CN118813112A - Polymer membrane for in-situ protection of lithium metal anode and its application - Google Patents

Abstract

The present invention provides a polymer film for in-situ protection of lithium metal negative electrodes and its application. The raw materials of the polymer film include polyepoxy group compounds, polyetheramines, lithium salts and specific types of active additives. In the present invention, the polyetheramine can be cross-linked with the polyepoxy group compound to obtain a polymer. When used for in-situ protection of lithium metal negative electrodes, the polymer can not only make the film effectively adhere to the surface of the negative electrode, but also actively react with lithium dendrites to prevent lithium dendrites from puncturing the diaphragm. The polymer can also effectively prevent the electrolyte from having side reactions with metallic lithium, which is beneficial to improving the coulombic efficiency of the battery; in addition, the specific types of active additives contained therein have good lithium ion conductivity, and cooperate with lithium salts and polymers to accelerate the lithium ion transmission effect, which is beneficial to improving the electrochemical performance of the negative electrode.

Description

Polymer membrane for in-situ protection of lithium metal anode and its application

Technical Field

The present invention relates to the technical field of lithium metal batteries, and in particular to a polymer film for in-situ protection of a lithium metal negative electrode and an application thereof.

Background Art

Due to its excellent energy density and long cycle life, lithium-ion batteries have become the most widely used and preferred secondary batteries in daily life. Traditional lithium-ion batteries use graphite as the negative electrode, and the rocking chair design can fully ensure safety, but it also limits the further development of energy density. Metal lithium batteries that replace graphite with metallic lithium are the theoretical best solution for improving energy density. However, metal lithium batteries are prone to lithium dendrite growth during use. On the one hand, lithium dendrites can easily puncture the diaphragm, causing internal short circuits in the battery, causing fires, explosions and other safety problems. On the other hand, they will react with the electrolyte. After the lithium dendrites fall off the electrode surface, they will become "dead lithium", affecting the battery capacity and cycle life.

Constructing a polymer film on the surface of lithium metal can effectively inhibit the growth of lithium dendrites on the surface of lithium metal. At present, most polymer coatings require the polymer raw materials to be dissolved in toxic solvents such as acetonitrile and methanol, and then heated and evaporated to remove the solvent to obtain a polymer film, such as CN113346052A. However, the above solvents are not only toxic and pose safety hazards, but the residual solvents will affect the electrical performance of subsequent lithium metal batteries.

Many high-energy-density secondary batteries, such as lithium-sulfur batteries and lithium-air batteries, use lithium metal as the negative electrode. Therefore, the research on lithium metal negative electrodes is the focus of the industry in the future, and protecting lithium metal is a development requirement of front-end technology. Effectively protecting the lithium metal negative electrode so that it takes into account both safety and electrochemical performance is an urgent problem to be solved before its actual commercialization.

Summary of the invention

The main purpose of the present invention is to provide a polymer film for in-situ protection of lithium metal negative electrodes and its application, so as to solve the problem that the lithium metal negative electrode protection method in the prior art cannot take into account environmental protection performance, safety performance and electrochemical performance.

In order to achieve the above object, according to one aspect of the present invention, a polymer membrane for in-situ protection of lithium metal negative electrode is provided. The raw materials of the polymer membrane include: a polyepoxy compound, a polyetheramine, a lithium salt and an active additive; wherein the active additive includes one or more of Li ₇ La ₃ Zr ₂ O ₁₂ , Li _6.4 La ₃ Zr _1.7 Ta _0.3 O ₁₂ , Li ₃ PS ₄ and Li ₇ P ₃ S _11. In the raw materials of the polymer membrane of the present invention, the polyepoxy compound and the polyetheramine are cross-linked to obtain a new polymer, and the polymer has a high ionic conductivity. When the polymer film of the present invention is used to in-situ protect the lithium metal negative electrode, on the one hand, the polymer can act as a binder to effectively adhere the film to the negative electrode surface, and on the other hand, the polymer can actively react with lithium dendrites to form a stable SEI layer, which is beneficial to inhibiting the growth of lithium dendrites on the surface of lithium metal, avoiding lithium dendrites from puncturing the diaphragm, and effectively reducing fires and explosions caused by diaphragm puncture, thereby greatly improving the safety of lithium metal batteries; at the same time, it can also avoid side reactions between electrolyte and metallic lithium, which is beneficial to improving the coulombic efficiency of the battery. The lithium metal negative electrode in-situ protected by the polymer film of the present invention has stable cycle performance and greatly improved safety. In addition, the raw materials of the polymer film of the present invention are widely available and inexpensive, which is convenient for large-scale industrial applications.

Furthermore, the polyepoxy compound is selected from cyanuric acid epoxy resin and/or octaglycidylpropylsiloxane. The polyepoxy compound of the above type can form a polymer with a stable three-dimensional cross-linked structure with polyetheramine, and the polymer has strong chemical stability and electrochemical stability, high conductivity, and good film-forming properties. When the polymer film containing a specific type of polyepoxy compound in the raw material is used for in-situ protection of lithium metal negative electrode, the polymer film has better adhesion on the negative electrode surface and is more conducive to the formation of SEI film, which can more effectively improve the safety performance and electrochemical performance of lithium metal batteries.

Furthermore, in the raw materials of the polymer film, the molar ratio of the epoxy group derived from the polyepoxy compound to the amino group derived from the polyetheramine is (0.25-4):1, preferably (0.5-2):1; and/or the molar mass of the polyetheramine is 230-5000 g/mol, preferably 230-800 g/mol. Under the above conditions, the polyetheramine can be more fully cross-linked with the polyepoxy compound to form a polymer, which is more conducive to inhibiting the growth of lithium dendrites on the surface of lithium metal and improving the safety performance of the battery.

Furthermore, the lithium salt is selected from one or more of LiTFSI, LiFSI, LiClO ₄ , LiTF and LiBOB. The above lithium salts have stronger dissociation ability and higher conductivity, which are more conducive to improving the electrochemical performance of the lithium metal negative electrode.

Further, in the raw material of the polymer film, the weight percentage of lithium salt is 0.1-40%, preferably 15-40%, more preferably 18-30%; and/or the weight percentage of active additives is 0.1-20%, preferably 0.5-10%, more preferably 1-5%; preferably, the weight ratio of the sum of polyepoxy compounds and polyetheramines to lithium salt is (2.3-4.5):1; and/or the weight ratio of the sum of polyepoxy compounds and polyetheramines to active additives is (19-99):1. Under the above conditions, the raw material components can be more fully contacted, which is more conducive to the reaction of polyepoxy compounds and polyetheramines, and the components of the polymer film are more evenly distributed, which is more conducive to effective protection of lithium metal negative electrodes. In addition, the cost of polymer film raw materials is lower.

According to another aspect of the present invention, a method for in-situ protection of a lithium metal negative electrode is provided, comprising the following steps: mixing and degassing the raw materials of the polymer film for in-situ protection of the lithium metal negative electrode to form a slurry; coating the slurry on the surface of the lithium metal negative electrode and solidifying it to form a polymer film on the surface of the lithium metal negative electrode. In the in-situ protection method of the lithium metal negative electrode of the present invention, the raw materials of the polymer film used do not contain solvents, are safe and environmentally friendly, can effectively reduce the steps of heating and volatilizing the solvent, shorten the synthesis process, are simple to operate, are conducive to improving production efficiency, and have a wide range of raw materials, which is convenient for large-scale industrial applications. In addition, the viscosity of the slurry is moderate, the synthesis process of the polymer is simple, and the obtained polymer film has a high ionic conductivity, which can effectively inhibit the growth of lithium dendrites of the lithium metal negative electrode and reduce the side reactions caused by the contact between the lithium metal negative electrode and the electrolyte. The lithium metal negative electrode protected by the polymer film has stable cycle performance and greatly improved safety.

Furthermore, the curing temperature is 20 to 150° C. and/or the curing time is 1 to 240 hours; preferably, when the curing temperature is 70 to 125° C., the curing time is 4 to 6 hours; when the curing temperature is 20 to 30° C., the curing time is 120 to 240 hours. Under the above conditions, the polyepoxy compound reacts more fully with the polyetheramine, the production efficiency is higher, and the side reactions are less.

Furthermore, the thickness of the polymer film is 0.1 to 100 μm, preferably 10 to 40 μm. Under the above conditions, it is more conducive to inhibiting the growth of lithium dendrites.

According to another aspect of the present invention, a modified lithium metal negative electrode is provided, which is treated using the above-mentioned in-situ protection method. The lithium metal negative electrode is coated with a polymer film containing specific components, which can effectively inhibit the growth of lithium dendrites and the occurrence of interface side reactions, thereby making the modified lithium metal negative electrode stable in battery cycling and greatly improving safety.

According to another aspect of the present invention, a lithium metal battery is provided, comprising the modified lithium metal negative electrode. The lithium metal battery has stable performance and high safety performance.

The raw materials of the polymer film used for in-situ protection of lithium metal negative electrodes of the present invention do not contain solvents, which can effectively reduce the safety hazards caused by toxic solvents, is not easy to cause environmental pollution, and can avoid the problem of battery performance degradation caused by residual solvents. In the raw materials of the polymer film of the present invention, polyetheramine can be cross-linked with a polyepoxy group compound to obtain a polymer, and the polymer has high ionic conductivity and exhibits good electrochemical stability and chemical stability to lithium metal. When the polymer film of the present invention is used for in-situ protection of lithium metal negative electrodes, on the one hand, the polymer can play the role of a binder and can effectively adhere to the surface of the negative electrode. On the other hand, the polymer can actively react with lithium dendrites to form a stable SEI layer, which is beneficial to inhibiting the growth of lithium dendrites on the surface of lithium metal, avoiding lithium dendrites from puncturing the diaphragm, and effectively reducing fires and explosions caused by diaphragm puncture, thereby greatly improving the safety of lithium metal batteries; at the same time, it can also avoid side reactions between electrolyte and metallic lithium, which is beneficial to improving the coulomb efficiency of the battery. In addition, the active additive in the present invention is a solid electrolyte powder with high conductivity and excellent lithium ion conductivity. It can cooperate with lithium salts and polymers to greatly improve the conductivity of the polymer, effectively reduce battery impedance, and improve the battery's cycle and rate performance.

The lithium metal negative electrode in-situ protected by the polymer membrane of the present invention has stable cycle performance and greatly improved safety. In addition, the raw materials of the polymer membrane of the present invention are widely available and inexpensive, which is convenient for large-scale industrial application.

DETAILED DESCRIPTION

It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

As described in the background of the present invention, the prior art has the problem that the lithium metal negative electrode protection method cannot take into account environmental protection performance, safety performance and electrochemical performance. In order to solve the above problems, in a typical embodiment of the present invention, a polymer film for in-situ protection of lithium metal negative electrodes is provided, and the raw materials of the polymer film include: a polyepoxy compound, a polyether amine, a lithium salt and an active additive; wherein the active additive includes one or more of Li ₇ La ₃ Zr ₂ O ₁₂ , Li _6.4 La ₃ Zr _1.7 Ta _0.3 O ₁₂ , Li ₃ PS ₄ and Li ₇ P ₃ S ₁₁ .

The raw materials of the polymer film for in-situ protection of lithium metal negative electrodes of the present invention do not contain solvents, which can effectively reduce the safety hazards caused by toxic solvents and is not easy to cause environmental pollution. In addition, the step of heating and volatilizing the solvent is reduced during preparation, which effectively shortens the synthesis process flow, is simple to operate, is conducive to improving production efficiency, and can avoid the problem of battery performance degradation caused by residual solvents.

The polymer film raw materials of the present invention include polyepoxy compound and polyetheramine. The polyetheramine has an active group and can be cross-linked with the polyepoxy compound to obtain a new polymer, and the polymer has a high ionic conductivity. When the polymer film of the present invention is used for in-situ protection of lithium metal negative electrode, on the one hand, the polymer can play the role of a binder, so that the film is effectively attached to the negative electrode surface, and on the other hand, the polymer can actively react with lithium dendrites to form a stable SEI layer, which is beneficial to inhibiting the growth of lithium dendrites on the surface of lithium metal, avoiding lithium dendrites from puncturing the diaphragm, and effectively reducing fires and explosions caused by diaphragm puncture, thereby greatly improving the safety of lithium metal batteries; at the same time, it can also avoid side reactions between electrolyte and metallic lithium, which is beneficial to improving the coulomb efficiency of the battery.

In addition, the polymer membrane raw material of the present invention also includes active additives, which include one or more of Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₃ PS ₄ and Li ₇ P ₃ S _11. The above-mentioned active additives have good lithium ion conductivity, can cooperate with lithium salts and polymers to accelerate the lithium ion transmission effect, and are beneficial to improving the electrochemical performance of the negative electrode.

The lithium metal negative electrode in-situ protected by the polymer membrane of the present invention has stable cycle performance and greatly improved safety. In addition, the raw materials of the polymer membrane of the present invention are widely available and inexpensive, which is convenient for large-scale industrial application.

In a preferred embodiment, the polyepoxy compound is a glycidol derivative, preferably cyanuric acid epoxy resin and/or octaglycidyl propyl siloxane. The inventor has found through a large number of experiments that when the polyepoxy compound is a glycidol derivative, especially when it is cyanuric acid epoxy resin and/or octaglycidyl propyl siloxane with more than three active epoxy groups, the polyepoxy compound can form a polymer with a stable three-dimensional cross-linked structure with polyetheramine, and the chemical stability and electrochemical stability of the polymer are strong. It should be noted that cyanuric acid epoxy resin has excellent high temperature resistance, chemical stability, resistance to ultraviolet light aging and weather resistance, and good mechanical properties and electrical properties, especially at high temperatures, it can maintain excellent mechanical properties and electrical properties. The polymer obtained by the reaction of the resin with polyetheramine inherits the excellent chemical stability and mechanical properties of cyanuric acid epoxy resin. In addition, octaglycidyl propyl siloxane has a uniformly distributed cubic structure, and the polymer obtained after cross-linking with polyetheramine shows excellent toughness and flexibility, and excellent high temperature stability and chemical stability.

The specific type of polyepoxy compound of the present invention can react with polyetheramine to obtain a polymer with high conductivity. The polymer has good film-forming property. When used for in-situ protection of lithium metal negative electrode, the polymer film has better adhesion on the negative electrode surface and is more conducive to the formation of SEI film, thereby more effectively improving the safety performance and electrochemical performance of lithium metal batteries. Among them, the reaction principle of cyanuric acid epoxy resin and polyetheramine is as follows:

In order to make the polyetheramine more fully cross-linked with the polyepoxy compound, thereby further inhibiting the growth of lithium dendrites on the surface of lithium metal and improving the safety performance of the battery, in a preferred embodiment, the raw material of the polymer film, the molar ratio of the epoxy group derived from the polyepoxy compound to the amino group derived from the polyetheramine is (0.25-4):1, preferably (0.5-2):1. If the molar ratio of the epoxy group in the polyepoxy compound to the amino group in the polyetheramine is less than 0.25, the conductivity of the polymer may be reduced and the electrochemical performance may be deteriorated. If the molar ratio is greater than 4, the reaction may be unsafe, and too much polyepoxy compound will greatly reduce the concentration of active amino groups in the polyetheramine in the system. Excessive epoxy resin molecules will play the role of dispersed phase, which may be unfavorable for the formation of bulk macromolecules, making the viscosity of the polymer low, which may easily lead to poor film-forming properties of the polymer, or even unable to solidify, thereby being unfavorable for the formation of a polymer film on the surface of the lithium metal negative electrode, and the protection effect on the negative electrode is poor.

In order to facilitate practical application, in a preferred embodiment, the molar mass of the polyetheramine is 230 to 5000 g/mol, preferably 230 to 800 g/mol.

In a preferred embodiment, the lithium salt is selected from one or more of LiTFSI, LiFSI, LiClO ₄ , LiTF and LiBOB. The above lithium salts have stronger dissociation ability and higher conductivity, which are more conducive to improving the electrochemical performance of the lithium metal negative electrode.

In a preferred embodiment, the weight percentage of lithium salt in the raw material of the polymer film is 0.1-40%, preferably 15-40%, more preferably 18-30%; and/or the weight percentage of active additives is 0.1-20%, preferably 0.5-10%, more preferably 1-5%. Under the above conditions, the raw material components can be more fully contacted, which is more conducive to the reaction of the polyepoxy compound and the polyetheramine. Moreover, the distribution of the components of the polymer film is more uniform, which is more conducive to the effective protection of the lithium metal negative electrode. In addition, the cost of the raw material of the polymer film is lower.

Based on similar reasons, in a preferred embodiment, in the raw materials of the polymer membrane, the weight ratio of the sum of the polyepoxide compounds and the polyetheramines to the lithium salt is (2.3-4.5):1; and/or the weight ratio of the sum of the polyepoxide compounds and the polyetheramines to the active additives is (19-99):1, preferably (50-99):1, and more preferably (78-81):1.

In another typical embodiment of the present invention, a method for in-situ protection of a lithium metal negative electrode is also provided, comprising the following steps: mixing and degassing the raw materials of the aforementioned polymer film for in-situ protection of the lithium metal negative electrode to form a slurry; coating the slurry on the surface of the lithium metal negative electrode and curing it to form a polymer film on the surface of the lithium metal negative electrode.

In the in-situ protection method of the lithium metal negative electrode of the present invention, the raw material of the polymer film used does not contain solvent, is safe and environmentally friendly, can effectively reduce the step of heating and volatilizing the solvent, shorten the synthesis process, is simple to operate, is conducive to improving production efficiency, and has a wide source of raw materials, which is convenient for large-scale industrial application. In addition, the viscosity of the slurry is moderate, the synthesis process of the polymer is simple, and the obtained polymer film has a high ionic conductivity, which can effectively inhibit the growth of lithium dendrites of the lithium metal negative electrode and reduce the side reactions caused by the contact between the lithium metal negative electrode and the electrolyte. The lithium metal negative electrode protected by the polymer film has stable cycle performance and greatly improved safety.

The present invention can adopt gradient temperature steps for curing, and the curing time can also be extended indefinitely. In a preferred embodiment, the curing temperature is 20 to 150°C; and/or the curing time is 1 to 240h. Preferably, when the curing temperature is 70 to 125°C, the curing time is 4 to 6h. When the curing temperature is 70 to 125°C, if the curing time is less than 4h, incomplete reaction may occur, and if the curing time is more than 6h, low production efficiency may result. Preferably, when the curing temperature is 20 to 30°C, the curing time is 120 to 240h. Under the above conditions, the polyepoxy compound reacts more fully with the polyetheramine, and there are fewer side reactions.

In a preferred embodiment, the thickness of the polymer film is 0.1 to 100 μm. Under the above conditions, it is more conducive to inhibiting the growth of lithium dendrites. If the thickness of the polymer film is less than 0.1 μm, the thickness is too thin, which may be unfavorable for film formation, and the uniformity of the polymer film is poor. If the thickness of the polymer film is greater than 100 μm, it is easy to cause impedance increase, affecting the overall rate and capacity of the lithium battery. In a preferred embodiment, the thickness of the polymer film is 10 to 40 μm.

The coating may be carried out by conventional means, preferably one or more of spin coating, blade coating, spray coating, dipping and electrospinning.

According to the actual application requirements, the slurry can be coated on one side or both sides of the negative electrode material, or only part of the effective area can be coated, both of which can achieve effective protection of the lithium metal negative electrode.

The present invention does not impose any restrictions on the mixing method, temperature environment control method, or equipment. A variety of equipment methods can achieve consistent results. Except for the recommendation to operate in a dry room with humidity controlled at a dew point of -30°C (it can also be prepared in a non-dry room, but the lithium salt will absorb a certain amount of moisture, affecting the later battery application), there are no special requirements.

In a preferred embodiment, a modified lithium metal negative electrode is also provided, which is treated using the above-mentioned in-situ protection method. In the obtained modified lithium metal negative electrode, the lithium metal negative electrode is treated using the above-mentioned in-situ protection method, and the lithium metal negative electrode is coated with a polymer film containing a polymer, a lithium salt, and an active additive, which can effectively inhibit the growth of lithium dendrites and the occurrence of interface side reactions, so that the modified lithium metal negative electrode has stable performance during battery cycles and greatly improved safety.

In a preferred embodiment, a lithium metal battery is provided, comprising a negative electrode, wherein the negative electrode is the modified lithium metal negative electrode. The lithium metal battery of the present invention has stable performance and high safety performance.

The lithium metal battery of the present invention further comprises an electrolyte and a positive electrode, and the electrolyte and the positive electrode can be selected from materials commonly used by those skilled in the art. In a preferred embodiment, the electrolyte comprises one or more of LiPF ₆ , ethylene carbonate, dimethyl carbonate and diethyl carbonate; and/or the material of the positive electrode is one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate and nickel cobalt manganese.

Typically but not limiting, in the raw materials of the polymer film, the molar ratio of the epoxy groups derived from the polyepoxy compound to the amino groups derived from the polyetheramine is 0.25:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1 or a range consisting of any two of them.

Typically but not limiting, in the raw materials of the polymer membrane, the weight percentage of lithium salt is 0.1%, 1%, 5%, 10%, 15%, 18%, 20%, 25%, 30%, 35%, 40% or a range consisting of any two of them; the weight percentage of active additives is 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20% or a range consisting of any two of them.

Typically but not limiting, in the raw materials of the polymer membrane, the weight ratio of the sum of the polyepoxy compounds and the polyetheramine to the lithium salt is 2.3:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or a range consisting of any two of them; the weight ratio of the sum of the polyepoxy compounds and the polyetheramine to the active additive is 19:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 78:1, 80:1, 81:1, 90:1, 99:1 or a range consisting of any two of them.

Typically but not limiting, the curing temperature is 20°C, 30°C, 50°C, 70°C, 100°C, 125°C, 150°C or a range consisting of any two of them; the curing time is 1h, 4h, 5h, 6h, 10h, 50h, 100h, 120h, 150h, 200h, 240h or a range consisting of any two of them.

Typically but not limiting, the polymer film has a thickness of 0.1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm or a range consisting of any two of these values.

The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

Example 1

In the raw material of the polymer membrane, the molar ratio of epoxy groups derived from the polyepoxy compound (triglycidyl cyanurate epoxy resin) to amino groups derived from the polyetheramine (molar mass of 230 g/mol) is 1:1. In terms of weight percentage, the lithium salt (lithium bis(fluorosulfonyl)imide) accounts for 21% of the raw material of the polymer membrane, and the active additive (Li ₃ PS ₄ ) accounts for 1% of the raw material of the polymer membrane.

In an argon atmosphere glove box, under the condition of dew point > -40°C, the polymer film raw materials were mixed evenly and degassed to obtain a slurry. The slurry was scraped onto the surface of a 200 μm thick negative electrode material lithium sheet and cured at 80°C for 4 hours to form a polymer film on the surface of the lithium sheet to obtain a modified lithium sheet. The thickness of the polymer film was 10 μm.

The positive electrode (the positive electrode material is lithium iron phosphate), electrolyte (1 mol/L LiPF ₆ /EC+DMC (dimethyl carbonate)+DEC (diethyl carbonate)), PE separator, and modified lithium sheet were assembled into a CR2032 buckle to obtain a lithium metal battery, and a charge and discharge cycle test was performed.

Example 2

The only difference from Example 1 is:

In the raw material of the polymer membrane, the molar ratio of epoxy groups derived from the polyepoxy compound (triglycidyl cyanurate epoxy resin) to amino groups derived from the polyetheramine (molar mass of 230 g/mol) is 1: 1. In terms of weight percentage, the lithium salt (lithium bis(fluorosulfonyl)imide) accounts for 18% of the raw material of the polymer membrane, and the active additive (Li ₇ P ₃ S ₁₁ ) accounts for 1% of the raw material of the polymer membrane.

Example 3

In the raw materials of the polymer membrane, the molar ratio of epoxy groups derived from the polyepoxy compound (triglycidyl cyanurate epoxy resin) to amino groups derived from the polyetheramine (molar mass of 230 g/mol) is 0.25: 1. In terms of weight percentage, the lithium salt (LiFSI) accounts for 0.1% of the raw materials of the polymer membrane, and the active additive (Li ₇ La ₃ Zr ₂ O ₁₂ ) accounts for 20% of the raw materials of the polymer membrane.

In an argon atmosphere glove box, under the condition of dew point > -40°C, the polymer film raw materials were mixed evenly and degassed to obtain a slurry. The slurry was scraped onto the surface of a 200 μm thick negative electrode material lithium sheet and cured at 70°C for 6 hours to form a polymer film on the surface of the lithium sheet to obtain a modified lithium sheet. The thickness of the polymer film was 0.1 μm.

The positive electrode (the positive electrode material is lithium cobalt oxide), electrolyte (1 mol/L LiPF ₆ /EC+DMC (dimethyl carbonate)+DEC (diethyl carbonate)), PE separator, and modified lithium sheet were assembled into a CR2032 buckle to obtain a lithium metal battery, and a charge and discharge cycle test was performed.

Example 4

In the raw materials of the polymer membrane, the molar ratio of epoxy groups derived from the polyepoxy compound (triglycidyl cyanurate epoxy resin) to amino groups derived from the polyetheramine (molar mass of 800 g/mol) is 4: 1. In terms of weight percentage, lithium salt (LiClO ₄ ) accounts for 40% of the raw materials of the polymer membrane, and active additives (Li _6.4 La ₃ Zr _1.7 Ta _0.3 O ₁₂ ) account for 0.1% of the raw materials of the polymer membrane.

In an argon atmosphere glove box, under the condition of dew point > -40°C, the polymer film raw materials were mixed evenly and degassed to obtain a slurry. The slurry was scraped onto the surface of a 200 μm thick negative electrode material lithium sheet and cured at 25°C for 7 days to form a polymer film on the surface of the lithium sheet to obtain a modified lithium sheet. The thickness of the polymer film was 100 μm.

The positive electrode (the positive electrode material is lithium iron phosphate), electrolyte (1 mol/L LiPF ₆ /EC+DMC (dimethyl carbonate)+DEC (diethyl carbonate)), PE separator, and modified lithium sheet were assembled into a CR2032 buckle to obtain a lithium metal battery, and a charge and discharge cycle test was performed.

Example 5

In the raw materials of the polymer membrane, the molar ratio of epoxy groups derived from the polyepoxy compound (triglycidyl cyanurate epoxy resin) to amino groups derived from the polyetheramine (molar mass of 400 g/mol) is 1:1. In terms of weight percentage, lithium salt (LiTF) accounts for 30% of the raw materials of the polymer membrane, and active additives (Li ₃ PS ₄ ) account for 5% of the raw materials of the polymer membrane.

In an argon atmosphere glove box, under the condition of dew point > -40°C, the polymer film raw materials were mixed evenly and degassed to obtain a slurry. The slurry was scraped onto the surface of a 200 μm thick negative electrode material lithium sheet and cured at 125°C for 4 hours to form a polymer film on the surface of the lithium sheet to obtain a modified lithium sheet. The thickness of the polymer film was 10 μm.

The positive electrode (the positive electrode material is lithium iron phosphate), electrolyte (1 mol/L LiPF ₆ /EC+DMC (dimethyl carbonate)+DEC (diethyl carbonate)), PE separator, and modified lithium sheet were assembled into a CR2032 buckle to obtain a lithium metal battery, and a charge and discharge cycle test was performed.

Example 6

In the raw materials of the polymer membrane, the molar ratio of epoxy groups derived from the polyepoxy compound (triglycidyl cyanurate epoxy resin) to amino groups derived from the polyetheramine (molar mass of 200 g/mol) is 2: 1. In terms of weight percentage, the lithium salt (LiBOB) accounts for 40% of the raw materials of the polymer membrane, and the active additive (Li ₇ P ₃ S ₁₁ ) accounts for 0.5% of the raw materials of the polymer membrane.

In an argon atmosphere glove box, under the condition of dew point > -40°C, the polymer film raw materials were mixed evenly and degassed to obtain a slurry. The slurry was scraped onto the surface of a 200 μm thick negative electrode material lithium sheet and cured at 30°C for 120 hours to form a polymer film on the surface of the lithium sheet to obtain a modified lithium sheet. The thickness of the polymer film was 40 μm.

The positive electrode (the positive electrode material is lithium iron phosphate), electrolyte (1 mol/L LiPF ₆ /EC+DMC (dimethyl carbonate)+DEC (diethyl carbonate)), PE separator, and modified lithium sheet were assembled into a CR2032 buckle to obtain a lithium metal battery, and a charge and discharge cycle test was performed.

Example 7

In the raw materials of the polymer membrane, the molar ratio of epoxy groups derived from the polyepoxy compound (triglycidyl cyanurate epoxy resin) to amino groups derived from the polyetheramine (molar mass of 5000 g/mol) is 0.5: 1. In terms of weight percentage, the lithium salt (LiTFSI) accounts for 15% of the raw materials of the polymer membrane, and the active additive (Li ₇ La ₃ Zr ₂ O ₁₂ ) accounts for 10% of the raw materials of the polymer membrane.

In an argon atmosphere glove box, under the condition of dew point > -40°C, the polymer film raw materials were mixed evenly and degassed to obtain a slurry. The slurry was sprayed onto the surface of a 200 μm thick negative electrode material lithium sheet and cured at 80°C for 4 hours to form a polymer film on the surface of the lithium sheet to obtain a modified lithium sheet. The thickness of the polymer film was 10 μm.

The positive electrode (the positive electrode material is lithium iron phosphate), electrolyte (1 mol/L LiPF ₆ /EC+DMC (dimethyl carbonate)+DEC (diethyl carbonate)), PE separator, and modified lithium sheet were assembled into a CR2032 buckle to obtain a lithium metal battery, and a charge and discharge cycle test was performed.

Example 8

The only difference from Example 1 is:

In the raw material of the polymer membrane, the molar ratio of epoxy groups derived from the polyepoxy compound (octaglycidylpropylsiloxane) to amino groups derived from the polyetheramine (molar mass of 230 g/mol) is 1: 1. In terms of weight percentage, the lithium salt (lithium bis(fluorosulfonyl)imide) accounts for 21% of the raw material of the polymer membrane, and the active additive (Li ₃ PS ₄ ) accounts for 1% of the raw material of the polymer membrane.

Comparative Example 1

The only difference from Example 1 is:

The lithium sheets are not coated.

The test results of the charge and discharge voltage range, first cycle discharge capacity, 200 cycle discharge capacity, and capacity retention rate of the batteries prepared in the above examples and comparative examples are shown in Table 1.

Test method:

Charge and discharge cycle test: The test was carried out under the conditions of 0.5C and 25℃. Each group included 3 parallel samples, and each group of test data adopted the average value of the 3 parallel samples.

Table 1

As can be seen from the above, in the raw materials of the polymer film of the embodiment of the present invention, the polyetheramine and the polyepoxy group compound can be cross-linked to obtain a polymer. Compared with the comparative example, when the polymer film of the embodiment of the present invention is used for in-situ protection of the lithium metal negative electrode, the polymer can not only play the role of a binder, so that the film is effectively attached to the surface of the negative electrode, but also can actively react with lithium dendrites, inhibit the growth of lithium dendrites on the surface of lithium metal, and avoid lithium dendrites from puncturing the diaphragm. In addition, the polymer can also effectively avoid the electrolyte and metallic lithium from having side reactions, which is beneficial to improving the coulomb efficiency of the battery. In addition, in the raw materials of the membrane of the present invention, a specific type of active additive has good lithium ion conductivity, and cooperates with lithium salts and polymers to accelerate the lithium ion transmission effect, which is beneficial to improving the electrochemical performance of the negative electrode. In addition, it can be seen that when each process parameter is within the preferred range of the present invention, the negative electrode has higher safety and better electrochemical performance.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (10)

1. A polymer film for in-situ protection of a lithium metal negative electrode, characterized in that: The raw materials of the polymer film include: polyepoxy group compound, polyether amine, lithium salt and active additive; Wherein, the active additive includes one or more of Li ₇ La ₃ Zr ₂ O ₁₂ , Li _6.4 La ₃ Zr _1.7 Ta _0.3 O ₁₂ , Li ₃ PS ₄ and Li ₇ P ₃ S ₁₁ . 2 . The polymer film according to claim 1 , wherein the polyepoxy compound is selected from cyanuric acid epoxy resin and/or octaglycidylpropylsiloxane. 3. The polymer film according to claim 1 or 2, characterized in that the raw materials of the polymer film are: The molar ratio of the epoxy group derived from the polyepoxy compound to the amino group derived from the polyetheramine is (0.25-4):1, preferably (0.5-2):1; and/or The molar mass of the polyetheramine is 230 to 5000 g/mol, preferably 230 to 800 g/mol. 4 . The polymer membrane according to claim 1 , wherein the lithium salt is selected from one or more of LiTFSI, LiFSI, LiClO ₄ , LiTF and LiBOB. 5 . 5. The polymer membrane according to any one of claims 1 to 4, characterized in that the weight percentage of the lithium salt in the raw material of the polymer membrane is 0.1 to 40%, preferably 15 to 40%, more preferably 18 to 30%; and/or The weight percentage of the active additive is 0.1-20%, preferably 0.5-10%, more preferably 1-5%; Preferably, the weight ratio of the sum of the polyepoxide compound and the polyetheramine to the lithium salt is (2.3-4.5):1; and/or The weight ratio of the sum of the polyepoxy compound and the polyetheramine to the active additive is (19-99):1. 6. A method for in-situ protection of a lithium metal negative electrode, characterized in that it comprises the following steps: The raw materials of the polymer film for in-situ protection of the lithium metal negative electrode according to any one of claims 1 to 5 are mixed and degassed to form a slurry; the slurry is applied to the surface of the lithium metal negative electrode and solidified to form a polymer film on the surface of the lithium metal negative electrode. 7. The in-situ protection method according to claim 6, characterized in that: The curing temperature is 20 to 150° C.; and/or the curing time is 1 to 240 hours; Preferably, when the curing temperature is 70-125° C., the curing time is 4-6 hours; when the curing temperature is 20-30° C., the curing time is 120-240 hours. 8 . The in-situ protection method according to claim 6 or 7 , characterized in that the thickness of the polymer film is 0.1 to 100 μm, preferably 10 to 40 μm. 9. A modified lithium metal negative electrode, characterized in that it is treated using the in-situ protection method described in any one of claims 6 to 8. 10. A lithium metal battery comprising a negative electrode, characterized in that the negative electrode is the modified lithium metal negative electrode according to claim 9.