Negative electrode material and preparation method therefor, and battery

Abstract

A negative electrode material and a preparation method therefor, and a battery, relating to the technical field of batteries. The negative electrode material comprises a silicon-based core and a coating layer at least partially covering the surface of the silicon-based core. The negative electrode material satisfies that the ratio of B:A is 1-100, wherein A is the mass ratio of an oxygen element to a lithium element in the negative electrode material, and B is the atomic ratio of the oxygen element to a silicon element in the negative electrode material measured by an X-ray photoelectron spectrometer. The preparation method for the negative electrode material comprises: enabling a carbon-coated pre-lithiated silicon-based material to react with an oxidizing agent to obtain a negative electrode material. The ratio of B:A in the negative electrode material actually indicates the degree of oxidation treatment of the surface layer of the negative electrode material; the larger the ratio is, the higher the degree of surface oxidation is; and the reaction between the silicon-based core and external moisture can be reduced, reducing the risk of hydrolysis and gas production, thereby greatly improving the water resistance of the negative electrode material, and improving the initial efficiency and cycle performance of the battery.

Description

Negative electrode material, preparation method thereof, and battery Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a negative electrode material, a preparation method thereof, and a battery. Background Art

[0002] Silicon-based negative electrode materials are one of the most promising materials for the next generation of lithium-ion battery applications. However, the main reason restricting the widespread application of silicon-based negative electrode materials is that the silicon-based negative electrode materials are accompanied by huge volume changes during the charging and discharging process, that is, the expansion rate is too large. Silicon-based negative electrode materials have a wider application prospect because their volume expansion changes are smaller than those of pure silicon negative electrode materials, but the initial efficiency of silicon-based negative electrode materials is low. In order to solve this problem, pre-lithiation technology is often used to pre-treat silicon-based negative electrode materials to form lithium silicate. While improving the initial efficiency, the hydrolysis of lithium silicate salts will make the solution more alkaline. This will result in poor processing performance of pre-lithiated silicon-based negative electrode materials during the preparation of slurry, poor slurry stability, inconvenience in production, and inability to be used in large-scale production.

[0003] Therefore, how to solve the processing problem of silicon-based negative electrode materials during the slurry preparation process is the key to their widespread application.

[0004] Summary of the Invention

[0005] The purpose of the present application is to provide a negative electrode material, a preparation method thereof, and a battery. By controlling the relationship between the pre-lithiation degree of the negative electrode material and the oxidation degree of the surface active silicon, the outward dissolution of lithium silicate in the pre-lithiation silicon-based material can be effectively reduced, and the generation of a higher pH value that destroys the stability of the aqueous slurry can be reduced; it can also reduce the contact between silicon particles in the negative electrode material and water, reduce the risk of gas production, and improve the safety performance of the negative electrode material in the battery.

[0006] The technical solution of this application is as follows:

[0007] In a first aspect, the present application provides a negative electrode material, comprising a silicon-based core and a coating layer at least partially coated on the surface of the silicon-based core;

[0008] The silicon-based core contains silicon and lithium silicate, and the negative electrode material satisfies a B:A ratio of 1-100, wherein A is the mass ratio of oxygen element to lithium element in the negative electrode material, and B is the atomic ratio of oxygen element to silicon element obtained by X-ray photoelectron spectrometer testing of the negative electrode material.

[0009] In a second aspect, the present application further provides a method for preparing the negative electrode material according to the first aspect, comprising:

[0010] The pre-lithiated silicon-based material having a coating layer is reacted with an oxidant to obtain the negative electrode material.

[0011] In a third aspect, the present application provides a battery comprising the negative electrode material described in the first aspect.

[0012] Beneficial effects of this application:

[0013] The mass ratio (A) of oxygen to lithium in the negative electrode material of this application reflects the degree of pre-lithiation. A lower A value indicates a higher lithium content and a higher degree of pre-lithiation in the negative electrode material, making hydrolysis more likely to occur, increasing the pH value in the negative electrode slurry and reducing the processing performance of the negative electrode slurry. The atomic ratio of oxygen to silicon in the surface layer of the negative electrode material can be measured using X-ray photoelectron spectroscopy. With the silicon atoms remaining unchanged, a higher B value indicates a higher number of oxygen atoms on the surface of the negative electrode material, indicating that surface oxidation reactions are occurring and the degree of oxidation is higher. The B:A ratio actually represents the relationship between the degree of pre-lithiation of the negative electrode material and the degree of oxidation of the surface active silicon. If the ratio falls within a certain range, the processing performance of the negative electrode material can be improved. Specifically, the active silicon on the surface of the negative electrode material has a certain degree of oxidation energy, which reduces the reaction of the core material with external moisture. On the one hand, this can reduce the dissolution of lithium silicates in the negative electrode material, which increases the pH value in the aqueous negative electrode slurry and damages the binder. On the other hand, it can also reduce the contact of active silicon with water, reducing the risk of gassing, thereby significantly improving the water resistance of the negative electrode material.

[0014] The present invention's negative electrode material preparation method utilizes an oxidant to promote in-situ oxidation on the surface of the pre-lithiated silicon-based material, thereby increasing the oxygen content of the negative electrode material's surface layer, reducing the reaction between the core material and external water, and improving the processing performance of the negative electrode material. The present invention's preparation method is simple, utilizes readily available raw materials, and can be used for large-scale production.

[0015] The above-mentioned negative electrode material is used in the negative electrode plate of the present application. The surface oxidized negative electrode material greatly delays and inhibits the hydrolysis reaction between the pre-lithiation silicon-based material inside the coating layer and external moisture, making the negative electrode plate more stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0017] FIG1 is a graph showing the viscosity change of the negative electrode slurry made from the negative electrode material of Example 1 of the present application on the first day and after being placed for 7 days. DETAILED DESCRIPTION

[0018] As used herein:

[0019] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus. The conjunction "consisting of" excludes any unspecified element, step, or component.

[0020] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed alone. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including the range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0021] In these examples, parts and percentages are by mass unless otherwise indicated.

[0022] "Parts by mass" refers to the basic unit of measurement used to express the mass ratio of multiple components. One part can represent any unit of mass, such as 1g or 2.689g. If we say that the mass of component A is a parts and the mass of component B is b parts, this means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, we could say that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number representing a multiplication factor). It's important to note that, unlike parts by mass, the sum of the mass of all components is not limited to 100 parts.

[0023] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0024] Although the silicon-based negative electrode material containing lithium silicates obtained by the pre-lithiation technology improves the initial efficiency, it is also easy to increase the alkalinity of the slurry after it is made into electrode slurry due to the hydrolysis of the lithium silicates. The alkaline environment causes the binder in the slurry to fail, the stability of the slurry deteriorates, and the processing performance of the negative electrode material deteriorates. In addition, the nano-silicon in the silicon-based negative electrode material has a very high reactivity and reacts with water to produce hydrogen. As the alkalinity of the slurry increases, the reaction rate will accelerate. When the lithium silicates in the silicon-based negative electrode material are hydrolyzed, the nano-silicon embedded in the lithium silicates is more easily exposed and reacts with water to produce gas, which further affects the coating process of the negative electrode slurry and affects the performance of the negative electrode sheet.

[0025] At present, the solution to the processing problems of pre-lithiation silicon-based negative electrode materials or amorphous silicon-based negative electrode materials is to perform secondary coating. Through different types of coating layers, the internal materials are not exposed to the aqueous solution when preparing the aqueous slurry, thereby slowing down the gas production during the material processing process. However, the existing secondary coating layers are mostly inorganic salts, organic polymer layers, etc., and most of them can only delay the gas production of the slurry. Therefore, it is necessary to improve the coating layer on the surface of the negative electrode material to reduce the dissolution of lithium silicates inside the silicon-based material, and at the same time reduce the contact reaction between the internal nano-silicon and water, thereby improving the processing performance of the negative electrode material. Even if the current silicon-based negative electrode materials are coated, there are still certain problems with the processing performance.

[0026] A first aspect of the present application provides a negative electrode material, comprising a silicon-based core and a coating layer at least partially coating the surface of the silicon-based core.

[0027] The negative electrode material of the present application contains silicon and lithium silicate. Further preferably, the lithium silicate includes at least one of Li2SiO3, Li2Si2O5, and Li4SiO4.

[0028] It should be noted that the silicon-based core of the negative electrode material of the present application is a pre-lithiated silicon-based material, specifically a pre-lithiated silicon-oxygen material, which can ensure that the negative electrode material has a high first coulombic efficiency. The silicon-oxygen material can generally be represented by the general formula SiO x , where 0<x≤2. After the silicon oxide material is pre-lithiated to form a silicon-based core, the active oxygen in the material reacts with exogenous lithium to form lithium silicate, which can be at least one of Li2SiO3, Li2Si2O5, and Li4SiO4. Lithium silicate can alleviate the consumption of active lithium in the formation of the SEI film in lithium-ion batteries, thereby improving the initial efficiency of the negative electrode material. At the same time, the coating layer on the surface of the silicon-based core can play a certain role in isolating moisture, reducing the chemical reaction between the silicon-based core and water, and improving the processing performance of the negative electrode material.

[0029] The negative electrode material of the present application satisfies a B:A ratio of 1-100, for example, 1, 5, 10, 20, 30, 50, 80, 100, or any value between 1 and 100. Wherein, A is the mass ratio of oxygen to lithium in the negative electrode material, and B is the atomic ratio of oxygen to silicon in the negative electrode material as measured by X-ray photoelectron spectroscopy.

[0030] In some embodiments of the present application, the A value of the negative electrode material is 1-20, for example, it can be 1, 3, 5, 8, 10, 12, 15, 18, 20 or any value between 1-20.

[0031] The A value mainly reflects the relationship between the content of all oxygen elements and lithium elements in the negative electrode material of this application. The lower the A value, the higher the content of Li, the higher the degree of pre-lithiation, and the worse the processing performance of the negative electrode slurry. Therefore, reducing the contact between the silicon-based core and water is the key to improving the slurry processing performance. The lithium element in the negative electrode material of this application mainly comes from Li2O, Li x Si, Li2SiO3, Li2Si2O5, Li4SiO4, etc. The oxygen element mainly comes from SiO, Li2SiO3, Li2Si2O5, Li4SiO4, etc. in the silicon-based core.

[0032] In some embodiments of the present application, the B value of the negative electrode material is 1-100, for example, it can be 1, 5, 10, 20, 30, 50, 70, 90, 100 or any value between 1-100.

[0033] It's understandable that X-ray photoelectron spectroscopy is a surface analysis technique that generally tests areas ≤10nm thick on the surface of a material. Therefore, the resulting B value primarily reflects the atomic ratio of O to Si in the anode material's surface. To improve the processing performance of anode materials, it's necessary to reduce the contact between the lithium silicate and active silicon in the silicon-based core and external water. A higher B value indicates a higher degree of oxidation of the active silicon on the anode material's surface.

[0034] The B:A ratio actually represents the relationship between the degree of pre-lithiation and the degree of surface active silicon oxidation in the negative electrode material. By controlling the B:A value, that is, by simultaneously maintaining a certain degree of pre-lithiation and surface active silicon oxidation, the negative electrode material of the present application can ensure a high initial efficiency while effectively reducing the active silicon content in the negative electrode material surface layer, reducing the contact between the silicon-based core and external water, and thus improving the processing performance of the negative electrode material.

[0035] In some embodiments of the present application, the negative electrode material satisfies B>A>1, and the ratio of B:A is 2-30, for example, it can be 2, 5, 10, 15, 20, 25, 30 or any value between 2-30.

[0036] It is understandable that when the B:A ratio is between 2 and 30, it means that the degree of pre-lithiation and the degree of oxidation of the surface active silicon in the negative electrode material are moderate, which will not affect the electrochemical properties of the negative electrode material, but can also use the higher degree of oxidation to isolate the contact between external substances and the silicon-based core, thereby improving the processing performance of the negative electrode material. For example, if the degree of oxidation of the active silicon on the surface of the negative electrode material is certain, and the degree of pre-lithiation is too high, then the A value is too small, and the B:A ratio will be too large, and the excessively high degree of pre-lithiation will significantly affect the processing performance; or if the degree of pre-lithiation is certain, when the degree of oxidation of the surface active silicon is too high, the active silicon content in the negative electrode material becomes less, which can easily lead to too low a first efficiency of the silicon-based material, thereby affecting the electrochemical performance of the negative electrode material.

[0037] In some embodiments of the present application, the atomic ratio of oxygen element to lithium element of the negative electrode material obtained by X-ray photoelectron spectrometry is C, where the C value is 1-10, for example, it can be 1, 2, 3, 5, 7, 10 or any value between 1-10.

[0038] The surface of the pre-lithiated silicon-based core, in addition to active silicon, may also contain residual lithium metal from the pre-lithiation process. This metal will react with external water, affecting the processing performance of the negative electrode material. Therefore, the C value is used to represent the atomic ratio of oxygen to lithium on the surface of the negative electrode material. A larger C value indicates a higher degree of oxidation on the surface of the negative electrode material and less residual lithium metal.

[0039] In some embodiments of the present application, the negative electrode material satisfies a C:A ratio of 0.5-10, for example, it can be 0.5, 1, 2, 3, 5, 7, 9, 10 or any value between 0.5-10.

[0040] The C:A ratio actually represents the relationship between the degree of pre-lithiation of the negative electrode material and the degree of oxidation of the residual lithium on the surface. When the degree of pre-lithiation is determined, a large C:A value indicates that the residual lithium metal on the surface is completely oxidized, which can greatly reduce the impact of the residual lithium metal on the processing performance of the negative electrode material. However, if the C:A value is too large, it means that there are too many oxygen atoms and too few lithium atoms on the surface of the material, which will affect the electrochemical performance of the negative electrode material.

[0041] In some embodiments of the present application, the coating layer contains a carbon material. The carbon material coating can not only isolate the silicon-based core from contact with external water, but also improve the conductivity of the negative electrode material.

[0042] In some embodiments of the present application, the negative electrode material contains an oxide, and the oxide is at least partially present on the surface of the silicon-based core. In other embodiments, the oxide forms an oxide layer, and at least a portion of the oxide layer is located on the surface of the silicon-based core of the negative electrode material. Further preferably, the oxide includes silicon oxide, and the general formula of silicon oxide is SiO x , where 0<x≤2.

[0043] It is understandable that the coating layer of carbon material on the surface of the negative electrode material is difficult to completely cover the silicon-based core, so a portion of the silicon-based core will be exposed to the outside world. Then, after the negative electrode material is oxidized, the active silicon on the surface of the exposed silicon-based core will be easily oxidized to silicon oxide to form an oxide layer. At least part of the oxide layer is located on the surface of the silicon-based core of the negative electrode material. Strictly speaking, part of the oxide layer formed is sandwiched between the silicon-based core and the carbon layer coating, while the other part of the oxide layer is directly exposed to the air. In some special cases, in addition to silicon oxide, the oxide layer formed by the oxidation treatment may also form lithium-containing oxides due to the residual Li metal on the surface of the silicon-based core.

[0044] In some embodiments of the present application, the pH value of the negative electrode material is 8-11.5, for example, it can be 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5 or any value between 8-11.5.

[0045] It is understandable that the silicon-based core of the present application has oxides on its surface, so it has a certain degree of oxidation, which reduces the contact between the lithium silicate in the silicon-based core and water, thereby reducing the pH value of the negative electrode material. If the negative electrode material has a high alkalinity, it will destroy the structure of the polymer binder in the slurry, causing its cross-linking to fail, thereby reducing the peeling force of the electrode. If the alkalinity is low, it will help slow down the rate at which the water solvent reacts with the lithium silicate and active silicon inside the negative electrode material to produce gas, further improving the stability of the electrode.

[0046] In some embodiments of the present application, the viscosity change of the negative electrode slurry containing the negative electrode material before and after being placed for 168 hours is ≤3000 mPa·s.

[0047] It should be noted that when the negative electrode material of the present application is used to prepare the negative electrode slurry, in addition to the silicon-based core, the negative electrode material has an outermost coating layer and an oxide formed by oxidation of the silicon-based core surface. The double layer protection of the oxide and the outermost coating layer greatly delays and inhibits the hydrolysis reaction of the lithium silicate inside the negative electrode material, and the water in the negative electrode slurry is not excessively consumed. Therefore, the negative electrode slurry has good stability during storage, and even after 7 days of storage, the viscosity of the slurry changes little, not exceeding 3000mPa·s.

[0048] The second aspect of the present application further provides a method for preparing the above-mentioned negative electrode material, comprising: reacting a pre-lithiated silicon-based material having a coating layer with an oxidant to obtain the negative electrode material.

[0049] In some embodiments of the present application, the oxidant includes at least one of oxygen, air, hypochlorous acid, hypochlorite, salts containing trivalent iron ions, salts containing copper ions, and hydrogen peroxide. These selected oxidants can oxidize the surface layer of the pre-lithiated silicon-based material, increasing the degree of oxidation and achieving the desired ratio of lithium, oxygen, and silicon.

[0050] In some embodiments of the present application, the reaction time of the pre-lithiated silicon-based material with a coating layer and the oxidant is 1h-12h, for example, it can be 1h, 2h, 3h, 5h, 8h, 10h, 12h or any value between 1h-12h.

[0051] In some embodiments of the present application, the mass ratio of the pre-lithiated silicon-based material with a coating layer to the oxidant is 100:1.5-5, for example, it can be 100:1.5, 100:2, 100:3, 100:4, 100:4.5, 100:5 or any value between 100:1.5-5.

[0052] In some embodiments of the present application, after the reaction with the oxidant is completed, the process further includes: subjecting the product after the reaction to a heat treatment to obtain a negative electrode material. Further, the heat treatment includes: heating the product to 400°C-800°C, for example, 400°C, 500°C, 600°C, 700°C, 800°C, or any value between 400°C and 800°C, under an inert gas atmosphere, and maintaining the temperature for 4 hours to 24 hours, for example, 4 hours, 8 hours, 12 hours, 15 hours, 20 hours, 24 hours, or any value between 4 hours and 24 hours.

[0053] It is understandable that heat treatment of the pre-lithiated silicon-based material having a coating layer after the oxidation reaction is completed can further enhance the coating effect of the coating layer on the surface of the silicon-based material and improve the strength of the negative electrode material.

[0054] In some embodiments of the present application, the preparation method of a pre-lithiated silicon-based material having a coating layer includes: mixing and sintering a silicon-based material with a carbon source to obtain a carbon-coated silicon-based material, and pre-lithiating the carbon-coated silicon-based material with a lithium source to obtain a pre-lithiated silicon-based material having a coating layer.

[0055] In some embodiments of the present application, the present application also provides another method for preparing a pre-lithiated silicon-based material with a coating layer, comprising: reacting a silicon-based material with a lithium source to obtain a pre-lithiated silicon-based material, and then mixing and sintering the pre-lithiated silicon-based material with a carbon source to obtain a pre-lithiated silicon-based material with a coating layer.

[0056] In some preferred embodiments, the carbon source includes at least one of alkanes, alkenes, alkynes, natural gas, toluene, glucose, sucrose, polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, polyvinylidene fluoride, and coal tar.

[0057] It should be noted that when silicon-based materials are used for preparation, silicon oxide materials, such as silicon monoxide, are often used. When using carbon sources to prepare the coating layer, vapor phase coating, liquid phase coating, or solid phase coating can be used. Among them, vapor phase coating often uses gases such as methane and acetylene to form a carbon coating layer through chemical vapor deposition; while liquid phase coating and solid phase coating processes use non-gaseous substances such as glucose and sucrose as carbon sources.

[0058] In some embodiments, the mass of the carbon-coated silicon oxide material is 100%, and the mass fraction of carbon is 2% to 8%, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8% or any value between 2% and 8%.

[0059] In some preferred embodiments, during pre-lithiation, the lithium source selected includes at least one of lithium hydride, LiOH, metallic lithium, and lithium-containing organic matter.

[0060] In some embodiments, the mass ratio of the carbon-coated silicon oxide material to the lithium source is 100:11-36, for example, 100:11, 100:15, 100:20, 100:25, 100:30, 100:36 or any value between 100:11-36.

[0061] In some preferred embodiments, the pre-lithiation treatment includes: heating to 500°C-1000°C in an inert gas atmosphere, for example, 500°C, 600°C, 800°C, 900°C, 1000°C or any value between 500°C and 1000°C, and keeping warm for 2h-10h, for example, 2h, 4h, 6h, 8h, 10h or any value between 2h-10h.

[0062] In a specific embodiment, the preparation method of the present application includes:

[0063] A silicon-based material and a carbon source are mixed and sintered to obtain a carbon-coated silicon-based material, and the carbon-coated silicon-based material and a lithium source are subjected to a pre-lithiation treatment to obtain a pre-lithiated silicon-based material having a coating layer, wherein the mass ratio of the carbon-coated silicon oxide material to the lithium source is 100:11-36, and the pre-lithiation treatment comprises: heating to 500° C.-1000° C. under an inert gas atmosphere;

[0064] A pre-lithiated silicon-based material having a coating layer is reacted with an oxidant, and a negative electrode material is obtained after heat treatment, wherein the oxidant includes at least one of oxygen, air, hypochlorous acid, hypochlorite, salts containing trivalent iron ions, salts containing copper ions, and hydrogen peroxide. The reaction time of the pre-lithiated silicon-based material having a coating layer and the oxidant is 1h-12h, and the mass ratio of the pre-lithiated silicon-based material having a coating layer to the oxidant is 100:1.5-5. The heat treatment includes: heating to 400°C-800°C in an inert gas atmosphere and keeping warm for 4h-24h.

[0065] The above preparation method uses an oxidant to promote an in-situ oxidation reaction on the surface of the pre-lithiated silicon-based material, thereby increasing the oxygen content of the surface layer of the negative electrode material, reducing the reaction between the core material and external water, and improving the processing performance of the negative electrode material. The preparation method of this application is simple, the raw materials are readily available, and it can be used for large-scale production.

[0066] The third aspect of the present application provides a negative electrode plate, comprising the above-mentioned negative electrode material.

[0067] In some embodiments of the present application, a method for preparing a negative electrode sheet includes: coating a negative electrode slurry containing a negative electrode material on a negative electrode current collector, rolling and drying the negative electrode sheet to obtain a negative electrode sheet.

[0068] The negative electrode slurry can be prepared according to the slurry production process of common batteries, and the preparation of the negative electrode plate can also be carried out according to the conventional production process of battery plates. If the viscosity of the negative electrode slurry is too high or too low, it will affect the coating process of the plate. If the viscosity is too high, the fluidity is poor, resulting in uneven coating; if the viscosity is too low, the coating thickness will be insufficient and the plate surface density requirements cannot be met. Therefore, the negative electrode material of the present application can make the viscosity of the prepared negative electrode slurry within an appropriate viscosity range to ensure the processing performance of the negative electrode plate.

[0069] A fourth aspect of the present application provides a battery comprising the above-mentioned negative electrode plate.

[0070] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0071] Example 1

[0072] This embodiment provides a negative electrode material, the preparation method of which includes:

[0073] (1) Using methane to carbon-coat silicon oxide (SiO), specifically, after adding silicon oxide to a rotary kiln, introducing methane gas, heating to 1000°C, and keeping warm for 8 hours, a carbon-coated silicon oxide material with a carbon content of 2-8% is obtained; then, the carbon-coated silicon oxide material is mixed with lithium hydride, the mass ratio of the carbon-coated silicon oxide material to lithium hydride is 100:12, wherein the mass content of lithium element is 11%, and heating to 600°C under an argon atmosphere, and keeping warm for 6 hours, to obtain a carbon-coated pre-lithiated silicon oxide material, wherein the mass content of lithium element is 10%.

[0074] (2) Sodium hypochlorite is mixed with deionized water to prepare a sodium hypochlorite solution with a concentration of 0.1 mol / L, wherein the mass ratio of the pre-lithiated silicon-based material with the coating layer to the sodium hypochlorite is 100:1.5; the carbon-coated pre-lithiated silicon oxide material obtained in step (1) is dispersed in the sodium hypochlorite solution under stirring and oxidized for 1 hour.

[0075] (3) The oxidized material is placed in a heat treatment furnace for heat treatment, the temperature is raised to 600°C, and the temperature is kept for 4 hours. The heat-treated material is then broken up to obtain the negative electrode material.

[0076] Example 2

[0077] The preparation method of the negative electrode material provided in this embodiment is the same as that in Example 1, except that the sodium hypochlorite in step (2) is replaced with copper chloride, the mass ratio of the pre-lithiated silicon-based material with a coating layer to the copper chloride is 100:5, and the concentration of the prepared solution is 0.2 mol / L.

[0078] Example 3

[0079] The preparation method of the negative electrode material provided in this embodiment is the same as that in Example 1, except that the sodium hypochlorite in step (2) is replaced with ferric chloride, the mass ratio of the pre-lithiated silicon-based material with a coating layer to the ferric chloride is 100:3, and the concentration of the prepared solution is 0.1 mol / L.

[0080] Example 4

[0081] The preparation method of the negative electrode material provided in this embodiment is the same as that in Example 1, except that the oxidation treatment time in step (2) is changed from 1 h to 4 h.

[0082] Example 5

[0083] The preparation method of the negative electrode material provided in this embodiment is the same as that in Example 1, except that the oxidation treatment time in step (2) is changed from 1 h to 12 h.

[0084] Example 6

[0085] The preparation method of the negative electrode material provided in this embodiment is the same as that in Example 1, except that the methane in step (1) is replaced with sucrose.

[0086] Example 7

[0087] The preparation method of the negative electrode material provided in this embodiment is the same as that in Example 1, except that the methane in step (1) is replaced by natural gas.

[0088] Example 8

[0089] The preparation method of the negative electrode material provided in this embodiment is the same as that in Example 1, except that the temperature after mixing with lithium hydride in step (1) is changed from 600°C to 800°C.

[0090] Example 9

[0091] The preparation method of the negative electrode material provided in this embodiment is the same as that in Example 1, except that the lithium hydride in step (1) is replaced with metallic lithium, wherein the mass ratio of the carbon-coated silicon dioxide material to the metallic lithium is 100:11.

[0092] Example 10

[0093] The preparation method of the negative electrode material provided in this embodiment is the same as that in Example 1, except that the holding time for mixing with lithium hydride in step (1) is changed from 6 hours to 12 hours.

[0094] Example 11

[0095] The preparation method of the negative electrode material provided in this embodiment is the same as that in Example 1, except that the heat treatment temperature in step (3) is changed from 600°C to 400°C.

[0096] Example 12

[0097] The preparation method of the negative electrode material provided in this embodiment is the same as that in Example 1, except that the heat treatment temperature in step (3) is changed from 600°C to 800°C.

[0098] Example 13

[0099] The preparation method of the negative electrode material provided in this embodiment is the same as that in Example 1, except that the holding time in step (3) is changed from 4 h to 12 h.

[0100] Example 14

[0101] The preparation method of the negative electrode material provided in this embodiment is the same as that in Example 1, except that the holding time in step (3) is changed from 4 h to 24 h.

[0102] Example 15

[0103] The preparation method of the negative electrode material provided in this embodiment is the same as that in Example 1, except that: in step (1), the mass ratio of the carbon-coated silicon oxide material to lithium hydride is 100:24, and the mass content of lithium element in the obtained carbon-coated pre-lithiated silicon oxide material is changed from 10% to 20%.

[0104] Example 16

[0105] The preparation method of the negative electrode material provided in this embodiment is the same as that in Example 1, except that: in step (1), the mass ratio of the carbon-coated silicon oxide material to lithium hydride is 100:24, the mass content of lithium element in the obtained carbon-coated pre-lithiated silicon oxide material is changed from 10% to 20%, and the oxidation treatment time in step (2) is changed from 1h to 4h.

[0106] Example 17

[0107] The preparation method of the negative electrode material provided in this embodiment is the same as that in Example 1, except that: in step (1), the mass ratio of the carbon-coated silicon oxide material to lithium hydride is 100:36, the mass content of lithium element in the obtained carbon-coated pre-lithiated silicon oxide material is changed from 10% to 30%, and the oxidation treatment time in step (2) is changed from 1h to 12h.

[0108] Comparative Example 1

[0109] This comparative example provides a negative electrode material, the preparation method of which includes:

[0110] After adding silicon oxide to a rotary kiln, methane gas is introduced, the temperature is raised to 1000°C, and the temperature is kept for 8 hours to obtain a carbon-coated silicon oxide material with a carbon content of 2-8%. The carbon-coated silicon oxide material is then mixed with lithium hydride, with a mass ratio of the carbon-coated silicon oxide material to lithium hydride being 100:12. The temperature is raised to 600°C under an argon atmosphere and the temperature is kept for 6 hours to obtain a carbon-coated pre-lithiated silicon oxide material, in which the mass content of lithium element is 10%.

[0111] Comparative Example 2

[0112] This comparative example provides a negative electrode material, and its preparation method is the same as that of comparative example 1, except that the mass content of lithium element in the prepared carbon-coated pre-lithiated silicon 2 oxide material is changed from 10% to 30%.

[0113] The element content and pH value of the negative electrode materials prepared in the above embodiments and comparative examples were tested, and the test results are shown in Table 1.

[0114] When testing the mass content of Li element in the negative electrode material, the test method is: full dissolution ICP measurement is used. The specific operation is: 0.5g of negative electrode material is calcined at 750℃ in air for 2 hours to completely remove the carbon element, and then it is completely dissolved in HCl / HNO3 / HF mixed acid and the volume is fixed in a 100mL plastic volumetric flask. Finally, the Li content is tested using an ICP spectrometer (Agilent 5800VDVICP-OES).

[0115] The O content in the negative electrode material was measured using an ONH elemental analyzer (ONH-2000). The weighed negative electrode material was placed in a graphite crucible and then tested in the ONH elemental analyzer to determine the O content. The A value was then calculated by comparing the O content with the Li content measured by ICP spectrometry.

[0116] The atomic counts of Si, Li, and O in the surface layer of the negative electrode material were measured using an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha). Al Kα radiation was used as the excitation source, with a beam spot size of 400 μm, a full-spectrum scan with a pass energy of 100 eV, and a step size of 1 eV. The full-spectrum scan data were analyzed using Avantage software to determine the atomic ratio of O to Si as the B value, and the atomic ratio of O to Li as the C value.

[0117] The pH value of the negative electrode material was tested by ultrasonically dispersing 5 g of the negative electrode material in 45 g of water, and then measuring the pH value using a pH meter.

[0118] In addition, the negative electrode materials obtained in Examples 1-17 and Comparative Examples 1-2 were used as negative electrode active materials, mixed evenly in a mass ratio of negative electrode active material: sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) = 96.5:1.5:2, and then coated on a copper foil current collector. After drying, a negative electrode sheet was obtained for use.

[0119] First, the obtained electrode was tested in a button cell battery. The battery was assembled in an argon glove box, using a metallic lithium sheet as the negative electrode, an electrolyte consisting of 1 mol / L LiPF6 + ethylene carbonate (EC) + ethyl methyl carbonate (EMC), and a separator consisting of a polyethylene / propylene composite microporous membrane. Electrochemical performance was measured on a battery tester, with the battery capacity set to a standard 480 mAh / g, charge and discharge voltages ranging from 0.01 V to 1.5 V, and a charge and discharge rate of 0.1 C. The electrochemical performance test results are shown in Table 2.

[0120] Viscosity test of negative electrode slurry: Use rheometer to test slurry viscosity, dynamic viscosity test (rotation mode), shear rate range 0.1s -1-300s -1 The test instruments are HAAKE MARS60, Anton Paar MCR302 and HAAKE MARS4.

[0121] Gas production test of negative electrode slurry: After the slurry is prepared, 20g of the slurry is weighed and sealed in an aluminum-plastic film, and then stored at room temperature for 168h. The volume change of the aluminum-plastic film before and after storage is measured by the drainage method to obtain the gas production of the slurry.

[0122] The test results of the viscosity and gas production of the negative electrode slurry are shown in Table 1. Figure 1 shows the viscosity of the negative electrode slurry prepared in Example 1 on the first day and after 7 days at a low shear rate (0.1s -1 -300s -1 ) under the change process.

[0123] Table 1 Test results of various embodiments and comparative examples

[0124] Table 2 Electrochemical test results of various embodiments and comparative examples

[0125] The results in Tables 1 and 2 demonstrate that, after treating the pre-lithiated silicon oxide material with an oxidant, the active Si particles and residual lithium exposed on the surface of the material can be oxidized to form an oxide layer. Compared to Comparative Examples 1 and 2, Examples 1-17, which all used an oxidant to treat the surface, exhibited superior gas production results when the B:A ratio ranged from 1 to 100.

[0126] Among them, Examples 1, 2, and 3 respectively used different oxidants, and the degree of surface treatment was similar, so they showed similar test results. In Examples 4 and 5, because the oxidation treatment time was extended, a thicker and denser oxide layer was obtained, and the gas production results were all 0, the same as in Examples 1 to 3, but the capacity was reduced to a certain extent. Examples 6 and 7 replaced the carbon source of the coating layer, which had little effect on the gas production results, but had a slight effect on the capacity first effect and cycle performance. Example 8 changed the pre-lithium reaction temperature to make the reaction more intense and sufficient, its first effect was higher, and other properties were not affected much. Example 9 changed the lithium source, and the overall performance was similar to Example 1. Example 10 increased the pre-lithium reaction time, which had no significant effect on the performance. Examples 11, 12, 13, and 14 changed the temperature and time of the heat treatment. When the heat treatment conditions changed, the outer layer oxidation treatment would be damaged to a certain extent as the temperature and time increased, which would have a certain effect on the gas production performance. In Example 15, the pre-lithium amount was increased, and its first effect was improved, but it had a certain effect on the gas production performance, and the gas production performance was weakened. In Examples 16 and 17, while increasing the amount of pre-lithium, the oxidation reaction time was increased. Although the overall gas production performance was improved compared to the comparative example, it did not reach the best level and still produced a small amount of gas. In Comparative Example 1, since no oxidation treatment was performed, its capacity and initial efficiency were relatively high, but its gas production performance was poor, the pH was high, the slurry viscosity changed greatly, and the processing performance was poor. In Comparative Example 2, due to the large increase in the amount of pre-lithium, the performance of the product after pre-lithium was unstable, and it was poor in gas production, capacity, and cycle performance.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

[0128] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and to form different embodiments. For example, any of the above-described claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background of this application and should not be construed as an admission or any form of implication that such information constitutes prior art known to those skilled in the art.

Claims

1. A negative electrode material, characterized in that: It comprises a silicon-based core and a coating layer at least partially coating the surface of the silicon-based core; The silicon-based core contains silicon and lithium silicate, and the negative electrode material satisfies a B:A ratio of 1-100, wherein A is the mass ratio of oxygen element to lithium element in the negative electrode material, and B is the atomic ratio of oxygen element to silicon element obtained by testing the negative electrode material through an X-ray photoelectron spectrometer.

2. The negative electrode material according to claim 1, characterized in that The negative electrode material contains an oxide, and the oxide is at least partially present on the surface of the silicon-based core.

3. The negative electrode material according to claim 2, characterized in that At least a portion of the oxide forms an oxide layer located on a surface of the silicon-based core.

4. The negative electrode material according to claim 1, characterized in that The lithium silicate includes at least one of Li2SiO3, Li2Si2O5, and Li4SiO4.

5. The negative electrode material according to claim 1, characterized in that The pH value of the negative electrode material is 8-11.

5.

6. The negative electrode material according to claim 1, characterized in that The A value of the negative electrode material is 1-20.

7. The negative electrode material according to claim 1, characterized in that The B value of the negative electrode material is 1-100.

8. The negative electrode material according to claim 1, characterized in that When the negative electrode material satisfies B>A>1, the ratio of B:A is 2-30.

9. The negative electrode material according to claim 1, characterized in that The atomic ratio of oxygen element to lithium element of the negative electrode material tested by an X-ray photoelectron spectrometer is C, wherein the C value is 1-10.

10. The negative electrode material according to claim 1, characterized in that The viscosity change of the negative electrode slurry containing the negative electrode material before and after being placed for 168 hours is ≤3000 mPa·s.

11. The negative electrode material according to claim 2, characterized in that The oxide includes silicon oxide, and the general formula of silicon oxide is SiO x , where 0<x≤2.

12. The negative electrode material according to claim 9, characterized in that The negative electrode material also satisfies a C:A ratio of 0.5-10.

13. The negative electrode material according to any one of claims 1 to 12, characterized in that: The coating layer contains a carbon material.

14. A method for preparing a negative electrode material according to any one of claims 1 to 13, characterized in that: include: The pre-lithiated silicon-based material having a coating layer is reacted with an oxidant to obtain the negative electrode material.

15. A battery, characterized in that: The negative electrode material comprises the negative electrode material according to any one of claims 1 to 13.

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