Composite negative electrode material for low-temperature lithium ion battery, preparation method and application

Abstract

The application discloses a composite negative electrode material for low-temperature lithium ion batteries, a preparation method and application. The composite negative electrode material is modified by a dual modification method of phosphorus compounding and carbon coating on tin antimonide, and has good electrochemical performance. In addition, the composite negative electrode material still has good cycle stability and safety under extreme conditions, thereby obtaining excellent low-temperature performance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion battery materials, and particularly relates to a composite negative electrode material for low-temperature lithium ion batteries, and further relates to a preparation method of the composite negative electrode material for low-temperature lithium ion batteries and application of the composite negative electrode material as a negative electrode material. BACKGROUND

[0002] In recent years, lithium ion batteries have become one of the energy storage devices that are focused on and researched due to high energy density, stable cycle performance, no memory performance and other advantages, and their application scenarios have been continuously widened, such as being applied to key fields such as power grid storage, national defense, space and deep sea operations. However, when lithium ion batteries are applied to some application fields under extreme conditions such as deep sea operations and polar scientific exploration, lithium precipitation occurs due to the sharply reduced electrochemical reaction kinetics, and therefore, in order to substantially improve the energy density, cycle life and safety performance of lithium ion batteries under low-temperature conditions, as a part that can play a decisive role in the performance of the battery, the negative electrode material still has good performance under extreme conditions and becomes a research hotspot in the field of lithium ion batteries.

[0003] The most widely used commercial lithium ion battery negative electrode material is graphite, but it has become increasingly difficult to meet the current demand for high energy density of lithium ion batteries, and more seriously, the low lithium intercalation potential of graphite and the slow lithium ion diffusion at low temperature lead to rapid capacity decay at low temperature and the risk of dendrite growth, and the low theoretical specific capacity of graphite and the safety problem of lithium precipitation at low temperature seriously hinder the application of lithium ion batteries under extreme conditions with high energy density requirements. In order to realize the normal operation of lithium ion batteries at low temperature, finding a suitable negative electrode material to replace graphite negative electrode has become the key to the problem.

[0004] As a very important lithium ion battery negative electrode material, tin-based negative electrode material has the advantages of high specific capacity, moderate lithium intercalation potential and abundant resources, unlike the deintercalation mechanism of graphite negative electrode, tin-based negative electrode mainly stores lithium through alloying and conversion reaction, and is less inhibited by low temperature, and has less risk of lithium precipitation under low-temperature fast charging conditions. In particular, antimony and tin in antimony tin, as a binary tin alloy material, can provide a buffer for the volume expansion of each other during the deintercalation of lithium at different potentials, and have better cycle stability than pure tin. However, the negative electrode material based on antimony tin has the defects of volume expansion and particle pulverization during the cycle process, and lacks fixed stable diffusion channels during the deintercalation of lithium, and how to improve it to make it have good electrochemical performance as a negative electrode material by taking advantage of the low risk of lithium precipitation under low-temperature fast charging conditions has become a new direction of research in the field of low-temperature lithium ion batteries. SUMMARY

[0005] In view of this, the application provides a composite negative electrode material for low-temperature lithium ion batteries, which is modified by a dual modification method of phosphorus compounding and carbon coating on tin antimonide, and has good electrochemical performance, overcoming the problems of tin antimonide as a negative electrode material.

[0006] In the first aspect of the application, a composite negative electrode material for low-temperature lithium ion batteries is provided, which comprises tin antimonide, phosphorus and expanded graphite, wherein the expanded graphite coats the tin antimonide and the phosphorus.

[0007] In the composite negative electrode material for low-temperature lithium ion batteries of the application, the electrochemical performance of the negative electrode material is improved by a dual modification method of phosphorus compounding and carbon coating. The use of phosphorus can improve the specific capacity of the whole as an active material, and can also regulate the lithium extraction kinetics of tin antimonide. At the same time, the presence of phosphorus produces Li3P in the electrode electrochemical reaction, which shows high affinity energy and ionic conductivity to lithium ions, and lithium ions have a low coordination number on the surface of Li3P, making it easier for lithium ions to desolvate and diffuse into the interior of the electrode material through the solid electrolyte membrane (SEI). In particular, the coating of expanded graphite can prevent direct contact between the electrolyte and the tin antimonide active material, thereby preventing the continuous decomposition of the electrolyte and the growth of the surface film, and can also provide a buffer for the volume expansion of the tin antimonide active material during the lithium extraction process, preventing the agglomeration and growth of tin antimonide active material particles. Therefore, the composite negative electrode material for low-temperature lithium ion batteries of the application has high specific capacity and fast charging characteristics, and still has good cycle stability and safety under extreme conditions, thereby obtaining excellent low-temperature performance.

[0008] Preferably, in the composite negative electrode material for low-temperature lithium ion batteries, the amount of tin antimonide is 60-85%, the amount of phosphorus is 7-10%, and the amount of expanded graphite is 9-30%, based on the total mass of the composite negative electrode material for low-temperature lithium ion batteries, and further preferably, the amount of tin antimonide is 65-80%, the amount of phosphorus is 7-10%, and the amount of expanded graphite is 10-30%.

[0009] In the composite negative electrode material for low-temperature lithium ion batteries, the tin antimonide is a matrix material, which has good electronic conductivity and ion conductivity, and the phosphorus is highly dispersed in the matrix or on the surface. On one hand, the phosphorus participates in the construction of SEI, and the Li3P generated by the phosphorus can reduce the desolvation energy of lithium ions and promote ion conduction. On the other hand, the phosphorus also participates in the alloying process of the electrode material and lithium, and can regulate and accelerate the alloying process of the tin antimonide and lithium. At the same time, the appropriate amount of expanded graphite coated with the phosphorus and the tin antimonide can inhibit the volume expansion of the phosphorus and the tin antimonide during the charging and discharging process, increase the stability of the entire composite negative electrode material, and also avoid the reaction of the charging and discharging products with the electrolyte, which is beneficial to the enhancement of the cycle stability of the battery.

[0010] Preferably, in the composite negative electrode material for low-temperature lithium ion batteries, the phosphorus can be red phosphorus and / or blue phosphorus.

[0011] In the present application, the thickness of the expanded graphite layer can be adjusted according to the size of the phosphorus and the tin antimonide as the core material, and can also be specifically adjusted by the amount or performance requirements of the expanded graphite. The expanded graphite layer completely covers the phosphorus and the tin antimonide, which can prevent the direct contact between the electrolyte and the tin antimonide active material, and further prevent the continuous decomposition of the electrolyte and the growth of the surface film. At the same time, the expanded graphite layer can provide a buffer for the volume expansion of the tin antimonide active material during the lithium extraction process, and prevent the agglomeration and growth of the tin antimonide active material particles. However, it is also necessary to avoid that the coating layer is too thick, which leads to the decline of the battery performance, such as affecting the release of active lithium.

[0012] Preferably, in the present application, the particle size of the composite negative electrode material for low-temperature lithium ion batteries is 1-15 μm, and more preferably 3-10 μm. If the particle size of the composite negative electrode material for low-temperature lithium ion batteries is too large, the particle will be severely pulverized. If the particle size of the composite negative electrode material for low-temperature lithium ion batteries is too small, the specific surface area will be too high, which will intensify the reaction with the electrolyte.

[0013] Preferably, in the composite negative electrode material for low-temperature lithium ion batteries, the mass ratio of the tin antimonide to the phosphorus is (7-10):1.

[0014] In the composite negative electrode material for low-temperature lithium ion battery, the tin antimonide and the phosphorus partially form chemical bonds, and partially form a highly dispersed system similar to an alloy system, which ensures sufficient contact between the two, can fully exert the advantages of the two, and can overcome the shortcomings of each other. Specifically, the high theoretical specific capacity and the extremely low lithium ion diffusion energy barrier of the phosphorus material, the high specific capacity, the moderate lithium intercalation potential and the suitability for low-temperature conditions of the tin antimonide, these advantages can be maintained, a negative electrode material for lithium ion battery suitable for extreme conditions can be obtained, which can realize high energy density and fast charging performance, and the composite conductive network of the tin antimonide and the phosphorus and the carbon coating means overcome the defects of particle pulverization of the tin antimonide and volume expansion of the tin antimonide and the phosphorus. Obviously, the composite negative electrode material for low-temperature lithium ion battery provides a prospect for further widening the application range of lithium ion battery.

[0015] In the second aspect of the present application, a preparation method of the above-mentioned composite negative electrode material for low-temperature lithium ion battery is provided, which comprises the following steps: firstly, ball milling the tin antimonide and the phosphorus to obtain a preliminary composite; and then adding expanded graphite and performing second ball milling to obtain the composite negative electrode material for low-temperature lithium ion battery.

[0016] Obviously, in the preparation method of the present application, the dual-modified composite negative electrode material of phosphorus composite and carbon coating is obtained by two-step ball milling. Firstly, the tin antimonide and the phosphorus are composited by the first step of ball milling. In the ball milling process, the tin antimonide and the phosphorus partially form chemical bonds, and the rest are highly dispersed to form an alloy-like dispersion system, which constructs an internal composite conductive network. Then, the expanded graphite is added to perform the second step of ball milling. In this process, the expanded graphite coats the preliminary composite formed in the first step of ball milling, so that the composite negative electrode material for low-temperature lithium ion battery retains the advantages of these single-component materials and overcomes their respective shortcomings, thereby providing a hard condition for the application of lithium ion battery under extreme conditions.

[0017] In the above method, the ball milling is implemented in a conventional ball milling manner in the art, such as tumbling ball milling, oscillation ball milling, grinding ball milling and high-energy ball milling, etc.

[0018] Preferably, in the above method, the grinding balls used in the ball milling are zirconium balls, i.e. zirconium oxide grinding balls, to avoid contamination of the raw materials. The diameter of the grinding balls is a conventional diameter in the art, which can be 5 mm, 8 mm, etc. The ball-to-material ratio can be 25-50:1.

[0019] Preferably, in the above method, the grinding balls used in the ball milling need to be cleaned before use, such as cleaning with one or more of anhydrous ethanol, acetone, isopropyl alcohol, and the like, and the cleaning can be performed once or more, such as 2 times, 3 times, and the like, and the cleaning needs to be followed by drying to remove the surface liquid residues, and the cleaning can avoid the influence of the impurities such as the powder attached to the periphery of the grinding balls on the raw materials, and further affect the performance of the product.

[0020] Preferably, in the above method, the ball milling process needs to be performed under an inert gas, and further, the inert gas is one or more of high-purity nitrogen, argon, and helium, and the inert gas can prevent the heat generated during the ball milling process from causing the raw materials to react in an oxygen environment.

[0021] Preferably, in the above method, the single continuous ball milling time is not more than 30 minutes, preferably 10-30 minutes, the room temperature cooling time is not less than 10 minutes, preferably 10-30 minutes, and the ball milling speed is 900-1200 rpm.

[0022] Preferably, in the above method, the cumulative ball milling time of the first step ball milling is 3-8 hours, and the cumulative ball milling time of the second step ball milling is 3-8 hours. During the ball milling process, the grinding balls collide and generate heat, and long-time continuous ball milling can cause the overall ball milling tank to cause the temperature in the ball milling tank to be too high, which affects the performance of the materials.

[0023] Exemplarily, in the above method, the ball milling method used is a swing ball milling, the ball milling machine speed is 900-1200 rpm, a bidirectional intermittent operation mode is used, that is, a forward and reverse rotation is alternately performed, the ball milling time of each time is 10 minutes, and the machine is stopped for 10 minutes.

[0024] Further specifically, when the swing ball milling is used for ball milling, the above-mentioned preparation method of the composite negative electrode material for low-temperature lithium ion batteries of the present application is specifically as follows:

[0025] S1. First step ball milling: the tin antimonide and phosphorus are loaded into a swing ball milling tank and the grinding balls are loaded at a ball-to-material ratio of 25-50:1, the swing ball milling tank is filled with an inert gas and sealed to perform swing ball milling, and a composite of the tin antimonide and phosphorus, that is, a preliminary composite, is obtained.

[0026] S2. Second step ball milling: the ball milling tank of step S1 is opened in an inert atmosphere, the expanded graphite is added, and then the second step ball milling is performed after sealing, and the composite negative electrode material for low-temperature lithium ion batteries is obtained.

[0027] In the above method, the inert gas is one or more of high-purity nitrogen, argon, and helium, the swing ball milling machine speed is 900-1200 rpm, the cumulative time of each step ball milling is 3-8 hours, a bidirectional intermittent operation mode is used, that is, a forward and reverse rotation is alternately performed, the ball milling time of each time is 10 minutes, and the machine is stopped for 10 minutes.

[0028] The grinding balls need to be cleaned before use, such as cleaning once or more times with one or more of anhydrous ethanol, acetone, isopropyl alcohol.

[0029] In addition, it should be noted that in the method of the present application, the first ball milling and the second ball milling can use the same or different ball milling methods, but in order to avoid unnecessary trouble, it is preferred to use the same ball milling method in the same ball mill.

[0030] Preferably, in the preparation method of the composite negative electrode material for low-temperature lithium ion batteries, the amount of tin antimonide is 60-85%, the amount of phosphorus is 7-10%, and the amount of expanded graphite is 9-30%, based on the total mass of the composite negative electrode material for low-temperature lithium ion batteries. Because the conductivity of phosphorus is poor, the amount of phosphorus cannot be too much, and too much expanded graphite as a coating material will cause the capacity of the composite material to decrease, and too little will result in poor coating effect.

[0031] Preferably, in the preparation method of the composite negative electrode material for low-temperature lithium ion batteries, the amount of tin antimonide is 65-80%, the amount of phosphorus is 7-10%, and the amount of expanded graphite is 10-30%, based on the total mass of the composite negative electrode material for low-temperature lithium ion batteries.

[0032] In the preparation method of the composite negative electrode material for low-temperature lithium ion batteries, the thickness of the expanded graphite layer coating the phosphorus and tin antimonide can be adjusted according to the size of the phosphorus and tin antimonide as the core material, or can be specifically adjusted by the amount or performance requirements of the expanded graphite.

[0033] Preferably, in the preparation method of the present application, the particle size of the obtained composite negative electrode material for low-temperature lithium ion batteries is 1-15 μm, more preferably 3-10 μm. If the particle size of the obtained composite negative electrode material for low-temperature lithium ion batteries is larger, the particle will be severely pulverized; if the particle size of the composite negative electrode material for low-temperature lithium ion batteries is smaller, it will have a higher specific surface area, which will intensify the reaction with the electrolyte.

[0034] Preferably, in the preparation method of the composite negative electrode material for low-temperature lithium ion batteries, the mass ratio of tin antimonide to phosphorus added in the first ball milling is (7-10):1.

[0035] Obviously, the preparation method of the composite negative electrode material for low-temperature lithium ion batteries of the present application can prepare a composite negative electrode material for low-temperature lithium ion batteries with higher specific capacity and better cycle performance, and good low-temperature performance by a simple and controllable ball milling method, and the method has the potential for large-scale production.

[0036] In a third aspect of the present application, a negative electrode sheet for a lithium ion battery is provided, the negative electrode sheet comprising the composite negative electrode material for a low-temperature lithium ion battery as described above.

[0037] Preferably, the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector, the negative electrode material layer comprising a negative electrode active material and a binder, the negative electrode active material comprising the composite negative electrode material for a low-temperature lithium ion battery as described above.

[0038] Further preferably, the mass fraction of the composite negative electrode material for a low-temperature lithium ion battery in the negative electrode material layer can be greater than or equal to 60 wt%, for example, 70-80 wt%, 80-90 wt%, 75 wt%, and the like.

[0039] Still further preferably, the negative electrode material layer can further comprise a conductive agent.

[0040] In the negative electrode sheet as described above, the negative electrode current collector is conventional in the art, and further preferably, the negative electrode current collector comprises, but is not limited to, a metal foil or an alloy foil, the surface of which can be etched or roughened to form a secondary structure for effective contact with the negative electrode material layer. Exemplary metal foils can be copper foils or carbon-coated copper foils, and exemplary alloy foils can be stainless steel foils, carbon-coated stainless steel foils, or copper alloy foils.

[0041] In the negative electrode sheet as described above, the amount and type of the binder and the conductive agent are conventional in the art, for example, the binder can specifically comprise, but is not limited to, one or more of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), lithium polyacrylate (Li-PAA), polyacrylate, polyacrylamide (PAM), polyimide (PI), and the like. The conductive agent can specifically comprise, but is not limited to, one or more of acetylene black, Ketjen black, Supper P conductive carbon black, graphite, graphene, carbon nanotubes, carbon fibers, Super C65, and single-walled carbon nanotubes (SWCNT), and the like.

[0042] In addition, in the negative electrode tab of the present application, the negative electrode active material can further include other negative electrode active components, which include but are not limited to one or more of lithium titanate, carbon-based materials, silicon-based materials, tin-based materials, germanium-based materials, antimony-based materials, and bismuth-based materials. Among them, the carbon-based materials can include graphite (such as natural graphite, artificial graphite), non-graphitized carbon (soft carbon, hard carbon, etc.); the silicon-based materials can include one or more of elemental silicon, silicon-based alloys, silicon oxides, and silicon-carbon composite materials, etc.; the tin-based materials can include one or more of elemental tin, tin alloys, tin oxides, etc.; the germanium-based materials can include one or more of elemental germanium, germanium alloys, germanium-carbon composite materials, germanium oxides, etc.; the antimony-based materials include one or more of antimony single substance, antimony alloys, etc.; and the bismuth-based materials include one or more of bismuth single substance, bismuth alloys, etc.

[0043] The other negative electrode active components can be dispersed in the negative electrode material layer together with the above-mentioned composite negative electrode material for low-temperature lithium ion batteries of the present application, and the two can exist independently or in the form of a composite material.

[0044] The negative electrode tab of the present application uses the above-mentioned composite negative electrode material for low-temperature lithium ion batteries of the present application, and has high specific capacity and stability during low-temperature charging and discharging cycles.

[0045] In the fourth aspect of the present application, a preparation method of the above-mentioned negative electrode tab for lithium ion batteries is provided, which includes the following steps:

[0046] SF1: Preparation of negative electrode slurry: uniformly mix the negative electrode active material, the binder, and the optional conductive agent in a solvent to prepare a negative electrode slurry;

[0047] SF2: Coating of negative electrode slurry: coat the negative electrode slurry prepared in step SF1 on the negative electrode current collector, and then dry to obtain the negative electrode tab for lithium ion batteries.

[0048] Obviously, the preparation method of the present application is simple and easy to implement, and can be prepared on a large scale. In step SF1, the negative electrode slurry is prepared in a manner conventional in the art, such as by a high-speed stirring defoaming machine.

[0049] Preferably, the solvent used in step SF1 is a solvent conventional in the art, such as water, an alcohol solvent, an amide solvent, an ether solvent, etc., and the amount used is also conventional in the art.

[0050] Further preferably, the negative active material comprises the composite negative material for low temperature lithium ion battery as described above and optional other negative active components, which include but are not limited to one or more of lithium titanate, carbon-based material, silicon-based material, tin-based material, germanium-based material, antimony-based material, bismuth-based material. Among them, the carbon-based material can include graphite (such as natural graphite, artificial graphite), non-graphitized carbon (soft carbon, hard carbon, etc.); the silicon-based material can include one or more of elemental silicon, silicon-based alloy, silicon oxide and silicon-carbon composite material, etc.; the tin-based material can include one or more of elemental tin, tin alloy, tin oxide, etc.; the germanium-based material can include one or more of elemental germanium, germanium alloy, germanium-carbon composite material, germanium oxide, etc.; the antimony-based material includes one or more of antimony element, antimony alloy, etc.; the bismuth-based material includes one or more of bismuth element, bismuth alloy, etc.

[0051] The other negative active components can be dispersed in the negative material layer together with the composite negative material for low temperature lithium ion battery as described above, and the two can exist independently or in the form of a composite material.

[0052] Further preferably, in the negative material layer formed by coating the negative slurry on the negative current collector, the mass percentage of the negative active material in the negative material layer is greater than or equal to 60wt%, and further preferably the mass percentage of the composite negative material for low temperature lithium ion battery in the negative material layer is greater than or equal to 60wt%, for example, 70-80wt%, 80-90wt%, 75wt%, etc.

[0053] In the above method, the negative current collector is conventional in the art, and further preferably, the negative current collector includes but is not limited to metal foil or alloy foil, the surface of which can be etched or roughened to form a secondary structure to facilitate effective contact with the negative material layer. Exemplary metal foils can be copper foil or carbon-coated copper foil, and exemplary alloy foils can be stainless steel foil, carbon-coated stainless steel foil, or copper alloy foil.

[0054] In the above method, the amount and type of the binder and the conductive agent are conventional in the art, and for example, the binder can specifically include but is not limited to one or more of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), lithium polyacrylate (Li-PAA), polyacrylate, polyacrylamide (PAM), polyimide (PI), etc. The conductive agent can specifically include but is not limited to one or more of acetylene black, Ketjen black, Supper P conductive carbon black, graphite, graphene, carbon nanotube, carbon fiber, Super C65 and single-walled carbon nanotube (SWCNT), etc.

[0055] Preferably, in the above method, in the step SF1, the mass ratio of the negative electrode active material, the binder, and the conductive agent is (7.5-8.5):(0.75-1.25):(0.75-1.25), and in this ratio, the negative electrode plate has better performance and can be better applied to extreme conditions.

[0056] Preferably, in the above method, in the step SF2, the coating thickness of the negative electrode slurry prepared in the step SF1 on the negative electrode current collector is 100-250 μm.

[0057] Preferably, in the above method, in the step SF2, after the negative electrode current collector coated with the negative electrode slurry is dried, the negative electrode current collector is rolled to a thickness of 60-80% of the thickness of the electrode plate after drying, so that the active material can be in closer contact, and the active material can be prevented from losing contact with the current collector after the electrolyte is soaked.

[0058] Preferably, in the above method, in the step SF2, the drying method of the negative electrode current collector coated with the negative electrode slurry is a conventional drying method in the art, such as drying or air drying, and is not strictly limited as long as the purpose can be achieved.

[0059] In a fifth aspect of the present application, a battery is provided, which is made of the above negative electrode plate.

[0060] The shape of the battery of the present application is not particularly limited, and can be cylindrical, button (coin type), flat, square, etc., which can be used in conventional terminal consumer products, and can also be used in some extreme conditions, such as deep sea operation, polar scientific exploration, etc.

[0061] Compared with the prior art, the present application modifies antimony tin by the dual means of phosphorus compounding and carbon coating, wherein the use of phosphorus can improve the overall specific capacity as an active material, and can also regulate the lithium extraction kinetics of antimony tin; at the same time, the presence of phosphorus produces Li3P in the electrode electrochemical reaction of the negative electrode material, which shows high affinity energy and ionic conductivity to lithium ions, and lithium ions have a low coordination number on the surface of Li3P, so that lithium ions are more easily desolvated and diffuse into the interior of the electrode material through the solid electrolyte membrane (SEI); at the same time, the coating of expanded graphite can prevent direct contact between the electrolyte and the antimony tin active material, thereby preventing the continuous decomposition of the electrolyte and the growth of the surface film, and can also provide a buffer for the volume expansion of the antimony tin active material during the lithium extraction process, thereby preventing the agglomeration and growth of antimony tin active material particles. Therefore, the composite negative electrode material for low-temperature lithium ion batteries has high specific capacity and fast charging characteristics, and still has good cycle stability and safety under extreme conditions, thereby obtaining excellent low-temperature performance.

[0062] In addition, the composite negative electrode material for low-temperature lithium ion batteries is efficiently prepared by a simple ball milling method, the preparation process is simple and controllable, no additional design equipment is needed, and the two-step ball milling method can achieve better composite effect of tin antimonide and phosphorus and better coating effect of expanded graphite. In the composite negative electrode material for low-temperature lithium ion batteries, the phosphorus regulates the lithium extraction and insertion process of the tin antimonide alloy, accelerates the alloying reaction process with lithium, and the phosphorus also has a high specific capacity, which can improve the overall capacity of the negative electrode; the expanded graphite as a carbon source achieves a good coating effect by regulating the proportion used, so that the material maintains better cycle stability during the cycle process. Finally, the composite negative electrode material for low-temperature lithium ion batteries has high specific capacity and stability during the charge and discharge cycle at low temperature, and can obtain a charge and discharge battery applied in extreme conditions. BRIEF DESCRIPTION OF DRAWINGS

[0063] Figure 1 X-ray diffraction spectra of the negative electrode materials prepared for Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4;

[0064] Figure 2 Scanning electron microscope images of the negative electrode materials prepared for Example 1, Example 2 and Example 3;

[0065] Figure 3 Normal temperature charge and discharge curves of the negative electrode materials prepared for Example 1, Example 2 and Example 3;

[0066] Figure 4 Normal temperature charge and discharge cycle diagrams of the negative electrode materials prepared for Example 1, Example 2 and Example 3;

[0067] Figure 5 Scanning electron microscope images of the negative electrode materials prepared for Comparative Example 1 and Comparative Example 2;

[0068] Figure 6 Normal temperature charge and discharge curves of the negative electrode materials prepared for Comparative Example 1 and Comparative Example 2;

[0069] Figure 7 Normal temperature charge and discharge cycle diagrams of the negative electrode materials prepared for Comparative Example 1 and Comparative Example 2;

[0070] Figure 8 Scanning electron microscope images of the negative electrode materials prepared for Comparative Example 3 and Comparative Example 4;

[0071] Figure 9 Normal temperature charge and discharge curves of the negative electrode materials prepared for Comparative Example 3 and Comparative Example 4;

[0072] Figure 10A charge-discharge cycle diagram at room temperature of the negative electrode material prepared for Comparative Example 3 and Comparative Example 4;

[0073] Figure 11 A charge-discharge cycle diagram at low temperature of the negative electrode material prepared for Example 2. DETAILED DESCRIPTION

[0074] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the specific embodiments will be explained below in conjunction with the drawings needed to be used.

[0075] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present application.

[0076] The raw materials used in the following examples are all commercially available, for example, the tin antimonide is purchased from Zhengzhou Alpha Company, the phosphorus is purchased from Aladdin Biochemical Technology Co., Ltd., and the expanded graphite is purchased from Henan Liugong Graphite Co., Ltd.

[0077] EMBODIMENT

[0078] EMBODIMENT 1

[0079] Preparation of a composite negative electrode material for low-temperature lithium ion batteries

[0080] S1 First step of ball milling: 0.9 g of tin antimonide powder and 0.1 g of red phosphorus powder are added to a swing ball mill tank, which is sealed under argon protection. Zirconia grinding balls with a mass ratio of 30:1 to the raw materials are loaded into the ball mill tank. The ball milling parameters are set as follows: the working mode is "two-way intermittent operation, timed stop" mode, the swing ball mill speed is 1000 rpm, the total ball milling time is 5 h, the forward running time is 10 min, the intermittent running time is 10 min, and then the reverse running time is 10 min, which is regarded as one cycle. The composite of tin antimonide and phosphorus, i.e. the preliminary composite, is obtained after 15 cycles.

[0081] S2 Second step of ball milling: the ball mill tank of the first step is opened under argon protection, and 0.1 g of expanded graphite is added. Then the ball mill tank is sealed and the ball milling is continued. The ball milling mode is the same as that in step S1. After ball milling, the composite negative electrode material for low-temperature lithium ion batteries, denoted as T-SPG1, is obtained.

[0082] Figure 1 The X-ray diffraction pattern of the T-SPG1 composite material prepared in this embodiment can be found that its crystal structure is consistent with that of SnSb, which is rhombohedral, R-3m structure. Figure 2Figure a is an image of the T-SPG1 negative electrode material prepared in this example under a scanning electron microscope, which appears as particles coated with expanded graphite sheets on the surface.

[0083] B Preparation of a negative electrode sheet for a lithium ion battery

[0084] SF1 Preparation of a negative electrode slurry: 0.4 g of the T-SPG1 prepared above, 0.05 g of a binder (sodium carboxymethyl cellulose, CMC), and 0.05 g of a conductive agent (Super C65 and SWCNT, mass ratio 50:1) were uniformly mixed, and a slurry was prepared by high-speed stirring with a defoaming machine using 3.5 g of deionized water as a solvent, which was the negative electrode slurry.

[0085] SF2 Coating of the negative electrode slurry: the prepared negative electrode slurry was uniformly coated on a battery-grade copper foil with a coating thickness controlled at 150 μm, and then dried in a vacuum drying oven at 80°C for 10 hours to completely remove water, and then a 12 mm diameter disc was punched to obtain a T-SPG1 negative electrode sheet; wherein the active material loading of T-SPG1 was about 1.5 mg / cm 2 .

[0086] C Preparation of a coin cell with the T-SPG1 negative electrode sheet prepared in this example as the anode and lithium metal as the counter electrode and electrochemical performance test

[0087] SC1 Preparation of a separator: a 19 mm Celgard 2325 was punched as a separator, and the separator was dried in a vacuum oven to remove residual moisture,

[0088] SC2 Preparation of a coin CR2016 half cell: this step needs to be carried out in an argon-filled glove box (Shanghai Micronano Machinery and Electrical Technology Co., Ltd.), and the water and oxygen content is strictly controlled to be less than 0.01 ppm, and the negative electrode sheet, separator and lithium metal counter electrode are assembled in order, and the electrolyte is used to fully soak them, and then a coin CR2016 half cell is assembled, wherein the electrolyte used is: a solution of lithium hexafluorophosphate with a concentration of 1 mol / L in a mixed solvent of ethylene carbonate, methyl ethyl carbonate and propylene carbonate with a volume ratio of 1:1:1, and additionally containing 10% by volume of fluoroethylene carbonate.

[0089] Electrochemical performance testing of SC3: The coin cell CR2016 half-cell prepared by SC2 was subjected to constant current charge-discharge test at room temperature under the following conditions on the LAND CT2001A battery test system: charge-discharge current density of 200mA / g and 1000mA / g, voltage range of 0.01V to 2V, and the charge-discharge process is as follows: first, the constant current was discharged to 0.01V at a current density of 200mA / g, and then allowed to stand for 3 minutes. Next, the current was charged to 2V at a current density of 200mA / g, and this was repeated 3 times for activation. Starting from the fourth cycle, the charge-discharge test was carried out at a current density of 1000mA / g.

[0090] It should be noted that when calculating the capacity retention rate, the statistics are based on the fourth cycle, i.e., the first cycle after activation and stabilization.

[0091] Figure 3 The first charge-discharge curve of the battery prepared using the T-SPG1 anode material prepared in this embodiment shows that its first discharge specific capacity is 886 mAh / g and its first coulombic efficiency is 88.24%. Figure 4 The data includes a charge-discharge cycle diagram at room temperature. After 150 cycles, the discharge specific capacity is 597.6 mAh / g, and the capacity retention rate is 71.3%.

[0092] Example 2

[0093] Preparation of composite anode materials for low-temperature lithium-ion batteries

[0094] The low-temperature lithium-ion battery composite anode material of this embodiment was prepared in accordance with the method described in Example 1, with the only difference being that the amount of expanded graphite used in the second ball milling step S2 was 0.2g, and the obtained low-temperature lithium-ion battery composite anode material was denoted as T-SPG2.

[0095] Figure 1 The X-ray diffraction pattern of the T-SPG2 composite material prepared in this embodiment shows that its crystal structure is consistent with SnSb, which is rhombohedral and has an R-3m structure. Figure 2 b is an image of the T-SPG2 negative electrode material prepared in this embodiment under a scanning electron microscope, which shows particles with expanded graphite sheets on their surface.

[0096] B. Negative electrode sheets used in the preparation of lithium-ion batteries

[0097] The negative electrode sheet for the lithium-ion battery of this embodiment is prepared in accordance with the method described in Example 1, except that the low-temperature lithium-ion battery composite negative electrode material used is T-SPG2.

[0098] C. The T-SPG2 negative electrode sheet prepared in this embodiment was used to fabricate a coin cell with lithium metal as the counter electrode, and its electrochemical performance was tested.

[0099] The T-SPG2 negative electrode sheet prepared in this example was prepared into a button cell with lithium metal as the counter electrode in the manner described in Example 1 and electrochemical performance testing was carried out.

[0100] Figure 3 The first charge-discharge curve of the button cell containing the T-SPG2 negative electrode material prepared in this example had a first discharge specific capacity of 815 mAh / g and a first coulombic efficiency of 87.10%. Figure 4 The normal temperature charge-discharge cycle diagram is shown. After 150 cycles, the discharge specific capacity was 646.5 mAh / g and the capacity retention rate was 83.2%.

[0101] The T-SPG2 negative electrode sheet prepared in this example was prepared into a button cell with lithium metal as the counter electrode and low temperature charge-discharge testing was carried out

[0102] The T-SPG2 negative electrode sheet prepared in this example was prepared into a button cell with lithium metal as the counter electrode in the manner described in Example 1, except that the electrolyte used in this example was a solution of 1 mol / L lithium hexafluorophosphate dissolved in a mixed solvent of tetrahydrofuran and dimethyltetrahydrofuran in a volume ratio of 1:1. The battery was tested in a thermostat at -10°C and -30°C, and the low temperature charge-discharge test conditions were: charge-discharge current density was 200 mA / g, and the voltage range was 0.01V-2V.

[0103] Figure 11 The low temperature charge-discharge cycle diagram of Example 2 is shown, which exhibits relatively high capacity and cycle stability at low temperature.

[0104] Example 3

[0105] Preparation of a composite negative electrode material for a low temperature lithium ion battery

[0106] The composite negative electrode material for a low temperature lithium ion battery of this example was prepared in the manner described in Example 1, except that the amount of expanded graphite used in the second step of ball milling in S2 was 0.3 g, and the composite negative electrode material for a low temperature lithium ion battery obtained was designated as T-SPG3.

[0107] Figure 1 The X-ray diffraction pattern of the T-SPG3 composite material prepared in this example was found to have a crystal structure consistent with SnSb, which was rhombohedral, R-3m structure. Figure 2 b is the image of the T-SPG3 negative electrode material prepared in this example under a scanning electron microscope, which showed particles coated with expanded graphite flakes, and it can be seen that there were a large number of un-complexed graphite flakes.

[0108] B Preparation of negative electrode sheet for lithium ion battery

[0109] The negative electrode sheet for lithium ion battery of this example was prepared in the same manner as described in Example 1, except that the low-temperature lithium ion battery composite negative electrode material used was T-SPG3.

[0110] C The T-SPG3 negative electrode sheet prepared in this example was prepared into a coin cell with lithium metal as the counter electrode and electrochemical performance testing was performed.

[0111] The T-SPG3 negative electrode sheet prepared in this example was prepared into a coin cell with lithium metal as the counter electrode and electrochemical performance testing was performed in the same manner as described in Example 1.

[0112] Figure 3 The first charge-discharge curve of the T-SPG3 negative electrode material prepared in this example had a first discharge specific capacity of 738.5 mAh / g and a first coulombic efficiency of 81.66%. Figure 4 The room temperature charge-discharge cycle diagram showed that after 150 cycles, the discharge specific capacity was 494.3 mAh / g and the capacity retention rate was 78.9%.

[0113] Comparative Example

[0114] Comparative Example 1

[0115] A Preparation of lithium ion battery composite negative electrode material

[0116] First, 0.9 g of tin antimony powder and 0.1 g of red phosphorus powder were added to a swing ball mill tank, followed by the addition of 0.1 g of expanded graphite. After sealing the tank under argon protection, swing ball milling was performed, with zirconium oxide grinding balls being loaded into the ball mill tank at a mass ratio of 30:1 to the raw materials. The ball milling parameters were set as follows: the working mode was "two-way intermittent operation, timed stop" mode, the swing ball milling speed was 1000 rpm, the total ball milling time was 5 h, the forward running time was 10 min, the intermittent running time was 10 min, and then the reverse running time was 10 min, which was taken as one cycle. After running for 15 times, the negative electrode powder was obtained and was denoted as SPG1.

[0117] Figure 1 The X-ray diffraction pattern of the SPG1 composite material prepared in this comparative example showed that its crystal structure was consistent with that of SnSb, which was rhombohedral and had an R-3m structure. Figure 5 a is the image of the SPG1 negative electrode material prepared in this comparative example under a scanning electron microscope, which showed that the particles were coated with expanded graphite sheets, but the expanded graphite sheets did not completely coat the particles.

[0118] B Preparation of negative electrode sheet for lithium ion battery

[0119] The negative electrode sheet for lithium ion battery of the present comparative example was prepared in the same manner as described in Example 1, except that the low-temperature lithium ion battery composite negative electrode material used was SPG1.

[0120] C The SPG1 negative electrode sheet prepared in the present comparative example was prepared into a coin cell with lithium metal as the counter electrode and electrochemical performance test was conducted.

[0121] The SPG1 negative electrode sheet prepared in the present comparative example was prepared into a coin cell with lithium metal as the counter electrode in the same manner as described in Example 1 and electrochemical performance test was conducted.

[0122] Figure 6 The first charge-discharge curve of the SPG1 negative electrode material prepared in the present comparative example had a first discharge specific capacity of 842.8 mAh / g and a first coulombic efficiency of 87.68%. Figure 7 The room-temperature charge-discharge cycle diagram showed that after 150 cycles, the discharge specific capacity was 443.7 mAh / g and the capacity retention rate was 55.8%.

[0123] Comparative Example 2

[0124] Preparation of lithium ion battery composite negative electrode material

[0125] The lithium ion battery composite negative electrode material of the present comparative example was prepared in the same manner as described in Comparative Example 1, except that the amount of expanded graphite used in the ball milling step was 0.2 g and the obtained lithium ion battery composite negative electrode material was denoted as SPG2.

[0126] Figure 1 The X-ray diffraction pattern of the SPG2 composite material prepared in the present comparative example showed that the crystal structure was consistent with that of SnSb, which was rhombohedral and had an R-3m structure. Figure 5 b The image of the SPG2 negative electrode material prepared in the present comparative example under a scanning electron microscope showed that the surface of the particles was coated with expanded graphite sheets, but the coating effect was poor.

[0127] Preparation of negative electrode sheet for lithium ion battery

[0128] The negative electrode sheet for lithium ion battery of the present comparative example was prepared in the same manner as described in Example 1, except that the lithium ion battery composite negative electrode material used was SPG2.

[0129] C The SPG2 negative electrode sheet prepared in the present comparative example was prepared into a coin cell with lithium metal as the counter electrode and electrochemical performance test was conducted.

[0130] The SPG2 negative electrode sheet prepared in the present comparative example was prepared into a coin cell with lithium metal as the counter electrode in the same manner as described in Example 1 and electrochemical performance test was conducted.

[0131] Figure 6 The first charge-discharge curve of the SPG2 negative electrode material prepared in the present comparative example has a first discharge specific capacity of 558.3 mAh / g and a first coulombic efficiency of 77.17%. Figure 7 The ambient temperature charge-discharge cycle diagram shows that after 150 cycles, the discharge specific capacity is 394.6 mAh / g and the capacity retention rate is 68.9%.

[0132] Comparative Example 3

[0133] Preparation of a composite negative electrode material for lithium ion batteries

[0134] The composite negative electrode material for lithium ion batteries of the present comparative example was prepared in the manner described in Example 1, with the exception that no red phosphorus was added in the first step of the ball milling process, only tin antimony powder was added, and the obtained composite negative electrode material for lithium ion batteries was designated as SPG3.

[0135] Figure 1 The X-ray diffraction pattern of the SPG3 negative electrode material prepared in the present comparative example is rhombohedral, with an R-3m structure. Figure 8 a is the image of the SPG3 negative electrode material prepared in the present comparative example under a scanning electron microscope.

[0136] B Preparation of a negative electrode sheet for lithium ion batteries

[0137] The negative electrode sheet for lithium ion batteries of the present example was prepared in the manner described in Example 1, with the exception that the low-temperature composite negative electrode material for lithium ion batteries used was SPG3.

[0138] C Preparation of a coin cell with lithium metal as the counter electrode using the SPG3 negative electrode sheet prepared in the present comparative example and testing of the electrochemical performance

[0139] The SPG3 negative electrode sheet prepared in the present comparative example was prepared into a coin cell with lithium metal as the counter electrode in the manner described in Example 1 and the electrochemical performance was tested.

[0140] Figure 9 The first charge-discharge curve of the SPG3 negative electrode material prepared in the present example has a first discharge specific capacity of 660.7 mAh / g and a first coulombic efficiency of 86.47%. Figure 10 The ambient temperature charge-discharge cycle diagram shows that after 150 cycles, the discharge specific capacity is 58.1 mAh / g and the capacity retention rate is only 9.6%.

[0141] Comparative Example 4

[0142] Preparation of a composite negative electrode material for lithium ion batteries

[0143] 0.9 g of tin-antimony powder and 0.1 g of red phosphorus powder were added into a swing ball mill tank, and the tank was sealed under argon protection. Zirconium oxide grinding balls were loaded into the tank in a mass ratio of 30:1 to the raw materials. The swing ball mill parameters were set as follows: the working mode was "two-way intermittent operation with fixed time stop", the swing ball mill speed was 1000 rpm, the total ball milling time was 5 h, the forward running time was 10 min, the intermittent running time was 10 min, and then the reverse running time was 10 min, which was taken as one cycle. The operation was repeated for 15 times to obtain a tin-antimony and phosphorus composite, i.e. a preliminary composite, as a composite negative electrode material for lithium ion batteries, denoted as SP.

[0144] Figure 1 The X-ray diffraction pattern of the SP negative electrode material prepared in this comparative example showed that its crystal structure was consistent with that of SnSb, i.e. rhombohedral crystal system and R-3m structure. Figure 8 b is an image of the SP negative electrode material prepared in this comparative example under a scanning electron microscope.

[0145] B Preparation of a negative electrode sheet for lithium ion batteries

[0146] The negative electrode sheet for lithium ion batteries of this comparative example was prepared in the same manner as described in Example 1, except that the low-temperature lithium ion battery composite negative electrode material used was SP.

[0147] C Preparation of a coin cell with lithium metal as the counter electrode using the SP negative electrode sheet prepared in this comparative example and electrochemical performance test

[0148] The SP negative electrode sheet prepared in this comparative example was prepared into a coin cell with lithium metal as the counter electrode and electrochemical performance test was carried out in the same manner as described in Example 1.

[0149] Figure 9 The first charge-discharge curve of the SP negative electrode material prepared in this comparative example showed that the first discharge specific capacity was 906.4 mAh / g and the first coulombic efficiency was 88.34%. Figure 10 The normal temperature charge-discharge cycle diagram showed that after 150 cycles, the discharge specific capacity was 58.7 mAh / g and the capacity retention rate was only 6.4%.

[0150] The above examples and comparative examples specifically show that the preparation of the negative electrode material for low-temperature lithium ion batteries has universality and effectiveness in improving the electrochemical performance of the negative electrode material for low-temperature lithium ion batteries from different material composition components, different preparation methods and the like, and it is proved that the composite negative electrode material for low-temperature lithium ion batteries obtained by the means of phosphorus compounding and carbon coating has higher specific capacity and good cycle stability. The example 2 of the present application has considerable specific capacity and cycle stability at low temperatures of-10 DEG C and-30 DEG C, which provides a material basis for realizing lithium ion batteries with high energy density, high rate performance and good low-temperature performance, and has certain enlightenment and help for breaking through the low-temperature fast-charging problem of lithium ion batteries.

[0151] According to the disclosure and teaching of the above description, those skilled in the art of the present application can also make changes and modifications to the above embodiments. Therefore, the present application is not limited to the specific embodiments disclosed and described above, and some modifications and changes of the application should fall within the protection scope of the claims of the present application. In addition, although some specific terms are used in the specification, these terms are only for convenience of description and do not constitute any limitation on the present application.

Claims

1. A composite negative electrode material for low-temperature lithium-ion batteries, characterized in that, It includes tin antimony, phosphorus, and expanded graphite, wherein the expanded graphite coats the tin antimony and phosphorus. Based on the total mass of the composite anode material for low-temperature lithium-ion batteries, the amount of tin antimony is 60-85%, the amount of phosphorus is 7-10%, and the amount of expanded graphite is 9-30%. The composite anode material for low-temperature lithium-ion batteries is prepared by the following method: First, tin antimonide and phosphorus are ball-milled to obtain a preliminary composite material; then expanded graphite is added and ball-milled a second time to obtain the composite anode material for low-temperature lithium-ion batteries of the present invention.

2. The composite negative electrode material for low-temperature lithium-ion batteries according to claim 1, characterized in that, The phosphorus is red phosphorus and / or blue phosphorus.

3. The composite negative electrode material for low-temperature lithium-ion batteries according to claim 1, characterized in that, Based on the total mass of the composite negative electrode material for the low-temperature lithium-ion battery, the amount of tin antimonide is 65-80%, the amount of phosphorus is 7-10%, and the amount of expanded graphite is 10-30%.

4. The composite negative electrode material for low-temperature lithium-ion batteries according to claim 1, characterized in that, The particle size of the composite negative electrode material for the low-temperature lithium-ion battery is 1-15 μm.

5. The composite negative electrode material for low-temperature lithium-ion batteries according to claim 1, characterized in that, The particle size of the composite negative electrode material for the low-temperature lithium-ion battery is 3-10 μm.

6. The composite negative electrode material for low-temperature lithium-ion batteries according to claim 1, characterized in that, The mass ratio of tin antimonide to phosphorus is (7-10):

1.

7. The composite negative electrode material for low-temperature lithium-ion batteries according to claim 1, characterized in that, The ball milling process needs to be carried out under an inert gas atmosphere.

8. A negative electrode sheet for a lithium-ion battery, characterized in that, The negative electrode sheet contains the composite negative electrode material for low-temperature lithium-ion batteries as described in any one of claims 1-7.

9. A battery, characterized in that, The battery includes the negative electrode sheet as described in claim 8.

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