Battery cell, battery device, and electric device

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a battery monomer, a battery device and a power utilization device. The battery monomer comprises an electrode assembly and an electrolyte, the electrolyte infiltrates the electrode assembly, the electrode assembly comprises a positive electrode sheet, a separator and a negative electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer, the positive electrode film layer comprises a lithium-containing transition metal phosphate; the negative electrode sheet comprises a negative electrode active material, the median of I D / I G of the negative electrode active material is 0.1-0.6, and the electrolyte comprises linear carbonic acid ester, cyclic carbonic acid ester and linear carboxylic acid ester in a mass ratio of (40-50):(30-40):(15-25). The median of I D / I G of the negative electrode active material is controlled to be 0.1-0.6, the amorphous carbon content is high, the interlayer spacing is large, the active sites are many, and the lithium embedding direction is multiple; the mixing of multiple solvents can reduce the freezing point of the electrolyte, improve the low-temperature ion conduction, and thus improve the low-temperature performance of the battery.

Description

Cross-reference to related applications

[0001] This application claims priority to international application No. PCT / CN2025 / 113079, filed on August 6, 2025, the entirety of which is incorporated herein by reference. Technical Field

[0002] This disclosure relates to the field of lithium-ion batteries, specifically to battery cells, battery devices, and electrical devices. Background Technology

[0003] Lithium-ion batteries, as a core technology for modern energy storage, have been applied in fields such as energy, transportation, and aerospace, demonstrating excellent environmental adaptability. However, despite the expanding application scenarios, existing battery cell technologies still face key technical challenges and require further improvement.

[0004] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0005] In a first aspect, this application proposes a battery cell comprising an electrode assembly and an electrolyte, wherein the electrolyte wets the electrode assembly, the electrode assembly comprising a positive electrode, a separator, and a negative electrode, the positive electrode comprising a positive current collector and a positive electrode film layer located on at least one side of the positive current collector, the positive electrode film layer comprising a positive active material, the positive active material comprising a lithium transition metal phosphate; the negative electrode comprising a negative current collector and a negative electrode film layer located on at least one side of the negative current collector, the negative electrode film layer comprising a negative active material, the negative active material comprising a graphite material, the negative active material comprising a... D / I G The median is 0.1-0.6, where I G This indicates that the Raman spectrum of the negative electrode active material is at 1580±100 cm⁻¹. -1 The intensity of peak G at I D This indicates that the Raman spectrum of the negative electrode active material is at 1350±100 cm⁻¹. -1The D peak intensity at the specified location; the electrolyte comprises linear carbonate, cyclic carbonate, and linear carboxylic acid ester; the mass ratio of the linear carbonate, cyclic carbonate, and linear carboxylic acid ester in the electrolyte is (40-50):(30-40):(15-25); the separator comprises a base film and a coating located on at least one side of the base film; the coating comprises a first coating and a second coating stacked sequentially, the first coating being located on the side closer to the positive electrode, the first coating comprising polyvinylidene fluoride, and the second coating comprising a ceramic material; the coating comprises a third coating on the side closer to the negative electrode, the third coating comprising polyvinylidene fluoride; the thickness of the first coating is 0.5μm-3μm; the thickness of the second coating is 0.5μm-3μm; the thickness of the third coating is 0.5μm-3μm.

[0006] This application controls the I of the negative electrode active material. D / I G The median is 0.1-0.6. The amorphous carbon content in the negative electrode active material is high, the interlayer spacing is large, there are many active sites, and there are many directions for lithium intercalation. The negative electrode accepts lithium ions quickly, that is, the lithium ion intercalation is fast, the lithium intercalation ability is increased, which is more conducive to lithium intercalation and reduces the risk of lithium plating on the negative electrode surface. Based on this, the electrolyte used in this application includes linear carbonates, cyclic carbonates and linear carboxylic esters in a mass ratio of (40-50):(30-40):(15-25). Multiple solvents can increase the disorder of the solvent, reduce the ordered arrangement of solvent molecules, lower the freezing point of the electrolyte, and delay the crystallization trend; multiple solvents can also improve low-temperature ion conduction. Therefore, the battery cell of this application has both fast charging performance and cycle life at low temperature. Carboxylic acid ester solvents have low viscosity. This application controls the content of carboxylic acid ester solvents to increase the electrolyte viscosity, slow down the lithium-ion transport rate, and better match it with the insertion rate of the negative electrode active material. This reduces lithium-ion accumulation on the negative electrode surface, reduces lithium dendrite growth, and thus reduces the probability of lithium dendrites piercing the separator and causing a short circuit in the battery cell. The ceramic material in the second coating of a specific thickness in this application can significantly improve the mechanical strength and heat resistance of the separator, improve puncture resistance and thermal shrinkage resistance, reduce lithium dendrite penetration during charge-discharge cycles, thereby reducing the risk of short circuits and comprehensively improving the fast-charging time and cycle performance of the battery cell. The first and third coatings of a specific thickness can enhance the bonding strength between the separator and the negative electrode sheet, improving the fast-charging time and cycle performance of the battery cell.

[0007] In some embodiments, the negative electrode active material I D / I G The median is 0.2-0.5. When the Raman spectrum of the negative electrode active material has an I... D / I GWhen the median is within the aforementioned range, there are more defect sites on the surface of the negative electrode active material, and the negative electrode active material has a stronger ability to accept lithium ions, which helps to reduce the occurrence of lithium plating side reactions and helps to improve the performance of the battery cell at high rates.

[0008] In some embodiments, the battery cell satisfies one or more of the following conditions: the linear carbonate content is 40%-50% based on the total mass of solvents and additives in the electrolyte; the cyclic carbonate content is 30%-40% based on the total mass of solvents and additives in the electrolyte; and the linear carboxylic acid ester content is 15%-25% based on the total mass of solvents and additives in the electrolyte. Controlling the content of linear carbonate can lower the freezing point of the electrolyte, reduce crystallization, and thus improve the fast-charging performance of the battery cell at low temperatures. Controlling the content of cyclic carbonate can form a stable solid electrolyte interphase (SEI) film, reduce lithium dendrites, and thus improve interface stability and extend cycle life at low temperatures. Controlling the content of linear carboxylic acid ester can further form a low-resistance SEI film and improve the ion mobility of the electrolyte at low temperatures. Therefore, controlling the content of linear carbonate, cyclic carbonate, and linear carboxylic acid ester in the electrolyte can further improve the fast-charging capability and cycle life of the battery cell at low temperatures.

[0009] In some embodiments, the battery cell satisfies one or more of the following conditions: the linear carbonate includes at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and methyl propyl carbonate (MPC); the cyclic carbonate includes at least one of ethylene carbonate (EC), propylene carbonate (PC), trimethylene cyclic carbonate (TMC), and 2,2-dimethyltrimethylene cyclic carbonate (DTC); the linear carboxylic acid ester includes at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate. The above-mentioned linear carbonates have low melting points, and their use can significantly reduce the freezing point of the electrolyte, improving the fast-charging performance of the battery cell at low temperatures. The above-mentioned cyclic carbonates can form a uniform and dense SEI film on the negative electrode surface, improving interface stability. The uniform SEI film can guide the uniform deposition of lithium metal and reduce the risk of lithium dendrite puncture. The aforementioned linear carboxylic acid esters have low viscosity and high ionic conductivity, which can accelerate the transport of lithium ions at low temperatures.

[0010] In some embodiments, the battery cell satisfies one or more of the following conditions: the mass percentage of dimethyl carbonate is 10%-50% based on the total mass of solvents and additives in the electrolyte; the mass percentage of ethyl methyl carbonate is 5%-30% based on the total mass of solvents and additives in the electrolyte; the mass percentage of ethylene carbonate is 10%-50% based on the total mass of solvents and additives in the electrolyte; the mass percentage of diethyl carbonate is 0.01%-20% based on the total mass of solvents and additives in the electrolyte; and the mass percentage of ethyl acetate is 15%-25% based on the total mass of solvents and additives in the electrolyte. Dimethyl carbonate has low viscosity and high ionic conductivity. Controlling the content of dimethyl carbonate can reduce lithium-ion transport resistance and improve fast-charging performance. Ethyl methyl carbonate has good interfacial compatibility. Controlling the content of ethyl methyl carbonate helps to form a uniform SEI film on the negative electrode, reduces solvent co-intercalation, and improves the cycle life of the battery cell. Ethyl carbonate has a high dielectric constant; controlling its content can increase the dissociation degree of lithium salt, thereby improving ionic conductivity. Controlling the content of diethyl carbonate can improve the low-temperature conductivity of the electrolyte, enhancing its low-temperature fast-charging capability. Ethyl acetate has a low melting point and viscosity, and can still improve electrolyte fluidity at low temperatures. Controlling its content can further form a low-impedance SEI film, improving the ion mobility of the electrolyte at low temperatures.

[0011] In some embodiments, the electrolyte comprises one of the cyclic carbonates, one of the linear carboxylic acid esters, and at least two of the linear carbonates. Thus, using the aforementioned multi-component solvent can further increase the solvent's disorder, reduce the ordered arrangement of solvent molecules, lower the electrolyte's freezing point, and delay the crystallization tendency; using the aforementioned solvent can also further provide continuous channels for ion conduction, improving low-temperature ion conduction.

[0012] In some embodiments, the electrolyte includes at least one selected from dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and ethyl acetate. Therefore, using the above solvents can further lower the freezing point of the electrolyte, improve SEI film stability, reduce low-temperature lithium plating, and significantly optimize the fast-charging performance and cycle life of battery cells at low temperatures.

[0013] In some embodiments, the electrolyte further includes a lithium salt, which includes at least two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate. Thus, a dynamic coordination structure can be formed between the lithium ions and anions in the solvated lithium salt and the solvent molecules, increasing the disorder of the electrolyte, lowering the freezing point, and improving the capacity retention at low temperatures.

[0014] In some embodiments, the electrolyte comprises lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. The anions of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide have different sizes, charge distributions, and lithium salt dissociation capabilities. In the electrolyte, the interaction modes between these anions and lithium ions are diversified, leading to a more complex solvated sheath structure, increased system disorder, and consequently, a lower freezing point of the electrolyte and improved low-temperature performance.

[0015] In some embodiments, at least one of the following conditions is met: the mass percentage of lithium hexafluorophosphate is 8%-16% based on the total mass of the electrolyte; the mass percentage of lithium difluorosulfonylimide is 1%-10% based on the total mass of the electrolyte. Thus, using the above-mentioned lithium salt can further increase the electrolyte's turbidity and improve the fast-charging capability of the battery cells at low temperatures.

[0016] In some embodiments, the electrolyte further includes BF4. - Therefore, BF4 - With a small ionic radius, it has a strong solubility at low temperatures, which can effectively reduce the viscosity of the electrolyte and improve the migration rate of lithium ions under low-temperature conditions.

[0017] In some embodiments, based on the total mass of the electrolyte, BF4 - The mass percentage is 0.01%-0.5%. This can improve the fast-charging performance of the electrolyte and reduce side reactions with the negative electrode active material at low potentials.

[0018] In some embodiments, the base film comprises one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. Therefore, the base film is widely available and suitable for various applications.

[0019] In some embodiments, the battery cell satisfies one or more of the following conditions: the thickness of the base film is 3μm-10μm; the thickness of the separator is 4μm-12μm. This results in superior mechanical strength of the base film. Controlling the thickness of the separator can shorten the lithium-ion transport path, allowing lithium ions to be transported to the surface of the negative electrode active material more quickly.

[0020] In some embodiments, at least one of the following conditions is met: the porosity of the separator is 25%-60%; the air permeability of the separator is 90s / 100cc-260s / 100cc. This facilitates sufficient wetting of the separator by the electrolyte and rapid passage of lithium ions through the separator during transfer between the positive and negative electrodes.

[0021] In some embodiments, the OI value of the negative electrode active material is 2-6. When the OI value of the negative electrode active material powder is 2-6, it is beneficial to improve the volume expansion and reaction kinetics of the negative electrode active material, enhance the isotropy of the negative electrode active material, accelerate the intercalation of lithium ions, effectively alleviate the volume expansion effect of the negative electrode sheet during cycling, and further improve the cycle performance of the battery cell at low temperatures.

[0022] In some embodiments, the volume average particle size Dv50 of the graphite material is 7 μm-13 μm. Therefore, the overall particle size of the negative electrode active material is small, the migration path of lithium ions within the negative electrode active material is short, and there are fewer side reactions between the negative electrode active material and the electrolyte.

[0023] In some embodiments, the graphite material comprises artificial graphite. Therefore, artificial graphite has more lithium-ion transport channels, which is beneficial for improving the lithium-ion insertion / extraction rate of the negative electrode active material.

[0024] In some embodiments, the graphite material comprises secondary particles formed from primary particles. Thus, the negative electrode active material exhibits isotropy during lithium intercalation, facilitating rapid lithium-ion insertion and improving the rate performance of the battery cell at low temperatures.

[0025] In some embodiments, the artificial graphite comprises a first component and a second component. The method for preparing the first component includes: crushing needle coke to obtain first primary graphite particles; granulating the first primary graphite particles to obtain secondary graphite particles; subjecting the secondary graphite particles to a first heat treatment to obtain an intermediate; mixing the intermediate with a coating agent and performing a second heat treatment to obtain the first component. The method for preparing the second component includes: crushing petroleum coke to obtain second primary graphite particles; mixing the second primary graphite particles with a coating agent and performing a third heat treatment to obtain the second component. Thus, a negative electrode active material with both superior rate performance and high capacity can be obtained through a simple and low-cost process. Furthermore, coating the graphite surface with an amorphous carbon layer expands the interlayer spacing and reduces lithium-ion intercalation resistance.

[0026] In some embodiments, the single-sided coating weight of the negative electrode film is 0.05 g / 1540.25 mm. 2 -0.2g / 1540.25mm 2 The lower coating weight of the negative electrode film results in a shorter migration path for lithium ions on the negative electrode film, which in turn facilitates the rapid and uniform insertion and extraction of lithium ions in the negative electrode film.

[0027] In some embodiments, the porosity of the negative electrode sheet is 20%-35%. This helps to improve the wettability of the electrolyte to the negative electrode sheet and improve the transport rate of lithium ions in the negative electrode sheet.

[0028] In some embodiments, at least one of the following conditions is met: the thickness of the negative electrode current collector is 2 μm-10 μm; the thickness of the negative electrode film is 40 μm-80 μm. When the thickness of the negative electrode current collector is within the above range, the breakage of the negative electrode current collector during coating, rolling, and cycling processes can be reduced, improving production yield and long-term reliability. When the thickness of the negative electrode film is within the above range, the negative electrode film is thinner, resulting in a faster lithium-ion insertion / extraction rate and higher energy density.

[0029] In some embodiments, the negative electrode film layer includes: a first negative electrode film layer disposed on at least one side of the negative electrode current collector; and a second negative electrode film layer disposed on the side of the first negative electrode film layer opposite to the negative electrode current collector; wherein the volume average particle size Dv50 of the graphite material in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the graphite material in the second negative electrode film layer. Therefore, the graphite material in the second negative electrode film layer can quickly receive lithium ions released from the positive electrode active material, reducing lithium plating, and transfer lithium ions to the first negative electrode film layer. This allows for effective storage of lithium ions by utilizing the high lithium intercalation capacity of the graphite material in the first negative electrode film layer.

[0030] In some embodiments, the single-sided coating weight of the positive electrode film is 0.200 g / 1540.25 mm. 2 -0.400g / 1540.25mm 2 Therefore, the positive electrode film has both high capacity and a short lithium-ion transport path.

[0031] In some embodiments, at least one of the following conditions is met: the thickness of the positive electrode current collector is 9 μm-15 μm; the thickness of the positive electrode film is 60 μm-90 μm. Therefore, when the thickness of the positive electrode current collector is within the above range, breakage during coating, rolling, and cycling processes can be reduced, improving production yield and long-term reliability. When the thickness of the positive electrode film is within the above range, the film is thinner, resulting in faster lithium-ion insertion / extraction rates and higher energy density.

[0032] In some embodiments, the chemical formula of the lithium-containing transition metal phosphate satisfies: Li m Fe x P y O j Q qWherein, Q includes one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, with 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.1. Therefore, modifying element Q can improve the lattice change rate of the positive electrode active material during lithium insertion / extraction, enhance the structural stability of the material, and thus improve the specific capacity of the material during low-temperature cycling.

[0033] In some embodiments, each of the positive and negative electrode plates includes a coating portion and a tab portion. The coating portion is provided with a film layer, and the tab portion is connected to the coating portion and extends out of the coating portion along the height direction of the battery cell. The tab portions of the positive and negative electrode plates are located on the same side of the electrode assembly. Therefore, the same-side arrangement of the positive and negative tabs ensures that the current transmission direction is consistent, reduces the lateral resistance of the current collector, and also reduces the uneven local current density of the electrodes caused by tabs on opposite sides, thereby reducing the risk of lithium plating during fast charging at low temperatures.

[0034] In some embodiments, the battery cell satisfies one or more of the following conditions: the dimension of the positive electrode sheet along the length direction of the electrode assembly is 150mm-400mm; the dimension of the negative electrode sheet along the length direction of the electrode assembly is 150mm-400mm. This results in a shorter electron transport path within the electrode sheet and higher internal current homogenization, reducing the risk of lithium plating during fast charging at low temperatures.

[0035] In some embodiments, the battery cell satisfies one or more of the following conditions: the dimension of the positive electrode sheet along the length direction of the electrode assembly is 150mm-300mm; the dimension of the negative electrode sheet along the length direction of the electrode assembly is 150mm-300mm. This further shortens the electron transport path within the electrode sheet, improving internal current homogenization.

[0036] In some embodiments, the electrode assembly is a stacked structure. The stacked electrode assembly is composed of multiple layers of stacked electrodes. The electrolyte can be simultaneously drawn back and wetted from the sides, top, and bottom of the electrode assembly. This multi-directional penetration path significantly reduces the flow resistance of the high-viscosity electrolyte, significantly enhances the back-drawing speed of the high-viscosity electrolyte, improves the wetting efficiency of the high-viscosity electrolyte on the electrode assembly, maintains the long-term wettability of the electrodes, and ensures that the interior of the electrode assembly is fully wetted, effectively improving the cycle performance of the battery cell at low temperatures.

[0037] In some embodiments, the electrolyte further includes at least one of vinylene carbonate and fluoroethylene carbonate. Thus, vinylene carbonate can form an elastic polymer on the surface of the negative electrode active material, which is superior to the electrolyte solvent, mitigating SEI film rupture and recombination caused by the expansion and contraction of the negative electrode active material. Fluoroethylene carbonate can form a LiF-rich SEI film on the surface of the negative electrode active material, reducing lithium dendrite growth and volume expansion of the negative electrode active material. Both can effectively improve the cycle performance of the battery cell at low temperatures.

[0038] In some embodiments, the mass percentage of vinylene carbonate is 0.05%-6.00% based on the total mass of solvent and additives in the electrolyte. Therefore, adding an appropriate amount of vinylene carbonate to the electrolyte helps improve the structural stability of the SEI film, and the resulting SEI film has a moderate thickness, having a minimal impact on the internal resistance of the battery cell.

[0039] In some embodiments, the electrolyte further includes one or more of tris(trimethylsilane) phosphate and trimethylfluorosilane. Thus, tris(trimethylsilane) phosphate and trimethylfluorosilane can preferentially form a structurally stable protective layer on the surface of the positive electrode film compared to linear or cyclic carbonates, reducing electrolyte corrosion of the aluminum foil and reducing electrolyte decomposition and gas generation.

[0040] In some embodiments, at least one of the following conditions is met: the mass percentage of the tris(trimethylsilane)phosphate is 0.01%-0.5% based on the total mass of the solvent and additives in the electrolyte; the mass percentage of the trimethylfluorosilane is 0.01%-0.5% based on the total mass of the solvent and additives in the electrolyte. Thus, a moderately thick and complete positive electrode electrolyte interface (CEI) film can be formed on the surface of the positive electrode active material, having a minimal impact on the lithium-ion extraction rate of the positive electrode active material, which helps improve the rate cycle performance of the battery cell and reduce costs.

[0041] In some embodiments, the electrolyte further includes POF3. During the charging and discharging process of a single battery cell, lithium hexafluorophosphate dissociates in the electrolyte to produce phosphorus pentafluoride. Phosphorus pentafluoride reacts with water to produce phosphorus trifluoride, which further reacts with the electrolyte to generate impurities that damage the membrane interface between the positive and negative electrodes.

[0042] In some embodiments, the mass percentage of POF3 is 0.04%-0.35% based on the total mass of the electrolyte. Therefore, by controlling the content of lithium hexafluorophosphate and adjusting the content of POF3 within the above range, the occurrence of chain reactions such as SEI film rupture and electrolyte decomposition can be effectively reduced, thereby improving the cycle stability of the battery cell.

[0043] In some embodiments, the electrolyte further includes SO3F- C2O4BF2 - One or more of them. Therefore, SO3F - C2O4BF2 - SEI and CEI films rich in inorganic components can be formed on the surface of active materials, which helps to reduce the internal resistance of battery cells.

[0044] In some embodiments, at least one of the following conditions is met: based on the total mass of the electrolyte, SO3F - The mass percentage is 0.01%-0.4%; based on the total mass of the electrolyte, C2O4BF2 - The mass percentage is 0.05%-0.5%. Therefore, while improving the lithium-ion migration rate, it can reduce the occurrence of gas-generating side reactions and the increase in electrolyte viscosity, thereby improving the cycle performance and fast-charging performance of individual battery cells at low temperatures.

[0045] In some embodiments, the electrolyte has an ionic conductivity of 11 mS / cm-15 mS / cm at 25°C. Therefore, lithium ions migrate relatively quickly in the electrolyte, making it suitable for high-rate charge / discharge scenarios.

[0046] In a second aspect, this application proposes a battery device comprising the aforementioned battery cell, wherein the battery device includes at least one of a battery module, a battery pack, and an energy storage device. Thus, this battery device possesses all the features and advantages of the aforementioned battery cell, which will not be repeated here.

[0047] In a third aspect, this application proposes an electrical device comprising the aforementioned battery cell. Therefore, this electrical device possesses all the features and advantages of the aforementioned battery cell, which will not be repeated here. Attached Figure Description

[0048] The foregoing aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application; Figure 2 This is an exploded view of a battery cell according to one embodiment of this application; Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application; Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application; Figure 5 yes Figure 4 An exploded view of the battery pack shown. Figure 6This is a schematic diagram of a power supply device for a battery cell power source according to an embodiment of this application.

[0049] Explanation of reference numerals in the attached figures: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0050] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0051] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0052] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0053] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0054] 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.

[0055] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. "First feature" and "second feature" may include one or more of the indicated feature.

[0056] In the description of this application, "multiple" means two or more.

[0057] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0058] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

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

[0060] The battery mentioned in the embodiments of this application can be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, or battery packs.

[0061] A battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. A battery cell can be cylindrical, cuboid, or other shapes, and the embodiments of this application are not limited in this respect. Figure 1 The example shown is a rectangular battery cell 5.

[0062] A single battery cell includes electrode components and electrolyte.

[0063] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode components and electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0064] In some embodiments, such as Figure 2 As shown, the 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 enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted according to requirements.

[0065] Electrode assemblies typically include positive and negative electrodes. The negative electrode is the electrode that absorbs or lithiates lithium ions during charging and releases or delithiates lithium during discharging. The positive electrode is the electrode that absorbs or delithiates lithium ions during charging and absorbs or lithiates lithium during discharging.

[0066] When there are multiple battery cells, they are connected in series, parallel, or mixed via a busbar. In some embodiments, the battery can be a battery module; when there are multiple battery cells, they are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed within the housing. In some embodiments, the housing can be part of the vehicle's chassis structure. For example, a portion of the housing can be at least part of the vehicle's floor, or a portion of the housing can be at least part of the vehicle's crossbeams and longitudinal beams.

[0067] In some embodiments, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0068] In some embodiments, individual battery cells can be assembled into a battery module, and the number of individual battery cells contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module. Figure 3This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0069] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0070] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0071] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0072] Lithium-containing transition metal phosphates exhibit low volume change rate and low lattice stress during lithium-ion insertion / extraction, making them less prone to structural collapse during fast-charging cycles and resulting in excellent cycle life. Furthermore, lithium-containing transition metal phosphates possess excellent thermal stability, significantly reducing the risk of thermal runaway during high-temperature fast charging, making them suitable for fast-charging battery systems. Moreover, there are fewer side reactions between lithium-containing transition metal phosphates and linear carboxylic acid esters. Linear carboxylic acid esters combine high ionic conductivity and low viscosity, and their use as a component of the electrolyte solution can effectively improve the ionic conductivity of the electrolyte, facilitating rapid lithium-ion transfer between the positive and negative electrodes and improving the fast-charging performance of individual battery cells. Therefore, the proportion of low-viscosity carboxylic acid esters in the electrolyte should be increased to enhance lithium-ion mobility, thereby leveraging the advantage of fewer side reactions between lithium-containing transition metal phosphates and linear carboxylic acid esters while also promoting lithium-ion transport within the electrolyte.

[0073] However, under low-temperature fast charging conditions, the inherent low heat generation characteristics of lithium transition metal phosphates interact with the low-temperature environment, posing a severe challenge to the performance of lithium transition metal phosphate batteries. At low temperatures, the ionic conductivity of the electrolyte decreases, and the diffusion rate of lithium ions in the electrode materials slows down, leading to a significant increase in charge transfer impedance and solid-phase diffusion impedance. This deterioration in kinetic performance directly affects the battery's fast-charging capability and makes it easier to trigger side reactions such as lithium deposition during high-current charging. During fast charging, although increased current brings more Joule heat, the low conductivity and slow temperature response of lithium transition metal phosphate materials limit the actual temperature rise. This slow temperature rise results in the battery remaining in an unfavorable low-temperature state for an extended period, further exacerbating polarization and creating a negative feedback loop of "low temperature - high impedance - low heat generation - sustained low temperature." Therefore, the electrochemical behavior and cycle life of lithium transition metal phosphate batteries require special consideration in low-temperature fast-charging scenarios.

[0074] To improve the lithium-ion transport rate within a single battery cell and achieve rapid lithium-ion insertion into the negative electrode active material, this application uses graphite as the negative electrode active material, while simultaneously controlling the Ig of the negative electrode active material. D / I G The median falls within the aforementioned range. Therefore, the amorphous carbon content in the negative electrode active material is high, resulting in large interlayer spacing, numerous active sites, and multiple lithium intercalation directions. This leads to faster lithium ion reception at the negative electrode, meaning faster lithium ion insertion and increased lithium intercalation capability, which is more conducive to lithium intercalation and reduces the risk of lithium plating on the negative electrode surface. However, a higher I... D / I G The median concentration presents a problem: the highly active sites on the amorphous carbon surface become nucleation sites for electrolyte crystallization, promoting crystallization at low temperatures. This leads to decreased low-temperature capacity retention and increased crystallization tendency under supercooled conditions, further deteriorating low-temperature performance. To alleviate this problem, this application mixes multiple solvents to increase solvent disorder and reduce the ordered arrangement of solvent molecules, thereby lowering the freezing point of the electrolyte and delaying the crystallization trend. This satisfies the requirements for lithium-ion transport rate in the electrolyte while reducing the possibility of electrolyte crystallization.

[0075] In a first aspect, this application provides a battery cell, which includes an electrode assembly and an electrolyte, wherein the electrolyte wets the electrode assembly. The electrode assembly includes a positive electrode, a separator, and a negative electrode. The positive electrode includes a positive current collector and a positive electrode film layer located on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes a lithium-containing transition metal phosphate. The negative electrode includes a negative current collector and a negative electrode film layer located on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes a graphite material. D / I G The median is 0.1-0.6, where I G This indicates that the Raman spectrum of the negative electrode active material is at 1580±100 cm⁻¹. -1 The intensity of peak G at I D This indicates that the Raman spectrum of the negative electrode active material is at 1350±100 cm⁻¹. -1 The intensity of peak D at that location; The electrolyte includes linear carbonates, cyclic carbonates, and linear carboxylic esters; the mass ratio of linear carbonates, cyclic carbonates, and linear carboxylic esters in the electrolyte is (40-50):(30-40):(15-25); The separator includes a base film and a coating located on at least one side of the base film; The coating includes a first coating and a second coating stacked sequentially. The first coating is located on the side closer to the positive electrode sheet and includes polyvinylidene fluoride. The second coating includes a ceramic material. The coating also includes a third coating near the negative electrode plate, which includes polyvinylidene fluoride; The thickness of the first coating is 0.5μm-3μm; the thickness of the second coating is 0.5μm-3μm; the thickness of the third coating is 0.5μm-3μm.

[0076] This application controls the I of the negative electrode active material. D / I GWith a median of 0.1-0.6, the amorphous carbon content in the negative electrode active material is relatively high, resulting in large interlayer spacing, numerous active sites, and multiple lithium intercalation directions. This leads to faster lithium ion reception at the negative electrode, meaning faster lithium ion insertion and increased lithium intercalation capability, which is more conducive to lithium intercalation and reduces the risk of lithium plating on the negative electrode surface. Based on this, the electrolyte used in this application includes linear carbonates, cyclic carbonates, and linear carboxylic acid esters in a mass ratio of (40-50):(30-40):(15-25). Multiple solvents can increase the disorder of the solvent, reduce the ordered arrangement of solvent molecules, lower the freezing point of the electrolyte, and delay the crystallization trend; multiple solvents can also improve low-temperature ion conduction. Therefore, the battery cell of this application has both fast charging performance and cycle life at low temperatures. Carboxylic acid ester solvents have low viscosity. This application controls the content of carboxylic acid ester solvents to increase the electrolyte viscosity, slow down the lithium-ion transport rate, and better match it with the insertion rate of the negative electrode active material. This reduces lithium-ion accumulation on the negative electrode surface, reduces lithium dendrite growth, and thus reduces the probability of lithium dendrites piercing the separator and causing a short circuit in the battery cell. The ceramic material in the second coating of a specific thickness in this application can significantly improve the mechanical strength and heat resistance of the separator, improve puncture resistance and thermal shrinkage resistance, reduce lithium dendrite penetration during charge-discharge cycles, thereby reducing the risk of short circuits and comprehensively improving the fast-charging time and cycle performance of the battery cell. The first and third coatings of a specific thickness can enhance the bonding strength between the separator and the negative electrode sheet, improving the fast-charging time and cycle performance of the battery cell.

[0077] The median is the value in the middle of a set of data. It is used to reflect the central tendency of the data. It is calculated by arranging the data in order of size and taking the middle number or range of values.

[0078] As an example, the I of the negative electrode active material D / I G The median can be 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, or any value between two of these.

[0079] In the Raman scattering analysis of the negative electrode active material, at a Raman shift of 1350±100 cm⁻¹ -1 and 1580±100cm -1 The positions of the scattering peaks are respectively, with the peak at a Raman shift of 1350±100 cm⁻¹. -1 The position has a carbon D-band scattering peak (referred to as the D peak), with a Raman shift of 1580±100 cm⁻¹. -1 The position of the peak is where the carbon sp(s) exhibits a scattering peak in the G band (referred to as the G peak). The G peak characterizes the carbon sp(s) spectrum. 2Hybrid structure; the D peak characterizes a disordered structure, where disorder refers to the irregular arrangement of carbon atoms within the structure. The peak intensity of the D peak is I. D Peak intensity I of G peak G The ratio can reflect the degree of defects in the negative electrode active material.

[0080] As an example, the I of the negative electrode active material D / I G The median can be obtained by testing as follows: The battery cell was disassembled to obtain the negative electrode sheet. The negative electrode sheet was cut into 6mm × 6mm squares using ceramic scissors. Dimethyl carbonate (DMC) was used to remove residual lithium salt from the negative electrode sheet. Then, the negative electrode film layer on the surface of the negative electrode current collector was scraped to collect the powder as a negative electrode active material sample. Raman surface scanning was then performed with a scanning range of 100μm × 100μm, a step size of 2μm, 2500 test points, a single-point time of 0.7s, and a power of 10%. The median I of the measured results was... 50 For I D / I G The median. By limiting I D / I G The median can better reflect the characteristics of the negative electrode active material and reduce the impact of scatter point value fluctuations on the accuracy of test results.

[0081] Understandably, the negative electrode film layer is dominated by negative electrode active materials, while the mass proportion of conductive agents, binders, and other substances is relatively low. This is relevant for I... D / I G The impact of the test results is negligible.

[0082] In some embodiments, the negative electrode active material I D / I G The median is 0.2-0.5. When the Raman spectrum of the negative electrode active material has an I... D / I G When the median is within the aforementioned range, there are more defect sites on the surface of the negative electrode active material, and the negative electrode active material has a stronger ability to accept lithium ions, which helps to reduce the occurrence of lithium plating side reactions and helps to improve the performance of the battery at high rates.

[0083] In some embodiments, the electrolyte of a lithium-ion battery includes an electrolyte salt, a solvent, and additives.

[0084] It is understood that solvents include linear carbonates, cyclic carbonates, and linear carboxylic acid esters. Additives can include additives for negative electrode film formation, additives for positive electrode film formation, 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. For example, additives can include vinylene carbonate (VC), fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (1,3-PS), tris(trimethylsilane) phosphate (TMSP), trimethylfluorosilane (TMFS), SO3F... - C2O4BF2 - One or more of them.

[0085] As an example, the mass ratio of linear carbonates, cyclic carbonates, and linear carboxylic acid esters in the electrolyte can be 40:30:15, 40:30:20, 40:30:25, 40:35:15, 40:35:20, 40:35:25, 40:40:15, 40:40:20, 40:40:25, 45:30:15, 45:30:20, 45:30:25, 45:40:15, 45:40:20, 45:40:25, 50:30:15, 50:30:20, 50:30:25, 50:40:15, 50:40:20, 50:40:25, or any range between the two.

[0086] The first coating is located on the side close to the positive electrode. The polyvinylidene fluoride in the first coating can form hydrogen bonds / van der Waals forces with the positive electrode, enhancing the adhesion strength between the separator and the positive electrode. In addition, polyvinylidene fluoride can provide lithium-ion transport pathways and improve the lithium-ion migration rate of the separator.

[0087] The second coating is located between the first coating and the base film. The ceramic material in the second coating can significantly improve the mechanical strength and heat resistance of the separator, enhance its puncture resistance and heat shrinkage resistance, and reduce the penetration of lithium dendrites during charge and discharge cycles, thereby reducing the risk of short circuits.

[0088] As an example, the thickness of the first coating can be 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, or any value between the two.

[0089] As an example, the thickness of the second coating can be 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, or any value between the two.

[0090] As an example, ceramic materials include one or more of alumina, boehmite, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, and barium sulfate.

[0091] As an example, the thickness of the third coating can be 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, or any value between the two.

[0092] In some embodiments, one or more of the following conditions are met: the mass percentage of linear carbonates is 40%-50% based on the total mass of solvents and additives in the electrolyte; the mass percentage of cyclic carbonates is 30%-40% based on the total mass of solvents and additives in the electrolyte; and the mass percentage of linear carboxylic esters is 15%-25% based on the total mass of solvents and additives in the electrolyte. Controlling the content of linear carbonates can lower the freezing point of the electrolyte, reduce crystallization, and thus improve the fast-charging performance of battery cells at low temperatures. Controlling the content of cyclic carbonates can form a stable solid electrolyte interphase (SEI) film, reduce lithium dendrites, and thus improve interfacial stability and extend cycle life at low temperatures. Controlling the content of linear carboxylic esters can further form a low-resistance SEI film and improve the ion mobility of the electrolyte at low temperatures. Therefore, controlling the contents of linear carbonates, cyclic carbonates, and linear carboxylic esters in the electrolyte can further improve the fast-charging capability and cycle life of battery cells at low temperatures.

[0093] As an example, based on the total mass of solvents and additives in the electrolyte, the mass percentage of linear carbonates can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or any value between the two.

[0094] As an example, based on the total mass of solvents and additives in the electrolyte, the mass percentage of cyclic carbonates can be 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, or any value between the two.

[0095] As an example, based on the total mass of solvent and additives in the electrolyte, the mass percentage of linear carboxylic acid esters can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or any value between the two.

[0096] As an example, the mass percentage of linear carbonates, cyclic carbonates, or linear carboxylic esters based on the total mass of solvents and additives in the electrolyte can be determined by the following method: Quantitative analysis of organic components using gas chromatography (GC). This method is for both qualitative and quantitative analysis and can be referenced in GB / T 9722-2023. The specific testing method is as follows: Disassemble a fresh battery to obtain the electrolyte, and analyze the components using a gas chromatograph to obtain the mass percentage of each component.

[0097] In some embodiments, one or more of the following conditions are met: linear carbonates include at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and methyl propyl carbonate (MPC); cyclic carbonates include at least one of ethylene carbonate (EC), propylene carbonate (PC), trimethylene cyclic carbonate (TMC), and 2,2-dimethyltrimethylene cyclic carbonate (DTC); linear carboxylic acid esters include at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate. The above-mentioned linear carbonates have low melting points, and their use can significantly reduce the freezing point of the electrolyte, improving the fast-charging performance of battery cells at low temperatures. The above-mentioned cyclic carbonates can form a uniform and dense SEI film on the negative electrode surface, improving interface stability. The uniform SEI film can guide the uniform deposition of lithium metal and reduce the risk of lithium dendrite puncture. The aforementioned linear carboxylic acid esters have low viscosity and high ionic conductivity, which can accelerate the transport of lithium ions at low temperatures.

[0098] As an example, based on the total mass of solvents and additives in the electrolyte, the components of linear carbonates, cyclic carbonates, or linear carboxylic esters can be determined by the following method: quantitative analysis of organic components using gas chromatography (GC). This method is for both qualitative and quantitative analysis and can be referenced in GB / T 9722-2023. The specific testing method is as follows: A fresh battery is disassembled to obtain the electrolyte, and the mass percentage of each component is obtained by injection analysis using a gas chromatograph.

[0099] In some embodiments, one or more of the following conditions are met: dimethyl carbonate accounts for 10%-50% of the total mass of solvents and additives in the electrolyte; ethyl methyl carbonate accounts for 5%-30% of the total mass of solvents and additives in the electrolyte; ethylene carbonate accounts for 10%-50% of the total mass of solvents and additives in the electrolyte; diethyl carbonate accounts for 0.01%-20% of the total mass of solvents and additives in the electrolyte; and ethyl acetate accounts for 15%-25% of the total mass of solvents and additives in the electrolyte. Dimethyl carbonate has low viscosity and high ionic conductivity. Controlling the content of dimethyl carbonate can reduce the lithium-ion transport resistance and improve fast-charging performance. Ethyl methyl carbonate has good interfacial compatibility. Controlling the content of ethyl methyl carbonate helps to form a uniform SEI film on the negative electrode, reduces solvent co-intercalation, and improves the cycle life of the battery cell. Ethyl carbonate has a high dielectric constant. Controlling the content of ethylene carbonate can increase the degree of lithium salt dissociation, thereby improving ionic conductivity. Controlling the diethyl carbonate content can improve the low-temperature conductivity of the electrolyte and enhance its low-temperature fast-charging capability. Ethyl acetate has a low melting point and viscosity, and can still improve the fluidity of the electrolyte at low temperatures. Controlling the ethyl acetate content can further form a low-impedance SEI film, thereby improving the ion mobility of the electrolyte at low temperatures.

[0100] As an example, based on the total mass of solvent and additives in the electrolyte, the mass percentage of dimethyl carbonate can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any value between the two.

[0101] As an example, based on the total mass of solvent and additives in the electrolyte, the mass percentage of methyl ethyl carbonate can be 5%, 8%, 11%, 14%, 15%, 17%, 20%, 23%, 26%, 29%, 30%, or any value between the two.

[0102] As an example, based on the total mass of solvent and additives in the electrolyte, the mass percentage of ethylene carbonate can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any value between the two.

[0103] As an example, based on the total mass of solvent and additives in the electrolyte, the mass percentage of diethyl carbonate can be 0.01%, 2.5%, 5.0%, 7.5%, 10.0%, 12.5%, 15.0%, 17.5%, 20%, or any value between the two.

[0104] As an example, based on the total mass of solvent and additives in the electrolyte, the mass percentage of ethyl acetate can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or any value between the two.

[0105] As an example, the mass percentage of dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, diethyl carbonate, or ethyl acetate, based on the total mass of solvents and additives in the electrolyte, can be determined using the following method: Gas chromatography-quantitative analysis of organic components (GC). This method is for both qualitative and quantitative analysis and can be referenced in GB / T 9722-2023. The specific testing method is as follows: Disassemble a fresh battery to obtain the electrolyte, and analyze the components using a gas chromatograph to obtain the mass percentage of each component.

[0106] In some embodiments, the electrolyte comprises a cyclic carbonate, a linear carboxylic acid ester, and at least two linear carbonates. Thus, using the aforementioned multi-component solvent can further increase the solvent's disorder, reduce the ordered arrangement of solvent molecules, lower the electrolyte's freezing point, and delay the crystallization tendency; using the aforementioned solvent can also further provide continuous channels for ion conduction, improving low-temperature ion conduction.

[0107] In some embodiments, the electrolyte includes at least one selected from dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and ethyl acetate. Therefore, using the above solvents can further lower the freezing point of the electrolyte, improve the stability of the SEI film, reduce low-temperature lithium plating, and significantly optimize the battery's fast-charging performance and cycle life at low temperatures.

[0108] In some embodiments, the electrolyte further includes a lithium salt, comprising at least two of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate. When the content of lithium difluorophosphate, lithium difluorooxalate borate, and lithium tetrafluoroborate in the solution is low (<0.5%), they can be considered lithium salt additives. Thus, a dynamic coordination structure can be formed between the lithium ions and anions in the solvated lithium salt and the solvent molecules, increasing the disorder of the electrolyte, lowering the freezing point, and improving the capacity retention at low temperatures.

[0109] In some embodiments, the electrolyte comprises lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. The anions of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide have different sizes, charge distributions, and lithium salt dissociation capabilities. In the electrolyte, the interaction modes between these anions and lithium ions are diversified, leading to a more complex solvated sheath structure, increased system disorder, and consequently, a lower freezing point of the electrolyte and improved low-temperature performance.

[0110] In some embodiments, at least one of the following conditions is met: the mass percentage of lithium hexafluorophosphate is 8%-16% based on the total mass of the electrolyte; the mass percentage of lithium difluorosulfonylimide is 1%-10% based on the total mass of the electrolyte. Thus, using the above-mentioned lithium salt can further increase the disorder of the electrolyte and improve the fast charging capability of the battery cell at low temperatures.

[0111] As an example, based on the total mass of the electrolyte, the mass percentage of lithium hexafluorophosphate can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, or any value between the two.

[0112] As an example, the mass percentage of lithium bis(fluorosulfonyl)imide can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value between the two, based on the total mass of the electrolyte.

[0113] As an example, the mass percentage of lithium hexafluorophosphate and lithium difluorosulfonylimide based on the total mass of the electrolyte can be determined by the following method: Ion chromatography (IC) is used for testing. This method is for qualitative and quantitative analysis and can be referenced in JY / T 020-1996. The specific testing method is as follows: 1) Provide standard substances for retention time calibration and establish a standard curve; 2) Disassemble a fresh battery, take a quantitative amount of electrolyte, with the diluent concentration at the midpoint of the standard curve, and dilute to 100 ml with ultrapure water. Automated injection and detection by ion chromatography will yield the mass percentage of lithium hexafluorophosphate and lithium difluorosulfonylimide in the electrolyte.

[0114] In some embodiments, the electrolyte also includes BF4. - Therefore, BF4 - With a small ionic radius, it has a strong solubility at low temperatures, which can effectively reduce the viscosity of the electrolyte and improve the migration rate of lithium ions under low-temperature conditions.

[0115] In some embodiments, BF4 is based on the total mass of the electrolyte. - The mass percentage is 0.01%-0.5%. This can improve the fast-charging performance of the electrolyte and reduce side reactions with the negative electrode active material at low potentials.

[0116] Lithium tetrafluoroborate dissociates in the electrolyte to form tetrafluoroborate ions and lithium ions. The tetrafluoroborate content in the electrolyte can be adjusted by changing the amount of lithium tetrafluoroborate added.

[0117] As an example, based on the total mass of the electrolyte, BF4 -The mass percentage can be 0.01%, 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, or any value range between the two.

[0118] As an example, based on the total mass of the electrolyte, BF4 - The mass percentage of LiBF4 in the electrolyte can be determined using the following method: Ion chromatography (IC) is employed. This method is for both qualitative and quantitative analysis and can be referenced in JY / T 020-1996. The specific testing method is as follows: 1) Provide a LiBF4 standard substance for retention time calibration and establish a standard curve; 2) Disassemble a fresh battery, take a measured amount of electrolyte, with the diluent concentration at the midpoint of the standard curve, and dilute to 100 ml with ultrapure water. Automated injection and ion chromatography are used to detect the LiBF4 mass percentage in the electrolyte, from which the LiBF4 mass percentage can be calculated. - The percentage of quality.

[0119] In some embodiments, the base film includes one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. Therefore, the base film is widely available and suitable for various applications.

[0120] In some embodiments, one or more of the following conditions are met: the thickness of the base film is 3μm-10μm; the thickness of the separator is 4μm-12μm.

[0121] As an example, the thickness of the base film can be 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or any value between the two.

[0122] As an example, the thickness of the isolation membrane can be 4μm, 6μm, 8μm, 10μm, 12μm or any value between the two.

[0123] Therefore, the base film has superior mechanical strength. By controlling the thickness of the separator, the lithium-ion transport path can be shortened, allowing lithium-ions to be transported to the surface of the negative electrode active material more quickly.

[0124] In some embodiments, at least one of the following conditions is met: the porosity of the separator is 25%-60%; the air permeability of the separator is 90s / 100cc-260s / 100cc. This facilitates sufficient wetting of the separator by the electrolyte and rapid passage of lithium ions through the separator during transfer between the positive and negative electrodes.

[0125] As an example, the porosity of the isolation membrane can be 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any value between two of these.

[0126] When the porosity of the separator is within the aforementioned range, the electrolyte has good wettability to the separator, the separator can provide more ion transport channels, and has high mechanical strength and puncture resistance.

[0127] As an example, the porosity of the isolation membrane can be tested using the following method: the isolation membrane is crumpled into a ball and inserted into a sample cup. The sample cup containing the sample is placed in a true density tester, the test system is sealed, and helium gas is introduced according to the procedure. By detecting the pressure of the gas in the sample chamber and the expansion chamber, the true volume is calculated according to Bohr's law (pV=nRT), thereby obtaining the porosity of the sample to be tested.

[0128] As an example, the air permeability of the separator can be 90s / 100cc, 110s / 100cc, 130s / 100cc, 150s / 100cc, 170s / 100cc, 190s / 100cc, 210s / 100cc, 230s / 100cc, 250s / 100cc, 260s / 100cc, or any value between the two.

[0129] When the permeability of the separator is within the aforementioned range, the lithium-ion migration path is short, the lithium-ion migration rate is fast, and the internal resistance of the battery cell is low, which is beneficial to improving the fast charging performance of the battery cell.

[0130] The unit of air permeability (s / 100cc) indicates the time required for 100 cubic centimeters (100cc) of air to pass through the isolation membrane under standard test conditions. For example, an air permeability of 260s / 100cc means that under standard test conditions, it takes 260 seconds for 100 cubic centimeters (100cc) of air to pass through the isolation membrane.

[0131] As an example, the air permeability of the separator can be tested using the Gurley method, referring to GB / T 458-2008. Specifically, the test is conducted using the Gurley method: a permeability meter is used, and under constant pressure difference, the time (in seconds) it takes for 100 cubic centimeters of gas to pass through the sample is recorded; the longer the time, the worse the permeability.

[0132] In some embodiments, the volume average particle size Dv50 of the graphite material is 7 μm-13 μm. As a result, the overall particle size of the negative electrode active material is smaller, forming a more compact packing structure. The migration path of lithium ions in the negative electrode active material is shorter. In addition, the surface current density distribution of the small-particle-size negative electrode active material is more uniform, the generated SEI film is more dense, and there are fewer side reactions with the electrolyte.

[0133] As an example, the volume average particle size Dv50 of the graphite material can be 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm or any value between the two.

[0134] The aforementioned volume average particle size Dv50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50%.

[0135] As an example, the volume average particle size Dv50 of graphite materials can be determined using laser diffraction particle size analysis. Specifically, the particle size of graphite materials can be determined using a laser particle size analyzer (e.g., MalvernMaster Size 3000) in accordance with standard GB / T 19077-2016.

[0136] In some embodiments, the OI value of the negative electrode active material is 2-6. When the OI value of the negative electrode active material powder is 2-6, it is beneficial to improve the volume expansion and reaction kinetics of the negative electrode active material, enhance the isotropy of the negative electrode active material, accelerate the intercalation of lithium ions, effectively alleviate the volume expansion effect of the negative electrode sheet during cycling, and further improve the cycle performance of the battery cell at low temperatures.

[0137] As an example, the OI value of the negative electrode active material can be 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0 or any value between the two.

[0138] After graphite material is slurry to form a negative electrode film, the arrangement direction (or orientation) of the graphite layered structure has a significant impact on lithium-ion migration. Since graphite can only intercalate and deintercalate lithium ions at its end faces, ideally, the graphite end faces should be perpendicular to the surface of the negative electrode for better lithium-ion migration. However, in actual preparation, it is difficult to precisely control the orientation of each graphite particle. X-ray diffraction (XRD) analysis can be used to test the orientation of graphite on the negative electrode. When performing diffraction pattern testing on a horizontally placed negative electrode sample, the diffraction signal of the (110) crystal plane can be collected from the graphite in the negative electrode film layer that is perpendicular to the surface of the negative electrode. The diffraction signals of the (002) and (004) crystal planes come from the graphite in the negative electrode film layer whose structure is parallel to the surface of the negative electrode. Therefore, the orientation of graphite can be described by the ratio of the intensity (or integrated area) of the (002) or (004) diffraction peak to the intensity (or integrated area) of the (110) diffraction peak, i.e., the OI value. The formula is described as: OI=I(002) / I(110) or OI=I(004) / I(110), where OI (orientation index) is the orientation of the negative electrode active material in the negative electrode film layer.

[0139] As an example, the OI value of the negative electrode active material can be obtained by the following method: disassemble the battery cell to obtain the negative electrode sheet, cut the negative electrode sheet into a 6mm×6mm square with ceramic scissors, soak it with dimethyl carbonate (DMC) to remove the residual lithium salt in the negative electrode sheet, then scrape the negative electrode film layer on the surface of the negative electrode sheet to collect the powder as a negative electrode active material sample, and then obtain the X-ray diffraction pattern by using an X-ray powder diffractometer (X'Pert PRO) according to the general rules of X-ray diffraction analysis and the method for determining the lattice parameters of graphite JB / T42202011. Calculate the orientation index of the negative electrode active material according to OI=I(004) / I(110), where I(004) is the peak area of ​​the characteristic diffraction peak of (004) and I(110) is the peak area of ​​the characteristic diffraction peak of (110).

[0140] It is understandable that the negative electrode film layer is mainly composed of negative electrode active materials, while the mass ratio of conductive agents, binders and other substances is relatively low, so their impact on the OI value test results can be ignored.

[0141] In some embodiments, the graphite material includes artificial graphite. Thus, lithium ions can be inserted from multiple directions into the artificial graphite, overcoming the bottleneck that natural graphite can only be inserted from the end face. The increased number of lithium ion transport channels is beneficial for improving the lithium ion insertion / extraction rate of the negative electrode active material and greatly alleviates surface lithium deposition.

[0142] In some embodiments, the graphite material comprises secondary particles formed from primary particles. Compared to primary particles, secondary particles exhibit isotropic behavior during lithium intercalation, facilitating rapid lithium-ion insertion and improving the rate performance of the battery cell at low temperatures. Secondary particles have uneven surfaces and offer better capacity utilization compared to primary particles of the same size, which is beneficial for further improving the battery's energy density. Relatively small primary particles easily embed into the surface of relatively large secondary particles. On the one hand, this facilitates further increasing the compaction density of the negative electrode sheet, thereby further improving the battery's energy density; on the other hand, it helps to form better structural porosity, improving the solid-liquid interface transport impedance between the negative electrode film and the electrolyte, and reducing the solid-phase transport impedance within the negative electrode film.

[0143] In some embodiments, the artificial graphite comprises a first component and a second component. The method for preparing the first component includes: crushing needle coke to obtain first primary graphite particles; granulating the first primary graphite particles to obtain secondary graphite particles; subjecting the secondary graphite particles to a first heat treatment to obtain an intermediate; mixing the intermediate with a coating agent and performing a second heat treatment to obtain the first component. The method for preparing the second component includes: crushing petroleum coke to obtain second primary graphite particles; mixing the second primary graphite particles with a coating agent and performing a third heat treatment to obtain the second component. Thus, a negative electrode active material with both superior rate performance and high capacity can be obtained through a simple and low-cost process. Furthermore, coating the graphite surface with an amorphous carbon layer expands the interlayer spacing and reduces lithium-ion insertion resistance.

[0144] As an example, the method for preparing the first component may include: granulating primary needle-shaped coke particles with a particle size of 7μm-10μm into secondary particles with a particle size of 13μm-16μm, subjecting them to a first heat treatment to produce a first graphitized product, adding a first coating agent and the first graphitized product to a reaction vessel at room temperature, subjecting them to a second heat treatment, thoroughly mixing and stirring to form a homogeneous product, and then carbonizing it to form a 14μm-20μm finished product; the first heat treatment may include a graphitization process; the temperature of the first heat treatment is 600℃-800℃; the first coating agent includes asphalt; the mass ratio of the first coating agent to the first graphitized product is (0.5-5):100; the temperature of the second heat treatment is 1100℃-1200℃. The graphite in the first component adopts high polymerization technology to form multidimensional oriented graphite, providing multidimensional lithium intercalation channels. Without affecting the initial efficiency and capacity of the battery cell, it can improve the lithium intercalation capability of artificial graphite, thus achieving a balance between energy density and fast charging performance in the battery.

[0145] As an example, the method for preparing the second component may include: preparing a second graphitized product by graphitizing primary isotropic petroleum coke with a particle size of 3μm-6μm; mixing the second coating agent and the second graphitized product uniformly at room temperature; and forming a 4μm-10μm finished product through a third heat treatment; the third heat treatment includes a carbonization process; the second coating agent includes asphalt; the mass ratio of the second coating agent to the second graphitized product is (0.5-5):100; and the temperature of the third heat treatment is 1100℃-1200℃. During the coating process of the graphite in the second component, the coating agent may include low-softening-point asphalt. The low-softening-point asphalt softens rapidly during high-temperature carbonization, promoting uniform and dense coating, thus giving the graphite in the second component a rapid lithium-ion intercalation / deintercalation rate. The particle size combination of the two components can significantly improve the lithium-ion intercalation / deintercalation rate of the graphite material while maintaining energy density.

[0146] In some embodiments, the single-sided coating weight of the negative electrode film is 0.05 g / 1540.25 mm. 2 -0.2g / 1540.25mm 2 The lower coating weight of the negative electrode film results in a shorter migration path for lithium ions on the negative electrode film, which in turn facilitates the rapid and uniform insertion and extraction of lithium ions in the negative electrode film.

[0147] As an example, the coating weight on one side of the negative electrode film can be 0.05g / 1540.25mm², 0.07g / 1540.25mm², 0.09g / 1540.25mm², 0.11g / 1540.25mm², 0.13g / 1540.25mm², 0.15g / 1540.25mm², 0.17g / 1540.25mm², 0.19g / 1540.25mm², 0.20g / 1540.25mm², or any value between the two.

[0148] As an example, the single-sided coating weight of the negative electrode film can be tested using the following method: Take a single-sided coated negative electrode sheet (if it is a double-sided coated electrode sheet, the negative 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, and record its weight as M1. Then wipe off the negative electrode film layer of the weighed negative electrode sheet, weigh the negative current collector, and record it as M0. The single-sided coating weight of the negative electrode film layer = (weight of the negative electrode sheet M1 - weight of the negative current collector M0) / S1.

[0149] In some embodiments, the porosity of the negative electrode sheet is 20%-35%. This helps to improve the wettability of the electrolyte to the negative electrode sheet and improve the transport rate of lithium ions in the negative electrode sheet.

[0150] As an example, the porosity of the negative electrode sheet can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or any value between the two.

[0151] When the porosity of the negative electrode sheet is within the aforementioned range, there are more contact points between particles in the negative electrode film, the electron transport path is stable, the particles are tightly bonded, the structural stability of the negative electrode film is high, there is more space in the negative electrode sheet that can be used for wetting the electrolyte, the electrolyte is fully wetted, which is conducive to shortening the lithium ion transport distance and improving the lithium ion transport efficiency.

[0152] As an example, the porosity of the negative electrode sheet can be determined by the gas displacement method. Specifically, refer to GB / T 24586-2009, and determine it through the following steps: Immerse the electrode sheet in ethyl methyl carbonate (EMC) for cleaning. Measure using the gas displacement method. The porosity is the percentage of pore volume to the total volume of the electrode sheet, calculated using the formula: Porosity = (V - V0) / V × 100%, where V0 is the true volume and V is the apparent volume.

[0153] In some embodiments, at least one of the following conditions is met: the thickness of the negative electrode current collector is 2 μm-10 μm; the thickness of the negative electrode film is 40 μm-80 μm.

[0154] As an example, the thickness of the negative electrode current collector can be 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or any value between the two.

[0155] When the thickness of the negative electrode current collector is within the above range, the breakage of the negative electrode current collector during coating, rolling and cycling processes can be reduced, thereby improving production yield and long-term reliability.

[0156] As an example, the thickness of the negative electrode film can be 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm or any value between the two.

[0157] The thickness of the negative electrode film refers to the thickness of the negative electrode film on one side of the negative electrode current collector. When double-sided coating is used, the thickness of the negative electrode film on either side can be within the aforementioned range.

[0158] When the thickness of the negative electrode film is within the above range, the thickness of the negative electrode film is relatively thin, the lithium ion insertion / extraction rate is faster, and the energy density is higher.

[0159] In some embodiments, the thickness of the negative electrode sheet is 82 μm-180 μm. As an example, the thickness of the negative electrode sheet can be 82 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm or any value range between the two.

[0160] When the thickness of the negative electrode sheet is within the above range, the space occupied by the negative electrode sheet is relatively small, which is beneficial to improving the volumetric energy density of the battery cell.

[0161] In some embodiments, the negative electrode film layer includes: a first negative electrode film layer disposed on at least one side of the negative electrode current collector; and a second negative electrode film layer disposed on the side of the first negative electrode film layer opposite to the negative electrode current collector; wherein the volume average particle size Dv50 of the graphite material in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the graphite material in the second negative electrode film layer. Therefore, the graphite material in the second negative electrode film layer can quickly receive lithium ions extracted from the positive electrode active material, reducing lithium plating, and transfer lithium ions to the first negative electrode film layer. This allows for effective storage of lithium ions by utilizing the high lithium intercalation capacity of the graphite material in the first negative electrode film layer.

[0162] 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 polymeric material substrate and a metal layer formed on at least one surface of the polymeric material 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 polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0163] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive includes at least one selected from 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).

[0164] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent includes at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0165] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0166] In some embodiments, the single-sided coating weight of the positive electrode film is 0.200 g / 1540.25 mm. 2 -0.400g / 1540.25mm 2 Therefore, the positive electrode film has both high capacity and a short lithium-ion transport path.

[0167] As an example, the coating weight on one side of the positive electrode film can be 0.200g / 1540.25mm², 0.250g / 1540.25mm², 0.300g / 1540.25mm², 0.350g / 1540.25mm², 0.400g / 1540.25mm², or any value between the two.

[0168] It is understood that the single-sided coating weight of the positive electrode film is a well-known definition in the field and can be measured using a similar method as that used for the single-sided coating weight of the negative electrode film.

[0169] In some embodiments, at least one of the following conditions is met: the thickness of the positive electrode current collector is 9 μm-15 μm; the thickness of the positive electrode film is 60 μm-90 μm.

[0170] As an example, the thickness of the positive current collector can be 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or any value between the two.

[0171] When the thickness of the positive electrode current collector is within the above range, the breakage of the positive electrode current collector during coating, rolling and cycling processes can be reduced, thereby improving production yield and long-term reliability.

[0172] As an example, the thickness of the positive electrode film can be 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, or any value between the two.

[0173] The thickness of the positive electrode film refers to the thickness of the positive electrode film on one side of the positive electrode current collector. When double-sided coating is used, the thickness of the positive electrode film on either side can be within the aforementioned range.

[0174] When the thickness of the positive electrode film is within the above range, the thickness of the positive electrode film is relatively thin, the lithium ion insertion / extraction rate is faster, and the energy density is higher.

[0175] In some embodiments, the thickness of the positive electrode is 70 μm-200 μm. As an example, the thickness of the positive electrode can be 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 100 μm, 110 μm, 120 μm, 125 μm, 140 μm, 155 μm, 170 μm, 185 μm, 200 μm, or any value between the two.

[0176] Lithium-containing transition metal phosphates refer to phosphate materials containing lithium and transition metal elements, and can be detected by any method known in the art. For example, they can be detected by combining X-ray diffraction (XRD) with energy dispersive spectroscopy (EDS).

[0177] In some embodiments, the chemical formula of the lithium transition metal phosphate satisfies: Li m Fe x P y O j Q q Wherein, Q includes one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, with 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.1. Therefore, modifying element Q can improve the lattice change rate of the positive electrode active material during lithium insertion / extraction, enhance the structural stability of the material, and thus improve the specific capacity of the material during low-temperature cycling.

[0178] As an example, m can be selected from 0.8, 0.85, 0.9, 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, or any value between two of these; x can be selected from 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, or any value between two of these; y The values ​​can be 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, or any value between two of these; j can be 3.5, 3.6, 3.7, 3.8, 3.9, 4, or any value between two of these; q can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any value between two of these.

[0179] In some embodiments, the positive electrode active material includes one or more of lithium iron phosphate and its doped and modified materials, and carbon-coated modified materials.

[0180] As an example, the types and contents of elements in the positive electrode active material can be tested using any method known in the art. For example, inductively coupled plasma atomic emission spectrometry (ICP-AES) is used to test the elements and their contents according to Appendix C of GB / T 33822-2017.

[0181] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0182] 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, polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0183] 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.

[0184] 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.

[0185] In some embodiments, each positive electrode and each negative electrode includes a coating portion and a tab portion. The coating portion is provided with a film layer, and the tab portion is connected to the coating portion and extends out of the coating portion along the height direction of the battery cell. The tab portions of the positive electrode and the negative electrode are located on the same side of the electrode assembly. Thus, the arrangement of the positive and negative tabs on the same side ensures that the current transmission direction is consistent, reduces the lateral resistance of the current collector, and can also reduce the uneven local current density of the electrodes caused by tabs on opposite sides, thereby reducing the risk of lithium plating during fast charging at low temperatures.

[0186] In some embodiments, one or more of the following conditions are met: the dimension of the positive electrode sheet along the length of the electrode assembly is 150mm-400mm; the dimension of the negative electrode sheet along the length of the electrode assembly is 150mm-400mm. This results in a shorter electron transport path within the electrode sheet and higher internal current homogenization, which can reduce the risk of lithium plating during fast charging at low temperatures.

[0187] As an example, the dimensions of the positive electrode along the length of the electrode assembly can be 150mm, 200mm, 250mm, 300mm, 350mm, 400mm, or any value between the two.

[0188] As an example, the dimension of the negative electrode sheet along the length of the electrode assembly can be 150mm, 200mm, 250mm, 300mm, 350mm, 400mm, or any value between the two.

[0189] In some embodiments, one or more of the following conditions are met: the dimension of the positive electrode sheet along the length of the electrode assembly is 150mm-300mm; the dimension of the negative electrode sheet along the length of the electrode assembly is 150mm-300mm. This further shortens the electron transport path within the electrode sheet, improving internal current homogenization.

[0190] In some embodiments, the electrode assembly is a stacked structure. The stacked electrode assembly is composed of multiple layers of electrode sheets stacked together. The electrolyte can be simultaneously drawn back and wetted from the sides, top, and bottom of the electrode assembly. The multi-directional penetration path significantly reduces the flow resistance of the high-viscosity electrolyte, significantly enhances the back-absorption rate of the high-viscosity electrolyte, improves the wetting efficiency of the high-viscosity electrolyte on the electrode assembly, maintains the long-term wettability of the electrode sheets, and allows the interior of the electrode assembly to be fully wetted, effectively improving the cycle performance of the battery cell at low temperatures.

[0191] In some embodiments, the electrolyte further includes at least one of vinylene carbonate (VC) and fluoroethylene carbonate (FEC). Thus, vinylene carbonate can form an elastic polymer on the surface of the negative electrode active material, which is superior to the electrolyte solvent, mitigating the SEI film rupture and recombination caused by the expansion and contraction of the negative electrode active material. Fluoroethylene carbonate can form a LiF-rich SEI film on the surface of the negative electrode active material, reducing lithium dendrite growth and volume expansion of the negative electrode active material. Both can effectively improve the cycle performance of the battery cell at low temperatures.

[0192] In some embodiments, the mass percentage of vinylene carbonate is 0.05%-6.00% based on the total mass of solvent and additives in the electrolyte. Therefore, adding an appropriate amount of vinylene carbonate to the electrolyte helps improve the structural stability of the SEI film, and the resulting SEI film has a moderate thickness, having a minimal impact on the internal resistance of the battery cell.

[0193] As an example, based on the total mass of solvent and additives in the electrolyte, the mass percentage of vinylene carbonate can be 0.05%, 0.80%, 1.55%, 2.30%, 3.05%, 3.80%, 4.55%, 5.30%, 6.00%, or any value between the two.

[0194] As an example, the mass percentage of vinylene carbonate based on the total mass of solvent and additives in the electrolyte can be determined using the following method: Gas chromatography-quantitative analysis of organic components (GC) is employed. This method is both qualitative and quantitative, and can be referenced in GB / T 9722-2023. The specific testing method is as follows: A fresh battery is disassembled, the electrolyte is collected, and the mass percentage of vinylene carbonate is obtained by gas chromatography analysis of organic components.

[0195] In some embodiments, the electrolyte further includes one or more of tris(trimethylsilane) phosphate (TMSP) and trimethylfluorosilane (TMFS). Thus, tris(trimethylsilane) phosphate and trimethylfluorosilane can preferentially form a structurally stable protective layer on the surface of the positive electrode film compared to linear or cyclic carbonates, reducing electrolyte corrosion of the aluminum foil and reducing electrolyte decomposition and gas generation.

[0196] In some embodiments, at least one of the following conditions is met: the mass percentage of tris(trimethylsilane)phosphate is 0.01%-0.5% based on the total mass of solvent and additives in the electrolyte; and the mass percentage of trimethylfluorosilane is 0.01%-0.5% based on the total mass of solvent and additives in the electrolyte. This allows for the formation of a moderately thick and complete positive electrode electrolyte interface (CEI) film on the surface of the positive electrode active material, minimizing its impact on the lithium-ion extraction rate of the positive electrode active material, thus contributing to improved rate cycle performance of the battery cell and reduced costs.

[0197] As an example, based on the total mass of solvent and additives in the electrolyte, the mass percentage of tris(trimethylsilane)phosphate can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, or any value between the two.

[0198] As an example, based on the total mass of solvent and additives in the electrolyte, trimethylfluorosilane can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, or any range between the two.

[0199] Tris(trimethylsilane) phosphate in the electrolyte will degrade to produce trimethylfluorosilane in a fluorine-containing environment (such as an electrolyte containing LiPF6). The content of trimethylfluorosilane in the electrolyte can be adjusted by changing the amount of tris(trimethylsilane) phosphate added.

[0200] As an example, based on the total mass of solvents and additives in the electrolyte, the mass percentages of tris(trimethylsilane)phosphate and trimethylfluorosilane can be determined using the following method: Gas chromatography-quantitative analysis (GC) of organic components is employed. This method is for both qualitative and quantitative analysis and can be referenced in GB / T 9722-2023. The specific testing method is as follows: A fresh battery is disassembled to obtain the electrolyte, and the mass percentages of the components are obtained through GC analysis of the organic components.

[0201] In some embodiments, the solvent in the electrolyte includes POF3. During the charging and discharging of a single battery cell, lithium hexafluorophosphate dissociates in the electrolyte to produce phosphorus pentafluoride. Phosphorus pentafluoride reacts with water to generate phosphorus trifluoride (POF3). Phosphorus trifluoride further reacts with the electrolyte to generate impurities that damage the membrane interface between the positive and negative electrodes.

[0202] In some embodiments, the mass percentage of POF3 is 0.04%-0.35% based on the total mass of the electrolyte. Therefore, by controlling the content of lithium hexafluorophosphate and adjusting the content of POF3 within the above range, the occurrence of chain side reactions such as SEI film rupture and electrolyte decomposition can be effectively reduced, thereby improving the cycle stability of the battery cell.

[0203] As an example, based on the total mass of the electrolyte, the mass percentage of POF3 can be 0.04%, 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, or any value between the two.

[0204] As an example, the mass percentage of POF3 based on the total mass of the electrolyte can be determined using the following method: Ion chromatography (IC) is employed for qualitative and quantitative analysis, and can be referenced in JY / T 020-1996. The specific testing method is as follows: 1) Provide POF3 standard material for retention time calibration and establish a standard curve; 2) Disassemble a fresh battery, take a measured amount of electrolyte, with the diluent concentration at the midpoint of the standard curve, and dilute to 100 ml with ultrapure water. Automated injection and detection using ion chromatography will yield the mass percentage of POF3 in the electrolyte.

[0205] In some embodiments, the electrolyte also includes SO3F - C2O4BF2 - One or more of them. Therefore, SO3F - C2O4BF2 - SEI and CEI films rich in inorganic components can be formed on the surface of active materials, which helps to reduce the internal resistance of battery cells.

[0206] In some embodiments, at least one of the following conditions is met: based on the total mass of the electrolyte, SO3F- The mass percentage is 0.01%-0.4%; based on the total mass of the electrolyte, C2O4BF2 - The mass percentage is 0.05%-0.5%. Therefore, while improving the lithium-ion migration rate, it can reduce the occurrence of gas-generating side reactions and the increase in electrolyte viscosity, thereby improving the cycle performance and fast-charging performance of individual battery cells at low temperatures.

[0207] Lithium bis(fluorosulfonyl)imide (LiFSI) dissociates in the electrolyte to form fluorosulfonate. The fluorosulfonate content in the electrolyte can be adjusted by changing the amount of LiFSI added.

[0208] As an example, based on the total mass of the electrolyte, SO3F - The mass percentage can be 0.01%, 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, or any value between the two.

[0209] Lithium difluorooxalate borate (LiDFOB) dissociates in the electrolyte to generate difluorooxalate borate ions and lithium ions. The content of difluorooxalate borate ions in the electrolyte can be adjusted by changing the amount of lithium difluorooxalate borate added.

[0210] As an example, based on the total mass of the electrolyte, C2O4BF2 - The mass percentage can be 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, or any value range between the two.

[0211] As an example, based on the total mass of the electrolyte, SO3F - C2O4BF2 - The mass percentage of SO3F can be determined using the following method: Ion chromatography (IC) is employed for qualitative and quantitative analysis, and can be referenced in JY / T 020-1996. The specific testing method is as follows: 1) Provide LiSO3F and LiC2O4BF2 standard substances for retention time calibration and establish a standard curve; 2) Disassemble a fresh battery, take a measured amount of electrolyte, with the diluent concentration at the midpoint of the standard curve, and dilute to 100 ml with ultrapure water. Automated injection analysis using ion chromatography is performed to obtain the mass percentage of LiSO3F and LiC2O4BF2 in the electrolyte, and then the SO3F content in the electrolyte can be calculated. - C2O4BF2 - The percentage of mass.

[0212] In some embodiments, the electrolyte has an ionic conductivity of 11 mS / cm-15 mS / cm at 25°C. Therefore, lithium ions migrate relatively quickly in the electrolyte, making it suitable for high-rate charge / discharge scenarios.

[0213] As an example, the ionic conductivity of the electrolyte at 25°C can be 11 mS / cm, 11.5 mS / cm, 12 mS / cm, 12.5 mS / cm, 13 mS / cm, 13.5 mS / cm, 14 mS / cm, 14.5 mS / cm, 15 mS / cm, or any value between the two.

[0214] In this application, unless otherwise specified, the term "ionic conductivity" of the electrolyte has a commonly known meaning in the art and can be tested and analyzed using existing methods in the field. Ionic conductivity can be obtained using a conductivity meter, such as the DDSJ-318 conductivity meter. The testing temperature can be 25±0.1℃. The testing method can be performed according to HG / T 4067-2015. Unless otherwise specified, the unit of ionic conductivity of the electrolyte is millisiemens per centimeter (mS / cm).

[0215] In a second aspect, this application proposes a battery device comprising the aforementioned battery cell, and the battery device further comprising at least one of a battery module, a battery pack, and an energy storage device. Thus, this battery device possesses all the features and advantages of the aforementioned battery cell, which will not be repeated here.

[0216] In a third aspect, this application proposes an electrical device comprising the aforementioned battery cell. Therefore, this electrical device possesses all the features and advantages of the aforementioned battery cell, which will not be repeated here.

[0217] Battery cells, battery modules, or battery packs can be used as power sources for electrical devices or as energy storage units for electrical devices. Electrical devices can include, but are not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0218] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0219] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0220] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0221] Example 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.

[0222] Example 1 (1) Preparation of positive electrode sheet: The positive electrode sheet includes a positive current collector aluminum foil and a positive electrode film layer coated on both sides of the positive current collector. The positive electrode film layer is formed by uniformly coating the surface of the positive current collector aluminum foil with a positive electrode slurry (solvent is N-methylpyrrolidone), and then drying and cold pressing. The positive electrode film layer includes positive electrode active material (lithium iron phosphate), conductive agent (Super P), and binder (polyvinylidene fluoride) in a weight ratio of 97.2:0.7:2.1.

[0223] The positive electrode active material is lithium iron phosphate with a carbon coating layer on at least part of its surface, and the mass fraction of the carbon coating layer in the positive electrode active material is 1%.

[0224] The coating weight of the single-layer positive electrode film is 0.29g / 1540.25mm. 2 The thickness of the single-layer positive electrode film is 75 μm, and the compaction density is 2.7 g / cm³. 3 The thickness of the positive electrode current collector is 13 μm.

[0225] 2) Preparation of the negative electrode sheet: The negative electrode sheet includes a negative current collector copper foil and a negative electrode film layer coated on both sides of the negative current collector. The negative electrode film layer is formed by uniformly coating the surface of the negative current collector copper foil with negative electrode slurry (solvent is deionized water), and then drying and cold pressing it.

[0226] The negative electrode film layer includes negative electrode active material in a weight ratio of 96.4:1.8:1.1:0.7, styrene-butadiene rubber (SBR) binder, sodium carboxymethyl cellulose (CMC-Na) thickener, and carbon black (Super P) conductive agent.

[0227] The negative electrode active material includes artificial graphite, and the OI value of the negative electrode active material is 2. D / I GThe median value is 0.2, the volume average particle size (Dv50) of the negative electrode active material is 10 μm, and the single-sided coating weight of the negative electrode film is 0.13 g / 1540.25 mm. 2 The compacted density is 1.65 g / cm³. 3 The porosity of the negative electrode sheet is 30%.

[0228] The thickness of the single-layer negative electrode film is 55 μm, and the thickness of the negative electrode current collector is 6 μm.

[0229] 3) Separating membrane: The separator comprises a base film, a first coating, a second coating, and a third coating. The first and second coatings are sequentially stacked on one side of the base film, and the third coating is located on the other side of the base film. The first coating is located on the side closer to the positive electrode, the second coating is located between the first coating and the base film, and the third coating is located on the side closer to the negative electrode. The base film is made of polyethylene with a thickness of 5.5 μm, and the thicknesses of the first, second, and third coatings are all 0.5 μm. The first coating is composed of polyvinylidene fluoride (PVDF). The second coating comprises alumina and PVDF, with alumina comprising 95% by mass and PVDF comprising 5% by mass. The third coating is composed of PVDF.

[0230] 4) Preparation of electrolyte: Solvents: dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and ethyl acetate, wherein, based on the total mass of solvents and additives in the electrolyte, the mass percentage of dimethyl carbonate is 30%, the mass percentage of ethyl methyl carbonate is 10%, the mass percentage of ethylene carbonate is 40%, and the mass percentage of ethyl acetate is 16%.

[0231] Lithium salts: Lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide are used, wherein, based on the total mass of the electrolyte, the mass percentage of lithium hexafluorophosphate is 8% and the initial mass percentage of lithium bis(fluorosulfonyl)imide is 1%.

[0232] Additives: vinylene carbonate, fluoroethylene carbonate, and tris(trimethylsilane) phosphate, wherein, based on the total mass of solvent and additives in the electrolyte, the initial mass percentage of vinylene carbonate is 2%, the initial mass percentage of fluoroethylene carbonate is 1.5%, and the initial mass percentage of tris(trimethylsilane) phosphate in the electrolyte is 0.5%.

[0233] The ionic conductivity of the electrolyte at 25℃ is 12.7±0.5mS / cm.

[0234] 5) Preparation of individual battery cells: The electrode assembly includes a positive electrode, a negative electrode, and a separator. The electrode assembly is a stacked electrode assembly, with the separator disposed between the positive and negative electrode. The electrode assembly is subjected to a series of processes including casing, liquid injection, settling, formation, and shaping to obtain a battery cell. In the battery cell, each positive electrode and each negative electrode includes a coating portion and a tab portion. The coating portion is provided with a film layer, and the tab portion is connected to the coating portion and extends out of the coating portion along the height direction of the battery cell. The tab portions of the positive electrode and the negative electrode are located on the same side of the electrode assembly. The dimension of the positive electrode along the length direction of the electrode assembly is 150 mm. The dimension of the negative electrode along the length direction of the electrode assembly is 150 mm.

[0235] The differences between the remaining embodiments and comparative examples and Embodiment 1 are shown in the table below. The batteries in the aforementioned embodiments and comparative examples were tested using the following methods, and the test results are shown in the table below. Specifically, compared to Embodiment 1, Comparative Example 1 adjusted the particle size of the artificial graphite and adjusted the I... D / I G The median was 0.05; Comparative Example 2 adjusted the I of the artificial graphite by adjusting the particle size of the artificial graphite. D / I G The median was 0.7; Comparative Example 3 omitted ethylene carbonate; Comparative Example 4 omitted ethyl acetate; Comparative Example 5 omitted dimethyl carbonate and ethyl methyl carbonate; Comparative Example 6 omitted the third coating; Comparative Example 7 omitted the second coating; Comparative Example 8 replaced the material of the second coating entirely with polyvinylidene fluoride; Comparative Example 9 replaced the material of the third layer entirely with alumina.

[0236] Test case The battery cells obtained in the examples and comparative examples were subjected to the following performance tests. The test results are shown in the table below.

[0237] 1. Fast charging performance test: -10℃ Three-electrode test Using copper wire as a reference electrode, the test was conducted at a constant temperature of -10℃ in a temperature chamber. After measuring the cell capacity, lithium plating was performed to activate the reference electrode. After calibrating, lithium plating boundary scanning was performed. The obtained data was processed to obtain the lithium plating current-SOC curve. Based on the obtained curve, the maximum fast charging time under unlimited current was calculated, thereby determining the battery's maximum fast charging capability at room temperature.

[0238] 2. DC internal resistance (DCR) test: At -20℃, the battery is charged at a constant current of 1 / 3C to 3.65V, and then charged at a constant voltage until the current is 0.05C. The battery is then discharged at a constant current of 1 / 3C for 90 minutes to adjust the battery to 50% SOC. The voltage of the battery at this time is recorded as U1. The battery is then discharged at a constant current of 1C for 30 seconds, with a sampling time of 0.1 seconds. The voltage at the end of the discharge is recorded as U2. The initial DC internal resistance (DCR) of the battery at 50% SOC is used to represent the initial DC internal resistance (DCR) of the battery. The initial DC internal resistance DCR of the battery is calculated as DCR = (U1 - U2) / 1C.

[0239] Table 1

[0240] As shown in Table 1, compared with Comparative Examples 1 and 2, the negative electrode active materials of Examples 1-4 have more surface defect sites and stronger lithium-ion acceptance capabilities, which helps to reduce the occurrence of lithium plating side reactions and improve the fast charging performance and cycle life of the battery cells.

[0241] Comparative Example 1: Adjusting the I of artificial graphite D / I G The median value of 0.05 leads to a longer fast-charging time for individual battery cells at low temperatures and an increase in DC internal resistance; Comparative Example 2 adjusts the I of artificial graphite. D / I G The median value is 0.7, which leads to a decrease in the fast charging performance and cycle life of individual battery cells.

[0242] Table 2

[0243] In Examples 5-7, the mass content of the solvent is calculated based on the total mass of the solvent and additives in the electrolyte. For example, in Example 5, based on the total mass of the solvent and additives in the electrolyte, the mass content of dimethyl carbonate is 0.5, the mass content of ethylene carbonate is 0.3, and the mass percentage of ethyl acetate is 0.16.

[0244] As shown in Table 2, controlling the content of linear carbonates, cyclic carbonates and linear carboxylic esters in the electrolyte within the above range can improve the fast charging capability and cycle life of battery cells at low temperatures.

[0245] Table 3

[0246] In Examples 8-10, based on the total mass of solvents and additives in the electrolyte, the mass percentage of linear carbonates was 40%, the mass percentage of cyclic carbonates was 40%, and the mass percentage of linear carboxylic esters was 16%.

[0247] As shown in Table 3, the use of different types of linear carbonates, cyclic carbonates and linear carboxylic esters can improve the fast charging capability and cycle life of battery cells at low temperatures.

[0248] Table 4

[0249] In Table 4, " / " indicates that the item does not exist. In Examples 1 and 11-13, the mass content of the solvent is calculated based on the total mass of the solvent and additives in the electrolyte. For example, in Example 11, based on the total mass of the solvent and additives in the electrolyte, the mass content of dimethyl carbonate is 0.3, the mass content of ethyl methyl carbonate is 0.1, the mass content of ethylene carbonate is 0.4, and the mass percentage of ethyl acetate is 0.16.

[0250] As shown in Table 4, compared with the comparative example, using the multi-electrode solvents in Table 4 can lower the freezing point of the electrolyte, improve the stability of SEI, reduce low-temperature lithium plating, and significantly optimize the fast-charging performance and cycle life of the battery cells at low temperatures.

[0251] Comparative Example 3 omitted ethylene carbonate, Comparative Example 4 omitted ethyl acetate, and Comparative Example 5 omitted dimethyl carbonate and ethyl methyl carbonate, all of which resulted in a decrease in the fast-charging performance and cycle life of the battery cells.

[0252] Table 5

[0253] In Examples 1 and 14-15, the mass content of lithium salts was calculated based on the total mass of the electrolyte. For example, in Example 14, based on the total mass of the electrolyte, the mass content of lithium hexafluorophosphate was 8%, and the mass content of lithium difluorosulfonylimide was 1%.

[0254] As shown in Table 5, the presence of both lithium hexafluorophosphate and lithium difluorosulfonylimide in the electrolyte increases the system disorder, thereby lowering the freezing point of the electrolyte and improving the low-temperature fast-charging performance and low-temperature cycling performance of the battery cells.

[0255] Table 6

[0256] As shown in Table 6, using different types of lithium-containing transition metal phosphates can improve the fast charging capability and cycle life of battery cells at low temperatures.

[0257] Table 7

[0258] As shown in Table 7, Comparative Example 6 omits the third coating. Compared with Comparative Example 6, the third coating of a specific thickness in Example 1 can enhance the bonding strength between the separator and the negative electrode sheet, and improve the fast charging time and cycle performance of the battery cell.

[0259] Comparative Example 7 omits the second coating. Compared to Comparative Example 7, the second coating of a specific thickness in Example 1 can significantly improve the mechanical strength and heat resistance of the separator, enhance puncture resistance and heat shrinkage resistance, reduce the penetration of lithium dendrites during charge and discharge cycles, thereby reducing the risk of short circuits and comprehensively improving the fast charging time and cycle performance of the battery cells.

[0260] Table 8

[0261] In Comparative Example 8, the material of the second coating was completely replaced with polyvinylidene fluoride. Compared with Comparative Example 8, the ceramic material in the second coating of Example 1 can significantly improve the mechanical strength and heat resistance of the separator, improve the puncture resistance and heat shrinkage resistance, reduce the penetration of lithium dendrites during charge and discharge cycles, thereby reducing the risk of short circuits and comprehensively improving the fast charging time and cycle performance of the battery cells.

[0262] In Comparative Example 9, the material of the third layer was completely replaced with aluminum oxide. Compared with Comparative Example 9, the polyvinylidene fluoride third coating of Example 1 can enhance the bonding strength between the separator and the negative electrode sheet, and improve the fast charging time and cycle performance of the battery cell.

[0263] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, The battery cell includes an electrode assembly and an electrolyte, wherein the electrolyte wets the electrode assembly. The electrode assembly includes a positive electrode, a separator, and a negative electrode. The positive electrode includes a positive current collector and a positive electrode film layer located on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a lithium-containing transition metal phosphate. The negative electrode sheet includes a negative current collector and a negative electrode film layer located on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes a graphite material. D / I G The median is 0.1-0.6, where I G This indicates that the Raman spectrum of the negative electrode active material is at 1580±100 cm⁻¹. -1 The intensity of peak G at I D This indicates that the Raman spectrum of the negative electrode active material is at 1350±100 cm⁻¹. -1 The intensity of peak D at that location; The electrolyte comprises linear carbonates, cyclic carbonates, and linear carboxylic esters; the mass ratio of the linear carbonates, cyclic carbonates, and linear carboxylic esters in the electrolyte is (40-50):(30-40):(15-25). The isolation membrane includes a base membrane and a coating located on at least one side of the base membrane; The coating comprises a first coating and a second coating stacked sequentially, the first coating being located on the side closer to the positive electrode sheet, the first coating comprising polyvinylidene fluoride, and the second coating comprising a ceramic material; The coating includes a third coating near the negative electrode sheet, the third coating comprising polyvinylidene fluoride; The thickness of the first coating is 0.5μm-3μm; the thickness of the second coating is 0.5μm-3μm; and the thickness of the third coating is 0.5μm-3μm.

2. The battery cell according to claim 1, characterized in that, The negative electrode active material I D / I G The median is 0.2-0.

5.

3. The battery cell according to claim 1, characterized in that, The battery cell satisfies one or more of the following conditions: Based on the total mass of solvent and additives in the electrolyte, the linear carbonate accounts for 40%-50% of the mass. Based on the total mass of solvent and additives in the electrolyte, the cyclic carbonate accounts for 30%-40% of the mass. Based on the total mass of solvent and additives in the electrolyte, the linear carboxylic acid ester accounts for 15%-25% of the mass.

4. The battery cell according to any one of claims 1-3, characterized in that, The battery cell satisfies one or more of the following conditions: the linear carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and methyl propyl carbonate; the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, trimethylene cyclic carbonate, and 2,2-dimethyltrimethylene cyclic carbonate; and the linear carboxylic acid ester includes at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate.

5. The battery cell according to claim 4, characterized in that, The battery cell meets one or more of the following conditions: the mass percentage of dimethyl carbonate is 10%-50% based on the total mass of solvent and additives in the electrolyte; Based on the total mass of solvent and additives in the electrolyte, the mass percentage of methyl ethyl carbonate is 5%-30%. Based on the total mass of solvent and additives in the electrolyte, the mass percentage of ethylene carbonate is 10%-50%. Based on the total mass of solvent and additives in the electrolyte, the mass percentage of diethyl carbonate is 0.01%-20%. Based on the total mass of solvent and additives in the electrolyte, the mass percentage of ethyl acetate is 15%-25%.

6. The battery cell according to any one of claims 1-3, characterized in that, The electrolyte comprises one of the cyclic carbonates, one of the linear carboxylic acid esters, and at least two of the linear carbonates.

7. The battery cell according to any one of claims 1-3, characterized in that, The electrolyte includes at least one of dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and ethyl acetate.

8. The battery cell according to any one of claims 1-3, characterized in that, The electrolyte further includes lithium salts, which include at least two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

9. The battery cell according to any one of claims 1-3, characterized in that, The electrolyte comprises lithium hexafluorophosphate and lithium difluorosulfonylimide.

10. The battery cell according to claim 9, characterized in that, The battery cell satisfies one or more of the following conditions: the mass percentage of lithium hexafluorophosphate is 8%-16% based on the total mass of the electrolyte; the mass percentage of lithium difluorosulfonylimide is 1%-10% based on the total mass of the electrolyte.

11. The battery cell according to any one of claims 1-3, characterized in that, The electrolyte also includes BF4. - .

12. The battery cell according to claim 11, characterized in that, Based on the total mass of the electrolyte, BF4 - The quality percentage is 0.01%-0.5%.

13. The battery cell according to any one of claims 1-3, characterized in that, The base film includes one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.

14. The battery cell according to claim 13, characterized in that, The battery cell meets one or more of the following conditions: the thickness of the base film is 3μm-10μm; the thickness of the separator is 4μm-12μm.

15. The battery cell according to any one of claims 1-3, characterized in that, The porosity of the isolation membrane is 25%-60%.

16. The battery cell according to any one of claims 1-3, characterized in that, The air permeability of the isolation membrane is 90s / 100cc-260s / 100cc.

17. The battery cell according to any one of claims 1-3, characterized in that, The OI value of the negative electrode active material is 2-6.

18. The battery cell according to any one of claims 1-3, characterized in that, The volume average particle size Dv50 of the graphite material is 7μm-13μm.

19. The battery cell according to any one of claims 1-3, characterized in that, The graphite material includes artificial graphite.

20. The battery cell according to any one of claims 1-3, characterized in that, The graphite material comprises secondary particles formed from primary particles.

21. The battery cell according to claim 19, characterized in that, The artificial graphite comprises a first component and a second component; wherein... The method for preparing the first component includes: crushing needle coke to obtain first primary graphite particles; granulating the first primary graphite particles to obtain secondary graphite particles; subjecting the secondary graphite particles to a first heat treatment to obtain an intermediate; mixing the intermediate with a coating agent and subjecting it to a second heat treatment to obtain the first component. The method for preparing the second component includes: crushing petroleum coke to obtain second primary graphite particles; mixing the second primary graphite particles with a coating agent and performing a third heat treatment to obtain the second component.

22. The battery cell according to any one of claims 1-3, characterized in that, The battery cell meets one or more of the following conditions: the single-sided coating weight of the negative electrode film is 0.05g / 1540.25mm. 2 -0.2g / 1540.25mm 2 The porosity of the negative electrode sheet is 20%-35%.

23. The battery cell according to any one of claims 1-3, characterized in that, The battery cell meets one or more of the following conditions: the thickness of the negative electrode current collector is 2μm-10μm; the thickness of the negative electrode film is 40μm-80μm.

24. The battery cell according to any one of claims 1-3, characterized in that, The negative electrode film layer includes: A first negative electrode film layer is disposed on at least one side of the negative electrode current collector; The second negative electrode film layer is disposed on the side of the first negative electrode film layer away from the negative electrode current collector; Wherein, the volume average particle size Dv50 of the graphite material in the first negative electrode film layer is greater than or equal to the volume average particle size Dv50 of the graphite material in the second negative electrode film layer.

25. The battery cell according to any one of claims 1-3, characterized in that, The single-sided coating weight of the positive electrode film is 0.200 g / 1540.25 mm. 2 -0.400g / 1540.25mm 2 .

26. The battery cell according to any one of claims 1-3, characterized in that, The battery cell meets one or more of the following conditions: the thickness of the positive electrode current collector is 9μm-15μm; the thickness of the positive electrode film is 60μm-90μm.

27. The battery cell according to any one of claims 1-3, characterized in that, The chemical formula of the lithium-containing transition metal phosphate satisfies: Li m Fe x P y O j Q q , Wherein, Q includes one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, with 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.

1.

28. The battery cell according to any one of claims 1-3, characterized in that, Each of the positive electrode and each of the negative electrode includes a coating portion and a tab portion. The coating portion is provided with a film layer, and the tab portion is connected to the coating portion and extends out of the coating portion along the height direction of the battery cell. The tabs of the positive electrode and the tabs of the negative electrode are located on the same side of the electrode assembly.

29. The battery cell according to any one of claims 1-3, characterized in that, The battery cell satisfies one or more of the following conditions: The positive electrode sheet has a dimension of 150mm-400mm along the length of the electrode assembly; The negative electrode sheet has a length of 150mm-400mm along the length of the electrode assembly.

30. The battery cell according to any one of claims 1-3, characterized in that, The battery cell satisfies one or more of the following conditions: The positive electrode sheet has a dimension of 150mm-300mm along the length of the electrode assembly; The negative electrode sheet has a length of 150mm-300mm along the length of the electrode assembly.

31. The battery cell according to any one of claims 1-3, characterized in that, The electrode assembly has a stacked structure.

32. The battery cell according to any one of claims 1-3, characterized in that, The electrolyte also includes at least one of vinylene carbonate and fluoroethylene carbonate.

33. The battery cell according to claim 32, characterized in that, Based on the total mass of solvent and additives in the electrolyte, the mass percentage of vinylene carbonate is 0.05%-6.00%.

34. The battery cell according to any one of claims 1-3, characterized in that, The electrolyte also includes one or more of tris(trimethylsilane) phosphate and trimethylfluorosilane.

35. The battery cell according to claim 34, characterized in that, The battery cell satisfies one or more of the following conditions: the mass percentage of tris(trimethylsilane) phosphate is 0.01%-0.5% based on the total mass of solvent and additives in the electrolyte; the mass percentage of trimethylfluorosilane is 0.01%-0.5% based on the total mass of solvent and additives in the electrolyte.

36. The battery cell according to any one of claims 1-3, characterized in that, The electrolyte also includes POF3.

37. The battery cell according to claim 36, characterized in that, Based on the total mass of the electrolyte, the mass percentage of POF3 is 0.04%-0.35%.

38. The battery cell according to any one of claims 1-3, characterized in that, The electrolyte also includes SO3F. - C2O4BF2 - One or more of them.

39. The battery cell according to claim 38, characterized in that, The battery cell satisfies one or more of the following conditions: based on the total mass of the electrolyte, SO3F - The mass percentage is 0.01%-0.4%; based on the total mass of the electrolyte, the C2O4BF2 - The quality percentage is 0.05%-0.5%.

40. The battery cell according to any one of claims 1-3, characterized in that, The electrolyte has an ionic conductivity of 11 mS / cm-15 mS / cm at 25°C.

41. A battery device, characterized in that, The battery device includes the battery cell according to any one of claims 1-40, and the battery device includes at least one of battery module, battery pack, and energy storage device.

42. An electrical appliance, characterized in that, Includes the battery cell as described in any one of claims 1-40.

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