Battery cells, battery devices, and electrical equipment

Abstract

The present application proposes a battery cell, a battery device and an electrical equipment, wherein the battery cell includes an electrode assembly and an electrolyte, wherein the electrode assembly includes a positive electrode plate; the electrolyte includes: a first solvent, wherein the first solvent includes one or both of ethylene carbonate and propylene carbonate, and the mass proportion of the first solvent is 20%-40% based on the total mass of the electrolyte; a first additive, wherein the first additive includes one or both of vinylene carbonate and ethylene carbonate derivatives, and the mass proportion of the first additive is 1%-8% based on the total mass of the electrolyte; a second additive, wherein the second additive includes a compound represented by formula I: R1-COOLiFormula I, wherein R1 includes any one of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, and a C1-C5 halogenated alkyl group, and the mass proportion of the second additive in the electrolyte is 0.5%-5% based on the total mass of the electrolyte.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to PCT patent application PCT / CN2025 / 086927, entitled “Battery Cell, Battery Device, and Electrical Equipment,” filed on April 2, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of batteries, and in particular, to battery cells, battery devices, and electrical equipment. Background Art

[0004] Batteries are not only used in energy storage systems such as hydropower, thermal, wind, and solar power plants, but are also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric vehicles, as well as in military equipment and aerospace. The HF generated during the cycling of lithium iron phosphate batteries can corrode the electrolyte interface film (SEI) on the negative electrode surface, reducing the battery's cycle life. Summary of the Invention

[0005] In a first aspect, the present application provides a battery cell, the battery cell comprising an electrode assembly and an electrolyte, the electrode assembly comprising a positive electrode sheet, wherein:

[0006] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium-containing phosphate;

[0007] The electrolyte comprises:

[0008] a first solvent, wherein the first solvent comprises one or both of ethylene carbonate and propylene carbonate, and the mass proportion of the first solvent is 20%-40% based on the total mass of the electrolyte;

[0009] The first additive includes one or two of vinylene carbonate and ethylene carbonate derivatives. Based on the total mass of the electrolyte, the mass proportion of the first additive is 1%-8%, and the ethylene carbonate derivative includes a compound represented by formula II:

[0010] Formula II,

[0011] wherein R1, R2, R3, and R4 are each independently selected from the group consisting of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, and a C1-C5 haloalkyl group, and R1, R2, R3, and R4 are not all hydrogen atoms at the same time;

[0012] The second additive comprises a compound represented by Formula I:

[0013] R1-COOLi Formula I,

[0014] Wherein, R1 includes any one of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, and a C1-C5 halogenated alkyl group, and based on the total mass of the electrolyte, the mass proportion of the second additive in the electrolyte is 0.1%-4%.

[0015] The battery cell proposed in this application can reduce the corrosion of HF on the SEI film and improve the cycle performance of the battery cell. At the same time, it can increase the transmission rate of lithium ions and improve the fast charging performance of the battery cell.

[0016] According to some embodiments of the present application, the second additive accounts for 0.5% to 2% of the total mass of the electrolyte, thereby reducing the viscosity of the electrolyte while combining with H2O.

[0017] According to some embodiments of the present application, the second additive includes one or more of lithium acetate, lithium difluoroacetate, and lithium trifluoroacetate, thereby reducing the hydrolysis of LiPF6 and the generation of HF, thereby reducing the corrosion of the SEI film.

[0018] According to some embodiments of the present application, the second additive includes lithium trifluoroacetate. Thus, after polyfluorine substitution, the acidity of the second additive is weakened, which can reduce corrosion to the aluminum foil.

[0019] According to some embodiments of the present application, the electrolyte further includes a second solvent, wherein the second solvent includes one or both of a carboxylate solvent and a linear carbonate solvent, thereby improving the conductivity of the electrolyte.

[0020] According to some embodiments of the present application, the mass of the second solvent accounts for 45%-65% of the total mass of the electrolyte, thereby improving the conductivity of the electrolyte.

[0021] According to some embodiments of the present application, the carboxylate solvent includes a compound represented by Formula III:

[0022] Formula III,

[0023] R5 comprises any one of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, or a C1-C5 haloalkyl group, and R6 comprises any one of a C1-C5 alkyl group or a C1-C5 haloalkyl group. As a result, these carboxylate solvents have a relatively low molecular weight, which can improve the ionic conductivity of the electrolyte and enhance the rate performance of the battery cells.

[0024] According to some embodiments of the present application, the carboxylate solvent includes one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate. As such, these carboxylate solvents have a relatively low molecular weight and can improve the ionic conductivity of the electrolyte, thereby enhancing the rate performance of the battery cells.

[0025] According to some embodiments of the present application, the linear carbonate solvent includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, thereby reducing the viscosity of the electrolyte and improving the ionic conductivity of the electrolyte.

[0026] According to some embodiments of the present application, when the second solvent includes a linear carbonate solvent, the mass of the first additive accounts for 1%-3% of the total mass of the electrolyte, thereby reducing film formation resistance.

[0027] According to some embodiments of the present application, the second solvent includes a carboxylate solvent and a linear carbonate solvent. Based on the total mass of the electrolyte, the mass of the carboxylate solvent accounts for 8%-60%, and the mass of the first additive accounts for 3%-8%. This allows more additives to participate in film formation, improves the stability of the negative electrode interface, and reduces side reactions between the electrolyte and the negative electrode interface.

[0028] According to some embodiments of the present application, the electrolyte further includes a lithium salt, wherein the lithium salt includes one or both of a fluorinated sulfonyl imide lithium salt and lithium hexafluorophosphate, thereby improving the ionic conductivity of the electrolyte.

[0029] According to some embodiments of the present application, the lithium salt accounts for 10% to 18% of the total mass of the electrolyte, thereby improving the ionic conductivity of the electrolyte while reducing the viscosity of the electrolyte.

[0030] According to some embodiments of the present application, the mass of the fluorinated sulfonyl imide lithium salt accounts for 4%-6% of the total mass of the electrolyte, thereby increasing the migration rate of lithium ions.

[0031] According to some embodiments of the present application, the fluorine-containing lithium sulfonyl imide salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium perfluorobutylsulfonyl imide, thereby increasing the migration rate of lithium ions.

[0032] According to some embodiments of the present application, the electrolyte further includes a third additive, wherein the third additive includes one or more of a sulfur-containing additive and a lithium salt additive, thereby improving the cycle performance and fast charging performance of the battery cell.

[0033] According to some embodiments of the present application, the sulfur-containing additive includes one or more of vinyl sulfate, vinyl disulfate, 1,3-propane sultone, butylene sulfite, vinyl sulfite, and methylene disulfonate, thereby reducing the impedance of the battery cell and improving the fast charging performance of the battery cell.

[0034] According to some embodiments of the present application, the sulfur-containing additive accounts for 0-2% by weight, thereby reducing the impedance of the battery cell and reducing the gas generation of the battery cell.

[0035] According to some embodiments of the present application, the sulfur-containing additive accounts for 0.5% to 2% of the total mass of the electrolyte, thereby reducing the impedance of the battery cell and reducing the gas generation of the battery cell.

[0036] According to some embodiments of the present application, the lithium salt additive includes one or more of lithium difluorophosphate, lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium bis(oxalatoborate), thereby reducing gas generation in battery cells under high temperature conditions.

[0037] According to some embodiments of the present application, the lithium salt additive accounts for 0-1% of the total mass of the electrolyte, thereby reducing gas production in the battery cells and lowering film formation resistance.

[0038] According to some embodiments of the present application, the lithium salt additive accounts for 0.2%-1% of the total mass of the electrolyte, thereby reducing gas production in the battery cells and lowering film formation resistance.

[0039] According to some embodiments of the present application, the lithium-containing phosphate includes: a substrate; and a first coating material, wherein the first coating material is located on at least a portion of the surface of the substrate and contains carbon. This improves the conductivity of the lithium-containing phosphate.

[0040] According to some embodiments of the present application, the mass proportion of the carbon element is 0.8%-2.3% based on the total mass of the lithium-containing phosphate. This improves the conductivity of the lithium-containing phosphate while increasing the loading of the lithium-containing phosphate on the positive electrode sheet, thereby increasing the energy density of the battery cell.

[0041] According to some embodiments of the present application, the first coating material includes a compound represented by Formula IV:

[0042] Li 3-d1 Fe 2-d1 M1 d1 (PO m1 ) n1 Formula IV,

[0043] Wherein, 0≤d1≤1, 3≤m1≤5, 2≤n1≤4, and M1 includes one or more of Ti, Zr, Hf, Ge, and Sn. This improves the ionic conductivity and specific capacity of the positive electrode active material, and enhances the fast charging performance and energy density of the battery cell.

[0044] According to some embodiments of the present application, the matrix includes a compound represented by Formula V:

[0045] Li x1 A y1 Me a1 M2 b1 P 1-c1 X c1 Y z1 Formula V,

[0046] Among them, 0.5≤x1≤1.3, 0≤y1≤1.3, 0.9≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5;

[0047] A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M2 includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of Cl, C, and N; and Y includes one or more of O and F. This improves the cycle performance and safety of the battery cell.

[0048] According to some embodiments of the present application, the matrix includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, and lithium cobalt phosphate, thereby improving the cycle performance and safety of the battery cell.

[0049] According to some embodiments of the present application, the compaction density of the positive electrode sheet of the battery cell at 0% state of charge is 2.46 g / cm 3 -2.8g / cm 3 This increases the energy density of the battery cell.

[0050] According to some embodiments of the present application, the single-sided coating weight of the positive electrode active material layer is 200 mg / 1540.25 mm 2 -400mg / 1540.25mm 2 This increases the energy density of the battery cell.

[0051] According to some embodiments of the present application, the electrode assembly further includes a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material, the negative electrode active material including one or both of a carbon-based material and a silicon-based material. This improves the energy density and cycle performance of the battery cell.

[0052] According to some embodiments of the present application, the carbon-based material includes graphite, thereby improving the cycle performance of the battery cell.

[0053] According to some embodiments of the present application, the graphite is a secondary particle formed by aggregation of primary particles, and at least a portion of the surface of the secondary particle is coated with a second coating material comprising amorphous carbon. This reduces side reactions between the negative electrode surface and the electrolyte, thereby improving the cycle performance of the battery cell.

[0054] According to some embodiments of the present application, the mass of the second coating material accounts for 2%-5% of the total mass of the graphite, thereby improving the cycle performance of the battery cell and the energy density of the battery cell.

[0055] According to some embodiments of the present application, the graphite has a volume average particle size Dv50 of 8.5 μm to 14.8 μm. This shortens the migration path of lithium ions in the solid phase, improves the fast charging capability of the battery cell, and reduces side reactions between the graphite and the electrolyte.

[0056] According to some embodiments of the present application, the negative electrode active material includes a silicon-based material, and the mass proportion of silicon is 0.3%-5% based on the total mass of the negative electrode active material layer, thereby improving the energy density of the battery cell.

[0057] According to some embodiments of the present application, the single-side coating weight of the negative electrode active material layer is 90 mg / 1540.25 mm 2 -185mg / 1540.25mm 2 This increases the energy density of the battery cell.

[0058] According to some embodiments of the present application, along the length direction of the battery cell, the size of the negative electrode active material layer is larger than the size of the positive electrode active material layer, and the difference between the size of the negative electrode active material layer and the size of the positive electrode active material layer is OH1; along the width direction of the battery cell, the size of the negative electrode active material layer is larger than the size of the positive electrode active material layer, and the difference between the size of the negative electrode active material layer and the size of the positive electrode active material layer is OH2, where OH1 is greater than or equal to OH2. In this way, while improving the energy density of the battery cell, lithium plating at the negative electrode is reduced.

[0059] According to some embodiments of the present application, 1 mm ≤ OH1 ≤ 4 mm, and 1 mm ≤ OH2 ≤ 3 mm. This improves the energy density of the battery cell while reducing lithium plating at the negative electrode.

[0060] According to some embodiments of the present application, the positive electrode tab is provided on the positive electrode sheet, and the negative electrode tab is provided on the negative electrode sheet. The positive electrode tab extends along the length or width of the positive electrode sheet; and / or the negative electrode tab extends along the length or width of the negative electrode sheet. This improves current transmission efficiency, reduces battery cell resistance, and enhances battery cell rate performance.

[0061] According to some embodiments of the present application, the electrode assembly further includes a separator having a porosity of 20%-70%, thereby improving the lithium ion transmission efficiency and the rate performance of the battery cell.

[0062] According to some embodiments of the present application, the porosity of the separator is 35%-60%, thereby improving the transmission efficiency of lithium ions and the rate performance of the battery cell.

[0063] According to some embodiments of the present application, the separator includes: a base film; a first functional layer located on at least one side of the base film, the first functional layer comprising a first inorganic material; and a second functional layer located on a side of the first functional layer away from the base film, the second functional layer comprising a second inorganic material and a non-fluoropolymer. This improves the heat resistance of the separator and enhances the safety of the battery cells.

[0064] According to some embodiments of the present application, the non-fluorinated polymer includes an acrylic copolymer, thereby improving the adhesion of the non-fluorinated polymer and reducing the risk of the second functional layer falling off.

[0065] According to some embodiments of the present application, the first inorganic substance and the second inorganic substance independently include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. This improves the heat resistance of the separator and the safety of the battery cell.

[0066] According to some embodiments of the present application, the base film has a thickness of 4 μm to 12 μm, thereby reducing the short circuit between the positive and negative electrodes while reducing the volume occupied by the separator in the battery cell, thereby improving the energy density of the battery cell.

[0067] According to some embodiments of the present application, the base film has a thickness of 5 μm to 9 μm, thereby reducing the volume occupied by the separator in the battery cell and improving the energy density of the battery cell.

[0068] According to some embodiments of the present application, the battery cell includes a housing and a cover assembly, the cover assembly being disposed at at least one end of the housing. The housing and the cover assembly define a receiving cavity, and the electrode assembly is disposed within the receiving cavity. The thickness of the housing on the larger surface of the battery cell is 0.1 mm to 0.5 mm. This improves the energy density of the battery cell.

[0069] According to some embodiments of the present application, the thickness of the large-surface shell is 0.2 mm to 0.35 mm, thereby increasing the energy density of the battery cell.

[0070] According to some embodiments of the present application, the cover plate assembly includes a first cover plate assembly and a second cover plate assembly, the first and second cover plate assemblies being disposed at opposite ends of the housing in the lengthwise or widthwise direction, the first cover plate assembly including a first cover plate and a first electrode terminal, and the second cover plate assembly including a second cover plate and a second electrode terminal, wherein the first and second electrode terminals have opposite polarities. This reduces the temperature rise of the battery cells during charging, thereby reducing the impedance of the battery cells.

[0071] According to some embodiments of the present application, the minimum cross-sectional area of ​​the first electrode terminal and / or the second electrode terminal is S and meets the requirement of 150 mm 2 ≤S≤1000mm 2 Thus, the current carrying capacity of the battery cell is improved.

[0072] A second aspect of the present application provides a battery device, comprising the battery cell provided in the first aspect of the present application, wherein the battery device is one or more of a battery module, a battery pack, and an energy storage device.

[0073] The third aspect of the present application provides an electrical device, comprising the battery cell provided by the first aspect of the present application or the battery device provided by the second aspect of the present application, wherein the battery cell or the battery device provides electrical energy for the electrical device.

[0074] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0076] Figure 1Schematic diagram of the dimensions of the positive electrode active material layer and the negative electrode active material layer according to one embodiment of the present application.

[0077] Figure 2 This is a schematic structural diagram of the positive electrode plate of an embodiment of the present application.

[0078] Figure 3 It is a structural schematic diagram of the positive electrode sheet of another embodiment of the present application.

[0079] Figure 4 It is a structural schematic diagram of the positive electrode sheet of another embodiment of the present application.

[0080] Figure 5 It is a structural schematic diagram of the positive electrode sheet of another embodiment of the present application.

[0081] Figure 6 It is a schematic structural diagram of the negative electrode plate of one embodiment of the present application.

[0082] Figure 7 It is a schematic structural diagram of the negative electrode sheet of another embodiment of the present application.

[0083] Figure 8 It is a structural schematic diagram of the negative electrode sheet of another embodiment of the present application.

[0084] Figure 9 It is a structural schematic diagram of the negative electrode sheet of another embodiment of the present application.

[0085] Figure 10 It is a schematic structural diagram of an isolation membrane according to an embodiment of the present application.

[0086] Figure 11 It is a structural schematic diagram of a shell of an embodiment of the present application.

[0087] Figure 12 It is a structural schematic diagram of a battery cell according to an embodiment of the present application.

[0088] Figure 13 It is a structural diagram of an electrical device according to an embodiment of the present application.

[0089] Description of reference numerals:

[0090] 1 battery cell; 11 housing; 111 large-surface housing; 121 positive electrode sheet; 1210 positive electrode tab; 1212 positive electrode active material layer; 122 negative electrode sheet; 1220 negative electrode tab; 1222 negative electrode active material layer; 123 separator; 1231 base film; 1232 first functional layer; 1233 second functional layer; 131 first electrode terminal; 132 second electrode terminal; 133 third electrode terminal; 134 fourth electrode terminal. DETAILED DESCRIPTION

[0091] The following embodiments of the technical solution of the present application are described in detail. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only used as examples and are not intended to limit the scope of protection of the present application.

[0092] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0093] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0094] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0095] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may 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.

[0096] Currently, market developments indicate that batteries are increasingly being used. They are not only used in energy storage systems such as hydropower, thermal, wind, and solar power plants, but are also widely used in electric vehicles like electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. As battery applications continue to expand, market demand is also growing.

[0097] The HF generated during the cycling of lithium iron phosphate battery cells can corrode the electrolyte interface film (SEI) on the negative electrode surface, reducing the battery's cycle life. Adding more carbonate additives to the electrolyte can improve the stability of the SEI film and extend the cycle life of the battery cells. However, excessive carbonate additives increase the viscosity of the electrolyte, affecting lithium ion transport and reducing the battery cell's fast-charging performance.

[0098] In a first aspect, the present application provides a battery cell, the battery cell comprising an electrode assembly and an electrolyte, the electrode assembly comprising a positive electrode sheet, wherein:

[0099] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium-containing phosphate;

[0100] The electrolyte comprises:

[0101] a first solvent, wherein the first solvent comprises one or both of ethylene carbonate and propylene carbonate, and the mass proportion of the first solvent is 20%-40% based on the total mass of the electrolyte;

[0102] The first additive includes one or both of vinylene carbonate and ethylene carbonate derivatives. Based on the total mass of the electrolyte, the mass proportion of the carbonate additive is 1%-8%, and the ethylene carbonate derivative includes a compound represented by formula II:

[0103] Formula II,

[0104] wherein R1, R2, R3, and R4 are each independently selected from the group consisting of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, and a C1-C5 haloalkyl group, and R1, R2, R3, and R4 are not all hydrogen atoms at the same time;

[0105] The second additive comprises a compound represented by Formula I:

[0106] R1-COOLi Formula I,

[0107] Wherein, R1 includes any one of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, and a C1-C5 halogenated alkyl group, and based on the total mass of the electrolyte, the mass proportion of the second additive in the electrolyte is 0.1%-4%.

[0108] In this application, after disassembling the battery cell to obtain the electrolyte, the first solvent, the first additive, and the second additive of the electrolyte can be qualitatively and quantitatively analyzed by gas chromatography with reference to GB / T9722-2023 "General Rules for Gas Chromatography of Chemical Reagents".

[0109] As an example, based on the total mass of the electrolyte, the mass proportion of the first solvent can be 20%, 25%, 30%, 35%, 40%, etc., or can be a range consisting of any of the above values.

[0110] As an example, based on the total mass of the electrolyte, the mass proportion of the carbonate additive can be 1%, 3%, 5%, 7%, 8%, etc., or can be a range consisting of any of the above values.

[0111] As an example, based on the total mass of the electrolyte, the mass proportion of the second additive in the electrolyte can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, etc., or can be a range consisting of any of the above values.

[0112] In the present application, the term "halogen atom" includes one or more of fluorine atom, chlorine atom and iodine atom.

[0113] As used herein, the term "C1-C5 alkyl" refers to a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, with no unsaturation present, having from one to five carbon atoms, and attached to the remainder of the molecule by a single bond. Examples include, but are not limited to, methyl, ethyl, propyl, isopropyl, 2-methyl-1-propyl, 2-methyl-2-propyl, 2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-3-butyl, 2,2-dimethyl-1-propyl, 2-methyl-1-pentyl, butyl, isobutyl, tert-butyl, pentyl, isopentyl, and neopentyl.

[0114] As used herein, the term "C1-C5 haloalkyl" refers to a C1-C5 alkyl group in which at least one hydrogen atom is replaced by a halogen atom, including but not limited to: -CF3, -CF2CH2, -CF2CH2CH3, -CF2CF2CH2CH3, and -CF2CH2CH2CH2CH3.

[0115] Additives refer to components with low content in the electrolyte, which generally account for no more than 10% of the mass of the electrolyte. They are highly targeted and used in small amounts, and can significantly optimize the performance of a certain aspect of the battery without changing the production process.

[0116] The battery cell proposed in the present application includes a first solvent in the electrolyte. The first solvent has a good solubility for the electrolyte salt in the electrolyte, and has a high dielectric constant and excellent chemical stability. It can improve the conduction rate of lithium ions, reduce the DC impedance of the battery, and improve the cycle stability of the battery cell. At the same time, the content of the first solvent is controlled to reduce the viscosity of the electrolyte while improving the conduction rate of lithium ions, thereby reducing the DC impedance of the battery cell. In addition, since the battery contains trace amounts of crystalline water that cannot be completely removed through the process, the commonly used lithium salts (such as lithium hexafluorophosphate, LiPF6) in the electrolyte will hydrolyze during the use of the battery to produce HF, which will corrode the SEI film. The present application adds a second additive R1-COOLi to the electrolyte. The second additive has a stronger binding energy with H2O and can preferentially combine with H2O to form R1-COO with a higher energy barrier. - -H2O, thereby reducing the hydrolysis of LiPF6 and the generation of HF, avoiding the consumption of the first additive caused by a large amount of HF corroding the SEI film during the battery cell cycle, reducing the consumption rate of the first additive, and thus reducing the amount of the first additive used, reducing the amount of the first additive to 1%-8%, avoiding the effect of excessive first additive on the viscosity of the electrolyte, which is beneficial to increasing the transmission speed of lithium ions in the electrolyte, reducing the DC impedance of the battery, and improving the fast charging performance of the battery. In addition, the R1-COOLi additive has a high donor number, and its anion has a strong coordination ability with Li, which can preferentially occupy the inner layer of the solvation shell, thereby reducing Li + The desolvation energy barrier is reduced, and the fast charging performance of the electrolyte is improved in systems containing a large amount of ethylene carbonate and / or propylene carbonate. By controlling the content of the second additive, while reducing the generation of HF, it is also possible to avoid the corrosion of the current collector caused by excessive second additives, improve the cycle stability of the battery cell, improve the film formation impedance deteriorated by excessive SEI film thickness, reduce the DC impedance of the battery, and improve the dynamic performance of the battery cell. In addition, the positive electrode active material contains an olivine-structured lithium-containing phosphate, which has excellent structural stability and can improve the cycle performance of the battery cell.

[0117] In the present application, vinylene carbonate and / or vinyl carbonate derivatives are added to the electrolyte. Vinylene carbonate and vinyl carbonate derivatives can preferentially participate in the formation of an SEI film on the negative electrode side over other components in the electrolyte, and the film formed with the participation of vinylene carbonate and vinyl carbonate derivatives has a high content of organic matter, which is beneficial to improving the overall flexibility of the SEI film, improving the stability of the interface between the SEI film and the negative electrode during the cycle, reducing the reaction between the negative electrode active material and the electrolyte, reducing the consumption of lithium ions, and improving the cycle performance and storage performance of the battery cell.

[0118] In summary, the present application can achieve both fast charging performance and cycle performance by collaboratively controlling the type and content of the first solvent, the type and content of the first additive, and the type and content of the second additive within an appropriate range.

[0119] According to some embodiments of the present application, the mass proportion of the second additive may be 0.5%-2% based on the total mass of the electrolyte, for example, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2%, etc., or any range thereof.

[0120] When the mass content of the second additive is within an appropriate range, it can combine with water, reduce HF generation, improve the cycle performance of the battery, and at the same time reduce the viscosity of the electrolyte, while taking into account the fast charging performance of the battery.

[0121] According to some embodiments of the present application, the second additive includes one or more of lithium acetate, lithium difluoroacetate, and lithium trifluoroacetate, thereby reducing the hydrolysis of LiPF6 and the generation of HF, thereby reducing the corrosion of the SEI film.

[0122] According to some embodiments of the present application, the second additive includes lithium trifluoroacetate. Therefore, when polyfluorinated lithium trifluoroacetate is selected as the second additive, the acidity of lithium trifluoroacetate is relatively weak, which can reduce corrosion to aluminum foil.

[0123] According to some embodiments of the present application, the electrolyte further includes a second solvent, and the second solvent includes one or both of a carboxylate solvent and a chain carbonate solvent.

[0124] Carboxylate ester solvents and chain carbonate solvents have low viscosity, thereby increasing the conductivity of the electrolyte.

[0125] According to some embodiments of the present application, the mass proportion of the second solvent can be 45%-65% based on the total mass of the electrolyte. For example, it can be 45%, 50%, 55%, 60%, 65%, etc., or any range consisting of the above values. This improves the conductivity of the electrolyte.

[0126] According to some embodiments of the present application, the carboxylate solvent includes a compound represented by Formula III:

[0127] Formula III,

[0128] R5 comprises any one of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, or a C1-C5 haloalkyl group, and R6 comprises any one of a C1-C5 alkyl group or a C1-C5 haloalkyl group. As a result, these carboxylate solvents have a relatively low molecular weight and low viscosity, which can improve the ionic conductivity of the electrolyte and enhance the rate performance of the battery cells.

[0129] According to some embodiments of the present application, the carboxylate solvent includes one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate. As such, these carboxylate solvents have a relatively low molecular weight and low viscosity, which can improve the ionic conductivity of the electrolyte and enhance the rate performance of the battery cells.

[0130] According to some embodiments of the present application, the linear carbonate solvent includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. This reduces the viscosity of the electrolyte and improves its ionic conductivity. When the electrolyte contains both cyclic carbonates (ethylene carbonate, propylene carbonate) and linear carbonates, the linear carbonates have low viscosity and high ionic conductivity, while the cyclic carbonates have a high dielectric constant and high solubility of lithium salts, thereby improving the overall performance of the electrolyte.

[0131] According to some embodiments of the present application, when the second solvent includes a chain carbonate solvent, the mass proportion of the first additive can be 1%-3% based on the total mass of the electrolyte. For example, it can be 1%, 1.5%, 2%, 2.5%, 3%, etc., or it can be a range composed of any of the above values. Compared with carboxylic acid ester solvents, chain carbonate solvents have reduced activity and fewer side reactions with the negative electrode interface. Relatively less first additive participates in film formation, which can make the battery cell have a better cycle life and prevent the first additive from increasing the film formation impedance too much.

[0132] According to some embodiments of the present application, the second solvent includes a carboxylate solvent and a chain carbonate solvent. Based on the total mass of the electrolyte, the mass proportion of the carboxylate solvent is 8%-60%, and the mass proportion of the first additive is 3%-8%. For example, it can be 3%, 4%, 5%, 6%, 7%, 8%, etc., or it can be a range composed of any of the above numerical values. Thus, when the electrolyte contains both a carboxylate solvent and a chain carbonate solvent, the electrolyte is more active and the side reaction between the electrolyte and the negative electrode interface is stronger. It is necessary to add more of the first additive to form a more stable SEI film, maintain the interface, and improve the cycle life of the battery cell.

[0133] In the present application, the type and content of the second solvent can be tested by referring to the aforementioned test methods for the type and content of the first solvent, the first additive, and the second additive.

[0134] According to some embodiments of the present application, the electrolyte further includes a lithium salt, which may include one or both of a fluorinated sulfonyl imide lithium salt and lithium hexafluorophosphate, thereby improving the ionic conductivity of the electrolyte.

[0135] When the electrolyte contains both fluorinated sulfonyl imide lithium salt and lithium hexafluorophosphate, the ion migration number of the fluorinated sulfonyl imide lithium is larger, which can increase the migration rate of lithium ions, and the stability of lithium hexafluorophosphate is better. The combination of the two can improve the stability and ionic conductivity of the electrolyte.

[0136] According to some embodiments of the present application, the lithium salt accounts for 10% to 18% of the total mass of the electrolyte. For example, it may be 10%, 12%, 14%, 16%, 18%, or any range thereof. This improves the ionic conductivity of the electrolyte while reducing its viscosity.

[0137] In this application, the test of the content of fluorinated sulfonyl imide lithium salt and lithium hexafluorophosphate can refer to the standard JY / T020-2002 "General Rules for Ion Chromatography Analysis Methods". For example, a freshly prepared electrolyte can be taken as a sample, the free electrolyte of a fresh battery can be taken as a sample, or a battery cell that has been fully discharged (discharged to the discharge cut-off voltage so that the battery cell has a charge state of approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery cell is used as a sample for testing using ion chromatography analysis. The inorganic ion chromatogram is tested, and the corresponding inorganic species are compared based on the chromatographic peak position. The corresponding inorganic ion content percentage is calculated based on the peak area, and then the ratio of the mass proportion of fluorinated sulfonyl imide lithium to the mass proportion of lithium hexafluorophosphate is calculated.

[0138] According to some embodiments of the present application, the mass percentage of the fluorinated sulfonyl imide lithium salt can be 4%-6% based on the total mass of the electrolyte. For example, it can be 4%, 4.5%, 5%, 5.5%, 6%, etc., or any range consisting of the above values. This improves the migration rate of lithium ions.

[0139] According to some embodiments of the present application, the fluorine-containing lithium sulfonyl imide salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium perfluorobutylsulfonyl imide, thereby increasing the migration rate of lithium ions.

[0140] According to some embodiments of the present application, the electrolyte further includes a third additive, wherein the third additive includes one or more of a sulfur-containing additive and a lithium salt additive, thereby improving the cycle performance and fast charging performance of the battery cell.

[0141] According to some embodiments of the present application, the sulfur-containing additive includes one or more of vinyl sulfate, vinyl disulfate, 1,3-propane sultone, butylene sulfite, vinyl sulfite, and methylene disulfonate, thereby reducing the impedance of the battery cell and improving the fast charging performance of the battery cell.

[0142] According to some embodiments of the present application, based on the total mass of the electrolyte, the mass proportion of the sulfur-containing additive can be 0%-2%, for example, 0.5%, 1%, 1.5%, 2%, etc., or can be a range composed of any of the above values. Thus, while reducing the impedance of the battery cell, the risk of the battery cell being oxidized at high potential to produce sulfur-containing free radicals is reduced, thereby reducing the decomposition of the solvent caused by the sulfur-containing free radicals and reducing the gas production of the battery cell. According to some embodiments of the present application, the mass proportion of the sulfur-containing additive can be 0.5%-2%.

[0143] According to some embodiments of the present application, the lithium salt additive includes one or more of lithium difluorophosphate, lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium bis(oxalatoborate), thereby reducing gas generation in battery cells under high temperature conditions.

[0144] According to some embodiments of the present application, based on the total mass of the electrolyte, the mass proportion of the lithium salt additive can be 0%-1%, for example, 0.2%, 0.4%, 0.6%, 0.8%, 1%, etc., or can be a range composed of any of the above values. In this way, while reducing the gas production of the battery cell, the content of inorganic components in the SEI film is reduced, and the film formation impedance is reduced. According to some embodiments of the present application, the mass proportion of the lithium salt additive can be 0.2%-1%.

[0145] It should be noted that since the additives in the electrolyte will be consumed during the formation and charge-discharge cycle to generate relevant components in the SEI film and / or CEI film, after disassembling the battery cell to obtain the electrolyte, when testing the content of sulfur-containing additives and lithium salt additives by gas chromatography, the content may be zero.

[0146] Specifically, taking the case where the mass content of the sulfur-containing additive is zero as an example, this could be because the freshly prepared electrolyte does not contain any sulfur-containing additives, or because the electrolyte obtained after disassembling the battery cell does not contain any sulfur-containing additives. This could be because the freshly prepared electrolyte does not contain any sulfur-containing additives, or because a small amount of sulfur-containing additives was added but participated in the SEI film formation reaction during the battery cell formation process, resulting in a mass content of zero during testing. Alternatively, the freshly prepared electrolyte does contain sulfur-containing additives.

[0147] Furthermore, regarding the addition of certain substances, such as additives, to the electrolyte, the content of additives in the battery cell electrolyte is related to the formation process, different battery life cycles, or different battery storage conditions due to the additives' role in film formation on the surface of the active material. Therefore, the additive content in a freshly prepared electrolyte may differ from that in an electrolyte obtained by reverse disassembling a battery cell. However, those skilled in the art can determine the approximate content range of the relevant substances in the fresh electrolyte based on the performance level of the battery cell (such as the number of cycles) and residual content. Similarly, those skilled in the art can also determine the approximate content range of the corresponding non-freshly prepared (i.e., after reverse disassembly) electrolyte based on the content of the freshly prepared additives, the performance requirements for the battery cell, the storage environment, etc.

[0148] Therefore, the additive content mentioned in the technical solution of the present application can be the content of the additive actively added to the fresh electrolyte, or it can be the content of the residual additive detected by reverse detection based on the actual battery status.

[0149] In the present application, the type and content of the sulfur-containing additive and the type and content of the lithium salt additive can be tested with reference to the aforementioned test methods for the type and content of the first solvent, the first additive, and the second additive.

[0150] In this application, additives refer to components with low content in the electrolyte, which generally account for no more than 10% by mass in the electrolyte. They are highly targeted and used in small amounts, and can significantly optimize the performance of a certain aspect of the battery without changing the production process.

[0151] According to some embodiments of the present application, the lithium-containing phosphate includes: a substrate; and a first coating material, the first coating material being located on at least a portion of the surface of the substrate and containing carbon. This forms a good conductive network between the lithium-containing phosphate particles, thereby improving the electronic conductivity of the lithium-containing phosphate.

[0152] According to some embodiments of the present application, based on the total mass of the lithium-containing phosphate, the mass proportion of the carbon element is 0.8%-2.3%. For example, it can be 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.3%, etc., or it can be a range composed of any of the above values. In this way, while improving the electronic conductivity of the lithium-containing phosphate, the impact on lithium ion transmission is reduced, the loading capacity of the lithium-containing phosphate on the positive electrode sheet is increased, and the energy density of the battery cell is improved.

[0153] The carbon content in materials is usually measured by infrared absorption, such as infrared carbon-sulfur instruments, or by indirect carbon determination methods. The latter can refer to pages 3-4 of the national standard GB / T 3521-2008 ("Chemical Analysis Methods of Graphite").

[0154] According to some embodiments of the present application, the first coating material includes a compound represented by Formula IV:

[0155] Li 3-d1 Fe 2-d1 M1 d1 (PO m1 ) n1 Formula IV,

[0156] Wherein, 0≤d1≤1, 3≤m1≤5, 2≤n1≤4, and M1 includes one or more of Ti, Zr, Hf, Ge, and Sn. This improves the ionic conductivity and specific capacity of the positive electrode active material, and enhances the fast charging performance and energy density of the battery cell.

[0157] The first cladding layer includes Li 3-d1 Fe 2-d1 M1 d1 (PO m1 ) n1 , which has excellent ion conductivity, and together with the carbon element with excellent conductivity in the coating layer, it improves the conductivity and ion conductivity of the material, which is beneficial to improving the fast charging performance of the battery.

[0158] According to some embodiments of the present application, the matrix includes a compound represented by Formula V:

[0159] Li x1 A y1 Me a1 M2 b1 P 1-c1 X c1 Y z1 Formula V,

[0160] Among them, 0.5≤x1≤1.3, 0≤y1≤1.3, 0.9≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5;

[0161] A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M2 includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of Cl, C, and N; and Y includes one or more of O and F. This improves the cycle performance and safety of the battery cell.

[0162] As an example, x1 may be 0.5, 0.7, 0.9, 1.1, 1.3, etc., or may be a range consisting of any of the above values.

[0163] It should be noted that due to the consumption of lithium ions during the formation and cycling of battery cells, the measured lithium content x1 in the positive electrode active material may be less than 1. Furthermore, if a lithium supplement is used in the positive and negative electrode sheets, the measured lithium content x1 in the positive electrode active material may be greater than 1 after the battery undergoes formation and cycling.

[0164] As an example, y1 may be 0, 0.3, 0.6, 0.9, 1.3, etc., or may be a range consisting of any of the above values.

[0165] As an example, a1 may be 0.9, 1.1, 1.3, 1.5, etc., or may be a range consisting of any of the above values.

[0166] As an example, b1 may be 0, 0.2, 0.4, 0.5, etc., or may be a range consisting of any of the above values.

[0167] As an example, c1 can be 0, 0.2, 0.4, 0.5, etc., or can be a range consisting of any of the above values.

[0168] As an example, z1 can be 3, 4, 5, etc., or can be a range consisting of any of the above values.

[0169] According to some embodiments of the present application, the matrix includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, and lithium cobalt phosphate, thereby improving the cycle performance and safety of the battery cell.

[0170] According to some embodiments of the present application, the compaction density of the positive electrode sheet of the battery cell at 0% state of charge is 2.46 g / cm 3 -2.8g / cm 3 For example, it can be 2.46 g / cm 3 , 2.5g / cm 3 , 2.6g / cm 3 , 2.7g / cm 3 , 2.8g / cm 3 The energy density of the battery cell can be increased by using any of the above numerical values.

[0171] The present application provides a method for testing the compaction density of a positive electrode: charge to 3.65V at a constant current of 1 / 3C, charge to 0.05C at a constant voltage of 3.65V, place the battery cell at 25°C, let it stand for 2h, and then discharge it to 2.0V at a rate of 0.33C. The battery cell is disassembled to remove the positive electrode sheet, for example, a single-sided coated positive electrode sheet (if it is a double-sided coated sheet, the positive electrode active material layer on one side can be wiped off first), punched into small discs with an area of ​​S1, weighed, recorded as M1, and its thickness H1 is measured. Then wipe off the positive electrode active material layer of the weighed positive electrode sheet, weigh the weight of the positive electrode collector, record it as M0, and measure its thickness H0. The single-side coating weight of the positive electrode active material layer = (M1-M0) / S1, the thickness of the positive electrode active material layer = H1-H0, and the compaction density of the positive electrode active material layer = the single-side coating weight of the positive electrode active material layer / the thickness of the positive electrode active material layer.

[0172] According to some embodiments of the present application, the single-sided coating weight of the positive electrode active material layer is 200 mg / 1540.25 mm 2 -400mg / 1540.25mm 2 For example, it can be 200mg / 1540.25mm 2 、250mg / 1540.25mm 2 、300mg / 1540.25mm 2 、340mg / 1540.25mm 2 、370mg / 1540.25mm 2 , 400mg / 1540.25mm 2 The energy density of the battery cell can be increased by using any of the above numerical values.

[0173] This application provides a method for testing the coating weight of the positive electrode active material layer: A battery cell is disassembled to remove the positive electrode sheet. For example, a single-sided coated positive electrode sheet (if a double-sided coated sheet is used, the positive electrode active material layer on one side can be wiped off first) is punched into small discs with an area of ​​S1. These discs are weighed and recorded as M1. The positive electrode active material layer of the weighed positive electrode sheet is then wiped off, and the weight of the positive electrode current collector is weighed and recorded as M0. The single-sided coating weight of the positive electrode active material layer = (M1 - M0) / S1.

[0174] According to some embodiments of the present application, the electrode assembly further includes a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material, the negative electrode active material including one or both of a carbon-based material and a silicon-based material. This improves the energy density and cycle performance of the battery cell.

[0175] According to some embodiments of the present application, the carbon-based material includes graphite, thereby improving the cycle performance of the battery cell.

[0176] According to some embodiments of the present application, the graphite is a secondary particle formed by aggregation of primary particles, at least a portion of the surface of the secondary particle has a second coating material, and the second coating material includes amorphous carbon.

[0177] Secondary particles are particles formed by the aggregation of two or more primary particles.

[0178] In this article, amorphous carbon refers to a transitional carbon material with a very low degree of graphitization and crystallization, nearly amorphous (or lacking a fixed shape and periodic structural regularity). In this application, amorphous carbon refers to the product of carbonization of an organic carbon source, which has a large number of end faces and defects and a high number of lithium ion sites.

[0179] Secondary particles can increase the migration rate of lithium ions, improve the transmission performance of lithium ions, facilitate the embedding and extraction of lithium ions, and help improve the ion conductivity of the material. The second coating material includes amorphous carbon, which can improve the conductivity of the composite graphite particles. The secondary particles in the inner core and the coating layer of amorphous carbon jointly improve the electronic and ion conductivity of the material, which helps to improve the fast charging performance of the battery cell.

[0180] According to some embodiments of the present application, the mass content of the second coating material is 2%-5% based on the total mass of the graphite. For example, it can be 2%, 3%, 4%, 5%, etc., or any range consisting of the above values. Controlling the mass content of the second coating material within a suitable range can improve the conductivity of the material and enhance the fast charging performance of the battery.

[0181] According to some embodiments of the present application, the volume average particle size Dv50 of the graphite is 8.5 μm-14.8 μm. For example, it can be 8.5 μm, 9.5 μm, 10.5 μm, 11.5 μm, 12.5 μm, 13.5 μm, 14.8 μm, etc., or it can be a range composed of any of the above values. As a result, the volume average particle size of the graphite is smaller, which can shorten the solid phase migration path of lithium ions and improve the fast charging capability of the battery cell. At the same time, by making the volume average particle size within the above range, the side reactions between the graphite negative electrode and the electrolyte can also be reduced.

[0182] In this application, Dv50 refers to the particle size at which the cumulative volume distribution percentage reaches 50%, as measured, for example, using a laser particle size analyzer (Malvern Master Size 2000) in accordance with GB / T 19077-2016 / ISO 13320:2009. The specific testing process is as follows: the battery cell is discharged to 0% SOC, then the negative electrode is disassembled and removed. A certain amount of powder on the electrode is scraped off with a blade, then cleaned 5-10 times with deionized water by repeated shaking. After drying, the sample is sintered in a tube furnace at 400°C for 2 hours. After sintering, an appropriate amount of the sample to be tested (the sample concentration should be 8%-12% obscuration) is taken, deionized water is added, and ultrasonic dispersion is performed to ensure complete dispersion of the sample. The sample is then measured in accordance with GB / T 19077-2016 / ISO 13320:2009.

[0183] According to some embodiments of the present application, the negative electrode active material includes a silicon-based material, and the mass percentage of silicon is 0.3%-5% based on the total mass of the negative electrode active material layer. For example, the mass percentage may be 0.3%, 1%, 3%, 5%, or any range thereof. This improves the energy density of the battery cell.

[0184] The qualitative and quantitative properties of each substance or element in this application can be detected using appropriate equipment and methods known to those skilled in the art. The relevant detection methods can refer to domestic and international detection standards, domestic and international enterprise standards, etc., and those skilled in the art can also adapt certain detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. A single detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0185] For example, the mass content of silicon in the negative electrode active material layer has a well-known meaning in the art and can be detected using equipment and methods well-known in the art. For example, the negative electrode plate is placed in a solvent such as water for immersion, the negative electrode active material is separated from the negative electrode current collector, and the various substances in the negative electrode active material layer are obtained by filtration. The substances are used as test samples, and the test samples are analyzed using an ICAP7400 model inductively coupled plasma-emission spectrometer from Thermo Fisher Scientific, USA, with reference to GB / T30902-2014 standard to obtain the silicon content.

[0186] According to some embodiments of the present application, the single-side coating weight of the negative electrode active material layer is 90 mg / 1540.25 mm 2 -185mg / 1540.25mm 2 For example, it can be 90mg / 1540.25mm 2、110mg / 1540.25mm 2 、125mg / 1540.25mm 2 、140mg / 1540.25mm 2 、185mg / 1540.25mm 2 etc., thereby increasing the energy density of the battery cell.

[0187] This application provides a method for measuring the coating weight of the negative electrode active material layer: A battery cell is disassembled to remove the negative electrode sheet. For example, a negative electrode sheet coated on one side (for double-sided sheets, the negative electrode active material layer can be wiped off on one side first) is punched into small discs with an area of ​​S2. These discs are weighed and recorded as M3. The negative electrode active material layer of the weighed negative electrode sheet is then wiped off, and the weight of the negative electrode current collector is weighed and recorded as M2. The single-sided coating weight of the negative electrode active material layer = (M3 - M2) / S2.

[0188] According to some embodiments of the present application, along the length direction of the battery cell, the size of the negative electrode active material layer is larger than the size of the positive electrode active material layer, and the difference between the size of the negative electrode active material layer and the size of the positive electrode active material layer is OH1; along the width direction of the battery cell, the size of the negative electrode active material layer is larger than the size of the positive electrode active material layer, and the difference between the size of the negative electrode active material layer and the size of the positive electrode active material layer is OH2, wherein OH1 is greater than or equal to OH2.

[0189] During fast charging, the overcurrent near the tab side is large, the temperature is higher, and the lithium ion migration rate is faster than other parts, making lithium deposition more likely. By making the size of the negative electrode active material layer larger than that of the positive electrode active material layer, more negative electrode active material layers can receive lithium ions, improving lithium deposition. And because the lithium ion diffusion path is longer along the length of the battery cell, by making OH1 greater than or equal to OH2, more negative electrode active material layers can receive lithium ions along the length direction, reducing the risk of lithium ion deposition at the edge.

[0190] Specifically, refer to Figure 1 , along the length direction of the battery cell, the size of the positive electrode active material layer 1212 is OH 11 , the size of the negative electrode active material layer 1222 is OH 21 The difference between the size of the negative electrode active material layer 1222 and the size of the positive electrode active material layer 1212 is OH1=OH 21 -OH 11 .

[0191] refer to Figure 1 , along the width direction of the battery cell, the size of the positive electrode active material layer 1212 is OH12 , the size of the negative electrode active material layer 1222 is OH 22 The difference between the size of the negative electrode active material layer 1222 and the size of the positive electrode active material layer 1212 is OH2=OH 22 -OH 12 .

[0192] According to some embodiments of the present application, 1 mm ≤ OH1 ≤ 4 mm. For example, it can be 1 mm, 2 mm, 3 mm, 4 mm, etc., or can be a range consisting of any of the above values.

[0193] According to some embodiments of the present application, 1 mm ≤ OH2 ≤ 3 mm. For example, it can be 1 mm, 2 mm, 3 mm, or any range of the above values. This reduces negative electrode lithium deposition while also taking into account the volumetric energy density of the battery cell.

[0194] According to some embodiments of the present application, the positive electrode tab is provided on the positive electrode sheet, and the negative electrode tab is provided on the negative electrode sheet. The positive electrode tab extends along the length or width of the positive electrode sheet; and / or the negative electrode tab extends along the length or width of the negative electrode sheet. This improves current transmission efficiency, reduces battery cell resistance, and enhances battery cell rate performance.

[0195] refer to Figure 2 , along the length direction of the positive electrode sheet 121, only one positive electrode tab 1210 extends out, referring to Figure 3 A positive electrode tab 1210 extends from each end along the length direction of the positive electrode sheet 121 .

[0196] refer to Figure 4 , along the width direction of the positive electrode sheet 121, only one positive electrode tab 1210 extends out, referring to Figure 5 A positive electrode tab 1210 extends from each end of the positive electrode sheet 121 along the width direction.

[0197] refer to Figure 6 , along the length direction of the negative electrode plate 122, only one negative electrode tab 1220 extends out, referring to Figure 7 A negative electrode tab 1220 extends from each end of the negative electrode sheet 122 along the length direction.

[0198] refer to Figure 8 , along the width direction of the negative electrode sheet 122, only one negative electrode tab 1220 extends out, referring to Figure 9 A negative electrode tab 1220 extends from each end of the negative electrode sheet 122 along the width direction.

[0199] According to some embodiments of the present application, the electrode assembly further includes a separator, and the porosity of the separator is 20%-70%. For example, it can be 20%, 30%, 40%, 50%, 60%, 70%, etc., or it can be a range consisting of any of the above values. This improves the transmission efficiency of lithium ions and the rate performance of the battery cell. According to some embodiments of the present application, the porosity of the separator is 35%-60%.

[0200] In this application, porosity refers to the percentage of the pore volume within the separator to the total volume of the separator. Porosity can be measured with reference to the standard GB / T 36363-2018, "Polyolefin Separators for Battery Cells." It should be noted that the actual testing process may vary slightly from the standard to obtain a more accurate test value, depending on instrument differences, test errors, and to minimize the impact of porosity on the test.

[0201] According to some embodiments of the present application, reference Figure 10 The separator 123 includes a base film 1231; a first functional layer 1232 located on at least one side of the base film 1231 and comprising a first inorganic material; and a second functional layer 1233 located on a side of the first functional layer 1232 away from the base film 1231 and comprising a second inorganic material and a non-fluoropolymer. This improves the heat resistance of the separator and enhances the safety of the battery cell.

[0202] According to some embodiments of the present application, the non-fluorinated polymer includes an acrylic copolymer, thereby improving the adhesion of the non-fluorinated polymer and reducing the risk of the second functional layer falling off.

[0203] According to some embodiments of the present application, the first inorganic substance and the second inorganic substance independently include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide. This improves the heat resistance of the separator and the safety of the battery cell.

[0204] According to some embodiments of the present application, the thickness of the base film is 4 μm-12 μm. For example, it can be 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, etc., or it can be a range consisting of any of the above values. In this way, while reducing the short circuit between the positive and negative electrodes, the volume occupied by the separator within the battery cell is reduced, thereby improving the energy density of the battery cell. According to some embodiments of the present application, the thickness of the base film is 5 μm-9 μm.

[0205] According to some embodiments of the present application, the battery cell includes a shell and a cover assembly, the cover assembly is arranged at at least one end of the shell, the shell and the cover assembly define a receiving cavity, and the electrode assembly is arranged in the receiving cavity. Figure 11 The battery cell includes a housing 11, and the thickness of the housing 111 on the large surface of the battery cell is 0.1 mm to 0.5 mm. Thus, the energy density of the battery cell is improved.

[0206] According to some embodiments of the present application, the thickness of the large-surface housing 111 is 0.2 mm to 0.35 mm, thereby increasing the energy density of the battery cell.

[0207] According to some embodiments of the present application, the cover plate assembly includes a first cover plate assembly and a second cover plate assembly, the first and second cover plate assemblies being disposed at opposite ends of the housing in the lengthwise or widthwise direction, the first cover plate assembly including a first cover plate and a first electrode terminal, and the second cover plate assembly including a second cover plate and a second electrode terminal, wherein the first and second electrode terminals have opposite polarities. This reduces the temperature rise of the battery cells during charging, thereby reducing the impedance of the battery cells.

[0208] According to some embodiments of the present application, reference Figure 12 The first cover plate assembly includes a first cover plate, a first electrode terminal 131, and a third electrode terminal 133, and the polarities of the first electrode terminal 131 and the third electrode terminal 133 are opposite. The second cover plate assembly includes a second cover plate, a second electrode terminal 132 and a fourth electrode terminal 134, and the polarities of the second electrode terminal 132 and the fourth electrode terminal 134 are opposite.

[0209] According to some embodiments of the present application, the minimum cross-sectional area of ​​the first electrode terminal and / or the second electrode terminal is S and meets the requirement of 150 mm 2 ≤S≤1000mm 2 As a result, the current capacity of the battery cell is improved, the heat generated by the electrode terminals is reduced, the internal resistance of the battery cell is reduced, and the cycle performance of the battery cell is improved.

[0210] In the present application, the minimum cross-sectional area of ​​the first electrode terminal refers to the minimum cross-sectional area of ​​the first electrode terminal along the direction perpendicular to the current flow, and the minimum cross-sectional area of ​​the second electrode terminal refers to the minimum cross-sectional area of ​​the second electrode terminal along the direction perpendicular to the current flow.

[0211] In the present application, when testing the minimum cross-sectional area of ​​the first electrode terminal and / or the second electrode terminal, the minimum cross-sectional area can be calculated based on the shape of the minimum cross-sectional area and the area calculation formula thereof. For example, if the minimum cross-sectional area of ​​the electrode terminal is circular, the minimum cross-sectional area can be obtained by measuring the radius of the circle; if the minimum cross-sectional area is square, the minimum cross-sectional area can be obtained by measuring the length and width of the square.

[0212] As an example, the minimum cross-sectional area S of the first electrode terminal and / or the second electrode terminal may be 150 mm 2 , 300mm 2 , 450mm 2 , 600mm 2 , 750mm 2 , 900mm 2 , 1000mm 2 etc., or can be within the range of any of the above numerical values.

[0213] The battery cells proposed in this application can be used in electrical devices that use battery cells as power sources or various energy storage systems that use batteries as energy storage elements. Electrical devices may include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0214] A second aspect of the present application provides a battery device, comprising the battery cell provided in the first aspect of the present application, wherein the battery device is one or more of a battery module, a battery pack, and an energy storage device.

[0215] The third aspect of the present application provides an electrical device, comprising the battery cell provided by the first aspect of the present application or the battery device provided by the second aspect of the present application, wherein the battery cell or the battery device provides electrical energy for the electrical device.

[0216] The electrical equipment may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0217] As the electrical equipment, a battery device can be selected according to its usage requirements.

[0218] Figure 13This is an example of an electric device. This electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the electric device, a battery pack or battery module can be used.

[0219] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0220] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the 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 actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0221] Example 1

[0222] 1. Preparation of positive electrode sheet

[0223] The positive electrode sheet includes a positive electrode collector, a positive electrode active material layer and a positive electrode conductive layer. The positive electrode active material layer is arranged on both sides of the positive electrode collector. The positive electrode conductive layer is located between the positive electrode collector and the positive electrode active material layer. The positive electrode collector is aluminum foil.

[0224] The positive conductive layer on the positive electrode current collector is a film layer formed by evenly mixing the positive electrode conductive agent superconducting carbon, the positive electrode binder polyvinylidene fluoride PVDF and the solvent N-methylpyrrolidone (NMP), and then coating it on the surface of the positive electrode current collector and drying it. The thickness is 1μm. The mass content of the positive electrode conductive agent in the positive electrode conductive layer is 40%, and the mass content of the positive electrode binder is 60%.

[0225] The positive electrode active material layer includes a film layer formed by uniformly coating the positive electrode slurry (solvent is NMP) on the surface of the positive electrode conductive layer, drying, and cold pressing. The positive electrode active material layer includes a positive electrode active material, a binder polyvinylidene fluoride (PVDF), and a conductive agent acetylene black in a mass ratio of 97:2:1.

[0226] The positive electrode active material includes lithium iron phosphate particles and a first coating material. The first coating material is coated on the surface of the lithium iron phosphate particles. The first coating material includes lithium iron titanium phosphate Li2FeTi(PO4)3 and carbon, and the mass content of carbon element is 1.12%.

[0227] The single-side coating weight of the positive electrode active material layer is 210 mg / 1540.25 mm 2 .

[0228] The compacted density of the positive electrode active material layer is 2.46 g / cm 3 .

[0229] 2. Preparation of negative electrode sheet

[0230] The negative electrode sheet includes a negative electrode current collector, a negative electrode active material layer and a negative electrode conductive layer. The negative electrode active material layer is arranged on both sides of the negative electrode current collector. The negative electrode conductive layer is located between the negative electrode current collector and the negative electrode active material layer. The negative electrode current collector is copper foil.

[0231] The negative electrode conductive layer on the negative electrode current collector is a film layer formed by evenly mixing the negative electrode conductive agent superconducting carbon, the negative electrode binder styrene-butadiene rubber (SBR), the thickener sodium carboxymethyl cellulose (CMC-Na) and the solvent water, and then coating it on the surface of the negative electrode current collector and drying it. The thickness is 1 μm, the mass content of the negative electrode conductive agent in the negative electrode conductive layer is 35%, the mass content of the negative electrode binder in the negative electrode conductive layer is 60%, and the mass content of the thickener in the negative electrode conductive layer is 5%.

[0232] The negative electrode active material layer includes a film layer formed by uniformly coating the negative electrode slurry (the solvent is deionized water) on the surface of the negative electrode conductive layer, drying, and cold pressing.

[0233] The negative electrode active material layer includes a negative electrode active material, a conductive agent acetylene black, a negative electrode binder styrene-butadiene rubber, and a thickener sodium carboxymethyl cellulose in a mass ratio of 96.5:0.5:2:1. The graphite particles include artificial graphite and a second coating material. The second coating material is coated on the surface of the artificial graphite. The mass content of carbon element in the second coating material is 3.5%, and the Dv50 of the graphite particles is 11.3 μm.

[0234] The single-side coating weight of the negative electrode active material layer is 97 mg / 1540.25 mm 2 .

[0235] The compaction density of the negative electrode active material layer is 1.35 g / cm 3 .

[0236] The length of the negative electrode active material layer is 4 mm greater than the length of the positive electrode active material layer, and the width of the negative electrode active material layer is 3 mm greater than the width of the positive electrode active material layer.

[0237] 3. Isolation film

[0238] The isolation film includes a base film and functional layers arranged on both sides of the base film. The base film includes a 7μm polyethylene film layer with a porosity of 42%;

[0239] The functional layer includes a first functional layer and a second functional layer. The first functional layer includes polyacrylate and aluminum oxide particles dispersed on the polyacrylate. The first functional layer is a film layer formed by applying the first slurry on one side of the base film. The thickness of the first functional layer is 1 μm, and the average particle size of the aluminum oxide particles is 10 nm. The first slurry includes aluminum oxide particles and a binder polyacrylate.

[0240] The second functional layer is a composite particle formed by polyacrylate and polyvinylidene fluoride (PVDF) particles dispersed on the polyacrylate. The second functional layer is a film layer formed by coating the second slurry on the other side of the base film. The thickness is 5μm and the average particle size of the PVDF particles is 10nm. The second slurry includes polyacrylate and PVDF particles.

[0241] 4. Preparation of Electrolyte

[0242] The electrolyte includes an organic solvent, lithium salt and additives.

[0243] After mixing the components of the organic solvents, lithium salt and additives are added to prepare an electrolyte solution.

[0244] The organic solvent includes a first solvent (ethylene carbonate) with a mass proportion of 20%, a second solvent dimethyl carbonate with a mass proportion of 31.7%, and a second solvent ethyl methyl carbonate with a mass proportion of 28%. The mass content of each component in the organic solvent is calculated based on the mass of the electrolyte.

[0245] The additives include 1% by mass of lithium trifluoroacetate, 1.5% by mass of vinylene carbonate VC, 1% by mass of fluoroethylene carbonate FEC, 1% by mass of vinyl sulfite ES, and 0.8% by mass of lithium difluorooxalatoborate LiDFOB.

[0246] The lithium salt includes 5% by mass of lithium bis(fluorosulfonyl)imide LiFSI and 10% by mass of lithium hexafluorophosphate LiPF6. The mass content of the lithium salt is calculated based on the mass of the electrolyte.

[0247] 5. Preparation of battery cells

[0248] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation, to obtain a laminated electrode assembly. The electrode assembly is placed in a shell, on which a positive terminal and a negative terminal are provided. After baking, the electrolyte is injected, and after vacuum packaging, standing, formation, shaping and other processes, a battery cell is obtained.

[0249] The outer shell is an aluminum shell with a rectangular parallelepiped structure, and the shell thickness corresponding to the surface with the largest area of ​​the rectangular parallelepiped structure is 0.5 mm.

[0250] Performance Testing

[0251] 1. DC internal resistance DCR test of battery cells

[0252] You can refer to the method in GB / T 31467 "Performance test specification for high-power lithium-ion power batteries for HEV".

[0253] For example, at room temperature, charge the battery cell to 3.65V at a constant current of 0.33C, then charge it to 0.05C at a constant voltage of 3.65V, let it stand for 30 minutes, and discharge it to 2.0V at a constant current of 0.33C. Record the discharge capacity A0 at this time in Ah, and then charge it for 0.5A0Ah at a constant current of 0.33C to adjust the SOC to 50%.

[0254] After the battery cell is placed at -20 ℃ for 2 hours, it is discharged at a constant current of 1C for 10 seconds and ∆U is recorded. 放电 , ∆I 放电 , the discharge DCR data of lithium-ion batteries is calculated by the following formula, R 放电 =∆U 放电 / ∆I 放电 ,

[0255] Where ∆U 放电 Indicates the voltage change within 10s after the discharge starts, ∆I 放电 Indicates the current value within 10 seconds after the start of discharge.

[0256] 2. Cycle performance

[0257] At 60°C, charge the battery cell at a constant current of 0.8C to a charge cutoff voltage of 3.6V. Then, charge it at a constant current of 0.1C to a charge cutoff voltage of 3.65V and let it rest for 30 minutes. Discharge it at a constant current of 1C to 3.1V and let it rest for 30 minutes. This constitutes one charge-discharge cycle. Repeat these charge-discharge cycles until the cycle capacity retention (i.e., Cn / C0 × 100%) reaches 70%. Record the number of cycles. A higher number of cycles indicates better cycling performance of the battery cell.

[0258] Comparative Example 1

[0259] The preparation method of the battery monomer is the same as that of Example 1, except that the mass proportion of ethylene carbonate is 15%, and the mass proportion of ethyl methyl carbonate is 33%.

[0260] Example 2

[0261] The preparation method of the battery monomer is the same as that of Example 1, except that the mass proportion of ethylene carbonate is 27.3%, and the mass proportion of ethyl methyl carbonate is 20.7%.

[0262] Example 3

[0263] The preparation method of the battery monomer is the same as that of Example 1, except that the mass proportion of ethylene carbonate is 40% and the mass proportion of ethyl methyl carbonate is 8%.

[0264] Comparative Example 2

[0265] The preparation method of the battery monomer is the same as that of Example 1, except that the mass proportion of ethylene carbonate is 45%, and the mass proportion of ethyl methyl carbonate is 3%.

[0266] The test results of the battery cells in Examples 1 to 3, Comparative Example 1, and Comparative Example 2 are shown in Table 1.

[0267] Table 1

[0268]

[0269] As shown in Table 1, when the contents of the first and second additives are within the scope of this application, the DCR and cycle performance of the battery cell can be adjusted by adjusting the content of the first solvent in the electrolyte. If the content of the first solvent is too low, the battery cell's DCR is low, but the cycle life is poor. When the content of the first solvent is too high, the battery cell's DCR is high and the cycle life is poor. When the content of the first solvent is within the range of 20%-40%, the battery cell can achieve both a low DCR and a good cycle life.

[0270] Comparative Example 3

[0271] The preparation method of the battery cell is the same as that of Example 2, except that the mass proportion of ethyl methyl carbonate is 21.7%, and the electrolyte does not contain lithium trifluoroacetate.

[0272] Example 4

[0273] The preparation method of the battery monomer is the same as that of Example 2, except that the mass proportion of ethyl methyl carbonate is 21.6%, and the mass proportion of lithium trifluoroacetate is 0.1%.

[0274] Example 5

[0275] The preparation method of the battery monomer is the same as that of Example 2, except that the mass proportion of ethyl methyl carbonate is 21.2%, and the mass proportion of lithium trifluoroacetate is 0.5%.

[0276] Example 6

[0277] The preparation method of the battery monomer is the same as that of Example 2, except that the mass proportion of ethyl methyl carbonate is 19.7%, and the mass proportion of lithium trifluoroacetate is 2%.

[0278] Example 7

[0279] The preparation method of the battery monomer is the same as that of Example 2, except that the mass proportion of ethyl methyl carbonate is 17.7%, and the mass proportion of lithium trifluoroacetate is 4%.

[0280] Comparative Example 4

[0281] The preparation method of the battery monomer is the same as that of Example 2, except that the mass proportion of ethyl methyl carbonate is 16.7%, and the mass proportion of lithium trifluoroacetate is 5%.

[0282] The test results of the battery cells in Examples 4 to 8, Comparative Example 3, and Comparative Example 4 are shown in Table 2.

[0283] Table 2

[0284]

[0285] As shown in Table 2, when the first solvent and the first additive are within the scope of protection of this application, the DCR and cycle life of the battery cell can be adjusted by adjusting the content of the second additive. If the electrolyte does not contain the second additive, trace amounts of water in the battery cell will hydrolyze the lithium hexafluorophosphate, and the resulting HF will corrode the SEI film, reducing the battery cell's cycle performance. If the electrolyte contains too much of the second additive, the strong acidity of the lithium trifluoroacetate will corrode the aluminum foil, similarly reducing the battery cell's cycle performance. When the content of the second additive is within the scope of protection of this application, the battery cell's cycle performance is excellent.

[0286] Comparative Example 5

[0287] The preparation method of the battery cell is the same as that of Example 2, except that the mass proportion of ethyl methyl carbonate is 22.7%, the mass proportion of VC is 0.3%, and the mass proportion of FEC is 0.2%.

[0288] Example 8

[0289] The preparation method of the battery cell is the same as that of Example 2, except that the mass proportion of ethyl methyl carbonate is 22.2%, the mass proportion of VC is 0.7%, and the mass proportion of FEC is 0.3%.

[0290] Example 9

[0291] The preparation method of the battery cell is the same as that of Example 2, except that the mass proportion of ethyl methyl carbonate is 20.2%, the mass proportion of VC is 2.5%, and the mass proportion of FEC is 0.5%.

[0292] Example 10

[0293] The preparation method of the battery cell is the same as that of Example 2, except that the mass proportion of ethyl methyl carbonate is 15.2%, the mass proportion of VC is 5%, and the mass proportion of FEC is 3%.

[0294] Comparative Example 6

[0295] The preparation method of the battery cell is the same as that of Example 2, except that the mass proportion of ethyl methyl carbonate is 13.2%, the mass proportion of VC is 7%, and the mass proportion of FEC is 3%.

[0296] The test results of the battery cells in Examples 8 to 10, Comparative Example 5, and Comparative Example 6 are shown in Table 3.

[0297] Table 3

[0298] As can be seen from Table 3, when the contents of the first solvent and the second additive are within the protection scope of this application and the contents are fixed, if the content of the first additive is too little, that is, the total amount of the second additive and the first additive in the electrolyte is relatively small, lithium hexafluorophosphate will hydrolyze to produce HF, resulting in the destruction of the SEI film and poor cycle performance of the battery cell; if the content of the first additive is too much, although the cycle performance of the battery cell is good, the film formation impedance is large, which will increase the internal resistance of the battery cell and seriously affect the fast charging performance of the battery. The addition of the second additive of this application can add 1%-8% of the first additive to the electrolyte, which can make the battery cell have better cycle performance.

[0299] Comparative Example 7

[0300] The preparation method of the battery cell is the same as that of Example 2, except that the electrolyte includes ethyl acetate, the mass proportion of ethyl acetate is 39%, the mass proportion of dimethyl carbonate is 15.4%, and the electrolyte does not contain ethyl methyl carbonate. The coating weight of the positive electrode sheet is 263 mg / 1540.25 mm 2 , negative electrode coating weight 120mg / 1540.25mm 2 .

[0301] Example 11

[0302] The preparation method of the battery cell is the same as that of Example 2, except that the electrolyte includes ethyl acetate, the mass proportion of ethyl acetate is 39%, the mass proportion of dimethyl carbonate is 12.9%, the electrolyte does not contain ethyl methyl carbonate, the mass proportion of VC is 2.5%, the mass proportion of FEC is 0.5%, and the coating weight of the positive electrode sheet is 263 mg / 1540.25 mm 2 , negative electrode coating weight 120mg / 1540.25mm 2 .

[0303] Example 12

[0304] The preparation method of the battery cell is the same as that of Example 2, except that the electrolyte includes ethyl acetate, the mass proportion of ethyl acetate is 39%, the mass proportion of dimethyl carbonate is 9.9%, the electrolyte does not contain ethyl methyl carbonate, the mass proportion of VC is 4%, the mass proportion of FEC is 2%, and the coating weight of the positive electrode sheet is 263 mg / 1540.25 mm 2 , negative electrode coating weight 120mg / 1540.25mm 2 .

[0305] Example 13

[0306] The preparation method of the battery cell is the same as that of Example 2, except that the electrolyte includes ethyl acetate, the mass proportion of ethyl acetate is 39%, the mass proportion of dimethyl carbonate is 7.9%, the electrolyte does not contain ethyl methyl carbonate, the mass proportion of VC is 5%, the mass proportion of FEC is 3%, and the coating weight of the positive electrode sheet is 263 mg / 1540.25 mm 2 , negative electrode coating weight 120mg / 1540.25mm 2 .

[0307] Comparative Example 8

[0308] The preparation method of the battery cell is the same as that of Example 2, except that the electrolyte includes ethyl acetate, the mass proportion of ethyl acetate is 39%, the mass proportion of dimethyl carbonate is 5.9%, the electrolyte does not contain ethyl methyl carbonate, the mass proportion of VC is 7%, the mass proportion of FEC is 3%, and the coating weight of the positive electrode sheet is 263 mg / 1540.25 mm 2 , negative electrode coating weight 120mg / 1540.25mm 2 .

[0309] The test results of the battery cells in Examples 11 to 13, Comparative Examples 7 and 8 are shown in Table 4.

[0310] Table 4

[0311]

[0312] As shown in Table 4, the electrolyte can also contain both linear carbonate solvents and carboxylic acid ester solvents. When ethyl acetate is included in the electrolyte, the side reaction between ethyl acetate and graphite is stronger. If the first additive content is too low, it cannot participate in film formation, resulting in poor cycle performance of the battery cell. If the first additive content is too high, although the battery cell cycle performance is good, the battery cell DCR is large, which is not conducive to fast charging.

[0313] Example 14

[0314] The preparation method of the battery cell is the same as that of Example 2, except that the mass proportion of ethyl methyl carbonate is 22.5%, and the electrolyte does not contain sulfur-containing additives and lithium salt additives.

[0315] Example 15

[0316] The preparation method of the battery monomer is the same as that of Example 2, except that the first solvent includes ethylene carbonate and propylene carbonate, the mass proportion of ethylene carbonate is 22.3%, the mass proportion of propylene carbonate is 5%, and the mass proportion of ethyl methyl carbonate is 20.7%.

[0317] Example 16

[0318] The preparation method of the battery cell is the same as that of Example 2, except that the second additive is lithium difluoroacetate.

[0319] Example 17

[0320] The preparation method of the battery cell is the same as that of Example 2, except that the second additive is lithium acetate.

[0321] Example 18

[0322] The preparation method of the battery cell is the same as that of Example 2, except that the mass proportion of ethyl methyl carbonate is 19.7%, and the mass proportion of ES is 2%.

[0323] Example 19

[0324] The preparation method of the battery cell is the same as that of Example 2, except that the sulfur-containing additive is vinyl sulfate.

[0325] Example 20

[0326] The preparation method of the battery cell is the same as that of Example 2, except that the lithium salt additive is lithium tetrafluoroborate.

[0327] The test results of the battery cells in Examples 14 to 20 are shown in Table 5.

[0328] Table 5

[0329]

[0330] It can be seen from Table 5 that when the contents of the first solvent, the first additive, and the second additive in the electrolyte are within the scope to be protected in this application, the type and content of the sulfur-containing additive and the type of lithium salt additive in the electrolyte can be adjusted to obtain battery cells with good cycle performance and low DCR.

[0331] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A battery cell comprising an electrode assembly and an electrolyte, wherein the electrode assembly comprises a positive electrode plate, characterized in that: The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a lithium-containing phosphate; The electrolyte comprises: a first solvent, wherein the first solvent comprises one or both of ethylene carbonate and propylene carbonate, and the mass proportion of the first solvent is 20%-40% based on the total mass of the electrolyte; The first additive includes one or two of vinylene carbonate and ethylene carbonate derivatives. Based on the total mass of the electrolyte, the mass proportion of the first additive is 1%-8%, and the ethylene carbonate derivative includes a compound represented by formula II: Formula II, wherein R1, R2, R3, and R4 are each independently selected from the group consisting of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, and a C1-C5 haloalkyl group, and R1, R2, R3, and R4 are not all hydrogen atoms at the same time; The second additive comprises a compound represented by Formula I: R1-COOLi Formula I, Wherein, R1 includes any one of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, and a C1-C5 halogenated alkyl group, and based on the total mass of the electrolyte, the mass proportion of the second additive in the electrolyte is 0.1%-4%.

2. The battery cell according to claim 1, wherein: Based on the total mass of the electrolyte, the mass proportion of the second additive is 0.5%-2%.

3. The battery cell according to claim 1, wherein: The second additive includes one or more of lithium acetate, lithium difluoroacetate, and lithium trifluoroacetate.

4. The battery cell according to claim 1, wherein: The second additive includes lithium trifluoroacetate.

5. The battery cell according to claim 1, characterized in that The electrolyte further includes a second solvent, and the second solvent includes one or both of a carboxylate solvent and a chain carbonate solvent.

6. The battery cell according to claim 5, characterized in that Based on the total mass of the electrolyte, the mass proportion of the second solvent is 45%-65%.

7. The battery cell according to claim 5, characterized in that The carboxylate solvent includes a compound represented by formula III: Formula III, Wherein, R5 includes any one of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, and a C1-C5 haloalkyl group, and R6 includes any one of a C1-C5 alkyl group and a C1-C5 haloalkyl group.

8. The battery cell according to claim 5, characterized in that The carboxylate solvent includes one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate.

9. The battery cell according to claim 5, characterized in that: The chain carbonate solvent includes one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

10. The battery cell according to claim 5, characterized in that When the second solvent includes a chain carbonate solvent, the mass of the first additive accounts for 1%-3% based on the total mass of the electrolyte.

11. The battery cell according to claim 5, characterized in that The second solvent includes a carboxylate solvent and a chain carbonate solvent. Based on the total mass of the electrolyte, the mass of the carboxylate solvent accounts for 8%-60%, and the mass of the first additive accounts for 3%-8%.

12. The battery cell according to claim 1, wherein The electrolyte further includes a lithium salt, and the lithium salt includes one or both of a fluorinated sulfonyl imide lithium salt and lithium hexafluorophosphate.

13. The battery cell according to claim 12, characterized in that: Based on the total mass of the electrolyte, the mass proportion of the lithium salt is 10%-18%.

14. The battery cell according to claim 12, characterized in that Based on the total mass of the electrolyte, the mass proportion of the fluorinated sulfonyl imide lithium salt is 4%-6%.

15. The battery cell according to claim 12, characterized in that The fluorine-containing lithium sulfonyl imide salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium perfluorobutylsulfonyl imide.

16. The battery cell according to any one of claims 1 to 15, characterized in that: The electrolyte further includes a third additive, and the third additive includes one or more of a sulfur-containing additive and a lithium salt additive.

17. The battery cell according to claim 16, characterized in that The sulfur-containing additive includes one or more of vinyl sulfate, vinyl disulfate, 1,3-propane sultone, butylene sulfite, vinyl sulfite, and methylene disulfonate.

18. The battery cell according to claim 16, characterized in that Based on the total mass of the electrolyte, the mass proportion of the sulfur-containing additive is 0-2%.

19. The battery cell according to claim 16, characterized in that Based on the total mass of the electrolyte, the mass proportion of the sulfur-containing additive is 0.5%-2%.

20. The battery cell according to claim 16, wherein: The lithium salt additive includes one or more of lithium difluorophosphate, lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium bis(oxalatoborate).

21. The battery cell according to claim 16, characterized in that Based on the total mass of the electrolyte, the mass proportion of the lithium salt additive is 0-1%.

22. The battery cell according to claim 16, characterized in that Based on the total mass of the electrolyte, the mass proportion of the lithium salt additive is 0.2%-1%.

23. The battery cell according to claim 1, characterized in that The lithium-containing phosphate comprises: matrix; A first coating material is located on at least a portion of the surface of the substrate, and the first coating material contains carbon.

24. The battery cell according to claim 23, characterized in that Based on the total mass of the lithium-containing phosphate, the mass proportion of the carbon element is 0.8%-2.3%.

25. The battery cell according to claim 23, characterized in that The first coating material includes a compound represented by formula IV: Li 3-d1 Fe 2-d1 M1 d1 (PO m1 ) n1 Formula IV Among them, 0≤d1≤1, 3≤m1≤5, 2≤n1≤4, and M1 includes one or more of Ti, Zr, Hf, Ge, and Sn.

26. The battery cell according to claim 23, characterized in that The matrix includes a compound shown in Formula V: Li x1 A y1 Me a1 M2 b1 P 1-c1 X c1 Y z1 Formula V Among them, 0.5≤x1≤1.3, 0≤y1≤1.3, 0.9≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5; Wherein, A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M2 includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of Cl, C, and N; and Y includes one or more of O and F.

27. The battery cell according to claim 23, characterized in that The matrix includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, and lithium cobalt phosphate.

28. The battery cell according to claim 1, characterized in that The battery cell is at 0% state of charge, and the compaction density of the positive electrode sheet is 2.46 g / cm 3 -2.8g / cm 3 .

29. The battery cell according to claim 1, characterized in that The single-side coating weight of the positive electrode active material layer is 200 mg / 1540.25 mm 2 -400mg / 1540.25mm 2 .

30. The battery cell according to claim 1, characterized in that The electrode assembly also includes a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material layer arranged on at least one side of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes one or both of a carbon-based material and a silicon-based material.

31. The battery cell according to claim 30, characterized in that The carbon-based material includes graphite.

32. The battery cell according to claim 31, characterized in that The graphite is a secondary particle formed by aggregation of primary particles. At least a portion of the surface of the secondary particle has a second coating material, and the second coating material includes amorphous carbon.

33. The battery cell according to claim 32, characterized in that Based on the total mass of the graphite, the mass proportion of the second coating material is 2%-5%.

34. The battery cell according to any one of claims 31 to 33, characterized in that: The volume average particle size Dv50 of the graphite is 8.5 μm-14.8 μm.

35. The battery cell according to claim 30, characterized in that The negative electrode active material includes a silicon-based material. Based on the total mass of the negative electrode active material layer, the mass proportion of silicon element is 0.3%-5%.

36. The battery cell according to claim 30, characterized in that The single-side coating weight of the negative electrode active material layer is 90 mg / 1540.25 mm 2 -185mg / 1540.25mm 2 .

37. The battery cell according to claim 30, characterized in that Along the length direction of the battery cell, the size of the negative electrode active material layer is larger than the size of the positive electrode active material layer, and the difference between the size of the negative electrode active material layer and the size of the positive electrode active material layer is OH1; Along the width direction of the battery cell, the size of the negative electrode active material layer is larger than the size of the positive electrode active material layer, and the difference between the size of the negative electrode active material layer and the size of the positive electrode active material layer is OH2, Among them, OH1 is greater than or equal to OH2.

38. The battery cell according to claim 37, characterized in that 1mm≤OH1≤4mm, 1mm≤OH2≤3mm.

39. The battery cell according to claim 30, characterized in that The positive electrode sheet is provided with a positive electrode tab, and the negative electrode sheet is provided with a negative electrode tab. The positive electrode tab extends along the length direction of the positive electrode sheet or along the width direction of the positive electrode sheet; and / or the negative electrode tab extends along the length direction of the negative electrode sheet or along the width direction of the negative electrode sheet.

40. The battery cell according to claim 1, wherein The electrode assembly further includes a separator having a porosity of 20% to 70%.

41. The battery cell according to claim 40, characterized in that The porosity of the isolation membrane is 35%-60%.

42. The battery cell according to claim 41 or 41, characterized in that: The isolation film includes: basement membrane; a first functional layer, located on at least one side of the base film, wherein the first functional layer comprises a first inorganic substance; The second functional layer is located on a side of the first functional layer away from the base film, and the second functional layer includes a second inorganic substance and a non-fluorine polymer.

43. The battery cell according to claim 42, characterized in that The non-fluorine polymer includes an acrylic copolymer.

44. The battery cell according to claim 42, characterized in that The first inorganic substance and the second inorganic substance independently include one or more of silicon oxide, aluminum oxide, boehmite, barium sulfate, calcium oxide, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, and tin oxide.

45. The battery cell according to claim 42, characterized in that The thickness of the isolation film is 4 μm-12 μm.

46. ​​The battery cell according to claim 42, characterized in that The thickness of the isolation film is 5 μm-9 μm.

47. The battery cell according to claim 1, characterized in that The battery cell includes a shell and a cover assembly, the cover assembly is arranged at at least one end of the shell, the shell and the cover assembly define a accommodating cavity, the electrode assembly is arranged in the accommodating cavity, and the shell thickness of the large surface of the battery cell is 0.1mm-0.5mm.

48. The battery cell according to claim 47, characterized in that The shell thickness of the large surface is 0.2mm-0.35mm.

49. The battery cell according to claim 47 or 48, characterized in that The cover plate assembly includes a first cover plate assembly and a second cover plate assembly, the first cover plate assembly and the second cover plate assembly are arranged at both ends of the shell in the length direction or the width direction, the first cover plate assembly includes a first cover plate and a first electrode terminal, the second cover plate assembly includes a second cover plate and a second electrode terminal, and the polarities of the first electrode terminal and the second electrode terminal are opposite.

50. The battery cell according to claim 49, characterized in that The minimum cross-sectional area of ​​the first electrode terminal and / or the second electrode terminal is S and meets the requirement of 150mm 2 ≤S≤1000mm 2 .

51. A battery device, characterized in that: The battery device comprises the battery cell according to any one of claims 1 to 50, wherein the battery device is at least one of a battery module and a battery pack.

52. An electrical device, characterized in that: The battery cell according to any one of claims 1 to 50 or the battery device according to claim 51 is provided, wherein the battery cell or the battery device provides electrical energy for the electrical device.

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