CN114284553A

CN114284553A - Lithium metal battery without negative electrode and preparation method thereof

Info

Publication number: CN114284553A
Application number: CN202111606056.8A
Authority: CN
Inventors: 宁晓辉; 余萌
Original assignee: Xian Jiaotong University
Current assignee: Xian Jiaotong University
Priority date: 2021-12-25
Filing date: 2021-12-25
Publication date: 2022-04-05

Abstract

The invention discloses a non-negative electrode lithium metal battery and a preparation method thereof, belonging to the research field of negative electrode materials of lithium ion batteries²⁺、Mg²⁺、Ni²⁺Or Sn²⁺A certain salt of the metal salt of (1). The additive X is added into the conventional electrolyte, so that a lithium alloy layer is formed on the surface of the copper current collector, and the deposition process of lithium is adjusted, thereby reducing the capacity loss of the battery and improving the cycle performance of the battery. The method is simple, convenient and economical, and has practical significance for the research and popularization of the lithium metal battery without the negative electrode.

Description

Lithium metal battery without negative electrode and preparation method thereof

Technical Field

The invention belongs to the technical field of research on lithium ion battery negative electrode materials, and particularly relates to a method for modifying cycle performance of a lithium metal battery without a negative electrode.

Background

Today the world faces two major energy challenges: the method has the advantages that firstly, the electric power production is converted from fuel combustion to sustainable development energy, secondly, the transportation is converted to electric power direction to be propelled, and namely, a new energy automobile is adopted to replace an automobile driven by a traditional internal combustion engine. With the increasing exhaustion of non-renewable energy sources (such as petroleum, coal, etc.), people have to further develop renewable energy sources, such as solar energy, wind energy, tidal energy, biomass energy, etc. However, the development and utilization of these new energy sources are largely influenced by seasonal, regional differences, so that the large-scale application of these new energy sources is limited. Since the last 90 s, lithium ion batteries have become the power choice for portable electronic devices due to their long cycle life, small size, and stable performance. Due to the vigorous development of the new energy automobile industry, the scale of the lithium ion battery industry in China is rapidly increased and is the first place in the world. However, the energy density of lithium ion batteries currently produced commercially is generally below 300Wh/kg, and only a few manufacturers are able to break through 300 Wh/kg. In order to meet the increasing development demand for energy density of lithium ion batteries, a new generation of lithium ion batteries with low cost and high energy density must be developed.

At present, the lower theoretical capacity (372mAh/g) of the graphite cathode is generally considered to be one of important factors limiting the energy density of the lithium ion battery. Compared with graphite, the lithium metal negative electrode has ultrahigh theoretical specific capacity (3860mAh/g) and lowest oxidation-reduction potential (-3.04V), and is considered to be the ultimate choice of the lithium ion battery negative electrode material. The lithium metal cathode can easily improve the energy density of the lithium battery to 400Wh/kg by matching with the traditional ternary cathode. Using S, O₂For high capacity positive electrodes, the energy density of lithium metal batteries would break through 600 Wh/kg. Therefore, the lithium metal cathode can well meet the planning requirement of the energy density of the battery. However, the content of the lithium metal negative electrode has an important influence on the energy density of the lithium battery. As the thickness of the negative electrode lithium sheet increases, the energy density of the lithium battery may significantly decrease. When the thickness of the lithium sheet exceeds 50 μm, the energy density of the lithium battery is even lower than that of the lithium ion battery using the graphite negative electrode. The lithium metal negative electrode will fully release its theoretical energy density only when the thickness of the lithium plate is 0, and the lithium source is fully provided by the lithium rich positive electrode. Among the lithium metal batteries, the lithium metal battery without the negative electrode has the highest energy density.

Compared with the traditional lithium ion battery, the lithium metal battery without the negative electrode directly adopts the copper foil as the substrate, and the energy density of the lithium metal battery without the negative electrode is obviously improved due to the saving of the quality and the volume of graphite, and meanwhile, the complicated pulping process of the graphite negative electrode can be avoided, thereby being beneficial to simplifying the manufacturing process and reducing the manufacturing cost; the lithium foil which is sensitive to air and water and has high processing difficulty does not need to be processed in the battery assembling process, so that the lithium resource is saved, and the manufacturing cost related to lithium is reduced; the battery is assembled and operated in a full discharge state and is in a state of lower energy, so that the safety is greatly improved, and the possibility of self-discharge of the battery is eliminated.

Despite numerous advantages, the cycling performance of the non-negative lithium metal battery is yet to be further improved. During charging and discharging, lithium from the positive electrode will be deposited directly on the copper current collector or stripped from the current collector. Lithium metal having high electrochemical activity may continuously react with the electrolyte to generate an SEI film, resulting in capacity loss. Also, lithium tends to deposit unevenly on copper current collectors creating lithium dendrites. The formation of dendrites exacerbates interfacial side reactions and also causes the production of inactive lithium during the stripping process and also causes short-circuiting problems in the battery. The generation of interfacial side reactions and inactive lithium continues to consume the lithium source, causing a rapid drop in capacity. The problem of capacity fade is particularly pronounced in non-negative lithium metal batteries because the positive electrode is the sole source of lithium and the lost capacity cannot be replenished by other means. The improvement of cycle performance and the reduction of capacity loss are problems to be solved urgently in the lithium metal battery without the negative electrode. The current commercial copper foil and electrolyte have poor effect in a lithium metal battery without a negative electrode, and can cause uneven deposition of lithium and generation of lithium dendrite in the circulation process, so that a large amount of interface side reaction and formation of non-active lithium are caused, and the capacity of the battery is rapidly attenuated.

Disclosure of Invention

The invention provides an electrolyte additive for adjusting a lithium deposition process aiming at the problem of rapid capacity attenuation of a lithium metal battery without a negative electrode, and the electrolyte additive can reduce the generation of interface side reaction and inactive lithium by controlling the lithium deposition process, reduce the capacity loss in a circulation process and further improve the circulation stability of the battery.

In order to achieve the purpose, the non-negative lithium metal battery comprises a negative electrode shell, wherein the positive electrode shell and the negative electrode shell are assembled to form a total shell, and the total shell is internally provided with a positive electrode shell, a positive electrode, a diaphragm and copper in sequenceA current collector, wherein the electrolyte consists of conventional electrolyte and an additive X, and the additive X contains Zn²⁺、Mg²⁺、Ni²⁺Or Sn²⁺The mass of the additive X is less than 5% of the mass of the conventional electrolyte.

Further, the mass of the additive X is 1-5% of that of the conventional electrolyte.

Further, the positive electrode is lithium iron phosphate coated on the aluminum current collector.

Furthermore, a spring plate and a gasket are arranged between the negative electrode shell and the copper current collector.

Furthermore, the materials of the positive electrode shell, the gasket, the elastic sheet and the negative electrode shell are all 304 stainless steel.

Further, the diaphragm is a polypropylene microporous membrane.

Further, the conventional electrolytic solution is composed of lithium hexafluorophosphate and an ethylene carbonate/diethyl carbonate mixed solvent.

The preparation method of the lithium metal battery without the negative electrode comprises the following steps:

s1, adding the additive X into the conventional electrolyte, and stirring and dissolving to obtain the electrolyte;

s2, assembling the battery in the glove box according to the sequence of the positive electrode shell, the positive electrode, the diaphragm, the negative electrode and the negative electrode shell; the electrolyte is added to the positive electrode and the diaphragm in the process of assembling the battery, the positive electrode is lithium iron phosphate coated on the aluminum foil, the negative electrode is a copper current collector, and the adding amount of the electrolyte of each battery is a constant value.

Further, in S1, the additive X is ground into powder and then added to the conventional electrolyte.

Further, in S2, the electrolyte is added once after the positive electrode is assembled, and the electrolyte is added once again after the separator is assembled.

Compared with the prior art, the invention has at least the following beneficial technical effects:

1) the invention adopts X as the electrolyte additive, and can adjust the appearance of the lithium deposited and stripped in the circulation process. In the presence of metal ions, lithium reacts with the copper current collector after primary deposition to form a lithium alloy layer, and the lithium alloy layer is firmly grown on the surface of the copper current collector. The alloy layer has lithium affinity, is beneficial to reducing the nucleation barrier of lithium, promotes the planar deposition of lithium, reduces the generation of dendritic crystals, and further reduces the occurrence of interface side reaction and inactive lithium, thereby reducing the capacity loss of the battery and improving the cycle performance of the battery. Moreover, the alloy layer generated by a small amount of electrolyte additive is very thin, and does not cause significant influence on the energy density of the battery.

2) The additive X provided by the invention is common metal salt, has wide source and lower cost. And the preparation method adopting the additive is very simple and convenient, and has practical significance for the research and popularization of the lithium metal battery without the negative electrode.

Furthermore, an elastic sheet and a gasket are arranged between the negative electrode shell and the copper current collector, the gasket and the elastic sheet play a compaction role, and a large gap is prevented from occurring in the battery, so that the internal resistance caused by the battery gap is reduced, and the stable transmission of electrons and lithium ions is ensured.

Furthermore, the anode is lithium iron phosphate coated on the aluminum current collector, and the lithium iron phosphate has a stable structure, a stable charging and discharging platform and good circulation stability.

The method has the advantages of simplicity and practicality. The adopted non-negative electrode structure has high energy density, and the use of an active lithium negative electrode is avoided, so that the battery is safer, and the cost is lower. The electrolyte additive is simple, convenient and efficient, and the adopted additive is common metal salt, has wide sources, and is economical and practical.

Further, in S1, the additive X is ground into powder and then added to the conventional electrolyte, which improves the manufacturing efficiency of the electrolyte.

Further, in S2, once electrolyte is added after the positive electrode is assembled, and once electrolyte is added after the diaphragm is assembled, the electrolyte is added twice to fully infiltrate the positive electrode, the diaphragm and the negative electrode, so as to ensure rapid transmission of lithium ions during the battery cycle, and the electrolyte addition amount of each battery is a constant value.

Drawings

FIG. 1 is a schematic diagram of a structure for preparing a lithium metal battery without a negative electrode using the present invention;

FIG. 2 is a schematic cross-sectional view of an assembled lithium metal battery without a negative electrode using the present invention;

FIG. 3 is a schematic diagram of a lithium deposition for a battery with a conventional electrolyte;

FIG. 4 is a schematic illustration of lithium deposition using the present invention after addition of electrolyte additives;

FIG. 5 is a graph of charge and discharge cycles for various levels of electrolyte additive according to the present invention;

fig. 6 is a charge-discharge cycle curve of the present invention after the addition of various additives.

In the drawings: 1-negative electrode shell, 2-elastic sheet, 3-gasket, 4-copper current collector, 5-diaphragm, 6-positive electrode, 7-positive electrode shell, 8-electrolyte, 9-lithium alloy layer and 10-lithium particle.

Detailed Description

In order to make the objects and technical solutions of the present invention clearer and easier to understand, the present invention will be further described in detail with reference to the accompanying drawings and examples, wherein the specific examples described herein are only used for explaining the present invention and are not used for limiting the present invention.

Referring to fig. 1 and 2, the non-negative lithium metal battery is a 2032 button cell structure, and includes an electrolyte 8, a positive electrode case 7, a positive electrode 6, a separator 5, a copper current collector 4, a gasket 3, an elastic sheet 2, and a negative electrode case 1. The positive electrode shell 7 and the negative electrode shell 1 form a total shell, the positive electrode 6, the diaphragm 5, the copper current collector 4, the gasket 3 and the elastic sheet 2 are sequentially arranged in the total shell, wherein the elastic sheet 2 is positioned on one side close to the negative electrode shell 1. The positive electrode 6 comprises a positive electrode current collector and a positive electrode material coated on the positive electrode current collector, and the positive electrode current collector is an aluminum foil. The negative current collector 4 is a copper foil, directly used as a negative electrode, the positive electrode and the negative electrode are separated by a separator, and a certain volume of electrolyte is injected between the positive electrode and the negative electrode. The diaphragm is a polypropylene microporous film.

The copper current collector 4 serves as a negative electrode, the gasket 3 and the elastic sheet 2 are used for compressing the negative electrode, and the diaphragm 5 is used for separating the positive electrode from the negative electrode. In the process of assembling the battery, the electrolyte 8 is added to fully soak the positive electrode, the negative electrode and the diaphragm 5.

The electrolyte consists of conventional electrolyte and additiveX is a Zn-containing compound²⁺、Mg²⁺、Ni²⁺Or Sn²⁺The content of the metal salt of (a) is less than 5% by mass of the conventional electrolyte. Zn²⁺、Mg²⁺、Ni²⁺Or Sn²⁺Is common metal salt ions, has wide sources and low cost. Meanwhile, lithium metal can replace the metal salt ions with corresponding simple substances of Zn, Mg, Ni or Sn, and further form a lithium alloy product with the simple substances of Zn, Mg, Ni or Sn, and the lithium alloy product grows on the copper current collector. The lithium alloy layer 9 can serve as a buffer layer between the lithium particles 10 and the copper current collector 4, has better lithium affinity than the copper current collector 4, and is beneficial to promoting the nucleation and dendrite-free growth of lithium to form a massive lithium deposit. The shape of the blocky lithium can effectively reduce the formation of interface side reaction and inactive lithium, thereby greatly reducing the capacity loss. The content of the additive X should not be too high, and when it exceeds 5% by mass of the conventional electrolyte, the lithium ion concentration in the conventional electrolyte is relatively insufficient, which easily causes capacity reduction and generation of dendrite.

Preferably, the content of the additive X is 1% -5% of the content of the conventional electrolyte.

Preferably, the conventional electrolyte is composed of lithium salt lithium hexafluorophosphate (LiPF)₆) With mixed ester solvents ethylene carbonate/diethyl carbonate (EC/DEC), LiPF₆The concentration in EC/DEC was 1mol/L, and the volume ratio of EC to DEC was 1: 1. The lithium ion in the conventional electrolyte has high conductivity and wide electrochemical window, and is a commercially and generally adopted electrolyte system.

Preferably, the anode material is lithium iron phosphate coated on the aluminum foil, and the lithium iron phosphate has a stable structure, a stable charging and discharging platform and good cycling stability.

and S1, grinding the additive X into powder, adding the powder into the conventional electrolyte, and stirring and dissolving to obtain the electrolyte 8. Wherein the additive X comprises Zn²⁺、Mg²⁺、Ni²⁺Or Sn²⁺The metal salt particles of (2) are less than 5% by mass of the conventional electrolyte.

And S2, assembling the 2032 type button cell in the glove box according to the sequence of the positive electrode shell 7, the positive electrode 6, the diaphragm 5, the negative electrode 4, the gasket 3, the elastic sheet 2 and the negative electrode shell 1. When the positive electrode 6 is assembled, a certain amount of electrolyte is added, and when the diaphragm 5 is assembled, the same amount of electrolyte is continuously added. The electrolyte is added twice, so that the electrolyte can be fully soaked in the anode 6, the diaphragm 5 and the cathode 4, the rapid transmission of lithium ions in the battery circulation process is ensured, and the adding amount of the electrolyte in each battery is a constant value.

Referring to fig. 3 and 4, in a charging process of a non-negative electrode lithium metal battery, when the electrolyte 8 is only a conventional electrolyte, lithium ions from the positive electrode 6 are directly deposited on the copper current collector 4. Due to the lithium-phobic nature of copper and the poor adhesion between lithium and copper, lithium tends to undergo non-planar deposition, growing as a one-dimensional dendritic structure on the copper surface. The lithium particles with the structure not only have larger surface area and aggravate the generation of interface side reaction, but also are easy to be cracked to generate inactive lithium during discharging and stripping, thereby causing the rapid attenuation of capacity. When the electrolyte 8 consists of a conventional electrolyte and an additive X, lithium ions from the positive electrode are still initially deposited on the copper current collector 4. Subsequently, the reduced metallic lithium and the additive X undergo a displacement reaction and an alloying reaction to form a thin lithium alloy layer on the surface of the copper current collector 4. Compared with copper, the lithium alloy layer has better affinity and adhesion to deposited lithium, promotes the planar growth of lithium and is beneficial to obtaining three-dimensional blocky lithium particles. The larger size and smooth surface of the lithium ion battery are beneficial to reducing the side reaction of the interface and reducing the generation of inactive lithium, thereby reducing the irreversible capacity loss in the circulating process and prolonging the circulating life of the battery.

Example 1

The utility model provides a no negative pole lithium metal battery, includes electrolyte 8, anodal shell 7, anodal 6, diaphragm 5, the mass flow body of copper 4, gasket 3, shell fragment 2 and negative pole shell 1, and anodal shell 7 and negative pole shell 1 constitute total casing, and anodal 6, diaphragm 5, the mass flow body of copper 4, gasket 3, shell fragment 2 set gradually in total casing, and wherein shell fragment 2 is located the one side of being close to negative pole shell 1. The positive electrode comprises a positive current collector and a lithium iron phosphate material coated on the positive current collector, and the surface capacity of the positive electrode is 2mAh/cm²The positive current collector is aluminum foil. The negative current collector is copper foil and is directly used as a negative electrode, the positive electrode and the negative electrode are separated by a diaphragm, and 15g/Ah of electrolyte is injected between the positive electrode and the negative electrode, so that the electrolyte infiltrates the positive electrode 6, the diaphragm 5 and the negative electrode 4. The diaphragm is a polypropylene microporous film. The electrolyte is added during the assembly of the battery and consists of a conventional electrolyte and an additive X. The conventional electrolyte was 1mol/L lithium hexafluorophosphate-ethylene carbonate/diethyl carbonate with a volume ratio of EC to DEC of 1: 1. Additive X is Zn-containing²⁺Metal salt of (1) ZnCl₂The content of the additive X is 1 percent of the mass of the conventional electrolyte, namely the mass ratio of the additive X to the conventional electrolyte is 1: 100. The battery is at 0.2mA/cm^-2The constant current charge and discharge test was performed at the current density of (1), and the charge and discharge curve is shown in fig. 5. It can be seen that: when ZnCl is present₂When the content is 1 percent, the first discharge capacity of the battery is 1.12mAh/cm^-2The attenuation amplitude of the first 10 cycles is relatively slow, the capacity retention rate of the 10 th cycle is 54%, then the capacity attenuation starts to become fast, and the capacity is 0.14mAh/cm after 20 weeks^-2。

Example 2

In this example, only ZnCl was used₂The content of the additive X was 3% of the mass of the conventional electrolyte, unlike example 1. The battery is at 0.2mA/cm^-2The constant current charge and discharge test was performed at the current density of (1), and the charge and discharge curve is shown in fig. 5. It can be seen that: when ZnCl is present₂When the content is 3 percent, the first discharge capacity of the battery is 1.28mAh/cm^-2The capacity attenuation is relatively gentle, and the discharge capacity after 20 weeks of circulation still has 0.51mAh/cm^-2。

Example 3

In this example, only ZnCl was used₂The content of the additive X is 5% of the mass of the conventional electrolyte, unlike example 1. The battery is at 0.2mA/cm^-2The constant current charge and discharge test was performed at the current density of (1), and the charge and discharge curve is shown in fig. 5. It can be seen that: when ZnCl is present₂When the content is 5 percent, the first discharge capacity of the battery is 1.35mAh/cm^-2The capacity decay in the first 14 cycles was relatively gradual, after which the decay began to become rapid, and the discharge capacity after 20 cycles was 0.44mAh/cm^-2。

Comparative example 1

In this comparative example, no additive was added, and only a conventional electrolyte was used. The conditions were exactly the same as in examples 1 to 3, except for the difference in the content of additive X. The battery is at 0.2mA/cm^-2The constant current charge and discharge test was performed at the current density of (1), and the charge and discharge curve is shown in fig. 5. It can be seen that: when no additive is added, the first discharge capacity of the battery is only 0.92mAh/cm^-2The capacity loss rate exceeds 50%. The capacity of the battery is quickly attenuated, and the battery is attenuated to 0.1mAh/cm after 10 cycles^-2The following.

Example 4

In this example, MgCl was used₂As additive, additive MgCl₂The content is 1 percent of the mass of the conventional electrolyte. The battery is at 0.2mA/cm^-2The constant current charge and discharge test was performed at the current density of (1), and the charge and discharge curve is shown in fig. 6. It can be seen that: when MgCl is present₂When the content is 1 percent, the first discharge capacity of the battery is up to 1.40mAh/cm^-2The capacity decayed rapidly in the first 3 cycles, with a discharge capacity of 0.97mAh/cm in the 3 rd cycle^-2The capacity decay is slower in the last 17 cycles, and the discharge capacity after 20 cycles is 0.48mAh/cm^-2。

Example 5

In this example, NiCl was used₂As additive, NiCl₂The content is 3 percent of the mass of the conventional electrolyte. The battery is at 0.2mA/cm^-2The constant current charge and discharge test was performed at the current density of (1), and the charge and discharge curve is shown in fig. 6. It can be seen that: when NiCl is added₂When the content is 3 percent, the first discharge capacity of the battery is 1.14mAh/cm^-2The capacity decayed rapidly in the first 5 cycles, with a 5 th discharge capacity of 0.52mAh/cm^-2The capacity decayed slowly in the following circulation, and the discharge capacity after 20 circles was 0.22mAh/cm^-2。

Example 6

In this example, SnCl was used₂As additive, additive SnCl₂The content is 5 percent of the mass of the conventional electrolyte. The battery is at 0.2mA/cm^-2The constant current charge and discharge test is carried out under the current density, and the charge and discharge curve is shown in the figureAnd 6. It can be seen that: when SnCl₂When the content is 5 percent, the first discharge capacity of the battery is 1.31mAh/cm^-2Shows gradual attenuation trend in 20 cycles, the attenuation rates are similar, and the discharge capacity after 20 cycles is 0.39mAh/cm^-2. The above results show that: the addition of the additive X obviously improves the capacity retention rate and the cycling stability of the battery. The method for improving the cycle performance of the lithium metal battery without the negative electrode is realized by adopting the electrolyte additive, the method is simple and convenient to operate, the adopted additive X is low in cost and wide in source, and the method has practical significance for the research and popularization of the lithium metal battery without the negative electrode.

The foregoing examples are provided for the purpose of clarity only and are not intended to be limiting. It should be noted that the invention can be implemented by those skilled in the art by similar alternatives and modifications based on the principle of the invention, and it is not possible to list all embodiments herein, so that obvious modifications or variations based on the invention are still within the scope of the invention.

Claims

1. The utility model provides a no negative pole lithium metal battery, its characterized in that includes negative pole shell (1), positive pole shell (7) and negative pole shell (1) equipment form total casing, positive pole shell (7), anodal (6), diaphragm (5) and copper mass flow body (4) have set gradually in the total casing, electrolyte (6) comprise conventional electrolyte and additive X, additive X is for containing Zn²⁺、Mg²⁺、Ni²⁺Or Sn²⁺The mass of the additive X is less than 5% of the mass of the conventional electrolyte.

2. The lithium metal battery of claim 1, wherein the additive X is 1-5% by mass of the conventional electrolyte.

3. The lithium metal battery of claim 1, wherein the positive electrode (6) is lithium iron phosphate coated on an aluminum current collector.

4. The lithium metal battery of claim 1, wherein a spring (2) and a gasket (3) are arranged between the negative casing (1) and the copper current collector (4).

5. The lithium metal battery without the negative electrode as claimed in claim 4, wherein the materials of the positive electrode case (7), the gasket (3), the elastic sheet (2) and the negative electrode case (1) are all 304 stainless steel.

6. The lithium metal battery of claim 1, wherein the separator (5) is a microporous polypropylene membrane.

7. The lithium metal battery of claim 1, wherein the conventional electrolyte is composed of lithium hexafluorophosphate and a mixed solvent of ethylene carbonate/diethyl carbonate.

8. The method of claim 1, comprising the steps of:

s1, adding the additive X into the conventional electrolyte, and stirring and dissolving to obtain the electrolyte (8);

s2, assembling the battery in the glove box according to the sequence of the positive electrode shell (7), the positive electrode (6), the diaphragm (5), the negative electrode (4) and the negative electrode shell (1); the electrolyte (8) is added to the positive electrode (6) and the diaphragm (5) in the process of assembling the battery, the positive electrode is lithium iron phosphate coated on an aluminum foil, the negative electrode is a copper current collector, and the addition amount of the electrolyte of each battery is a constant value.

9. The method of claim 8, wherein in step S1, the additive X is ground into powder and then added to a conventional electrolyte.

10. The method of claim 8, wherein in step S2, the electrolyte is added once after the positive electrode (6) is assembled, and the electrolyte is added once after the separator (5) is assembled.