Battery cell, battery device, and electric device

Abstract

The invention provides a battery monomer, a battery device and a power utilization device. The battery monomer comprises a positive pole piece, an isolating membrane, a negative pole piece and electrolyte, and the positive pole piece, the isolating membrane and the negative pole piece are arranged in a laminated manner; the positive pole piece comprises a positive current collector and a positive active layer arranged on at least one side of the positive current collector, the negative pole piece comprises a negative current collector and a negative active layer arranged on at least one side of the negative current collector, and the positive active layer comprises lithium iron phosphate primary particles; the isolating membrane comprises a base membrane and a bonding layer, the bonding layer is of a porous continuous structure, and the bonding layer is at least arranged on one side, facing the positive electrode active layer, of the base membrane; the electrolyte comprises a first solvent, and the first solvent comprises one or more of dimethyl carbonate and linear carboxylic ester. The battery monomer has relatively good cycle performance.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular, to a battery cell, a battery device, and an electrical device. Background Art

[0002] The battery core of a stacked battery is composed of an alternating stack of a positive electrode sheet and a negative electrode sheet. Compared with a wound battery, a stacked battery can achieve a higher energy density. The reasons are as follows: (1) There are no corners in the battery core of a stacked battery, and the space utilization rate inside the battery is higher; (2) Limited by the current winding process, the unfolded length of a wound battery is usually less than 300 mm, while the length of the battery core of a stacked battery is not limited by this.

[0003] However, compared with a wound battery, the binding effect of a stacked battery on materials is smaller, making it easy for the active material layer and the separator to have poor contact. Especially when lithium iron phosphate is used as the positive electrode active material, the problem of electrode sheet misalignment is very likely to occur, reducing the cycle performance of the stacked battery. Summary of the Invention

[0004] Based on this, the present application provides a battery cell, a battery device, and an electrical device with good cycle performance.

[0005] In a first aspect of the present application, there is provided a battery cell, including a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. The positive electrode sheet, the separator, and the negative electrode sheet are stacked; the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer provided on at least one side of the positive electrode current collector. The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer provided on at least one side of the negative electrode current collector. The positive electrode active layer contains lithium iron phosphate primary particles; the separator includes a base film and a bonding layer. The bonding layer is a porous continuous structure, and the bonding layer is provided at least on one side of the base film facing the positive electrode active layer; the electrolyte includes a first solvent, and the first solvent includes one or more of dimethyl carbonate and linear carboxylic acid esters. The structural general formula of the linear carboxylic acid ester is R1-COO-R2, and R1 and R2 each independently include a C1-C5 alkyl group or a halogenated C1-C5 alkyl group.

[0006] As described above, when the lithium iron phosphate primary particles are used as the positive electrode active material and the laminated battery cell in the present application, the energy density and cycle performance of the battery are improved. At the same time, a separator including a porous continuous structure adhesive layer is used. The presence of this adhesive layer can play a good bonding role, making the connection between the separator and the positive electrode active layer containing lithium iron phosphate primary particles tight. Furthermore, it can withstand the stress changes generated by the lithium iron phosphate primary particles, enhance the bonding stability between the positive electrode active layer and the separator, ensure good contact between the two, and thus reduce the occurrence of pole piece misalignment, effectively improving the cycle performance of the laminated battery. At the same time, the introduction of this adhesive layer will reduce the ion transport performance of the separator. Therefore, a suitable electrolyte solvent needs to be used to effectively improve the wettability of the electrolyte to the introduced separator, reduce the internal resistance of the battery, and enhance the ion transport performance, thereby comprehensively improving the cycle performance of the battery cell.

[0007] In some embodiments, the thickness of the adhesive layer on one side is 0.5 μm to 2.5 μm. By reasonably controlling the thickness of the adhesive layer, on the one hand, it can better resist the stress of the lithium iron phosphate primary particles and enhance the stability of the battery structure. On the other hand, a higher energy density and a lower internal resistance of the battery can be obtained, thereby comprehensively improving the cycle performance.

[0008] In some embodiments, the porosity of the separator is 40% to 60%. By reasonably controlling the porosity of the separator, on the one hand, better adhesion can be obtained and the stability of the battery structure can be enhanced. On the other hand, a higher ion transport efficiency can be obtained, the internal resistance of the battery can be reduced, and thus the cycle performance can be comprehensively improved.

[0009] In some embodiments, the adhesive layer includes one or more of polyvinylidene fluoride and polyvinylidene fluoride - hexafluoropropylene copolymer.

[0010] In some embodiments, the separator further includes an inorganic ceramic layer, and the inorganic ceramic layer is disposed between the base film and the adhesive layer. By setting the inorganic ceramic layer between the adhesive layer and the base film, its good hydrophilic property can improve the wettability of the electrolyte to the separator, thereby reducing the internal resistance of the battery and improving the cycle performance of the battery.

[0011] In some embodiments, the inorganic ceramic layer includes one or more of aluminum oxide, silicon oxide, and boehmite.

[0012] In some of these embodiments, the average particle size of the lithium iron phosphate primary particles is 100 nm to 800 nm. Using lithium iron phosphate primary particles with a suitable particle size can, on the one hand, shorten the lithium ion diffusion path, and on the other hand, reduce the expansion and contraction of the particle volume caused by the insertion and extraction of lithium ions. Combined with the binding effect of the bonding layer, the structural stability of the laminated sheet is improved, and thus the cycle performance is comprehensively improved. Further, the average particle size of the lithium iron phosphate primary particles is 500 nm to 800 nm.

[0013] In some of these embodiments, the lithium iron phosphate primary particles comprise a doped or undoped lithium iron phosphate material, and the doped elements include one or more of Al, V, and Ti.

[0014] In some of these embodiments, the conductivity of the electrolyte at room temperature is 9.5 ms / cm to 18 ms / cm. The electrolyte used has a high conductivity, which can further reduce the internal resistance of the battery and improve the cycle performance of the battery.

[0015] In some of these embodiments, based on the mass of the electrolyte, the mass percentage of the first solvent is 10% to 60%.

[0016] In some of these embodiments, the electrolyte further comprises a lithium salt, the lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is (1.2 to 3):1. Using lithium bis(fluorosulfonyl)imide in combination with lithium hexafluorophosphate and reasonably controlling the mass ratio of the two can, while reducing costs, better improve the conductivity of the electrolyte, thereby reducing the internal resistance of the separator film introducing the bonding layer and improving the cycle performance of the battery.

[0017] In some of these embodiments, based on the mass of the electrolyte, the mass percentage of the lithium salt is 12% to 18%.

[0018] In some of these embodiments, the electrolyte further comprises an additive, and the additive includes one or more of vinylene carbonate, fluoroethylene carbonate, and 1,3 - propane sultone.

[0019] In some of these embodiments, based on the mass of the electrolyte, the mass percentage of the additive is 0.1% to 5%.

[0020] In some of these embodiments, the negative electrode active layer includes a first active layer and a second active layer. The first active layer is disposed between the negative electrode current collector and the second active layer. The first active layer includes first graphite, and the second active layer includes second graphite. The average value of the longest diameter of the first graphite is 7 μm to 18 μm, and the average value of the longest diameter of the second graphite is 6 μm to 10 μm, and the average value of the longest diameter of the first graphite is greater than the average value of the longest diameter of the second graphite. By adopting a double-layer active layer design for the negative electrode and reasonably controlling the particle sizes of the two layers of graphite, among which the particle size of the first graphite is larger, which can improve the compaction density of the negative electrode sheet, and the particle size of the second graphite is smaller, which can shorten the lithium ion transmission path and improve the cycling performance.

[0021] In some of these embodiments, each of the first graphite and the second graphite independently includes a graphite particle body and an amorphous carbon coating layer disposed on the surface of the graphite particle body, and the thickness of the amorphous carbon coating layer is 100 nm to 500 nm; and / or,

[0022] The volume average particle size Dv50 of each of the first graphite and the second graphite is independently 7 μm to 20 μm; and / or,

[0023] The graphitization degree of each of the first graphite and the second graphite is independently 90% to 94%.

[0024] In addition, by reasonably controlling the coating amount per unit area, compaction density, etc. of the positive electrode active layer in the positive electrode sheet and / or the negative electrode active layer in the negative electrode sheet, while introducing the binder layer, the battery cell can have good ion transmission efficiency, achieve good cycling performance, and at the same time obtain a high energy density.

[0025] In some of these embodiments, the coating amount per unit area on one side of the positive electrode active layer is 0.3 g / 1540.25 mm 2 ~0.45 g / 1540.25 mm 2 ; and / or,

[0026] The coating amount per unit area on one side of the negative electrode active layer is 0.13 g / 1540.25 mm 2 ~0.22 g / 1540.25 mm 2 .

[0027] In some of these embodiments, the compaction density of the positive electrode active layer is 2.3 g / cm 3 ~2.65 g / cm 3 ; and / or,

[0028] The compaction density of the negative electrode active layer is 1.3 g / cm 3~1.52 g / cm 3 。

[0029] In some of these embodiments, the positive electrode tab includes a bottom-coated carbon layer, and the thickness of the bottom-coated carbon layer is 0.5 μm to 3 μm. By providing the bottom-coated carbon layer in the positive electrode tab, the conductivity of the tab can be improved, the increase in the internal resistance of the battery after introducing the binder layer can be reduced, and the cycling performance can be improved.

[0030] In some of these embodiments, the thickness ratio of the positive electrode active layer on one side to the positive electrode current collector is (10~20):1; and / or,

[0031] The thickness ratio of the negative electrode active layer on one side to the negative electrode current collector is (15~25):1.

[0032] In some of these embodiments, the positive electrode tab includes a positive electrode main body portion and a positive electrode tab portion connected to the positive electrode main body portion, and the ratio of the long side dimension to the short side dimension of the positive electrode main body portion is (3~8):1.

[0033] In some of these embodiments, the battery cell further includes a soft package shell, and the positive electrode tab, the separator, the negative electrode tab, and the electrolyte are disposed inside the soft package shell.

[0034] In a second aspect of the present application, there is provided a battery device including the battery cell according to the first aspect.

[0035] In a third aspect of the present application, there is provided an electrical device including the battery cell according to the first aspect or the battery device according to the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] To better describe and illustrate the embodiments or examples provided in the present application, one or more drawings may be referred to. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, and the currently understood best mode of these applications. Moreover, in all the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0037] Figure 1 is a schematic structural diagram of a separator constructed with an oil-based binder in a battery cell according to an embodiment of the present application;

[0038] Figure 2 is a schematic structural diagram of a separator constructed with an aqueous binder in a conventional method;

[0039] Figure 3 is a schematic structural diagram of a positive electrode tab in a battery cell according to an embodiment of the present application;

[0040] Figure 4 Schematic diagram of the structure of the negative electrode plate in a battery cell according to an embodiment of the present application;

[0041] Figure 5 Schematic diagram of an electrical device powered by a secondary battery according to an embodiment of the present application. Specific embodiments

[0042] To facilitate the understanding of the present application, the present application will be described more comprehensively below with reference to the relevant drawings. Preferred embodiments of the present application are shown in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used in the description of the present application in this specification are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0044] The "range" disclosed in the present application can be 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 boundary of a particular range. The range defined in this way can include or not include the end values, and any one of the end values can be independently included or not included, 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 also listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise specified, the numerical range "a~b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between "0~5" have been fully listed herein, and "0~5" is only an abbreviated representation of these numerical combinations. In addition, when a certain parameter is expressed as an integer ≥2, it is equivalent to listing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a certain parameter is expressed as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0045] In this application, the terms "a plurality of", "multiple types", etc., unless otherwise specified, mean greater than or equal to 2 in quantity. For example, "one or more types" means one type or two or more types.

[0046] If there is no special explanation, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0047] The mention of "embodiment" in this text means that the specific features, structures or characteristics described in connection with the embodiment can be included in at least one embodiment or implementation manner of this application. The appearance of this phrase at various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments. The understanding of "implementation manner" mentioned in this text is similar.

[0048] Those skilled in the art can understand that in the methods of each embodiment or implementation manner, the writing order of each step does not mean a strict execution order that constitutes any limitation on the implementation process, and the detailed execution order of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of this application can be carried out in sequence or randomly, and 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.

[0049] In this application, unless otherwise stated, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0050] In this application, "optionally", "optional", "option" mean that it can be either present or absent, that is, it refers to any one of the two parallel options of "present" or "absent". If "optional" appears multiple times in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction relationship, each "optional" is independent of each other.

[0051] Lithium iron phosphate usually exists in the form of primary particles distributed in the positive electrode active layer, with a high degree of particle packing, so it has a high energy density. However, compared with the secondary particle lithium iron phosphate, the stress generated by the primary particles of lithium iron phosphate during the cycling process will concentrate at the particle interface. And compared with secondary particles, the primary particles lack an internal buffer space (secondary particles can release this stress through internal pores and grain boundaries), and the stress generated by the primary particles is more likely to be conducted to the entire positive electrode active material layer. Therefore, during the stress release process, it is easy to cause poor contact between the positive electrode active layer and the separator. At the same time, compared with wound battery cells, the stacked battery cells have no corner areas, which can effectively improve the space utilization rate of the battery, thereby increasing the volume energy density; and the absence of corner areas helps to reduce the stress concentration phenomenon, reduce the probability of film layer peeling, and reduce the risk of battery capacity degradation. However, compared with wound batteries, the binding effect of the stacked battery cells on the contact between the positive electrode active layer and the separator is smaller, specifically manifested as follows: the wound structure formed by the winding process makes the contact between the positive electrode active layer and the separator tight, with a strong circumferential binding force; while the electrode sheets in the stacked battery are combined in a planar stacking manner, and are mainly fixed by adhesives between layers, and the binding force between the positive electrode active layer and the separator is weak. Therefore, when applying the primary particles of lithium iron phosphate to stacked battery cells, the problem of electrode sheet misalignment is very likely to occur, reducing the cycling performance of the stacked battery cells.

[0052] Based on this, an embodiment of the present application provides a battery cell, including a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte. The positive electrode sheet, the separator and the negative electrode sheet are stacked; the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer provided on at least one side of the positive electrode current collector, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer provided on at least one side of the negative electrode current collector, the positive electrode sheet includes a positive electrode active layer, and the positive electrode active layer contains primary particles of lithium iron phosphate; the separator includes a base film and a bonding layer, the bonding layer is a porous continuous structure, and the bonding layer is provided at least on one side of the base film facing the positive electrode active layer; the electrolyte includes a first solvent, the first solvent includes one or more of dimethyl carbonate and linear carboxylic acid esters, and the structural general formula of the linear carboxylic acid ester is R1-COO-R2, and R1 and R2 each independently include a C1-C5 alkyl group or a halogenated C1-C5 alkyl group.

[0053] As mentioned above, the present application uses lithium iron phosphate primary particles as the positive electrode active material and the laminated battery core to improve the energy density and cycle performance of the battery, and at the same time, cooperates with the use of a separator including a porous continuous structure bonding layer. The presence of the bonding layer can play a good bonding role, so that the separator and the positive electrode active layer containing lithium iron phosphate primary particles are tightly connected, and then can withstand the stress changes generated by the lithium iron phosphate primary particles, improve the bonding stability between the positive electrode active layer and the separator, so that the two are in good contact, thereby reducing the occurrence of pole piece misalignment, and effectively improving the cycle performance of the laminated battery. At the same time, the introduction of the bonding layer will reduce the ion transmission performance of the separator, so it is necessary to cooperate with the use of one or more of dimethyl carbonate and linear carboxylic acid ester as a solvent in the electrolyte. The solvent has a lower viscosity and is conducive to improving the conductivity of the electrolyte, improving the wettability of the electrolyte to the introduced separator, reducing the internal resistance of the battery, and improving the ion transmission performance, thereby comprehensively improving the cycle performance of the battery cell.

[0054] In some of the embodiments, the battery cell also has a lower self-discharge rate and better storage performance.

[0055] It can be understood that the above-mentioned battery cells are laminated battery cells.

[0056] It is understood that "primary particles" are the basic unit of particles in lithium iron phosphate. It is understood that there are primary particles in lithium iron phosphate. In the positive electrode active material, the primary particles can be in a non-agglomerated state or can be formed into agglomerates by multiple primary particles. The non-agglomerated primary particles can be called "non-agglomerated primary particles", and the agglomerates formed by multiple primary particles can be called "secondary particles".

[0057] The presence and particle size of lithium iron phosphate primary particles can be observed by conventional methods in the art. For example, a battery that has been fully discharged (discharged to the lower limit cut-off voltage so that the battery is charged to about 0% SOC) is disassembled, and a positive electrode sheet including a positive electrode active layer is obtained as a sample to be tested. The sample to be tested is placed on a sample table, and then the sample table is placed in a vacuum sample chamber and fixed. The power of an argon ion cross-section polisher (for example, the IB-09010CP argon ion cross-section polisher of JEOL, Japan) is turned on and vacuumed (for example, to 10 -7 Pa), set the argon flow rate (e.g. 0.12MPa) and polishing time (e.g. 90min), adjust the sample stage to the swing mode and start polishing. After polishing, observe the cross section of the sample under the scanning electron microscope, and you can see the primary lithium iron phosphate particles. The particle size of the primary lithium iron phosphate particles can be measured with the help of the measurement software provided by the scanning electron microscope.

[0058] It can be understood that "the adhesive layer is disposed at least on one side of the base film facing the positive electrode active layer" means that the adhesive layer can be disposed only on one side of the base film facing the positive electrode active layer, or can be disposed on both sides of the base film, that is, the adhesive layer is also disposed on the side of the base film facing the negative electrode active layer.

[0059] It should be noted that the adhesive layer used in this application is a continuous layer structure, mainly constructed by an oil-based binder, that is, an organic solvent is used to disperse the binder and then coated into a film, and the formed adhesive layer is a continuous structure, which is different from the traditional water-based binder. The traditional water-based binder mainly disperses the binder with water and then coats it into a film, and the formed adhesive layer is an island structure. On the one hand, this island structure adhesive layer is beneficial to provide gaps for the expansion of the battery cell, and on the other hand, it is convenient for manufacturing, but the bonding area is small and the bonding force is weak. This problem is particularly obvious in laminated batteries. In this application, a porous adhesive layer with a continuous layer structure is adopted for the battery monomer. By improving the bonding force, the bonding stability between the positive electrode active layer and the separator is improved, so that the two are in good contact, and further the situation of pole piece misalignment is reduced, and the cycle performance of the battery monomer is improved.

[0060] Without limitation, the separator structure constructed by the oil-based binder can be as Figure 1 shown, including a base film 101 and an adhesive layer 103 disposed on at least one side of the base film 101. The adhesive layer 103 is a continuous layer with a porous structure, and the separator is connected to the positive electrode plate and / or the negative electrode plate through the adhesive layer 103. Further, the separator further includes a ceramic coating 102, and the ceramic coating 102 is disposed between the base film 101 and the adhesive layer 103. The separator structure constructed by the water-based binder can be as Figure 2 shown, and its base film and ceramic coating can be similar to Figure 1 , but its adhesive layer 103 is an island structure, and the separator is connected to the positive electrode plate and / or the negative electrode plate through the adhesive layer 103.

[0061] It can be understood that the continuous adhesive layer may break and deform into a block structure during the manufacturing or cycling process of the pole piece due to contact or extrusion stress with the positive electrode plate or the negative electrode plate. The continuous structure referred to in this application means that at the microscopic level, such as observed under a scanning electron microscope or an optical microscope, the adhesive layer of the separator is continuous. In order to reflect the true morphology of the separator, during the sampling process, it is preferably sampled in the area where the adhesive layer of the separator in the battery has not bonded with the positive electrode plate or the negative electrode plate. As an example, sampling is performed at the position of the separator beyond the positive electrode plate and the negative electrode plate; or sampling is performed on the separator near the surface of the electrode assembly. The bonding between this separator sampling area and the positive electrode plate or the negative electrode plate is less, and it can better reflect the true state of the separator.

[0062] Without limitation, the morphology of the adhesive layer can be observed under a scanning electron microscope (SEM), specifically as follows:

[0063] Disassemble a battery that has been fully discharged (discharged to the lower cut-off voltage so that the charged state of the battery is approximately 0% SOC), select the separator in the middle of the battery, and cut a 5 mm × 5 mm separator with scissors as the test sample. Place the sample in absolute ethanol and gently shake it. After removing the sample, dry it to remove the residual electrolyte and electrode debris on the surface of the sample. Place the dried separator sample on a glass slide and observe the morphology of the adhesive layer on the separator through a scanning electron microscope.

[0064] Without limitation, the method for preparing the separator including the adhesive layer includes the following steps:

[0065] Dissolve the binder and the pore former in an organic solvent to obtain a binder solution;

[0066] Apply the binder solution on the porous base film, and remove the pore former after drying to form the adhesive layer on the porous base film.

[0067] Further, the linear carboxylic acid ester includes one or more of ethyl acetate, methyl acetate, methyl propionate, propyl acetate, ethyl formate, and isopropyl formate.

[0068] In some embodiments, the thickness of the adhesive layer on one side is 0.5 μm to 2.5 μm. By reasonably controlling the thickness of the adhesive layer, on the one hand, it can better resist the stress of the primary lithium iron phosphate particles and improve the stability of the battery structure. On the other hand, it can obtain a higher energy density and a lower internal resistance of the battery, thereby comprehensively improving the cycle performance. Specifically, the thickness of the adhesive layer includes but is not limited to: 0.5 μm, 0.7 μm, 1 μm, 1.2 μm, 1.5 μm, 1.7 μm, 2 μm, 2.3 μm, 2.5 μm, or the range between any two of the foregoing. Further, the thickness of the adhesive layer is 1 μm to 2 μm.

[0069] The thickness of the adhesive layer in the separator can be measured by conventional methods in the art. Exemplarily, disassemble a battery that has been fully discharged (discharged to the lower cut-off voltage so that the charged state of the battery is approximately 0% SOC), obtain the separator including the adhesive layer as the sample to be tested, paste the sample to be tested on the sample stage, then place the sample stage in the vacuum sample chamber and fix it, turn on the power of the argon ion cross-section polisher (such as the IB-09010CP type argon ion cross-section polisher of JEOL Ltd., Japan) and evacuate (such as evacuating to 10 -7Pa), set the argon flow rate (e.g. 0.12MPa) and polishing time (e.g. 90min), adjust the sample stage to the swing mode and start polishing. After polishing, observe the cross section of the sample under a scanning electron microscope. Since there are a large number of pores in the base film, the base film and the bonding layer can be distinguished in the cross section of the isolation film. The thickness of the bonding layer can be measured using the measurement software provided by the scanning electron microscope.

[0070] In some embodiments, the porosity of the separator is 40% to 60%. By rationally controlling the porosity of the separator, on the one hand, the stability of the battery structure can be improved, and on the other hand, a higher ion transfer efficiency can be obtained, the internal resistance of the battery can be reduced, and the cycle performance can be comprehensively improved. Specifically, the porosity of the separator includes but is not limited to: 40%, 45%, 50%, 55%, 60% or a range between any two of the foregoing.

[0071] The porosity of the separator can be measured by conventional methods in the art. For example, a battery that has been fully discharged (discharged to the lower limit cut-off voltage so that the battery is charged at about 0% SOC) is disassembled to obtain a separator as a sample to be tested. The AccuPyc II 1340 fully automatic true density tester of Micromeritics, USA, is used. Referring to the porosity test method in GB / T24586-2009, 30 small discs with a diameter of 14 mm are cut from the sample to be tested, and the thickness of the separator is measured. Based on the principle of gas adsorption, an inert gas such as helium or nitrogen is used as a medium to test the true volume of 30 small discs with a diameter of 14 mm. Then, the relationship between the apparent volume and the true volume of the separator is calculated based on the area, thickness and number of the small discs, and the porosity is calculated.

[0072] Without limitation, the bonding layer includes one or more of polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene copolymer.

[0073] In some embodiments, the isolation membrane further includes an inorganic ceramic layer, which is disposed between the base membrane and the bonding layer. The introduction of the bonding layer will increase the internal resistance of the battery to a certain extent. The non-polar ceramic layer is disposed between the bonding layer and the base membrane, and its good hydrophilicity can improve the wettability of the electrolyte to the isolation membrane, thereby reducing the internal resistance of the battery and improving the cycle performance of the battery.

[0074] Furthermore, the inorganic ceramic layer comprises one or more of aluminum oxide, silicon oxide and boehmite.

[0075] Further, the thickness of the inorganic ceramic layer is 1 μm to 4 μm. Specifically, the thickness of the inorganic ceramic layer includes but is not limited to: 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, or the range between any two of the foregoing.

[0076] Without limitation, the base film can be selected from any well-known porous base film with good chemical stability and mechanical stability. For example, it can be one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. Without limitation, the thickness of the base film is 6 μm to 18 μm. Specifically, the thickness of the base film includes but is not limited to: 6 μm, 8 μm, 10 μm, 13 μm, 15 μm, 16 μm, 18 μm, or the range between any two of the foregoing.

[0077] In some embodiments, the average particle size of the lithium iron phosphate primary particles is 100 nm to 800 nm. Using lithium iron phosphate primary particles with a suitable particle size can, on the one hand, shorten the lithium ion diffusion path, and on the other hand, reduce the expansion and contraction of the particle volume caused by the insertion and extraction of lithium ions. With the binding effect of the binding layer, the structural stability of the laminated sheet is improved, and thus the cycle performance is comprehensively improved. Specifically, the average particle size of the lithium iron phosphate primary particles includes but is not limited to: 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, or the range between any two of the foregoing. Further, the average particle size of the lithium iron phosphate primary particles is 500 nm to 800 nm.

[0078] Without limitation, the lithium iron phosphate primary particles can be doped or undoped lithium iron phosphate materials, and the doping elements include one or more of Al, V, and Ti. Specifically, the doping concentration of Al is 200 ppm to 2500 ppm; the doping concentration of V is 300 ppm to 2000 ppm; the doping concentration of Ti is 1500 ppm to 3500 ppm.

[0079] In some of these embodiments, the conductivity of the electrolyte at room temperature is 9.5 ms / cm to 18 ms / cm. The electrolyte used has a relatively high conductivity, which can further reduce the internal resistance of the battery and improve the cycling performance of the battery. Specifically, the conductivity of the electrolyte at room temperature includes, but is not limited to: 9.5 ms / cm, 10 ms / cm, 10.5 ms / cm, 11 ms / cm, 12 ms / cm, 13 ms / cm, 14 ms / cm, 15 ms / cm, 16 ms / cm, 17 ms / cm, 18 ms / cm, or the range between any two of the foregoing. Further, the conductivity of the electrolyte at room temperature is 10 ms / cm to 16 ms / cm.

[0080] In this application, the conductivity of the electrolyte can be tested by methods known in the art. The electrolyte to be tested can be the prepared electrolyte or the electrolyte obtained by disassembling the battery. Hereinafter, the latter will be taken as an example to illustrate the testing process. Disassemble the battery that has been discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) to obtain the electrolyte, and use the obtained electrolyte as the sample to be tested. The testing method follows HG / T 4067-2015, and use a conductivity meter to test the conductivity of the electrolyte to be tested: Take about 100 mL of the sample to be tested with a dry, clean and corrosion-resistant sample bottle, seal it and place it in a constant temperature water bath at 25 ± 0.5 °C. When the temperature of the sample to be tested is constant, replace the sample bottle cap with a rubber stopper with electrodes inserted. When the temperature is within the range of 25 ± 0.5 °C, read the data, which is the conductivity of the sample to be tested.

[0081] Without limitation, based on the mass of the electrolyte, the mass percentage of the first solvent is 10% to 60%. Specifically, the mass percentage of the first solvent includes, but is not limited to: 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or the range between any two of the foregoing. Further, the mass percentage of the first solvent is 15% to 35%.

[0082] It can be understood that the electrolyte may further include a second solvent, and the second solvent is a conventional solvent in the art. For example, it may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate ( ),(FEC), 1,4 - butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone, or one or more thereof. In some embodiments, the second solvent includes a carbonate solvent. Further, in the electrolyte, the mass percentage of the second solvent is 25% - 73%.

[0083] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes a combination of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide (LiFSI). Further, the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide (LiFSI) is (1.2 - 3):1. Lithium hexafluorophosphate is a commonly used lithium salt due to its low cost. In this application, by using lithium bis(fluorosulfonyl)imide in combination with lithium hexafluorophosphate and reasonably controlling the mass ratio of the two, while reducing the cost, it can better improve the conductivity of the electrolyte, thereby reducing the internal resistance of the separator film introduced into the adhesive layer and enhancing the cycling performance of the battery. Specifically, the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide includes, but is not limited to: 1.2:1, 1.5:1, 1.7:1, 2:1, 2.2:1, 2.5:1, 2.7:1, 3:1, or the range between any two of the foregoing.

[0084] Without limitation, based on the mass of the electrolyte, the mass percentage of the lithium salt is 12% - 18%. Specifically, the mass percentage of the lithium salt includes, but is not limited to: 12%, 13%, 14%, 15%, 16%, 17%, 18%, or the range between any two of the foregoing.

[0085] In some embodiments, the electrolyte further includes an additive, and the additive includes one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), and 1,3 - propane sultone (PS). By using a suitable additive, an SEI film can be formed on the negative electrode, improving the interfacial compatibility between the negative electrode active layer and the adhesive layer, reducing the interfacial impedance, and thereby enhancing the cycling performance of the battery.

[0086] In some embodiments, based on the mass of the electrolyte, the mass percentage of the additive is 0.1% - 5%. By reasonably controlling the dosage of the additive, on the one hand, the effect of reducing the interfacial impedance as described above is achieved, and on the other hand, side reactions caused by excessive addition amount are reduced. Specifically, the mass percentage of the additive includes, but is not limited to: 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or the range between any two of the foregoing. Further, the mass percentage of the additive is 0.5% - 3%.

[0087] In this application, the types and contents of the organic components in the electrolyte can be detected by using the equipment and methods well-known in the art. For example, qualitative and quantitative analysis of the organic components in the electrolyte can be carried out by gas chromatography with reference to GB / T9722-2006 General Rules for Gas Chromatography of Chemical Reagents. In the embodiments of this application, freshly prepared electrolyte can be taken as a sample, the free electrolyte of a fresh battery can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be taken as a sample for detection by ion chromatography analysis method.

[0088] In the embodiments of this application, the types and contents of the inorganic components / lithium salt concentration in the electrolyte have the meanings well-known in the art and can be detected by using the equipment and methods well-known in the art. For example, qualitative or quantitative analysis of the inorganic components / lithium salt concentration in the electrolyte can be carried out by ion chromatography with reference to the standard JY / T020-1996 General Rules for Ion Chromatography Analysis Method. In the embodiments of this application, freshly prepared electrolyte can be taken as a sample, the free electrolyte of a fresh battery can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be taken as a sample for detection by ion chromatography analysis method.

[0089] In the embodiments of this application, after the components in the electrolyte are quantitatively and qualitatively detected, the solvent components and the mass contents of each solvent in the electrolyte can be determined.

[0090] It should be noted that during the cyclic use of the battery cell, the content of the additive in the electrolyte may change. Based on this proportion range and considering the consumption after cyclic use, the content of the additive may not be within this proportion range, but it should also be understood to be within the protection scope of this application.

[0091] In some of these embodiments, the negative electrode active layer includes a first active layer and a second active layer. The first active layer is disposed between the negative electrode current collector and the second active layer. The first active layer includes a first graphite, and the second active layer includes a second graphite. The average longest diameter particle size of the first graphite is 7 μm to 18 μm, and the average longest diameter particle size of the second graphite is 6 μm to 10 μm, and the average value of the longest diameter of the first graphite is greater than the average value of the longest diameter of the second graphite. A double-layer active layer design is adopted for the negative electrode, and the particle sizes of the two layers of graphite are reasonably controlled. Among them, the particle size of the first graphite is larger, which can improve the compaction density of the negative electrode sheet, and the particle size of the second graphite is smaller, which can shorten the lithium ion transmission path and improve the cycle performance. Specifically, the average longest diameter particle size of the first graphite includes, but is not limited to: 7 μm, 10 μm, 12 μm, 15 μm, 18 μm, or the range between any two of the foregoing; the average longest diameter particle size of the second graphite includes, but is not limited to: 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or the range between any two of the foregoing.

[0092] It can be understood that the "average value of the longest diameter" means that the longest diameter of each graphite particle is taken, and the average value of the longest diameters of multiple graphite particles is calculated. Specifically, in this application, the test method is to perform a cross-section test (CP) of graphite particles using SEM, select 50 particles, and measure their longest diameters and take the average value.

[0093] Without limitation, the first graphite and the second graphite each independently include artificial graphite, or a combination of artificial graphite and natural graphite.

[0094] Without limitation, the thickness of the second active layer accounts for 30% to 70% of the total thickness of the first active layer and the second active layer. Specifically, the thickness of the second active layer accounting for the total thickness of the first active layer and the second active layer includes, but is not limited to: 30%, 40%, 50%, 60%, 70%, or the range between any two of the foregoing.

[0095] In some of these embodiments, the first graphite and the second graphite each independently include a graphite particle body and an amorphous carbon coating layer disposed on the surface of the graphite particle body. The thickness of the amorphous carbon coating layer is 100 nm to 500 nm. Specifically, the thickness of the amorphous carbon coating layer includes, but is not limited to: 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, or the range between any two of the foregoing.

[0096] In some of these embodiments, the first graphite and the second graphite each independently comprise secondary particles, and the volume average particle size Dv50 thereof is each independently 7 μm to 20 μm. Specifically, the volume average particle size Dv50 of the secondary particles each independently includes but is not limited to: 7 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, or the range between any two of the foregoing.

[0097] In some of these embodiments, the graphitization degree of the first graphite and the second graphite is each independently 90% to 94%. Reasonably controlling the graphitization degree of the first graphite and the second graphite can reduce defect sites, thereby reducing side reactions, reducing the consumption of lithium ions, and at the same time being conducive to the insertion and extraction of lithium ions, improving the cycle performance of the battery.

[0098] In addition, reasonably controlling the coating amount per unit area, the compaction density, etc. of the positive electrode active layer in the positive electrode sheet and / or the negative electrode active layer in the negative electrode sheet can, while introducing the binder layer, enable the battery cell to have good ion transport efficiency, achieve good cycle performance, and at the same time obtain a high energy density.

[0099] In some of these embodiments, the coating amount per unit area on one side of the positive electrode active material layer is 0.3 g / 1540.25 mm 2 ~0.45 g / 1540.25 mm 2 . Specifically, the coating amount per unit area includes but is not limited to: 0.3 g / 1540.25 mm 2 , 0.33 g / 1540.25 mm 2 , 0.34 g / 1540.25 mm 2 , 0.35 g / 1540.25 mm 2 , 0.37 g / 1540.25 mm 2 , 0.40 g / 1540.25 mm 2 , 0.43 g / 1540.25 mm 2 , 0.45 g / 1540.25 mm 2 or the range between any two of the foregoing. Further, the coating amount per unit area on one side of the positive electrode active material layer is 0.33 g / 1540.25 mm 2 ~0.4 g / 1540.25 mm 2 .

[0100] In some of these embodiments, the coating amount per unit area on one side of the negative electrode active layer is 0.13 g / 1540.25 mm 2 ~0.22 g / 1540.25 mm 2. Specifically, the coating amount per unit area includes, but is not limited to: 0.13 g / 1540.25 mm 2 , 0.14 g / 1540.25 mm 2 , 0.15 g / 1540.25 mm 2 , 0.17 g / 1540.25 mm 2 , 0.195 g / 1540.25 mm 2 , 0.20 g / 1540.25 mm 2 , 0.22 g / 1540.25 mm 2 or the range between any two of the above. Further, the coating amount per unit area on one side of the negative electrode active layer is 0.14 g / 1540.25 mm 2 ~0.195 g / 1540.25 mm 2 .

[0101] In some embodiments, the tap density of the positive electrode active layer is 2.3 g / cm 3 ~2.65 g / cm 3 . Specifically, the tap density includes, but is not limited to: 2.3 g / cm 3 , 2.35 g / cm 3 , 2.4 g / cm 3 , 2.45 g / cm 3 , 2.5 g / cm 3 , 2.55 g / cm 3 , 2.6 g / cm 3 , 2.65 g / cm 3 or the range between any two of the above. Further, the tap density of the positive electrode active layer is 2.35 g / cm 3 ~2.6 g / cm 3 .

[0102] In some embodiments, the tap density of the negative electrode active layer is 1.3 g / cm 3 ~1.52 g / cm 3 . Specifically, the tap density includes, but is not limited to: 1.3 g / cm 3 , 1.35 g / cm 3 , 1.4 g / cm 3 , 1.45 g / cm 3 , 1.50 g / cm 3 , 1.52 g / cm 3 or the range between any two of the above. Further, the tap density of the negative electrode active layer is 1.35 g / cm 3 ~1.5 g / cm 3 .

[0103] In the embodiments of the present application, the tap density of the positive electrode active layer refers to the tap density of the positive electrode active layer of the battery cell at 0% state of charge (SOC). The following method can be used for detection. The positive electrode plate is disassembled from the battery cell at 0% SOC, and the tap density of the positive electrode active layer is measured. For example, for a single-sided coated positive electrode plate (if it is a double-sided coated plate, the positive electrode active layer on one side can be wiped off first), it is punched into small round pieces with an area of S1, weighed, and recorded as M1, and its thickness H1 is measured. Then, the positive electrode active layer of the above-mentioned weighed positive electrode plate is wiped off, and the weight of the positive electrode current collector is weighed and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the positive electrode plate = (the weight M1 of the positive electrode plate - the weight M0 of the positive electrode current collector) / S1, the thickness of the positive electrode active layer = the thickness H1 of the positive electrode plate - the thickness H0 of the positive electrode current collector, and the tap density of the positive electrode active layer = the single-sided coating weight of the positive electrode active layer / the thickness of the positive electrode active layer. The tap density of the negative electrode plate is the same and will not be elaborated.

[0104] In some of the embodiments, the positive electrode plate includes a bottom carbon coating layer, and the thickness of the bottom carbon coating layer is 0.5 μm to 3 μm. By providing a bottom carbon coating layer in the positive electrode plate, the conductivity of the electrode plate can be improved, the increase in the internal resistance of the battery after introducing the binder layer can be reduced, and the cycling performance can be improved. Specifically, the thickness of the bottom carbon coating layer includes but is not limited to: 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or the range between any two of the foregoing. Further, the thickness of the bottom carbon coating layer is 0.5 μm to 1.5 μm. It can be understood that the bottom carbon coating layer is provided between the positive electrode current collector and the positive electrode active layer.

[0105] In addition, reasonably controlling the thickness ratio of the active layer to the current collector in the positive and negative electrode plates can obtain a higher energy density while achieving better ion transport performance.

[0106] In some of the embodiments, the thickness ratio of the positive electrode active layer on one side to the positive electrode current collector is (10 to 20):1. Specifically, the thickness ratio includes but is not limited to: 10:1, 13:1, 15:1, 17:1, 20:1, or the range between any two of the foregoing.

[0107] In some of the embodiments, the thickness ratio of the negative electrode active layer on one side to the negative electrode current collector is (15 to 25):1. Specifically, the thickness ratio includes but is not limited to: 15:1, 17:1, 20:1, 22:1, 25:1, or the range between any two of the foregoing.

[0108] In some of these embodiments, the positive electrode tab includes a positive electrode main body portion and a positive electrode tab ear connected to the positive electrode main body portion. The ratio of the long side dimension to the short side dimension of the positive electrode main body portion is (3 to 8):1. It can be understood that the "positive electrode main body portion" refers to the main part of the positive electrode tab, and the positive electrode active layer is mainly arranged in this area, and an insulating coating can be arranged at its edge; the positive electrode tab ear refers to the conductive area extending from the positive electrode main body portion for connecting to an external circuit, and the positive electrode active layer is usually not arranged on the positive electrode tab ear, and an insulating coating can be arranged at the root of the positive electrode tab ear. This ratio can reflect the overall aspect ratio design of the battery cell, especially the laminated battery. For battery cells with a relatively large aspect ratio, the expansion is more obvious when introducing large-particle-size graphite. The above solution of using a bonding layer in this application is particularly suitable for battery cells with a relatively large aspect ratio to improve their cycling performance. Specifically, the ratio of the long side dimension to the short side dimension of the positive electrode main body portion includes but is not limited to: 3:1, 4:1, 5:1, 6:1, 7:1, 8:1 or the range between any two of the foregoing. Further, the ratio of the long side length to the short side length of the positive electrode main body portion is (4 to 6):1.

[0109] Without limitation, as Figure 3 and Figure 4 shown, the battery cell is a laminated battery. The battery cell includes a positive electrode tab 1, a separator 2, a negative electrode tab 3, and an electrolyte. The positive electrode tab 1 and the negative electrode tab 3 are stacked, and the separator 2 is arranged between the positive electrode tab 1 and the negative electrode tab 3.

[0110] The positive electrode tab 1 includes a positive electrode main body portion 11 and a positive electrode tab ear 12 connected to the positive electrode main body portion 11. The long side dimension of the positive electrode main body portion 11 is as Figure 3 shown as d1 in Figure 3 and the short side dimension is as shown as d2 in

[0111] In some of these embodiments, the positive electrode tab ear 12 is connected to the short side of the positive electrode main body portion 11, and the negative electrode tab ear 32 is connected to the short side of the negative electrode main body portion 31. Arranging the positive electrode tab ear 12 on one side of the short side of the positive electrode main body portion 11 and the negative electrode tab ear 32 on one side of the short side of the negative electrode main body portion 31 is beneficial to improving the energy density of the battery cell compared with the scheme of arranging the tab ear on the long side.

[0112] In some of these embodiments, the battery cell further includes a soft-pack housing, and the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte are disposed within the soft-pack housing. Without limitation, the soft-pack housing includes an aluminum-plastic film. Further, the thickness of the aluminum-plastic film is 70 μm to 200 μm. Reasonably controlling the thickness of the aluminum-plastic film can, on the one hand, obtain a higher energy density, and on the other hand, improve the mechanical strength of the housing and inhibit the swelling of the battery cell to a certain extent. Specifically, the thickness of the aluminum-plastic film includes, but is not limited to: 70 μm, 100 μm, 120 μm, 150 μm, 170 μm, 200 μm, or the range between any two of the foregoing.

[0113] Some other embodiments of the present application provide a battery device including the battery cell as described above.

[0114] Some other embodiments of the present application provide an electrical device including the battery cell or the battery device as described above.

[0115] The battery cell and the electrical device of the present application will be described below with appropriate reference to the drawings.

[0116] Generally, a battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly functioning to prevent short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0117] The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector, and the positive electrode active layer includes a positive electrode active material.

[0118] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode active layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0119] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0120] In some embodiments, as described above, the positive electrode active material includes lithium iron phosphate primary particles, and related technical solutions will not be elaborated herein.

[0121] In some embodiments, the positive electrode active layer may optionally further include a binder. As non-limiting examples, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0122] In some embodiments, the positive electrode active layer may optionally further include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0123] In some embodiments, the positive electrode plate may 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 to form a positive electrode slurry; coating the positive electrode slurry on at least one surface of the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained. The type of the solvent may be selected from, but not limited to, any one of the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry may be a single surface of the positive electrode current collector or two surfaces of the positive electrode current collector. The solid content of the positive electrode slurry may be 40 wt% to 80 wt%. The viscosity of the positive electrode slurry at room temperature may be adjusted to 5000 mPa·s to 25000 mPa·s. The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, and the negative electrode active layer includes a negative electrode active material.

[0124] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active layer is provided on either or both of the two opposite surfaces of the negative electrode current collector.

[0125] In some embodiments, the negative electrode tab includes a negative electrode current collector and a negative electrode active layer provided on at least one surface of the negative electrode current collector. The negative electrode active layer includes a first active layer and a second active layer. The first active layer is disposed between the negative electrode current collector and the second active layer. The first active layer includes a first graphite, and the second active layer includes a second graphite. The average value of the longest diameter of the first graphite is 7 μm to 18 μm, and the average value of the longest diameter of the second graphite is 6 μm to 10 μm, and the average value of the longest diameter of the first graphite is greater than the average value of the longest diameter of the second graphite. Related technical solutions will not be elaborated herein.

[0126] 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 can 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 obtained by forming a metal material on the polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material can include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc. In the negative electrode current collector, non-limiting examples of the polymer material substrate can include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0127] In some embodiments, the negative electrode active layer may further optionally include a binder. The binder can include one or more 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).

[0128] In some embodiments, the negative electrode active layer may further optionally include a conductive agent. The conductive agent can include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0129] In some embodiments, the negative electrode active layer may further optionally include other additives, such as a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0130] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet described above, such as the negative electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one surface of the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or two surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40 wt% to 60 wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet.

[0131] It can be understood that the electrolyte includes a lithium salt and a solvent.

[0132] In some embodiments, the lithium salt can include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluoro bis(oxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0133] In some embodiments, as described above, the lithium salt includes a combination of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the related technical solutions will not be elaborated herein.

[0134] In some embodiments, as described above, the electrolyte includes a first solvent and optionally includes a second solvent, and the related technical solutions will not be elaborated herein.

[0135] In some embodiments, the electrolyte may also optionally include additives. For example, the additives can include negative electrode film-forming additives, positive electrode film-forming additives, and can also include additives that can improve certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0136] In some embodiments, as described above, the additives include one or more of vinylene carbonate, fluorinated ethylene carbonate, and 1,3-propane sultone, and the related technical solutions will not be elaborated herein.

[0137] In some embodiments, the secondary battery further includes a separator, as described above, and the related technical solutions will not be elaborated herein.

[0138] In some of the embodiments, for laminated batteries, the positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly through a lamination process.

[0139] In some embodiments, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0140] In some embodiments, for a soft pack battery, the outer packaging of the battery cell is a soft pack, such as a bag-type soft pack. The material of the soft pack may be plastic, and further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate. In some embodiments, as described above, the outer packaging of the battery cell includes an aluminum-plastic film, and the related technical solutions are not repeated here.

[0141] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode sheet, a negative electrode sheet and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0142] The battery device includes at least one battery cell. The number of battery cells contained in the battery device can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery device.

[0143] In the battery device, the plurality of battery cells may be arranged in sequence along the length direction of the battery device. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells may be fixed by fasteners.

[0144] Optionally, the battery device may further include a housing having a receiving space, and the plurality of battery cells are received in the receiving space.

[0145] In some of the embodiments, the battery devices described above may also be assembled into a battery pack. The number of battery devices contained in the battery pack may be one or more. Those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0146] The battery pack may include a battery box and a plurality of battery devices disposed in the battery box. The battery box includes an upper box body and a lower box body, and the upper box body can cover the lower box body and form a closed space for accommodating the battery devices. The plurality of battery devices can be arranged in the battery box in any manner.

[0147] In addition, the present application also provides an electrical device, which includes the battery device provided by the present application. The battery device can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can include mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto. Among them, the mobile device can be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle can be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but is not limited thereto.

[0148] As the electrical device, the battery device can be selected according to its usage requirements.

[0149] Figure 5 This is the electrical device 2 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 secondary battery for this electrical device, a battery pack or a battery module can be adopted.

[0150] Another example of the device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires being thin and light, and a battery cell can be adopted as the power source.

[0151] In order to make the technical problems, technical solutions, and beneficial effects solved by the present application clearer, the present application will be further described in detail below with reference to the embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way constitutes a limitation to the present application and its application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0152] For those technical or conditions not specified in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0153] Example 1

[0154] 1) Preparation of the positive electrode sheet

[0155] The lithium iron phosphate primary particles without doping of the positive electrode active material (average particle size is 500 nm), conductive carbon black SP, and binder PVDF are dispersed in the solvent NMP according to a weight ratio of 98:1:1 and mixed evenly to obtain the positive electrode slurry; aluminum foil is used as the positive electrode current collector. The positive electrode current collector includes a positive electrode main body part and a positive electrode tab connected to the positive electrode main body part. The positive electrode tab is connected to the short side of the positive electrode main body part; a primer slurry containing PVDF and conductive carbon is coated on both surfaces of the positive electrode main body part of the positive electrode current collector, and after curing, a primer layer with a thickness of 1 μm is formed. The mass ratio of PVDF to conductive carbon in the primer slurry is 1:5. The above-prepared positive electrode slurry is evenly coated on the primer layer on both surfaces of the positive electrode main body part, dried to form the positive electrode active layer, and then cold-pressed and slit to obtain the positive electrode sheet.

[0156] Among them, the ratio of the long side dimension to the short side dimension of the positive electrode main body part of the positive electrode sheet is 4.85:1, and the ratio of the thickness of the positive electrode active layer to the positive electrode current collector is 7.1:1. The tap density of the positive electrode active layer is 2.36 g / cm 3 , and the single-sided coating areal density is 0.384 g / 1540.25 mm 2 .

[0157] 2) Preparation of the negative electrode sheet

[0158] The first artificial graphite (average value of the longest diameter is 12 μm, thickness of the amorphous carbon coating layer is 300 nm, Dv50 is 12 μm, graphitization degree is 92%), thickening agent sodium carboxymethylcellulose, binder styrene-butadiene rubber, and conductive agent acetylene black are mixed according to a mass ratio of 97:1:1:1, and deionized water is added, and the first negative electrode slurry is obtained under the action of a vacuum mixer;

[0159] The second artificial graphite (average value of the longest diameter is 8 μm, thickness of the amorphous carbon coating layer is 300 nm, Dv50 is 12 μm, graphitization degree is 92%), thickening agent sodium carboxymethylcellulose, binder styrene-butadiene rubber, and conductive agent acetylene black are mixed according to a mass ratio of 97:1:1:1, and deionized water is added, and the second negative electrode slurry is obtained under the action of a vacuum mixer;

[0160] The first negative electrode slurry is evenly coated on both surfaces of the negative electrode current collector copper foil, dried to form the first active layer; the second negative electrode slurry is evenly coated on the surface of the first active layer, dried to form the second active layer; and then cold-pressed and slit to obtain the negative electrode sheet.

[0161] Among them, the ratio of the total thickness of the negative electrode active layer to the negative electrode current collector is 10.4:1, the thickness of the second active layer accounts for 50% of the total thickness of the negative electrode active layer, and the tap density of the negative electrode active layer is 1.45 g / cm 3 , and the single-sided coating areal density is 0.185 g / 1540.25 mm2 。

[0162] 3) Separator membrane

[0163] Dissolve polyvinylidene fluoride in N-methylpyrrolidone, add polyethylene glycol as a pore-forming agent after stirring evenly, and stir well to obtain a binder layer solution. Among them, the mass contents of polyvinylidene fluoride and polyethylene glycol are 20% and 15% of the total mass of the binder layer solution respectively.

[0164] Apply the above-mentioned binder layer solution on both sides of a polyethylene-based membrane with ceramic layers on both sides. After pre-volatilization at 80 °C and drying at 110 °C, immerse it in deionized water to dissolve polyethylene glycol, obtaining a separator membrane with a porous continuous structure on both sides. The porosity of the separator membrane is 50%. Among them, the thickness of the polyethylene-based membrane is 7 μm, the single-sided thickness of the ceramic layer is 2 μm, and the single-sided thickness of the binder layer is 1.5 μm. The binder in the ceramic coating is polyvinylidene fluoride, and the inorganic ceramic particles are alumina.

[0165] 4) Preparation of electrolyte

[0166] In an argon atmosphere glove box with a water content < 10 ppm, mix ethyl acetate (EA), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) to obtain an organic solvent, add dry lithium salts LiPF6 and LiFSI, and configure them into a solution; add fluoroethylene carbonate (FEC) and ethylene sulfite (VC) as additives to the above solution to obtain an electrolyte.

[0167] Among them, relative to the mass percentage of the electrolyte, EA is 15%, DMC is 15%, EMC is 30%, EC is 23%, the sum of the mass percentages of LiPF6 and LiFSI is 15%, the mass ratio of LiPF6 and LiFSI is 2.5:1, FEC is 0.5%, and VC is 1.5%. The conductivity of the electrolyte at 25 °C is 12 mS / cm.

[0168] 5) Preparation of battery

[0169] Stack the positive electrode sheet, separator membrane, and negative electrode sheet prepared above in sequence, with the separator membrane playing an isolating role between the positive electrode sheet and the negative electrode sheet. Hot press to connect the binder layer on the separator membrane with the positive electrode sheet and the negative electrode sheet to obtain a stacked bare battery cell. Place the stacked bare battery cell in a soft package shell made of polypropylene with a thickness of 100 μm, inject the electrolyte after drying, and obtain a lithium stacked battery monomer through processes such as vacuum packaging, standing, forming, and shaping.

[0170] The battery monomers of Examples 2-5 are similar to the preparation method of Example 1, and the main difference is that: lithium iron phosphate primary particles with different average particle sizes are used.

[0171] The battery cell of Example 6 was prepared in a similar manner to that of Example 1, with the main difference being that the second active layer was not provided in the negative electrode sheet, and the total thickness of the negative active layer remained unchanged.

[0172] The battery cells of Examples 7 - 8 were prepared in a similar manner to that of Example 1, with the main difference being that the single - side thickness of different binder layers was set.

[0173] The battery cells of Examples 9 - 10 were prepared in a similar manner to that of Example 1, with the main difference being that the porosity of different separator films was set, which was obtained by adjusting the dosage of the pore - forming agent.

[0174] The battery cell of Example 11 was prepared in a similar manner to that of Example 1, with the main difference being that EA was not used in the organic solvent of the electrolyte, and the dosage of DMC was used to make up the deficiency.

[0175] The battery cells of Examples 12 - 13 were prepared in a similar manner to that of Example 1, with the main difference being that different total mass percentages of EA and DMC were used. Among them, the mass ratio of EA and DMC remained unchanged at 1:1, and at the same time, the mass percentage of EMC was adjusted to make the electrolyte composition meet 100%.

[0176] The battery cell of Example 14 was prepared in a similar manner to that of Example 1, with the main difference being that only LiPF6 was used as the lithium salt, and the total mass percentage of the lithium salt remained unchanged.

[0177] The main parameters of the examples are summarized in Table 1 below.

[0178] Table 1

[0179]

[0180]

[0181] Note: "The mass percentage of the first solvent" refers to the total mass percentage of EA and DMC based on the mass of the electrolyte.

[0182] The battery cell of Comparative Example 1 was prepared in a similar manner to that of Example 1, with the main difference being that the binder layer was a traditional aqueous binder layer. In the corresponding preparation method of the separator film, water was used to replace N - methylpyrrolidone, and polyethylene glycol was not added, resulting in an island - like and discontinuous binder layer.

[0183] The battery cell of Comparative Example 2 was prepared in a similar manner to that of Example 1, with the main difference being that PC was used to replace EA and DMC in the organic solvent of the electrolyte in equal mass percentage.

[0184] Test Example:

[0185] (1) Cycling performance:

[0186] Step 1: Charge the battery cell at 0.33C to 3.65V at 25 °C, then perform constant voltage charging at 3.65V until the current reaches 0.05C; let it stand for 5 minutes; discharge it at 0.33C to 2V, and record the capacity at this time as C0 (this step is to measure the initial capacity during actual testing);

[0187] Step 2: Then charge the battery at 0.5C0 to 3.45V and at 0.33C0 to 3.65V; let it stand for 10 minutes; discharge it at 1C0 to 2V and at 0.33C to 2V until the capacity decays to less than or equal to 80% of the initial capacity, and record the number of cycles at this time.

[0188] (2) Self-discharge performance:

[0189] Let the battery cell stand for 1h at room temperature, and use a 6 1 / 2-digit digital multimeter to measure the initial open circuit voltage (Open Circuit Voltage, OCV) value, denoted as OCV1; after the test, let the battery cell stand for 120h at 45 °C, then stand for 1h at room temperature, and measure the open circuit voltage value again, denoted as OCV2, and calculate the self-discharge rate. The formula for calculating the self-discharge rate is: (OCV2 - OCV1) / 120. Measure 10 battery cells and take the average value.

[0190] The test results are shown in Table 2 below.

[0191] Table 2

[0192]

[0193] From the comparison between Examples 1-14 and Comparative Examples 1-2, it can be seen that by using a separator including a porous continuous structure bonding layer and cooperating with a suitable electrolyte solvent system, the present application can effectively improve the cycle performance of the battery and at the same time achieve a lower self-discharge rate.

[0194] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0195] The above-described embodiments only represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A battery cell, characterized in that, It includes a positive electrode plate, a separator, a negative electrode plate and an electrolyte. The positive electrode plate, the separator and the negative electrode plate are stacked; the positive electrode plate includes a positive current collector and a positive active layer provided on at least one side of the positive current collector. The negative electrode plate includes a negative current collector and a negative active layer provided on at least one side of the negative current collector. The positive active layer contains lithium iron phosphate primary particles; the separator includes a base film and a bonding layer. The bonding layer is a porous continuous structure and is provided at least on one side of the base film facing the positive active layer; the electrolyte includes a first solvent. The first solvent includes one or more of dimethyl carbonate and linear carboxylic acid esters. The structural general formula of the linear carboxylic acid ester is R1-COO-R2, and R1 and R2 each independently include a C1-C5 alkyl group or a halogenated C1-C5 alkyl group.

2. The battery cell according to claim 1, wherein The thickness of the bonding layer on one side is 0.5μm - 2.5μm.

3. The battery cell according to claim 1, wherein The porosity of the separator is 40% - 60%.

4. The battery cell according to claim 1, characterized in that, The bonding layer includes one or more of polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene copolymer.

5. The battery cell according to any one of claims 1 to 4, characterized in that, The separator further includes an inorganic ceramic layer, and the inorganic ceramic layer is provided between the base film and the bonding layer.

6. The battery cell according to claim 5, characterized in that, The inorganic ceramic layer contains one or more of alumina, silica and boehmite.

7. The battery cell according to any one of claims 1 to 4, characterized in that, The average particle size of the lithium iron phosphate primary particles is 100nm - 800nm.

8. The battery cell according to claim 7, wherein The average particle size of the lithium iron phosphate primary particles is 500nm - 800nm.

9. The battery cell according to any one of claims 1 to 4, characterized in that, The lithium iron phosphate primary particles contain doped or undoped lithium iron phosphate materials, and the doped elements include one or more of Al, V and Ti.

10. The battery cell according to any one of claims 1 to 4, characterized in that, The conductivity of the electrolyte at room temperature is 9.5ms / cm - 18ms / cm.

11. The battery cell according to any one of claims 1 to 4, characterized in that, Based on the mass of the electrolyte, the mass percentage of the first solvent is 10% - 60%.

12. The battery cell according to any one of claims 1 to 4, characterized in that, The electrolyte further includes a lithium salt. The lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is (1.2 - 3):

1.

13. The battery cell according to claim 12, wherein Based on the mass of the electrolyte, the mass percentage of the lithium salt is 12% - 18%.

14. The battery cell according to any one of claims 1 to 4, characterized in that, The electrolyte further includes an additive. The additive includes one or more of vinylene carbonate, fluoroethylene carbonate and 1,3-propane sultone.

15. The battery cell according to claim 14, wherein Based on the mass of the electrolyte, the mass percentage of the additive is 0.1% - 5%.

16. The battery cell according to any one of claims 1 to 4, characterized in that, The negative active layer includes a first active layer and a second active layer. The first active layer is provided between the negative current collector and the second active layer. The first active layer includes first graphite, and the second active layer includes second graphite. The average value of the longest diameter of the first graphite is 7μm - 18μm, and the average value of the longest diameter of the second graphite is 6μm - 10μm, and the average value of the longest diameter of the first graphite is greater than the average value of the longest diameter of the second graphite.

17. The battery cell according to claim 16, wherein, The first graphite and the second graphite each independently include a graphite particle body and an amorphous carbon coating layer provided on the surface of the graphite particle body. The thickness of the amorphous carbon coating layer is 100nm - 500nm; and / or, The volume average particle size Dv50 of the first graphite and the second graphite are each independently 7 μm to 20 μm; and / or, The graphitization degrees of the first graphite and the second graphite are each independently 90% to 94%.

18. The battery cell according to any one of claims 1 to 4, characterized in that, The coating amount per unit area on one side of the positive electrode active layer is 0.3 g / 1540.25 mm 2 ~0.45 g / 1540.25 mm 2 ; and / or, The coating amount per unit area on one side of the negative electrode active layer is 0.13 g / 1540.25 mm 2 ~0.22 g / 1540.25 mm 2 .

19. The battery cell according to any one of claims 1 to 4, characterized in that, The tap density of the positive electrode active layer is 2.3 g / cm 3 ~2.65 g / cm 3 ; and / or, The tap density of the negative electrode active layer is 1.3 g / cm 3 ~1.52 g / cm 3 .

20. The battery cell according to any one of claims 1 to 4, characterized in that, The positive electrode tab includes a bottom-coated carbon layer, and the thickness of the bottom-coated carbon layer is 0.5 μm to 3 μm.

21. The battery cell according to any one of claims 1 to 4, characterized in that, The thickness ratio of the single-sided positive electrode active layer to the positive electrode current collector is (10 to 20):1; and / or, The thickness ratio of the single-sided negative electrode active layer to the negative electrode current collector is (15 to 25):

1.

22. The battery cell according to any one of claims 1 to 4, characterized in that, The positive electrode tab includes a positive electrode main body portion and a positive electrode tab ear portion connected to the positive electrode main body portion, and the ratio of the long side dimension to the short side dimension of the positive electrode main body portion is (3 to 8):

1.

23. The battery cell according to any one of claims 1 to 4, characterized in that, The battery cell further includes a soft package case, and the positive electrode tab, the separator, the negative electrode tab, and the electrolyte are disposed inside the soft package case.

24. A battery device, characterized in that, Comprising the battery cell according to any one of claims 1 to 23.

25. An electrical device, characterized in that, Comprising the battery cell according to any one of claims 1 to 23 or the battery device according to claim 24.

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