Negative electrode material and preparation method therefor, and lithium-ion secondary battery

Abstract

A negative electrode material and a preparation method therefor, and a lithium-ion secondary battery. The negative electrode material comprises a silicon-based active substance, and the silicon-based active substance has an Si-R bond on the surface thereof, wherein R comprises at least one of H, COOH, CHO and NH2, and the pH value of the silicon-based active substance is 3-7. The negative electrode material is beneficial for maintaining the interface stability of the silicon-based active substance, reducing side reactions of the silicon-based active substance, and improving the cycling performance of the negative electrode material.

Description

Negative electrode material and preparation method thereof, lithium ion secondary battery Technical Field

[0001] The present invention relates to the technical field of negative electrode materials, and in particular to a negative electrode material and a preparation method thereof, and a lithium ion secondary battery. Background Art

[0002] Lithium-ion batteries are widely used in electric vehicles and consumer electronics due to their high energy density, long cycle life, low environmental pollution, and lack of memory effect. The rapid development of electric vehicles in recent years has led to a growing demand for lithium-ion batteries with higher energy density, prompting researchers to search for battery materials with higher energy density and better cycle performance. Positive and negative electrode materials are the core of the battery and determine its operating efficiency. Currently, the commercialized negative electrode material is graphite, whose capacity is close to its theoretical upper limit, with limited potential for further improvement. Therefore, there is an urgent need to develop a new generation of high-energy-density negative electrode materials. Silicon-based negative electrode materials are widely considered to be the next generation of battery negative electrode materials, offering advantages such as high capacity, abundant sources, and relative safety.

[0003] However, the silicon negative electrode experiences a dramatic volume expansion effect during the cycle, causing the material to pulverize and break, and the battery cycle decays rapidly. To address this problem, there are currently multiple solutions, including structural design of silicon, such as the use of nano- and porous technologies, or improvements such as composite coating, or modifications such as new electrolytes and adhesives to improve silicon pole pieces. Among them, nano-scaling is one of the current mainstream directions. Reducing the size of silicon to nanometers helps reduce silicon expansion and prevent silicon pulverization. However, existing nano-scaling solutions still have many shortcomings in solving silicon performance problems, and there is still much room for improvement in long-cycle performance.

[0004] Summary of the Invention

[0005] The purpose of the present application is to provide a negative electrode material and a preparation method thereof, as well as a lithium-ion secondary battery using the negative electrode material. The negative electrode material provided in the present application is conducive to maintaining the interface stability of silicon-based active substances, reducing the side reactions of silicon-based active substances, and thus improving the cycle performance of the negative electrode material.

[0006] In a first aspect, the present application provides a negative electrode material, which includes a silicon-based active substance, the surface of which has a Si-R bond, wherein R includes at least one of H, COOH, CHO and NH2, and the pH value of the silicon-based active substance is 3 to 9.

[0007] In some embodiments, the average particle size of the silicon-based active material is 1 nm to 500 nm.

[0008] In some embodiments, the silicon-based active material includes at least one of crystalline silicon, amorphous silicon, and a composite of crystalline silicon and amorphous silicon.

[0009] In some embodiments, the silicon-based active material includes at least one of silicon oxide and a silicon alloy.

[0010] In some embodiments, the silicon-based active material includes silicon particles and a silicon oxide layer located on the surface of the silicon particles.

[0011] In some embodiments, the silicon-based active material includes silicon particles and a silicon oxide layer located on the surface of the silicon particles. Based on the mass of the silicon-based active material being 100%, the mass percentage of oxygen atoms in the silicon-based active material is 1% to 18%.

[0012] In some embodiments, the negative electrode material further includes a carbon material located on at least a portion of the surface of the silicon-based active material.

[0013] In some embodiments, the mass percentage of silicon in the silicon-based active material is greater than or equal to 99%.

[0014] In some embodiments, the carbon material exists on the surface of the silicon-based active material and / or is dispersed among the silicon-based active materials.

[0015] In some embodiments, the carbon material includes at least one of amorphous carbon, graphene, graphite, carbon nanotubes, and carbon fibers.

[0016] In some embodiments, the median particle size of the negative electrode material is 1 μm to 10 μm.

[0017] In some embodiments, the specific surface area of ​​the negative electrode material is ≤5m 2 / g.

[0018] In some embodiments, the silicon-based active material is mixed with ethanol to form a slurry with a solid content of 5% to 30%. The Zeta potential of the slurry is tested using a Zeta potential tester, and the absolute value of the Zeta potential of the slurry is ≥20 mV.

[0019] In a second aspect, the present application provides a method for preparing a negative electrode material, comprising the following steps:

[0020] The silicon raw material is subjected to a first surface treatment to obtain primary particles with exposed surfaces;

[0021] The primary particles are surface-modified to obtain a silicon-based active substance; the negative electrode material includes the silicon-based active substance, the surface of the silicon-based active substance includes Si-R bonds, wherein R includes at least one of H, COOH, CHO and NH2, and the pH value of the silicon-based active substance is 3 to 7.

[0022] In some embodiments, the first surface treatment includes at least one of a crushing treatment and an etching treatment.

[0023] In some embodiments, the surface modification treatment includes at least one of an amination treatment and an acid leaching treatment.

[0024] In a third aspect, the present application further provides a lithium-ion secondary battery, which comprises the negative electrode material described in the first aspect or the negative electrode material prepared by the negative electrode material preparation method described in the second aspect.

[0025] Compared with the prior art, the technical solution of this application has at least the following beneficial effects:

[0026] The negative electrode material provided by the present application includes a silicon-based active material, the surface of the silicon-based active material includes a Si-R bond, R includes at least one of -H, -COOH, -CHO and -NH2, and the Si-R bond will hydrolyze in an aqueous solution to release H + , thereby improving the pH value of the silicon-based active material, reducing the situation where the pH value of the silicon-based active material is too acidic or too alkaline, reducing the combination of the silicon-based active material with other elements (especially oxygen), and reducing the impact on the activity of the silicon-based active material.

[0027] In addition, during the production process of silicon-based active substances, since silicon-based active substances are nano-scale and have a large specific surface area, they can easily adhere to the human body surface. Controlling the pH value of nano-scale silicon-based active substances within the range of 3 to 7 can reduce the damage caused by nano-scale silicon-based active substances to human skin.

[0028] The preparation method of the negative electrode material provided by the present application, by performing a first surface treatment on the silicon raw material, the surface of the silicon raw material can be cleaned, thereby obtaining a primary particle with an exposed surface, and the lattice terminates at the exposed surface of the primary particle, so that each silicon atom located on the outermost layer of the primary particle surface has an unpaired electron, that is, there is an unsaturated bond, which is called a dangling bond. Due to the rich dangling bonds on the exposed surface of the primary particle, in the process of surface modification of the primary particle, the dangling bonds on the surface of the primary particle can be used as active sites, and compounded with -H, -COOH, -CHO or -NH2 to form a strong Si-H bond, Si-COOH bond, Si-CHO bond or Si-NH2 bond, reducing the silicon-based active material from combining with other elements (especially oxygen), affecting the activity of the silicon-based active material. Moreover, when the negative electrode material is used in a battery, there is inevitably water in the electrolyte of the battery. After the negative electrode material contacts the electrolyte, the pH value of the silicon-based active material is controlled to be 3 to 7, which can reduce the side reactions between the negative electrode material and the electrolyte and improve the cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be further described below with reference to the accompanying drawings and examples.

[0030] FIG1 is an infrared spectrum of the silicon-based active material prepared in Example 1 of the present application;

[0031] FIG2 is a scanning electron microscope (SEM) image of the negative electrode material prepared in Example 1 of the present application;

[0032] FIG3 is an XRD pattern of the negative electrode material prepared in Example 1 of the present application;

[0033] FIG4 is the first charge and discharge curve of the negative electrode material prepared in Example 1 of the present application;

[0034] FIG5 is a cycle performance curve of the negative electrode material prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0035] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0036] It should be understood that the embodiments described are only a portion of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0037] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "an", "the" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0038] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0039] In a first aspect, the present application provides a negative electrode material, wherein the negative electrode material is a silicon-based active substance, the surface of the silicon-based active substance has a Si-R bond, wherein R includes at least one of H, COOH, CHO and NH2, and the pH value of the silicon-based active substance is 3 to 7.

[0040] The negative electrode material provided by the present application includes a silicon-based active material, the surface of the silicon-based active material includes a Si-R bond, R includes at least one of -H, -COOH, -CHO and -NH2, and the Si-R bond will hydrolyze in an aqueous solution to release H + , thereby improving the pH value of the silicon-based active material, reducing the situation where the pH value of the silicon-based active material is too acidic or too alkaline, reducing the combination of the silicon-based active material with other elements (especially oxygen), and reducing the impact on the activity of the silicon-based active material.

[0041] In addition, during the production process of silicon-based active substances, since silicon-based active substances are nano-scale and have a large specific surface area, they can easily adhere to the human body surface. Controlling the pH value of nano-scale silicon-based active substances within the range of 3 to 7 can reduce the damage caused by nano-scale silicon-based active substances to human skin.

[0042] Specifically, the pH value of the silicon-based active material can be 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.8, 4, 4.3, 4.5, 4.6, 4.7, 5, 5.3, 5.5, 5.7, 5.8, 5.9, 6 or 7, etc., which is not limited here.

[0043] In some embodiments, the average particle size of the silicon-based active material is 1 nm to 500 nm, and specifically can be 1 nm, 5 nm, 10 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, or 500 nm, etc., and of course other values ​​within the above range are also possible and are not limited here. Preferably, the average particle size of the silicon-based active material is 1 nm to 200 nm, and more preferably, the average particle size of the silicon-based active material is 5 nm to 100 nm.

[0044] In some embodiments, the silicon-based active material includes at least one of crystalline silicon, amorphous silicon, or a composite of crystalline silicon and amorphous silicon.

[0045] In some embodiments, the silicon-based active material includes at least one of silicon oxide and a silicon alloy.

[0046] In some embodiments, the silicon-based active material includes silicon particles and a silicon oxide layer located on the surface of the silicon particles. The silicon oxide layer includes silicon oxide, and the general formula of silicon oxide is SiOx, where 0.5≤x<2. Specifically, SiOx can be SiO0.5, SiO0.7, SiO0.9, SiO, SiO1.2, SiO1.5, SiO1.8, SiO1.9, etc., without limitation herein.

[0047] In some embodiments, the silicon-based active material includes silicon particles and a silicon oxide layer located on the surface of the silicon particles. Based on the mass of the silicon-based active material being 100%, the mass percentage of oxygen atoms in the silicon-based active material is 1% to 18%. Specifically, the mass percentage of oxygen atoms in the silicon-based active material can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, or 18%, etc., without limitation herein. Controlling the mass percentage of oxygen atoms in the silicon-based active material within the above range is conducive to forming a stable silicon oxide layer on the surface of the silicon particles, which can reduce direct contact between the silicon particles and the electrolyte, thereby reducing side reactions between the silicon-based active material and the electrolyte, and improving the cycle stability of the negative electrode material. It can also ensure that the silicon-based active material has stable activity and improve the specific capacity of the negative electrode material.

[0048] In some embodiments, the negative electrode material further includes a carbon material located on at least a portion of the surface of the silicon-based active material.

[0049] In some embodiments, the mass percentage of silicon in the silicon-based active material is ≥99%. The mass percentage of silicon in the silicon-based active material within the above range is beneficial to improving the purity of the silicon-based active material and reducing impurities.

[0050] In some embodiments, the carbon material exists on the surface of the silicon-based active material and / or is dispersed among the silicon-based active materials.

[0051] In some embodiments, the carbon material includes at least one of amorphous carbon, graphene, graphite, carbon nanotubes, and carbon fibers.

[0052] In some embodiments, the median particle size of the negative electrode material is 1 μm to 10 μm, specifically 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, etc., and of course other values ​​within the above range are also possible, and are not limited here. Controlling the median particle size of the negative electrode material within the above range is beneficial to improving the capacity and cycle performance of the negative electrode material.

[0053] In some embodiments, the specific surface area of ​​the negative electrode material is ≤5m 2 / g, specifically 0.5m 2 / g、1m 2 / g, 1.5m 2 / g, 2m 2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g or 5m 2 / g, etc., and of course other values ​​within the above range are also possible and are not limited here. It can be understood that controlling the specific surface area of ​​the negative electrode material within the above range is beneficial to suppressing volume expansion and improving the cycle performance of the material.

[0054] In some embodiments, the silicon-based active material is mixed with ethanol to form a slurry with a solid content of 5% to 30%, and the Zeta potential of the slurry is tested using a zeta potential analyzer. The absolute value of the Zeta potential of the slurry is ≥20mV, and can specifically be 20mV, 25mV, 30mV, 35mV, 40mV, 45mV or 50mV, etc., and of course, it can also be other values ​​within the above range, which is not limited here. It can be understood that controlling the absolute value of the Zeta potential of the slurry within the above range can improve the dispersibility and stability of the slurry, inhibit the aggregation and deposition of particles, reduce the resistance and polarization of the electrode, and also improve the interfacial stability of the silicon-based active material, reduce the side reactions at the interface of the silicon-based active material, thereby improving the cycle performance of the negative electrode material.

[0055] In a second aspect, the present application provides a method for preparing a negative electrode material, comprising the following steps:

[0056] The silicon raw material is subjected to a first surface treatment to obtain primary particles with exposed surfaces;

[0057] The primary particles are surface-modified to obtain a silicon-based active substance, the negative electrode material includes the silicon-based active substance, the surface of the silicon-based active substance includes Si-R bonds, wherein R includes at least one of H, COOH, CHO and NH2, and the pH value of the silicon-based active substance is 3 to 7.

[0058] The preparation method of the negative electrode material provided by the present application, by performing a first surface treatment on the silicon raw material, the surface of the silicon raw material can be cleaned, thereby obtaining a primary particle with an exposed surface, and the lattice terminates at the exposed surface of the primary particle, so that each silicon atom located on the outermost layer of the primary particle surface has an unpaired electron, that is, there is an unsaturated bond, which is called a dangling bond. Due to the rich dangling bonds on the exposed surface of the primary particle, in the process of surface modification of the primary particle, the dangling bonds on the surface of the primary particle can be used as active sites, and compounded with -H, -COOH, -CHO or -NH2 to form a strong Si-H bond, Si-COOH bond, Si-CHO bond or Si-NH2 bond, reducing the silicon-based active material from combining with other elements (especially oxygen), affecting the activity of the silicon-based active material. Moreover, when the negative electrode material is used in a battery, there is inevitably water in the electrolyte of the battery. After the negative electrode material contacts the electrolyte, the pH value of the silicon-based active material is controlled to be 3 to 7, which can reduce the side reactions between the negative electrode material and the electrolyte and improve the cycle performance of the battery.

[0059] In some embodiments, the silicon feedstock includes silicon particles.

[0060] In some embodiments, the silicon raw material includes silicon particles, and the silicon particles include crystalline silicon and / or amorphous silicon.

[0061] In some embodiments, the silicon raw material includes silicon particles, and the average particle size of the silicon particles is 1nm to 100nm, specifically 1nm, 5nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0062] In some embodiments, the silicon raw material includes silicon particles, and the mass percentage of silicon element in the silicon particles is greater than or equal to 97%.

[0063] In some embodiments, the silicon raw material is prepared from a silicon source precursor.

[0064] In some embodiments, the silicon raw material is prepared from a silicon source precursor, and the silicon source precursor includes at least one of a gas-phase silicon source and a liquid-phase silicon source.

[0065] In some embodiments, the silicon raw material is prepared from a silicon source precursor, the silicon source precursor includes a gas-phase silicon source, and the gas-phase silicon source includes at least one of monosilane, disilane, monochlorosilane, and dichlorosilane.

[0066] In some embodiments, the silicon raw material is prepared from a silicon source precursor, the silicon source precursor includes a liquid silicon source, and the liquid silicon source includes at least one of trichlorosilane and tetrachlorosilane.

[0067] In some embodiments, the first surface treatment includes at least one of a crushing treatment and an etching treatment.

[0068] In some embodiments, the step of performing a first surface treatment on the silicon raw material includes: etching the silicon raw material using an etching solution.

[0069] In some embodiments, the step of performing a first surface treatment on the silicon raw material includes: etching the silicon raw material with an etching solution, wherein the etching solution includes at least one of potassium hydroxide solution, ammonia hydroxide solution, tetramethylhydroxylamine solution, hydrofluoric acid solution, buffered oxide etchant BOE, HF / EG solution and SC1 solution.

[0070] Specifically, the buffered oxide etchant (BOE) is a mixture of HF and NH4F in varying proportions, with HF serving as the primary etchant and NH4F acting as a buffer. Concentrated HF etches silicon material too quickly, while the buffered oxide etchant (BOE) offers advantages such as fast etching, easy controllable etching, and high dissolving power. Using BOE on silicon material facilitates controlled etching rates.

[0071] Specifically, the HF / EG solution is a mixture of 49% hydrofluoric acid and ethylene glycol in a ratio of approximately 4:96.

[0072] Specifically, SC1 solution is a mixture of ammonium hydroxide, hydrogen peroxide, and water. At 60°C to 70°C, SC1 (ammonium hydroxide: hydrogen peroxide: water = 1:2:50) has a low etching rate for silicon raw materials, about The etching rate of silicon raw materials can be finely controlled.

[0073] In some embodiments, the step of subjecting the silicon raw material to a first surface treatment includes: etching the silicon raw material with an etching solution, wherein the concentration of hydrogen ions in the etching solution is 1 mol / L to 12 mol / L, specifically 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, 11 mol / L or 12 mol / L, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0074] In some embodiments, the step of subjecting the silicon raw material to a first surface treatment includes: crushing the silicon raw material to obtain primary particles, and the average particle size of the primary particles is 1μm to 100μm, specifically 1μm, 5μm, 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm or 100μm, etc., of course, it can also be other values ​​within the above range, which is not limited here.

[0075] In some embodiments, the surface modification treatment includes at least one of an amination treatment and an acid leaching treatment.

[0076] In some embodiments, the surface modification treatment includes an amination treatment, and the amination treatment is performed in a compound containing an amino group.

[0077] In some embodiments, the surface modification treatment includes an amination treatment, and the amination treatment is carried out in a substance containing an amino group, and the amino group-containing compound includes at least one of ammonia, ammonium chloride, ammonium sulfate, ammonium bicarbonate, ammonium carbonate, ammonium bisulfate, ammonium nitrate, ammonium fluoride, ammonium iodide, ammonium bromide, methanol ammonium and hydrazine.

[0078] In some embodiments, the surface modification treatment includes an acid leaching treatment, and the acid leaching treatment is performed in a compound containing a carboxyl group.

[0079] In some embodiments, the surface modification treatment includes an acid leaching treatment, wherein the acid leaching treatment is performed in a compound containing a carboxyl group, and the compound containing a carboxyl group includes at least one of a fatty acid and an aromatic acid.

[0080] In some embodiments, the surface modification treatment includes an acid leaching treatment, wherein the acid leaching treatment is performed in a compound containing a carboxyl group, and the compound containing a carboxyl group includes at least one of formic acid, acetic acid, propionic acid, and octanoic acid.

[0081] In some embodiments, the surface modification treatment includes an acid leaching treatment, wherein the acid leaching treatment is performed in a compound containing a carboxyl group, and the compound containing a carboxyl group includes at least one of benzoic acid, phenylacetic acid, phthalic acid, and 3-nitrophthalic acid.

[0082] In some embodiments, the surface modification treatment comprises a physical treatment.

[0083] In some embodiments, the surface modification treatment comprises a physical treatment, and the physical treatment comprises at least one of ball milling, sand milling, and jet milling.

[0084] In some embodiments, the surface modification treatment comprises a physical treatment performed under a protective atmosphere.

[0085] In some embodiments, the protective atmosphere comprises at least one of nitrogen, helium, neon, argon, krypton, and xenon.

[0086] In some embodiments, the method further comprises:

[0087] The silicon-based active material obtained by the cooling process is subjected to carbon coating treatment to obtain a negative electrode material; the carbon coating treatment includes at least one of solid phase carbon coating, liquid phase carbon coating and gas phase carbon coating.

[0088] In the above technical solution, the surface of the silicon-based active material is carbon-coated to form a coating layer on the surface of the silicon-based active material, which can reduce the side reactions caused by the electrolyte entering the interior of the negative electrode material, resulting in a decrease in the initial coulombic efficiency and specific capacity, and can further solve the problem of large volume expansion of the negative electrode material, improve the conductivity of the negative electrode material, and thereby reduce the volume expansion of the entire negative electrode material and reduce the swelling of the electrode sheet.

[0089] In some embodiments, the carbon coating treatment step specifically includes: heating the silicon-based active material obtained by the cooling treatment, introducing a protective gas and a carbon source gas, and thermally cracking the carbon source gas to obtain a negative electrode material.

[0090] In some embodiments, the carbon coating treatment step specifically includes: heating the silicon-based active material obtained by cooling treatment, introducing protective gas and carbon source gas, and thermally cracking the carbon source gas to obtain a negative electrode material, wherein the carbon source gas is a hydrocarbon.

[0091] In some embodiments, the carbon coating treatment step specifically includes: heating the silicon-based active material obtained by cooling treatment, introducing protective gas and carbon source gas, and thermally cracking the carbon source gas to obtain a negative electrode material; wherein the carbon source gas includes at least one of methane, ethylene, acetylene, propyne, propylene, propane, toluene, benzene, styrene and phenol.

[0092] In some embodiments, the carbon coating treatment step specifically includes: heating the silicon-based active material obtained by the cooling treatment, introducing a protective gas and a carbon source gas, and thermally cracking the carbon source gas to obtain a negative electrode material; wherein the thermal cracking temperature is 600°C to 1000°C, and the thermal cracking time is 30 minutes to 24 hours.

[0093] Specifically, the thermal cracking temperature can be 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C or 1000°C, and the thermal cracking time can be 30 min, 1 h, 3 h, 5 h, 8 h, 10 h, 12 h, 15 h, 18 h, 20 h or 24 h, etc., which are not limited here.

[0094] In some embodiments, the carbon coating step specifically includes: carbonizing a mixture of the silicon-based active material obtained by the cooling treatment and a solid carbon source to obtain a negative electrode material.

[0095] In some embodiments, the carbon coating step specifically includes: carbonizing a mixture obtained by mixing the silicon-based active material obtained by cooling with a solid-phase carbon source to obtain a negative electrode material; wherein the carbonization temperature is 500°C to 1000°C, and the carbonization time is 30 minutes to 24 hours.

[0096] The temperature of the carbonization treatment can be 500°C, 600°C, 700°C, 800°C, 900°C or 1000°C, and the time of the carbonization treatment can be 30 min, 1 h, 3 h, 5 h, 8 h, 10 h, 12 h, 15 h, 18 h, 20 h or 24 h, etc., which are not limited here.

[0097] In some embodiments, the carbon coating step specifically includes: carbonizing the mixture obtained by mixing the silicon-based active material obtained by cooling treatment with a solid carbon source to obtain a negative electrode material; wherein the solid carbon source includes at least one of sugars, esters, hydrocarbons, organic acids and high molecular polymers.

[0098] In some embodiments, the carbon coating step specifically includes: carbonizing a mixture obtained by mixing the silicon-based active material obtained by cooling treatment with a solid carbon source to obtain a negative electrode material; wherein the solid carbon source includes at least one of polyvinyl chloride, polyvinyl butyral, polyacrylonitrile, polyacrylic acid, polyethylene glycol, polypyrrole, polyaniline, sucrose, glucose, maltose, citric acid, asphalt, furfural resin, epoxy resin and phenolic resin.

[0099] In some embodiments, the carbon coating step specifically includes: carbonizing a mixture obtained by mixing the silicon-based active material obtained by cooling treatment with a solid-phase carbon source to obtain a negative electrode material; wherein the mass ratio of the solid-phase carbon source to the silicon-based active material is (10-100): (5-80), specifically 10:5, 10:10, 10:20, 10:30, 20:50, 30:70, 40:60, 50:60, 80:70, 90:70 or 100:80, etc., of course, it can also be other values ​​within the above range, which is not limited here.

[0100] In a third aspect, the present application further provides a lithium-ion secondary battery, which comprises the negative electrode material described in the first aspect or the negative electrode material prepared by the negative electrode material preparation method described in the second aspect.

[0101] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0102] Example

[0103] Example 1

[0104] (1) Weigh 0.5 kg of commercially available nano-silicon (median particle size of 45 nm) and add it to a prepared acid solution (HF and HCl in a volume ratio of 1:15). React for 1 hour and then dry to obtain surface-purified primary particles.

[0105] (2) The primary particles in step (1) were added to 1000 g of butanol, stirred and dispersed, and then 10 g of acetic acid was added. The mixture was refluxed at 50° C. for 6 h under argon protection, and dried to obtain a silicon-based active material with Si-COOH bonds on the surface.

[0106] (3) The silicon-based active material and glucose were mixed in a mass ratio of 100:44, and then heat-treated at 880°C for 5 h to obtain a negative electrode material.

[0107] The negative electrode material prepared in this embodiment includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material. The median particle size of the negative electrode material is 5.8 μm and the specific surface area is 3.1 m 2 / g. The silicon-based active material was tested by Fourier infrared spectrometer, and the obtained spectrum is shown in Figure 1. As can be seen from Figure 1, the silicon-based active material of this embodiment has a wavelength of 1700-1750cm -1 There is a peak in the wave number of , which is speculated to be the Si-COOH bond, thus proving that the surface of the silicon-based active material contains Si-COOH bonds.

[0108] FIG1 is an infrared spectrum of the silicon-based active material prepared in Example 1 of the present application.

[0109] FIG2 is a scanning electron microscope (SEM) image of the negative electrode material prepared in Example 1.

[0110] FIG3 is an XRD pattern of the negative electrode material prepared in Example 1. As shown in FIG3 , it can be observed that a silicon peak exists in the negative electrode material.

[0111] FIG4 is the first charge and discharge curve of the negative electrode material prepared in Example 1. As shown in FIG4 , the first charge and discharge capacity of the negative electrode material is relatively high, and the first coulombic efficiency is also high.

[0112] FIG5 is a cycle performance curve of the negative electrode material prepared in Example 1. As shown in FIG5 , the negative electrode material has excellent cycle performance, and its capacity retention rate after 100 cycles is 94.0%.

[0113] Example 2

[0114] (1) Weigh 10 kg of metallic silicon (median particle size of 25 μm), of which the silicon content is 99%, put it into an argon protector, place it in a plasma reactor, heat it to 2400°C, and then quickly cool it to obtain primary particles with pure surface.

[0115] (2) Continue to introduce a mixture of hydrogen and nitrogen (the volume ratio of ammonia to nitrogen is 1:15) into the plasma reactor of step (1), raise the temperature to 600°C, and keep it warm for 2 hours to obtain the silicon-based active material containing Si-H bonds on the surface.

[0116] (3) The silicon-based active material and glucose were mixed in a mass ratio of 100:44, and then heat-treated at 880°C for 5 h to obtain a negative electrode material.

[0117] The negative electrode material prepared in this embodiment includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material. The median particle size of the negative electrode material is 7.9 μm and the specific surface area is 3.0 m 2 / g. The silicon-based active material was tested by Fourier infrared spectrometer and the results were in the range of 1900-2200cm -1 There is a peak at the wavenumber position of , which is speculated to be the Si-H bond, thereby proving that the surface of the silicon-based active material contains Si-H bonds.

[0118] Example 3

[0119] (1) Weigh 10 kg of metallic silicon (median particle size of 12 μm), wherein the silicon content is 99%, place the silicon powder in HF vapor for 2 hours, and then vacuum dry to obtain primary particles.

[0120] (2) The primary particles in step (1) were added to a high-energy ball mill, and anhydrous ethanol and formaldehyde were added to form a slurry. The solid content of the slurry was controlled to be 33%, the ball-to-material ratio was 10:1, the speed of the ball mill was set to 300 rpm, and the ball milling was continued for 30 hours to obtain a silicon-based active material containing Si-CHO bonds on the surface.

[0121] (3) The silicon-based active material and glucose were mixed in a mass ratio of 100:44, and then heat-treated at 880°C for 5 h to obtain a negative electrode material.

[0122] The negative electrode material prepared in this embodiment includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material. The median particle size of the negative electrode material is 4.6 μm and the specific surface area is 4.1 m 2 / g. The silicon-based active substances were tested by Fourier infrared spectrometer at 2600-2850cm -1 There is a peak at the wave number of , which is speculated to be the Si-CHO bond, thus proving that the surface of the silicon-based active material contains Si-CHO bonds.

[0123] Example 4

[0124] (1) Weigh 5 kg of metallic silicon (median particle size of 5 μm), of which the silicon content is 99%, and add it to a prepared acid solution (HF and HCl in a volume ratio of 1:20). The mixture is acid-washed and stirred for 10 h, then washed with water until neutral, and vacuum-dried to obtain primary particles.

[0125] (2) The primary particles were added to a sand mill, and acetone and acetic acid were added in a volume ratio of 100:1 to form a slurry. The solid content of the slurry was controlled to 25%, the ball-to-material ratio was 12:1, the speed of the sand mill was set to 350 rpm, and the sand milling was continued for 30 hours to obtain a silicon-based active material with Si-COOH bonds on the surface.

[0126] (3) The silicon-based active material and glucose were mixed in a mass ratio of 100:44, and then heat-treated at 880°C for 5 h to obtain a negative electrode material.

[0127] The negative electrode material prepared in this embodiment includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material. The median particle size of the negative electrode material is 9.1 μm and the specific surface area is 2.8 m 2 / g. The silicon-based active material was tested using a Fourier infrared spectrometer, and the spectrum obtained was at 1700-1750cm -1 There is a peak in the wave number of , which is speculated to be the Si-COOH bond, thus proving that the surface of the silicon-based active material contains Si-COOH bonds.

[0128] Example 5

[0129] (1) A mixed gas of silane and nitrogen (the volume ratio of silane to nitrogen is 1:15) is introduced into a chemical vapor deposition apparatus, and the temperature is raised to 500°C and kept at this temperature for 2 hours to obtain primary particles.

[0130] (2) Continue to introduce a mixed gas of ammonia and nitrogen into the chemical vapor deposition equipment, wherein the volume ratio of ammonia to nitrogen is 0.5:10, raise the temperature to 800°C and keep it for 3 hours to obtain a silicon-based active material with Si-NH2 bonds on the surface.

[0131] (3) Continue to introduce a mixture of carbon source gas and nitrogen into the chemical vapor deposition equipment, wherein the volume ratio of carbon source gas to nitrogen is 100:40, raise the temperature to 1000° C. and keep it for 5 hours to obtain the negative electrode material.

[0132] The negative electrode material prepared in this embodiment comprises a silicon-based active material and a carbon material located on the surface of the silicon-based active material. The median particle size of the negative electrode material is 2.9 μm and the specific surface area is 3.3 m 2 / g. The silicon-based active substances were tested by Fourier infrared spectrometer at 800-1200cm -1 There is a peak at the wave number of , which is speculated to be the Si-NH2 bond, thus proving that the surface of the silicon-based active material contains Si-NH2 bonds.

[0133] Example 6

[0134] Different from Example 1, in step (3), a liquid phase carbon coating process is used to coat the silicon-based active material to obtain the negative electrode material.

[0135] The negative electrode material prepared in this embodiment includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material. The median particle size of the negative electrode material is 6.5 μm and the specific surface area is 2.8 m 2 / g. The silicon-based active material was tested using a Fourier infrared spectrometer, and the spectrum obtained was at 1700-1750cm -1 There is a peak in the wave number of , which is speculated to be the Si-COOH bond, thus proving that the surface of the silicon-based active material contains Si-COOH bonds.

[0136] Example 7

[0137] Different from Example 1, in step (3), a vapor phase carbon coating process is used to coat the silicon-based active material to obtain the negative electrode material.

[0138] The negative electrode material prepared in this embodiment includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material. The median particle size of the negative electrode material is 6.0 μm and the specific surface area is 3.5 m 2 / g. The silicon-based active material was tested using a Fourier infrared spectrometer, and the spectrum obtained was at 1700-1750cm -1 There is a peak in the wave number of , which is speculated to be the Si-COOH bond, thus proving that the surface of the silicon-based active material contains Si-COOH bonds.

[0139] Example 8

[0140] Different from Example 1, in step (2), a mixed gas of ammonia and nitrogen is introduced into the device for placing the primary particles in step (1), wherein the volume ratio of ammonia to nitrogen is 5:10, and the temperature is raised to 800°C and kept warm for 3 hours to obtain a silicon-based active substance containing Si-NH2 bonds on the surface.

[0141] The negative electrode material prepared in this embodiment includes a silicon-based active material and a carbon material located on at least a portion of the surface of the silicon-based active material. The median particle size of the negative electrode material is 6.0 μm and the specific surface area is 3.5 m 2 / g. The silicon-based active substances were tested by Fourier infrared spectrometer at 800-1200cm -1 There is a peak at the wave number of , which is speculated to be the Si-NH2 bond, thus proving that the surface of the silicon-based active material contains Si-NH2 bonds.

[0142] Comparative Example 1

[0143] The negative electrode material was prepared in a method substantially the same as that of Example 1, except that no HF was added for treatment in step (1).

[0144] Comparative Example 2

[0145] The negative electrode material was prepared in a method substantially the same as that of Example 1, except that acetic acid was not added for treatment in step (2).

[0146] Comparative Example 3

[0147] Silicon particles with a median particle size of 50 nm were placed in a chemical vapor deposition device, and a mixed gas of carbon source gas and nitrogen was introduced into the chemical vapor deposition device, wherein the volume ratio of carbon source gas to nitrogen was 100:40. The temperature was raised to 1000°C and kept for 5 hours to obtain a negative electrode material.

[0148] Test method:

[0149] (1) Testing method for Si-R bond on the surface of silicon-based active materials:

[0150] Fourier transform infrared spectrometer was used to test the Si-R valence bonds on the surface of silicon-based active materials.

[0151] (2) Testing method for pH value of silicon-based active substances:

[0152] Tested according to ISO3071-1980 method.

[0153] (3) Testing method for the absolute value of zeta potential of slurry:

[0154] A silicon-based active substance was mixed with ethanol to form a slurry with a solids content of 5% to 30%. The zeta potential was measured using a 90Plus PALS Zeta Potential Tester from Brookhaven, USA. The sample was selected for testing, with a volume concentration below 0.5% and a volume of 1.5-3 ml. The sample was placed in a sample cell and allowed to stabilize for 5 minutes. The test was then performed with 3 cycles, 3 runs, a dwell time of 5 seconds, and a temperature of 5-70°C.

[0155] (4) Test method for average particle size of silicon-based active materials:

[0156] The particle size distribution of the composite anode material is measured using a Malvern laser particle size analyzer. Alternatively, the silicon-based active material can be observed using a field emission scanning electron microscope or transmission electron microscope. The particle sizes of 5-10 silicon-based active materials can be directly measured using a scale, and the average of the particle sizes is taken as the final particle size of the silicon-based active material.

[0157] (5) Testing method for median particle size D50 of materials:

[0158] The D50 was measured using a laser particle size analyzer and showed a symmetrical distribution similar to a normal distribution. In the volume-based distribution, the cumulative 50% diameter is D50, and so on, the cumulative 90% diameter is D90, and the cumulative 10% diameter is D10.

[0159] (6) Test method for the mass percentage of oxygen atoms in silicon-based active materials:

[0160] The range of oxygen content in the negative electrode material is tested by an oxygen, nitrogen and hydrogen tester.

[0161] (7) Test method for specific surface area of ​​negative electrode material:

[0162] The dynamic specific surface area rapid tester JW-DX produced by Beijing Jingwei Gaobo Science and Technology Co., Ltd. is used for testing, and the unit is m2 / g.

[0163] (8) Electrochemical performance test:

[0164] The negative electrode materials, conductive agent, and binder prepared in Examples 1-7 and Comparative Examples 1-3 were dissolved in deionized water in a ratio of 94:1:5 by mass, mixed to a solids content of 50%, coated onto a copper foil current collector, and vacuum-dried to produce a negative electrode. 18650 cylindrical cells were then assembled using conventional production processes using a ternary positive electrode (lithium nickel cobalt manganese oxide NCM523) prepared using a conventional, mature process, a 1 mol / L lithium hexafluorophosphate (LiPF6) / (ethylene carbonate EC + dimethyl carbonate DMC + ethyl methyl carbonate EMC) (v / v = 1:1:1) electrolyte, a Celgard 2400 separator, and a housing. Cylindrical cells were tested for charge and discharge at room temperature using a LAND battery test system from Wuhan Jinnuo Electronics Co., Ltd., with a constant current of 0.2C and a charge and discharge voltage limit of 2.75-4.2V. Initial specific capacity, first cycle charge capacity, and first cycle discharge capacity were obtained. First coulombic efficiency = first cycle discharge capacity / first cycle charge capacity.

[0165] The above test results are detailed in Table 1 and Table 2.

[0166] Table 1 Performance parameters of silicon-based active materials in various embodiments and comparative examples

[0167] Table 2 Electrochemical performance test results of each embodiment and comparative example

[0168] According to the test data in Table 1 and Table 2, the negative electrode materials prepared in Examples 1 to 8 include a silicon-based active material, the surface of the silicon-based active material includes a Si-R bond, R includes at least one of -H, -COOH, -CHO or -NH2, and the Si-R bond will hydrolyze in an aqueous solution to release H + , thereby improving the pH value of the silicon-based active material, reducing the situation where the pH value of the silicon-based active material is too acidic or too alkaline, reducing the combination of the silicon-based active material with other elements (especially oxygen), and reducing the impact on the activity of the silicon-based active material.

[0169] Compared with Example 1, during the preparation process of the negative electrode material of Comparative Example 1, HF was not added to treat the silicon raw material, so the surface of the silicon raw material could not be cleaned, and an oxide layer existed on the surface of the obtained primary particles. The presence of the oxide layer made it difficult for the primary particles to form dangling bonds, and could not combine with -COOH bonds to form Si-COOH bonds, or very few Si-COOH bonds were formed. The primary particles easily reacted with oxygen to form inactive silicon oxide, which reduced the specific capacity of the negative electrode material. After the negative electrode material was applied to the battery, the pH value of the silicon-based active substance was not improved, the side reaction with the electrolyte was aggravated, the consumption of active lithium ions increased, and the first efficiency and cycle performance of the battery were significantly reduced.

[0170] Compared with Example 1, during the preparation of the negative electrode material of Comparative Example 2, acetic acid was not added to treat the primary particles, and Si-COOH bonds could not be formed on the surface of the silicon-based active material. The primary particles easily reacted with oxygen to form inactive silicon oxide, resulting in a decrease in the specific capacity of the negative electrode material. After the negative electrode material was applied to the battery, the pH value of the silicon-based active material did not improve, the side reaction with the electrolyte was intensified, the consumption of active lithium ions increased, and the first efficiency and cycle performance of the battery were significantly reduced.

[0171] Compared with Example 1, in Comparative Example 3, the silicon particles are directly compounded with the carbon material without undergoing the first surface treatment and surface modification treatment. Si-R bonds cannot be formed on the surface of the silicon particles, and the silicon particles easily react with oxygen to form inactive silicon oxide, which greatly reduces the specific capacity of the negative electrode material. After the negative electrode material is applied to the battery, the pH value of the silicon particles does not improve, the side reaction between the silicon particles and the electrolyte is intensified, the consumption of active lithium ions increases, and the first efficiency and cycle performance of the battery are greatly reduced.

Claims

1. A negative electrode material, characterized in that: The negative electrode material includes a silicon-based active substance, the surface of the silicon-based active substance has a Si-R bond, wherein R includes at least one of H, COOH, CHO or NH2, and the pH value of the silicon-based active substance is 3-7.

2. The negative electrode material according to claim 1, characterized in that The average particle size of the silicon-based active material is 1 nm to 500 nm.

3. The negative electrode material according to any one of claims 1 to 2, characterized in that: The silicon-based active material includes at least one of crystalline silicon, amorphous silicon, and a composite of crystalline silicon and amorphous silicon.

4. The negative electrode material according to any one of claims 1 to 2, characterized in that: The silicon-based active material includes at least one of silicon oxide and silicon alloy.

5. The negative electrode material according to any one of claims 1 to 4, characterized in that: It includes at least one of the following features (1) and (2): (1) The silicon-based active material includes silicon particles and a silicon oxide layer located on the surface of the silicon particles; (2) The silicon-based active material includes silicon particles and a silicon oxide layer located on the surface of the silicon particles. Taking the mass of the silicon-based active material as 100%, the mass percentage of oxygen atoms in the silicon-based active material is 1% to 18%.

6. The negative electrode material according to claim 1, characterized in that The negative electrode material further includes a carbon material located on at least a portion of the surface of the silicon-based active material.

7. The negative electrode material according to claim 6, characterized in that The mass percentage of silicon in the silicon-based active material is greater than or equal to 99%.

8. The negative electrode material according to any one of claims 6 to 7, characterized in that: The carbon material exists on the surface of the silicon-based active material and / or is dispersed among the silicon-based active materials.

9. The negative electrode material according to any one of claims 6 to 8, characterized in that: The carbon material includes at least one of amorphous carbon, graphene, graphite, carbon nanotubes and carbon fibers.

10. The negative electrode material according to any one of claims 1 to 9, characterized in that: The median particle size of the negative electrode material is 1 μm to 10 μm.

11. The negative electrode material according to any one of claims 1 to 10, characterized in that: The specific surface area of ​​the negative electrode material is ≤5m 2 / g.

12. The negative electrode material according to any one of claims 6 to 11, characterized in that: The silicon-based active material is mixed with ethanol to form a slurry with a solid content of 5% to 30%. The Zeta potential of the slurry is tested by a Zeta potential analyzer. The absolute value of the Zeta potential of the slurry is ≥20mV.

13. A method for preparing a negative electrode material, characterized in that: The steps include: The silicon raw material is subjected to a first surface treatment to obtain primary particles with exposed surfaces; The primary particles are subjected to surface modification treatment to obtain a silicon-based active substance; the negative electrode material includes the silicon-based active substance, the surface of the silicon-based active substance includes Si-R bonds, wherein R includes at least one of H, COOH, CHO and NH2, and the pH value of the silicon-based active substance is 3 to 7.

14. The preparation method according to claim 13, characterized in that: The preparation method comprises at least one of the following features (1) to (2): (1) The first surface treatment includes at least one of a crushing treatment or an etching treatment; (2) The surface modification treatment includes at least one of an amination treatment and an acid leaching treatment.

15. A lithium ion secondary battery, characterized in that: The lithium-ion secondary battery comprises the negative electrode material according to any one of claims 1 to 12 or the negative electrode material prepared by the method for preparing the negative electrode material according to any one of claims 13 to 14.

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