Surface modification method of lithium negative electrode, lithium negative electrode and lithium metal battery

Abstract

The invention provides a surface modification method of a lithium negative electrode, the lithium negative electrode and a lithium metal battery, the surface modification method of the lithium negative electrode comprises the following steps: dispersing graphite fluoride in a defluorination solvent for defluorination reaction to obtain a fluorinated solution; coating the surface of the lithium negative electrode with the fluorination liquid to carry out fluorination reaction, and forming a functional interface layer on the surface of the lithium negative electrode; removing redundant fluorination liquid on the surface of the functional interface layer to obtain the surface-modified lithium negative electrode; wherein the lithium negative electrode functional interface layer contains LiF. According to the surface modification method of the lithium negative electrode, SEI with LiF as a main component is artificially constructed on the surface of the lithium negative electrode, so that decomposition of an electrolyte and excessive consumption of lithium metal when SEI is generated in the running process of a lithium metal battery can be effectively reduced; when the obtained surface-modified lithium negative electrode is applied to a lithium metal battery, the cycling stability and safety of the lithium metal battery can be effectively improved. In addition, the modification method also has the advantages of higher stability, higher efficiency, simplicity in operation, safety and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium metal batteries, and in particular to a surface modification method of a lithium negative electrode, a lithium negative electrode and a lithium metal battery. Background Art

[0002] Since their commercialization in the 1990s, lithium-ion batteries have been widely used in consumer electronics, electric vehicles, and aerospace due to their advantages, such as high energy density, long cycle life, and lack of memory effect. However, with technological advancements and growing market demand, the demand for battery systems with higher energy density is becoming increasingly urgent. Conventional lithium-ion batteries use graphite as the anode material, with a theoretical specific capacity of 372 mAh / g. Although stable and reliable, they are no longer able to meet the requirements of future high-energy-density batteries. Lithium metal, as an ideal anode material, is considered the preferred anode material for next-generation high-energy-density batteries due to its ultra-high theoretical capacity of 3860 mAh / g and extremely low electrochemical potential (-3.040 V vs. standard hydrogen electrode). In particular, when paired with high-energy-density conversion cathode materials such as sulfur, oxygen, or fluoride, lithium metal batteries (LMBs) can achieve energy densities of up to 800 Wh / kg or more, significantly outperforming traditional lithium-ion batteries.

[0003] However, lithium metal faces a major challenge during use as an anode material: the growth of lithium dendrites. Not only can lithium dendrites penetrate the solid electrolyte interphase (SEI), leading to electrolyte decomposition and excessive lithium metal consumption, but they also continue to grow, increasing the risk of internal short circuits in the battery and seriously threatening the safety and lifespan of lithium metal batteries. Furthermore, the growth of lithium dendrites in lithium metal batteries is accompanied by significant volume changes, which can cause the SEI to rupture and peel, forming irreversible "dead lithium," accelerating the degradation of battery performance and further shortening the lifespan of lithium metal batteries.

[0004] To overcome the lithium dendrite problem, existing approaches have been proposed, primarily including the use of electrolyte additives, the construction of an artificial SEI, the modification of separators, and the design of three-dimensional lithium metal anodes. Among these, the construction of a functional SEI layer on the lithium metal surface has shown great potential due to its flexible design and long-lasting durability. This strategy typically involves optimizing the SEI composition and regulating its morphology to effectively inhibit lithium dendrite growth.

[0005] Prior art methods for constructing SEI films primarily include physical deposition, electrochemical deposition, and polymer coating. While these methods overcome the problem of lithium dendrite growth to some extent, potentially paving the way for the commercialization of lithium metal batteries, existing methods are limited in terms of operational complexity, cost, and efficiency. Therefore, developing a simple, low-cost, and highly efficient method for constructing an artificial SEI layer is of great significance for advancing lithium metal battery technology. To this end, the present invention is proposed. Summary of the Invention

[0006] The main purpose of the present invention is to provide a surface modification method for a lithium negative electrode, a lithium negative electrode, and a lithium metal battery. The purpose is to provide a surface modification method for a lithium negative electrode that is simple to operate, low in cost, and highly efficient, and to construct a functionalized interface layer containing LiF on the surface of the lithium negative electrode, thereby further achieving the purpose of further improving the safety and life of the lithium metal battery.

[0007] The present application provides a method for surface modification of a lithium negative electrode, which comprises the following steps: dispersing graphite fluoride in a defluorination solvent to carry out a defluorination reaction to obtain a fluoride liquid; applying the fluoride liquid to the surface of the lithium negative electrode to carry out a fluorination reaction to form a functionalized interface layer on the surface of the lithium negative electrode; removing excess fluoride liquid on the surface of the functionalized interface layer to obtain a surface-modified lithium negative electrode; wherein the functionalized interface layer of the lithium negative electrode contains LiF. The method of constructing a functionalized interface layer on the surface of a lithium negative electrode using a fluoride liquid prepared from graphite fluoride can not only efficiently generate LiF, but also ensure the safety, controllability and cost-effectiveness of the preparation process, and the constructed functionalized interface layer has the advantages of being uniform, stable and dense. The obtained surface-modified lithium negative electrode is used in a lithium metal battery to effectively solve the problem of lithium dendrites in the lithium metal battery and improve the cycle stability and safety of the lithium metal battery.

[0008] Furthermore, the fluorine content of the fluorinated graphite is 30 to 70 wt %, preferably 50 to 62 wt %. Controlling the fluorine content of the fluorinated graphite within the above range enables the fluorinated graphite to release an appropriate amount of free hydrogen fluoride in the fluorination solution, which is beneficial for further improving the stability and safety of lithium metal batteries.

[0009] Furthermore, the defluorination reaction time is 0.5 to 5 hours, and the defluorination reaction temperature is 25 to 200°C; preferably, the defluorination reaction time is 2 to 5 hours, and the defluorination reaction temperature is 60 to 100°C; preferably, the fluorination reaction time is 3 to 10 minutes; preferably, the thickness of the lithium negative electrode functionalized interface layer is 10 to 200 nm; more preferably, the thickness of the lithium negative electrode functionalized interface layer is 20 to 80 nm. Controlling the thickness of the lithium negative electrode functionalized interface layer within the above range can not only more effectively passivate the lithium metal negative electrode surface, reduce the occurrence of side reactions during the operation of the lithium metal battery, and improve the coulombic efficiency of the lithium metal battery; at the same time, the thickness will not excessively increase the internal resistance of the battery, thereby improving the performance of the lithium metal battery and achieving the best balance between performance and effect.

[0010] Furthermore, the weight content of fluorinated graphite in the defluorination solvent is 0.02-0.06 g / mL. Preferably, the weight content of element F in the functionalized interface layer of the surface-modified lithium negative electrode is 10-50%; more preferably, the weight content of element F in the functionalized interface layer of the surface-modified lithium negative electrode is 15-40%. Preferably, the lithium negative electrode material is at least one of metallic lithium or a lithium-metal alloy. Controlling the weight content of fluorine in the functionalized interface layer within the above range can better utilize the function of the functionalized interface layer, which is beneficial for further improving the electrochemical performance and safety of lithium metal batteries.

[0011] Furthermore, the coating method is spraying or brushing; preferably, the coating process is carried out in a glove box or a dry room.

[0012] Furthermore, the defluorination solvent is one or more of benzylamine, tetramethylethylenediamine and ethylenediamine.

[0013] Furthermore, the operation of removing excess fluoride liquid on the surface of the functionalized interface layer includes: washing away excess fluoride liquid on the surface of the functionalized interface layer with an organic solvent, and then vacuum drying it to obtain a surface-modified lithium negative electrode; or, the operation of removing excess fluoride liquid on the surface of the functionalized interface layer includes: drying the lithium negative electrode including the functionalized interface layer containing excess fluoride liquid to obtain a surface-modified lithium negative electrode.

[0014] Furthermore, the organic solvent is one or more of ethylene glycol dimethyl ether, 1,3-dioxolane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; preferably, the drying temperature is 20-80°C and the drying time is 0.5-2h; preferably, the drying temperature is 150-180°C and the time is 8-15min.

[0015] According to another aspect of the present invention, a lithium negative electrode is provided. The lithium negative electrode is a surface-modified lithium negative electrode obtained by the above-mentioned modification method.

[0016] According to a third aspect of the present invention, a lithium metal battery is further provided, comprising the above-mentioned lithium negative electrode.

[0017] In the surface modification method of the lithium negative electrode provided by the present invention, the fluorinated graphite is first subjected to a defluorination reaction in a defluorinating solvent to generate a fluoride liquid containing free hydrogen fluoride; the obtained fluoride liquid is then applied to the surface of the lithium negative electrode, and the free hydrogen fluoride in the fluoride liquid reacts with the lithium element on the surface of the lithium negative electrode to generate a LiF compound, thereby constructing a functionalized interface layer on the surface of the lithium negative electrode to achieve the purpose of modifying the surface of the lithium negative electrode; finally, the excess fluoride liquid on the surface of the functionalized interface layer is removed to obtain a surface-modified lithium negative electrode. The surface modification method of the lithium negative electrode provided by the present invention can effectively reduce the decomposition of the electrolyte and excessive consumption of lithium metal when the battery generates SEI during operation by artificially constructing a SEI whose main component is LiF on the surface of the lithium negative electrode. In addition, the functionalized interface layer containing LiF generated by the surface modification method of the lithium negative electrode according to the present invention has the advantages of being more stable and more efficient, and the preparation process is safe and simple, without the need to introduce expensive HF gas or other fluorinating agents. Furthermore, graphite fluoride, as an industrial raw material, is relatively low in cost, which not only reduces the cost of constructing the SEI membrane but also improves the economic benefits of the entire battery manufacturing process. The preparation method of the present invention is particularly suitable for large-scale production of surface-modified lithium anodes.

[0018] In summary, the method of constructing a functionalized interfacial layer on the surface of a lithium anode using a fluorinated solution prepared from graphite fluoride not only efficiently generates LiF, but also ensures a safe, controllable, and cost-effective preparation process. The constructed functionalized interfacial layer is uniform, stable, and dense. The resulting surface-modified lithium anode is used in lithium metal batteries to effectively solve the problem of lithium dendrites in lithium metal batteries and improve their cycling stability and safety. DETAILED DESCRIPTION

[0019] 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 with reference to the embodiments.

[0020] As described in the background technology section, the growth problem of lithium dendrites is a major challenge faced by metallic lithium in the application process of batteries. Lithium dendrites can not only penetrate the solid electrolyte interface layer (SEI), leading to electrolyte decomposition and excessive consumption of lithium metal, but also continue to grow, increasing the risk of internal short circuits in the battery, seriously threatening the safety and life of the battery. In addition, the growth of lithium dendrites is also accompanied by volume changes, which may cause the rupture and peeling of SEI, forming irreversible "dead lithium", accelerating the decay of battery performance, and reducing the cycle stability of lithium metal batteries. Therefore, finding a surface modification method for lithium negative electrodes that is simple to operate, low in cost, and high in efficiency, constructing a functionalized interface layer on the surface of the lithium negative electrode, and improving the safety and life of the battery is the key to overcoming the lithium dendrite problem and improving the service life and safety of lithium metal batteries.

[0021] In order to solve the above problems, the present invention provides a surface modification method for a lithium negative electrode, which comprises the following steps: dispersing fluorinated graphite in a defluorinating solvent to perform a defluorination reaction to obtain a fluorinated liquid; applying the fluorinated liquid to the surface of the lithium negative electrode to perform a fluorination reaction to form a functionalized interface layer on the surface of the lithium negative electrode; removing excess fluorinated liquid on the surface of the functionalized interface layer to obtain a surface-modified lithium negative electrode; wherein the functionalized interface layer of the lithium negative electrode contains LiF. In the above surface modification method for a lithium negative electrode, the fluorinated graphite is first subjected to a defluorination reaction in a defluorinating solvent to generate a fluorinated liquid containing free hydrogen fluoride; the obtained fluorinated liquid is then applied to the surface of the lithium negative electrode. During this process, the free hydrogen fluoride in the fluorinated liquid can react with the lithium element on the surface of the lithium negative electrode to generate a functionalized interface layer containing LiF; finally, the excess fluorinated liquid on the surface of the functionalized interface layer is removed to obtain a surface-modified lithium negative electrode.

[0022] As mentioned above, during the operation of lithium metal batteries, the formation of a solid electrolyte interface layer (SEI) whose main component is LiF will lead to the decomposition of the electrolyte in the battery and excessive consumption of lithium metal in the lithium negative electrode. In addition, the SEI in the battery will continue to grow as the battery operates, increasing the risk of internal short circuits in the battery, seriously threatening the safety and life of the battery. The construction of artificial SEI can effectively alleviate the above effects. On the one hand, LiF has high mechanical strength, which can enhance the stability and toughness of the SEI layer, effectively prevent the penetration and growth of lithium dendrites, and at the same time reduce the direct contact between the electrolyte and lithium metal, reduce the occurrence of side reactions, and improve coulombic efficiency. On the other hand, the presence of LiF can also reduce the resistance of the SEI layer and optimize the electrochemical performance.

[0023] The surface modification method of the lithium negative electrode described in the present invention, by artificially constructing a SEI with LiF as the main component on the surface of the lithium negative electrode, can effectively reduce the decomposition of the electrolyte and excessive consumption of lithium metal when the SEI is generated during the operation of the battery. The functionalized interface layer containing LiF generated by the surface modification method of the lithium negative electrode described in the present invention has the advantages of being more stable and more efficient. First, the fluorinated graphite in the fluoridation liquid can serve as a continuous fluorine source, which can ensure the formation of a uniform and dense LiF functionalized interface layer on the surface of the lithium negative electrode. Second, the surface modification method of the lithium negative electrode described above has the advantages of strong controllability, simple operation, and high safety. The fluoridation liquid prepared using graphite fluoride can further adjust the parameters of the defluorination reaction and fluorination reaction to accurately control the amount of LiF generated and the characteristics of the constructed SEI layer, thereby achieving controllable modification process. At the same time, the fluorinated graphite can gently release HF in the defluorination solvent, avoiding the safety risks of directly using HF gas for treatment and reducing the danger during the treatment process. The generation and release of HF are carried out in a closed system, further ensuring operational safety. In addition, graphite fluoride, as an industrial raw material, is relatively low-cost and has a simple preparation process, without the need for the introduction of expensive HF gas or other fluorinating agents. This further reduces the cost of constructing the SEI membrane and improves the economic benefits of the entire battery manufacturing process.

[0024] In summary, the method of constructing a functionalized interface layer on the surface of a lithium anode using a fluorinated solution prepared from graphite fluoride not only efficiently generates LiF, but also ensures a safe, controllable, and cost-effective preparation process. The constructed functionalized interface layer has the advantages of being uniform, stable, and dense. The resulting surface-modified lithium anode is used in lithium metal batteries to effectively solve the problem of lithium dendrites in lithium metal batteries and improve the cycling stability and safety of lithium metal batteries.

[0025] In a preferred embodiment, the fluorine content in the fluorinated graphite is 30-70 wt%, specifically, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any content between any two of the above; controlling the fluorine content in the fluorinated graphite within the above range can enable the fluorinated graphite to release a suitable amount of free hydrogen fluoride in the fluorinated liquid, and the appropriate amount of free hydrogen fluoride is conducive to the rapid and uniform generation of a dense LiF layer, thereby forming a dense and efficient functionalized interface layer containing LiF on the surface of the lithium negative electrode, which is conducive to further improving the stability and safety of the lithium metal battery. Preferably, the fluorine content in the fluorinated graphite is 50-62 wt%; specifically, for example, 50%, 52%, 54%, 56%, 58%, 60%, 62%, or any content between any two of the above. Controlling the fluorine content in the fluorinated graphite within the above preferred range has a better effect on the surface modification of the lithium negative electrode.

[0026] In a preferred embodiment, the defluorination reaction time is 0.5 to 5 hours, and the defluorination reaction temperature is 25 to 200°C. Controlling the defluorination reaction time and defluorination reaction temperature within the above ranges is conducive to better defluorination reaction performance, and can make the content of free hydrofluoric acid in the fluorination solution within a more appropriate range, which is conducive to further improving the effect of the functionalized interface layer formed on the surface of the lithium negative electrode. Preferably, the defluorination reaction time is 2 to 5 hours, and the defluorination reaction temperature is 60 to 100°C. Controlling the defluorination reaction temperature and time within the above preferred ranges can further improve the effect of the functionalized interface layer formed on the surface of the lithium negative electrode.

[0027] Preferably, the fluorination reaction time is 3 to 10 minutes; preferably, the thickness of the lithium negative electrode functionalized interface layer is 10 to 200 nm; specifically, for example, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, or any thickness between any two of the above; controlling the fluorination reaction time within the above range can enable the LiF functionalized interface layer to be more fully formed. Controlling the thickness of the lithium negative electrode functionalized interface layer within the above range can more effectively passivate the surface of the lithium metal negative electrode, thereby facilitating the avoidance of direct contact between the lithium metal negative electrode and the electrolyte and lithium metal, reducing the occurrence of side reactions during the operation of the lithium metal battery, and improving the coulombic efficiency of the lithium metal battery; at the same time, the thickness will not excessively increase the internal resistance of the battery, thereby improving the performance of the lithium metal battery and achieving the best balance between performance and effect. More preferably, the thickness of the lithium negative electrode functionalized interface layer is 20 to 80 nm, for example, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, or any thickness between any two of the above; when the thickness of the lithium negative electrode functionalized interface layer is controlled within the above range, the above effect is better, which is conducive to further improving the electrochemical performance of lithium metal batteries.

[0028] In a preferred embodiment, the weight content of fluorinated graphite in the defluorination solvent is 0.02 to 0.06 g / mL; controlling the weight content of fluorinated graphite in the defluorination solvent within the above range is conducive to better progress of the defluorination reaction, and at the same time can further control the concentration of free hydrogen fluoride in the fluorination liquid, which is conducive to the subsequent fluorination liquid being able to better form a functional interface layer on the surface of the lithium negative electrode. Preferably, the weight content of the F element in the functional interface layer of the surface-modified lithium negative electrode is 10 to 50%; specifically, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any weight content between any two of the above; controlling the weight content of the fluorine element in the functional interface layer within the above range can better play the role of the functional interface layer, which is conducive to further improving the electrochemical performance and safety of the lithium metal battery. More preferably, the weight content of the F element in the functional interface layer of the surface-modified lithium negative electrode is 15 to 40%; controlling the weight content of the F element in the functional interface layer within the above range will achieve even better results. More preferably, the weight content of the F element in the functionalized interface layer of the surface-modified lithium negative electrode is 20-35%. Controlling the weight content of the F element in the functionalized interface layer within the above range is beneficial for further improving the electrochemical performance of lithium metal batteries. Preferably, the material of the lithium negative electrode is at least one of metallic lithium or a lithium metal alloy. The use of metallic lithium or a lithium metal alloy (specifically, lithium aluminum alloy, lithium magnesium alloy, lithium zinc alloy, lithium tin alloy, lithium indium alloy, and lithium antimony alloy) as the material of the lithium negative electrode can cause a fluorination reaction with the fluoride solution to form a lithium negative electrode functionalized interface layer containing LiF.

[0029] In a preferred embodiment, the coating method is spraying or brushing. In fact, the present application does not strictly limit the coating method. Any method that can evenly coat the fluorinated liquid on the surface of the lithium negative electrode is acceptable, and spraying or brushing is easier to control the coating thickness and uniform coating effect. Preferably, the coating process is carried out in a glove box or dry room. The water-free and oxygen-free conditions in the glove box or dry room avoid the corrosion of lithium metal by moisture and oxygen in the air, ensure the purity and stability of the functionalized interface layer of the lithium negative electrode, and help to make the functionalized interface layer formed on the surface of the lithium negative electrode have better performance.

[0030] In a preferred embodiment, the defluorinating solvent is one or more of benzylamine, tetramethylethylenediamine and ethylenediamine. The above-mentioned defluorinating solvents have active amino groups and can undergo nucleophilic substitution reactions with fluorinated graphite, thereby allowing the fluorinated graphite to undergo a mild defluorination reaction to generate a fluorinated liquid. In addition, the above-mentioned defluorinating solvents have good solubility and low toxicity, and are more suitable for large-scale production.

[0031] In a preferred embodiment, the operation of removing excess fluorine liquid on the surface of the functionalized interface layer includes: washing away excess fluorine liquid on the surface of the functionalized interface layer with an organic solvent, and then vacuum drying it to obtain a surface-modified lithium negative electrode; or, the operation of removing excess fluorine liquid on the surface of the functionalized interface layer includes: drying the lithium negative electrode including the functionalized interface layer containing excess fluorine liquid to obtain a surface-modified lithium negative electrode. The method of washing the surface of the functionalized interface layer with an organic solvent and then vacuum drying it can remove the residual unreacted fluorine liquid; the operation of directly drying the lithium negative electrode of the functionalized interface layer can, on the one hand, volatilize the residual organic solvent, and on the other hand, further convert the metallic lithium into a molten state, so that the residual fluorinated graphite and the defluorinated graphite together with LiF form an SEI protective film. Both of the above-mentioned post-treatment methods can achieve the purpose of further improving the performance of the functionalized interface layer of the lithium negative electrode.

[0032] Preferably, the organic solvent is one or more of ethylene glycol dimethyl ether, 1,3-dioxolane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. All of the above organic solvents are chemically stable and do not react with lithium metal. Preferably, the drying temperature is 20-80°C and the drying time is 0.5-2 hours; preferably, the drying temperature is 150-180°C and the drying time is 8-15 minutes. The above-mentioned operation of removing the fluorinated liquid from the surface of the functionalized interface layer of the lithium negative electrode can further enhance the barrier effect of the functionalized interface layer on the surface of the lithium negative electrode. Controlling the drying temperature and drying time, and the drying temperature and drying time within the above-mentioned ranges, can achieve better organic solvent removal.

[0033] According to another aspect of the present invention, a lithium anode is provided, which is a surface-modified lithium anode obtained by the above-mentioned modification method. It should be further noted that due to the specificity of the field, the surface-modified lithium anode prepared by the above-mentioned preparation method in this application cannot be fully characterized. However, experiments have demonstrated that the surface-modified lithium anode has significant properties in improving the cycling stability and safety of lithium metal batteries.

[0034] According to a third aspect of the present invention, a lithium metal battery is provided, comprising the lithium anode described above. The lithium anode with a functionalized interface layer prepared using the method of the present invention is used in the lithium metal battery to effectively inhibit the growth of lithium dendrites during cycling, significantly improving the cycling stability and safety of the lithium metal battery.

[0035] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0036] Example 1

[0037] 0.45 g of fluorinated graphite (fluorine content in fluorinated graphite is 62.7 wt%) was dispersed in 7 mL of benzylamine and stirred at 65 ° C for 2 h to obtain a fluorinated solution. The fluorinated solution was sprayed on the surface of the lithium metal negative electrode and allowed to stand for 3 min to undergo a fluorination reaction, thereby forming a functionalized interface layer containing LiF on the surface of the lithium metal negative electrode; wherein the amount of fluorinated solution sprayed on the surface of the lithium metal negative electrode was 2 mg / cm 2 After using ethylene glycol dimethyl ether to remove excess fluorine liquid on the surface of the functionalized interface layer, the lithium metal anode was dried at 50°C for 1 hour to obtain a surface-modified lithium anode. The thickness of the functionalized interface layer of the surface-modified lithium anode was 46 nm.

[0038] The surface-modified lithium anode was assembled into a lithium metal symmetric battery in an argon atmosphere glove box for electrochemical testing.

[0039] Example 2

[0040] 0.45 g of fluorinated graphite (fluorine content in fluorinated graphite is 62.7 wt%) was dispersed in 7 mL of benzylamine and stirred at 90 ° C for 2 h to obtain a fluorinated solution. The fluorinated solution was sprayed on the surface of the lithium metal negative electrode and allowed to stand for 3 min to undergo a fluorination reaction, thereby forming a functionalized interface layer containing LiF on the surface of the lithium metal negative electrode; wherein the amount of fluorinated solution sprayed on the surface of the lithium metal negative electrode was 2 mg / cm 2 The lithium metal anode was dried at 180° C. for 10 min to obtain a surface-modified lithium anode. The thickness of the functionalized interface layer of the surface-modified lithium anode was 80 nm.

[0041] The surface-modified lithium anode was assembled into a lithium metal symmetric battery in an argon atmosphere glove box for electrochemical testing.

[0042] Example 3

[0043] 0.45 g of fluorinated graphite (fluorine content in fluorinated graphite is 30 wt%) was dispersed in 7 mL of tetramethylethylenediamine and stirred at 25 ° C for 5 h to obtain a fluorinated solution. The fluorinated solution was sprayed on the surface of the lithium metal negative electrode and allowed to stand for 10 min to undergo a fluorination reaction, thereby forming a functionalized interface layer containing LiF on the surface of the lithium metal negative electrode; wherein the amount of fluorinated solution sprayed on the surface of the lithium metal negative electrode was 2 mg / cm 2 After using ethylene glycol dimethyl ether to remove excess fluorine liquid on the surface of the functionalized interface layer, the lithium metal anode was dried at 20°C for 2 hours to obtain a surface-modified lithium anode. The thickness of the obtained surface-modified lithium anode functionalized interface layer was 40 nm.

[0044] The surface-modified lithium anode was assembled into a lithium metal symmetric battery in an argon atmosphere glove box for electrochemical testing.

[0045] Example 4

[0046] 0.45 g of fluorinated graphite (fluorine content in fluorinated graphite is 70 wt%) was dispersed in 7 mL of ethylenediamine and stirred at 200 ° C for 0.5 h to obtain a fluorinated solution. The fluorinated solution was sprayed on the surface of the lithium metal negative electrode and allowed to stand for 3 minutes to undergo a fluorination reaction, thereby forming a functionalized interface layer containing LiF on the surface of the lithium metal negative electrode; wherein the amount of fluorinated solution sprayed on the surface of the lithium metal negative electrode was 2 mg / cm 2 After using ethylene glycol dimethyl ether to remove excess fluorine liquid on the surface of the functionalized interface layer, the lithium metal anode was dried at 80°C for 0.5h to obtain a surface-modified lithium anode. The thickness of the surface-modified lithium anode functionalized interface layer was 30nm.

[0047] The surface-modified lithium anode was assembled into a lithium metal symmetric battery in an argon atmosphere glove box for electrochemical testing.

[0048] Example 5

[0049] 0.45 g of fluorinated graphite (fluorine content in fluorinated graphite is 50 wt%) was dispersed in 7 mL of benzylamine and stirred at 60 ° C for 2 h to obtain a fluorinated solution. The fluorinated solution was sprayed on the surface of the lithium metal negative electrode and allowed to stand for 3 min to undergo a fluorination reaction, thereby forming a functionalized interface layer containing LiF on the surface of the lithium metal negative electrode; wherein the amount of fluorinated solution sprayed on the surface of the lithium metal negative electrode was 2 mg / cm 2 After using ethylene glycol dimethyl ether to remove excess fluorine liquid on the surface of the functionalized interface layer, the lithium metal anode was dried at 50°C for 1 hour to obtain a surface-modified lithium anode. The thickness of the functionalized interface layer of the surface-modified lithium anode was 36 nm.

[0050] The surface-modified lithium anode was assembled into a lithium metal symmetric battery in an argon atmosphere glove box for electrochemical testing.

[0051] Example 6

[0052] 0.45 g of fluorinated graphite (fluorine content in fluorinated graphite is 62 wt%) was dispersed in 7 mL of benzylamine and stirred at 100 ° C for 2 h to obtain a fluorinated solution. The fluorinated solution was sprayed on the surface of the lithium metal negative electrode and allowed to stand for 3 min to undergo a fluorination reaction, thereby forming a functionalized interface layer containing LiF on the surface of the lithium metal negative electrode; wherein the amount of fluorinated solution sprayed on the surface of the lithium metal negative electrode was 2 mg / cm 2 After using ethylene glycol dimethyl ether to remove excess fluorine liquid on the surface of the functionalized interface layer, the lithium metal anode was dried at 50°C for 1 hour to obtain a surface-modified lithium anode. The thickness of the functionalized interface layer of the surface-modified lithium anode was 50 nm.

[0053] The surface-modified lithium anode was assembled into a lithium metal symmetric battery in an argon atmosphere glove box for electrochemical testing.

[0054] Example 7

[0055] The difference between Example 7 and Example 1 is that the amount of fluoride solution sprayed on the surface of the lithium metal negative electrode is 1 mg / cm 2 The fluorination reaction time is 1 min, and the thickness of the surface-modified lithium negative electrode functional interface layer is 10 nm.

[0056] Example 8

[0057] The difference between Example 8 and Example 1 is that the amount of fluoride solution sprayed on the surface of the lithium metal negative electrode is 5 mg / cm 2 The fluorination reaction time is 3 minutes, and the thickness of the surface-modified lithium negative electrode functional interface layer is 200 nm.

[0058] Example 9

[0059] The difference between Example 9 and Example 1 is that the amount of fluoride solution sprayed on the surface of the lithium metal negative electrode is 1 mg / cm 2 The fluorination reaction time is 3 min, and the thickness of the surface-modified lithium negative electrode functional interface layer is 20 nm.

[0060] Example 10

[0061] The difference between Example 10 and Example 1 is that the amount of fluoride solution sprayed on the surface of the lithium metal negative electrode is 5 mg / cm 2 The fluorination reaction time is 3 min, and the thickness of the surface-modified lithium negative electrode functional interface layer is 50 nm.

[0062] Example 11

[0063] 0.45 g of fluorinated graphite (fluorine content in fluorinated graphite is 20 wt%) was dispersed in 7 mL of benzylamine and stirred at 30 ° C for 10 min to obtain a fluorination solution. The fluorination solution was sprayed on the surface of the lithium metal negative electrode and allowed to stand for 1 min to undergo a fluorination reaction, thereby forming a functionalized interface layer containing LiF on the surface of the lithium metal negative electrode; wherein the amount of fluorination solution sprayed on the surface of the lithium metal negative electrode was 2 mg / cm 2 After using ethylene glycol dimethyl ether to remove excess fluorine liquid on the surface of the functionalized interface layer, the lithium metal anode was dried at 50°C for 1 hour to obtain a surface-modified lithium anode. The thickness of the functionalized interface layer of the surface-modified lithium anode was 8 nm.

[0064] The surface-modified lithium anode was assembled into a lithium metal symmetric battery in an argon atmosphere glove box for electrochemical testing.

[0065] Example 12

[0066] 0.45 g of fluorinated graphite (fluorine content in fluorinated graphite is 70 wt%) was dispersed in 7 mL of benzylamine and stirred at 100 ° C for 2 min to obtain a fluorinated solution. The fluorinated solution was sprayed on the surface of the lithium metal negative electrode and allowed to stand for 15 min to undergo a fluorination reaction, thereby forming a functionalized interface layer containing LiF on the surface of the lithium metal negative electrode; wherein the amount of fluorinated solution sprayed on the surface of the lithium metal negative electrode was 2 mg / cm 2 After using ethylene glycol dimethyl ether to remove excess fluorine liquid on the surface of the functionalized interface layer, the lithium metal anode was dried at 50°C for 1 hour to obtain a surface-modified lithium anode. The thickness of the functionalized interface layer of the surface-modified lithium anode was 300 nm.

[0067] The surface-modified lithium anode was assembled into a lithium metal symmetric battery in an argon atmosphere glove box for electrochemical testing.

[0068] Comparative Example 1

[0069] The unmodified lithium metal negative electrode in Example 1 was used as the negative electrode of the lithium metal symmetric battery.

[0070] The fluorine content in the lithium negative electrode functionalized interface layer prepared in the above embodiment was first tested, and the test results are shown in Table 1. The weight content of fluorine in the negative electrode lithium negative electrode functionalized interface layer was determined by measuring the fluorine content in the formed functionalized interface layer using the XPS test method to determine the weight content of fluorine in the negative electrode lithium negative electrode functionalized interface layer.

[0071] The lithium metal anode with the functionalized interface layer prepared in the above examples and the unmodified lithium metal anode in the comparative example were used to prepare lithium metal symmetric batteries. The electrochemical performance of the corresponding lithium metal symmetric batteries was tested, and the test results are shown in Table 2. The preparation process and test parameters of the lithium metal symmetric batteries are as follows.

[0072] Preparation of lithium metal symmetrical battery: electrolyte: 1 mol / L LiTFSI / DOL:DME with added 1 wt% LiNO3, wherein the volume ratio of DOL (1,3-dioxolane) to DME (ethylene glycol dimethyl ether) is 1:1; diaphragm: Celgard 2400; assembly of lithium metal symmetrical battery: assemble the battery in the order of positive electrode shell, lithium metal negative electrode with functionalized interface layer, electrolyte, diaphragm, lithium metal negative electrode with functionalized interface layer, and negative electrode shell, and press and seal with a fully automatic packaging machine to obtain a lithium metal symmetrical battery.

[0073] Performance test of lithium metal symmetrical battery: After the lithium metal symmetrical battery prepared above was left to stand for 24 hours, electrochemical test was carried out using Xinwei test cabinet; the electrochemical test was carried out at 25 ° C, mainly including constant current charge and discharge test, respectively at a current density of 1mA / cm 2 , with a capacity of 1 mAh / cm 2 Under the conditions of current density 3mA / cm 2 , with a capacity of 3 mAh / cm 2 The battery's stable charge and discharge overpotential, cycle life, and safety are tested under certain conditions. A lithium metal battery is considered to have better electrochemical performance if it exhibits lower stable charge and discharge overpotential, longer service life, and is less susceptible to short circuits.

[0074] Table 1

[0075]

[0076]

[0077] Table 2

[0078]

[0079]

[0080] Table 3

[0081]

[0082] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0083] In Examples 1 to 12, the surface of the lithium negative electrode was modified using a fluorinated liquid prepared by reacting graphite fluoride with a defluorinating solvent to obtain a lithium negative electrode containing a functionalized interface layer of LiF, and the surface-modified lithium negative electrode was used to prepare a lithium metal battery. According to the results in Tables 1, 2, and 3, the cycle life of the lithium metal batteries corresponding to the above examples was greatly improved, and the safety performance of the corresponding lithium metal batteries was also better. In particular, in Examples 1 to 10, the parameters in the modification process of the lithium negative electrode were controlled within the preferred range, and the corresponding lithium metal battery had a better cycle life and a lower stable overpotential for charge and discharge.

[0084] In contrast, in Comparative Example 1, an unmodified lithium metal negative electrode is used as the negative electrode of a lithium metal symmetric battery. Although the corresponding lithium metal battery has a stable charge and discharge overpotential at a low level, its cycle life is significantly lower than that of the embodiments of the present application. In addition, the safety of the lithium metal battery corresponding to Comparative Example 1 is also poor, making it difficult to meet basic usage requirements.

[0085] In summary, the method provided by the present application is used to artificially construct a SEI whose main component is LiF on the surface of a lithium negative electrode, which can effectively reduce the decomposition of the electrolyte and the excessive consumption of lithium metal when the battery generates SEI during operation, and inhibit the growth of lithium dendrites. The generated functionalized interface layer containing LiF not only has the advantages of being more stable and more efficient, but also has a simple and safe preparation process and low preparation cost. The lithium metal negative electrode with a functionalized interface layer prepared by the present invention is used in a lithium metal battery, and the obtained lithium metal battery has good cycle stability and rate performance, and has broad application prospects in the fields of portable electronic devices, electric vehicles, aerospace, etc.

[0086] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for surface modification of a lithium negative electrode, characterized in that: The method comprises the following steps: dispersing the fluorinated graphite in a defluorinating solvent to perform a defluorinating reaction to obtain a fluorinated liquid; The fluorination liquid is applied to the surface of the lithium negative electrode to perform a fluorination reaction, thereby forming a functionalized interface layer on the surface of the lithium negative electrode; excess fluorination liquid on the surface of the functionalized interface layer is removed to obtain a surface-modified lithium negative electrode; wherein the lithium negative electrode functionalized interface layer contains LiF.

2. The surface modification method of the lithium negative electrode according to claim 1, characterized in that: The fluorine content in the fluorinated graphite is 30 to 70 wt%; Preferably, the fluorine content in the fluorinated graphite is 50-62 wt%.

3. The surface modification method of the lithium negative electrode according to claim 1, characterized in that: The defluorination reaction time is 0.5 to 5 hours, and the defluorination reaction temperature is 25 to 200°C; Preferably, the defluorination reaction time is 2 to 5 hours, and the defluorination reaction temperature is 60 to 100°C; Preferably, the fluorination reaction time is 3 to 10 minutes; Preferably, the thickness of the lithium negative electrode functionalized interface layer is 10 to 200 nm; more preferably, the thickness of the lithium negative electrode functionalized interface layer is 20 to 80 nm.

4. The surface modification method of a lithium negative electrode according to any one of claims 1 to 3, characterized in that: The weight content of the fluorinated graphite in the defluorination solvent is 0.02 to 0.06 g / mL; Preferably, the weight content of the F element in the functionalized interface layer of the surface-modified lithium negative electrode is 10 to 50%; More preferably, the weight content of the F element in the functionalized interface layer of the surface-modified lithium negative electrode is 15 to 40%; Preferably, the material of the lithium negative electrode is at least one of metallic lithium or a lithium metal alloy.

5. The surface modification method of a lithium negative electrode according to any one of claims 1 to 3, characterized in that: The coating method is spraying or brushing; Preferably, the coating process is carried out in a glove box or a dry room.

6. The surface modification method of a lithium negative electrode according to any one of claims 1 to 3, characterized in that: The defluorination solvent is one or more of benzylamine, tetramethylethylenediamine and ethylenediamine.

7. The surface modification method of a lithium negative electrode according to any one of claims 1 to 3, characterized in that: The operation of removing the excess fluorinated liquid on the surface of the functionalized interface layer comprises: washing the excess fluorinated liquid on the surface of the functionalized interface layer with an organic solvent, and then vacuum drying the organic solvent to obtain the surface-modified lithium negative electrode; or The operation of removing the excess fluoride liquid on the surface of the functionalized interface layer includes: drying the lithium negative electrode including the functionalized interface layer of the excess fluoride liquid to obtain the surface-modified lithium negative electrode.

8. The surface modification method of the lithium negative electrode according to claim 7, characterized in that: The organic solvent is one or more of ethylene glycol dimethyl ether, 1,3-dioxolane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; Preferably, the drying temperature is 20-80°C, and the drying time is 0.5-2h; Preferably, the drying temperature is 150-180° C., and the drying time is 8-15 minutes.

9. A lithium negative electrode, characterized in that The lithium negative electrode is a surface-modified lithium negative electrode obtained by the modification method according to any one of claims 1 to 8.

10. A lithium metal battery, characterized in that: The lithium metal battery comprises the lithium negative electrode according to claim 9.

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