Negative electrode active material and preparation method therefor, and related device

Abstract

A negative electrode active material and a preparation method therefor, and a related device. The negative electrode active material comprises a negative electrode active substance and a coating layer. The coating layer is coated on the surface of the negative electrode active substance, and the coating layer comprises at least one of polymethyl methacrylate, sodium maleate, and oleic acid diethanolamide borate. The cycle performance and the initial coulombic efficiency of batteries are improved.

Description

Negative electrode active material, preparation method thereof and related device

[0001] Cross-references

[0002] This application claims priority to a Chinese application filed with the Patent Office of China on June 20, 2023, with application number 202310732590.6 and invention name “Negative electrode active material, preparation method thereof and related device”, all contents of which are incorporated into this application by application. Technical Field

[0003] The present application relates to the field of battery technology, and more specifically, to a negative electrode active material and a preparation method thereof, a negative electrode plate, a battery cell, a battery, and an electrical device. Background Art

[0004] In recent years, lithium-ion batteries have been used in an increasingly diverse range of applications, including energy storage applications such as wind power, hydropower, thermal power, and solar cells, as well as in electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. As lithium-ion batteries have made significant progress, so too have their performance requirements been placed on a wider range of applications.

[0005] Therefore, how to improve the performance of lithium-ion batteries is an urgent problem that needs to be solved.

[0006] Summary of the Invention

[0007] This application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode active material and its preparation method, a negative electrode plate, a battery cell, a battery and an electrical device, which improve the cycle performance and the first-cycle coulombic efficiency of the battery.

[0008] The first aspect of the present application provides a negative electrode active material, comprising: a negative electrode active substance and a coating layer, wherein the coating layer is coated on the surface of the negative electrode active substance, and the coating layer comprises at least one of polymethyl methacrylate, sodium maleate and oleic acid diethanolamide borate.

[0009] In an embodiment of the present application, the negative electrode active material includes a negative electrode active material and a coating layer, wherein the coating layer is coated on the surface of the negative electrode active material, and the coating layer includes at least one of polymethyl methacrylate, sodium maleate, and oleic acid diethanolamide borate. By coating the surface of the negative electrode active material with a coating layer including at least one of polymethyl methacrylate, sodium maleate, and oleic acid diethanolamide borate, such a coating layer has a flexible property, which can not only reduce damage to the material structure of the coating layer caused by multiple conduction of lithium ions, but also inhibit the interfacial reaction between the electrolyte and the negative electrode surface, reduce the consumption of irreversible active ions, and improve the efficiency of lithium ion deintercalation, thereby improving the first-cycle coulombic efficiency and cycle performance of the battery.

[0010] In a possible implementation manner, the coating layer has a thickness of 5 nm to 50 nm. Optionally, the coating layer has a thickness of 10 nm to 20 nm.

[0011] In the embodiments of this application, if the coating layer is too thin, the coating layer will not fully cover the negative electrode active material, and its effect on suppressing the negative electrode interface reaction will be insignificant. If the coating layer is too thick, the lithium ion transmission rate will be affected. Therefore, by setting the coating layer thickness to 5nm-50nm, and particularly to 10nm-20nm, it helps to further improve the battery's cycling performance and first-cycle coulombic efficiency.

[0012] In one possible implementation, the molecular weight of the polymethyl methacrylate is 500,000-2,000,000. Optionally, the molecular weight of the polymethyl methacrylate is 1,000,000-1,500,000.

[0013] In the embodiment of the present application, a negative electrode active material including a negative electrode active material and a coating layer is formed by polymerizing methyl methacrylate and a negative electrode active material. This preparation method is simple and has abundant raw materials, which is conducive to wide application in industrial production. In addition, the molecular weight of polymethyl methacrylate is 500,000-2,000,000, especially 1,000,000-1,500,000. Polymethyl methacrylate with a high degree of polymerization is used as the coating layer of the negative electrode active material, which is conducive to the coating layer to fully exert its function.

[0014] In one possible embodiment, the negative electrode active material includes at least one of graphite and silicon-based materials. Optionally, the silicon-based material includes at least one of elemental silicon, silicon oxides, silicon carbon compounds, silicon nitrogen compounds, and composites of elemental silicon, silicon oxides, and silicon carbon compounds. Optionally, the silicon oxides include Si a O b , wherein a=1, 1≤b≤2; Optionally, the silicon carbon compound includes Si c C d , where c=1, d=1.

[0015] In the embodiment of the present application, at least one of graphite and silicon-based materials is used as the negative electrode active material, and further, at least one of elemental silicon, silicon oxide compounds, silicon carbon compounds, silicon nitrogen compounds and composites of elemental silicon, silicon oxide compounds and silicon carbon compounds is used, and further, Si is used. a O b 、Si c C d At least one of the following, where a=1, 1≤b≤2, c=1, and d=1, is used as a negative electrode active material to help improve the energy density of the battery.

[0016] The second aspect of the present application provides a method for preparing a negative electrode active material, comprising: providing a negative electrode active material and a coating material; mixing the negative electrode active material and the coating material, and treating them to obtain the negative electrode active material and a coating layer coated on the surface of the negative electrode active material; wherein the coating material includes at least one of methyl methacrylate, sodium maleate and oleic acid diethanolamide borate.

[0017] In the embodiments of the present application, a negative electrode active material and a coating material are mixed and treated to obtain a negative electrode active material comprising the negative electrode active material and a coating layer coated on the surface of the negative electrode active material; wherein the coating material comprises at least one of methyl methacrylate, sodium maleate, and oleic acid diethanolamide borate. The negative electrode active material prepared by this preparation method can enable a battery containing the negative electrode active material to have good cycling performance and first-cycle coulombic efficiency.

[0018] In a possible implementation manner, the coating layer has a thickness of 5 nm to 50 nm. Optionally, the coating layer has a thickness of 10 nm to 20 nm.

[0019] In the embodiments of the present application, by setting the thickness of the coating layer to 5 nm-50 nm, particularly 10 nm-20 nm, it helps to further improve the cycle performance and first-cycle coulombic efficiency of the battery.

[0020] In a possible implementation, the methyl methacrylate is polymerized to form the coating layer, and the coating layer includes polymethyl methacrylate; wherein the molecular weight of the polymethyl methacrylate is 500,000-2,000,000, optionally, the molecular weight of the polymethyl methacrylate is 1,000,000-2,000,000.

[0021] In the embodiment of the present application, a coating layer is formed by polymerizing methyl methacrylate to form a negative electrode active material including a negative electrode active material and a coating layer. This preparation method is simple and has abundant raw materials, which is conducive to wide application in industrial production. In addition, the molecular weight of polymethyl methacrylate is 500,000-2,000,000, and polymethyl methacrylate with a high degree of polymerization is used as the coating layer of the negative electrode active material, which is conducive to the coating layer to fully exert its function.

[0022] In a possible implementation, the mass ratio of the methyl methacrylate to the negative electrode active material is 1-5. Optionally, the mass ratio of the methyl methacrylate to the negative electrode active material is 1.5-3.

[0023] In the examples of this application, the mass ratio of the negative electrode active material to methyl methacrylate directly affects the thickness of the coating layer. Therefore, by setting the mass ratio of methyl methacrylate to the negative electrode active material to 1-5, particularly 1.5-3, the coating layer can have a more reasonable thickness, thereby enhancing the coating layer's effectiveness.

[0024] In a possible embodiment, the treatment temperature of the negative electrode active material and the methyl methacrylate is not less than 60°C. Optionally, the treatment temperature is 60°C-220°C.

[0025] In the embodiments of this application, methyl methacrylate is polymerized to form polymethyl methacrylate, which serves as a coating layer around the negative electrode active material. If the processing temperature is too low, the polymethyl methacrylate may fail to polymerize; if the processing temperature is too high, the relative molecular weight of the polymethyl methacrylate may be affected, resulting in reduced performance. Therefore, by maintaining the processing temperature of the negative electrode active material and methyl methacrylate at no less than 60°C, particularly between 60°C and 220°C, the resulting polymethyl methacrylate exhibits superior performance, helping to further enhance battery performance.

[0026] In a possible implementation manner, the negative electrode active material and the methyl methacrylate are treated for 1 hour to 8 hours. Optionally, the treatment time is 3 hours to 5 hours.

[0027] In the embodiment of the present application, by maintaining the treatment time of the negative electrode active material and methyl methacrylate at 1 hour to 8 hours, particularly at 3 hours to 5 hours, the polymethyl methacrylate can have a reasonable thickness, thereby improving the battery performance.

[0028] In a possible implementation, the catalyst, the negative electrode active material, and the methyl methacrylate are mixed. Optionally, the catalyst includes at least one of an organic peroxide and an azo compound.

[0029] In the embodiments of the present application, a catalyst is added to the reaction between methyl methacrylate and the negative electrode active material. The catalyst can reduce the activation energy of the polymerization reaction and accelerate the polymerization reaction. Therefore, by adding a catalyst to the polymerization process of polymethyl methacrylate, and the catalyst can be at least one of an organic peroxide and an azo compound, the formation of polymethyl methacrylate can be accelerated.

[0030] In one possible embodiment, the coating material includes at least one of sodium maleate and oleic acid diethanolamide borate; the treatment temperature of the negative electrode active material and at least one of sodium maleate and oleic acid diethanolamide borate is not less than 40°C, optionally, the treatment temperature is 40°C-120°C.

[0031] In the embodiment of the present application, a negative electrode active material including a negative electrode active material and a coating layer can be obtained by mixing the negative electrode active material with sodium maleate or oleic acid diethanolamide borate. The processing temperature of the two is maintained at not less than 40°C, especially 40°C-120°C, so as not to destroy the activity of the coating layer and thus improve the performance of the battery.

[0032] In one possible embodiment, the mass ratio of at least one of the sodium maleate and the oleic acid diethanolamide borate to the negative electrode active material is 1-3. Optionally, the mass ratio of at least one of the sodium maleate and the oleic acid diethanolamide borate to the negative electrode active material is 1-2.

[0033] In the embodiments of the present application, when at least one of sodium maleate and oleic acid diethanolamide borate is used as a coating layer to coat the negative electrode active material, the two can be directly mixed at a certain temperature. By setting the mass ratio of at least one of sodium maleate and oleic acid diethanolamide borate to the negative electrode active material to 1-3, particularly 1-2, the coating layer can have an appropriate thickness, thereby improving battery performance.

[0034] In one possible embodiment, the negative electrode active material includes at least one of graphite and silicon-based materials. Optionally, the silicon-based material includes at least one of elemental silicon, silicon oxides, silicon carbon compounds, silicon nitrogen compounds, and composites of elemental silicon, silicon oxides, and silicon carbon compounds. Optionally, the silicon oxides include Si a O b , wherein a=1, 1≤b≤2; Optionally, the silicon carbon compound includes Si c C d , where c=1, d=1.

[0035] The third aspect of the present application provides a negative electrode plate, comprising the negative electrode active material described in any one of the embodiments of the first aspect, and / or comprising the negative electrode active material prepared by the preparation method of the negative electrode active material described in any one of the embodiments of the second aspect.

[0036] A fourth aspect of the present application provides a battery cell comprising the negative electrode sheet described in the third aspect.

[0037] A fifth aspect of the present application provides a battery comprising the battery cell described in the fourth aspect.

[0038] The sixth aspect of the present application provides an electrical device comprising the battery described in the fifth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] 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 of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0040] FIG1 is a schematic structural diagram of a negative electrode active material according to an embodiment of the present application;

[0041] FIG2 is a TEM image of a negative electrode active material according to an embodiment of the present application;

[0042] FIG3 is a flow chart of preparing a negative electrode active material according to an embodiment of the present application;

[0043] FIG4 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0044] FIG5 is a schematic structural diagram of a battery cell according to another embodiment of the present application;

[0045] FIG6 is a schematic diagram of a battery according to an embodiment of the present application;

[0046] FIG7 is a schematic structural diagram of a battery according to an embodiment of the present application;

[0047] FIG8 is a schematic structural diagram of an electrical device according to an embodiment of the present application. DETAILED DESCRIPTION

[0048] The following describes in detail, with appropriate reference to the accompanying drawings, embodiments of the negative electrode active material and its preparation method, negative electrode sheet, battery cell, battery, and electrical device of the present application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. In addition, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0049] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of specific range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0050] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0051] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0052] Unless otherwise specified, all steps of the present application may be performed sequentially, randomly, or optionally sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0053] The terms "above", "below", "greater than" or "less than" as used in this application are inclusive of the number, for example, "at least one" means one or more, and "at least one of A and B" means "A", "B" or "A and B".

[0054] The cycle life of a lithium battery is related to the stability of interfaces (such as the interface between the electrode plate and the electrolyte). The formation of the interface is often accompanied by the irreversible consumption of lithium ions, especially the interface between the negative electrode plate and the electrolyte. This is because when the battery is first charged and discharged, the solid electrolyte interface (SEI) film formed consumes a large amount of lithium ions, and this part of the lithium ion consumption is irreversible. If too many lithium ions are consumed, it will have a significant impact on the performance of the battery. Therefore, how to reduce the irreversible consumption of limited lithium ions is the key to restricting the cycle stability and coulombic efficiency of lithium batteries.

[0055] To address these issues, one approach is to supplement active lithium, such as by adding lithium-supplementing materials or constructing lithium-supplementing structures into the battery. However, lithium-supplementing materials are generally highly active and require high processing conditions for the battery, making their commercialization unlikely. Another approach is to reduce active lithium consumption, such as by applying a polymeric aluminum foil layer to the surface of the negative electrode active material. However, this method is complex and unlikely to be commercialized. Therefore, finding a more direct way to reduce active lithium ion consumption and thus improve battery cycle performance is a pressing issue.

[0056] In view of this, the present application provides a negative electrode active material and a preparation method thereof. The negative electrode active material comprises: a negative electrode active material and a coating layer, wherein the coating layer is coated on the surface of the negative electrode active material, and the coating layer comprises at least one of polymethyl methacrylate, sodium maleate, and oleic acid diethanolamide borate. By directly coating the substrate surface with at least one of polymethyl methacrylate, sodium maleate, and oleic acid diethanolamide borate, the cycling performance and first-cycle coulombic efficiency of a battery using the negative electrode active material can be improved.

[0057] The negative electrode active material and its preparation method, negative electrode sheet, battery cell, battery and electrical device of the present application are described below with reference to the accompanying drawings.

[0058] In addition, the technical solution of the present application is applicable to lithium-ion batteries or lithium metal batteries, and the present application does not limit this; for the convenience of description, the following description will take lithium-ion batteries as an example.

[0059] [Negative electrode active material]

[0060] Figure 1 is a schematic structural diagram of a negative electrode active material according to one embodiment of the present application, and Figure 2 is a TEM image of the negative electrode active material according to one embodiment of the present application. As shown in Figures 1 and 2, the negative electrode active material 122 includes a negative electrode active material 1221 and a coating layer 1222. The coating layer 1222 is coated on the surface of the negative electrode active material 1221 and includes at least one of polymethyl methacrylate, sodium maleate, and oleic acid diethanolamide borate.

[0061] Coating the surface of the negative electrode active material with at least one of polymethyl methacrylate, sodium maleate and oleic acid diethanolamide borate can improve the cycle performance and the first-cycle coulombic efficiency of the battery.

[0062] The covering here can be full covering as shown in FIG1 , or partial covering as shown in FIG2 .

[0063] In the embodiment of the present application, the negative electrode active material includes a negative electrode active material 1221 and a coating layer 1222. Furthermore, the coating layer 1222 is coated on the surface of the negative electrode active material 1221 and includes at least one of polymethyl methacrylate, sodium maleate, and oleic acid diethanolamide borate. By coating the surface of the negative electrode active material 1221 with the coating layer 1222, which includes at least one of polymethyl methacrylate, sodium maleate, and oleic acid diethanolamide borate, the coating layer 1222 has a flexible nature. This not only reduces damage to the coating layer 1222's material structure caused by multiple lithium ion conduction, but also inhibits interfacial reactions between the electrolyte and the surface of the negative electrode plate 122. This reduces the consumption of irreversible active ions and improves the efficiency of lithium ion intercalation and deintercalation, thereby improving the battery's first-cycle coulombic efficiency and cycling performance.

[0064] It should be noted that during battery cycling, a solid electrolyte interface (SEI) film forms on the surface of the negative electrode 122. Since the coating layer 1222 is relatively close to this SEI film, it can act as an "artificial" SEI film, forming a double SEI film with the SEI film already formed in the battery, thereby inducing the formation of a more stable and thin SEI film.

[0065] The SEI membrane is a passivation layer formed on the surface of the active material during the initial charge and discharge process of a lithium-ion battery. The coating layer 1222 is considered an "artificial" SEI membrane, meaning it can function as an SEI membrane, but it is not a true SEI membrane.

[0066] In addition, it should be understood that the "lithium insertion" and "intercalation" processes described in this application refer to the process in which lithium ions are embedded in the positive electrode active material or the negative electrode active material due to an electrochemical reaction, and the "deintercalation" and "deintercalation" processes described in this application refer to the process in which lithium ions are released from the positive electrode active material or the negative electrode active material due to an electrochemical reaction.

[0067] In some embodiments, the thickness d1 of the coating layer 1222 is 5 nm-50 nm. Optionally, the thickness d1 of the coating layer is 10 nm-20 nm.

[0068] In the above scheme, if the coating layer 1222 is too thin, the coating layer 1222 will not fully cover the negative electrode active material 1221, and its effect on suppressing negative electrode interface reactions will be ineffective. If the coating layer 1222 is too thick, the transmission rate of metal ions will be affected. Therefore, by setting the thickness of the coating layer 1222 to 5nm-50nm, and particularly to 10nm-20nm, it helps to further improve the battery's cycling performance and first-cycle coulombic efficiency.

[0069] It should be noted here that the thickness of the coating layer can be 5 nm, 15 nm, 20 nm, 40 nm, or any value within the above range.

[0070] In some embodiments, the molecular weight of the polymethyl methacrylate is 500,000-2,000,000. Optionally, the molecular weight of the polymethyl methacrylate is 1,000,000-15,000,000.

[0071] In the embodiment of the present application, methyl methacrylate and the negative electrode active material 1221 are polymerized to form a negative electrode active material 122 including the negative electrode active material 1221 and the coating layer 1222. This preparation method is simple and has abundant raw materials, which is conducive to its wide application in industrial production. In addition, the molecular weight of polymethyl methacrylate is 500,000-2,000,000, especially 1,000,000-15,000,000. Polymethyl methacrylate with a high degree of polymerization is used as the coating layer 1222 of the negative electrode active material 1221, which is conducive to the coating layer 1222 to fully exert its function.

[0072] It should be noted that the molecular weight of polymethyl methacrylate can be 500,000, 800,000, 1,000,000, 1,500,000, or any value within the above range.

[0073] In addition, the molecular weight of polymethyl methacrylate varies depending on its thickness.

[0074] In some embodiments, the negative electrode active material 1221 includes at least one of graphite and silicon-based materials. Optionally, the silicon-based material includes at least one of elemental silicon, silicon oxides, silicon carbon compounds, silicon nitrogen compounds, and composites of elemental silicon, silicon oxides, and silicon carbon compounds. Optionally, the silicon oxides include Si a O b , wherein a=1, 1≤b≤2; Optionally, the silicon carbon compound includes Si c C d , where c=1, d=1.

[0075] In the above scheme, at least one of graphite and silicon-based materials is used as the negative electrode active material, and further, at least one of elemental silicon, silicon oxide, silicon carbon compound, silicon nitrogen compound and a compound of elemental silicon, silicon oxide and silicon carbon compound is used. a O b 、Si c C d At least one of the following, where a=1, 1≤b≤2, c=1, and d=1, is used as a negative electrode active material to help improve the energy density of the battery.

[0076] The composite of elemental silicon, silicon oxide, and silicon carbon compound may include composites formed of any two of these three, for example, a multilayer composite structure formed of Si, SiO2, and C, namely, Si@SiO2@C.

[0077] [Method for preparing negative electrode active material]

[0078] The second aspect of the present application provides a method for preparing a negative electrode active material. FIG3 is a flow chart of the preparation of a negative electrode active material according to an embodiment of the present application. As shown in FIG3 , the preparation method of the negative electrode active material includes:

[0079] S101, providing a negative electrode active material and a coating material;

[0080] S102, mixing the negative electrode active material and the coating material, and treating them to obtain the negative electrode active material and a coating layer coated on the surface of the negative electrode active material; wherein the coating material includes at least one of methyl methacrylate, sodium maleate and oleic acid diethanolamide borate.

[0081] The coating material refers to the material state before the coating layer is formed. If the coating material is methyl methacrylate, the resulting coating layer is polymethyl methacrylate; if the coating material is sodium maleate and oleic acid diethanolamide borate, the coating layer is sodium maleate and oleic acid diethanolamide borate. Therefore, in the following text, sodium maleate and oleic acid diethanolamide borate can be referred to as the coating material or coating layer, but methyl methacrylate should not be referred to as the coating layer, nor should polymethyl methacrylate be referred to as the coating material.

[0082] In the above scheme, the negative electrode active material 1221 and the coating material are mixed and treated to obtain a negative electrode active material 122 comprising the negative electrode active material 1221 and a coating layer 1222 coating the surface of the negative electrode active material 1221. The coating material comprises at least one of methyl methacrylate, sodium maleate, and oleic acid diethanolamide borate. The negative electrode active material 122 prepared by this preparation method can provide a battery containing the negative electrode active material 122 with excellent cycling performance and first-cycle coulombic efficiency.

[0083] In some embodiments, the thickness of the coating layer 1222 is 5 nm to 50 nm. Optionally, the thickness of the coating layer 1222 is 10 nm to 20 nm.

[0084] In the above solution, by making the thickness of the coating layer 1222 5 nm-50 nm, especially 10 nm-20 nm, it helps to further improve the cycle performance and the first-cycle coulombic efficiency of the battery.

[0085] In some embodiments, methyl methacrylate is polymerized to form the coating layer 1222 , and the coating layer 1222 includes polymethyl methacrylate; wherein the molecular weight of the polymethyl methacrylate is 500,000-2,000,000, optionally, the molecular weight of the polymethyl methacrylate is 1,000,000-1,500,000.

[0086] Polymerization here refers to a polymerization reaction, which is the process of converting low molecular weight monomers into high molecular weight polymers.

[0087] In addition, before the process of polymerizing methyl methacrylate to form polymethyl methacrylate, methyl methacrylate can be directly mixed with the negative electrode active material 1221 , so that the negative electrode active material 122 with the coating layer 1222 can be directly formed.

[0088] In the above scheme, the coating layer 1222 is formed by polymerizing methyl methacrylate, and the negative electrode active material 122 including the negative electrode active material 1221 and the coating layer 1222 is formed. This preparation method is simple and has abundant raw materials, which is conducive to its wide application in industrial production. In addition, the molecular weight of polymethyl methacrylate is 500,000-2,000,000, and polymethyl methacrylate with a high degree of polymerization is used as the coating layer 1222 of the negative electrode active material 1221, which is conducive to the coating layer 1222 to fully exert its function.

[0089] In some embodiments, the mass ratio of methyl methacrylate to the negative electrode active material 1221 is 1-5. Optionally, the mass ratio of methyl methacrylate to the negative electrode active material 1221 is 1.5-3.

[0090] In the above solution, the different mass ratios of methyl methacrylate to negative electrode active material 1221 directly affect the thickness of coating layer 1222. Therefore, by setting the mass ratio of methyl methacrylate to negative electrode active material 1221 to 1-5, particularly 1.5-3, coating layer 1222 can have a more reasonable thickness, thereby enhancing the effectiveness of coating layer 1222.

[0091] It should be noted that the mass ratio of methyl methacrylate to the negative electrode active material 1221 can be 1.5, 2.8, 4.2, 5, or any other value within the above range.

[0092] In some embodiments, the treatment temperature of the negative electrode active material 1221 and methyl methacrylate is not less than 60°C. Optionally, the treatment temperature is 60°C-220°C.

[0093] In the above scheme, methyl methacrylate polymerizes to form polymethyl methacrylate, which serves as a coating layer 1222 that covers the negative electrode active material 1221. If the processing temperature is too low, the polymerization of polymethyl methacrylate may fail. If the processing temperature is too high, the relative molecular weight of polymethyl methacrylate will be affected, and its performance will also be reduced. Therefore, by maintaining the processing temperature of the negative electrode active material 1221 and methyl methacrylate at no less than 60°C, and particularly within a range of 60°C to 220°C, the resulting polymethyl methacrylate exhibits better performance, helping to further improve battery performance.

[0094] It should be noted that the treatment temperature may be 60° C., 100° C., 150° C., 170° C., or any value within the above range.

[0095] In some embodiments, the negative electrode active material 1221 and methyl methacrylate are treated for 1 hour to 8 hours. Optionally, the treatment time is 3 hours to 5 hours.

[0096] In the above scheme, by maintaining the treatment time of the negative electrode active material 1221 and methyl methacrylate at 1 hour to 8 hours, especially at 3 hours to 5 hours, better polymethyl methacrylate can be formed.

[0097] It should be noted here that the above-mentioned processing time can be 1.5 hours, 3 hours, 5 hours, 8 hours and any value within the above-mentioned range.

[0098] In some embodiments, a catalyst, negative electrode active material 1221 and methyl methacrylate are mixed. Optionally, the catalyst includes at least one of an organic peroxide and an azo compound.

[0099] A catalyst generally refers to a substance that increases the reaction rate without changing the change in the total standard Gibbs free energy of the reaction. It can also be described as a substance that can increase the chemical reaction rate without changing the chemical equilibrium, and whose mass and chemical properties do not change before and after the chemical reaction.

[0100] Organic peroxides refer to organic compounds containing a -O- peroxide functional group formed by replacing the hydrogen atom in hydrogen peroxide with an organic group such as an alkyl group, an acyl group, or an aromatic group, including but not limited to benzoic acid peroxide and methyl ethyl ketone peroxide.

[0101] Azo compounds are compounds formed by connecting an azo group (─N=N─) with two hydrocarbon groups, with the general formula R─N=N─R, such as azobisisobutyronitrile.

[0102] In the above scheme, a catalyst is added to the reaction between methyl methacrylate and negative electrode active material 1221. The catalyst can reduce the activation energy of the polymerization reaction and accelerate the polymerization reaction. Therefore, by adding a catalyst during the polymerization of polymethyl methacrylate, and the catalyst can be at least one of an organic peroxide and an azo compound, the formation of polymethyl methacrylate can be accelerated.

[0103] In some embodiments, the coating material includes at least one of sodium maleate and oleic acid diethanolamide borate; the treatment temperature of the negative electrode active material 1221 and at least one of sodium maleate and oleic acid diethanolamide borate is not less than 40°C, optionally, the treatment temperature is 40°C-120°C.

[0104] In the above scheme, by mixing the negative electrode active material 1221 with sodium maleate or oleic acid diethanolamide borate, a negative electrode active material 122 including the negative electrode active material 1221 and the coating layer 1222 can be obtained. Maintaining the processing temperature of the two at no less than 40°C, especially 40°C-120°C, can not destroy the activity of the coating layer 1222, thereby improving the performance of the battery.

[0105] It should be noted that the treatment temperature may be 45° C., 60° C., 80° C., 100° C., or any value within the above range.

[0106] In some embodiments, the mass ratio of at least one of sodium maleate and oleic acid diethanolamide borate to the negative electrode active material 1221 is 1-3. Optionally, the mass ratio of at least one of sodium maleate and oleic acid diethanolamide borate to the negative electrode active material 1221 is 1-2.

[0107] In the above scheme, when at least one of sodium maleate and oleic acid diethanolamide borate is used as the coating layer 1222 to coat the negative electrode active material 1221, the two can be directly mixed at a certain temperature. By setting the mass ratio of at least one of sodium maleate and oleic acid diethanolamide borate to the negative electrode active material 1221 to be 1-3, particularly 1-2, the coating layer 1222 can have an appropriate thickness, thereby improving battery performance.

[0108] It should be noted that the mass ratio of at least one of sodium maleate and oleic acid diethanolamide borate to the negative electrode active material 1221 can be 1.2, 1.5, 2, 3, or any value within the above range.

[0109] In some embodiments, the negative electrode active material 1221 includes at least one of graphite and silicon-based materials. Optionally, the silicon-based material includes Si a O b 、Si c C d At least one of the following, wherein a=1, 1≤b≤2, c=1, d=1, and optionally, the silicon-based material includes Si@SiO2@C.

[0110] It should be noted here that if graphite is used as the negative electrode active material 1221, it can be fresh graphite or waste graphite, that is, used graphite.

[0111] Typically, a battery cell consists of a positive electrode, a separator, a negative electrode, and an electrolyte. During the battery's charge and discharge processes, active ions are embedded in and extracted from the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0112] It should be noted here that the “positive electrode sheet” and “negative electrode sheet” mentioned in the embodiments of the present application refer to the positive electrode sheet and the negative electrode sheet as a whole including active materials, current collectors or other additives.

[0113] [Negative electrode]

[0114] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material 122 .

[0115] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0116] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.), or a current collector that combines support capabilities with functional elements, such as carbon cloth, carbon film, carbonaceous, porous current collector, alloyed modified current collector, and lithium-philic modified current collector.

[0117] In some embodiments, the negative electrode plate can be a rolled metal foil or a surface coated with an inert layer of metal powder coated on the current collector; it can be a functional coating negative electrode, such as a carbon material coating (including single-arm, multi-arm conductive carbon tubes, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers, soft carbon and hard carbon, etc.), lithium-philic / sodium-philic metal composite coating, etc.

[0118] In some embodiments, the negative electrode plate is an alkali metal negative electrode. The alkali metal negative electrode can be a current collector with an alkali metal layer pre-applied thereon, or it can be a negative electrode current collector that forms an alkali metal layer on the negative electrode current collector during charge and discharge. This application is not limited to this.

[0119] In some embodiments, the negative electrode active material 1221 in the negative electrode active material 122 may also use negative electrode active materials for batteries that are well known in the art. As an example, the negative electrode active material 1221 may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0120] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0121] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0122] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0123] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material 122, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0124] [Positive electrode]

[0125] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0126] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0127] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0128] In some embodiments, the positive electrode active material may be a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0129] The battery's charge and discharge processes involve the intercalation and deintercalation of lithium, leading to different molar Li contents at different discharge states. The molar Li contents listed in this application for cathode materials refer to the initial state of the material, i.e., the state before addition of the materials. When the cathode material is used in a battery system, the molar Li content will change after charge and discharge cycles.

[0130] In the list of positive electrode materials in the application, the molar content of O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0131] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0132] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0133] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry, and the positive electrode slurry is coated on the positive electrode current collector. After drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0134] [Electrolytes]

[0135] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0136] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0137] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0138] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0139] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0140] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0141] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0142] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG4 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0143] Figure 5 is a schematic structural diagram of a battery cell in another embodiment of the present application. As shown in Figure 5, the outer packaging of the battery cell 100 includes a shell 11 and a cover plate 13. Among them, the shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the battery cell 100 can be one or more, and those skilled in the art can select according to specific actual needs.

[0144] In some embodiments, the battery cells 100 may be assembled into a battery module. The battery module may contain one or more battery cells 100. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0145] Figure 6 is a schematic diagram of a battery according to one embodiment of the present application, and Figure 7 is a schematic diagram of the structure of a battery according to one embodiment of the present application. Referring to Figures 6 and 7, a battery 400 may include a battery box and a plurality of battery cells 100 disposed within the battery box. The battery box includes an upper box body 401 and a lower box body 402. The upper box body 401 can be placed over the lower box body 402 to form an enclosed space for accommodating the battery cells 100. The plurality of battery cells 100 can be arranged in any manner within the battery box.

[0146] In addition, the present application also provides an electrical device, which includes at least one of the battery cell 100 or battery 400 provided in the present application. The battery cell 100 or battery 400 can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0147] For example, FIG8 is a schematic structural diagram of an electric device according to an embodiment of the present application. As shown in FIG8 , the electric device is a vehicle 1. Vehicle 1 may be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A motor 500, a controller 600 and a battery 400 may be provided inside the vehicle 1. The controller 600 is used to control the battery 400 to supply power to the motor 500. For example, a battery 400 may be provided at the bottom, front or rear of the vehicle 1. The battery 400 may be used to power the vehicle 1. For example, the battery 400 may be used as an operating power source for the vehicle 1, for the circuit system of the vehicle 1, for example, for the working power requirements during the start-up, navigation and operation of the vehicle 1. In another embodiment of the present application, the battery 400 may not only be used as an operating power source for the vehicle 1, but may also be used as a driving power source for the vehicle 1, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1.

[0148] As the electrical device, a battery cell 100 or a battery 400 may be selected according to its usage requirements.

[0149] The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the electric device's requirements for high power and high energy density of the battery, a battery cell 100 or a battery 400 may be used.

[0150] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use the battery cell 100 as a power source.

[0151] [Example]

[0152] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0153] [Example 1]

[0154] 1). Preparation of lithium-ion batteries

[0155] 1.11) Preparation of negative electrode active material: Methyl methacrylate (MMA), a coating material, and graphite, a negative electrode active material, were weighed in a mass ratio of 3:1 and dispersed in 45 mL of deionized water. Benzoic acid peroxide was added as a catalyst and ultrasonically emulsified for 10 minutes to obtain a negative electrode active material mixture. The negative electrode active material mixture was then poured into a three-necked flask and polymerized at 80°C under an argon (Ar) atmosphere for 4 hours to obtain a negative electrode active material, wherein the negative electrode active material was artificial graphite and the coating layer was polymethyl methacrylate (PMMA).

[0156] 1.12) Preparation of negative electrode sheets: The negative electrode active material, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are thoroughly stirred and mixed in a suitable amount of deionized water solvent system at a weight ratio of 97.5%:0.7%:1.8%:1% to obtain the negative electrode active material. The negative electrode active material is coated on Cu foil, and then dried, cold pressed, and cut to obtain the negative electrode sheet.

[0157] 1.2) Preparation of positive electrode sheets: The positive electrode active material lithium iron phosphate LiFePO4, the conductive agent carbon nanotubes (CNT), and the binder polyvinylidene fluoride (PVDF) are dissolved in a solvent N-methylpyrrolidone (NMP) at a weight ratio of 96%:2%:2%, and the mixture is thoroughly stirred and mixed to obtain the positive electrode active material. The positive electrode active material is coated on Al foil, and then dried, cold pressed, and cut to obtain the positive electrode sheet.

[0158] 1.3) Preparation of diaphragm: PE porous polymer film is used as the isolation membrane.

[0159] 1.4) Electrolyte: Dissolve EC / EMC / DMC in 1M LiPF6 at a volume ratio of 1:1:1 and stir evenly.

[0160] 1.5) Assembly: The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide separation. Winding is done to form an electrode assembly, and electrolyte is added. The lithium-ion battery is then hot-pressed at 100°C and 250 MPa for 2 minutes.

[0161] In the lithium-ion battery of Example 1, the coating material is methyl methacrylate, the coating layer is polymethyl methacrylate, the coating layer thickness is 20 nm, the mass ratio of the coating material to the negative electrode active material is 3, the treatment time is 4 h, the treatment temperature is 80°C, the coating layer molecular weight is 1530000, and the catalyst is benzoic acid peroxide.

[0162] [Example 2]

[0163] The lithium ion battery of Example 2 is substantially the same as the lithium ion battery of Example 1, except that, in the lithium ion battery of Example 2, the mass ratio of the coating material to the negative electrode active material is 1, and the thickness of the coating layer is 5 nm.

[0164] [Example 3]

[0165] The lithium ion battery of Example 3 is substantially the same as the lithium ion battery of Example 1, except that, in the lithium ion battery of Example 3, the mass ratio of the coating material to the negative electrode active material is 5, and the thickness of the coating layer is 50 nm.

[0166] [Example 4]

[0167] The lithium ion battery of Example 4 is substantially the same as the lithium ion battery of Example 1, except that, in the lithium ion battery of Example 4, the mass ratio of the coating material to the negative electrode active material is 1.5, and the thickness of the coating layer is 10 nm.

[0168] [Example 5]

[0169] The lithium ion battery of Example 5 is substantially the same as the lithium ion battery of Example 1, except that, in the lithium ion battery of Example 5, the mass ratio of the coating material to the negative electrode active material is 4, and the thickness of the coating layer is 30 nm.

[0170] [Example 6]

[0171] The lithium ion battery of Example 6 is substantially the same as the lithium ion battery of Example 1, except that, in the lithium ion battery of Example 6, the treatment time is 1 h and the coating layer thickness is 2 nm.

[0172] [Example 7]

[0173] The lithium ion battery of Example 7 is substantially the same as the lithium ion battery of Example 1, except that, in the lithium ion battery of Example 7, the treatment time is 8 h and the coating layer thickness is 60 nm.

[0174] [Example 8]

[0175] The lithium ion battery of Example 8 is substantially the same as the lithium ion battery of Example 1, except that, in the lithium ion battery of Example 8, the treatment time is 3 h and the coating layer thickness is 12 nm.

[0176] [Example 9]

[0177] The lithium ion battery of Example 9 is substantially the same as the lithium ion battery of Example 1, except that, in the lithium ion battery of Example 9, the treatment time is 5 h and the coating layer thickness is 45 nm.

[0178] [Example 10]

[0179] The lithium ion battery of Example 10 is substantially the same as the lithium ion battery of Example 1, except that, in the lithium ion battery of Example 10, the processing temperature is 60° C., and the coating layer thickness is 11 nm.

[0180] [Example 11]

[0181] The lithium ion battery of Example 11 is basically the same as the lithium ion battery in Example 1, except that, in the lithium ion battery of Example 11, the coating material is sodium maleate, and sodium maleate is directly mixed with the negative electrode active material to obtain a negative electrode active material having a coating layer of sodium maleate; wherein the coating layer thickness is 28 nm, the mass ratio of the coating material to the negative electrode active material is 4.5, and the processing temperature is 60°C.

[0182] [Example 12]

[0183] The lithium ion battery of Example 12 is substantially the same as the lithium ion battery of Example 11, except that, in the lithium ion battery of Example 12, the coating layer thickness is 13 nm, and the mass ratio of the coating material to the negative electrode active material is 2.5.

[0184] [Example 13]

[0185] The lithium ion battery of Example 13 is substantially the same as the lithium ion battery of Example 11, except that, in the lithium ion battery of Example 13, the coating layer has a thickness of 10 nm and a mass ratio of the coating material to the negative electrode active material is 2.

[0186] [Example 14]

[0187] The lithium ion battery of Example 14 is substantially the same as the lithium ion battery of Example 11, except that, in the lithium ion battery of Example 14, the coating layer has a thickness of 5 nm and a mass ratio of the coating material to the negative electrode active material is 1.

[0188] [Example 15]

[0189] The lithium ion battery of Example 15 is basically the same as the lithium ion battery in Example 1, except that, in the lithium ion battery of Example 15, the coating material is oleic acid diethanolamide borate, and oleic acid diethanolamide borate is directly mixed with the negative electrode active material to obtain a negative electrode active material having a coating layer of oleic acid diethanolamide borate; wherein the coating layer thickness is 10 nm, the mass ratio of the coating material to the negative electrode active material is 1, and the processing temperature is 40°C.

[0190] [Example 16]

[0191] The lithium ion battery of Example 16 is substantially the same as the lithium ion battery of Example 1, except that, in the lithium ion battery of Example 16, the catalyst is peroxyketal.

[0192] [Example 17]

[0193] The lithium-ion battery of Example 17 is substantially the same as the lithium-ion battery of Example 1, except that, in the lithium-ion battery of Example 17, the negative electrode active material is SiO2@Si@C.

[0194] [Comparative Example 1]

[0195] The lithium ion battery of Comparative Example 1 is substantially the same as the lithium ion battery of Example 1, except that, in the lithium ion battery of Comparative Example 1, the negative electrode active material only includes negative electrode active material, ie, graphite.

[0196] [Comparative Example 2]

[0197] The lithium ion battery of Comparative Example 2 is substantially the same as the lithium ion battery of Example 1, except that, in the lithium ion battery of Comparative Example 2, the negative electrode active material only includes SiO 2 —Si—C negative electrode active material.

[0198] [Comparative Example 3]

[0199] The lithium ion battery of Comparative Example 3 is substantially the same as the lithium ion battery of Example 1, except that, in the lithium ion battery of Comparative Example 3, the coating layer is aluminum oxide (Al 2 O 3 ).

[0200] [Comparative Example 4]

[0201] The lithium ion battery of Comparative Example 4 is substantially the same as the lithium ion battery of Example 1, except that, in the lithium ion battery of Comparative Example 4, the coating layer is 3(3-nitrophenyl)acrylonitrile / olefin sulfonic acid copolymer.

[0202] 2) Physical characterization of negative electrode active materials

[0203] 2.1) Coating thickness measurement: directly observe and measure through scanning electron microscope (SEM) or transmission electron microscope (TEM).

[0204] 2.2) Molecular weight measurement: Direct measurement can be performed using a light scattering detector.

[0205] Table 1 Specific experimental parameters of Examples 1-17 and Comparative Examples 1-4

[0206] 3). Lithium-ion battery performance characterization

[0207] 3.1) Capacity retention rate test: Use the Blue Power test system to perform charge and discharge tests on the battery.

[0208] At 45°C, maintain the battery charge and discharge voltage range at 2.5-3.65V, cycle at a current density of 1C, and record the battery capacity retention rate after 1000 cycles. See Table 2 for the test results.

[0209] 3.2) Measurement of first-cycle coulombic efficiency: Use the Blue Electric test system to perform charge and discharge tests on the battery.

[0210] At 45°C, the battery was cycled at a current density of 1C while maintaining a charge-discharge voltage range of 2.5-3.65V. The charge and discharge capacity of the battery during the third cycle was recorded, and the ratio of discharge to charge capacity was calculated. The test results are shown in Table 2. (It should be noted that the first cycle of the battery is the formation stage, and the third cycle is more stable than the second cycle. Therefore, the third cycle is selected as the first cycle in the actual sense of this application.)

[0211] Table 2 Performance parameters of Examples 1-17 and Comparative Examples 1-4

[0212] The embodiment of the present application uses the capacity retention rate to characterize the cycle performance of the battery. When the capacity retention rate is higher, it means that the capacity of the battery is retained higher after a certain number of cycles, that is, the cycle performance of the battery is better.

[0213] According to Examples 1-17 and Comparative Examples 1-4, coating the surface of the negative electrode active material with at least one of polymethyl methacrylate, sodium maleate and oleic acid diethanolamide borate can improve the first-cycle coulombic efficiency and cycle performance of the battery.

[0214] According to Examples 1-10, by making the thickness of the coating layer 5nm-50nm, the first-cycle coulombic efficiency and cycle performance of the battery can be improved; further, making the thickness of the coating layer 10nm-20nm helps to further improve the cycle performance and first-cycle coulombic efficiency of the battery.

[0215] According to Examples 1-10, when the coating layer is polymethyl methacrylate, by setting the molecular weight of the coating layer to 500,000-2,000,000, especially 1,000,000-1,500,000, the cycle performance and the first-cycle coulombic efficiency of the battery can be further improved.

[0216] According to Examples 1-5, when the coating material is methyl methacrylate and the coating layer formed is polymethyl methacrylate, the mass ratio of methyl methacrylate to the negative electrode active material is 1-5, especially 1.5-3, which can make the coating layer have a more suitable thickness, thereby helping to further improve the cycle performance and first-cycle coulombic efficiency of the battery.

[0217] According to Examples 6-10, when the coating material is methyl methacrylate and the formed coating layer is polymethyl methacrylate, a treatment time of 1 h-8 h, especially 3 h-5 h, helps to further improve the cycle performance and first-cycle coulombic efficiency of the battery.

[0218] According to Examples 1 and 10, when the coating material is methyl methacrylate and the formed coating layer is polymethyl methacrylate, the cycle performance and the first-cycle coulombic efficiency of the battery can be further improved by setting the treatment temperature to not less than 60°C.

[0219] According to Examples 1, 11-14 and 15, coating the surface of the negative electrode active material with polymethyl methacrylate, sodium maleate or oleic acid diethanolamide borate can improve the performance of the battery.

[0220] According to Examples 11-14, when the coating layer is sodium maleate, the mass ratio of sodium maleate to the negative electrode active material is 1-3, especially 1.5-2, which can improve the cycle performance and the first-cycle coulombic efficiency of the battery.

[0221] It can be seen from Examples 1 and 16 that a variety of catalysts are suitable for the technical solution of this application.

[0222] It can be seen from Examples 1 and 17 that a variety of negative electrode active materials are suitable for the technical solution of this application.

[0223] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode active material, characterized in that: include: A negative electrode active material and a coating layer, wherein the coating layer is coated on the surface of the negative electrode active material, and the coating layer comprises at least one of polymethyl methacrylate, sodium maleate and oleic acid diethanolamide borate.

2. The negative electrode active material according to claim 1, characterized in that The coating layer has a thickness of 5nm-50nm. Optionally, the coating layer has a thickness of 10nm-20nm.

3. The negative electrode active material according to claim 1 or 2, characterized in that: The molecular weight of the polymethyl methacrylate is 500,000-2,000,000. Optionally, the molecular weight of the polymethyl methacrylate is 1,000,000-1,500,000.

4. The negative electrode active material according to any one of claims 1 to 3, characterized in that The negative electrode active material includes at least one of graphite and silicon-based materials. Optionally, the silicon-based material includes at least one of elemental silicon, silicon-oxygen compounds, silicon-carbon compounds, and composites of elemental silicon, silicon-oxygen compounds, and silicon-carbon compounds; Optionally, the silicon oxide compound includes Si a O b , where a=1, 1≤b≤2; Optionally, the silicon carbon compound includes Si c C d , where c=1, d=1.

5. A method for preparing a negative electrode active material, characterized in that: include: Providing negative electrode active material and coating material; The negative electrode active material and the coating material are mixed and treated to obtain the negative electrode active material and a coating layer coated on the surface of the negative electrode active material; Wherein, the coating material includes at least one of methyl methacrylate, sodium maleate and oleic acid diethanolamide borate.

6. The preparation method according to claim 5, characterized in that: include: The coating layer has a thickness of 5nm-50nm. Optionally, the coating layer has a thickness of 10nm-20nm.

7. The preparation method according to claim 5 or 6, characterized in that: The negative electrode active material and the coating material are mixed, and the treatment comprises: The methyl methacrylate is polymerized to form the coating layer, and the coating layer includes polymethyl methacrylate; Wherein, the molecular weight of the polymethyl methacrylate is 500,000-2,000,000. Optionally, the molecular weight of the polymethyl methacrylate is 1,000,000-1,500,000.

8. The preparation method according to claim 7, characterized in that: The mass ratio of the methyl methacrylate to the negative electrode active material is 1-5. Optionally, the mass ratio of the methyl methacrylate to the negative electrode active material is 1.5-3.

9. The preparation method according to claim 7 or 8, characterized in that: The treatment temperature of the negative electrode active material and the methyl methacrylate is not less than 60°C. Optionally, the treatment temperature is 60°C-220°C.

10. The preparation method according to any one of claims 7 to 9, characterized in that: The treatment time of the negative electrode active material and the methyl methacrylate is 1 hour to 8 hours. Optionally, the treatment time is 3 hours to 5 hours.

11. The preparation method according to any one of claims 5 to 10, characterized in that: The negative electrode active material and the coating material are mixed and processed, including: mixing the catalyst, the negative electrode active material and the methyl methacrylate; Optionally, the catalyst comprises at least one of an organic peroxide and an azo compound.

12. The preparation method according to claim 5, characterized in that: The negative electrode active material and the coating material are mixed and processed, including: The coating material includes at least one of sodium maleate and oleic acid diethanolamide borate; The treatment temperature of the negative electrode active material and at least one of the sodium maleate and oleic acid diethanolamide borate is not less than 40°C. Optionally, the treatment temperature is 40°C-120°C.

13. The preparation method according to claim 12, characterized in that: The mass ratio of at least one of the sodium maleate and the oleic acid diethanolamide borate to the negative electrode active material is 1-3. Optionally, the mass ratio of at least one of the sodium maleate and the oleic acid diethanolamide borate to the negative electrode active material is 1-2.

14. The preparation method according to any one of claims 5 to 13, characterized in that: The negative electrode active material includes at least one of graphite and silicon-based materials. Optionally, the silicon-based material includes at least one of elemental silicon, silicon-oxygen compounds, silicon-carbon compounds, silicon-nitrogen compounds, and composites of elemental silicon, silicon-oxygen compounds, and silicon-carbon compounds; Optionally, the silicon oxide compound includes Si a O b , where a=1, 1≤b≤2; Optionally, the silicon carbon compound includes Si c C d , where c=1, d=1.

15. A negative electrode plate, characterized in that: The invention comprises the negative electrode active material according to any one of claims 1 to 4, and / or the negative electrode active material prepared by the method for preparing the negative electrode active material according to any one of claims 5 to 14.

16. A battery cell, characterized in that: Including the negative electrode sheet as described in claim 15.

17. A battery, characterized in that: Comprising a battery cell as claimed in claim 16.

18. An electrical device, characterized in that: Comprising the battery of claim 17.

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