Battery cell, battery device, and electric device

Abstract

The invention discloses a battery monomer, a battery device and a power utilization device. The battery monomer comprises an electrode assembly and an electrolyte; wherein the electrode assembly comprises a positive electrode plate and a negative electrode plate, a positive electrode film layer of the positive electrode plate comprises a positive electrode active material, the positive electrode active material comprises lithium-containing phosphate, and the porosity of the positive electrode plate is 20-30%; a negative electrode film layer of the negative electrode plate comprises a negative electrode active material, the negative electrode active material comprises graphite, and the porosity of the negative electrode plate is 24-33%; the electrolyte comprises an electrolyte salt and a solvent, the solvent comprises chain carboxylic ester and chain carbonic ester, the mass ratio of the chain carboxylic ester in the electrolyte is 8.5%-40%, and the mass ratio of the chain carbonic ester in the electrolyte is 8.5%-50%. According to the technical scheme, good fast charging performance, good cycle performance and high energy density of the battery are considered.

Description

[0001] This application claims the priority of the PCT international application "Battery Cell, Battery Device, and Electrical Device" with the application number PCT / CN2025 / 077646 filed on February 17, 2025, and the entire content of this application is incorporated into this application by reference. Technical Field

[0002] This application relates to the technical field of batteries, and specifically relates to a battery cell, a battery device, and an electrical device. Background Art

[0003] In recent years, with the increasingly wide application range of batteries, batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.

[0004] With the application and popularization of batteries, the requirements for the fast charging performance and cycling performance of batteries are getting higher and higher. Summary of the Invention

[0005] This application is made in view of the above problems, and its purpose is to provide a battery cell, a battery device, and an electrical device, aiming to balance good fast charging performance, good cycling performance, and high energy density of the battery.

[0006] In a first aspect, this application provides a battery cell, which includes an electrode assembly and an electrolyte; wherein, the electrode assembly includes a positive electrode tab and a negative electrode tab. The positive electrode tab 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 active material, and the positive active material includes a lithium-containing phosphate. The porosity of the positive electrode tab is 20% - 30%; the negative electrode tab 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 active material, and the negative active material includes graphite. The porosity of the negative electrode tab is 24% - 33%; the electrolyte includes an electrolyte salt and a solvent. The solvent includes a chain carboxylic ester and a chain carbonate. The mass ratio of the chain carboxylic ester in the electrolyte is 8.5% - 40%, and the mass ratio of the chain carbonate in the electrolyte is 8.5% - 50%.

[0007] In the battery cell provided by this application, through the cooperation of the chain carboxylic ester and the chain carbonate with the above mass ratios in the electrolyte and the positive electrode tab and the negative electrode tab with the above porosities, it can not only reduce the decomposition of the electrolyte during cycling, improve the cycling performance of the battery, but also improve the wetting ability of the electrolyte to the electrode tab, shorten the ion transport distance in the electrode material, improve the fast charging performance of the battery cell, and at the same time, is conducive to obtaining a high energy density. Thus, it balances good fast charging performance, good cycling performance, and high energy density of the battery.

[0008] In any embodiment, the porosity of the positive electrode sheet is 25% to 30%. Thus, it is beneficial for the battery cell to have good fast charging performance while taking into account high energy density.

[0009] In any embodiment, the porosity of the negative electrode sheet is 25% to 30%. Thus, it is beneficial for the battery cell to have good fast charging performance while taking into account high energy density.

[0010] In any embodiment, the mass ratio of the chain carboxylic acid ester in the electrolyte is 10% to 25.5%. Thus, it is beneficial for further optimizing the fast charging performance and cycling performance of the battery cell.

[0011] In any embodiment, the mass ratio of the chain carbonate in the electrolyte is 10% to 42.5%. Thus, it is beneficial for further optimizing the fast charging performance and cycling performance of the battery cell.

[0012] In any embodiment, the chain carboxylic acid ester includes the chain carboxylic acid ester represented by Formula I, Formula I wherein, R 1 includes any one of an alkyl group having 1 to 3 carbon atoms and an alkenyl group having 2 to 4 carbon atoms; R 2 includes an alkyl group having 1 to 3 carbon atoms. The chain carboxylic acid ester having the above structure has a suitable viscosity, which is beneficial for reducing the ion transport resistance in the electrolyte.

[0014] In any embodiment, the chain carboxylic acid ester includes at least one of ethyl acrylate, propyl acetate, and ethyl propionate. Thus, it is beneficial for further reducing the ion transport resistance in the electrolyte.

[0015] In any embodiment, the chain carbonate includes the chain carbonate represented by Formula II, Formula II wherein, R 3 and R 4 independently include an alkyl group having 1 to 3 carbon atoms. The addition of the chain carbonate is beneficial for reducing the generation of gas during the cycling of the battery cell, thereby improving the cycling performance.

[0017] In any embodiment, the chain carbonate includes at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The above chain carbonate has a suitable viscosity, which is beneficial for reducing the ion transport resistance in the electrolyte while being beneficial for reducing the generation of gas during the cycling of the battery cell, thereby improving the cycling performance.

[0018] In any embodiment, the solvent further includes cyclic carbonate. The addition of cyclic carbonate is beneficial to reducing the solvation effect of the electrolyte, decreasing the binding ability between the solvent and ions, making it easier for ions to dissociate from the solvent, and thus further improving the fast charging performance.

[0019] In any embodiment, the cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate. The above-mentioned suitable cyclic carbonate is beneficial to exerting its function of reducing the solvation effect of the electrolyte.

[0020] In any embodiment, the mass percentage of the cyclic carbonate in the electrolyte is 10% - 51.5%. Thus, it is beneficial to further optimize the fast charging performance of the battery cell.

[0021] In any embodiment, the electrolyte further includes a first additive, and the first additive includes at least one of lithium difluorophosphate and lithium fluorosulfonate. The addition of the first additive is beneficial to improving the SEI film, enhancing the ionic conductivity of the electrolyte, and further improving the fast charging performance and cycling performance of the battery cell.

[0022] In any embodiment, the mass percentage of the first additive in the electrolyte is 0.02% - 2%. Thus, it is beneficial to exert the function of the first additive to improve the SEI film and enhance the ionic conductivity of the electrolyte.

[0023] In any embodiment, the electrolyte further includes a second additive, and the second additive includes at least one of vinylene carbonate, fluoroethylene carbonate, and 1,3 - propanesultone. The addition of the second additive is beneficial to improving the SEI film and further improving the cycling performance of the battery cell.

[0024] In any embodiment, the mass percentage of the second additive in the electrolyte is 3% - 7%. Thus, it is beneficial to exert the function of the second additive to improve the SEI film.

[0025] In any embodiment, the ionic conductivity of the electrolyte at 25°C is 11 - 13 mS / cm. Thus, the suitable ionic conductivity is beneficial to the rapid migration of ions between the electrodes.

[0026] In any embodiment, the negative electrode film layer includes a first film layer and a second film layer. The first film layer is disposed on at least one surface of the negative electrode current collector, and the second film layer is disposed on the surface of the first film layer facing away from the current collector; Among them, the first film layer contains a first negative electrode active material; the second film layer contains a second negative electrode active material; the average longest diameter particle size of graphite in the second negative electrode active material is smaller than that of graphite in the first negative electrode active material. Thus, the average longest diameter particle size of graphite used in the second film layer is relatively smaller, and the ion transport distance of ions in the second film layer is relatively shorter, which is beneficial to further improving the fast charging performance of the battery cell. The average longest diameter particle size of graphite used in the first film layer is relatively larger, and the tap density of the first film layer is relatively higher, which is beneficial to taking into account good energy density.

[0027] In any embodiment, the average longest diameter particle size of graphite in the first negative electrode active material is 7 - 18 μm. Thus, it is beneficial to exert the effect that the tap density of the first film layer is relatively higher.

[0028] In any embodiment, the graphite in the first negative electrode active material includes at least one of artificial graphite and natural graphite.

[0029] In any embodiment, the graphite in the first negative electrode active material includes a negative electrode active material with a secondary particle morphology.

[0030] In any embodiment, the volume distribution particle size Dv50 of graphite in the first negative electrode active material is 7 - 15 μm.

[0031] In any embodiment, the graphite in the first negative electrode active material includes a carbon coating layer, and the thickness of the carbon coating layer is 100 - 500 nm. The carbon coating layer is beneficial to improving the conductivity of graphite.

[0032] In any embodiment, the graphitization degree of graphite in the first negative electrode active material is 90 - 94%.

[0033] In any embodiment, the first negative electrode active material further includes a silicon material, and the mass ratio of silicon element in the silicon material in the first negative electrode active material is 0.5 - 10%. The addition of the silicon material is beneficial to further improving the energy density of the battery cell.

[0034] In any embodiment, the average longest diameter particle size of graphite in the second negative electrode active material is 6 - 10 μm. Thus, it is beneficial to exert the effect that the ion transport distance of ions in the second film layer is relatively shorter.

[0035] In any embodiment, the graphite in the second negative electrode active material includes at least one of artificial graphite and natural graphite.

[0036] In any embodiment, the graphite in the second negative electrode active material includes graphite with a secondary particle morphology.

[0037] In any embodiment, the volume distribution particle size Dv50 of graphite in the second negative electrode active material is 7 to 15 μm.

[0038] In any embodiment, the graphite in the second negative electrode active material includes a carbon coating layer, and the thickness of the carbon coating layer is 100 to 500 nm. The carbon coating layer is beneficial to improving the conductivity of graphite.

[0039] In any embodiment, the graphitization degree of graphite in the second negative electrode active material is 90 to 94%.

[0040] In any embodiment, the second negative electrode active material further includes a silicon material, and the mass ratio of silicon element in the silicon material in the second negative electrode active material is 0.5 to 10%. The addition of the silicon material is beneficial to further improving the energy density of the battery cell. In any embodiment, the thickness of the first film layer is 30% to 70% of the total thickness of the negative electrode film layer. Thus, it is beneficial to play the role of the first film layer in taking into account the energy density of the battery cell.

[0041] In any embodiment, the thickness of the second film layer is 30% to 70% of the total thickness of the negative electrode film layer. Thus, it is beneficial to further improve the fast charging performance of the battery cell.

[0042] In any embodiment, under the condition that the state of charge SOC of the battery cell is 0%, the compaction density of the single-sided negative electrode film layer of the negative electrode plate is 1.3 to 1.52 g / cc. Thus, the appropriate compaction density is beneficial to further adjusting the porosity of the negative electrode plate within a suitable range.

[0043] In any embodiment, the areal density of the single-sided negative electrode film layer of the negative electrode plate is 0.12 to 0.18 g / 1540.25 mm 2 . Thus, the appropriate areal density is beneficial to further adjusting the porosity of the negative electrode plate within a suitable range.

[0044] In any embodiment, under the condition that the state of charge SOC of the battery cell is 0%, the compaction density of the single-sided positive electrode film layer of the positive electrode plate is 2.3 to 2.6 g / cc. Thus, the appropriate compaction density is beneficial to further adjusting the porosity of the positive electrode plate within a suitable range.

[0045] In any embodiment, the areal density of the single-sided positive electrode film layer of the positive electrode plate is 0.25 to 0.33 g / 1540.25 mm 2 . Thus, the appropriate areal density is beneficial to further adjusting the porosity of the positive electrode plate within a suitable range.

[0046] In any embodiment, the lithium-containing phosphate includes lithium iron phosphate, and the lithium iron phosphate includes metal elements, and the metal elements include at least one of aluminum, titanium, and vanadium. Adding the above metal elements to lithium iron phosphate is beneficial to improving the tap density of the positive electrode active material.

[0047] In any embodiment, the metal element includes aluminum, and the mass ratio of aluminum in the lithium-containing phosphate is 0.02% to 0.25%. Thus, it is beneficial to play the role of aluminum doping in improving the tap density of the positive electrode active material and further improving the cycle performance of the battery cell.

[0048] In any embodiment, the metal element includes titanium, and the mass ratio of the titanium in the lithium-containing phosphate is 0.15% to 0.35%. Thus, it is beneficial to play the role of titanium doping in improving the tap density of the positive electrode active material and further increasing the battery capacity.

[0049] In any embodiment, the metal element includes vanadium, and the mass ratio of the vanadium in the lithium-containing phosphate is 0.03% to 0.2%. Thus, it is beneficial to play the role of vanadium doping in improving the tap density of the positive electrode active material and further improving the charge and discharge performance of the battery cell.

[0050] In any embodiment, the lithium-containing phosphate includes lithium-containing phosphate with a primary particle morphology and lithium-containing phosphate with a secondary particle morphology. Mixing the primary particles and the secondary particles is beneficial to further adjusting the tap density of the positive electrode active material.

[0051] In any embodiment, the average longest diameter of the lithium-containing phosphate with a primary particle morphology is 300 to 800 nm. Thus, it is beneficial to shorten the ion transport distance and further improve the fast charging performance.

[0052] In any embodiment, the average longest diameter of the lithium-containing phosphate with a secondary particle morphology is 8 μm to 15 μm. The secondary particles are usually composed of lithium-containing phosphate of primary particles with smaller particle sizes, which is beneficial to shortening the ion transport distance.

[0053] In any embodiment, the lithium-containing phosphate with a secondary particle morphology is spherical or quasi-spherical.

[0054] In any embodiment, the volume distribution particle size Dv50 of the lithium-containing phosphate is 5 to 15 μm.

[0055] In a second aspect, the present application provides a battery device, including the battery cell of the first aspect of the present application.

[0056] In a third aspect, the present application provides an electrical device, including the battery device of the second aspect of the present application. Description of the Drawings

[0057] Figure 1 It is a schematic diagram of a battery cell according to an embodiment of the present application; Figure 2 is Figure 1 an exploded view of the battery cell according to an embodiment of the present application shown in the figure; Figure 3 It is a schematic diagram of a battery module according to an embodiment of the present application; Figure 4 It is a schematic diagram of a battery pack according to an embodiment of the present application; Figure 5 is Figure 4 an exploded view of the battery pack according to an embodiment of the present application shown in the figure; Figure 6 It is a schematic diagram of an electrical device using the battery cell according to an embodiment of the present application as a power source.

[0058] Explanation of reference numerals: 1 Battery pack; 2 Upper box body; 3 Lower box body; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Specific embodiments

[0059] Hereinafter, embodiments of the battery cell, battery device, and electrical device of the present application will be specifically disclosed in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0060] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, 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, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In this application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any combination of real numbers between a and b, where both a and b are real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" are fully listed herein, and "0 - 5" is just an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0061] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form a new technical solution.

[0062] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0063] If there is no special instruction, all steps of this application can be carried out in sequence or randomly, preferably in sequence. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0064] If there is no special instruction, the "including" and "comprising" mentioned in this application mean open-ended or can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can only include or comprise the listed components.

[0065] In the embodiments of the present application, the battery mentioned may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present application may include battery cells, battery modules, battery packs, etc.

[0066] A battery cell is the smallest unit that makes up a battery and can independently perform the functions of charging and discharging. When there are multiple battery cells, the multiple battery cells are connected in series, parallel, or in a hybrid connection through a busbar component. The present application does not particularly limit the shape of the battery cell, and it can be cylindrical, square, or any other shape. For example, Figure 1 is a battery cell 5 with a square structure as an example.

[0067] In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, and the battery pack includes a box body and battery cells, and the battery cells or battery modules are accommodated in the box body. In some embodiments, the box body may be part of the chassis structure of a vehicle. For example, part of the box body may become at least part of the vehicle floor, or part of the box body may become at least part of the crossbeam and longitudinal beam of the vehicle. In some embodiments, the battery may be an energy storage device. The energy storage device includes an energy storage container, an energy storage cabinet, etc. In some embodiments, the battery cells can be assembled into a battery module. The number of battery cells included in the battery module can be one or more, and those skilled in the art can select the specific number according to the application and capacity of the battery module.

[0068] Figure 3 is a battery module 4 as an example. Refer to Figure 3 , in the battery module 4, multiple battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other way. Further, the multiple battery cells 5 can be fixed through fasteners.

[0069] Optionally, the battery module 4 may further include a housing with an accommodation space, and the multiple battery cells 5 are accommodated in the accommodation space.

[0070] In some embodiments, the above-mentioned battery cells and battery modules can also be assembled into a battery pack. The number of battery modules included in the battery pack can be one or more, and those skilled in the art can select the specific number according to the application and capacity of the battery pack.

[0071] Figure 4 and Figure 5 is a battery pack 1 as an example. Refer to Figure 4 and Figure 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0072] The battery provided by the embodiment of the present application may include a lithium-ion battery.

[0073] The battery cell includes an electrode assembly and an electrolyte.

[0074] The electrode assembly includes a positive electrode tab and a negative electrode tab. During the charging and discharging process of the battery, active ions are embedded and extracted back and forth between the positive electrode tab and the negative electrode tab.

[0075] In some embodiments, the battery cell may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0076] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed, etc.

[0077] In some embodiments, referring to Figure 2 , the outer package may include a housing 51 and a cover plate 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate. The bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0078] The fast charging performance refers to the performance of the battery for fast charging. The fast charging performance is closely related to the ion transport kinetics. To improve the fast charging performance, it is required that ions can be transported quickly and efficiently between the electrodes and ions can be transported quickly in the electrode material. In order to improve the fast charging performance of the battery cell, it is desirable to use a solvent with better conductivity. Therefore, chain carboxylic esters are usually used in the electrolyte, but chain carboxylic esters are easily decomposed to generate gas during the cycling process of the battery cell, resulting in a decline in the battery cycling performance.

[0079] Based on the above problems, an embodiment of the present application provides a battery cell, including an electrode assembly and an electrolyte; wherein, the electrode assembly includes a positive electrode tab and a negative electrode tab, the positive electrode tab 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 active material, the positive active material includes a lithium-containing phosphate, and the porosity of the positive electrode tab is 20% to 30%; the negative electrode tab 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 active material, the negative active material includes graphite, and the porosity of the negative electrode tab is 24% to 33%; the electrolyte includes an electrolyte salt and a solvent, the solvent includes a chain carboxylic ester and a chain carbonate, the mass ratio of the chain carboxylic ester in the electrolyte is 8.5% to 40%, and the mass ratio of the chain carbonate in the electrolyte is 8.5% to 50%.

[0080] In this article, the porosity of the positive electrode tab and the porosity of the negative electrode tab can be tested by methods known in the art. For example, it is tested based on the national standard GB / T24586-2009. The electrode tab is immersed in ethylene methyl carbonate (EMC) for cleaning; the true density meter (AccuPycII1340 of Micromeritics, USA) is used to measure based on the gas displacement method. Among them, the percentage of the pore volume in the electrode tab accounting for the total volume of the electrode tab is the porosity of the electrode tab, and the calculation formula is: porosity = (V - V0) / V × 100%, where V0 is the true volume of the electrode tab and V is the apparent volume of the electrode tab.

[0081] In this article, the types and mass contents of the components in the electrolyte can be obtained by detecting the electrolyte by any method known to those skilled in the art. As an example, the composition and content of the electrolyte can be characterized by one or more of gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), and gas chromatography-mass spectrometry (GC-MS). Exemplarily, referring to GB / T-9722-2006 / GB / T6041-2002, gas chromatography and mass spectrometry are used in combination. After the components in the sample are separated by gas chromatography, each component is broken into ion fragments in the mass spectrometry and separated according to the mass-to-charge ratio (m / z) to form a specific mass spectrum, and the qualitative analysis of each organic component in the electrolyte is obtained. Then, each organic component in the electrolyte is separated in the chromatographic column to generate a detection signal spectrum of each component, and the components are qualitatively analyzed using the retention time, and the peak area is calibrated with a standard to achieve quantification, and the quantitative test analysis of the organic components in the electrolyte is obtained. Referring to JY / T0578-2020, nuclear magnetic resonance spectroscopy (NMR) is used to obtain the qualitative and quantitative analysis of the components in the electrolyte.

[0082] The electrolyte referred to in this article can be either fresh electrolyte or electrolyte obtained by disassembling a battery cell. The electrolyte obtained by disassembling a battery cell can be either the free electrolyte in the battery case or the electrolyte centrifuged from the electrode sheets.

[0083] Optionally, the porosity of the positive electrode sheet can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30% or any numerical range composed of any two of the above values. The porosity of the negative electrode sheet can be 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34% or any numerical range composed of any two of the above values.

[0084] Optionally, the mass percentage of the chain carboxylic ester in the electrolyte can be 8.5%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40% or any numerical range composed of any two of the above values. Optionally, the mass percentage of the chain carbonate in the electrolyte can be 8.5%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50% or any numerical range composed of any two of the above values.

[0085] The addition of chain carboxylic acid ester solvents to the electrolyte not only helps to improve the lithium-ion conductivity of the electrolyte, but also can reduce the viscosity of the electrolyte, increase the transport rate of lithium ions at the solid-liquid interface of the battery monomer, and improve the fast charging performance of the battery. However, chain carboxylic acid ester solvents have high reactivity and are prone to decomposition during battery cycling, resulting in gas generation in the battery. Adding a certain amount of chain carbonate to the chain carboxylic acid ester solvent can reduce the amount of chain carboxylic acid ester solvent in the electrolyte, reduce the degree of side reactions of the chain carboxylic acid ester solvent, and improve the battery cycling performance. At the same time, by using a positive electrode plate with a porosity of 20-30% and a negative electrode plate with a porosity of 24-33%, in combination with the chain carboxylic acid ester and chain carbonate in the electrolyte, it is beneficial to improve the wetting ability of the electrolyte for the electrode plate and shorten the transport distance of ions in the electrode material, thereby further facilitating the improvement of the fast charging performance of the battery monomer. Moreover, it is also beneficial to obtain a high energy density. Thus, the good fast charging performance, good cycling performance, and high energy density of the battery are taken into account.

[0086] In some embodiments, the porosity of the positive electrode plate is 25-30%. Thereby, it is beneficial for the battery monomer to have good fast charging performance while taking into account high energy density.

[0087] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector. As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on either one or both of the two opposite surfaces of the positive electrode current collector.

[0088] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0089] In some embodiments, the positive electrode film layer may optionally further include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0090] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0091] In some embodiments, the positive electrode plate can be prepared by the following method: dispersing the components for preparing the positive electrode plate, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0092] In some embodiments, the porosity of the negative electrode plate is 25% to 30%. Thereby, it is beneficial for the battery cell to have good fast charging performance while taking into account high energy density.

[0093] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0094] In some embodiments, the negative electrode film layer may further optionally include a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0095] In some embodiments, the negative electrode film layer may further optionally include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0096] In some embodiments, the negative electrode film layer may further optionally include other additives, such as a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0097] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet can be obtained.

[0098] In some embodiments, the electrolyte salt in the electrolyte can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0099] In some embodiments, the battery cell further includes a separator. The material of the base film of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The base film of the separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the base film of the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0100] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly by a winding process or a stacking process.

[0101] In some embodiments, the mass percentage of the chain carboxylic ester in the electrolyte is 10% - 25.5%. Thereby, it is beneficial to further optimize the fast charging performance and cycling performance of the battery cell.

[0102] In some embodiments, the mass percentage of the chain carbonate in the electrolyte is 10% - 42.5%. Thereby, it is beneficial to further optimize the fast charging performance and cycling performance of the battery cell.

[0103] In some embodiments, the chain carboxylic ester includes the chain carboxylic ester represented by Formula I, Formula I wherein, R 1 includes any one of an alkyl group having 1 - 3 carbon atoms and an alkenyl group having 2 - 4 carbon atoms; R 2 includes an alkyl group having 1 - 3 carbon atoms. The chain carboxylic ester having the above structure has a suitable viscosity, which is beneficial to reducing the transport resistance of ions in the electrolyte.

[0105] As used herein, "alkyl group having 1 to 3 carbon atoms" refers to a straight-chain or branched-chain hydrocarbon chain group composed only of carbon and hydrogen atoms, without unsaturation in the group, having 1 to 3 carbon atoms, and attached to the rest of the molecule by a single bond. Examples include, but are not limited to: methyl (-CH3), ethyl (-CH2CH3), 1-propyl (-CH2CH2CH3), 2-propyl (-CH(CH3)2).

[0106] As used herein, "alkenyl group having 2 to 4 carbon atoms" is a straight-chain or branched-chain hydrocarbon group having 2 to 4 carbon atoms and at least one carbon-carbon double bond. Examples include, but are not limited to: vinyl, 1-propenyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl.

[0107] In some embodiments, the chain carboxylic acid ester includes at least one of ethyl acrylate, propyl acetate, and ethyl propionate. Thus, it is beneficial to further reduce the ion transport resistance in the electrolyte.

[0108] In some embodiments, the chain carbonate includes the chain carbonate represented by Formula II, Formula II wherein R 3 and R 4 independently include an alkyl group having 1 to 3 carbon atoms. The addition of the chain carbonate is beneficial to reduce the generation of gas during the cycling of the battery monomer, thereby improving the cycling performance.

[0110] In some embodiments, the chain carbonate includes at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. The above chain carbonates have appropriate viscosities, which are beneficial to reduce the ion transport resistance in the electrolyte and are also beneficial to reduce the generation of gas during the cycling of the battery monomer, thereby improving the cycling performance.

[0111] In some embodiments, the solvent further includes a cyclic carbonate. The addition of the cyclic carbonate is beneficial to reduce the solvation effect of the electrolyte, reduce the binding ability of the solvent to ions, and make it easier for ions to dissociate from the solvent, thereby further improving the fast charging performance.

[0112] In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate. The above appropriate cyclic carbonate is beneficial to exert its function of reducing the solvation effect of the electrolyte.

[0113] In some embodiments, the mass percentage of the cyclic carbonate in the electrolyte is 10% - 51.5%. Thereby, it is beneficial to further optimize the fast charging performance of the battery cell. The mass percentage of the cyclic carbonate in the electrolyte can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 51.5% or any numerical range composed of any two of the above values.

[0114] In some embodiments, the electrolyte further includes a first additive, and the first additive includes at least one of lithium difluorophosphate and lithium fluorosulfonate. The addition of the first additive is beneficial to improving the SEI film, enhancing the ionic conductivity of the electrolyte, and further improving the fast charging performance and cycling performance of the battery cell.

[0115] In some embodiments, the mass percentage of the first additive in the electrolyte is 0.02% - 2%. Thereby, it is beneficial to exert the function of the first additive in improving the SEI film and enhancing the ionic conductivity of the electrolyte. The mass percentage of the first additive in the electrolyte can be 0.02%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, 1.05%, 1.1%, 1.15%, 1.2%, 1.25%, 1.3%, 1.35%, 1.4%, 1.45%, 1.5%, 1.55%, 1.6%, 1.65%, 1.7%, 1.75%, 1.8%, 1.85%, 1.9%, 1.95%, 2% or any numerical range composed of any two of the above values.

[0116] In some embodiments, the electrolyte further includes a second additive, and the second additive includes at least one of vinylene carbonate, fluoroethylene carbonate, and 1,3 - propane sultone. The addition of the second additive is beneficial to improving the SEI film and further improving the cycling performance of the battery cell.

[0117] In some embodiments, the mass percentage of the second additive in the electrolyte is 3% to 7%. Thus, it is beneficial to exert the role of the second additive in improving the SEI film. The mass percentage of the second additive in the electrolyte can be 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7% or any numerical range composed of any two of the above values.

[0118] In some embodiments, the ionic conductivity of the electrolyte at 25 °C is 11 to 13 mS / cm. Thus, the appropriate ionic conductivity is beneficial to the rapid migration of ions between the electrodes. 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 or any numerical range composed of any two of the above values.

[0119] In the present application, the ionic conductivity of the electrolyte describes the ability of the ions dissociated from the electrolyte to conduct electricity through the directional movement in an electric field, and can be tested by any well-known method in the art. As an example, disassemble the battery cell, take about 100 mL of the electrolyte sample with a dry, clean and corrosion-resistant sample bottle, seal it and place it in a constant temperature water bath, shake the sample from time to time, and keep the temperature constant at 25 °C (deviation ±0.5 °C). After the temperature of the sample is constant, use a commercially available conductivity meter to test its conductivity. After wiping the conductivity meter clean with the calibration solution, vertically place it into the liquid to be tested, click to start the test, and record the test result after the data is stable for more than 10 s.

[0120] In some embodiments, the negative electrode film layer includes a first film layer and a second film layer. The first film layer is disposed on at least one surface of the negative electrode current collector, and the second film layer is disposed on the surface of the first film layer facing away from the current collector; Wherein, the first film layer contains a first negative electrode active material; the second film layer contains a second negative electrode active material; the average longest diameter of the graphite in the second negative electrode active material is smaller than the average longest diameter of the graphite in the first negative electrode active material.

[0121] In this article, the "average longest diameter" means that the pole piece is ion-polished and cut along the thickness direction of the pole piece to expose the cross-section of the film layer. The cross-section of the film layer can be tested by a scanning electron microscope (SEM). At a magnification of 1000 times in the SEM scene, randomly take more than 50 particles, measure the length of the longest straight line passing through the center point of each particle and extending to the outer periphery of the particle, and then take the average value of the lengths of the longest straight lines of these particles.

[0122] The average longest diameter particle size of the graphite used in the second film layer is relatively smaller, and the ion transport distance of ions in the second film layer is relatively shorter, which is beneficial to further improving the fast charging performance of the battery cell. The average longest diameter particle size of the graphite used in the first film layer is relatively larger, and the compaction density of the first film layer is relatively higher, which is beneficial to taking into account good energy density.

[0123] In some embodiments, the average longest diameter particle size of the graphite in the first negative electrode active material is 7-18 μm. Thus, it is beneficial to play the role of the relatively higher compaction density of the first film layer. The average longest diameter particle size of the graphite in the first negative electrode active material can be 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm or any numerical range composed of any two of the above values.

[0124] In some embodiments, the graphite in the first negative electrode active material includes at least one of artificial graphite and natural graphite.

[0125] Artificial graphite and natural graphite can be distinguished by the SEM cross-sectional view taken by scanning electron microscope (SEM). There are voids between flake structures in the SEM cross-sectional view of natural graphite, and the SEM cross-sectional view of artificial graphite is dense and has no obvious gaps, or can be distinguished by the XRD spectrum obtained by X-ray diffraction method. There are obvious 2H phase and 3R phase in the XRD spectrum of natural graphite, and only 2H phase exists in the XRD spectrum of artificial graphite.

[0126] In some embodiments, the graphite in the first negative electrode active material includes graphite with a secondary particle morphology.

[0127] In this application, the particle with a primary particle morphology refers to a primary particle. A primary particle is the smallest unit of a particle within a certain observation range. There may be any form of defects inside the primary particle, but smaller particles cannot be defined within the primary particle. Primary particles may aggregate under physical actions such as van der Waals force, but this aggregation is easily depolymerized under external forces such as ultrasonic, stirring, and rolling, so that the main composition form of the active material in the film layer is still primary particles.

[0128] In this application, the particle with a secondary particle morphology refers to a secondary particle. A secondary particle is formed by the aggregation of primary particles and is not easily dispersed under external forces such as ultrasonic, but after cutting the cross-section of the secondary particle, it can be seen that the secondary particle is formed by the aggregation of numerous primary particles.

[0129] In some embodiments, the volume-based median diameter Dv50 of graphite in the first negative electrode active material is 7 to 15 μm. The volume-based median diameter Dv50 of graphite in the first negative electrode active material can be 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or a numerical range composed of any two of the above values.

[0130] In this application, the volume-based median diameter Dv50 of a material represents the particle diameter corresponding to when the cumulative volume distribution percentage of the material reaches 50%, and can be measured using instruments and methods known in the art. For example, it can be conveniently measured by referring to GB / T19077-2016 Laser Diffraction Method for Particle Size Distribution and using a laser particle size analyzer. The test instrument can be the Mastersizer 3000 type laser particle size analyzer of Malvern Instruments Limited, UK.

[0131] In some embodiments, the graphite in the first negative electrode active material includes a carbon coating layer, and the thickness of the carbon coating layer is 100 to 500 nm. The carbon coating layer is beneficial to improving the conductivity of graphite. The thickness of the carbon coating layer can be 100 nm, 150 nm, 200 nm, 350 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or a numerical range composed of any two of the above values.

[0132] The thickness of the coating layer can be characterized by transmission electron microscopy (TEM) testing. Observe the negative electrode active material through transmission electron microscopy. According to the difference in lattice fringes, the coating layer coated on the surface of the negative electrode active material can be clearly observed. Randomly select 5 positions in the coating layer for testing, and calculate the average value as the average thickness of the coating layer.

[0133] In some embodiments, the graphitization degree of graphite in the first negative electrode active material is 90 to 94%. A high graphitization degree of the material indicates a small graphite layer spacing, less lattice rotation, less disordered stacking of the layers, ordered arrangement, a high specific capacity of the material, and is beneficial to obtaining a battery cell with a high energy density. The graphitization degree of graphite in the first negative electrode active material can be 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, or a numerical range composed of any two of the above values.

[0134] In this article, the term "graphitization degree" macroscopically characterizes the proportion of the material that reaches a complete graphite crystal structure; microscopically, it refers to the degree to which different transitional carbon structures approach an ideal graphite crystal.

[0135] In this application, the graphitization degree of graphite can be tested by instruments and methods known in the art. For example, it can be tested using an X-ray diffractometer (such as Bruker D8 Discover), and the test can refer to JISK 0131-1996 and JB / T4220-2011 to obtain the average layer spacing d002 of the C(002) crystal plane in the crystal structure of the material, and then the graphitization degree can be calculated according to the formula g=(0.344-d002) / (0.344-0.3354)×100%. In the above formula, d002 is the average layer spacing of the C(002) crystal plane in the crystal structure of the material expressed in nanometers (nm).

[0136] In some embodiments, the first negative electrode active material further includes a silicon material, and the mass ratio of silicon element in the silicon material in the first negative electrode active material is 0.5-10%. The addition of the silicon material is beneficial to further improve the energy density of the battery cell. The mass ratio of silicon element in the silicon material in the first negative electrode active material can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10% or any numerical range composed of any two of the above values.

[0137] In this application, the content of silicon element can be tested by instruments and methods known in the art. For example, the negative electrode active material can be placed in an appropriate digestion solvent, concentrated nitric acid solvent, and digested by the plate digestion method. Finally, it is dissolved in hydrochloric acid to extract the solvent, and then the obtained solution is fixed to an appropriate volume and quantitatively tested using an inductively coupled plasma optical emission spectrometer ICP-OES.

[0138] In some embodiments, the average longest diameter particle size of graphite in the second negative electrode active material is 6-10 μm. Thus, it is beneficial to play the role that the ion transport distance in the second film layer is relatively shorter. The average longest diameter particle size of graphite in the second negative electrode active material can be 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or any numerical range composed of any two of the above values.

[0139] In some embodiments, the graphite in the second negative electrode active material includes at least one of artificial graphite and natural graphite.

[0140] In some embodiments, the graphite in the second negative electrode active material includes a negative electrode active material with a secondary particle morphology.

[0141] In some embodiments, the volume-based median diameter Dv50 of the graphite in the second negative electrode active material is 7 to 15 μm. The volume-based median diameter Dv50 of the graphite in the second negative electrode active material can be 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or a numerical range composed of any two of the above values.

[0142] In some embodiments, the graphite in the second negative electrode active material includes a carbon coating layer, and the thickness of the carbon coating layer is 100 to 500 nm. The carbon coating layer is beneficial to improving the conductivity of the negative electrode active material. The thickness of the carbon coating layer can be 100 nm, 150 nm, 200 nm, 350 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or a numerical range composed of any two of the above values.

[0143] In some embodiments, the graphitization degree of the graphite in the second negative electrode active material is 90 to 94%. A high graphitization degree of the material indicates a small graphite layer spacing, less lattice rotation, less disordered stacking of the layers, more ordered arrangement, a high specific capacity of the material, and is beneficial to obtaining a battery cell with a high energy density. The graphitization degree of the graphite in the second negative electrode active material can be 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, or a numerical range composed of any two of the above values.

[0144] In some embodiments, the second negative electrode active material further includes a silicon material, and the mass ratio of silicon element in the silicon material in the second negative electrode active material is 0.5 to 10%. The addition of the silicon material is beneficial to further improving the energy density of the battery cell. The mass ratio of silicon element in the silicon material in the second negative electrode active material can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or a numerical range composed of any two of the above values.

[0145] In some embodiments, the thickness of the first film layer is 30% to 70% of the total thickness of the negative electrode film layer. Thus, it is beneficial to play the role of the first film layer in taking into account the energy density of the battery cell. The thickness of the first film layer can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% of the total thickness of the negative electrode film layer, or a numerical range composed of any two of the above values.

[0146] In some embodiments, the thickness of the second film layer is 30% to 70% of the total thickness of the negative electrode film layer. Thus, it is beneficial to further improve the fast charging performance of the battery cell. The thickness of the second film layer can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or any numerical range composed of any two of the above values of the total thickness of the negative electrode film layer.

[0147] The thicknesses of the first film layer and the second film layer can be characterized by transmission electron microscopy (TEM) testing. Observe the cross-section of the negative electrode sheet through transmission electron microscopy, and observe the thicknesses of the first film layer and the second film layer according to the difference in the average longest diameter particle size of the active materials in the first film layer and the second film layer. Take the average value after observing, for example, 5 times.

[0148] In some embodiments, under the condition that the state of charge (SOC) of the battery cell is 0%, the tap density of the single-sided negative electrode film layer of the negative electrode sheet is 1.3 to 1.52 g / cc. Thus, a suitable tap density is beneficial to further adjust the porosity of the negative electrode sheet within a suitable range. Under the condition that the state of charge (SOC) of the battery cell is 0%, the tap density of the single-sided negative electrode film layer of the negative electrode sheet can be 1.3 g / cc, 1.31 g / cc, 1.32 g / cc, 1.33 g / cc, 1.34 g / cc, 1.35 g / cc, 1.36 g / cc, 1.37 g / cc, 1.38 g / cc, 1.39 g / cc, 1.4 g / cc, 1.41 g / cc, 1.42 g / cc, 1.43 g / cc, 1.44 g / cc, 1.45 g / cc, 1.46 g / cc, 1.47 g / cc, 1.48 g / cc, 1.49 g / cc, 1.5 g / cc, 1.51 g / cc, 1.52 g / cc or any numerical range composed of any two of the above values.

[0149] In this application, the tap density of the electrode sheet has the meaning well-known in the art and can be tested by methods known in the art. Under the condition that the state of charge (SOC) of the battery cell is 0%, remove the electrode sheet from the lithium-ion battery, take a certain area of the electrode sheet, and measure the mass and thickness of the electrode sheet and the current collector after removing the film layer respectively. According to the following formula, calculate the tap density of the electrode sheet. Tap density of the electrode sheet = (mass of the electrode sheet - mass of the current collector) / [(thickness of the electrode sheet - thickness of the current collector) × area of the electrode sheet].

[0150] In some embodiments, the areal density of the single-sided negative electrode film layer of the negative electrode sheet is 0.12 to 0.18 g / 1540.25 mm 2 . Thus, a suitable areal density is beneficial to further adjust the porosity of the negative electrode sheet within a suitable range. The areal density of the single-sided negative electrode film layer of the negative electrode sheet can be 0.12 g / 1540.25 mm 2, 0.13 g / 1540.25 mm 2 , 0.14 g / 1540.25 mm 2 , 0.15 g / 1540.25 mm 2 , 0.16 g / 1540.25 mm 2 , 0.17 g / 1540.25 mm 2 , 0.18 g / 1540.25 mm 2 or a numerical range composed of any two of the above values.

[0151] In this application, the areal density of the film layer has the meaning well-known in the art and can be measured by methods known in the art. For example, take a single-sided coated and cold-pressed electrode sheet (if it is a double-sided coated electrode sheet, the film layer on one side can be wiped off), punch it into small round pieces with an area of S1, weigh it, and record it as M1. Then wipe off the film layer of the above-mentioned weighed electrode sheet and weigh the weight of the current collector, and record it as M0. The areal density of the single-sided film layer = (M1 - M0) / S1. To ensure the accuracy of the test results, multiple groups (such as 10 groups) of samples to be tested can be tested, and the average value can be calculated as the test result.

[0152] In some embodiments, under the condition that the state of charge SOC of the battery cell is 0%, the compaction density of the single-sided positive electrode film layer of the positive electrode sheet is 2.3 - 2.6 g / cc. Thus, a suitable compaction density is beneficial to further adjust the porosity of the positive electrode sheet within a suitable range. Under the condition that the state of charge SOC of the battery cell is 0%, the compaction density of the single-sided positive electrode film layer of the positive electrode sheet can be 2.3 g / cc, 2.31 g / cc, 2.32 g / cc, 2.33 g / cc, 2.34 g / cc, 2.35 g / cc, 2.36 g / cc, 2.37 g / cc, 2.38 g / cc, 2.39 g / cc, 2.4 g / cc, 2.41 g / cc, 2.42 g / cc, 2.43 g / cc, 2.44 g / cc, 2.45 g / cc, 2.46 g / cc, 2.47 g / cc, 2.48 g / cc, 2.49 g / cc, 2.5 g / cc, 2.51 g / cc, 2.52 g / cc, 2.53 g / cc, 2.54 g / cc, 2.55 g / cc, 2.56 g / cc, 2.57 g / cc, 2.58 g / cc, 2.59 g / cc, 2.6 g / cc or a numerical range composed of any two of the above values.

[0153] In some embodiments, the areal density of the single-sided positive electrode film layer of the positive electrode sheet is 0.25 - 0.33 g / 1540.25 mm 2Thus, a suitable areal density is beneficial to further adjust the porosity of the positive electrode sheet within a suitable range. The areal density of the single-sided positive electrode film layer of the positive electrode sheet can be 0.25 g / 1540.25 mm 2 , 0.26 g / 1540.25 mm 2 , 0.27 g / 1540.25 mm 2 , 0.28 g / 1540.25 mm 2 , 0.29 g / 1540.25 mm 2 , 0.3 g / 1540.25 mm 2 , 0.31 g / 1540.25 mm 2 , 0.32 g / 1540.25 mm 2 , 0.33 g / 1540.25 mm 2 or a numerical range composed of any two of the above values.

[0154] In some embodiments, the lithium-containing phosphate includes lithium iron phosphate, and the lithium iron phosphate includes metal elements, and the metal elements include at least one of aluminum, titanium, and vanadium. Adding the above metal elements to lithium iron phosphate is beneficial to improving the tap density of the positive electrode active material.

[0155] In the present application, the contents of aluminum, titanium, and vanadium in the lithium-containing phosphate can be tested by instruments and methods known in the art. For example, the lithium-containing phosphate can be placed in a proper digestion solvent, concentrated nitric acid solvent, and digested by the plate digestion method. Finally, it is dissolved with hydrochloric acid to extract the solvent, and then the obtained solution is fixed to an appropriate volume and quantitatively tested using an inductively coupled plasma optical emission spectrometer ICP-OES.

[0156] In some embodiments, the metal element includes aluminum, and the mass ratio of aluminum in the lithium-containing phosphate is 0.02% - 0.25%. Thus, it is beneficial to exert the role of aluminum doping in improving the tap density of the positive electrode active material and further improving the cycle performance of the battery cell. The mass ratio of aluminum in the lithium-containing phosphate can be 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25% or a numerical range composed of any two of the above values.

[0157] In some embodiments, the metal element includes titanium, and the mass ratio of titanium in the lithium-containing phosphate is 0.15% to 0.35%. Thus, it is beneficial to play the role of titanium doping in improving the tap density of the cathode active material and further improving the battery capacity. The mass ratio of titanium in the lithium-containing phosphate can be 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.3%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35% or a numerical range composed of any two of the above values.

[0158] In some embodiments, the metal element includes vanadium, and the mass ratio of vanadium in the lithium-containing phosphate is 0.03% to 0.2%. Thus, it is beneficial to play the role of vanadium doping in improving the tap density of the cathode active material and further improving the charge and discharge performance of the battery cell. The mass ratio of vanadium in the lithium-containing phosphate can be 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.2% or a numerical range composed of any two of the above values.

[0159] In some embodiments, the lithium-containing phosphate includes a lithium-containing phosphate with a primary particle morphology and a lithium-containing phosphate with a secondary particle morphology. The mixed use of primary particles and secondary particles is beneficial to further adjust the tap density of the cathode active material.

[0160] In some embodiments, the average longest diameter of the lithium-containing phosphate with a primary particle morphology is 300 to 800 nm. Thus, it is beneficial to shorten the ion transport distance, thereby improving the fast charging performance. The average longest diameter of the lithium-containing phosphate with a primary particle morphology can be 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm or a numerical range composed of any two of the above values.

[0161] In some embodiments, the average longest diameter of the lithium-containing phosphate in the secondary particle morphology is 8 μm to 15 μm. The secondary particles are usually composed of lithium-containing phosphates of primary particles with smaller particle sizes, which is beneficial to shortening the ion transport distance. The average longest diameter of the lithium-containing phosphate in the secondary particle morphology can be 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm or any numerical range composed of any two of the above values.

[0162] In some embodiments, the lithium-containing phosphate in the secondary particle morphology is spherical or quasi-spherical. Spherical refers to a material with a sphericity of 1, and quasi-spherical refers to a material with a sphericity close to 1 but not 1.

[0163] In some embodiments, the volume distribution particle size Dv50 of the lithium-containing phosphate is 5 to 15 μm. The volume distribution particle size Dv50 of the lithium-containing phosphate can be 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm or any numerical range composed of any two of the above values.

[0164] The embodiment of the present application also provides a battery device, including the battery cell provided by the present application.

[0165] As the electrical device, the battery cell, battery module or battery pack can be selected according to its usage requirements.

[0166] Figure 6 is an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the battery cell, a battery pack or battery module can be used.

[0167] Another example of the device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires thinning, and a battery cell can be used as the power source.

[0168] The embodiment of the present application also provides an electrical device, including the battery device provided by the present application.

[0169] Embodiment The embodiments of the present application will be described below. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those where specific technologies or conditions are not indicated in the embodiments, the technologies or conditions described in the literature in the art or according to the product specifications are followed. For reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial purchases.

[0170] Example 1 1. Preparation of the positive electrode sheet The positive electrode sheet includes a positive current collector and a positive electrode film layer. The positive electrode film layer is disposed on both sides of the positive current collector, and the positive current collector is aluminum foil.

[0171] The positive electrode film layer is formed by uniformly coating a positive electrode slurry (solvent: N-methylpyrrolidone NMP) on the surface of the positive current collector and then drying and cold pressing. The positive electrode film layer includes a positive active material, a binder polyvinylidene fluoride (PVDF), and a conductive agent acetylene black with a weight ratio of 90:5:5.

[0172] The positive active material includes lithium iron phosphate particles and metal elements located in the lithium iron phosphate particles. The metal elements include Al, V, and Ti. Among them, the mass ratio of Al, V, and Ti in the lithium iron phosphate particles is 0.15% each.

[0173] The lithium iron phosphate particles include primary particles and secondary particles formed by the aggregation of primary particles. The secondary particles are spherical and quasi-spherical. The average longest diameter of the primary particles is 600 nm, and the average longest diameter of the secondary particles is 10 μm. The volume distribution particle size Dv50 of the lithium iron phosphate particles is 7 μm.

[0174] The areal density of the single-sided positive electrode film layer is 0.28 g / 1540.25 mm 2 .

[0175] Under the condition that the state of charge SOC of the battery cell is 0%, the tap density of the single-sided positive electrode film layer of the positive electrode sheet is 2.4 g / cc.

[0176] The porosity of the positive electrode sheet is 25%.

[0177] 2. Preparation of the negative electrode sheet The negative electrode sheet includes a negative current collector and a negative electrode film layer. The negative electrode film layer is disposed on both sides of the negative current collector, and the negative current collector is copper foil.

[0178] The negative electrode film layer includes a first film layer and a second film layer formed by uniformly coating a negative electrode slurry (solvent: deionized water) on the surface of the negative current collector and then drying and cold pressing.

[0179] The first film layer is disposed on the surface of the negative electrode current collector, and it includes a first negative electrode active material, acetylene black as a conductive agent, styrene-butadiene rubber as a negative electrode binder, and sodium carboxymethyl cellulose as a thickening agent, with a mass ratio of 96.5:0.5:2:1. The negative electrode active material includes graphite and silicon oxide, and the mass proportion of silicon element in the first negative electrode active material is 5%. The graphite includes artificial graphite and a carbon coating layer, the carbon coating layer covers the surface of the artificial graphite, the thickness of the carbon coating layer is 200 nm, the graphitization degree of the graphite is 92%. The average longest diameter particle size of the graphite is 12 μm.

[0180] The second film layer is disposed on the surface of the negative electrode current collector, and it includes a negative electrode active material, acetylene black as a conductive agent, styrene-butadiene rubber as a negative electrode binder, and sodium carboxymethyl cellulose as a thickening agent, with a mass ratio of 96.5:0.5:2:1. The negative electrode active material includes graphite and silicon oxide, and the mass proportion of silicon element in the first negative electrode active material is 5%. The graphite includes artificial graphite and a carbon coating layer, the carbon coating layer covers the surface of the artificial graphite, the thickness of the carbon coating layer is 200 nm, the graphitization degree of the graphite is 92%. The average longest diameter particle size of the graphite is 9 μm.

[0181] The thickness of the first film layer is 50% of the total thickness of the negative electrode film layer, and the thickness of the second film layer is 50% of the total thickness of the negative electrode film layer.

[0182] The areal density of the single-sided negative electrode film layer is 0.13 g / 1540.25 mm 2 。

[0183] Under the condition that the state of charge SOC of the battery cell is 0%, the tap density of the single-sided negative electrode film layer of the negative electrode plate is 1.4 g / cc.

[0184] The porosity of the negative electrode plate is 28%.

[0185] 3. Separator The separator is a 7-μm polyethylene film layer.

[0186] 4. Preparation of electrolyte The electrolyte includes organic solvents, lithium salts and additives. After mixing the components of each organic solvent, lithium salts and additives are added to prepare the electrolyte. The organic solvents include ethyl acrylate, dimethyl carbonate and propylene carbonate. Based on the total mass of the electrolyte, the mass proportion of ethyl acrylate is 20%, the mass proportion of dimethyl carbonate is 20%, and the mass proportion of propylene carbonate is 40%. The lithium salt is lithium hexafluorophosphate, and based on the total mass of the electrolyte, the mass proportion of lithium hexafluorophosphate is 15%. The additives include lithium difluorophosphate and vinylene carbonate. Based on the total mass of the electrolyte, the mass proportion of lithium difluorophosphate is 1%, and the mass proportion of vinylene carbonate is 4%.

[0187] 5. Preparation of battery cell Stack the above-mentioned positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an insulating role, obtaining a stacked electrode assembly. Place the electrode assembly in an outer packaging case, and set a positive terminal and a negative terminal on the outer packaging case. After baking, inject the electrolyte, and through processes such as vacuum packaging, standing, forming, and shaping, obtain a battery cell.

[0188] Examples 2-13 and Comparative Examples 1-6 were used to prepare battery cells by a method similar to that of Example 1. The differences from Example 1 are shown in Table 1. Among them, after the mass ratios of the chain carboxylic acid ester and the chain carbonate are changed, the mass ratio of propylene carbonate is changed accordingly to meet the requirement that the total mass ratio of the total organic solvents is 80%, the mass ratio of lithium hexafluorophosphate is 15%, the mass ratio of lithium difluorophosphate is 1%, and the mass ratio of vinylene carbonate is 4% based on the total mass of the electrolyte.

[0189] Performance test: (1) Battery fast charging performance test: Charge and discharge the batteries of the above examples and comparative examples for the first time at a current of 1C. Specifically, at 25 °C, charge the battery at a constant current of 1C rate until the voltage reaches 3.65V, then charge at a constant voltage until the current ≤ 0.05C, stand for 5 minutes, and then discharge at a constant current of 0.33C rate until the voltage reaches 2.5V. Record its actual capacity as C0. Then charge the battery at a constant current of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0, 5C0 to the full battery charging cut-off voltage of 3.65V, and record the SOC state corresponding to the battery when it is charged to 3.65V at each rate. After each charge is completed, discharge at 1C0 to the full battery discharge cut-off voltage of 2.1V, draw a curve graph of different SOC - charging rates, and read the charging rates corresponding to 10% SOC, 20% SOC... 80% SOC from this curve graph, and record them as C(10%SOC), C(20%SOC), C(30%SOC), C(40%SOC), C(50%SOC), C(60%SOC), C(70%SOC), C(80%SOC) respectively, to obtain the maximum charging rate under the corresponding state of charge, that is, the fast charging window. The charging time from 10 - 80% is 6 / C(10%SOC)+6 / C(20%SOC)+ 6 / C(30%SOC) +6 / C(40%SOC) +6 / C(50%SOC) +6 / C(60%SOC) +6 / C(70%SOC)+6 / C(80%SOC), with the unit of minutes.

[0190] (2) Cycle performance test: At 25°C, the battery cell is charged at a constant current of 1C to a charging cut-off voltage of 3.65V, then charged at a constant current of 0.05C to a charging cut-off voltage of 3.65V, and left standing for 30 minutes; it is discharged at a constant current of 1C to 2.5V and left standing for 30 minutes. This is one charge-discharge cycle. Repeat the above charge-discharge cycle steps until the cycle capacity retention rate (i.e., Cn / C0×100%) reaches 80%, and record the number of cycles.

[0191] (3)Energy density test: At 25°C, the assembled battery is fully charged at a rate of 0.5C and fully discharged at a rate of 0.5C, and the actual discharge energy at this time is recorded; at 25°C, the battery is weighed using an electronic balance; the ratio of the actual discharge energy of the battery at 0.5C to the battery weight is the energy density of the battery.

[0192]

[0193] In Comparative Example 1, the mass content of the chain carboxylic acid ester is relatively low, and the fast charging performance cannot be effectively improved.

[0194] In Comparative Example 2, the mass content of the chain carboxylic acid ester is relatively high, and the fast charging performance is good, but the cycle performance drops sharply.

[0195] In Comparative Example 3 and Comparative Example 5, the porosity of the electrode sheet is relatively low, which can improve the energy density of the battery, but the low porosity results in a large internal resistance, which is not conducive to fast charging, the charging time is too long, and the low porosity is prone to incomplete reaction and the risk of lithium deposition, resulting in poor cycle performance.

[0196] In Comparative Example 4 and Comparative Example 6, the porosity of the electrode sheet is relatively high, which is conducive to the movement of ions, the improvement of fast charging and cycle performance, but the energy density of the battery drops too much.

[0197] In the embodiments of the present application, by adjusting the mass ratio of the chain carboxylic acid ester in the electrolyte to 8.5% - 40% and the mass ratio of the chain carbonate in the electrolyte to 8.5% - 50%, and at the same time adjusting the porosity of the positive electrode sheet to 20 - 30% and the porosity of the negative electrode sheet to 24 - 33%. It can not only reduce the decomposition of the electrolyte during the cycle, improve the cycle performance of the battery, but also improve the wetting ability of the electrolyte to the electrode sheet, shorten the transmission distance of ions in the electrode material, and improve the fast charging performance of the battery cell. Thus, it takes into account the good fast charging performance and cycle performance of the battery, and can also ensure the high energy density of the battery.

[0198] As can be seen from Examples 1 - 3, as the porosity of the positive electrode sheet increases, the charging time decreases, the number of cycle increases, and the energy density decreases. As can be seen from Examples 1, 4 - 5, as the porosity of the negative electrode sheet increases, the charging time decreases, the number of cycle increases, and the energy density decreases.

[0199] As can be seen from Examples 1, 6 - 7, as the mass ratio of the chain carboxylic acid ester increases, the charging time decreases and the number of cycles decreases.

[0200] As can be seen from Examples 1, 10 - 13, by using different chain carboxylic acid esters and different chain carbonates, it is also possible to achieve good fast - charging performance, cycling performance, and high energy density.

[0201] In Examples 14 - 17, battery monomers were prepared using a method similar to that of Example 1. The differences from Example 1 are shown in Table 2.

[0202] Table 2

[0203] As can be seen from Examples 1 and 14, when the average longest diameter of graphite in the two film layers of the negative electrode tab is the same, although the number of cycles and energy density increase to a certain extent, the fast - charging performance deteriorates. In Example 1, the average longest diameters of graphite in the two film layers are different. After particle size grading, while achieving better fast - charging performance, good cycling performance and energy density are also taken into account. The average longest diameter of graphite used in the second film layer of Example 1 is relatively smaller, and the ion transport distance in the second film layer is relatively shorter, which is beneficial to further improving the fast - charging performance of the battery monomer. And the average longest diameter of graphite used in the first film layer is relatively larger, and the compaction density of the first film layer is relatively higher, which is beneficial to taking into account good energy density.

[0204] As can be seen from Examples 1 and 15, by increasing the average longest diameter of graphite in the first film layer, the compaction density of the first film layer increases, the energy density is improved, but the fast - charging performance and cycling performance decline.

[0205] As can be seen from Examples 1 and 16, by reducing the average longest diameter of graphite in the second film layer, the solid - phase ion transport distance is shortened, the fast - charging performance is improved, but the cycling performance is reduced.

[0206] As can be seen from Examples 1 and 17, by reducing the average longest diameter of primary particles and secondary particles in the positive electrode tab, it is beneficial to improve the fast - charging performance, but the cycling performance is reduced.

[0207] It should be noted that the present application is not limited to the above - mentioned embodiments. The above - mentioned embodiments are only examples, and embodiments with the same structure in essence as the technical idea and achieving the same effect within the technical scope of the present application are all included in the technical scope of the present application. In addition, within the scope not departing from the gist of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A battery cell, characterized in that: The invention comprises an electrode assembly and an electrolyte; wherein the electrode assembly comprises a positive electrode sheet and a negative electrode sheet, The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, the positive electrode active material includes a lithium-containing phosphate, and the porosity of the positive electrode sheet is 20-30%; The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes graphite, and the porosity of the negative electrode sheet is 24-33%; The electrolyte includes an electrolyte salt and a solvent, the solvent includes a chain carboxylate and a chain carbonate, the chain carboxylate accounts for 8.5% to 40% by mass in the electrolyte, and the chain carbonate accounts for 8.5% to 50% by mass in the electrolyte.

2. The battery cell according to claim 1, characterized in that: The porosity of the positive electrode sheet is 25-30%.

3. The battery cell according to claim 1 or 2, characterized in that: The porosity of the negative electrode plate is 25-30%.

4. The battery cell according to claim 1, characterized in that: The mass proportion of the chain carboxylic acid ester in the electrolyte is 10% to 25.5%.

5. The battery cell according to claim 1, characterized in that: The mass proportion of the linear carbonate in the electrolyte is 10% to 42.5%.

6. The battery cell according to claim 1, characterized in that: The chain carboxylic acid ester includes the chain carboxylic acid ester described in Formula I, Formula I Among them, R1 includes any one of an alkyl group having 1 to 3 carbon atoms and an alkenyl group having 2 to 4 carbon atoms; R2 includes an alkyl group having 1 to 3 carbon atoms.

7. The battery cell according to claim 1, characterized in that: The chain carboxylic acid ester includes at least one of ethyl acrylate, propyl acetate and ethyl propionate.

8. The battery cell according to claim 1, characterized in that: The chain carbonate includes the chain carbonate described in formula II, Formula II Wherein, R3 and R4 independently include an alkyl group having 1 to 3 carbon atoms.

9. The battery cell according to claim 1, characterized in that: The chain carbonate includes at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

10. The battery cell according to claim 1, characterized in that: The solvent also includes cyclic carbonates.

11. The battery cell according to claim 10, characterized in that: The cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate.

12. The battery cell according to claim 10 or 11, characterized in that: The mass proportion of the cyclic carbonate in the electrolyte is 10% to 51.5%.

13. The battery cell according to claim 1, characterized in that: The electrolyte also includes a first additive, which includes at least one of lithium difluorophosphate and lithium fluorosulfonate.

14. The battery cell according to claim 13, characterized in that: The mass proportion of the first additive in the electrolyte is 0.02% to 2%.

15. The battery cell according to claim 1, characterized in that: The electrolyte also includes a second additive, which includes at least one of vinylene carbonate, fluoroethylene carbonate, and 1,3-propane sultone.

16. The battery cell according to claim 15, characterized in that: The mass proportion of the second additive in the electrolyte is 3% to 7%.

17. The battery cell according to claim 1, characterized in that: The ionic conductivity of the electrolyte at 25° C. is 11-13 ms / cm.

18. The battery cell according to claim 1, characterized in that: The negative electrode film layer comprises a first film layer and a second film layer, wherein the first film layer is arranged on at least one surface of the negative electrode current collector, and the second film layer is arranged on a surface of the first film layer that is opposite to the current collector; The first film layer contains a first negative electrode active material; the second film layer contains a second negative electrode active material; the longest average particle size of graphite in the second negative electrode active material is smaller than the longest average particle size of graphite in the first negative electrode active material.

19. The battery cell according to claim 18, characterized in that: The longest average particle size of graphite in the first negative electrode active material is 7-18 μm.

20. The battery cell according to claim 18 or 19, characterized in that: The graphite in the first negative electrode active material includes at least one of artificial graphite and natural graphite.

21. The battery cell according to claim 18, characterized in that: The graphite in the first negative electrode active material includes graphite in a secondary particle morphology.

22. The battery cell according to claim 18, characterized in that: The volume distribution particle size Dv50 of graphite in the first negative electrode active material is 7-15 μm.

23. The battery cell according to claim 18, characterized in that: The graphite in the first negative electrode active material includes a carbon coating layer, and the thickness of the carbon coating layer is 100-500 nm.

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

25. The battery cell according to claim 18, characterized in that: The first negative electrode active material further includes a silicon material, and the mass proportion of silicon element in the silicon material in the first negative electrode active material is 0.5-10%.

26. The battery cell according to claim 18, characterized in that: The longest average particle size of graphite in the second negative electrode active material is 6-10 μm.

27. The battery cell according to claim 18, characterized in that: The graphite in the second negative electrode active material includes at least one of artificial graphite and natural graphite.

28. The battery cell according to claim 18, characterized in that: The graphite in the second negative electrode active material includes a negative electrode active material in the form of secondary particles.

29. The battery cell according to claim 18, characterized in that: The volume distribution particle size Dv50 of graphite in the second negative electrode active material is 7-15 μm.

30. The battery cell according to claim 18, characterized in that The graphite in the second negative electrode active material includes a carbon coating layer, and the thickness of the carbon coating layer is 100-500 nm.

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

32. The battery cell according to claim 18, characterized in that The second negative electrode active material further includes a silicon material, and the mass proportion of silicon element in the silicon material in the second negative electrode active material is 0.5-10%.

33. The battery cell according to claim 18, characterized in that: The thickness of the first film layer is 30% to 70% of the total thickness of the negative electrode film layer.

34. The battery cell according to claim 18, characterized in that The thickness of the second film layer is 30% to 70% of the total thickness of the negative electrode film layer.

35. The battery cell according to claim 1, characterized in that When the state of charge (SOC) of the battery cell is 0%, the compaction density of the negative electrode film layer on a single side of the negative electrode plate is 1.3-1.52 g / cc.

36. The battery cell according to claim 1, characterized in that The surface density of the negative electrode film layer on a single side of the negative electrode plate is 0.12-0.18 g / 1540.25 mm 2 .

37. The battery cell according to claim 1, characterized in that When the state of charge (SOC) of the battery cell is 0%, the compaction density of the single-sided positive electrode film layer of the positive electrode sheet is 2.3-2.6 g / cc.

38. The battery cell according to claim 1, characterized in that The surface density of the single-sided positive electrode film layer of the positive electrode plate is 0.25-0.33 g / 1540.25 mm 2 .

39. The battery cell according to claim 1, characterized in that: The lithium-containing phosphate includes lithium iron phosphate, the lithium iron phosphate includes a metal element, and the metal element includes at least one of aluminum, titanium, and vanadium.

40. The battery cell according to claim 39, characterized in that The metal element includes aluminum, and the mass proportion of the aluminum in the lithium-containing phosphate is 0.02% to 0.25%.

41. The battery cell according to claim 39 or 40, characterized in that: The metal element includes titanium, and the mass proportion of the titanium in the lithium-containing phosphate is 0.15% to 0.35%.

42. The battery cell according to claim 39, characterized in that The metal element includes vanadium, and the mass proportion of the vanadium in the lithium-containing phosphate is 0.03% to 0.2%.

43. The battery cell according to claim 1, characterized in that The lithium-containing phosphate includes lithium-containing phosphate in the form of primary particles and lithium-containing phosphate in the form of secondary particles.

44. The battery cell according to claim 43, characterized in that The longest average particle size of the lithium-containing phosphate in the primary particle morphology is 300-800 nm.

45. The battery cell according to claim 43 or 44, characterized in that: The longest average particle size of the lithium-containing phosphate in the secondary particle morphology is 8 μm to 15 μm.

46. ​​The battery cell according to claim 43, characterized in that The lithium-containing phosphate in the secondary particle morphology is spherical or quasi-spherical.

47. The battery cell according to claim 1, characterized in that The volume distribution particle size Dv50 of the lithium-containing phosphate is 5-15 μm.

48. A battery device, characterized in that: Comprising a battery cell as claimed in any one of claims 1 to 47.

49. An electrical device, characterized in that: Comprising a battery device as claimed in claim 48.

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