A lithium-ion battery

Abstract

To overcome the problems of insufficient battery cycle performance and safety performance in existing high-voltage lithium cobalt oxide batteries with silicon-doped negative electrodes, the present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. The non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte salt, and an additive. The non-aqueous organic solvent comprises 2,2-difluoroethyl acetate. The additive comprises a first additive and a second additive. The first additive comprises a sulfur-containing additive represented by structural formula 1: #imgabs0# Structural formula 1, and the second additive comprises a nitrile compound. The lithium-ion battery satisfies the following conditions: #imgabs1#, and 0.1≤a≤3, 0.5≤b≤5, 1≤c≤40, 0.2≤d≤7, and 5≤e≤30. The lithium-ion battery provided by the present invention can achieve both excellent high-temperature cycle stability and good thermal shock resistance and safety performance.

Description

Technical Field

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

[0002] Lithium-ion batteries, with their advantages of high operating voltage, wide operating temperature range, high energy and power density, no memory effect, and long cycle life, have been widely used in 3C digital products such as mobile phones and laptops, as well as in new energy vehicles. In recent years, with the continuous development of lightweight and thin 3C digital products, the battery industry has increasingly demanded higher energy density in lithium-ion batteries. At the same time, for user considerations, good safety performance has become a basic requirement for batteries.

[0003] In terms of the positive electrode, lithium cobalt oxide has a higher volumetric energy density among many positive electrode materials, and also has good rate performance. However, as the battery voltage gradually increases, lithium cobalt oxide enters a higher delithiation state, and the material structure stability deteriorates. The Co in the positive electrode is prone to disproportionation reaction and dissolves in the electrolyte in the form of ions, causing damage to the positive electrode structure and the risk of thermal runaway under high temperature and high pressure. In addition, the dissolved Co migrates to the negative electrode interface, undergoing ion exchange with the lithium in the negative electrode, occupying the negative electrode lithium insertion position, resulting in a decrease in the negative electrode's lithium storage capacity and a deterioration in various battery performances, specifically manifested as: battery gassing, rapid increase in internal resistance, and a sharp decrease in capacity. Battery gassing will lead to increased internal pressure, and further development may develop into dangerous situations such as battery explosion and combustion. Therefore, high-voltage batteries need to be matched with electrolytes with better safety performance.

[0004] Regarding the negative electrode, silicon-doping graphite anodes has become a common practice in the industry to increase energy density. This boosts battery energy density, allowing for larger capacity within the same volume. For example, cells with capacities of 5000mAh or higher have become standard in flagship smartphones. However, due to their large capacity, these larger cells experience high temperature rise during fast charging and high-rate discharge, posing safety challenges.

[0005] Therefore, when using a battery system with high-voltage lithium cobalt oxide and a silicon-doped negative electrode, how to balance battery cycle performance and safety performance is currently a difficult problem in the industry. Summary of the Invention

[0006] Aiming at the problem that existing high-voltage lithium cobalt oxide batteries with silicon-doped negative electrodes have insufficient battery cycle performance and safety performance, the present invention provides a lithium-ion battery.

[0007] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0008] The present invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the separator is located between the positive electrode and the negative electrode, the positive electrode comprising a positive electrode material layer containing a positive electrode active material, the positive electrode active material comprising lithium cobalt oxide or lithium cobalt oxide modified by doping and / or coating with any one or more elements selected from the group consisting of Ni, Mg, Al, Zr, W, F, B, Cr, Mo, and rare earth elements, the negative electrode comprising a negative electrode material layer comprising a silicon-based material, the separator comprising a base film and a ceramic coating disposed on at least one side of the base film, the non-aqueous electrolyte comprising a non-aqueous organic solvent, an electrolyte salt, and an additive, the non-aqueous organic solvent comprising 2,2-difluoroethyl acetate, the additive comprising a first additive and a second additive, the first additive comprising a sulfur-containing additive represented by structural formula 1:

[0009] ;

[0010] wherein n is 0 or 1, A is selected from C or O, and X is selected from or , R1, R2 are each independently selected from H, or , R1 and R2 are not simultaneously selected from H, and X, R1 and R2 contain at least one sulfur atom;

[0011] The second additive includes a nitrile compound;

[0012] The lithium-ion battery meets the following conditions:

[0013] 0.2≤ ≤33, and 0.1≤a≤3, 0.5≤b≤5, 1≤c≤40, 0.2≤d≤7, 5≤e≤30;

[0014] Wherein, a is the mass percentage of the first additive in the non-aqueous electrolyte, and the unit is %;

[0015] b is the mass percentage of the second additive in the non-aqueous electrolyte, unit is %;

[0016] c is the mass percentage of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, unit is %;

[0017] d is the thickness of the ceramic coating, in μm;

[0018] e is the mass percentage of silicon element in the negative electrode material layer, in %.

[0019] Optionally, the lithium-ion battery meets the following conditions:

[0020] 0.6≤ ≤14.

[0021] Optionally, the lithium-ion battery meets at least one of the following conditions:

[0022] (1) The mass percentage a of the first additive in the non-aqueous electrolyte is 0.5% to 2%;

[0023] (2) The mass percentage content b of the second additive in the non-aqueous electrolyte is 1% to 4%;

[0024] (3) The mass percentage c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte is 3% to 40%;

[0025] (4) The thickness d of the ceramic coating is 0.3-4 μm;

[0026] (5) The mass percentage e of silicon element in the negative electrode material layer is 10% to 30%;

[0027] (6) 0.6≤ ≤14.

[0028] Optionally, the sulfur-containing additive shown in Structural Formula 1 includes at least one of the following compounds:

[0029] .

[0030] Optionally, the second additive includes one or more of succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,4-dicyano-2-butene or 1,2,3-tris(2-cyanoethoxy)propane.

[0031] Optionally, the non-aqueous organic solvent further comprises a non-fluorinated carboxylate;

[0032] The non-aqueous electrolyte satisfies the following conditions:

[0033] 0.5≤c / f≤2;

[0034] Wherein, c is the mass percentage of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, unit is %;

[0035] f is the mass percentage of non-fluorinated carboxylic acid ester in the non-aqueous electrolyte, in %.

[0036] Optionally, the mass percentage f% of the non-fluorinated carboxylic acid ester in the non-aqueous electrolyte is 10% to 30%; and / or,

[0037] 13≤c+f≤45.

[0038] Optionally, the non-fluorinated carboxylic acid ester includes one or more of ethyl acetate, methyl acetate, methyl propionate, propyl propionate or ethyl propionate.

[0039] Optionally, the ceramic coating includes ceramic particles, and the ceramic particles include one or more of aluminum oxide, boehmite, silicon dioxide, zirconium dioxide, barium sulfate, magnesium hydroxide, fluorapatite, fluorphlogopite, mullite, aluminum titanate, copper oxide, titanium dioxide, and zinc oxide.

[0040] Optionally, the negative electrode material layer includes a negative electrode active material, and the silicon-based material includes one or more of silicon element, silicon oxide, silicon-carbon composite material and silicon alloy material.

[0041] Optionally, the charging cut-off voltage of the lithium-ion battery is ≥4.45V.

[0042] According to the lithium-ion battery provided by the present invention, lithium cobalt oxide is used as the positive electrode, and silicon is doped in the negative electrode, so that the battery has a higher volume energy density. In order to solve the safety performance problems caused by lithium cobalt oxide and silicon, the inventors adapted and adjusted the non-aqueous electrolyte and found that when the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive in the non-aqueous electrolyte, the mass percentage c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, the thickness d of the ceramic coating, and the mass percentage e of the silicon element in the negative electrode material layer meet the conditions of 0.2≤ When ≤33, and 0.1≤a≤3, 0.5≤b≤5, 1≤c≤40, 0.2≤d≤7, and 5≤e≤30, the obtained lithium-ion battery can have both excellent high-temperature cycle stability and good thermal shock resistance safety performance while having a higher energy density. It is speculated that the thickness of the ceramic coating provided on the surface of the diaphragm can improve the safety of the battery, but it will also lead to a decrease in the ion conduction efficiency. In the battery formation stage, the first additive, the second additive and 2,2-difluoroethyl acetate jointly participate in the formation of the solid electrolyte interface film on the surface of the positive and negative electrodes. By regulating the content of the three, a solid electrolyte interface film with low impedance, high ion conduction efficiency and high high-temperature stability can be formed. By adapting the solid electrolyte interface film and the ceramic coating, the high-temperature stability and safety of the battery can be improved without significantly increasing the impedance. Furthermore, the content of silicon in the negative electrode material layer will affect the volume change of the negative electrode during charging and discharging, leading to the rupture of the solid electrolyte interface film. Therefore, the relative contents of the first additive, the second additive and 2,2-difluoroethyl acetate need to be adjusted according to different silicon contents to obtain a solid electrolyte interface film suitable for the corresponding negative electrode, and finally obtain a lithium-ion battery with high energy density, excellent high-temperature cycle performance and high-temperature safety performance. DETAILED DESCRIPTION

[0043] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0044] An embodiment of the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the separator is located between the positive electrode and the negative electrode, the positive electrode comprising a positive electrode material layer containing a positive electrode active material, the positive electrode active material comprising lithium cobalt oxide or lithium cobalt oxide modified by doping and / or coating with any one or more elements selected from Ni, Mg, Al, Zr, W, F, B, Cr, Mo, and rare earth elements, the negative electrode comprising a negative electrode material layer comprising a silicon-based material, the separator comprising a base film and a ceramic coating disposed on at least one side of the base film, the non-aqueous electrolyte comprising a non-aqueous organic solvent, an electrolyte salt, and an additive, the non-aqueous organic solvent comprising 2,2-difluoroethyl acetate, the additive comprising a first additive and a second additive, the first additive comprising a sulfur-containing additive represented by structural formula 1:

[0045] ;

[0046] wherein n is 0 or 1, A is selected from C or O, and X is selected from or , R1, R2 are each independently selected from H, or , R1 and R2 are not simultaneously selected from H, and X, R1 and R2 contain at least one sulfur atom;

[0047] The second additive includes a nitrile compound;

[0048] The lithium-ion battery meets the following conditions:

[0049] 0.2≤ ≤33, and 0.1≤a≤3, 0.5≤b≤5, 1≤c≤40, 0.2≤d≤7, 5≤e≤30;

[0050] Wherein, a is the mass percentage of the first additive in the non-aqueous electrolyte, and the unit is %;

[0051] b is the mass percentage of the second additive in the non-aqueous electrolyte, unit is %;

[0052] c is the mass percentage of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, unit is %;

[0053] d is the thickness of the ceramic coating, in μm;

[0054] e is the mass percentage of silicon element in the negative electrode material layer, in %.

[0055] In order to solve the safety performance problems caused by lithium cobalt oxide and silicon, the inventors adapted and adjusted the non-aqueous electrolyte and found that when the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive in the non-aqueous electrolyte, the mass percentage c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, the thickness d of the ceramic coating and the mass percentage e of the silicon element in the negative electrode material layer meet the conditions 0.2≤ When ≤33, and 0.1≤a≤3, 0.5≤b≤5, 1≤c≤40, 0.2≤d≤7, and 5≤e≤30, the obtained lithium-ion battery can have both excellent high-temperature cycle stability and good thermal shock resistance safety performance while having a higher energy density. It is speculated that the thickness of the ceramic coating provided on the surface of the diaphragm can improve the safety of the battery, but it will also lead to a decrease in the ion conduction efficiency. In the battery formation stage, the first additive, the second additive and 2,2-difluoroethyl acetate jointly participate in the formation of the solid electrolyte interface film on the surface of the positive and negative electrodes. By regulating the content of the three, a solid electrolyte interface film with low impedance, high ion conduction efficiency and high high-temperature stability can be formed. By adapting the solid electrolyte interface film and the ceramic coating, the high-temperature stability and safety of the battery can be improved without significantly increasing the impedance. Furthermore, the content of silicon in the negative electrode material layer will affect the volume change of the negative electrode during charging and discharging, leading to the rupture of the solid electrolyte interface film. Therefore, the relative contents of the first additive, the second additive and 2,2-difluoroethyl acetate need to be adjusted according to different silicon contents to obtain a solid electrolyte interface film suitable for the corresponding negative electrode, and finally obtain a lithium-ion battery with high energy density, excellent high-temperature cycle performance and high-temperature safety performance.

[0056] In some embodiments, in the sulfur-containing additive shown in structural formula 1, R1 and R2 are each independently selected from or , and X, R1 and R2 contain at least one sulfur atom.

[0057] When the sulfur-containing additive shown in Structural Formula 1 meets the above conditions, the sulfur-containing additive shown in Structural Formula 1 has a three-ring structure. Compared with the two-ring structure, the three-ring structure is open and participates in the formation of the interface film on the electrode surface, which has the effect of improving the strength of the interface film structure, thereby helping to improve its high-temperature stability.

[0058] As an example, the sulfur-containing additive represented by Structural Formula 1 is selected from one or more of the following compounds:

[0059] .

[0060] In some embodiments, in the sulfur-containing additive represented by Structural Formula 1, X, R1, and R2 do not contain sulfur atoms at the same time.

[0061] When the sulfur-containing additive shown in Structural Formula 1 meets the above conditions, the sulfur-containing additive shown in Structural Formula 1 has a tricyclic structure, and the sulfur-containing additive shown in Structural Formula 1 includes both a sulfur-containing cyclic structure and a carbonate-containing cyclic structure, wherein the carbonate cyclic structure is conducive to the formation of a lithium carbonate component in the electrode interface film. Compared with simple sulfur-containing decomposition products, the interface film component formed by the carbonate cyclic structure and the sulfur-containing cyclic structure is more stable and dense.

[0062] In some embodiments, in the sulfur-containing additive shown in structural formula 1, R1 is selected from H, X is selected from , R2 is selected from ;or,

[0063] R1 is selected from H, X is selected from , R2 is selected from or .

[0064] When the sulfur-containing additive shown in Structural Formula 1 meets the above conditions, the sulfur-containing additive shown in Structural Formula 1 has a bicyclic structure, and the sulfur-containing additive shown in Structural Formula 1 includes both a sulfur-containing cyclic structure and a carbonate-containing cyclic structure. Compared with simple sulfur-containing decomposition products, the interfacial film component formed by the carbonate cyclic structure and the sulfur-containing cyclic structure is more stable and dense.

[0065] In some embodiments, when lithium cobalt oxide is coated and modified with any one or more elements selected from Ni, Mg, Al, Zr, W, F, B, Cr, Mo and rare earth elements, the coating is performed with oxides of one or more of these elements.

[0066] In a preferred embodiment, the lithium-ion battery meets the following conditions:

[0067] 0.6≤ ≤14.

[0068] When the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive in the non-aqueous electrolyte, the mass percentage c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, the thickness d of the ceramic coating, and the mass percentage e of the silicon element in the negative electrode material layer further meet the above conditions, it is beneficial to further improve the high-temperature cycle life and thermal shock resistance safety performance of the lithium-ion battery.

[0069] In a specific embodiment, the mass percentage a of the first additive in the non-aqueous electrolyte can be 0.10%, 0.25%, 0.41%, 0.56%, 0.71%, 0.86%, 1.02%, 1.17%, 1.32%, 1.47%, 1.63%, 1.78%, 1.93%, 2.08%, 2.24%, 2.39%, 2.54%, 2.69%, 2.85%, 3.00% or a range therebetween.

[0070] In a preferred embodiment, the mass percentage a of the first additive in the non-aqueous electrolyte is 0.5% to 2%.

[0071] The first additive can decompose on the surface of the positive and negative electrodes and construct a solid electrolyte interface film. The solid electrolyte interface film can effectively isolate the positive and negative electrodes from the non-aqueous electrolyte, reduce the side reactions of the non-aqueous electrolyte at the positive and negative electrode interfaces under high temperature and high voltage conditions, and improve its high-temperature stability. If the mass percentage a of the first additive is too small, it is difficult to generate a complete solid electrolyte interface film, resulting in a decrease in the high-temperature stability of the non-aqueous electrolyte; if the mass percentage a of the first additive is too high, the thickness of the generated solid electrolyte interface film will be larger, resulting in a significant increase in the interface impedance, affecting the battery rate performance, and generating more Joule heat during the charge and discharge process, further threatening the safety and stability of the battery.

[0072] In a specific embodiment, the mass percentage b of the second additive in the non-aqueous electrolyte can be 0.50%, 0.56%, 0.71%, 0.86%, 1.02%, 1.17%, 1.32%, 1.47%, 1.63%, 1.78%, 1.93%, 2.08%, 2.24%, 2.39%, 2.54%, 2.69%, 2.85%, 3.00%, 3.50%, 4.00%, 4.50%, 5.00% or a range therebetween.

[0073] In a preferred embodiment, the mass percentage b of the second additive in the non-aqueous electrolyte is 1% to 4%.

[0074] The second additive plays an important role in the battery system. On the one hand, it can effectively stabilize the positive electrode interface, significantly improve the thermal safety performance of the battery, and reduce the risk of thermal runaway of the battery under harsh working conditions such as high temperature. On the other hand, it will also affect the composition of the negative electrode solid electrolyte interface membrane, and by adjusting the composition of the solid electrolyte interface membrane, it can potentially affect the charge and discharge performance of the battery. When the content of the second additive is too low, it is difficult to fully exert the effect of stabilizing the positive electrode interface, the improvement of the thermal safety performance of the battery is not obvious, and the tolerance to high temperature environment is poor. When the content of the second additive is too high, the battery impedance will increase significantly. At the same time, due to the high reactivity of the cyanide group in the second additive, it is not conducive to improving the high temperature stability of the non-aqueous electrolyte.

[0075] In a specific embodiment, the mass percentage c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte can be 1.0%, 2.9%, 4.9%, 6.8%, 8.8%, 10.7%, 12.7%, 14.6%, 16.6%, 18.5%, 20.5%, 22.4%, 24.4%, 26.3%, 28.3%, 30.2%, 32.2%, 34.1%, 36.1%, 38.0%, 40.0% or a range therebetween.

[0076] In a preferred embodiment, the mass percentage c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte is 3% to 40%.

[0077] The 2,2-difluoroethyl acetate also participates in the formation of the solid electrolyte interface film during the battery formation stage. At the same time, compared to other non-aqueous organic solvents, 2,2-difluoroethyl acetate has higher high-temperature and high-voltage stability, reducing the side reactions of non-aqueous organic solvents at the positive and negative electrode interfaces under high-voltage conditions, thereby improving fast-charge cycle performance. When the content of the 2,2-difluoroethyl acetate is too low, the high-temperature and high-voltage stability of the non-aqueous electrolyte will decrease. During high-temperature cycling, the non-aqueous electrolyte will decompose and produce gas due to side reactions, resulting in capacity reduction and battery expansion. When the content of the 2,2-difluoroethyl acetate is too high, it will affect the content of the components derived from the first additive and the second additive in the solid electrolyte interface film, affecting the high-temperature stability of the solid electrolyte interface film.

[0078] In a specific embodiment, the thickness d of the ceramic coating can be 0.2μm, 0.5μm, 0.8μm, 1μm, 1.2μm, 1.4μm, 1.7μm, 2μm, 2.2μm, 2.4μm, 2.7μm, 3μm, 3.2μm, 3.4μm, 3.7μm, 4μm, 4.2μm, 4.4μm, 4.7μm, 5μm, 5.4μm, 5.8μm, 6μm, 6.4μm, 6.8μm, 7μm or a range therebetween.

[0079] In a preferred embodiment, the thickness d of the ceramic coating is 0.3-4 μm.

[0080] The ceramic coating can improve the heat resistance and mechanical properties of the diaphragm. On the one hand, it avoids the short circuit of the positive and negative electrodes caused by the shrinkage of the diaphragm under high temperature conditions, and on the other hand, it avoids the problem of the generated lithium dendrites piercing the diaphragm. If the thickness of the ceramic coating is too low, it is difficult to achieve better heat resistance and anti-lithium dendrite performance. If the thickness of the ceramic coating is too high, it will lead to a decrease in the energy density of the battery, and at the same time affect the conduction of lithium ions between the positive and negative electrodes, and finally deteriorate the rapid discharge performance of the battery.

[0081] In a specific embodiment, the mass percentage e of the silicon element in the negative electrode material layer can be 5.0%, 6.3%, 7.6%, 8.9%, 10.2%, 11.5%, 12.8%, 14.1%, 15.4%, 16.7%, 18.0%, 19.3%, 20.6%, 21.9%, 23.2%, 24.5%, 25.8%, 27.1%, 28.4%, 29.7%, 30.0% or a range therebetween.

[0082] In a preferred embodiment, the mass percentage e of silicon element in the negative electrode material layer is 10% to 30%.

[0083] Compared with conventional carbon materials, silicon materials can accommodate more lithium ions. By doping silicon elements in the negative electrode material layer, the energy density of the negative electrode can be effectively improved. However, the volume change of silicon materials during the charging and discharging process is also relatively large. When the silicon content in the negative electrode material layer is too low, it is difficult to improve the energy density of the lithium-ion battery. When the silicon content in the negative electrode material layer is too high, the volume change of the negative electrode during charging and discharging is too large, resulting in frequent rupture and recombination of the solid electrolyte interface film on the electrode surface, leading to the consumption of active lithium, increased impedance, and a lower cycle life of the battery.

[0084] In some embodiments, the second additive includes one or more of succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,4-dicyano-2-butene, or 1,2,3-tris(2-cyanoethoxy)propane.

[0085] In some embodiments, the additive further includes a third additive, and the third additive includes at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, a phosphate compound, and a borate compound;

[0086] Preferably, based on the total mass of the non-aqueous electrolyte being 100%, the content of the third additive is 0.01% to 30%.

[0087] In some embodiments, the cyclic sulfate compound is selected from vinyl sulfate, propylene sulfate, methyl vinyl sulfate, At least one of;

[0088] The sultone compound is selected from at least one of 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone;

[0089] The cyclic carbonate compound is selected from at least one of vinylene carbonate, ethylene carbonate, methylene carbonate, fluoroethylene carbonate or the compound shown in structural formula 2.

[0090] ;

[0091] In the structural formula 2, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 Each is independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group;

[0092] The phosphate compound includes at least one of the compounds shown in structural formula 3:

[0093] ;

[0094] In the structural formula 3, R 31 、R 32 、R 33 Each independently selected from C1-C5 saturated hydrocarbon group, unsaturated hydrocarbon group, halogenated hydrocarbon group, -Si(C m H 2m+1 )3, m is a natural number from 1 to 3;

[0095] In a preferred embodiment, the phosphate compound shown in the structural formula 3 may be at least one of tris(trimethylsilane)phosphate, tris(triethylsilane)phosphate, tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl-2,2,2-trifluoroethyl phosphate, dipropargyl-3,3,3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate;

[0096] The borate compound includes at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate.

[0097] In other embodiments, the additives may also include other additives that can improve battery performance: for example, additives that enhance battery safety, such as flame retardant additives such as fluorophosphates and cyclophosphazenes, or overcharge prevention additives such as tert-amylbenzene and tert-butylbenzene.

[0098] It should be noted that, unless otherwise specified, under normal circumstances, the content of any one of the optional substances in the additives in the non-aqueous electrolyte is less than 10%, preferably, the content is 0.1%-5%, and more preferably, the content is 0.1%-2%. Specifically, the content of any one of the optional substances in the additives can be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, or 10%.

[0099] In some embodiments, when the auxiliary additive is selected from fluoroethylene carbonate, the amount of the fluoroethylene carbonate added is 0.05% to 30% based on the total mass of the non-aqueous electrolyte as 100%.

[0100] In some embodiments, the non-aqueous organic solvent further comprises a non-fluorinated carboxylate;

[0101] The non-aqueous electrolyte satisfies the following conditions:

[0102] 0.5≤c / f≤2;

[0103] Wherein, c is the mass percentage of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, and the unit is %;

[0104] f is the mass percentage of non-fluorinated carboxylic acid ester in the non-aqueous electrolyte, in %.

[0105] In the battery system provided by the present invention, the additional addition of a non-fluorinated carboxylate is beneficial for reducing the viscosity of the non-aqueous electrolyte, improving the penetration of the non-aqueous electrolyte into the positive and negative electrodes, reducing the internal resistance of the battery, and compensating for the problem of increased internal resistance caused by providing a ceramic coating on the separator. However, the non-fluorinated carboxylate itself has insufficient high-temperature stability and needs to be adapted to 2,2-difluoroethyl acetate to improve its stability. Therefore, when the mass percentage c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte and the mass percentage f of the non-fluorinated carboxylate in the non-aqueous electrolyte meet the condition 0.5≤c / f≤2, it is beneficial to comprehensively consider the effects of the non-fluorinated carboxylate and 2,2-difluoroethyl acetate on the battery impedance and high-temperature stability, thereby improving the discharge performance and high-temperature performance of the lithium-ion battery.

[0106] In some embodiments, the mass percentage f% of the non-fluorinated carboxylic acid ester in the non-aqueous electrolyte is 10% to 30%.

[0107] In a preferred embodiment, the non-aqueous electrolyte satisfies the following conditions:

[0108] 13≤c+f≤45.

[0109] In the battery system provided by the present invention, when the total mass of non-fluorinated carboxylic acid ester and 2,2-difluoroethyl acetate in the non-aqueous electrolyte is less than 13%, the synergistic effect between the non-fluorinated carboxylic acid ester and 2,2-difluoroethyl acetate is difficult to achieve, and the improvement effect on the lithium-ion battery is limited; when the total mass of non-fluorinated carboxylic acid ester and 2,2-difluoroethyl acetate in the non-aqueous electrolyte is higher than 45%, it is easy to cause the high-temperature stability of the non-aqueous electrolyte to decrease, affecting the high-temperature cycle performance of the lithium-ion battery.

[0110] In some embodiments, the non-fluorinated carboxylic acid ester includes one or more of ethyl acetate, methyl acetate, methyl propionate, propyl propionate, or ethyl propionate.

[0111] In some embodiments, the non-aqueous organic solvent further comprises one or more of cyclic carbonates, linear carbonates, and ether solvents.

[0112] In some embodiments, the cyclic carbonate may be, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); the chain carbonate may be, but is not limited to, at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). The content of the cyclic carbonate is not particularly limited and may be any amount that does not significantly impair the performance of the lithium-ion battery of the present invention. However, when a single cyclic carbonate is used, its lower limit is generally 3% by volume or greater, preferably 5% by volume or greater, relative to the total volume of the non-aqueous electrolyte solvent. This range avoids a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte, facilitating the achievement of excellent high-current discharge characteristics, stability relative to the negative electrode, and cycling characteristics of the non-aqueous electrolyte battery. The upper limit is generally 90% by volume or less, preferably 85% or less, and more preferably 80% or less. By setting this scope, the oxidation / reduction tolerance of nonaqueous electrolytic solution can be improved, thus the stability during helping to improve high temperature storage.The content of linear carbonate is not particularly limited, and relative to the total amount of solvent of nonaqueous electrolytic solution, is usually more than 15% by volume, preferably more than 20% by volume, more preferably more than 25% by volume. In addition, usually volume ratio is below 90%, preferably below 85% by volume, more preferably below 80% by volume. By making the content of linear carbonate in above-mentioned scope, easily make the viscosity of nonaqueous electrolytic solution reach appropriate range, suppress the reduction of ionic conductivity, and then help make the output characteristics of nonaqueous electrolyte battery reach good scope. When using two or more linear carbonates in combination, make the total amount of linear carbonate meet above-mentioned scope.

[0113] In some embodiments, the ether solvent includes cyclic ethers or chain ethers and their fluorinated derivatives, preferably chain ethers with 3 to 10 carbon atoms and cyclic ethers with 3 to 6 carbon atoms. The cyclic ethers may be, but are not limited to, at least one of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF). The chain ethers may be, but are not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Because chain ethers have high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are particularly preferred due to their low viscosity and high ionic conductivity. The ether compound can be used alone or in any combination and ratio. There is no special restriction on the content of the ether compound, and it is arbitrary within the range that does not significantly damage the effect of the high-density lithium-ion battery of the present invention. In the non-aqueous solvent volume ratio of 100%, the volume ratio is usually 1% or more, preferably 2% or more, and more preferably 3% or more. In addition, the volume ratio is usually 30% or less, preferably 25% or less, and more preferably 20% or less. When two or more ether compounds are used in combination, the total amount of the ether compound can be made to meet the above range. When the content of the ether compound is within the above-mentioned preferred range, it is easy to ensure the improvement effect of the ionic conductivity brought about by the increase in the lithium ion dissociation degree of the chain ether and the reduction in viscosity. In addition, when the negative electrode active material is a carbon-based material, the phenomenon of co-embedding of the chain ether and lithium ions can be suppressed, so that the input and output characteristics and the charge and discharge rate characteristics can reach an appropriate range.

[0114] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass content of the non-aqueous organic solvent is 65% to 90%.

[0115] Specifically, based on the total mass of the non-aqueous electrolyte as 100%, the mass content of the non-aqueous organic solvent can be 65%, 68%, 71%, 74%, 76%, 78%, 79%, 80%, 81.5%, 82%, 84%, 85%, 86%, 87%, 89%, 90% or a range consisting of any two of these values.

[0116] In some embodiments, the electrolyte salt is selected from lithium salts, including LiPF6, LiODFP, LiODFB, LiBOB, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, Li2B 10 Cl 10 , lithium chloroborane, lithium trioxalophosphate, a lower aliphatic carboxylic acid lithium having 4 or less carbon atoms, or at least one of lithium tetraphenylborate.

[0117] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol / L to 8 mol / L. In a preferred embodiment, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 mol / L to 2.5 mol / L. Specifically, the concentration of the lithium salt in the non-aqueous electrolyte can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, or 2.5 mol / L.

[0118] In some embodiments, the ceramic coating includes ceramic particles, and the ceramic particles include one or more of aluminum oxide, boehmite, silicon dioxide, zirconium dioxide, barium sulfate, magnesium hydroxide, fluorapatite, fluorphlogopite, mullite, aluminum titanate, copper oxide, titanium dioxide, and zinc oxide.

[0119] In some embodiments, the ceramic coating further includes a binder.

[0120] In some embodiments, the binder includes acrylic resin; polyvinylidene fluoride, copolymer of vinylidene fluoride, polytetrafluoroethylene, copolymer of vinylidene fluoride-hexafluoropropylene, copolymer of tetrafluoroethylene-hexafluoropropylene, copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, copolymer of ethylene-tetrafluoroethylene, copolymer of vinylidene fluoride-tetrafluoroethylene, copolymer of vinylidene fluoride-trifluoroethylene, copolymer of vinylidene fluoride-trichloroethylene, copolymer of vinylidene fluoride-fluoroethylene, copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, thermoplastic resins such as polyethylene and polypropylene; and at least one of styrene butadiene rubber.

[0121] In some embodiments, the base film includes one or more of polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), polyimide (PI), and polyester resin (such as PET).

[0122] In some embodiments, the negative electrode material layer includes a negative electrode active material, the negative electrode active material includes a silicon-based negative electrode, and the silicon-based negative electrode includes one or more of silicon material, silicon oxide, silicon-carbon composite material, and silicon alloy material.

[0123] In some embodiments, the negative electrode further comprises a negative electrode current collector, and the negative electrode material layer covers the surface of the negative electrode current collector. The negative electrode current collector comprises an electron-conducting metal material, preferably comprising at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0124] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductor, and the negative electrode active material, the negative electrode binder and the negative electrode conductor are blended to obtain the negative electrode material layer.

[0125] The negative electrode binder includes polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, a thermoplastic resin such as polyethylene and polypropylene; an acrylic resin; and at least one of styrene butadiene rubber.

[0126] The negative electrode conductive agent includes at least one of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0127] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductor, and the positive electrode active material, the positive electrode binder and the positive electrode conductor are blended to obtain the positive electrode material layer.

[0128] The positive electrode binder includes polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, a thermoplastic resin such as polyethylene and polypropylene; an acrylic resin; and at least one of styrene butadiene rubber.

[0129] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0130] In some embodiments, the positive electrode current collector includes a metal material that can conduct electrons. Preferably, the positive electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive electrode current collector is selected from aluminum foil.

[0131] In some embodiments, the charging cut-off voltage of the lithium-ion battery is ≥4.45V, thereby achieving high energy density and expanding its application range.

[0132] The present invention is further described below with reference to the following examples.

[0133] Table 1

[0134]

[0135] Example 1

[0136] This embodiment is used to illustrate the lithium ion and preparation method disclosed in the present invention, including the following steps:

[0137] Preparation of positive electrode

[0138] The positive electrode active material LiCoO2 (hereinafter referred to as LCO), conductive carbon black and binder PVDF are dispersed in the solvent NMP and mixed evenly to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and after drying, rolling and cutting, a positive electrode sheet is obtained. The weight ratio of the positive electrode active material, conductive carbon black and binder PVDF is 96:2:2.

[0139] Preparation of negative electrode sheet

[0140] The negative electrode active material graphite, silicon material, conductive agent, CMC (sodium carboxymethyl cellulose) and SBR (styrene-butadiene rubber) were dispersed in deionized water and stirred to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on the negative electrode current collector copper foil, dried, rolled and cut to obtain a negative electrode sheet with a compaction of 1.7 g / cc. The mass percentage of silicon element in the negative electrode material layer is shown in Table 1.

[0141] Preparation of non-aqueous electrolyte

[0142] 2,2-difluoroethyl acetate, a non-fluorinated carboxylic acid ester and ethylene carbonate are mixed to obtain a non-aqueous organic solvent, wherein the selection and mass content of 2,2-difluoroethyl acetate and the non-fluorinated carboxylic acid ester are as shown in Table 1, and ethylene carbonate is used to make up the balance. 1 mol / L LiPF6 is dissolved in the above non-aqueous organic solvent, and the first additive and the second additive are added as shown in Table 1 to obtain a non-aqueous electrolyte, wherein the first additive is compound 7, the second additive is succinonitrile, and the non-fluorinated carboxylic acid ester is ethyl propionate.

[0143] Preparation of diaphragm

[0144] A polypropylene porous membrane served as the substrate layer. A ceramic coating was applied to one surface of the membrane. The ceramic coating consisted of boehmite and an acrylic binder, with boehmite accounting for 90% of the total weight of the ceramic coating. The membrane was then dried in an oven to form a heat-resistant layer, resulting in a separator. The thickness of the ceramic coating is shown in Table 1.

[0145] Preparation of lithium-ion batteries

[0146] The positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence using the lamination process, and then the top and side are sealed, the electrolyte is injected, and the battery is packaged and formed to make a soft-pack battery.

[0147] Examples 2 to 24

[0148] Examples 2 to 24 are used to illustrate the non-aqueous electrolyte for lithium ion batteries and the preparation method thereof disclosed in the present invention, and include most of the operating steps in Example 1, except that:

[0149] The selection of 2,2-difluoroethyl acetate, non-fluorinated carboxylic acid ester, first additive, second additive in the non-aqueous electrolyte and their mass percentages, and the mass percentage of silicon in the negative electrode material layer are shown in Table 1.

[0150] Comparative Examples 1 to 17

[0151] Comparative Examples 1 to 17 are used to illustrate the non-aqueous electrolyte for lithium ion batteries and the preparation method thereof disclosed in the present invention, and include most of the operating steps in Example 1, except that:

[0152] The mass percentages of 2,2-difluoroethyl acetate, non-fluorinated carboxylic acid ester, the first additive, and the second additive in the non-aqueous electrolyte, and the mass percentage of silicon in the negative electrode material layer are shown in Table 1.

[0153] Performance Testing

[0154] (1) Thermal shock test

[0155] At 25°C, place the lithium-ion battery aside for 5 minutes, charge it at a constant current rate of 1C to 4.53V, then charge it at a constant voltage until the current is less than or equal to 0.05C, and then place it aside for 5 minutes. The battery is then placed in a high-temperature box, and the temperature of the high-temperature box is set to increase from 25°C to 133°C at a heating rate of 2°C / min and kept warm for 1 hour. The battery surface temperature and battery status are monitored during the heating and holding processes. The battery passes the test if no thermal runaway problem occurs at the end of the test.

[0156] (2) High temperature cycle performance test

[0157] At 45°C, place the lithium-ion secondary battery aside for 5 minutes, charge it at a constant current rate of 1C to 4.53V, then charge it at a constant voltage until the current is less than or equal to 0.05C, then place it aside for 5 minutes, and then discharge it at a constant current rate of 1C to 3.0V. Perform 800 cycles of charge and discharge test in this manner, recording the discharge capacity of each cycle. The capacity retention rate after 800 cycles is calculated as follows:

[0158] Capacity retention rate after 800 cycles (%) = discharge capacity at the 800th cycle / discharge capacity at the 1st cycle×100%.

[0159] 1. The test results of Examples 1 to 11 and Comparative Examples 1 to 17 are entered into Table 2.

[0160] Table 2

[0161]

[0162] It can be seen from the test results of Examples 1 to 11 and Comparative Examples 1 to 17 that in a battery system using lithium cobalt oxide as the positive electrode, by regulating the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive in the non-aqueous electrolyte, the mass percentage c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, the thickness d of the ceramic coating, and the mass percentage e of the silicon element in the negative electrode material layer, the condition 0.2 ≤ When the values ​​of a ≤ 33, a ≤ 3, b ≤ 5, c ≤ 40, d ≤ 7, and e ≤ 30 are used, the resulting lithium-ion battery exhibits excellent high-temperature cycling performance and safety. This indicates that the thickness of the ceramic coating on the separator surface improves battery safety in lithium-ion batteries, but increasing thickness leads to a decrease in ion conduction efficiency. During the battery formation stage, the first and second additives, along with 2,2-difluoroethyl acetate, participate in the formation of the solid electrolyte interface (SEI) film on the positive and negative electrode surfaces. By precisely controlling the contents of these three components, an SEI film with low impedance, high ion conduction efficiency, and excellent high-temperature stability can be constructed. Further optimizing the compatibility of the SEI film with the ceramic coating can simultaneously improve the battery's high-temperature stability and safety without significantly increasing battery impedance. Furthermore, the silicon content in the negative electrode material layer directly affects the volume change of the negative electrode during charge and discharge; excessive volume change may lead to SEI film rupture. Therefore, the relative proportions of the three additives mentioned above must be adjusted according to the silicon content of the anode material to produce an SEI film that matches the specific silicon-containing anode. Ultimately, this synergistic regulation strategy can produce lithium-ion batteries with high energy density, excellent high-temperature cycling performance, and outstanding high-temperature safety performance.

[0163] From the test results of Examples 1 to 11, it can be seen that when the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive in the non-aqueous electrolyte, the mass percentage c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, the thickness d of the ceramic coating, and the mass percentage e of silicon in the negative electrode material layer further satisfy the condition 0.6≤ ≤14, and 0.5≤a≤2, 1≤b≤4, 3≤c≤40, 0.3≤d≤4, 10≤e≤30, it is beneficial to further improve the high temperature cycle life and thermal shock resistance safety performance of lithium-ion batteries.

[0164] From the test results of Comparative Examples 1 to 11, it can be seen that when the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive in the non-aqueous electrolyte, the mass percentage c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, the thickness d of the ceramic coating, and the mass percentage e of the silicon element in the negative electrode material layer are not within their respective limited ranges, even if 0.2≤ The condition of ≤33 still cannot be achieved. This shows that the values ​​of a, b, c, and d are closely related in affecting the ion conduction efficiency between the solid electrolyte interface membrane and the ceramic coating. Any change in any of these values ​​will affect the high-temperature cycle performance and safety performance of the battery.

[0165] Similarly, according to the test results of Comparative Examples 12 to 17, when the a value, b value, c value and d value are all within the specified range, If the value of does not meet the above-mentioned preset conditions, the safety performance and high-temperature cycle performance of the lithium-ion battery will not be improved. This further shows that only when the values ​​of a, b, c, and d are in a coordinated state can the safety performance and high-temperature cycle performance of the lithium-ion battery be effectively improved.

[0166] 2. The test results of Examples 12 to 24 are entered into Table 3.

[0167] Table 3

[0168]

[0169] From the comparison of the test results of Examples 1 to 11 and Examples 12 to 15, it can be seen that in the battery system provided by the present invention, the further addition of a non-fluorinated carboxylic acid ester is beneficial to reducing the viscosity of the non-aqueous electrolyte. At the same time, when the mass percentage c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte and the mass percentage f of the non-fluorinated carboxylic acid ester in the non-aqueous electrolyte further satisfy the condition 0.5≤c / f≤2, it is beneficial to comprehensively consider the effects of the non-fluorinated carboxylic acid ester and 2,2-difluoroethyl acetate on the battery impedance and high temperature stability, thereby improving the discharge performance and high temperature performance of the lithium-ion battery.

[0170] From the comparison of the test results of Examples 1 to 11 and Examples 16 to 24, it can be seen that in the electrolyte system provided by the present invention, by further limiting the total mass of the non-fluorinated carboxylic acid ester and 2,2-difluoroethyl acetate to be within the range of 13≤c+f≤45, it is beneficial to ensure that the non-fluorinated carboxylic acid ester and 2,2-difluoroethyl acetate improve the performance of the non-aqueous electrolyte, while avoiding the excessive addition of non-fluorinated carboxylic acid ester or 2,2-difluoroethyl acetate, which affects the high temperature stability of the non-aqueous electrolyte and ensures the high temperature cycle performance of the lithium ion battery.

[0171] Examples 25 to 34

[0172] Examples 25 to 34 are used to illustrate the non-aqueous electrolyte for lithium ion batteries and the preparation method thereof disclosed in the present invention, and include most of the operating steps in Example 1, except that:

[0173] The types of the first additive, the second additive, and the non-fluorinated carboxylic acid ester in the non-aqueous electrolyte are shown in Table 4.

[0174] The thermal shock test and high temperature cycle performance test were carried out using the above method, and the test results were filled in Table 4.

[0175] Table 4

[0176]

[0177] From the test results of Examples 1 and 25 to 34, it can be seen that in the battery system provided by the present invention, the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive in the non-aqueous electrolyte, the mass percentage c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, the thickness d of the ceramic coating, and the mass percentage e of the silicon element in the negative electrode material layer meet the condition 0.2≤ ≤33, and 0.1≤a≤3, 0.5≤b≤5, 1≤c≤40, 0.2≤d≤7, 5≤e≤30, even if different first additives, second additives and non-fluorinated carboxylates are used, the high temperature cycle performance and safety performance of the lithium ion battery can still be improved to a certain extent, which shows that the battery system provided by the present invention has good applicability to different first additives, second additives and non-fluorinated carboxylates.

[0178] Examples 35-38

[0179] Examples 35 to 38 are used to illustrate the non-aqueous electrolyte for lithium ion batteries and the preparation method thereof disclosed in the present invention, and include most of the operating steps in Example 1, except that:

[0180] The types of positive electrode active materials are shown in Table 5.

[0181] The thermal shock test and high temperature cycle performance test were carried out using the above method, and the test results were filled in Table 5.

[0182] Table 5

[0183]

[0184] From the test results of Examples 1 and 35 to 38, it can be seen that in the battery system provided by the present invention, the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive in the non-aqueous electrolyte, the mass percentage c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, the thickness d of the ceramic coating, and the mass percentage e of the silicon element in the negative electrode material layer meet the condition 0.2≤ Under the premise that ≤33, 0.1≤a≤3, 0.5≤b≤5, 1≤c≤40, 0.2≤d≤7, and 5≤e≤30, even if different combinations of lithium cobalt oxide positive active materials are used, the high temperature cycle performance and safety performance of the lithium ion battery can still be improved to a certain extent, which shows that the battery system provided by the present invention has good applicability for lithium cobalt oxide materials.

[0185] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A lithium-ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte, wherein the separator is located between the positive electrode and the negative electrode, the positive electrode comprises a positive electrode material layer containing a positive electrode active material, the positive electrode active material comprises lithium cobalt oxide or lithium cobalt oxide modified by doping and / or coating with any one or more elements selected from Ni, Mg, Al, Zr, W, F, B, Cr, Mo and rare earth elements, the negative electrode comprises a negative electrode material layer containing a silicon-based material, the separator comprises a base film and a ceramic coating provided on at least one side of the base film, the non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte salt and an additive, the non-aqueous organic solvent comprises 2,2-difluoroethyl acetate, the additive comprises a first additive and a second additive, the first additive comprises a sulfur-containing additive represented by structural formula 1: ； wherein n is 0 or 1, A is selected from C or O, and X is selected from or , R1, R2 are each independently selected from H, or , R1 and R2 are not simultaneously selected from H, and X, R1 and R2 contain at least one sulfur atom; The second additive includes a nitrile compound; The lithium-ion battery meets the following conditions: 0.2≤ ≤33, and 0.1≤a≤3, 0.5≤b≤5, 1≤c≤40, 0.2≤d≤7, 5≤e≤30; Wherein, a is the mass percentage of the first additive in the non-aqueous electrolyte, and the unit is %; b is the mass percentage of the second additive in the non-aqueous electrolyte, unit is %; c is the mass percentage of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, unit is %; d is the thickness of the ceramic coating, in μm; e is the mass percentage of silicon element in the negative electrode material layer, in %.

2. The lithium-ion battery according to claim 1, wherein The lithium-ion battery meets at least one of the following conditions: (1) The mass percentage a of the first additive in the non-aqueous electrolyte is 0.5% to 2%; (2) The mass percentage content b of the second additive in the non-aqueous electrolyte is 1% to 4%; (3) The mass percentage c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte is 3% to 40%; (4) The thickness d of the ceramic coating is 0.3-4 μm; (5) The mass percentage e of silicon element in the negative electrode material layer is 10% to 30%; （6）0.6≤ ≤14。 3. The lithium-ion battery according to claim 1, wherein The sulfur-containing additive shown in Structural Formula 1 includes at least one of the following compounds: 。 4. The lithium-ion battery according to claim 1, wherein The second additive includes one or more of succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,4-dicyano-2-butene, or 1,2,3-tris(2-cyanoethoxy)propane.

5. The lithium-ion battery according to claim 1, wherein The non-aqueous organic solvent further comprises a non-fluorinated carboxylic acid ester; The non-aqueous electrolyte satisfies the following conditions: 0.5≤c / f≤2; Wherein, c is the mass percentage of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, unit is %; f is the mass percentage of non-fluorinated carboxylic acid ester in the non-aqueous electrolyte, in %.

6. The lithium-ion battery according to claim 5, characterized in that The mass percentage f% of the non-fluorinated carboxylic acid ester in the non-aqueous electrolyte is 10% to 30%; and / or, 13≤c+f≤45.

7. The lithium-ion battery according to claim 6, characterized in that The non-fluorinated carboxylic acid ester includes one or more of ethyl acetate, methyl acetate, methyl propionate, propyl propionate or ethyl propionate.

8. The lithium-ion battery according to claim 1, wherein The ceramic coating includes ceramic particles, and the ceramic particles include one or more of aluminum oxide, boehmite, silicon dioxide, zirconium dioxide, barium sulfate, magnesium hydroxide, fluorapatite, fluorphlogopite, mullite, aluminum titanate, copper oxide, titanium dioxide, and zinc oxide.

9. The lithium-ion battery according to claim 1, wherein The silicon-based material includes one or more of silicon element, silicon oxide, silicon-carbon composite material and silicon alloy material.

10. The lithium-ion battery according to claim 1, wherein The charging cut-off voltage of the lithium-ion battery is ≥4.45V.

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