolyte comprises a positive active material, and the surface of the positive active material is coated with the chalcogenide solid electrolyte; the positive electrode active material is Li2S; the sulfur-based solid electrolyte is Li3PS4。
2. The method for preparing the positive electrode active material coated with the sulfur-based electrolyte according to claim 1, wherein the mass ratio of the positive electrode active material to the sulfur-based solid electrolyte is 0.55-4: 1.
3. An all-solid-state lithium-sulfur battery comprising a positive electrode layer, a solid electrolyte layer and a negative electrode layer, the solid electrolyte layer being disposed between the positive electrode layer and the negative electrode layer, characterized in that the positive electrode layer comprises an all-solid-state lithium-sulfur battery composite positive electrode material made of the chalcogenide electrolyte-coated positive electrode active material according to claim 1 or 2 and a conductive carbon material.
4. The all-solid-state lithium-sulfur battery according to claim 3, wherein the positive electrode layer comprises the following components in percentage by mass:
20 to 30 percent of conductive carbon material,
70-80% of positive active material coated with sulfur electrolyte.
5. The all-solid-state lithium-sulfur battery according to claim 3 or 4, wherein the conductive carbon material is at least one of acetylene black, superconducting carbon, graphene, carbon nanotubes, carbon nanofibers, and activated carbon; the negative electrode layer contains a negative electrode active material; the negative active material is at least one of a metal lithium sheet and an indium lithium alloy sheet; the solid electrolyte layer is an all-solid sulfide electrolyte materialFeeding; the all-solid-state sulfide electrolyte material is Li3PS4Or Li10GeP2S12。
6. The all-solid-state lithium-sulfur battery according to claim 3 or 4, wherein the thickness of the positive electrode layer is 0.1 to 50 μm; the thickness of the solid electrolyte layer is 100-1000 μm.
7. A method for preparing the all-solid-state lithium-sulfur battery according to any one of claims 3 to 6, comprising the steps of:
(1) cold press molding the all-solid-state sulfide electrolyte material to prepare a solid-state electrolyte layer;
(2) placing the composite positive electrode material of the all-solid-state lithium-sulfur battery on one side of the solid electrolyte layer obtained in the step (1) for cold press molding to obtain a positive electrode layer/solid electrolyte layer material;
(3) and (3) taking the solid electrolyte layer as an intermediate layer, and placing the negative electrode active material on the other side of the solid electrolyte layer in the positive electrode layer/solid electrolyte layer material obtained in the step (2) for cold press molding to obtain the all-solid-state lithium-sulfur battery.
8. The production method of the all-solid-state lithium-sulfur battery according to claim 7, wherein in the step (1), the all-solid-state sulfide electrolyte material is produced by: under the protection of argon atmosphere, adding P2S5Powder or P2S5And GeS2Mixed powder of (2) with Li2Mixing S powder, ball-milling for 5-20 h at the rotation speed of 380-510 rpm, ball-milling for 40min each time in the ball-milling process, and standing and cooling for 20 min; carrying out heat treatment on the product obtained after ball milling at 240-280 ℃ for 0.5-3 h to obtain an all-solid sulfide electrolyte material; the pressure in the cold press molding process is 191-637 MPa;
in the step (2), the all-solid-state lithium-sulfur battery composite positive electrode material is prepared by the following method: mixing the positive electrode active material coated with the sulfur electrolyte and the conductive carbon material, and ball-milling for 1-5 h at the rotating speed of 380-510 rpm to obtain the all-solid-state lithium-sulfur battery composite positive electrode material; the pressure in the cold press molding process is 191-637 MPa;
in the step (3), the pressure in the cold press molding process is 128MPa to 255 MPa.
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