Battery, electric device, and box body

Abstract

The present application belongs to the technical field of batteries. Provided are a battery cell and a preparation method thereof, and a battery and an electric apparatus. The battery cell comprises an electrode assembly, which comprises a positive electrode sheet, a negative electrode sheet and a separator, wherein the negative electrode sheet contains a negative-electrode active material, which contains a silicon-carbon composite material and a carbon material. The electrode assembly comprises a flat region and two bending regions, wherein two ends of the flat region are respectively connected to the two bending regions, and a bonding layer is provided on the surface of the separator in each of the bending regions, which bonding layer contains polymer particles. With regard to the battery cell in the present application, a silicon-carbon composite material is added into the negative-electrode active material, such that the volumetric energy density of the battery cell is increased; moreover, bonding layers are provided on surfaces of separators in bending regions, and since the bonding layers have a relatively large compressibility, a relatively large expansion space or gap is reserved for the volume expansion of the silicon-carbon composite material, thereby ameliorating lithium plating in the bending regions, and thus enabling the battery cell to have both a relatively high energy density and a relatively good cycle performance.

Description

A battery, electrical device and enclosure Cross-reference to related applications

[0001] This application claims priority to Chinese Patent Application No. 202411822793.5, filed on December 11, 2024, entitled “A battery cell and a method for preparing the same, a battery and an electrical device thereof”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, and more specifically, to a battery cell and its preparation method, a battery, and an electrical device. Background Technology

[0003] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Due to the significant advancements in lithium-ion battery technology, higher requirements have been placed on its energy density, cycle performance, and safety performance.

[0004] However, the theoretical specific capacity of graphite anodes is constantly approaching the theoretical value (372mAh / g), making it very difficult to improve the volumetric energy density (VED) of batteries by increasing the specific capacity of graphite anodes and thus solve the current range anxiety of electric vehicles.

[0005] Currently, the most effective way to rapidly improve the VED (Volume Effect) of a battery cell while simultaneously enhancing its fast-charging capability is silicon doping at the anode. However, the massive volume expansion (>300%) of silicon during charging and discharging severely reduces the cell's cycle stability. The severe volume expansion of silicon-carbon composite materials makes it easier for the electrodes at the cell corners to squeeze against each other, thereby squeezing out the electrolyte between the electrodes. This leads to lithium plating at the cell corners, causing a sharp drop in cell cycle performance and even triggering other safety issues. Summary of the Invention

[0006] This application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell and its preparation method, battery and power device, which can improve the lithium plating problem at the corner of the battery cell and make it balance energy density and cycle performance.

[0007] To achieve the above objectives, a first aspect of this application provides a battery cell comprising an electrode assembly, the electrode assembly including a positive electrode, a negative electrode, and a separator, the separator being disposed between the positive and negative electrode, the negative electrode including a negative electrode active material, the negative electrode active material including a silicon-carbon composite material and a carbon material, the electrode assembly including a straight region and two bending regions, the two ends of the straight region being respectively connected to the two bending regions, and an adhesive layer comprising polymer particles being disposed on the surface of the separator in the bending regions.

[0008] Therefore, the battery cell of this application, on the one hand, can improve the volumetric energy density of the battery cell by adding silicon-carbon composite material to the negative electrode active material. Furthermore, the addition of silicon-carbon composite material can reduce the amount of carbon material used while maintaining the same specific capacity, making the negative electrode thinner and effectively improving the kinetic performance of the battery cell. On the other hand, because the silicon-carbon composite material expands significantly during cycling, the electrodes will be squeezed together, causing the electrolyte to be squeezed out. The bending region is more prone to lithium deposition than the straight region. To reduce lithium deposition in the bending region, the electrolyte reflux in the bending region needs to be made smoother. By setting an adhesive layer on the surface of the separator in the bending area, the adhesive layer is made of raw materials including polymer particles. This results in larger gaps between polymer particles in the adhesive layer, lower packing density, and greater compressibility. This allows for more expansion space or gaps for the volume expansion of the silicon-carbon composite material, reducing or avoiding problems such as electrolyte squeezing out between electrodes in the bending area, difficulty in electrolyte reflux, and uneven electrolyte distribution caused by the expansion of the silicon-carbon composite material. This improves the lithium plating problem in the bending area, enabling the battery cell to have both high energy density and long cycle performance.

[0009] In any embodiment, the mass of silicon in the silicon-carbon composite material accounts for 1.5% to 6% of the mass of the negative electrode active material, and the volume distribution particle size Dv50 of the polymer particles is 2 μm to 22 μm. By ensuring that the mass of the silicon-carbon composite material accounts for the mass of the negative electrode active material and that the silicon content in the silicon-carbon composite material is within the above range, the volumetric energy density of the battery cell can be increased without sacrificing initial efficiency as much as possible. By controlling the particle size of the polymer particles within the above range, the volume expansion of the silicon-carbon composite material and the compressibility of the adhesive layer are matched. The reserved expansion space or gap can not only meet the migration of lithium ions or sodium ions, but also accommodate the volume expansion of the silicon-carbon composite material, thus improving the lithium plating problem in the bending region. This allows the battery cell to have both high energy density and long cycle performance.

[0010] In any embodiment, when silicon accounts for 1.5% to 3% of the mass of the negative electrode active material in the silicon-carbon composite material, the volume distribution particle size Dv50 of the polymer particles is 7 μm to 12 μm; and / or when silicon accounts for 3% to 4.5% of the mass of the negative electrode active material in the silicon-carbon composite material, the volume distribution particle size Dv50 of the polymer particles is 12 μm to 15 μm; and / or when silicon accounts for 4.5% to 6% of the mass of the negative electrode active material in the silicon-carbon composite material, the volume distribution particle size Dv50 of the polymer particles is 15 μm to 20 μm. The particle size of polymer particles is related to the mass ratio of silicon to the negative electrode active material in the silicon-carbon composite material. The larger the mass ratio of silicon to the negative electrode active material in the silicon-carbon composite material, the greater the volume expansion of the silicon-carbon composite material. When using polymer particles with larger particle sizes, under the premise of the same thickness of adhesive layer, the larger polymer particles can provide a greater compressibility for the adhesive layer. This allows the reserved expansion space or gap to not only meet the migration of lithium ions or sodium ions, but also to accommodate the volume expansion of the silicon-carbon composite material. This improves the lithium plating problem in the bending area, enabling the battery cell to have both high energy density and long cycle performance.

[0011] In any embodiment, the mass percentage of silicon in the silicon-carbon composite material is 30% to 60%. By keeping the mass percentage of silicon in the silicon-carbon composite material within the above range, the first-efficiency matching of the positive and negative electrodes of the battery cell can be achieved. This is beneficial for increasing the volumetric energy density of the battery cell without sacrificing the first-efficiency. At the same time, the addition of the silicon-carbon composite material can reduce the amount of carbon material used while meeting the same specific capacity, making the thickness of the negative electrode thinner, thereby effectively improving the kinetic performance of the battery cell.

[0012] In any embodiment, the volumetric capacity of the negative electrode sheet is 630 mAh / cm³ to 770 mAh / cm³. In this application embodiment, the volumetric capacity of the negative electrode sheet, the mass ratio of the silicon-carbon composite material to the mass of the negative electrode active material, and the silicon content in the silicon-carbon composite material are matched. By ensuring that the volumetric capacity of the negative electrode sheet is within the above range, it is beneficial to achieve a higher energy density in the battery cell.

[0013] In any embodiment, the spacing between the positive and negative electrode plates in the bending region is 40 μm to 100 μm. By ensuring that the spacing between the positive and negative electrode plates in the bending region of the battery cell is within the above range, the migration of lithium ions or sodium ions can be satisfied.

[0014] In any embodiment, the polymer includes a polyvinylidene fluoride (PVDF) polymer, which includes at least one of the following: PVDF polymer, PVDF-hexafluoropropylene copolymer, PVDF-pentafluoropropylene copolymer, PVDF-tetrafluoropropylene copolymer, PVDF-trifluoropropylene copolymer, PVDF-perfluorobutene copolymer, PVDF-tetrafluoroethylene copolymer, PVDF-trifluoroethylene copolymer, PVDF-trifluorochloroethylene copolymer, and PVDF-vinyl fluoride copolymer. By selecting the above-mentioned materials for the polymer, the polymer particles can be stably adhered to the surface of the separator, and the compressibility of the adhesive layer can be increased, thereby reserving more expansion space or gap for the volume expansion of the silicon-carbon composite material.

[0015] The second aspect of this application provides a method for preparing a battery cell, comprising: coating an adhesive layer slurry onto a separator to form an adhesive layer; then winding a positive electrode sheet, a negative electrode sheet, and a separator to form an electrode assembly; the electrode assembly includes a straight region and two bending regions, with the two ends of the straight region respectively connected to the two bending regions; and hot-pressing the electrode assembly by applying pressure to the straight region; wherein the negative electrode sheet includes a negative electrode active material, the negative electrode active material includes a silicon-carbon composite material and a carbon material, and the adhesive layer includes polymer particles.

[0016] Therefore, the battery cell preparation method of this application forms an adhesive layer by coating an adhesive slurry on the separator. The adhesive layer fills the space between the separator and the electrode, increasing the spacing between the electrode. Since the spacing between the electrode in the straight area is still sufficient, hot pressing makes the adhesive layer in the straight area form a very thin structure, which can reduce the volume of the electrode assembly and thus improve the volumetric energy density of the battery cell. The adhesive layer in the bending area is hardly affected by hot pressing, so the polymer inside does not deform and remains granular. This makes the adhesive layer in the bending area maintain a low packing density and has a large compressibility, thus reserving more expansion space or gap for the volume expansion of the silicon-carbon composite material. This reduces or avoids problems such as electrolyte extrusion between the electrode in the bending area, difficulty in electrolyte reflux, and uneven electrolyte distribution caused by the expansion of the silicon-carbon composite material. It also improves the lithium plating problem in the bending area, enabling the battery cell to have both high energy density and long cycle performance.

[0017] In any embodiment, the coating amount of the adhesive layer slurry is 1.5 mg to 2.5 mg / 1540.25 mm². By keeping the coating amount of the adhesive layer slurry within the above range, it is beneficial to ensure that the spacing between the positive and negative electrode sheets meets the requirements for the migration of lithium ions or sodium ions. At the same time, the adhesive layer formed by the adhesive layer slurry can be compressed to a large extent, which can reserve more expansion space or gap for the volume expansion of the silicon-carbon composite material.

[0018] In any embodiment, the hot-pressing temperature is 70°C to 100°C, and the hot-pressing time is 70s to 100s. By keeping the hot-pressing temperature and time within the above range, the adhesive layer in the straight area can be formed into a very thin structure during the hot-pressing process, while the adhesive layer in the bending area is almost unaffected by the hot-pressing process.

[0019] In any embodiment, when the volume distribution particle size Dv50 of the polymer particles is 7μm to 12μm, the hot-pressing time is 70s to 80s; and / or when the volume distribution particle size Dv50 of the polymer particles is 12μm to 15μm, the hot-pressing time is 80s to 90s; and / or when the volume distribution particle size Dv50 of the polymer particles is 15μm to 20μm, the hot-pressing time is 90s to 100s. The hot-pressing time is related to the particle size of the polymer particles. The larger the particle size of the polymer particles, the longer the hot-pressing time, so that the adhesive layer in the flat region is formed into a very thin structure during the hot-pressing process, thereby improving the energy density of the battery cell.

[0020] In any embodiment, the method of coating the adhesive layer slurry onto the separator includes dot coating. Dot coating can both create spacing between the electrodes and reduce the amount of adhesive layer used, thereby increasing the energy density of the battery cell.

[0021] A third aspect of this application provides a battery comprising the battery cell described in the above embodiments or a battery cell prepared according to the preparation method of the battery cell described in the above embodiments.

[0022] A fourth aspect of this application provides an electrical device that includes the battery described in the above embodiments, the battery being used to provide electrical energy. Attached Figure Description

[0023] Figure 1 is a schematic diagram of an electrode assembly according to an embodiment of this application.

[0024] Figure 2 is a partial schematic diagram of the electrode assembly of one embodiment of the present application shown in Figure 1.

[0025] Figure 3 is a schematic diagram of a battery cell according to one embodiment of this application.

[0026] Figure 4 is an exploded view of a battery cell according to an embodiment of this application, as shown in Figure 3.

[0027] Figure 5 is a schematic diagram of a battery module according to one embodiment of this application.

[0028] Figure 6 is a schematic diagram of a battery pack according to one embodiment of this application.

[0029] Figure 7 is an exploded view of the battery pack of one embodiment of this application shown in Figure 6.

[0030] Figure 8 is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to an embodiment of this application.

[0031] Explanation of reference numerals in the attached figures:

[0032] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 521 Straight area; 522 Bending area; 523 Positive electrode; 524 Negative electrode; 525 Separator; 526 Adhesive layer; 53 Cover plate. Detailed Implementation

[0033] The following detailed description, with appropriate reference to the accompanying drawings, discloses a battery cell, its preparation method, the battery, and an electrical device according to this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known facts and repetitive descriptions of identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0034] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0036] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0037] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0038] Since the positive electrode active material is already close to its theoretical specific capacity, improving the volumetric energy density (VED) of the battery can only be achieved by improving the negative electrode. Graphite's specific capacity is also nearing its theoretical value; to improve battery capacity using graphite, one must increase the coating weight and compaction density. However, this leads to more severe particle breakage after cold pressing, and the exposure of more fresh surface consumes a large amount of lithium ions, thus deteriorating the cycle performance. The introduction of silicon-carbon composite materials, while improving the battery's VED, also significantly increases the volume expansion of the negative electrode. This massive volume expansion causes the positive electrode, separator, and negative electrode at the corners of the electrode assembly to be squeezed together. The electrolyte impregnated between these three elements at the corners is squeezed out, reducing their porosity and causing electrolyte deficiency between the positive and negative electrodes. This easily leads to lithium plating at the corners, affecting battery safety.

[0039] Based on this, this application proposes a battery cell and its preparation method, a battery and an electrical device. The following provides a more detailed description of this application and optional embodiments.

[0040] Please refer to Figures 1 and 2. This application provides a battery cell including an electrode assembly 52. ​​The electrode assembly 52 includes a positive electrode 523, a negative electrode 524, and a separator 525. The separator 525 is disposed between the positive electrode 523 and the negative electrode 524. The negative electrode 524 includes a negative electrode active material, which includes a silicon-carbon composite material and a carbon material. The electrode assembly 52 includes a straight region 521 and two bending regions 522. The two ends of the straight region 521 are respectively connected to the two bending regions 522. An adhesive layer 526 is disposed on the surface of the separator 525 in the bending region 522. The adhesive layer 526 includes polymer particles.

[0041] Among them, silicon-carbon composite material is a composite material composed of two elements, silicon (Si) and carbon (C). Compared with carbon materials, silicon-carbon composite material has a higher theoretical specific capacity and has a significant advantage in improving the volumetric energy density (VED) of batteries.

[0042] Carbon materials are materials with carbon as the main component, including graphite, hard carbon, soft carbon, carbon nanotubes, and graphene. Carbon materials have advantages such as high conductivity, high specific capacity, good cycle stability, high safety, and low cost, and are widely used as negative electrode active materials in batteries.

[0043] Optionally, the carbon material is graphite.

[0044] The flat region 521 refers to the region in the electrode assembly 52 that has a parallel structure, that is, the surfaces of the negative electrode 524, the positive electrode 523 and the separator 525 in the flat region 521 are all planar.

[0045] The bending region 522 refers to the area in the electrode assembly 52 that has a bending structure, that is, the negative electrode 524, the positive electrode 523 and the separator 525 in the bending region 522 are all bent, that is, the surface of each layer of negative electrode 524, positive electrode 523 and separator 525 in the bending region 522 of the electrode assembly 52 is curved.

[0046] The adhesive layer 526 is a layered structure formed by hot pressing an adhesive layer precursor including polymer particles.

[0047] It should be noted that the adhesive layer 526 can be disposed on one or both sides of the release membrane 525, preferably both sides of the release membrane 525.

[0048] The battery cell of this application improves the volumetric energy density of the battery cell by adding silicon-carbon composite material to the negative electrode active material. Furthermore, the addition of silicon-carbon composite material reduces the amount of carbon material used while maintaining the same specific capacity, resulting in a thinner negative electrode and effectively improving the kinetic performance of the battery cell. On the other hand, by providing an adhesive layer 526 on the surface of the separator 525 in the bending region 522, the adhesive layer 526 is formed by stacking raw materials including polymer particles. This results in larger gaps between polymer particles in the adhesive layer 526, lower packing density, and greater compressibility. This allows for more expansion space or gaps for the volume expansion of the silicon-carbon composite material, reducing or avoiding problems such as electrolyte extrusion between the electrodes in the bending region 522, difficulty in electrolyte recirculation, and uneven electrolyte distribution caused by the expansion of the silicon-carbon composite material. This improves the lithium plating problem in the bending region 522, enabling the battery cell to possess both high energy density and long cycle performance.

[0049] In some embodiments, the silicon mass in the silicon-carbon composite material accounts for 1.5% to 6% of the mass of the negative electrode active material, and the volume distribution particle size Dv50 of the polymer particles is 5 μm to 22 μm.

[0050] Although silicon-carbon composite materials have a high theoretical specific capacity, the huge volume expansion of silicon during charge and discharge (>300%) can severely reduce the cycle stability of individual cells. Using silicon-carbon composite materials in combination with carbon materials is an option, but because silicon's initial coulombic efficiency is much lower than that of carbon materials (such as graphite), the initial film formation requires a large amount of lithium ions. To ensure a good match between the initial efficiencies of the positive and negative electrodes in the individual cells, the mass of the silicon-carbon composite material should account for 3% to 9% of the mass of the negative electrode active material.

[0051] As an example, the mass of silicon in the silicon-carbon composite material accounts for 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, or 6% of the mass of the negative electrode active material.

[0052] As an example, the volume distribution particle size Dv50 of the polymer particles can be 5μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm or 22μm.

[0053] By ensuring that the mass of the silicon-carbon composite material accounts for the mass of the negative electrode active material and that the silicon content in the silicon-carbon composite material is within the aforementioned range, the volumetric energy density of the battery cell can be increased without sacrificing initial efficiency as much as possible. Furthermore, by controlling the particle size of the polymer particles within the aforementioned range, the volume expansion of the silicon-carbon composite material and the compressibility of the adhesive layer 526 can be matched. The reserved expansion space or gap can not only meet the migration of lithium ions or sodium ions but also accommodate the volume expansion of the silicon-carbon composite material, thus improving the lithium plating problem in the bending region 522. This allows the battery cell to have both high energy density and long cycle performance.

[0054] In some embodiments, when silicon accounts for 1.5% to 3% of the mass of the negative electrode active material in the silicon-carbon composite material, the volume distribution particle size Dv50 of the polymer particles is 7 μm to 12 μm; and / or when silicon accounts for 3% to 4.5% of the mass of the negative electrode active material in the silicon-carbon composite material, the volume distribution particle size Dv50 of the polymer particles is 12 μm to 15 μm; and / or when silicon accounts for 4.5% to 6% of the mass of the negative electrode active material in the silicon-carbon composite material, the volume distribution particle size Dv50 of the polymer particles is 15 μm to 20 μm.

[0055] As an example, when silicon accounts for 1.5% to 3% of the mass of the negative electrode active material in the silicon-carbon composite material, the volume distribution particle size Dv50 of the polymer particles can be 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm or 12μm.

[0056] When silicon accounts for 3% to 4.5% of the mass of the negative electrode active material in the silicon-carbon composite material, the volume distribution particle size Dv50 of the polymer particles can be 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm or 15μm.

[0057] When silicon accounts for 4.5% to 6% of the mass of the negative electrode active material in the silicon-carbon composite material, the volume distribution particle size Dv50 of the polymer particles can be 15μm, 15.5μm, 16μm, 16.5μm, 17μm, 17.5μm, 18μm, 18.5μm, 19μm, 19.5μm or 20μm.

[0058] The particle size of polymer particles is related to the mass ratio of silicon to negative electrode active material in silicon-carbon composite materials. The larger the mass ratio of silicon to negative electrode active material in silicon-carbon composite materials, the greater the volume expansion of silicon-carbon composite materials. By using polymer particles with larger particle sizes, under the premise of the same thickness of adhesive layer 526, larger polymer particles can provide greater compressibility for adhesive layer 526. This allows the reserved expansion space or gap to not only meet the migration of lithium ions or sodium ions, but also to accommodate the volume expansion of silicon-carbon composite materials. This improves the lithium plating problem in the bending region 522, enabling the battery cell to have both high energy density and long cycle performance.

[0059] In some embodiments, the mass percentage of silicon in the silicon-carbon composite material is 30% to 60%.

[0060] As an example, the mass percentage of silicon in silicon-carbon composite materials can be 30%, 35%, 40%, 45%, 50%, 55%, or 60%.

[0061] This application does not limit the source or preparation method of silicon-carbon composite materials. Embodiments of this application provide a method for preparing silicon-carbon composite materials:

[0062] Preparation of silicon-carbon composite materials: Porous hard carbon was heated to 500℃ and held at that temperature for 2 hours under an argon atmosphere to remove air adsorbed within the pores. A mixture of silane and argon was then introduced into a container. Subsequently, the temperature of the rotary kiln was raised to 600℃, and a mixture of acetylene and argon was introduced to coat the particles. The specific surface area of ​​the porous hard carbon was 1650 m². 2 / g, total pore volume is 0.8cm³ 3 / g, micropore volume is 0.6cm³ 3 / g, with an average pore size of 1.8nm.

[0063] By ensuring that the mass percentage of silicon in the silicon-carbon composite material is within the aforementioned range, the first-efficiency matching of the positive and negative electrodes of the battery cell can be achieved. This not only helps to increase the volumetric energy density of the battery cell without sacrificing the first-efficiency, but also reduces the amount of carbon material required while maintaining the same specific capacity, making the negative electrode thinner and thus effectively improving the dynamic performance of the battery cell.

[0064] In some embodiments, the negative electrode 524 has a volumetric capacity of 630 mAh / cm³. 3 ~770mAh / cm 3 .

[0065] As an example, the volumetric capacity of the negative electrode 524 can be 630 mAh / cm³. 3 640mAh / cm 3 650mAh / cm 3 660mAh / cm 3 670mAh / cm 3 680mAh / cm 3 690mAh / cm 3 700mAh / cm 3 710mAh / cm 3 720mAh / cm 3 730mAh / cm 3 740mAh / cm 3 750mAh / cm 3 760mAh / cm 3 Or 770mAh / cm 3 .

[0066] In this embodiment, the unit volume capacity of the negative electrode 524 and the mass of the silicon-carbon composite material relative to the mass of the negative electrode active material are matched, as is the silicon content in the silicon-carbon composite material. By ensuring that the unit volume capacity of the negative electrode 524 is within the above range, it is beneficial to enable the battery cell to have a higher energy density.

[0067] In some embodiments, the spacing between the positive electrode 523 and the negative electrode 524 in the bending region 522 is 40 μm to 100 μm.

[0068] As an example, the spacing between the positive electrode 523 and the negative electrode 524 in the bending region 522 can be 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm or 100μm.

[0069] By ensuring that the spacing between the positive electrode 523 and the negative electrode 524 in the bending region 522 of the battery cell is within the aforementioned range, the migration of lithium ions or sodium ions can be satisfied.

[0070] In some embodiments, the polymer includes a polyvinylidene fluoride (PVDF) polymer, which includes at least one of the following: PVDF polymer, PVDF-hexafluoropropylene copolymer, PVDF-pentafluoropropylene copolymer, PVDF-tetrafluoropropylene copolymer, PVDF-trifluoropropylene copolymer, PVDF-perfluorobutene copolymer, PVDF-tetrafluoroethylene copolymer, PVDF-trifluoroethylene copolymer, PVDF-trifluorochloroethylene copolymer, and PVDF-vinyl fluoride copolymer.

[0071] The polyvinylidene fluoride polymer used in this application includes at least one of the following: polyvinylidene fluoride polymer, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-pentafluoropropylene copolymer, polyvinylidene fluoride-tetrafluoropropylene copolymer, polyvinylidene fluoride-trifluoropropylene copolymer, polyvinylidene fluoride-perfluorobutene copolymer, polyvinylidene fluoride-tetrafluoroethylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-trifluorochloroethylene copolymer, or polyvinylidene fluoride-vinyl fluoride copolymer; that is, the polyvinylidene fluoride polymer may include one or more of the above-mentioned polyvinylidene fluoride polymers, and there is no specific limitation.

[0072] By selecting the aforementioned materials for the polymer, it is possible to ensure that the polymer particles can be stably bonded to the surface of the separator 525, and to increase the compressibility of the adhesive layer 526, thereby reserving more expansion space or gap for the volume expansion of the silicon-carbon composite material.

[0073] This application also provides a method for preparing a battery cell, comprising: coating an adhesive layer slurry onto a separator to form an adhesive layer; then winding a positive electrode sheet, a negative electrode sheet, and a separator to form an electrode assembly; the electrode assembly includes a flat region and two bending regions, with the two ends of the flat region respectively connected to the two bending regions; and hot-pressing the electrode assembly by applying pressure to the flat region; wherein the negative electrode sheet includes a negative electrode active material, the negative electrode active material includes a silicon-carbon composite material and a carbon material, and the adhesive layer includes polymer particles.

[0074] The adhesive layer slurry includes polymer particles and solvent.

[0075] It should be noted that the solvent can be a poor solvent for polymer particles. In this way, after the adhesive layer slurry is made, the polymer particles will not dissolve in the solvent, thus maintaining their original particle shape and size before hot pressing.

[0076] For example, when the polymer particles are polyvinylidene fluoride polymer particles, the solvent can be water.

[0077] The battery cell preparation method of this application forms an adhesive layer by coating an adhesive slurry onto the separator. The adhesive layer fills the space between the separator and the electrode, increasing the spacing between the electrode. The adhesive layer in the straight area forms a very thin structure during hot pressing, while the adhesive layer in the bending area is almost unaffected by hot pressing. Therefore, the internal polymer does not deform and remains granular, resulting in a lower packing density in the adhesive layer of the bending area. This allows for greater compressibility, reserving more expansion space or gap for the volume expansion of the silicon-carbon composite material. This reduces or avoids problems such as electrolyte extrusion between the electrode in the bending area, difficulty in electrolyte reflux, and uneven electrolyte distribution caused by the expansion of the silicon-carbon composite material. It also improves the lithium plating problem in the bending area, enabling the battery cell to have both high energy density and long cycle performance.

[0078] In some embodiments, the coating amount of the adhesive layer slurry is 1.5 mg to 2.5 mg / 1540.25 mm. 2 .

[0079] As an example, the coating amount of the adhesive layer slurry can be 1.5 mg / 1540.25 mm. 2 1.8mg / 1540.25mm 2 2mg / 1540.25mm 2 2.2mg / 1540.25mm 2 Or 2.5mg / 1540.25mm 2 .

[0080] By ensuring that the amount of adhesive layer slurry applied is within the above range, it is beneficial to ensure that the spacing between the positive and negative electrode sheets meets the requirements for the migration of lithium or sodium ions. At the same time, the adhesive layer formed by the adhesive layer slurry can be compressed to a greater extent, which can reserve more expansion space or gap for the volume expansion of silicon-carbon composite materials.

[0081] In some embodiments, the hot pressing temperature is 70°C to 100°C, and the hot pressing time is 70s to 100s.

[0082] As an example, the hot pressing temperature can be 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, or 100°C.

[0083] The hot pressing time can be 70s, 75s, 80s, 85s, 90s, 95s or 100s.

[0084] By keeping the temperature and time of hot pressing within the above range, the adhesive layer in the straight area can be formed into a very thin structure during the hot pressing process, while the adhesive layer in the bending area is almost unaffected by the hot pressing process.

[0085] In some embodiments, when the volume distribution particle size Dv50 of the polymer particles is 7μm to 12μm, the hot pressing time is 70s to 80s, and / or when the volume distribution particle size Dv50 of the polymer particles is 12μm to 15μm, the hot pressing time is 80s to 90s, and / or when the volume distribution particle size Dv50 of the polymer particles is 15μm to 20μm, the hot pressing time is 90s to 100s.

[0086] As an example, when the volume distribution particle size Dv50 of the polymer particles is 7μm to 12μm, the hot pressing time can be 70s, 75s or 80s.

[0087] When the volume distribution particle size Dv50 of the polymer particles is 12μm to 15μm, the hot pressing time can be 80s, 85s or 90s.

[0088] When the volume distribution particle size Dv50 of the polymer particles is 15μm to 20μm, the hot pressing time can be 90s, 95s or 100s.

[0089] The hot pressing time is related to the particle size of the polymer particles. The larger the particle size of the polymer particles, the longer the hot pressing time, which makes the adhesive layer in the flat area form a very thin structure during the hot pressing process, thereby improving the energy density of the battery cell.

[0090] In some embodiments, the adhesive layer slurry is applied to the release membrane by dot-matrix coating.

[0091] Dot-matrix coating can create spacing between electrodes and reduce the amount of adhesive layer used, thereby increasing the energy density of individual battery cells.

[0092] In addition, the following description, with appropriate reference to the accompanying drawings, describes a battery cell, its preparation method, the battery, and the power-consuming device of this application.

[0093] [Battery cell]

[0094] This application does not impose any particular restrictions on the type of battery cell; for example, the battery cell can be a lithium-ion battery, etc.

[0095] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0096] This application does not impose any particular limitation on the type of electrolyte, which can be selected according to actual needs. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions). This includes battery cells using electrolyte solutions and some battery cells using solid electrolytes.

[0097] [Positive electrode plate]

[0098] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0099] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0100] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0101] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25Mn 0.25 O2 (which can also be abbreviated as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be abbreviated as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be abbreviated as NCM 811 )、lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2) and at least one of its modified compounds, etc. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon.

[0102] In some embodiments, in order to further improve the energy density of the battery cell, the positive electrode active material for a lithium-ion battery may include a lithium transition metal oxide represented by the general formula Li a Ni b Co c M d O e A f and one or more of its modified compounds. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0103] In some embodiments, by way of example, the positive electrode active material for a lithium-ion battery may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co0.15 Al 0.05 One or more of O2, LiFePO4 and LiMnPO4.

[0104] In this application, the modified compounds of the above-mentioned positive electrode active materials may be those that have undergone doping modification and / or surface coating modification of the positive electrode active materials.

[0105] As an optional technical approach in this application, the polyanionic compound can be Li 1+x Mn 1-y A y P 1-z R z O4; where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from B, S, Si and N;

[0106] As an optional technical approach in this application, the polyanionic compound can be Li a A e Mn 1-f B f P 1-g C g O 4-n D n Wherein, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from B, S, Si, and N; D includes one or more elements selected from S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the second positive electrode active material is electrically neutral.

[0107] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of cathode materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before feeding. When the cathode material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0108] In the enumeration of the cathode material in this application, the molar content of O is only the theoretical value, and the lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0109] As an optional technical solution of this application, the polyanionic compound can be Na 4+x R 3-y P 4-m O 15 / C; wherein, 0 < x < 0.5, 0 < y ≤ 0.5, 0 < m ≤ 0.2, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W and Pb.

[0110] As an optional technical solution of this application, the polyanionic compound can be Na x-a A a V y-b M b (PO4) 2-2c (DO4) 2c F z- d Q d , where the A element represents an alkali metal element that dopes and replaces the Na element, the M element represents a metal element that replaces the V element, the D element represents a doping element that replaces the P element, the Q element represents a doping element that replaces the F element, the D element includes at least one of Si and S, and the Q element includes at least one of Cl and O; 3.5 ≤ x ≤ 4.5, 0 ≤ a ≤ 0.15x, 0.8 ≤ y ≤ 1.1, 0 ≤ b ≤ 0.3y, 0 ≤ c ≤ 0.15, 0.8 ≤ z ≤ 1.1, 0 ≤ d ≤ 0.2z. Optionally, the A element includes at least one of K and Li; the M element includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu and Co.

[0111] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer formed on at least a part of the surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material can include at least one of sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium ion batteries can also be used.

[0112] As an optional technical solution of this application, in the sodium transition metal oxide, the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The sodium transition metal oxide is, for example, Na xMO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, 0 <x≤1。

[0113] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The price state.

[0114] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0115] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, n represents the valence state of V; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0116] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3, NaM'PO4F (where M' is one or more of V, Fe, Mn, and Ni) and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0117] Prussian blue compounds can be a class of compounds containing sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Examples of Prussian blue compounds include Na. a Me b Me' c(CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 <a≤2,0<b<1,0<c<1。

[0118] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0119] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0120] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0121] [Negative electrode plate]

[0122] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

[0123] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0124] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0125] In some embodiments, the negative electrode film layer comprises a negative electrode active material. The negative electrode active material may be a negative electrode active material known in the art for use in batteries.

[0126] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of 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).

[0127] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0128] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0129] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0130] In other embodiments, the current collector of the negative electrode sheet typically includes a current collector body and a base coating. The base coating can be disposed on at least one side of the current collector body. The base coating basically does not contain negative electrode active material, and may include a small amount of carbon material. However, the carbon material forms a thin coating and cannot function as a negative electrode active material. In this embodiment, the negative electrode sheet can be an electrode sheet without a negative electrode active material layer. For a negative electrode sheet without a negative electrode active material layer, when the current collector of the negative electrode sheet does not contain a base coating, the film layer can be disposed on the surface of at least one side of the current collector; when the current collector of the negative electrode sheet includes a base coating, the film layer can be disposed on the surface of the base coating away from the current collector.

[0131] In some embodiments, the film layer may further include a binder for fixing the additive to the negative electrode sheet. The type of binder is not particularly limited, and those skilled in the art can choose flexibly according to actual needs.

[0132] [Electrolytes]

[0133] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0134] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0135] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0136] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0137] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0138] [Isolation membrane]

[0139] In some embodiments, the battery cell also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0140] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0141] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding process.

[0142] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0143] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0144] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 shows a square battery cell 5 as an example.

[0145] In some embodiments, referring to FIG4, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 by a winding process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0146] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0147] Figure 5 shows a battery module 4 as an example. Referring to Figure 5, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0148] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0149] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0150] Figures 6 and 7 illustrate a battery pack 1 as an example. Referring to Figures 6 and 7, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0151] In addition, this application also provides an electrical device, which includes at least one of the battery cell, battery module, or battery pack provided in this application. The battery cell, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0152] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0153] Figure 8 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the individual battery cells, a battery pack or battery module can be used.

[0154] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0155] Example

[0156] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0157] The relevant parameters of the battery cells of Examples 1-10 and Comparative Examples 1-3 are shown in Table 1 below.

[0158] Table 1. Relevant parameters of the battery cells in Examples 1-10 and Comparative Examples 1-3.

[0159] The gap between the positive and negative electrode plates in the bending region was measured using the following method:

[0160] Before winding, record the thickness information of the cathode electrode (dc), anode electrode (da), and separator (ds) (taking 15 layers as an example). After the cell is injected with liquid and left to stand at high temperature, measure the distance between the JR electrodes under X-Ray along the horizontal and oblique angles. Measure the distance between the JR electrodes at four different angles: up+, up-, down+, and down-. Take the value (dⅠ, dⅡ, dⅢ) every 5 folds. The gap between the anode and cathode electrodes is (dⅠ+dⅡ+dⅢ)-5×(dc+da+2ds)) / 10) / 3.

[0161] Examples 1-10 of this application provide a battery cell and a method for preparing the same, which includes the following steps:

[0162] S1. Preparation of the positive electrode sheet

[0163] Lithium iron phosphate (LiFePO4), a positive electrode active material, acetylene black, a conductive agent, and polyvinylidene fluoride (PVDF), a binder, were mixed in a weight ratio of 97.9:0.5:1.6 and dissolved in N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry was then uniformly coated onto a 15 μm aluminum foil, thoroughly dried, cold-pressed, die-cut, and slit to obtain the positive electrode sheet.

[0164] S2. Preparation of negative electrode sheet

[0165] The negative electrode active material, conductive agent carbon black, thickener CMC, binder, and carbon nanotubes were mixed in a weight ratio of 96.4:0.5:1:2:0.1, and deionized water was added. The mixture was stirred evenly under vacuum to obtain a negative electrode slurry. The negative electrode slurry was then coated onto a 6μm copper foil, dried, cold-pressed, die-cut, and slit to obtain the negative electrode sheet. The negative electrode active material consisted of silicon-carbon composite material and artificial graphite.

[0166] Silicon-carbon composite materials are prepared by the following methods:

[0167] Porous hard carbon was heated to 500℃ and held for 2 hours under an argon atmosphere to remove adsorbed air from the pores. A mixture of silane and argon (silane to argon volume ratio 1:4, flow rate 4 L / min) was then introduced into a container. The rotary kiln temperature was then raised to 600℃, and a mixture of acetylene and argon (acetylene to argon volume ratio 1:4, flow rate 3 L / min) was introduced to coat the particles. The specific surface area of ​​the porous hard carbon was 1650 m². 2 / g, total pore volume is 0.8cm³ 3 / g, micropore volume is 0.6cm³ 3 / g, with an average pore size of 1.8nm.

[0168] The mass percentage of elemental silicon in the silicon-carbon composite material is 47%, the grain size of elemental silicon is ≤5.5nm, the specific capacity of the silicon-carbon composite material is 1800, and the volume distribution particle size Dv50 of the silicon-carbon composite material is about 9μm.

[0169] S3. Preparation of the isolation membrane

[0170] Using a conventional PE base film with a thickness of 5μm, ceramic fiber, styrene-butadiene rubber, polyvinylidene fluoride and water are mixed evenly in a mass ratio of 4:0.9:0.1:5 to obtain a ceramic fiber slurry. The slurry is then uniformly coated onto the surface of the base film using a gravure coating method to form a ceramic fiber layer, and dried at 45℃ to obtain a separator membrane.

[0171] S4. Apply adhesive slurry to form an adhesive layer.

[0172] First, the ethylene-hexafluoropropylene copolymer particles and water are mixed evenly at a mass ratio of 4:6 to obtain an adhesive layer slurry. Then, the adhesive layer slurry is coated onto the surface of the ceramic fiber layer of the separator in a dot-coating manner to form an adhesive layer.

[0173] S5. Preparation of electrolyte

[0174] In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC), ethyl methyl carbonate, and dimethyl carbonate (DMC) are mixed in a volume ratio of 3:3:4. Then, lithium hexafluorophosphate (LiPF6) is uniformly dissolved in the solvent, and FEC is added to obtain the electrolyte.

[0175] S6, Assembly

[0176] The positive electrode, separator, and negative electrode are prepared in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound, hot-pressed and shaped by applying pressure to the flat area, and welded to obtain the electrode assembly. The electrode assembly is placed in a square aluminum shell, vacuum dried, and then injected with electrolyte. After standing, formation testing, aging, and capacity testing, a battery cell with a final volume of 0.411L is obtained.

[0177] Comparative Examples 1-3 of this application provide a battery cell and a method for preparing the same, which includes the following steps:

[0178] S1. Preparation of the positive electrode sheet

[0179] Lithium iron phosphate (LiFePO4), a positive electrode active material, acetylene black, a conductive agent, and polyvinylidene fluoride (PVDF), a binder, were mixed in a weight ratio of 97.9:0.5:1.6 and dissolved in N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry was then uniformly coated onto a 15 μm aluminum foil, thoroughly dried, cold-pressed, die-cut, and slit to obtain the positive electrode sheet.

[0180] S2. Preparation of negative electrode sheet

[0181] The negative electrode active material, conductive agent carbon black, thickener CMC, binder, and carbon nanotubes were mixed in a weight ratio of 96.4:0.5:1:2:0.1, and deionized water was added. The mixture was stirred evenly under vacuum to obtain a negative electrode slurry. The negative electrode slurry was then coated onto a 6μm copper foil, dried, cold-pressed, die-cut, and slit to obtain the negative electrode sheet. The negative electrode active material consisted of silicon-carbon composite material and artificial graphite.

[0182] Silicon-carbon composite materials are prepared by the following methods:

[0183] Porous hard carbon was heated to 500℃ and held for 2 hours under an argon atmosphere to remove adsorbed air from the pores. A mixture of silane and argon (silane to argon volume ratio 1:4, flow rate 4 L / min) was then introduced into a container. The rotary kiln temperature was then raised to 600℃, and a mixture of acetylene and argon (acetylene to argon volume ratio 1:4, flow rate 3 L / min) was introduced to coat the particles. The specific surface area of ​​the porous hard carbon was 1650 m². 2 / g, total pore volume is 0.8cm³ 3 / g, micropore volume is 0.6cm³ 3 / g, with an average pore size of 1.8nm.

[0184] The mass percentage of elemental silicon in the silicon-carbon composite material is 47%, the grain size of elemental silicon is ≤5.5nm, the specific capacity of the silicon-carbon composite material is 1800, and the volume distribution particle size Dv50 of the silicon-carbon composite material is about 9μm.

[0185] S3. Preparation of the isolation membrane

[0186] Using a conventional PE base film with a thickness of 5μm, ceramic fiber, styrene-butadiene rubber, polyvinylidene fluoride and water are mixed evenly in a mass ratio of 4:0.9:0.1:5 to obtain a ceramic fiber slurry. The slurry is then uniformly coated onto the surface of the base film using a gravure coating method to form a ceramic fiber layer, and dried at 45℃ to obtain a separator membrane.

[0187] S4. Apply adhesive slurry to form an adhesive layer.

[0188] First, the vinylidene fluoride-hexafluoropropylene copolymer and dimethylacetamide are mixed evenly at a mass ratio of 4:6 to obtain an adhesive layer slurry. Then, the adhesive layer slurry is coated onto the surface of the ceramic fiber layer of the separator in a dot-coating manner to form an adhesive layer.

[0189] S5. Preparation of electrolyte

[0190] In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC), ethyl methyl carbonate, and dimethyl carbonate (DMC) are mixed in a volume ratio of 3:3:4. Then, lithium hexafluorophosphate (LiPF6) is uniformly dissolved in the solvent, and FEC is added to obtain the electrolyte.

[0191] S6, Assembly

[0192] The positive electrode, separator, and negative electrode are prepared in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound, hot-pressed and shaped by applying pressure to the flat area, and welded to obtain the electrode assembly. The electrode assembly is placed in a square aluminum shell, vacuum dried, and then injected with electrolyte. After standing, formation testing, aging, and capacity testing, a battery cell with a final volume of 0.411L is obtained.

[0193] In addition, the apparent volume, true volume and porosity of the bent separator in Example 1 were measured, and the results are shown in Table 2; the unit volume capacity, first efficiency, energy density and cycle capacity retention of the negative electrode sheets of Examples 1 to 10 and Comparative Examples 1 to 3 were measured, and the results are shown in Table 3.

[0194] The testing method is as follows:

[0195] (1) Apparent volume

[0196] Apparent volume V1 = S * H ​​* A, where: S - area, cm² 2 H - thickness, cm; A - number of samples, EA.

[0197] (2) True volume

[0198] The test utilizes the displacement method of an inert gas (helium) with a small molecular diameter, combined with Archimedes' principle (F=ρgV) and Bohr's law (PV=k), to accurately measure the true volume V2 of the material being tested.

[0199] (3) Porosity

[0200] The percentage of the sample well volume to the total area is calculated as follows: Porosity = (V1 - V2) / V1 * 100%, where V1 is the apparent volume of the sample and V2 is the actual volume of the sample.

[0201] (4) Capacity per unit volume of the negative electrode sheet

[0202] Clean the active material layer on any one side of the double-sided negative electrode sheet. Use a mold to cut the remaining single-sided negative electrode sheet into small circular pieces with a radius of 7mm and an area S = 0.49π. Use a micrometer to measure the thickness h of the active layer (excluding the thickness of the current collector). Calculate the volume using the formula V = Sh. Dry the single-sided negative electrode sheet with volume V and transfer it to a glove box to make a pair of lithium half-cells. Then, use Wuhan Landian testing equipment to test the delithiation capacity Q of the above circular pieces. Finally, obtain the unit volume capacity of the negative electrode sheet by Q ÷ V.

[0203] (5) First-efficiency and energy density of individual battery cells

[0204] The battery cells were placed in a negative pressure environment at 45°C for 20 minutes and then charged at a rate of 0.05C to 20% SOC (the theoretical battery cell capacity C can be calculated based on the cathode size after winding) to obtain the formation capacity C0. The cells were then left to stand at 45°C for 48 hours before being transferred to room temperature and pressure and charged at a rate of 0.2C to 3.65V. They were then charged at a constant voltage of 3.65V to 0.05C to obtain the charging capacity C1. Finally, the cells were discharged at a rate of 0.1C to 2V at room temperature and pressure to obtain the discharge capacity C2, and the discharge energy E (Wh) was also obtained.

[0205] (6) Cyclic capacity retention

[0206] The battery cell was placed in a 25°C environment and charged to 80% SOC at a 1C2 rate, then charged to 3.8V at a 0.33C2 rate, and finally charged at a constant voltage of 3.8V. After full charging, it was left to stand for 10 minutes, and then discharged to 2V at a 1C2 rate to obtain the discharge capacity C. 10 Repeat the above steps until the battery cell is cycled to 90% SOH, obtaining the discharge capacity C at 2V. 100 Calculate the cycle capacity retention rate = C 100 ÷C 10 *100%.

[0207] Table 2. Apparent volume, true volume, and porosity of the bent diaphragm in Example 1.

[0208] As shown in Table 2, the bent diaphragm in Example 1 has a large apparent volume, a low true volume, and a high porosity.

[0209] Table 3 shows the electrical performance of the battery cells in Examples 1-10 and Comparative Examples 1-3.

[0210] As shown in Examples 1-3, when the mass of silicon in the silicon-carbon composite material accounts for 1.5% of the mass of the negative electrode active material, and the particle size of the polymer particles is selected as 5μm, 7μm, and 12μm, the unit volume capacity of the negative electrode sheet is 630mAh / cm³. 3 The battery cell has an initial efficiency of ≥91.4%, an energy density of 430Wh / L, and a cycle capacity retention of ≥1192 cycles@90%SOH; and when the polymer particle size is 7μm, the battery cell has the highest cycle capacity retention of 1358 cycles@90%SOH.

[0211] As shown in Examples 4-6, when the mass of silicon in the silicon-carbon composite material accounts for 4% of the mass of the negative electrode active material, and the particle size of the polymer particles is selected as 7μm, 12μm, and 20μm, the unit volume capacity of the negative electrode sheet is 715mAh / cm³. 3 The battery cell has an initial efficiency of ≥90.8%, an energy density of 443Wh / L, and a cycle capacity retention of ≥805 cycles@90%SOH; and when the polymer particle size is 12μm, the battery cell has a maximum cycle capacity retention of 920 cycles@90%SOH.

[0212] As shown in Examples 7-10, when the mass of silicon in the silicon-carbon composite material accounts for 4% of the mass of the negative electrode active material, and the particle size of the polymer particles is selected as 7μm, 12μm, 20μm, and 22μm, the unit volume capacity of the negative electrode sheet is 770mAh / cm³. 3 The battery cell has an initial efficiency of ≥89.6%, an energy density of 452Wh / L, and a cycle capacity retention of ≥339 cycles@90%SOH; and when the polymer particle size is 20μm, the battery cell has a maximum cycle capacity retention of 606 cycles@90%SOH.

[0213] As can be seen from the comparison of Comparative Example 1 and Examples 1-3, when there are no polymer particles in the adhesive layer, compared with the scheme where there are polymer particles in the adhesive layer, the bending gap is reduced and the number of cycles of the battery cell at 90% SOH is reduced.

[0214] As can be seen from the comparison between Comparative Example 2 and Examples 4-6, when there are no polymer particles in the adhesive layer, compared with the scheme where there are polymer particles in the adhesive layer, the bending gap is reduced and the number of cycles of the battery cell at 90% SOH is reduced.

[0215] As can be seen from the comparison of Comparative Example 3 and Examples 7-10, when there are no polymer particles in the adhesive layer, the bending gap is reduced compared to the scheme with polymer particles in the adhesive layer, and the number of cycles of the battery cell at 90% SOH is reduced.

[0216] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, wherein, The battery cell includes an electrode assembly, which includes a positive electrode, a negative electrode, and a separator. The separator is disposed between the positive and negative electrode. The negative electrode includes a negative active material, which includes a silicon-carbon composite material and a carbon material. The electrode assembly includes a straight region and two bending regions. The two ends of the straight region are respectively connected to the two bending regions. An adhesive layer is disposed on the surface of the separator in the bending region, and the adhesive layer includes polymer particles.

2. The battery cell according to claim 1, wherein, In the silicon-carbon composite material, silicon accounts for 1.5% to 6% of the mass of the negative electrode active material, and the volume distribution particle size Dv50 of the polymer particles is 5 μm to 22 μm.

3. The battery cell according to claim 2, wherein, When silicon accounts for 1.5% to 3% of the mass of the negative electrode active material in the silicon-carbon composite material, the volume distribution particle size Dv50 of the polymer particles is 7 μm to 12 μm, and / or; When silicon accounts for 3% to 4.5% of the mass of the negative electrode active material in the silicon-carbon composite material, the volume distribution particle size Dv50 of the polymer particles is 12 μm to 15 μm, and / or; When silicon accounts for 4.5% to 6% of the mass of the negative electrode active material in the silicon-carbon composite material, the volume distribution particle size Dv50 of the polymer particles is 15 μm to 20 μm.

4. The battery cell according to claim 2 or 3, wherein, The silicon-carbon composite material contains 30% to 60% silicon by mass.

5. The battery cell according to any one of claims 2 to 4, wherein, The negative electrode has a unit volume capacity of 630mAh / cm3 to 770mAh / cm3.

6. The battery cell according to any one of claims 1 to 5, wherein, The distance between the positive electrode and the negative electrode in the bending region is 40μm to 100μm.

7. The battery cell according to any one of claims 1 to 6, wherein, The polymer includes a polyvinylidene fluoride (PVDF) polymer, which includes at least one of the following: PVDF polymer, PVDF-hexafluoropropylene copolymer, PVDF-pentafluoropropylene copolymer, PVDF-tetrafluoropropylene copolymer, PVDF-trifluoropropylene copolymer, PVDF-perfluorobutene copolymer, PVDF-tetrafluoroethylene copolymer, PVDF-trifluoroethylene copolymer, PVDF-trifluorochloroethylene copolymer, and PVDF-vinyl fluoride copolymer.

8. A method for preparing a single battery cell, wherein, The method for preparing the battery cell includes: coating an adhesive layer slurry on a separator to form an adhesive layer, and then winding a positive electrode sheet, a negative electrode sheet and a separator to form an electrode assembly. The electrode assembly includes a flat region and two bending regions. The two ends of the flat region are respectively connected to the two bending regions, and the electrode assembly is hot-pressed by applying pressure to the flat region. The negative electrode sheet includes a negative electrode active material, which includes a silicon-carbon composite material and a carbon material, and the adhesive layer includes polymer particles.

9. The method for preparing a battery cell according to claim 8, wherein, The coating amount of the adhesive layer slurry is 1.5mg~2.5mg / 1540.25mm. 2 .

10. The method for preparing a battery cell according to claim 8 or 9, wherein, The hot pressing temperature is 70℃~100℃, and the hot pressing time is 70s~100s.

11. The method for preparing a battery cell according to claim 10, wherein, When the volume distribution particle size Dv50 of the polymer particles is 7μm to 12μm, the hot pressing time is 70s to 80s, and / or; The volume distribution particle size Dv50 of the polymer particles is 12μm to 15μm, the hot pressing time is 80s to 90s, and / or; The volume distribution particle size Dv50 of the polymer particles is 15μm to 20μm, and the hot pressing time is 90s to 100s.

12. The method for preparing a battery cell according to any one of claims 8 to 11, wherein, The adhesive layer slurry is applied to the release membrane by a dot-matrix coating method.

13. A battery, wherein, The battery comprises a battery cell according to any one of claims 1 to 7 or a battery cell prepared by any one of claims 8 to 12.

14. An electrical appliance, wherein, The electrical device includes the battery of claim 13, the battery being used to provide electrical energy.

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