Battery cell, battery device, and electric device

Abstract

A battery cell, a battery device, and an electric device. The battery cell comprises an electrode assembly and an electrolyte, wherein the electrode assembly comprises a positive electrode sheet and a negative electrode sheet; the positive electrode sheet comprises a lithium-containing phosphate; the negative electrode sheet comprises graphite particles; the electrolyte comprises a carboxylate ester solvent, a linear carbonate solvent, and an additive; the mass content of the carboxylate ester solvent is 10% to 30%; the mass content of the linear carbonate solvent is 10% to 50%; the mass content of the additive is 3% to 9%; the additive comprises 1,3-propane sultone having a mass content greater than or equal to 0, an ethylene carbonate derivative having a mass content greater than or equal to 0, and vinylene carbonate having a mass content greater than 0; and the ethylene carbonate derivative comprises a compound represented by formula A, wherein in formula A, Q1, Q2, Q3, and Q4 each independently comprise any one of a hydrogen atom, a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 haloalkyl group, and Q1, Q2, Q3, and Q4 are not simultaneously hydrogen atoms.

Description

Battery cell, battery device and electric device TECHNICAL FIELD

[0001] The present application relates to a battery cell, a battery device and an electric device. BACKGROUND

[0002] Battery cells have characteristics of high capacity and long service life, and are widely used in electronic devices such as mobile phones, notebook computers, electric vehicles, electric cars, electric planes, electric ships and electric tools, etc. With the development of the application field of lithium ion batteries, higher requirements are put forward for the performance of battery cells, such as the rapid charging performance and cycle performance of battery cells. SUMMARY

[0003] The present application provides a battery cell, a battery device and an electric device, which can improve the rapid charging performance and cycle performance of the battery cell.

[0004] 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 and a negative electrode sheet stacked along a thickness direction of the battery cell; the positive electrode sheet comprising a positive current collector and a positive film layer arranged on at least one side of the positive current collector, the positive film layer comprising a lithium-containing olivine phosphate; the negative electrode sheet comprising a negative current collector and a negative film layer arranged on at least one side of the negative current collector, the negative film layer comprising graphite particles.

[0005] The electrolyte comprises a carboxylic acid ester solvent, a linear carbonate solvent and an additive, wherein the mass content of the carboxylic acid ester solvent is 10% to 30% based on the mass of the electrolyte, and the mass content of the linear carbonate solvent is 10% to 50%; the mass content of the additive is 3% to 9%, and the additive comprises 1,3-propanesultone with a mass content ≥0, a vinyl carbonate derivative with a mass content ≥0, and vinylene carbonate with a mass content >0, the vinyl carbonate derivative comprising a compound represented by formula A,

[0006] In formula A, Q1, Q2, Q3 and Q4 each independently comprise any one of a hydrogen atom, a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 halogenated alkyl group, and Q1, Q2, Q3 and Q4 are not simultaneously a hydrogen atom.

[0007] Therefore, in the charging process, the active ions such as lithium ions migrated out from the positive electrode tab can migrate into the negative electrode tab through the electrolyte, the electrolyte includes carboxylic ester solvents, which can reduce the viscosity of the electrolyte and improve the migration rate of lithium ions in the electrolyte; with the increase of the mass content of the carboxylic ester solvents, the viscosity of the electrolyte is reduced, the conductivity is improved, and the migration rate of lithium ions in the electrolyte can be further improved, which is beneficial to the improvement of the rapid charging performance; however, with the further increase of the mass content of the carboxylic ester solvents, the side reaction between the carboxylic ester solvents and the negative active material is more serious, and the gas production is increased; the electrolyte further includes linear carbonate solvents, the addition of the linear carbonate solvents can make the electrolyte have relatively high conductivity even if the addition amount of the carboxylic ester solvents is low, so as to improve the migration rate of lithium ions; and since the mass content of the carboxylic ester solvents is relatively low, the side reaction is slowed down, and the gas production is reduced; further, the electrolyte further includes an additive, and the additive includes vinylene carbonate; the reaction potential of the vinylene carbonate is close to that of the carboxylic ester solvents, and there is a competitive reaction between the two solvents; the vinylene carbonate can participate in the formation of a dense SEI film containing organic components on the negative side, so that the carboxylic ester solvents are not easy to penetrate the SEI film to the negative active material, thereby further alleviating the side reaction between the carboxylic ester solvents and the negative active material and further reducing the gas production; and since the additive is within a proper content range, the impedance of the film formed on the negative side is not too large, and the rapid charging performance is not deteriorated. Therefore, the embodiments of the present application can improve the rapid charging capability and the cycle performance of the battery cell

[0008] In some embodiments, the mass content of the additive is 5% to 8%. When the mass content of the additive is within the above range, the cycle performance and the rapid charging performance of the battery cell can be further improved.

[0009] In some embodiments, the mass content of the vinylene carbonate is 0.8% to 7%, and can be 2% to 6%. When the mass content of the vinylene carbonate is within the above range, a dense SEI film containing organic components can be formed on the negative side, and the impedance of the SEI film is relatively low, which can reduce the side reaction on the negative side and improve the cycle performance and the rapid charging capability of the battery cell.

[0010] In some embodiments, the mass content of the 1,3-propanesultone in the electrolyte is 0 to 0.5%. When the mass content of the 1,3-propanesultone is within the above range, the impedance of the SEI film formed thereby will not be too high, which can reduce the impedance on the basis of alleviating the side reaction and improve the rapid charging performance and the cycle performance of the battery cell.

[0011] In some embodiments, the mass content of the ethylene carbonate derivative in the electrolyte is 0-2.55%. The ethylene carbonate derivative can preferentially form a film, optimize the composition of the SEI film, reduce the impedance of the SEI film, and effectively improve the rapid charging performance and cycle performance of the battery cell.

[0012] In some embodiments, at least one of Q1, Q2, Q3, and Q4 comprises a halogen atom or a C1-C5 halogenated alkyl group. In the case where the ethylene carbonate derivative comprises a fluorine atom, the ethylene carbonate derivative can form a film layer rich in F and Li on the negative electrode side, can make the impedance of the film layer lower on the basis of protecting the negative electrode active material, and can more effectively improve the cycle performance and rapid charging performance of the battery cell.

[0013] In some embodiments, the ethylene carbonate derivative comprises at least one of the compounds shown in formula A-1 to formula A-3,

[0014] The above-mentioned materials can further improve the cycle performance and rapid charging performance of the battery cell.

[0015] In some embodiments, the electrolyte has an electrical conductivity of 11-14 ms / cm. The high electrical conductivity of the electrolyte is conducive to improving the rapid charging performance of the battery cell.

[0016] In some embodiments, the carboxylic acid ester solvent comprises at least one of ethyl acrylate, propyl acetate, ethyl propionate, ethyl formate, propyl formate, ethyl acetate, and butyl propionate. The above-mentioned materials have low viscosity, which can further improve the rapid charging performance of the battery cell.

[0017] In some embodiments, the linear carbonate solvent comprises at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. The above-mentioned materials have relatively low viscosity, which can improve the electrical conductivity of the electrolyte at room temperature and improve the rapid charging capacity of the battery cell.

[0018] In some embodiments, the electrolyte further comprises a cyclic carbonate solvent, and the mass content of the cyclic carbonate solvent in the electrolyte is 20-50%. The cyclic carbonate solvent has excellent desolvation ability, which can make lithium ions quickly release from the solvation structure at the interface between the positive and negative electrodes, improve the transmission rate of lithium ions at the interface, and thus further improve the rapid charging capacity of the battery cell.

[0019] In some embodiments, the cyclic carbonate solvent comprises at least one of ethylene carbonate, propylene carbonate, and butylene carbonate. The above-mentioned materials have excellent desolvation ability, which can improve the transmission rate of lithium ions at the interface, and thus further improve the rapid charging capacity of the battery cell.

[0020] In some embodiments, the electrolyte further comprises a lithium salt additive, and the lithium salt additive comprises at least one of lithium difluorophosphate, lithium fluorosulfonate, lithium difluoro oxalate borate, lithium tetrafluoroborate, lithium bis-oxalate borate. The above-mentioned additive can improve the SEI film performance on the negative electrode side, which is beneficial to improve the rapid charging performance of the battery monomer and improve the cycle performance.

[0021] In some embodiments, the mass content of the lithium salt additive in the electrolyte is 0.02% to 0.5%. The lithium salt additive and the additive cooperate to participate in film formation, which can optimize the film layer composition of the SEI film. The lithium salt additive can participate in the formation of an SEI film rich in inorganic matter, which can improve the high-temperature stability and high-pressure stability of the SEI film and improve the cycle performance of the battery monomer.

[0022] In some embodiments, the compaction density of the negative electrode film layer of the battery monomer at 0% state of charge is 1.30 g / cm 3 to 1.52 g / cm 3 . When the compaction density of the negative electrode film layer is in the above range, it is beneficial to improve the energy density of the battery monomer, and because the negative electrode active material in the negative electrode film layer is more tightly packed, the contact resistance between particles is smaller, which can further reduce the resistance of the pole piece, thereby reducing heat generation, reducing the amount of gas generated by the decomposition of carboxylate solvents due to heat accumulation, and improving the cycle performance of the battery monomer.

[0023] In some embodiments, the single-side coating weight of the negative electrode film layer is 120 mg / 1540.25 mm 2 to 180 mg / 1540.25 mm 2 . When the single-side coating weight of the negative electrode film layer is in the above range, the heat generation per unit area of the negative electrode pole piece will not be too large, which can improve the cycle performance of the battery monomer.

[0024] In some embodiments, the graphite particles comprise graphite bulk particles and a negative electrode coating layer coated on the surface of the graphite bulk particles, the graphite bulk particles comprise secondary particles, and the negative electrode coating layer comprises carbon elements.

[0025] In some embodiments, the graphite bulk particles comprise at least one of artificial graphite and natural graphite.

[0026] In some embodiments, the graphitization degree of the graphite particles is 90% to 94%. When the graphitization degree of the graphite particles is in the above range, the conductive performance of the graphite particles is relatively excellent, which can reduce the heat generation of the negative electrode pole piece, reduce the heat generation of the battery monomer, and improve the rapid charging performance of the battery monomer.

[0027] In some embodiments, the volume average particle size Dv50 of the graphite particles is 7-15 μm. The volume average particle size of the graphite particles is relatively small, so that the solid phase migration path of lithium ions is short, which can improve the rapid charging capability of the battery cell.

[0028] In some embodiments, the thickness of the negative electrode coating layer is 100-500 nm. When the thickness of the negative electrode coating layer is in the above range, the conductivity of the graphite particles can be further improved, the internal resistance of the negative electrode sheet is reduced, the heat generation of the battery cell is reduced, and the cycle performance of the battery cell can be improved.

[0029] In some embodiments, the negative electrode film layer further comprises a silicon-based material, and the mass content of silicon element in the silicon-based material in the negative electrode film layer is 0.5%-10.0%. When the mass content of silicon element in the silicon-based material is in the above range, the capacity of the negative electrode active material can be improved, and the energy density of the battery cell is improved.

[0030] In some embodiments, the negative electrode film layer comprises a first negative electrode film layer and a second negative electrode film layer, the first negative electrode film layer is arranged on the surface of the negative electrode current collector, and the second negative electrode film layer is arranged on the side of the first negative electrode film layer away from the negative electrode current collector, wherein the first negative electrode film layer and the second negative electrode film layer both comprise graphite particles, and the average longest diameter of the graphite particles in the first negative electrode film layer is greater than or equal to the average longest diameter of the graphite particles in the second negative electrode film layer.

[0031] Therefore, the particle size of the particles in the first negative electrode film layer and the second negative electrode film layer is different, which can improve the rapid charging performance of the battery cell. Specifically, during the rapid charging process, the overpotential of the second negative electrode film layer is usually high, and the bottleneck of the rapid charging is mainly in the second negative electrode film layer. In the embodiments of the present application, the particle size of the particles in the second negative electrode film layer is relatively small, which can shorten the solid phase transmission path of lithium ions, improve the rapid charging performance, and improve the problem of lithium extraction from the surface layer of the negative electrode sheet.

[0032] In some embodiments, the average longest diameter of the graphite particles in the first negative electrode film layer is 7-18 μm. When the average longest diameter of the graphite particles in the first negative electrode film layer is in the above range, on the one hand, the solid phase transmission path of lithium ions can be shortened, and the rapid charging performance can be improved, and on the other hand, the material is not easy to agglomerate during preparation, and the stability of the material can be improved.

[0033] In some embodiments, the average longest diameter of the graphite particles in the second negative electrode film is 6 μm to 10 μm. When the average longest diameter of the graphite particles in the second negative electrode film is within this range, it can shorten the solid-phase transport path of lithium ions and improve fast charging performance. On the other hand, the material is less prone to agglomeration during preparation, which can improve the stability of the material. Furthermore, the combination of the negative electrode active material in the second negative electrode film within the above particle size range and the negative electrode active material in the first negative electrode film is beneficial to constructing a gradient porosity difference between the second and first negative electrode films, reducing the tortuosity of lithium ion transport, and improving the fast charging performance of the battery cell.

[0034] In some embodiments, the ratio of the thickness of the second negative electrode film to the thickness of the negative electrode film is 0.3 to 0.7. By adjusting the thickness ratio of the first negative electrode film, the gradient porosity difference between the upper and lower layers can be further increased, the tortuosity of lithium-ion transport can be reduced, and the fast charging capability of the battery cell can be improved.

[0035] In some embodiments, the compaction density of the positive electrode film layer is 2.3 / cm² when the battery cell is at 0% SOC. 3 Up to 2.6 g / cm 3 When the compaction density of the positive electrode film is within the above range, it is beneficial to improve the energy density of the battery cell. Furthermore, since the positive electrode active material in the positive electrode film is densely packed, the contact resistance between particles is small, which can further reduce the resistance of the electrode, thereby reducing heat generation under fast charging and improving the cycle performance and fast charging performance of the battery cell.

[0036] In some embodiments, the single-sided coating weight of the positive electrode film is 250 mg / 1540.25 mm. 2 Up to 330mg / 1540.25mm 2 When the single-sided coating weight of the positive electrode film is within the above range, the heat generation per unit area of ​​the positive electrode sheet will not be too large, thus improving the cycle performance and fast charging performance of the battery cell.

[0037] In some embodiments, the lithium phosphate includes at least one of primary particles and secondary particles, wherein the secondary particles include a plurality of primary particles and are spherical and / or quasi-spherical. The migration path of lithium ions in the primary particles is shorter, which can improve the migration rate of lithium ions; moreover, the spherical and / or quasi-spherical shape of the secondary particles provides more migration paths, which can further improve the migration rate of lithium ions and improve the fast-charging performance of the battery cell.

[0038] In some embodiments, the average longest diameter of the primary particles is between 300 nm and 800 nm. When the average longest diameter of the primary particles is within this range, the solid-phase transport distance of lithium ions is shorter, which can further improve the migration rate of lithium ions and improve the fast charging performance of the battery cell.

[0039] In some embodiments, the average particle size of the secondary particles is 5-15 μm. When the average particle size of the secondary particles is in the above range, the solid phase transmission distance of lithium ions is shorter, which can further improve the migration rate of lithium ions and improve the rapid charging performance of the battery cell.

[0040] In some embodiments, the lithium-containing phosphate includes phosphate particles and positive electrode additive elements in the phosphate particles, and the positive electrode additive elements include at least one of aluminum, vanadium, titanium and niobium. The above positive electrode additive elements can improve the crystal structure stability of the positive electrode active material, improve the pressure resistance of the lithium-containing phosphate, and be beneficial to improving the compaction density of the positive electrode film layer and the energy density and cycle performance of the battery cell.

[0041] In some embodiments, the mass content of aluminum in the lithium-containing phosphate is 200-2500 ppm. When the mass content of aluminum is in the above range, the pressure resistance of the lithium-containing phosphate can be improved, which is beneficial to improving the compaction density of the positive electrode film layer and the energy density and cycle performance of the battery cell.

[0042] In some embodiments, the mass content of vanadium in the lithium-containing phosphate is 300-2000 ppm. When the mass content of vanadium is in the above range, the compaction density of the positive electrode film layer can be improved, and the energy density and cycle performance of the battery cell can be improved.

[0043] In some embodiments, the mass content of titanium in the lithium-containing phosphate is 1500-3500 ppm. When the mass content of titanium is in the above range, the crystal structure of the positive electrode active material can be further improved, and the cycle performance can be improved.

[0044] In some embodiments, the mass content of niobium in the lithium-containing phosphate is 300-2000 ppm. When the mass content of niobium is in the above range, the crystal structure of the positive electrode active material can be further improved, and the cycle performance can be improved.

[0045] In some embodiments, the phosphate particles include one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate and lithium cobalt phosphate. The above materials have excellent cycle stability, which can improve the cycle performance of the battery cell.

[0046] In some embodiments, the lithium-containing phosphate includes a general formula of Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1A compound of formula (I), wherein 0.5≤x1≤1.3, 0≤y1≤1.3, 0.5≤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, A comprises at least one of Na, K and Mg; Me comprises at least one of Mn, Fe, Co and Ni; M comprises at least one 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 comprises at least one of Cl, C, N; Y comprises at least one of O and F. The lithium-containing phosphate has excellent cycle stability, which is beneficial to improve the cycle performance of the battery cell.

[0047] In some embodiments, the positive tab includes at least one positive tab, and the at least one positive tab is connected to the positive current collector and extends out of the positive current collector along the length direction of the battery cell. This arrangement is beneficial to reduce the occupied space of the tab and improve the energy density of the battery cell.

[0048] In some embodiments, the negative tab includes at least one negative tab, and the at least one negative tab is connected to the negative current collector and extends out of the negative current collector along the length direction of the battery cell. This arrangement is beneficial to reduce the occupied space of the tab and improve the energy density of the battery cell.

[0049] In some embodiments, the positive tab satisfies: n*W1 / W2 is 0.9 to 1.0; n represents the number of all positive tabs located on the same side of the positive current collector; W1 represents the average size of the positive tab along the width direction of the battery cell; and W2 represents the size of the positive current collector along the width direction.

[0050] Thus, when n*W1 / W2 satisfies the above range, the overcurrent area of the positive tab is relatively large, which is beneficial to improve the rapid charging performance of the battery cell.

[0051] In some embodiments, the negative tab satisfies: m*W3 / W4 is 0.9 to 1.0; m represents the number of all negative tabs located on the same side of the negative current collector; W3 represents the average size of the negative tab along the width direction of the battery cell; and W4 represents the size of the negative current collector along the width direction.

[0052] Thus, when m*W3 / W4 satisfies the above range, the overcurrent area of the negative tab is relatively large, which is beneficial to improve the rapid charging performance of the battery cell.

[0053] In some embodiments, the battery cell further comprises a positive terminal and a positive adapter, the positive terminal is arranged on at least one side of the electrode assembly along the width direction of the battery cell, and the positive terminal is connected to the positive tab through the positive adapter. Through the connection of the positive adapter, the overcurrent capacity between the positive terminal and the positive tab can be improved, and the rapid charging capacity of the battery cell can be improved.

[0054] In some embodiments, the battery cell further comprises a negative terminal and a negative adapter, the negative terminal is arranged on at least one side of the electrode assembly along the width direction, and the negative terminal is connected to the negative tab through the negative adapter. Through the connection of the negative adapter, the overcurrent capacity between the negative terminal and the negative tab can be improved, and the rapid charging capacity of the battery cell can be improved.

[0055] In some embodiments, the thickness of the positive adapter is 1.25mm to 3.00mm. The thickness of the positive adapter is relatively thick, the overcurrent capacity is relatively excellent, and the rapid charging capacity of the battery cell can be further improved.

[0056] In some embodiments, the thickness of the negative adapter is 1.50mm to 2.50mm. The thickness of the negative adapter is relatively thick, the overcurrent capacity is relatively excellent, and the rapid charging capacity of the battery cell can be further improved.

[0057] In some embodiments, the positive adapter comprises a first positive adapter part and a second positive adapter part, the first positive adapter part is connected to the positive tab, the second positive adapter part is connected to the first positive adapter part and protrudes from the first positive adapter part along the length direction, and the second positive adapter part is connected to the positive terminal. The ratio of the size of the first positive adapter part along the width direction to the width of the battery cell is 0.2 to 0.5. When the ratio of the size of the first positive adapter part along the width direction to the width of the battery cell is in the above range, the path of electrons from the positive tab to the positive terminal through the positive adapter is relatively short, and the rapid charging capacity of the battery cell 7 can be improved.

[0058] In some embodiments, the ratio of the size of the second positive adapter part along the length direction to the length of the battery cell is 0.05 to 0.2. When the ratio of the size of the second positive adapter part along the length direction to the length of the battery cell is in the above range, the path of electrons from the positive tab to the positive terminal through the positive adapter is relatively short, and the rapid charging capacity of the battery cell can be improved.

[0059] In some embodiments, the negative adapter includes a first negative adapter portion and a second negative adapter portion, the first negative adapter portion is connected to the negative tab, the second negative adapter portion is connected to the first negative adapter portion and protrudes from the first negative adapter portion along a length direction, and the second negative adapter portion is connected to the negative terminal; a ratio of a size of the first negative adapter portion along a width direction to a width of the battery cell is 0.2 to 0.5; when the ratio of the size of the first negative adapter portion along the width direction to the width of the battery cell is within the above range, a path of electrons from the negative tab to the negative terminal through the negative adapter is relatively short, and the fast charging capability of the battery cell can be improved.

[0060] In some embodiments, a ratio of a size of the second negative adapter portion along a length direction to a length of the battery cell is 0.05 to 0.2; when the ratio of the size of the second negative adapter portion along the length direction to the length of the battery cell is within the above range, a path of electrons from the negative tab to the negative terminal through the negative adapter is relatively short, and the fast charging capability of the battery cell can be improved.

[0061] In some embodiments, the length of the battery cell is 200 mm to 400 mm; when the length of the battery cell is within the above range, the energy density of the battery cell can be improved, and the transmission path of the electrons along the length direction is not too long, which is beneficial to improve the fast charging capability of the battery cell.

[0062] In some embodiments, the width of the battery cell is 80 mm to 130 mm; when the width of the battery cell is within the above range, the energy density of the battery cell can be improved, and the transmission path of the electrons along the width direction is not too long, which is beneficial to improve the fast charging capability of the battery cell.

[0063] In some embodiments, the thickness of the battery cell is 25 mm to 60 mm; when the thickness of the battery cell is within the above range, the battery cell can quickly release internal heat, slow down the risk of electrolyte decomposition due to heat accumulation, and improve the cycle performance of the battery cell.

[0064] In a second aspect, the present application provides a battery device, the battery device including one or more battery cells according to any of the embodiments of the first aspect of the present application.

[0065] In a third aspect, the present application provides a power consumption device, the power consumption device including the battery device according to any of the embodiments of the second aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0066] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments of the present application. Obviously, the drawings described below only constitute some of the embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of the drawings.

[0067] FIG. 1 is a structural schematic diagram of a battery cell provided by some embodiments of the present application,

[0068] FIG. 2 is an exploded schematic diagram of a battery cell provided by some embodiments of the present application,

[0069] FIG. 3 is a structural schematic diagram of an electrode assembly of a battery cell provided by some embodiments of the present application,

[0070] FIG. 4 is a structural schematic diagram of a positive electrode sheet of a battery cell provided by some embodiments of the present application,

[0071] FIG. 5 is a structural schematic diagram of a positive electrode sheet of a battery cell provided by some other embodiments of the present application,

[0072] FIG. 6 is a structural schematic diagram of a positive electrode sheet of a battery cell provided by some other embodiments of the present application,

[0073] FIG. 7 is a structural schematic diagram of a positive electrode sheet of a battery cell provided by some other embodiments of the present application,

[0074] FIG. 8 is a structural schematic diagram of a negative electrode sheet of a battery cell provided by some embodiments of the present application,

[0075] FIG. 9 is a structural schematic diagram of a negative electrode sheet of a battery cell provided by some other embodiments of the present application,

[0076] FIG. 10 is an exploded schematic diagram of a battery cell provided by some other embodiments of the present application,

[0077] FIG. 11 is a structural schematic diagram of a positive electrode adapter of a battery cell provided by some embodiments of the present application,

[0078] FIG. 12 is a structural schematic diagram of a negative electrode adapter of a battery cell provided by some embodiments of the present application,

[0079] FIG. 13 is a structural schematic diagram of a battery module provided by some embodiments of the present application,

[0080] FIG. 14 is a structural schematic diagram of a battery pack provided by some embodiments of the present application,

[0081] FIG. 15 is a structural schematic diagram of a power utilization device provided by some embodiments of the present application.

[0082] The drawings are not necessarily drawn according to the actual scale.

[0083] The following reference signs are used in the drawings: X, thickness direction; Y, width direction; Z, length direction; 1, electric device; 2, battery pack; 3, controller; 4, motor; 5, case; 5a, first case portion; 5b, second case portion; 5c, accommodation space; 6, battery module; 7, battery cell; 10, electrode assembly; 11, positive electrode tab; 111, first end; 112, positive electrode current collector; 12, negative electrode tab; 121, second end; 122, negative electrode current collector; 13, separator; 20, housing; 21, case; 22, end cap; 31, positive electrode terminal; 32, negative electrode terminal; 41, positive electrode adapter; 411, first positive electrode adapter portion; 412, second positive electrode adapter portion; 42, negative electrode adapter; 421, first negative electrode adapter portion; 422, second negative electrode adapter portion. DETAILED DESCRIPTION

[0084] Hereinafter, embodiments of the battery cell, battery device, and electric device of the present application are specifically disclosed while appropriately referring to the drawings. However, there are cases where unnecessary detailed explanations are omitted. For example, there are cases where detailed explanations of matters that are already well known, repeated explanations of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following explanations are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0085] The "ranges" disclosed in the present application are defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The ranges defined in this manner can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, then the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In the present application, unless otherwise stated, a numerical range "a to b" indicates a shorthand manner of describing an arbitrarily selected combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" indicates that all real numbers between "0 to 5" have been listed herein, and "0 to 5" is merely a shorthand manner of describing these numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0086] If there is no special indication, all the embodiments and optional embodiments of the present application can be combined to form new technical solutions.

[0087] If there is no special indication, all the technical features and optional technical features of the present application can be combined to form new technical solutions.

[0088] If there is no special indication, all the steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, it is mentioned that the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0089] The battery monomer comprises an electrode assembly and an electrolyte, the electrode assembly comprises a positive electrode sheet and a negative electrode sheet, the negative electrode sheet comprises a negative electrode active material, and a side interface of the negative electrode may have a side reaction with the electrolyte, which deteriorates the cycle; as the charging rate of the battery monomer increases, the side reaction of the negative electrode side interface is further intensified, which further deteriorates the cycle, which is not conducive to fast charging.

[0090] In view of the above problems, the embodiments of the present application reasonably design the system of the battery monomer, which can improve the cycle performance and fast charging capacity of the battery monomer; specifically, the positive electrode active material comprises lithium-containing phosphate with olivine structure, and the negative electrode active material comprises graphite particles, and the above material system has excellent cycle stability;

[0091] During charging, active ions such as lithium ions migrated out of the positive electrode sheet migrate to the negative electrode sheet through the electrolyte, and the electrolyte comprises a carboxylic acid ester solvent, which can reduce the viscosity of the electrolyte and improve the migration rate of lithium ions in the electrolyte; as the mass content of the carboxylic acid ester solvent increases, the viscosity of the electrolyte decreases, the conductivity increases, and the migration rate of lithium ions in the electrolyte can be further improved, which is conducive to the improvement of the fast charging performance; but as the mass content of the carboxylic acid ester solvent further increases, the side reaction between the carboxylic acid ester solvent and the negative electrode active material is more serious, and the gas production increases;

[0092] The electrolyte further comprises a linear carbonate solvent, and the addition of the linear carbonate solvent can make the addition amount of the carboxylic acid ester solvent relatively low, so that the electrolyte has relatively high conductivity and improves the migration rate of lithium ions; and because the mass content of the carboxylic acid ester solvent is relatively low, the side reaction is slowed down and the gas production is reduced;

[0093] Further, the electrolyte further comprises an additive, the additive comprises vinylene carbonate, the reaction potential of the vinylene carbonate is close to that of the carboxylic acid ester solvent, and the carboxylic acid ester solvent has a competitive reaction, the vinylene carbonate can participate in the formation of a dense solid electrolyte interface (SEI) film containing organic components on the negative electrode side, so that the carboxylic acid ester solvent is not easy to penetrate the SEI film to the negative electrode active material, thereby further alleviating the side reaction of the carboxylic acid ester solvent and the negative electrode active material, and further reducing the gas production; and because the additive is within an appropriate content, the film impedance formed by the additive on the negative electrode side is not too large, and the rapid charging performance is not substantially deteriorated.

[0094] Therefore, the embodiments of the present application can improve the rapid charging capability and cycle performance of the battery cell.

[0095] Battery cell

[0096] In a first aspect, the embodiments of the present application provide a battery cell.

[0097] The battery cell comprises an electrode assembly and an electrolyte, the electrode assembly comprises a positive electrode sheet and a negative electrode sheet, the positive electrode sheet and the negative electrode sheet are stacked along the thickness direction of the battery cell; the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, the positive electrode film layer comprises a positive electrode active material, the positive electrode active material comprises a lithium-containing phosphate with an olivine structure; the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, and the negative electrode active material comprises graphite particles;

[0098] The electrolyte comprises an organic solvent and an additive, wherein the organic solvent comprises a carboxylic acid ester solvent and a linear carbonate solvent, the mass content of the carboxylic acid ester solvent in the electrolyte is 10% to 30%, and the mass content of the linear carbonate solvent is 10% to 50%;

[0099] The mass content of the additive is 3% to 9% based on the mass of the electrolyte, the additive comprises 1,3-propane sultone with a mass content of ≥0, a vinyl carbonate derivative with a mass content of ≥0, and vinylene carbonate with a mass content of >0, the vinyl carbonate derivative comprises a compound represented by formula A,

[0100] In formula A, Q1, Q2, Q3, and Q4 each independently comprise any one of a hydrogen atom, a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 halogenated alkyl group, and Q1, Q2, Q3, and Q4 are not simultaneously hydrogen atoms.

[0101] The positive electrode active material comprises a lithium-containing phosphate with an olivine structure, and the negative electrode active material comprises graphite particles, and the above material system has excellent cycle stability.

[0102] During the charging process, active ions such as lithium ions migrated out of the positive electrode sheet migrate into the negative electrode sheet through the electrolyte, which includes a mass content of greater than or equal to 10% of carboxylic acid ester solvent, can reduce the viscosity of the electrolyte, improve the migration rate of lithium ions in the electrolyte, and improve the rapid charging capacity of the battery cell;

[0103] As the mass content of the carboxylic acid ester solvent increases, the viscosity of the electrolyte decreases, the conductivity increases, and the migration rate of lithium ions in the electrolyte can be further improved, which is beneficial to the improvement of the rapid charging performance; but as the mass content of the carboxylic acid ester solvent further increases, the side reaction of the carboxylic acid ester solvent and the negative active material is more serious, and the gas production increases;

[0104] The electrolyte also includes a linear carbonate solvent, and the addition of 10% to 50% of the linear carbonate solvent can make the addition amount of the carboxylic acid ester solvent relatively low, so that the electrolyte has relatively high conductivity and improves the migration rate of lithium ions; and because the mass content of the carboxylic acid ester solvent is relatively low, for example, less than or equal to 30%, the side reaction on the negative side can be slowed down, and the gas production is reduced;

[0105] Further, the electrolyte also includes an additive, and the additive includes vinylene carbonate, the reaction potential of the vinylene carbonate and the carboxylic acid ester solvent is close, and there is a competitive reaction with the carboxylic acid ester solvent. The vinylene carbonate can participate in the formation of a dense solid-state electrolyte interface film SEI film containing organic components on the negative side, so that the carboxylic acid ester solvent is not easy to penetrate the SEI film to the negative active material, thereby further alleviating the side reaction of the carboxylic acid ester solvent and the negative active material, and further reducing the gas production; and because the additive is within an appropriate content, the impedance of the film formed on the negative side is not too large, and the rapid charging performance is not substantially deteriorated.

[0106] Therefore, the embodiments of the present application can improve the rapid charging capacity and cycle performance of the battery cell.

[0107] [Electrolyte]

[0108] The battery cell includes an electrolyte. During the charging and discharging process of the battery cell, active ions such as lithium ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet, and the electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0109] In some embodiments, the conductivity of the electrolyte is 11 mS / cm to 14 mS / cm. For example, the conductivity of the electrolyte is 11 mS / cm, 11.5 mS / cm, 12 mS / cm, 12.5 mS / cm, 13 mS / cm, 13.5 mS / cm, 14 mS / cm, or a range formed by any two of the above values.

[0110] When the conductivity of the electrolyte at room temperature, for example, 25℃, is in the above range, the migration rate of lithium ions in the electrolyte is higher, which can further reduce the internal resistance of the battery monomer, thereby reducing the heat generation and improving the rapid charging performance of the battery monomer.

[0111] In the embodiments of the present application, the conductivity of the electrolyte at room temperature, for example, 25℃, is the ionic conductivity, which can be detected by using the devices and methods known in the art, for example, by referring to the industry standard HG-T 4067-2015 for testing.

[0112] The electrolyte comprises an organic solvent and an electrolyte salt.

[0113] The organic solvent comprises a carboxylic acid ester solvent, and the mass content of the carboxylic acid ester solvent in the electrolyte is 10% to 30%. Illustratively, the mass content of the carboxylic acid ester solvent is 10%, 15%, 20%, 25%, 30%, or a range formed by any two of the above values. When the mass content of the carboxylic acid ester solvent is greater than or equal to 10%, the viscosity of the electrolyte system is relatively small, which is beneficial to the migration of lithium ions; when the mass content of the carboxylic acid ester solvent is less than or equal to 30%, the side reaction between the carboxylic acid ester solvent and the negative active material is relatively small, which is beneficial to improve the cycle performance.

[0114] In some embodiments, the carboxylic acid ester solvent can comprise at least one of a linear carbonate solvent and a cyclic carboxylic acid ester solvent, and optionally a linear carbonate solvent. The linear carbonate solvent has lower viscosity, which can further improve the migration rate of lithium ions and improve the rapid charging capability of the battery monomer.

[0115] Due to the lower viscosity and better flowability of the linear carbonate solvent, it is more beneficial to the rapid infiltration of the electrode sheet. Under fast charging conditions, local lithium precipitation is less likely to occur on the surface of the negative electrode sheet, thereby improving the use reliability of the battery monomer.

[0116] Illustratively, the carboxylic acid ester solvent comprises at least one of ethyl acrylate, propyl acetate, ethyl propionate, ethyl formate, propyl formate, ethyl acetate, and butyl propionate, and optionally ethyl acrylate.

[0117] The above material has lower viscosity, which can further improve the rapid charging performance of the battery monomer.

[0118] In the embodiments of the present application, the organic solvent further comprises a linear carbonate solvent, and the mass content of the linear carbonate solvent in the electrolyte is 10% to 50%. Illustratively, the mass content of the linear carbonate solvent in the electrolyte is 10%, 15%, 20%, 25%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 40%, 45%, 48%, 50%, or a range formed by any two of the above values.

[0119] The linear carbonate solvent in the above mass content can further improve the conductivity of the electrolyte at room temperature, is conducive to the migration of lithium ions, and improves the rapid charging capability of the battery cell.

[0120] Illustratively, the linear carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, and can be dimethyl carbonate.

[0121] The viscosity of the above material is relatively low, which can improve the conductivity of the electrolyte at room temperature, and improve the rapid charging capability of the battery cell.

[0122] In some embodiments, the organic solvent further includes a cyclic carbonate solvent, and the mass content of the cyclic carbonate solvent in the electrolyte is 20% to 50%. Illustratively, the mass content of the cyclic carbonate solvent in the electrolyte is 20%, 25%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 40%, 45%, 48%, 50%, or a range composed of any two of the above values. The cyclic carbonate solvent has excellent desolvation capacity, which can make lithium ions quickly release from the solvation structure at the positive and negative electrode interface, improve the transmission rate of lithium ions at the interface, and thus further improve the rapid charging capability of the battery cell.

[0123] Illustratively, the cyclic carbonate includes one or more of vinyl carbonate, propylene carbonate, and butylene carbonate, and can be vinyl carbonate.

[0124] The above material has excellent desolvation capacity, which can improve the transmission rate of lithium ions at the interface, and thus further improve the rapid charging capability of the battery cell.

[0125] In the embodiments of the present application, the electrolyte further includes an additive, and the additive includes 1,3-propane sultone with a mass content ≥0, vinyl carbonate derivative with a mass content ≥0, and vinylene carbonate with a mass content >0.

[0126] In the embodiments of the present application, the mass content of the additive is 3% to 9%, for example, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, or a range composed of any two of the above values.

[0127] When the mass content of the additive is less than 3%, the film layer formed on the negative electrode side is thin, which is not conducive to the protection of the negative electrode active material; with the increase of the mass content of the additive, the film forming effect on the negative electrode side is more excellent, which can play an excellent protective role on the negative electrode active material, reduce the risk of carboxylic acid ester solvent penetrating the SEI film into the negative electrode film layer, reduce the side reaction on the negative electrode side, reduce the gas production, and improve the cycle performance; but with the further increase of the mass content of the additive, the SEI film formed on the negative electrode side has high impedance, which is not conducive to fast charging; therefore, the mass content of the additive in the embodiment of the application is controlled to be 3% to 9%, which can improve the cycle performance and fast charging performance of the battery cell.

[0128] The additive includes vinylene carbonate with a mass content of >0, in other words, vinylene carbonate is a necessary component of the electrolyte.

[0129] When the mass content of 1,3-propanesultone and vinyl carbonate derivative is 0, it means that the sum of the mass content of 1,3-propanesultone and the mass content of vinyl carbonate derivative is 0, in this case, the additive can only include vinylene carbonate, and the mass content of vinylene carbonate can be 3% to 9%;

[0130] Specifically, taking the case of 0 mass content of vinyl carbonate derivative as an example,

[0131] It can be that no vinyl carbonate derivative is added in the freshly prepared electrolyte,

[0132] Or the electrolyte obtained after disassembling the battery cell does not contain vinyl carbonate derivative, which may be that the freshly prepared electrolyte does not add vinyl carbonate derivative, or a small amount of vinyl carbonate derivative is added, but participates in the film forming reaction of SEI film during the formation process of the battery cell, so that the mass content of vinyl carbonate derivative is 0 in the detection process. Alternatively, the freshly prepared electrolyte includes vinyl carbonate derivative.

[0133] Further, for adding certain substances, such as additives, in the electrolyte, due to the characteristics that the additives participate in the film formation on the surface of the active material, the content of the additives in the electrolyte of the battery cell is related to the formation, different battery life cycles or different battery storage states, so the content of the additives in the electrolyte obtained from the reverse disassembled battery cell can be different from that in the freshly prepared electrolyte, but the skilled person in the art can know the approximate range of the content of the related substances in the fresh electrolyte corresponding to the performance level (such as the number of cycles) of the battery cell, the residual content, etc. Similarly, the skilled person in the art can also know the approximate range of the content corresponding to the non-fresh preparation (i.e. after reverse) according to the content of the freshly prepared additives, according to the performance requirements of the battery cell, the storage environment, etc.

[0134] Therefore, the content of the additives mentioned in the technical scheme of the present application can be the content of the additives actively added to the fresh electrolyte, or the content of the residual additives detected reversely according to the actual battery state.

[0135] In some embodiments, the mass content of vinylene carbonate in the electrolyte is 0.8% to 7%, for example, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7% or a range consisting of any two of the above values. When the mass content of vinylene carbonate is in the above range, a dense SEI film containing organic components can be formed on the negative side, and the impedance of the SEI film is relatively low, which can reduce the side reaction on the negative side, and improve the cycle performance and fast charging capability of the battery cell. Alternatively, the mass content of vinylene carbonate in the electrolyte is 2% to 6%.

[0136] The additive further includes at least one of 1,3-propane sultone and vinyl carbonate derivative with a mass content > 0, the additive can include 1,3-propane sultone, or the additive can include vinyl carbonate derivative, or the additive can include 1,3-propane sultone and vinyl carbonate derivative.

[0137] In some embodiments, the mass content of 1,3-propane sultone in the electrolyte is 0 to 0.5%, for example, 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% or a range consisting of any two of the above values.

[0138] In the case that the mass content of 1,3-propanesultone is 0, it means that 1,3-propanesultone can not be added in the freshly prepared electrolyte, or the electrolyte obtained after disassembling the battery cell does not contain 1,3-propanesultone. Generally speaking, since 1,3-propanesultone is less consumed in the film forming process, the mass content of 1,3-propanesultone in the freshly prepared electrolyte is slightly greater than that in the disassembled electrolyte.

[0139] Both 1,3-propanesultone and vinylene carbonate can form a dense SEI film on the negative electrode side, which can effectively alleviate the risk of side reactions between carboxylic ester solvents and negative active materials penetrating through the SEI film.

[0140] In the case that the mass content of 1,3-propanesultone is greater than 0 and less than or equal to 0.5%, the impedance of the formed SEI film will not be too high, which can reduce the impedance on the basis of alleviating the side reaction and improve the rapid charging performance and cycle performance of the battery cell.

[0141] In some embodiments, the mass content of the vinyl carbonate derivative in the electrolyte is 0 to 2.55%, for example, 0, 0.5%, 1%, 1.5%, 2%, 2.5%, 2.55%, or a range composed of any two of the above values.

[0142] Alternatively, the freshly prepared electrolyte includes a vinyl carbonate derivative, and the mass content of the vinyl carbonate derivative in the freshly prepared electrolyte is greater than 0. The vinyl carbonate derivative preferentially forms a film, and after adding a certain content of the vinyl carbonate derivative in the freshly prepared electrolyte, the battery cell obtained after disassembly can also not detect the vinyl carbonate derivative due to the large consumption of the vinyl carbonate derivative in the film forming stage.

[0143] Vinylene carbonate continuously participates in the formation of the SEI film during the cycle of the battery cell, alleviating the risk of carboxylic ester solvents penetrating through the SEI film, but the organic component content of the SEI film is relatively high, making the impedance of the SEI film relatively high; while the vinyl carbonate derivative can preferentially form a film, which can optimize the components of the SEI film, reduce the impedance of the SEI film, and effectively improve the rapid charging performance and cycle performance of the battery cell.

[0144] In the rapid charging, the three types of substances jointly participate in the formation of the SEI film, which can reinforce the SEI film through the low content of 1,3-propane sultone, and the vinylene carbonate can further reinforce the film, reduce the risk of carboxylate solvent penetrating the SEI film, and improve the cycle performance of the battery cell; the appropriate content of the vinyl carbonate derivative can reduce the film forming impedance and improve the fast charging performance, and the mass content of the vinyl carbonate derivative cannot be too high, which can reduce the risk of high temperature decomposition and further improve the cycle performance of the battery cell; thereby improving the rapid charging performance and cycle performance of the battery cell.

[0145] In the embodiments of the present application, the vinyl carbonate derivative refers to at least one hydrogen atom of the vinyl carbonate being replaced, and the substituent group can be one, two, three, or four, etc.

[0146] Exemplarily, the vinyl carbonate derivative includes a compound shown in formula A,

[0147] In formula A, Q1, Q2, Q3, and Q4 each independently include any one of a hydrogen atom, a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 halogenated alkyl group, and Q1, Q2, Q3, and Q4 are not hydrogen atoms at the same time.

[0148] Q1, Q2, Q3, and Q4 are not hydrogen atoms at the same time, in other words, at least one of Q1, Q2, Q3, and Q4 includes a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 halogenated alkyl group.

[0149] Exemplarily, one of Q1, Q2, Q3, and Q4 includes a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 halogenated alkyl group, and the rest are hydrogen atoms.

[0150] Exemplarily, at least two of Q1, Q2, Q3, and Q4 include a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 halogenated alkyl group.

[0151] Exemplarily, at least three of Q1, Q2, Q3, and Q4 include a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 halogenated alkyl group.

[0152] Exemplarily, Q1, Q2, Q3, and Q4 each independently include a halogen atom, a C1 to C5 alkyl group, or a C1 to C5 halogenated alkyl group.

[0153] Optionally, at least one of Q1, Q2, Q3 and Q4 comprises a halogen atom, or a C1 to C5 halogenated alkyl group. The halogen atom comprises a fluorine atom, a bromine atom, or a chlorine atom, etc., and is optionally a fluorine atom. The C1 to C5 halogenated alkyl group comprises a C1 to C5 fluorinated alkyl group, a C1 to C5 brominated alkyl group, or a C1 to C5 chlorinated alkyl group, etc., and is optionally a fluorine atom. For example, the C1 to C5 fluorinated alkyl group comprises a fluoromethyl group, a fluoroethyl group, a fluoropropyl group, a fluorobutyl group, or a fluoropentyl group.

[0154] In the case that the ethylene carbonate derivative comprises a fluorine atom, the ethylene carbonate derivative is capable of forming a film layer rich in F and Li on the negative electrode side, is capable of making the impedance of the film layer lower on the basis of protecting the negative electrode active material, and is capable of more effectively balancing the improvement of the cycle performance and the fast charging performance of the battery cell.

[0155] For example, the ethylene carbonate derivative comprises at least one of a compound represented by Formula A-1 to a compound represented by Formula A-6,

[0156] The above material is capable of further improving the cycle performance and the fast charging performance of the battery cell.

[0157] Optionally, the ethylene carbonate derivative comprises at least one of a compound represented by Formula A-1, a compound represented by Formula A-2, and a compound represented by Formula A-3, and further optionally, the ethylene carbonate derivative comprises a compound represented by Formula A-1.

[0158] In some embodiments, the additive further comprises a lithium salt additive, and the lithium salt additive comprises at least one of lithium difluorophosphate, lithium fluorosulfonate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, and lithium bis(oxalato)borate. The above additive is capable of improving the SEI film performance on the negative electrode side, is conducive to improving the fast charging performance and the cycle performance of the battery cell.

[0159] In some embodiments, the mass content of the lithium salt additive in the electrolyte is 0.02% to 0.5%, such as 0.02%, 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, or a range composed of any two of the above values. The lithium salt additive and the additive cooperate to participate in film formation, which is capable of optimizing the film layer composition of the SEI film. The lithium salt additive is capable of participating in the formation of an SEI film rich in inorganic matter, which is capable of improving the high-temperature stability and the high-pressure stability of the SEI film, and improving the cycle performance of the battery cell.

[0160] For example, the lithium salt additive comprises lithium difluorophosphate, and the mass content of the lithium difluorophosphate in the electrolyte is 0.02% to 0.5%.

[0161] Exemplarily, the lithium salt additive includes lithium fluorosulfonate, and the mass content of lithium fluorosulfonate in the electrolyte is 0.02% to 0.5%.

[0162] In some embodiments, the electrolyte salt includes a lithium salt, and the lithium salt includes lithium hexafluorophosphate LiPF6. Optionally, the electrolyte further includes a lithium-containing sulfurylimide salt, which can improve the cycle performance of the battery cell.

[0163] Optionally, the lithium-containing sulfurylimide includes one or more of lithium bisfluorosulfonylimide LiFSI and lithium bis(trifluoromethylsulfonyl)imide LiTFSI.

[0164] In some embodiments, the mass content of the lithium salt is 5% to 18%, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, or a range between any two of the above values.

[0165] In the embodiments of the present application, the types and contents of inorganic components / lithium salts in the electrolyte are the meanings known in the art, and can be detected by using the devices and methods known in the art, for example, the qualitative or quantitative analysis of the inorganic components / lithium salts in the electrolyte can be performed by ion chromatography according to the standard JY / T020-1996 “General Ion Chromatography Analysis Method”. In the embodiments of the present application, the freshly prepared electrolyte can be taken as a sample, the free electrolyte of a fresh battery can be taken as a sample, or the free electrolyte obtained from a battery cell that has been discharged (discharged to a discharge cut-off voltage so that the charged state of the battery cell is about 0% SOC) can be taken as a sample, and the ion chromatography analysis method is used for detection.

[0166] In the embodiments of the present application, the types and contents of organic components in the electrolyte are the meanings known in the art, and can be detected by using the devices and methods known in the art, for example, the qualitative and quantitative analysis of the organic components in the electrolyte can be performed by gas chromatography according to the standard GB / T9722-2006 “General Gas Chromatography Method for Chemical Reagents”.

[0167] [Negative electrode sheet]

[0168] The negative electrode sheet includes a negative current collector and a negative film layer including a negative active material and arranged on at least one surface of the negative current collector. For example, the negative current collector has two surfaces opposite in the thickness direction of the negative current collector, and the negative film layer is arranged on any one or both of the two opposite surfaces of the negative current collector.

[0169] The charging upper limit voltage and discharging cut-off voltage of the battery cell are different according to different positive active materials. For example, when the phosphate material includes lithium iron phosphate, the charging upper limit voltage can be 3.65V, and the discharging cut-off voltage can be 2.0V. For example, when the phosphate material includes lithium manganese iron phosphate, the charging upper limit voltage can be 4.2V, and the discharging cut-off voltage can be 2.0V. Next, taking the charging upper limit voltage of 3.65V and the discharging cut-off voltage of 2.0V as an example, the state of the battery cell is described: in the embodiments of the present application, the 100% state of charge SOC and the 0% state of charge SOC of the battery cell are defined as follows,

[0170] The battery cell is charged to the charging upper limit voltage at a constant current charging rate of 0.33C, and then charged to 0.05C at a constant voltage, corresponding to the state of 100% SOC of the battery cell. The battery cell is discharged to the cut-off voltage at a constant current discharging rate of 0.33C, corresponding to the state of 0% SOC of the battery cell.

[0171] In some embodiments, the compaction density of the negative electrode film layer of the battery cell at 0% state of charge is 1.30g / cm 3 to 1.52g / cm 3 . For example, the compaction density of the negative electrode film layer of the battery cell at 0% state of charge is 1.30g / cm 3 , 1.32g / cm 3 , 1.35g / cm 3 , 1.40g / cm 3 , 1.45g / cm 3 , 1.50g / cm 3 , 1.52g / cm 3 , or a range composed of any two of the above values.

[0172] When the compaction density of the negative electrode film layer is in the above range, it is beneficial to improve the energy density of the battery cell, and because the negative active material of the negative electrode film layer is packed more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the pole piece, thereby reducing heat generation, reducing the amount of gas generated by decomposition of the carboxylate solvent due to heat accumulation, and improving the cycle performance of the battery cell.

[0173] In some embodiments, the single-sided coating weight of the negative electrode film layer is 120mg / 1540.25mm 2 to 180mg / 1540.25mm 2 . For example, the single-sided coating weight of the negative electrode film layer is 120mg / 1540.25mm 2 , 122mg / 1540.25mm 2 , 125mg / 1540.25mm 2, 128 mg / 1540.25 mm 2 , 130 mg / 1540.25 mm 2 , 132 mg / 1540.25 mm 2 , 135 mg / 1540.25 mm 2 , 137 mg / 1540.25 mm 2 , 140 mg / 1540.25 mm 2 , 145 mg / 1540.25 mm 2 , 150 mg / 1540.25 mm 2 , 155 mg / 1540.25 mm 2 , 160 mg / 1540.25 mm 2 , 165 mg / 1540.25 mm 2 , 170 mg / 1540.25 mm 2 , 175 mg / 1540.25 mm 2 , 180 mg / 1540.25 mm 2 or a range formed by any two of the above values. Alternatively, the single-side coating weight of the negative electrode film layer is 125 mg / 1540.25 mm 2 to 160 mg / 1540.25 mm 2 .

[0174] When the single-side coating weight of the negative electrode film layer is within the above range, the heat generation per unit area of the negative electrode tab will not be too large, and the cycle performance of the battery cell can be improved.

[0175] In the embodiments of the present application, the single-side coating weight of the negative electrode film layer is a meaning known in the art, and can be detected by using devices and methods known in the art. The negative electrode tab is taken out from a battery cell at 0% state of charge (SOC), the tap density of the negative electrode film layer is measured, for example, a single-side coated negative electrode tab (if it is a double-side coated tab, the negative electrode film layer on one side can be wiped off first) is punched into a small disc with an area of S1, weighed, recorded as M1, and its thickness H1 is measured. Then the negative electrode film layer of the above weighed negative electrode tab is wiped off, the weight of the negative electrode current collector is weighed, recorded as M0, and its thickness H0 is measured. The single-side coating weight of the negative electrode film layer = (the weight of the negative electrode tab M1 - the weight of the negative electrode current collector M0) / S1, the thickness of the negative electrode film layer = the thickness of the negative electrode tab H1 - the thickness of the negative electrode current collector H0, and the tap density of the negative electrode film layer = the single-side coating weight of the negative electrode film layer / the thickness of the negative electrode film layer.

[0176] In the embodiments of the present application, the negative active material comprises a carbon-based material, the carbon-based material comprises graphite particles, the graphite particles have high cycle stability, and the cycle performance of the battery monomer can be improved. The positive active material of the present application is mainly a lithium-containing phosphate system with an olivine structure, and the negative active material is mainly a carbon-based material system. The combination of the two has excellent cycle performance of the battery monomer.

[0177] In some embodiments, the graphitization degree of the graphite particles is 90% to 94%. For example, the graphitization degree of the graphite particles is 90%, 91%, 92.0%, 92.5%, 93%, 93.5%, 94%, or a range formed by any two of the above values.

[0178] When the graphitization degree of the graphite particles is in the above range, the conductivity of the graphite particles is excellent, which can reduce the heat generation of the negative electrode sheet, reduce the heat generation of the battery monomer, and improve the rapid charging performance of the battery monomer.

[0179] In some embodiments, the volume average particle size Dv50 of the graphite particles is 7 μm to 15 μm, for example, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 9.8 μm, 10 μm, 10.2 μm, 10.5 μm, 10.8 μm, 11 μm, 11.2 μm, 11.5 μm, 11.8 μm, 12 μm, 12.2 μm, 12.5 μm, 12.8 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, or a range formed by any two of the above values.

[0180] The volume average particle size of the graphite particles is relatively small, so that the solid phase migration path of lithium ions is short, which can improve the rapid charging capacity of the battery monomer. However, under the condition of rapid charging, the active surface of the small particle size graphite particles is large, and the side reaction with the carboxylic acid ester solvent in the electrolyte is more violent. The electrolyte further adds an additive, the additive can form a film on the negative electrode side, which has excellent protective effect on the negative active material, reduces the risk of side reaction on the negative electrode side, and improves the cycle performance of the battery monomer.

[0181] In the embodiments of the present application, the volume average particle size Dv50 of the material refers to the particle size corresponding to 50% in the volume distribution, which can be detected by using devices and methods known in the art. For example, the negative active material is used as a sample, the Dv50 of the particles is tested by a Mastersizer 2000E laser particle size analyzer according to the test standard GB / T 19077-2016, and the like.

[0182] In some embodiments, the graphite particles include graphite bulk particles and a negative electrode coating layer. The graphite bulk particles include secondary particles, which in turn include multiple primary particles. The negative electrode coating layer coats the surface of the graphite bulk particles and comprises carbon elements. The carbon in the negative electrode coating layer is mainly amorphous carbon, which refers to transitional carbon materials with a very low degree of graphitization and crystallization, exhibiting an approximately amorphous morphology (or lacking a fixed shape and periodic structural regularity). In this application, amorphous carbon refers to the product after carbonization treatment of an organic carbon source.

[0183] The graphite bulk particles include secondary particles. There are multiple migration paths for lithium ions in the graphite bulk particles, and the migration paths in the primary particles are shorter, which can improve the migration rate of lithium ions. The negative electrode coating layer has more end faces and defects, which increases the number of sites where lithium ions can be inserted or extracted. This results in better conductivity of the negative electrode coating layer, which can reduce the internal resistance of the negative electrode sheet, reduce the heat generation of the battery cell, and improve the fast charging performance and cycle performance of the battery cell.

[0184] For example, the graphite bulk particles include at least one of artificial graphite and natural graphite, optionally artificial graphite.

[0185] Optionally, the thickness of the negative electrode coating layer is from 100 nm to 500 nm. For example, the thickness of the negative electrode coating layer is 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm or any two of the above values.

[0186] When the thickness of the negative electrode coating is within the above range, it can further improve the conductivity of graphite particles, reduce the internal resistance of the negative electrode sheet, reduce the heat generation of the battery cell, and improve the cycle performance of the battery cell.

[0187] In the embodiments of this application, the graphite particles can be prepared using methods known in the art. Taking artificial graphite as an example, the preparation method includes: providing artificial graphite and an organic carbon source, mixing the two, and then carbonizing them to form a negative electrode coating layer on at least a portion of the surface of the artificial graphite particles.

[0188] Optionally, the organic carbon source includes one or more of coal tar pitch, petroleum asphalt, phenolic resin, and coconut shell. Further optionally, the organic carbon source includes petroleum asphalt. Optionally, the softening point of coal tar pitch or petroleum asphalt is below 250°C.

[0189] Optionally, the carbonization temperature is between 700°C and 1800°C. Optionally, the carbonization temperature is between 1000°C and 1300°C. Within a suitable range, the carbonization temperature allows the organic carbon source to be carbonized, forming a negative electrode coating layer containing amorphous carbon on at least a portion of the surface of the artificial graphite.

[0190] Optionally, the carbonization treatment time is 1 hour to 6 hours.

[0191] In some embodiments, the carbon-based material may further include natural graphite. Specifically, the carbon-based material may include graphite particles, or it may include both graphite particles and natural graphite. Optionally, the carbon-based material is graphite particles.

[0192] In some embodiments, the negative electrode active material may include silicon-based materials in addition to graphite particles. The introduction of silicon-based materials can increase the capacity of the negative electrode active material and improve the energy density of the battery cell.

[0193] Optionally, based on the mass of the negative electrode film, the mass content of silicon element in the silicon-based material is from 0.5% to 10.0%. Exemplarily, the mass content of silicon element in the silicon-based material is 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.8%, 8%, 8.2%, 8.5%, 8.8%, 9%, 9.2%, 9.5%, 9.8%, 10%, or a range of any two of the above values.

[0194] When the mass content of silicon in silicon-based materials is within the above range, it can increase the capacity of the negative electrode active material, thereby improving the energy density of the battery cell.

[0195] Optionally, the silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy.

[0196] In some embodiments, the negative electrode active material may include, in addition to the aforementioned carbon-based materials and optionally silicon-based materials, at least one of tin-based materials and lithium titanate. Tin-based materials may include at least one of elemental tin, tin oxides, and tin alloys.

[0197] The qualitative and quantitative analysis of each substance or element in this application can be performed using suitable equipment and methods known to those skilled in the art. Relevant testing methods can be referenced from domestic and international testing standards and enterprise standards. Furthermore, those skilled in the art can adaptively modify certain testing steps / instrument parameters from the perspective of testing accuracy to obtain more accurate results. One testing method can be used for qualitative or quantitative analysis, or several testing methods can be used in combination for qualitative or quantitative determination.

[0198] For example, this application can combine JIS / K0131-1996 General Rules for X-ray Diffraction Analysis to perform X-ray powder diffraction tests and qualitative analysis on negative electrode sheets or negative electrode active materials.

[0199] Artificial graphite and natural graphite can be distinguished by SEM cross-sectional images taken by scanning electron microscope (SEM). Natural graphite has gaps between the sheet-like structures in its SEM cross-section, while artificial graphite has a dense structure with no obvious gaps. Alternatively, they can be distinguished by XRD patterns obtained by X-ray diffraction. Natural graphite has obvious 2H and 3R phases in its XRD pattern, while artificial graphite only has the 2H phase in its XRD pattern.

[0200] In the embodiments of this application, the negative electrode film layer includes at least one film layer, which can be a single film layer or at least two film layers. The negative electrode film layer can include two film layers, three film layers, four film layers, or even more film layers. Optionally, the negative electrode film layer includes at least two film layers.

[0201] When the negative electrode film is a single layer, the negative electrode active material in the negative electrode film includes carbon-based materials, and optionally also includes silicon-based materials.

[0202] When the negative electrode film layer employs at least two film layers, the negative electrode active material in the negative electrode film layer includes a carbon-based material, and optionally also includes a silicon-based material. The silicon-based material can be located in one of the at least two film layers, or in at least two of the at least two film layers. The negative electrode film layer can include two film layers, three film layers, four film layers, or even more film layers.

[0203] In some embodiments, the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer. The first negative electrode film layer is disposed on the surface of the negative electrode current collector. The carbon-based material in the first negative electrode film layer includes graphite particles. The second negative electrode film layer is connected to the side of the first negative electrode film layer away from the negative electrode current collector. The carbon-based material in the second negative electrode film layer also includes graphite particles. The graphite particles in the first negative electrode film layer and the graphite particles in the second negative electrode film layer may be the same or different.

[0204] The interface between the first negative electrode film and the second negative electrode film can be regular or irregular, and can optionally be irregular.

[0205] Optionally, the carbon-based material in the first negative electrode film layer may also include natural graphite.

[0206] The negative electrode film consists of at least two layers, and layered coating is beneficial for improving the fast charging performance of the battery cell. In particular, when there are differences between the first and second negative electrode films, it can create porosity differences in the negative electrode films, reduce the tortuosity of lithium-ion transport, and improve the fast charging performance of the battery cell.

[0207] Optionally, both the first negative electrode film and the second negative electrode film include graphite particles, wherein the average longest diameter of the graphite particles in the first negative electrode film is greater than or equal to the average longest diameter of the graphite particles in the second negative electrode film. Further optionally, the average longest diameter of the graphite particles in the first negative electrode film is greater than the average longest diameter of the graphite particles in the second negative electrode film.

[0208] The difference in particle size between the first and second negative electrode layers can improve the fast charging performance of the battery cell. Specifically, during fast charging, the overpotential of the second negative electrode layer is usually higher, and the bottleneck of fast charging is mainly in the second negative electrode layer. However, in the embodiments of this application, the particle size of the second negative electrode layer is relatively small, which can shorten the solid-phase transport path of lithium ions, improve fast charging performance, and improve the problem of lithium deposition on the surface of the negative electrode sheet.

[0209] Optionally, the average longest diameter of the graphite particles in the first negative electrode film layer is between 7 μm and 18 μm. For example, the average longest diameter of the graphite particles in the first negative electrode film layer is 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 14.6 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, or a range consisting of any two of the above values.

[0210] When the average longest diameter of the graphite particles in the first negative electrode film is within the above range, it can shorten the solid-phase transport path of lithium ions and improve fast charging performance. On the other hand, the material is less prone to agglomeration during the preparation process, which can improve the stability of the material.

[0211] Optionally, the average longest diameter of the graphite particles in the second negative electrode film layer is 6 μm to 10 μm. For example, the average longest diameter of the graphite particles in the second negative electrode film layer is 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8.0 μm, 8.2 μm, 8.5 μm, 8.8 μm, 9 μm, 9.2 μm, 9.5 μm, 9.8 μm, 10 μm, or a range consisting of any two of the above values.

[0212] When the average longest diameter of the graphite particles in the second negative electrode film is within the above-mentioned range, it can shorten the solid-phase transport path of lithium ions and improve fast charging performance. On the other hand, the material is less prone to agglomeration during the preparation process, which can improve the stability of the material. Furthermore, the combination of the negative electrode active material in the second negative electrode film within the above-mentioned particle size range and the negative electrode active material in the first negative electrode film is conducive to building a gradient porosity difference between the second negative electrode film and the first negative electrode film, reducing the tortuosity of lithium ion transport, and improving the fast charging performance of the battery cell.

[0213] Optionally, the thickness ratio of the second negative electrode film to the total negative electrode film is 0.3 to 0.7. For example, the thickness ratio of the second negative electrode film to the total negative electrode film is 0.3, 0.4, 0.5, 0.6, 0.7, or any combination of two of the above values. By adjusting the thickness ratio of the first negative electrode film, the gradient porosity difference between the upper and lower layers can be further increased, reducing the tortuosity of lithium-ion transport and improving the fast-charging capability of the battery cell.

[0214] In this embodiment, the negative electrode sheet is cut along its thickness direction to expose the cross-section of the negative electrode film layer. This can also be understood as a cross-section of the negative electrode film layer along its own thickness direction. The longest diameter of the graphite particles is determined by performing scanning electron microscopy (SEM) testing on the cross-section of the negative electrode film layer. For example, the "longest diameter" of a particle refers to the longest straight line that passes through the center point of the particle and extends to the outer periphery of the particle.

[0215] In a cross-section of the negative electrode film along its own thickness direction, the longest diameter of all graphite particles in the cross-section is counted, and the average value is calculated as the average longest diameter.

[0216] In a cross-section along the thickness direction of the negative electrode film, measure the dimensions of the second negative electrode film and the negative electrode film, and calculate the size ratio of the second negative electrode film.

[0217] In some embodiments, the negative electrode film layer further includes a negative electrode binder, which includes at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass content of the negative electrode binder is ≤5% based on the total weight of the negative electrode film layer.

[0218] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose particular limitations on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the negative electrode conductive agent is ≤5% based on the total weight of the negative electrode film layer.

[0219] In some embodiments, the negative electrode film layer may optionally include other additives. As examples, other additives may include thickeners, dispersants, etc., such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass content of other additives is ≤2% based on the total weight of the negative electrode film layer.

[0220] In some embodiments, the negative current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one foil made of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. A composite current collector may include a polymer base material and a metal material layer formed on at least one surface of the polymer base material. As an example, the metal material layer may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer base material may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0221] The negative electrode film is typically formed by coating a negative electrode slurry onto the negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0222] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the present application further includes a negative electrode conductive layer sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0223] In some embodiments, the negative electrode sheet further includes a negative electrode conductive layer, which is located between the negative electrode film layer and the negative electrode current collector. The negative electrode conductive layer can further improve the conductivity of the negative electrode sheet, reduce the heat generation of the negative electrode sheet, thereby reducing the heat generation of the battery cell and improving the fast charging performance and cycle performance of the battery cell.

[0224] [Positive electrode plate]

[0225] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0226] In some embodiments, the compaction density of the positive electrode film layer at 0% state of charge (SOC) of the battery cell is 2.3 g / cm³. 3 Up to 2.6 g / cm 3 For example, at 0% state of charge (SOC), the compaction density of the positive electrode film in a single battery cell is 2.3 g / cm³. 3 2.35g / cm 32.4g / cm 3 2.45g / cm 3 2.50g / cm 3 2.52g / cm 3 2.55g / cm 3 2.56 g / cm 3 2.57g / cm 3 2.58g / cm 3 2.60g / cm 3 Or a range consisting of any two of the above values. Optionally, at 0% state of charge (SOC), the compaction density of the positive electrode film is 2.4 g / cm³. 3 Up to 2.55 g / cm 3 .

[0227] When the compaction density of the positive electrode film is within the above range, it is beneficial to improve the energy density of the battery cell. Furthermore, since the positive electrode active material in the positive electrode film is packed more tightly, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode, thereby reducing heat generation under fast charging and improving the cycle performance and fast charging performance of the battery cell.

[0228] In some embodiments, the single-sided coating weight of the positive electrode film is 250 mg / 1540.25 mm. 2 Up to 330mg / 1540.25mm 2 For example, 250mg / 1540.25mm 2 260mg / 1540.25mm 2 270mg / 1540.25mm 2 280mg / 1540.25mm 2 290mg / 1540.25mm 2 300mg / 1540.25mm 2 310mg / 1540.25mm 2 320mg / 1540.25mm 2 330mg / 1540.25mm 2 Or a range consisting of any two of the above values. Optionally, the single-sided coating weight of the positive electrode film is 275 mg / 1540.25 mm. 2 Up to 320mg / 1540.25mm 2 .

[0229] When the single-sided coating weight of the positive electrode film is within the above range, the heat generation per unit area of ​​the positive electrode sheet will not be too large, thus improving the cycle performance and fast charging performance of the battery cell.

[0230] In this embodiment, the compaction density of the positive electrode film layer of a single battery cell at 0% State of Charge (SOC) can be detected by the following method: The positive electrode sheet of the single battery cell at 0% SOC is disassembled, and the compaction density of the positive electrode film layer is measured. For example, a single-sided coated positive electrode sheet (if it is a double-sided coated sheet, the positive electrode film layer on one side can be wiped off first) is taken, cut into small circular pieces with an area of ​​S1, weighed, and recorded as M1, and its thickness H1 is measured. Then, the positive electrode film layer of the weighed positive electrode sheet is wiped off, the weight of the positive current collector is weighed and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the positive electrode film layer = (weight of the positive electrode sheet M1 - weight of the positive current collector M0) / S1, the thickness of the positive electrode film layer = thickness of the positive electrode sheet H1 - thickness of the positive current collector H0, and the compaction density of the positive electrode film layer = single-sided coating weight of the positive electrode film layer / thickness of the positive electrode film layer.

[0231] In some embodiments, the lithium phosphate includes at least one of primary particles and secondary particles, wherein the secondary particles include a plurality of primary particles, in other words, the secondary particles are formed by the agglomeration of a plurality of primary particles, and the secondary particles are spherical and / or quasi-spherical.

[0232] The migration path of lithium ions in primary particles is relatively short, which can improve the migration rate of lithium ions; moreover, the secondary particles are spherical and / or quasi-spherical, resulting in more migration paths, which can further improve the migration rate of lithium ions and improve the fast charging performance of battery cells.

[0233] In some embodiments, the average longest diameter of the primary particles is between 300 nm and 800 nm, such as 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, or any combination of two of the above values. When the average longest diameter of the primary particles is within the above range, the solid-phase transport distance of lithium ions is shorter, which can further improve the migration rate of lithium ions and improve the fast charging performance of the battery cell.

[0234] In some embodiments, the average particle size of the secondary particles is from 5 μm to 15 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or any combination of two of the above values. When the average particle size of the secondary particles is within the above range, the solid-phase transport distance of lithium ions is shorter, which can further improve the migration rate of lithium ions and improve the fast charging performance of the battery cell.

[0235] In this embodiment, the positive electrode sheet is cut along its thickness direction to expose the cross-section of the positive electrode film layer. This can also be understood as a cross-section of the positive electrode film layer along its own thickness direction. By performing scanning electron microscopy (SEM) testing on the cross-section of the positive electrode film layer, the average longest diameter of the primary particles containing lithium phosphate and the average particle size of the secondary particles are determined. For example, the "longest diameter" of a particle refers to the longest straight line that passes through the center point of the particle and extends to the outer periphery of the particle.

[0236] In a cross-section of the positive electrode film along its own thickness direction, the longest diameter of each primary particle containing lithium phosphate is counted, and the average of the longest diameters of each primary particle containing lithium phosphate is calculated; then the average of the longest diameters of multiple, for example, 50 primary particles containing lithium phosphate is counted as the average longest diameter.

[0237] In a cross-section along the thickness direction of the positive electrode film, the particle size of all secondary particles containing lithium phosphate in the cross-section is statistically analyzed, and the average particle size of the secondary particles containing lithium phosphate is calculated as the average particle size of the secondary particles.

[0238] In this embodiment of the application, the lithium phosphate with olivine structure can be phosphate particles or a material obtained by modifying them. For example, the lithium phosphate with olivine structure includes phosphate particles and positive electrode additives. The positive electrode additives are located in the phosphate particles, either inside the phosphate particles or on the surface of the phosphate particles. The positive electrode additives include at least one element selected from aluminum (Al), vanadium (V), titanium (Ti), and niobium (Nb).

[0239] The aforementioned cathode additives can improve the crystal structure stability of the cathode active material, enhance the withstand voltage of lithium phosphate, improve the compaction density of the cathode film, and increase the energy density and cycle performance of the battery cell.

[0240] In some embodiments, the mass content of aluminum in the lithium phosphate is between 200 ppm and 2500 ppm, for example, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, 2100 ppm, 2200 ppm, 2300 ppm, 2400 ppm, 2500 ppm, or any combination of two of the above values. When the mass content of aluminum is within the above range, it can improve the withstand voltage of the lithium phosphate, which is beneficial for increasing the compaction density of the positive electrode film, and improving the energy density and cycle performance of the battery cell.

[0241] In some embodiments, the vanadium content in the lithium phosphate is between 300 ppm and 2000 ppm by mass, for example, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, or any combination of two of the above values. A vanadium content within the above range is beneficial for increasing the compaction density of the positive electrode film, thereby improving the energy density and cycle performance of the battery cell.

[0242] In some embodiments, the mass content of titanium in the lithium phosphate is between 1500 ppm and 3500 ppm, for example, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, 2100 ppm, 2200 ppm, 2300 ppm, 2400 ppm, 2500 ppm, 2600 ppm, 2700 ppm, 2800 ppm, 2900 ppm, 3000 ppm, 3100 ppm, 3200 ppm, 3300 ppm, 3400 ppm, 3500 ppm, or any combination of two of the above values. When the mass content of titanium is within the above range, the crystal structure of the positive electrode active material can be further improved, thereby enhancing cycle performance.

[0243] In some embodiments, the niobium content in the lithium phosphate is between 300 ppm and 2000 ppm by mass, for example, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, or any combination of two of the above values. When the niobium content is within the above range, the crystal structure of the positive electrode active material can be further improved, thereby enhancing cycle performance.

[0244] Examples of phosphate particles include, but are not limited to, one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, and lithium cobalt phosphate. The above materials exhibit excellent cycle stability and can improve the cycle performance of individual battery cells.

[0245] In some embodiments, lithium phosphates include those with the general formula Li x1 A y1 Me a1 Mb1 P 1-c1 X c1 Y z1 The compound, wherein 0.5≤x1≤1.3, 0≤y1≤1.3, 0.5≤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, A includes at least one of Na, K and Mg; Me includes at least one of Mn, Fe, Co and Ni; M includes at least one 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 at least one of Cl, C, N and P; Y includes at least one of O and F.

[0246] Lithium phosphates exhibit superior cycle stability, which is beneficial for improving the cycle performance of individual battery cells.

[0247] For example, phosphate particles include one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. During the charging and discharging process, active ions such as Li are de-intercalated and consumed in a single battery cell, resulting in different molar contents of Li in different discharged states. In the examples of positive electrode active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4, the molar contents of Li represent the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar contents of Li may change after charge-discharge cycles. In the embodiments of this application, the molar contents of oxygen (O) in the examples of positive electrode active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4 are only theoretical values. Lattice oxygen release can cause changes in the molar contents of oxygen (O). In reality, the molar contents of oxygen (O) may fluctuate, and all of the above situations are within the scope of protection of this application.

[0248] In this embodiment, the elemental content in the positive electrode active material is defined in a way known in the art and can be detected using equipment and methods known in the art. For example, referring to EPA 6010D-2014, it can be tested by inductively coupled plasma atomic emission spectrometry (ICP-OES, instrument model: Thermo ICAP7400). After discharging the battery cell to 0% state of charge (SOC), the positive electrode sheet is disassembled, cleaned and dried with DMC, and then calcined at high temperature to remove impurities. 0.4g of the positive electrode active material is weighed and 10ml (50% concentration) of aqua regia is added. Then it is placed on a plate at 180°C for 30min. After digestion on the plate, the volume is adjusted to 100mL, and quantitative testing is performed using the standard curve method.

[0249] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose particular limitations on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the positive electrode conductive agent is ≤5% based on the mass of the positive electrode film layer.

[0250] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose particular limitations on the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. In some embodiments, the mass content of the positive electrode binder is ≤5% based on the mass of the positive electrode film layer.

[0251] In some embodiments, the positive current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one foil made of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. A composite current collector may include a polymer base material and a metal material layer formed on at least one surface of the polymer base material. As an example, the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer base material may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0252] The positive electrode film is typically formed by coating a positive electrode slurry onto the positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0253] The positive electrode sheet does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of the present application further includes a positive electrode conductive layer sandwiched between the positive electrode current collector and the positive electrode film layer and disposed on the surface of the positive electrode current collector. In other embodiments, the positive electrode sheet of the present application further includes a protective layer covering the surface of the positive electrode film layer.

[0254] [Isolation membrane]

[0255] In this embodiment, the separator is disposed between the positive electrode and the negative electrode to isolate the positive electrode and the negative electrode.

[0256] In some embodiments, the porosity of the separator is 20% to 70%, optionally 35% to 60%. Exemplarily, the porosity of the separator is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any range of two of the above values.

[0257] When the porosity of the separator in the embodiments of this application is within the above-mentioned range, it can enhance the migration ability of lithium ions in the separator, further reduce the internal resistance of the battery cell, and thus reduce heat generation.

[0258] In this embodiment, porosity refers to the percentage of the volume of the pores in the separator to the total volume of the separator. Porosity can be tested according to the standard GB / T 36363-2018 "Polyolefin Separators for Battery Cells". It should be noted that the actual testing process may differ slightly from the standard due to differences in testing instruments, testing errors, and to minimize the impact on porosity testing, in order to obtain more accurate test values.

[0259] In some embodiments, the thickness of the separator is from 4 μm to 12 μm, optionally from 5 μm to 9 μm. Exemplarily, the thickness of the base film is 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, or any range of two of the above values.

[0260] When the thickness of the separator is within the above range, the migration path of lithium ions in the separator is shorter, which can further reduce the internal resistance of the battery cell and thus reduce heat generation.

[0261] In this embodiment, the separator can be a base film. Optionally, the separator further includes a functional layer disposed on at least one side of the base film. The functional layer may include inorganic particles to improve the heat resistance of the separator. Optionally, the functional layer is disposed on both sides of the base film.

[0262] In some embodiments, the base film includes at least one of glass fiber, nonwoven fabric, and polyolefin. The base film can be a single-layer film or a multi-layer composite film, without particular limitation. When the base film is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0263] Optionally, the polyolefin includes at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0264] In some embodiments, the functional layer may include an adhesive, optionally including at least one of a fluorinated adhesive or a polyacrylic adhesive, such as polyvinylidene fluoride.

[0265] In some embodiments, the functional layer may include inorganic particles, which may 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. These inorganic particles can improve the heat resistance of the functional layer.

[0266] In the embodiments of this application, the thickness of the separator is defined in the sense of a known concept in the art. It can be tested using known concepts and equipment in the art. For example, a newly prepared separator can be used as a sample, or a battery cell that has been completely discharged (discharged to the discharge cutoff voltage so that the battery's state of charge is about 0% SOC) can be disassembled in reverse, the separator can be obtained from the battery cell, and the separator can be dried and used as a sample. The separator can be cut with an ion beam cutter to form a cross section, and then the thickness of the separator and its various layers can be measured using a scanning electron microscope.

[0267] In some implementations, the positive electrode, separator, and negative electrode can be fabricated into an electrode assembly using a stacking process.

[0268] Figures 1 and 2 show schematic diagrams of the structure of a single battery cell.

[0269] In some embodiments, the battery cell 7 may include a housing 20.

[0270] The outer casing 20 can be of various shapes, such as a cylinder or a cuboid. The shape of the outer casing 20 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 is a cylindrical structure, the outer casing 20 can be a cylindrical structure. If the electrode assembly 10 is a cuboid structure, the outer casing 20 can be a cuboid structure. Optionally, the electrode assembly 10 can be a cuboid structure.

[0271] The outer casing 20 can be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc., and this application embodiment does not impose any special limitations on this. Optionally, the inner wall of the outer casing 20 may also include an insulating layer, which can separate the outer casing 20 from the electrode assembly 10. The material of the insulating layer can be selected from materials commonly used in the art, and is not particularly limited here.

[0272] The electrode assembly 10 housed within the housing 20 may be one or more.

[0273] In some embodiments, the housing 20 includes a housing 21 and an end cap 22, the housing 21 having an opening and the end cap 22 closing the opening, the housing 21 containing the electrode assembly 10 and the electrolyte.

[0274] In some embodiments, the casing 21 is made of steel, which has high mechanical strength, is not easily deformed, and can improve the reliability and cycle performance of the battery cells. Optionally, steel is the material with the highest mass percentage in the casing 21.

[0275] In some embodiments, the length of the battery cell 7 is between 200 mm and 400 mm, for example, 200 mm, 210 mm, 220 mm, 230 mm, 240 mm, 250 mm, 260 mm, 270 mm, 280 mm, 290 mm, 300 mm, 310 mm, 320 mm, 330 mm, 340 mm, 350 mm, 360 mm, 370 mm, 380 mm, 390 mm, 400 mm, or any combination of two of the above values. When the length of the battery cell 7 is within the above range, it is beneficial to increase the energy density of the battery cell 7; moreover, the electron transport path in the length direction is not too long, which is beneficial to improving the fast charging capability of the battery cell 7. Z1 shown in Figure 1 represents the length of the battery cell 7.

[0276] The electrolyte has relatively high conductivity, low viscosity, and excellent fluidity, which allows it to quickly wet the electrode in the length direction, resulting in a more uniform reaction degree in the electrode in the length direction. When active ions migrate to the negative electrode 12, problems such as lithium plating are less likely to occur, which is beneficial to improving the reliability and cycle performance of the battery cell 7.

[0277] In some embodiments, the width of the battery cell 7 is between 80 mm and 130 mm, for example, 80 mm, 90 mm, 100 mm, 110 mm, 120 mm, 130 mm, or any combination of two of the above values. A width within this range is advantageous for increasing the energy density of the battery cell 7; moreover, the electron transport path in the width direction is not excessively long, which is beneficial for improving the fast charging capability of the battery cell 7. Y1 shown in Figure 1 represents the width of the battery cell 7.

[0278] In some embodiments, the thickness of the battery cell 7 is between 25 mm and 60 mm, for example, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, or any combination of two of the above values. A thickness within this range facilitates the rapid release of internal heat from the battery cell 7, mitigating the risk of electrolyte decomposition due to heat accumulation and improving the cycle performance of the battery cell 7. X1 in Figure 1 represents the thickness of the battery cell 7.

[0279] The following explanation will take the electrode assembly 10, which has a stacked structure, as an example.

[0280] As shown in Figure 3, when the electrode assembly 10 has a stacked structure, there are multiple positive electrode plates 11 and multiple negative electrode plates 12, which are stacked along the thickness direction X of the battery cell 7. Optionally, the electrode assembly 10 also includes a separator 13, which is located between the positive electrode plates 11 and the negative electrode plates 12.

[0281] In some embodiments, as shown in FIG4, the positive electrode 11 includes at least one positive electrode tab 111, which is connected to the positive current collector 112 and extends out of the positive current collector 112 along the length direction Z of the battery cell 7. This arrangement helps to reduce the space occupied by the tab and improve the energy density of the battery cell.

[0282] For example, at least one positive electrode tab 111 may be provided on the same side of the positive current collector 112 along the length direction Z.

[0283] For example, as shown in Figure 5, there are multiple positive electrode tabs 111 in the same positive electrode sheet 11. These multiple positive electrode tabs 111 can be disposed on both sides of the positive current collector 112 along the length direction Z. The positive electrode tabs 111 disposed on both sides of the positive current collector 112 can shorten the electron transport path in the length direction Z, improve the electron transport rate, and improve the fast charging capability of the battery cell 7.

[0284] As shown in Figures 5 and 6, in some embodiments, the positive electrode 11 satisfies: n*W1 / W2 is 0.9 to 1.0;

[0285] n represents the number of all positive electrode tabs 111 located on the same side of the positive electrode current collector 112;

[0286] W1 represents the average dimension of the positive electrode tab 111 along the width direction Y;

[0287] W2 represents the dimension of the positive current collector 112 along the width direction Y.

[0288] For example, n*W1 / W2 is 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00 or a range of any two of the above values.

[0289] When n*W1 / W2 meets the above range, the overcurrent area of ​​the positive electrode tab 111 is relatively large, which is beneficial to improving the fast charging performance of the battery cell 7.

[0290] W1 represents the average dimension of the positive electrode tab 111 along the width direction Y.

[0291] When the positive electrode tab 111 has an irregular shape, for example, along the length direction Z, the dimension of the positive electrode tab 111 gradually increases along the width direction Y. In this case, the dimensions of the positive electrode tab 111 along the width direction Y at multiple locations can be measured, and the average dimension of the positive electrode tab 111 along the width direction Y can be calculated. Of course, the dimension of the positive electrode tab 111 along the width direction Y at all locations can be the same value. In this case, this value can be used as the average dimension of the positive electrode tab 111.

[0292] There can be one or more positive electrode tabs 111, for example, n is 1 to 4. When there are multiple positive electrode tabs 111 located on the same side of the positive electrode current collector 112, the average size of each positive electrode tab 111 can be measured separately, and the average size of each size can be summed and divided by the number of positive electrode tabs 111 to calculate the average size of the positive electrode tab 111.

[0293] The positive electrode tab 111 is connected to the positive current collector 112. The positive electrode tab 111 includes a first end 1111 connected to the positive current collector 112. When n*W1 / W2 meets the above range, it means that the cross-section of the first end 1111 along the thickness direction of the positive electrode tab 111 itself is relatively large, the contact surface between the positive electrode tab 111 and the positive current collector 112 is relatively large, and the current carrying capacity of the positive electrode tab 111 is strong, which can improve the fast charging performance and cycle performance of the battery cell 7.

[0294] Optionally, the positive electrode tab 111 and the positive current collector 112 are integrated into one structure, which makes the internal resistance of the positive electrode 11 lower and can further improve the cycle performance of the battery cell 7.

[0295] As shown in FIG7, in some other embodiments, at least one positive electrode tab 111 may also be connected to the positive electrode current collector 112 and extend out of the positive electrode current collector 112 along the width direction Y of the battery cell 7.

[0296] As shown in Figures 8 and 9, in some embodiments, the negative electrode plate 12 includes at least one negative electrode tab 121, which is connected to the negative current collector 122 and extends out of the negative current collector 122 along the length direction Z of the battery cell 7. Alternatively, at least one negative electrode tab 121 may also be connected to the negative current collector 122 and extend out of the negative current collector 122 along the width direction Y of the battery cell 7.

[0297] For example, as shown in FIG8, at least one negative electrode tab 121 may be disposed on the same side of the negative electrode current collector 122 along the length direction Z.

[0298] For example, as shown in Figure 9, there are multiple negative electrode tabs 121 in the same negative electrode sheet 12. These multiple negative electrode tabs 121 can be disposed on both sides of the negative electrode current collector 122 along the length direction Z. The negative electrode tabs 121 disposed on both sides of the negative electrode current collector 122 can shorten the electron transport path in the length direction Z, improve the electron transport rate, and improve the fast charging capability of the battery cell 7.

[0299] In some implementations, the negative electrode 12 satisfies: m*W3 / W4 is 0.9 to 1.0;

[0300] m represents the number of all negative electrode tabs 121 located on the same side of the negative electrode current collector 122;

[0301] W3 represents the average dimension of the negative electrode tab 121 along the width direction Y;

[0302] W4 represents the dimension of the negative electrode current collector 122 along the width direction Y.

[0303] For example, m*W3 / W4 is 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00 or a range of any two of the above values.

[0304] When m*W3 / W4 meets the above range, the overcurrent area of ​​the negative electrode tab 121 is relatively large, which is beneficial to improving the fast charging performance of the battery cell 7.

[0305] W3 represents the average dimension of the negative electrode tab 121 along the width direction Y. There can be one or more negative electrode tabs 121, for example, m is 1 to 4. When there are multiple negative electrode tabs 121, the average dimension can be calculated by measuring the dimensions of each negative electrode tab 121 with a micrometer.

[0306] The negative electrode tab 121 is connected to the negative electrode current collector 122. The negative electrode tab 121 includes a second end 1211 connected to the negative electrode current collector 122. When n*W3 / W4 meets the above range, it means that the cross-section of the second end 1211 along the thickness direction of the negative electrode tab 121 itself is relatively large, the contact surface between the negative electrode tab 121 and the negative electrode current collector 122 is relatively large, the current carrying capacity of the negative electrode tab 121 is strong, and it can improve the fast charging performance and cycle performance of the battery cell 7.

[0307] Optionally, the negative electrode tab 121 and the negative electrode current collector 122 are integrated into one structure, which makes the internal resistance of the negative electrode 12 lower and can further improve the fast charging performance and cycle performance of the battery cell 7.

[0308] As shown in Figure 10, in some embodiments, the battery cell 7 further includes a positive terminal 31, which is disposed on the housing 20 and may be disposed on the housing 21 or the end cap 22.

[0309] The positive terminal 31 is electrically connected to the positive electrode tab 111. Optionally, the positive terminal 31 and the positive electrode tab 111 are welded together. The positive terminal 31 and the positive electrode tab 111 can be connected through a positive electrode adapter 41, or they can be connected directly without a positive electrode adapter. This can reduce the resistance at the connection point and help reduce the overall internal resistance of the battery cell 7.

[0310] Optionally, the positive terminal 31 is disposed on at least one side of the electrode assembly 10 along the width direction Y of the battery cell 7, and the positive terminal 31 is connected to the positive electrode tab 111 via a positive adapter 41. The connection via the positive adapter 41 can improve the overcurrent capacity between the positive terminal 31 and the positive electrode tab 111, thereby improving the fast charging capability of the battery cell 7.

[0311] Optionally, the thickness of the positive electrode adapter 41 is from 1.25mm to 3.00mm, such as 1.25mm, 1.50mm, 1.75mm, 2.00mm, 2.25mm, 2.50mm, 2.75mm, 3.00mm, or any combination of two of the above values. The relatively thicker positive electrode adapter 41 provides superior current carrying capacity, further improving the fast charging capability of the battery cell 7.

[0312] For example, the material of the positive electrode adapter 41 may include aluminum, copper, aluminum alloy, copper alloy, etc.

[0313] As shown in Figures 10 and 11, optionally, the positive electrode adapter 41 includes a first positive electrode adapter portion 411 and a second positive electrode adapter portion 412. The first positive electrode adapter portion 411 is connected to the positive electrode tab 111, and the second positive electrode adapter portion 412 is connected to the first positive electrode adapter portion 411 and protrudes from the first positive electrode adapter portion 411 along the length direction Z. The second positive electrode adapter portion 412 is connected to the positive terminal 31. The first positive electrode adapter portion 411 and the second positive electrode adapter portion 412 can electrically connect the positive electrode tab 111 and the positive terminal 31, and can improve the overcurrent capacity of the positive electrode tab 111 and the positive terminal 31, thereby improving the fast charging capability of the battery cell 7.

[0314] Optionally, the ratio of the dimension of the first positive electrode adapter 411 along the width direction Y to the width of the battery cell 7 is 0.2 to 0.5, for example, 0.2, 0.3, 0.4, 0.5, or any two of the above values. When the ratio of the dimension of the first positive electrode adapter 411 along the width direction Y to the width of the battery cell 7 is within the above range, the path for electrons to travel from the positive electrode tab 111 through the positive electrode adapter 41 to the positive terminal 31 is relatively short, which can improve the fast charging capability of the battery cell 7. In Figure 11, Y2 represents the dimension of the first positive electrode adapter 411 along the width direction Y, and Y2 / Y1 represents the ratio of the dimension of the first positive electrode adapter 411 along the width direction Y to the width of the battery cell 7.

[0315] Optionally, the ratio of the dimension of the second positive electrode adapter 412 along the length direction Z to the length of the battery cell 7 is 0.05 to 0.2, for example, 0.05, 0.1, 0.15, 0.2, or any two of the above values. When the ratio of the dimension of the second positive electrode adapter 412 along the length direction Z to the length of the battery cell 7 is within the above range, the path for electrons to travel from the positive electrode tab 111 through the positive electrode adapter 41 to the positive terminal 31 is relatively short, which can improve the fast charging capability of the battery cell 7. In Figure 11, Z2 represents the dimension of the first positive electrode adapter 411 along the length direction Z, and Z2 / Z1 represents the ratio of the dimension of the second positive electrode adapter 412 along the length direction Z to the length of the battery cell 7.

[0316] In some embodiments, the battery cell 7 also includes a negative terminal 32, which is disposed on the housing 20, and may be disposed on the housing 21 or the end cap 22.

[0317] The negative terminal 32 is electrically connected to the negative electrode tab 121. Optionally, the negative terminal 32 and the negative electrode tab 121 are welded together. The negative terminal 32 and the negative electrode tab 121 can be connected by an adapter, or they can be directly welded together without an adapter. This can reduce the resistance at the connection point and help reduce the overall internal resistance of the battery cell 7.

[0318] Optionally, the negative terminal 32 is disposed on at least one side of the electrode assembly 10 along the width direction Y of the battery cell 7, and the negative terminal 32 is connected to the negative electrode tab 121 via the positive terminal adapter 41. The connection via the negative terminal adapter 42 can improve the overcurrent capacity between the negative terminal 32 and the negative electrode tab 121, thereby improving the fast charging capability of the battery cell 7.

[0319] Optionally, the thickness of the negative electrode adapter 42 is from 1.25mm to 3.00mm, such as 1.25mm, 1.50mm, 1.75mm, 2.00mm, 2.25mm, 2.50mm, 2.75mm, 3.00mm, or any combination of two of the above values. The relatively thicker negative electrode adapter 42 provides superior current carrying capacity, further improving the fast charging capability of the battery cell 7.

[0320] For example, the material of the negative electrode adapter 42 may include aluminum, copper, aluminum alloy, copper alloy, etc.

[0321] As shown in Figure 12, optionally, the negative electrode adapter 42 includes a first negative electrode adapter 421 and a second negative electrode adapter 422. The first negative electrode adapter 421 is connected to the negative electrode tab 121, and the second negative electrode adapter 422 is connected to the first negative electrode adapter 421 and protrudes from the first negative electrode adapter 421 along the length direction Z. The second negative electrode adapter 422 is connected to the negative terminal 32. The first negative electrode adapter 421 and the second negative electrode adapter 422 can electrically connect the negative electrode tab 121 and the negative terminal 32, and can improve the overcurrent capacity of both, thereby improving the fast charging capability of the battery cell 7.

[0322] Optionally, the ratio of the dimension of the first negative electrode adapter 421 along the width direction Y to the width of the battery cell 7 is 0.2 to 0.5, for example, 0.2, 0.3, 0.4, 0.5, or any two of the above values. When the ratio of the dimension of the first negative electrode adapter 421 along the width direction Y to the width of the battery cell 7 is within the above range, the path for electrons to travel from the negative electrode tab 121 through the negative electrode adapter 42 to the negative terminal 32 is relatively short, which can improve the fast charging capability of the battery cell 7. In Figure 12, Y3 represents the dimension of the first negative electrode adapter 421 along the width direction Y, and Y3 / Y1 represents the ratio of the dimension of the first negative electrode adapter 421 along the width direction Y to the width of the battery cell 7.

[0323] Optionally, the ratio of the dimension of the second negative electrode adapter 422 along the length direction Z to the length of the battery cell 7 is 0.05 to 0.2, for example, 0.05, 0.1, 0.15, 0.2, or any two of the above values. When the ratio of the dimension of the second negative electrode adapter 422 along the length direction Z to the length of the battery cell 7 is within the above range, the path for electrons to travel from the negative electrode tab 121 through the negative electrode adapter 42 to the negative terminal 32 is relatively short, which can improve the fast charging capability of the battery cell 7. In Figure 12, Z3 represents the dimension of the second negative electrode adapter 422 along the length direction Z, and Z3 / Z1 represents the ratio of the dimension of the second negative electrode adapter 422 along the length direction Z to the length of the battery cell 7.

[0324] As shown in Figure 13, the battery cell 7 of the present application embodiment can be assembled into a battery module 6. The number of battery cells 7 contained in the battery module 6 can be one or more, and the specific number can be adjusted according to the application and capacity of the battery module 6.

[0325] If there are multiple battery cells 7, they can be connected in series, parallel, or in a mixed configuration. A mixed configuration means that some battery cells 7 are connected in series while others are connected in parallel. Multiple battery cells 7 can be directly connected in series, parallel, or in a mixed configuration, and then the entire assembly of these battery cells 7 is housed within the housing of the battery module 6. Alternatively, multiple battery cells 7 can first be connected in series, parallel, or in a mixed configuration to form the battery module 6, and then the multiple battery modules 6 can be connected in series, parallel, or in a mixed configuration to form a whole, which is then housed within the housing. Optionally, the battery module 6 may also include a housing with a accommodating space, within which multiple battery cells 7 are housed.

[0326] Multiple battery cells 7 of the battery module 6 can be electrically connected through a busbar to achieve parallel, series, or mixed connection of the multiple battery cells 7 of the battery module 6. There can be one or more busbars, and each busbar is used to electrically connect at least two battery cells 7.

[0327] As shown in Figure 14, in some embodiments, the battery module 6 can also be assembled into a battery pack 2, and the number of battery modules 6 contained in the battery pack 2 can be adjusted according to the application and capacity of the battery pack. The battery device described herein can be a battery module 6, a battery pack 2, or a battery cell 7, with the battery cell 7 being the smallest unit constituting the battery device.

[0328] The battery pack 2 may include a housing 5 and a plurality of battery modules 6 disposed in the housing 5. The housing 5 includes a first housing portion 5a and a second housing portion 5b, and the housing 5 has a receiving space 5c. The first housing portion 5a is used to cover the second housing portion 5b and form a closed space for receiving the battery modules 6. The plurality of battery modules 6 can be arranged in the housing 5 in any manner.

[0329] The first housing portion 5a and the second housing portion 5b overlap each other, and together they define a receiving space 5c for accommodating a single battery cell. The second housing portion 5b can be a hollow structure with one open end, and the first housing portion 5a can be a plate-like structure. The first housing portion 5a covers the open side of the second housing portion 5b to form a housing 5 with the receiving space 5c. Alternatively, both the first housing portion 5a and the second housing portion 5b can be hollow structures with one open side, with the open side of the first housing portion 5a covering the open side of the second housing portion 5b to form a housing 5 with the receiving space 5c. Of course, the first housing portion 5a and the second housing portion 5b can be of various shapes, such as cylinders, cuboids, etc.

[0330] To improve the sealing performance after the first housing part 5a and the second housing part 5b are connected, a sealing element, such as sealant or sealing ring, can also be provided between the first housing part 5a and the second housing part 5b.

[0331] Assuming that the first box section 5a covers the top of the second box section 5b, the first box section 5a can also be called the upper box cover, and the second box section 5b can also be called the lower box.

[0332] Electrical appliances

[0333] The second aspect of this application provides an electrical device, which includes a battery device as described in this application, such as a battery cell, battery module, or battery pack. The battery cell, battery module, or battery pack can be the power source of the electrical device or the energy storage unit of the electrical device. The electrical device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, and power tool, etc. Vehicles can be gasoline-powered vehicles, natural gas-powered vehicles, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.; spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc.; electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc.; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose any special limitations on the above-described electrical device.

[0334] Electrical devices can be equipped with individual battery cells, battery modules, or battery packs depending on their usage requirements.

[0335] Figure 15 is a schematic diagram of an example electrical device 1. This electrical device 1 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device 1, a battery pack or battery module can be used.

[0336] The electrical device 1 is equipped with a battery pack 2, which can be located at the bottom, head, or tail of the electrical device 1. The battery pack 2 can be used to supply power to the electrical device 1. For example, the battery pack 2 can serve as the operating power source for the electrical device 1, and can also serve as the driving power source for the electrical device 1, replacing or partially replacing fuel oil or natural gas to provide driving power for the electrical device 1.

[0337] Electrical device 1 may also include controller 3 and motor 4. Controller 3 is used to control battery pack 2 to supply power to motor 4, for example, to meet the power needs of electrical device 1 during startup, navigation and driving.

[0338] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0339] Example

[0340] The following embodiments describe the contents of the embodiments disclosed in this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of the embodiments of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0341] Example 1

[0342] 1. Preparation of positive electrode sheet

[0343] The positive electrode includes a positive current collector and a positive electrode film layer. The positive electrode film layer is disposed on both sides of the positive current collector, which is an aluminum foil.

[0344] The positive electrode film layer comprises a film layer formed by uniformly coating the surface of the positive electrode current collector with a positive electrode slurry (solvent being N-methylpyrrolidone NMP), followed by drying and cold pressing. The positive electrode film layer comprises positive electrode active material, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black in a weight ratio of 97:2:1.

[0345] The positive electrode active material includes lithium iron phosphate particles and positive electrode additives located in the lithium iron phosphate particles. The positive electrode additives include Al, V, Ti, and Nb, with a mass content of 1500 ppm and a mass ratio of 1:1:1:1 for the four elements.

[0346] The lithium phosphate includes primary particles and secondary particles formed by the agglomeration of primary particles. The secondary particles are spherical and / or quasi-spherical. In the cross section along the thickness direction of the positive electrode film, the average longest diameter of the primary particles is 600 nm, and the average particle size of the secondary particles is 10 μm.

[0347] The single-sided coating weight of the positive electrode film is 290 mg / 1540.25 mm. 2 .

[0348] 2. Preparation of negative electrode sheet

[0349] The negative electrode includes a negative current collector and a negative electrode film layer. The negative electrode film layer is disposed on both sides of the negative current collector, which is a copper foil.

[0350] The negative electrode film layer comprises a film layer formed by uniformly coating the surface of the negative electrode current collector with negative electrode slurry (solvent is deionized water), and then drying and cold pressing.

[0351] The first negative electrode film layer is disposed on the surface of the negative electrode current collector. It 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 negative electrode active material includes graphite particles and silicon oxide. The graphite particles include artificial graphite and a negative electrode coating layer. The negative electrode coating layer is coated on the surface of the artificial graphite. The negative electrode coating layer includes carbon elements. The graphitization degree of the graphite particles is 92.5%, and the volume average particle size of the graphite particles is 8.5 μm.

[0352] The second negative electrode film layer is disposed on the surface of the negative electrode current collector. It includes a negative electrode active material in a mass ratio of 96.5:0.5:2:1, a conductive agent acetylene black, a negative electrode binder styrene-butadiene rubber, and a thickener sodium carboxymethyl cellulose. The negative electrode active material includes graphite particles and silicon oxide. The graphite particles include artificial graphite and a negative electrode coating layer. The negative electrode coating layer is coated on the surface of the artificial graphite. The carbon content of the negative electrode coating layer is 2% by mass. The graphitization degree of the graphite particles is 92.5%, and the volume average particle size of the graphite particles is 7 μm.

[0353] The mass content of silicon in the negative electrode film is 0.7%.

[0354] In a cross-section along the thickness direction of the negative electrode film, the average longest diameter of the graphite particles in the first negative electrode film is 11.5 μm, and the thickness of the negative electrode coating layer of the graphite particles in the first negative electrode film is 200 nm. The average longest diameter of the graphite particles in the second negative electrode film is 10 μm, and the thickness of the negative electrode coating layer of the graphite particles in the second negative electrode film is 200 nm.

[0355] The single-sided coating weight of the negative electrode film is 130 mg / 1540.25 mm. 2 .

[0356] 3. Separating membrane

[0357] The separator is a 7μm polyethylene membrane with a porosity of 35%.

[0358] 4. Preparation of electrolyte

[0359] The electrolyte comprises an organic solvent, a lithium salt, and additives. The components of the organic solvent are mixed, and then the lithium salt and additives are added to prepare the electrolyte.

[0360] The organic solvents include 16.3% by mass of carboxylic acid ester solvents, 35.7% by mass of linear carbonate solvents, and 26.3% by mass of cyclic carbonate solvents.

[0361] The additive has a mass content of 6.4%, which includes vinylene carbonate (VC), 1,3-propanesulfonic acid lactone, and fluoroethylene carbonate (FEC) in a mass ratio of 4:0.4:2.

[0362] The electrolyte also includes 0.2% lithium difluorophosphate and 0.1% lithium fluorosulfonate.

[0363] The lithium salt includes lithium hexafluorophosphate (LiPF6) with a mass content of 15%.

[0364] The conductivity of the electrolyte is 12.8 mS / cm.

[0365] 5. Preparation of battery cells

[0366] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes, to obtain a stacked electrode assembly. The electrode assembly is placed in a housing, with the positive and negative terminals set on the housing. After baking, electrolyte is injected. After vacuum sealing, settling, formation, and shaping, a battery cell is obtained.

[0367] The compaction density of the positive electrode film layer of the battery cell at 0% SOC is 2.52 g / cm³. 3 The compaction density of the negative electrode film at 0% SOC is 1.35 g / cm³. 3 .

[0368] The outer shell is a rectangular aluminum shell, and the thickness of the shell corresponding to the largest surface area of ​​the rectangular structure is 0.5mm.

[0369] Examples 2-1 to 2-5

[0370] Battery cells were prepared using a method similar to that of Example 1. The difference from Example 1 is that the mass content of each solvent was adjusted in Examples 2-1 to 2-4, and the material of the solvent was adjusted in Example 2-5.

[0371] Comparative Example 1-1 and Comparative Example 1-2

[0372] Battery cells were prepared using a method similar to that of Example 1, except that the mass content of each solvent was adjusted.

[0373] Performance testing

[0374] 1. Fast charging test of individual battery cells

[0375] At 25°C, the battery cell

[0376] Charge from 0% SOC to 10% SOC at a constant current of 0.33C;

[0377] Charge from 10% SOC to 15% SOC at a constant current of 5.0C;

[0378] Charge from 15% SOC to 20% SOC at a constant current of 4.6C;

[0379] Charge from 20% SOC to 35% SOC at a constant current of 4.2C;

[0380] Charge from 35% SOC to 45% SOC at a constant current of 3.8C;

[0381] Charge from 45% SOC to 50% SOC at a constant current of 3.6C;

[0382] Charge from 50% SOC to 60% SOC at a constant current of 3.4C;

[0383] Charge from 60% SOC to 70% SOC at a constant current of 3.0C;

[0384] Charge from 70% SOC to 75% SOC at a constant current of 2.8C;

[0385] Charge from 75% SOC to 80% SOC at a constant current of 2.4C;

[0386] Record the fast charging time of a single battery cell from 10% SOC to 80% SOC.

[0387] 2. Number of cycles required for a single battery cell to reach 80% SOH

[0388] At 25°C, the battery cells are charged at a constant current of 1C to the charging cutoff voltage of 3.65V, then charged at a constant current of 0.05C to the charging cutoff voltage of 3.65V, and allowed to rest for 30 minutes; then discharged at a constant current of 1C to 2.5V, and allowed to rest for 30 minutes. This constitutes one charge-discharge cycle. The above charge-discharge cycle steps are repeated until the cycle capacity retention rate (i.e., Cn / C0×100%) is 80%, and the number of cycles is recorded. The more cycles, the better the cycle performance of the battery cell.

[0389] In the above-mentioned charge and discharge test of battery cells, the battery cells can be assembled in the battery device, and the required charge and discharge strategy can be controlled by the battery management system for testing.

[0390] The test results are shown in Table 1.

[0391] Table 1

[0392] In Table 1,

[0393] EA stands for ethyl acetate;

[0394] EP stands for ethyl propionate;

[0395] DMC stands for dimethyl carbonate;

[0396] DEC represents diethyl carbonate; in Examples 1, 2-1 to 2-4, Comparative Examples 1-1 and 1-2, the mass ratio of DMC to DEC was 1:1.

[0397] EMC stands for ethyl methyl carbonate. In Examples 2-5, the mass ratio of EMC to DEC is 1:1.

[0398] EC stands for ethylene carbonate.

[0399] The composition of the electrolytes in the examples and comparative examples was analyzed.

[0400] The electrolyte in Comparative Example 1-1 has a relatively low mass content of carboxylic acid ester solvents. Although the introduction of linear carbonate solvents can reduce the viscosity of the electrolyte to some extent, the overall viscosity of the electrolyte is still high, resulting in high impedance, which is not conducive to fast charging.

[0401] The electrolytes in Comparative Examples 1-2 also contain a certain amount of linear carbonate. Although this can appropriately reduce the amount of carboxylic acid ester solvent additives, the mass content of carboxylic acid ester solvents in Comparative Examples 1-2 is still relatively high, resulting in lower electrolyte viscosity and lower impedance, which is beneficial for fast charging. However, the side reactions between carboxylic acid ester solvents and negative electrode active materials are more serious, which deteriorates the cycle performance.

[0402] This application embodiment, by adjusting the mass content of carboxylic acid ester solvent within an appropriate range, such as 10% to 30%, and combining it with 10% to 50% linear carbonate solvent, can reduce the viscosity of the electrolyte and increase the migration rate of lithium ions in the electrolyte. Moreover, the use of carboxylic acid ester solvent in combination with linear carbonate solvent ensures that the mass content of carboxylic acid ester solvent is not too high, which can alleviate the side reactions between carboxylic acid ester solvent and negative electrode active material. Furthermore, the electrolyte also includes additives, which can form an excellent and low-impedance solid electrolyte interphase (SEI) film on the negative electrode side, which can further alleviate side reactions, improve cycle performance, and enhance fast charging capability.

[0403] Examples 2-1 to 2-5 show that by adjusting the mass content of carboxylic acid ester solvents and linear carbonate solvents, the conductivity can be adjusted. As the conductivity increases, it is beneficial for the migration of lithium ions in the electrolyte, which can improve the fast charging performance of the battery cell and shorten the charging time.

[0404] For example, in Examples 1, 2-1, and 2-2, as the mass content of carboxylic acid ester solvent increases, the conductivity of the electrolyte improves, and the migration rate of lithium ions in the electrolyte accelerates, which can improve the fast charging performance of the battery cells and shorten the charging time. However, due to the increased mass content of carboxylic acid ester solvent, the degree of side reactions on the negative electrode side is greater, which can deteriorate the cycle performance to some extent.

[0405] In Examples 2-3 and 2-4, as the mass content of linear carbonate solvent increases, the conductivity of the electrolyte also improves, which can enhance the fast charging performance of the battery cells and shorten the charging time.

[0406] Carboxylic acid ester solvents are suitable for different materials, and linear carbonate solvents are suitable for different materials. For example, Examples 2-5 and Example 1 use different solvent materials, which can also improve the fast charging and cycle performance of battery cells.

[0407] Examples 3-1 to 3-8

[0408] Battery cells were prepared using a method similar to that of Example 1. The difference from Example 1 was that one of the materials and mass content of the additives was adjusted. The mass content of the organic solvent was adjusted accordingly based on the adjustment of the mass content of the additives and other components. For example, if the mass content of the additives increased by 1%, the mass content of the organic solvent decreased by 1%. The mass ratio of each component in the organic solvent remained unchanged, as shown in Table 2.

[0409] The electrolytes in Examples 3-8 do not contain lithium difluorophosphate or lithium fluorosulfonate.

[0410] The test results are shown in Table 2.

[0411] Table 2

[0412] In Table 2,

[0413] VC stands for vinylene carbonate;

[0414] PS stands for 1,3-propanesulfonyl lactone;

[0415] FEC stands for fluoroethylene carbonate;

[0416] DFEC stands for difluoroethylene carbonate;

[0417] The amount of additives added to the electrolyte in Comparative Example 2-1 was too low. For example, the amount of vinylene carbonate added was too low. Although the impedance of the SEI film on the negative electrode side was relatively low, the relatively poor protective effect of the SEI film made it easy for carboxylic acid ester solvents to react with the negative electrode active material, thus worsening the cycle.

[0418] The electrolyte in Comparative Example 2-2 had an excessive amount of additives, such as vinylene carbonate. While vinylene carbonate can form a dense organic SEI film on the negative electrode side, mitigating the side reactions between carboxylic acid ester solvents and negative electrode active materials, the high impedance of the SEI film hinders the rapid migration of lithium ions, resulting in a longer charging time for the battery cells.

[0419] In this embodiment, the amount of additive added to the electrolyte is within an appropriate range, with a mass content of 3% to 9%. The reaction potentials of the additive vinylene carbonate and carboxylic acid ester solvents are close, and they compete for reaction with the carboxylic acid ester solvents. The vinylene carbonate can participate in the formation of a dense SEI film on the negative electrode side, making it difficult for the carboxylic acid ester solvent to penetrate the SEI film to the graphite particles. This alleviates the side reaction between the carboxylic acid ester solvent and the graphite particles and reduces the amount of gas produced. Moreover, since the additive is within an appropriate content, the film impedance formed on the negative electrode side is relatively small, which is beneficial to improving cycle performance and reducing the risk of lithium plating.

[0420] Examples 3-1 to 3-8 show that by controlling the mass content of vinylene carbonate, 1,3-propanesulfonic acid lactone, and ethylene carbonate derivatives, a SEI film with relatively low impedance can be obtained, thereby improving the fast charging performance and cycle performance of the battery cell.

[0421] In Examples 1, 3-1, and 3-2, as the mass content of vinylene carbonate increases, the protection performance on the negative electrode side is improved, which is beneficial to improving cycle performance; however, the impedance of the SEI film increases, and the fast charging time increases.

[0422] Examples 1, 3-3, and 3-4, by controlling the mass content of 1,3-propanesulfonate lactone, show that increasing the mass content of 1,3-propanesulfonate lactone optimizes the SEI membrane composition, improves its protective effect, and enhances cycle performance. However, the impedance of the SEI membrane also increases slightly, which may slightly degrade the fast-charging performance of the battery cells. Therefore, the mass content of 1,3-propanesulfonate lactone is set to 0 to 0.5%, preferably 0.2% to 0.5%, to balance the improvement of both cycle performance and fast-charging performance of the battery cells.

[0423] Examples 1, 3-5, and 3-6 involved controlling the mass content of fluoroethylene carbonate. Increasing the mass content of fluoroethylene carbonate optimized the SEI film composition, reduced its impedance, and facilitated rapid lithium-ion migration, thus improving the fast-charging performance of the battery cell. However, while increasing the mass content of fluoroethylene carbonate improved the protection performance on the negative electrode side, it also increased the impedance of the formed SEI film, leading to a longer charging time. Therefore, the mass content of the ethylene carbonate derivative in the electrolyte was set between 0 and 2.55% to balance improving both the cycle performance and fast-charging performance of the battery cell.

[0424] When the electrolyte includes fluoroethylene carbonate, the mass content of vinylene carbonate can be appropriately reduced, which is beneficial to both improving the cycle performance and fast charging performance of the battery cells.

[0425] Using ethylene carbonate derivatives of different materials, such as fluoroethylene carbonate and difluoroethylene carbonate, can effectively improve the cycle performance and fast charging performance of battery cells.

[0426] Compared to Examples 3-8, Example 1 also includes lithium fluorosulfonate and lithium difluorophosphate, which can further optimize the composition of the SEI film on the negative electrode side, improve the protection performance on the negative electrode side, and improve the cycle performance.

[0427] Examples 4-1 and 4-2

[0428] Battery cells were prepared using a method similar to that of Example 1, except that...

[0429] Example 4-1 adjusted the coating weight on one side of the positive and negative electrode films;

[0430] Example 4-2 adjusted the compaction density of the positive and negative electrode films.

[0431] The test results are shown in Table 3.

[0432] Table 3

[0433] Compared to Example 1, the single-sided coating weight of the positive and negative electrode films in Example 4-1 is smaller, resulting in a relatively lower energy density of the battery cell. The migration path of lithium ions in the positive and negative electrode films is shortened, which is more conducive to achieving fast charging and shortening the charging time. Moreover, due to the reduction in single-sided coating weight, the total amount of active material participating in the negative electrode side reaction is reduced, which is beneficial to improving cycle performance.

[0434] The increased compaction density of the positive and negative electrode films in Example 4-2 resulted in a relatively higher energy density for the battery cells. However, the increased resistance to lithium ion migration in the positive and negative electrode films led to a longer charging time. Furthermore, due to the increased compaction density, the total amount of active material participating in the negative electrode side reaction increased, resulting in a slight deterioration in cycle performance.

[0435] Example 5

[0436] Battery cells were prepared using a similar preparation method to Example 1, except that the volume average particle size of the graphite particles was adjusted.

[0437] Example 6

[0438] Battery cells were prepared using a similar preparation method as in Example 1. However, unlike Example 1, the negative electrode film layer in Example 6 consisted of a single-layer film layer formed by uniformly coating a negative electrode slurry (with deionized water as the solvent) onto the surface of the negative electrode current collector, followed by drying and cold pressing.

[0439] The negative electrode film layer is disposed on the surface of the negative electrode current collector and includes negative electrode active material (in a mass ratio of 96.5:0.5:2:1), conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose. The negative electrode active material includes graphite particles and silicon dioxide. The graphite particles include artificial graphite and a negative electrode coating layer. The negative electrode coating layer coats the surface of the artificial graphite. The carbon content of the negative electrode coating layer is 2% by mass. The graphitization degree of the graphite particles is 92.5%, and the volume average particle size of the graphite particles is 8.5 μm. The silicon content in the negative electrode film layer is 0.7% by mass.

[0440] Example 7

[0441] Battery cells were prepared using a similar preparation method to Example 1, except that the mass content of silicon in the negative electrode film was adjusted to 3.0%.

[0442] Example 8

[0443] Battery cells were prepared using a similar preparation method to Example 1, except that the particle size of the lithium phosphate was adjusted.

[0444] Example 9

[0445] Battery cells were prepared using a similar preparation method to Example 1, except that no positive electrode additives were added to the lithium phosphate.

[0446] Example 10

[0447] Battery cells were prepared using a similar preparation method to Example 1. The difference from Example 1 was that the types and mass contents of the positive electrode additives containing lithium phosphate were adjusted.

[0448] The test results are shown in Table 4.

[0449] Table 4

[0450] The graphite particles in Examples 1 and 5 have different volume average particle sizes. As the volume average particle size of the graphite particles decreases, the solid-phase transport path of lithium ions is shortened, which is beneficial to shorten the fast charging time and improve the fast charging performance of the battery. However, the active surface area of ​​the graphite particles may be greater, which may increase the side reactions and slightly deteriorate the cycle performance of the battery.

[0451] Example 6 uses a single-layer negative electrode film. Compared with the single-layer negative electrode film, the double-layer film of Example 1 is more conducive to building a porous structure, improving the fast charging capability of the battery cell, and shortening the fast charging time. Since the graphite particles in Example 6 have a relatively large particle size, the exposed active surface can be reduced, thus improving cycle performance.

[0452] The silicon content of the negative electrode film in Examples 1 and 7 is different. As the silicon content increases, the volumetric energy density of the battery cell increases, but the side reactions on the negative electrode side are aggravated, which worsens the cycle. Moreover, due to the repeated expansion of the silicon-based material during charging and discharging, the SEI film needs to be constantly repaired, which may increase the impedance of the SEI film and potentially increase the fast charging time of the battery cell.

[0453] The lithium phosphates in Examples 1 and 8 have different particle sizes. As the particle size decreases, the solid-phase transport path of lithium ions is shortened, which is beneficial to shorten the fast charging time and improve the fast charging performance of the battery. However, the active surface area of ​​the lithium phosphate may be greater, which may increase the number of side reactions and slightly deteriorate the cycle performance of the battery.

[0454] Compared to the lithium phosphate in Example 9 which did not contain any positive electrode additives, the lithium phosphates in Examples 1 and 10 contained positive electrode additives, which improved the cycle stability and cycle performance of the lithium phosphate. The improvement effect was even better with the appropriate increase of the positive electrode additives.

[0455] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A battery cell, comprising an electrode assembly and an electrolyte, wherein the electrode assembly comprises a positive electrode and a negative electrode stacked along the thickness direction of the battery cell; The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector, the positive electrode film layer including a lithium phosphate with an olivine structure; The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector, the negative electrode film layer including graphite particles; The electrolyte comprises carboxylic acid ester solvents, linear carbonate solvents, and additives. in, Based on the mass meter of the electrolyte The mass content of the carboxylic acid ester solvent is 10% to 30%, and the mass content of the linear carbonate solvent is 10% to 50%. The additive has a mass content of 3% to 9%, and the additive includes 1,3-propanesulfonic acid lactone with a mass content ≥0, ethylene carbonate derivatives with a mass content ≥0, and vinylene carbonate with a mass content >0. The ethylene carbonate derivatives include compounds represented by formula A. In Formula A, Q1, Q2, Q3 and Q4 each independently include any one of hydrogen atoms, halogen atoms, C1 to C5 alkyl groups, or C1 to C5 haloalkyl groups, and Q1, Q2, Q3 and Q4 are not all hydrogen atoms at the same time.

2. The battery cell according to claim 1, wherein, The additive has a mass content of 5% to 8%.

3. The battery cell according to claim 1 or 2, wherein, The vinylene carbonate content is 0.8% to 7% by mass.

4. The battery cell according to claim 3, wherein, The vinylene carbonate content is 2% to 6% by mass.

5. The battery cell according to any one of claims 1 to 4, wherein, The 1,3-propanesulfonate lactone has a mass content of 0 to 0.5% in the electrolyte.

6. The battery cell according to any one of claims 1 to 5, wherein, The ethylene carbonate derivative has a mass content of 0 to 2.55% in the electrolyte.

7. The battery cell according to any one of claims 1 to 6, wherein, At least one of Q1, Q2, Q3 and Q4 includes a halogen atom or a C1 to C5 haloalkyl group.

8. The battery cell according to any one of claims 1 to 7, wherein, The ethylene carbonate derivatives include at least one compound represented by formula A-1 to formula A-3.

9. The battery cell according to any one of claims 1 to 8, wherein, The conductivity of the electrolyte is 11 ms / cm to 14 ms / cm.

10. The battery cell according to any one of claims 1 to 9, wherein, The carboxylic acid ester solvent includes at least one of ethyl acrylate, propyl acetate, ethyl propionate, ethyl formate, propyl formate, ethyl acetate, and butyl propionate; and / or The linear carbonate solvents include at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

11. The battery cell according to any one of claims 1 to 10, wherein, The electrolyte also includes a cyclic carbonate solvent, wherein the cyclic carbonate solvent has a mass content of 20% to 50% in the electrolyte.

12. The battery cell according to claim 11, wherein, The cyclic carbonate solvents include at least one of ethylene carbonate, propylene carbonate, and butene carbonate.

13. The battery cell according to any one of claims 1 to 12, wherein, The electrolyte also includes lithium salt additives, which include at least one of lithium difluorophosphate, lithium fluorosulfonate, lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium dioxalate borate.

14. The battery cell according to claim 13, wherein, The lithium salt additive is present in the electrolyte at a mass content of 0.02% to 0.5%.

15. The battery cell according to any one of claims 1 to 14, wherein, When the battery cell is at 0% charge, the compaction density of the negative electrode film is 1.30 g / cm³. 3 Up to 1.52 g / cm 3 , and / or The single-sided coating weight of the negative electrode film is 120 mg / 1540.25 mm. 2 Up to 180mg / 1540.25mm 2 .

16. The battery cell according to any one of claims 1 to 15, wherein, The graphite particles include graphite body particles and a negative electrode coating layer covering the surface of the graphite body particles. The graphite body particles include secondary particles, and the negative electrode coating layer includes carbon elements.

17. The battery cell according to claim 16, wherein, The graphite bulk particles include at least one of artificial graphite and natural graphite.

18. The battery cell according to claim 16 or 17, wherein, The graphite particles have a graphitization degree of 90% to 94%; and / or The volume average particle size Dv50 of the graphite particles is 7 μm to 15 μm; and / or The thickness of the negative electrode coating layer is 100 nm to 500 nm.

19. The battery cell according to any one of claims 1 to 18, wherein, The negative electrode film layer also includes a silicon-based material, wherein the silicon content of the silicon element in the negative electrode film layer is 0.5% to 10.0% by mass.

20. The battery cell according to any one of claims 1 to 19, wherein, The negative electrode film layer includes: The first negative electrode film layer is disposed on the surface of the negative electrode current collector; The second negative electrode film layer is disposed on the side of the first negative electrode film layer away from the negative electrode current collector. Both the first negative electrode film layer and the second negative electrode film layer include graphite particles, and the average longest diameter of the graphite particles in the first negative electrode film layer is greater than or equal to the average longest diameter of the graphite particles in the second negative electrode film layer.

21. The battery cell according to claim 20, wherein, The average longest diameter of the graphite particles in the first negative electrode film is 7 μm to 18 μm; and / or The average longest diameter of the graphite particles in the second negative electrode film is 6 μm to 10 μm.

22. The battery cell according to claim 20 or 21, wherein, The ratio of the thickness of the second negative electrode film to the thickness of the negative electrode film is 0.3 to 0.

7.

23. The battery cell according to any one of claims 1 to 22, wherein, When the battery cell is at 0% SOC, the compaction density of the positive electrode film is 2.3 / cm². 3 Up to 2.6 g / cm 3 ; and / or The single-sided coating weight of the positive electrode film is 250 mg / 1540.25 mm. 2 Up to 330mg / 1540.25mm 2 .

24. The battery cell according to any one of claims 1 to 23, wherein, The lithium phosphate includes at least one of primary particles and secondary particles, wherein the secondary particles include a plurality of primary particles and the secondary particles are spherical and / or quasi-spherical.

25. The battery cell according to claim 24, wherein, The average longest diameter of the primary particles is 300 nm to 800 nm; and / or The average particle size of the secondary particles is 5 μm to 15 μm.

26. The battery cell according to any one of claims 1 to 25, wherein, The lithium-containing phosphate includes: Phosphate particles, and The positive electrode additive element located in the phosphate particles, wherein the positive electrode additive element comprises at least one element selected from aluminum, vanadium, titanium and niobium.

27. The battery cell according to claim 26, wherein, The aluminum content in the lithium phosphate is between 200 ppm and 2500 ppm by mass; and / or The vanadium content in the lithium phosphate is from 300 ppm to 2000 ppm by mass; and / or The mass content of titanium in the lithium phosphate is from 1500 ppm to 3500 ppm; and / or The mass content of niobium in the lithium phosphate is between 300 ppm and 2000 ppm.

28. The battery cell according to claim 26 or 27, wherein, The phosphate particles include one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, and lithium cobalt phosphate.

29. The battery cell according to any one of claims 1 to 28, wherein, The lithium-containing phosphate includes those with the general formula Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 compounds, Wherein, 0.5≤x1≤1.3, 0≤y1≤1.3, 0.5≤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, A includes at least one of Na, K, and Mg; Me includes at least one of Mn, Fe, Co, and Ni; M includes at least one 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 at least one of Cl, C, and N; Y includes at least one of O and F.

30. The battery cell according to any one of claims 1 to 29, wherein, The positive electrode includes at least one positive electrode tab, the at least one positive electrode tab being connected to the positive current collector and extending out of the positive current collector along the length direction of the battery cell; and / or The negative electrode sheet includes at least one negative electrode tab, which is connected to the negative current collector and extends out of the negative current collector along the length direction of the battery cell.

31. The battery cell according to claim 30, wherein, The positive electrode plate satisfies the following condition: n*W1 / W2 is 0.9 to 1.0; n represents the number of all positive electrode tabs located on the same side of the positive current collector; W1 represents the average dimension of the positive electrode tab along the width direction of the battery cell; W2 represents the dimension of the positive current collector along the width direction; and / or The negative electrode sheet satisfies the following condition: m*W3 / W4 is 0.9 to 1.0; m represents the number of all negative electrode tabs located on the same side of the negative electrode current collector; W3 represents the average dimension of the negative electrode tab along the width direction of the battery cell; W4 represents the dimension of the negative current collector along the width direction.

32. The battery cell according to claim 30 or 31, wherein, The battery cell further includes a positive terminal and a positive electrode adapter. The positive terminal is disposed on at least one side of the electrode assembly along the width direction of the battery cell, and the positive terminal is connected to the positive electrode tab via the positive electrode adapter; and / or The battery cell further includes a negative terminal and a negative terminal adapter. The negative terminal is disposed on at least one side of the electrode assembly along the width direction, and the negative terminal is connected to the negative terminal tab through the negative terminal adapter.

33. The battery cell according to claim 32, wherein, The thickness of the positive electrode adapter is 1.25 mm to 3.00 mm; and / or The thickness of the negative electrode adapter is 1.50 mm to 2.50 mm.

34. The battery cell according to claim 32 or 33, wherein, The positive electrode adapter includes a first positive electrode adapter portion and a second positive electrode adapter portion. The first positive electrode adapter portion is connected to the positive electrode tab, and the second positive electrode adapter portion is connected to the first positive electrode adapter portion and protrudes from the first positive electrode adapter portion along the length direction. The second positive electrode adapter portion is connected to the positive electrode terminal. The ratio of the dimension of the first positive electrode adapter portion along the width direction to the width of the battery cell is 0.2 to 0.5; and / or The ratio of the dimension of the second positive electrode adapter along the length direction to the length of the battery cell is 0.05 to 0.

2.

35. The battery cell according to any one of claims 32 to 34, wherein, The negative electrode adapter includes a first negative electrode adapter portion and a second negative electrode adapter portion. The first negative electrode adapter portion is connected to the negative electrode tab, and the second negative electrode adapter portion is connected to the first negative electrode adapter portion and protrudes from the first negative electrode adapter portion along the length direction. The second negative electrode adapter portion is connected to the negative electrode terminal. The ratio of the dimension of the first negative electrode adapter portion along the width direction to the width of the battery cell is 0.2 to 0.5; and / or The ratio of the dimension of the second negative electrode adapter along the length direction to the length of the battery cell is 0.05 to 0.

2.

36. The battery cell according to any one of claims 1 to 35, wherein, The length of the battery cell is 200mm to 400mm; and / or The width of the battery cell is 80mm to 130mm; and / or The thickness of the battery cell is 25mm to 60mm.

37. A battery device comprising a battery cell according to any one of claims 1 to 36.

38. An electrical device comprising the battery device as described in claim 37.

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