Negative electrode material and secondary battery

Abstract

The invention discloses a negative pole piece and a secondary battery, and belongs to the technical field of electrochemical energy storage, and the negative pole piece is characterized in that solid electrolyte particles with a specific edge coefficient are introduced into a negative pole material substance layer containing silicon-based material particles, and meanwhile, the particle size ratio of the two particles is regulated and controlled; the volume expansion effect of the silicon-based material can be effectively relieved, meanwhile, the ion conduction resistance of the pole piece is reduced, the expansion rate of the pole piece in the circulation process is low, and the corresponding secondary battery can have both long cycle life and excellent low-temperature performance.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, specifically to negative electrode sheets and secondary batteries. Background Technology

[0002] Silicon-based materials have significant advantages in energy density and theoretical capacity when used as negative electrode materials for battery cells. However, their volume expansion rate during lithium insertion / extraction is as high as 300%, resulting in high expansion rate, poor stability, and short cycle life of the electrode during cycling. On the other hand, the ion transport resistance of the electrode is high at low temperatures, and the conductivity of traditional silicon-based negative electrodes is already low. Coupled with the volume expansion effect, the electrochemical performance of secondary batteries deteriorates severely at low temperatures, especially at high rates. Summary of the Invention

[0003] The purpose of this application is to overcome the shortcomings of the existing technology and provide a negative electrode sheet. By introducing solid electrolyte particles with a specific angular coefficient into the negative electrode material layer containing silicon-based material particles, and controlling the particle size ratio of the two types of particles, the volume expansion effect of silicon-based materials can be effectively alleviated, and the ion conduction resistance of the electrode sheet can be reduced. The electrode sheet has a low expansion rate during cycling, and the corresponding secondary battery can take into account both long cycle life and excellent low-temperature performance.

[0004] To achieve the above objectives, in a first aspect of this application, a negative electrode sheet is provided, comprising a negative electrode material layer, wherein the negative electrode material layer comprises a silicon-based material and a solid electrolyte; The solid electrolyte has an edge factor greater than or equal to 1 and less than or equal to 1.5; The negative electrode plate satisfies: 0.01≤D1 / D2≤0.5; Where D1 is the average particle size of the solid electrolyte and D2 is the average particle size of the silicon-based material.

[0005] In some implementations, 0.08μm≤D1≤4μm.

[0006] In some implementations, the 5μm≤D2≤12μm.

[0007] In some embodiments, the negative electrode sheet satisfies: 0.6≤K≤1.8, where K is the ratio of the angularity coefficient of the solid electrolyte to that of the silicon-based material.

[0008] In some embodiments, the negative electrode sheet satisfies: 0.5% ≤ 100% × M1 / ​​(M1 + M2) ≤ 20%, where M1 is the mass of the solid electrolyte and M2 is the mass of the silicon-based material.

[0009] In some embodiments, the silicon-based material includes at least one of elemental silicon, silicon oxide, and silicon-carbon composite materials.

[0010] In some embodiments, the solid electrolyte includes at least one of lithium lanthanum zirconium tantalum oxide (LLZTO), LATP (lithium aluminum titanium phosphate), LLZO (lithium lanthanum zirconium oxide), alumina, lithium lanthanum titanium oxide (LLTO), and lithium germanium phosphorus sulfide (LGPS).

[0011] In a second aspect, this application provides a secondary battery, including the negative electrode sheet described in this application.

[0012] In some embodiments, the secondary battery satisfies: 50 ≤ A / K ≤ 278, where AN / m is the peel strength of the negative electrode in the secondary battery.

[0013] In some implementations, 30 N / m ≤ A ≤ 500 N / m.

[0014] The beneficial effects of this application are as follows: This application provides a negative electrode sheet. By introducing solid electrolyte particles with a specific angular coefficient into a negative electrode material layer containing silicon-based material particles, and simultaneously controlling the particle size ratio of the two types of particles, it can not only effectively alleviate the volume expansion effect of silicon-based materials, but also reduce the ion conduction resistance of the electrode sheet. The electrode sheet has a low expansion rate during cycling, and the corresponding secondary battery can achieve both long cycle life and excellent low-temperature performance. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0016] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0017] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0018] The present application is further illustrated below with specific embodiments: A negative electrode sheet includes a negative electrode material layer, wherein the negative electrode material layer includes a silicon-based material and a solid electrolyte; The solid electrolyte has an edge factor greater than or equal to 1 and less than or equal to 1.5; The negative electrode plate satisfies: 0.01≤D1 / D2≤0.5; Where D1 is the average particle size of the solid electrolyte and D2 is the average particle size of the silicon-based material.

[0019] To overcome the problems of poor cycle performance and low-temperature performance (especially at high rates) of existing silicon-based negative electrode sheets due to low conductivity and severe volume expansion, this application's technical solution introduces a solid electrolyte component in addition to silicon as the active material in the negative electrode material layer. This component not only has high ionic conductivity, effectively improving the ion conduction efficiency of the entire negative electrode material layer, but also, by controlling the particle size of both types of particles, allows the solid electrolyte particles to precisely fill the voids in the silicon particles. This physically confines and suppresses the volume expansion of the silicon material, providing abundant transport channels for ion conduction. It also avoids electrolyte retention during wetting due to excessively large inter-particle voids, or excessive agglomeration of small solid electrolyte or silicon particles affecting lithium-ion transport efficiency. This approach simultaneously improves the cycle performance and low-temperature performance of the corresponding secondary battery. While solid electrolytes offer high dimensional stability and structural stability, the angularity coefficient needs to be controlled during their introduction. Excessive angularity increases surface roughness, leading to more irregular dead angles between particles. This can cause stress concentration points after the negative electrode material layer is formed, resulting in poor surface density uniformity of the electrode and reduced ion conductivity. Furthermore, it may puncture the binder film during cycling, weakening the binding effect of the binder in the negative electrode material layer and reducing the binding effect on the volume expansion of the silicon-based material. Conversely, excessively low angularity results in a smooth surface, making it difficult to effectively fill and fix the irregular gaps within the particles when combined with silicon-based materials. This leads to poor particle stacking and even particle agglomeration, reducing lithium-ion transport channels, further decreasing ion conduction speed, decreasing structural stability, and resulting in poor low-temperature performance, especially low-temperature rate performance.

[0020] When the negative electrode sheet is made of silicon-based material and solid electrolyte, and the angularity coefficient of the solid electrolyte and the particle size ratio of the two particles are controlled, the cycle performance and low-temperature performance of the negative electrode sheet when applied to secondary batteries can be effectively balanced, and both can be effectively improved.

[0021] In some embodiments, the angularity factor of the solid electrolyte can be a range of one or both of 1, 1.1, 1.2, 1.3, 1.4, and 1.5.

[0022] It should be noted that the angularity factor of the solid electrolyte described in this application can be confirmed by, but is not limited to, the following methods: Carefully scrape the composite powder from the surface of the negative electrode sheet and perform gold sputtering on the powder (ensuring the sample remains dry). Under a high-resolution scanning electron microscope (SEM) at 100 kx, locate and capture clear images of structurally complete solid electrolyte particles (solid electrolytes are typically brighter and can also aid in EDS analysis). Import the SEM images into ImageJ image processing software and measure the actual perimeter (P0.05) of each solid electrolyte particle. 实际 Given the 2D area (A) of the image and the particle area, we fit and calculate the circumference of the equivalent circle with the same area: , Then the angle coefficient = P 实际 / P 等效圆 The average value of the calculation results of 20 samples is calculated and rounded to one decimal place to obtain the angularity coefficient of the solid electrolyte.

[0023] In some implementations, D1 / D2 can be a range of one or both of the following: 0.01, 0.02, 0.05, 0.08, 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, and 0.5.

[0024] More preferably, 0.02≤D1 / D2≤0.4.

[0025] The average particle size ratio of silicon-based particles to solid electrolytes affects product performance. On the one hand, if the silicon-based material particles are too large and the solid electrolyte particles are too small, there will be large gaps between the particles after they are stacked. This is not only detrimental to the uniform wetting of the electrolyte, but also reduces the physical binding effect of the solid electrolyte on the volume expansion of the silicon-based particles, and may even lead to the agglomeration of small particles. On the other hand, if the silicon-based material particles are too small and the solid electrolyte particles are too large, the uniformity of the solid electrolyte particles in the negative electrode material layer will be poor. The binder in the material layer cannot effectively coat the solid electrolyte, and there may be a risk of separation at the interlayer interface. In addition, the gaps between the silicon-based particles cannot be fully filled, resulting in low ion conduction efficiency. When the ratio of the two is limited to the range of 0.01 to 0.5, and more preferably within the above range, the two particles have high packing density, good dispersion, good electrolyte wettability, better volume expansion suppression effect of silicon-based material in the negative electrode material layer, further improved ion conduction efficiency, lower expansion rate of electrode after cycling, corresponding to longer cycle life of secondary battery and better low temperature performance.

[0026] It should be noted that the average particle size of the silicon-based material and solid electrolyte described in this application can be confirmed by, but is not limited to, the following methods: The negative electrode material layer of the negative electrode sheet was scraped into powder, and the resulting powder was soaked and dispersed in N-methylpyrrolidone for 5 hours. The remaining material was filtered, washed with ethanol and water, dried, and dispersed to prepare a sample. The sample was observed under a scanning electron microscope (JEOL SM-74190UEC model) at a magnification of 100X~1000X. At the maximum magnification, elemental analysis was used to confirm the silicon-based material particles and solid electrolyte particles. Twenty silicon-based material particles and twenty solid electrolyte particles with intact morphology were screened respectively. The particle diameter was measured using measurement software, and the average value was calculated to obtain the average particle size of the silicon-based material particles and the average particle size of the solid electrolyte particles, respectively.

[0027] In some implementations, 0.08μm≤D1≤4μm.

[0028] In some implementations, D1 can be a range of one or any two of 0.08μm, 0.1μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, and 4μm.

[0029] In some implementations, the 5μm≤D2≤12μm.

[0030] In some implementations, D2 can be a range of one or any two of the following: 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, and 12μm.

[0031] In some embodiments, the negative electrode sheet satisfies: 0.6≤K≤1.8, where K is the ratio of the angularity coefficient of the solid electrolyte to that of the silicon-based material.

[0032] In some implementations, K can be a range of one or any two of 0.6, 0.7, 0.8, 1, 1.2, 1.4, 1.5, 1.6, and 1.8.

[0033] More preferably, the negative electrode sheet satisfies: 0.8 ≤ K ≤ 1.5 As mentioned above, the angularity coefficient of the solid electrolyte affects its filling effect between particles and the overall distribution uniformity. Therefore, it needs to be controlled within a specific range. Based on this, the angularity coefficient of the silicon-based material is further optimized so that when the ratio K of the angularity coefficients of the two is within the above-mentioned preferred range, better contact and particle stacking effect can be achieved between the two types of particles. At the same time, the binding effect with the anode material layer is better, which is more conducive to improving ion conduction efficiency and suppressing the volume expansion effect of silicon-based materials during cycling, resulting in better overall performance of the secondary battery.

[0034] In some embodiments, the angularity factor of the silicon-based material is greater than or equal to 1 and less than or equal to 1.5.

[0035] It should be noted that the angularity coefficient of the solid electrolyte described in this application can be controlled by process conditions such as sintering temperature and time during the preparation process, or by subsequent ball milling or crushing treatment. For silicon-based materials, the surface angularity of the particles can be controlled by methods such as air jet milling, which can drive the particles to collide and rub against each other, without significantly changing the particle size. The angularity coefficient can also be changed by coating the surface of the particles with a thin layer, such as carbon coating, so that the particle size remains basically unchanged. However, it is not limited to this. Those skilled in the art can also control the angularity coefficient of these two types of particles in other ways. At the same time, due to differences in actual conditions, if there are existing materials with different angularity coefficients, these existing materials can be used directly to prepare products to obtain final products with different angularity coefficients.

[0036] It should be noted that the test method for the angularity coefficient of the silicon-based material described in this application is the same as that for solid electrolytes, and will not be repeated here.

[0037] In some embodiments, the negative electrode sheet satisfies: 0.5% ≤ 100% × M1 / ​​(M1 + M2) ≤ 20%, where M1 is the mass of the solid electrolyte and M2 is the mass of the silicon-based material.

[0038] In some implementations, 100%×M1 / (M1+M2) can be a range of one or any two of the following: 0.5%, 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 15%, 18%, 20%.

[0039] More preferably, the negative electrode sheet satisfies: 1%≤100%×M1 / (M1+M2)≤10%.

[0040] In the negative electrode material layer, the solid electrolyte plays a role in both suppressing the volume expansion of the silicon-based material and improving the overall ion conduction efficiency of the material. Therefore, when the total mass ratio of the solid electrolyte to the silicon-based material changes, the application effect of the corresponding negative electrode sheet also varies. On the one hand, when its content is low, the improvement effect brought by the solid electrolyte is insufficient; the ion conduction efficiency and dimensional stability of the electrode sheet are low. On the other hand, since the solid electrolyte has strong rigidity, its introduction will reduce the overall flexibility of the electrode sheet. If too much is introduced, cracking may occur due to the inability to relieve the internal stress of the electrode sheet, which is also not conducive to improving the performance of the electrode sheet. When the solid electrolyte content of the negative electrode sheet is preferably within the above range, the improvement effect of the solid electrolyte and the flexibility of the negative electrode sheet can be balanced, further improving its performance.

[0041] It should be noted that, in the negative electrode sheet described in this application, M1 and M2 can be identified in, but is not limited to, the following ways: The negative electrode material layer of the negative electrode sheet is scraped into powder. XRD and elemental analysis tests are performed in advance to confirm the types of solid electrolyte and silicon-based materials contained in the negative electrode sheet. Then, in-situ EDS testing with scanning electron microscopy is used to confirm the specific element content of the solid electrolyte and silicon-based materials (such as lithium in the solid electrolyte and silicon in the silicon-based materials). M1 and M2 are obtained by calculation.

[0042] In some embodiments, the silicon-based material includes at least one of elemental silicon, silicon oxide, and silicon-carbon composite materials.

[0043] In some embodiments, the solid electrolyte includes at least one of lithium lanthanum zirconium tantalum oxide (LLZTO), LATP (lithium aluminum titanium phosphate), LLZO (lithium lanthanum zirconium oxide), alumina, lithium lanthanum titanium oxide (LLTO), and lithium germanium phosphorus sulfide (LGPS).

[0044] It should be noted that the silicon-based material and solid electrolyte described in this application can be commercially available products, self-made products, or products obtained by secondary modification of commercially available products. There are no specific limitations on this. For example, it is acceptable to purchase solid electrolytes with the same type of substance but different average particle sizes and different angularity coefficients, or to purchase silicon-based materials with the same type of substance but different average particle sizes and different angularity coefficients and combine them to meet the scope of this application. Alternatively, it is acceptable to purchase silicon-based materials with the same average particle size and angularity coefficient and coat them with a carbon coating layer on their surface to control the angularity coefficient while keeping the average particle size basically unchanged.

[0045] In some embodiments, the negative electrode material layer further includes a conductive agent and a binder.

[0046] In some embodiments, the negative electrode includes a current collector and a layer of negative electrode material.

[0047] In some embodiments, the mass ratio of the silicon-based material to the mixture of solid electrolyte, conductive agent, and binder is (80~85.5):(0.5~5):(5~10).

[0048] It should be noted that the conductive agent described in this application is used to provide conductivity, and any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity and does not significantly cause adverse chemical changes in the battery. For example, the conductive agent includes, but is not limited to, at least one of carbon nanotubes, carbon black, graphite, carbon fibers, activated carbon, mesoporous carbon, and fullerenes, wherein carbon fibers are, for example, carbon nanofibers; and carbon black is, for example, SP (Super P), acetylene black, Ketjen black, etc.

[0049] The binder is used to improve the adhesion between the active material and the conductive agent particles, and the adhesion between the negative electrode material layer and the current collector. Any binder can be used without particular limitation, as long as it has suitable adhesive properties and does not significantly cause adverse chemical changes in the battery. For example, the binder includes, but is not limited to, fluorinated polyolefin binders, including, but not limited to, polyvinylidene fluoride (PVDF), PVDF copolymers or their modified derivatives (e.g., modified with carboxylic acid, acrylic acid, acrylonitrile, etc.), styrene-butadiene rubber (SBR), carboxymethyl cellulose or its salts, etc.

[0050] In some embodiments, the compaction density of the negative electrode sheet is 0.8~1.5 g / cm³. 3 .

[0051] In some embodiments, the current collector includes at least one of metal, alloy, and conductive polymer, specifically a copper current collector, a copper alloy current collector, a conductive polymer current collector, or a composite structure of the above current collectors, etc., without any particular limitation.

[0052] In a second aspect, this application provides a secondary battery, including the negative electrode sheet described in this application.

[0053] In some embodiments, the secondary battery satisfies: 50 ≤ A / K ≤ 278, where AN / m is the peel strength of the negative electrode in the secondary battery.

[0054] In some implementations, A / K can be a range of one or both of the following: 50, 60, 80, 100, 120, 150, 180, 200, 220, 250, 270, 278.

[0055] More preferably, the secondary battery satisfies: 80≤A / K≤250.

[0056] The peel strength of the negative electrode is mainly related to the packing density of the active material particles on the electrode, the inter-particle connectivity, and the connection strength between the negative electrode material layer and the current collector. Lower peel strength indicates weaker inter-particle connectivity and a lower connection between the negative electrode material layer and the current collector. This may lead to detachment or interlayer separation during cycling due to the volume expansion effect of the silicon-based material, affecting electrode efficiency. Furthermore, a larger contact area with the electrolyte can easily cause more side reactions, increasing internal heat generation and further exacerbating electrode expansion. However, excessively high peel strength can lead to a denser packing density between particles. If the solidity is too high, the flexibility of the electrode is low, making it prone to cracking due to concentrated stress. Furthermore, the wetting effect of the electrolyte is reduced, and the ion transport channels are not fully utilized. Therefore, after limiting the relationship between the angularity coefficient and particle size ratio of the silicon-based material and the solid electrolyte, the angularity coefficient ratio of the two materials is further synergistically controlled with the peel strength of the negative electrode. The balance between the rigidity and flexibility of the electrode, the balance between electrolyte wettability and the degree of side reactions can be adjusted through the micro-aggregation between particles. This results in better stability of the electrode during cycling and a higher ion transport rate, which is more conducive to improving the cycle performance and low-temperature performance of the secondary battery.

[0057] In some implementations, 30 N / m ≤ A ≤ 500 N / m.

[0058] It should be noted that A described in this application can be confirmed by, but is not limited to, the following methods: After discharging the secondary battery, the negative electrode sheet is sampled: the electrode sheet to be tested is cut into strips with a width of W (20mm) and a length of 150mm using a cutter. Adhesive tape is used at one end of the sample (about 10-20mm along the length) to separate the active material coating of the negative electrode sheet from the foil to create an initial peeling area for clamping and initiating peeling. The peeling speed is set (200mm / min), and the test is started. The clamp on the equipment will move upward at a constant speed, peeling the coating off the foil. The effective peeling length H is recorded. The effective peeling length should usually be greater than 50mm. The effective peeling tensile force N is recorded. Then the peeling strength of the electrode sheet = N / H. 10 sets of data are repeated and the average value A is recorded.

[0059] In the scheme described in this application, the peel strength of the negative electrode sheet can be controlled by the type and content of the binder. For example, the binder can be PU, PAA, PVDF, etc., with different weights, and the content of the binder can be adjusted in the range of 0.1% to 15% to achieve the control of the peel strength. However, it is not limited to this. Those skilled in the art can also use other methods, such as changing the type of binder or using different electrode preparation methods, to make the peel strength of the negative electrode sheet different. No specific limitation is made here.

[0060] In some embodiments, the secondary battery further includes an electrolyte comprising a solvent and a lithium salt.

[0061] In some embodiments, the solvent includes at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, sulfone solvents, nitrile solvents, and phosphate ester solvents.

[0062] Exemplary examples include, but are not limited to, at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC); carboxylic acid ester solvents include, but are not limited to, at least one of ethyl acetate, methyl formate, and 1,4-butyrolactone; ether solvents include, at least one of dimethyltetrahydrofuran, tetrahydrofuran, and 1,2-dimethoxyethane; sulfone solvents include, at least one of methyl sulfone and dimethyl sulfoxide; nitrile solvents include, at least one of propionitrile, butyronitrile, 1-(2-cyanoethyl)pyrrole, and 1,3,6-hexanetrionitrile; and phosphate ester solvents include, at least one of trimethyl triphosphate and triethyl phosphate.

[0063] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium trifluoromethanesulfonate, lithium difluoromethanesulfonylimide, lithium ditrifluoromethanesulfonylimide, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0064] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.5~2 mol / L.

[0065] In some embodiments, the secondary battery further includes a separator located between the positive electrode and the negative electrode.

[0066] It should be noted that the separator can be any of the battery separator materials available in the art. For example, the separator may include, but is not limited to, at least one of polypropylene and polyethylene.

[0067] In some embodiments, the secondary battery further includes a positive electrode sheet, which includes a current collector and a positive active material layer, the positive active material layer including a positive electrode material.

[0068] In some embodiments, the cathode material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and lithium iron phosphate.

[0069] In some embodiments, the positive electrode active material layer further includes a binder and a conductive agent.

[0070] In some embodiments, the mass ratio of the positive electrode material, binder, and conductive agent is (70~90):(5~10):(5~10).

[0071] In some embodiments, the adhesive includes at least one selected from polyvinylidene fluoride, polyvinyl butyral, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, and polyvinyl alcohol.

[0072] In some embodiments, the conductive agent includes at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0073] The present invention is further illustrated below with specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention: Materials used: Solid electrolytes: LLZTO, LATP, LLZO (Shanghai Xiba, LO115) series products, different series have different mesh sizes and various angular coefficient specifications; Silicon-based materials: Silicon-carbon composite materials, with silicon content of 5%~100%, BTR series products, different series have different mesh sizes and various angular coefficient specifications.

[0074] Example 1 An embodiment of a negative electrode sheet and a secondary battery, wherein the method for preparing the negative electrode sheet includes the following steps: Preparation of the negative electrode sheet: A slurry is prepared by mixing a silicon-based material and a solid electrolyte with conductive agent SP and binder sodium carboxymethyl cellulose in a mass ratio of 85:5:10 and dispersing them in N-methylpyrrolidone. The slurry is coated onto copper foil, and then cold-pressed and slit to obtain the negative electrode sheet. The compacted density of the negative electrode sheet is 1 g / cm³. 3 ; Preparation of the positive electrode sheet: Commercially available lithium cobalt oxide with an average particle size of 15 μm was used as the positive electrode material. It was compounded with conductive agent acetylene black, conductive agent carbon nanotubes, and binder polyvinylidene fluoride in a mass ratio of 97.8:0.6:0.4:1.2 and dispersed in N-methylpyrrolidone to prepare a slurry. This slurry was coated onto aluminum foil, cold-pressed, and slit to obtain the positive electrode sheet. The compacted density of the positive electrode sheet was 3.5 g / cm³. 3 ; Electrolyte preparation: EC:DMC:EMC were mixed in a volume ratio of 3:5:2 to obtain a mixed solution. Then, LiPF6 was added to the above mixed solution to prepare a concentration of 1 mol / L to complete the electrolyte preparation. The positive electrode, negative electrode, and commercially available PP separator are stacked together, and an electrolyte is added to assemble a secondary battery. The battery is then packaged, tested for capacity, and formed to obtain the secondary battery.

[0075] Examples 2-15, Comparative Examples 1-3 An embodiment of a negative electrode sheet and a secondary battery differs from Embodiment 1 only in that the parameters of the negative electrode sheet during preparation and in the finished product are different, as shown in Tables 1 and 2. However, it is not limited to this. Those skilled in the art can adjust these parameters in other ways. In the preparation method, some silicon-based materials are also carbon-coated: the silicon-based material is mixed and ground with 3 wt% glucose, and then calcined in a closed tube furnace at 500°C under an argon atmosphere for 1 hour. The average particle size change of the obtained silicon-based material does not exceed 2%, and it is considered that the average particle size of the silicon-based material does not change after carbon coating treatment, only the angularity coefficient changes. In Table 1, when the binder changes during the preparation of the negative electrode sheet, the ratio between the mixture of silicon-based material and solid electrolyte and the conductive agent is still 85:5.

[0076] In Table 2, M = 100% × M1 / ​​(M1 + M2).

[0077] Table 1 Table 2 Electrochemical performance tests were performed on the battery products of each embodiment and comparative example: (1) Electrode expansion rate test: Each secondary battery was tested using an in-situ thickness measuring instrument: at 25℃, 300 cycles were performed at a 0.2C rate in the working range of 2.6~4.53V. The original thickness H0 of the electrode was recorded during battery preparation. After the test, the battery was disassembled and the thickness H1 of the negative electrode was measured. The electrode expansion rate was 100%×(H1-H0) / H0. (2) Cyclic performance test: Each secondary battery was subjected to 500 cycles at 25°C and 0.5C rate in the known range of 2.6~4.53V. The discharge capacity a0 of the first cycle and the discharge capacity a1 of the last cycle were recorded. The cycle capacity retention rate of the secondary battery = 100% × a1 / a0. (3) Low temperature rate performance test: Using a low temperature battery test system, each secondary battery was first charged at 0.5C to the highest cutoff voltage of 4.53V at 25℃ (constant voltage until current < 0.02C), and the charging capacity C1 at 25℃ was recorded; then the temperature was lowered to -10℃ and left to stand for 2 hours until the temperature inside the cell was constant, and discharged at 0.5C rate to the lowest cutoff voltage of 2.6V, and the discharge capacity C2 was recorded; the low temperature rate discharge capacity ratio = (C2 / C1) × 100% was calculated.

[0078] The test results are shown in Table 3.

[0079] Table 3 As can be seen from Table 3, the negative electrode sheet described in this application introduces a solid electrolyte compound into the negative electrode material layer of silicon-based material, and regulates the angularity coefficient of the solid electrolyte and the particle size ratio of silicon-based material and solid electrolyte particles. This not only effectively suppresses the volume expansion effect of silicon-based material, but also ensures high electrode size stability. The electrode expansion rate after cycling does not exceed 10%, and the cycle stability is excellent. After 500 cycles, the capacity retention rate can still reach more than 80%. At the same time, it can also effectively reduce the ion transport resistance of the electrode sheet. The electrode sheet has high structural stability at high rates. Therefore, the rate capacity ratio of the secondary battery at high rates in low-temperature environments can reach more than 70%.

[0080] In contrast, the product described in Comparative Example 1 did not introduce a solid electrolyte, resulting in a high electrode expansion rate, significant electrode transport resistance, and poor structural stability. Consequently, the corresponding secondary battery exhibited low cycle performance and low-temperature rate performance. The solid electrolyte used in Comparative Example 2 had an excessively large angularity coefficient and low particle regularity, leading to numerous transport dead zones. Furthermore, when combined with silicon-based materials, it resulted in many unfillable pores, resulting in a low effect on suppressing the volume expansion of silicon-based materials. Consequently, the performance of the corresponding secondary battery was also substandard. In Comparative Examples 3 and 4, the particle size ratios of the two types of particles were too close or too different, preventing the particles from forming a gradient distribution. Small particles could not effectively fill the gaps between large particles, which was insufficient for improving ion transport within the electrode or enhancing the electrode's dimensional and structural stability. This could even lead to the agglomeration of small particles or the inability to fully release interparticle stress, resulting in electrode cracking and other issues, ultimately leading to poor product performance.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this article and are not intended to limit the scope of protection of this article. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this article without departing from the essence and scope of the technical solutions of this article.

Claims

1. A negative electrode sheet, characterized by, The negative electrode material substance layer comprises a silicon-based material and a solid-state electrolyte; The solid-state electrolyte has an angular coefficient greater than or equal to 1 and less than or equal to 1.5; The negative electrode sheet satisfies 0.01≤D1 / D2≤0.5, wherein D1 is the average particle size of the solid-state electrolyte, and D2 is the average particle size of the silicon-based material. The 0.08μm≤D1≤4μm.

2. The negative electrode sheet according to claim 1, wherein The 5μm≤D2≤12μm.

3. The negative electrode sheet according to claim 1, wherein The negative electrode sheet satisfies 0.6≤K≤1.8, wherein K is the ratio of the angular coefficients of the solid-state electrolyte and the silicon-based material.

4. The negative electrode sheet according to claim 1, wherein The negative electrode sheet satisfies 0.5%≤100%×M1 / (M1+M2)≤20%, wherein M1 is the mass of the solid-state electrolyte, and M2 is the mass of the silicon-based material.

5. The negative electrode sheet according to claim 1, wherein The silicon-based material comprises at least one of elemental silicon, silicon oxide, and silicon-carbon composite material.

6. The negative electrode sheet according to claim 1, wherein The solid-state electrolyte comprises at least one of lithium lanthanum zirconium tantalum oxide, LATP, LLZO, aluminum oxide, lithium lanthanum titanium oxide, and lithium germanium phosphorus sulfur.

7. The negative electrode sheet according to claim 1, wherein The secondary battery comprises the negative electrode sheet according to any one of claims 1-7.

8. A secondary battery characterized by comprising: The secondary battery satisfies 50≤A / K≤278, wherein AN / m is the peeling strength of the negative electrode sheet in the secondary battery.

9. The secondary battery according to claim 8, wherein the negative electrode is a lithium metal electrode. The 30N / m≤A≤500N / m.

10. The secondary battery according to claim 9, wherein the negative electrode is a lithium metal electrode. ​

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