Lithium ion battery

Abstract

The invention discloses a lithium ion battery, belongs to the technical field of lithium ion batteries, and solves the problems of capacity fading and high thermal runaway risk caused by easy dissolution of cobalt in element-doped lithium cobalt oxide in the prior art. The positive electrode active material of the lithium ion battery comprises lithium cobalt oxide, and the lithium cobalt oxide comprises doping elements Al and Y; on the basis of the mass of lithium cobalt oxide, the mass content of Y is A, and A is 200-1000 ppm; on the basis of the mass of lithium cobalt oxide, the mass content of Al is B, and B is equal to 4000-15000 ppm; the electrolyte comprises a first additive # imgabs0 # R1, wherein the first additive # imgabs0 # R1 comprises an alkenyl group and / or an alkynyl group. According to the lithium ion battery, the attenuation rate of capacity can be reduced, the cycle life is prolonged, and the electrical property and the safety are higher.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a lithium ion battery. Background Art

[0002] Lithium-ion batteries offer advantages such as high volumetric energy density, environmental friendliness, and rapid internal ion transport. Lithium cobalt oxide, a common cathode material for lithium-ion batteries, boasts high specific capacity and operating voltage, with a theoretical specific capacity of up to 274 mAh / g. It also delivers high energy in practice, meeting the demands for miniaturization and high-performance power supplies, enabling devices to extend battery life within limited space. It is widely used in products such as mobile phones, tablets, and laptops. Further increasing the cutoff voltage of lithium cobalt oxide materials will help increase the energy density of lithium-ion batteries, meeting the demand for high-performance batteries in consumer electronics.

[0003] However, at high voltages (≥4.48V), the crystal structure of lithium cobalt oxide is prone to phase transition from a layered structure to a spinel structure, resulting in volume changes and deterioration of material properties, causing battery performance degradation. Doping with elements can stabilize the crystal structure of lithium cobalt oxide, reduce structural changes during the charge and discharge process, slow capacity decay, and extend the cycle life of the battery.

[0004] However, doping elements expand the crystal lattice, weakening the chemical bonds around the cobalt ions and increasing the likelihood of cobalt dissolution. The dissolved cobalt ions deposit at the material interface, prompting side reactions between the surface atoms and the electrolyte, leading to capacity decay, increased heat generation, and the risk of thermal runaway. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the problem of cobalt dissolution in element-doped lithium cobalt oxide in the prior art, which leads to capacity decay and a high risk of thermal runaway, thereby providing a lithium-ion battery. The lithium-ion battery of the present application can reduce the capacity decay rate, increase the cycle life, and improve electrical performance and safety.

[0006] To this end, the present invention provides the following technical solutions:

[0007] A lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, and a separator and an electrolyte disposed between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer, wherein the positive electrode active layer comprises a positive electrode active material, wherein the positive electrode active material comprises lithium cobaltate, wherein the lithium cobaltate comprises doping elements Al, Y, and M, wherein M comprises Al and Y, and further comprises at least one of Na, Mg, Ti, Zr, Ni, Sr, W, Sc, B, Si, Sn, Tb, Nb, Sb, Se, Ce, and Te;

[0008] Based on the mass of lithium cobalt oxide, the mass content of Y is A, where A = 200 to 1000 ppm;

[0009] Based on the mass of lithium cobalt oxide, the mass content of Al is B, B = 4000 to 15000 ppm;

[0010] The electrolyte includes a first additive Wherein, R1 includes alkenyl and / or alkynyl.

[0011] In a possible implementation, the mass content of the first additive in the electrolyte is 0.2-2 wt %.

[0012] In one possible embodiment, the first additive includes One or more of;

[0013] wherein R2 is selected from -(CH2) n - and -O- at least one, n is a natural number of 0 to 3, R3 is selected from at least one of -CH2- or -O-, and R4 is selected from C2 to C4 unsaturated alkanes;

[0014] m is 0 or 1, and R5 is selected from C2-C4 unsaturated alkanes.

[0015] In one possible implementation, Selected from

[0016] At least one of;

[0017] In one possible implementation, Selected from At least one of .

[0018] In a possible implementation, the electrolyte further includes a second additive containing a phosphorus-oxygen double bond and a cyano group, and the mass content of the second additive in the electrolyte is 0.1 to 6 wt %.

[0019] In one possible embodiment, the structure of the second additive is

[0020] R6, R7, and R8 are independently selected from at least one of -CH2- and -O-, R9, R 10 、R 11 are independently selected from substituted or unsubstituted C1 to C4 alkyl groups, and R9, R 10 、R 11 At least one of them is a C1-C4 alkyl group substituted with a cyano group;

[0021] In one possible embodiment, the second additive includes

[0022] At least one of .

[0023] In one possible embodiment, the electrolyte further includes a third additive containing both an ether bond and a cyano group, and the mass content of the third additive in the electrolyte is 0.2 to 5 wt%;

[0024] In one possible embodiment, the third additive includes at least one of ethylene glycol bis(propionitrile) ether, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,3,4-tetrakis(2-cyanoethoxy)butane, tetrakis(2-cyanoethoxymethyl)methane, 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane, and 1,2,3,4,5-penta(2-cyanoethoxy)pentane.

[0025] In a possible embodiment, the electrolyte further includes a fourth additive containing boron, and the mass content of the fourth additive in the electrolyte is 0.01 to 2 wt%;

[0026] In a possible implementation, the fourth additive includes at least one of lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluorooxalatoborate.

[0027] In a possible embodiment, the electrolyte further includes a fluorine-containing solvent, and the mass content of the fluorine-containing solvent in the electrolyte is 10 to 65 wt%;

[0028] In one possible embodiment, the fluorine-containing solvent includes bis(2,2,2-trifluoroethyl) carbonate, trifluoroethyl methyl carbonate, methyl difluoroacetate, ethyl difluoroacetate, methyl trifluoroacetate, ethyl trifluoroacetate, 2,2-difluoroethyl trifluoromethanesulfonate, 2,2,2-trifluoroethyl methanesulfonate, fluoroethylene carbonate, difluoroethylene carbonate, 4-trifluoromethylethylene carbonate, perfluoropentyl-1,3-dioxolane-2-one, monofluorobenzene, p-difluorobenzene, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) carbonate, perfluoroheptyl ether, bis(2,2,2-trifluoroethyl) ether, and at least one of perfluorohexyl methyl ether.

[0029] In one possible embodiment, the volume particle size distribution curve of the positive electrode active material includes a first volume distribution peak and a second volume distribution peak;

[0030] The particle size corresponding to the maximum peak intensity of the first volume distribution peak is 1 to 8 μm, and the particle size corresponding to the maximum peak intensity of the second volume distribution peak is 10 to 25 μm.

[0031] In one possible embodiment, the compaction density of the positive electrode active layer is 3.5 to 5.5 g / cm 3 .

[0032] The technical solution of the present invention has the following advantages:

[0033] The present application provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, and a separator and an electrolyte disposed between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer. The positive electrode active layer comprises a positive electrode active material. The positive electrode active material comprises lithium cobalt oxide. The lithium cobalt oxide comprises doping elements Al and Y. Based on the mass of the lithium cobalt oxide, the mass content of Y is A, A=200-1000ppm; based on the mass of the lithium cobalt oxide, the mass content of Al is B, B=4000-15000ppm; the electrolyte comprises a first additive Wherein, R1 includes alkenyl and / or alkynyl. The first additive in the electrolyte The lone pair of electrons in the nitrogen element of the imidazole ring forms a coordination compound with the metal ions on the surface of the lithium cobalt oxide, inhibiting the dissolution of Co ions. Simultaneously, unsaturated bonds polymerize on the surface of the cathode active material to form a stable CEI film, preventing side reactions between the electrolyte and the cathode active material surface and improving interfacial stability. The doping elements Al and Y in the cathode active material form stable chemical bonds in the lattice, enhancing the material's mechanical strength and inhibiting lattice collapse.

[0034] At the same time, Al and Y have stronger metallic properties than Co, which can increase the adsorption capacity of the material surface to the first additive, improve the utilization rate of the first additive, further protect the positive electrode interface, and jointly improve the stability of the battery. The lithium-ion battery of this application can further reduce the capacity decay rate, increase the cycle life, avoid excessive heat generation, and reduce the risk of thermal runaway. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 is the volume particle size distribution curve of the positive electrode active material in Example 1. DETAILED DESCRIPTION

[0037] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0038] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0039] Doping elements can improve the crystal structure stability of lithium cobalt oxide at high voltages, thereby reducing the rate of capacity decay and extending the cycle life of the battery. However, doping elements also expand the crystal lattice, weakening the chemical bonds around the cobalt ions, which increases the possibility of cobalt dissolution during cycling. The dissolved cobalt ions deposit at the material interface, prompting side reactions between the atoms on the material surface and the electrolyte, resulting in a certain degree of capacity decay, reducing the effectiveness of doping elements in reducing the rate of capacity decay.

[0040] In order to solve the above problems, the present application provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, and a separator and an electrolyte disposed between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer, wherein the positive electrode active layer comprises a positive electrode active material, wherein the positive electrode active material comprises lithium cobalt oxide, and wherein the lithium cobalt oxide comprises doping elements Al and Y;

[0041] Based on the mass of lithium cobalt oxide, the mass content of Y is A, where A = 200 to 1000 ppm;

[0042] Based on the mass of lithium cobalt oxide, the mass content of Al is B, B = 4000 to 15000 ppm; the electrolyte includes a first additive Wherein, R1 includes alkenyl and / or alkynyl.

[0043] Illustratively, A can be 200 ppm, 300, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, or 1000 ppm; and B can be 4000, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm, 10000 ppm, 11000 ppm, 12000 ppm, 13000 ppm, 14000 ppm, or 15000 ppm.

[0044] Y and Al elements support the layered structure of lithium cobalt oxide, inhibiting structural collapse at high voltages, reducing the rate of battery capacity decay, and extending the battery's cycle life. Furthermore, doping increases the interlayer spacing of the positive electrode active material, enhancing lithium ion insertion and extraction, and improving the battery's rate performance. Y doping improves the crystal interface, providing good interfacial contact between lithium cobalt oxide primary particles, reducing interparticle resistance, improving electron conduction efficiency, and facilitating smoother lithium ion insertion and extraction. Al replaces Co by altering the transition metal layer state, increasing interlayer slip resistance, stabilizing the lithium cobalt oxide crystal structure, and minimizing structural changes during charge and discharge. When the Y and Al content are too high, the doping elements occupy lithium ion diffusion channels or active sites, hindering lithium ion insertion and extraction, resulting in a decrease in the battery's reversible capacity. When the Y / Al ratio is too low, the positive electrode material's performance cannot be effectively improved, making it difficult to achieve the desired material modification effect. A is in the range of 200-1000ppm, and B is in the range of 4000-15000ppm, which can improve the stability of the crystal structure under high voltage and make the battery have better rate performance and higher reversible capacity. The lone pair of electrons in the nitrogen element of the imidazole ring forms a coordination compound with the metal ions on the surface of the lithium cobalt oxide, inhibiting the dissolution of Co ions. Simultaneously, unsaturated bonds polymerize on the surface of the cathode active material to form a stable CEI film, preventing side reactions between the electrolyte and the cathode active material surface and improving interfacial stability. The doping elements Al and Y in the cathode active material form stable chemical bonds in the lattice, enhancing the material's mechanical strength and inhibiting lattice collapse.

[0045] At the same time, Al and Y have stronger metallic properties than Co, which can increase the adsorption capacity of the material surface to the first additive, improve the utilization rate of the first additive, further protect the positive electrode interface, and jointly improve the stability of the battery. The lithium-ion battery of this application can further reduce the capacity decay rate, increase the cycle life, avoid excessive heat generation, and reduce the risk of thermal runaway.

[0046] In one possible embodiment, the lithium cobalt oxide further includes a doping element M, where M includes at least one of Na, Mg, Ti, Zr, Ni, Sr, W, Sc, B, Si, Sn, Tb, Nb, Sb, Se, Ce, and Te. These elements can interact with Y and Al to form a stable solid solution, thereby improving the thermal conductivity of the lithium cobalt oxide, allowing heat to be more easily transferred from the interior of the material to the exterior, reducing local heat accumulation, and thus lowering the risk of thermal runaway.

[0047] The method for testing the mass content of each doping element in lithium cobalt oxide is as follows: prepare a series of standard solutions of Y, Al, Na, Mg, Ti, Zr, Ni, Sr, W, Sc, B, Si, Sn, Tb, Nb, Sb, Se, Ce, and Te at varying concentrations, test these standard solutions using ICP, and plot a standard curve for each element. Accurately weigh a certain amount of lithium cobalt oxide sample, add strong acid, heat to completely dissolve, and transfer to a volumetric flask to a constant volume to obtain the test solution. The test sample solution is introduced into the ICP instrument, tested under the specified parameters, and the spectral intensity of each element is recorded. Based on the spectral intensities obtained, the content of each element in the sample is directly calculated from the standard curve.

[0048] In one possible embodiment, the mass content of the first additive in the electrolyte is 0.2 to 2 wt%. If the content of the first additive is greater than 2 wt%, the formed CEI is too thick, which increases the internal resistance and affects the cycle and furnace temperature performance. If the content of the first additive is less than 0.2 wt%, the interface protection is insufficient, and it is difficult to achieve the improvement of the cycle performance and furnace temperature performance. The mass content of the first additive in the electrolyte is in the range of 0.2 to 2 wt%, which can increase the cycle life while reducing the internal resistance and reducing the risk of thermal runaway. Exemplary, it can be 0.2 wt%, 0.3 wt%, 0.5 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt% or 2 wt%. In one possible embodiment, the first additive includes One or more of;

[0049] wherein R2 is selected from -(CH2) n - and -O-, n is a natural number of 0 to 3, R3 is selected from at least one of -CH2- or -O-, and R4 is selected from C2 to C4 unsaturated alkanes; illustratively, n can be 0, 1, 2 or 3;

[0050] m is 0 or 1, and R5 is selected from C2-C4 unsaturated alkanes.

[0051] Optional, Selected from At least one of;

[0052] Optional, Selected from At least one of .

[0053] In one possible embodiment, the electrolyte further includes a second additive containing a phosphorus-oxygen double bond and a cyanide group, and the mass content of the second additive in the electrolyte is 0.1 to 6 wt%. The second additive can be adsorbed to further improve the stability of the positive electrode. The second additive also contains a phosphorus-oxygen double bond, and the unsaturated bond in the first additive and the phosphorus-oxygen double bond of the second additive interact through π-π to synergistically form an interface film with a two-dimensional network structure, thereby promoting the adsorption of nitrogen atoms on the active sites on the positive electrode surface, thereby further reducing the attenuation of the battery capacity and improving the thermal stability of the battery. Exemplarily, the mass content of the second additive in the electrolyte can be 0.1 wt%, 0.3 wt%, 0.5 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt% or 6 wt%.

[0054] In one possible embodiment, the structure of the second additive is

[0055] R6, R7, and R8 are independently selected from at least one of -CH2- and -O-, R9, R 10 、R 11 are independently selected from substituted or unsubstituted C1 to C4 alkyl groups, and R9, R 10 、R 11 At least one of them is a C1-C4 alkyl group substituted with a cyano group;

[0056] Optionally, the second additive includes (diethyl cyanophosphate), (tris(2-cyanoethyl)phosphate), At least one of .

[0057] In one possible embodiment, the electrolyte further includes a third additive containing both an ether bond and a cyano group, and the mass content of the third additive in the electrolyte is 0.2 to 5 wt%. The third additive containing an ether bond can decompose under high voltage to form a CEI film. The third additive interacts with the first additive through hydrogen bonds, thereby improving the stability of the CEI film, further inhibiting the dissolution of Co ions, and improving battery performance. The mass content of the third additive in the electrolyte is in the range of 0.2 to 5 wt%, which can improve the positive electrode interface stability and optimize the battery's cycle, rate, and safety performance. Exemplarily, the mass content of the third additive in the electrolyte can be 0.2 wt%, 0.3 wt%, 0.5 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt% or 5 wt%.

[0058] Optionally, the third additive includes at least one of ethylene glycol bis(propionitrile) ether, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,3,4-tetrakis(2-cyanoethoxy)butane, tetrakis(2-cyanoethoxymethyl)methane, and 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane.

[0059] In one possible embodiment, the electrolyte further includes a fourth additive containing boron. The introduction of the first additive to form a CEI film will cause the battery interface impedance to increase. The fourth additive containing boron can complex with the anions in the electrolyte, reduce the decomposition of lithium salts to generate other components such as lithium carbonate and lithium fluoride, and thus reduce the increase in battery interface impedance. The mass content of the fourth additive in the electrolyte is 0.01 to 2 wt%. If the content of the fourth additive is too low, it is difficult to achieve the optimization effect. If the content is too high, the fourth additive may form a poor quality SEI film at the negative electrode, deteriorating the negative electrode interface. Exemplary, it can be 0.01 wt%, 0.03 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt% or 2 wt%.

[0060] In a possible embodiment, the fourth additive includes a boron-containing lithium salt. Optionally, the boron-containing lithium salt includes at least one of lithium tetrafluoroborate, lithium bis(oxalatoborate), and lithium difluorooxalatoborate.

[0061] In one possible embodiment, the electrolyte further includes a fluorinated solvent, the mass content of which in the electrolyte is 10 to 65 wt%. Due to the high electron-withdrawing tendency of the -F group, the fluorinated solvent can resist high-voltage oxidation, thereby increasing the high-voltage stability of the electrolyte, preventing the electrolyte components from undergoing side reactions at the positive electrode under high voltage, destroying the CEI film formed by the first additive, and further improving the stability of the battery under high voltage. Exemplarily, the mass content of the fluorinated solvent in the electrolyte can be 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, or 65 wt%.

[0062] Optionally, the fluorine-containing solvent includes bis(2,2,2-trifluoroethyl) carbonate, trifluoroethyl methyl carbonate, methyl difluoroacetate, ethyl difluoroacetate, methyl trifluoroacetate, ethyl trifluoroacetate, 2,2-difluoroethyl trifluoromethanesulfonate, 2,2,2-trifluoroethyl methanesulfonate, fluoroethylene carbonate, difluoroethylene carbonate, 4-trifluoromethylethylene carbonate, and perfluoropentyl-1,3-dioxolane-2-one. Wherein ethyl difluoroacetate refers to replacing two fluorine atoms at any position of ethyl acetate, preferably including at least one of 2,2-difluoroethyl acetate and 2,2-difluoroethyl acetate.

[0063] In one possible embodiment, the volume particle size distribution curve of the positive electrode active material includes a first volume distribution peak and a second volume distribution peak;

[0064] The particle size corresponding to the maximum peak intensity of the first volume distribution peak is 1 to 8 μm, and the particle size corresponding to the maximum peak intensity of the second volume distribution peak is 10 to 25 μm. For example, the particle size corresponding to the maximum peak intensity of the first volume distribution peak may be 1, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, or 8 μm; the particle size corresponding to the maximum peak intensity of the second volume distribution peak may be 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 20 μm, 22 μm, or 25 μm.

[0065] Volume particle size distribution curve of positive electrode active material: soak the positive electrode sheet in DMC for more than 3 hours to remove attached substances, and then dry it in a drying room; put the dried positive electrode sheet into a crucible, put it into a muffle furnace, raise the temperature from room temperature to 400℃ at 5℃ / min, keep it warm for 3 hours, and then cool it to room temperature; take out the calcined positive electrode sheet, use a brush to brush off the substances on the positive electrode current collector, and then test it with a laser particle size analyzer.

[0066] In this application, the positive electrode active material is graded with large and small particles. Large particles can form a dense packing, and small particles can fill the gaps between large particles, making the material more dense as a whole. This can reduce stress concentration and structural damage in the electrode during charge and discharge, maintain the integrity of the electrode structure, and thus extend the cycle life of the battery. The close packing of large and small particles can reduce internal voids and prevent a large amount of the first additive from entering the particles and forming an excessively thick CEI.

[0067] In one possible embodiment, the compaction density of the positive electrode active layer is 3.5 to 5.5 g / cm 3 For example, it can be 3.5g / cm 3 , 4g / cm 3 , 4.5g / cm 3 , 5g / cm 3 or 5.5g / cm 3 .

[0068] Example

[0069] This embodiment provides a lithium-ion battery, the preparation method of which includes:

[0070] (1) Preparation of positive electrode sheet:

[0071] Lithium cobalt oxide, binder polyvinylidene fluoride (PVDF 520), and conductive carbon material (Super P: carbon nanotube mass ratio = 1:1) were mixed in N-methylpyrrolidone (NMP) solvent at a weight ratio of 97.5:1.3:1.2. The mixture was stirred continuously in a blender to form a uniform positive electrode slurry. The slurry was then coated onto 10μm-thick aluminum foil and dried in a 120°C vacuum oven for 6 hours. The resulting positive electrode sheets were then rolled and slit.

[0072] (2) Preparation of negative electrode sheet:

[0073] A mixture of 97.5wt% graphite, 1.3wt% sodium carboxymethyl cellulose (CMC) binder, and 1.2wt% styrene-butadiene rubber (SBR) binder is mixed in water and continuously stirred in a blender to form a uniform, fluid negative electrode slurry. The slurry is then coated on a 10μm-thick copper foil current collector and dried in a 120°C vacuum oven for 6 hours. The resulting negative electrode sheets are then rolled and slit.

[0074] (3) Preparation of electrolyte:

[0075] In an argon-filled glove box (moisture <1 ppm, oxygen <1 ppm), a fluorinated solvent (with a mixed solution of propyl propionate, propylene carbonate, and ethylene carbonate (mass ratio 35:15:15)) was mixed into a uniform solvent. LiPF6 accounting for 15 wt% of the total mass of the electrolyte was slowly added to the above solvent, and various additives were added according to Table 2. After stirring evenly, the desired lithium-ion battery electrolyte was obtained.

[0076] (4) Preparation of diaphragm:

[0077] A 1.5 μm thick boehmite layer was coated on one side of a 7 μm polyethylene substrate, and then a 1 μm thick polyvinylidene fluoride adhesive layer was coated on both sides.

[0078] (5) Preparation of lithium-ion batteries:

[0079] After the prepared positive electrode sheet, separator and negative electrode sheet are wound to prepare a bare cell, the bare cell is placed in an aluminum-plastic film package, and the prepared electrolyte is injected into the dried bare cell. After vacuum packaging, room temperature standing, high-temperature formation and other processes, the required lithium-ion battery is obtained.

[0080] The electrolyte of Example 1 includes a first additive 0.5wt%, no fluorinated solvent was added. The volume particle size distribution curve of the positive electrode active material is shown in Figure 1As shown, it includes a first volume distribution peak and a second volume distribution peak; the particle size corresponding to the maximum peak intensity of the first volume distribution peak is 5.3 μm, the particle size corresponding to the maximum peak intensity of the second volume distribution peak is 15.8 μm, and the compaction density of the positive electrode active layer is 4.22 g / cm 3 .

[0081] Examples 2 to 6 are basically the same as Example 1, except that the content or type of doping elements in lithium cobalt oxide is different, see Table 1 for details.

[0082] Table 1

[0083]

[0084] Example 8 and Example 9 are basically the same as Example 1, except that the mass content of the first additive in the electrolyte is 0.2 wt % and 2 wt %, respectively.

[0085] Example 10 and Example 11 are basically the same as Example 1, except that the types of the first additive are

[0086] Comparative Example 1 is substantially the same as Example 1, except that the first additive is not added to the electrolyte.

[0087] Comparative Example 2 is substantially the same as Example 1, except that the doping element in the lithium cobalt oxide does not contain Y.

[0088] Comparative Example 3 is substantially the same as Example 1, except that the doping element in the lithium cobalt oxide does not contain Al.

[0089] Example 12 is basically the same as Example 1, except that the electrolyte further includes a second additive. 0.1wt%.

[0090] Example 13 and Example 14 are basically the same as Example 12, except that the mass content of the second additive in the electrolyte is 3 wt % and 6 wt %, respectively.

[0091] Example 15 and Example 16 are basically the same as Example 13, except that the types of the second additives are

[0092] Examples 17 to 31 are substantially the same as Example 13, except that they further include other additives and / or solvents, as detailed in Table 2.

[0093] Table 2

[0094]

[0095]

[0096] Example 32 is basically the same as Example 1, except that the electrolyte further includes a third additive 1,2,3,4,5-penta(2-cyanoethoxy)pentane 2.5 wt%.

[0097] Example 33 is basically the same as Example 1, except that the electrolyte further includes a fourth additive, lithium tetrafluoroborate, 1 wt%.

[0098] Example 34 is basically the same as Example 1, except that the electrolyte further includes 35 wt% of fluorine-containing solvent 2,2-difluoroethyl acetate.

[0099] Test Method

[0100] The electrochemical performance of the lithium-ion batteries obtained in the above comparative examples and embodiments was tested, as shown below:

[0101] (1) Cyclic stability test

[0102] The batteries obtained in the above examples and comparative examples were placed at an ambient temperature of (25±2)°C, charged to 4.53V at a constant current density of 1.3C, and discharged to 3.0V at a constant current density of 0.5C. The discharge capacity was recorded as the initial capacity Q0, and the discharge capacity Q1 when the cycle reached 500 cycles was obtained. The capacity retention rate (Q1 / Q0) was obtained, and the calculation results are recorded in Table 3.

[0103] (2) Furnace temperature test

[0104] The batteries prepared in the examples and comparative examples were placed in an ambient temperature of (25±2)°C and charged at 1.3C to an upper limit voltage of 4.53V and a cutoff current of 0.05C. The batteries were then placed in a 130°C hot box, heated to 130°C at a rate of 5°C / min±2°C / min, and maintained for 60 minutes. The battery passed the test if it did not smoke, catch fire, or explode. The results are recorded in Table 3.

[0105] (3) Rate experiment

[0106] The batteries obtained in the above examples and comparative examples were placed at an ambient temperature of (25±2)°C and charged to 4.53V at a current density of 1.3C. They were then discharged to 3.0V at a current density of 0.5C. The discharge capacity was recorded as the initial capacity Q2. After 5 minutes of rest, the batteries were fully charged according to the above charging procedure again and discharged to 3V at a rate of 5C. The discharge capacity Q3 was recorded to obtain the capacity retention ratio (Q3 / Q2). The results are recorded in Table 3.

[0107] Table 3 Lithium-ion battery performance

[0108]

[0109]

[0110] As can be seen from Table 3, the cycle capacity retention rate and rate performance of the battery of the present application are significantly improved, and the high-temperature safety performance is also significantly improved.

[0111] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer, wherein the positive electrode active layer comprises a positive electrode active material, characterized in that: The positive electrode active material includes lithium cobalt oxide, and the lithium cobalt oxide includes doping elements Al and Y. The mass content of Y is A based on the mass of the lithium cobalt oxide, and A=200-1000 ppm; Based on the mass of lithium cobalt oxide, the mass content of Al is B, B = 4000 to 15000 ppm; The electrolyte includes a first additive Wherein, R1 includes alkenyl and / or alkynyl.

2. The lithium-ion battery according to claim 1, characterized in that The mass content of the first additive in the electrolyte is 0.2 to 2 wt%; and / or The lithium cobalt oxide further includes a doping element M, where M includes at least one of Na, Mg, Ti, Zr, Ni, Sr, W, Sc, B, Si, Sn, Tb, Nb, Sb, Se, Ce, and Te.

3. The lithium-ion battery according to claim 2, wherein The first additive includes One or more of; wherein R2 is selected from -(CH2) n - and -O- at least one, n is a natural number of 0 to 3, R3 is selected from at least one of -CH2- or -O-, and R4 is selected from C2 to C4 unsaturated alkanes; m is 0 or 1, R5 is selected from C2-C4 unsaturated alkanes; Optional, Selected from At least one of; Optional, Selected from At least one of .

4. The lithium-ion battery according to any one of claims 1 to 3, wherein: The electrolyte further includes a second additive containing a phosphorus-oxygen double bond and a cyano group, and the mass content of the second additive in the electrolyte is 0.1 to 6 wt %.

5. The lithium-ion battery according to claim 4, characterized in that The structure of the second additive is R6, R7, and R8 are independently selected from at least one of -CH2- and -O-, R9, R 10 、R 11 are independently selected from substituted or unsubstituted C1 to C4 alkyl groups, and R9, R 10 、R 11 At least one of them is a C1-C4 alkyl group substituted with a cyano group; Optionally, the second additive includes At least one of .

6. The lithium-ion battery according to any one of claims 1 to 3, characterized in that: The electrolyte further comprises a third additive containing both an ether bond and a cyano group, wherein the mass content of the third additive in the electrolyte is 0.2 to 5 wt %; Optionally, the third additive includes at least one of ethylene glycol bis(propionitrile) ether, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,3,4-tetrakis(2-cyanoethoxy)butane, tetrakis(2-cyanoethoxymethyl)methane, 1,2,3,4,5,6-hexa(2-cyanoethoxy)hexane, and 1,2,3,4,5-penta(2-cyanoethoxy)pentane.

7. The lithium-ion battery according to any one of claims 1 to 3, characterized in that: The electrolyte further comprises a fourth additive containing boron, wherein the mass content of the fourth additive in the electrolyte is 0.01 to 2 wt %; Optionally, the fourth additive includes at least one of lithium tetrafluoroborate, lithium bis(oxalatoborate), and lithium difluorooxalatoborate.

8. The lithium-ion battery according to any one of claims 1 to 3, characterized in that: The electrolyte further comprises a fluorine-containing solvent, wherein the mass content of the fluorine-containing solvent in the electrolyte is 10 to 65 wt %; Optionally, the fluorine-containing solvent includes at least one of bis(2,2,2-trifluoroethyl) carbonate, trifluoroethyl methyl carbonate, methyl difluoroacetate, ethyl difluoroacetate, methyl trifluoroacetate, ethyl trifluoroacetate, 2,2-difluoroethyl trifluoromethanesulfonate, 2,2,2-trifluoroethyl methanesulfonate, fluoroethylene carbonate, difluoroethylene carbonate, 4-trifluoromethylethylene carbonate, perfluoropentyl-1,3-dioxolane-2-one, monofluorobenzene, p-difluorobenzene, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) carbonate, perfluoroheptyl ether, bis(2,2,2-trifluoroethyl) ether, and perfluorohexyl methyl ether.

9. The lithium-ion battery according to any one of claims 1 to 3, characterized in that: The volume particle size distribution curve of the positive electrode active material includes a first volume distribution peak and a second volume distribution peak; The particle size corresponding to the maximum peak intensity of the first volume distribution peak is 1 to 8 μm, and the particle size corresponding to the maximum peak intensity of the second volume distribution peak is 10 to 25 μm.

10. The lithium-ion battery according to claim 9, characterized in that The compaction density of the positive electrode active layer is 3.5 to 5.5 g / cm 3 .

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