Negative electrode material and preparation method thereof, negative electrode sheet and battery

Abstract

The present application provides a negative electrode material and a preparation method thereof, a negative electrode plate and a battery, and relates to the field of battery technology. The negative electrode material of the present application includes a silicon-based core and a coating layer that is at least partially coated on the surface of the silicon-based core; 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. The preparation method of the negative electrode material comprises: reacting a carbon-coated pre-lithiated silicon-based material with an oxidant to obtain a negative electrode material. The B:A ratio in the negative electrode material of the present application actually represents the degree of oxidation treatment of the surface layer of the negative electrode material. The larger the ratio, the higher the degree of surface oxidation, which can reduce the reaction of the silicon-based core material with external moisture, reduce 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

Technical Field

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

[0004] The purpose of the present application is to provide a negative electrode material and a preparation method thereof, a negative electrode plate and a battery. By oxidizing the surface of the silicon-based material, the dissolution of lithium silicate in the pre-lithiation silicon-based material can be effectively reduced, and the generation of a high 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.

[0005] To achieve the above objectives, the technical solutions of this application are as follows:

[0006] 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;

[0007] The negative electrode material 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.

[0008] Optionally, the negative electrode material satisfies at least one of the following conditions:

[0009] a. The negative electrode material further comprises an oxide layer, at least a portion of the oxide layer being located between the silicon-based core and the coating layer;

[0010] b. The lithium silicate includes at least one of Li2SiO3, Li2Si2O5, Li4SiO4;

[0011] c. The pH value of the negative electrode material is 8-11.5;

[0012] d. The A value of the negative electrode material is 1-20;

[0013] e. The B value of the negative electrode material is 1-100;

[0014] f. When the negative electrode material satisfies B>A>1, the ratio of B:A is 2-30;

[0015] g. The atomic ratio of oxygen to lithium obtained by the negative electrode material tested by X- ray photoelectron spectrometer is C, wherein the C value is 1-10;

[0016] h. The viscosity change of the negative electrode slurry containing the negative electrode material before and after standing for 7 days is ≤3000 mPa·s.

[0017] Preferably, the negative electrode material further satisfies at least one of the following conditions:

[0018] i. The oxide layer includes silicon oxide, the general formula of which is SiO x , where 0<x≤2;

[0019] j. The negative electrode material also satisfies a C:A ratio of 0.5-10.

[0020] Optionally, the coating layer comprises a carbon layer.

[0021] In a second aspect, the present application further provides a method for preparing the negative electrode material according to the first aspect, comprising:

[0022] The pre-lithiated silicon-based material having a coating layer is reacted with an oxidant to obtain the negative electrode material.

[0023] Optionally, the preparation method of the negative electrode material satisfies at least one of the following conditions:

[0024] l. The oxidant comprises at least one of oxygen, air, hypochlorous acid, hypochlorite, salts containing trivalent iron ions, salts containing copper ions, and hydrogen peroxide;

[0025] m. After the reaction with the oxidant is completed, further comprising: heat treating the product after the reaction to obtain the negative electrode material;

[0026] n. The method for preparing the pre-lithiation silicon-based material having a coating layer comprises:

[0027] Mixing a silicon-based material with a carbon source and sintering the mixture to obtain a carbon-coated silicon-based material, and subjecting the carbon-coated silicon-based material to a pre-lithiation treatment with a lithium source to obtain the pre-lithiation silicon-based material having a coating layer;

[0028] Alternatively, a silicon-based material is reacted with a lithium source to obtain the pre-lithiated silicon-based material, and the pre-lithiated silicon-based material is mixed with a carbon source and sintered to obtain the pre-lithiated silicon-based material with a coating layer.

[0029] Preferably, the method for preparing the negative electrode material further satisfies at least one of the following conditions:

[0030] o. The heat treatment comprises: heating to 400°C-800°C in an inert gas atmosphere and holding for 4h-24h;

[0031] p. The carbon source comprises at least one of alkanes, alkenes, alkynes, natural gas, toluene, glucose, sucrose, polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, polyvinylidene fluoride and coal tar;

[0032] q. The lithium source comprises at least one of lithium hydride, LiOH, metallic lithium, and lithium-containing organic matter;

[0033] r. The pre-lithiation treatment comprises: heating to 400°C-800°C in an inert gas atmosphere and keeping the temperature for 2h-12h.

[0034] Optionally, the reaction time of the pre-lithiated silicon-based material having the coating layer and the oxidant is 1 hour to 12 hours.

[0035] In a third aspect, the present application provides a negative electrode plate comprising the negative electrode material described in the first aspect.

[0036] Optionally, the method for preparing the negative electrode sheet includes: coating a negative electrode slurry including the negative electrode material on a negative electrode current collector, rolling and drying, to obtain the negative electrode sheet.

[0037] In a fourth aspect, the present application provides a battery comprising the negative electrode sheet described in the third aspect.

[0038] Beneficial effects of this application:

[0039] 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. This increases the pH in the negative electrode slurry and reduces the processing performance of the negative electrode slurry. The atomic ratio of oxygen to silicon on the surface of the negative electrode material can be measured using an X-ray photoelectron spectroscopy. With the silicon atoms remaining constant, 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 oxidation of the active silicon on the surface of the negative electrode material can block the reaction between the core material and external moisture. This can reduce the dissolution of lithium silicates in the negative electrode material, which can generate a higher pH and damage the binder in the aqueous negative electrode slurry. It can also reduce the contact of the active silicon with water, reducing the risk of gassing, thereby significantly improving the water resistance of the negative electrode material.

[0040] 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, blocking the reaction between the core material and external water, and improving the negative electrode material's processing performance. The present invention's preparation method is simple, utilizes readily available raw materials, and can be used for large-scale production.

[0041] The negative electrode plate of the present application adopts the above-mentioned negative electrode material. By using the surface-oxidized negative electrode material, the hydrolysis reaction between the pre-lithiation material inside the coating layer and the external moisture is greatly delayed and suppressed, making the negative electrode plate more stable.

[0042] The battery of the present application uses the above-mentioned negative electrode plate, which has high initial coulombic efficiency and good cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] 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.

[0044] Figure 1 This is a graph showing the viscosity change of the negative electrode slurry made from the negative electrode material of Example 1 on the first day and after being placed for 7 days. DETAILED DESCRIPTION

[0045] As used herein:

[0046] "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.

[0047] 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.

[0048] In these examples, parts and percentages are by mass unless otherwise indicated.

[0049] "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.

[0050] "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).

[0051] Although pre-lithiation technology improves the initial efficiency of silicon-based negative electrode materials, it is also easy to increase the alkalinity of the slurry after the electrode slurry is made due to the hydrolysis of the lithium silicate therein, resulting in binder failure and poor stability of the slurry, which in turn deteriorates the processing performance of the negative electrode material. In addition, the nano-silicon in the silicon-based negative electrode material has a very high reactivity and reacts with water to produce hydrogen, and the reaction rate accelerates as the alkalinity of the slurry increases. When the lithium silicate in the silicon-based material is hydrolyzed, the nano-silicon embedded in the lithium silicate is more easily exposed and reacts with water to produce gas, which further affects the coating process of the negative electrode slurry and the performance of the negative electrode sheet.

[0052] Currently, the solution to the processing problems of pre-lithiated silicon-based anode materials or amorphous silicon-based anode 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 anode material to reduce the dissolution of lithium silicates inside the silicon-based material, while also reducing the contact reaction between the internal nano-silicon and water, thereby improving the processing performance of the anode material.

[0053] 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.

[0054] 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.

[0055] 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 oxide material, which can ensure that the negative electrode material has a high first coulombic efficiency. Silicon oxide materials are generally a new structure in which silicon and silicon dioxide are mixed, in which silicon, silicon dioxide and silicon suboxidation states exist. After the silicon oxide material is pre-lithiated to form a silicon-based core, the active oxygen in the material will react with exogenous lithium to form a lithium-containing silicate, for example, it can be at least one of Li2SiO3, Li2Si2O5, and Li4SiO4. Lithium silicate can alleviate the active lithium consumed by lithium-ion batteries in the process of forming the SEI film, thereby improving the first effect of the negative electrode material. At the same time, the coating layer on the surface of the silicon-based core can play a certain insulating role against moisture, reducing the chemical reaction between the silicon-based core and water, and improving the processing performance of the negative electrode material.

[0056] 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.

[0057] 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.

[0058] The A value mainly reflects the content of all oxygen and lithium elements in the negative electrode material of this application. The lower the A value, the higher the Li content and the higher the pre-lithiation degree, 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.

[0059] 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.

[0060] It's understandable that X-ray photoelectron spectroscopy is a surface analysis technique, so the B value obtained from the test primarily reflects the atomic ratio of O to Si in the surface layer of the negative electrode material. To improve the processing performance of the negative electrode material, it's necessary to reduce the contact between the lithium silicate and active silicon in the silicon-based core material and external water. Therefore, if the active silicon exposed on the surface of the silicon-based core is oxidized, when sufficient silicon oxide is generated, it can isolate the silicon-based core material from external water. Therefore, a larger B value indicates a higher degree of oxidation of the active silicon on the surface of the negative electrode material.

[0061] The B:A ratio actually represents the relationship between the degree of pre-lithiation in the anode material and the degree of surface active silicon oxidation. Given a certain degree of pre-lithiation, a larger B:A value indicates a greater atomic ratio of oxygen to silicon, meaning a higher degree of surface oxidation in the anode material. This effectively reduces the active silicon content in the anode material's surface. The silicon oxide formed by oxidation, in turn, reduces contact between the silicon-based core material and external water, thereby improving the processing performance of the anode material.

[0062] 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.

[0063] It is understandable that when the ratio of B:A 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 oxidation reaction to isolate the contact between external substances and the silicon-based core material, 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, the degree of pre-lithiation is too high, the A value is too small, and the ratio of B:A will be too large, and the excessively high degree of pre-lithiation will obviously 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.

[0064] 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.

[0065] In addition to active silicon, the surface of pre-lithiated silicon-based core materials may also contain residual lithium metal from the pre-lithiation process. This metal can 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.

[0066] 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.

[0067] 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.

[0068] In some embodiments of the present application, the coating layer includes a carbon layer. The carbon layer can not only isolate the silicon-based core material from contact with external water, but also improve the conductivity of the negative electrode material.

[0069] In some embodiments of the present application, the negative electrode material further comprises an oxide layer, at least part of which is located between the silicon-based core and the coating layer of the negative electrode material. Further preferably, the oxide layer comprises silicon oxide, the general formula of which is SiO x , where 0<x≤2.

[0070] It is understandable that the carbon coating on the surface of the negative electrode material is difficult to completely cover the silicon-based core material, so a portion of the silicon-based core material 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 material will be easily oxidized into silicon oxide to form an oxide layer. Strictly speaking, part of the oxide layer formed is sandwiched between the silicon-based core and the carbon 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 material.

[0071] 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.

[0072] It is understandable that the surface oxidation treatment of the negative electrode material of this application reduces the contact between the lithium silicate in the silicon-based core and water, thereby lowering the pH of the negative electrode material. A high alkalinity in the negative electrode material would destroy the structure of the polymer binder in the slurry, causing its crosslinking to fail and thus reducing the peel strength of the electrode. A low alkalinity would help slow the rate at which the aqueous solvent reacts with the Si grains within the material to produce gas, further improving the stability of the electrode.

[0073] 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.

[0074] 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 material, 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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 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.

[0079] It is understandable that heat treatment of the silicon-based material after the oxidation reaction is completed can further enhance the coating effect of the surface coating layer of the silicon-based material and improve the strength of the negative electrode material.

[0080] 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 carbon-coated pre-lithiated silicon-based material having a coating layer as a carbon layer.

[0081] 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, including: 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 carbon-coated pre-lithiated silicon-based material having a coating layer as a carbon layer.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] The third aspect of the present application provides a negative electrode plate, comprising the above-mentioned negative electrode material.

[0087] 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.

[0088] 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.

[0089] A fourth aspect of the present application provides a battery comprising the above-mentioned negative electrode plate.

[0090] 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.

[0091] Example 1

[0092] This embodiment provides a silicon-based negative electrode material for a lithium-ion battery, and the preparation method thereof includes:

[0093] (1) Using methane to carbon-coat silicon oxide, specifically, after adding silicon oxide into a rotary kiln, introducing methane gas, heating to 1000°C, and keeping warm for 8 hours to obtain a carbon-coated silicon oxide material; then, mixing the carbon-coated silicon oxide material with lithium hydride, 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%.

[0094] (2) Sodium hypochlorite is mixed with deionized water to prepare a sodium hypochlorite solution with a concentration of 0.1 mol / L; the carbon-coated pre-lithiated silicon dioxide material obtained in step (1) is dispersed in the sodium hypochlorite solution under stirring and oxidized for 1 hour.

[0095] (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 a silicon-based negative electrode material.

[0096] Example 2

[0097] The preparation method of the silicon-based 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, and the concentration of the prepared solution is 0.2 mol / L.

[0098] Example 3

[0099] The preparation method of the silicon-based 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, and the concentration of the prepared solution is 0.1 mol / L.

[0100] Example 4

[0101] The preparation method of the silicon-based 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.

[0102] Example 5

[0103] The preparation method of the silicon-based 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.

[0104] Example 6

[0105] The preparation method of the silicon-based 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.

[0106] Example 7

[0107] The preparation method of the silicon-based 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.

[0108] Example 8

[0109] The preparation method of the silicon-based 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.

[0110] Example 9

[0111] The preparation method of the silicon-based 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.

[0112] Example 10

[0113] The preparation method of the silicon-based 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.

[0114] Example 11

[0115] The preparation method of the silicon-based 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.

[0116] Example 12

[0117] The preparation method of the silicon-based 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.

[0118] Example 13

[0119] The preparation method of the silicon-based 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.

[0120] Example 14

[0121] The preparation method of the silicon-based 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 hours to 24 hours.

[0122] Example 15

[0123] The preparation method of the silicon-based negative electrode material provided in this embodiment is the same as that in Example 1, except that the mass content of lithium element in the carbon-coated pre-lithiated silicon monoxide material obtained in step (1) is changed from 10% to 20%.

[0124] Example 16

[0125] The preparation method of the silicon-based negative electrode material provided in this embodiment is the same as that in Example 1, except that the mass content of lithium element in the carbon-coated pre-lithiated silicon dioxide material obtained in step (1) is changed from 10% to 20%, and the oxidation treatment time in step (2) is changed from 1h to 4h.

[0126] Comparative Example 1

[0127] This comparative example provides a silicon-based negative electrode material for a lithium-ion battery, the preparation method of which includes:

[0128] 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; then the carbon-coated silicon oxide material is mixed with lithium hydride, 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%.

[0129] Comparative Example 2

[0130] This comparative example provides a silicon-based negative electrode material for a lithium-ion battery. The preparation method is the same as that of comparative example 1, except that the mass content of lithium in the prepared carbon-coated pre-lithiated silicon monoxide material is changed from 10% to 30%.

[0131] The element content and pH value of the silicon-based negative electrode materials prepared in the above embodiments and comparative examples were tested, and the test results are shown in Table 1.

[0132] 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).

[0133] 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.

[0134] The number of Si, Li, and O atoms in the surface layer of the negative electrode material was tested using an X-ray photoelectron spectrometer (Thermo Scientific K-Alpha). The excitation source used was Al Kα radiation, the beam spot was 400 μm, the full spectrum scan energy was 100 eV, and the step size was 1 eV. Finally, the full spectrum scan data was 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.

[0135] 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.

[0136] In addition, the negative electrode materials obtained in Examples 1-16 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] The test results of the viscosity and gas production of the negative electrode slurry are shown in Table 1. Figure 1 The negative electrode slurry prepared in Example 1 was given in the table 1 and after 7 days of storage at a low shear rate (0.1s -1 -300s -1 ) under the change process.

[0141] Table 1 Test results of various embodiments and comparative examples

[0142]

[0143]

[0144]

[0145] Table 2 Electrochemical test results of various embodiments and comparative examples

[0146]

[0147]

[0148] 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 1-16, all of which used an oxidant to treat the surface, exhibited better gas production results than Comparative Example 1 when the B:A ratio ranged from 1 to 100.

[0149] 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 Example 16, 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, because 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.

[0150] 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.

[0151] 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 comprising a silicon-based core and a coating layer at least partially coating the surface of the silicon-based core; The negative electrode material contains silicon and lithium silicate, and the A value of the negative electrode material is 1-20; The B value of the negative electrode material is 1-100; The negative electrode material satisfies B>A>1, and the ratio of B:A is 2-30; 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, wherein At least one of the following conditions is met: a. The negative electrode material further comprises an oxide layer, at least a portion of the oxide layer being located between the silicon-based core and the coating layer; b. The lithium silicate includes at least one of Li2SiO3, Li2Si2O5, Li4SiO4; c. The pH value of the negative electrode material is 8-11.5; g. The atomic ratio of oxygen to lithium obtained by the negative electrode material tested by X- ray photoelectron spectrometer is C, wherein the C value is 1-10; h. 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.

3. The negative electrode material according to claim 2, wherein At least one of the following conditions is also met: i. The oxide layer includes silicon oxide, the general formula of which is SiO x , where 0<x≤2; j. The negative electrode material also satisfies a C:A ratio of 0.5-10.

4. The negative electrode material according to any one of claims 1 to 3, wherein The coating layer includes a carbon layer.

5. A method for preparing the negative electrode material according to any one of claims 1 to 4, 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.

6. The preparation method according to claim 5, wherein At least one of the following conditions is met: l. The oxidant comprises at least one of oxygen, air, hypochlorous acid, hypochlorite, salts containing trivalent iron ions, salts containing copper ions, and hydrogen peroxide; m. After the reaction with the oxidant is completed, further comprising: heat treating the product after the reaction to obtain the negative electrode material; n. The method for preparing the pre-lithiation silicon-based material having a coating layer comprises: Mixing a silicon-based material with a carbon source and sintering the mixture to obtain a carbon-coated silicon-based material, and subjecting the carbon-coated silicon-based material to a pre-lithiation treatment with a lithium source to obtain the pre-lithiation silicon-based material having a coating layer; Alternatively, a silicon-based material is reacted with a lithium source to obtain a pre-lithiated silicon-based material, and the pre-lithiated silicon-based material is mixed with a carbon source and sintered to obtain the pre-lithiated silicon-based material with a coating layer.

7. The preparation method according to claim 6, wherein At least one of the following conditions is also met: o. The heat treatment comprises: heating to 400°C-800°C in an inert gas atmosphere and holding for 4h-24h; p. The carbon source comprises at least one of alkanes, alkenes, alkynes, natural gas, toluene, glucose, sucrose, polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, polyvinylidene fluoride and coal tar; q. The lithium source comprises at least one of lithium hydride, LiOH, metallic lithium, and lithium-containing organic matter; r. The pre-lithiation treatment comprises heating to 400-800°C in an inert gas atmosphere and keeping the temperature for 2-12 hours.

8. The preparation method according to any one of claims 5 to 7, characterized in that: The reaction time of the pre-lithiated silicon-based material with the coating layer and the oxidant is 1 hour to 12 hours.

9. A negative electrode plate, characterized in that: The negative electrode material comprises the negative electrode material according to any one of claims 1 to 4.

10. A battery, characterized in that: Including the negative electrode sheet according to claim 9.

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