Battery cells, battery packs and electrical devices

Abstract

This application provides a battery cell, a battery device, and an electrical device. The battery cell includes a stacked electrode assembly and an electrolyte. The stacked electrode assembly includes a positive electrode, a separator, and a negative electrode stacked together. The separator includes a base film and coatings disposed on both sides of the base film. The coatings include an adhesive layer, wherein the adhesive layer is a continuous layer with a porous structure and includes a fluoropolymer. The electrolyte includes a chain carbonate, and the mass content of the chain carbonate is 43%-71% based on the total mass of the electrolyte. The battery cell has a high energy density and good cycle performance.

Description

Technical Field

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

[0002] In recent years, with the increasingly wide range of applications, rechargeable 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 vehicles, aerospace, and many other fields. Among these numerous applications, the consumer market has consistently maintained a high demand for batteries that are miniaturized, have high capacity, and have long lifespan.

[0003] With the widespread application and rapid development of secondary batteries, people have put forward higher requirements for their energy density and cycle performance. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell, a battery device and an electrical device, wherein the battery cell has a stable cell structure and can balance energy density and cycle performance.

[0005] To achieve the above objectives, a first aspect of this application provides a battery cell. The battery cell includes a stacked electrode assembly and an electrolyte. The stacked electrode assembly includes a positive electrode, a separator, and a negative electrode stacked together. The separator includes a base film and coatings disposed on both sides of the base film. The coatings include an adhesive layer, wherein the adhesive layer is a continuous layer with a porous structure, and the adhesive layer includes a fluoropolymer. The electrolyte includes a chain carbonate, and based on the total mass of the electrolyte, the mass content of the chain carbonate is 43%-71%.

[0006] The battery cell employs a stacked electrode assembly to achieve high energy density, and utilizes a separator with adhesive layers on both sides. These adhesive layers comprise a fluoropolymer and are a continuous, porous layer, ensuring good adhesion between the electrodes and the separator. This results in a battery cell with high energy density and a stable cell structure. Chain carbonates, used as solvents in the anhydrous electrolyte, have lower viscosity compared to cyclic carbonates. When the electrolyte contains 43%-71% chain carbonates, the viscosity is effectively reduced, improving the wetting of the electrode assembly. Therefore, the battery cell of this application not only has a stable cell structure but also balances energy density and cycle performance.

[0007] In some embodiments, the chain carbonate content is 52%-62% based on the total mass of the electrolyte. This allows for better wettability of the electrode assembly.

[0008] In some embodiments, the chain carbonate includes one or both of dimethyl carbonate and ethyl methyl carbonate. When DMC is used in combination with EMC, it can effectively reduce the viscosity of the electrolyte and improve the wettability of the electrolyte without causing a decrease in the low-temperature performance of the battery.

[0009] In some embodiments, the electrolyte further includes cyclic carbonates. Cyclic carbonates facilitate the dissociation of lithium salts and improve the conductivity of the electrolyte. Furthermore, cyclic carbonates can form a stable SEI film on the negative electrode surface, thereby improving the cycle stability and safety of the battery.

[0010] In some embodiments, the cyclic carbonate content is 14%-42% based on the total mass of the electrolyte. A cyclic carbonate content within this range is beneficial for improving the conductivity of the electrolyte without affecting the wettability of the electrolyte to the electrode assembly.

[0011] In some embodiments, the fluoropolymer includes one or more of polyvinylidene fluoride, vinylidene fluoride-trifluorochloroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluorochloroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, and vinylidene fluoride-trifluorochloroethylene-tetrafluoroethylene-hexafluoropropylene copolymer.

[0012] These polymers can dissolve in oily solvents, allowing their molecular chains to open and form a more uniform slurry. This results in a unified film structure during coating, significantly improving adhesion to the electrode.

[0013] In some embodiments, the thickness of the adhesive layer on one side is 0.15 μm to 2 μm. Within this thickness range, the adhesion strength between the separator and the electrode is within a suitable range without affecting lithium-ion transport, which is beneficial to the cycle performance and safety of the battery cell.

[0014] In some embodiments, the coating further includes a ceramic layer disposed between the base film and the adhesive layer. The presence of a ceramic layer between the base film and the adhesive layer improves the wettability of the electrolyte to the separator, promotes electrolyte flow, and helps to further mitigate the performance degradation of the battery cell caused by insufficient electrolyte wetting, thereby improving the cycle performance of the individual battery cells.

[0015] In some embodiments, the ceramic layer comprises one or more ceramic particles selected from alumina, boehmite, silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, yttrium oxide, zinc oxide, silicon carbide, magnesium fluoride, barium sulfate, barium titanate, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide.

[0016] In some embodiments, the thickness of the ceramic layer on one side is 0.5 μm to 4 μm. Within this thickness range, the wettability and electrolyte retention of the electrolyte can be improved, which is beneficial to the cycle performance and safety performance of the battery cell.

[0017] In some embodiments, the thickness of the base film is 7 μm-9 μm.

[0018] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive active material, which comprises particles containing lithium transition metal phosphate. The lithium transition metal phosphate particles include a lithium transition metal phosphate matrix and a coating layer located on at least a portion of the surface of the lithium transition metal phosphate matrix. The coating layer contains carbon. The chemical formula of the lithium transition metal phosphate matrix is ​​represented as: Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 Wherein, 0.5≤x1≤1.3, 0≤y1≤0.8, 0.9≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5; A includes one or more of Na, K and Mg; Me includes one or more of Mn, Fe, Co and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La and Ce; X includes one or more of S, Si, Cl, B, C, N and P; Y includes one or more of O and F.

[0019] In some embodiments, the lithium-containing transition metal phosphate includes lithium iron phosphate.

[0020] Lithium iron phosphate (LFP) cathode active materials exhibit good cycle performance and high safety, but their specific capacity is relatively low. By employing a stacked electrode assembly arrangement, the energy density of LFP cells can be effectively improved.

[0021] In some embodiments, the lithium-containing transition metal phosphate includes Ti, with the Ti content being 0.05%-0.2% by mass based on the weight of the lithium-containing transition metal phosphate. In the lithium-containing transition metal phosphate, Ti can lower the lithium-ion transport barrier, increase the lithium-ion diffusion rate, thereby improving the battery's kinetic performance and cycle performance.

[0022] In some embodiments, the cumulative particle size distribution curve of the lithium transition metal phosphate particles, measured in a cross-section along the thickness direction of the positive electrode film, shows the D-value of the lithium transition metal phosphate particles. A50 70nm-3μm, D A50 This represents the particle size value corresponding to a cumulative area ratio of 50% along the vertical axis in the cumulative particle size area distribution curve. The D-value of the positive electrode active material particles... A50 On the one hand, it can shorten the lithium-ion diffusion path, and on the other hand, it can reduce the expansion and contraction of particle volume caused by lithium-ion insertion and extraction. Combined with the binding effect of the binder layer, it can improve the structural stability of the stack and thus comprehensively improve the cycle performance.

[0023] In some embodiments, the cumulative distribution curve of the spheroidal area of ​​the lithium transition metal phosphate particles measured in a cross-section of the positive electrode film along the thickness direction of the positive electrode sheet, wherein the spheroidal degree L A50 The value is 0.70-0.75, L A50 This represents the sphericity when the cumulative area along the vertical axis of the cumulative sphericity area distribution curve accounts for 50%. L of lithium transition metal phosphate particles. A50 Within a certain range, relative slippage is more likely to occur between particles. This slippage releases the internal stress of the electrode, thereby mitigating the damage to the electrode structure caused by stress release and improving battery performance.

[0024] In some embodiments, the porosity of the positive electrode sheet is 23%-32%. A certain porosity in the positive electrode film layer can simultaneously ensure high compaction and good wetting, thereby ensuring that the battery cell has high energy density and good cycle performance.

[0025] In some embodiments, the compaction density of the positive electrode sheet is 2.25 g / cm³. 3 -2.65g / cm 3 .

[0026] In some embodiments, the compaction density of the positive electrode sheet is 2.3 g / cm³. 3 -2.45g / cm 3 .

[0027] The compaction density of the positive electrode sheet within the above range enables the cell to have a high energy density, while also facilitating electrolyte wetting and ensuring battery cycle performance.

[0028] In some embodiments, the single-sided coating weight of the positive electrode film is 0.33 g / 1540.25 mm. 2 -0.43g / 1540.25mm 2 .

[0029] In some embodiments, the single-sided coating weight of the positive electrode film is 0.36 g / 1540.25 mm. 2 -0.40g / 1540.25mm 2 .

[0030] When the single-sided coating weight of the positive electrode film is within a suitable range, the cell can have a high energy density and is conducive to ion transport.

[0031] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, and the porosity of the negative electrode sheet is 23% to 32%.

[0032] Within this range, the porosity of the negative electrode film can simultaneously ensure high compaction and good wetting, thereby ensuring that the cell has high energy density and good cycle performance.

[0033] In some embodiments, the compaction density of the negative electrode sheet is 1.3 g / cm³. 3 -1.55g / cm 3 .

[0034] In some embodiments, the compaction density of the negative electrode sheet is 1.4 g / cm³. 3 -1.5g / cm 3 .

[0035] The compaction density of the negative electrode sheet within the above range enables the cell to have a high energy density, while also facilitating electrolyte wetting and ensuring battery cycle performance.

[0036] In some embodiments, the single-sided coating weight of the negative electrode film is 0.15g / 1540.25mm. 2 -0.207g / 1540.25mm 2 .

[0037] In some embodiments, the single-sided coating weight of the negative electrode film is 0.17 g / 1540.25 mm. 2 - 0.2g / 1540.25mm 2 .

[0038] When the single-sided coating weight of the negative electrode film is within a suitable range, the cell can have a high energy density and is conducive to ion transport.

[0039] In some embodiments, the negative electrode sheet includes a negative electrode film layer, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes graphite, and the particle size Dv50 of the graphite is 13μm-22μm.

[0040] In some embodiments, the graphite has a particle size Dv50 of 14.5 μm-20 μm.

[0041] Using graphite with a larger particle size (Dv50) within the aforementioned range is beneficial for increasing the compaction density of the electrode, thereby improving the volumetric energy density of the battery. The electrolyte containing a certain amount of chain carbonate solvent exhibits good fluidity, effectively improving the wetting of the negative electrode, thus enhancing both the volumetric energy density and cycle performance.

[0042] In some embodiments, the porosity of the separator is 28% to 50%.

[0043] In some embodiments, the porosity of the separator is 31% to 40%.

[0044] The porosity of the base membrane within the above-mentioned range is conducive to the passage of active ions.

[0045] A second aspect of this application provides a battery device including the aforementioned battery cell.

[0046] A third aspect of this application provides an electrical device including the aforementioned battery device. The battery device and electrical device of this application, by including the aforementioned battery cell, also possess the advantages described above. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the microstructure of the surface of the isolation membrane in this application;

[0048] Figure 2 This is a schematic diagram of the microstructure of a traditional separator surface;

[0049] Figure 3 This is a schematic diagram of a battery cell according to one embodiment of this application;

[0050] Figure 4 yes Figure 3 An exploded view of a battery cell according to one embodiment of this application is shown.

[0051] Figure 5 This is a schematic diagram of a battery module according to one embodiment of this application;

[0052] Figure 6 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0053] Figure 7 yes Figure 6 An exploded view of a battery pack according to one embodiment of this application is shown;

[0054] Figure 8 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0055] Explanation of reference numerals in the attached figures:

[0056] 10. Separator of this application; 11. Porous continuous adhesive layer; 111 pores; 12. Ceramic layer; 20. Conventional separator; 21. Island adhesive; 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Top cover assembly. Detailed Implementation

[0057] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the lithium-ion secondary battery 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 this application.

[0058] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0059] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0060] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0061] 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.

[0062] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0063] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0064] The market demands increasingly higher capacity and lifespan for rechargeable batteries. One existing technology employs a stacked electrode assembly arrangement to improve cell energy density. The stacked structure involves sequentially stacking positive and negative electrodes, separated by a separator. However, during battery manufacturing, electrode slippage and misalignment can easily occur. During battery cycling, the parallel stacking of electrodes in the stacked cell results in weak interfacial adhesion, and volume expansion during charging and discharging can lead to interlayer separation. These issues pose safety risks such as lithium plating. To address the safety concerns of stacked batteries, a solution has been proposed: using a separator with adhesive layers on both sides. These adhesive layers strengthen the bond between the separator and the electrodes, stabilizing the cell structure.

[0065] However, research has found that when using a separator with an adhesive layer in a stacked electrode assembly, either the adhesion is not strong enough, and electrode misalignment and lithium plating still occur during use, or the cycle performance of a secondary battery with good adhesion is not ideal.

[0066] Based on this, this application provides a battery cell, a battery device, and an electrical device. The battery cell has a stable cell structure and can also ensure good cycle performance. The following provides a more detailed description of this application and its optional embodiments.

[0067] battery cell

[0068] This application provides a battery cell in a first aspect. The battery cell includes a stacked electrode assembly and an electrolyte. The stacked electrode assembly includes a positive electrode, a separator, and a negative electrode stacked together. The separator includes a base film and coatings disposed on both sides of the base film. The coatings include an adhesive layer, wherein the adhesive layer is a continuous layer with a porous structure, and the adhesive layer includes a fluoropolymer. The electrolyte includes a chain carbonate solvent, and the chain carbonate solvent has a mass content of 43%-71% based on the total mass of the electrolyte.

[0069] The adhesive layer used in this application is a porous, continuous layer structure, mainly constructed using an oil-based adhesive, i.e., the adhesive is dispersed using an organic solvent and then coated to form a film. The resulting adhesive layer has a continuous structure (see...). Figure 1 The diagram schematically illustrates the microstructure of the surface of the release membrane 10 of this application. This structure differs from traditional water-based adhesive layers, which are primarily formed by dispersing the adhesive with an aqueous solvent before coating. The resulting adhesive layer exhibits an island-like structure (see [reference]). Figure 2 The diagram schematically illustrates the microstructure of the separator 20 formed using a conventional aqueous binder. While island-shaped binder layers are easy to manufacture, they have a small bonding area and weak adhesion, a problem particularly pronounced in stacked batteries, leading to misalignment of the electrodes and consequently affecting cycle performance. Therefore, the battery cell of this invention employs a stacked electrode assembly and a separator with a continuous binder layer on both sides having the aforementioned porous structure. This results in better adhesion between the electrodes and the separator, leading to a battery cell with high energy density and a stable cell structure. On one hand, the continuous film layer allows for a larger contact area with the electrodes, enhancing the adhesion between the separator and the electrodes; on the other hand, the porous structure facilitates the transport of active ions from the electrolyte between the separator layers.

[0070] However, as mentioned earlier, research has found that even when using a separator with such good adhesion, the battery's cycle performance is still not ideal, and lithium plating still occurs. Further research revealed that this phenomenon is because when the bonding area between the electrode and the separator is large and the bonding force is strong, it affects the wetting of the electrode components by the electrolyte, leading to insufficient local wetting and thus worsening the battery's cycle life.

[0071] Therefore, this application proposes using a chain carbonate solvent with the aforementioned mass content range in the electrolyte of the battery cell. As a solvent for anhydrous electrolytes, the chain carbonate solvent has a lower viscosity compared to cyclic carbonates. When the electrolyte includes 43%-71% cyclic carbonates, the viscosity of the electrolyte is effectively reduced, improving the wettability of the electrolyte to the electrode components. Thus, the battery cell of this application not only has a stable cell structure but also achieves good energy density and cycle performance.

[0072] The morphology of the continuous porous structure of the adhesive layers on both sides of the separator can be observed using an electron microscope. For example, the separator can be disassembled from a single battery cell, cleaned, and then observed under a scanning electron microscope, for example. To reflect the true morphology of the separator, it is preferable to sample areas in the battery where the adhesive layer of the separator is not bonded to the positive or negative electrode. As an example, sampling can be performed at locations where the separator's projection extends beyond the positive and negative electrode plates; or sampling can be performed near the surface of the electrode assembly. These sampling areas have less adhesion between the separator and the positive or negative electrode plates, thus better reflecting the true state of the separator.

[0073] Furthermore, it is understood that during electrode manufacturing or cycling, the continuous structure may become blocky due to contact with or compression of the positive or negative electrode. The continuous structure referred to in this application does not mean that the adhesive layer is continuous throughout the entire battery. Rather, it refers to a network-like continuous layer with a porous structure at the microscopic level, as observed under an electron microscope, rather than an island-like structure.

[0074] The following details the battery cell of this application.

[0075] electrolyte

[0076] The electrolyte in the battery cell of this application includes an electrolyte salt and an organic solvent. As previously mentioned, the electrolyte includes a chain carbonate solvent with a mass content of 43%-71%. Exemplarily, based on the total mass of the electrolyte, the mass content of the chain carbonate solvent is any value from 43%, 45%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 65%, 70%, and 71%, or a range between any two of these values. Optionally, based on the total mass of the electrolyte, the mass content of the chain carbonate solvent is 52%-62%.

[0077] In some embodiments, the chain carbonate solvent includes one or both of dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC). Optionally, the chain carbonate solvent includes DMC and EMC. Further optionally, the chain carbonate is DMC and EMC.

[0078] DMC has a lower viscosity than EMC, making it more effective at reducing electrolyte viscosity. However, DMC has a higher crystallization temperature, resulting in relatively poor low-temperature performance as it is prone to crystallization at low temperatures. When DMC is used in combination with EMC, it can effectively reduce electrolyte viscosity and improve electrolyte wettability without causing a decrease in the battery's low-temperature performance.

[0079] This application does not impose any particular limitation on the ratio of DMC to EMC, which can be adjusted as needed. In some embodiments, the DMC content is 8%-43% based on the total mass of the electrolyte. For example, the DMC content can be any value or a range of any two values ​​from 8%, 10%, 12%, 15%, 17%, 20%, 122%, 25%, 27%, 30%, 32%, 35%, 37%, 40%, to 43% based on the total mass of the electrolyte. Optionally, the DMC content is 20% to 35% based on the total mass of the electrolyte. A DMC content within the above range allows it to fully exert its effect of reducing electrolyte viscosity without affecting the battery's low-temperature performance.

[0080] In other embodiments, the chain carbonate may also include diethyl carbonate (DEC).

[0081] In some embodiments, the organic solvent also includes cyclic carbonates. Cyclic carbonates facilitate the dissociation of lithium salts and improve the conductivity of the electrolyte. Furthermore, cyclic carbonates can form a stable SEI film on the negative electrode surface, thereby improving the cycle stability and safety of the battery.

[0082] In some embodiments, the cyclic carbonate may include ethylene carbonate (EC) and / or propylene carbonate (PC).

[0083] In some embodiments, the cyclic carbonate content is 14%-42% by mass based on the total mass of the electrolyte. Exemplarily, the cyclic carbonate content, based on the total mass of the electrolyte, is any value from 14%, 17%, 20%, 23%, 24%, 26%, 28%, 30%, 32%, 33%, 36%, 39%, and 42%, or a range of any two values. Optionally, the cyclic carbonate content is 23%-33% by mass based on the total mass of the electrolyte. A cyclic carbonate content within the above range is beneficial for improving the conductivity of the electrolyte without affecting the wettability of the electrolyte to the electrode assembly.

[0084] In some embodiments, the solvent may further include one or more of dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethyl 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.

[0085] In some embodiments, the organic solvent content is 82%-92% by mass, optionally 84%-89%, based on the total mass of the electrolyte. For example, the solvent content in the electrolyte is any value from 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, or a range between any two of these values.

[0086] This application does not impose any particular limitation on the electrolyte salt. In some embodiments, the electrolyte salt includes lithium salts. The lithium salt includes one or more selected from 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. Optionally, the lithium salt includes one or more selected from lithium hexafluorophosphate, lithium difluorophosphate, and lithium bis(fluorosulfonyl)imide.

[0087] In some embodiments, the mass content of the electrolyte salt is 8%-18%, optionally 11%-15%, based on the total mass of the electrolyte.

[0088] In some embodiments, the electrolyte may also include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc. Exemplarily, the additives include one or more of vinylene carbonate, fluoroethylene carbonate, and fluorobenzene. Based on the total mass of the electrolyte, the mass content of the additives is 0.4%-5%, optionally 0.7%-3%. Exemplarily, in the electrolyte, the mass content of the additives is any value from 0.5%, 0.7%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a value within a range of any two values.

[0089] In this application, the types and contents of organic components in the electrolyte can be detected using equipment and methods known in the art. For example, the organic components in the electrolyte can be qualitatively and quantitatively analyzed by gas chromatography using GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents". In the embodiments of this application, freshly prepared electrolyte can be used as a sample, the free electrolyte of a fresh battery can be used as a sample, or a battery that has been completely discharged (discharged to the lower limit cutoff voltage so that the battery's state of charge is approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be used as a sample for detection by gas chromatography analysis.

[0090] In this application, the types and contents of inorganic components / lithium salt concentrations in the electrolyte are defined in the art and can be detected using equipment and methods known in the art. For example, the concentrations of inorganic components / lithium salts in the electrolyte can be qualitatively or quantitatively analyzed using ion chromatography, referring to standard JY / T020-1996 "General Rules for Ion Chromatography Analysis". In the embodiments of this application, freshly prepared electrolyte can be used as a sample, the free electrolyte from a fresh battery can be used as a sample, or a fully discharged battery (discharged to the lower cutoff voltage so that the battery's state of charge is approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be used as a sample for detection using ion chromatography.

[0091] Separating membrane

[0092] As previously stated, the separator of this application includes a base film and a coating disposed on both sides of the base film, the coating including an adhesive layer.

[0093] This application does not impose any particular limitation on the type of base membrane; any known porous structure base membrane with good chemical and mechanical stability can be selected. In some embodiments, the base membrane material includes one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The base membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the base membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. Optionally, the base membrane is polyethylene.

[0094] In some embodiments, the thickness of the base film is 7 μm to 9 μm, a thickness range that is beneficial for improving the safety performance of the battery cell. Exemplarily, the thickness of the base film is any value among 7 μm, 8 μm, and 9 μm, or a value within a range consisting of any two of these values.

[0095] The coating is located on both sides of the base film and includes an adhesive layer, which is a continuous layer with a porous structure. In some embodiments, the adhesive layer is disposed on the surface of the base film and in contact with the base film. In other embodiments, there are other intercalary layers between the adhesive layer and the base film, such as ceramic layers as detailed below.

[0096] The adhesive layer comprises a fluoropolymer. Specifically, the fluoropolymer includes one or more of polyvinylidene fluoride (PVDF), vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, and vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene-hexafluoropropylene copolymer. Optionally, the fluoropolymer includes polyvinylidene fluoride (PVDF).

[0097] This application does not impose any particular restrictions on the specific fluoropolymers used; commercially available fluoropolymers, especially those suitable as adhesives, may be used, but are not limited thereto.

[0098] These polymers exhibit different solubilities in aqueous and oil-based solvents. Typically, fluoropolymers are insoluble in aqueous solvents, existing as particulate dispersions, but they dissolve in oil-based solvents, allowing the molecular chains to open and form a more uniform slurry. This results in a monolithic film layer during coating, rather than a discrete point distribution. Furthermore, the addition of pore-forming agents can create a non-uniform porous structure in the coating, significantly improving adhesion to the electrode and allowing active ions from the electrolyte to transport across the separator membrane through these pores.

[0099] In the porous structure of the adhesive layer of this application, the pore size is typically less than 15 micrometers, and the area ratio of pores per unit area is 15%-50%.

[0100] In some embodiments, the thickness of the adhesive layer on one side is 0.15 μm to 2 μm. Within this thickness range, the adhesion strength between the separator and the electrode is within a suitable range, which is beneficial to the cycle performance and safety of the battery cell. Exemplarily, the thickness of the adhesive layer on one side is any value selected from 0.15 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, and 2 μm, or a value within a range of any two values.

[0101] Therefore, the "one-sided thickness of the adhesive layer" mentioned in this application refers to the average thickness of the film layer containing adhesive material, without including the pores in the film layer where no adhesive material is present.

[0102] In some embodiments, the coatings on both sides of the base film further include a ceramic layer disposed between the base film and the adhesive layer.

[0103] The ceramic layer comprises one or more ceramic particles selected from alumina, boehmite, silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, barium sulfate, yttrium oxide, zinc oxide, silicon carbide, magnesium fluoride, barium titanate, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide. Optionally, the ceramic layer comprises alumina and / or boehmite.

[0104] The ceramic layer exhibits excellent wetting properties for the electrolyte. During cycling, the ceramic layer promotes electrolyte wetting on the separator surface and enhances the separator's electrolyte retention capacity. Placing a ceramic layer between the base film and the adhesive layer improves the electrolyte's wettability to the separator, promotes electrolyte flow, and helps to further mitigate interface problems in the electrode assembly caused by insufficient electrolyte wetting, thereby improving the cycle performance of the battery cell. In some embodiments, the average particle size of the ceramic material is 0.2 μm to 2.5 μm; optionally, it is 0.5 μm to 1.5 μm. Controlling the average particle size of the ceramic material within this range is beneficial for improving the separator's electrolyte retention capacity, thereby further improving lithium plating and ultimately enhancing the cycle performance and safety performance of the battery cell. For example, the average particle size of the ceramic material is any value among 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, and 2.5μm, or a value between any two of these values.

[0105] In addition to ceramic particles, the ceramic layer also includes a binder. In some embodiments, the mass ratio of ceramic particles to binder is (3:1) to (10:1); optionally, it is 5:1. This application does not particularly limit the type of binder, which can also be a fluoropolymer, such as polyvinylidene fluoride (PVDF), vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, or vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene-hexafluoropropylene copolymer. Optionally, the binder includes polyvinylidene fluoride (PVDF).

[0106] A certain mass ratio of the above-mentioned binder can enable ceramic particles to form a uniform and dense film layer, and also helps to make the base film, ceramic layer and binder layer tightly bonded.

[0107] The ceramic layer may further include an optional thickener. The thickener helps to ensure the uniformity and stability of the slurry used to coat the ceramic layer, thereby facilitating the formation of a uniform ceramic layer. This application does not particularly limit the type of thickener. For example, the thickener may include at least one of hydroxyethyl cellulose, methyl hydroxyethyl cellulose, sodium carboxymethyl cellulose, polyacrylamide, or sodium alginate. This application does not particularly limit the content of the thickener in the oily adhesive layer; those skilled in the art can select it according to actual needs.

[0108] In some embodiments, the thickness of the ceramic layer on one side is 0.5 μm to 4 μm. Within this thickness range, the wettability and electrolyte retention of the ceramic layer can be improved, which is beneficial to the cycle performance and safety of the battery cell. Exemplarily, the thickness of the ceramic layer on one side is any value selected from 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, and 4 μm, or a value within a range of any two values.

[0109] The presence of the adhesive layer and optional ceramic layer in the separator removed from the electrode assembly can be observed under a scanning electron microscope (SEM).

[0110] To accurately reflect the true morphology of the separator, sampling is preferably performed in areas of the battery where the separator adhesive layer is not bonded to the positive or negative electrode. For example, sampling can be conducted at locations where the separator's projection extends beyond the positive and negative electrode surfaces; or sampling can be performed near the surface of the electrode assembly. These sampling areas have less adhesion to the positive or negative electrode, thus better reflecting the separator's true condition.

[0111] Specific methods include observing the coating thickness from a cross-section along the thickness direction of the separator membrane using the methods described below. Alternatively, the morphology of the coating can be observed on the surface of the separator membrane under a scanning electron microscope (SEM). As mentioned earlier, after removing the separator membrane from the battery cell and sampling from a suitable area, the surface of the separator membrane sample is cleaned, and the surface can be observed using SEM. See [link to relevant documentation]. Figure 1 A schematic diagram of the microstructure of the separator surface is shown. According to the separator 10 of this application, the porous continuous adhesive layer 11 has a morphology of a continuous membrane layer with a porous structure, including multiple pores 111. If a ceramic layer is present, ceramic particles in the ceramic layer 12 beneath the adhesive layer can be observed through the pores 111 of the adhesive layer 11. Unlike the separator of this application, Figure 2 A schematic diagram of the microstructure of the surface of a conventional release membrane 20 obtained using a conventional aqueous adhesive coating method is shown. See also Figure 2 The surface of the conventional separator 20 also has a ceramic layer 12, on which island-shaped adhesive 21 is applied. (Comparison) Figure 1 and Figure 2 As can be seen, the adhesive layer of this application has a relatively much larger bonding area.

[0112] In the embodiments of this application, the thickness of the base film, the thickness of the adhesive layer on one side, and the thickness of the ceramic layer on one side have conventional meanings in the art. The thickness of the base film and coatings in the separator can be detected using methods and equipment known in the art. For example, a newly prepared separator can be used as a sample, or a fully discharged battery cell (discharged to the lower cutoff voltage so that the battery's state of charge is approximately 0% SOC) can be disassembled in reverse, and the separator can be obtained from the battery cell and dried as a sample. The separator is cut along the thickness direction using an ion beam cutter to expose the cut surface, and then the thickness of the separator and its various layers is measured using a scanning electron microscope. By adjusting the microscope to a suitable magnification, the separator base film, ceramic layer, and adhesive layer can be observed completely, and then a mapping test is performed on the separator. The coating containing metal elements in the test results is the ceramic layer, and the coating with higher carbon and fluorine content is the adhesive layer. Then, the thickness T1 of the ceramic coating and the thickness t1 of the adhesive layer on one side of the base film are measured respectively. Following the above steps, further test the thicknesses T2, T3, T4, and T5 of the ceramic layer and the organic coating in four different fields of view. Calculate the average values ​​for both the ceramic coating and the adhesive layer.

[0113] The specific materials of the adhesive layer and optional ceramic layer can be tested using the following methods: For separators removed from the electrode assembly at 0% state of charge (SOC), if only the adhesive layer exists, the separator can be dissolved in a suitable solvent (such as N-methylpyrrolidone, NMP) and then tested using an infrared spectroscopy analyzer. Alternatively, the entire surface of the separator sample can be tested directly using an infrared spectroscopy analyzer, and the type of adhesive layer material can be identified by recognizing characteristic peaks in the infrared spectrum. For separators containing both an adhesive layer and a ceramic layer, the separator can be placed in a suitable solvent (such as NMP) and sonicated at 60°C for 60 minutes to remove the coating. The solid material can then be collected and subjected to X-ray diffraction (XRD) testing. The type of ceramic material can be determined by the XRD pattern. Alternatively, the separator can be dissolved in a suitable solvent (such as NMP) and then tested using an infrared spectroscopy analyzer. Alternatively, the entire surface of the separator sample can be tested directly using an infrared spectroscopy analyzer, and the type of adhesive layer material can be identified by recognizing characteristic peaks in the infrared spectrum.

[0114] In some embodiments, the porosity of the separator is 28%-50%. A porosity within this range facilitates the passage of active ions. Exemplarily, the porosity of the separator is any value from 28%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 45%, and 50%, or a range consisting of any two of these values. Optionally, the porosity of the separator is 31%-40%.

[0115] In this application, porosity refers to the percentage of the volume of the pores in the separator to the total volume of the separator. Porosity can be tested according to standard GB / T 24586-2009. For example, as described above, the separator can be obtained by disassembling a battery cell at 0% state of charge (SOC), cut into 3mm × 3mm pieces, and the apparent volume V0 of the sample (the apparent volume of the sample is the thickness of the positive electrode film layer × the area of ​​the sample) can be measured. Then, the true volume of the sample is tested using a true density meter. Specifically, the sample is placed in the sample test chamber, nitrogen gas is introduced into the sample test chamber, and the sample test chamber is connected to the reference chamber. The pressure after stabilization is recorded. By detecting the pressure before the reference chamber and the sample chamber are connected and the pressure after the connection is stabilized, the pore volume is calculated according to Bohr's law PV=nRT. The porosity of the sample = pore volume / apparent volume. It should be noted that the actual testing process may differ slightly from the standard due to differences in testing instruments, testing errors, and to minimize the influence on the porosity test, in order to obtain more accurate test values.

[0116] Without limitation, the separator of the present invention can be prepared by the following method: dissolving an adhesive and a pore-forming agent in an organic solvent to obtain an adhesive solution; applying the adhesive solution onto a porous base membrane, and removing the pore-forming agent after drying to form the adhesive layer on the porous base membrane.

[0117] This application does not impose any particular limitation on the preparation method of the separator membrane. For example, it can be prepared by the following method.

[0118] The separator with a ceramic layer is first coated with a ceramic layer. Ceramic particles forming the ceramic layer and a binder (e.g., a mass ratio of 5:1, and if applicable, a thickener) are dispersed in a solvent (e.g., N-methylpyrrolidone NMP) to form a ceramic layer slurry. The ceramic layer slurry is coated onto both sides of a base film, and after drying to remove the solvent, a separator with ceramic layers on both sides of the base film is obtained.

[0119] Next, an adhesive layer is coated. A fluoropolymer (such as PVDF, with a final mass content of 20%) is dissolved in an organic solvent (such as NMP), and a pore-forming agent (such as PEG, with a final mass content of 15%) is added. The mixture is then thoroughly mixed to obtain the adhesive layer solution. The liquid is coated onto the surface of the ceramic layer (or directly onto the base film surface for films without a ceramic layer). Part of the solvent is pre-evaporated at 80°C, and then dried at 110°C. The dried membrane is then immersed in deionized water to dissolve and wash away the PEG, thus forming an adhesive layer with a porous structure.

[0120] Positive electrode sheet

[0121] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material.

[0122] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the opposite surfaces of the positive current collector. In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0123] This application does not impose any particular limitation on the positive electrode active material. Exemplarily, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3Co 1 / 3 Mn 1 / 3 O2 (NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.1 Al 0.05O2) and its modified compounds, etc. Examples of lithium-containing phosphates with olivine structure may include, but are not limited to, lithium transition metal phosphates, such as lithium iron phosphate (e.g., LiFePO4 (LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (e.g., LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0124] In some embodiments, the positive electrode active material comprises particles containing lithium transition metal phosphate. The lithium transition metal phosphate particles comprise a lithium transition metal phosphate matrix and a coating layer covering at least a portion of the surface of the lithium transition metal phosphate matrix. The coating layer contains carbon. The lithium transition metal phosphate matrix is ​​represented by the following chemical formula.

[0125] Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1

[0126] Wherein, 0.5≤x1≤1.3, 0≤y1≤0.8, 0.9≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5; A includes one or more of Na, K and Mg; Me includes one or more of Mn, Fe, Co and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La and Ce; X includes one or more of S, Si, Cl, B, C, N and P; Y includes one or more of O and F.

[0127] This disclosure does not impose any particular limitation on the type of lithium-containing transition metal phosphate matrix. For example, it can be selected from at least one of lithium iron phosphate (LFP), lithium manganese phosphate, and lithium manganese iron phosphate. In some embodiments, the lithium-containing transition metal phosphate includes lithium iron phosphate. Lithium iron phosphate-based cathode active materials have good cycle performance and high safety, but their specific capacity is relatively low. By using a stacked electrode assembly arrangement, the energy density of lithium iron phosphate cells can be effectively improved.

[0128] At least a portion of the surface of the lithium transition metal phosphate matrix is ​​coated with a carbon coating layer. Carbon has excellent electrical conductivity, which is beneficial for electron transport. The carbon coating layer can significantly improve the electronic conductivity of lithium transition metal phosphate materials, compensating for the poor electronic conductivity of lithium transition metal phosphate materials.

[0129] Carbon coatings deposited on at least a portion of the surface of lithium-containing transition metal phosphates can be detected using any method known in the art. As an example, carbon coatings deposited on at least a portion of the surface of lithium-containing transition metal phosphates can be observed by characterizing the phosphates using transmission electron microscopy coupled with energy dispersive spectroscopy. It should be noted that the elements in the carbon coating are not limited to carbon, but may also include other non-carbon elements. Carbon coatings are not limited to film-like forms, but also include island-like, irregular, or discontinuous coatings.

[0130] In some embodiments, the lithium-containing transition metal phosphate includes titanium (Ti). Based on the mass of the lithium-containing transition metal phosphate, the mass content of Ti is 0.05% to 0.2%. For example, the mass content of Ti is any value from 0.05%, 0.08%, 0.1%, 0.13%, 0.15%, 0.17%, and 0.2%, or a range of any two values. In the lithium-containing transition metal phosphate, Ti can lower the lithium-ion transport barrier, increase the lithium-ion diffusion rate, thereby improving the battery's kinetic performance and cycle performance.

[0131] In some embodiments, the cumulative particle size distribution curve of the lithium transition metal phosphate particles, measured in a cross-section along the thickness direction of the positive electrode film, shows the D-value of the lithium transition metal phosphate particles. A50 The range is 70nm to 3μm, D A50 This represents the particle size value corresponding to a cumulative area ratio of 50% on the vertical axis of the cumulative particle size area distribution curve.

[0132] In this application, the term "particle" refers to a particle in the positive electrode film layer that has a recognizable complete boundary in the field of view at a certain magnification, such as 10,000x. Defects and scratches may exist inside the particle, but a complete boundary sufficient to divide the particle cannot be identified inside the particle.

[0133] The particle identification method is as follows: The positive electrode film layer is cut along the thickness direction of the electrode sheet using an argon ion beam. After exposing the cut surface, a scanning electron microscope (SEM) is used to observe the cut surface along the thickness direction of the positive electrode film layer. Using a field emission scanning electron microscope (FET) at a non-edge location in the cut surface of the positive electrode film layer (after observing the electrode edge under the SEM, the field of view is adjusted to the center of the sample), images are acquired in secondary electron mode. Electron micrographs are taken at 10kx magnification, and the particles in the electron micrographs are analyzed using ImageJ software (1.46r, Win64 version). The specific usage of ImageJ software is as follows: Load the SEM image to be analyzed; use the Cellpose plugin software to identify particles, and perform manual corrections; use ImageJ to read and analyze data. The specific method for identifying particles using the Cellpose plugin software is as follows: Set the segmentation diameter parameter (diameter in the Segmentation module) to 15 pixels, click "run cyto3" to identify particles, and manually mark particles in the image that were not identified by the software, were not fully identified by the software, or had identification errors. The particles in the image that were not recognized by the software, were not fully recognized by the software, or were recognized with errors mainly include the following: 1. Due to the particle being too large or having scratches on its surface, the particle cannot be recognized or cannot be fully recognized; 2. During the argon ion beam cutting process, scratches will be generated on the particle surface. The software may misjudge the scratches as particle boundaries during the recognition process, thus causing recognition errors; 3. Due to the particle being too small, it was not successfully recognized; 4. The particle is located at the edge of the electron microscope field of view, and the interior of the particle is penetrated by the edge, so the morphology cannot be fully displayed. The part is recognized instead of the whole, resulting in recognition errors. For the unidentified or misidentified particles mentioned above, manual calibration is performed. The specific process is as follows: 1. Delete large particles located around the edges of the scanning electron microscope that are not fully displayed. 2. Determine if any unidentified or misidentified particles have internal cracks or scratches. If no cracks or scratches are found, classify it as a single particle and manually mark it based on the observed particle boundary. 3. If cracks or scratches are found inside the particle, determine if they penetrate the particle. If not, classify it as a single particle and manually mark it. 4. If cracks or scratches penetrate the particle, determine if they are linear or irregular. 5. If the cracks or scratches are irregular, classify them as the boundary between particles and divide the particles along this boundary. 6. If the cracks or scratches are linear, perform contrast comparison. 7. If the contrast is not obvious and there is no crack-like appearance, classify it as a scratch and mark it as a single particle. 8. If the contrast is strong and there is a crack-like appearance, classify it as the boundary between particles and mark it as two particles. After manual marking, delete information irrelevant to the particles from the automatic image processing, thus completing the particle identification and marking in the image.

[0134] The cross-sectional morphology of the positive electrode film along the thickness direction differs from that of the positive electrode active material in Malvern laser scattering and also from that observed directly under a scanning electron microscope. Under roller pressure, the particles in the positive electrode film exhibit good dispersion, making observation of the positive electrode film beneficial for effectively characterizing the particle size, area, and quantity.

[0135] It is understandable that the particles in the cross-section of the positive electrode film along the thickness direction of the electrode sheet, especially those larger than 50 nm, mainly originate from the positive electrode active material. Therefore, this application can accurately and objectively reflect the distribution of positive electrode active material particles in the electrode sheet by observing and statistically analyzing the particle size in the cross-section of the positive electrode film.

[0136] In existing technologies, Malvern laser diffraction is commonly used to statistically analyze the particle size of cathode active materials. However, studies have shown that because lithium phosphate readily agglomerates, the test results obtained by Malvern laser diffraction based on the principle of laser scattering often only reflect the particle size of the agglomerates, failing to accurately reflect the particle size within the cathode active material, let alone its dispersion state in the film layer. This is because the dispersion of the cathode active material in the film layer increases during the film-forming rolling process. The test results obtained by Malvern laser diffraction are closely related to the particle size, specific surface area, and degree of agglomeration of the cathode active material. Therefore, the particle size obtained by Malvern laser diffraction cannot be equated with or analogized to the particle size statistically obtained in this application.

[0137] D A50 Test method: In a cross-section of the positive electrode film along the thickness direction of the electrode, the D of the particles... A50The calculation method is as follows. Following the method described above, the images after particle identification and labeling are imported into ImageJ software for analysis. Based on the scanning electron microscope (SEM) images, scale settings are completed. The Feret diameter and Area of ​​the particle cross-section in the cross-section along the electrode thickness direction of the positive electrode film are analyzed using the "Feret diameter," "Area," "Round," and "Solidity" analysis functions. According to the software manual (ImageJ User Guide IJ 1.46r), the obtained "Feret" parameter represents the maximum spacing between all parallel lines of the particle's cross-section, thus characterizing the particle size; and the obtained "Area" parameter represents the pixel area of ​​the particle. Since particles with a diameter less than 50 nm have a large error in the statistical process and are difficult to accurately identify, and the particle size of conductive agents is generally less than 50 nm, which will introduce a large error into the statistical results, particles with a diameter less than 50 nm are not counted in the particle size statistics process of this application, and the particle statistics data corresponding to Area, Round, or Solidity being displayed as "NaN" are deleted. Following the above method, to ensure a statistically significant sample size, at least 10 non-overlapping scanning electron microscope (SEM) images were acquired for each electrode, and the particle size of at least 5000 particles was statistically analyzed. The particle sizes of the at least 5000 particle cross-sections were arranged in ascending order, and the cumulative area distribution curve of the particles in the positive electrode film was obtained by plotting particle size on the horizontal axis and the cumulative area percentage calculated from the particle's "area" on the vertical axis. A50 This represents the particle size value corresponding to a cumulative area ratio of 50% on the vertical axis of the cumulative area distribution curve.

[0138] For example, the D of particles containing lithium transition metal phosphate A50 The value can be any value from 70nm, 100nm, 500nm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, or a range between any two values. Optionally, the D of the lithium transition metal phosphate particles... A50 The particle size is 100nm-2.5μm. Using lithium iron phosphate particles with appropriate particle size can shorten the lithium-ion diffusion path and reduce the expansion and contraction of particle volume caused by lithium-ion insertion and extraction. Combined with the binding effect of the binder layer, it can improve the structural stability of the stack and thus comprehensively improve the cycle performance.

[0139] In some embodiments, the particles of the positive electrode active material include particles containing lithium transition metal phosphate, or particles containing lithium transition metal phosphate.

[0140] In some implementations, the lithium transition metal phosphate particles can be designed with a combination of large and small particles to increase the compaction density of the cathode, thereby increasing the energy density of the battery.

[0141] In some embodiments, the cumulative distribution curve of the spheroidal area of ​​the lithium transition metal phosphate particles measured in a cross-section of the positive electrode film along the thickness direction of the positive electrode sheet, wherein the spheroidal degree L A50 The value is 0.70-0.75, L A50 This represents the sphericity when the cumulative area along the vertical axis of the cumulative sphericity area distribution curve accounts for 50%. Sphericity L of lithium-containing transition metal phosphate particles. A50 Within a certain range, relative slippage is more likely to occur between particles. This slippage releases internal stress in the electrode, thereby mitigating stress release and reducing its destructive effects on the electrode structure, thus improving battery performance. For example, sphericity L... A50 It can be any value from 0.70, 0.71, 0.72, 0.73, 0.74, 0.75 or a value between any two values.

[0142] The method for determining the cumulative distribution curve of spheroidity area is as follows. Specifically, the method for testing the spheroidity of particles in the cross-section of the positive electrode film along the electrode thickness direction is as follows: The image after particle identification and labeling is imported into ImageJ software for analysis. The scale is set according to the scanning electron microscope image. The particle size and area in the cross-section of the positive electrode film along the electrode thickness direction are analyzed using the "Feret diameter," "Area," "Round," and "Solidity" analysis functions. According to the software manual (ImageJ User Guide IJ 1.46r), the "Feret" parameter represents the maximum spacing between all parallel lines in the two-dimensional projection of the particle, thus characterizing the particle size; the "Area" parameter represents the pixel area of ​​the particle, thus characterizing the particle area. Since particles with a diameter less than 50 nm have a large error in the statistical process and are difficult to accurately identify, and the particle size of the conductive agent is generally less than 50 nm, it will produce a large error in the statistical results. Therefore, in the particle size statistics process of this application, particles with a diameter less than 50 nm are not counted, and the statistical data corresponding to particles whose Area is displayed as "NaN" are deleted. The "Round" parameter represents the ratio of the pixel area of ​​a particle to the area of ​​a circle with the fitted major axis as its diameter, and can be used to characterize the sphericity of the particle. The closer the particle is to a sphere, the closer the ratio of the pixel area to the area of ​​the circle with the fitted major axis as its diameter is to 1. Therefore, the "Round" parameter of the particle obtained from the analysis is used to characterize the sphericity of the particle.

[0143] The sphericity of at least 5000 particles was arranged in ascending order, and the cumulative sphericity distribution curve of the particles in the positive electrode film was obtained with sphericity as the horizontal axis and cumulative area percentage as the vertical axis. L A50 This represents the L-value of sphericity when the cumulative area under the vertical axis of the cumulative distribution curve of L-values ​​accounts for 50%.A50 Compared to point values, it can reflect the overall sphericity of particles in the positive electrode film, that is, the degree to which they are approximately spherical; compared to mean values, it can reduce the influence of extreme values ​​during the test and improve the confidence of the test results.

[0144] 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 positive electrode active materials in this application, the molar Li content refers to the initial state of the material, i.e., before feeding. When the positive electrode active material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0145] In the examples of positive electrode active 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.

[0146] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0147] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0148] In some embodiments, the porosity of the positive electrode film is 23%-32%. A certain porosity in the positive electrode film ensures both high compaction and good wetting, thereby ensuring the cell has high energy density and good cycle performance. For example, the porosity of the positive electrode film is any value from 23%, 25%, 27%, 29%, 30%, and 32%, or a range of any two values.

[0149] In this application, the porosity of the positive electrode sheet can be determined using instruments and methods known in the art. For example, it can be determined using a true density meter, referring to GB / T24586-2009. Specifically: the positive electrode sheet in a battery cell at 0% state of charge (SOC) is disassembled, cut into 3mm × 3mm pieces, and the apparent volume V0 of the sample is measured (the apparent volume of the sample is the thickness of the positive electrode film × the area of ​​the sample). Then, the true volume of the sample is measured using a true density meter. Specifically, the sample is placed in the sample testing chamber, nitrogen gas is introduced into the sample testing chamber, and the sample testing chamber is connected to the reference chamber. The pressure after stabilization is recorded. By detecting the pressure before the reference chamber and the sample chamber are connected and the pressure after the connection is stabilized, the pore volume is calculated according to Bohr's law PV=nRT. The porosity of the sample = pore volume / apparent volume.

[0150] In some embodiments, the compaction density of the positive electrode sheet is 2.25 g / cm³. 3 -2.65g / cm 3 The compaction density of the positive electrode sheet within the aforementioned range allows the battery cell to have a high energy density, while also facilitating electrolyte wetting and ensuring battery cycle performance. For example, the compaction density of the positive electrode sheet is 2.25 g / cm³. 3 2.30g / cm 3 2.35g / cm 3 2.40 g / cm 3 2.45g / cm 3 2.50g / cm 3 2.60g / cm 3 2.65g / cm 3 The value can be any value in the range or any two values ​​within a given range. Optionally, the compaction density of the positive electrode sheet is 2.3 g / cm³. 3 -2.45g / cm 3 .

[0151] In this application, the compaction density of the positive electrode sheet refers to the compaction density of the positive electrode sheet of the battery cell at 0% state of charge (SOC), which can be detected by the following method: Disassemble the battery cell at 0% SOC to separate the positive electrode sheet, and measure the compaction density of the positive electrode sheet. For example, take a single-sided coated positive electrode sheet (if it is a double-sided coated electrode sheet, the positive electrode film layer on one side can be wiped off first), cut it into a small circular piece with an area of ​​S1, weigh it, record its weight as M1, and measure its thickness H1. Then wipe off the positive electrode film layer of the weighed positive electrode sheet, weigh the positive current collector, record its weight as M0, and measure its thickness H0. The coating weight of the positive electrode sheet on one side = (weight of the positive electrode sheet M1 - weight of the positive current collector M0) / S1, the thickness of the positive electrode film = the thickness of the positive electrode sheet H1 - the thickness of the positive current collector H0, and the compaction density of the positive electrode sheet = the coating weight of the positive electrode film on one side / the thickness of the positive electrode film.

[0152] In some embodiments, the single-sided coating weight of the positive electrode film is 0.33 g / 1540.25 mm. 2 ~0.43g / 1540.25mm 2 A suitable single-sided coating weight for the positive electrode film can result in a high energy density in the battery cell and is beneficial for ion transport. For example, the single-sided coating weight of the positive electrode film is 0.33 g / 1540.25 mm. 2 0.35g / 1540.25mm 2 0.36g / 1540.25mm 2 0.37g / 1540.25mm 2 0.38g / 1540.25mm 2 0.39g / 1540.25mm 2 0.40g / 1540.25mm 2 0.41g / 1540.25mm 2 0.43g / 1540.25mm 2 Optionally, the single-sided coating weight of the positive electrode film is 0.36g / 1540.25mm. 2 ~0.40g / 1540.25mm 2 .

[0153] In this application, the single-sided coating weight of the positive electrode film can be tested using methods known in the art. The positive electrode sheet to be tested can be a pre-prepared positive electrode sheet or a positive electrode sheet obtained by disassembling a battery. The latter will be used as an example to illustrate the testing process below. A positive electrode sheet is obtained by disassembling a 0% state of charge (SOC) battery, and the positive electrode sheet is cut into pieces with an area of ​​1540.25 mm². 2Take a circular wafer, weigh it as m1, then remove the positive electrode film layer on one side of the wafer, weigh the wafer as m2, and take m1-m2 as the single-sided coating weight of the positive electrode film layer.

[0154] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0155] Negative electrode sheet

[0156] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material.

[0157] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0158] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0159] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, 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 batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0160] In some embodiments, the negative electrode active material includes graphite. The graphite particle size Dv50 is 13μm-22μm. Using graphite with a larger particle size Dv50 within the above range is beneficial to increasing the compaction density of the electrode sheet, thereby increasing the volumetric energy density of the battery. Although graphite in this particle size range will lengthen the transport path of lithium ions in the graphite, increase polarization, and be detrimental to the cell cycle performance, in the single cell of this application, the electrolyte containing a certain amount of chain carbonate solvent has good fluidity, which can effectively improve the wetting of the negative electrode sheet, thereby improving the volumetric energy density of the battery while taking into account the cycle performance. For example, the graphite particle size Dv50 is any value or any combination of two values ​​from 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm. Optionally, the graphite particle size Dv50 is 14.5 μm-20 μm.

[0161] In the embodiments of this application, the volume average particle size Dv50 of the material refers to the particle size corresponding to 50% of the volume distribution, and the volume average particle size Dv10 of the material refers to the particle size corresponding to 10% of the volume distribution. They can be detected using equipment and methods known in the art. For example, the negative electrode active material can be used as a sample, or the negative electrode sheet can be disassembled from a battery cell at 0% state of charge (SOC), and the negative electrode film layer can be scraped off to remove organic matter and obtain the negative electrode active material. According to the testing standard GB / T19077-2016, the Dv50 of the particles can be tested using a Mastersizer 2000E laser particle size analyzer.

[0162] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive 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).

[0163] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0164] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0165] In some embodiments, the porosity of the negative electrode film is 23%-32%. This porosity range ensures both high compaction and good wetting, thereby guaranteeing high energy density and good cycle performance of the battery cell. For example, the porosity of the negative electrode film is any value from 23%, 32%, 25%, 27%, 30%, 32%, or any combination of two values.

[0166] In some embodiments, the compaction density of the negative electrode sheet is 1.3 g / cm³. 3 -1.55g / cm 3 The compaction density of the negative electrode sheet within the aforementioned range allows the battery cell to achieve a high energy density while also facilitating electrolyte wetting and ensuring battery cycle performance. For example, the compaction density of the negative electrode sheet is 1.3 g / cm³. 3 1.35g / cm 3 1.4g / cm 3 1.45g / cm 3 1.5g / cm 3 1.55g / cm 3 The value can be any value in the range or any two values ​​within a given range. Optionally, the compaction density of the negative electrode sheet is 1.4 g / cm³. 3 -1.5g / cm 3 .

[0167] In some embodiments, the single-sided coating weight of the negative electrode film is 0.15g / 1540.25mm. 2 -0.207g / 1540.25mm 2 A suitable single-sided coating weight for the negative electrode film can result in a high energy density in the battery cell and is beneficial for ion transport. For example, the single-sided coating weight of the positive electrode film is 0.15g / 1540.25mm. 2 0.17g / 1540.25mm 2 0.18g / 1540.25mm 2 0.19g / 1540.25mm 2 0.20g / 1540.25mm 2 0.207g / 1540.25mm 2 Optionally, the single-sided coating weight of the negative electrode film is 0.17g / 1540.25mm. 2 -0.2g / 1540.25mm 2 .

[0168] In this application, the methods for determining the porosity, compaction density, and single-sided coating weight of the negative electrode sheet are basically the same as the corresponding methods for determining the positive electrode sheet, and will not be repeated here.

[0169] 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, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0170] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0171] In the battery cell of this application, the aforementioned positive electrode, negative electrode, and separator are fabricated into an electrode assembly using a stacking process. This application does not impose any particular restrictions on the stacking process; conventional methods can be employed for fabrication.

[0172] In some embodiments, the hot pressing of the stacked electrode assembly is maintained at 2MPa~4MPa and 60℃~100℃ for 90s~200s. Through hot pressing, the adhesive layer can be melted, thereby bonding the positive and negative electrode sheets on both sides of the separator to the separator.

[0173] In some embodiments, the battery cell may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and the electrolyte described above.

[0174] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0175] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 The example shown is a square-structured battery cell 5.

[0176] In some implementations, refer to Figure 4The outer packaging may include a housing 51 and a top cover assembly 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 top cover assembly 53 can cover the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 through 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 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0177] Battery device

[0178] A second aspect of this application further provides a battery device.

[0179] The battery apparatus 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 as described in the first aspect, wherein the multiple battery cells are connected in series, parallel, or mixed connections via a busbar.

[0180] In some implementations, a battery cell assembly is typically formed by arranging multiple battery cells.

[0181] 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.

[0182] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0183] 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.

[0184] 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.

[0185] In some implementations, 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.

[0186] In some implementations, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0187] Figure 5 This is battery module 4 as an example. (See reference...) Figure 5 In the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other way. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0188] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0189] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 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.

[0190] Electrical appliances

[0191] The third aspect of this application provides an electrical device, which includes the battery device provided in the second aspect of this application.

[0192] The electrical device mentioned in the embodiments of this application includes the battery device provided in the second aspect of this application. The battery device can be the power source of the electrical device or the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0193] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0194] Figure 8 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 the secondary battery for this device, a battery pack or battery module can be used.

[0195] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0196] Example

[0197] 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.

[0198] Example 1

[0199] (1) Preparation of positive electrode sheet

[0200] The positive electrode active material (lithium iron phosphate with carbon coating, molecular formula: LiFePO4, particle size Da50 of 700nm, carbon content 2%), polyvinylidene fluoride, and conductive carbon black were mixed in a weight ratio of 97:2.2:0.8 and then added to the solvent N-methylpyrrolidone. The mixture was stirred evenly and the viscosity was adjusted to form a positive electrode slurry. The positive electrode slurry was then coated onto both sides of the positive electrode current collector aluminum foil (15µm thick) to form a positive electrode film layer (single-sided coating weight 0.38g / 1540.25mm). 2 After drying and hot pressing, a positive electrode sheet is obtained with a porosity of 29% and a compacted density of 2.4 g / cm³. 3 .

[0201] (2) Preparation of negative electrode sheet

[0202] A negative electrode active material (Dv50 is 15μm graphite), conductive agent (conductive carbon black), binder (styrene-butadiene rubber (SBR)), and thickener (sodium carboxymethyl cellulose (CMC)) were mixed in a mass ratio of 95.5:1.0:2.0:1.5. Deionized water was added and stirred to disperse the mixture into a negative electrode slurry. The negative electrode slurry was then coated onto both sides of a Cu foil (coating weight on one side: 0.185g / 1540.25mm²). After drying, compaction, slitting, and sheet preparation, a negative electrode sheet was obtained with a porosity of 28% and a compaction density of 1.4g / cm³. 3 .

[0203] (3) Preparation of electrolyte

[0204] In an argon-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed thoroughly. Lithium hexafluorophosphate was then added and dissolved in the organic solvent to achieve an electrolyte concentration of 1.05 mol / L. Ethylene carbonate (VC) was then added and the mixture was stirred until homogeneous, yielding the electrolyte of Example 1.

[0205] Based on the total mass of the electrolyte, the mass content of dimethyl carbonate is 27.2%, the mass content of ethyl methyl carbonate is 29.9%, the mass content of ethylene carbonate is 28.1%, and the mass content of vinylene carbonate is 2.6%.

[0206] (4) Separating membrane

[0207] A 7μm polyethylene film was used as the base membrane. A ceramic layer slurry was prepared by mixing alumina powder (1μm particle size) and polyvinylidene fluoride (PVDF) as a binder in N-methylpyrrolidone (alumina:PVDF:solvent mass ratio 5:1:10). The ceramic layer slurry was coated onto both sides of the base membrane and dried to form the ceramic layer. A binder layer solution was prepared by mixing PVDF with N-methylpyrrolidone, followed by the addition of polyethylene glycol (PEG) as a pore-forming agent, where PVDF accounted for 20% of the mass and PEG for 10%. The binder layer solution was coated onto the ceramic layer, pre-evaporated at 80℃ and dried at 110℃, and then immersed in deionized water to dissolve the PEG, yielding the separator membrane. The prepared separator membrane was measured to have a single-sided thickness of 1.6μm for the ceramic layer, a single-sided thickness of 0.65μm for the binder layer, and a porosity of 35%.

[0208] (5) Preparation of battery cells

[0209] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then formed through a stacking process. The electrode assembly is placed in outer packaging, dried, and then injected with the electrolyte. After vacuum sealing, settling, formation, and shaping, a single battery cell is obtained.

[0210] Separator membrane characteristic test

[0211] (1) Coating thickness

[0212] The separator was polished along its thickness direction using an argon ion cross-section polisher (e.g., JEOL IB-09010 CP type argon ion cross-section polisher, Japan) (argon flow rate 0.12 MPa, polishing time 90 min) to obtain a cross-section of the separator along its thickness direction. Under a field emission scanning electron microscope, the base film, ceramic layer, and adhesive layer were observed simultaneously in the field of view. Five sites were selected in five different fields of view to measure the thickness of the ceramic layer and adhesive layer on one side of the base film, and the average value was calculated.

[0213] (2) Porosity of the isolation membrane

[0214] The porosity of the separator was determined according to standard GB / T 24586-2009.

[0215] Electrode performance testing

[0216] (1) Electrode compaction density

[0217] The compaction density is tested using the method described above and calculated by dividing the mass of the electrode film by the volume of the electrode film.

[0218] (2) Testing of electrode porosity

[0219] Referring to GB / T24586-2009, the positive and negative electrode sheets were cut into 3mm×3mm pieces. A true density meter was used, and nitrogen gas was introduced to determine the porosity of the positive and negative electrode sheets, respectively.

[0220] Battery cell performance testing

[0221] Cyclic performance test

[0222] At 25℃, the battery cell was charged to 3.65V at a constant power of 0.5P, allowed to stand for 30 minutes, and then discharged to 2.5V at a constant power of 0.5P, allowed to stand for 2 hours, and the discharge capacity was recorded. This test was repeated 1000 times. The capacity retention rate after 1000 cycles is calculated as (discharge capacity after the 1000th cycle / discharge capacity of the first cycle) × 100%.

[0223] Examples 2-8

[0224] The preparation methods of Examples 2-8 are similar to those of Example 1, except that the composition of the organic solvent in the electrolyte and the thickness of the separator coating are adjusted according to Table 1.

[0225] Example 9

[0226] The preparation method of Example 9 is similar to that of Example 1, except that the isolation membrane does not have a ceramic layer.

[0227] Comparative Examples 1-2

[0228] The preparation methods of Comparative Examples 1 and 2 are similar to those of Example 1, except that the composition of the organic solvent in the electrolyte is adjusted according to Table 1.

[0229] Comparative Examples 3-4

[0230] The preparation methods of Comparative Examples 3-4 are similar to those of Example 1, except that the composition of the organic solvent in the electrolyte is adjusted according to Table 1, and the separator does not have a ceramic layer.

[0231] The performance of the battery cells prepared in Examples 2 to 9 and Comparative Examples 1 to 4 were measured using the same test method as in Example 1. The specific results are shown in Table 1.

[0232] Table 1

[0233]

[0234] As can be seen from Table 1 above, the separators with an oil-based coating adhesive layer, combined with electrolytes containing 43-71% chain carbonate, according to Examples 1-9 of this application, all achieved significantly improved cycle performance compared to Comparative Examples 1 and 2, which used the same separator as in Example 1 but had lower or higher chain carbonate contents, and Comparative Examples 3 and 4, which used the same separator as in Example 9 but had lower or higher chain carbonate contents. These results suggest that an appropriate content of chain carbonate can improve the wettability of the electrolyte to a separator with good adhesion, thereby improving the cycle performance of the battery.

[0235] 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 assembly includes a stacked electrode assembly and an electrolyte. The stacked electrode assembly comprises a positive electrode, a separator, and a negative electrode stacked together. The separator includes a base membrane and a coating disposed on both sides of the base membrane. The coating includes an adhesive layer, wherein the adhesive layer is a continuous layer with a porous structure and the adhesive layer includes a fluoropolymer. The electrolyte comprises chain carbonates and cyclic carbonates, wherein the chain carbonates include dimethyl carbonate and ethyl methyl carbonate; Based on the total mass of the electrolyte, the total mass content of the chain carbonates is 43%-71%, and the mass content of the cyclic carbonates is 14%-42%. The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes particles containing lithium transition metal phosphate. The particles containing lithium transition metal phosphate include a lithium transition metal phosphate matrix and a coating layer located on at least a portion of the surface of the lithium transition metal phosphate matrix. The coating layer contains carbon. In the cumulative particle size distribution curve of the lithium transition metal phosphate particles measured along the thickness direction of the positive electrode film layer, the Dsize of the lithium transition metal phosphate particles is... A50 70nm-3μm, D A50 This represents the particle size value corresponding to a cumulative area ratio of 50% on the vertical axis of the cumulative particle size area distribution curve. The negative electrode sheet includes a negative electrode film layer, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes graphite, and the particle size D of the graphite is... v50 The range is 14.5μm-20μm.

2. The battery cell according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass content of the chain carbonate is 52%-62%.

3. The battery cell according to claim 1, characterized in that, The fluoropolymers include one or more of polyvinylidene fluoride, vinylidene fluoride-trifluorochloroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluorochloroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, and vinylidene fluoride-trifluorochloroethylene-tetrafluoroethylene-hexafluoropropylene copolymer.

4. The battery cell according to claim 1 or 2, characterized in that, The thickness of the adhesive layer on one side is 0.15μm-2μm.

5. The battery cell according to claim 1, characterized in that, The coating also includes a ceramic layer disposed between the base film and the adhesive layer.

6. The battery cell according to claim 5, characterized in that, The ceramic layer comprises one or more ceramic particles selected from alumina, boehmite, silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, barium sulfate, yttrium oxide, zinc oxide, silicon carbide, magnesium fluoride, barium titanate, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide.

7. The battery cell according to claim 5 or 6, characterized in that, The thickness of the ceramic layer on one side is 0.5μm-4μm.

8. The battery cell according to claim 1, characterized in that, The thickness of the base film is 7μm-9μm.

9. The battery cell according to claim 1, characterized in that, The chemical formula of the lithium-containing transition metal phosphate matrix is: Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 Wherein, 0.5≤x1≤1.3, 0≤y1≤0.8, 0.9≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5; A includes one or more of Na, K and Mg; Me includes one or more of Mn, Fe, Co and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La and Ce; X includes one or more of S, Si, Cl, B, C, N and P; Y includes one or more of O and F.

10. The battery cell according to claim 9, characterized in that, The lithium-containing transition metal phosphates include lithium iron phosphate.

11. The battery cell according to claim 9 or 10, characterized in that, The lithium-containing transition metal phosphate contains Ti, and the mass content of Ti is 0.05%-0.2% based on the mass of the lithium-containing transition metal phosphate.

12. The battery cell according to claim 9 or 10, characterized in that, In the cumulative distribution curve of the spheroidal area of ​​the lithium transition metal phosphate particles measured in a cross-section along the thickness direction of the positive electrode film, the spheroidal degree L... A50 The value is 0.70-0.75, L A50 This represents the sphericity when the cumulative area ratio of the vertical axis in the cumulative distribution curve of sphericity area is 50%.

13. The battery cell according to claim 9, characterized in that, The porosity of the positive electrode sheet is 23%-32%.

14. The battery cell according to claim 9 or 10, characterized in that, The compaction density of the positive electrode sheet is 2.25 g / cm³. 3 -2.65g / cm 3 .

15. The battery cell according to claim 14, characterized in that, The compaction density of the positive electrode sheet is 2.3 g / cm³. 3 -2.45g / cm 3 .

16. The battery cell according to claim 9 or 10, characterized in that, The single-sided coating weight of the positive electrode film is 0.33g / 1540.25mm. 2 -0.43g / 1540.25mm 2 .

17. The battery cell according to claim 16, characterized in that, The single-sided coating weight of the positive electrode film is 0.36g / 1540.25mm. 2 -0.40g / 1540.25mm 2 .

18. The battery cell according to claim 1 or 2, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, and the porosity of the negative electrode sheet is 23%~32%.

19. The battery cell according to claim 1 or 2, characterized in that, The compaction density of the negative electrode sheet is 1.3 g / cm³. 3 -1.55g / cm 3 .

20. The battery cell according to claim 19, characterized in that, The compaction density of the negative electrode sheet is 1.4 g / cm³. 3 -1.5g / cm 3 .

21. The battery cell according to claim 18, characterized in that, The single-sided coating weight of the negative electrode film is 0.15g / 1540.25mm. 2 -0.207g / 1540.25mm 2 .

22. The battery cell according to claim 21, characterized in that, The single-sided coating weight of the negative electrode film is 0.17g / 1540.25mm. 2 -0.2g / 1540.25mm 2 .

23. The battery cell according to claim 1 or 2, characterized in that, The porosity of the isolation membrane is 28%~50%.

24. The battery cell according to claim 23, characterized in that, The porosity of the isolation membrane is 31%~40%.

25. A battery device, characterized in that, Includes the battery cell according to any one of claims 1 to 24.

26. An electrical appliance, characterized in that, Includes the battery device as described in claim 25.

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