Battery monomer and preparation method thereof, battery device and power utilization device

Abstract

The invention provides a battery monomer and a preparation method thereof, a battery device and a power utilization device, the battery monomer comprises a positive pole piece, an isolating membrane, a negative pole piece and an electrolyte, the positive pole piece and the negative pole piece are laminated, and the isolating membrane is arranged between the positive pole piece and the negative pole piece; the positive pole piece comprises a positive pole main body part and a positive pole lug part, and the ratio of the long side size to the short side size of the positive pole main body part is (3-8): 1; the isolating membrane comprises a base membrane and a bonding layer arranged on at least one side of the base membrane, and the bonding layer is a continuous layer of a porous structure; the electrolyte comprises a first solvent, and the first solvent comprises one or more of dimethyl carbonate and linear carboxylic ester with a structure as shown in a formula (1); in the formula (1), R1 and R2 respectively and independently comprise C1-C5 alkyl or halogenated alkyl. The battery monomer has relatively high energy density, relatively good cycle performance and relatively low self-discharge.

Description

Technical Field

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

[0002] In recent years, with the increasingly wide application scope of secondary batteries, secondary batteries are widely used in energy storage power systems such as hydraulic power stations, thermal power stations, wind power stations, and solar power stations, as well as in multiple fields such as electric tools, electric bicycles, electric motorcycles, and electric vehicles.

[0003] Due to the great development of secondary batteries, higher requirements are also put forward for the performance of secondary batteries. Seeking a battery with a relatively high energy density, good cycle performance, and low self-discharge is one of the key concerns of those skilled in the art. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a battery cell, a preparation method thereof, a battery device, and an electric device, and the battery cell has a relatively high energy density, good cycle performance, and low self-discharge.

[0005] To achieve the above object, a first aspect of the present application provides a battery cell, including a positive electrode plate, a separator, a negative electrode plate, and an electrolyte. The positive electrode plate and the negative electrode plate are stacked, and the separator is disposed between the positive electrode plate and the negative electrode plate;

[0006] The positive electrode plate includes a positive electrode main body portion and a positive electrode tab 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;

[0007] The separator includes a base film and a bonding layer disposed on at least one side of the base film, and the bonding layer is a continuous layer with a porous structure;

[0008] The electrolyte includes a first solvent, and the first solvent includes one or more of dimethyl carbonate and a linear carboxylic acid ester having the structure shown in formula (1):

[0009] R1-(C=O)-O-R2 formula (1);

[0010] Wherein, R1 and R2 each independently include an alkyl or haloalkyl group having 1 to 5 carbon atoms.

[0011] By controlling the ratio of the long side dimension to the short side dimension of the positive electrode main body of the positive electrode plate within (3-8):1, and using the positive electrode plate with a relatively large aspect ratio to form a laminated battery, the battery space occupied by the tab can be relatively smaller, which is beneficial to improving the energy density of the battery cell; by using one or more of dimethyl carbonate and linear carboxylic acid esters having the structure shown in formula (1) as the first solvent in the electrolyte, the above-mentioned first solvent has a lower viscosity and is beneficial to improving the conductivity of the electrolyte, and can solve the problem of insufficient infiltration of the electrolyte in the laminated battery with a relatively large aspect ratio of the electrode plate, so that the battery cell can have good cycle performance; by providing a bonding layer on at least one side of the base film of the separator, using this porous continuous bonding layer, the separator can be well connected to the positive electrode plate and / or the negative electrode plate, reducing the self-discharge of the battery caused by the misalignment of the positive and negative electrode plates due to gas generation during the cycle of the low-viscosity solvent, so that the battery cell can have a lower self-discharge. Through the setting of the aspect ratio of the electrode plate, the electrolyte solvent and the structure of the separator, and the synergistic cooperation of the above factors, the battery cell not only has a high energy density, but also has good cycle performance and low self-discharge.

[0012] In any embodiment, the thickness of the bonding layer on one side is 0.5 μm to 5 μm. In this way, it is more beneficial for the battery cell to have a high energy density and a low self-discharge.

[0013] In any embodiment, the thickness of the bonding layer on one side is 1 μm to 4 μm. In this way, it is more beneficial for the battery cell to better balance a high energy density and a low self-discharge.

[0014] In any embodiment, the material of the bonding layer includes one or more of polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene copolymer. In this way, it is beneficial for the bonding layer to have good bonding performance.

[0015] In any embodiment, the separator further includes a ceramic coating, the ceramic coating is provided between the base film and the bonding layer, and the material of the ceramic coating includes a binder and inorganic ceramic particles. In this way, it is beneficial to improve the thermal stability and mechanical strength of the separator.

[0016] In any embodiment, the ratio of the long side dimension to the short side dimension of the positive electrode main body is (4-6):1. In this way, it is beneficial for the battery cell to better balance a high energy density, good cycle performance and low self-discharge.

[0017] In any embodiment, the linear carboxylic acid ester includes one or more of ethyl acetate, methyl acetate, methyl propionate, propyl acetate, ethyl formate, and isopropyl formate. Thus, it is beneficial to improve the problem of insufficient electrolyte infiltration in the stacked battery with a large aspect ratio of the electrode sheet, so that the battery cell can take into account better cycle performance while having a large energy density.

[0018] In any embodiment, based on the mass of the electrolyte, the mass fraction of the first solvent is 10% - 60%. Thus, it is beneficial to make the electrolyte have appropriate viscosity and high conductivity, beneficial to improving the problem of insufficient electrolyte infiltration in the stacked battery with a large aspect ratio of the electrode sheet, and enabling the battery cell to better take into account the cycle performance.

[0019] In any embodiment, based on the mass of the electrolyte, the mass fraction of the first solvent is 15% - 35%. Thus, it is beneficial to enable the battery cell to better take into account high energy density, good cycle performance, and low self-discharge.

[0020] In any embodiment, the conductivity of the dimethyl carbonate and the linear carboxylic acid ester at room temperature is 10 mS / cm - 16 mS / cm. Thus, it is beneficial to improve the cycle performance of the battery cell.

[0021] In any embodiment, the electrolyte further includes a lithium salt, and the lithium salt includes one or more of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; based on the mass of the electrolyte, the total mass fraction of the lithium hexafluorophosphate and / or the lithium bis(fluorosulfonyl)imide is 12% - 18%. Thus, it is beneficial to increase the conductivity of the electrolyte and improve the cycle performance and kinetic performance of the battery cell.

[0022] In any embodiment, the mass ratio of the lithium hexafluorophosphate to the lithium bis(fluorosulfonyl)imide is (1.2 - 3):1. Thus, it is beneficial to increase the conductivity of the electrolyte, improve the problem of insufficient electrolyte infiltration in the stacked battery with a large aspect ratio of the electrode sheet, and improve the cycle performance and kinetic performance of the battery cell.

[0023] In any embodiment, the electrolyte further includes an additive, and the additive includes one or more of vinylene carbonate, fluoroethylene carbonate, and 1,3 - propane sultone; based on the mass of the electrolyte, the mass fraction of the additive is less than or equal to 5%. Thus, it is more beneficial to enable the battery cell to better take into account the cycle performance and kinetic performance.

[0024] In any embodiment, based on the mass of the electrolyte, the mass fraction of the additive is 0.5% - 3%. Thus, it is beneficial to enable the battery cell to better take into account the cycle performance and kinetic performance.

[0025] In any implementation manner, the battery cell further includes a soft-pack outer shell, the positive electrode plate, the separator, the negative electrode plate and the electrolyte are arranged in the soft-pack outer shell, and the thickness of the soft-pack outer shell is 70 μm to 200 μm. In this way, it is beneficial to improve the energy density of the battery cell; and it can also improve the problem that the soft-pack outer shell bulges due to gas generation during the circulation of the low-viscosity solvent.

[0026] In any implementation manner, the negative electrode plate includes a negative electrode main body portion and a negative electrode tab connected to the negative electrode main body portion. The negative electrode main body portion includes a negative electrode current collector and a negative electrode film layer. The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer arranged on the negative electrode current collector. The first negative electrode film layer is located between the negative electrode current collector and the second negative electrode film layer;

[0027] Both the first negative electrode film layer and the second negative electrode film layer include graphite. The average value of the longest diameter of the graphite in the first negative electrode film layer is 7 μm to 18 μm, and the average value of the longest diameter of the graphite in the second negative electrode film layer is 6 μm to 10 μm, and the average value of the longest diameter of the graphite in the first negative electrode film layer is greater than the average value of the longest diameter of the graphite in the second negative electrode film layer. In this way, it is beneficial for the battery cell to better balance the fast charging performance and the energy density.

[0028] In any implementation manner, the graphite in the first negative electrode film layer and the second negative electrode film layer independently includes a graphite particle body and an amorphous carbon coating layer arranged on the surface of the graphite particle body. The thickness of the amorphous carbon coating layer is 100 nm to 500 nm. In this way, it is beneficial to improve the conductivity of the graphite particles and further improve the kinetic performance of the battery.

[0029] In any implementation manner, the graphitization degree of the graphite in the first negative electrode film layer and the second negative electrode film layer is independently 90% to 94%. In this way, it is beneficial to improve the negative electrode specific capacity and the battery energy density.

[0030] In any implementation manner, the positive electrode tab is connected to the short side of the positive electrode main body portion, and the negative electrode tab is connected to the short side of the negative electrode main body portion. In this way, it is beneficial to improve the energy density of the battery cell.

[0031] In any implementation manner, the single-sided coating areal density of the negative electrode film layer is 0.13 g / 1540.25 mm 2 ~0.22 g / 1540.25 mm 2 。In this way, it is beneficial for the battery cell to better balance the fast charging performance and the energy density.

[0032] In any embodiment, the compaction density of the negative electrode plate is 1.3 g / cc to 1.52 g / cc. In this way, it is beneficial for the battery cell to better balance the fast charging performance and energy density.

[0033] In any embodiment, the positive electrode main body includes a positive electrode current collector and a positive electrode film layer. The positive electrode film layer is disposed on the positive electrode current collector. The positive electrode film layer includes a lithium-containing transition metal phosphate. The lithium-containing transition metal phosphate includes one or more of aluminum element with a mass content of 200 ppm to 2500 ppm, vanadium element with a mass content of 300 ppm to 2000 ppm, and titanium element with a mass content of 1500 ppm to 3500 ppm. In this way, the fast charging performance, cycle performance, and / or energy density of the battery cell are improved.

[0034] In any embodiment, the positive electrode main body further includes a bottom coating layer. The bottom coating layer is disposed between the positive electrode current collector and the positive electrode film layer. The bottom coating layer includes a conductive agent, and the thickness of the bottom coating layer is 0.5 μm to 3 μm. In this way, it is beneficial to reduce the internal resistance of the battery and improve the kinetic performance of the battery.

[0035] In any embodiment, the single-sided coating areal density of the positive electrode film layer is 0.33 g / 1540.25 mm 2 ~0.45 g / 1540.25 mm 2 。In this way, it is beneficial for the battery cell to better balance the fast charging performance and energy density.

[0036] In any embodiment, the compaction density of the positive electrode plate is 2.3 g / cc to 2.65 g / cc. In this way, it is beneficial for the battery cell to better balance the fast charging performance and energy density.

[0037] According to the second aspect of the present application, there is provided a method for manufacturing the battery cell of the first aspect of the present application, including the following steps:

[0038] Stack the positive electrode plate, the separator, and the negative electrode plate in sequence to form an electrode assembly; place the electrode assembly in an outer package to form a dry battery, and inject an electrolyte into the dry battery;

[0039] Wherein, the positive electrode plate includes a positive electrode main body and a positive electrode tab connected to the positive electrode main body. The ratio of the long side dimension to the short side dimension of the positive electrode main body is (3 to 8):1;

[0040] The separator includes a base film and an adhesive layer disposed on at least one side of the base film. The adhesive layer is a continuous layer with a porous structure;

[0041] The electrolyte includes a first solvent, and the first solvent includes one or more of dimethyl carbonate and linear carboxylic acid esters having the structure shown in formula (1):

[0042] R1-(C=O)-O-R2 formula (1);

[0043] wherein, R1 and R2 each independently include an alkyl group or a haloalkyl group having 1 to 5 carbon atoms.

[0044] Thus, through the setting of the aspect ratio of the electrode tab, the electrolyte solvent, and the structure of the adhesive layer in the separator, through the synergistic cooperation of the above factors, the prepared battery cell not only has a high energy density, but also has good cycle performance and low self-discharge.

[0045] In any embodiment, the preparation method of the separator includes the following steps: dissolving a binder and a pore-forming agent in an organic solvent to obtain a binder solution; applying the binder solution on a base film, and removing the pore-forming agent after drying to form the adhesive layer on the base film. Thus, an adhesive layer with a porous continuous structure can be prepared, which is beneficial to reducing the self-discharge of the battery.

[0046] According to the third aspect of the present application, a battery device is provided, including one or more of the battery cells of the first aspect of the present application and the battery cells prepared by the preparation method of the battery cells of the second aspect of the present application.

[0047] According to the fourth aspect of the present application, an electrical device is provided, including one or more of the battery cells of the first aspect of the present application, the battery cells prepared by the preparation method of the battery cells of the second aspect of the present application, and the battery device of the third aspect of the present application.

[0048] Details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the specification, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] To better describe and illustrate the embodiments or examples provided by 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. And in all the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0050] Figure 1 is a schematic structural diagram of a positive electrode tab in a battery cell according to an embodiment of the present application;

[0051] Figure 2Schematic structural diagram of the negative electrode plate in a battery cell according to an embodiment of the present application;

[0052] Figure 3 Schematic structural diagram of the separator in a battery cell according to an embodiment of the present application;

[0053] Figure 4 Schematic diagram of an electrical device powered by a battery device according to an embodiment of the present application.

[0054] Description of reference numerals:

[0055] 1. Positive electrode plate; 11. Positive electrode main body; 12. Positive electrode tab; 2. Separator; 21. Base film; 22. Adhesive layer; 23. Ceramic coating; 3. Negative electrode plate; 31. Negative electrode main body; 32. Negative electrode tab; 6. Electrical device. Detailed embodiments

[0056] Hereinafter, embodiments of the battery cell of the present application, its preparation method, battery device, and electrical device are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where non-essential details are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0057] The "range" disclosed in this 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 boundaries of a particular range. The range defined in this way can include or exclude the end values. Any end value can be independently included or excluded, 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 of 1 and 2 are listed, and if the maximum range values of 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 this 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" are fully listed herein, and "0~5" is only an abbreviated representation of these numerical combinations. Additionally, when it is stated that a certain parameter is 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 it is stated that a certain parameter is an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0058] In this application, when it comes to "multiple", "a variety of", etc., unless otherwise specified, it means greater than 2 or equal to 2 in quantity. For example, "one or more" means one or greater than or equal to two.

[0059] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form a new technical solution.

[0060] Referring to "embodiment" in this text means that the specific features, structures, or characteristics described in combination 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 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 same understanding applies to the "implementation manner" mentioned in this text.

[0061] Those skilled in the art can understand that in the methods of various embodiments or examples, the written order of each step does not mean a strict execution order that constitutes any limitation to the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or may include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0062] In this application, in an open technical feature or technical solution described by words such as "containing", "including", "comprising", etc., without other instructions, additional members other than the listed members are not excluded, and it can be regarded as providing both a closed feature or solution composed of the listed members and an open feature or solution that further includes additional members outside the listed members. For example, A includes a1, a2 and a3. Without other instructions, it may also include other members, or may not include additional members, and can be regarded as providing both a feature or solution of "A is composed of a1, a2 and a3" and a feature or solution of "A not only includes a1, a2 and a3, but also includes other members". In this application, without other instructions, A (such as B) means that B is a non-limiting example in A, and it can be understood that A is not limited to B.

[0063] In this application, "optionally", "optional", "option" mean that it can be either present or absent, that is, it refers to any one of two alternative schemes of "present" or "absent". If "optional" appears multiple times in a technical solution, without special instructions and without contradictions or mutual constraints, each "optional" is independent of each other.

[0064] Currently, due to the great development of secondary batteries, higher requirements are also put forward for the performance of secondary batteries. Seeking a battery with a relatively high energy density and capable of having good cycle performance and low self-discharge is one of the key concerns of those skilled in the art.

[0065] Based on this, please refer to Figure 1 、 Figure 2 and Figure 3 , a first aspect of this application provides a battery cell. The battery cell is a laminated battery. The battery cell includes a positive electrode plate 1, a separator 2, a negative electrode plate 3 and an electrolyte. The positive electrode plate 1 and the negative electrode plate 3 are stacked, and the separator 2 is disposed between the positive electrode plate 1 and the negative electrode plate 3.

[0066] Among them, the positive electrode tab 1 includes a positive electrode main body portion 11 and a positive electrode tab portion 12 connected to the positive electrode main body portion 11. The ratio of the long side dimension (such as d1 shown in Figure 1 it) to the short side dimension (such as d2 shown in Figure 1 it) of the positive electrode main body portion 11 is (3 to 8):1; the separator 2 includes a base film 21 and an adhesive layer 22 provided on at least one side of the base film 21, and the adhesive layer 22 is a continuous layer with a porous structure; the electrolyte includes a first solvent, and the first solvent includes one or more of dimethyl carbonate and a linear carboxylic acid ester having the structure shown in formula (1);

[0067] R1-(C=O)-O-R2 formula (1);

[0068] In formula (1), R1 and R2 each independently include an alkyl group or a haloalkyl group having 1 to 5 carbon atoms.

[0069] In this application, the positive electrode main body portion 11 is the main part of the positive electrode tab 1. The positive electrode film layer is mainly arranged in this area, and an insulating coating can be arranged at its edge; the positive electrode tab portion 12 refers to the conductive area extending from the positive electrode main body portion 11 for connecting an external circuit, and an insulating coating can be arranged at the root of the positive electrode tab portion 12; the long side of the positive electrode main body portion 11 refers to the side with a longer length in the plane where the positive electrode main body portion 11 is located, and the short side of the positive electrode main body portion 11 refers to the side with a shorter length in the plane where the positive electrode main body portion 11 is located. The long side dimension and the short side dimension of the positive electrode main body portion 11 can be directly measured by disassembling the laminated battery.

[0070] The morphology of the adhesive layer 22 can be observed by a scanning electron microscope (SEM). Without limitation, the battery cell can be fully discharged and disassembled in a glove box, the electrode assembly is taken out, and the positive electrode tab 1, the negative electrode tab 3 and the separator 2 are peeled off. Select the separator 2 in the middle of the battery, and cut off a 5 mm×5 mm separator 2 with scissors as a test sample. The sample is placed in absolute ethanol and gently shaken, and after taking out the sample, it is dried to remove the electrolyte and electrode debris remaining on the surface of the sample. The dried separator 2 sample is placed on a glass slide, and the morphology of the adhesive layer 22 on the separator 2 is observed through a scanning electron microscope.

[0071] In this application, the types and contents of organic components in the electrolyte can be detected by using 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, newly prepared electrolyte can be taken as a sample, 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.

[0072] In the embodiments of this application, the types and contents of inorganic components / lithium salt concentration in the electrolyte have the meanings well-known in the art and can be detected by using 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, newly prepared electrolyte can be taken as a sample, 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.

[0073] In the embodiments of this application, after quantitatively and qualitatively detecting each component in the electrolyte, the solvent components in the electrolyte and the mass content of each solvent can be determined.

[0074] The above battery cell controls the ratio of the long side dimension to the short side dimension of the positive electrode main body portion 11 of the positive electrode tab 1 to be (3-8):1. By using the positive electrode tab 1 with a relatively large aspect ratio to form a laminated battery, the battery space occupied by the electrode ear portion can be relatively smaller, which is beneficial to improving the energy density of the battery cell. However, when the aspect ratio of the positive electrode tab 1 of the laminated battery is relatively large, the penetration path of the electrolyte along the battery length direction is longer, and it is easy to occur that the electrolyte infiltration in some areas of the electrode tab is insufficient, affecting the cycle performance of the battery. In this application, one or more of dimethyl carbonate and linear carboxylate having the structure shown in formula (1) are used as the first solvent in the electrolyte. The above first solvent has a relatively low viscosity and is beneficial to improving the conductivity of the electrolyte, and can improve the problem of insufficient electrolyte infiltration in the laminated battery with a relatively large aspect ratio of the electrode tab, so that the battery cell can take into account better cycle performance; the above low-viscosity first solvent is prone to gas generation during the cycle, resulting in misalignment of the positive and negative electrode tabs. Especially in the laminated battery cell, since the electrode tab assembly is formed by stacking multiple independent electrode tabs, compared with the wound battery cell formed by winding a whole electrode tab, the probability of misalignment between the electrode tabs in the laminated battery cell in the battery width direction under the action of electrolyte gas generation is greater, resulting in battery self-discharge caused by misalignment of the positive and negative electrode tabs. In this application, a bonding layer 22 is provided on at least one side of the base film 21 of the separator 2. By using the porous continuous bonding layer 22, the separator 2 can be well connected to the positive electrode tab 1 and / or the negative electrode tab 3, reducing the battery self-discharge caused by misalignment of the positive and negative electrode tabs due to gas generation of the low-viscosity solvent during the cycle, so that the battery cell can take into account a lower self-discharge. Through the setting of the aspect ratio of the electrode tab, the electrolyte solvent and the structure of the separator 2, and the coordinated cooperation of the above factors, the battery cell not only has a relatively high energy density, but also has better cycle performance and lower self-discharge.

[0075] It can be understood that the ratio of the long side dimension to the short side dimension of the positive electrode main body portion 11 can be 3:1, 3.2:1, 3.5:1, 3.8:1, 4:1, 4.2:1, 4.5:1, 4.8:1, 5:1, 5.2:1, 5.5:1, 5.8:1, 6:1, 6.2:1, 6.5:1, 6.8:1, 7:1, 7.2:1, 7.5:1, 7.8:1, 8:1 and any ratio within the range formed by any two of the above ratios.

[0076] It should be noted that the adhesive layer 22 is a continuous layer with a porous structure, which means that there are multiple pores in the adhesive layer 22 that are either interconnected or non-interconnected, and the pores are interconnected by a solid skeleton to form a continuous three-dimensional layered structure. Compared with a discontinuous adhesive layer composed of multiple isolated island-like structures, the adhesive layer 22 with a porous continuous structure can better connect the separator 2 with the positive electrode plate 1 and / or the negative electrode plate 3, making the connection between the positive electrode plate 1, the separator 2, and the negative electrode plate 3 more firm. During the battery cycling process, it is beneficial to maintain the interfacial contact between the positive and negative electrode plates and the separator 2, and it is beneficial to reduce the self-discharge of the battery caused by the misalignment of the positive and negative electrode plates due to gas generation during the cycling process of the low-viscosity solvent.

[0077] Especially in a laminated battery using a lithium-containing transition metal phosphate (such as lithium iron phosphate) as the positive active material, the lithium-containing transition metal phosphate particles have a large rebound during the battery cycling process. Coupled with the gas generation of the low-viscosity solvent during the cycling process, it is easy to cause the release of the positive and negative electrode plates and the slippage and misalignment of the positive and negative electrode plates relative to the separator 2, resulting in battery self-discharge. By providing an adhesive layer 22 with a porous continuous structure on the separator 2, the self-discharge of such batteries can be effectively reduced.

[0078] In some embodiments, the thickness of the single-sided adhesive layer 22 is 0.5 μm to 5 μm. Controlling the thickness of the single-sided adhesive layer 22 within the above range is more beneficial for the battery monomer to have a higher energy density and lower self-discharge. It can be understood that the thickness of the single-sided adhesive layer 22 can be, but is not limited to, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, and any value within the range formed by any two of the above values.

[0079] The thickness of the adhesive layer 22 can be directly measured from the scanning electron microscope image of the cross-section of the separator 2 after cutting the separator 2 along the thickness direction. Without limitation, the thickness values of the adhesive layer 22 at multiple (such as 10) positions can be measured at intervals in the scanning electron microscope image of the cross-section of the separator 2, and then the average value is taken.

[0080] Further optionally, the thickness of the single-sided adhesive layer 22 is 1 μm to 4 μm. In this way, it is beneficial for the battery monomer to better balance a higher energy density and lower self-discharge.

[0081] In some of these embodiments, the material of the adhesive layer 22 includes one or more of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - HFP). Using the above - mentioned organic polymer as the binder of the adhesive layer 22 has good bonding performance.

[0082] In some of these embodiments, the separator 2 further includes a ceramic coating 23. The ceramic coating 23 is disposed between the base film 21 and the adhesive layer 22. The material of the ceramic coating 23 includes a binder and inorganic ceramic particles. By providing the above - mentioned ceramic coating 23 between the base film 21 and the adhesive layer 22, it is beneficial to improve the thermal stability and mechanical strength of the separator 2. It can be understood that the binder in the ceramic coating 23 can use the commonly used binders in the art, such as PVDF, and the inorganic ceramic particles can be, but are not limited to, alumina, zirconia, titanium oxide, boehmite, etc.

[0083] In some of these embodiments, the ratio of the long - side dimension to the short - side dimension of the positive - electrode main body 11 is (4 - 6):1. Controlling the ratio of the long - side dimension to the short - side dimension of the positive - electrode main body 11 within the above range is beneficial for the battery cell to better balance higher energy density, better cycle performance, and lower self - discharge.

[0084] In some of these embodiments, the linear carboxylic ester includes one or more of ethyl acetate, methyl acetate, methyl propionate, propyl acetate, ethyl formate, and isopropyl formate. The above - mentioned types of linear carboxylic esters have low viscosities, which is beneficial for the infiltration of the electrolyte, improving the problem of insufficient electrolyte infiltration in the stacked - film battery with a large aspect ratio of the electrode sheet, and thus is beneficial for the battery cell to balance better cycle performance while having a large energy density.

[0085] In some of these embodiments, based on the mass of the electrolyte, the mass fraction of the first solvent is 10% - 60%. Controlling the mass fraction of the first solvent in the electrolyte within the above range is beneficial for the electrolyte to have a suitable viscosity and a high conductivity, beneficial for improving the problem of insufficient electrolyte infiltration in the stacked - film battery with a large aspect ratio of the electrode sheet, and enabling the battery cell to better balance cycle performance.

[0086] It can be understood that the mass fraction of the first solvent can be, but is not limited to, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60% and any value within the range formed by any two of the above values. The electrolyte can include dimethyl carbonate but not include linear carboxylic esters, or can include linear carboxylic esters but not include dimethyl carbonate, or can include both dimethyl carbonate and linear carboxylic esters.

[0087] Further, in some embodiments, based on the mass of the electrolyte, the mass fraction of the first solvent is 15% to 35%. Controlling the mass fraction of the first solvent in the electrolyte within the above range is beneficial for the battery cell to better balance higher energy density, better cycling performance, and lower self-discharge.

[0088] In some embodiments, the conductivity of the electrolyte at room temperature is 9.5 mS / cm to 20 mS / cm. Adding dimethyl carbonate and / or linear carboxylic acid ester as the first solvent to the electrolyte is beneficial for the electrolyte to have a relatively high conductivity. Controlling the conductivity of the electrolyte within the above range is beneficial for improving the cycling performance of the battery cell.

[0089] It can be understood that the conductivity of the electrolyte at room temperature can be, but is not limited to, 9.5 mS / cm, 10 mS / cm, 10.5 mS / cm, 11 mS / cm, 11.5 mS / cm, 12 mS / cm, 12.5 mS / cm, 13 mS / cm, 13.5 mS / cm, 14 mS / cm, 14.5 mS / cm, 15 mS / cm, 15.5 mS / cm, 16 mS / cm, 16.5 mS / cm, 17 mS / cm, 17.5 mS / cm, 18 mS / cm, 18.5 mS / cm, 19 mS / cm, 19.5 mS / cm, 20 mS / cm, and any value within the range formed by any two of the above values. Among them, room temperature generally refers to 20°C to 25°C.

[0090] In some specific examples, the conductivity of the electrolyte at room temperature is 10 mS / cm to 16 mS / cm.

[0091] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI); based on the mass of the electrolyte, the sum of the mass fractions of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide is 12% to 18%.

[0092] By compounding lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide as the lithium salt and controlling the sum of the mass fractions of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide within the above range, it is beneficial to improve the conductivity of the electrolyte and the cycling performance and kinetic performance of the battery cell.

[0093] It can be understood that the sum of the mass fractions of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in the electrolyte can be, but is not limited to, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, and any value within the range formed by any two of the above values.

[0094] In some of these embodiments, the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is (1.2 to 3):1. Controlling the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide within the above range is conducive to improving the conductivity of the electrolyte, alleviating the problem of insufficient electrolyte infiltration in a stacked battery with a relatively large aspect ratio of the electrode sheet, and improving the cycle performance and kinetic performance of the battery cell. It can be understood that the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide can be, but is not limited to, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3:1, and any ratio within the range formed by any two of the above ratios.

[0095] In some of these 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 adding the above additives to the electrolyte, the SEI (Solid Electrolyte Interface) film can be optimized, which is conducive to enabling the battery cell to better balance the cycle performance and kinetic performance.

[0096] In some of these embodiments, based on the mass of the electrolyte, the mass fraction of the additive is less than or equal to 5%. Excessive use of the additive will increase the impedance of the battery cell. In the stacked battery with a relatively large aspect ratio of the electrode sheet in this application, using the above additive with a mass fraction of less than 5% based on the mass of the electrolyte is more conducive to enabling the battery cell to better balance the cycle performance and kinetic performance.

[0097] It can be understood that the mass fraction of the additive in the electrolyte can be, but is not limited to, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, and any value within the range formed by any two of the above values.

[0098] Furthermore, in some specific examples, based on the mass of the electrolyte, the mass fraction of the additive is 0.5% to 3%. In this way, it is conducive to enabling the battery cell to better balance the cycle performance and kinetic performance.

[0099] In some of these embodiments, the battery cell further includes a pouch case, and the positive electrode sheet 1, the separator 2, the negative electrode sheet 3, and the electrolyte are disposed inside the pouch case. The thickness of the pouch case is 70 μm to 200 μm. That is, the battery cell of the present application can be a pouch battery cell. Controlling the thickness of the pouch case within the above range is beneficial to improving the energy density of the battery cell; and can also make the case have greater strength, and improve the problem that the pouch case bulges due to gas generation during cycling of the low-viscosity solvent.

[0100] It can be understood that the thickness of the pouch case can be, but is not limited to, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, and any value within the range formed by any two of the above values.

[0101] In some specific examples, the material of the pouch case can be plastic. Further, non-limiting examples of the plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0102] In some of these embodiments, the negative electrode sheet 3 includes a negative electrode main body portion 31 and a negative electrode tab portion 32 connected to the negative electrode main body portion 31. The negative electrode main body portion 31 includes a negative electrode current collector and a negative electrode film layer. The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer disposed on the negative electrode current collector. The first negative electrode film layer is located between the negative electrode current collector and the second negative electrode film layer. Both the first negative electrode film layer and the second negative electrode film layer include graphite. The average value of the longest diameter of the graphite in the first negative electrode film layer is 7 μm to 18 μm, and the average value of the longest diameter of the graphite in the second negative electrode film layer is 6 μm to 10 μm, and the average value of the longest diameter of the graphite in the first negative electrode film layer is greater than the average value of the longest diameter of the graphite in the second negative electrode film layer.

[0103] In the present application, the negative electrode main body portion 31 is the main part of the negative electrode sheet 3, and the negative electrode film layer is mainly disposed in this area; the negative electrode tab portion 32 refers to the conductive area extending from the negative electrode main body portion 31 for connecting to an external circuit.

[0104] By setting the negative electrode film layer with an upper and lower two-layer structure, controlling the average value of the longest diameters of the graphite in the first negative electrode film layer and the second negative electrode film layer within the above range, and making the average value of the longest diameters of the graphite in the first negative electrode film layer greater than the average value of the longest diameters of the graphite in the second negative electrode film layer; using graphite with a smaller particle size in the second negative electrode film layer located above can provide more lithium-ion insertion sites, making it easier for lithium ions to be inserted into the negative electrode film layer from the electrolyte, which is beneficial to improving the fast charging performance of the battery cell; using graphite with a larger particle size in the first negative electrode film layer located below is beneficial to improving the compaction density of the negative electrode film layer, enabling the battery cell to better balance the fast charging performance and energy density.

[0105] It can be understood that the average value of the longest diameters of the graphite in the first negative electrode film layer can be 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, and any value within the range formed by any two of the above values; the average value of the longest diameters of the graphite in the second negative electrode film layer can be 6μm, 7μm, 8μm, 9μm, 10μm, and any value within the range formed by any two of the above values.

[0106] Among them, the test method for the average value of the longest diameter is: in the scanning electron microscope image, randomly select 500 graphite particles, measure the longest diameters of each graphite particle and then take the average value. The longest diameter of the graphite particle refers to the maximum length dimension that can be measured in all possible measurement directions of the particle in the above SEM image.

[0107] Furthermore, the ratio of the thickness of the second negative electrode film layer to the total thickness of the negative electrode sheet can be 30% - 70%.

[0108] In some embodiments, the graphite in the first negative electrode film layer and the second negative electrode film layer each independently includes a graphite particle body and an amorphous carbon coating layer provided on the surface of the graphite particle body, and the thickness of the amorphous carbon coating layer is 100nm - 500nm. That is, the graphite in the first negative electrode film layer can include an amorphous carbon coating layer, the graphite in the second negative electrode film layer can include an amorphous carbon coating layer, or the graphite in both the first negative electrode film layer and the second negative electrode film layer includes an amorphous carbon coating layer. By providing the amorphous carbon coating layer with the above thickness on the surface of the graphite, it is beneficial to further improve the conductivity of the graphite particles and further improve the kinetic performance of the battery.

[0109] Understandably, the thickness of the amorphous carbon coating layer on the surface of the graphite particle body can be, but is not limited to, 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm, and any value within the range formed by any two of the above values.

[0110] Further, the graphite in the first negative electrode film layer and the second negative electrode film layer can each independently be artificial graphite or a mixture of artificial graphite and natural graphite.

[0111] In some embodiments, the graphitization degree of the graphite in the first negative electrode film layer and the second negative electrode film layer is each independently 90% - 94%. Using graphite with the above graphitization degree is more conducive to the insertion of lithium ions and is beneficial to improving the specific capacity of the negative electrode and the energy density of the battery.

[0112] In some embodiments, the positive electrode ear 12 is connected to the short side of the positive electrode main body 11, and the negative electrode ear 32 is connected to the short side of the negative electrode main body 31. In this way, by arranging the positive electrode ear 12 on one side of the short side of the positive electrode main body 11 and the negative electrode ear 32 on one side of the short side of the negative electrode main body 31, compared with the scheme of arranging the ear on the long side, it is more conducive to improving the energy density of the battery cell.

[0113] In some embodiments, the single-sided coating areal density of the negative electrode film layer is 0.13 g / 1540.25 mm 2 ~0.22 g / 1540.25 mm 2 . Controlling the single-sided coating areal density of the negative electrode film layer within the above range is beneficial for the battery cell to better balance the fast charging performance and the energy density. Understandably, the single-sided coating areal density of the negative electrode film layer can be, 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 , 0.16 g / 1540.25 mm 2 , 0.17 g / 1540.25 mm 2 , 0.18 g / 1540.25 mm 2 , 0.19 g / 1540.25 mm 2 , 0.20 g / 1540.25 mm 2 , 0.21 g / 1540.25 mm 2 , 0.22 g / 1540.25 mm 2 and any value within the range formed by any two of the above values.

[0114] Further optionally, the single-sided coating areal density of the negative electrode film layer is 0.14 g / 1540.25 mm 2 ~0.195 g / 1540.25 mm 2 .

[0115] In some embodiments, the compaction density of the negative electrode tab at 0% state of charge is 1.3 g / cc to 1.52 g / cc. Controlling the compaction density of the negative electrode tab within the above range is beneficial to better balance the fast charging performance and energy density of the battery cell. Understandably, the compaction density of the negative electrode tab can be, but is not limited to, 1.3 g / cc, 1.31 g / cc, 1.32 g / cc, 1.33 g / cc, 1.34 g / cc, 1.35 g / cc, 1.36 g / cc, 1.37 g / cc, 1.38 g / cc, 1.39 g / cc, 1.4 g / cc, 1.41 g / cc, 1.42 g / cc, 1.43 g / cc, 1.44 g / cc, 1.45 g / cc, 1.46 g / cc, 1.47 g / cc, 1.48 g / cc, 1.49 g / cc, 1.50 g / cc, 1.51 g / cc, 1.52 g / cc, and any value within the range formed by any two of the above values.

[0116] Further optionally, the compaction density of the negative electrode tab is 1.35 g / cc to 1.50 g / cc.

[0117] In some embodiments, the positive electrode main body 11 includes a positive electrode current collector and a positive electrode film layer. The positive electrode film layer is disposed on the positive electrode current collector. The positive electrode film layer includes a lithium-containing transition metal phosphate. The lithium-containing transition metal phosphate includes one or more of aluminum element with a mass content of 200 ppm to 2500 ppm, vanadium element with a mass content of 300 ppm to 2000 ppm, and titanium element with a mass content of 1500 ppm to 3500 ppm.

[0118] By adding the above content of aluminum element to the lithium-containing transition metal phosphate, it is beneficial to improve the electronic conductivity of the positive electrode active material and improve the fast charging performance and cycle performance of the battery cell; by adding the above content of vanadium element to the lithium-containing transition metal phosphate, it is beneficial to increase the specific capacity of the positive electrode active material, and thus beneficial to increase the energy density of the battery cell; by adding the above content of titanium element to the lithium-containing transition metal phosphate, it is beneficial to improve the crystal structure stability of the positive electrode active material, thereby enhancing the cycle performance of the battery cell.

[0119] Understandably, the content of aluminum element in the lithium-containing transition metal phosphate can be, but is not limited to, 200 ppm, 500 ppm, 800 ppm, 1000 ppm, 1200 ppm, 1500 ppm, 1800 ppm, 2000 ppm, 2200 ppm, 2500 ppm, and any value within the range formed by any two of the above values; the content of vanadium element in the lithium-containing transition metal phosphate can be, but is not limited to, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, and any value within the range formed by any two of the above values; the content of titanium element in the lithium-containing transition metal phosphate can be, but is not limited to, 1500 ppm, 1800 ppm, 2000 ppm, 2200 ppm, 2500 ppm, 2800 ppm, 3000 ppm, 3200 ppm, 3500 ppm, and any value within the range formed by any two of the above values.

[0120] In some embodiments, the positive electrode main body 11 further includes a bottom coating, which is disposed between the positive electrode current collector and the positive electrode film layer. The bottom coating includes a conductive agent, and the thickness of the bottom coating is 0.5 μm to 3 μm. In a stacked battery with a relatively large aspect ratio of the electrode length and width, the distance for electrons to transfer from the positive electrode main body 11 to the positive electrode tab 12 is relatively long, resulting in a relatively large internal resistance (DCR) of the battery cell; by providing the above bottom coating between the positive electrode current collector and the positive electrode film layer, it is beneficial to reduce the battery internal resistance and improve the kinetic performance of the battery.

[0121] Understandably, the thickness of the bottom coating can be, but is not limited to, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, and any value within the range formed by any two of the above values.

[0122] In some embodiments, the single-sided coating areal density of the positive electrode film layer is 0.33 g / 1540.25 mm 2 ~0.45 g / 1540.25 mm 2 . Controlling the single-sided coating areal density of the positive electrode film layer within the above range is beneficial for the battery cell to better balance the fast charging performance and energy density. Understandably, the single-sided coating areal density of the positive electrode film layer can be, but is not limited to, 0.33 g / 1540.25 mm 2 、0.34 g / 1540.25 mm2 、0.35 g / 1540.25 mm 2 、0.36 g / 1540.25 mm 2 、0.37 g / 1540.25 mm 2 、0.38 g / 1540.25 mm 2 、0.39 g / 1540.25 mm 2 、0.40 g / 1540.25 mm 2 、0.41 g / 1540.25 mm 2 、0.42 g / 1540.25 mm 2 、0.43 g / 1540.25 mm 2 、0.44 g / 1540.25 mm 2 、0.45 g / 1540.25 mm 2 and any value within the range formed by any two of the above values.

[0123] Further optionally, the single-sided coating areal density of the positive electrode film layer is 0.30 g / 1540.25 mm 2 ~0.40 g / 1540.25 mm 2 .

[0124] In some embodiments, the compaction density of the positive electrode sheet at 0% state of charge is 2.3 g / cc to 2.65 g / cc. Controlling the compaction density of the positive electrode sheet within the above range is beneficial for the battery cell to better balance the fast charging performance and energy density. Understandably, the compaction density of the positive electrode sheet can be, but is not limited to, 2.3 g / cc, 2.32 g / cc, 2.35 g / cc, 2.38 g / cc, 2.4 g / cc, 2.42 g / cc, 2.45 g / cc, 2.48 g / cc, 2.5 g / cc, 2.52 g / cc, 2.55 g / cc, 2.58 g / cc, 2.6 g / cc, 2.62 g / cc, 2.65 g / cc and any value within the range formed by any two of the above values.

[0125] Further optionally, the compaction density of the negative electrode sheet is 2.35 g / cc to 2.6 g / cc.

[0126] In some embodiments, the ratio of the thickness of the positive electrode sheet 1 to the thickness of the positive current collector is (10~20):1, and the ratio of the thickness of the negative electrode sheet 3 to the thickness of the negative current collector is (15~25):1. In this way, the thickness proportion of the positive current collector in the positive electrode sheet 1 is small, and the thickness proportion of the negative current collector in the negative electrode sheet 3 is small, which is beneficial to further improve the energy density of the battery cell.

[0127] The second aspect of the present application provides a method for preparing the above-mentioned battery cell, including the following steps:

[0128] Stack the positive electrode plate 1, the separator 2, and the negative electrode plate 3 in sequence to form an electrode assembly; place the electrode assembly in an outer package to form a dry battery, and inject electrolyte into the dry battery.

[0129] Among them, the positive electrode plate 1 includes a positive electrode main body portion 11 and a positive electrode tab portion 12 connected to the positive electrode main body portion 11, and the ratio of the long side dimension to the short side dimension of the positive electrode main body portion 11 is (3-8):1;

[0130] The separator 2 includes a base film 21 and a bonding layer 22 provided on at least one side of the base film 21, and the bonding layer 22 is a continuous layer with a porous structure;

[0131] The electrolyte includes a first solvent, and the first solvent includes one or more of dimethyl carbonate and a linear carboxylic acid ester having the structure shown in formula (1):

[0132] R1-(C=O)-O-R2 Formula (1);

[0133] Among them, R1 and R2 each independently include an alkyl or haloalkyl group having 1 to 5 carbon atoms.

[0134] In the above-mentioned method for preparing a battery cell, through the setting of the aspect ratio of the electrode plate, the electrolyte solvent, and the structure of the bonding layer 22 in the separator 2, and through the synergistic cooperation of the above factors, the prepared battery cell not only has a high energy density, but also has good cycle performance and low self-discharge.

[0135] In some embodiments, the method for preparing the separator 2 includes the following steps: Dissolve the binder and the pore-forming agent in an organic solvent to obtain a binder solution; Apply the binder solution on the base film 21, and remove the pore-forming agent after drying to form the bonding layer 22 on the base film 21.

[0136] Through the above-mentioned preparation method, a bonding layer 22 with a porous continuous structure can be prepared on the base film 21, which is beneficial to improving the connection force between the separator 2 and the positive electrode plate 1 and the negative electrode plate 3 after hot pressing of the electrode assembly, and reducing the battery self-discharge caused by the misalignment of the positive and negative electrode plates due to gas generation of the low-viscosity solvent during the cycle.

[0137] In some specific examples, the binder is one or more of PVDF or PVDF-HFP; the pore-forming agent is polyethylene glycol (PEG), and the organic solvent is N-methylpyrrolidone (NMP).

[0138] The third aspect of the present application provides a battery device, which includes one or more of the battery cells of the first aspect of the present application and the battery cells prepared by the preparation method of the second aspect of the present application.

[0139] After a plurality of battery cells are interconnected and arranged in a certain order, they can be directly placed in a box body to assemble and form a battery device. Alternatively, one or more battery cells can be first formed into a battery module, and then a plurality of battery modules are interconnected to form an integral body, and finally the whole of the battery modules is placed in a box body to form a battery device.

[0140] In some specific examples, the battery device is a battery module, and the battery module may include one or more of the above-mentioned battery cells. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module. In the battery module, a plurality of battery cells may be arranged in sequence along the length direction of the battery module. Of course, they can also be arranged in any other way. Further, the plurality of battery cells can be fixed by fasteners.

[0141] Optionally, the battery module may further include a housing having an accommodation space, and a plurality of battery cells are accommodated in the accommodation space.

[0142] In some specific examples, the battery device is a battery pack further assembled from a plurality of the above-mentioned battery modules. The number of battery modules included in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0143] The battery pack may include a battery box and a plurality of battery modules disposed in the battery box. The battery box includes an upper box body and a lower box body. The upper box body can cover the lower box body and form a closed space for accommodating the battery modules. The plurality of battery modules can be arranged in the battery box in any way.

[0144] The fourth aspect of the present application provides an electrical device, which includes one or more of the battery cells of the first aspect of the present application, the battery cells prepared by the preparation method of the battery cells of the second aspect of the present application, and the battery device of the third aspect.

[0145] The battery cells and electrical devices of the present application will be described below with appropriate reference to the drawings.

[0146] Unless otherwise specified, the components, material types or contents of the battery mentioned are applicable to both lithium-ion batteries and sodium-ion batteries.

[0147] In one embodiment of the present application, a battery cell is provided.

[0148] Under normal circumstances, a battery cell includes a positive electrode plate, a negative electrode plate, 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 plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows ions to pass through.

[0149] The positive electrode plate includes a positive current collector and a positive electrode film layer provided on at least one surface of the positive current collector.

[0150] As a non-limiting example, the positive current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on either or both of the two opposite surfaces of the positive current collector.

[0151] In some embodiments, the positive current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material substrate 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 a polymer material substrate. In the positive current collector, non-limiting examples of the metal material can include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc. In the positive 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).

[0152] In some embodiments, the positive electrode active material can include positive electrode active materials known in the art for batteries.

[0153] As a non-limiting example, the positive electrode active material of a lithium-ion battery may include one or more of the following materials: lithium-containing phosphates with an olivine structure, lithium-containing transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as the positive electrode active material of a battery can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of the lithium-containing transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and their modified compounds. Non-limiting examples of the lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon. Non-limiting examples of lithium cobalt oxide may include LiCoO2; non-limiting examples of lithium nickel oxide may include LiNiO2; non-limiting examples of lithium manganese oxide may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxide may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be abbreviated as NCM 811 ), etc.; non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.85 Co 0.1 Al 0.05 O2.

[0154] Understandably, during the charge and discharge process of the battery, the insertion and extraction as well as consumption of lithium (Li) will occur, and the content of Li in the positive electrode sheet is different when the battery is discharged to different states. In the listing of the positive electrode materials in this application, unless otherwise specified, the content of Li is the initial state of the material. When the positive electrode material is applied to the positive electrode sheet in the battery system, after charge and discharge cycles, the content of Li in the positive electrode material contained in the sheet usually changes. Among them, the content of Li can be measured by molar content, but is not limited to this. Regarding "the content of Li is the initial state of the material", the initial state of the material refers to the state before being fed into the positive electrode slurry. It can be understood that new materials obtained by appropriately modifying the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode materials, and non-limiting examples include coating modification.

[0155] In the listing of the positive electrode materials in this application, the content of oxygen (O) is only the theoretical state value, and the release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual content of O will fluctuate. Among them, the content of O can be measured by molar content, but is not limited to this.

[0156] As a non-limiting example, the positive electrode active material of a sodium-ion battery may include one or more of the following materials: one or more of sodium transition metal oxides, polyanion-type compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventionally well-known materials that can be used as the positive electrode active material of a sodium-ion battery can also be used.

[0157] As an optional technical solution of this application, the polyanion-type compound can be a type of compound having sodium ions, transition metal ions, and a tetrahedral (YO4) n- anion unit. The transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be one or more of P, S, and Si; n represents the valence state of (YO4) n- .

[0158] The polyanion-type compound can also be a type of compound having sodium ions, transition metal ions, a tetrahedral (YO4) n- anion unit, and a halogen anion. The transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be one or more of P, S, and Si, n represents the valence state of (YO4) n- ; the halogen can be one or more of F, Cl, and Br.

[0159] The polyanion-type compound can also be a type of compound having sodium ions, a tetrahedral (YO4) n- anion unit, a polyhedral unit (ZOy ) m+ and a class of compounds of optional halogen anions. Y can be one or more of P, S, and Si, and n represents the valence state of (YO4) n- ; Z represents a transition metal, which can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and m represents the valence state of (ZO y ) m+ ; The halogen can be one or more of F, Cl, and Br.

[0160] Polyanionic compounds such as NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM’PO4F (M’ is one or more of V, Fe, Mn, and Ni), and Na3(VO y )2(PO4)2F 3-2y (0 ≤ y ≤ 1).

[0161] Prussian blue compounds can be a class of compounds having sodium ions, transition metal ions, and cyanide ions (CN - ). The transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds such as Na a Me b Me’ c (CN)6, where Me and Me’ are each independently one or more of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0162] The weight ratio of the positive electrode active material in the positive electrode film layer is 80 wt% to 100 wt%, based on the total weight of the positive electrode film layer.

[0163] In some embodiments, the positive electrode film layer may further optionally include a binder. As a non-limiting example, 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. The weight ratio of the binder in the positive electrode film layer is 0 wt% to 20 wt%, based on the total weight of the positive electrode film layer.

[0164] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As a non-limiting example, 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. The weight ratio of the conductive agent in the positive electrode film layer is 0 wt% to 20 wt%, based on the total weight of the positive electrode film layer.

[0165] In some embodiments, the positive electrode tab can be prepared by the following method: dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry, coating the positive electrode slurry on both surfaces of the positive electrode current collector, and forming the positive electrode tab after drying and cold pressing by a cold rolling mill.

[0166] The negative electrode tab includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0167] 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 film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0168] In some of these embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. Among them, in the negative electrode current collector, non-limiting examples of the metal material may 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 may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0169] In some of these embodiments, the negative electrode active material can be a negative electrode active material for batteries well-known in the art.

[0170] As a non-limiting example, the negative electrode active material of a lithium-ion battery may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based materials may include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0171] As a non-limiting example, the negative electrode active material of a sodium-ion battery is usually hard carbon material, two-dimensional metal carbides or nitrides. Preferably, the negative electrode active material of a sodium-ion secondary battery is usually hard carbon material.

[0172] In some embodiments, the negative electrode film layer may optionally further include a binder. The binder may 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).

[0173] In some embodiments, the negative electrode film layer may optionally further include a conductive agent. 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.

[0174] In some embodiments, the negative electrode film layer may optionally further include other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0175] In some embodiments, the negative electrode plate can be prepared in the following manner: dispersing the components for preparing the negative electrode plate, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry on at least one surface of the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate 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.

[0176] The electrolyte has the function of conducting ions between the positive electrode plate and the negative electrode plate.

[0177] In some embodiments, the electrolyte includes an electrolyte salt and a solvent.

[0178] In some embodiments, the electrolyte salt of the lithium-ion battery includes lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI); it may also include one or more of lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluoro(dioxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0179] In some embodiments, the solvent includes one or more of dimethyl carbonate (DMC) and a linear carboxylic acid ester having the structure shown in formula (1); R1-(C=O)-O-R2 formula (1); wherein, R1 and R2 each independently include an alkyl or haloalkyl group having 1 to 5 carbon atoms. It may also include one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0180] In some embodiments, the battery cell further includes a separator. The separator includes a base film and an adhesive layer provided on at least one side of the base film, and the adhesive layer is a continuous layer with a porous structure.

[0181] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator are made into an electrode assembly by a lamination process.

[0182] In some embodiments, the battery cell may include an outer package. The outer package can be used to encapsulate the above electrode assembly and electrolyte.

[0183] In some embodiments, the outer package of the battery cell can be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic. Further, non-limiting examples of the plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.

[0184] In this application, unless otherwise specified, a "battery cell" refers to a basic unit capable of converting chemical energy and electrical energy into each other. Further, generally, it includes at least a positive electrode sheet, a negative electrode sheet, and an electrolyte. 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 plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0185] In addition, the present application also provides an electrical device, which includes at least one of the battery cells or battery devices provided by the present application. The battery cell and 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 (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0186] As the electrical device, the battery cell or the battery device can be selected according to its usage requirements.

[0187] Figure 4 Shown is an electrical device 6 as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the electrical device for the battery, a battery device can be adopted.

[0188] 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.

[0189] 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 in conjunction with embodiments and 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 fall within the scope of protection of the present application.

[0190] For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For the reagents or instruments not specified in terms of the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0191] Embodiment 1:

[0192] (1) Preparation of the positive electrode plate

[0193] The positive electrode active material lithium iron phosphate (LFP), the conductive agent Super P, and the binder PVDF are mixed in a mass ratio of 97:1:2, and the solvent N-methylpyrrolidone is added and stirred evenly to obtain the positive electrode paste. Aluminum foil is used as the positive electrode current collector, and the positive electrode current collector includes a positive electrode main body part and a positive electrode tab part connected to the positive electrode main body part, and the positive electrode tab part is connected to the short side of the positive electrode main body part.

[0194] On both sides of the positive electrode main body of the positive electrode current collector, a primer slurry containing PVDF and conductive carbon is coated, 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 positive electrode slurry prepared above is uniformly coated on the primer layer on both sides of the positive electrode main body, and after drying, cold pressing, and slitting, a positive electrode sheet is obtained.

[0195] Among them, the ratio of the long side dimension to the short side dimension of the positive electrode main body of the positive electrode sheet is 5:1. The compaction density of the positive electrode sheet is 2.5 g / cc, and the single-side coating areal density is 0.4 g / 1540.25 mm 2 。

[0196] (2)Negative electrode sheet preparation

[0197] After mixing artificial graphite, conductive agent Super P, thickening agent sodium carboxymethyl cellulose, and binder styrene-butadiene rubber in a mass ratio of 96:1:1.2:1.8, deionized water as a solvent is added, and after stirring evenly, a first negative electrode slurry is obtained; among them, the average value of the longest diameter of the artificial graphite is 12 μm; the artificial graphite includes a graphite particle body and an amorphous carbon coating layer with a thickness of 200 nm provided on the surface of the graphite particle body. The graphitization degree of the artificial graphite is 92%.

[0198] Copper foil is used as the negative electrode current collector. The negative electrode current collector includes a negative electrode main body and a negative electrode tab connected to the negative electrode main body. The negative electrode tab is connected to the short side of the negative electrode main body. The first negative electrode slurry prepared above is uniformly coated on both sides of the negative electrode main body, and after drying and cold pressing, a first negative electrode film layer is obtained; the single-side coating areal density of the first negative electrode film layer is 0.1 g / 1540.25 mm 2 。

[0199] After mixing artificial graphite, conductive agent Super P, thickening agent sodium carboxymethyl cellulose, and binder styrene-butadiene rubber in a mass ratio of 96:1:1.2:1.8, deionized water as a solvent is added, and after stirring evenly, a second negative electrode slurry is obtained; among them, the average value of the longest diameter of the artificial graphite is 8 μm; the artificial graphite includes a graphite particle body and an amorphous carbon coating layer with a thickness of 200 nm provided on the surface of the graphite particle body. The graphitization degree of the artificial graphite is 92%.

[0200] The second negative electrode slurry prepared above is uniformly coated on the first negative electrode film layer on both sides of the negative electrode main body, and after drying and cold pressing, a second negative electrode film layer is obtained; after slitting, a negative electrode sheet is obtained. The single-side coating areal density of the second negative electrode film layer is 0.1 g / 1540.25 mm 2 。The total single-side coating areal density of the negative electrode film layer is 0.2 g / 1540.25 mm 2 。The compaction density of the negative electrode sheet is 1.42 g / cc.

[0201] (3) Separator

[0202] Polyvinylidene fluoride was dissolved in N-methylpyrrolidone. After stirring evenly, polyethylene glycol was added as a pore-forming agent, and the mixture was stirred thoroughly to obtain a binder layer solution. Among them, the mass contents of polyvinylidene fluoride and polyethylene glycol were 20% and 15% of the total mass of the binder layer solution, respectively.

[0203] The above-mentioned binder layer solution was coated on both sides of a polyethylene-based film with ceramic layers on both sides. After pre-volatilization at 80 °C and drying at 110 °C, it was immersed in deionized water to dissolve polyethylene glycol, obtaining a separator with a porous continuous structure on both sides. Among them, the thickness of the polyethylene-based film was 7 μm, the single-sided thickness of the ceramic layer was 2 μm, and the single-sided thickness of the binder layer was 1.5 μm. The binder in the ceramic coating was polyvinylidene fluoride, and the inorganic ceramic particles were alumina.

[0204] (4)Electrolyte

[0205] In a glove box with an argon atmosphere where the water content < 10 ppm, dimethyl carbonate, ethylene carbonate, and methyl acetate were mixed to obtain an organic solvent, and dry lithium salts LiPF6 and LiFSI were added. Fluoroethylene carbonate with a mass content of 1% was added as an additive to the above solution to obtain an electrolyte. Among them, the total mass fraction of dimethyl carbonate and methyl acetate in the electrolyte was 50%, and the volume ratio of dimethyl carbonate to methyl acetate was 1:1; the sum of the mass fractions of LiPF6 and LiFSI was 18%, and the mass ratio of LiPF6 to LiFSI was 2:1. The conductivity of the electrolyte at 25 °C was 15 mS / cm.

[0206] (5)Battery assembly

[0207] The positive electrode plate, separator, and negative electrode plate prepared above were stacked in sequence, with the separator between the positive electrode plate and the negative electrode plate to play an isolation role. Heat pressing was used to connect the binder layer on the separator with the positive electrode plate and the negative electrode plate, obtaining a stacked bare battery cell. The stacked bare battery cell was placed in a soft package shell made of polypropylene with a thickness of 100 μm. After drying, the electrolyte was injected, and through processes such as vacuum packaging, standing, forming, and shaping, a single lithium battery was obtained.

[0208] Example 2:

[0209] This example is basically the same as Example 1, except that in step (1), by adjusting the length of the positive electrode plate, the ratio of the long side dimension to the short side dimension of the positive electrode main body of the positive electrode plate was 3:1, and the short side dimension of the positive electrode main body remained unchanged.

[0210] Example 3:

[0211] This embodiment is basically the same as Embodiment 1, except that: in step (1), by adjusting the length of the positive electrode plate, the ratio of the long side dimension to the short side dimension of the positive electrode main body of the positive electrode plate is 8:1, and the short side dimension of the positive electrode main body remains unchanged.

[0212] Embodiment 4:

[0213] This embodiment is basically the same as Embodiment 1, except that: in step (3), the single-sided thickness of the bonding layer is 0.5 μm.

[0214] Embodiment 5:

[0215] This embodiment is basically the same as Embodiment 1, except that: in step (3), the single-sided thickness of the bonding layer is 2.5 μm.

[0216] Embodiment 6:

[0217] This embodiment is basically the same as Embodiment 1, except that: in step (4), ethylene carbonate, methyl acetate and ethyl acetate are mixed to obtain an organic solvent, and dry lithium salts LiPF6 and LiFSI are added; 0.3% by mass of fluoroethylene carbonate is added as an additive to the above solution to obtain an electrolyte. Among them, the total mass fraction of methyl acetate and ethyl acetate in the electrolyte is 20%, and the volume ratio of methyl acetate to ethyl acetate is 1:1; the sum of the mass fractions of LiPF6 and LiFSI is 12%, and the mass ratio of LiPF6 to LiFSI is 1.2:1. The conductivity of the electrolyte at 25 °C is 10 mS / cm.

[0218] Embodiment 7:

[0219] This embodiment is basically the same as Embodiment 1, except that: in step (2), by adjusting the types of artificial graphite in the first negative electrode paste and the second negative electrode paste, the average value of the longest diameter of the artificial graphite in the first negative electrode film layer is 18 μm, and the average value of the longest diameter of the artificial graphite in the second negative electrode film layer is 10 μm.

[0220] Embodiment 8:

[0221] This embodiment is basically the same as Embodiment 1, except that: in step (2), the average value of the longest diameter of the artificial graphite in the first negative electrode paste is 8 μm; the average value of the longest diameter of the artificial graphite in the second negative electrode paste is 6 μm.

[0222] Comparative Example 1:

[0223] This comparative example is basically the same as Example 1, except that: in step (3), water is used instead of N-methylpyrrolidone as the solvent of the adhesive layer solution, and polyvinyl alcohol is not added to the adhesive layer solution. The obtained adhesive layer is a discontinuous adhesive layer composed of multiple isolated island-shaped bonded particles.

[0224] Comparative Example 2:

[0225] This comparative example is basically the same as Example 1, except that: in step (1), by adjusting the length of the positive electrode plate, the ratio of the long side dimension to the short side dimension of the positive electrode main body of the positive electrode plate is 10:1, and the short side dimension of the positive electrode main body remains unchanged.

[0226] Comparative Example 3:

[0227] This comparative example is basically the same as Example 1, except that: in step (4), ethylene carbonate and propylene carbonate are mixed in a volume ratio of 1:1 to obtain an organic solvent.

[0228] Test method:

[0229] (1) Energy density test

[0230] Charge the battery cell at 0.33C to 3.65V at 25 °C, and then charge it at a constant voltage of 3.65V to 0.05C; let it stand for 5 minutes; discharge it at 0.33C to 2V, and record the total discharge capacity C0 of the battery cell. The total discharge energy is E0, unit: Wh;

[0231] Measure the length, width and thickness of the battery cell, and calculate the volume and record it as V, unit: L;

[0232] The volume energy density of the battery cell = E0 / V, unit: Wh / L.

[0233] (2) Cycle performance test

[0234] First step: Charge the battery cell at 0.33C to 3.65V at 25 °C, and then charge it at a constant voltage of 3.65V to 0.05C; let it stand for 5 minutes; discharge it at 0.33C to 2V, and record the capacity at this time and denote it as C0 (this step is the actual test initial capacity);

[0235] Second step: Then charge the battery at 0.5C0 to 3.45V, and charge it at 0.33C0 to 3.65V; let it stand for 10 minutes; discharge it at 1C0 to 2V, and discharge it 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.

[0236] (3) Self-discharge performance test of the battery

[0237] The battery cell was left standing for 1 h at room temperature, and the initial open circuit voltage (OCV) value of the battery cell was measured using a 6 1 / 2-digit digital multimeter and denoted as OCV1. After the measurement, the battery cell was left standing for 120 h at 45 °C and then for 1 h at room temperature, and the open circuit voltage value was measured again and denoted as OCV2. The self-discharge rate was calculated. The formula for calculating the self-discharge rate is: (OCV2 - OCV1) / 120. Ten battery cells were measured and the average value was taken.

[0238] (4)Measurement of the coating areal density of the film layer

[0239] The coating areal density was measured using the following method: Fifteen pieces each of the electrode sheet and the current collector (with the same production batch number as the current collector used for the electrode sheet) with a size of 1540.25 mm 2 were punched out, weighed, and the average value was obtained. The average mass of the electrode sheets was M1 (unit: g), and the average mass of the current collectors was M2 (unit: g); when the film layer was arranged on both sides of the current collector, the unilateral coating areal density was: (M1 - M2) / 2S.

[0240] (5)Measurement of the compaction density of the electrode sheet

[0241] The electrode sheet was taken from the 0% SOC battery cell monomer after disassembly and punched into small round pieces with a size of 1540.25 mm 2 . The weight M and thickness L of the small round pieces were measured; for another layer of electrode sheet, the film layer on the surface was wiped off to leave only the empty current collector foil, which was also punched into small round pieces with a size of 1540.25 mm 2 . The mass M0 of the empty current collector foil was weighed, then the compaction density PD = (M - M0) / 1.54025 / (L - L0), where L0 is the thickness of the current collector foil.

[0242] (6)Measurement of the average value of the longest diameter of graphite

[0243] In the scanning electron microscope (SEM) image of the negative electrode film layer, 500 graphite particles were randomly selected, and the longest diameter of each graphite particle was measured and the average value was taken. Among them, the longest diameter of the graphite particle refers to the maximum length dimension that can be measured in all possible measurement directions of the particle in the above SEM image.

[0244] The parameters and performance data of the battery cell monomers in the above examples and comparative examples are shown in Table 1. " / " in Table 1 indicates non-existence.

[0245] Table 1

[0246]

[0247] As can be seen from Table 1, the battery cell of the embodiment of the present application has a high energy density, and at the same time has good cycle performance and low self-discharge. Compared with Example 1, in Comparative Example 1, water is used instead of N-methylpyrrolidone as the solvent of the adhesive layer solution, and polyvinyl alcohol is not added to the adhesive layer solution. Since the formed adhesive layer is an island-shaped discontinuous adhesive layer, the adhesion between the separator and the positive and negative electrode sheets is poor, and the cycle performance of the battery cell is poor and the self-discharge is large. Compared with Example 1, in Comparative Example 2, the ratio of the long side dimension to the short side dimension of the positive electrode main body portion of the positive electrode sheet is too large. Although the energy density of the battery cell is improved, the cycle performance is significantly reduced. Compared with Example 1, in Comparative Example 3, dimethyl carbonate and the linear carboxylic acid ester having the structure of formula (1) are not used in the electrolyte solvent, and the cycle performance of the battery cell is significantly reduced.

[0248] The above descriptions of the various embodiments tend to emphasize the differences between the various embodiments. The same or similar parts can be referred to each other. For the sake of brevity, they will not be elaborated herein.

[0249] It should be noted that the present application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same composition and the same effect as the technical idea within the technical solution scope of the present application are included in the technical scope of the present application. In addition, within the scope not departing from the gist of the present application, various modifications that can be conceived by those skilled in the art to the embodiments and other ways constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present application.

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 and the negative electrode plate are stacked, and the separator is disposed between the positive electrode plate and the negative electrode plate; The positive electrode plate includes a positive electrode main body portion and a positive electrode tab 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 (3-8):1; The separator includes a base film and an adhesive layer disposed on at least one side of the base film. The adhesive layer is a continuous layer with a porous structure; The electrolyte includes a first solvent. The first solvent includes one or more of dimethyl carbonate and a linear carboxylic acid ester having the structure shown in formula (1): R1-(C=O)-O-R2 Formula (1); Wherein, R1 and R2 each independently include an alkyl or haloalkyl group of C1-C5.

2. The battery cell according to claim 1, characterized in that, The thickness of the adhesive layer on one side is 0.5μm-5μm.

3. The battery cell according to claim 2, wherein, The thickness of the adhesive layer on one side is 1μm-4μm.

4. The battery cell according to any one of claims 1 to 3, characterized in that The adhesive 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 3, characterized in that The separator further includes a ceramic coating. The ceramic coating is disposed between the base film and the adhesive layer. The material of the ceramic coating includes inorganic ceramic particles.

6. The battery cell according to any one of claims 1 to 3, characterized in that, The ratio of the long side dimension to the short side dimension of the positive electrode main body portion is (4-6):

1.

7. The battery cell according to any one of claims 1 to 3, characterized in that, The linear carboxylic acid ester includes one or more of ethyl acetate, methyl acetate, methyl propionate, propyl acetate, ethyl formate and isopropyl formate.

8. The battery cell according to any one of claims 1 to 3, characterized in that, Based on the mass of the electrolyte, the mass fraction of the first solvent is 10%-60%.

9. The battery cell according to claim 8, wherein Based on the mass of the electrolyte, the mass fraction of the first solvent is 15%-35%.

10. The battery cell according to any one of claims 1 to 3 and 9, characterized in that, The conductivity of the dimethyl carbonate and the linear carboxylic acid ester at room temperature is 10ms / cm-16ms / cm.

11. The battery cell according to any one of claims 1 to 3 and 9, characterized in that, The electrolyte further includes a lithium salt. The lithium salt includes one or more of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; based on the mass of the electrolyte, the total mass fraction of the lithium hexafluorophosphate and / or the lithium bis(fluorosulfonyl)imide is 12%-18%.

12. The battery cell according to claim 11, wherein, The mass ratio of the lithium hexafluorophosphate to the lithium bis(fluorosulfonyl)imide is (1.2-3):

1.

13. The battery cell according to any one of claims 1 to 3, 9, and 12, wherein The electrolyte further includes an additive. The additive includes one or more of vinylene carbonate, fluorinated ethylene carbonate and 1,3-propane sultone; based on the mass of the electrolyte, the mass fraction of the additive is less than or equal to 5%.

14. The battery cell according to claim 13, wherein, Based on the mass of the electrolyte, the mass fraction of the additive is 0.5%-3%.

15. The battery cell according to any one of claims 1 to 3, 9, 12, and 14, characterized in that, The battery cell further includes a soft package shell. The positive electrode plate, the separator, the negative electrode plate and the electrolyte are disposed inside the soft package shell. The thickness of the soft package shell is 70μm-200μm.

16. The battery cell according to any one of claims 1 to 3, 9, 12, and 14, characterized in that, The negative electrode plate includes a negative electrode main body portion and a negative electrode tab connected to the negative electrode main body portion. The negative electrode main body portion includes a negative electrode current collector and a negative electrode film layer. The negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer disposed on the negative electrode current collector. The first negative electrode film layer is located between the negative electrode current collector and the second negative electrode film layer; Both the first negative electrode film layer and the second negative electrode film layer include graphite. The average value of the longest diameter of the graphite in the first negative electrode film layer is 7 μm to 18 μm, and the average value of the longest diameter of the graphite in the second negative electrode film layer is 6 μm to 10 μm, and the average value of the longest diameter of the graphite in the first negative electrode film layer is greater than the average value of the longest diameter of the graphite in the second negative electrode film layer.

17. The battery cell according to claim 16, wherein, The graphite in the first negative electrode film layer and the second negative electrode film layer each independently includes a graphite particle body and an amorphous carbon coating layer provided on the surface of the graphite particle body, and the thickness of the amorphous carbon coating layer is 100 nm to 500 nm.

18. The battery cell according to claim 16, characterized in that, The graphitization degree of the graphite in the first negative electrode film layer and the second negative electrode film layer is each independently 90% to 94%.

19. The battery cell according to claim 16, wherein, The positive electrode tab is connected to the short side of the positive electrode main body, and the negative electrode tab is connected to the short side of the negative electrode main body.

20. The battery cell according to claim 16, characterized in that, The single-sided coating areal density of the negative electrode film layer is 0.13 g / 1540.25 mm 2 ~0.22 g / 1540.25 mm 2 .

21. The battery cell according to any one of claims 1 to 3, 9, 12, 14, 17 to 20, characterized in that, The compaction density of the negative electrode sheet is 1.3 g / cc to 1.52 g / cc.

22. The battery cell according to any one of claims 1 to 3, 9, 12, 14, 17 to 20, characterized in that, The positive electrode main body includes a positive electrode current collector and a positive electrode film layer. The positive electrode film layer is provided on the positive electrode current collector. The positive electrode film layer includes a lithium-containing transition metal phosphate. The lithium-containing transition metal phosphate includes one or more of aluminum element with a mass content of 200 ppm to 2500 ppm, vanadium element with a mass content of 300 ppm to 2000 ppm, and titanium element with a mass content of 1500 ppm to 3500 ppm.

23. The battery cell according to claim 22, characterized in that, The positive electrode main body further includes a bottom coating layer. The bottom coating layer is provided between the positive electrode current collector and the positive electrode film layer. The bottom coating layer includes a conductive agent, and the thickness of the bottom coating layer is 0.5 μm to 3 μm.

24. The battery cell according to claim 22, wherein, The single-sided coating areal density of the positive electrode film layer is 0.33 g / 1540.25 mm 2 ~0.45 g / 1540.25 mm 2 .

25. The battery cell according to any one of claims 1 to 3, 9, 12, 14, 17 to 20, 23 to 24, characterized in that, The compaction density of the positive electrode sheet is 2.3 g / cc to 2.65 g / cc.

26. A preparation method of a battery cell, characterized in that, Comprising the following steps: Stack the positive electrode sheet, the separator, and the negative electrode sheet in sequence to form an electrode assembly; place the electrode assembly in an outer package to form a dry battery, and inject an electrolyte into the dry battery; Wherein, the positive electrode sheet includes a positive electrode main body and a positive electrode tab connected to the positive electrode main body. The ratio of the long side dimension to the short side dimension of the positive electrode main body is (3 to 8):1; The separator includes a base film and a bonding layer provided on at least one side of the base film. The bonding layer is a continuous layer with a porous structure; The electrolyte includes a first solvent. The first solvent includes one or more of dimethyl carbonate and a linear carboxylic acid ester having the structure shown in formula (1): R1-(C=O)-O-R2 Formula (1); Wherein, R1 and R2 each independently include an alkyl or haloalkyl group of C1 to C5.

27. The preparation method of the battery cell according to claim 26, wherein, The preparation method of the separator includes the following steps: Dissolve a binder and a pore-forming agent in an organic solvent to obtain a binder solution; Apply the binder solution on the base film, and remove the pore-forming agent after drying to form the bonding layer on the base film.

28. A battery device, characterized in that, Comprising one or more of the battery monomers described in any one of claims 1 to 25 and the battery monomers prepared by the preparation method of the battery monomers described in any one of claims 26 to 27.

29. An electrical device, characterized in that, One or more of the battery cells described in any one of claims 1 to 25, the battery cells prepared by the method for preparing a battery cell described in any one of claims 26 to 27, and the battery device described in claim 28.

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