Negative electrode sheet and preparation method therefor, and battery

Abstract

A negative electrode sheet, and a preparation method therefor and the use thereof. The negative electrode sheet comprises a negative electrode active material layer and a negative electrode current collector, wherein the negative electrode active material layer is attached to the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material, which comprises a first material and a second material, wherein the first material comprises a pre-magnesiated silicon oxide material, which is a pre-magnesiated silicon oxide body surface-modified with nitrogen; and the second material comprises graphite.

Description

A negative electrode sheet, a preparation method thereof and a battery

[0001] Cross-reference to Related Applications

[0002] This application claims priority to Chinese Patent Application No. 202411348543.2, filed on September 26, 2024, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of secondary batteries, and in particular to a negative electrode sheet, a preparation method thereof and a battery. BACKGROUND

[0004] Silicon negative electrodes have been widely used in high-energy batteries due to their high capacity, wide source and low price. However, silicon negative electrodes have the disadvantage of high expansion rate, which can cause particle pulverization, electrode structure damage, and repeated growth of solid electrolyte interphase (SEI), thereby affecting the long cycle stability of the battery. To solve the problem of silicon negative electrode expansion, silicon-oxygen materials for preparing silicon negative electrodes have emerged. The inert buffer provided by silicon-oxygen materials can significantly inhibit the expansion of silicon negative electrodes, but they also have the problem of low initial efficiency. To solve this problem, silicon-oxygen materials are pre-lithiated or pre-magnesiated. Pre-magnesiated silicon-oxygen materials have attracted widespread attention due to their low cost and the absence of the need for expensive lithium raw materials. However, since the pre-magnesiated silicon-oxygen material is coated with a layer of magnesium silicate on the surface, the pre-magnesiated silicon-oxygen material can promote the insertion and extraction of lithium ions, thereby improving the capacity and cycle life of the battery. However, the lithium ion conductivity of this layer of magnesium silicate is very poor, which adversely affects the rate and cycle performance of the battery, and thus the electrochemical performance is poor. SUMMARY

[0005] By utilizing one or more embodiments of the present disclosure, a negative electrode sheet, a preparation method thereof and a battery are provided to improve the electrochemical performance of pre-magnesiated silicon-oxygen materials.

[0006] In a first aspect, the present disclosure provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer being attached to the negative electrode current collector; the negative electrode active material layer comprising a negative electrode active material, the negative electrode active material comprising a first material and a second material, the first material comprising a pre-magnesiated silicon-oxygen material, the pre-magnesiated silicon-oxygen material being a pre-magnesiated silicon-oxygen body with a surface modified with nitrogen, and the second material comprising graphite.

[0007] In a second aspect, the present disclosure provides a preparation method of a negative electrode sheet, comprising: obtaining a pre-magnesia silicon-oxygen material, the pre-magnesia silicon-oxygen material being a pre-magnesia silicon-oxygen body with a surface modified with nitrogen; and preparing a slurry of the pre-magnesia silicon-oxygen material and graphite, and coating the slurry on a negative electrode current collector to obtain the negative electrode sheet.

[0008] In a third aspect, the present disclosure provides a battery, the battery comprising the negative electrode sheet provided in the first aspect.

[0009] In a fourth aspect, the present disclosure provides a battery, the battery comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer being attached to the negative electrode current collector; the negative electrode active material layer comprising a negative electrode active material, the negative electrode active material comprising a first material and a second material, the first material comprising a pre-magnesia silicon-oxygen material, the pre-magnesia silicon-oxygen material comprising a pre-magnesia silicon-oxygen body and a coating layer coated on the pre-magnesia silicon-oxygen body, the material of the coating layer comprising Li3N, and the second material comprising graphite. BRIEF DESCRIPTION OF DRAWINGS

[0010] The accompanying drawings, which are incorporated herein and constitute part of the specification, illustrate embodiments consistent with the present disclosure and serve to explain the principles of the present disclosure together with the specification.

[0011] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the related technical solutions, the accompanying drawings needed to be used in the embodiments or the related technical description will be briefly introduced. Obviously, those skilled in the art can obtain other drawings according to these drawings without any creative effort.

[0012] FIG. 1 shows a flowchart of a preparation method of a negative electrode sheet according to some embodiments of the present disclosure;

[0013] FIG. 2 shows a flowchart of obtaining a pre-magnesia silicon-oxygen material in FIG. 1; and

[0014] FIG. 3 shows a graph of the cycle performance test results of the half-batteries provided in Example 1 and Comparative Example 1 of the present disclosure. Embodiments of the present disclosure

[0015] In order to make the objects, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be described clearly and completely below with reference to the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only some of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without any creative effort fall within the scope of protection of the present disclosure.

[0016] Unless otherwise specifically indicated, various materials, reagents, instruments and equipment and the like used in the present disclosure can be purchased or prepared by existing methods.

[0017] The present disclosure intends to provide a long-circulation pre-magnesia silicon-oxygen-based negative electrode sheet, a preparation method thereof and a battery. By modifying the surface of the pre-magnesia silicon-oxygen body with nitrogen, a Li3N layer with high ionic conductivity can be constructed in situ on the negative electrode sheet during charging and discharging. The in-situ generated Li3N is a stable inorganic substance with high ionic conductivity, which can improve the poor lithium ion conductivity caused by the original surface coverage of magnesium silicate of the pre-magnesia silicon-oxygen material.

[0018] The present disclosure provides a negative electrode sheet. The negative electrode sheet includes a negative electrode active material layer and a negative electrode current collector, and the negative electrode active material layer is attached to the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material includes a first material and a second material. The first material includes a pre-magnesia silicon-oxygen material. The pre-magnesia silicon-oxygen material is a pre-magnesia silicon-oxygen body modified with nitrogen on the surface. The second material includes graphite.

[0019] The negative electrode sheet modifies the surface of the pre-magnesia silicon-oxygen material with nitrogen. During the charging and discharging process, when a solid-state electrolyte film is generated on the surface of the pre-magnesia silicon-oxygen material, a large amount of Li3N component will be generated at the same time. The in-situ generated Li3N is a stable inorganic substance with high ionic conductivity, which can improve the poor lithium ion conductivity caused by the original surface coverage of magnesium silicate of the pre-magnesia silicon-oxygen material, thereby improving the rate and cycle performance of the battery, thereby improving the electrochemical performance of the pre-magnesia silicon-oxygen body.

[0020] In some embodiments, the mass ratio of nitrogen to the pre-magnesia silicon-oxygen body in the pre-magnesia silicon-oxygen material is (1:27) to (1:72). By controlling the mass ratio of nitrogen to the pre-magnesia silicon-oxygen body, an appropriate amount of Li3N can be formed, thereby facilitating ion conduction of the pre-magnesia silicon-oxygen material. The pre-magnesia silicon-oxygen body can be a carbon-coated silicon monoxide material.

[0021] In some embodiments, the mass ratio of the pre-magnesia silicon-oxygen material to graphite is (30-40):(60-70).

[0022] For example, the mass ratio of the pre-magnesia silicon-oxygen material to graphite can be 30:70, 31:69, 32:68, 33:67, 34:66, 35:65, 36:64, 37:63, 38:62, 39:61 or 40:60, etc. It can also be any value within the range of (30-40):(60-70).

[0023] In some embodiments, the negative active material layer further comprises a conductive agent and a binder, and the mass ratio of the negative active material, the conductive agent and the binder is (93-95):(0.5-1.5):(4-6). For example, the mass ratio of the negative active material, the conductive agent and the binder can be 94:1:5, and can also be any value within the range of (93-95):(0.5-1.5):(4-6).

[0024] In some embodiments, the conductive agent comprises carbon black and carbon nanotubes, and the mass ratio of the carbon black and the carbon nanotubes is (5-7):(3-5).

[0025] For example, the mass ratio of the carbon black and the carbon nanotubes can be 5:5, 5.5:4.5, 6:4, 6.5:3.5, 7:3, or the like, and can also be any value within the range of (5-7):(3-5).

[0026] In some embodiments, the binder comprises polyacrylic acid (PAA) and polymerized styrene butadiene rubber (SBR), and the mass ratio of the polyacrylic acid and the polymerized styrene butadiene rubber is (0.5-1.5):(0.5-1.5).

[0027] For example, the mass ratio of the polyacrylic acid and the polymerized styrene butadiene rubber can be 0.5:0.5, 1:0.5, 1.5:0.5, 0.5:1, 0.5:1.5, 1:0.5, 1:1.5, or the like, and can also be any value within the range of (0.5-1.5):(0.5-1.5).

[0028] FIG. 1 shows a flowchart of a method for preparing a negative electrode sheet according to some embodiments of the present disclosure. As shown in FIG. 1, based on a general inventive concept, the present disclosure further provides a method for preparing a negative electrode sheet.

[0029] The method is used for preparing the negative electrode sheet described above, and the specific content of the negative electrode sheet can refer to the above embodiments. Since the method adopts part or all of the technical solutions of the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be repeated here.

[0030] In some embodiments, the method for preparing the negative electrode sheet comprises steps S1-S2.

[0031] In step S1, a pre-magnesia silicon-oxygen material is obtained, and the pre-magnesia silicon-oxygen material is a pre-magnesia silicon-oxygen body with a surface modified with nitrogen.

[0032] In step S2, the pre-magnesia silicon-oxygen material and graphite are prepared into a slurry, and the slurry is coated on a negative electrode current collector to obtain a negative electrode sheet.

[0033] In some embodiments, the method for preparing the negative electrode sheet comprises:

[0034] obtaining a first material, the first material comprising a pre-magnesia silicon-oxygen material, the pre-magnesia silicon-oxygen material being a pre-magnesia silicon-oxygen body with a surface modified with nitrogen; and,

[0035] mixing the first material and a second material to obtain a negative electrode active material, configuring the negative electrode active material, a conductive agent, and a binder into a slurry, and coating the slurry on a negative electrode current collector to obtain the negative electrode sheet.

[0036] FIG. 2 shows a flowchart of obtaining the pre-magnesia silicon-oxygen material in FIG. 1. In some embodiments, as shown in FIG. 2, obtaining the pre-magnesia silicon-oxygen material can comprise steps S1.1-S1.3:

[0037] In step S1.1, a pre-magnesia silicon-oxygen body, a nitrogen source, and a carbon source are mixed to obtain a first mixed solution.

[0038] In step S1.2, the first mixed solution is heated and dispersed to obtain a second mixed solution, and the second mixed solution is cooled and precipitated to obtain an intermediate.

[0039] In step S1.3, the intermediate is calcined to obtain the pre-magnesia silicon-oxygen material.

[0040] In some embodiments, obtaining the pre-magnesia silicon-oxygen material can comprise:

[0041] mixing the nitrogen source, the carbon source, and a solute to obtain a first mixed solution;

[0042] heating the first mixed solution, adding a magnesia silicon-oxygen body to the heated first mixed solution to obtain a second mixed solution;

[0043] ultrasonic dispersing the second mixed solution, and cooling and precipitating the ultrasonic dispersed second mixed solution to obtain an intermediate;

[0044] calcining the intermediate to obtain the pre-magnesia silicon-oxygen material.

[0045] In some embodiments, the nitrogen source can comprise at least one of melamine, dicyandiamide, and thiourea.

[0046] In some embodiments, the carbon source can comprise citric acid.

[0047] In some embodiments, the mass ratio of the pre-magnesia silicon-oxygen body to the nitrogen source is (5-8): 1.

[0048] For example, the mass ratio of the pre-magnesia silicon-oxygen bulk and the carbon source can be 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, or 10:1, etc., which can also be any value within the range of (6-10):1.

[0049] In some embodiments, the mass ratio of the pre-magnesia silicon-oxygen bulk and the carbon source is (6-10):1.

[0050] For example, the mass ratio of the pre-magnesia silicon-oxygen bulk and the carbon source can be 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1, or 10:1, etc., which can also be any value within the range of (6-10):1.

[0051] In some embodiments, the heating temperature is 60-80°C. For example, the heating temperature can be 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C, or 80°C, etc., which can also be any value within the range of 60-80°C.

[0052] In some embodiments, the heating time is 0.5-1 h. For example, the heating time can be 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, or 1 h, etc., which can also be any value within the range of 0.5-1 h.

[0053] In some embodiments, the dispersion is ultrasonic dispersion, and the dispersion time is 4-6 min. For example, the dispersion time can be 4 min, 4.2 min, 4.4 min, 4.6 min, 4.8 min, 5 min, 5.2 min, 5.4 min, 5.6 min, 5.8 min, or 6 min, etc., which can also be any value within the range of 4-6 min.

[0054] In some embodiments, the calcination temperature is 700-800°C. For example, the calcination temperature can be 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, or 800°C, etc., which can also be any value within the range of 700-800°C.

[0055] In some embodiments, the calcination time is 2-5 h. For example, the calcination time can be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, or 5 h, etc., which can also be any value within the range of 2-5 h.

[0056] In some embodiments, the preparation process of the pre-magnesia silicon-oxygen material can be as follows: first, dispersing the pre-magnesia silicon-oxygen body in a heated desalted aqueous solution in which a nitrogen source and citric acid are dissolved to obtain a first mixed solution. The nitrogen source can be one of melamine, dicyandiamide, and thiourea, and citric acid serves as a carbon source; the mass ratio of the pre-magnesia silicon-oxygen body to the nitrogen source ranges from (5:1) to (8:1), and the mass ratio of the pre-magnesia silicon-oxygen body to citric acid ranges from (6:1) to (10:1). The first mixed solution is dispersed to obtain a second mixed solution. The heating temperature is 60-80°C, and the heating time is 0.5-1 h; the first mixed solution is dispersed by ultrasonic dispersion, and the dispersion time is 4-6 min. Then, the second mixed solution is cooled, and the solid precipitated after cooling is calcined at high temperature in a mixed argon-hydrogen gas to obtain a pre-magnesia silicon-oxygen body with a surface nitrogen modification (pre-magnesia silicon-oxygen material). Alternatively, the second mixed solution can be cooled to room temperature first, and a solid is precipitated to form a turbid liquid; the turbid liquid is centrifuged, and the obtained solid is washed with desalted water and ethanol and then dried; the dried solid is calcined at high temperature in a mixed argon-hydrogen gas with a hydrogen content of 10%, and the calcination temperature is 700-800°C and the calcination time is 2-5 h, to obtain a pre-magnesia silicon-oxygen body with a surface nitrogen modification (pre-magnesia silicon-oxygen material).

[0057] In some embodiments, the preparation of the negative electrode tab can be as follows: the obtained pre-magnesia silicon-oxygen body with a surface nitrogen modification (pre-magnesia silicon-oxygen material) is used as a first material in the negative electrode tab main material (negative electrode active material), and graphite is used as a second material in the negative electrode active material; the first material, the second material, a binder, and a conductive agent are prepared into a slurry, the slurry is coated on a negative electrode current collector to obtain a negative electrode tab. The components of the negative electrode active material layer include the negative electrode active material (negative electrode tab main material), the conductive agent, and the binder, and the ratio of the negative electrode active material, the conductive agent, and the binder is 94:1:5; the ratio of the pre-magnesia silicon-oxygen body with a surface nitrogen modification (pre-magnesia silicon-oxygen material) to graphite is 35:65, the ratio of carbon black to carbon tube in the conductive agent is 6:4, and the ratio of PAA to SBR in the binder is 1:1; it should be noted that desalted water can be added to the raw materials during the preparation of the slurry, and then the negative electrode tab can be obtained through coating, drying, rolling, and die cutting operations.

[0058] Based on the overall inventive concept, the disclosure also provides a battery comprising the above negative electrode tab.

[0059] The battery provided by the embodiments of the present disclosure includes the negative pole sheet provided by the technical scheme, and thus the battery provided by the present disclosure has all the beneficial effects of the negative pole sheet, which will not be described herein. The negative pole sheet includes a negative pole active material layer and a negative pole current collector, and the negative pole active material layer is attached to the negative pole current collector. The negative pole active material layer includes a negative pole active material, and the negative pole active material includes a first material and a second material. The first material includes a pre-magnesium silicon-oxygen material, and the pre-magnesium silicon-oxygen material is a pre-magnesium silicon-oxygen body with a surface decorated with nitrogen. The second material includes graphite. The battery is a new battery that has not been charged and discharged. At this time, the nitrogen on the surface of the pre-magnesium silicon-oxygen body in the pre-magnesium silicon-oxygen material has not reacted with lithium.

[0060] Based on the overall inventive concept, the embodiments of the present disclosure also provide a battery including a negative pole sheet, the negative pole sheet including a negative pole active material layer and a negative pole current collector, the negative pole active material layer being attached to the negative pole current collector; the negative pole active material layer including a negative pole active material, the negative pole active material including a first material and a second material, the first material including a pre-magnesium silicon-oxygen material, the pre-magnesium silicon-oxygen material including a pre-magnesium silicon-oxygen body and a coating layer coated on the pre-magnesium silicon-oxygen body, the material of the coating layer including Li3N, and the second material including graphite. The battery is a battery that has been charged and discharged, that is, during the charging and discharging process of the above-mentioned new battery that has not been charged and discharged, the nitrogen on the surface of the pre-magnesium silicon-oxygen body in the pre-magnesium silicon-oxygen material reacts with lithium ions to generate Li3N, thereby forming a coating layer on the surface of the pre-magnesium silicon-oxygen body to coat the pre-magnesium silicon-oxygen body.

[0061] The technical solutions of the present disclosure will be further described below in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate the present disclosure and not to limit the scope of the present disclosure. The experimental methods not specified in the following embodiments are generally determined according to national standards. If there is no corresponding national standard, the general international standard, the conventional condition, or the condition suggested by the manufacturer is used.

[0062] Embodiment 1

[0063] A negative pole sheet is prepared as follows:

[0064] 1) Melamine and citric acid are added to desalted water, heated at 80°C for 1 h to dissolve the melamine and citric acid, and then pre-magnesium silicon-oxygen bodies are added and ultrasonically dispersed for 5 min. The mass ratio of the pre-magnesium silicon-oxygen bodies to the melamine is 5:1, and the mass ratio of the pre-magnesium silicon-oxygen bodies to the citric acid is 8:1. After the ultrasonic dispersion, the dispersion liquid is cooled to room temperature and then centrifuged. The obtained solid is washed with desalted water and ethanol and then dried. The obtained solid after drying is calcined in an argon-hydrogen mixed gas with a hydrogen content of 10%, and calcined at 750°C for 3 h to obtain pre-magnesium silicon-oxygen bodies with a surface decorated with nitrogen (pre-magnesium silicon-oxygen material).

[0065] 2) The surface nitrogen-modified pre-magnesia silicon-oxygen body (pre-magnesia silicon-oxygen material) obtained is used as a first material in a negative electrode active material, graphite is used as a second material in the negative electrode active material, the first material, the second material, a binder, and a conductive agent are prepared into a slurry, the slurry is coated on a negative electrode current collector to obtain a negative electrode sheet. The ratio of the negative electrode active material, the conductive agent, and the binder is 94:1:5; the ratio of the surface nitrogen-modified pre-magnesia silicon-oxygen body (pre-magnesia silicon-oxygen material) to the graphite in the negative electrode active material is 35:65, the ratio of the carbon black to the carbon tube in the conductive agent is 6:4, and the ratio of the PAA to the SBR in the binder is 1:1; during the preparation of the slurry, desalted water can be added to the raw materials to mix the slurry, and then coating, drying, rolling, and die cutting operations are performed to obtain the negative electrode sheet.

[0066] Example 2

[0067] A negative electrode sheet is prepared as follows:

[0068] 1) Thiourea and citric acid are added to desalted water, heated at 80°C for 1 h to dissolve the thiourea and citric acid, and then pre-magnesia silicon-oxygen bodies are added and ultrasonically dispersed for 5 min. The mass ratio of the pre-magnesia silicon-oxygen bodies to the thiourea is 5:1, and the mass ratio of the pre-magnesia silicon-oxygen bodies to the citric acid is 8:1. After the ultrasonic dispersion, the dispersion liquid is cooled to room temperature and then centrifuged. The obtained solid is washed with desalted water and ethanol and then dried. The dried solid is calcined in an argon-hydrogen mixed gas with a hydrogen content of 10% at a high temperature, and calcined at 750°C for 3 h to obtain a surface nitrogen-modified pre-magnesia silicon-oxygen body (pre-magnesia silicon-oxygen material).

[0069] 2) The surface nitrogen-modified pre-magnesia silicon-oxygen body (pre-magnesia silicon-oxygen material) obtained is used as a first material in a negative electrode active material (negative electrode main material), graphite is used as a second material in the negative electrode active material, the first material, the second material, a binder, and a conductive agent are prepared into a slurry, the slurry is coated on a negative electrode current collector to obtain a negative electrode sheet. The ratio of the negative electrode active material, the conductive agent, and the binder is 94:1:5; the ratio of the surface nitrogen-modified pre-magnesia silicon-oxygen body (pre-magnesia silicon-oxygen material) to the graphite in the negative electrode active material is 35:65, the ratio of the carbon black to the carbon tube in the conductive agent is 6:4, and the ratio of the PAA to the SBR in the binder is 1:1; during the preparation of the slurry, desalted water can be added to the raw materials to mix the slurry, and then coating, drying, rolling, and die cutting operations are performed to obtain the negative electrode sheet.

[0070] Example 3

[0071] A negative electrode sheet is prepared as follows:

[0072] 1) dicyandiamide and citric acid were added into the desalted water, heated at 65℃ for 1 h to dissolve dicyandiamide and citric acid, and then the pre-magnesia silicon body was ultrasonically dispersed for 5 min. The mass ratio of the pre-magnesia silicon body to dicyandiamide was 8:1, and the mass ratio of the pre-magnesia silicon body to citric acid was 10:1. After the dispersion liquid was cooled to room temperature, centrifugal separation was performed, and the obtained solid was washed with desalted water and ethanol and then dried. The obtained solid was calcined in an argon-hydrogen mixed gas with a hydrogen content of 10% at a high temperature, and calcined at 800℃ for 5 h to obtain a pre-magnesia silicon body with surface nitrogen modification (pre-magnesia silicon material).

[0073] 2) The obtained pre-magnesia silicon body with surface nitrogen modification (pre-magnesia silicon material) was used as a first material in a negative electrode active material (negative electrode main material), and graphite was used as a second material in the negative electrode active material. The first material, the second material, a binder, and a conductive agent were prepared into a slurry, and the slurry was coated on a negative electrode current collector to obtain a negative electrode sheet. The ratio of the negative electrode active material, the conductive agent, and the binder was 94:1:5; the ratio of the pre-magnesia silicon body with surface nitrogen modification (pre-magnesia silicon material) to graphite in the negative electrode active material was 35:65, the ratio of carbon black to carbon tube in the conductive agent was 6:4, and the ratio of PAA to SBR in the binder was 1:1; desalted water was added to the raw materials during the preparation of the slurry, and then coating, drying, rolling, and die cutting were performed to obtain the negative electrode sheet.

[0074] Comparative Example 1

[0075] A negative electrode sheet was prepared by the following process:

[0076] A pre-magnesia silicon body was used as a first material in a negative electrode active material (negative electrode main material), and graphite was used as a second material in the negative electrode active material. The first material, the second material, a binder, and a conductive agent were prepared into a slurry, and the slurry was coated on a negative electrode current collector to obtain a negative electrode sheet. The components of the negative electrode active material layer included the negative electrode active material, the conductive agent, and the binder, and the ratio of the negative electrode active material, the conductive agent, and the binder was 94:1:5; the ratio of the pre-magnesia silicon body to graphite in the negative electrode active material was 35:65, the ratio of carbon black to carbon tube in the conductive agent was 6:4, and the ratio of PAA to SBR in the binder was 1:1; desalted water was added to the raw materials during the preparation of the slurry, and then coating, drying, rolling, and die cutting were performed to obtain the negative electrode sheet.

[0077] The negative electrode pole pieces provided by each of the examples and the comparative examples were cut into 12 mm diameter round pieces and assembled into button-type half batteries (the counter electrode was lithium metal) for cycle performance testing. The test results are shown in FIG. 2. It should be noted that, since the results of Examples 1 to 3 are similar, only the results of Example 1 are shown and described in the figure.

[0078] As can be seen from FIG. 3, the battery composed of the negative electrode pole piece prepared by the method provided by the embodiments of the present disclosure has significantly higher cycle performance under the premise of meeting high capacity.

[0079] The above technical solutions provided by the embodiments of the present disclosure have at least the following advantages compared with related art:

[0080] The negative electrode pole piece provided by the embodiments of the present disclosure, by modifying the surface of the pre-magnesium silicon-oxygen body with nitrogen, in the charging and discharging process, the nitrogen decorated on the surface of the pre-magnesium silicon-oxygen body can generate more Li3N components in situ with lithium; the in-situ generated Li3N is a stable and high ionic conductivity inorganic substance, which can improve the poor lithium ion conductivity problem caused by the original surface of the pre-magnesium silicon-oxygen body magnesium silicate, and further improve the rate and cycle performance of the battery, so as to improve the electrochemical performance of the pre-magnesium silicon-oxygen body.

[0081] Various embodiments of the present disclosure can exist in the form of a range; it should be understood that the description in the form of a range is only for the convenience and brevity, and should not be understood as a hard limit on the scope of the present disclosure; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single values within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated in this document, it refers to any cited number (fraction or integer) within the indicated range.

[0082] In the present disclosure, the orientation words such as "upper" and "lower" are specifically the directions of the drawing surface in the drawings unless otherwise stated. In addition, in the description of the present disclosure, the terms "comprise", "contain" and the like mean "including but not limited to". In this text, the relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. In this text, "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B can represent: the case of A alone, the case of A and B existing at the same time, and the case of B alone. Wherein A, B can be singular or plural. In this text, "at least one" means one or more, and "multiple" means two or more. "At least one", "at least one of the following" or the like means any combination of these items, including any combination of single item or multiple items. For example, "at least one of a, b or c", or "at least one of a, b and c", can represent a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, wherein a, b, c can be single or multiple.

[0083] The above is only a specific embodiment of the present disclosure, which enables those skilled in the art to understand or implement the present disclosure. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure will not be limited to these embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied herein.

Claims

1. A negative electrode sheet, comprising a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer being attached to the negative electrode current collector; the negative electrode active material layer comprising a negative electrode active material, the negative electrode active material comprising a first material and a second material, the first material comprising a pre-magnesia silicon-oxygen material, the pre-magnesia silicon-oxygen material being a pre-magnesia silicon-oxygen body with a surface modified with nitrogen, the second material comprising graphite.

2. The negative electrode sheet according to claim 1, wherein The mass ratio of nitrogen to the pre-magnesia silicon-oxygen body in the pre-magnesia silicon-oxygen material is (1:27) to (1:72).

3. The negative electrode sheet according to claim 1, wherein The mass ratio of the pre-magnesia silicon-oxygen material to the graphite is (30-40) to (60-70).

4. The negative electrode sheet according to claim 1, wherein The negative electrode active material layer further comprises a conductive agent and a binder, and the mass ratio of the negative electrode active material, the conductive agent and the binder is (93-95) to (0.5-1.5) to (4-6).

5. The negative electrode sheet according to claim 4, wherein The conductive agent comprises carbon black and carbon nanotubes, and the mass ratio of the carbon black to the carbon nanotubes is (5-7) to (3-5); and / or The binder comprises polyacrylic acid and styrene butadiene rubber, and the mass ratio of the polyacrylic acid to the styrene butadiene rubber is (0.5-1.5) to (0.5-1.5). 6.A method for preparing a negative electrode sheet, comprising: obtaining a pre-magnesia silicon-oxygen material, the pre-magnesia silicon-oxygen material being a pre-magnesia silicon-oxygen body with a surface modified with nitrogen; and preparing a slurry of the pre-magnesia silicon-oxygen material and graphite, and coating the slurry on a negative electrode current collector to obtain a negative electrode sheet. The obtaining of the pre-magnesia silicon-oxygen material comprises:

7. The method of producing a negative electrode sheet according to claim 6, wherein mixing a pre-magnesia silicon-oxygen body, a nitrogen source and a carbon source to obtain a first mixed solution; heating and dispersing the first mixed solution to obtain a second mixed solution, and cooling and precipitating the second mixed solution to obtain an intermediate; calcining the intermediate to obtain the pre-magnesia silicon-oxygen material. 8.A method for preparing a negative electrode sheet, comprising: obtaining a first material, the first material comprising a pre-magnesia silicon-oxygen material, the pre-magnesia silicon-oxygen material being a pre-magnesia silicon-oxygen body with a surface modified with nitrogen; and mixing the first material and a second material to obtain a negative electrode active material, and preparing a slurry of the negative electrode active material, a conductive agent and a binder, and coating the slurry on a negative electrode current collector to obtain a negative electrode sheet. The obtaining of the pre-magnesia silicon-oxygen material comprises:

9. The method of producing a negative electrode sheet according to claim 8, wherein mixing a nitrogen source, a carbon source and a solute to obtain a first mixed solution; heating the first mixed solution, and adding a pre-magnesia silicon-oxygen body to the heated first mixed solution to obtain a second mixed solution; ultrasonic dispersing the second mixed solution, and cooling and precipitating the ultrasonic dispersed second mixed solution to obtain an intermediate; calcining the intermediate to obtain the pre-magnesia silicon-oxygen material. The nitrogen source comprises at least one of melamine, dicyandiamide and thiourea; and / or 10. The method of producing a negative electrode sheet according to claim 7 or 9, wherein The carbon source comprises citric acid; and / or The mass ratio of the pre-magnesia silicon-oxygen body to the nitrogen source is (5-8) to 1; and / or The mass ratio of the pre-magnesia silicon-oxygen body to the carbon source is (6-10) to 1; and / or The heating temperature is 60-80℃; and / or ​ The heating time is 0.5 h to 1 h; and / or The dispersion is ultrasonic dispersion; and / or The dispersion time is 4 min to 6 min; and / or The calcination temperature is 700 DEG C to 800 DEG C; and / or The calcination time is 2 h to 5 h. 11.A battery comprising the negative electrode sheet according to any one of claims 1 to 5. 12.A battery comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer being attached to the negative electrode current collector; the negative electrode active material layer comprising a negative electrode active material, the negative electrode active material comprising a first material and a second material, the first material comprising a pre-magnesia silicon-oxygen material, the pre-magnesia silicon-oxygen material comprising a pre-magnesia silicon-oxygen bulk and a coating layer coated on the pre-magnesia silicon-oxygen bulk, the material of the coating layer comprising Li 3 N, the second material comprising graphite.

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