Negative electrode sheet, cell, battery, and electric device

Abstract

The present disclosure provides a negative electrode sheet, a cell, a battery, and an electric device. The negative electrode sheet comprises: a negative electrode current collector; a first active layer, arranged on at least one side surface of the negative electrode current collector, a negative electrode active material in the first active layer comprising first graphite and silicon-carbon; and a second active layer, arranged on the side of the first active layer away from the negative electrode current collector, a negative electrode active material in the second active layer comprising second graphite and silicon monoxide. The particle size of the silicon-carbon ranges from 4 μm to 7 μm. The active layers can be prevented from peeling off and falling off from the negative electrode current collector, ensuring that the battery formed from the negative electrode sheet has a high energy density, and enabling the negative electrode sheet to have good electrochemical performance and electrode sheet stability.

Description

Negative plate, pole core, battery and electric device

[0001] The present disclosure claims priority to the Chinese patent application No. 202410854235.0, filed on June 27, 2024, and entitled "Negative plate, pole core, battery and electric device", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present disclosure relates to the technical field of materials, in particular, to a negative plate, a pole core, a battery and an electric device. BACKGROUND

[0003] In the field of modern battery technology, silicon-based materials are considered as ideal candidate materials for the next generation of high-energy-density batteries due to their high theoretical capacity.

[0004] However, when pure silicon materials are used as negative electrode materials of lithium-ion batteries, the silicon materials will undergo significant volume expansion and contraction during the charging and discharging process of the battery due to the deintercalation of lithium ions. Such volume change is prone to cause the active material to peel off from the electrode, thereby seriously affecting the stability of the battery.

[0005] SUMMARY

[0006] An object of embodiments of the present disclosure is to provide a new technical solution for a negative plate, a pole core, a battery and an electric device.

[0007] According to a first aspect of embodiments of the present disclosure, a negative plate is provided, comprising:

[0008] a negative current collector;

[0009] a first active layer, the first active layer being arranged on at least one side surface of the negative current collector, a negative active material in the first active layer comprising a first graphite and silicon-carbon;

[0010] a second active layer, the second active layer being arranged on a side of the first active layer away from the negative current collector, a negative active material in the second active layer comprising a second graphite and silicon monoxide;

[0011] wherein the particle size range of the silicon-carbon is 4-7 μm.

[0012] Optionally, the silicon-carbon comprises a carbon matrix and silicon filled in the carbon matrix.

[0013] The carbon matrix is a porous hard carbon, and the average pore size range of the carbon matrix is 3-11 nm.

[0014] Optionally, the pore volume range of the silicon-carbon is 0.6-1.0 mL / g.

[0015] Optionally, the particle size of the first graphite ranges from 15 to 19 μm.

[0016] Optionally, the mass percentage of the silicon-carbon in the negative active material of the first active layer ranges from 1% to 20%.

[0017] Optionally, the gravimetric capacity of the silicon-carbon ranges from 1300 to 2000 mAh / g.

[0018] Optionally, the particle size of the second graphite ranges from 11 to 15 μm, and the particle size of the silicon monoxide ranges from 9 to 12 μm.

[0019] Optionally, the mass percentage of the silicon monoxide in the negative active material of the second active layer ranges from 1% to 20%.

[0020] Optionally, the ratio of the number of silicon atoms to the number of oxygen atoms in the silicon monoxide ranges from (2:1) to (1.1:1).

[0021] Optionally, the thickness ratio of the first active layer to the second active layer ranges from (1:2) to (2:1).

[0022] According to a second aspect of the embodiments of the present disclosure, there is provided a pole core, which comprises the negative electrode sheet of the first aspect.

[0023] Optionally, the pole core comprises a positive electrode sheet and a separator.

[0024] The separator is arranged between the positive electrode sheet and the negative electrode sheet.

[0025] According to a third aspect of the embodiments of the present disclosure, there is provided a battery, which comprises the pole core of the second aspect.

[0026] According to a fourth aspect of the embodiments of the present disclosure, there is provided an electrical device, which comprises the battery of the third aspect.

[0027] One technical effect of the present disclosure is that:

[0028] The embodiments of the present disclosure provide a negative electrode sheet, which comprises a negative electrode current collector, a first active layer arranged on at least one side surface of the negative electrode current collector, and a second active layer arranged on a side of the first active layer away from the negative electrode current collector. The negative active material in the first active layer comprises first graphite and silicon-carbon, and the negative active material in the second active layer comprises second graphite and silicon monoxide. The particle size of the silicon-carbon ranges from 4 to 7 μm, which can prevent the active layer from peeling off from the negative electrode current collector, and ensure that the battery formed by the negative electrode sheet has high energy density, and the negative electrode sheet has good electrochemical performance and pole sheet stability.

[0029] Other features of the present disclosure, and its particular advantages, will become apparent to those skilled in the art from the following detailed description, along with the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0030] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure.

[0031] FIG. 1 is a schematic view of a negative electrode sheet according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0032] Various exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of the components and steps set forth in the embodiments, numerical expressions, and numerical values, unless specifically stated otherwise, do not limit the scope of the present disclosure.

[0033] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the scope of the disclosure, its application or uses.

[0034] Techniques, methods, and devices known to those of ordinary skill in the relevant art can not be discussed in detail herein. However, where appropriate, such techniques, methods, and devices can be viewed as part of the specification.

[0035] In all of the examples shown and discussed herein, any specific values should be interpreted as merely illustrative and not as a limitation. Thus, other examples of exemplary embodiments can have different values.

[0036] It should be noted that like reference numerals and letters refer to like items throughout the drawings, and once an item is defined in one drawing, it need not be discussed further in subsequent drawings.

[0037] Referring to FIG. 1, a negative electrode sheet according to an embodiment of the present disclosure includes:

[0038] a negative current collector 1;

[0039] a first active layer 2 disposed on at least one side surface of the negative current collector 1, the negative active material in the first active layer 2 including a first graphite and silicon carbon;

[0040] a second active layer 3 disposed on a side of the first active layer 2 distal from the negative current collector 1, the negative active material in the second active layer 3 including a second graphite and silicon monoxide;

[0041] wherein the silicon carbon has a particle size range of 4-7 μm.

[0042] In this embodiment, the first active layer 2 can be arranged on one side surface of the negative current collector 1 to obtain a negative electrode sheet with single-side coating of the negative current collector 1, or the first active layer 2 can be arranged on both side surfaces of the negative current collector 1 to obtain a negative electrode sheet with double-side coating of the negative current collector 1; the second active layer 3 is arranged on the side of the first active layer 2 away from the negative current collector 1, and the second active layer 3 is arranged correspondingly to the first active layer 2, for example, when the first active layer 2 is arranged on one side, the second active layer 3 is also arranged on the side of the first active layer 2 away from the negative current collector 1; when the first active layer 2 is arranged on both sides, the second active layer 3 is also arranged on the side of the first active layer 2 away from the negative current collector 1, to form a double-layer active structure of the first active layer 2 and the second active layer 3 on the surface of the negative current collector 1 in sequence.

[0043] In this embodiment, the negative active material in the first active layer 2 includes silicon-carbon, which is different from silicon carbide, and is a substance obtained by depositing silicon particles on carbon material. The capacity of silicon-carbon is high but the initial efficiency is low, while the negative active material in the second active layer 3 includes silicon monoxide, which has a high initial efficiency. The use of silicon monoxide (SiOx, also known as silicon-oxygen, x is in the range of 1-2, for example, x is 1, 1.2, 1.5 or 1.8) partially alleviates the low initial efficiency problem caused by pure silicon-carbon, ensures that the active lithium of the positive electrode material in the battery is more fully embedded and extracted in the active material of the negative electrode sheet, and improves the utilization efficiency of the active lithium.

[0044] At the same time, in the process of charging and discharging of the battery, the expansion of silicon-carbon is smaller than that of silicon monoxide. The combination of inner silicon-carbon and outer silicon monoxide can reduce the stress difference between the inner and outer layers during charging and discharging, making the structure of the negative electrode sheet more stable and preventing the problem of peeling between the inner and outer layers, thereby increasing the service life of the negative electrode sheet.

[0045] In this embodiment, the first active layer 2 and the second active layer 3 both contain specific negative active materials (such as graphite) and silicon materials (silicon-carbon or silicon monoxide) with specific structures, for example, the first graphite and silicon-carbon in the first active layer 2 are uniformly mixed in the slurry preparation process, and the second graphite and silicon monoxide in the second active layer 3 are uniformly mixed in the slurry preparation process, which can prevent the active layer from peeling off from the negative current collector 1, ensure that the battery formed by the negative electrode sheet has high energy density, and make the negative electrode sheet have good electrochemical performance and electrode sheet stability.

[0046] In this embodiment, the particle size range of silicon-carbon is 4-7 μm, that is, small particles of silicon-carbon are added to the first graphite in the first active layer 2. The silicon-carbon can be a small-size diamond structure as shown in FIG. 1. The silicon-carbon has the characteristics of small expansion and good long-term stability. The combination of silicon-carbon and large-particle graphite can effectively improve the compaction density of the negative electrode sheet and the energy density of the battery containing the negative electrode sheet.

[0047] In one embodiment, the silicon-carbon includes a carbon matrix and silicon filled in the carbon matrix.

[0048] The carbon matrix is a porous hard carbon, and the average pore size of the carbon matrix ranges from 3 to 11 nm.

[0049] In this embodiment, when the average pore size of the carbon matrix ranges from 3 to 11 nm, the size of the silicon particles in the carbon matrix can be prevented from being too large on the basis of ensuring the deposition amount of silicon in the carbon matrix, thereby ensuring the stability of the battery during the charging and discharging process.

[0050] When the average pore size of the carbon matrix is too small, the deposition amount of silicon in the carbon matrix is low, which leads to a high processing difficulty of the silicon-carbon; when the average pore size of the carbon matrix is too large, the size of the silicon particles deposited in the carbon matrix is too large, which affects the stability of the silicon during the charging and discharging process, thereby leading to the deterioration of the performance of the battery.

[0051] In one embodiment, the pore volume of the silicon-carbon ranges from 0.6 to 1.0 mL / g.

[0052] In this embodiment, when the pore volume of the silicon-carbon ranges from 0.6 to 1.0 mL / g, the capacity of the negative active material can be ensured on the basis of ensuring the stability of the structure of the silicon-carbon. When the pore volume of the silicon-carbon is too large, the carbon skeleton is unstable, which leads to the fact that the negative active material is easily broken during the charging and discharging process of the battery; when the pore volume of the silicon-carbon is too small, the amount of the deposited silicon in the silicon-carbon is too low, which limits the capacity of the negative active material.

[0053] In one embodiment, the particle size of the first graphite ranges from 15 to 19 μm.

[0054] In this embodiment, small-particle silicon-carbon is added to the first graphite of the first active layer 2. The silicon-carbon can be a small-size rhombus structure as shown in FIG. 1. The silicon-carbon has the characteristics of small expansion and good long-term stability. The silicon-carbon is matched with large-particle graphite, which can effectively improve the compaction density of the negative electrode sheet and the energy density of the battery containing the negative electrode sheet. On the other hand, the reasonable particle size matching also significantly improves the rate charging and discharging capacity of the battery.

[0055] In one embodiment, the first graphite can be natural graphite or artificial graphite, and the particle size (D50) of the first graphite can be selected as 16 μm, 17 μm or 18 μm; the particle size (D50) of the silicon-carbon can be selected as 6 μm or 6.5 μm. The compaction degree of the negative electrode sheet is improved by matching the silicon-carbon and the graphite.

[0056] In one embodiment, the mass percentage of the silicon-carbon in the negative active material of the first active layer 2 ranges from 1% to 20%.

[0057] In this embodiment, the mass percentage of silicon and carbon in the negative active material of the first active layer can be selected as 8%, 10%, 12%, 13.5%, or 15%. When the mass percentage of silicon and carbon in the negative active material of the first active layer is increased, the energy density of the battery can be improved while ensuring the performance of the battery.

[0058] In one embodiment, the gram capacity of the silicon-carbon is in the range of 1300-2000 mAh / g.

[0059] In this embodiment, when the gram capacity of the silicon-carbon is controlled in the range of 1300-2000 mAh / g, the structural stability of the negative electrode sheet can be ensured while ensuring the capacity of the battery. When the capacity of the silicon-carbon is too large, for example, the gram capacity of the silicon-carbon is greater than 2000 mAh / g, the material structure of the electrode sheet will change more during the charge and discharge cycle, reducing the cycle stability of the battery. When the capacity of the silicon-carbon is too small, for example, the gram capacity of the silicon-carbon is less than 1300 mAh / g, the energy density of the battery will be reduced accordingly.

[0060] In one embodiment, the gram capacity of the silicon-carbon can be selected in the range of 1300-1700 mAh / g, to further ensure the structural stability of the negative electrode sheet.

[0061] In one embodiment, the gram capacity of the first graphite is in the range of 355-365 mAh / g, for example, the gram capacity of the first graphite is selected as 360 mAh / g, to ensure the capacity of the negative electrode sheet.

[0062] In one embodiment, the particle size of the second graphite is in the range of 11-15 μm, and the particle size of the silicon monoxide is in the range of 9-12 μm.

[0063] In this embodiment, large particles of silicon monoxide are added to the second graphite of the second active layer 3. The silicon monoxide has a high initial efficiency, and the large particles of silicon monoxide are matched with large particles of graphite to provide more capacity and initial efficiency to the negative electrode sheet, further improving the energy density of the battery.

[0064] At the same time, the particle size of the silicon monoxide particles is similar to that of the second graphite particles, ensuring that the second active layer 3 has good porosity. Since the second active layer 3 is located at the outermost layer of the negative electrode sheet, the negative electrode sheet has good wettability.

[0065] In one embodiment, the second graphite can be natural graphite or artificial graphite, and the particle size (D50) of the second graphite can be selected as 12 μm, 13 μm, or 14 μm. The particle size (D50) of the silicon monoxide can be selected as 9.5 μm, 10 μm, or 10.5 μm. The combination of silicon monoxide and graphite can improve the capacity and initial efficiency of the negative electrode sheet.

[0066] In one embodiment, the mass percentage of silicon monoxide in the negative active material of the second active layer 3 ranges from 1% to 20%.

[0067] In this embodiment, the mass percentage of silicon monoxide in the negative active material of the second active layer can be selected as 8%, 10%, 12%, 13.5%, or 15%. When the mass percentage of silicon monoxide in the negative active material of the second active layer increases, the initial efficiency of the battery can be improved, and the battery has a higher capacity.

[0068] In one embodiment, the mass capacity of the second graphite ranges from 345 mAh / g to 355 mAh / g, for example, the mass capacity of the second graphite is selected as 350 mAh / g to ensure the capacity of the negative electrode sheet.

[0069] In one embodiment, the ratio of the number of silicon atoms to the number of oxygen atoms in the silicon monoxide ranges from (2:1) to (1.1:1).

[0070] In this embodiment, in the silicon monoxide of the second active layer, the number of silicon atoms is greater than the number of oxygen atoms, for example, the ratio of the number of silicon atoms to the number of oxygen atoms ranges from 1.1:1 to 2:1, to ensure the specific capacity of the silicon monoxide and improve the capacity of the negative electrode sheet.

[0071] In one embodiment, the thickness ratio of the first active layer 2 to the second active layer 3 ranges from (1:2) to (2:1).

[0072] In this embodiment, the thickness of the first active layer 2 can be less than the thickness of the second active layer 3, for example, the thickness ratio of the first active layer 2 to the second active layer 3 ranges from (1:2) to (1:1), to improve the capacity of the negative electrode sheet through the silicon monoxide in the second active layer 3; or the thickness of the first active layer 2 can be greater than the thickness of the second active layer 3, for example, the thickness ratio of the first active layer 2 to the second active layer 3 ranges from (1:1) to (2:1), to ensure the structural stability of the negative electrode sheet through the silicon carbon in the first active layer 2.

[0073] In one embodiment, the first active layer of the negative electrode sheet includes graphite, silicon carbon, a binder, and a conductive agent, and the mass ratio of graphite: silicon carbon: binder: conductive agent is (10-90):(5-20):(0.5-3):(0.55-6); the second active layer of the negative electrode sheet includes graphite, silicon monoxide, a binder, and a conductive agent, and the mass ratio of graphite: silicon monoxide: binder: conductive agent is (10-90):(5-20):(0.5-3):(0.55-6).

[0074] The conductive agent includes one or a combination of both of conductive carbon black and carbon nanotubes, and the binder includes one or a combination of PAA, CMC, and SBR.

[0075] The embodiment of the present disclosure provides an electrode core, which comprises the negative electrode sheet.

[0076] In the embodiment, small-particle silicon-carbon is added to the first graphite of the first active layer 2, and the silicon-carbon can be small-size rhombus structures in FIG. 1. The silicon-carbon has the characteristics of small expansion and good long-term stability, and the silicon-carbon is matched with large-particle graphite, which can effectively improve the compaction density of the negative electrode sheet and the energy density of the electrode core.

[0077] In one embodiment, the electrode core comprises a positive electrode sheet and a separator;

[0078] The separator is arranged between the positive electrode sheet and the negative electrode sheet.

[0079] In the embodiment, the negative electrode sheet of the electrode core comprises a negative electrode current collector 1, a first active layer 2 and a second active layer 3, and the second active layer 3 is arranged on the side of the first active layer 2 away from the negative electrode current collector 1, so as to form a double-layer active structure of the first active layer 2 and the second active layer 3 on the surface of the negative electrode current collector 1, thereby ensuring that the battery formed by the negative electrode sheet has high energy density, and the negative electrode sheet has good electrochemical performance and electrode sheet stability.

[0080] The embodiment of the present disclosure provides a battery, which comprises the electrode core.

[0081] The embodiment of the present disclosure provides an electric device, which comprises the battery.

[0082] In the battery formed by the negative electrode sheet, the positive electrode active material in the positive electrode sheet of the battery can be a high-nickel ternary material.

[0083] The technical solutions of the present disclosure are further illustrated by specific embodiments and comparative examples, wherein the thicknesses of the negative electrode sheets obtained by the embodiments and the comparative examples are the same.

[0084] Embodiment 1

[0085] The negative electrode sheet:

[0086] The negative electrode active material (graphite 90 g, silicon-carbon 10 g) for the first active layer, the conductive agent (SP conductive carbon black), the thickening agent (CMC-sodium carboxymethyl cellulose), the adhesive (SBR butadiene rubber), and the binder PAA are mixed according to the mass ratio of graphite:silicon-carbon:SP:CMC:SBR:PAA:H2O:NMP = 90:10:1:0.7:0.8:1.5:68:3 to obtain the negative electrode slurry for the first active layer;

[0087] The negative active material for the second active layer (graphite 90 g, silicon monoxide 10 g), conductive agent (SP conductive carbon black), thickening agent (CMC-sodium carboxymethyl cellulose), adhesive (SBR butadiene rubber), and binder PAA were mixed in a mass ratio of graphite: silicon monoxide: SP: CMC: SBR: PAA: H2O: NMP = 90: 10: 1: 0.7: 0.8: 1.5: 68: 3 to prepare a negative electrode slurry for the second active layer;

[0088] Then the negative electrode slurry for the first active layer and the negative electrode slurry for the second active layer were coated in turn on the negative current collector (copper foil) by a double-layer coating device in a thickness ratio of 1:1, one side was coated first, and the other side was coated then (double-sided coating on the negative current collector), and after rolling and slitting, a negative electrode sheet was obtained;

[0089] The positive electrode sheet:

[0090] After the active material NCM (nickel-cobalt-manganese ternary material), conductive agent (ketjen black), and binder polyvinylidene fluoride (PVDF) were mixed uniformly in a mass ratio of 97: 1.5: 1.5 in an N-methyl pyrrolidone (NMP) solvent system, they were coated on an aluminum foil, one side was coated first, and the other side was coated then (double-sided coating on the aluminum foil), and after rolling and slitting, a positive electrode sheet was obtained.

[0091] The separator:

[0092] A PE ceramic film was used.

[0093] The electrolyte:

[0094] The lithium salt was lithium hexafluorophosphate LiPF6, and the organic solvent included ethylene carbonate (EC), methyl ethyl carbonate (EMC), and dimethyl carbonate (DMC).

[0095] The positive electrode sheet, the negative electrode sheet, and the separator were wound to obtain a roll core, packaged with an aluminum plastic film, and after baking for 48 h in a vacuum state to remove moisture, the electrolyte was injected, and after formation and capacity distribution, a soft package battery was prepared.

[0096] Example 2

[0097] A battery was prepared in this example, which was different from example 1 only in that:

[0098] The thickness ratio of the first active layer to the second active layer was 1:2;

[0099] Example 3

[0100] A battery was prepared in this example, which was different from example 1 only in that:

[0101] The thickness ratio of the first active layer to the second active layer was 2:1;

[0102] Example 4

[0103] A battery was prepared in this example, which was different from Example 1 only in that:

[0104] The negative active material for the first active layer (graphite 80 g, silicon carbon 20 g), conductive agent (SP conductive carbon black), thickening agent (CMC - Na carboxymethyl cellulose sodium), adhesive (SBR styrene butadiene rubber), and binder PAA were mixed in a mass ratio of graphite: silicon carbon: SP: CMC: SBR: PAA: H2O: NMP = 80:20:1:0.7:0.8:1.5:68:3 to prepare a negative electrode slurry for the first active layer.

[0105] The negative active material for the second active layer (graphite 80 g, silicon monoxide 20 g), conductive agent (SP conductive carbon black), thickening agent (CMC - Na carboxymethyl cellulose sodium), adhesive (SBR styrene butadiene rubber), and binder PAA were mixed in a mass ratio of graphite: silicon monoxide: SP: CMC: SBR: PAA: H2O: NMP = 80:20:1:0.7:0.8:1.5:68:3 to prepare a negative electrode slurry for the second active layer.

[0106] Example 5

[0107] A battery was prepared in this example, which was different from Example 1 only in that:

[0108] The negative active material for the first active layer (graphite 99 g, silicon carbon 1 g), conductive agent (SP conductive carbon black), thickening agent (CMC - Na carboxymethyl cellulose sodium), adhesive (SBR styrene butadiene rubber), and binder PAA were mixed in a mass ratio of graphite: silicon carbon: SP: CMC: SBR: PAA: H2O: NMP = 99:1:1:0.7:0.8:1.5:68:3 to prepare a negative electrode slurry for the first active layer.

[0109] The negative active material for the second active layer (graphite 99 g, silicon monoxide 1 g), conductive agent (SP conductive carbon black), thickening agent (CMC - Na carboxymethyl cellulose sodium), adhesive (SBR styrene butadiene rubber), and binder PAA were mixed in a mass ratio of graphite: silicon monoxide: SP: CMC: SBR: PAA: H2O: NMP = 99:1:1:0.7:0.8:1.5:68:3 to prepare a negative electrode slurry for the second active layer.

[0110] Example 6

[0111] A battery was prepared in this example, which was different from Example 1 only in that:

[0112] The particle size of the silicon carbon was 6 μm.

[0113] Example 7

[0114] A battery was prepared in this example, which was different from Example 1 only in that:

[0115] The particle size of the silicon carbon was 8 μm;

[0116] Example 8

[0117] A battery was prepared in this example, which was different from Example 1 only in that:

[0118] The particle size of the first graphite was 19 μm;

[0119] Example 9

[0120] A battery was prepared in this example, which was different from Example 1 only in that:

[0121] The particle size of the first graphite was 22 μm;

[0122] Example 10

[0123] A battery was prepared in this example, which was different from Example 1 only in that:

[0124] The particle size of the silicon monoxide was 8 μm;

[0125] Example 11

[0126] A battery was prepared in this example, which was different from Example 1 only in that:

[0127] The particle size of the silicon monoxide was 15 μm;

[0128] Example 12

[0129] A battery was prepared in this example, which was different from Example 1 only in that:

[0130] The particle size of the second graphite was 15 μm;

[0131] Example 13

[0132] A battery was prepared in this example, which was different from Example 1 only in that:

[0133] The particle size of the second graphite was 18 μm.

[0134] Comparative Example 1

[0135] A battery was prepared in this example, which was different from Example 1 only in that: the negative electrode sheet was coated in a single layer, and the negative electrode slurry preparation process was as in the first active layer negative electrode slurry configuration process of Example 1.

[0136] Comparative Example 2

[0137] A battery was prepared in the same manner as in Example 1, except that the negative electrode sheet was coated with a single layer, and the negative electrode slurry preparation process was as follows: the negative electrode active material (see Table 1 for details), conductive agent (SP conductive carbon black), thickening agent (CMC - sodium carboxymethyl cellulose), binder (SBR butadiene rubber), and adhesive were mixed in a mass ratio of graphite: SiC: SiOx: SP: CMC: SBR: PAA: H2O: NMP = 90: 5: 5: 1: 0.7: 0.8: 1.5: 68: 3 to prepare the negative electrode slurry.

[0138] Comparative Example 3

[0139] A battery was prepared in the same manner as in Example 1, except that the negative electrode sheet was coated with a single layer, and the negative electrode slurry preparation process was as follows: the negative electrode active material (see Table 1 for details), conductive agent (SP conductive carbon black), thickening agent (CMC - sodium carboxymethyl cellulose), binder (SBR butadiene rubber), and adhesive were mixed in a mass ratio of graphite: SiC: SiOx: SP: CMC: SBR: PAA: H2O: NMP = 90: 5: 5: 1: 0.7: 0.8: 1.5: 68: 3 to prepare the negative electrode slurry.

[0140] Comparative Example 4

[0141] A battery was prepared in the same manner as in Example 1, except that the second active layer slurry of Example 1 was used as the first active layer coating of the comparative example, and the first active layer slurry of Example 1 was coated on the second active layer of the comparative example;

[0142] Comparative Example 5

[0143] A battery was prepared in the same manner as in Example 1, except that:

[0144] The particle size of the silicon-carbon was 3 μm;

[0145] Comparative Example 6

[0146] A battery was prepared in the same manner as in Example 1, except that:

[0147] The particle size of the silicon-carbon was 9 μm.

[0148] All the above experiments were prepared under the same conditions, and tested under the same conditions.

[0149] Table 1 Parameters in Examples and Comparative Examples

[0150] wherein the thickness ratio is the thickness ratio of the first active layer to the second active layer, and the total thickness of the first active layer and the second active layer is the same.

[0151] Performance test:

[0152] 25℃ 1.0C / 1.0C normal temperature cycle test:

[0153] Charge at 1.0C (design capacity) to 4.25V at 25℃, constant voltage 4.25V to 0.05C0 cutoff current, then discharge the battery at 1.0C, record the discharge capacity as C0 (actual capacity, that is, the capacity of the first circle discharge), then repeat the charge and discharge at 0.5C0 / 1C0 until the capacity retention rate reaches 80%, then record the cycle number.

[0154] 35℃1.0C / 1.0C fast charging cycle test:

[0155] Charge at 0.33C0 constant current for 13.635min, 4C0 constant current for 1.5min, 3.5C0 constant current for 1.2min, 3C0 constant current for 3min, 2.5C0 constant current for 3.63min, 2C0 constant current for 2.4min, 1.5C0 constant current for 2min, 1C0 constant current for 6min (each current setting time and voltage jump, the upper limit of the jump is 4.25V), 0.33C0 constant current constant voltage charge 4.25V cutoff current 0.05C0, then discharge the battery at 1.0C to 2.75V, repeat the above steps of charge and discharge until the capacity retention rate reaches 80%, then record the cycle number.

[0156] 45℃1.0C / 1.0C high temperature cycle test:

[0157] Charge at 0.5C0 constant current to 4.25V at 45℃, constant voltage 4.25V to 0.05C0 cutoff current, then discharge the battery at 1.0C0 constant current, repeat the charge and discharge at 0.5C0 / 1C0 until the capacity retention rate reaches 80%, then record the cycle number.

[0158] The room temperature cycle performance, 45℃ high temperature cycle performance and 35℃ fast charging cycle performance of the batteries in the above examples and comparative examples are as follows in Table 2.

[0159] Table 2

[0160] As can be seen from Table 2, the cycle life at room temperature of the battery of the negative electrode sheet of Example 1 to Example 13 can reach more than 1300 times, such as the cycle life at room temperature of the battery of Example 5 can reach 1900 times, the cycle life at 45℃ of the battery can reach more than 830 times, such as the cycle life at 45℃ of the battery of Example 5 can reach 1410 times, the cycle life of the battery at 35℃ fast charging can reach more than 700 times, such as the cycle life at 35℃ fast charging of the battery of Example 5 can reach 1100 times, the initial efficiency of the battery can reach more than 84%, such as the initial efficiency of the battery of Example 5 can reach 92%, and the energy density of the battery can reach more than 240 Wh / kg, such as the energy density of the battery of Example 4 can reach 320 Wh / kg.

[0161] In the negative electrode sheet of Comparative Example 1, the current collector surface only has one layer of active material, and the active material only includes silicon carbon, resulting in the initial efficiency of the battery being only 80%; in the negative electrode sheet of Comparative Example 2, the current collector surface only has one layer of active material, and the active material only includes silicon monoxide, resulting in poor cycle life of the battery; in the negative electrode sheet of Comparative Example 3, the current collector surface also only has one layer of active material, which limits the capacity and cycle life of the battery; in the negative electrode sheet of Comparative Example 4, the silicon monoxide is located inside the silicon carbon in the two layers of active material on the surface of the current collector, resulting in excessive stress on the negative electrode sheet, affecting the stability and cycle life of the negative electrode sheet of the battery; in the negative electrode sheet of Comparative Example 4, the particle size of the silicon carbon is too small, which limits the capacity and cycle life of the battery; in the negative electrode sheet of Comparative Example 4, the particle size of the silicon carbon is too large, resulting in poor cycle life.

[0162] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present disclosure, and not to limit them; although the present disclosure has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent replacements for some technical features therein; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. A negative electrode sheet, wherein, The negative electrode sheet comprises: a negative current collector (1); a first active layer (2) provided on at least one side surface of the negative current collector (1), the negative active material in the first active layer (2) comprising a first graphite and silicon-carbon; a second active layer (3) provided on the side of the first active layer (2) away from the negative current collector (1), the negative active material in the second active layer (3) comprising a second graphite and silicon monoxide; wherein the particle size of the silicon-carbon ranges from 4 to 7 μm.

2. The negative electrode sheet according to claim 1, wherein The silicon-carbon comprises a carbon matrix and silicon filled in the carbon matrix. The carbon matrix is porous hard carbon, and the average pore size of the carbon matrix ranges from 3 to 11 nm.

3. The negative electrode sheet according to claim 1, wherein The pore volume of the silicon-carbon ranges from 0.6 to 1.0 mL / g.

4. The negative electrode sheet according to claim 1, wherein The particle size of the first graphite ranges from 15 to 19 μm.

5. The negative electrode sheet according to claim 1, wherein The mass percentage of the silicon-carbon in the negative active material of the first active layer (2) ranges from 1% to 20%.

6. The negative electrode sheet according to claim 1, wherein The specific capacity of the silicon-carbon ranges from 1300 to 2000 mAh / g.

7. The negative electrode sheet according to claim 1, wherein The particle size of the second graphite ranges from 11 to 15 μm, and the particle size of the silicon monoxide ranges from 9 to 12 μm.

8. The negative electrode sheet according to claim 1, wherein The mass percentage of the silicon monoxide in the negative active material of the second active layer (3) ranges from 1% to 20%.

9. The negative electrode sheet according to claim 1, wherein The ratio of the number of silicon atoms to the number of oxygen atoms in the silicon monoxide ranges from (2:1) to (1.1:1).

10. The negative electrode sheet according to claim 1, wherein The thickness ratio of the first active layer (2) to the second active layer (3) ranges from (1:2) to (2:1).

11. A core, wherein, The battery comprises the negative electrode sheet according to any one of claims 1 to 10.

12. The pole core of claim 11, wherein, The battery comprises the negative electrode sheet according to any one of claims 1 to 10.

13. A battery, wherein, The battery comprises the negative electrode sheet according to any one of claims 1 to 10.

14. An electrical device, comprising: The battery comprises the negative electrode sheet according to any one of claims 1 to 10.

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