A battery

Abstract

This application discloses a battery. It includes a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode comprises a silicon-based material. At 0% SOC, in any 20μm × 20μm section along the thickness direction of the negative electrode active layer, the area ratio of the silicon-based material is 65%–85%. The roughness Ra μm of the first surface of the negative electrode active layer satisfies 1 ≤ Ra ≤ 5. The separator includes a binder layer, which comprises a porous structure formed by a first polymer. The glass transition temperature Tg ℃ of the first polymer satisfies -40 ≤ Tg ≤ -18. By simultaneously optimizing the physicochemical properties of the negative electrode surface and the separator binder layer, not only can good static contact between the two be ensured, but the separator can also better adapt to the dynamic volume changes of silicon. Ultimately, while ensuring high energy density, the battery's cycle stability is significantly improved, and the degree of interface lithium plating is effectively alleviated, thus extending the battery's cycle life.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a battery. Background Technology

[0002] With the rapid development of lithium-ion battery technology and its widespread application in portable mobile electronic devices such as laptops and smartphones, the market has placed higher demands on battery energy density.

[0003] Currently, the use of graphite-doped silicon-carbon anode systems has become the main technical approach to improve battery energy density. This involves increasing the silicon-carbon content in the anode active material to achieve higher energy density. In this context, traditional low-silicon-content doping methods are no longer sufficient to meet the current market's urgent demand for high-energy-density batteries.

[0004] However, when the amount of silicon-carbon material is further increased, the adhesion between particles and between particles and the separator deteriorates, leading to a decrease in the cycle performance of the battery and inducing a serious risk of lithium plating, which severely restricts the application of silicon-carbon materials in high-energy-density batteries. Summary of the Invention

[0005] In view of this, the technical problem to be solved by this application is to overcome the defects of poor cycle performance and easy lithium plating in the existing high-silicon battery system, and to provide a battery with high energy density, good cycle performance and the ability to alleviate the degree of interface lithium plating.

[0006] To achieve the above objectives, this application adopts the following technical solution.

[0007] According to an embodiment of this application, a battery is provided, including a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode includes a negative electrode current collector and a negative electrode active layer disposed on at least one side surface of the negative electrode current collector in the thickness direction, the negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material; at 0% SOC, in any 20μm×20μm range in a cross-section of the negative electrode active layer along its thickness direction, the area ratio of the silicon-based material is 65%-85%; The negative electrode active layer has a first surface away from the negative electrode current collector, and the roughness Ra μm of the first surface satisfies 1≤Ra≤5; The separator includes a substrate layer and an adhesive layer disposed on at least one side surface of the substrate layer in the thickness direction, the adhesive layer being at least facing the negative electrode sheet; the adhesive layer includes a porous structure formed of a first polymer, the glass transition temperature Tg ℃ of the first polymer satisfying -40≤Tg≤-18.

[0008] In some alternative implementations, at least one of the following conditions is met: (1) The sphericity of the silicon-based material is at least 0.9; (2) The particle size Dv50 of the silicon-based material is denoted as D1, which satisfies 7μm≤D1≤11μm; (3) The particle size Dv90 of the silicon-based material is denoted as D2, which satisfies 12μm≤D2≤20μm; (4) The silicon-based material includes at least one of silicon-carbon composite material and silicon-oxygen composite material.

[0009] In some alternative embodiments, the negative electrode active material further includes a carbon-based material that satisfies at least one of the following conditions: (1) The carbon-based material includes at least one of graphite, soft carbon, and hard carbon; (2) The particle size Dv50 of the carbon-based material is denoted as D3, which satisfies 4μm≤D3≤8μm; (3) The particle size Dv90 of the carbon-based material is denoted as D4, which satisfies 10μm≤D4≤14μm; (4) The mass content of carbon-based materials in the negative electrode active material is less than or equal to 20%.

[0010] In some alternative implementations, at least one of the following conditions is met: (1) The first polymer includes a fluoropolymer; (2) The substrate layer of the separator includes a base film and a ceramic layer, wherein the ceramic layer is located on at least one side surface of the base film in the thickness direction, and the ceramic layer is at least facing the positive electrode sheet; (3) The puncture strength of the diaphragm is 400gf~600gf; (4) The porosity of the diaphragm is 15%-45%.

[0011] Furthermore, in some optional embodiments, the fluoropolymer includes a polymer formed by polymerizing at least one monomer selected from vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene.

[0012] In some alternative embodiments, the negative electrode further includes a binder comprising a second polymer comprising at least one functional group selected from cyano and ester groups.

[0013] In some optional embodiments, the mass ratio of the second polymer to the negative electrode active material is (1~8):(85~92); Furthermore, in some optional embodiments, the monomers of the second polymer include at least one of acrylonitrile, acrylate, and methyl methacrylate.

[0014] Further, in some optional embodiments, the second polymer comprises a polymer formed by polymerizing at least one monomer selected from acrylonitrile, acrylate, and methyl methacrylate with at least one monomer selected from acrylic acid, acrylate, and acrylamide; the acrylate comprises at least one selected from sodium acrylate, lithium acrylate, potassium acrylate, calcium acrylate, and magnesium acrylate.

[0015] Furthermore, in some alternative embodiments, the second polymer comprises a copolymer formed by polymerizing acrylonitrile monomer, acrylate monomer, and acrylate monomer.

[0016] In some optional embodiments, the areal density of the negative electrode active layer is 2.3 mg / cm³. 2 ~3.3mg / cm 2 .

[0017] In some optional embodiments, the thickness of the negative electrode active layer on one side surface of the negative electrode current collector in the thickness direction is 20 μm to 40 μm.

[0018] In some alternative embodiments, the peel force between the separator and the negative electrode is 5 N / m-14 N / m.

[0019] In some optional embodiments, the positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one side surface of the positive current collector in the thickness direction. The positive active layer includes a positive active material, which includes lithium cobalt oxide, and the particle size Dv50 μm of the lithium cobalt oxide is 13 μm to 20 μm.

[0020] In some optional embodiments, the areal density of the positive electrode active layer is 19 mg / cm³. 2 ~26 mg / cm 2 .

[0021] In some alternative embodiments, the thickness of the positive electrode is 100 μm to 125 μm.

[0022] In some alternative embodiments, the electrolyte includes lithium salt, organic solvent, and additives; The lithium salt includes at least one of lithium hexafluorophosphate, lithium dioxaborate, lithium difluorooxaborate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide, and the concentration of the lithium salt in the electrolyte is 1.2 mol / L to 1.8 mol / L; The organic solvent includes at least two of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, ethyl propionate, methyl butyrate, and ethyl butyrate. The additive includes fluoroethylene carbonate, and the mass content of the fluoroethylene carbonate is 1.5% based on the mass of the electrolyte.

[0023] In some alternative embodiments, the swelling rate of the adhesive layer of the diaphragm in the electrolyte is 1%-5%.

[0024] The technical solution of this application has the following advantages: The battery provided in this application includes a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode active layer in the negative electrode includes a silicon-based material. At 0% SOC, in any 20μm×20μm section along the thickness direction of the negative electrode active layer, the area ratio of the silicon-based material is 65%-85%. The negative electrode active layer has a first surface away from the negative electrode current collector, and the roughness Ra μm of the first surface satisfies 1≤Ra≤5. The separator includes a substrate layer and an adhesive layer disposed on at least one side surface of the substrate layer in the thickness direction, the adhesive layer facing at least the negative electrode. The adhesive layer includes a porous structure formed by a first polymer, and the glass transition temperature Tg ℃ of the first polymer satisfies -40≤Tg≤-18.

[0025] This application optimizes the physicochemical properties of both the negative electrode surface and the separator adhesive layer, ensuring good static contact between them and enabling the separator to better adapt to the dynamic volume changes of silicon. This jointly ensures the stability and integrity of the electrode interface in the high-silicon system, ultimately guaranteeing the high energy density of the battery while significantly improving the cycle stability and effectively reducing the degree of lithium plating at the interface, thus extending the battery cycle life.

[0026] Additional aspects and advantages of the embodiments of this application will be described and shown in part in the following description, or illustrated by practice of the embodiments of this application. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the specific embodiments of this application, the drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 This is a SEM image of the surface of the negative electrode sheet in one embodiment of this application; Figure 2 This is a SEM image of a cross-section of the negative electrode sheet along its thickness direction in one embodiment of this application. Detailed Implementation

[0029] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0030] It should be noted in the description of this application that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, the technical features involved in the different embodiments of this application described below may be combined with each other as long as they do not conflict with each other.

[0031] To address the shortcomings of high-silicon battery systems in related technologies, such as poor cycle performance and easy lithium deposition, this application proposes the following solutions.

[0032] A battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode includes a negative electrode current collector and a negative electrode active layer disposed on at least one side surface of the negative electrode current collector in the thickness direction, the negative electrode active layer including a negative electrode active material, the negative electrode active material including a silicon-based material; at 0% SOC, in any 20μm×20μm range of a cross-section of the negative electrode active layer along its thickness direction, the area ratio of the silicon-based material is 65%-85%; the negative electrode active layer has a first surface away from the negative electrode current collector, the roughness Ra μm of the first surface satisfying 1≤Ra≤5; the separator includes a substrate layer and an adhesive layer disposed on at least one side surface of the substrate layer in the thickness direction, the adhesive layer facing at least the negative electrode; the adhesive layer includes a porous structure formed of a first polymer, the glass transition temperature Tg ℃ of the first polymer satisfying -40≤Tg≤-18.

[0033] It should be noted that the State of Charge (SOC) is a core parameter measuring the ratio of a battery's remaining usable capacity to its fully charged capacity, ranging from 0 to 1 (equivalent to 0% to 100%). 0% SOC refers to the battery being fully discharged, at which point the discharge cutoff voltage is 2.8V. Under 0% SOC conditions, the volume of the silicon-based material in the negative electrode active layer shrinks to its minimum, and the negative electrode sheet is in its most stable contracted state. At this point, scanning electron microscopy (SEM) is used to observe the cross-section of the negative electrode active layer along its thickness. Within any 20μm × 20μm range of this cross-section, the area ratio of silicon-based material is controlled between 65% and 85%, indicating a high silicon content in the battery, i.e., a high-silicon battery system. This provides sufficient lithium storage space for the battery, thus laying the foundation for achieving high energy density.

[0034] The roughness Ra of the first surface of the negative electrode active layer refers to the absolute value of the average height deviation of the negative electrode active layer surface from an ideal plane at the microscale after the electrode is rolled, and is used to measure the smoothness of the surface. The roughness Ra value is the average value of the absolute value of the profile deviation from the center line within the sampling length; the smaller the Ra value, the smoother and flatter the surface. This application, by controlling the roughness of the first surface of the negative electrode active layer within the range of 1μm-5μm, can ensure that the negative electrode surface has a high degree of flatness, thereby effectively increasing the contact area between the negative electrode surface and the separator adhesive layer, improving the interfacial adhesion state, increasing the interfacial adhesion strength, enhancing the interfacial stability, and thus suppressing capacity decay, interfacial lithium plating, and other phenomena caused by interfacial peeling or local stress concentration.

[0035] The glass transition temperature (Tg) of the first polymer refers to the characteristic temperature at which the polymer transitions from a glassy state to a rubbery state, reflecting the flexibility of the polymer molecular chain segments. In the separator adhesive layer, the Tg value of the first polymer determines the mechanical state and viscoelastic behavior of the amorphous molecular chains within the battery's operating temperature range: when the ambient temperature is below Tg, the amorphous molecular chains are in a glassy state, with restricted molecular chain movement, resulting in a rigid adhesive layer with poor flexibility; conversely, when the ambient temperature is above Tg, the amorphous molecular chains enter a rubbery state, allowing free movement of the molecular chain segments, leading to a soft and elastic adhesive layer. Therefore, selecting a polymer with a suitable Tg value to construct the separator adhesive layer has a significant impact on improving the interfacial compatibility between the separator and the negative electrode surface, enhancing the separator's buffering capacity against the volume expansion of silicon-based materials, and improving structural stability during long-term cycling.

[0036] This application constructs a porous separator adhesive layer by selecting a first polymer with a glass transition temperature (Tg) between -40℃ and -18℃. This ensures that the separator adhesive layer has suitable viscoelasticity within the battery's operating temperature range, can moderately swell in the electrolyte, and form good interfacial compatibility with the negative electrode surface. This improves the interfacial adhesion strength between the separator and the negative electrode, effectively buffers the volume expansion effect of silicon-based materials during charging and discharging, and thus improves the battery's cycle stability and suppresses lithium plating.

[0037] In summary, to address the issues of hindered capacity utilization and easy lithium plating at the interface in high-silicon batteries, this application simultaneously optimizes the physicochemical properties of the negative electrode surface and the separator adhesive layer. This not only ensures good static contact between the two but also allows the separator to better adapt to the dynamic volume changes of silicon. Thus, they jointly ensure the stability and integrity of the electrode interface in the high-silicon system. Ultimately, while ensuring the high energy density of the battery, this application significantly improves the cycle stability of the battery, effectively reduces the degree of lithium plating at the interface, and extends the cycle life of the battery.

[0038] In this application, the area ratio of silicon-based material within a 20μm×20μm range of the cross-section along the thickness direction of the negative electrode active layer can be obtained by conventional methods. As an example, the specific testing method includes: disassembling the negative electrode sheet under the condition that the battery is at 0% SOC, cutting out the cross-section along the thickness direction of the negative electrode sheet by argon ion flow, and taking an image under SEM in backscattered electron mode. Using image processing software such as ImageJ, the pores, graphite and silicon-based materials are identified and distinguished by different gray levels, and the area ratio of silicon-based material within a 20μm×20μm range is calculated.

[0039] For example, the area ratio of silicon-based material in the cross section of the negative electrode active layer along its thickness direction within a range of 20μm×20μm can be, for example, 65%, 67%, 69%, 70%, 72%, 74%, 76%, 78%, 79%, 81%, 83%, 85%, etc., or values ​​within the range of any two of the above values.

[0040] For example, see Figure 1 , Figure 1 This is a SEM image of the surface of the negative electrode sheet in one embodiment of this application. Figure 1 As can be seen, the negative electrode active layer is mainly composed of spherical silicon-based materials. The silicon-based material particles have regular morphology and high sphericity, with particle sizes ranging from 2μm to 20μm. This is beneficial for maintaining structural integrity and reducing the risk of breakage during electrode rolling. Simultaneously, the negative electrode active layer also contains a small amount of graphite particles, with particle sizes ranging from 2μm to 15μm. These graphite particles fill the gaps between the silicon-based particles, improving the packing density and surface smoothness of the negative electrode active layer. By controlling the content and particle size distribution of silicon-based and graphite materials, a good particle size distribution is achieved between the silicon-based materials and graphite. This allows for the formation of a tightly packed and uniformly structured electrode framework in the negative electrode active layer, which is beneficial for enhancing interfacial contact stability and ion transport performance, thereby synergistically improving the battery's energy density, cycle stability, and suppressing lithium plating.

[0041] This study found that if the roughness of the first surface of the negative electrode active layer away from the negative electrode current collector is too small (less than 1 μm), the negative electrode surface is too smooth, resulting in insufficient physical anchoring between it and the separator adhesive layer, making it difficult to form an effective interfacial bond. Furthermore, during the repeated volume expansion and contraction of silicon-based materials, the interface is prone to slippage or peeling, leading to contact failure, which in turn induces lithium plating and accelerates cycle decay. If the roughness is too large (greater than 5 μm), the negative electrode surface becomes uneven, reducing the actual contact area with the separator adhesive layer. Local voids or stress concentration points exist at the interface, which also weakens the interfacial bond strength. At the same time, excessive roughness may cause uneven pressure on the separator, increasing the risk of local lithium plating.

[0042] It should be noted that the arithmetic mean deviation of the profile (Ra) reflects the average height of the overall surface undulations, but is not sensitive to extreme peaks and valleys. The surface profile can be measured using a contact profilometer / laser scanner, or directly by a surface roughness meter. Specific testing methods include: using a high-powered microscope, laying the sample to be tested flat under the microscope lens, selecting a 10X magnification lens, and adjusting the focus until the interface is clear; using 3D scanning, opening the microscope operation interface, adjusting the upper and lower limits of 3D scanning, and then clicking the "3D Scan" button to perform a 3D scan; after the 3D scan is completed, the surface roughness of the sample is automatically calculated.

[0043] For example, the roughness of the first surface of the negative electrode active layer away from the negative electrode current collector can be, for example, 1.0, 1.4, 1.9, 2.3, 2.8, 3.2, 3.7, 4.1, 4.6, 5.0, etc., or a value within the range of any two of the above values.

[0044] If the glass transition temperature of the first polymer is too low (below -40℃), the molecular chain movement of the adhesive layer is too active at the battery operating temperature, exhibiting an excessively soft and easily swollen state. The adhesion between the excessively swollen adhesive layer and the negative electrode surface is weakened, and the interface is prone to slippage or peeling. It cannot provide effective buffering and anchoring during the repeated volume expansion and contraction of silicon-based materials, but instead exacerbates interface degradation, leading to a decrease in battery cycle performance and an increased risk of lithium plating. If the glass transition temperature of the first polymer is too high (above -18℃), the molecular chain segment movement of the adhesive layer is restricted at the battery operating temperature, exhibiting a glassy state or excessive rigidity, lacking sufficient viscoelasticity and deformability, making it difficult to form a tight bond with the negative electrode surface with a certain degree of roughness. Microscopic voids or local stress concentrations are prone to exist at the interface. During charging and discharging, the rigid adhesive layer cannot dynamically adapt to the volume change of the electrode, and the interface stress cannot be effectively released, leading to local peeling or contact failure, which in turn destroys the integrity of the interface structure, aggravates the degree of lithium plating, and accelerates the decay of battery capacity.

[0045] The specific test method for the glass transition temperature (Tg) of the first polymer includes the following steps: First, after stabilizing and zeroing the crucible at room temperature, remove it and add 5 mg of the first polymer particles to the crucible, then secure the crucible edges. Next, gently place the crucible containing the sample onto a support and use a nitrogen gas flow protection at a rate of 20-50 mL / min. Retrieve the latest calibration baseline, input the sample number, sample name, and sample weight according to the software process, edit the heating rate and heating range, save the file name, and click "Start" after confirming the input parameters are correct. The differential scanning calorimeter is then used to begin the temperature rise test. The instrument is set to a heating rate of 10℃ / min, and the test temperature is from -50℃ to 200℃. After holding at -50℃ for 10 minutes, the temperature rise begins. The midpoint of the temperature rise curve is located; the corresponding temperature is the glass transition temperature (Tg) of the first polymer.

[0046] For example, the glass transition temperature of the first polymer may be -40.0℃, -37.6℃, -35.1℃, -32.7℃, -30.2℃, -27.8℃, -25.3℃, -22.9℃, -20.4℃, -18.0℃, or a value within the range of any two of the above values.

[0047] In some implementations, by controlling the sphericity of the silicon-based material to be at least 0.9, the shape of the silicon-based particles can be made closer to a sphere, reducing the stress concentration of the particles themselves. This effectively suppresses the breakage or cracking of silicon-based particles during the negative electrode rolling process. In addition, silicon-based particles with higher sphericity can form a more compact and uniform stacking structure in the active layer, which helps maintain the mechanical integrity and interface flatness of the electrode, effectively improving the interfacial bonding state between the separator and the negative electrode sheet. This effectively mitigates lithium desorption in high-silicon content systems and improves the cycle performance of the battery.

[0048] If the sphericity of silicon-based materials is less than 0.9, it means that the shape of silicon-based particles is not regular enough. During the rolling process, they are prone to breakage due to stress concentration. The sharp edges and fine particles formed after breakage will damage the flatness of the negative electrode surface, weaken the tight contact with the separator adhesive layer, and at the same time exacerbate the interface side reaction, leading to the deterioration of the interface structure. This will increase the risk of lithium plating and cycle degradation of batteries in high-silicon systems.

[0049] It is understandable that the sphericity of silicon-based materials can be expressed by the formula: E=4πA / P 2 The calculations show that A is the projected area of ​​the silicon-based material, and P is the projected perimeter of the silicon-based material.

[0050] In some embodiments, by controlling the particle size D1 of the silicon-based material to be in the range of 7μm-11μm and D2 to be in the range of 12μm-20μm, the silicon-based material in the negative electrode active layer can have a more suitable particle size distribution, which is beneficial to forming a good particle size distribution with carbon-based materials such as graphite, enhancing the structural stability and interfacial contact of the electrode, and thus simultaneously improving the energy density, cycle performance and rate performance of the battery.

[0051] Understandably, particle size D1 reflects the overall particle size level of silicon-based materials, while particle size D2 is mainly used to assess the upper limit of particle size distribution and help identify whether there are excessively large particles.

[0052] If the particle size of silicon-based materials is generally too large (D1 > 11 μm or D2 > 20 μm), not only will the diffusion path of lithium ions within the particles be prolonged and the diffusion resistance increased, which is detrimental to fast charging performance, but also excessively large particles are prone to breakage due to stress concentration during rolling, compromising the integrity of the electrode structure. Furthermore, the mismatch between excessively large particles and graphite particle size will affect the uniform stacking of the active layer, leading to poor interfacial contact. Conversely, if the particle size of silicon-based materials is generally too small (D1 < 7 μm or D2 < 12 μm), the specific surface area of ​​the silicon particles will be too large, which will exacerbate side reactions with the electrolyte, leading to increased irreversible capacity loss. At the same time, excessively small particles are difficult to achieve high compaction density, affecting the energy density of the electrode and hindering the maintenance of structural stability during long-term cycling.

[0053] It should be noted that the particle sizes D1 and D2 of silicon-based materials can be measured using a laser particle size analyzer (such as the Malvern MasterSize 3000) according to GB / T19077-2016 / ISO 13320:2009, with units in micrometers (μm). For example, D1 can be 7.0μm, 7.4μm, 7.9μm, 8.3μm, 8.8μm, 9.2μm, 9.7μm, 10.1μm, 10.6μm, 11.0μm, or values ​​within any two of the above ranges; D2 can be 12.0μm, 12.9μm, 13.8μm, 14.7μm, 15.6μm, 16.4μm, 17.3μm, 18.2μm, 19.1μm, 20.0μm, or values ​​within any two of the above ranges.

[0054] For example, the silicon-based material includes at least one of silicon-carbon composite materials and silicon-oxygen composite materials.

[0055] Preferably, the silicon-carbon composite material can be a CVD silicon-carbon material obtained by in-situ deposition of silane gas (SiH4) into the interior of a porous carbon skeleton in a fluidized bed reactor using chemical vapor deposition (CVD) technology.

[0056] In some embodiments, the negative electrode active material also includes carbon-based materials. By controlling the particle size D3 of the carbon-based material to be in the range of 4μm-8μm and D4 to be in the range of 10μm-14μm, the carbon-based material in the negative electrode active layer can have a smaller and more concentrated particle size distribution, which is beneficial for filling the gaps between silicon-based material particles, improving the packing density and surface smoothness of the negative electrode active layer. At the same time, the small particle size carbon-based material can construct a more uniform and dense conductive network, significantly improving the electron transport capability of the active layer, reducing polarization, and further mitigating the risk of lithium desorption.

[0057] Understandably, the particle size D3 of carbon-based materials reflects the overall particle size level of carbon-based materials, determining the filling behavior and distribution uniformity of carbon-based materials in the active layer; while the particle size D4 of carbon-based materials is used to evaluate the upper limit of particle size distribution, helping to identify whether there are excessively large particles that may affect the smoothness.

[0058] If the particle size of carbon-based materials is generally too large (e.g., D3 greater than 8 μm or D4 greater than 14 μm), the carbon-based materials will have difficulty effectively filling the gaps between silicon-based particles, resulting in increased surface roughness of the negative electrode and poorer interfacial contact. At the same time, excessively large carbon-based particles may disrupt the structural uniformity of the active layer during the rolling process, weakening the continuity of the conductive network. Conversely, if the particle size of carbon-based materials is generally too small (e.g., D3 less than 4 μm or D4 less than 10 μm), the specific surface area of ​​the carbon-based particles will be too large, consuming more binder, affecting the mechanical strength of the active layer, and making it easy for particles to agglomerate during cycling, which will worsen the conductivity and interfacial stability.

[0059] It should be noted that the particle size D3 and D4 of carbon-based materials can be tested using a laser particle size analyzer (such as Malvern MasterSize 3000) in accordance with GB / T19077-2016 / ISO 13320:2009, with the unit being micrometers (μm). For example, D3 can be 4.0μm, 4.2μm, 4.4μm, 4.7μm, 4.9μm, 5.1μm, 5.3μm, 5.6μm, 5.8μm, 6.0μm, 7.0μm, 8.0μm, or a value within the range of any two of the above values; D4 can be 10.0μm, 10.4μm, 10.9μm, 11.3μm, 11.8μm, 12.2μm, 12.7μm, 13.1μm, 13.6μm, 14.0μm, or a value within the range of any two of the above values.

[0060] For example, the carbon-based material includes at least one of graphite, soft carbon, and hard carbon.

[0061] In some implementations, by controlling the mass content of carbon-based materials in the negative electrode active material to be less than or equal to 20%, a high-capacity framework with silicon-based materials as the main component in the negative electrode active layer can be formed, fully leveraging its high-capacity characteristics and ensuring the battery has a high energy density. Simultaneously, as an auxiliary component, carbon-based materials can effectively fill the gaps between silicon particles and construct a continuous conductive network, improving the conductivity and structural uniformity of the active layer, thereby improving the surface smoothness and interfacial contact of the negative electrode. Within this content range, the proportion of carbon-based materials is sufficient to fulfill its filling and conductive functions, while preventing the capacity advantage of silicon-based materials from being weakened due to excessive carbon-based material content, or problems such as discontinuous conductive networks and interfacial stress concentration due to excessively low carbon-based material content. This synergistically improves the structural stability and interfacial reliability of the electrode, effectively suppressing the deterioration effect caused by the volume expansion of silicon-based materials during cycling. Thus, without sacrificing energy density, the battery's cycle performance is significantly improved, and the risk of lithium release is mitigated.

[0062] It should be noted that the mass content of carbon-based materials in the negative electrode active material can be obtained by thermogravimetric analysis (TGA). For example, the mass content of carbon-based materials in the negative electrode active material can be 0.0%, 2.2%, 4.4%, 6.7%, 8.9%, 11.1%, 13.3%, 15.6%, 17.8%, 20.0%, or a value within any two of the above ranges.

[0063] In some embodiments, the first polymer includes a fluoropolymer. Fluoropolymers, due to the presence of stable carbon-fluorine bonds in their molecular chains, exhibit excellent electrochemical stability and oxidation resistance, maintaining structural stability within the battery's operating voltage range and being less prone to decomposition or side reactions. Simultaneously, fluoropolymers possess a moderate affinity for the electrolyte, forming a gel state after absorbing a small amount of electrolyte, thus maintaining the integrity of the porous structure and enhancing the interfacial bonding with the negative electrode surface. Furthermore, the glass transition temperature (Tg) of fluoropolymers can be easily controlled through copolymerization or modification, allowing it to fall within a suitable range of -40°C to -18°C. This provides both good flexibility and structural stability at the battery's operating temperature, effectively buffering the volume expansion of silicon-based materials and improving the interfacial compatibility between the separator and the negative electrode. Furthermore, the fluoropolymer includes polymers formed by polymerizing at least one monomer selected from vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene, such as polyvinylidene fluoride (PVDF) and vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP). These materials not only have good film-forming properties and mechanical strength, but their viscoelasticity and swelling behavior can also be further optimized by adjusting the copolymerization ratio, so as to better meet the requirements for interfacial stability and cycle performance in high-silicon systems.

[0064] Based on this, by using the above-mentioned fluoropolymer to form the adhesive layer, the peel force between the separator and the negative electrode can be stabilized in the range of 5 N / m-14 N / m, thereby providing a reliable guarantee for the structural integrity of the electrode interface during cycling and further verifying the effective improvement of the interface bonding strength.

[0065] It should be noted that the peel force between the separator and the negative electrode sheet can be obtained by testing according to standard GB / T 2792-2014. For example, the peel force between the separator and the negative electrode sheet can be 5 N / m, 6 N / m, 7 N / m, 8 N / m, 9 N / m, 10 N / m, 11 N / m, 12 N / m, 13 N / m, 14 N / m, etc., or a value within any two of the above ranges.

[0066] In some embodiments, the substrate layer of the separator includes a base film and a ceramic layer, wherein the ceramic layer is located on at least one surface of the base film in the thickness direction, and the ceramic layer faces at least the positive electrode. By setting a ceramic layer on the surface of the base film, the thermal stability and mechanical strength of the separator can be significantly improved, and the thermal shrinkage rate of the separator under high temperature conditions can be reduced, thereby effectively preventing internal short circuits between the positive and negative electrodes due to separator shrinkage. At the same time, the inorganic particles (such as alumina, boehmite, etc.) in the ceramic layer have good oxidation resistance and insulation properties, and can withstand the high potential environment on the positive electrode side, reducing the risk of oxidation decomposition when the separator is in direct contact with the positive electrode. In addition, the porous structure of the ceramic layer helps to absorb and retain electrolyte, improves ion transport performance, and can buffer the mechanical stress caused by the volume changes of the electrode during charging and discharging. Arranging the ceramic layer at least facing the positive electrode side can give full play to its advantages of high voltage resistance and high temperature resistance, forming a functional complement with the adhesive layer facing the negative electrode side, jointly improving the safety performance and cycle stability of the battery. Preferably, the ceramic layer can be coated on a single surface or both sides of the base film, which can be adjusted according to the design requirements of the battery.

[0067] In some implementations, by controlling the puncture strength of the separator within the range of 400 gf to 600 gf, the separator can possess sufficient mechanical strength to resist the risk of physical puncture from electrode surface protrusions, sharp edges generated by the breakage of active particles, or conductive agent dendrites, effectively reducing the probability of micro-short circuits or short circuit failures inside the battery and improving the battery's safety performance. At the same time, the separator within this puncture strength range can prevent the increase in thickness or decrease in porosity caused by excessive toughness of the separator while ensuring mechanical protection capabilities, thereby maintaining good ion conductivity and energy density.

[0068] It should be noted that the puncture strength of the diaphragm can be obtained by testing according to standard GB / T 36363-2018. For example, the puncture strength of the diaphragm can be 400.0 gf, 422.2 gf, 444.4 gf, 466.7 gf, 488.9 gf, 511.1 gf, 533.3 gf, 555.6 gf, 577.8 gf, 600.0 gf, or a value within the range of any two of the above values.

[0069] In some implementations, by controlling the porosity of the separator within the range of 15%-45%, sufficient and uniform ion transport channels can be formed inside the separator, which is beneficial for the rapid migration of lithium ions between the positive and negative electrodes, reducing the internal resistance of the battery, and thus improving the rate performance and power characteristics of the battery. If the porosity of the separator is too low (below 15%), the ion transport path is blocked, the internal resistance of the battery increases significantly, and the rate performance and low-temperature discharge capability are severely affected. In addition, too low porosity also means that the liquid absorption capacity of the separator is reduced, which can easily lead to local liquid shortage at the interface, exacerbating lithium plating and cycle degradation. If the porosity of the separator is too high (above 45%), the mechanical strength of the separator decreases, the puncture resistance and thermal stability are weakened, and deformation or cracking is more likely to occur during battery assembly or cycling, increasing the risk of internal short circuits. At the same time, too high porosity is often accompanied by an increase in separator thickness or a decrease in material density, which is not conducive to improving the energy density of the battery.

[0070] It should be noted that the porosity of the membrane can be obtained by mercury porosimetry according to standard GB / T 21650.2-2008. For example, the porosity of the membrane can be 15.0%, 18.3%, 21.7%, 25.0%, 28.3%, 31.7%, 35.0%, 38.3%, 41.7%, 45.0%, or a value within any two of the above ranges.

[0071] In some embodiments, the negative electrode further includes a binder comprising a second polymer containing at least one functional group selected from cyano and ester groups. These functional groups possess strong electronegativity and coordination ability, enabling them to form strong interactions with the surface of the negative electrode current collector (such as copper foil), and simultaneously generate hydrogen bonds or complexes with the hydroxyl groups or oxide layers on the surface of silicon-based material particles. This significantly enhances the interfacial bonding force between the binder and the active material and current collector. During the repeated volume expansion and contraction of the silicon-based material, the robust bonding network effectively maintains the integrity of the electrode structure, inhibits cracking or detachment of the active layer, and reduces the risk of lithium plating caused by interfacial failure. Furthermore, polymers containing cyano functional groups (such as polyacrylonitrile polymers) can form hydrogen bonds or dipole interactions with fluorinated polymers (such as polyvinylidene fluoride) in the separator adhesive layer, while polymers containing ester functional groups (such as polyacrylate polymers) help improve the compatibility and flexibility of the binder and electrolyte. Both can synergistically form interfacial properties on the negative electrode surface that are conducive to tight adhesion of the adhesive layer, significantly improving the bonding strength between the separator and the negative electrode. This cross-interfacial synergistic enhancement helps maintain stable interfacial contact during cycling, further buffering the volume expansion effect of silicon-based materials, improving the cycle reliability of the battery, and suppressing lithium plating.

[0072] Further, the monomers of the second polymer include at least one of acrylonitrile, acrylate, and methyl methacrylate; further, the second polymer comprises a polymer formed by polymerizing at least one monomer of acrylonitrile, acrylate, and methyl methacrylate with at least one monomer of acrylic acid, acrylate, and acrylamide, wherein the acrylate includes at least one of sodium acrylate, lithium acrylate, potassium acrylate, calcium acrylate, and magnesium acrylate; even further, the second polymer comprises a copolymer formed by polymerizing acrylonitrile monomer, acrylate monomer, and acrylate monomer. By introducing monomers with different functional groups and adjusting the copolymer composition, the viscoelasticity, flexibility, and compatibility with the electrolyte of the polymer can be synergistically optimized, making it better adaptable to the volume changes of silicon-based materials during charging and discharging, while improving the interfacial bonding strength between the polymer and the separator layer and current collector.

[0073] In some embodiments, by controlling the mass ratio of the second polymer to the negative electrode active material to be (1~8):(85~92), the second polymer containing cyano functional groups can form a moderate and uniform distribution in the active layer. This provides sufficient bonding strength to suppress particle shedding caused by the volume expansion of the silicon-based material, while preventing excessive binder from coating the surface of the active material and hindering lithium-ion transport. Simultaneously, the strong polarity of the cyano functional groups can form a stable chemical or physical bond with the surface of the silicon-based particles and the current collector, constructing a strong and tough bonding network, thereby effectively maintaining the integrity of the electrode structure. If the mass ratio of the second polymer to the negative electrode active material is too low (below 1:92), the bonding strength is insufficient, easily leading to cracking or peeling of the active layer; if the mass ratio of the second polymer to the negative electrode active material is too high (above 8:85), it will clog pores, increase polarization, and impair the cycle and rate performance of the battery.

[0074] It should be noted that the mass ratio of the second polymer to the negative electrode active material can be obtained by thermogravimetric analysis (TGA). For example, the mass ratio of the second polymer to the negative electrode active material can be 1:92, 3:87, 4:90, 4:85, 5:88, 6:91, 6:86, 7:89, 8:92, 8:85, or a value within any two of the above ranges.

[0075] For example, see Figure 2 , Figure 2 This is a SEM image of a cross-section of the negative electrode sheet along its thickness direction in one embodiment of this application. Figure 2As can be seen, the silicon-based material in the negative electrode active layer exhibits a continuous and uniform distribution, with complete particle morphology and clear outlines, occupying a dominant position in the active layer. Further confirmation through image grayscale recognition and area statistics reveals that the silicon-based material accounts for approximately 65%-85% of the area per unit cross-sectional area, consistent with the area proportion range measured under discharge cutoff voltage conditions. This verifies the effectiveness of the silicon-based material content control in this application. Furthermore, from... Figure 2 As can be observed, the binder is distributed in a network in the active layer, penetrating between active particles and the interface area between particles and current collectors, forming a continuous three-dimensional bonding network structure. This network-distributed binder can tightly anchor silicon-based particles, enhance the interfacial bonding force between particles and between particles and current collectors, effectively maintain the integrity of the electrode structure during the repeated volume expansion and contraction of silicon-based materials, inhibit cracking or detachment of the active layer, thereby synergistically improving the cycle stability of the battery and suppressing the degree of lithium plating.

[0076] In some embodiments, the areal density of the negative electrode active layer is controlled at 2.3 mg / cm³. 2 ~3.3mg / cm 2 Within this range, the loading of active materials in the active layer can be moderate, ensuring a high energy density in the battery while maintaining rapid diffusion of lithium ions within the electrode, reducing concentration polarization, and thus effectively mitigating the risk of lithium plating caused by limited ion transport during charging and discharging. If the areal density is too low (below 2.3 mg / cm³),... 2 If the areal density is too high (above 3.3 mg / cm³), the active material loading will be insufficient, and the battery's energy density will be difficult to meet design requirements; if the areal density is too high (above 3.3 mg / cm³), the battery will be unable to meet design requirements. 2 If the diffusion distance of lithium ions in the active layer increases, the transport kinetics deteriorate, which can easily lead to insufficient lithium ion supply at the bottom of the electrode or in local areas, exacerbating lithium plating and accelerating cycle decay.

[0077] It should be noted that the areal density of the negative electrode active layer can be obtained by the disc weighing method. The specific testing method includes: cutting the negative electrode sheet into small discs of a specific area, weighing the total weight of the discs using a precision electronic balance, then wiping away the negative electrode active layer using solvents such as water and N-methylpyrrolidone to obtain the weight of the negative electrode current collector foil. The difference between the total weight of the discs and the weight of the foil is the weight of the active layer. Dividing the active layer weight by the disc area gives the areal density of the negative electrode active layer. For example, the areal density of the negative electrode active layer can be 2.30 mg / cm³. 2 2.41 mg / cm 2 2.52 mg / cm 2 2.63 mg / cm 2 2.74 mg / cm 2 2.86 mg / cm 22.97 mg / cm 2 3.08 mg / cm 2 3.19 mg / cm 2 3.30 mg / cm 2 Values ​​that are equal to or fall within the range of any two of the above values.

[0078] In some implementations, controlling the thickness of the negative electrode active layer on one side of the negative electrode current collector surface in the thickness direction to be between 20 μm and 40 μm can ensure that the active layer contributes sufficient capacity while forming a more uniform and stable interface contact between the negative electrode and the separator. This helps reduce local stress concentration, thereby further improving the interface bonding strength and cycle reliability. It also prevents the negative electrode from being too thick (greater than 40 μm), which would increase the transport resistance of lithium ions in the thickness direction, intensify polarization, and induce lithium plating, thus impairing rate performance. Conversely, it prevents the negative electrode from being too thin (less than 20 μm), which would result in limited capacity contribution of the active layer and hinder energy density improvement.

[0079] It should be noted that the thickness of the negative electrode active layer on one side of the negative electrode current collector's thickness direction can be obtained using a scanning electron microscope or a micrometer. For example, the thickness of the negative electrode active layer on one side of the negative electrode current collector's thickness direction can be 20.0 μm, 22.2 μm, 24.4 μm, 26.7 μm, 28.9 μm, 31.1 μm, 33.3 μm, 35.6 μm, 37.8 μm, 40.0 μm, or a value within any two of the above ranges.

[0080] In some implementations, by controlling the particle size Dv50 of lithium cobalt oxide within the range of 13μm to 20μm, the positive electrode active material can have a suitable particle size, which is beneficial to forming a compact and uniform particle packing structure and improving the compaction density and energy density of the positive electrode.

[0081] Understandably, Dv50, as the volumetric median particle size, reflects the main particle size level of lithium cobalt oxide particles. If Dv50 is too small (below 13μm), the specific surface area of ​​lithium cobalt oxide particles is too large, which will aggravate the side reactions with the electrolyte and make them prone to agglomeration or breakage; if Dv50 is too large (above 20μm), the lithium ion diffusion path is prolonged, the diffusion resistance increases, which is not conducive to rate performance, and large particles are prone to cracking due to stress concentration during cycling.

[0082] It should be noted that the particle size Dv50 of lithium cobalt oxide can be obtained using a laser particle size analyzer. For example, the particle size Dv50 of lithium cobalt oxide can be 13.0 μm, 13.8 μm, 14.6 μm, 15.3 μm, 16.1 μm, 16.9 μm, 17.7 μm, 18.4 μm, 19.2 μm, 20.0 μm, or a value within any two of the above ranges.

[0083] In some implementations, the areal density of the positive electrode active layer is controlled at 19 mg / cm³. 2 ~26mg / cm 2 Within a certain range, the positive electrode active material can have a suitable loading, which is beneficial to maintaining the rapid insertion / extraction kinetics of lithium ions inside the positive electrode, reducing polarization, thereby improving the rate performance and cycle stability of the battery while ensuring a high energy density.

[0084] On the other hand, by controlling the thickness of the positive electrode sheet between 100μm and 125μm, the positive electrode sheet can maintain good mechanical strength and processing adaptability while having sufficient capacity contribution. This helps to form a uniform and stable interface contact with the separator, reduce interface stress concentration, and further improve the cycle reliability and safety performance of the battery.

[0085] It should be noted that the areal density of the positive electrode active layer can be obtained by the disc weighing method. The specific testing method includes: cutting the positive electrode sheet into small discs of a specific area, weighing the total weight of the discs using a precision electronic balance, then wiping away the positive electrode active layer with an organic solvent such as N-methylpyrrolidone to obtain the weight of the positive electrode current collector foil. The difference between the total weight of the discs and the weight of the foil is the weight of the positive electrode active layer. Dividing the active layer weight by the disc area gives the areal density of the positive electrode active layer. For example, the areal density of the positive electrode active layer can be 19.0 mg / cm³. 2 19.8 mg / cm 2 20.6 mg / cm 2 21.3 mg / cm 2 22.1 mg / cm 2 22.9 mg / cm 2 23.7 mg / cm 2 24.4 mg / cm 2 25.2 mg / cm 2 26.0 mg / cm 2 Values ​​that are equal to or fall within the range of any two of the above values.

[0086] The thickness of the positive electrode can be obtained using a scanning electron microscope or a micrometer. For example, the thickness of the positive electrode can be 100.0 μm, 102.8 μm, 105.6 μm, 108.3 μm, 111.1 μm, 113.9 μm, 116.7 μm, 119.4 μm, 122.2 μm, 125.0 μm, or a value within any two of the above ranges.

[0087] In some embodiments, the electrolyte includes a lithium salt, an organic solvent, and additives; the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium dioxalate borate, lithium difluorooxalate borate, lithium bisfluorosulfonyl imide (LiFSI), and lithium bistrifluoromethanesulfonyl imide (LiTFSI). By controlling the concentration of the lithium salt in the electrolyte to be between 1.2 mol / L and 1.8 mol / L, the electrolyte can have suitable ionic conductivity and lithium-ion supply capacity. This ensures the lithium source requirement for the electrode reaction and prevents problems such as insufficient conductivity and increased polarization due to excessively low lithium salt concentration (below 1.2 mol / L) or excessive viscosity and poor wettability due to excessively high lithium salt concentration (above 1.8 mol / L), thereby improving the rate performance and cycle stability of the battery.

[0088] For example, the organic solvent includes at least two of ethylene carbonate (EC), propylene carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate, ethyl acetate, ethyl propionate, methyl butyrate, and ethyl butyrate.

[0089] The additive includes fluoroethylene carbonate (FEC). Based on the mass of the electrolyte, by controlling the mass content of fluoroethylene carbonate within the range of 2%-25%, FEC can be preferentially reduced and decomposed on the negative electrode surface, participating in the formation of a stable and dense solid electrolyte interface film. This helps to construct a tough SEI layer rich in LiF, enhances the mechanical stability and flexibility of the interface structure, and effectively inhibits the damage to the SEI film caused by the volume expansion of silicon-based materials. Thus, while ensuring the stability of the high-silicon negative electrode interface, the cycle life and rate performance of the battery are also taken into account.

[0090] It should be noted that the concentration of lithium salt can be obtained by inductively coupled plasma optical emission spectrometry (ICP-OES) or by titration (such as ion-selective electrode method). The mass content of fluoroethylene carbonate can be obtained by gas chromatography (GC) or high-performance liquid chromatography (HPLC). For example, the mass content of fluoroethylene carbonate can be 2.0%, 4.6%, 7.1%, 9.7%, 12.2%, 14.8%, 17.3%, 19.9%, 22.4%, or 25.0%; the concentration of lithium salt can be 1.20 mol / L, 1.27 mol / L, 1.33 mol / L, 1.40 mol / L, 1.47 mol / L, 1.53 mol / L, 1.60 mol / L, 1.67 mol / L, 1.73 mol / L, 1.80 mol / L, or values ​​within any two of the above ranges.

[0091] In some embodiments, by controlling the swelling rate of the adhesive layer of the separator in the electrolyte to be between 1% and 5%, the adhesive layer can be moderately swollen to enhance the interfacial adhesion and bonding strength with the negative electrode surface, while maintaining the integrity and mechanical strength of the porous structure. This provides a stable interfacial bonding force during cycling, effectively buffers the volume expansion effect of silicon-based materials, and improves the cycle stability and interfacial reliability of the battery.

[0092] It should be noted that the swelling rate of the adhesive layer in the electrolyte can be obtained by immersion weighing. The specific test method includes: placing the membrane adhesive layer sample in the electrolyte, immersing it at a set temperature until swelling equilibrium is reached, removing it, wiping off excess electrolyte from the surface, weighing the swollen sample, and then weighing the initial weight after drying. The swelling rate is calculated as (swollen weight - initial weight) / initial weight × 100%. For example, the swelling rate of the adhesive layer in the electrolyte can be 1.0%, 1.3%, 1.6%, 1.9%, 2.1%, 2.4%, 2.7%, 3.0%, 3.3%, 3.6%, 3.9%, 4.1%, 4.4%, 4.7%, 5.0%, or a value within any two of the above ranges.

[0093] The present application will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application. Where specific experimental steps or conditions are not specified in the embodiments and comparative examples, they can be performed according to the conventional experimental steps or conditions described in the literature in the art. Reagents or instruments used, unless otherwise specified, are all commercially available conventional reagent products.

[0094] Example 1 This embodiment provides a method for preparing a battery, including the following steps: Step 1: Preparation of the negative electrode The negative electrode active material is composed of silicon carbon and graphite, with a mass ratio of 90%:10%. The silicon carbon is spherical with a median particle size Dv50 of 9 μm and Dv90 of 14 μm. The graphite is small-particle graphite with a median particle size Dv50 of 4 μm and Dv90 of 13 μm. The binder is a polyacrylonitrile polymer, and the conductive agent is single-walled carbon nanotubes and multi-walled carbon nanotubes. The mass ratio of the negative electrode active material, conductive agent, and binder is 92%:3%:5%. The thickness of the active layer on one side of the negative electrode sheet is 30 μm, the total thickness of the negative electrode sheet is 68 μm, and the areal density of the active layer on one side is 3.0 mg / cm³. 2 .

[0095] Step 2: Preparation of the positive electrode sheet The positive electrode active material is lithium cobalt oxide with a median particle size Dv50 of 16 μm; the conductive agent is carbon nanotubes, and the binder is polyvinylidene fluoride; the weight percentage of positive electrode active material: conductive agent: binder is 95%:3%:2%; the thickness of the positive electrode sheet is 110 μm, and the areal density of the positive electrode active layer is 22 mg / cm³. 2 .

[0096] Step 3: Preparation of the diaphragm The base membrane used is a polyethylene membrane with a puncture strength of 500 gf. A boehm ceramic coating is coated on one side of the polyethylene membrane, and a PVDF adhesive layer is coated on the surface of the ceramic coating away from the base membrane and on the other side of the base membrane. The adhesive layer is in contact with the negative electrode. The resulting separator has a porosity of 42% and a thickness of 11 μm.

[0097] Step 4: Preparation of electrolyte The electrolyte is a 1.5 mol / L organic mixed solution of lithium salts, wherein the lithium salts are a mixture of LiPF6 and LiTFSI in a mass ratio of 13:7, which is added to the mixed solvent. The organic solvents EC : EMC : DMC = 30% : 30% : 40% by volume. FEC (4% by mass of the total electrolyte) and succinate (1% by mass of the total electrolyte) are added as film-forming additives.

[0098] Step 5: Battery fabrication The negative electrode sheet prepared in the first step, the positive electrode sheet prepared in the second step, and the separator prepared in the third step are assembled into a bare cell through a stacking process. Then, the bare cell is welded with tabs, placed into the battery casing, and injected with the electrolyte prepared in the fourth step. After standing, aging, formation, secondary sealing, aging and sorting processes, the desired battery is finally obtained.

[0099] The preparation methods of Examples 2-26 and Comparative Examples 1-4 are basically the same as those of Example 1. The differences are shown in Tables 1-3.

[0100] Table 1

[0101] Table 2

[0102] Table 3

[0103] Test case 1. Cyclic performance test The battery was subjected to repeated charge-discharge tests under constant current / constant voltage (CC / CV) conditions of 2C / 4.55V, a charging cutoff current of 0.05C, and a discharge cutoff program of 0.5C / 3.0V. The cycle stability of the battery was determined by recording the ratio of the cycle capacity to the initial capacity. The capacity retention rate (%) in each cycle was calculated using the following formula: [(discharge capacity of a specific cycle) / (discharge capacity of the first cycle)] × 100%. The test temperature was room temperature.

[0104] 2. Volumetric energy density test At 25°C, the battery is charged to 4.55V at a constant current of 0.5C, with a cutoff current of 0.02C. After resting for 5 minutes, it is discharged to 2.8V at 0.2C. The energy released is recorded as the discharge energy. The volumetric energy density (VED) is defined as the ratio between the discharge energy and the volume of the battery at 3.85V, with units of Wh / L.

[0105] 3. Lithium plating test By disassembling and cycling the battery cells, the degree and area of ​​lithium plating can be determined. For high-silicon content (80%~100%) cells at 100% SOC, unlike the golden-yellow surface of graphite and low-silicon-carbon content (0%~50%) negative electrodes, the surface of high-silicon content negative electrodes is black. The degree of lithium plating can be judged by the area percentage of white and gray lithium plating spots on the entire electrode. Area percentage below 1% is considered no lithium plating, below 5% is considered slight lithium plating, and above 20% is considered severe lithium plating.

[0106] The test results are shown in Table 4.

[0107] Table 4

[0108] As can be seen from Tables 1-4, by simultaneously optimizing the physicochemical properties of the negative electrode surface and the separator adhesive layer, this application can not only ensure good static contact between the two, but also enable the separator to better adapt to the dynamic volume change of silicon, thereby jointly ensuring the stability and integrity of the electrode interface in the high silicon system. Ultimately, while ensuring the high energy density of the battery, it significantly improves the cycle stability of the battery and effectively improves the degree of lithium plating at the interface, thus extending the cycle life of the battery.

[0109] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode comprising a negative current collector and a negative active layer disposed on at least one surface of the negative current collector in the thickness direction, the negative active layer comprising a negative active material, the negative active material comprising a silicon-based material; characterized in that, When the battery is at 0% SOC, the area ratio of the silicon-based material in any 20μm×20μm range along the thickness direction of the negative electrode active layer is 65%-85%; The negative electrode active layer has a first surface that is far away from the negative electrode current collector, and the roughness Ra μm of the first surface satisfies 1≤Ra≤5; The separator includes a substrate layer and an adhesive layer disposed on at least one side surface of the substrate layer in the thickness direction, the adhesive layer being at least facing the negative electrode sheet; the adhesive layer includes a porous structure formed of a first polymer, the glass transition temperature Tg ℃ of the first polymer satisfying -40≤Tg≤-18.

2. The battery of claim 1, wherein, At least one of the following conditions must be met: (1) The sphericity of the silicon-based material is at least 0.9; (2) The particle size Dv50 of the silicon-based material is denoted as D1, which satisfies 7μm≤D1≤11μm; (3) The particle size Dv90 of the silicon-based material is denoted as D2, which satisfies 12μm≤D2≤20μm; (4) The silicon-based material includes at least one of silicon-carbon composite material and silicon-oxygen composite material.

3. The battery of claim 1, wherein, The negative electrode active material also includes carbon-based materials that meet at least one of the following conditions: (1) The carbon-based material includes at least one of graphite, soft carbon, and hard carbon; (2) The particle size Dv50 of the carbon-based material is denoted as D3, which satisfies 4μm≤D3≤8μm; (3) The particle size Dv90 of the carbon-based material is denoted as D4, which satisfies 10μm≤D4≤14μm; (4) The mass content of carbon-based materials in the negative electrode active material is less than or equal to 20%.

4. The battery of claim 1, wherein, At least one of the following conditions must be met: (1) The first polymer includes a fluoropolymer, preferably, the fluoropolymer includes a polymer formed by polymerizing at least one monomer selected from vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene; (2) The substrate layer of the separator includes a base film and a ceramic layer, wherein the ceramic layer is located on at least one side surface of the base film in the thickness direction, and the ceramic layer is at least facing the positive electrode sheet; (3) The puncture strength of the diaphragm is 400gf~600gf; (4) The porosity of the diaphragm is 15%-45%.

5. The battery according to any one of claims 1 to 4, characterized in that, The negative electrode sheet further includes a binder, the binder comprising a second polymer, the second polymer comprising at least one functional group selected from cyano and ester groups, and / or the mass ratio of the second polymer to the negative electrode active material is (1~8):(85~92); Preferably, the monomers of the second polymer include at least one of acrylonitrile, acrylate, and methyl methacrylate; Preferably, the second polymer comprises a polymer formed by polymerizing at least one monomer selected from acrylonitrile, acrylate, and methyl methacrylate with at least one monomer selected from acrylic acid, acrylate, and acrylamide; wherein the acrylate comprises at least one selected from sodium acrylate, lithium acrylate, potassium acrylate, calcium acrylate, and magnesium acrylate. More preferably, the second polymer comprises a copolymer formed by polymerizing acrylonitrile monomer, acrylate monomer, and acrylate monomer.

6. The battery according to any one of claims 1 to 4, wherein The areal density of the negative electrode active layer is 2.3 mg / cm 2 3.3 mg / cm 2 ; And / or, the thickness of the negative electrode active layer on one side surface of the negative electrode current collector in the thickness direction is 20μm~40μm; And / or, the peel force between the diaphragm and the negative electrode is 5 N / m-14 N / m.

7. The battery of claim 1, wherein, The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one side surface of the positive current collector in the thickness direction. The positive active layer includes a positive active material, which includes lithium cobalt oxide, and the particle size Dv50 μm of the lithium cobalt oxide is 13 μm to 20 μm.

8. The battery according to claim 1 or 7, characterized by The face density of the positive electrode active layer is 19 mg / cm 2 26 mg / cm 2 ; And / or, the thickness of the positive electrode is 100μm~125μm.

9. The battery of claim 1, wherein, The electrolyte includes lithium salt, organic solvent, and additives; The lithium salt includes at least one of lithium hexafluorophosphate, lithium dioxaborate, lithium difluorooxaborate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide, and the concentration of the lithium salt in the electrolyte is 1.2 mol / L to 1.8 mol / L; The organic solvent includes at least two of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl acetate, ethyl propionate, methyl butyrate, and ethyl butyrate. The additive includes fluoroethylene carbonate, and the mass content of the fluoroethylene carbonate is 2%-25% based on the mass of the electrolyte.

10. The battery according to claim 1 or 9, characterized in that, The swelling rate of the adhesive layer of the diaphragm in the electrolyte is 1%-5%.

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