Negative electrode sheets, lithium-ion batteries, and electrical equipment

Abstract

The present application discloses a negative electrode sheet, a lithium-ion battery, and an electrical device. The negative electrode sheet includes a negative electrode current collector layer arranged in sequence; a first negative electrode active material layer, including silicon carbon, a first graphite, and a first hard carbon; a second negative electrode active material layer, including a second graphite and a second hard carbon; the median particle size of the first graphite is 12 to 15 μm, and the median particle size of the second graphite is 3 to 10 μm. The bottom hard carbon is fully combined with the silicon carbon, which can suppress the volume expansion problem of silicon carbon and improve the overall compaction and low-temperature performance; the surface hard carbon is combined with the fast-charging graphite, and the large interlayer spacing and isotropic structure of the hard carbon can effectively shorten the lithium ion transmission path, improve the surface dynamics, and improve the problem of lithium deposition in the corners of the battery cell. Through the combination of the first and second negative electrode active material layers, while ensuring that the high energy density of the silicon carbon material is fully utilized, the corner lithium deposition caused by insufficient dynamics is significantly improved, and the rebound expansion problem of the battery cell under the high silicon system can be significantly suppressed.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to negative electrode sheets, lithium-ion batteries, and electrical equipment. Background Art

[0002] While lithium-ion batteries are widely used, they are also subject to increasingly high consumer demands, such as high energy density, fast charging speed, and long battery life. As the market's demand for energy density continues to rise, silicon-carbon anode materials with high gram capacity are gaining popularity and becoming the mainstream development trend. However, silicon-carbon batteries also suffer from the disadvantages of large volume expansion, poor low-temperature performance, and severe lithium deposition in corners. Therefore, suppressing the expansion of silicon-carbon materials during cycling has become a top priority.

[0003] The current mainstream method usually uses a double-layer coating technology, which mixes silicon-carbon materials with high-ED graphite and coats them on the bottom layer, and then coats the surface with fast-charging graphite materials. This method can, to a certain extent, suppress the expansion problem of silicon-carbon while ensuring the fast-charging performance of the battery system. However, research has found that this also inevitably leads to serious lithium deposition in the corners. Therefore, it is necessary to improve the problem of lithium deposition in the corners of the battery cells while improving the energy density and fast charging of the battery cells. Summary of the Invention

[0004] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application proposes a negative electrode sheet and an electrical device.

[0005] In a first aspect of the present application, a negative electrode sheet is provided, the negative electrode sheet comprising:

[0006] negative electrode current collector layer;

[0007] a first negative electrode active material layer, wherein the first negative electrode active material in the first negative electrode active material layer includes silicon carbon, first graphite and first hard carbon;

[0008] a second negative electrode active material layer, wherein the second negative electrode active material in the second negative electrode active material layer includes a second graphite and a second hard carbon;

[0009] Among them, the median particle size D of the first graphite 1 50 is 12μm~15μm, the median particle size D of the second graphite 3 50 is 3μm~10μm.

[0010] The negative electrode sheet according to the first aspect of the present application has the following beneficial effects:

[0011] The negative electrode sheet of the present application forms two active material layers on the negative electrode current collector. The composition of the first negative electrode active material layer at the bottom layer close to the negative electrode current collector includes silicon carbon, a first graphite with high ED and a first hard carbon, and the composition of the second negative electrode active material layer on the surface includes a second graphite with good fast charging performance and a second hard carbon. The bottom hard carbon is fully combined with silicon carbon, which can significantly suppress the volume expansion problem of silicon carbon and improve the overall compaction and low-temperature performance; the surface hard carbon is combined with the fast-charging graphite, and the large interlayer spacing and isotropic structure of the hard carbon can effectively shorten the lithium ion transmission path, improve the surface dynamics, and improve the problem of lithium deposition in the corners of the battery cell. Therefore, through the combination of the above-mentioned first negative electrode active material layer and the second negative electrode active material layer, while ensuring that the high energy density of the silicon-carbon material is fully utilized, the lithium deposition in the corners caused by insufficient dynamics is significantly improved. More importantly, it can significantly suppress the rebound expansion problem of the battery cell under the high silicon system. Specifically:

[0012] (1) The interlayer spacing of hard carbon (e.g., 0.380 nm) is larger than that of graphite (e.g., 0.335 nm), which is conducive to the rapid insertion and removal of lithium ions. At the same time, hard carbon has an isotropic structure, and lithium ions can be inserted from all directions at the same time, which is conducive to accelerating the efficiency of lithium insertion. Therefore, the surface mixed with hard carbon can make up for the defect of the long migration distance of lithium ions in the double-layer coating surface and improve the kinetics.

[0013] (2) Silicon carbon has a high gram capacity and is usually mixed with graphite. However, the volume expansion effect of silicon carbon itself makes the battery cell prone to failure during cycling. Hard carbon materials have more voids and a larger specific surface area. Mixing with silicon carbon can provide more space for stress release, thereby suppressing its cyclic expansion problem. At the same time, the voids in hard carbon can effectively store electrolyte, which is beneficial to improving the battery cell's liquid retention capacity under high-pressure and dense systems.

[0014] (3) The hard carbon itself has a low compaction. By introducing high-compacted graphite into the bottom layer and regulating the content and median particle size ratio of the bottom layer graphite to hard carbon, it is possible to ensure the compaction of the bottom layer without losing energy density while allowing the bottom layer to exert the high dynamic performance of hard carbon and improve the overall charging capacity of the battery cell.

[0015] In some embodiments of the present application, the mass ratio w2 of the first hard carbon in the first negative electrode active material is 2.5-10%, for example, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0016] In some embodiments of the present application, the mass ratio w4 of the second hard carbon in the second negative electrode active material is 2.5-7.5%, for example, it can be 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, or 7.5%.

[0017] In some embodiments of the present application, the mass ratio w1 of the first graphite in the first negative electrode active material is 70-92.5%, for example, it can be 70%, 72%, 74%, 75%, 76%, 78%, 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, or 92.5%.

[0018] In some embodiments of the present application, the mass ratio w5 of silicon and carbon in the first negative electrode active material is 5-20%, for example, it can be 5%, 6%, 8%, 10%, 12%, 14%, 15%, 16%, 18%, or 20%.

[0019] In some embodiments of the present application, the mass ratio w3 of the second graphite in the second negative electrode active material is 92.5-97.5%, for example, it can be 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, or 97.5%.

[0020] In some embodiments of the present application, the median particle size D of the first hard carbon is 2 50 is 3 μm to 5 μm, for example, 3 μm, 4 μm, and 5 μm.

[0021] In some embodiments of the present application, the median particle size D of silicon carbon is 5 50 is 6 μm to 10 μm, for example, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm.

[0022] In some embodiments of the present application, the median particle size D of the second hard carbon is 4 50 is 3 μm to 5 μm, for example, 3 μm, 4 μm, and 5 μm.

[0023] In some embodiments of the present application, the first negative electrode active material layer satisfies 0.56≤(D 1 50×w1+D 2 50×w2) / (D 1 50+D 2 50)≤0.71.

[0024] In some embodiments of the present application, the second negative electrode active material layer satisfies 0.44≤(D 3 50×w3+D 4 50×w4) / (D 3 50+D 4 50)≤0.7.

[0025] In some embodiments of the present application, the second negative electrode active material layer and the first negative electrode active material layer satisfy 0.06≤(D 4 50×w4+D 550×w5) / (D 5 50+D 4 50) ≤ 0.22. The hard carbon content in the second negative electrode active material layer is similarly related to the silicon-carbon content in the first negative electrode active material layer. A higher silicon-carbon content increases the hard carbon content in the first negative electrode active material layer to suppress its expansion. However, to maintain the battery cell's chargeability, the hard carbon content in the second negative electrode active material layer must be reduced. When this relationship is met, both good chargeability and low expansion can be achieved.

[0026] By controlling the median particle size and mass ratio of the different active materials in the first and second negative electrode active material layers, the resulting negative electrode sheets achieve both high gram capacity and excellent kinetic performance, significantly improving the problem of lithium deposition in the cell corners. Most importantly, breakthrough progress has been made in addressing the issue of cyclic expansion in silicon-based batteries.

[0027] In some embodiments of the present application, the mass ratio of the first negative electrode active material layer to the second negative electrode active material layer is 9:1 to 1:9, for example, it can be 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, or 1:9.

[0028] In some embodiments of the present application, the specific surface area S of the first hard carbon and the specific surface area S of the second hard carbon are independently 6 to 15 m 2 / g, for example, it can be 6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g、10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g、15m 2 / g. Generally speaking, the smaller the particle size, the larger the specific surface area, which can effectively release the stress caused by silicon expansion.

[0029] In some embodiments of the present application, the raw materials of the first negative electrode active material layer and / or the second negative electrode active material layer further include at least one of a conductive agent and a binder. The conductive agent includes but is not limited to conductive graphite (such as KS-6, KS-15, SFG-6, SFG-15, SO, etc.), conductive carbon black (such as Super P, Super S, 350G, acetylene black, Ketjen black, etc.), conductive carbon fiber (such as VGCF, CNT) and graphene, etc. The binder includes but is not limited to at least one of polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, polyvinyl alcohol, polyvinyl butyral, etc.

[0030] In some embodiments of the present application, the first (second) negative electrode active material layer includes 70-99 wt % of the first (second) negative electrode active material, 0.5-6 wt % of a conductive agent, and 0.5-20 wt % of a binder.

[0031] In some embodiments of the present application, when the first (second) negative electrode active material, conductive agent and binder are made into a negative electrode sheet, the first negative electrode active material, conductive agent and binder are dispersed in a solvent and then coated on the negative electrode collector, dried, and then the second negative electrode active material, conductive agent and binder are dispersed in a solvent and then continued to be coated and dried to obtain a negative electrode sheet.

[0032] The present invention also provides a method for preparing a negative electrode sheet, which comprises the following steps:

[0033] Coating a slurry of a first negative electrode active material on a current collector to form a semi-finished negative electrode sheet;

[0034] The slurry of the second negative electrode active material is further coated on the semi-finished negative electrode sheet to form a finished negative electrode sheet.

[0035] In a second aspect of the present application, a lithium-ion battery is provided. The lithium-ion battery includes the aforementioned negative electrode sheet.

[0036] In some embodiments of the present application, a lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The positive electrode sheet, the negative electrode sheet, and the separator are wound together to form a battery cell and a lithium-ion battery.

[0037] In some embodiments, the positive electrode sheet includes a positive electrode current collector layer and a positive electrode active material layer.

[0038] In some embodiments, the positive electrode current collector layer and the negative electrode current collector layer are independently selected from at least one metal material including metal foil (such as aluminum foil, silver foil, tin foil, iron foil, titanium foil, nickel foil, copper foil or alloy foil of the above metals), metal mesh (such as aluminum mesh, silver mesh, tin mesh, iron mesh, titanium mesh, nickel mesh, copper mesh or alloy mesh of the above metals).

[0039] In some embodiments, the positive electrode current collector layer is aluminum foil, and the negative electrode current collector layer is copper foil.

[0040] In some embodiments, the positive electrode active material layer includes a positive electrode active material, which is at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium nickel manganese aluminum oxide.

[0041] In some embodiments, the raw materials of the positive electrode active material layer further include at least one of a conductive agent and a binder. The conductive agent includes, but is not limited to, conductive graphite (such as KS-6, KS-15, SFG-6, SFG-15, SO, etc.), conductive carbon black (such as Super P, Super S, 350G, acetylene black, Ketjen black, etc.), conductive carbon fiber (such as VGCF, CNT), and graphene. The binder includes, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, polyvinyl alcohol, and polyvinyl butyral.

[0042] In some embodiments, the positive electrode active material layer includes 70 to 99 wt % of a positive electrode active material, 0.5 to 6 wt % of a conductive agent, and 0.5 to 20 wt % of a binder.

[0043] In some embodiments, the electrolyte may be at least one of a solid electrolyte or an electrolyte solution.

[0044] In some embodiments, the electrolyte includes an electrolyte salt and an organic solvent, wherein the specific types and compositions of the electrolyte salt and the organic solvent are not subject to specific restrictions, and include positive electrode film-forming additives, negative electrode film-forming additives, and cycle-improving and low-temperature additives, etc.

[0045] In some embodiments, the separator includes, but is not limited to, one or more polymers selected from polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), etc. In some embodiments, the separator further includes a coating (such as ceramic) covering the polymer material.

[0046] In a fourth aspect of the present application, an electrical device is provided, which includes the aforementioned lithium-ion battery.

[0047] Electric equipment refers to any device that can utilize electrical energy and convert it into one or more other forms of energy, such as mechanical energy, thermal energy, light energy, etc., such as electric motors, electric heat generators, electric light sources, etc. This includes mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Mobile devices can be mobile phones, laptops, drones, robot vacuums, electronic cigarettes, etc.; electric vehicles can be pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.

[0048] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the concept and technical effects of this application in conjunction with the embodiments to fully understand the purpose, features and effects of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments of this application, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of this application.

[0050] The embodiments of the present application are described in detail below. The described embodiments are exemplary and are only used to explain the present application, and should not be understood as limiting the present application.

[0051] In the description of this application, "several" means more than one, "plurality" means more than two, "greater than," "less than," and "exceed" are understood to exclude the number itself, while "above," "below," and "within" are understood to include the number itself. "About" means within the range of ±20%, 10%, 8%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.2%, 0.1%, etc. of the number itself. The terms "first" and "second" are used solely to distinguish technical features and are not to be construed as indicating or implying relative importance, or as implicitly indicating the quantity of the indicated technical features, or as implicitly indicating the order of the indicated technical features.

[0052] In the description of this application, reference to the terms "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of this application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples.

[0053] The present application is described below with reference to specific embodiments.

[0054] Examples 1 to 17

[0055] Examples 1 to 17 provide a lithium-ion battery, the composition and preparation of each part of which are as follows:

[0056] (1) Positive electrode

[0057] The active material LiCoO2, conductive agent superconducting carbon (Super P), conductive agent carbon nanotubes, and binder polyvinylidene fluoride (PVDF) are fully dispersed and evenly coated on the aluminum foil current collector in an N-methylpyrrolidone solvent system in a mass ratio of 97.6:0.6:0.5:1.3, and then cold-pressed and stripped to obtain the positive electrode sheet.

[0058] (2) Negative electrode

[0059] The negative electrode active material, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and carbon black conductive agent are mixed in a mass ratio of 97.8:0.6:0.6:1 in the slurry of the first negative electrode active material and the slurry of the second negative electrode active material, and mixed with deionized water to form the negative electrode slurry. The two slurries are sequentially coated on the corresponding primer copper foil current collector through a double-layer coating process, dried, and then cold-pressed and stripped to obtain the negative electrode sheet.

[0060] (3) Diaphragm

[0061] A ceramic mixture is coated on the surface of the PE film as a diaphragm.

[0062] (4) Electrolyte

[0063] Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) are mixed in a volume ratio of 1:1:4:4, and then the fully dried lithium salt LiPF6 is dissolved in a mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte.

[0064] (5) Full battery preparation

[0065] The above-mentioned positive electrode sheet, separator, and negative electrode sheet are made into a bare battery cell, which is then encapsulated and injected with electrolyte to produce a finished lithium-ion battery.

[0066] The compositions of the first negative electrode active material and the second negative electrode active material in the first negative electrode active material layer and the second negative electrode active material layer are shown in the following table:

[0067] Table 1. Negative electrode composition

[0068]

[0069]

[0070] In addition, Comparative Examples 1 to 9 were set with reference to the above-mentioned Examples 1 to 17.

[0071] The performance of the negative electrode sheets and lithium batteries of the embodiments and comparative examples were tested by the following methods:

[0072] (1) Negative electrode sheet half-charge rebound compaction: disassemble the battery cell after capacity division, take the negative electrode sheet and use a micrometer to measure the thickness. The obtained electrode sheet thickness and current collector thickness are calculated by double-sided coating surface density / (electrode sheet thickness-foil thickness), and the unit is g / cm 3 The greater the rebound compaction, the smaller the rebound thickness of the negative electrode sheet, and the less energy density the battery cell loses.

[0073] (2) Energy density: calculated according to the following formula: discharge capacity per cell / (cell width × cell thickness × cell length), unit: Wh / L.

[0074] (3) Cycle retention rate: The battery cell is charged to 4.1V at 2.5C, 4.2V at 2C, 4.3V at 1.5C, and 4.53V at 1C. After 500 cycles, the remaining capacity is the percentage of the initial capacity.

[0075] (4) Cyclic expansion rate: The cell is charged at a rate of 2.5C to 4.1V, a rate of 2C to 4.2V, a rate of 1.5C to 4.3V, and a rate of 1C to 4.53V. The difference between the thickness of the cell after 500 cycles and the initial half-charge thickness (i.e., the thickness of the cell at half-charge voltage of 3.9V) is the percentage of the initial half-charge thickness.

[0076] (5) Rate discharge: Fully charge the cell to 4.53V, and then discharge it at 0.2C to 3.0V to obtain the initial capacity. After fully charging the cell, discharge it at 2.5C to 3.0V to obtain the percentage of the initial capacity of the cell.

[0077] (6) Corner lithium deposition interface: obtained by disassembling the battery cell after 500 cycles.

[0078] The results are shown in Table 2:

[0079] Table 2. Performance test results of examples and comparative examples

[0080]

[0081] Comparing Example 1 and Comparative Examples 1 to 3, compared to the case where no hard carbon is added to the first negative electrode active material layer and the second negative electrode active material layer, after adding hard carbon to the first negative electrode active material layer or the second negative electrode active material layer, the negative electrode sheet half-electric rebound compaction, the battery's energy density, room temperature cycle retention rate, and 2.5C rate discharge all showed significant improvements, the expansion rate after 500 cycles at room temperature decreased significantly, and the lithium precipitation situation improved significantly. However, when a certain amount of hard carbon is added to the first negative electrode active material layer and the second negative electrode active material layer at the same time, the improvement in the negative electrode sheet half-electric rebound compaction, the battery's energy density, room temperature cycle retention rate, and 2.5C rate discharge is much greater than the improvement brought by the addition of either alone and the sum of the increases brought by the two. The same is true for the decrease in the expansion rate after 500 cycles at room temperature. The improvement in the lithium precipitation situation is even more obvious. The improvement in the lithium precipitation situation is not obvious when added alone. Only when it is added to the first negative electrode active material layer and the second negative electrode active material layer at the same time can it be significantly improved.

[0082] Comparing Example 1 and Comparative Example 2, after adding hard carbon to the first negative electrode active material layer, the half-electric rebound compaction of the negative electrode sheet, the energy density of the battery, the room temperature cycle retention rate, and the 2.5C rate discharge are greatly improved. The expansion rate after 500 cycles of room temperature cycling has dropped significantly, and the lithium plating situation has improved significantly.

[0083] Comparing Example 1 with Comparative Examples 4 to 5, when the median particle size of the graphite in the first active material layer is too small or too large, (D 1 50×w1+D 2 50×w2) / (D 1 50+D 2 50) is not within the range of 0.56 to 0.71, the energy density and room temperature cycle retention rate of the battery are reduced to varying degrees, and the lithium plating situation is worsened.

[0084] Comparing Example 1 with Comparative Examples 6 to 7, when the median particle size of the graphite in the first active material layer is too small or too large, that is, (D 3 50×w3+D 4 50×w4) / (D 3 50+D 4 50) is not within the range of 0.44 to 0.7, the energy density and room temperature cycle retention rate of the battery are reduced to varying degrees, and the lithium plating situation is worsened.

[0085] Comparing Example 1 with Comparative Examples 8 to 9, when the silicon carbon content in the first active material layer is too little or too much, that is, (D 4 50×w4+D 5 50×w5) / (D 5 50+D 4 50) is not between 0.06 and 0.22 or (D1 50×w1+D 2 50×w2) / (D 1 50+D 2 50) is not within the range of 0.56 to 0.71, the battery's energy density, room temperature cycle retention rate, and lithium plating at the negative electrode corner are all affected to varying degrees.

[0086] Comparing Examples 1 to 3, with the increase of the hard carbon content in the first negative electrode active material layer, the half-charge rebound compaction and 2.5C rate discharge of the negative electrode sheet gradually increased, and the energy density and room temperature cycle of the battery first increased and then decreased. This was mainly due to the loss of capacity caused by the addition of hard carbon, while the expansion rate of 500 cycles at room temperature gradually decreased, and the lithium plating situation gradually improved.

[0087] Comparing Examples 1, 4, and 5, increasing the hard carbon content in the second negative electrode active material layer shows that the negative electrode sheet half-charge rebound compaction, battery energy density, and room temperature cycle retention first increase and then decrease. Expansion after 500 cycles of room temperature cycling first decreases and then increases, 2.5C rate discharge gradually increases, and lithium deposition performance also gradually improves. The 5% hard carbon content in Example 1 is optimal.

[0088] Comparing Examples 1, 6, and 7, as the silicon-carbon content in the first negative electrode active material layer increases, the half-charge rebound compaction of the negative electrode sheet gradually decreases, the energy density of the battery first increases and then decreases, the room temperature cycle retention rate gradually decreases, the expansion rate after 500 cycles of room temperature cycling gradually increases, the 2.5C rate discharge gradually decreases, and the lithium plating situation gradually deteriorates.

[0089] Comparing Examples 1, 8, and 9, as the median particle size of silicon carbon in the first negative electrode active material layer gradually increases, the half-electric rebound compaction of the negative electrode sheet gradually decreases, the energy density and room temperature cycle retention of the battery first increase and then decrease, the expansion of 500 cycles of room temperature cycle first decreases and then increases, and the 2.5C rate discharge gradually decreases.

[0090] Comparing Examples 1, 10, and 11, as the median particle size of graphite in the first negative electrode active material layer gradually increases, the half-electric rebound compaction of the negative electrode sheet gradually decreases, the energy density and room temperature cycle retention of the battery first increase and then decrease, the expansion of 500 cycles of room temperature cycle first decreases and then increases, the 2.5C rate discharge gradually decreases, and the lithium plating situation gradually improves.

[0091] Comparing Examples 1, 12, and 13, as the median particle size of the hard carbon in the first negative electrode active material layer gradually increases, the half-electric rebound compaction of the negative electrode sheet, the energy density of the battery, and the room temperature cycle retention first increase and then decrease, the expansion of the room temperature cycle for 500 weeks first decreases and then increases, the 2.5C rate discharge gradually decreases, and the lithium plating situation gradually improves.

[0092] Comparing Examples 1, 14, and 15, as the median particle size of graphite in the second negative electrode active material layer gradually increases, the half-electric rebound compaction of the negative electrode sheet, the energy density of the battery, the room temperature cycle retention rate, and the 2.5C rate discharge first increase and then decrease, and the expansion after 500 cycles of room temperature cycling first decreases and then increases, and the lithium deposition situation is good.

[0093] Comparing Examples 1, 16, and 17, as the median particle size of the hard carbon in the second negative electrode active material layer gradually increases, the half-electric rebound compaction of the negative electrode sheet gradually decreases, the energy density and room temperature cycle retention of the battery first increase and then decrease, the expansion rate of 500 cycles of room temperature cycling gradually increases, the 2.5C rate discharge gradually decreases, and the lithium plating situation deteriorates.

[0094] Based on the above results, when the first active material layer of the prepared negative electrode sheet meets the following requirements: 0.56≤(D 1 50×w1+D 2 50×w2) / (D 1 50+D 2 50)≤0.71; the second active material layer satisfies: 0.44≤(D 3 50×w3+D 4 50×w4) / (D 3 50+D 4 50)≤0.7; and at the same time: 0.06≤(D 4 50×w4+D 5 50×w5) / (D 5 50+D 4 50)≤0.22, the prepared battery cell has the best energy density, cycle retention rate, cycle expansion rate and lithium deposition interface.

[0095] The present application has been described in detail above with reference to the embodiments. However, the present application is not limited to the above embodiments. Various modifications can be made within the scope of knowledge possessed by a person of ordinary skill in the art without departing from the purpose of the present application. In addition, the embodiments of the present application and the features of the embodiments can be combined with each other unless there is a conflict.

Claims

1. A negative electrode sheet, characterized in that: The negative electrode sheet includes: negative electrode current collector layer; The first negative electrode active material layer includes a first negative electrode active material comprising silicon carbon, a first graphite and a first hard carbon, and the median particle size D of the first graphite is 1 50 is 13 μm; The second negative electrode active material layer includes a second negative electrode active material including a second graphite and a second hard carbon, and the median particle size D of the second graphite is 3 50 is 6 μm~10 μm; The mass ratio w2 of the first hard carbon in the first negative electrode active material is 7.5-10%, the mass ratio w5 of the silicon carbon in the first negative electrode active material is 5-10%, and the mass ratio w1 of the first graphite in the first negative electrode active material is 80-87.5%. The mass ratio w4 of the second hard carbon in the second negative electrode active material is 5-7.5%; The mass ratio w3 of the second graphite in the second negative electrode active material is 92.5-95%; The median particle size D of the first hard carbon 2 50 is 3 μm~5 μm; the median particle size D of the silicon carbon 5 50 is 6 μm~10 μm; the median particle size D of the second hard carbon 4 50 is 3 μm~4 μm; The first negative electrode active material layer satisfies 0.56≤(D 1 50×w1+D 2 50×w2) / (D 1 50+D 2 50)≤0.71; The second negative electrode active material layer satisfies 0.44≤(D 3 50×w3+ D 4 50×w4) / (D 3 50+D 4 50)≤0.7; The second negative electrode active material layer and the first negative electrode active material layer satisfy 0.06≤(D 4 50×w4+ D 5 50×w5) / (D 5 50+D 4 50)≤0.

22.

2. The negative electrode sheet according to claim 1, characterized in that: The mass ratio of the first negative electrode active material layer to the second negative electrode active material layer is 9:1 to 1:

9.

3. The negative electrode sheet according to claim 1, characterized in that: The specific surface area of ​​the first hard carbon and the specific surface area of ​​the second hard carbon are independently 6 to 15 m 2 / g.

4. A lithium-ion battery, characterized in that The negative electrode sheet comprises the negative electrode sheet according to any one of claims 1 to 3.

5. Electrical equipment, characterized in that: The negative electrode sheet according to any one of claims 1 to 3, or the lithium-ion battery according to claim 4.

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