Battery cell, secondary battery and power utilization device

Abstract

The invention discloses a battery cell, a secondary battery and a power utilization device, and relates to the technical field of batteries. The invention provides a battery cell. The battery cell comprises a positive plate, a negative plate and a diaphragm, the positive plate, the diaphragm and the negative plate are wound to form a battery cell main body, the battery cell main body comprises a straight part and a corner part adjacent to the straight part, and the corner part is arc-shaped; the positive plate comprises a positive current collector, at least one surface of the positive current collector is provided with a first coating and a second coating, and the positive current collector, the first coating and the second coating are arranged in sequence; the first coating comprises a first positive electrode active material layer; the second coating comprises second positive electrode active material layers and ceramic layers which are alternately arranged in the length direction of the positive plate, the second positive electrode active material layers are located at the straight parts, and the ceramic layers are located at the corner parts; the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer is smaller than the particle size Dv50 of the positive electrode active material in the second positive electrode active material layer.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, in particular to a battery cell, a secondary battery and an electrical device. Background Art

[0002] Current commercial lithium-ion batteries pursue higher energy density (ED). Silicon-based materials, with a theoretical capacity of up to 4212 mAh / g—an 11.3-fold increase over graphite—show potential to break through this energy density bottleneck. However, the volume of silicon anodes undergoes significant changes during charge and discharge, expanding by over 300% during charging and contracting by the same amount during discharge. This volume change induces significant internal stress, pushing the silicon material to its mechanical limits, ultimately leading to breakage and disintegration. Therefore, addressing silicon's volume expansion is crucial.

[0003] To address the above issues, existing technologies focus on silicon modification research, including: 1) carbon-based coating technology, such as graphitized carbon layer coating silicon particles; 2) porous carbon matrix composite technology, such as reserving silicon expansion space through microporous / mesoporous structure; Although changing the structural properties of the coating material can inhibit part of the silicon expansion, there are significant defects in actual applications: when the silicon content is high, irreversible structural distortion will still occur inside the composite system, resulting in an imbalance in the electrode porosity and obstructed ion transport, which cannot meet the customer's cyclic expansion requirements.

[0004] In view of this, this application is filed. Summary of the Invention

[0005] Based on this, the object of the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a battery cell, a secondary battery and an electrical device.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] In a first aspect of the present invention, the present invention provides a battery cell, comprising a positive electrode sheet, a negative electrode sheet, and a separator; the positive electrode sheet, the separator, and the negative electrode sheet are wound to form a battery cell body, the battery cell body comprising a straight portion and a corner portion adjacent to the straight portion, the corner portion being arc-shaped;

[0008] The positive electrode sheet includes a positive electrode current collector, at least one side of which is provided with a first coating layer and a second coating layer, wherein the positive electrode current collector, the first coating layer and the second coating layer are provided in sequence;

[0009] The first coating layer includes a first positive electrode active material layer; the second coating layer includes a second positive electrode active material layer and a ceramic layer alternately arranged along the length direction of the positive electrode sheet, the second positive electrode active material layer is located in the straight portion, and the ceramic layer is located in the corner portion; the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer is less than the particle size Dv50 of the positive electrode active material in the second positive electrode active material layer.

[0010] As an embodiment of the present invention, the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer is 7-9 μm.

[0011] As an embodiment of the present invention, the particle size Dv50 of the positive electrode active material in the second positive electrode active material layer is 14-16 μm.

[0012] As an embodiment of the present invention, the difference between the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer and the Dv50 of the positive electrode active material in the second positive electrode active material layer is mμm, satisfying 5≤m≤10.

[0013] As an embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector, at least one side of the negative electrode current collector is provided with a negative electrode active material layer, the weight percentage of silicon-carbon material and / or silicon-oxygen material in the negative electrode active material layer is C, the percentage of the thickness of the second coating layer to the total thickness of the first coating layer and the second coating layer is h, and h=2*C-10%.

[0014] As an embodiment of the present invention, the weight percentage of the silicon-carbon material and / or silicon-oxygen material in the negative electrode active material layer is C, and satisfies 5%<C≤50%.

[0015] As an embodiment of the present invention, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-carbon material and / or a silicon-oxygen material.

[0016] As an embodiment of the present invention, the negative electrode active material may further include graphite.

[0017] As an embodiment of the present invention, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes at least one of a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material, a lithium cobaltate material, a lithium iron phosphate material, a lithium manganese oxide material, a lithium manganese iron phosphate material and a nickel manganese spinel material.

[0018] In a second aspect of the present invention, the present invention provides a secondary battery comprising the battery cell.

[0019] In a third aspect of the present invention, the present invention provides an electrical device comprising the secondary battery.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The particle size Dv50 of the positive electrode active material layer of the first coating and the second coating provided on the positive electrode current collector of the present invention is different, and the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer is less than the particle size Dv50 of the positive electrode active material in the second positive electrode active material layer. The small particle layer has a high specific surface area and can preferentially embed lithium ions, which can shorten the diffusion path of lithium ions inside the positive electrode, preferentially release high lithium ion flux at the initial stage of charging, reduce interface polarization, and reduce the non-uniform lithium embedding of the silicon negative electrode caused by local supersaturation of lithium ions; the large particle layer can form a low tortuosity pore structure, provide a fast ion diffusion channel in the middle and late stages of charging, balance the lithium ion embedding rate of the silicon negative electrode as a whole, and inhibit the anisotropic expansion of silicon particles caused by the lithium concentration gradient. The specific design of the present invention makes the lithium ion deintercalation rate tend to be uniform, which can avoid the non-uniform expansion of the local area of ​​the silicon negative electrode caused by the sudden increase in the lithium ion concentration gradient.

[0022] The present invention uses a gradient structural design and local reinforcement of the positive electrode sheet to synergistically suppress the volume expansion problem of the silicon negative electrode from two dimensions: mechanical stress regulation and ion transport optimization. After the battery cell is wound, the corners have a small radius of curvature. During charging and discharging, the positive and negative electrode sheets are subjected to a superposition of bidirectional bending stress at the corners, which leads to an increase in the expansion restriction of the silicon negative electrode. The present invention provides a ceramic layer at the corner of the positive electrode sheet. Its elastic modulus is much higher than that of the positive electrode active material, which can form a local rigid support frame. At the same time, the ceramic layer reduces the extrusion deformation of the positive electrode on the silicon negative electrode at the corner by dispersing the bending stress.

[0023] The specific battery cell structure design of the present invention can better improve the lithium plating at the negative electrode corner, delay the cycle attenuation, extend the service life of the battery cell, and ensure high volume energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 1 is a top view and a side view of the positive electrode sheet; wherein 1 is the first positive electrode active material layer, 2 is the second positive electrode active material layer, and 3 is the ceramic layer. DETAILED DESCRIPTION

[0025] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below with reference to the accompanying drawings and specific examples. Its purpose is to understand the content of the present invention in detail, rather than to limit the present invention. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise specified, the experimental reagents and instruments designed for the implementation and comparative examples of the present invention are all commonly used ordinary reagents and instruments, which can be obtained from commercial channels. In the implementation and comparative examples, the experimental methods used are all conventional methods unless otherwise specified; and unless otherwise specified, the raw materials used in parallel experiments are from the same batch of raw materials.

[0026] According to a first aspect of the present invention, the present invention provides a battery cell, comprising a positive electrode sheet, a negative electrode sheet, and a separator; the positive electrode sheet, the separator, and the negative electrode sheet are wound to form a battery cell body, the battery cell body comprising a straight portion and a corner portion adjacent to the straight portion, the corner portion being arc-shaped;

[0027] The positive electrode sheet includes a positive electrode current collector, at least one side of which is provided with a first coating layer and a second coating layer, wherein the positive electrode current collector, the first coating layer and the second coating layer are provided in sequence;

[0028] The first coating layer includes a first positive electrode active material layer 1; the second coating layer includes a second positive electrode active material layer 2 and a ceramic layer 3 alternately arranged along the length direction of the positive electrode sheet, the second positive electrode active material layer 2 is located in the straight part, and the ceramic layer 3 is located in the corner part; the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer 1 is less than the particle size Dv50 of the positive electrode active material in the second positive electrode active material layer 2.

[0029] The present invention uses a gradient structural design and local reinforcement of the positive electrode sheet to synergistically suppress the volume expansion problem of the silicon negative electrode from two dimensions: mechanical stress regulation and ion transport optimization. After the battery cell is wound, the corners have a small radius of curvature. During charging and discharging, the positive and negative electrode sheets are subjected to a superposition of bidirectional bending stress at the corners, which leads to an increase in the expansion restriction of the silicon negative electrode. The present invention provides a ceramic layer 3 at the corner of the positive electrode sheet. Its elastic modulus is much higher than that of the positive electrode active material, which can form a local rigid support frame. At the same time, the ceramic layer 3 reduces the extrusion deformation of the positive electrode on the silicon negative electrode at the corner by dispersing the bending stress.

[0030] The particle size Dv50 of the positive electrode active material layer of the first coating and the second coating provided on the positive electrode current collector of the present invention is different, the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer 1 is less than the particle size Dv50 of the positive electrode active material in the second positive electrode active material layer 2, the small particle layer has a high specific surface area, can preferentially embed lithium ions, can shorten the diffusion path of lithium ions inside the positive electrode, preferentially release high lithium ion flux at the initial stage of charging, reduce interface polarization, and reduce the non-uniform lithium embedding of the silicon negative electrode caused by local supersaturation of lithium ions; the large particle layer can form a low tortuosity pore structure, provide a fast ion diffusion channel in the middle and late stages of charging, balance the lithium ion embedding rate of the silicon negative electrode as a whole, and inhibit the anisotropic expansion of silicon particles due to the lithium concentration gradient. The specific design of the present invention makes the lithium ion deintercalation rate tend to be uniform, which can avoid the non-uniform expansion of the local area of ​​the silicon negative electrode due to the sudden increase in the lithium ion concentration gradient.

[0031] The advantages of the ceramic layer 3 of the present invention being located at the corner are as follows: first, it increases the N / P ratio of the positive and negative electrodes in the corner area of ​​the positive electrode, which is beneficial to improving the lithium plating situation; second, by coating the ceramic at the corner position instead of coating the ceramic on the complete electrode piece, the thickening of the battery cell caused by coating the ceramic at the corner can be minimized to improve the energy density; third, ceramics have the ability to absorb and retain liquid, and the ceramic layer 3 at the corner can increase the amount of electrolyte retained at the corner position, ensure the fluidity of the electrolyte, improve local lithium plating at the corner, improve battery cell deformation, and prolong the cycle life; fourth, it can inhibit the release of lithium ions in the corner area of ​​the positive electrode plane, improve the lithium plating at the corner from the root, and prolong the cycle life; fifth, it can block the direct contact between the positive electrode active material and the electrolyte in the corner area, increase the voltage platform, reduce the system polarization, and prolong the cycle life.

[0032] The specific battery cell structure design of the present invention can better improve the lithium plating at the negative electrode corner, delay the cycle attenuation, extend the service life of the battery cell, and ensure high volume energy density.

[0033] In some embodiments, the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer 1 is 7-9 μm. Specifically, the Dv50 of the first positive electrode active material layer 1 can be any point value or any two points in the range of 7-9 μm, for example, 7 μm, 7.2 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, etc.

[0034] In some embodiments, the particle size Dv50 of the positive electrode active material in the second positive electrode active material layer 2 is 14-16 μm. Specifically, the Dv50 of the second positive electrode active material layer 2 can be any point value or any two points in the range of 14-16 μm, for example, 14 μm, 14.2 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, etc.

[0035] The particle size Dv50 of the positive electrode active material in the first positive electrode active material layer 1 of the present invention is 7-9 μm. When the particle size Dv50 is greater than 9 μm, on the one hand, the specific surface area of ​​the first positive electrode active material layer 1 is insufficient, exacerbating local overlithiation of the silicon negative electrode; on the other hand, the diffusion rate of lithium ions is hindered, the system dynamics deteriorate, and the system polarization increases, which is not conducive to cycle life. When the particle size Dv50 of the first positive electrode active material layer 1 is less than 7 μm, on the one hand, the slurry viscosity is too high, and the coating uniformity deteriorates; on the other hand, the surface area of ​​the lower layer is too small, and the interfacial free energy, interfacial tension, interfacial defects, and interfacial thermodynamic effects are significantly increased, placing more stringent requirements on the system.

[0036] The particle size Dv50 of the positive electrode active material in the second positive electrode active material layer 2 of the present invention is 14-16μm. When the particle size Dv50 of the second positive electrode active material layer 2 is higher than 16μm, the surface particles are too large, the lubricity and wettability of the electrolyte and the positive electrode surface are insufficient, and the diffusion of lithium ions encounters greater resistance, resulting in lithium ions being easily deposited on the surface, forming more local purple spots on the interface; when the particle size Dv50 is lower than 14μm, an effective lithium ion diffusion mechanism cannot be formed with the lower layer, and the kinetics are insufficient.

[0037] In some embodiments, a difference between the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer and the particle size Dv50 of the positive electrode active material in the second positive electrode active material layer is m μm, satisfying 5≤m≤10.

[0038] Specifically, the difference m can be any point value within the range or any two point range values, for example, it can be 5, 6, 7, 8, 9, 10, etc.

[0039] The difference m between the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer and the particle size Dv50 of the positive electrode active material in the second positive electrode active material layer of the present invention satisfies 5≤m≤10, which can ensure that the difference in the mechanical modulus of the two layers is large enough to form a progressive stress transfer interface and avoid interlayer shear failure. If the positive electrode active material layer has a single particle size and the modulus is uniform within the layer, the positive electrode as a whole will undergo rigid deformation when the silicon negative electrode expands, resulting in a sudden stress change at the positive-negative electrode interface and initiating interlayer shear cracks. When the difference m is too small, it means that the difference in particle size between the upper and lower layers is small, and no effective mechanism is formed for the migration of lithium ions, resulting in the worst kinetics and the worst system kinetic window, and the required charging regime cannot be achieved. When the difference m is too large, on the one hand, more energy will be consumed in the formation of CEI during cell formation, the surface tension at the connection will be greater, and the migration of lithium ions will encounter greater resistance, resulting in increased thermodynamic utility and increased Gibbs free energy, which will lead to poor system stability and unfavorable cycle life; on the other hand, when the gap between particles at the connection is too large, it will also lead to increased liquid phase polarization and increased system polarization, which is not conducive to the cycle life of the system.

[0040] In some embodiments, the negative electrode sheet includes a negative electrode current collector, at least one side of the negative electrode current collector is provided with a negative electrode active material layer, the weight percentage of silicon-carbon material and / or silicon-oxygen material in the negative electrode active material layer is C, the percentage of the thickness of the second coating layer to the total thickness of the first coating layer and the second coating layer is h, and h=2*C-10%.

[0041] By establishing a relationship between h and C, the present invention significantly improves the volume expansion problem of silicon, achieving a coordinated optimization of the dynamic adaptation of silicon expansion space and the stability of the electrode structure. The second coating thickness ratio increases with increasing C, providing additional space for expansion and significantly reducing the risk of electrode cracking. When the second coating thickness ratio increases, the lithium ion diffusion rate is increased. By establishing a relationship between h and C, the present invention can ensure a dynamic balance between silicon content and ion transmission capacity.

[0042] In some embodiments, the weight percentage of the silicon-carbon material and / or silicon-oxygen material in the negative electrode active material layer is C, and satisfies 5%<C≤50%. Specifically, the weight percentage C of the silicon-carbon material and / or silicon-oxygen material in the negative electrode active material layer can be any value or any two values ​​within the range of 5%-50%, for example, 6%, 7%, 8%, 9%, 15%, 18%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.

[0043] When the weight percentage of silicon-carbon material and / or silicon-oxygen material in the negative electrode active material layer is ≤5, the positive electrode sheet can improve the lithium deposition at the negative electrode corner and delay cycle attenuation without the need for a second coating.

[0044] In some embodiments, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-carbon material and / or a silicon-oxygen material.

[0045] In some embodiments, the negative electrode active material may further include graphite.

[0046] In some embodiments, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes at least one of a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material, a lithium cobaltate material, a lithium iron phosphate material, a lithium manganese oxide material, a lithium iron manganese phosphate material, and a nickel-manganese spinel material.

[0047] In the battery cell of the present invention, the active materials on the positive and negative electrode sheets can be matched with different types of materials as needed, and both can achieve good electrochemical activity and safety and stability.

[0048] In some embodiments, the positive electrode current collector is a metal foil, and the metal foil may be an aluminum foil.

[0049] In some embodiments, the negative electrode current collector is a metal foil, and the metal foil may be a copper foil.

[0050] In some embodiments, the material of the ceramic layer includes at least one of aluminum oxide, zirconium oxide, aluminum nitride, silicon nitride, and silicon carbide.

[0051] In some embodiments, the first coating layer, the second coating layer, and the ceramic layer each independently further comprise a conductive agent and a binder.

[0052] In some embodiments, the mass percentage of the conductive agent is 0.20%-15%, and the mass percentage of the binder is 0.30%-11%.

[0053] In some embodiments, the conductive agent includes one or more of superconducting carbon, acetylene black, conductive carbon black, Ketjen black, carbon nanotubes, graphene, and carbon nanofibers.

[0054] In some embodiments, the binder includes one or more of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0055] In some embodiments, the diaphragm may be an existing conventional diaphragm.

[0056] In some embodiments, the separator includes at least one of a polypropylene separator, a polyethylene separator, and a polyvinylidene fluoride separator.

[0057] In some embodiments, the battery cell further includes an electrolyte.

[0058] In some embodiments, the electrolyte is an electrolyte obtained by dissolving lithium hexafluorophosphate in a mixed solvent of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) in a volume ratio of 1:1:4:4.

[0059] In a second aspect of the present invention, the present invention provides a secondary battery comprising the battery cell.

[0060] In a third aspect of the present invention, the present invention provides an electrical device comprising the secondary battery.

[0061] Exemplarily, the above-mentioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

[0062] During the research and experimental process, the inventors conducted a large number of research experiments, including designing and preparing different positive electrode sheets and lithium-ion batteries, and testing battery performance. Some of these experimental cases and test results are listed below to illustrate this application:

[0063] Example 1

[0064] See also Figure 1 Top view and side view of the positive electrode sheet, positive electrode sheet preparation:

[0065] The positive electrode sheet comprises a positive electrode current collector aluminum foil, and both sides of the positive electrode current collector are provided with a first coating layer and a second coating layer, respectively. The positive electrode current collector, the first coating layer and the second coating layer are provided in sequence;

[0066] The first coating layer is a first positive electrode active material layer 1; the second coating layer includes a second positive electrode active material layer 2 and a ceramic layer 3 alternately arranged along the length direction of the positive electrode sheet, the second positive electrode active material layer 2 is located in the straight portion, and the ceramic layer 3 is located in the corner portion;

[0067] The first positive electrode active material layer 1 includes the following components in mass percentage: 0.80% conductive agent (conductive carbon black) + 1.21% binder (polyvinylidene fluoride (PVDF) + 0.03% dispersant (polyacrylamide) + 97.96% lithium cobalt oxide material;

[0068] The second positive electrode active material layer 2 includes the following components in percentage by mass: 0.91% conductive carbon black + 0.95% binder (polyvinylidene fluoride (PVDF) + 0.02% dispersant (polyacrylamide) + 98.12% lithium cobalt oxide material;

[0069] The ceramic layer 3 comprises the following components in percentage by mass: 12% conductive carbon black + 88% aluminum oxide;

[0070] The components of the first positive electrode active material layer 1 are mixed uniformly to prepare a positive electrode slurry A for a lithium-ion battery cell; the positive electrode slurry A is coated on a current collector aluminum foil and dried at 85°C;

[0071] The components of the second positive electrode active material layer 2 are mixed uniformly to prepare a positive electrode slurry B for a lithium-ion battery cell; the positive electrode slurry B is coated on the flat portion of the first positive electrode active material layer and dried at 85°C;

[0072] The components in the ceramic layer 3 are mixed uniformly to prepare a positive electrode slurry C for a lithium-ion battery cell. The positive electrode slurry C is applied to the corner of the first positive electrode active material layer and dried at 85°C.

[0073] The positive electrode sheet was prepared by cold pressing, slitting, drying at 85°C under vacuum conditions for 4 hours, and welding the tabs.

[0074] Preparation of secondary batteries:

[0075] 1. Preparation of electrolyte: The electrolyte is prepared by dissolving lithium hexafluorophosphate in ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) in a volume ratio of 1:1:

[0076] The electrolyte obtained by mixing the lithium hexafluorophosphate and the mixed solvent in a ratio of 4:4; the mass ratio of lithium hexafluorophosphate and the mixed solvent is 8:92;

[0077] 2. Preparation of negative electrode sheet: The negative electrode active material, dispersant (sodium carboxymethyl cellulose CMC), binder (styrene-butadiene rubber SBR) and CNT (carbon nanotube) are mixed in a weight ratio of 96.75:2.7:0.3:0.25 to prepare a negative electrode active material slurry. The negative electrode active material is silicon-carbon material and graphite, and the silicon content (the weight percentage of silicon-carbon material in the negative electrode active material (silicon carbon and graphite)) is 10%; the active material slurry is coated on the current collector copper foil, dried at 85°C and cold pressed, and then trimmed and striped, and dried at 85°C under vacuum conditions for 12 hours, and the tabs are welded to obtain the negative electrode sheet.

[0078] 3. Preparation of wound secondary batteries: Please refer to Figure 1 , a secondary battery, including a battery cell, the battery cell including a positive electrode sheet, a negative electrode sheet, and a separator (PE film); the positive electrode sheet, the separator, and the negative electrode sheet are wound to form a battery cell body, the battery cell body including a straight portion and a corner portion adjacent to the straight portion, and the corner portion is arc-shaped; the prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed in the middle of the positive and negative electrode sheets, and wound to obtain a bare battery cell; the battery cell is designed to have a capacity of 6.0Ah and a voltage range of 3.0-4.55V. The bare battery cell is placed in an aluminum-plastic film outer packaging for packaging, and then the battery cell is placed in a vacuum oven at 85°C for baking for 48 hours. The electrolyte is injected into the dried battery cell, and the battery cell is packaged, left to stand, formed, shaped, and capacity divided.

[0079] Then, the second sealing is performed, and the liquid retention coefficient is 1.1 g / Ah, completing the preparation of the wound secondary battery.

[0080] Example 2-Example 9

[0081] A wound secondary battery. The difference between this embodiment and embodiment 1 is that the particle size Dv50 of the first positive electrode active material layer 1 is different; specifically, the particle size Dv50 is as shown in Table 1, and the lithium cobalt oxide is purchased from Zhejiang Bamo Technology Co., Ltd.

[0082] Examples 10-17

[0083] A wound secondary battery. The difference between this embodiment and embodiment 5 is that the particle size Dv50 of the second positive electrode active material layer 2 is different. Specifically, the particle size Dv50 is as shown in Table 1. The lithium cobalt oxide is purchased from Zhejiang Bamo Technology Co., Ltd.

[0084] Examples 18-20

[0085] A wound secondary battery, the difference between this embodiment and embodiment 5 is that the weight percentage C of the silicon-carbon material in the negative electrode active material layer is different. By adjusting the proportion of silicon-carbon material in the negative electrode active material in the negative electrode sheet, the weight percentage C of silicon-carbon material in the negative electrode active material in the final negative electrode active material layer is adjusted. Specifically, the negative electrode active material silicon-carbon material and graphite are purchased from Jiangxi Zichen Technology Co., Ltd.; wherein, the silicon doping amount (the weight percentage of silicon-carbon material in the negative electrode active material) in the negative electrode sheet of embodiment 18 is 8%; the silicon doping amount (the weight percentage of silicon-carbon material in the negative electrode active material) in the negative electrode sheet of embodiment 19 is 20%; the silicon doping amount (the weight percentage of silicon-carbon material in the negative electrode active material) in the negative electrode sheet of embodiment 20 is 30%;

[0086] Examples 21-23

[0087] A wound secondary battery, the difference between this embodiment and embodiment 5 is that the percentage h of the second coating thickness to the total thickness of the first coating and the second coating is different, and is adjusted by adjusting the thickness of the first and second coatings.

[0088] Comparative Example 1

[0089] A wound secondary battery. The difference between this comparative example and Example 5 is that the preparation of the positive electrode sheet is different. Specifically, the first coating layer is a first positive electrode active material layer 1; the second coating layer is a second positive electrode active material layer 2, and does not contain a ceramic layer 3.

[0090] Comparative Example 2

[0091] A wound secondary battery. The difference between this comparative example and Example 5 is that the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer 1 in the positive electrode sheet is greater than the particle size Dv50 of the positive electrode active material in the second positive electrode active material layer 2.

[0092] Specifically, the particle size Dv50 is shown in Table 1, and the lithium cobalt oxide is purchased from Zhejiang Bamo Technology Co., Ltd.

[0093] Comparative Example 3

[0094] A wound secondary battery. The difference between this comparative example and Example 5 is that the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer 1 in the positive electrode sheet is equal to the particle size Dv50 of the positive electrode active material in the second positive electrode active material layer 2.

[0095] Specifically, the particle size Dv50 is shown in Table 1, and the lithium cobalt oxide is purchased from Zhejiang Bamo Technology Co., Ltd.

[0096] The specific adjustments and parameters of the above embodiments and comparative examples are shown in Table 1.

[0097] Performance Verification

[0098] In order to verify the performance of the wound secondary battery obtained by the technical solution of the present application, the wound secondary batteries prepared in each embodiment and comparative example were subjected to the following performance tests:

[0099] The finished battery cells were subjected to RT cycle testing using the following cycle schedules: 2.8C CC to 4.25V, CV to 1.8C; 1.8C CC to 4.30V, CV to 1.5C; 1.5C CC to 4.35V, CV to 1.2C; and 1.2C CC to 4.58V, CV to 0.02C. The thickness of the fully charged battery cells was tested every 100 cycles, and the fully charged cells were disassembled to observe lithium deposition at their corners.

[0100] Specifically: Charging process: First, charge to 4.25V at a constant current (CC) of 2.8C, then switch to constant voltage (CV) charging mode until the charging current drops to 1.8C. Then charge to 4.30V at a constant current of 1.8C, then switch to constant voltage charging to reduce the current to 1.5C. Then charge to 4.35V at a constant current of 1.5C, then switch to constant voltage charging to reduce the current to 1.2C. Finally, charge to 4.58V at a constant current of 1.2C, then continue constant voltage charging until the current drops to 0.02C.

[0101] RT cycle test: The finished battery cells are subjected to repeated charge and discharge cycle tests according to the above charging system at room temperature to simulate the conditions of the battery in actual use and examine the performance changes and stability of the battery.

[0102] 700cls-Swelling, the expansion rate of the battery cell during the cycle. The test method is: use PPG to test the battery cell thickness when the battery cell is initially half-charged, then cycle the battery cell for 700 cycles, fully charge the battery cell, and test the PPG thickness when the battery cell is fully charged.

[0103] (3) The number of folds of lithium deposition at the corner: The number of folds from the corner where lithium deposition starts is the first fold, and the number of folds from the corner where lithium deposition ends is the last fold. Count the number of folds from the first fold to the last fold, which is the number of folds of lithium deposition at the corner.

[0104] The test results are shown in Table 2.

[0105] The Dv50 of the positive electrode active material in the first positive electrode active material layer is expressed as Dv A 50 represents that the Dv50 of the positive electrode active material in the second positive electrode active material layer is expressed as Dv B50; the first coating thickness is represented by X, and the second coating thickness is represented by Y; the weight percentage of silicon-carbon material and / or silicon-oxygen material in the negative electrode active material layer is C, and the percentage of the second coating thickness to the total thickness of the first coating and the second coating is h, satisfying h=2*C-10%; the difference between the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer and the particle size Dv50 of the positive electrode active material in the second positive electrode active material layer is mμm.

[0106] The Dv50 test method is as follows: weigh a certain mass of the material to be tested, mix the material to be tested with a dispersant by ultrasonic or magnetic stirring, and then add it dropwise into the laser particle size analyzer with a dropper (different materials require different shading degrees of 8%-14%) until the refractive index reaches 1.54, and then start testing to obtain the particle size of the material;

[0107] The coating thickness test method is as follows: first, apply the first coating layer and then use a micrometer to measure the thickness of the first coating layer. Then, apply the second coating layer and then measure the thickness of the entire electrode. The difference between the two is the thickness of the second coating layer.

[0108] Table 1

[0109]

[0110]

[0111]

[0112] Table 2

[0113]

[0114]

[0115] As shown in the table above, the wound secondary battery cells described in this application exhibit excellent performance in each embodiment. The wound secondary battery cells exhibited an expansion rate of less than 20% after 700 cycles, and a corner lithium deposition factor of ≤15. The specific cell structure design of the present invention can further improve negative electrode corner lithium deposition, slow cycle degradation, extend the cell life, and ensure high volumetric energy density.

[0116] From the comparison of Examples 1-9, it can be seen that when the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer is 7-9μm, the comprehensive performance is better, the expansion rate after 700 cycles is lower, and the corner lithium deposition fold is lower. From the comparison of Examples 5 and 10-17, it can be seen that when the particle size Dv50 of the positive electrode active material in the second positive electrode active material layer is 14-16μm, the comprehensive performance is better. From the comparison of Examples 1-17, it can be seen that when the difference between the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer and the particle size Dv50 of the positive electrode active material in the second positive electrode active material layer is mμm, and 5≤m≤10 is satisfied, the comprehensive performance is better, the expansion rate after 700 cycles is lower, and the corner lithium deposition fold is lower.

[0117] From the comparison of Example 5 and Examples 18-20, it can be seen that the weight percentage C of the silicon-carbon material and / or silicon-oxygen material in the negative electrode active material layer of the wound secondary battery cell of the present invention can meet a large range, and good performance can be achieved in the range of 5%<C≤50%; the expansion rate of the battery cell during 700 cycles is less than 20%, and the corner lithium deposition fold is ≤15.

[0118] From the comparison of Example 5 and Examples 21-23, it can be seen that the weight percentage of silicon-carbon material and / or silicon-oxygen material in the negative electrode active material layer is C, and the percentage of the thickness of the second coating layer to the total thickness of the first coating layer and the second coating layer is h. When h=2*C-10%, the overall performance is better, the expansion rate after 700 cycles is lower, and the corner lithium deposition fold is lower.

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A battery cell, characterized in that: The battery cell comprises a positive electrode sheet, a negative electrode sheet, and a separator; the positive electrode sheet, the separator, and the negative electrode sheet are wound to form a battery cell body, the battery cell body comprising a straight portion and a corner portion adjacent to the straight portion, the corner portion being arc-shaped; The positive electrode sheet includes a positive electrode current collector, at least one side of which is provided with a first coating layer and a second coating layer, wherein the positive electrode current collector, the first coating layer and the second coating layer are provided in sequence; The first coating layer includes a first positive electrode active material layer; the second coating layer includes a second positive electrode active material layer and a ceramic layer alternately arranged along the length direction of the positive electrode sheet, the second positive electrode active material layer is located in the straight portion, and the ceramic layer is located in the corner portion; the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer is less than the particle size Dv50 of the positive electrode active material in the second positive electrode active material layer.

2. The battery cell according to claim 1, wherein: The particle size Dv50 of the positive electrode active material in the first positive electrode active material layer is 7-9 μm.

3. The battery cell according to claim 1, wherein: The particle size Dv50 of the positive electrode active material in the second positive electrode active material layer is 14-16 μm.

4. The battery cell according to claim 1, wherein: The difference between the particle size Dv50 of the positive electrode active material in the first positive electrode active material layer and the particle size Dv50 of the positive electrode active material in the second positive electrode active material layer is m μm, satisfying 5≤m≤10.

5. The battery cell according to claim 1, wherein: The negative electrode sheet includes a negative electrode current collector, at least one side of the negative electrode current collector is provided with a negative electrode active material layer, the weight percentage of silicon-carbon material and / or silicon-oxygen material in the negative electrode active material layer is C, the percentage of the second coating thickness to the total thickness of the first coating and the second coating is h, and h=2*C-10%.

6. The battery cell according to claim 5, characterized in that The weight percentage of the silicon-carbon material and / or silicon-oxygen material in the negative electrode active material layer is C, and satisfies 5%<C≤50%.

7. The battery cell according to claim 5, characterized in that The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes at least one of a silicon-oxygen composite material and a silicon-carbon composite material.

8. The battery cell according to claim 1, wherein: The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes at least one of a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material, a lithium cobaltate material, a lithium iron phosphate material, a lithium manganese oxide material, a lithium iron manganese phosphate material, and a nickel-manganese spinel material.

9. A secondary battery, characterized in that: The battery cell comprises the battery cell according to any one of claims 1 to 8.

10. An electrical device, characterized in that: The secondary battery according to claim 9 is included.

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