Battery cell, method of manufacturing a battery cell, battery device, and electric device

Abstract

The present application provides a battery cell, a method for preparing a battery cell, a battery device and a power utilization device. The battery cell of the present application comprises an electrode assembly, the electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, the separator is located between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer located on at least one side of the positive electrode current collector, the positive electrode active layer comprises a positive electrode active material; the compaction density of the positive electrode active layer is 2.3 g / cm 3 - 3.35 g / cm 3 ; the separator comprises a base layer and a polymer layer located on the side of the base layer facing the positive electrode sheet, the polymer layer comprises a fluorine-containing polymer with a crystallinity less than or equal to 50%. The fluorine-containing polymer layer of the battery cell of the present application can melt and cover the burrs of the positive electrode current collector and the positive electrode active layer, thereby improving the cycle performance and safety performance of the battery cell.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a battery cell, a method for preparing a battery cell, a battery device, and an electrical device. Background Technology

[0002] In recent years, with the increasingly wide range of applications, batteries 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 cars, military equipment, aerospace, and many other fields. Due to the significant advancements in battery technology, higher requirements have been placed on their cycle performance and safety performance. Summary of the Invention

[0003] This application addresses the aforementioned issues and aims to provide a battery cell, a method for preparing a battery cell, a battery device, and an electrical device. The fluoropolymer layer in the battery cell of this application can melt-coat the burrs of the positive electrode current collector and the positive electrode active layer, thereby improving the cycle performance and safety performance of the battery cell.

[0004] To achieve the above objectives, the first aspect of this application provides a battery cell including an electrode assembly, the electrode assembly including a positive electrode, a negative electrode and a separator, the separator being located between the positive electrode and the negative electrode.

[0005] The positive electrode includes a positive current collector and a positive active layer located on at least one side of the positive current collector. The positive active layer includes a positive active material; the compaction density of the positive active layer is 2.3 g / cm³. 3 - 3.35 g / cm 3 ;

[0006] The separator includes a base layer and a polymer layer located on the side of the base layer facing the positive electrode. The polymer layer includes a fluorinated polymer with a crystallinity of less than or equal to 50%.

[0007] Therefore, by using fluoropolymers with a crystallinity of less than or equal to 50% in the polymer layer, the positive electrode current collector and the burrs at the edge of the positive electrode active layer as well as the burrs in the non-edge areas of the positive electrode active layer can be melt-coated. Furthermore, the compaction density of the positive electrode active layer within the above range helps to reduce the number of burrs at the edge and non-edge areas of the positive electrode active layer and improve the structural stability of the positive electrode sheet, thereby reducing the risk of burrs puncturing the separator and causing a short circuit, and thus improving the cycle performance and safety performance of the battery cell.

[0008] In any embodiment of the first aspect, the crystallinity of the fluoropolymer is 20%-50%.

[0009] Therefore, the crystallinity range of the aforementioned fluoropolymer can, on the one hand, melt-coat the burrs at the edges of the positive electrode current collector and the positive electrode active layer, as well as the non-edge burrs of the positive electrode active layer, to reduce the risk of short circuits caused by burrs piercing the separator, thereby improving the cycle performance and safety performance of the battery cell. On the other hand, if the crystallinity of the fluoropolymer decreases, its structural stability will decrease, making it easier to dissolve into the electrolyte, resulting in increased electrolyte viscosity, decreased lithium-ion transport rate, increased impedance of the battery cell, and impact on the cycle performance of the battery cell. The aforementioned range reduces this impact.

[0010] In any embodiment of the first aspect, the weight-average molecular weight of the fluoropolymer is 120,000 to 800,000.

[0011] In any embodiment of the first aspect, the weight-average molecular weight of the fluoropolymer is 150,000 to 500,000.

[0012] Therefore, the aforementioned weight-average molecular weight range of the fluoropolymers has two advantages. First, it makes the polymer viscosity more suitable for coating the burrs on the positive electrode current collector and the edge of the positive electrode active layer, as well as the non-edge burrs on the positive electrode active layer. This reduces the risk of burrs puncturing the separator and causing a short circuit, thereby improving the cycle performance and safety performance of the battery cell. Second, a decrease in weight-average molecular weight may cause the fluoropolymers to easily dissolve in the electrolyte, resulting in an increase in electrolyte viscosity and affecting the cycle performance of the battery cell. The aforementioned range reduces this impact.

[0013] In any embodiment of the first aspect, the thickness of the polymer layer is 0.2 μm - 5 μm.

[0014] In any embodiment of the first aspect, the thickness of the polymer layer is 0.5 μm - 3 μm.

[0015] Therefore, on the one hand, the aforementioned polymer layer thickness range can cover the burrs on the positive electrode current collector and the edge of the positive electrode active layer, as well as the non-edge burrs of the positive electrode active layer, to a greater extent, thereby reducing the damage of burrs to the separator and improving the cycle performance and safety performance of the battery cell. On the other hand, increasing the polymer layer thickness may increase the lithium-ion transport distance, thus affecting the fast charging performance of the battery cell, and increasing the polymer layer thickness may affect the energy density of the battery cell. The aforementioned thickness range reduces these effects.

[0016] In any embodiment of the first aspect, the ratio of the area of ​​the polymer layer to the area of ​​the base layer is 65%-100%.

[0017] This allows for greater coverage of burrs on the positive electrode current collector and the edges of the positive electrode active layer, as well as burrs in the non-edge areas of the positive electrode active layer. This reduces the risk of burrs puncturing the separator, thereby improving the cycle performance and safety of the battery cells. It also facilitates a strong bond between the electrodes and the separator. Furthermore, when the polymer layer partially covers the base layer in the aforementioned proportion, it helps to create a gap between the positive electrode and the separator, which in turn facilitates electrolyte penetration and improves lithium-ion transport.

[0018] In any embodiment of the first aspect, the fluoropolymer includes one or more of polyvinylidene fluoride, vinylidene fluoride-trifluorochloroethylene copolymer, vinylidene fluoride-trifluorochloroethylene-tetrafluoroethylene copolymer, vinylidene fluoride-trifluorochloroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-trifluorochloroethylene-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-acrylic acid copolymer, and vinylidene fluoride-acrylate copolymer.

[0019] Therefore, the aforementioned fluoropolymer can melt the burrs covering the positive electrode current collector and the edge of the positive electrode active layer, as well as the burrs in the non-edge areas of the positive electrode active layer, reducing the risk of burrs puncturing the separator, thereby improving the cycle performance and safety performance of the battery cell.

[0020] In any embodiment of the first aspect, the diaphragm further includes an inorganic material layer located between the base layer and the polymer layer.

[0021] Therefore, the inorganic material layer has high mechanical strength and strong resistance to thermal shrinkage, which can reduce the risk of burrs on the positive electrode current collector and the edge of the positive electrode active layer, as well as burrs in the non-edge areas of the positive electrode active layer, piercing the separator during high-temperature cycling, thereby improving the cycle performance and safety performance of the battery cell. In addition, the inorganic material layer has a high electrolyte wetting rate, which can reduce impedance and is beneficial to lithium ion transport.

[0022] In any embodiment of the first aspect, the inorganic material layer includes one or more inorganic materials selected from alumina, boehmite, titanium dioxide, and silicon dioxide.

[0023] In any embodiment of the first aspect, the average particle size of the positive electrode active material is 0.35 μm - 2.1 μm.

[0024] In any embodiment of the first aspect, the average particle size of the positive electrode active material is 0.5 μm - 1.5 μm.

[0025] Therefore, on the one hand, keeping the average particle size of the positive electrode active material within the upper limit helps reduce the number of burrs at the edge and non-edge regions of the positive electrode active layer, thereby reducing the risk of burrs puncturing the separator, improving the cycle performance and safety performance of the battery cell, and also helping to increase the energy density of the battery cell; on the other hand, reducing the average particle size of the positive electrode active material may allow the positive electrode active material particles to pass through the separator pores, which may affect the self-discharge and safety performance of the battery cell. The above-mentioned average particle size range reduces this impact.

[0026] In any embodiment of the first aspect, the areal density of the positive electrode active layer is 0.15 mg / mm². 2 - 0.4mg / mm 2 .

[0027] Therefore, on the one hand, having a surface density of the positive electrode active layer that is not lower than the lower limit is beneficial to improving the energy density of the battery cell. On the other hand, increasing the surface density of the positive electrode active layer leads to an increase in the thickness of the positive electrode active layer, which may easily generate edge burrs during processing. The above-mentioned range of surface density of the positive electrode active layer reduces this impact.

[0028] In any embodiment of the first aspect, the positive electrode active material comprises undoped lithium iron phosphate or doped lithium iron phosphate, wherein the doping element comprises one or more of Ti, Zr, Mn, Co, and V.

[0029] Therefore, among commonly used positive electrode active materials, lithium iron phosphate materials have a smaller particle size and fewer burrs on the edges and non-edges of their positive electrode active layer, reducing the risk of burrs puncturing the separator and improving the cycle performance and safety performance of the battery cell.

[0030] In any embodiment of the first aspect, the mass content of the dopant element in the doped lithium iron phosphate is 500-5000 ppm.

[0031] Therefore, the above-mentioned range of doping element content is beneficial to improving the lithium-ion diffusion coefficient of the positive electrode active layer and increasing the discharge power of the battery cell.

[0032] In any embodiment of the first aspect, the thickness of the base layer is 5 μm - 12 μm.

[0033] Therefore, on the one hand, the aforementioned thickness range of the base layer can improve the liquid retention capacity of the battery cells and reduce the impedance of the battery cells through the micropores and capillary forces of the base layer, and can also improve the mechanical strength of the separator, thereby improving the rate performance and cycle performance of the battery cells. On the other hand, increasing the thickness of the base layer may increase the resistance to lithium-ion transport and affect the rate performance of the battery cells. The aforementioned range reduces this impact.

[0034] In any embodiment of the first aspect, the porosity of the separator is 19% - 50%. Thus, on the one hand, a separator porosity not lower than the aforementioned lower limit is beneficial to improving the liquid phase transport of the battery cell and enhancing the discharge performance of the battery cell; on the other hand, an increase in separator porosity may weaken the insulating effect of the separator and affect the safety of the battery cell, and the aforementioned range reduces this impact.

[0035] In any embodiment of the first aspect, the positive electrode active layer further includes a positive electrode conductive agent, which includes a single-arm carbon nanotube.

[0036] Therefore, the entanglement effect of single-arm carbon nanotubes can entangle and anchor the positive electrode active material particles onto the positive electrode current collector. Furthermore, the single-arm carbon nanotubes can buffer the volume change of the positive electrode active material particles during cycling to reduce particle shedding. This is beneficial for the positive electrode active material particles to adhere to the positive electrode current collector and also helps to improve the electronic conductivity, thereby increasing the discharge power of the battery cell.

[0037] In any embodiment of the first aspect, the positive electrode active layer further includes a polymeric positive electrode binder, wherein the weight-average molecular weight of the polymeric positive electrode binder is greater than or equal to the weight-average molecular weight of the fluoropolymer.

[0038] Therefore, it is beneficial to firmly bond the positive electrode active material particles to the positive electrode current collector using polymer-based positive electrode binders, thereby reducing the loss of positive electrode active material and improving the cycle life of the battery cell.

[0039] In any embodiment of the first aspect, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on at least one side of the negative electrode current collector, wherein the negative electrode active layer includes a negative electrode active material; wherein,

[0040] Negative electrode active materials include graphite materials.

[0041] Therefore, using graphite materials in the negative electrode active material is beneficial to improving the cycle life of the battery cell.

[0042] In any embodiment of the first aspect, the degree of graphitization of the negative electrode active material is 90% - 94%.

[0043] Therefore, on the one hand, maintaining the graphitization degree of the negative electrode active material at or above the lower limit is beneficial for improving the rate performance, energy density, and cycle life of the battery cell; on the other hand, increasing the graphitization degree of the negative electrode active material may lead to a decrease in the capacity of the battery cell and a deterioration in fast charging performance, and the above range reduces this impact.

[0044] In any embodiment of the first aspect, the average particle size of the negative electrode active material is 8 μm - 20 μm.

[0045] Therefore, on the one hand, having an average particle size of negative electrode active material that is not lower than the aforementioned lower limit is beneficial for reducing the specific surface area of ​​negative electrode active material, reducing the contact area between negative electrode active material and electrolyte, reducing side reactions, and thus improving the cycle life of battery cells. On the other hand, an increase in the average particle size of negative electrode active material may lead to gelation of negative electrode slurry, making processing difficult, and may also lead to a deterioration in the fast charging performance of battery cells. The aforementioned range reduces this impact.

[0046] In any embodiment of the first aspect, the battery cell further includes an electrolyte, which comprises electrolyte additives, including unsaturated carbonate additives and / or sulfonate additives. Therefore, using the aforementioned electrolyte additives is beneficial for improving the cycle life of the battery cell.

[0047] In any embodiment of the first aspect, the unsaturated carbonate additive includes one or more of vinylene carbonate, fluoroethylene carbonate, and vinylene carbonate; and / or,

[0048] Sulfonate additives include one or more of 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, methylene disulfonate, vinyl sulfate, and ethyl sulfite.

[0049] In any embodiment of the first aspect, the electrolyte further includes a solvent, the solvent including a cyclic carbonate solvent, the cyclic carbonate solvent being 20% ​​- 40% of the solvent mass.

[0050] Therefore, on the one hand, having a cyclic carbonate solvent content not lower than the aforementioned lower limit is beneficial to improving the cycle life of the battery cell; on the other hand, having a cyclic carbonate solvent content not exceeding the aforementioned upper limit is beneficial to reducing the electrolyte viscosity under low-temperature conditions, thereby improving the low-temperature charge and discharge power of the battery cell.

[0051] In any embodiment of the first aspect, the electrode assembly is cuboid in shape, and the ratio of the length to the width of the electrode assembly is 2–8.

[0052] Since the crystallinity of the fluoropolymer in the polymer layer is less than or equal to 50%, the mechanical strength of the electrode assembly formed after the diaphragm is bonded to the positive electrode sheet through the polymer layer is reduced. The above-mentioned length-to-width ratio of the electrode assembly makes it easier to load and unload the electrode assembly for subsequent processing.

[0053] In any embodiment of the first aspect, the electrode assembly is a stacked structure.

[0054] A second aspect of this application provides a method for preparing a battery cell, comprising the following steps:

[0055] The positive electrode, separator, and negative electrode are arranged sequentially and hot-pressed at 80℃-150℃ under pressures of 2kN-8kN to obtain an electrode assembly. This electrode assembly is then used to fabricate a single battery cell.

[0056] The positive electrode includes a positive current collector and a positive active layer located on at least one side of the positive current collector. The positive active layer includes a positive active material; the compaction density of the positive active layer is 2.3 g / cm³. 3 - 3.35 g / cm 3 ;

[0057] The separator includes a base layer and a polymer layer located on the side of the base layer facing the positive electrode. The polymer layer includes a fluorinated polymer with a crystallinity of less than or equal to 50%.

[0058] Therefore, hot pressing under the above conditions can melt and coat the positive electrode current collector and the burrs at the edge of the positive electrode active layer and the non-edge burrs of the positive electrode active layer with a crystallinity of less than or equal to 50%. At the same time, limiting the compaction density of the positive electrode active layer within the above range helps to reduce the number of burrs at the edge and non-edge areas of the positive electrode active layer and improve the structural stability of the positive electrode sheet, thereby reducing the risk of short circuit caused by burrs piercing the separator, and thus improving the cycle performance and safety performance of the battery cell.

[0059] In any embodiment of the second aspect, the hot pressing time is 40 s - 180 s.

[0060] In any embodiment of the second aspect, the battery cell is as described in the first aspect.

[0061] In any embodiment of the second aspect, the diaphragm further includes an inorganic material layer located between the base layer and the polymer layer.

[0062] In any embodiment of the second aspect, the polymer layer is prepared by the following steps:

[0063] A fluoropolymer is mixed with an oily solvent to obtain a polymer slurry;

[0064] The polymer slurry is coated onto the substrate or inorganic material layer facing the positive electrode, and then dried to obtain the polymer layer.

[0065] In any embodiment of the second aspect, the oily solvent includes one or more of N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, and dimethylacetamide.

[0066] A third aspect of this application provides a battery device, including a battery cell according to the first aspect of this application or a battery cell prepared by the method of the second aspect of this application.

[0067] The fourth aspect of this application provides an electrical device, including a battery cell of the first aspect of this application or a battery device of the third aspect of this application. Attached Figure Description

[0068] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0069] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0070] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0071] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0072] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0073] Figure 6 This is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to one embodiment of this application.

[0074] Explanation of reference numerals in the attached figures:

[0075] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0076] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery module, battery pack, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically 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.

[0077] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0078] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0079] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means 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.

[0080] [Battery cell]

[0081] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0082] The battery cell can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, sodium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc., and the embodiments of this application are not limited to this.

[0083] A single battery cell typically includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator positioned between the positive and negative electrodes. During the charging and discharging process of a single battery cell, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits while allowing active ions to pass through.

[0084] One embodiment of this application provides a lithium-ion battery cell, including an electrode assembly, the electrode assembly including a positive electrode, a negative electrode and a separator, the separator being located between the positive electrode and the negative electrode;

[0085] The positive electrode includes a positive current collector and a positive active layer located on at least one side of the positive current collector. The positive active layer includes a positive active material; the compaction density of the positive active layer is 2.3 g / cm³. 3 - 3.35 g / cm 3 (e.g., 2.3 g / cm) 3 2.4 g / cm 3 2.48 g / cm 3 2.5 g / cm 3 2.55 g / cm 3 2.6 g / cm 3 2.63 g / cm 3 2.7 g / cm 3 2.8g / cm 3 2.9 g / cm3 3.0 g / cm 3 3.1 g / cm 3 3.2 g / cm 3 3.3 g / cm 3 3.35 g / cm 3 Or a range of any of the above values);

[0086] The separator includes a base layer and a polymer layer located on the side of the base layer facing the positive electrode. The polymer layer includes a fluoropolymer with a crystallinity of less than or equal to 50% (e.g., 10%, 18%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any range of the above values).

[0087] In a single battery cell, burrs are prone to form on the edges of the positive current collector and the positive active layer, as well as in the non-edge areas of the positive active layer. These burrs can puncture the separator, causing a short circuit and leading to battery safety issues.

[0088] Although the mechanism is not yet clear, the applicant unexpectedly discovered that fluorinated polymers with a crystallinity of less than or equal to 50% in the polymer layer can melt-coat the burrs on the edge of the positive electrode current collector and the positive electrode active layer, as well as the burrs in the non-edge areas of the positive electrode active layer, thereby reducing the sharpness and conductivity of the burrs. At the same time, limiting the compaction density of the positive electrode active layer within the above range helps to reduce the number of burrs on the edge and non-edge areas of the positive electrode active layer and improve the structural stability of the positive electrode sheet, thereby reducing the risk of short circuit caused by burrs piercing the separator, and thus improving the cycle performance and safety performance of the battery cell.

[0089] Battery cell electrode assemblies include various structures, and traditional electrode assembly structures all suffer from burr problems in the positive electrode sheet. For example, burrs easily appear on the cutting edge of the positive current collector in a wound electrode assembly. However, in the later stages of cycling, uneven stress distribution in wound electrode assemblies can easily lead to increased electrode spacing, and local polarization in corner areas can cause corner lithium plating and increased internal resistance. Stacked electrode assemblies can avoid these corner problems. However, in stacked electrode assemblies, burrs easily form on the edges of the positive current collector and the positive active layer, as well as in the non-edge areas of the positive active layer. The fluoropolymer in the polymer layer of this application can coat the burrs on the positive electrode sheet, and the number of burrs on the edges and non-edge areas of the positive active layer is reduced, thereby improving the cycle performance and safety performance of the battery cell.

[0090] In some embodiments, the crystallinity of the fluoropolymer is 20%-50%.

[0091] Therefore, the crystallinity range of the aforementioned fluoropolymer can, on the one hand, melt-coat the burrs at the edges of the positive electrode current collector and the positive electrode active layer, as well as the non-edge burrs of the positive electrode active layer, to reduce the risk of short circuits caused by burrs piercing the separator, thereby improving the cycle performance and safety performance of the battery cell. On the other hand, if the crystallinity of the fluoropolymer decreases, its structural stability will decrease, making it easier to dissolve into the electrolyte, resulting in increased electrolyte viscosity, decreased lithium-ion transport rate, increased impedance of the battery cell, and impact on the cycle performance of the battery cell. The aforementioned range reduces this impact.

[0092] In this application, the crystallinity of the fluoropolymer was tested using conventional methods in the art. For example, the battery cell was disassembled, the separator was removed, and the polymer (fluoropolymer) on the surface of the separator facing the positive electrode was scraped off. The fluoropolymer was then tested using a Differential Scanning Calorimeter (DSC) model 250 from TA Instruments in a nitrogen atmosphere at a heating rate of 10 °C / min within a temperature range of -100 °C to 400 °C. The purge gas flow rate was 50 ml / min, and the protective gas flow rate was 70 ml / min. The resulting DSC curve was obtained, and the crystallinity of the fluoropolymer was calculated using the following formula. The peak area of ​​the DSC curve is the enthalpy of fusion ΔH (in J / g), and ΔHm100% is the standard enthalpy of fusion (heat of fusion in crystalline state, in J / g) of the fluoropolymer. For example, the ΔHm100% of polyvinylidene fluoride is 104.7 J / g.

[0093] The crystallinity of fluoropolymers = 100% × ΔH / (ΔHm × 100%).

[0094] In some embodiments, the weight-average molecular weight of the fluoropolymer is 120,000 to 800,000, for example, 120,000, 150,000, 200,000, 250,000, 300,000, 350,000, 400,000, 450,000, 500,000, 550,000, 600,000, 650,000, 700,000, 750,000, 800,000 or any combination of the above values.

[0095] In some embodiments, the weight-average molecular weight of the fluoropolymer is 150,000 to 500,000.

[0096] Therefore, the aforementioned weight-average molecular weight range of the fluoropolymers has two advantages. First, it makes the polymer viscosity more suitable for coating the burrs on the positive electrode current collector and the edge of the positive electrode active layer, as well as the non-edge burrs on the positive electrode active layer. This reduces the risk of burrs puncturing the separator and causing a short circuit, thereby improving the cycle performance and safety performance of the battery cell. Second, a decrease in weight-average molecular weight may cause the fluoropolymers to easily dissolve in the electrolyte, resulting in an increase in electrolyte viscosity and affecting the cycle performance of the battery cell. The aforementioned range reduces this impact.

[0097] In this application, the weight-average molecular weight of the fluoropolymer is tested using conventional methods in the art. For example, the battery cell is disassembled, the separator is removed, and the polymer (i.e., the fluoropolymer) on the surface of the separator facing the positive electrode is scraped off. A 3.0% (w / w) fluoropolymer solution is prepared using a purified solvent (e.g., N-methylpyrrolidone), and allowed to stand for one day for later use. Gel chromatography (e.g., a Waters 2695 Isocratic HPLC with a 2141 differential refractive index detector) is used for detection. The chromatographic column is oil-based: Styragel HT5 DMF7.8*300mm + Styragel HT4, with an injection volume of 5 ml. A 3.0% (w / w) polystyrene solution sample is used as a reference. The gel chromatography can calculate the weight-average molecular weight of the polymer being tested based on the weight-average molecular weight of the reference sample.

[0098] In some embodiments, the thickness of the polymer layer is 0.2 μm to 5 μm, for example, 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or any combination of the above values.

[0099] In some embodiments, the thickness of the polymer layer is 0.5 μm - 3 μm.

[0100] Therefore, on the one hand, the aforementioned polymer layer thickness range can cover the burrs on the positive electrode current collector and the edge of the positive electrode active layer, as well as the non-edge burrs of the positive electrode active layer, to a greater extent, thereby reducing the damage of burrs to the separator and improving the cycle performance and safety performance of the battery cell. On the other hand, increasing the polymer layer thickness may increase the lithium-ion transport distance, thus affecting the fast charging performance of the battery cell, and increasing the polymer layer thickness may affect the energy density of the battery cell. The aforementioned thickness range reduces these effects.

[0101] In this application, the thickness of the polymer layer is tested using conventional methods in the art; for example, by disassembling the battery cell, removing the separator, cutting it along the thickness direction, and observing the cross-section along the thickness direction using a scanning electron microscope, the base layer, inorganic material layer, and polymer layer of the separator can be distinguished, thereby directly measuring the thickness of the polymer layer; or the thickness of the polymer layer can be measured multiple times at different sites, and then the average value is taken as the thickness of the polymer layer to improve the accuracy of the measurement.

[0102] In some implementations, the polymer layer being located on the side of the substrate facing the positive electrode means that the polymer layer can cover both the edge and non-edge areas of the substrate facing the positive electrode.

[0103] In some embodiments, the ratio of the area of ​​the polymer layer to the area of ​​the base layer is 65% - 100% or 70% - 100% or 70% - 99%, for example, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, 100% or any of the above values.

[0104] This allows for greater coverage of burrs on the positive electrode current collector and the edges of the positive electrode active layer, as well as burrs in the non-edge areas of the positive electrode active layer. This reduces the risk of burrs puncturing the separator, thereby improving the cycle performance and safety of the battery cells. It also facilitates a strong bond between the electrodes and the separator. Furthermore, when the polymer layer partially covers the base layer in the aforementioned proportion, it helps to create a gap between the positive electrode and the separator, which in turn facilitates electrolyte penetration and improves lithium-ion transport.

[0105] In some embodiments, the fluoropolymer includes one or more of polyvinylidene fluoride, vinylidene fluoride-trifluorochloroethylene copolymer, vinylidene fluoride-trifluorochloroethylene-tetrafluoroethylene copolymer, vinylidene fluoride-trifluorochloroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-trifluorochloroethylene-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-acrylic acid copolymer, and vinylidene fluoride-acrylate copolymer.

[0106] Therefore, the aforementioned fluoropolymer can melt the burrs covering the positive electrode current collector and the edge of the positive electrode active layer, as well as the burrs in the non-edge areas of the positive electrode active layer, reducing the risk of burrs puncturing the separator, thereby improving the cycle performance and safety performance of the battery cell.

[0107] In this application, conventional methods in the art were used to confirm the structure of the fluoropolymer. For example, the battery cell was disassembled, the separator was removed, and a 0.5cm × 0.5cm separator sample was cut and tested using a scanning electron microscope and energy dispersive spectroscopy (SEM) (equipment model: Sigma300). The test was conducted according to JY / T010-1996 to confirm whether it contained fluorine. Material (excluding the base film and inorganic material layer) was scraped from the surface of the separator facing the positive electrode and tested using an infrared spectrometer (model: IS10) according to the national standard GB / T6040-2002. The characteristic peaks of fluorine-carbon bonds (CF2 symmetric stretching vibration peak, CF2 asymmetric stretching vibration peak, CF2 bending vibration peak, and CF2 torsional vibration peak are located at 1140 cm⁻¹) were obtained. -1 Left and right, 1210 cm -1 Left and right, 650 cm -1 Left and right and 540 cm -1 The CF stretching vibration peak (around 1200 cm⁻¹) and the characteristic peaks of carbon-hydrogen bonds can confirm the main characteristic peaks in the polymer, and combined with nuclear magnetic resonance (NMR) (e.g., the peak at 1200 cm⁻¹), the main characteristic peaks in the polymer can be identified. 1 H NMR,13 C NMR and 19 The structure of fluoropolymers can be confirmed by identifying the repeating unit structure of polymers using fluoropolymer NMR.

[0108] In some embodiments, the diaphragm further includes an inorganic material layer located between the base layer and the polymer layer.

[0109] Therefore, the inorganic material layer has high mechanical strength and strong resistance to thermal shrinkage, which can reduce the risk of burrs on the positive electrode current collector and the edge of the positive electrode active layer, as well as burrs in the non-edge areas of the positive electrode active layer, piercing the separator during high-temperature cycling, thereby improving the cycle performance and safety performance of the battery cell. In addition, the inorganic material layer has a high electrolyte wetting rate, which can reduce impedance and is beneficial to lithium ion transport.

[0110] In some embodiments, the inorganic material layer includes one or more inorganic materials selected from alumina, boehmite, titanium dioxide, and silicon dioxide.

[0111] In this application, the specific substances of the inorganic materials are identified using conventional methods in the art. For example, the battery cell is disassembled, the separator is removed, the polymer on the side of the separator facing the positive electrode is scraped off, and then the inorganic material layer powder (binders and other additives do not produce interfering diffraction peaks) is taken out. The specific substances of the inorganic materials can be identified by comparing the obtained XRD pattern with a standard PDF card.

[0112] In some embodiments, the average particle size of the positive electrode active material is 0.35 μm to 2.1 μm, for example, 0.35 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.3 μm, 1.5 μm, 1.7 μm, 2 μm, 2.1 μm or any range of the above values.

[0113] In some embodiments, the average particle size of the positive electrode active material is 0.5 μm - 1.5 μm.

[0114] Therefore, on the one hand, keeping the average particle size of the positive electrode active material within the upper limit helps reduce the number of burrs at the edge and non-edge regions of the positive electrode active layer, thereby reducing the risk of burrs puncturing the separator, improving the cycle performance and safety performance of the battery cell, and also helping to increase the energy density of the battery cell; on the other hand, reducing the average particle size of the positive electrode active material may allow the positive electrode active material particles to pass through the separator pores, which may affect the self-discharge and safety performance of the battery cell. The above-mentioned average particle size range reduces this impact.

[0115] In this application, the average particle size of the positive electrode active material is tested using conventional methods in the art. For example, the battery cell is disassembled, the positive electrode sheet is removed, and cut into 6mm × 6mm pieces. The positive electrode sheet is then cut along its thickness direction using an argon ion beam (for example, a Leica EM TIC 3X CP device can be used, operating voltage: 6kV, operating time: 6h). After exposing the cut surface, a scanning electron microscope (for example, a Hitachi SU8230 device can be used, operating voltage: 3kV, beam current: high, probe type: U (LA100), working distance <5mm) is used to observe the cut surface of the positive electrode active layer along its thickness direction. Images are acquired in secondary electron mode at non-edge locations within the cut surface of the positive electrode active layer using a field emission scanning electron microscope, and several electron microscope images are taken at a certain magnification (e.g., 10kx magnification). Analyzing the particles in the electron microscope image using Avizo software will yield the particle size information, "EqDiameter (nm)". Since conductive agents and other additives are usually smaller than 50 nm, particles with "EqDiameter (nm)" smaller than 50 nm should be removed when calculating the average particle size to avoid interference. At the same time, to ensure the accuracy of the data, the number of particles counted should be ≥5000. The average particle size is obtained by summing the "EqDiameter (nm)" parameters of the counted positive electrode active material particles and taking the average value.

[0116] In some embodiments, the areal density of the positive electrode active layer is 0.15 mg / mm². 2 - 0.4 mg / mm 2 For example, 0.15 mg / mm 2 0.2 mg / mm 2 0.276 mg / mm 2 0.3 mg / mm 2 0.364 mg / mm 2 0.4 mg / mm 2 Or a range consisting of any of the above values.

[0117] Therefore, on the one hand, having a surface density of the positive electrode active layer that is not lower than the lower limit is beneficial to improving the energy density of the battery cell. On the other hand, increasing the surface density of the positive electrode active layer leads to an increase in the thickness of the positive electrode active layer, which may easily generate edge burrs during processing. The above-mentioned range of surface density of the positive electrode active layer reduces this impact.

[0118] In this application, the compaction density and areal density of the positive electrode active layer can be tested using conventional methods in the art. For example, the battery cell is disassembled, the positive electrode sheet is removed and cleaned and dried with an organic solvent, a fixed area of ​​positive electrode sheet is cut and weighed, and the weight of a positive electrode current collector of the same area is weighed beforehand; the areal density of the positive electrode active layer is obtained by subtracting the weight of the positive electrode current collector from the weight of the positive electrode sheet and then dividing by the fixed area; the average thickness of the positive electrode active layer on the positive electrode sheet is then measured by scanning electron microscopy, and the compaction density of the positive electrode active layer is obtained by dividing the areal density of the positive electrode active layer by the average thickness of the positive electrode active layer.

[0119] In some embodiments, the surface of the positive electrode active material has a carbon-containing coating layer. When the average particle size of the primary particles of the positive electrode active material decreases while the coating layer thickness remains unchanged, the carbon coating content in the positive electrode active material increases, making it difficult for the positive electrode active material particles to be compacted, resulting in a decrease in the compaction density of the positive electrode active layer. Conversely, when the average particle size of the primary particles of the positive electrode active material increases while the coating layer thickness remains unchanged, the positive electrode active material particles are easier to compact, resulting in an increase in the compaction density of the positive electrode active layer.

[0120] In some embodiments, the positive electrode active material includes undoped lithium iron phosphate or doped lithium iron phosphate, wherein the doping element includes one or more of Ti, Zr, Mn, Co, and V.

[0121] Therefore, among commonly used positive electrode active materials, lithium iron phosphate materials have a smaller particle size and fewer burrs on the edges and non-edges of their positive electrode active layer, reducing the risk of burrs puncturing the separator and improving the cycle performance and safety performance of the battery cell.

[0122] In some embodiments, the mass content of the dopant element in the doped lithium iron phosphate is 500-5000 ppm, for example, 500 ppm, 800 ppm, 900 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm or any range of the above values.

[0123] Therefore, the above-mentioned range of doping element content is beneficial to improving the lithium-ion diffusion coefficient of the positive electrode active layer and increasing the discharge power of the battery cell.

[0124] In this application, conventional methods in the art are used to confirm the positive electrode active material and the content of its doping elements. For example, the battery cell is placed at 25°C and left to stand for 30 minutes, then discharged at 0.33C to 2.0V to obtain a fully discharged battery cell. The battery cell is then disassembled, the positive electrode is removed, and material is scraped from the surface of the positive electrode current collector. The material is subjected to XRD testing, and the specific substance of the positive electrode active material is confirmed by comparing the obtained XRD pattern with a standard PDF card. The scraped material is placed in an appropriate amount of concentrated nitric acid solvent and digested using a plate digestion method. The digested solution is then diluted with 7% (v / v) hydrochloric acid solution. After the obtained solution is brought to a fixed volume, it is tested using an inductively coupled plasma optical emission spectrometer (ICP=OES). The mass content of the doping elements is calculated based on the test results.

[0125] Another embodiment of this application provides a method for preparing a battery cell, comprising the following steps:

[0126] The positive electrode, separator, and negative electrode are arranged sequentially and hot-pressed at 80℃-150℃ (e.g., 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃ or any combination of the above values), with a hot-pressing pressure of 2 kN-8 kN (e.g., 2 kN, 3 kN, 4 kN, 5 kN, 6 kN, 7 kN, 8 kN or any combination of the above values), to obtain an electrode assembly. A battery cell is then fabricated using this electrode assembly.

[0127] The positive electrode includes a positive current collector and a positive active layer located on at least one side of the positive current collector. The positive active layer includes a positive active material; the compaction density of the positive active layer is 2.3 g / cm³. 3 - 3.35 g / cm 3 ;

[0128] The separator includes a base layer and a polymer layer located on the side of the base layer facing the positive electrode. The polymer layer includes a fluorinated polymer with a crystallinity of less than or equal to 50%.

[0129] Therefore, hot pressing under the above conditions can melt and coat the positive electrode current collector and the burrs at the edge of the positive electrode active layer and the non-edge burrs of the positive electrode active layer with a crystallinity of less than or equal to 50%. At the same time, limiting the compaction density of the positive electrode active layer within the above range helps to reduce the number of burrs at the edge and non-edge areas of the positive electrode active layer and improve the structural stability of the positive electrode sheet, thereby reducing the risk of short circuit caused by burrs piercing the separator, and thus improving the cycle performance and safety performance of the battery cell.

[0130] In some embodiments, the hot pressing time is 40 s - 180 s or 50 s - 150 s, for example, 40 s, 50 s, 60 s, 70 s, 80 s, 90 s, 100 s, 120 s, 130 s, 140 s, 150 s, 160 s, 170 s, 180 s or any range of the above values.

[0131] In some implementations, the battery cells are as described above.

[0132] In some embodiments, the diaphragm further includes an inorganic material layer located between the base layer and the polymer layer.

[0133] In some embodiments, the polymer layer is prepared by the following steps:

[0134] A fluoropolymer is mixed with an oily solvent to obtain a polymer slurry;

[0135] The polymer slurry is coated onto the substrate or inorganic material layer facing the positive electrode, and then dried to obtain the polymer layer.

[0136] Therefore, using an oily solvent when preparing polymer slurry can result in a higher coverage of the slurry on the base layer or inorganic material layer, thus obtaining a polymer layer with higher coverage. This helps reduce the risk of the positive electrode burrs puncturing the separator, thereby improving the cycle performance and safety performance of the battery cell.

[0137] In some embodiments, the oily solvent includes one or more of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and dimethylacetamide (DMAc).

[0138]

Isolation Components

[0139] In some implementations, the spacer is a spacer membrane.

[0140] In some implementations, the thickness of the substrate is 5μm to 12μm, for example, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm or any range of the above values.

[0141] Therefore, on the one hand, the aforementioned thickness range of the base layer can improve the liquid retention capacity of the battery cells and reduce the impedance of the battery cells through the micropores and capillary forces of the base layer, and can also improve the mechanical strength of the separator, thereby improving the rate performance and cycle performance of the battery cells. On the other hand, increasing the thickness of the base layer may increase the resistance to lithium-ion transport and affect the rate performance of the battery cells. The aforementioned range reduces this impact.

[0142] In this application, the method for testing the thickness of the substrate is similar to the aforementioned method for testing the thickness of the polymer layer.

[0143] In some embodiments, the porosity of the diaphragm is 19% to 50%, for example, 19%, 19.9%, 20%, 24%, 26%, 26.6%, 28%, 29.8%, 30%, 31.4%, 33%, 35%, 35.8%, 37%, 37.7%, 39%, 40%, 40.2%, 41%, 44%, 46%, 48%, 50%, or any range of the above values.

[0144] Therefore, on the one hand, a membrane porosity not lower than the aforementioned lower limit is beneficial to improving the liquid phase transport of the battery cell and enhancing the discharge performance of the battery cell. On the other hand, an increase in membrane porosity may weaken the insulating effect of the membrane and affect the safety of the battery cell. The aforementioned range reduces this impact.

[0145] In this application, the porosity of the separator is tested using conventional methods in the art. For example, the battery cell is disassembled, the separator is removed, soaked in a solvent (e.g., dimethyl carbonate) for 20 minutes, rinsed twice, dried, and then the porosity of the separator is determined using a fully automated mercury porosimeter (instrument model: Quanta PoreMaster-33).

[0146] As an example, the main material of the substrate can be selected from at least one of glass fiber, non-woven fabric, polyethylene, and polypropylene. The substrate can be a single-layer film or a multi-layer composite film, without particular limitations. The separator can be a separate component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes.

[0147] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0148]

Positive Electrode

[0149] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0150] As an example, the positive current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0151] As an example, the positive electrode active material may further include at least one of the following materials: lithium phosphate, lithium transition metal oxide, and their respective modified compounds. Examples of lithium phosphate include, but are not limited to, at least one of lithium manganese phosphate (e.g., LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (e.g., 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 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Modified compounds refer to substances obtained by doping or coating, etc., based on the aforementioned substances. However, this application is not limited to these materials; other conventional materials that can be used as battery cathode materials may also be used. These cathode materials may be used alone or in combination of two or more.

[0152] 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.

[0153] In the examples of cathode materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0154] In some embodiments, the polymeric positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0155] In some embodiments, the positive electrode conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0156] In some embodiments, the positive electrode active layer further includes a positive electrode conductive agent, which includes a single-arm carbon nanotube.

[0157] Therefore, the entanglement effect of single-arm carbon nanotubes can entangle and anchor the positive electrode active material particles onto the positive electrode current collector. Furthermore, the single-arm carbon nanotubes can buffer the volume change of the positive electrode active material particles during cycling to reduce particle shedding. This is beneficial for the positive electrode active material particles to adhere to the positive electrode current collector and also helps to improve the electronic conductivity, thereby increasing the discharge power of the battery cell.

[0158] In some embodiments, the positive electrode active layer further includes a polymeric positive electrode binder, wherein the weight-average molecular weight of the polymeric positive electrode binder is greater than or equal to the weight-average molecular weight of the fluoropolymer.

[0159] Therefore, it is beneficial to firmly bond the positive electrode active material particles to the positive electrode current collector using polymer-based positive electrode binders, thereby reducing the loss of positive electrode active material and improving the cycle life of the battery cell.

[0160] In this application, the test method for the weight-average molecular weight of polymeric cathode binders is similar to the test method for the weight-average molecular weight of fluoropolymers.

[0161] 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, positive conductive agent, positive 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 current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0162] [Negative electrode plate]

[0163] In some embodiments, the negative electrode current collector may be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals may be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material substrate and a metal layer. The composite current collector can be formed by forming a metal material (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0164] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0165] As an example, the negative electrode active material may further include at least one of the following materials: natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for battery cells may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0166] In some embodiments, the negative electrode active material includes graphite material; and / or,

[0167] Negative electrode active materials include artificial graphite materials.

[0168] Therefore, using graphite materials in the negative electrode active material is beneficial to improving the cycle life of the battery cell.

[0169] In some embodiments, the graphitization degree of the negative electrode active material is 90%-94%, for example, 90%, 92%, 92.6%, 93%, 94% or any range of the above values.

[0170] Therefore, on the one hand, maintaining the graphitization degree of the negative electrode active material at or above the lower limit is beneficial for improving the rate performance, energy density, and cycle life of the battery cell; on the other hand, increasing the graphitization degree of the negative electrode active material may lead to a decrease in the capacity of the battery cell and a deterioration in fast charging performance, and the above range reduces this impact.

[0171] In this application, the graphitization degree of the negative electrode active material is tested using conventional methods in the art. For example, the battery cell is disassembled, the negative electrode sheet is removed, and material from the negative electrode current collector is scraped off. This material is then sintered at a certain temperature for a period of time (e.g., sintering at 250°C for 3 hours) to remove binders and other additives, as well as SEI film materials, to obtain the negative electrode active material. The negative electrode active material is tested according to Appendix E of the national standard GB / T24533-2019 "Graphite-based Negative Electrode Materials for Lithium-ion Batteries." Artificial graphite is also applicable to the Chinese machinery industry standard JB / T4220-2011 "Method for Determining Lattice Parameters of Artificial Graphite." Specific testing steps are detailed below. The graphitization degree G of the negative electrode active material was determined by automatically recording the 002, 004, 110, and 112 diffraction lines of carbon using an XRD diffractometer, while simultaneously reading the diffraction angle (2θobs)c. The corrected diffraction angle (2θcor)c was obtained using the internal standard method and substituted into the interplanar spacing formula to calculate the graphite interlayer spacing d002. The d002 data value was then substituted into the Mering-Maire formula: G = [(3.440 - d002) / (3.440 - 3.354)] × 100% to obtain the graphitization degree G.

[0172] In some embodiments, the average particle size of the negative electrode active material is 8 μm to 20 μm, for example, 8 μm, 8.7 μm, 9 μm, 10 μm, 11 μm, 13 μm, 15 μm, 17 μm, 18 μm, 19 μm, 20 μm or any combination of the above values.

[0173] Therefore, on the one hand, having an average particle size of negative electrode active material that is not lower than the aforementioned lower limit is beneficial for reducing the specific surface area of ​​negative electrode active material, reducing the contact area between negative electrode active material and electrolyte, reducing side reactions, and thus improving the cycle life of battery cells. On the other hand, an increase in the average particle size of negative electrode active material may lead to gelation of negative electrode slurry, making processing difficult, and may also lead to a deterioration in the fast charging performance of battery cells. The aforementioned range reduces this impact.

[0174] In this application, the method for testing the average particle size of the negative electrode active material is similar to the method for testing the average particle size of the positive electrode active material.

[0175] As an example, negative electrode material can be filled or / and deposited inside the negative electrode current collector.

[0176] In some embodiments, the positive current collector can be made of aluminum, and the negative current collector can be made of copper.

[0177] In some embodiments, the negative electrode material may optionally include a negative electrode binder. As an example, 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).

[0178] In some embodiments, the negative electrode material may optionally include a negative electrode conductive agent. As an example, 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.

[0179] In some embodiments, the negative electrode material may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0180] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, negative electrode conductive agent, negative electrode 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.

[0181] Electrolytes

[0182] In some embodiments, the battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. The electrolyte can be liquid or gel-like.

[0183] Liquid electrolytes include electrolyte salts and solvents.

[0184] 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.

[0185] 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. The solvent may also be an ether solvent. Ether solvents may include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ethers.

[0186] In some embodiments, the electrolyte further includes a solvent, including a cyclic carbonate solvent, wherein the mass of the cyclic carbonate solvent is 20% to 40% of the solvent mass, for example, 20%, 25%, 30%, 34%, 36%, 40%, or any range of the above values.

[0187] Therefore, on the one hand, having a cyclic carbonate solvent content not lower than the aforementioned lower limit is beneficial to improving the cycle life of the battery cell; on the other hand, having a cyclic carbonate solvent content not exceeding the aforementioned upper limit is beneficial to reducing the electrolyte viscosity at low temperatures, thereby improving the low-temperature charge and discharge power of the battery cell.

[0188] In some embodiments, the cyclic carbonate solvent includes one or more of ethylene carbonate (EC), propylene carbonate (PC), and γ-butyrolactone (γ-GBL).

[0189] 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 additives that can improve certain properties of the battery cell, such as additives that improve the overcharge / fast charge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature performance of the battery cell.

[0190] In some embodiments, the battery cell further includes an electrolyte, which comprises electrolyte additives, including unsaturated carbonate additives and / or sulfonate additives. Therefore, using the aforementioned electrolyte additives is beneficial for improving the cycle life of the battery cell.

[0191] In some embodiments, the unsaturated carbonate additives include one or more of vinylene carbonate, fluoroethylene carbonate, and vinylene carbonate.

[0192] In some embodiments, the sulfonate additives include one or more of 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, methylene disulfonate, vinyl sulfate, and ethyl sulfite.

[0193] The gel electrolyte includes a polymer as a backbone network and can be used in conjunction with an ionic liquid-lithium salt.

[0194] [Structure of the Electrode Assembly]

[0195] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0196] In some implementations, the electrode assembly is a wound structure. The positive and negative electrode sheets are wound into a wound structure.

[0197] In some embodiments, the electrode assembly is cuboid in shape, and the ratio of the length to the width of the electrode assembly is 2-8, for example, 2, 3, 4, 5, 6, 7, 8 or any range of the above values.

[0198] Since the crystallinity of the fluoropolymer in the polymer layer is less than or equal to 50%, the mechanical strength of the electrode assembly formed after the diaphragm is bonded to the positive electrode sheet through the polymer layer is reduced. The above-mentioned length-to-width ratio of the electrode assembly makes it easier to load and unload the electrode assembly for subsequent processing.

[0199] In some embodiments, the cuboid electrode assembly has three directions: length, width, and thickness. The dimension in the length direction is greater than the dimension in the width direction, which is greater than the dimension in the thickness direction. Therefore, the length and width dimensions of the electrode assembly can be determined based on the dimensional differences in the three directions.

[0200] In some implementations, the electrode assembly is a stacked structure.

[0201] As an example, multiple positive and negative electrodes can be set, and multiple positive and multiple negative electrodes can be stacked alternately.

[0202] As an example, multiple positive electrode plates can be provided, and negative electrode plates can be folded to form multiple stacked folded segments, with a positive electrode plate sandwiched between adjacent folded segments.

[0203] As an example, both the positive and negative electrode plates are folded to form multiple stacked folded segments.

[0204] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0205] As an example, the separators can be continuously arranged, either by folding or rolling between any adjacent positive or negative electrode plates.

[0206] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0207] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0208]

shell

[0209] In some embodiments, the battery cell may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0210] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not have any particular limitations.

[0211] In some embodiments, the housing includes an end cap and a housing, the housing having an opening, and the end cap covering the opening. The housing may have one or more openings. The end cap may also have one or more.

[0212] Electrode terminals

[0213] In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab, or it can be indirectly connected to the tab through a current collector. The electrode terminal can be provided on the end cap or on the housing.

[0214] Pressure relief mechanism

[0215] In some embodiments, a pressure relief mechanism is provided on the casing. The pressure relief mechanism is used to release the internal gas of the battery cell.

[0216] As an example, the internal pressure or temperature of a battery cell is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the battery cell reaches the predetermined threshold, the pressure relief mechanism is activated or a weak structure in the pressure relief mechanism is broken, thereby creating an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the battery cell.

[0217] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0218] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0219] The term "actuation" as used in this application refers to the activation or actuation of the pressure relief mechanism to a certain state, thereby releasing the internal pressure and temperature of the battery cell. The actions of the pressure relief mechanism may include, but are not limited to: movement of components within the mechanism to form an exhaust channel, rupture, breakage, tearing, or opening of at least a portion of the mechanism, etc. When the pressure relief mechanism is activated, the high-temperature, high-pressure substances inside the battery cell are discharged as waste from the activated portion. This method allows for pressure and temperature relief of the battery cell under controllable pressure or temperature, thereby preventing potentially more serious accidents.

[0220] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be configured as a through hole for venting gas inside the battery cell.

[0221] The emissions from battery cells mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode plates, fragments of separators, high-temperature and high-pressure gases generated by the reaction, flames, etc.

[0222] [Battery Device]

[0223] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0224] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0225] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0226] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0227] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0228] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0229] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0230] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0231] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0232] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0233] For example, Figure 1 The example shown is a square-structured battery cell 5.

[0234] In some implementations, refer to Figure 2The outer packaging may include a housing 51 and a cover 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 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking 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 a single battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0235] 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.

[0236] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0237] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0238] 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.

[0239] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 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.

[0240] 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 the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, 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.

[0241] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0242] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of individual battery cells, a battery pack or battery module can be used.

[0243]

Example

[0244] 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.

[0245] Example 1

[0246] (1) Preparation of the positive electrode sheet:

[0247] A lithium iron phosphate cathode active material with an average particle size of 0.8 μm and doped with Ti (Ti element content in lithium iron phosphate is 800 ppm by mass, and its surface has a carbon coating layer), polyvinylidene fluoride (PVDF) binder (weight average molecular weight of 700,000), single-arm carbon nanotube conductive agent, and polyvinylpyrrolidone surfactant were mixed in a mass ratio of 97.2:1.8:0.4:0.6. A certain amount of solvent N-methylpyrrolidone (NMP) was added, and the mixture was stirred to form a homogeneous slurry. The cathode slurry was uniformly coated onto a cathode current collector aluminum foil, and then dried, cold-pressed, and slit to obtain the cathode electrode sheet. The cathode electrode sheet includes a cathode current collector and cathode active layers located on both sides of the cathode current collector. The areal density of the cathode active layer is 0.364 mg / mm². 2 The compacted density is 2.55 g / cm³. 3 .

[0248] (2) Preparation of the diaphragm:

[0249] Prepare a polyethylene base layer with a thickness of 7 μm; mix boehmite (inorganic material), polyvinylidene fluoride (weight average molecular weight of 400,000), acrylic emulsion (concentration of 35% by mass), and deionized water in a mass ratio of 40%, 1.8%, 4.7%, and 54.5% respectively to form an inorganic slurry. Apply the inorganic slurry to the side of the base layer facing the positive electrode using slit coating. After drying, an inorganic material layer with a thickness of 1 μm is obtained on the side of the base layer facing the positive electrode.

[0250] Polyvinylidene fluoride (PVDF) with a crystallinity of 25% and a weight-average molecular weight of 400,000 was mixed with the oily solvent N-methylpyrrolidone (NMP) to prepare a polymer slurry. The polymer slurry was then coated onto the inorganic material layer facing the positive electrode using slot coating. After drying and slitting, a separator was obtained. The thickness of the polymer layer loaded on the inorganic material layer facing the positive electrode in the separator was 1 μm, the separator porosity was 37.7%, and the ratio of the polymer layer area to the substrate area was 87%.

[0251] (3) Preparation of negative electrode sheet:

[0252] Artificial graphite anode active material, styrene-butadiene rubber (SBR) anode binder, sodium carboxymethyl cellulose (CMC-Na) anode thickener, and carbon black (Super P) anode conductive agent were thoroughly mixed in an appropriate amount of deionized water at a mass ratio of 96:1.5:0.5:2 to form a uniform anode slurry. The anode slurry was then coated onto the surface of a copper foil anode current collector, and the anode sheet was prepared by drying, cold pressing, and slitting. The anode sheet includes a cathode current collector and a cathode active layer located on both sides of the cathode current collector. The cathode active layer includes a cathode active material with an average particle size of 8.7 μm and a graphitization degree of 92.6%.

[0253] (4) Preparation of electrolyte:

[0254] Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1 to obtain a non-aqueous solvent. Then, the electrolyte salt LiPF6 and the electrolyte additive vinylene carbonate were dissolved in the non-aqueous solvent to obtain the electrolyte. The concentration of the electrolyte salt LiPF6 in the electrolyte was 1 mol / L, the mass content of the additive vinylene carbonate in the electrolyte was 5%, and the mass content of ethylene carbonate (EC) in the solvent was 34%.

[0255] (5) Fabrication of individual battery cells:

[0256] The positive electrode, separator, and negative electrode are stacked sequentially and then hot-pressed (hot-pressing temperature 95℃, hot-pressing pressure 4000 N, hot-pressing time 120s) to bond the three together. The polymer layer of the separator wraps around the edges and sharp burrs of the non-edge areas of the positive electrode. Finally, the stacked battery cell is obtained through processes such as encapsulation, liquid injection, high-temperature standing, formation aging, and coating.

[0257] Battery test

[0258] (1) Energy density test of individual battery cells:

[0259] Under a constant temperature environment of 25℃, the battery cell is charged at a constant current of 0.33C to the upper limit voltage of 3.8V, then charged at a constant voltage to the current of 0.05C. After standing for 10 minutes, it is discharged at a constant current of 0.33C to the lower limit voltage of 2.0V. The discharge capacity A0 and the discharge plateau voltage V are recorded at this time. The length, thickness and height of the battery cell are measured with calipers (generally calculated based on the outer shell size of the battery cell, excluding the height of the electrode terminals and the insulating film outside the shell), and the volume of the battery cell V0 is calculated. The volumetric energy density of the battery cell VED = (A0 × V) / V0, in Wh / L.

[0260] (2) Battery cell DC impedance test at 20% SOC (-20℃):

[0261] Under a constant temperature environment of 25℃, the battery cell is charged at a constant current of 0.33C to the upper limit voltage of 3.8V, then charged at a constant voltage of 3.8V to a current of 0.05C, left to stand for 10 minutes, and then discharged at a constant current of 0.33C to the lower limit voltage of 2.0V. The discharge capacity C0 at this time is recorded. After standing for 10 minutes, it is charged at a constant current of 0.33C to 0.20 C0 (i.e., 20% SOC). After standing for 60 minutes under a -20℃ environment, it is discharged at 0.36 C0 for 30 seconds. The DC impedance is calculated according to the following formula. The smaller the impedance value, the greater the discharge power and the higher the rate performance.

[0262] DC impedance = (voltage before discharge 30s - voltage after discharge 30s) / discharge current.

[0263] (3) Self-discharge rate test of individual battery cells:

[0264] Under a constant temperature environment of 25℃, the battery cell is charged to 3.8V at a constant current of 0.33C, then charged at a constant voltage of 3.8V until the current is below 0.05C. After standing for 10 minutes, it is discharged to 2.0V at a constant current of 0.33C to obtain the discharge capacity C0. After standing for 10 minutes, it is charged to 0.3C0 (i.e., 30% SOC) at a constant current of 0.33C. After standing for 10 minutes, the open circuit voltage of the battery cell is tested as V1 (in V). Then the battery cell is placed in an oven at 45℃ for 48 hours, and the open circuit voltage of the battery is tested as V2 (in V). The self-discharge rate of the battery cell is (V1-V2)×1000 / 48.

[0265] (4) High-temperature cycle performance test of individual battery cells:

[0266] Under a constant temperature environment of 45℃, the battery cells are charged at a constant current of 0.5C to the upper limit voltage of 3.8V, then charged at a constant voltage until the current is ≤0.05C, left to stand for 5 minutes, and then discharged at a constant current of 1C to the lower limit voltage of 2.0V. This constitutes one cycle of charge and discharge. The discharge capacity at this point is recorded as the discharge capacity of the first cycle. The battery cells are cycled using the above method, and the discharge capacity after each cycle is recorded until the discharge capacity of the battery cells decreases to 75% of the discharge capacity of the first cycle. The number of cycles at this point is recorded.

[0267] Examples 2-7

[0268] (2) Preparation of the diaphragm:

[0269] Polymer slurries were prepared by mixing polyvinylidene fluoride (PVDF) with a crystallinity of 20% and a weight-average molecular weight of 350,000, polyvinylidene fluoride (PVDF) with a crystallinity of 50% and a weight-average molecular weight of 400,000, polyvinylidene fluoride (PVDF) with a crystallinity of 25% and a weight-average molecular weight of 150,000, polyvinylidene fluoride (PVDF) with a crystallinity of 25% and a weight-average molecular weight of 500,000, polyvinylidene fluoride (PVDF) with a crystallinity of 18% and a weight-average molecular weight of 120,000, and polyvinylidene fluoride (PVDF) with a crystallinity of 50% and a weight-average molecular weight of 800,000 with an oily solvent N-methylpyrrolidone (NMP). The rest was the same as in step (2) of Example 1.

[0270] (5) Fabrication of individual battery cells:

[0271] The hot pressing conditions used were as follows: hot pressing temperature 95℃, hot pressing pressure 4000 N, hot pressing time 90s; hot pressing temperature 95℃, hot pressing pressure 4000 N, hot pressing time 150s; hot pressing temperature 95℃, hot pressing pressure 4000 N, hot pressing time 90s; hot pressing temperature 95℃, hot pressing pressure 4000 N, hot pressing time 150s; hot pressing temperature 95℃, hot pressing pressure 4000 N, hot pressing time 90s; hot pressing temperature 105℃, hot pressing pressure 4000 N, hot pressing time 150s; the rest were the same as in step (5) of Example 1.

[0272] Steps (1) and (3)-(4) are the same as steps (1) and (3)-(4) in Example 1.

[0273] Comparative Example 1

[0274] (2) Preparation of the diaphragm:

[0275] Polymer slurry was prepared by mixing polyvinylidene fluoride (PVDF) with a crystallinity of 55% and a weight-average molecular weight of 400,000 with an oily solvent N-methylpyrrolidone (NMP), and the rest was the same as in step (2) of Example 1.

[0276] (5) Fabrication of individual battery cells:

[0277] The hot pressing conditions used were a hot pressing temperature of 95°C, a hot pressing pressure of 4000 N, and a hot pressing time of 180 s; the rest were the same as in step (5) of Example 1.

[0278] Steps (1) and (3)-(4) are the same as steps (1) and (3)-(4) in Example 1.

[0279] Comparative Example 2

[0280] (2) Preparation of the diaphragm:

[0281] Polymer slurry was prepared by mixing polymethyl methacrylate (PMMA) with a crystallinity of 25% and a weight-average molecular weight of 400,000 with an oily solvent, N-methylpyrrolidone (NMP), and the rest was the same as in step (2) of Example 1.

[0282] Steps (1) and (3)-(5) are the same as steps (1) and (3)-(5) in Example 1.

[0283] Table 1: Partial parameters and test results of Examples 1-7 and Comparative Examples 1-2

[0284] serial number Polymer (also known as P) P crystallinity P's Mw Diaphragm porosity Energy density (Wh / L) 20% SOC DC resistance (mΩ) Self-discharge rate (mV / h) 45℃, 75% of cycle count Example 1 PVDF 25% 400,000 37.70% 427.6 10.1 0.013 5877 Example 2 Same as Example 1 20% 350,000 35.8% 427.6 9.6 0.014 5548 Example 3 Same as Example 1 50% 400,000 39% 427.6 10.4 0.021 5481 Example 4 Same as Example 1 25% 150,000 35% 427.6 10.2 0.01 5470 Example 5 Same as Example 1 25% 500,000 41% 427.6 10 0.018 5600 Example 6 Same as Example 1 18% 120,000 29.80% 427.6 12.6 0.011 5201 Example 7 Same as Example 1 50% 800,000 37.70% 427.6 9.9 0.022 5344 Comparative Example 1 Same as Example 1 55% Same as Example 1 39.10% 427.6 10.5 0.029 4587 Comparative Example 2 PMMA 25% Same as Example 1 37.70% 427.6 10.6 0.03 4379 .

[0285] It can be seen from the above table:

[0286] Compared with the fluoropolymer in Comparative Example 1, which has a crystallinity greater than 50%, the safety and cycle performance of the battery cells in Examples 1-7 of this application are significantly improved.

[0287] Compared with the polymer layer of Comparative Example 2 which uses a fluorine-free polymer, the safety performance and cycle performance of the battery cells in Examples 1-7 of this application are significantly improved.

[0288] Compared with the fluoropolymer of Example 6, which has lower crystallinity and lower weight-average molecular weight, the battery cells of Examples 1-5 of this application have significantly lower DC resistance and significantly improved cycle performance.

[0289] Compared with the larger weight-average molecular weight of the fluoropolymer in Example 7, the safety performance and cycle performance of the battery cells in Examples 1-5 of this application are significantly improved.

[0290] Examples 8-11

[0291] (2) Preparation of the diaphragm:

[0292] Adjust the amount of polymer slurry coated on the inorganic material layer facing the positive electrode sheet using slit coating, so that the thickness of the polymer layer is 0.5 μm, 3 μm, 0.2 μm, and 5 μm respectively, and the rest is the same as in step (2) of Example 1;

[0293] (5) Fabrication of individual battery cells:

[0294] The hot pressing conditions used were as follows: hot pressing temperature 95℃, hot pressing pressure 4000 N, hot pressing time 90s; hot pressing temperature 95℃, hot pressing pressure 4000 N, hot pressing time 120s; hot pressing temperature 95℃, hot pressing pressure 4000 N, hot pressing time 90s; hot pressing temperature 95℃, hot pressing pressure 4000 N, hot pressing time 150s; the rest were the same as in step (5) of Example 1.

[0295] Steps (1) and (3)-(4) are the same as steps (1) and (3)-(4) in Example 1.

[0296] Examples 12-13

[0297] (2) Preparation of the diaphragm:

[0298] Adjust the coating area of ​​the polymer slurry applied to the inorganic material layer on the side facing the positive electrode using slit coating, so that the ratio of the polymer layer area to the base layer area is 70% and 100%, respectively, and the rest is the same as in step (2) of Example 1;

[0299] (5) Fabrication of individual battery cells:

[0300] The hot pressing conditions used were as follows: hot pressing temperature 95℃, hot pressing pressure 4000 N, hot pressing time 90s; hot pressing temperature 95℃, hot pressing pressure 4000 N, hot pressing time 100s; the rest were the same as in step (5) of Example 1.

[0301] Steps (1) and (3)-(4) are the same as steps (1) and (3)-(4) in Example 1.

[0302] Example 14

[0303] (2) Preparation of the diaphragm:

[0304] Polyvinylidene fluoride (PVDF) with a crystallinity of 25% and a weight-average molecular weight of 400,000 was mixed with deionized water to prepare a polymer slurry. The polymer slurry was coated on the inorganic material layer facing the positive electrode sheet using slit coating. The rest was the same as in step (2) of Example 1.

[0305] Steps (1) and (3)-(5) are the same as steps (1) and (3)-(5) in Example 1.

[0306] Comparative Example 3

[0307] (2) Preparation of the diaphragm:

[0308] The polymer slurry was coated on the four edges of the inorganic material layer facing the positive electrode sheet using slit coating (the middle part of the positive electrode material layer was not coated). The ratio of the total area of ​​the polymer layer to the base layer area was 45%, and the rest was the same as in step (2) of Example 1.

[0309] (5) Fabrication of individual battery cells:

[0310] The hot pressing conditions used were: hot pressing temperature 95℃, hot pressing pressure 4000 N, hot pressing time 90s, and the rest were the same as in step (5) of Example 1;

[0311] Steps (1) and (3)-(4) are the same as steps (1) and (3)-(4) in Example 1.

[0312] Table 2: Partial parameters and test results of Examples 1, 8-14 and Comparative Example 3

[0313] serial number Polymer layer thickness (μm) Polymer layer to base layer area ratio Diaphragm porosity Energy density (Wh / L) 20% SOC DC resistance (mΩ) Self-discharge rate (mV / h) 45℃, 75% of cycle count Example 1 1 87% 37.70% 427.6 10.1 0.013 5877 Example 8 0.5 Same as Example 1 40.20% 429.8 10.1 0.023 5289 Example 9 3 Same as Example 1 26.60% 422.6 10.6 0.01 5800 Example 10 0.2 Same as Example 1 41.00% 430.3 10 0.025 4899 Example 11 5 Same as Example 1 26% 419.9 13 0.01 5789 Example 12 Same as Example 1 70% 39% 427.6 9.9 0.016 5679 Example 13 Same as Example 1 100% 31.40% 427.6 10.7 0.011 5919 Example 14 Same as Example 1 65% 37.70% 427.6 9.6 0.022 5702 Comparative Example 3 Same as Example 1 45% 45% 427.6 9.6 0.035 4180

[0314] It can be seen from the above table:

[0315] Compared with Comparative Example 3, which only prepared a polymer layer at the edge of the inorganic material layer, the safety performance and cycle performance of the battery cells in Examples 1, 8-14 of this application are significantly improved.

[0316] Compared to the thinner polymer layer in Example 10, the safety and cycle performance of the battery cells in Examples 1 and 8-9 of this application are significantly improved.

[0317] Compared to the thicker polymer layer in Example 11, the energy density of the battery cells in Examples 1 and 8-9 of this application is significantly improved and the DC impedance is significantly reduced.

[0318] Compared with Example 14, which uses deionized water to prepare polymer slurry, Examples 1 and 12-13 of this application have a larger area ratio of polymer layer to base layer, resulting in significantly improved safety and cycle performance of the battery cells.

[0319] Example 15

[0320] (2) Preparation of the diaphragm:

[0321] The preparation of the inorganic material layer is omitted, and the rest is the same as in step (2) of Example 1; the membrane porosity is 37%;

[0322] Steps (1) and (3)-(5) are the same as steps (1) and (3)-(5) in Example 1.

[0323] Examples 16-19

[0324] (1) Preparation of the positive electrode sheet:

[0325] Lithium iron phosphate cathode materials doped with Ti (with a Ti element content of 800 ppm in lithium iron phosphate and a carbon coating layer of constant thickness on the surface) with average particle sizes of 0.5 μm, 1.5 μm, 0.35 μm, and 2.1 μm were used respectively, and the rest was the same as in step (1) of Example 1; the compaction density of the cathode active layer was 2.48 g / cm³. 3 2.63 g / cm 3 2.3 g / cm 3 2.8 g / cm 3 ;

[0326] Steps (2)-(5) are the same as steps (2)-(5) in Example 1.

[0327] Example 20

[0328] (5) Fabrication of individual battery cells:

[0329] The hot-pressing conditions were adjusted to a hot-pressing temperature of 95°C, a hot-pressing pressure of 4000 N, and a hot-pressing time of 40 s, with the rest being the same as in step (5) of Example 1; the membrane porosity was 37.7%;

[0330] Steps (1)-(4) are the same as steps (1)-(4) in Example 1.

[0331] Example 21

[0332] (1) Preparation of the positive electrode sheet:

[0333] The positive electrode active material LiNi with an average particle size of 4.5 μm 0.5 Co 0.2 Mn 0.3 O2 (NCM523), polyvinylidene fluoride (PVDF) binder (weight-average molecular weight 700,000), single-arm carbon nanotube conductive agent, and polyvinylpyrrolidone surfactant were mixed in a mass ratio of 97.2:1.8:0.4:0.6. A certain amount of N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred into a homogeneous slurry. This positive electrode slurry was then uniformly coated onto a positive electrode current collector aluminum foil. After drying, cold pressing, and slitting, the positive electrode sheet was obtained. The positive electrode sheet includes a positive electrode current collector and positive electrode active layers located on both sides of the current collector. The areal density of the positive electrode active layers is 0.276 mg / mm². 2 The compacted density is 3.35 g / cm³. 3 .

[0334] Steps (2)-(5) are the same as steps (2)-(5) in Example 1.

[0335] Example 22

[0336] (1) Preparation of the positive electrode sheet:

[0337] A mixture of lithium iron phosphate positive electrode active material (with a carbon coating layer on its surface), polyvinylidene fluoride (PVDF) binder (weight-average molecular weight of 300,000), Super P conductive agent, and polyvinylpyrrolidone surfactant in a mass ratio of 97.2:1.8:0.4:0.6 was prepared by adding a certain amount of N-methylpyrrolidone (NMP) solvent and stirring to form a homogeneous slurry. The positive electrode slurry was then uniformly coated onto a positive electrode current collector aluminum foil, and the resulting material was dried, cold-pressed, and slit to obtain the positive electrode sheet. The positive electrode sheet comprises a positive electrode current collector and positive electrode active layers located on both sides of the current collector. The areal density of the positive electrode active layers is 0.364 mg / mm². 2 The compacted density is 2.55 g / cm³. 3 .

[0338] Steps (2)-(5) are the same as steps (2)-(5) in Example 1.

[0339] Example 23

[0340] (2) Preparation of the diaphragm:

[0341] The thickness of the polyethylene base layer was adjusted to 5 μm, and the rest was the same as in step (2) of Example 1; the membrane porosity was 19.9%;

[0342] Steps (1) and (3)-(5) are the same as those in Steps (1) and (3)-(5) of Example 1.

[0343] Table 3: Partial parameters and test results of Examples 1 and 15-23

[0344] serial number Inorganic material layer Average particle size (μm) of positive electrode active material Positive electrode active material Base layer thickness (μm) Positive conductive agent Polymer-based positive electrode binder Mw Hot pressing conditions Energy density (Wh / L) 20% SOC DC resistance (mΩ) Self-discharge rate (mV / h) 45℃, 75% of cycle count Example 1 have 0.8 Ti-doped lithium iron phosphate 7 Single-arm carbon nanotubes 700,000 95℃, 4000N, 120s 427.6 10.1 0.013 5877 Example 15 none Same as Example 1 Same as Example 1 Same as Example 1 Same as Example 1 Same as Example 1 95℃, 4000N, 90s 428.1 11.3 0.02 5407 Example 16 have 0.5 Same as Example 1 Same as Example 1 Same as Example 1 Same as Example 1 Same as Example 1 419 8.8 0.012 5856 Example 17 have 1.5 Same as Example 1 Same as Example 1 Same as Example 1 Same as Example 1 Same as Example 1 434.8 13 0.011 5805 Example 18 have 0.35 Same as Example 1 Same as Example 1 Same as Example 1 Same as Example 1 Same as Example 1 410.2 8.5 0.018 5338 Example 19 have 2.1 Same as Example 1 Same as Example 1 Same as Example 1 Same as Example 1 Same as Example 1 443.2 14.5 0.021 5348 Example 20 have Same as Example 1 Same as Example 1 Same as Example 1 Same as Example 1 Same as Example 1 95℃, 4000N, 40s 427.6 10.5 0.018 5670 Example 21 have 4.5 NCM523 Same as Example 1 Same as Example 1 Same as Example 1 Same as Example 1 543.1 13 0.02 4577 Example 22 have Same as Example 1 Lithium iron phosphate Same as Example 1 Super P 300,000 Same as Example 1 427.6 11.1 0.014 5566 Example 23 have Same as Example 1 Same as Example 1 5 Same as Example 1 Same as Example 1 Same as Example 1 429.7 11 0.012 5481 .

[0345] It can be seen from the above table:

[0346] Compared with Example 15, which did not have an inorganic material layer, the battery cell of Example 1 of this application has lower impedance and higher safety and cycle performance.

[0347] Compared to the smaller average particle size of the positive electrode active material in Example 18, the battery cells in Examples 1 and 16-17 of this application have significantly higher safety and cycle performance.

[0348] Compared with the larger average particle size of the positive electrode active material in Example 19, the battery cells in Examples 1 and 16-17 of this application have lower DC resistance and higher safety and cycle performance.

[0349] Compared to the shorter hot-pressing time in Example 20, the battery cell in Example 1 of this application has significantly higher safety and cycle performance.

[0350] Compared with the lithium nickel cobalt manganese oxide cathode active material used in Example 21, the Ti-doped lithium iron phosphate cathode active material in Example 1 of this application has a smaller average particle size and higher safety and cycle performance of the battery cell.

[0351] Compared with Example 22, which uses lithium iron phosphate cathode active material without Ti doping, particulate cathode conductive agent, and cathode binder with a weight-average molecular weight lower than that of fluoropolymer, the battery cell of Example 1 of this application has lower DC impedance and higher cycle performance.

[0352] Compared to the thinner substrate of Example 23, the battery cell of Example 1 of this application has lower DC impedance and improved cycle performance.

[0353] 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, characterized in that, The battery cell includes an electrode assembly, which includes a positive electrode, a negative electrode, and a separator, with the separator located between the positive electrode and the negative electrode. The positive electrode sheet includes a positive current collector and a positive active layer located on at least one side of the positive current collector. The positive active layer includes a positive active material and a polymeric positive electrode binder. The compaction density of the positive active layer is 2.3 g / cm³. 3 - 3.35 g / cm 3 ; The separator includes a base layer and a polymer layer located on the side of the base layer facing the positive electrode sheet. The polymer layer includes a fluorinated polymer with a crystallinity of 20%-50% and a weight-average molecular weight of 120,000-800,000. Furthermore, the weight-average molecular weight of the polymeric positive electrode binder is greater than or equal to the weight-average molecular weight of the fluorinated polymer.

2. The battery cell according to claim 1, characterized in that, The weight-average molecular weight of the fluoropolymer is 150,000 to 500,000.

3. The battery cell according to claim 1, characterized in that, The thickness of the polymer layer is 0.2 μm - 5 μm.

4. The battery cell according to claim 1, characterized in that, The thickness of the polymer layer is 0.5 μm - 3 μm.

5. The battery cell according to claim 1, characterized in that, The ratio of the area of ​​the polymer layer to the area of ​​the base layer is 65% - 100%.

6. The battery cell according to claim 1, characterized in that, The fluoropolymers include one or more of the following: polyvinylidene fluoride, vinylidene fluoride-trifluorochloroethylene copolymer, vinylidene fluoride-trifluorochloroethylene-tetrafluoroethylene copolymer, vinylidene fluoride-trifluorochloroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-trifluorochloroethylene-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-acrylic acid copolymer, and vinylidene fluoride-acrylate copolymer.

7. The battery cell according to claim 1, characterized in that, The diaphragm also includes an inorganic material layer, which is located between the base layer and the polymer layer.

8. The battery cell according to claim 7, characterized in that, The inorganic material layer includes one or more inorganic materials selected from alumina, boehmite, titanium dioxide, and silicon dioxide.

9. The battery cell according to claim 1, characterized in that, The average particle size of the positive electrode active material is 0.35 μm - 2.1 μm.

10. The battery cell according to claim 1, characterized in that, The average particle size of the positive electrode active material is 0.5 μm - 1.5 μm.

11. The battery cell according to claim 1, characterized in that, The areal density of the positive electrode active layer is 0.15 mg / mm². 2 - 0.4mg / mm 2 .

12. The battery cell according to claim 1, characterized in that, The positive electrode active material includes undoped lithium iron phosphate or doped lithium iron phosphate, wherein the doping element includes one or more of Ti, Zr, Mn, Co, and V.

13. The battery cell according to claim 12, characterized in that, The mass content of the doped element in the lithium iron phosphate is 500-5000 ppm.

14. The battery cell according to claim 1, characterized in that, The thickness of the base layer is 5μm - 12μm.

15. The battery cell according to claim 1, characterized in that, The porosity of the diaphragm is 19% - 50%.

16. The battery cell according to claim 1, characterized in that, The positive electrode active layer also includes a positive electrode conductive agent, which includes a single-arm carbon nanotube.

17. The battery cell according to claim 1, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer located on at least one side of the negative electrode current collector, wherein the negative electrode active layer includes a negative electrode active material; wherein, The negative electrode active material includes graphite.

18. The battery cell according to claim 17, characterized in that, The graphitization degree of the negative electrode active material is 90% - 94%.

19. The battery cell according to claim 17, characterized in that, The average particle size of the negative electrode active material is 8 μm - 20 μm.

20. The battery cell according to claim 1, characterized in that, The battery cell also includes an electrolyte, which includes electrolyte additives, including unsaturated carbonate additives and / or sulfonate additives.

21. The battery cell according to claim 20, characterized in that, The unsaturated carbonate additives include one or more of vinylene carbonate, fluoroethylene carbonate, and vinylene carbonate; and / or, The sulfonate additives include one or more of 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, methylene disulfonate, vinyl sulfate, and ethyl sulfite.

22. The battery cell according to claim 20, characterized in that, The electrolyte also includes a solvent, which includes a cyclic carbonate solvent, wherein the mass of the cyclic carbonate solvent is 20% - 40% of the total mass of the solvent.

23. The battery cell according to any one of claims 1 to 22, characterized in that, The electrode assembly is rectangular, and the ratio of its length to its width is 2–8; and / or, The electrode assembly has a stacked structure.

24. A method for preparing a battery cell, characterized in that, The method includes the following steps: The positive electrode, separator, and negative electrode are arranged sequentially and hot-pressed at 80℃-150℃ under a pressure of 2kN-8kN to obtain an electrode assembly. A battery cell is then fabricated using this electrode assembly. The positive electrode sheet includes a positive current collector and a positive active layer located on at least one side of the positive current collector. The positive active layer includes a positive active material and a polymeric positive electrode binder. The compaction density of the positive active layer is 2.3 g / cm³. 3 - 3.35 g / cm 3 ; The separator includes a base layer and a polymer layer located on the side of the base layer facing the positive electrode sheet. The polymer layer includes a fluorinated polymer with a crystallinity of 20%-50% and a weight-average molecular weight of 120,000-800,000. Furthermore, the weight-average molecular weight of the polymeric positive electrode binder is greater than or equal to the weight-average molecular weight of the fluorinated polymer.

25. The method according to claim 24, characterized in that, The hot pressing time is 40 s - 180 s; and / or, The battery cell is the battery cell described in any one of claims 1 to 23.

26. The method according to claim 24, characterized in that, The diaphragm also includes an inorganic material layer, which is located between the base layer and the polymer layer.

27. The method according to claim 24, characterized in that, The polymer layer is prepared by the following steps: The fluoropolymer is mixed with an oily solvent to obtain a polymer slurry; The polymer slurry is coated onto the side of the base layer facing the positive electrode sheet, and then dried to obtain the polymer layer.

28. The method according to claim 26, characterized in that, The polymer layer is prepared by the following steps: The fluoropolymer is mixed with an oily solvent to obtain a polymer slurry; The polymer slurry is coated onto the inorganic material layer on the side facing the positive electrode, and then dried to obtain the polymer layer.

29. The method according to claim 27 or 28, characterized in that, The oily solvent includes one or more of N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, and dimethylacetamide.

30. A battery device, characterized in that, The battery device comprises a battery cell according to any one of claims 1 to 23 or a battery cell prepared by the method according to any one of claims 24 to 29.

31. An electrical device, characterized in that, The electrical device includes a single battery cell as described in any one of claims 1 to 23 or a battery device as described in claim 30.

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