Battery

Abstract

The embodiment of the invention relates to the technical field of batteries, and provides a battery which comprises a positive plate, a negative plate, electrolyte and a diaphragm arranged between the positive plate and the negative plate, the positive plate comprises a positive current collector and a positive active material coating at least one surface of the positive current collector, and the negative plate comprises a negative active material coating at least one surface of the negative current collector. The positive active material comprises a lithium cobalt oxide material and a ternary material, and the ternary material and / or the lithium cobalt oxide material are / is doped with metalloid elements; the electrolyte comprises a boron-containing additive and a compound as shown in a formula 1, the metalloid element is doped in the ternary material and / or the lithium cobalt oxide material, and the boron-containing additive and the compound as shown in the formula 1 are added into the electrolyte, so that the cycle stability of the battery can be effectively improved and the floating air blowing phenomenon can be improved by utilizing the common synergistic effect of the ternary material, the boron-containing additive and the compound as shown in the formula 1.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a battery. Background Art

[0002] Since lithium cobaltate material has advantages such as high platform voltage, high tap density, and stable crystal structure, it is regarded as an ideal cathode material for high-energy-density lithium-ion batteries and has been widely used in consumer portable electronic products such as mobile phones, laptop computers, and Bluetooth headsets.

[0003] However, the mineral resources of cobalt are relatively scarce, making the cost of lithium cobaltate-based batteries remain high. Since ternary materials also have a high lithium storage capacity and a high voltage platform, appropriately blending ternary cathode materials into lithium cobaltate cathodes is an effective way to reduce the cost of batteries.

[0004] However, after the lithium cobaltate material and the ternary material are mixed, at high temperature and high voltage, the ternary material and / or the lithium cobaltate material are prone to problems such as oxygen release, nickel dissolution, and cobalt dissolution, inducing the decomposition of the electrolyte to generate gas, resulting in poor cycle stability of the battery and the phenomenon of floating charge and bulging. Summary of the Invention

[0005] Embodiments of the present application provide a battery, which can effectively improve the cycle stability of the battery and improve the phenomenon of floating charge and bulging.

[0006] Embodiments of the present application provide a battery, including: a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator disposed between the positive electrode sheet and the negative electrode sheet;

[0007] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material coated on at least one surface of the positive electrode current collector. The positive electrode active material includes a lithium cobaltate material and / or a ternary material, and a metalloid element is doped in the ternary material and / or the lithium cobaltate material;

[0008] The electrolyte includes a boron-containing additive and a compound represented by Formula 1; the mass percentage content Y of the boron-containing additive in the electrolyte is 0.1 wt% - 5 wt%, and the mass percentage content X of the compound of Formula 1 in the electrolyte is 1 wt% - 30 wt%;

[0009]

[0010] In Formula 1, R1-R6 are independently selected from a hydrogen atom, a fluorine atom, a carbon-containing alkyl group or a fluoroalkyl group, and at least one of R1-R6 is a fluorine atom.

[0011] In some embodiments, the boron-containing additive includes at least one of lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium dicyanooxalate borate, lithium bis(malonato)borate, lithium (2-fluoromalonato)difluoroborate, lithium bis(salicylato)borate, lithium methanedisulfonato difluoroborate, lithium bis(difluorophosphoryloxy)difluoroborate, trimethyl borate, triethyl borate, tripropyl borate, tris(2,2,2-trifluoroethyl) borate, triphenyl borate, lithium bis(1,1,1,4,4,4-hexafluorobutane-2,3-diol) borate, tripropargyl borate, 2,4,6-trimethylcyclotriboroxane, sodium difluorooxalate borate, potassium difluorooxalate borate, cesium difluorooxalate borate;

[0012] and / or, the mass percentage content Y of the boron-containing additive in the electrolyte is 0.1 wt% - 3 wt%.

[0013] In some embodiments, the compound shown in Formula 1 is selected from at least one of the following structures:

[0014]

[0015]

[0016] In some embodiments, the metalloid element includes boron (B);

[0017] and / or, the mass content Z1 of the metalloid element in the ternary material is 50 - 5000 ppm;

[0018] and / or, the mass content Z2 of the metalloid element in the lithium cobaltate material is 50 - 5000 ppm.

[0019] In some embodiments, the lithium cobaltate material is doped with an alkali metal element.

[0020] In some embodiments, the mass content W of the alkali metal element in the lithium cobaltate material is 50 - 5000 ppm.

[0021] In some embodiments, the alkali metal element includes at least one of Na and K elements.

[0022] In some embodiments, the lithium cobaltate material and the ternary material satisfy the following formula:

[0023] 1 ≤ A / B ≤ 8;

[0024] wherein, A is the mass percentage content of the lithium cobaltate material in the positive electrode sheet, and B is the mass percentage content of the ternary material in the positive electrode sheet.

[0025] In some embodiments, the D50 particle size of the lithium cobaltate material is 8-20 μm, and / or the D50 particle size of the ternary material is 4-18 μm;

[0026] and / or,

[0027] The D50 particle size C of the lithium cobaltate material and the D50 particle size D of the ternary material satisfy the following formula:

[0028] 1.3 ≤ C / D ≤ 4.

[0029] In some embodiments, the electrolyte further includes: other fluorinated solvents; the other fluorinated solvents include at least one of difluoroethyl acetate, ethyl difluoroacetate, methyl 2,2-difluoroethyl carbonate, bis(2-fluoroethyl) carbonate, methyl trifluoroethyl carbonate, ethyl 2-fluoropropionate, ethyl 2,2-difluoropropionate, difluoroethyl propionate, trifluoroethyl propionate, ethyl difluoropropionate.

[0030] In some embodiments, the mass percentage content M of the fluorinated carboxylate and / or fluorinated carbonate in the electrolyte is 3 wt% - 30 wt%.

[0031] In some embodiments, the separator includes: a porous substrate, a ceramic coating coated on at least one side of the porous substrate, and an aqueous binder layer coated on one side of the ceramic coating and / or the porous substrate;

[0032] The thickness of the aqueous binder layer is 0.5-5 μm;

[0033] and / or;

[0034] The total thickness of the separator is 3-30 μm;

[0035] and / or;

[0036] The air permeability (Gurley) value of the separator is greater than 20 s / 100 cc and less than 200 s / 100 cc.

[0037] The battery provided by the embodiments of the present application, by doping a metalloid element in the ternary material and / or the lithium cobaltate material, due to the electron-deficient structure on the surface of the metalloid element, can strongly coordinate with the surrounding oxygen, thereby inhibiting the oxygen release behavior of the ternary material or the lithium cobaltate material during charging. However, due to the differences in various metal elements inside the material and the presence of vacancies and distorted crystal defects, the internal structure is in a dynamic equilibrium state. During high temperature or repeated lithium insertion and extraction processes, the doped elements and the vacancies in the lattice are still prone to behaviors such as position exchange, which affects the stability of local oxygen elements, especially the oxygen elements on the surface of the material.

[0038] After adding a boron-containing additive to the electrolyte, since boron (B) still has empty electron orbitals on its surface, it can coordinate with oxygen atoms in the cathode material to form a stable covalent bond similar to the B-O structure, making the oxygen on the surface of the cathode material in a charge balance state similar to that of the oxygen inside the material. Therefore, the stability of oxygen elements in the cathode material can be improved, and further the structural stability of the cathode material can be enhanced. However, the boron-containing additive will form a solid electrolyte interphase (SEI) film on the positive and negative electrodes of the battery. The flexibility of this SEI film is relatively low and it is prone to cracking during the battery cycling process, resulting in further consumption of the electrolyte and a decrease in battery performance.

[0039] Fluorobenzene solvents (compounds shown in Formula 1) have certain characteristics such as cathode film-forming ability and low surface energy. When a fluorobenzene solvent and a boron-containing additive are simultaneously added to the electrolyte, under the combined action of the fluorobenzene solvent and the boron-containing additive, a SEI film with good flexibility can be formed on the positive electrode of the battery, reducing the probability of the SEI film cracking due to low flexibility on the surface during the battery cycling process, thereby effectively improving the cycling stability of the battery.

[0040] In addition, using only fluorobenzene solvents cannot avoid the decomposition and gas generation of the electrolyte in the floating charge process due to being in a highly oxidized state for a long time. After the boron-containing additive forms a film on the positive and negative electrodes, on the one hand, it can inhibit the decomposition and gas generation of the electrolyte, making the SEI film on the surface of the positive and negative electrode materials stable. On the other hand, it can improve the bonding effect between B and O to stabilize the oxygen on the surface of the cathode material and inhibit the oxygen release during floating charge on the cathode side.

[0041] Doping a quasi-metal element in the ternary material and / or lithium cobalt oxide material, and adding a boron-containing additive and the compound shown in Formula 1 to the electrolyte. Through the combined synergistic effect of the three, the cycling stability of the battery can be effectively improved and the floating charge bulging phenomenon can be improved. Detailed Embodiments

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0043] It should be noted that in the embodiments of the present application, words such as "exemplary" or "for example" are used to represent examples, illustrations, or explanations. Any embodiment or design solution described as "exemplary" or "for example" in the present application should not be construed as being more preferred or having more advantages than other embodiments or design solutions. Exactly, using words such as "exemplary" or "for example" is intended to present related concepts in a specific manner.

[0044] As described above, for a battery prepared with a mixed cathode material that is a mixture of lithium cobaltate and ternary materials, oxygen evolution, nickel dissolution, cobalt dissolution, etc. are likely to occur at high temperatures and high voltages, inducing the decomposition of the electrolyte to produce gas, resulting in poor cycle stability of the battery and the phenomenon of floating charge and bulging. In addition, in the mixed cathode, due to the differences in the surface interfaces, lithium insertion / extraction rates, and stress / strain between the lithium cobaltate and ternary materials, the interfaces between the cathode material particles are more complex, making gas production failure more likely. Moreover, existing electrolytes cannot be well adapted to lithium-ion batteries with mixed cathodes, further degrading the battery performance.

[0045] To address the above problems, an embodiment of the present application provides a battery, which includes: a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator disposed between the positive electrode sheet and the negative electrode sheet.

[0046] The positive electrode sheet includes a positive electrode current collector and an active material coated on at least one surface of the positive electrode current collector. The active material includes lithium cobaltate and ternary materials, and a metalloid element is doped in the ternary material and / or lithium cobaltate.

[0047] Among them, a metalloid element can also be called a semi-metal element or a metalloid element, and its chemical properties can exhibit both metallic and non-metallic properties.

[0048] In some embodiments, the metalloid element can be selected from one or more of boron (B), silicon (Si), germanium (Ge), antimony (Sb), and tellurium (Te).

[0049] The electrolyte includes a compound represented by Formula 1 and a boron-containing additive.

[0050]

[0051] In Formula 1, R1-R6 can each independently be selected from a hydrogen atom, a fluorine atom, a carbon-containing alkyl group, or a fluoroalkyl group, and at least one of R1-R6 is a fluorine atom. Preferably, at least two of R1-R6 are fluorine atoms.

[0052] Optionally, the compound represented by Formula 1 can be called a fluorobenzene analog solvent.

[0053] In the embodiments of the present application, the carbon-containing alkyl group can refer to a chain alkyl group containing 1-2 carbon atoms, and the chain alkyl group can be a saturated straight-chain alkyl group. The chain alkyl group can be a methyl group, an ethyl group, etc.

[0054] In the embodiments of the present application, the fluoroalkyl group can refer to an alkyl group in which one or more hydrogen atoms are replaced by fluorine atoms, and the carbon-containing fluoroalkyl group can refer to a chain fluoroalkyl group containing 1-2 carbon atoms.

[0055] The boron-containing additive can be selected from one or more of lithium difluorooxalate borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium dicyanooxalate borate, lithium bis(malonato)borate, lithium (2-fluoromalonato)difluoroborate, lithium bis(salicylato)borate, lithium methanedisulfonatodifluoroborate, lithium bis(difluorophosphoryloxy)difluoroborate, trimethyl borate, triethyl borate, tripropyl borate, tris(2,2,2-trifluoroethyl) borate, triphenyl borate, lithium bis(1,1,1,4,4,4-hexafluorobutyl-2,3-diol) borate, tripropargyl borate, 2,4,6-trimethylcyclotriboroxane, sodium difluorooxalate borate, potassium difluorooxalate borate, cesium difluorooxalate borate, etc.

[0056] In the embodiments of the present application, there are no specific limitations on the specific sources of the quasi-metal element, the boron-containing additive, and the compound shown in Formula 1. Commercially available products well-known to those skilled in the art or products prepared by conventional preparation methods can be used.

[0057] In the present application, when a quasi-metal element is doped into the ternary material and / or the lithium cobaltate material, due to the electron-deficient structure on the surface of the quasi-metal element, it can strongly coordinate with the surrounding oxygen, thereby inhibiting the oxygen release behavior of the ternary material or the lithium cobaltate material during charging. However, due to the differences in various metal elements inside the material and the existence of vacancies and distorted crystal defects, the internal structure is in a state of dynamic equilibrium. During high-temperature or repeated lithium insertion and extraction processes, the doped elements and the vacancies in the crystal lattice are still prone to behaviors such as position exchange, which affects the stability of local oxygen elements, especially the oxygen elements on the surface of the material.

[0058] After adding the boron-containing additive to the electrolyte, since boron (B) still has empty electron orbitals on its surface, it can coordinate with the oxygen atoms in the positive electrode material to form a stable covalent bond similar to the B-O structure, making the oxygen on the surface of the positive electrode material in a charge balance state similar to that of the oxygen inside the material. Therefore, the stability of oxygen elements in the positive electrode material can be improved, oxygen release can be inhibited, and thus the structural stability of the positive electrode material can be further enhanced. However, the boron-containing additive will form a solid electrolyte interphase (SEI) film on the positive and negative electrodes of the battery. The flexibility of this SEI film is relatively low, and it is prone to cracking during the battery cycle, resulting in further consumption of the electrolyte and a decrease in battery performance.

[0059] The fluorobenzene solvent (the compound shown in Formula 1) has certain characteristics such as positive electrode film-forming property and low surface energy. When the fluorobenzene solvent and the boron-containing additive are added to the electrolyte simultaneously, under the combined action of the fluorobenzene solvent and the boron-containing additive, a solid electrolyte interphase (SEI) film with better flexibility can be formed on the positive electrode of the battery, reducing the probability of cracking of the SEI film due to its relatively low flexibility during the battery cycle, thereby effectively improving the cycle stability of the battery.

[0060] In addition, using fluorobenzene solvents alone cannot avoid the decomposition and gas generation of the electrolyte during the floating charge process due to the long-term high oxidation state. After the boron-containing additive forms a film on the positive and negative electrodes, on the one hand, it can inhibit the decomposition and gas generation of the electrolyte, keeping the solid electrolyte film on the surface of the positive and negative electrode materials stable. On the other hand, it can improve the bonding between B and O to stabilize the oxygen on the surface of the positive electrode material and inhibit the floating charge oxygen release on the positive electrode side.

[0061] In summary, in the embodiments of the present application, by doping a metalloid element in the ternary material and / or lithium cobaltate material, adding a fluorobenzene solvent and a boron-containing additive to the electrolyte, through the combined action of the above three substances, the phenomenon of floating charge and bulging of the battery can be effectively reduced, and the cycle stability of the battery can be improved, and the kinetic performance of the battery can be enhanced.

[0062] In one embodiment, the metalloid element preferably includes boron element. Due to the small atomic size of the boron element, it is easier for the boron element to be doped into the lattice of the ternary material and / or lithium cobaltate material compared with other metalloid elements, and the valence state of boron is relatively rich, which can replace various metal elements in the ternary material / lithium cobaltate material. Therefore, it can be doped more uniformly and is not prone to segregation and precipitation. In addition, the bond between boron and oxygen is closer to a covalent bond and is not easily broken, so it has a good effect on stabilizing the oxygen in the ternary material and / or lithium cobaltate material.

[0063] In one embodiment, the general formula of the ternary material is LiNi 1-x-y Co x Mn y O2.

[0064] Wherein, 0.5 ≤ 1 - x - y ≤ 0.95, 0.025 ≤ x ≤ 0.4, 0.025 ≤ x ≤ 0.4. High content of Ni and low content of Co are beneficial for the ternary material to have advantages such as high capacity and low cost, and to maintain structural stability.

[0065] The mass content Z1 of the metalloid element doped in the ternary material in the ternary material is 50 - 5000 ppm. For example, the atomic percentage content Z of the metalloid element in the ternary material can be 50 ppm, 100 ppm, 200 ppm, 500 ppm, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, or the range composed of any two of the above values.

[0066] The mass percentage content Z2 of the quasi-metal element doped in the lithium cobaltate material in the lithium cobaltate material is 50 - 5000 ppm. For example, the atomic percentage content Z of the quasi-metal element in the ternary material can be 50 ppm, 100 ppm, 200 ppm, 500 ppm, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, or a range composed of any two of the above values.

[0067] When the mass content of the quasi-metal element in the ternary material and / or the lithium cobaltate material is within the above range, the oxygen evolution behavior of the positive electrode material during charging can be effectively inhibited, and the stability of the positive electrode material at high voltages can be improved. If the doping amount of the quasi-metal element is too small, the improvement effect of the quasi-metal element on the high-voltage stability of the positive electrode material is not obvious; if the doping amount is too large, since the quasi-metal element replaces too many metal or oxygen sites, it is easy to cause serious lattice distortion, deteriorate the stability of the positive electrode material, and affect the improvement of the performance of the lithium-ion battery such as cycling and floating charge.

[0068] In one embodiment, the mass percentage content X of the compound of Formula 1 in the electrolyte is 1 wt% - 30 wt%. For example, the mass percentage content X of the compound of Formula 1 in the electrolyte can be 1 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, 13 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, or a range composed of any two of the above values. When the mass percentage content X of the compound of Formula 1 in the electrolyte is within the above range, the kinetic performance of the battery can be effectively improved. If the addition amount of the compound of Formula 1 in the electrolyte is too small, the improvement of the electrolyte viscosity and kinetic performance is limited; if the addition amount is too large, the solubility of the lithium salt will be reduced, resulting in interface problems such as lithium precipitation or poor lithium intercalation.

[0069] In one embodiment, the mass percentage content Y of the boron-containing additive in the electrolyte is 0.1 wt% - 5 wt%. For example, the mass percentage content Y of the boron-containing additive in the electrolyte can be 0.1 wt%, 0.2 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.5 wt%, 3 wt%, 4 wt%, 5 wt%, or any range composed of any two of the above values. When the mass percentage content Y of the boron-containing additive in the electrolyte is within the above range, in cooperation with the compound of Formula 1, if the addition amount of the boron-containing additive is too small, the boron-containing additive cannot form a uniform and stable solid electrolyte film on the surface of the cathode material, resulting in continuous decomposition of the electrolyte solvent, and ultimately deteriorating the cycle and kinetic performance of the lithium-ion battery; if the addition amount is too large, the formed solid electrolyte film will be too thick, with poor flexibility, deteriorating the kinetic and cycle performance.

[0070] In one embodiment, the compound shown in Formula 1 includes at least one of the following compounds:

[0071]

[0072] When the compound shown in Formula 1 includes the above compounds, it can cooperate better with the boron-containing additive to further improve the floating charge gas evolution and cycle stability of the lithium-ion battery.

[0073] When the compound shown in Formula 1 is a mixture of the foregoing multiple compounds, the present invention does not make specific limitations on the ratio between the specific compounds.

[0074] In one embodiment, the lithium cobaltate material is further doped with an alkali metal element. The alkali metal element can be selected from one or more of Na, K, Cs, Rb; preferably, the alkali metal element includes at least one of Na and K elements.

[0075] By doping an alkali metal element in the lithium cobaltate material, these doping elements can slightly replace the Li lattice sites in the lithium cobaltate crystal. During the charging process of the lithium-ion battery, these doped elements can act as pillars to support the Co-O layer and maintain the stability of the material structure. In addition, the larger ionic size of the doping elements also makes the lithium ion layer in the lithium cobaltate larger, making the insertion and extraction of lithium ions more convenient, and at the same time can inhibit the phase change or interlayer slip of the cathode material. Therefore, after doping, the cycle stability and kinetic performance of the lithium cobaltate material are both improved, and the cycle and floating charge performance are both improved.

[0076] In one embodiment, the lithium cobalt oxide material may also be doped with alkaline earth metal elements. The alkaline earth metal elements may be selected from one or more of Be, Mg, Ca, Sr, and Ba. The alkaline earth metal can have a similar effect of stabilizing the lithium cobalt oxide cathode material.

[0077] In some embodiments, the doping element in the lithium cobalt oxide material is preferably Na. Since Na and Li are in the same main group in the periodic table, the physical and chemical properties of Na and Li are closer. Doping with Na has little effect on the crystal structure of lithium cobalt oxide and the chemical states of each element. In addition, the ionic radius of Na is relatively small, and doping with Na has little effect on the lattice distortion around the doping element, and at the same time can meet the role of a pillar. Therefore, doping with Na can enable lithium cobalt oxide to obtain better cycle stability and kinetic performance.

[0078] In some embodiments, the mass content W of the alkali metal element or alkaline earth metal element in the lithium cobalt oxide material is 50 - 5000 ppm. For example, the mass content W of the alkali metal element or alkaline earth metal element (doping element) in the lithium cobalt oxide material can be 50 ppm, 100 ppm, 200 ppm, 500 ppm, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, or any range composed of any two of the above values. When the doping element is within the above range, the cycle stability of the lithium cobalt oxide material can be effectively improved. If the doping amount of the doping element is too small, the stability and kinetic performance of the material are hardly improved; if the doping amount of the doping element is too large, since the doping element is an inert component, it will not only cause a decrease in the lithium storage capacity of the material, but also block the transmission of lithium ions.

[0079] In some embodiments, based on the total mass of the positive electrode sheet, the addition amount of the lithium cobalt oxide material in the positive electrode sheet is A wt%, and the addition amount of the ternary material in the positive electrode sheet is B wt%. A and B satisfy the following formula:

[0080] 1 ≤ A / B ≤ 8;

[0081] In the positive electrode sheet, since the ternary material has more surface defects and a more unstable structure under high voltage compared with the lithium cobalt oxide material, adjusting the ratio between the addition amounts of the lithium cobalt oxide material and the ternary material to be within the range of the above formula can not only obtain the effects of higher energy density and cost reduction, but also take into account better floating charge resistance performance.

[0082] In some embodiments, the median particle size D50 of the lithium cobalt oxide material is 8 - 20 μm. For example, the median particle size D50 of the lithium cobalt oxide material is 8 μm, 10 μm, 12 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or any range composed of any two of the above values.

[0083] In some embodiments, the particle size D90 of the lithium cobalt oxide material is 20 - 30 μm. For example, the particle size D90 of the lithium cobalt oxide material is 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, or any range composed of any two of the above values.

[0084] In some embodiments, the median particle size D50 of the ternary material is 4 - 18 μm. For example, the median particle size D50 of the ternary material is 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 15 μm, 18 μm, or any range composed of any two of the above values.

[0085] In some embodiments, the particle size D90 of the ternary material is 12 - 25 μm. For example, the particle size D90 of the ternary material is 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or any range composed of any two of the above values.

[0086] Adjusting the overall particle size of the ternary material to be smaller than that of the lithium cobalt oxide material is beneficial for the positive electrode sheet of the mixed positive electrode to have a higher tap density, reduce the porosity and specific surface area of the electrode sheet, thereby reducing the contact area between the electrolyte and the positive electrode sheet to improve floating charge gas generation.

[0087] In some embodiments, the D50 particle size C of the lithium cobalt oxide material and the D50 particle size D of the ternary material satisfy the following formula:

[0088] 1 ≤ C / D ≤ 4.

[0089] Adjusting the ratio of the D50 particle sizes of the two within 1 ≤ D / C ≤ 4 can, to a certain extent, control the contact interface between the two within a suitable range without affecting the energy density, thereby improving floating charge gas production.

[0090] In some embodiments, the electrolyte further includes: other fluorinated solvents. By further adding other fluorinated solvents to the electrolyte, the antioxidant property of the electrolyte can be further improved.

[0091] In some embodiments, the fluorinated solvent is selected from fluorinated carboxylates and / or fluorinated carbonates. Among them, the fluorinated carboxylates and / or fluorinated carbonates may refer to linear fluorinated carboxylates and / or linear fluorinated carbonates, or non-linear fluorinated carboxylates and / or non-linear fluorinated carbonates. Since the kinetics and stability of linear fluorinated carboxylates and / or linear fluorinated carbonates are better, the fluorinated solvent is preferably selected from linear fluorinated carboxylates and / or linear fluorinated carbonates.

[0092] Due to the fluorinated alkyl groups surrounding the carboxylate and carbonate groups in linear fluorinated carboxylates and / or carbonates, the direct contact between the carbonate and carboxylate bonds and the surface of the positive electrode particles is blocked. Therefore, their antioxidant properties are significantly improved compared to substances containing benzene rings. Adding an appropriate amount of them to the electrolyte can further improve the antioxidant properties of the electrolyte, thereby improving the floating charge performance of lithium-ion batteries.

[0093] In some embodiments, the fluorinated carboxylate may include one or more of ethyl fluoroacetate, methyl fluoropropionate, ethyl fluoropropionate, methyl fluoroacetate, propyl fluoropropionate, isopropyl fluoropropionate, isopropyl fluoroacetate, ethyl fluorobutyrate, ethyl isofluorobutyrate, methyl isofluorobutyrate, butyl fluoroacetate, isobutyl fluoroacetate, tert-butyl fluoroacetate.

[0094] The fluorinated carbonate may include one or more of ethyl methyl fluorocarbonate, fluorinated propylene carbonate, diethyl fluorocarbonate, dimethyl fluorocarbonate.

[0095] Preferably, the fluorinated carboxylate and / or fluorinated carbonate may include: difluoroethyl acetate, ethyl difluoroacetate, methyl 2,2-difluoroethyl carbonate, bis(2-fluoroethyl) carbonate, methyl trifluoroethyl carbonate, ethyl 2-fluoropropionate, ethyl 2,2-difluoropropionate, difluoroethyl propionate, trifluoroethyl propionate, ethyl difluoropropionate, etc.

[0096] In some embodiments, the mass percentage content M of the fluorinated carboxylate and / or fluorinated carbonate in the electrolyte is 3 wt% - 30 wt%. For example, the mass percentage content M of the fluorinated carboxylate and / or fluorinated carbonate in the electrolyte may be 3 wt%, 5 wt%, 8 wt%, 10 wt%, 15 wt%, 18 wt%, 20 wt%, 25 wt%, 30 wt%, or a range composed of any two of the above values. When the addition amount of the fluorinated carboxylate and / or fluorinated carbonate in the electrolyte is less than 3 wt%, the improvement of the antioxidant property of the electrolyte is less, and it cannot effectively improve the floating charge and inhibit the impedance growth; when the addition amount is higher than 30 wt%, due to the high viscosity of the fluorinated solvent, the kinetics of the electrolyte will be deteriorated, resulting in a poor charging window of the lithium-ion battery.

[0097] The present application does not specifically limit the specific source of the fluorinated solvent, and products commercially available or prepared by conventional preparation methods well-known to those skilled in the art can be used.

[0098] When the fluorinated solvent is a mixture of the aforementioned specific compounds, the present application does not overly limit the ratio between the specific compounds.

[0099] In some embodiments, during the floating charge process of a lithium-ion battery, although it is always in a small-current charging state, if the local current is too concentrated, it will cause lithium deposition at the local part of the negative electrode. In severe cases, it can penetrate the separator, form a micro short circuit and an excessive local temperature rise, and further deteriorate the gas generation. Therefore, the separator can be optimized to further improve the floating charge gas bulging of the battery.

[0100] In some embodiments, the separator includes a porous substrate, a ceramic coating coated on at least one side of the porous substrate, and an aqueous binder layer coated on one side of the ceramic coating and / or the porous substrate.

[0101] For example, a ceramic coating is coated on one side of the porous substrate, and the aqueous binder layer can be coated on the ceramic coating, or the aqueous binder layer can be coated on the other side of the porous substrate, or coated on the ceramic coating and on the other side of the porous substrate.

[0102] For example, ceramic coatings are coated on both sides of the porous substrate, and the aqueous binder layer can be coated on at least one side of the ceramic coatings.

[0103] Preferably, when only one layer of the aqueous binder layer is coated in the separator, the aqueous binder layer is coated on the side close to the negative electrode.

[0104] It should be understood that when only one layer of the aqueous binder layer is coated in the separator, the other binder layer can be an oil-based binder layer, or other binder layers, and the present application does not limit this.

[0105] In some embodiments, the porous substrate is composed of a porous film of polyethylene or polypropylene, and the thickness of the porous substrate is 2 - 20 μm. For example, the thickness of the porous substrate can be 2 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 12 μm, 15 μm, 20 μm, or a range composed of any two of the above values.

[0106] In some embodiments, the ceramic coating includes ceramic particles and a binder.

[0107] In some embodiments, the ceramic particles are selected from one or more of inert substances such as boehmite, alumina, and silica.

[0108] In some embodiments, the binder is selected from oxygen-containing binders and / or oxygen-free binders.

[0109] In some embodiments, the oxygen-containing binder may be selected from one or more of polymethyl methacrylate, polymethacrylic acid, polyethyl methacrylate, sodium carboxymethyl cellulose, sodium alginate, polyvinyl alcohol, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, carboxylated chitosan.

[0110] In some embodiments, the oxygen-free binder may be selected from one or more of polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, ethylene-difluoroethylene copolymer, polytetrafluoroethylene, polyvinylidene fluoride-tetrafluoroethylene copolymer, polyvinylidene fluoride-hexafluoropropylene copolymer.

[0111] In some embodiments, when the ceramic coating is coated only on one side of the porous substrate, the ceramic coating is closer to the positive electrode sheet. When the ceramic coating is coated on both sides of the porous substrate, the substances included in the ceramic coatings on both sides may be the same or different.

[0112] In some embodiments, when the ceramic coating is coated on both sides of the porous substrate, the ceramic coating closer to the positive electrode sheet includes ceramic particles and an oxygen-free binder, and the ceramic coating closer to the negative electrode sheet includes ceramic particles and an oxygen-containing binder.

[0113] In some embodiments, the median particle size D50 of the ceramic particles is 0.05 - 5 μm. For example, the median particle size D50 of the ceramic particles is 0.05 μm, 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1.0 μm, 1.5 μm, 2.0 μm, 3.0 μm, 4.0 μm, 5.0 μm, or a range composed of any two of the above values.

[0114] In some embodiments, the thickness of the ceramic coating is 0.5 - 10 μm. For example, the thickness of the ceramic coating may be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 5 μm, 8 μm, 10 μm, or a range composed of any two of the above values.

[0115] In some embodiments, the aqueous binder layer near the positive electrode plate may be selected from one or more of polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, ethylene-difluoroethylene copolymer, polytetrafluoroethylene, polyvinylidene fluoride-tetrafluoroethylene copolymer, polyvinylidene fluoride-hexafluoropropylene copolymer, etc. Due to the high fluorine content of the above binder materials, they can resist the strong oxidative environment on the positive electrode side and avoid gas generation and deterioration of battery performance caused by oxidative degradation. At the same time, if a ceramic coating is applied near the positive electrode side, since the aqueous binder layer is selected from binders similar to those in the ceramic coating, it can have better adhesion with the ceramic coating.

[0116] In some embodiments, the aqueous binder layer near the negative electrode plate is selected from one or more of polymethyl methacrylate, polymethacrylic acid, polyethyl methacrylate, sodium carboxymethyl cellulose, sodium alginate, polyvinyl alcohol, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, carboxylated chitosan. Since the above binder materials are all oxygen-containing aqueous binders, the oxygen-containing aqueous binder has certain interactions with carbonates, carboxylates and lithium salts in the electrolyte due to having functional groups such as ester groups, carboxyl groups, hydroxyl groups, ether groups, etc., which can improve the wettability and liquid retention of the electrolyte, make the distribution of lithium ions more uniform, and avoid too concentrated local current, thereby inhibiting the occurrence of lithium deposition on the negative electrode.

[0117] The present application does not specifically limit the specific sources of the binders in the aqueous binder layer and the ceramic coating, and products commercially available to those skilled in the art or products prepared by conventional preparation methods can be used.

[0118] When the binders in the aqueous binder layer and the ceramic coating are mixtures of the foregoing specific compounds, the present application does not overly limit the ratio between the various specific compounds.

[0119] In some embodiments, the thickness of the aqueous binder layer is 0.5 - 5 μm. For example, the thickness of the aqueous binder layer can be 0.5 μm, 0.8 μm, 1 μm, 1.3 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 4 μm, 5 μm, or a range composed of any two of the above values. When the thickness of the aqueous binder layer is within the above range, it can provide good adhesion for the separator. When the aqueous binder layer is too thin, the adhesion with the positive and negative electrode plates and the corresponding ceramic coating is weak, and it is easy for the material to separate during the cyclic expansion and contraction of the lithium-ion battery, resulting in interface problems such as black spots and lithium deposition at the interface inside the lithium-ion battery; when the binder layer is too thick, during the preparation of the soft-pack lithium-ion battery, due to the action of heating and extrusion, some pores in the binder layer will be closed, thereby deteriorating the interface of the lithium-ion battery.

[0120] In some embodiments, the thickness of the separator is 3-30 μm. For example, the thickness of the separator can be 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 13 μm, 15 μm, 18 μm, 20 μm, 25 μm, 30 μm, or any range formed by any two of the above values. When the thickness of the separator is within the above range, problems such as battery short circuit or excessive self-discharge caused by too thin a separator can be avoided, and negative impacts such as poor kinetic performance of the lithium-ion battery and decreased battery energy density caused by too thick a separator can also be weakened.

[0121] In some embodiments, the air permeability of the separator (characterized by Gurley value) is greater than 20 s / 100 cc and less than 200 s / 100 cc. For example, the Gurley value of the separator can be 20 s / 100 cc, 40 s / 100 cc, 60 s / 100 cc, 80 s / 100 cc, 100 s / 100 cc, 120 s / 100 cc, 140 s / 100 cc, 160 s / 100 cc, 18 s / 100 cc, 200 s / 100 cc, or any range formed by any two of the above values. If the Gurley value of the separator is too high, the air permeability of the separator is too poor. Although the separator is not easily pierced by lithium dendrites and has good local high-temperature resistance and better floating charge performance, the kinetics deteriorate, which is not conducive to the cycle performance; if the Gurley value is too low, the air permeability of the separator is too good, the barrier to the interaction between the positive and negative electrodes on both sides of the separator is weakened, and the lithium-ion battery is more likely to form a micro short circuit, which is not conducive to the improvement of the floating charge performance.

[0122] It should be understood that the Gurley value of the separator can be tested by the following method: the time required for 100 mL of air to pass through a 1 square inch separator under a pressure of 1.22 kPa can be tested on a Gurley 4110N type air permeability detector or a Wang Yan type air permeability instrument.

[0123] It should be understood that the positive electrode sheet in the battery provided by the present application includes a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material layer also includes a conductive agent and a binder. The mass percentage content of each component in the positive electrode active material layer is: 90-99 wt% of the positive electrode active material, 0.5-5 wt% of the conductive agent, and 0.5-5 wt% of the binder.

[0124] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material layer also includes a conductive agent and a binder.

[0125] The negative electrode active material can be selected from one or more of natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, nano-silicon, amorphous silicon, silicon nanowires, silicon-carbon materials, silicon-oxygen materials, or their composites. If the negative electrode active material contains a silicon-based material, the silicon-based material accounts for less than or equal to 50% of the total mass of the negative electrode active material.

[0126] The mass percentage content of each component in the negative electrode active material layer is: 90-99 wt% of the negative electrode active material, 0.5-5 wt% of the conductive agent, and 0.5-5 wt% of the binder.

[0127] The conductive agent in the positive electrode sheet and the negative electrode sheet can both be selected from at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, and metal powder.

[0128] The binder in the positive electrode sheet can be selected from one or more of polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, ethylene-difluoroethylene copolymer, polytetrafluoroethylene, polyvinylidene fluoride-tetrafluoroethylene copolymer, and polyvinylidene fluoride-hexafluoropropylene copolymer.

[0129] The binder in the negative electrode sheet can be selected from one or more of styrene-butadiene rubber latex, polymethyl methacrylate, polymethacrylic acid, polyethyl methacrylate, sodium carboxymethyl cellulose, sodium alginate, polyvinyl alcohol, polyacrylic acid, lithium polyacrylate, and sodium polyacrylate.

[0130] The electrolyte further includes other solvents, lithium salts, and other additives. The other solvents can be selected from common carbonates and carboxylates, such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propionate (MP), methyl butyrate (MB), ethyl butyrate (EB), ethyl acetate (EA), propyl acetate (PA), etc. The other solvents account for 15 wt%-50 wt% of the total mass of the electrolyte.

[0131] The lithium salt can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium hexafluoroantimonate (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methyl, and lithium difluorobis(oxalato)phosphate. The lithium salt accounts for 12 wt%-25 wt% of the total mass of the electrolyte.

[0132] The other additives may be selected from one or more common additives to further improve the cycle performance or high and low temperature performance of the battery, such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), propylene sulfonic acid lactone (PST), methylene methanedisulfonate (MMDS), 1,3 - propane sulfonic acid lactone (PS), ethylene sulfate (DTD), bis(ethylene sulfate) (BiDTD), tetravinylsilane (TVS), tris(trimethylsilyl) borate (TMSB), hexamethyldisilazane (HMDS), fluorobenzene (FB), triphenyl phosphite (TPPi), pentafluoroethoxy cyclotriphosphazene (PFPN), and so on. The total mass ratio of the other additives in the electrolyte is 8wt% - 25wt%.

[0133] The positive current collector may be a conventional current collector in the art. For example, aluminum foil is selected as the positive current collector.

[0134] The negative current collector may be a conventional current collector in the art. For example, copper foil is selected as the negative current collector.

[0135] This application does not specifically limit the sources of the binder, conductive agent, current collector, and other solvents. Commercially available products or products prepared by conventional preparation methods well-known to those skilled in the art can be used.

[0136] Hereinafter, the battery including the present application will be introduced in detail through specific examples.

[0137] Example 1

[0138] (1) Preparation of the negative electrode sheet:

[0139] The negative electrode active material (composed of 93wt% artificial graphite + 7wt% silicon-carbon composite material), polymethyl methacrylate, lithium polyacrylate, conductive carbon black (SP), and carbon nanotubes (CNTs) are mixed evenly according to a mass ratio of 97:1.0:0.5:1.0:0.5. Subsequently, an appropriate amount of deionized water is added step by step, and a negative electrode slurry is obtained under the action of a vacuum mixer; the negative electrode active slurry is evenly coated on both surfaces of the copper foil; the coated copper foil is air-dried at room temperature until the surface is dry, then transferred to an 80°C oven for drying, and then rolled and slit to obtain the negative electrode sheet.

[0140] (2) Preparation of the positive electrode sheet:

[0141] The lithium cobaltate (B / Na-LiCoO2) material doped with boron and sodium, the ternary material doped with boron (B-LiNi 0.6 Co 0.2 Mn 0.2(O2), polyvinylidene fluoride (PVDF), SP, and carbon nanotubes (CNTs) were dry-mixed in a mass ratio of 77.6:19.4:1.5:1.0:0.5. Subsequently, an appropriate amount of N-methylpyrrolidone (NMP) was gradually added under the action of a vacuum mixer to form a homogeneous slurry. Subsequently, the positive electrode active slurry was evenly coated on both surfaces of the aluminum foil using a coater; the coated aluminum foil was dried and then rolled and slit to obtain the required positive electrode sheet. In this embodiment, the doping amount of sodium in lithium cobaltate was 2000 ppm, the doping amount of boron was 1000 ppm, and the doping amount of boron in the ternary material was 1000 ppm. The D50 particle size of the used B / Na-LiCoO2 was 18 μm, and the particle size of B-LiNi 0.6 Co 0.2 Mn 0.2 O2 was 8 μm.

[0142] (3) Preparation of the separator:

[0143] A layer of aluminum oxide layer with a thickness of 1.5 μm (composed of 96 wt% aluminum oxide and 4 wt% methyl methacrylate) was coated on the first surface of a porous polyethylene (PE) substrate with a thickness of 5 μm, and the average particle size of the aluminum oxide particles was 0.2 μm. Subsequently, a porous binder layer composed of polymethyl methacrylate was coated on top of this layer, and the thickness of the binder layer was 1.5 μm; then, a ceramic coating with a thickness of 1.5 μm and a binder layer with a thickness of 1.5 μm were coated on the second surface of the substrate opposite to the first surface. The composition of this ceramic coating was 96 wt% aluminum oxide and 4 wt% PVDF, and the material of the binder layer was also PVDF.

[0144] (4) Preparation of the electrolyte:

[0145] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), difluoroethyl acetate (DFEA), and p-difluorobenzene (Formula 1-1) were mixed evenly in a mass ratio of 20:30:20:15:15. Then, 15 wt% of LiPF6 based on the total mass of the electrolyte was quickly added thereto, and after dissolution, 10 wt% of FEC, 2.0 wt% of HTCN, 2.0 wt% of PS, and 1.0 wt% of LiODFB based on the total mass of the electrolyte were added. After stirring evenly and passing the tests for moisture, free acid, chromaticity, etc., the required electrolyte was obtained. In this electrolyte, the content of p-difluorobenzene (Formula 2-1) in the electrolyte was 10.5 wt%. The content of DFEA in the electrolyte was 10.5 wt%

[0146] (5) Preparation of the lithium-ion battery:

[0147] Stack the negative electrode sheet, separator, and positive electrode sheet in a certain manner so that the separator completely separates the positive and negative electrodes, and at the same time, the negative electrode paste completely covers the positive electrode paste. Then, a wound core with a certain thickness and width is formed by winding. The PVDF adhesive layer in the separator faces the positive electrode sheet, and the polymethyl methacrylate binder layer faces the negative electrode sheet. Subsequently, it is packaged with an aluminum-plastic film and the electrolyte prepared in the above steps is injected. After vacuum packaging, processes such as aging, formation, shaping, and sorting are carried out to obtain a soft-pack lithium-ion battery with certain specifications. The prepared lithium-ion battery has a voltage test window of 3.0 - 4.45V.

[0148] The preparation methods of the lithium-ion batteries in Examples 2 - 26 are basically the same as those in Example 1, except that the types or contents of the compounds shown in Formula 1 are different, the types or contents of the boron additives are different, and the types or contents of the quasi-metal elements doped in the ternary material and / or lithium cobaltate material are different. The specific adjustments are shown in Table 1.

[0149] The preparation methods of the lithium-ion batteries in Examples 27 - 36 are basically the same as those in Example 1, except that the contents or types of the alkali metal elements doped in the lithium cobaltate material are different, and the mixing ratios of the ternary material and the lithium cobaltate material in the positive electrode sheet are different. The specific adjustments are shown in Table 2.

[0150] The preparation methods of the lithium-ion batteries in Examples 37 - 40 are basically the same as those in Example 1, except that the particle sizes D50 of the lithium cobaltate material and / or the ternary material are different. The specific adjustments are shown in Table 3.

[0151] The preparation methods of the lithium-ion batteries in Examples 41 - 46 are basically the same as those in Example 1, except that the types and contents of the fluorine-containing solvents added to the electrolyte are different. The specific adjustments are shown in Table 4.

[0152] The preparation methods of the lithium-ion batteries in Examples 47 - 50 are basically the same as those in Example 1, except that there are differences in the thicknesses of the components in the separator and the coated binder layer. The specific adjustments are shown in Table 5.

[0153] Comparative Example 1: The preparation method of the lithium-ion battery in this comparative example is basically the same as that in Example 1, except that the compound shown in Formula 1 - 1 is not included in the electrolyte.

[0154] Comparative Example 2: The preparation method of the lithium-ion battery in this comparative example is basically the same as that in Example 1, except that the boron-containing additive is not included in the electrolyte.

[0155] Comparative Example 3: The preparation method of the lithium-ion battery in this comparative example is basically the same as that in Example 1, except that the ternary material and the lithium cobaltate material are not doped.

[0156] Comparative Example 4: The preparation method of the lithium-ion battery in this comparative example is basically the same as that of Example 1, except that the content of the compound shown in Formula 1-1 in the electrolyte is adjusted to 0.5 wt%, the content of the boron-containing additive in the electrolyte is adjusted to 0.05 wt%, and the content of the metalloid doped in the ternary material and the lithium cobaltate material is adjusted to 30 ppm.

[0157] Comparative Example 5: The preparation method of the lithium-ion battery in this comparative example is basically the same as that of Example 1, except that the content of the compound shown in Formula 1-1 in the electrolyte is adjusted to 40 wt%, the content of the boron-containing additive in the electrolyte is adjusted to 8 wt%, and the content of the metalloid doped in the ternary material and the lithium cobaltate material is adjusted to 10,000 ppm.

[0158] Experimental Example

[0159] 1. Test the cycle performance and floating charge performance of the lithium-ion batteries in Examples 1 - X and Comparative Examples 1 - 5.

[0160] 1) Cycle performance test: In a constant temperature oven at 25°C, charge at an initial rate of 2C in a stepped manner to the upper limit voltage, and then charge at a constant voltage until the current drops to 0.05C as one charging process. After the charging process is completed, let it stand for 10 minutes, and then discharge at a rate of 0.7C to 3.0V. One charge-discharge process is one cycle. The cycle life of the battery is represented by the capacity of the battery dropping to 80% of the initial capacity.

[0161] 2) Floating charge performance test: In a constant temperature oven at 45°C, charge at a rate of 0.5C to the upper limit voltage, and continue to charge at a constant voltage. Measure the thickness of the battery every 5 days. The floating charge life of the lithium-ion battery is represented by the number of days of floating charge when the thickness of the battery does not exceed 15% of the initial thickness.

[0162] The test results are shown in Table 6.

[0163] Table 1 (Note: The doping amount data in the table are all approximate numbers)

[0164]

[0165]

[0166] Table 2

[0167]

[0168]

[0169] Table 3

[0170]

[0171] Table 4

[0172] Fluorinated solvent Addition amount of fluorinated solvent wt% Example 1 DFEA 10.5 Example 41 Propyl fluoropropionate 10.5 Example 42 Ethyl methyl fluorocarbonate (FEMC) 10.5 Example 43 DFEA, FEMC 5.5+5 Example 44 DFEA 3 Example 45 DFEA 30 Example 46 / 0

[0173] Table 5

[0174]

[0175]

[0176] Table 6

[0177]

[0178]

[0179]

[0180] After testing:

[0181] 1. As can be seen from Table 1 and Table 6, for the lithium-ion batteries in Examples 1 - 26, compared with Comparative Examples 1 - 5, by adding the compound shown in Formula 1 and a boron-containing additive to the electrolyte, doping a metalloid element in the ternary material and / or lithium cobalt oxide material, and when the addition amount of the compound shown in Formula 1 in the electrolyte is in the range of 1 wt% - 30 wt% and the addition amount of the boron-containing additive in the electrolyte is in the range of 0.1 wt% - 5 wt%, the cycle life (increased by more than 400 cycles) and floating charge life (increased by more than 30 days) of the lithium-ion battery can be effectively improved, thereby improving the battery's performance.

[0182] 2. As can be seen from Table 2 and Table 6, when an alkali metal element is doped in the lithium cobalt oxide material and the doping amount of the alkali metal element is controlled within the range of 50 - 5000 ppm, the cycle life of the lithium-ion battery can be effectively improved.

[0183] In addition, when the ratio of the percentage content A of the lithium cobalt oxide material in the positive electrode sheet to the content B of the ternary material in the positive electrode sheet is controlled within the range of 1 - 8, the lithium-ion battery has a better floating charge life.

[0184] 3. As can be seen from Table 3 and Table 6, when the D50 particle size of the lithium cobalt oxide material is controlled within the range of 8 - 20 μm, the D50 particle size of the ternary material is controlled within the range of 4 - 18 μm, and the ratio between the D50 particle size of the lithium cobalt oxide material and the D50 particle size of the ternary material is controlled within the range of 1.3 - 4, the cycle life of the lithium-ion battery can be effectively improved.

[0185] 4. As can be seen from Table 4 and Table 6, after adding a fluorinated solvent to the electrolyte, the cycle life and floating charge life of the lithium-ion battery can be effectively improved.

[0186] 5. As can be seen from Table 5 and Table 6, compared with Example 47 (with a water-based binder layer coated on one side), in Example 1, the water-based binder layer is coated on both sides of the separator, and the lithium-ion battery has better cycle life and floating charge life.

[0187] In addition, when the thickness of the water-based binder layer is controlled within 0.5 - 5 μm and the total thickness of the separator is controlled within 3 - 30 μm, the air permeability of the separator is appropriate, and the lithium-ion battery has better cycle life and floating charge life.

[0188] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery, comprising: A positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, characterized in that: The positive electrode sheet includes a positive electrode current collector and a positive electrode active material coated on at least one surface of the positive electrode current collector. The active material includes a lithium cobaltate material and a ternary material, and a metalloid element is doped in the lithium cobaltate material and / or the ternary material; The electrolyte includes a boron-containing additive and a compound represented by Formula 1. The mass percentage content Y of the boron-containing additive in the electrolyte is 0.1 wt% - 5 wt%, and the mass percentage content X of the compound of Formula 1 in the electrolyte is 1 wt% - 30 wt%; In Formula 1, R1-R6 are independently selected from a hydrogen atom, a fluorine atom, a carbon-containing alkyl group or a fluoroalkyl group, and at least one of R1-R6 is a fluorine atom.

2. The battery according to claim 1, wherein The boron-containing additive includes at least one of lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium dicyanooxalate borate, lithium bis(malonato)borate, lithium (2-fluoromalonato)difluoroborate, lithium bis(salicylato)borate, lithium methanedisulfonato difluoroborate, lithium bis(difluorophosphoryloxy)difluoroborate, trimethyl borate, triethyl borate, tripropyl borate, tris(2,2,2-trifluoroethyl) borate, triphenyl borate, lithium bis(1,1,1,4,4,4-hexafluorobutyl-2,3-diol) borate, tripropargyl borate, 2,4,6-trimethylcyclotriboroxane, sodium difluorooxalate borate, potassium difluorooxalate borate, cesium difluorooxalate borate; And / or, the mass percentage content Y of the boron-containing additive in the electrolyte is 0.1 wt% - 3 wt%.

3. The battery according to claim 1, wherein The compound represented by Formula 1 is selected from at least one of the following structures:

4. The battery according to any one of claims 1 to 3, characterized in that, The metalloid element includes boron (B); And / or, the mass content Z1 of the metalloid element in the ternary material is 50 - 5000 ppm; And / or, the mass content Z2 of the metalloid element in the lithium cobaltate material is 50 - 5000 ppm.

5. The battery according to any one of claims 1-3, characterized in that, An alkali metal element is doped in the lithium cobaltate material; Preferably, the mass content W of the alkali metal element in the lithium cobaltate material is 50 - 5000 ppm; Preferably, the alkali metal element includes at least one of Na and K elements.

6. The battery according to any one of claims 1 to 3, characterized in that, The lithium cobaltate material and the ternary material satisfy the following formula: 1 ≤ A / B ≤ 8; Wherein, A is the mass percentage content of the lithium cobaltate material in the positive electrode sheet, and B is the mass percentage content of the ternary material in the positive electrode sheet.

7. The battery according to any one of claims 1 to 3, characterized in that, The D50 particle size C of the lithium cobaltate material is 8 - 20 μm, and / or, the D50 particle size D of the ternary material is 4 - 18 μm.

8. The battery according to any one of claims 1 to 3, characterized in that, The electrolyte includes other fluorinated solvents, and the other fluorinated solvents include at least one of difluoroethyl acetate, ethyl difluoroacetate, methyl 2,2-difluoroethyl carbonate, bis(2-fluoroethyl) carbonate, methyltrifluoroethyl carbonate, ethyl 2-fluoropropionate, ethyl 2,2-difluoropropionate, ethyl difluoropropionate, ethyl trifluoropropionate, ethyl difluoropropionate; 9. The battery according to claim 8, characterized in that, The mass percentage content M of the other fluorinated solvents in the electrolyte is 3 wt% - 30 wt%.

10. The battery according to any one of claims 1-3, characterized in that, The separator includes: a porous substrate, a ceramic coating coated on at least one side of the porous substrate, and an aqueous binder layer coated on one side of the ceramic coating and / or the porous substrate; The thickness of the aqueous binder layer is 0.5 - 5 μm; and / or; The total thickness of the separator is 3 - 30 μm; and / or; The air permeability of the separator is greater than 20 s / 100 cc and less than 200 s / 100 cc.

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