Secondary battery cell and electric device

Abstract

A secondary battery cell and an electric device. The secondary battery cell comprises: a housing; and an electrode assembly and an electrolyte that are contained in the housing. The electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator, the separator being located between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprises graphite, and the powder OI of the graphite is 10-25. The electrolyte comprises an organic solvent, the organic solvent comprises a chain carbonate and a cyclic carbonate, and the mass ratio of the chain carbonate to the cyclic carbonate is 1.5-2.

Description

Secondary battery cell and power consuming device

[0001] Related Applications

[0002] The present application claims priority to the Chinese patent application No. 2024110951929, filed on August 9, 2024, entitled "Secondary battery cell and power consuming device", the contents of which are hereby incorporated by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of batteries, and in particular to a secondary battery cell and a power consuming device. BACKGROUND

[0004] In recent years, batteries such as lithium ion batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc.

[0005] With the continuous deepening of battery research, the performance of the battery has been greatly improved, but it is still difficult to balance high energy density and good cycle performance. SUMMARY

[0006] Based on the above problems, the first aspect of the present application provides a secondary battery cell, comprising: a shell; and an electrode assembly and an electrolyte contained in the shell. The electrode assembly comprises a positive electrode sheet, a negative electrode sheet and a separator film between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprises graphite, and the powder OI of the graphite is 10-25. The electrolyte comprises an organic solvent, the organic solvent comprises a chain carbonate and a cyclic carbonate, and the mass ratio of the chain carbonate to the cyclic carbonate is 1.5-2.

[0007] In the above-mentioned secondary battery cell, the graphite with a larger powder OI is easy to be compacted, so as to improve the energy density of the secondary battery cell. However, the graphite with a larger powder OI can increase the internal resistance of the secondary battery cell, and since the viscosity of the chain carbonate is usually low, the introduction of the chain carbonate in the electrolyte can reduce the internal resistance of the battery cell. However, the introduction of the chain carbonate can increase the gas production of the battery cell and affect the cycle performance. Therefore, in the above-mentioned battery cell, by using the graphite negative electrode active material with a specific powder OI, and matching the chain carbonate and the cyclic carbonate with a suitable mass ratio, the battery cell can have high energy density while balancing good cycle performance.

[0008] In some embodiments, the powder OI of the graphite is 12-20.

[0009] In some implementations, graphite includes synthetic graphite.

[0010] In some implementations, the graphite includes a primary grain morphology.

[0011] In some embodiments, the volumetric particle size distribution (DV50) of graphite is 8 μm-15 μm.

[0012] In some embodiments, the volumetric particle size distribution (DV10) of graphite is 4 μm-6 μm.

[0013] In some embodiments, the volumetric particle size distribution (DV90) of graphite is 20 μm-28 μm.

[0014] In some embodiments, the volumetric particle size distribution (DV99) of graphite is 30 μm-40 μm.

[0015] The volume distribution of graphite with particle sizes Dv50, Dv10, Dv90, and Dv99 within the above range can further improve the fast-charging performance of battery cells while ensuring that the battery cells have a high energy density.

[0016] In some embodiments, the graphitization degree of the graphite is 91%-95%. Graphite with a graphitization degree in this range is beneficial for further improving the energy density of the battery cell.

[0017] In some embodiments, the coating weight of the negative electrode film is 9 mg / cm³. 2 -14mg / cm 2 The coating weight of the negative electrode film within this range can further improve the energy density of the battery cell.

[0018] In some embodiments, the compaction density of the negative electrode film is 1.3 g / cm³. 3 -1.6g / cm 3 The compaction density of the negative electrode film within this range can further improve the energy density of the battery cell.

[0019] In some embodiments, the mass ratio of chain carbonate to cyclic carbonate is 1.6-1.9. Maintaining this mass ratio in the organic solvent allows for better matching of the amounts of both, more effectively promoting the reduction of internal resistance in the secondary battery cell, reducing gas production in the battery cell, and further improving the cycle performance of the battery cell.

[0020] In some embodiments, the chain carbonate accounts for 60%-70% of the organic solvent by mass.

[0021] In some embodiments, the cyclic carbonate accounts for 30%-40% by mass in the organic solvent.

[0022] In some embodiments, the chain carbonate includes at least two of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0023] In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate.

[0024] In some embodiments, the chain carbonate includes dimethyl carbonate, and the mass percentage of the dimethyl carbonate in the organic solvent is 10%-50%. The dimethyl carbonate has a small viscosity, which can effectively improve the internal resistance of the battery. Meanwhile, controlling the mass percentage of the dimethyl carbonate in the above range can balance the gas production of the dimethyl carbonate, which is conducive to further improving the cycle performance of the battery monomer.

[0025] In some embodiments, the mass percentage of the dimethyl carbonate in the organic solvent is 12%-30%.

[0026] In some embodiments, the chain carbonate includes methyl ethyl carbonate, and the mass percentage of the methyl ethyl carbonate in the organic solvent is 15%-45%. The mass percentage of the methyl ethyl carbonate in the organic solvent in the range can make the electrolyte have a good wettability effect, which can further improve the cycle performance of the battery monomer.

[0027] In some embodiments, the mass percentage of the methyl ethyl carbonate in the organic solvent is 20%-40%.

[0028] In some embodiments, the chain carbonate includes diethyl carbonate, and the mass percentage of the diethyl carbonate in the organic solvent is 5%-20%. The mass percentage of the diethyl carbonate in the organic solvent in the range can make the electrolyte have a good wettability effect, which can further improve the cycle performance of the battery monomer.

[0029] In some embodiments, the mass percentage of the diethyl carbonate in the organic solvent is 5%-15%.

[0030] In some embodiments, the electrolyte further includes an additive, and the additive includes at least one of vinylene carbonate and fluoroethylene carbonate.

[0031] In some embodiments, the positive electrode tab includes a positive electrode current collector and a positive electrode film layer arranged on the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a lithium-containing phosphate.

[0032] In some embodiments, the particle size distribution curve of the positive electrode active material includes two characteristic peaks. This represents that the positive electrode active material includes two materials with different particle sizes. The two materials with different particle sizes can improve the compaction density of the positive electrode tab, and further improve the energy density of the secondary battery monomer.

[0033] In some embodiments, the peak intensity of one of the two characteristic peaks is 0.5 μm-1.0 μm, and the peak intensity of the other characteristic peak is 1.2 μm-2.0 μm.

[0034] In some embodiments, the positive electrode film layer further comprises carbon nanotubes. The carbon nanotubes can improve the conductivity of the positive electrode tab, and further reduce the direct current internal resistance of the secondary battery cell.

[0035] In some embodiments, the carbon nanotubes are multi-walled carbon nanotubes.

[0036] In some embodiments, the diameter of the carbon nanotubes is 7 nm-12 nm.

[0037] In some embodiments, the coating weight of the positive electrode film layer is 19 mg / cm 2 -30 mg / cm 2 . The coating weight of the positive electrode film layer in this range can further reduce the heat generation of the battery cell and improve the safety performance of the battery cell.

[0038] In some embodiments, the compaction density of the positive electrode film layer is 2.3 g / cm 3 -2.6 g / cm 3 . The compaction density of the positive electrode film layer in this range can further improve the energy density of the battery cell.

[0039] In some embodiments, the length of the secondary battery cell is 500 mm-1200 mm. The secondary battery cell has a larger length, which can increase the amount of active material and further improve the energy density of the secondary battery cell.

[0040] In some embodiments, the length of the secondary battery cell is 700 mm-1100 mm.

[0041] In some embodiments, the width of the secondary battery cell is 90 mm-150 mm.

[0042] In some embodiments, the width of the secondary battery cell is 110 mm-150 mm.

[0043] In some embodiments, the thickness of the secondary battery cell is 15 mm-30 mm.

[0044] In some embodiments, the thickness of the secondary battery cell is 20 mm-30 mm.

[0045] In some embodiments, the length-width ratio of the secondary battery cell is 5-12. The length-width ratio of the secondary battery cell in this range can enable better overall arrangement of more secondary battery cells, and further promote the improvement of battery energy density.

[0046] In some embodiments, the ratio of the width to the thickness of the secondary battery cell is 3.2-11.5.

[0047] In some embodiments, the secondary battery cell further comprises a first electrode terminal, a second electrode terminal, a first tab and a second tab, the first electrode terminal and the second electrode terminal are respectively connected to the shell, the first electrode terminal and the first tab are directly electrically connected, and the second electrode terminal and the second tab are directly electrically connected; the polarity of the first tab is opposite to that of the second tab. The direct electrical connection between the first electrode terminal and the first tab and the direct electrical connection between the second electrode terminal and the second tab cancel the current collecting member between the electrode terminal and the tab, which can further reduce the internal resistance of the secondary battery cell. At the same time, since the current collecting member is omitted, the volume of the secondary battery cell can be reduced, thereby improving the energy density of the secondary battery cell.

[0048] In some embodiments, the ratio of the width of the first tab to the width of the secondary battery cell is 0.5-1. The ratio of the width of the first tab to the width of the secondary battery cell in this range can promote heat dissipation of the secondary battery cell, reduce heat accumulation during use of the secondary battery cell, and further improve the safety performance of the battery cell.

[0049] In some embodiments, the ratio of the width of the first tab to the width of the secondary battery cell is 0.7-1.

[0050] In some embodiments, the ratio of the width of the second tab to the width of the secondary battery cell is 0.5-1. The ratio of the width of the second tab to the width of the secondary battery cell in this range can promote heat dissipation of the secondary battery cell, reduce heat accumulation during use of the secondary battery cell, and further improve the safety performance of the battery cell.

[0051] In some embodiments, the ratio of the width of the second tab to the width of the secondary battery cell is 0.7-1.

[0052] In some embodiments, the width of the first tab and the width of the second tab are different.

[0053] In some embodiments, the first tab is a positive tab, and the second tab is a negative tab, the ratio of the width of the positive tab to the width of the secondary battery cell is denoted as W1, and the ratio of the width of the negative tab to the width of the secondary battery cell is denoted as W2, then W1>W2.

[0054] In some embodiments, the extension direction of the first tab and the second tab is the same as the length direction of the secondary battery cell, and the first tab and the second tab are respectively arranged at both ends of the electrode assembly.

[0055] In some embodiments, the number of the first tab is 1-2.

[0056] In some embodiments, the number of the first tabs is 2, and the 2 first tabs are arranged at an end of the electrode assembly.

[0057] In some embodiments, the number of the second tabs is 1-2.

[0058] In some embodiments, the number of the second tabs is 2, and the 2 second tabs are arranged at an end of the electrode assembly.

[0059] The second aspect of the present application provides a power consuming device comprising the secondary battery cell of the first aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0060] For better understanding and illustrating the embodiments or examples provided by the present application, one or more drawings can be referred to. Additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the presently described embodiments or examples, and any one of the best modes of these applications presently understood. Moreover, the same reference numerals are used to represent the same components throughout the drawings. In the drawings:

[0061] Fig. 1 is an exploded view of a secondary battery cell according to an embodiment of the present application.

[0062] Fig. 2 is a schematic view of an electrode assembly of a secondary battery cell according to an embodiment of the present application.

[0063] Fig. 3 is a schematic view of an electrode assembly of a secondary battery cell according to another embodiment of the present application.

[0064] Fig. 4 is a schematic view of a battery pack according to an embodiment of the present application.

[0065] Fig. 5 is an exploded view of the battery pack of Fig. 4.

[0066] Fig. 6 is a schematic view of a power consuming device according to an embodiment of the present application.

[0067] Marked description in the drawings: 1, battery pack; 2, upper box body; 3, lower box body; 4, battery module; 5, secondary battery cell; 51, shell; 52, electrode assembly; 521, body; 522, first tab; 523, second tab; 53, end cover; 54, first electrode terminal; 55, second electrode terminal; 6, power consuming device. DETAILED DESCRIPTION

[0068] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the related drawings. The preferred embodiments of the present application are shown in the drawings. However, the present application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive. DETAILED DESCRIPTION

[0069] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0070] "Ranges" disclosed herein are of the type where the lower limit and the upper limit of a given range are selected, the selected lower limit and upper limit define the boundaries of a particular range. Ranges defined in this manner can be inclusive or exclusive of the end values, either end value can be included or excluded independently, and can be combined in any manner. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. In addition, if a minimum range value of 1 and 2 are listed, and if a maximum range value of 3, 4, and 5 are also listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, a numerical range "a-b" indicates a shorthand way of describing each and every

[0071] In this application, references to "a plurality" or "a plurality of" or "plurality" or "a plurality of something" refer to one or more than one, and are equivalent to the term "one or more" unless otherwise stated.

[0072] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, if not specifically stated.

[0073] Reference to "an embodiment" herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment or implementation of the application. The appearances of the phrase "in an embodiment" or "in implementations" in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. Those skilled in the art will appreciate that embodiments described herein can be combined with other embodiments unless otherwise specified. Reference to "implementations" herein has a similar understanding.

[0074] Those skilled in the art will understand that, in the methods of various implementations or embodiments, the order of the steps written is not meant to imply a strict execution order and does not constitute any limitation on the implementation process, and the detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the application can be performed sequentially or randomly. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, it is mentioned that the method can also include step (c), which means that step (c) can be added to the method in any order, for example, the method can include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0075] In this application, the open technical features or technical solutions described with the words "containing", "including", "comprising" and the like, if not otherwise specified, do not exclude additional members from the listed members, which can be regarded as providing both a closed feature or solution composed of the listed members, and an open feature or solution including additional members in addition to the listed members. For example, A includes a1, a2 and a3, if not otherwise specified, it can also include other members, or it can not include additional members, which can be regarded as providing the feature or solution that "A is composed of a1, a2 and a3", and also providing the feature or solution that "A includes a1, a2 and a3, and also includes other members".

[0076] In this application, "A, such as B" means that B is a non-limiting example of A, and A can be understood as not limited to B.

[0077] In this application, "optionally", "optional" and "optional" mean that it can or can not be present, that is, it means to choose from the two parallel schemes of "yes" or "no". If there are multiple "optional" in a technical solution, if not otherwise specified, and there is no contradictory relationship or mutual restriction, each "optional" is independent.

[0078] In the present application, unless otherwise specified, the "secondary battery cell" refers to a basic unit capable of realizing mutual conversion between chemical energy and electrical energy, and further, generally includes at least a positive electrode sheet, a negative electrode sheet, and an electrolyte. In the process of charging and discharging the battery, active ions are embedded and de-embedded 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.

[0079] An embodiment of the present application provides a secondary battery cell. The secondary battery cell includes a housing; and an electrode assembly and an electrolyte contained in the housing. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator film between the positive electrode sheet and the negative electrode sheet. The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector, the negative electrode film layer including a negative electrode active material, the negative electrode active material including graphite, and a powder OI of the graphite being 10-25. The electrolyte includes an organic solvent, the organic solvent including a chain carbonate and a cyclic carbonate, and a mass ratio of the chain carbonate to the cyclic carbonate being 1.5-2.

[0080] Graphite is a widely used negative electrode active material in secondary battery cells. The powder OI of graphite represents the orientation of the material, and the level of orientation will affect the embedding and de-embedding rate of active ions on the surface of the graphite negative electrode, thereby affecting the overall performance of the battery cell. Therefore, the powder OI is one of the key indicators for evaluating the performance of graphite negative electrode active materials. The inventors found in the process of exploring secondary battery cells that the orientation of graphite with a larger powder OI during cold pressing of the negative electrode sheet may be more easily oriented in one direction, making it easier to be compacted. Therefore, the selection of graphite with a powder OI of 10-25 in the present application helps to improve the energy density of the secondary battery cell. However, graphite with a larger powder OI usually has poor kinetics, which increases the internal resistance of the secondary battery cell. Since the viscosity of chain carbonates is usually low, the introduction of chain carbonates in the electrolyte can reduce the internal resistance of the battery cell. However, the introduction of chain carbonates usually increases the gas production of the battery cell, affecting the cycle performance of the battery cell. Therefore, in the above-mentioned battery cell, by using graphite negative electrode active material with a specific powder OI, and at the same time matching the mass ratio of chain carbonate and cyclic carbonate, the battery cell can have both high energy density and good cycle performance.

[0081] Negative electrode sheet

[0082] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0083] As a non-limiting example, the negative electrode current collector has two opposite surfaces in the thickness direction of itself, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0084] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be obtained by forming a metal material on a polymer material base layer. Non-limiting examples of the metal material in the negative current collector can include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, and the like. Non-limiting examples of the polymer material base layer in the negative current collector can include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0085] In some embodiments, the negative active material can further include a negative active material for a battery known in the art. As non-limiting examples, the negative active material can include one or more of other carbon-based materials other than the above-described graphite having a value of 10-25 for the powder OI, silicon-based materials, tin-based materials, and lithium titanate, and the like. The silicon-based material can include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material can include one or more of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone or in combination with two or more.

[0086] In some embodiments, the negative film layer can further optionally include a binder. The binder can include one or more of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0087] In some embodiments, the negative film layer can further optionally include a conductive agent. The conductive agent can include one or more of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0088] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as a thickening agent. Optionally, the thickening agent includes sodium carboxymethyl cellulose (CMC-Na) and the like.

[0089] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, in a solvent, for example, deionized water, to form a negative electrode slurry; coating the negative electrode slurry on at least one side surface of the negative electrode current collector, and after processes such as drying, cold pressing, etc., the negative electrode sheet can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be on a single surface of the negative electrode current collector, or on both surfaces of the negative electrode current collector.

[0090] Some optional examples of the powder OI of graphite are 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, and any value within the range formed by any two of the above-mentioned values. For example, the powder OI of graphite can be 11-25, 11-20, 11-18, 12-25, 12-20, 12-18, 13-25, 13-20, 13-18, 14-25, 14-20, 14-18, 15-25, 15-20, 15-18.

[0091] The powder OI of graphite in the present application can be measured by the following test method: using an X-ray powder diffractometer, according to the general method for X-ray diffraction analysis and the method for measuring the lattice parameters of graphite JIS K 0131-1996, JB / T 4220-2011, obtaining the X-ray diffraction spectrum, OI value = C004 / C110, wherein C004 is the peak area of the 004 crystal plane diffraction peak, and C110 is the peak area of the 110 crystal plane diffraction peak. Specifically, the test method for the powder OI value of the negative electrode active material is as follows: a certain mass of negative electrode active material powder is placed in an X-ray powder diffractometer, the peak area of the 004 crystal plane diffraction peak and the peak area of the 110 crystal plane diffraction peak are obtained by X-ray diffraction analysis, and then the powder OI value of the negative electrode active material particles is obtained. The X-ray powder diffractometer can be a Bruker D8 Discover.

[0092] In some embodiments, the graphite includes artificial graphite.

[0093] In some embodiments, the graphite includes primary particle morphology. It can be understood that the primary particle generally refers to a particle that has not undergone agglomeration. The morphology of the graphite material can be tested by using a scanning electron microscope. The test can refer to JY / T 0584-2020. The scanning electron microscope can be a ZEISS Sigma 300.

[0094] In some embodiments, the volume distribution particle size Dv50 of the graphite is 8 microns (referred to as: μm) - 15 μm. Alternatively, the volume distribution particle size Dv50 of the graphite can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, and any value within the range formed by any two of the above values.

[0095] In some embodiments, the volume distribution particle size Dv10 of the graphite is 4 μm - 6 μm. The volume distribution particle size Dv10 of the graphite can be 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, and any value within the range formed by any two of the above values.

[0096] In some embodiments, the volume distribution particle size Dv90 of the graphite is 20 μm - 28 μm. The volume distribution particle size Dv90 of the graphite can be 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, and any value within the range formed by any two of the above values.

[0097] In some embodiments, the volume distribution particle size Dv99 of the graphite is 30 μm - 40 μm. The volume distribution particle size Dv99 of the graphite can be 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, 40 μm, and any value within the range formed by any two of the above values.

[0098] The volume distribution particle sizes Dv50, Dv10, Dv90, Dv99 of the graphite within the above ranges can further improve the fast charging performance of the battery monomer on the basis of having a higher energy density of the battery monomer.

[0099] The Dv10, Dv50, Dv90, Dv99 of the graphite are meanings known in the art, and can be tested using methods known in the art. For example, reference can be made to the standard GB / T 19077-2016, and determination can be made using a laser particle size analyzer, which can be a Malvern Master Size 3000. The physical definitions of Dv10, Dv50, Dv90, Dv99 are as follows: Dv10: the particle size corresponding to the cumulative volume distribution percentage of the graphite reaching 10%. Dv50: the particle size corresponding to the cumulative volume distribution percentage of the graphite reaching 50%. Dv90: the particle size corresponding to the cumulative volume distribution percentage of the graphite reaching 90%. Dv99: the particle size corresponding to the cumulative volume distribution percentage of the graphite negative active material reaching 99%.

[0100] In some embodiments, the graphitization degree of the graphite is 91%-95%. The graphite with the graphitization degree in this range is beneficial to further improve the energy density of the battery cell. Alternatively, the graphitization degree of the graphite can be 91%, 92%, 93%, 94%, 95%, and any value in the range formed by any two of the above values.

[0101] The graphitization degree of the graphite can be tested using an X-ray diffractometer, which can be Bruker D8 Discover, according to JIS K 0131-1996, JB / T 4220-2011, and GB / T 24533-2019. Specifically, the size of d002 is first measured, and then the graphitization degree is calculated according to the formula G=(0.344-d002) / (0.344-0.3354) x 100%, wherein d002 is the interlayer spacing in the graphite crystal structure, expressed in nanometers (abbreviated as nm). In the X-ray diffraction analysis test, a copper target can be used as an anode target, CuKα ray is used as the radiation source, and the wavelength of the ray is 0.15406 nm. The scanning 2θ angle range is 20°-80°, and the scanning rate can be 4° / min.

[0102] In some embodiments, the coating weight of the negative electrode film layer is 9 milligrams per square centimeter (abbreviated as mg / cm 2 -14 mg / cm 2 . The coating weight of the negative electrode film layer in this range can further improve the energy density of the battery cell. Alternatively, the coating weight of the negative electrode film layer can be 9 mg / cm 2 , 10 mg / cm 22 , 11 mg / cm 2 , 12 mg / cm 2 , 13 mg / cm 2 , 14 mg / cm 2 , and any value in the range formed by any two of the above values.

[0103] The coating weight of the negative electrode film layer can be measured by using instruments and methods known in the art. For example, the negative electrode sheet after cold pressing is cut into small round pieces with an area of S1, weighed, and recorded as M1. Then the negative electrode film layer of the above weighed negative electrode sheet is wiped off, the weight of the negative electrode current collector is weighed and recorded as M0, and the coating weight of the negative electrode film layer=(weight of the negative electrode sheet M1-weight of the negative electrode current collector M0) / S1.

[0104] In some embodiments, the compaction density of the negative electrode film layer is 1.3 grams per cubic centimeter (abbreviated as g / cm 3 -1.6 g / cm 3The compaction density of the negative electrode film layer in this range can further improve the energy density of the battery cell. Alternatively, the compaction density of the negative electrode film layer can be any value in the range of 1.35 g / cm 3 1.38 g / cm 3 1.4 g / cm 3 1.42 g / cm 3 1.45 g / cm 3 1.48 g / cm 3 1.5 g / cm 3 1.52 g / cm 3 1.55 g / cm 3 and any value in the range formed by any two of the above values.

[0105] The compaction density of the negative electrode film layer can be tested by the following method: taking a single-sided coated and cold-pressed negative electrode tab, if it is a double-sided coated tab, wiping off the film layer on one side first, punching into a small disc with an area of S1, weighing it, and recording it as M1; measuring the thickness of the negative electrode tab film layer, and recording it as T; then wiping off the above weighed negative electrode film layer, weighing the negative electrode current collector, and recording it as M0. The compaction density PD of the negative electrode film layer = (M1-M0) / (S1xT).

[0106] Electrolyte

[0107] The electrolyte has the function of conducting ions between the positive electrode tab and the negative electrode tab. The type of electrolyte is not particularly limited in the present application and can be selected according to the needs. For example, the electrolyte can be liquid, gel or all-solid.

[0108] In some embodiments, the electrolyte uses electrolyte solution. The electrolyte solution includes electrolyte salt and organic solvent. The organic solvent includes chain carbonate and cyclic carbonate, and the mass ratio of chain carbonate to cyclic carbonate is 1.5-2.

[0109] In some embodiments, the mass ratio of the chain carbonate to the cyclic carbonate in the organic solvent can be 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.86, 1.9, 1.95, 2, and any value within a range defined by any two of the above values. For example, the mass ratio of the chain carbonate to the cyclic carbonate in the organic solvent can be 1.5-1.95, 1.5-1.95, 1.55-1.95, 1.55-1.9, 1.6-2, 1.6-1.95, 1.6-1.9, 1.6-2, 1.6-1.95, 1.6-1.9, 1.65-2, 1.65-1.95, 1.65-1.9, 1.7-2, 1.7-1.95, 1.7-1.9, 1.75-2, 1.75-1.95, 1.75-1.9, 1.8-2, 1.8-1.95, 1.8-1.9. The mass ratio of the chain carbonate to the cyclic carbonate in the organic solvent within the range can better adapt the use amount of the two, more fully promote the reduction of the secondary battery cell internal resistance, reduce the gas production of the battery cell, and further improve the cycle performance of the battery cell.

[0110] In some embodiments, the mass percentage of the chain carbonate in the organic solvent is 60%-70%. Alternatively, the mass percentage of the chain carbonate in the organic solvent is 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, and any value within a range defined by any two of the above values.

[0111] In some embodiments, the mass percentage of the cyclic carbonate in the organic solvent is 30%-40%. Alternatively, the mass percentage of the cyclic carbonate in the organic solvent is 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, and any value within a range defined by any two of the above values.

[0112] In some embodiments, the chain carbonate includes at least two of dimethyl carbonate (abbreviated as: DMC), diethyl carbonate (abbreviated as: DEC), and ethyl methyl carbonate (abbreviated as: EMC).

[0113] In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate (abbreviated as: EC) and propylene carbonate (abbreviated as: PC).

[0114] In some embodiments, the chain carbonate includes dimethyl carbonate, and the mass percentage of dimethyl carbonate in the organic solvent is 10%-50%. The viscosity of dimethyl carbonate is small, which can effectively improve the internal resistance of the battery. At the same time, by controlling the mass percentage of dimethyl carbonate in the above range, the gas production of dimethyl carbonate can be balanced, which is conducive to further improving the cycle performance of the battery monomer. Optionally, the mass percentage of dimethyl carbonate in the organic solvent can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, and any value within the range formed by any two of the above values. Further optionally, the mass percentage of dimethyl carbonate in the organic solvent is 12%-30%.

[0115] In some embodiments, the chain carbonate includes methyl ethyl carbonate, and the mass percentage of methyl ethyl carbonate in the organic solvent is 15%-45%. The mass percentage of methyl ethyl carbonate in the organic solvent in this range can make the electrolyte have a good wetting effect, which can further improve the cycle performance of the battery monomer. Optionally, the mass percentage of methyl ethyl carbonate in the organic solvent can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, and any value within the range formed by any two of the above values. Further optionally, the mass percentage of methyl ethyl carbonate in the organic solvent is 20%-40%.

[0116] In some embodiments, the chain carbonate includes dimethyl carbonate, and the mass percentage of dimethyl carbonate in the organic solvent is 10%-50%. The viscosity of dimethyl carbonate is small, which can effectively improve the internal resistance of the battery. At the same time, by controlling the mass percentage of dimethyl carbonate in the above range, the gas production of dimethyl carbonate can be balanced, which is conducive to further improving the cycle performance of the battery monomer. Optionally, the mass percentage of dimethyl carbonate in the organic solvent can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, and any value within the range formed by any two of the above values. Further optionally, the mass percentage of dimethyl carbonate in the organic solvent is 12%-30%.

[0117] In some embodiments, the organic solvent can also include one or more of dipropyl carbonate (abbreviation: DPC), methyl propyl carbonate (abbreviation: MPC), ethyl propyl carbonate (abbreviation: EPC), butylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0118] It can be understood that the electrolyte will be consumed in the preparation process of the secondary battery cell and in the subsequent use process of the secondary battery, but the consumption has little effect on the mass ratio of the chain carbonate and the cyclic carbonate, which can be basically ignored. The mass ratio of the chain carbonate and the cyclic carbonate of the secondary battery cell obtained in any state is within the scope of the present application and belongs to the protection scope of the present application.

[0119] In some embodiments, the electrolyte further includes an additive. The additive includes at least one of vinylene carbonate and fluoroethylene carbonate. Optionally, the electrolyte can further include an additive capable of improving certain performance of the secondary battery cell, such as an additive capable of improving overcharge performance of the secondary battery cell, an additive capable of improving high-temperature or low-temperature performance of the battery, etc.

[0120] In some embodiments, the electrolyte salt can include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluoro-oxalato-borate (LiDFOB), lithium bis-oxalato-borate (LiBOB), lithium difluoro-bis-oxalato-phosphate (LiDFOP), and lithium tetrafluoro-oxalato-phosphate (LiTFOP).

[0121] Positive electrode tab

[0122] The positive electrode tab includes a positive current collector and a positive film layer disposed on at least one surface of the positive current collector, the positive film layer including a positive active material.

[0123] As a non-limiting example, the positive current collector has two opposite surfaces in the thickness direction of itself, and the positive film layer is disposed on either one or both of the two opposite surfaces of the positive current collector.

[0124] In some embodiments, the positive electrode current collector can employ a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be obtained by forming a metal material on a polymer material base material. Non-limiting examples of the metal material in the positive electrode current collector can include one or more of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, and the like. Non-limiting examples of the polymer material base material in the positive electrode current collector can include one or more of a polypropylene (PP), a polyethylene terephthalate (PET), a polybutylene terephthalate (PBT), a polystyrene (PS), a polyethylene (PE), and the like.

[0125] In some embodiments, the positive electrode active material includes a lithium-containing phosphate. Optionally, the lithium-containing phosphate includes one or more of lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon, which has a small amount of gas generation, and can further improve the safety performance of the secondary battery cell.

[0126] In some embodiments, the positive electrode active material includes a lithium-containing phosphate, and the particle size distribution curve of the positive electrode active material includes two characteristic peaks. This represents that the positive electrode active material includes two materials with different particle sizes. The two materials with different particle sizes can increase the compaction density of the positive electrode sheet, and further improve the energy density of the secondary battery cell.

[0127] In some embodiments, the peak intensity of one of the characteristic peaks is 0.5 μm-1.0 μm. Optionally, the peak intensity of one of the peaks can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, and any value within a range defined by any two of the above values.

[0128] In some embodiments, the peak intensity of the other characteristic peak is 1.2 μm-2.0 μm. Optionally, the peak intensity of the other characteristic peak can be 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, and any value within a range defined by any two of the above values.

[0129] The particle size distribution curve of the positive electrode active material can be determined using a laser particle size analyzer in accordance with the standard GB / T 19077-2016, and the laser particle size analyzer can be a Malvern Master Size 3000.

[0130] In some embodiments, the positive electrode film layer also includes carbon nanotubes. Carbon nanotubes can improve the conductivity of the positive electrode, further reducing the DC internal resistance of the secondary battery cell.

[0131] In some embodiments, carbon nanotubes include multi-walled carbon nanotubes.

[0132] In some embodiments, the diameter of the carbon nanotubes is 7 nm to 12 nm. Optionally, the diameter of the carbon nanotubes can be 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, or any value within the range of any two of the above values.

[0133] In some embodiments, the coating weight of the positive electrode film is 19 mg / cm³. 2 -30mg / cm 2 Within this range, the coating weight of the positive electrode film can further reduce heat generation in the battery cell and improve its safety performance. Optionally, the coating weight of the positive electrode film can be 19 mg / cm³. 2 20mg / cm 2 21mg / cm 2 22mg / cm 2 23mg / cm 2 24mg / cm 2 25mg / cm 2 26mg / cm 2 27mg / cm 2 28g / cm 2 29mg / cm 2 30mg / cm 2 And any value within the range consisting of any two of the above values.

[0134] The coating weight of the positive electrode film can be determined using instruments and methods known in the art. For example, take a cold-pressed positive electrode sheet, cut it into small circular pieces with an area of ​​S1, weigh them, and record their weight as M1. Then wipe off the positive electrode film of the weighed positive electrode sheet, weigh the positive current collector, and record it as M0. The coating weight of the positive electrode film = (weight of the positive electrode sheet M1 - weight of the positive current collector M0) / S1.

[0135] In some embodiments, the compaction density of the positive electrode film is 2.3 g / cm³. 3 -2.6g / cm 3 The compaction density of the positive electrode film within this range can further improve the energy density of the battery cell. Optionally, the compaction density of the positive electrode film can be 2.35 g / cm³. 3 2.4g / cm 3 2.45g / cm 32.5 g / cm 3 2.55 g / cm 3 2.6 g / cm 3 and any value within a range defined by any two of the above values.

[0136] The compaction density of the positive electrode film layer can be tested by the following method: taking a single-side coated and cold-pressed positive electrode sheet, if it is a double-side coated sheet, wiping off the film layer on one side first, punching into a small disc with an area of S1, weighing it, and recording it as M1; measuring the thickness of the positive electrode film layer, and recording it as T; then wiping off the above weighed positive electrode film layer, weighing the positive electrode current collector, and recording it as M0. The compaction density of the positive electrode film layer = (M1-M0) / (S1xT).

[0137] In some embodiments, the positive electrode active material can include other positive electrode active materials known in the art in addition to lithium-containing phosphates. As non-limiting examples, the known positive electrode active materials include lithium transition metal oxides. Examples of lithium transition metal oxides can 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, lithium nickel cobalt aluminum oxide, and modified compounds thereof, etc. Non-limiting examples of lithium cobalt oxide can include LiCoO2; non-limiting examples of lithium nickel oxide can include LiNiO2; non-limiting examples of lithium manganese oxide can include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxide can include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(referred to as: NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2(referred to as: NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(referred to as: NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(referred to as: NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(referred to as: NCM 811 ), etc. Non-limiting examples of lithium nickel cobalt aluminum oxide can include LiNi 0.8 Co 0.15 Al 0.05 O2.

[0138] In some embodiments, the positive electrode film layer can further optionally include a binder. As a non-limiting example, the binder can include one or more of polyvinylidene fluoride (abbreviated as: PVDF), polytetrafluoroethylene (abbreviated as: PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0139] In some embodiments, the positive electrode film layer can further optionally include a conductive agent. As a non-limiting example, the conductive agent can include one or more of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, and graphene.

[0140] In some embodiments, the positive electrode tab can be prepared by 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 to form a positive electrode slurry; coating the positive electrode slurry on at least one side surface of the positive electrode current collector, and then drying, cold-pressing, or the like to obtain the positive electrode tab. The type of the solvent can be selected from, but is not limited to, any of the above-mentioned embodiments, such as N-methylpyrrolidone (abbreviated as: NMP). The positive electrode slurry can be coated on a single surface of the positive electrode current collector, or on both surfaces of the positive electrode current collector.

[0141] Separator film

[0142] The secondary battery cell further includes a separator film. The type of the separator film is not particularly limited in the present application, and any publicly known porous structure separator film having good chemical stability and mechanical stability can be used.

[0143] In some embodiments, the material of the separator film can include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0144] In some embodiments, the separator film further includes a coating layer.

[0145] In some embodiments, the coating layer can include one or more of a heat-resistant coating layer or an adhesive coating layer.

[0146] In some embodiments, the heat-resistant coating layer includes one or more of organic heat-resistant particles or inorganic heat-resistant particles.

[0147] In some embodiments, the inorganic heat-resistant particles include one or more of boehmite (abbreviation: γ-AlOOH), alumina (abbreviation: Al2O3), barium sulfate (abbreviation: BaSO4), magnesium oxide (abbreviation: MgO), magnesium hydroxide (abbreviation: Mg(OH)2), silicon dioxide (abbreviation: SiO2), tin dioxide (abbreviation: SnO2), titanium oxide (abbreviation: TiO2), calcium oxide (abbreviation: CaO), zinc oxide (abbreviation: ZnO), zirconium oxide (abbreviation: ZrO2), yttrium oxide (abbreviation: Y2O3), nickel oxide (abbreviation: NiO), cerium oxide (abbreviation: CeO2), zirconium titanate (abbreviation: SrTiO3), barium titanate (abbreviation: BaTiO3), and magnesium fluoride (abbreviation: MgF2).

[0148] In some embodiments, the organic heat-resistant particles include one or more of phenol formaldehyde resin, polystyrene, polyethylene, polypropylene, polyimide, cellulose, polyester, polyphenylene sulfide, polyaramid, polyamide-imide, and polyimide.

[0149] In some embodiments, the adhesive coating layer includes organic binder particles.

[0150] The heat-resistant coating layer or the adhesive coating layer further includes a binder for fixing the above-mentioned particulate materials. Optionally, the binder includes one or more of a homopolymer or a copolymer of acrylic monomer units, a homopolymer or a copolymer of acrylate monomer units, a homopolymer or a copolymer of fluorine-containing vinyl monomer units, a homopolymer or a copolymer of unsaturated nitrile monomer units, and polyvinylpyrrolidone.

[0151] In some embodiments, the positive electrode tab, the negative electrode tab, and the separator film can be made into an electrode assembly through a winding process or a stacking process.

[0152] In some embodiments, the length of the secondary battery cell is 500 millimeters (abbreviation: mm) to 1200 mm. The secondary battery cell has a large length, which can increase the amount of active material, and further improve the energy density of the secondary battery cell. Optionally, the length of the secondary battery cell can be 500 mm, 600 mm, 700 mm, 800 mm, 900 mm, 1000 mm, 1100 mm, 1200 mm, and any value within a range defined by any two of the above values. Optionally, the length of the secondary battery cell is 700 mm to 1100 mm.

[0153] In some embodiments, the width of the secondary battery cell is 90mm-150mm. Alternatively, the width of the secondary battery cell can be 90mm, 95mm, 100mm, 105mm, 110mm, 115mm, 120mm, 125mm, 130mm, 135mm, 140mm, 145mm, 150mm, and any value within the range defined by any two of the above values. Further alternatively, the width of the secondary battery cell is 120mm-140mm. The width of the secondary battery cell within this range can enable the electrolyte to maintain a good wetting effect on the electrode assembly, thereby further improving the cycle performance of the secondary battery cell on the basis of a high volumetric energy density.

[0154] In some embodiments, the thickness of the secondary battery cell is 15mm-30mm. Alternatively, the thickness of the secondary battery cell can be 15mm, 16mm, 17mm, 18mm, 19mm, 20mm, 20.5mm, 21mm, 21.5mm, 22mm, 22.5mm, 23mm, 23.5mm, 24mm, 24.5mm, 25mm, 25.5mm, 26mm, 26.5mm, 27mm, 27.5mm, 28mm, 30mm, and any value within the range defined by any two of the above values. For example, the thickness of the secondary battery cell can be 15mm-28mm, 15mm-26mm, 15mm-25mm, 18mm-28mm, 18mm-26mm, 18mm-25mm, 20mm-28mm, 20mm-26mm, 20mm-25mm.

[0155] In some embodiments, the aspect ratio of the secondary battery cell is 5-12. The aspect ratio of the secondary battery cell within this range can enable better overall arrangement of more secondary battery cells, thereby further promoting the improvement of the energy density of the battery. Alternatively, the aspect ratio of the secondary battery cell can be 5, 6, 7, 8, 9, 10, 11, 12, and any value within the range defined by any two of the above values. For example, the aspect ratio of the secondary battery cell can be 5-11, 5-10, 5-9, 6-11, 6-10, 6-9, 7-11, 7-10, 7-9, 7.5-11, 7.5-10, 7.5-9, 8-11, 8-10, 8-9. It can be understood that the aspect ratio of the secondary battery cell represents the ratio of the length to the width of the secondary battery cell.

[0156] In some embodiments, the width-to-thickness ratio of the secondary battery cell is 3.2-11.5. For example, the width-to-thickness ratio of the secondary battery cell can be 3.2, 4, 5, 6, 7, 8, 9, 10, 11, 11.5, and any value within the range defined by any two of the above values. For example, the width-to-thickness ratio of the secondary battery cell can be 3.2-11.5, 3.2-10, 3.2-8, 3.2-6, 3.2-5, 4-11.5, 4-10, 4-8, 4-6, 4-5. It can be understood that the width-to-thickness ratio of the secondary battery cell represents the ratio of the width and the thickness of the secondary battery cell.

[0157] When other designs of the battery remain unchanged, for example, the length of the secondary battery cell is determined, if the battery achieves the required energy density, the width and thickness of the secondary battery cell need to be reasonably adjusted. If the width or thickness is designed too small, the design requirement of energy density cannot be met; if the thickness is designed too large, the heat dissipation performance of the secondary battery cell will be affected; if the width is designed too large, the cycle performance of the secondary battery cell will be affected. Therefore, the width-to-thickness ratio of the secondary battery cell needs to be controlled within a certain range, so that the secondary battery cell can have good heat dissipation performance and cycle performance at the same time.

[0158] It can be understood that the shell can have various shapes, for example, a hollow cylindrical body, a hollow cuboid, and other hollow three-dimensional structures, and the electrode assembly is accommodated in the accommodation cavity of the hollow three-dimensional structure. The shape of the shell can be determined according to the shape of the electrode assembly. If the electrode assembly is a cylindrical structure, the shell can be a hollow cylindrical structure; if the electrode assembly is a cuboid structure, the shell can be a hollow cuboid structure. The material of the shell can be a conductive material such as copper, iron, aluminum, stainless steel, and aluminum alloy, or an insulating material such as plastic and rubber. Optionally, the shell is a hard shell. Further optionally, the hard shell includes an aluminum shell. The aluminum shell has good heat dissipation performance, which can promote the improvement of the heat dissipation performance of the battery cell.

[0159] In some embodiments, as shown in FIGS. 1-3, the secondary battery cell 5 includes a shell 51 and an electrode assembly 52 and an electrolyte accommodated in the shell 51. The shell 51 has an opening. The secondary battery cell 5 further includes an end cover 53 for covering the opening. The electrode assembly 52 includes a body 521 and a tab, the body 521 includes a positive electrode sheet, a negative electrode sheet, and a separator, and the separator is located between the positive electrode sheet and the negative electrode sheet. Optionally, the tab includes a first tab 522 and a second tab 523. The polarity of the first tab 522 and the second tab 523 is opposite.

[0160] The shell 51 is a hollow cuboid structure, and the opening is rectangular. The opening can be one or two. Optionally, when the opening is one, it can be arranged on any one face of the hollow cuboid shell 51. When the opening is two, it can be arranged on two opposite sides of the hollow cuboid shell 51, or on the top and bottom faces of the cuboid shell 51. When the number of openings is more, it is determined according to the actual situation.

[0161] The end cover 53 is used to cover the opening of the shell 51 to form a sealed space for accommodating the electrode assembly 52 and the electrolyte. The end cover 53 is a carrier of other components such as electrode terminals. The end cover 53 can serve as an output pole of the battery monomer, which is a part of the battery monomer connected to other components and outputs the electrical energy of the battery monomer.

[0162] The end cover 53 and other components arranged on the end cover 53 can be collectively referred to as an end cover assembly, which can include explosion-proof valves, liquid injection holes, insulating pieces, etc. The end cover assembly can be one or more.

[0163] The electrode terminals are arranged on the end cover 53, and the electrode terminals are output components for outputting the electrical energy of the battery monomer. The number of electrode terminals can be one or more, and the material can be a conductive material such as copper, iron, aluminum, stainless steel, and aluminum alloy. The electrode terminals conduct the electrical energy generated by the electrode assembly 52 to the electrical device through the electrical connection of the tabs and the electrical device. In some embodiments, the electrode terminals and the tabs are directly electrically connected.

[0164] In some embodiments, the opening of the shell 51 is two, the two openings are arranged on the opposite sides of the shell 51, and the end cover assembly is two, the two end cover assemblies cover the two openings of the shell 51 respectively.

[0165] In some embodiments, the end cover assembly can also include a pressure relief mechanism mounted on the end cover 53, which is used to release the pressure inside the battery monomer when the internal pressure or temperature of the battery monomer reaches a threshold value. Of course, if the end cover assembly in the battery monomer is one, the pressure relief mechanism can be mounted on the end cover 53 of the end cover assembly. If the end cover assembly in the battery monomer is two, the pressure relief mechanism can be mounted on the end cover 53 of each end cover assembly, or only on the end cover 53 of one end cover assembly. Exemplarily, the pressure relief mechanism can be an explosion-proof valve, an explosion-proof sheet, a gas valve, a pressure relief valve, or a safety valve, etc.

[0166] In some embodiments, as shown in FIGS. 1-3, the secondary battery cell 5 further comprises a first electrode terminal 54, a second electrode terminal 55, a first tab 522 and a second tab 523, the first electrode terminal 54 and the second electrode terminal 55 are respectively connected to the shell 51, the first electrode terminal 54 and the first tab 522 are directly electrically connected, the second electrode terminal 55 and the second tab 523 are directly electrically connected; the polarity of the first tab 522 and the second tab 523 is opposite. The first electrode terminal 54 and the first tab 522 are directly electrically connected, and the second electrode terminal 55 and the second tab 523 are directly electrically connected. The secondary battery cell 5 of the present application cancels the current collecting member between the electrode terminal and the tab, further reducing the internal resistance of the secondary battery cell 5. At the same time, since the current collecting member is omitted, the volume of the secondary battery cell 5 can be reduced, thereby improving the energy density of the secondary battery cell 5. Alternatively, the first tab 522 and the first electrode terminal 54 are directly welded, and the second tab 523 and the second electrode terminal 55 are directly welded.

[0167] In some embodiments, as shown in FIG. 2, the extension direction of the first tab 522 and the second tab 523 is the same as the length direction of the secondary battery cell 5, and the first tab 522 and the second tab 523 are respectively arranged at both ends of the battery cell.

[0168] In some embodiments, the ratio of the width of the first tab 522 to the width of the secondary battery cell 5 is 0.5-1. The ratio of the width of the first tab 522 to the width of the secondary battery cell 5 in this range can promote heat dissipation of the secondary battery cell 5, reduce heat accumulation during use of the secondary battery cell 5, and further improve the safety performance of the battery cell. Alternatively, the ratio of the width of the first tab 522 to the width of the secondary battery cell 5 can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1 and any value in the range formed by any two of the above values. Further alternatively, the ratio of the width of the first tab 522 to the width of the secondary battery cell 5 is 0.7-1.

[0169] In some embodiments, the ratio of the width of the second tab 523 to the width of the secondary battery cell 5 is 0.5-1. The ratio of the width of the second tab 523 to the width of the secondary battery cell 5 in this range can facilitate heat dissipation of the secondary battery cell 5, reduce heat accumulation during use of the secondary battery cell 5, and further improve the safety performance of the battery cell. Alternatively, the ratio of the width of the second tab 523 to the width of the secondary battery cell 5 can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, and any value in the range formed by any two of the above values. Further alternatively, the ratio of the width of the second tab 523 to the width of the secondary battery cell 5 is 0.7-1.

[0170] In some embodiments, the widths of the first tab 522 and the second tab 523 are different.

[0171] In some embodiments, the first tab 522 is a positive electrode tab, and the second tab 523 is a negative electrode tab. The ratio of the width of the positive electrode tab to the width of the secondary battery cell 5 is denoted as W1, and the ratio of the width of the negative electrode tab to the width of the secondary battery cell 5 is denoted as W2. Then W1>W2.

[0172] In some embodiments, the number of the first tabs 522 is 1-2.

[0173] In some embodiments, as shown in FIG. 2, the number of the first tabs 522 is 1.

[0174] In some embodiments, as shown in FIG. 3, the number of the first tabs 522 is 2, and the two first tabs 522 are arranged at one end of the battery cell. The arrangement of the two first tabs 522 can obtain better flow guiding capacity, and promote the improvement of the battery performance.

[0175] In some embodiments, the number of the second tabs 523 is 1-2.

[0176] In some embodiments, as shown in FIG. 2, the number of the second tabs 523 is 1.

[0177] In some embodiments, as shown in FIG. 3, the number of the second tabs 523 is 2, and the two second tabs 523 are arranged at one end of the battery cell. The arrangement of the two second tabs 523 can obtain better flow guiding capacity, and promote the improvement of the secondary battery performance.

[0178] It can be understood that, in order to ensure that no fusing occurs when passing a large current, the first tab 522 and / or the second tab 523 are usually arranged in multiple layers. The number of the first tab 522 or the second tab 523 refers to the number of the first tab 522 or the second tab 523 after being arranged in layers.

[0179] The application also provides a secondary battery, which comprises the secondary battery cell 5 provided by the application.

[0180] When there are multiple secondary battery cells, the multiple secondary battery cells are connected in series, in parallel or in a mixed manner through the current collection component.

[0181] In some embodiments, the secondary battery can be a battery module; when there are multiple secondary battery cells, the multiple battery cells are arranged and fixed to form a battery module.

[0182] In some embodiments, the secondary battery can be a battery pack, which comprises a box body and a secondary battery cell, and the battery cell or the battery module is accommodated in the box body.

[0183] FIG. 4 and FIG. 5 are a battery pack 1 as an example. Referring to FIG. 4 and FIG. 5, the battery pack 1 can comprise a battery box and multiple battery modules 4 arranged in the battery box. The battery box comprises an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in the battery box in any manner.

[0184] The application also provides a power consuming device, which comprises the secondary battery cell 5 provided by the application. The secondary battery cell 5 can be used as a power source of the power consuming device, or can be used as an energy storage unit of the power consuming device. The power consuming device can comprise a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto. The mobile device can be a mobile phone, a notebook computer, etc., for example, and the electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but is not limited thereto.

[0185] As the power consuming device, the battery can be selected according to the use requirement thereof.

[0186] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the battery cell can be used as a power source.

[0187] In some embodiments, as shown in FIG. 6, the battery pack 1 can be part of the chassis structure of the electric vehicle as the power consuming device. For example, part of the box body can become at least part of the floor of the vehicle, or part of the box body can become at least part of the cross beam and the longitudinal beam of the vehicle.

[0188] In order to make the technical problems, technical solutions and beneficial effects solved in the present application clearer, the present application will be further described in detail below in combination with embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way limiting on the application or its applications. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0189] Unless otherwise specified in the embodiments, the techniques or conditions are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions. Unless otherwise specified, the reagents or instruments used are all conventional products that can be obtained commercially.

[0190] Embodiment 1

[0191] (1) Preparation of positive electrode sheet

[0192] The positive electrode active material lithium iron phosphate, the conductive agent SP, the conductive agent CNT and the binder polyvinylidene fluoride are mixed in a weight ratio of 96.2%:1.0%:0.5%:2.3% and dissolved in the solvent N-methyl pyrrolidone NMP to prepare a positive electrode slurry. Then the positive electrode slurry is coated on the current collector aluminum foil, and after drying, cold pressing, edge cutting, sheet cutting, striping and the like are carried out to obtain a positive electrode sheet. In the particle size distribution curve of the positive electrode active material, two characteristic peaks are included, one of which has a peak intensity of 0.8 μm and the other has a peak intensity of 1.5 μm.

[0193] (2) Preparation of negative electrode sheet

[0194] The negative electrode active material artificial graphite, the conductive agent SP, the thickening agent CMC and the binder SBR are mixed in a weight ratio of 96.4%:0.6%:1.0%:2.0% and dissolved in the solvent deionized water to prepare a negative electrode slurry, and the negative electrode slurry is obtained under the action of a vacuum stirrer. Then the negative electrode slurry is coated on the current collector copper foil, and after drying, cold pressing, edge cutting, sheet cutting, striping and the like are carried out to obtain a negative electrode sheet. The powder OI of the artificial graphite is shown in Table 1. The artificial graphite also satisfies: the volume distribution particle size Dv50 is 13.0 μm, the volume distribution particle size Dv10 is 6.0 μm, the volume distribution particle size Dv90 is 24.8 μm, and the volume distribution particle size Dv99 is 37.6 μm; mainly in primary particle morphology, i.e.: more than 80% of the particles are in primary particle morphology; the graphitization degree of the artificial graphite is 93%.

[0195] (3) Preparation of electrolyte

[0196] In an argon atmosphere glove box with water content <10 ppm, lithium hexafluorophosphate LiPF6 was uniformly dissolved in an organic solvent, and then additives VC and FEC were added to obtain an electrolyte. The molar concentration of LiPF6 in the electrolyte was 1 mol / L. The mass percentage of VC in the electrolyte was 3%, and the mass percentage of FEC in the electrolyte was 0.5%. The composition of the organic solvent is shown in Table 1.

[0197] (4) Separator film

[0198] PP with a thickness of 12 μm was used as the separator film.

[0199] (5) Preparation of secondary battery monomer

[0200] The positive electrode sheet, the separator film, and the negative electrode sheet were stacked in order, and the separator film was arranged between the positive electrode sheet and the negative electrode sheet to play a role of isolation, thereby obtaining an electrode assembly with a stacked structure. The electrode assembly was placed in a square aluminum shell, and the positive electrode tab and the positive terminal on the shell end cover were welded, so that the positive electrode tab was directly connected to the positive terminal. The negative electrode tab and the negative terminal on the shell end cover were welded, so that the negative electrode tab was directly connected to the negative terminal. After vacuum drying, the electrolyte was injected, and then the battery monomer was obtained after standing, formation testing, and aging. The length of the secondary battery monomer was 950 mm, the width was 120 mm, and the thickness was 28 mm.

[0201] Examples 2-6 and Comparative Examples 1-2 had substantially the same preparation steps as Example 1, and the differences are shown in Table 1.

[0202] Test Example

[0203] (1) The volume energy density of the secondary battery monomer was tested. The test method was as follows: at 25 degrees Celsius (abbreviated as: ℃), the secondary battery monomer was discharged at a constant current of 0.33 Coulomb (abbreviated as: C) to 2.5 volts (abbreviated as: V); after standing for 5 minutes (abbreviated as: min), the battery was charged at a constant current of 0.33 C to an upper limit cutoff voltage of 3.65 V, and then charged at a constant voltage until the current was 0.05 C. The discharge capacity C0 and the discharge energy E0 at this time were recorded. The volume energy density = E0 / monomer volume, and the unit volume was in liters. The test results are shown in Table 1.

[0204] (2) 25℃ cycle performance, test method: at 25℃, the secondary battery was charged at a constant current of 0.5C to a cutoff voltage of 3.65V, and then discharged at a constant current of 0.5C to 2.5V. This step was repeated until the capacity retention rate reached 80% C0 cutoff, and the cycle number at this time was recorded. The test results are shown in Table 1.

[0205] Table 1

[0206] As can be seen from Table 1, when the mass ratio of the chain carbonate and the cyclic carbonate in the electrolyte and the powder OI of the graphite are both controlled in the specific range of the application, the battery cell can have both high energy density and good cycle performance.

[0207] The technical features of the above embodiments can be combined in any manner. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described, but as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the description.

[0208] The above embodiments only express several implementation manners of the application, and the description is specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the application, a number of modifications and improvements can be made, which are all within the protection scope of the application. Therefore, the protection scope of the patent of the application should be subject to the appended claims.

Claims

1. A secondary battery cell, comprising: a housing; and an electrode assembly and an electrolyte contained in the housing; the electrode assembly comprises a positive electrode tab, a negative electrode tab, and a separator membrane between the positive electrode tab and the negative electrode tab; the negative electrode tab comprises a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprises graphite, and a powder OI of the graphite is 10-25; the electrolyte comprises an organic solvent, the organic solvent comprises a chain carbonate and a cyclic carbonate, and a mass ratio of the chain carbonate to the cyclic carbonate is 1.5-2. the powder OI of the graphite is 12-20.

2. The secondary battery cell according to claim 1, wherein the graphite satisfies at least one of the following (1)-(7):

3. The secondary battery cell according to claim 1 or 2, wherein (1) the graphite comprises artificial graphite; (2) the graphite comprises primary particle morphology; (3) a volume distribution particle size Dv50 of the graphite is 8-15 μm; (4) a volume distribution particle size Dv10 of the graphite is 4-6 μm; (5) a volume distribution particle size Dv90 of the graphite is 20-28 μm; (6) a volume distribution particle size Dv99 of the graphite is 30-40 μm; (7) a graphitization degree of the graphite is 91-95%. the mass ratio of the chain carbonate to the cyclic carbonate is 1.6-1.

9.

4. The secondary battery cell according to any one of claims 1 to 3, wherein The coating weight of the negative electrode film layer is 9 mg / cm 2 - 14 mg / cm 2 ; and / or, The compaction density of the negative electrode film layer is 1.3 g / cm 3 -1.6 g / cm 3 .

5. The secondary battery cell according to any one of claims 1 to 4, wherein 6.The secondary battery cell according to any one of claims 1-5, wherein a mass proportion of the chain carbonate in the organic solvent is 60-70%; and / or a mass proportion of the cyclic carbonate in the organic solvent is 30-40%; and / or the chain carbonate comprises at least two of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; and / or the cyclic carbonate comprises at least one of ethylene carbonate and propylene carbonate. the chain carbonate comprises dimethyl carbonate, and a mass proportion of the dimethyl carbonate in the organic solvent is 10-50%, optionally 12-30%.

7. The secondary battery cell according to any one of claims 1 to 6, wherein the chain carbonate comprises methyl ethyl carbonate, and a mass proportion of the methyl ethyl carbonate in the organic solvent is 15-45%, optionally 20-40%.

8. The secondary battery cell according to any one of claims 1 to 7, wherein the chain carbonate comprises diethyl carbonate, and a mass proportion of the diethyl carbonate in the organic solvent is 5-20%, optionally 5-15%.

9. The secondary battery cell according to any one of claims 1 to 8, wherein the electrolyte further comprises an additive, and the additive comprises at least one of vinylene carbonate and fluoroethylene carbonate.

10. The secondary battery cell according to any one of claims 1 to 9, wherein the positive electrode tab comprises a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer comprises a positive electrode active material, and the positive electrode active material comprises lithium-containing phosphate.

11. The secondary battery cell according to any one of claims 1 to 10, wherein the positive electrode active material comprises two characteristic peaks in a particle size distribution curve thereof.

12. The secondary battery cell of claim 11, wherein, one of the two characteristic peaks has a peak intensity of 0.5-1.0 μm, and the other has a peak intensity of 1.2-2.0 μm.

13. The secondary battery cell of claim 12, wherein, the positive electrode film layer further comprises carbon nanotubes; 14. The secondary battery cell of any one of claims 11-13, wherein, optionally, the carbon nanotubes comprise multi-walled carbon nanotubes. ​ Optionally, the diameter of the carbon nanotube is 7-12 nm.

15. The secondary battery cell of any one of claims 11-14, wherein, The coating weight of the positive electrode film layer is 19 mg / cm 2 - 30 mg / cm 2 ; and / or, The compacted density of the positive electrode film layer is 2.3 g / cm 3 - 2.6 g / cm 3 .

16. The secondary battery cell of any one of claims 1-15, wherein, The length of the secondary battery cell is 500-1200 mm, optionally 700-1100 mm; and / or, The width of the secondary battery cell is 90-150 mm, optionally 110-150 mm; and / or, The thickness of the secondary battery cell is 15-30 mm, optionally 20-30 mm.

17. The secondary battery cell of any one of claims 1-16, wherein, The aspect ratio of the secondary battery cell is 5-12; and / or, The width-thickness ratio of the secondary battery cell is 3.2-11.

5.

18. The secondary battery cell of any one of claims 1-17, wherein, The secondary battery cell further comprises a first electrode terminal, a second electrode terminal, a first tab and a second tab; the first electrode terminal and the second electrode terminal are connected to the shell respectively, the first electrode terminal and the first tab are directly electrically connected, the second electrode terminal and the second tab are directly electrically connected; the polarity of the first tab is opposite to that of the second tab.

19. The secondary battery cell of claim 18, wherein, The secondary battery cell satisfies at least one of the following (1)-(4): (1) The ratio of the width of the first tab to the width of the secondary battery cell is 0.5-1, optionally 0.7-1; (2) The ratio of the width of the second tab to the width of the secondary battery cell is 0.5-1, optionally 0.7-1; (3) The width of the first tab is different from that of the second tab; (4) The first tab is a positive tab, the second tab is a negative tab, the ratio of the width of the positive tab to the width of the secondary battery cell is denoted as W1, the ratio of the width of the negative tab to the width of the secondary battery cell is denoted as W2, then W1>W2.

20. The secondary battery cell of claim 18 or 19, wherein, The extension direction of the first tab and the second tab is the same as the length direction of the secondary battery cell, and the first tab and the second tab are arranged at two ends of the electrode assembly respectively.

21. The secondary battery cell of claim 20, wherein, The number of the first tab is 1-2; optionally, the number of the first tab is 2, and the two first tabs are arranged at one end of the electrode assembly in an interval; and / or, The number of the second tab is 1-2; optionally, the number of the second tab is 2, and the two second tabs are arranged at one end of the electrode assembly in an interval.

22. An electric device comprising the secondary battery cell according to any one of claims 1-21.

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