Lithium ion battery

Abstract

In order to solve the problem that an existing battery with high-voltage lithium cobalt oxide matched with a silicon-doped negative electrode is insufficient in cycle performance and safety performance, the invention provides a lithium ion battery which comprises a positive electrode, a negative electrode, a diaphragm and a non-aqueous electrolyte, and the non-aqueous electrolyte comprises a non-aqueous organic solvent, electrolyte salt and an additive, the non-aqueous organic solvent comprises acetic acid 2, 2-difluoroethyl ester, the additives comprise a first additive and a second additive, the first additive comprises a sulfur-containing additive as shown in a structural formula 1: # imgabs0 # structural formula 1, and the second additive comprises a nitrile compound; the lithium ion battery satisfies the following conditions: # imgabs 1 #, 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 invention has relatively excellent high-temperature cycling stability and relatively good thermal shock resistance safety performance.

Description

Technical Field

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

[0002] Lithium-ion batteries have been widely used in the fields of 3C digital products such as mobile phones and laptop computers, as well as new energy vehicles due to their advantages of high working voltage, wide working temperature range, large energy density and power density, no memory effect, and long cycle life. In recent years, with the continuous development of the thinning of 3C digital products, the battery industry has higher and higher requirements for the high energy density of lithium-ion batteries. At the same time, considering the user side, good safety performance has become a basic requirement for batteries.

[0003] In terms of the positive electrode, lithium cobaltate has a relatively high volumetric energy density among many positive electrode materials and good rate performance. However, as the battery voltage gradually increases, lithium cobaltate enters a higher delithiated state, and the structural stability of the material will deteriorate. 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 posing a risk of thermal runaway under high temperature and high pressure. Moreover, the dissolved Co migrates to the negative electrode interface, undergoes ion exchange with lithium in the negative electrode, occupies the lithium intercalation position in the negative electrode, resulting in a decrease in the lithium storage capacity of the negative electrode and deterioration of various battery performances. Specifically, it is manifested as: gas generation in the battery, rapid increase in internal resistance, and sharp drop in capacity. Gas generation in the battery will cause an increase in internal pressure, and further may develop into dangerous situations such as explosion and combustion of the battery. Therefore, high-voltage batteries require electrolytes with better safety performance.

[0004] In terms of the negative electrode, in order to improve the energy density, doping silicon into the graphite negative electrode has become a commonly used method in the industry. After doping silicon, the energy density of the battery is improved, and the battery capacity can be made larger under the same volume. For example, existing ≥5000mAh battery cells have become the standard configuration of flagship mobile phones. However, due to their large capacity, such large battery cells have high temperature rise during fast charging and high-rate discharging, and there are challenges in safety performance.

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

[0006] Aiming at the problems of insufficient battery cycle performance and safety performance in existing batteries with high-voltage lithium cobaltate and a silicon-doped negative electrode, 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: The present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte. 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 cobaltate or lithium cobaltate doped and / or coated and modified by any one or several 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 surface 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, X is selected from or , R 1 , R 2 are each independently selected from H, or , R 1 and R 2 are not simultaneously selected from H, and at least one of X, R 1 and R 2 contains a sulfur atom; The second additive comprises a nitrile compound; The lithium-ion battery satisfies 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 content of the first additive in the non-aqueous electrolyte, in %; b is the mass percentage content of the second additive in the non-aqueous electrolyte, in %; c is the mass percentage content of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, in %; d is the thickness of the ceramic coating, in μm; e is the mass percentage content of silicon element in the negative electrode material layer, in %.

[0008] Optionally, the lithium-ion battery satisfies the following conditions: 0.6 ≤ ≤ 14.

[0009] Optionally, the lithium-ion battery satisfies at least one of the following conditions: (1) The mass percentage content 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 content 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 to 4 μm; (5) The mass percentage content e of silicon element in the negative electrode material layer is 10% to 30%; (6) 0.6 ≤ ≤ 14.

[0010] Optionally, the sulfur-containing additive shown in Structural Formula 1 includes at least one of the following compounds: .

[0011] Optionally, the second additive includes one or more of succinonitrile, adiponitrile, 1,3,6-hexanetricarbonitrile, 1,4-dicyano-2-butene, or 1,2,3-tris(2-cyanoethoxy)propane.

[0012] Optionally, the non-aqueous organic solvent further includes non-fluorinated carboxylic acid esters; The non-aqueous electrolyte satisfies the following conditions: 0.5 ≤ c / f ≤ 2; wherein, c is the mass percentage content of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, with the unit of %; f is the mass percentage content of non-fluorinated carboxylic acid esters in the non-aqueous electrolyte, with the unit of %.

[0013] Optionally, the mass percentage content f% of non-fluorinated carboxylic acid esters in the non-aqueous electrolyte is 10% to 30%; and / or, 13 ≤ c + f ≤ 45.

[0014] Optionally, the non-fluorinated carboxylic acid esters include one or more of ethyl acetate, methyl acetate, methyl propionate, propyl propionate, or ethyl propionate.

[0015] 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, fluorophlogopite, mullite, aluminum titanate, copper oxide, titanium dioxide, zinc oxide.

[0016] Optionally, the negative electrode material layer includes a negative electrode active material, and the silicon-based material includes one or more of silicon, silicon oxide, silicon-carbon composite material, and silicon alloy material.

[0017] Optionally, the charging cut-off voltage of the lithium-ion battery is ≥ 4.45V.

[0018] For the lithium-ion battery provided by the present invention, lithium cobaltate is used as the positive electrode, and silicon element is doped in the negative electrode at the same time, so that the battery has a high volumetric energy density. To solve the safety performance problems brought by lithium cobaltate and silicon, the inventor adjusted and adapted the non-aqueous electrolyte and found that when the mass percentage content a of the first additive, the mass percentage content b of the second additive, the mass percentage content c of 2,2-difluoroethyl acetate, the thickness d of the ceramic coating, and the mass percentage content e of silicon element in the negative electrode material layer in the non-aqueous electrolyte satisfy the condition 0.2 ≤ ≤ 33, and 0.1 ≤ a ≤ 3, 0.5 ≤ b ≤ 5, 1 ≤ c ≤ 40, 0.2 ≤ d ≤ 7, 5 ≤ e ≤ 30, the obtained lithium-ion battery can take into account better high-temperature cycle stability and better thermal shock resistance safety performance on the premise of having a high energy density. It is speculated that the thickness of the ceramic coating provided on the surface of the separator can improve the safety of the battery, but it will also lead to a decrease in the ion conduction efficiency. During 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 surfaces of the positive and negative electrodes. By regulating the contents 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. Moreover, the content of silicon element in the negative electrode material layer will affect the volume change of the negative electrode during charge and discharge, resulting in the rupture of the solid electrolyte interface film. Therefore, it is necessary to adjust the relative contents of the first additive, the second additive, and 2,2-difluoroethyl acetate 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 implementation manners

[0019] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0020] An embodiment of the present invention provides a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. The separator is located between the positive electrode and the negative electrode. The positive electrode includes a positive electrode material layer containing a positive electrode active material. The positive electrode active material includes lithium cobaltate or lithium cobaltate doped and / or coated and modified by any one or several elements selected from Ni, Mg, Al, Zr, W, F, B, Cr, Mo, and rare earth elements. The negative electrode includes a negative electrode material layer containing a silicon-based material. The separator includes a base film and a ceramic coating provided on at least one surface of the base film. The non-aqueous electrolyte includes a non-aqueous organic solvent, an electrolyte salt, and an additive. The non-aqueous organic solvent includes 2,2-difluoroethyl acetate. The additive includes a first additive and a second additive. The first additive includes 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 , R 1 , R 2 are each independently selected from H, or , R 1 and R 2 are not simultaneously selected from H, and at least one of X, R 1 and R 2 contains a sulfur atom; The second additive includes a nitrile compound; The lithium-ion battery satisfies 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 content of the first additive in the non-aqueous electrolyte, in %; b is the mass percentage content of the second additive in the non-aqueous electrolyte, in %; c is the mass percentage content of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, in %; d is the thickness of the ceramic coating, in μm; e is the mass percentage content of silicon element in the negative electrode material layer, in %.

[0021] To solve the safety performance problems brought by lithium cobaltate and silicon, the inventor made an adaptation adjustment to the non-aqueous electrolyte and found that when the mass percentage content a of the first additive in the non-aqueous electrolyte, the mass percentage content b of the second additive in the non-aqueous electrolyte, the mass percentage content c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, the thickness d of the ceramic coating, and the mass percentage content e of silicon element in the negative electrode material layer satisfy the condition 0.2 ≤ When ≤ 33, and 0.1 ≤ a ≤ 3, 0.5 ≤ b ≤ 5, 1 ≤ c ≤ 40, 0.2 ≤ d ≤ 7, 5 ≤ e ≤ 30, the obtained lithium-ion battery can achieve better high-temperature cycle stability and better thermal shock resistance safety performance on the premise of having a high energy density. It is speculated that the thickness of the ceramic coating on the diaphragm surface can improve the safety of the battery, but it will also lead to a decrease in ion conduction efficiency. During 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 positive and negative electrode surfaces. By regulating the contents of the three, a solid electrolyte interface film with low impedance, high ion conduction efficiency, and high high-temperature stability can be formed. By matching 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. Moreover, the content of silicon element in the negative electrode material layer will affect the volume change of the negative electrode during charge and discharge, resulting in the rupture of the solid electrolyte interface film. Therefore, it is necessary to adjust the relative contents of the first additive, the second additive, and 2,2-difluoroethyl acetate 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.

[0022] In some embodiments, in the sulfur-containing additive represented by Structural Formula 1, R 1 、R 2 are each independently selected from or , and at least one of X, R 1 and R 2 contains a sulfur atom.

[0023] When the sulfur-containing additive represented by Structural Formula 1 satisfies the above conditions, the sulfur-containing additive represented by Structural Formula 1 has a tricyclic structure at this time. Compared with the bicyclic structure, each ring of the tricyclic structure opens to participate in the formation of the interface film on the electrode surface, which has the effect of improving the structural strength of the interface film, and thus is beneficial to enhancing its high-temperature stability.

[0024] As an example, the sulfur-containing additive represented by Structural Formula 1 is selected from one or more of the following compounds: .

[0025] In some embodiments, in the sulfur-containing additive represented by Structural Formula 1, X, R 1 and R 2 do not contain sulfur atoms simultaneously.

[0026] When the sulfur-containing additive represented by Structural Formula 1 meets the above conditions, the sulfur-containing additive represented by Structural Formula 1 has a tricyclic structure, and the sulfur-containing additive represented by Structural Formula 1 includes both a sulfur-containing cyclic structure and a cyclic structure containing a carbonate. The cyclic structure of the carbonate is conducive to the formation of lithium carbonate components in the electrode interface film. Compared with the simple sulfur-containing decomposition products, the interfacial film components formed by the combination of the cyclic structure of the carbonate and the sulfur-containing cyclic structure are more stable and dense.

[0027] In some embodiments, in the sulfur-containing additive represented by Structural Formula 1, R 1 is selected from H, X is selected from , R 2 is selected from ; or, R 1 is selected from H, X is selected from , R 2 is selected from or .

[0028] When the sulfur-containing additive represented by Structural Formula 1 meets the above conditions, the sulfur-containing additive represented by Structural Formula 1 has a bicyclic structure, and the sulfur-containing additive represented by Structural Formula 1 includes both a sulfur-containing cyclic structure and a cyclic structure containing a carbonate. Compared with the simple sulfur-containing decomposition products, the interfacial film components formed by the combination of the cyclic structure of the carbonate and the sulfur-containing cyclic structure are more stable and dense.

[0029] In some embodiments, when using any one or several of the elements Ni, Mg, Al, Zr, W, F, B, Cr, Mo and rare earth elements to coat and modify lithium cobaltate, oxides of one or more of these elements are used for coating.

[0030] In a preferred embodiment, the lithium ion battery meets the following conditions: 0.6 ≤ ≤ 14.

[0031] When the mass percentage content a of the first additive in the non-aqueous electrolyte, the mass percentage content b of the second additive in the non-aqueous electrolyte, the mass percentage content c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, the thickness d of the ceramic coating, and the mass percentage content e of 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.

[0032] In a specific embodiment, the mass percentage content a of the first additive in the non-aqueous electrolyte may 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 between any two of them.

[0033] In a preferred embodiment, the mass percentage content a of the first additive in the non-aqueous electrolyte is 0.5% - 2%.

[0034] The first additive can decompose on the surfaces of the positive and negative electrodes and form 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 content a of the first additive is too small, it is difficult to form a complete solid electrolyte interface film, resulting in a decrease in the high temperature stability of the non-aqueous electrolyte; if the mass percentage content a of the first additive is too high, it will lead to a relatively large thickness of the formed solid electrolyte interface film, resulting in a significant increase in the interfacial 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.

[0035] In a specific embodiment, the mass percentage content b of the second additive in the non-aqueous electrolyte may 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 between any two of them.

[0036] In a preferred embodiment, the mass percentage content b of the second additive in the non-aqueous electrolyte is 1% - 4%.

[0037] The second additive plays an important role in the battery system. On the one hand, it can effectively stabilize the cathode 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 also affects the composition of the solid electrolyte interface film on the anode, and potentially affects the charge and discharge performance of the battery by adjusting the composition of the solid electrolyte interface film. When the content of the second additive is too low, it is difficult to fully exert the effect of stabilizing the cathode interface, the improvement of the battery thermal safety performance is not obvious, and the tolerance to high temperature environment is poor. When the content of the second additive is too high, it will cause a significant increase in the battery impedance. At the same time, due to the high reactivity of the cyano group in the second additive, it is also not conducive to improving the high temperature stability of the non-aqueous electrolyte.

[0038] In a specific embodiment, the mass percentage content 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 between any two of them.

[0039] In a preferred embodiment, the mass percentage content c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte is 3% - 40%.

[0040] 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 with 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 the fast charge and discharge cycle performance. When the content of the 2,2-difluoroethyl acetate is too low, it will lead to a decrease in the high temperature and high voltage stability of the non-aqueous electrolyte, and the non-aqueous electrolyte decomposes and generates gas due to side reactions during high temperature cycling, resulting in problems such as capacity decline and battery swelling. When the content of the 2,2-difluoroethyl acetate is too high, it will affect the component content of the solid electrolyte interface film derived from the first additive and the second additive, and affect the high temperature stability of the solid electrolyte interface film.

[0041] 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 between any two of them.

[0042] In a preferred embodiment, the thickness d of the ceramic coating is 0.3 to 4 μm.

[0043] The ceramic coating can improve the heat resistance and mechanical properties of the separator. On the one hand, it avoids the short circuit between the positive and negative electrodes caused by the shrinkage of the separator under high temperature conditions. On the other hand, it also avoids the problem of lithium dendrites piercing the separator. If the thickness of the ceramic coating is too low, it is difficult to achieve good improvement in heat resistance and lithium dendrite resistance. 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.

[0044] In a specific embodiment, the mass percentage content e of 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 the range between any two of them.

[0045] In a preferred embodiment, the mass percentage content e of silicon element in the negative electrode material layer is 10% to 30%.

[0046] Silicon material can accommodate more lithium ions compared to conventional carbon materials. By doping silicon element in the negative electrode material layer, the energy density of the negative electrode can be effectively improved. However, the volume change of silicon material during charge and discharge is relatively large. When the content of silicon element in the negative electrode material layer is too low, it is difficult to achieve good improvement in the energy density of the lithium ion battery. When the content of silicon element in the negative electrode material layer is too high, due to the excessive volume change of the negative electrode during charge and discharge, the solid electrolyte interface film on the electrode surface will frequently break and reorganize, resulting in the consumption of active lithium, an increase in impedance, and a lower cycle life of the battery.

[0047] In some embodiments, the second additive includes one or more of succinonitrile, adiponitrile, 1,3,6 - hexanetricarbonitrile, 1,4 - dicyano - 2 - butene or 1,2,3 - tris(2 - cyanoethoxy)propane.

[0048] In some embodiments, the additive further includes a third additive, and the third additive includes at least one of cyclic sulfate compounds, sulfonic acid lactone compounds, cyclic carbonate compounds, phosphate compounds and borate compounds; Preferably, based on the total mass of the non - aqueous electrolyte being 100%, the content of the third additive is 0.01% to 30%.

[0049] In some embodiments, the cyclic sulfate compounds are selected from at least one of ethylene sulfate, propylene sulfate, vinyl methyl sulfate, and the like; The sultone compounds are selected from at least one of 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone; The cyclic carbonate compounds are selected from at least one of vinylene carbonate, ethylene vinylene carbonate, ethylene methylene carbonate, fluoroethylene carbonate, or the compound shown in Structural Formula 2, ; In Structural Formula 2, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 are each independently selected from a hydrogen atom, a halogen atom, or a C1-C5 group; The phosphate compounds include at least one of the compounds shown in Structural Formula 3: ; In Structural Formula 3, R 31 , R 32 , R 33 are each independently selected from a C1-C5 saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group, -Si(C m H 2m+1 ) 3 , and m is a natural number from 1 to 3; In a preferred embodiment, the phosphate compounds shown in Structural Formula 3 can be at least one of tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, tripropargyl 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, diallyl 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, diallyl hexafluoroisopropyl phosphate; The borate compounds include at least one of tris(trimethylsilyl) borate and tris(triethylsilyl) borate.

[0050] In some other embodiments, the additive may further include other additives that can improve battery performance: for example, additives that enhance battery safety performance, specifically, flame retardant additives such as fluorophosphate esters and cyclophosphazenes, or overcharge prevention additives such as tert-amylbenzene and tert-butylbenzene.

[0051] It should be noted that, unless otherwise specified, generally, the content of any optional substance in the additive 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 optional substance in the additive 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%, 10%.

[0052] In some embodiments, when the auxiliary additive is selected from vinylidene fluoride carbonate, based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of vinylidene fluoride carbonate is 0.05%~30%.

[0053] In some embodiments, the non-aqueous organic solvent further includes non-fluorinated carboxylic acid esters; The non-aqueous electrolyte satisfies the following conditions: 0.5≤c / f≤2; Wherein, c is the mass percentage content of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, with the unit of %; f is the mass percentage content of non-fluorinated carboxylic acid esters in the non-aqueous electrolyte, with the unit of %.

[0054] In the battery system provided by the present invention, adding non-fluorinated carboxylic acid esters is beneficial to 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 is beneficial to compensating for the problem of increased internal resistance caused by setting a ceramic coating on the separator. However, the non-fluorinated carboxylic acid esters themselves have insufficient high-temperature stability and need to be adapted with 2,2-difluoroethyl acetate to improve their stability. Therefore, when the mass percentage content c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte and the mass percentage content f of non-fluorinated carboxylic acid esters in the non-aqueous electrolyte satisfy the condition 0.5≤c / f≤2, it is beneficial to comprehensively consider the effects of non-fluorinated carboxylic acid esters and 2,2-difluoroethyl acetate on battery impedance and high-temperature stability, and improve the discharge performance and high-temperature performance of the lithium-ion battery.

[0055] In some embodiments, the mass percentage content f% of non-fluorinated carboxylic acid esters in the non-aqueous electrolyte is 10%~30%.

[0056] In a preferred embodiment, the non-aqueous electrolyte satisfies the following conditions: 13 ≤ c + f ≤ 45.

[0057] In the battery system provided by the present invention, when the total mass of the non-fluorinated carboxylic acid ester and 2,2-difluoroethyl acetate in the non-aqueous electrolyte is less than 13%, it is difficult to achieve the synergistic effect between the non-fluorinated carboxylic acid ester and 2,2-difluoroethyl acetate, and the improvement effect on the lithium-ion battery is limited; when the total mass of the non-fluorinated carboxylic acid ester and 2,2-difluoroethyl acetate in the non-aqueous electrolyte is higher than 45%, it is likely to cause a decrease in the high-temperature stability of the non-aqueous electrolyte, affecting the high-temperature cycle performance of the lithium-ion battery.

[0058] 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.

[0059] In some embodiments, the non-aqueous organic solvent further includes one or more of cyclic carbonates, linear carbonates, and ether solvents.

[0060] In some embodiments, the cyclic carbonate may specifically be, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); the linear carbonate may specifically 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 arbitrary within the range that does not significantly damage the effect of the lithium-ion battery of the present invention. However, when using only one kind, the lower limit of its content is usually 3% or more, preferably 5% or more, by volume, relative to the total amount of the solvents of the non-aqueous electrolyte. By setting this range, it is possible to avoid a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte, and it is easy to bring the high-current discharge characteristics, stability with respect to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery into a good range. In addition, the upper limit is usually 90% or less, preferably 85% or less, more preferably 80% or less, by volume. By setting this range, the oxidation / reduction resistance of the non-aqueous electrolyte can be improved, which helps to improve the stability during high-temperature storage. The content of the linear carbonate is not particularly limited and is usually 15% or more, preferably 20% or more, more preferably 25% or more, by volume, relative to the total amount of the solvents of the non-aqueous electrolyte. In addition, it is usually 90% or less, preferably 85% or less, more preferably 80% or less, by volume. By making the content of the linear carbonate within the above range, it is easy to bring the viscosity of the non-aqueous electrolyte into an appropriate range, suppress a decrease in ionic conductivity, and further help to bring the output characteristics of the non-aqueous electrolyte battery into a good range. When using two or more linear carbonates in combination, it is only necessary to make the total amount of the linear carbonates satisfy the above range.

[0061] In some embodiments, the ether solvent includes cyclic ethers or linear ethers and their fluorinated derivatives, preferably linear ethers having 3 to 10 carbon atoms and cyclic ethers having 3 to 6 carbon atoms. The cyclic ethers may specifically be, but are not limited to, 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH 3 -THF), 2-trifluoromethyltetrahydrofuran (2-CF 3At least one of the following: 1,2 - dimethoxyethane, 1,2 - diethoxyethane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, γ - butyrolactone, sulfolane, 1,3 - dioxolane, 4 - methyl - 1,3 - dioxolane, 1,3 - dioxane, 4 - methyl - 1,3 - dioxane, tetrahydrofuran (THF). The chain - like ethers can specifically be, but are not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di - n - propyl ether, ethylene glycol di - n - butyl ether, diethylene glycol dimethyl ether. Since chain - like ethers have a high solvation ability for lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which have low viscosity and can impart high ionic conductivity, are particularly preferred. The ether compounds can be used alone or in combination of two or more in any combination and ratio. The content of the ether compounds is not particularly limited and is arbitrary within the range that does not significantly damage the effect of the high - compaction lithium - ion battery of the present invention. In a non - aqueous solvent with a volume ratio of 100%, the volume ratio is generally 1% or more, preferably 2% or more, more preferably 3% or more, and generally 30% or less, preferably 25% or less, more preferably 20% or less. When using a combination of two or more ether compounds, the total amount of the ether compounds should meet the above range. When the content of the ether compounds is within the above - mentioned preferred range, it is easy to ensure the improvement effect of ionic conductivity brought about by the increase in lithium - ion dissociation degree and the decrease in viscosity of the chain - like ether. In addition, when the negative electrode active material is a carbon - based material, the phenomenon of co - intercalation of the chain - like ether and lithium ions can be inhibited, so that the input - output characteristics and charge - discharge rate characteristics can reach an appropriate range.

[0062] 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% - 90%.

[0063] Specifically, based on the total mass of the non - aqueous electrolyte being 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 any range composed of any two of these values.

[0064] In some embodiments, the electrolyte salt is selected from lithium salts, and the lithium salts include LiPF 6 , LiODFP, LiODFB, LiBOB, LiPO 2 F 2 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiN(SO 2 F) 2 , LiN(SO 2 CF 3 ) 2 , LiN(SO 2 C 2 F 5) 2 , LiC(SO 2 CF 3 ) 3 , LiClO 4 , LiAlCl 4 , LiCF 3 SO 3 , LiSO 3 F, Li 2 B 10 Cl 10 , at least one of lithium chloroborane, lithium trioxalato phosphate, lithium lower aliphatic carboxylate having less than 4 carbon atoms, or lithium tetraphenylborate.

[0065] In some embodiments, in the non-aqueous electrolyte, the concentration of the lithium salt is 0.1 mol / L to 8 mol / L. In a preferred embodiment, in the non-aqueous electrolyte, the concentration of the lithium salt is 0.5 mol / L to 2.5 mol / L. Specifically, in the non-aqueous electrolyte, the concentration of the lithium salt can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L.

[0066] 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, fluorophlogopite, mullite, aluminum titanate, copper oxide, titanium dioxide, zinc oxide.

[0067] In some embodiments, the ceramic coating further includes a binder.

[0068] In some embodiments, the binder includes acrylic resins; thermoplastic resins such as polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene, copolymers of tetrafluoroethylene - hexafluoropropylene, copolymers of tetrafluoroethylene - perfluoroalkyl vinyl ether, copolymers of ethylene - tetrafluoroethylene, copolymers of vinylidene fluoride - tetrafluoroethylene, copolymers of vinylidene fluoride - trifluoroethylene, copolymers of vinylidene fluoride - trichloroethylene, copolymers of vinylidene fluoride - fluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; and at least one of styrene butadiene rubber.

[0069] In some embodiments, the base film includes one or more of polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), polyimide (PI), polyester resins (such as PET).

[0070] 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 materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials.

[0071] In some embodiments, the negative electrode further includes 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 includes a metal material capable of conducting electrons. Preferably, the negative electrode current collector includes 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 foils.

[0072] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder, and the negative electrode conductive agent are blended to obtain the negative electrode material layer.

[0073] The negative electrode binder includes at least one of thermoplastic resins such as polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene, copolymers of tetrafluoroethylene - hexafluoropropylene, copolymers of tetrafluoroethylene - perfluoroalkyl vinyl ether, copolymers of ethylene - tetrafluoroethylene, copolymers of vinylidene fluoride - tetrafluoroethylene, copolymers of vinylidene fluoride - trifluoroethylene, copolymers of vinylidene fluoride - trichloroethylene, copolymers of vinylidene fluoride - fluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0074] The negative electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0075] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent, and the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent are blended to obtain the positive electrode material layer.

[0076] The positive electrode binder includes at least one of thermoplastic resins such as polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene, copolymers of tetrafluoroethylene - hexafluoropropylene, copolymers of tetrafluoroethylene - perfluoroalkyl vinyl ether, copolymers of ethylene - tetrafluoroethylene, copolymers of vinylidene fluoride - tetrafluoroethylene, copolymers of vinylidene fluoride - trifluoroethylene, copolymers of vinylidene fluoride - trichloroethylene, copolymers of vinylidene fluoride - fluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0077] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0078] In some embodiments, the positive electrode current collector includes a metal material capable of conducting 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.

[0079] In some embodiments, the charging cut-off voltage of the lithium-ion battery is ≥ 4.45V, thereby achieving the purpose of realizing high energy density and expanding its application range.

[0080] The present invention is further illustrated by the following examples.

[0081] Table 1

[0082] Example 1 This example is used to illustrate the lithium ions and their preparation method disclosed in the present invention, and includes the following operation steps: Preparation of the positive electrode sheet Disperse the positive electrode active material LiCoO 2 (subsequently referred to as LCO), conductive carbon black, and the binder PVDF into the solvent NMP for uniform mixing to obtain a positive electrode slurry; uniformly coat the positive electrode slurry on the positive electrode current collector aluminum foil, and after drying, rolling, and cutting, obtain a positive electrode sheet. The weight ratio of the positive electrode active material, conductive carbon black, and the binder PVDF is 96:2:2.

[0083] Preparation of the negative electrode sheet Disperse the negative electrode active material graphite, silicon material, conductive agent, CMC (sodium carboxymethyl cellulose), and SBR (styrene-butadiene rubber) in deionized water for stirring to obtain a negative electrode slurry; uniformly coat the negative electrode slurry on the negative electrode current collector copper foil, and after drying, rolling, and cutting, obtain a negative electrode sheet with a compaction of 1.7 g / cc. The mass percentage content of silicon element in the negative electrode material layer is shown in Table 1.

[0084] Preparation of the non-aqueous electrolyte Mix 2,2-difluoroethyl acetate, non-fluorinated carboxylic acid ester, and ethylene carbonate to obtain a non-aqueous organic solvent. The selection and mass content of 2,2-difluoroethyl acetate and non-fluorinated carboxylic acid ester are shown in Table 1, and ethylene carbonate is used to make up the balance. Dissolve 1 mol / L of LiPF 6 in the above non-aqueous organic solvent, and add the first additive and the second additive according to Table 1 to obtain a non-aqueous electrolyte. The first additive is compound 7, the second additive is succinonitrile, and the non-fluorinated carboxylic acid ester is ethyl propionate.

[0085] Preparation of separator Using a polypropylene porous membrane as the base layer, a ceramic coating is coated on one surface of the polypropylene porous membrane. The ceramic coating includes boehmite and an acrylic binder. Based on the mass of the ceramic coating, the mass ratio of boehmite is 90%. Subsequently, drying is completed in an oven to form a heat-resistant layer, thereby obtaining a separator. The thickness of the ceramic coating is shown in Table 1.

[0086] Preparation of lithium-ion battery Using the stacking process, the positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence, and then top-side sealed, injected with electrolyte, encapsulated, and formed to make a soft-pack battery.

[0087] Examples 2 to 24 Examples 2 to 24 are used to illustrate the non-aqueous electrolyte of the lithium-ion battery and its preparation method disclosed in the present invention, including most of the operation steps in Example 1. The differences are as follows: The selection and mass percentage content 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 content of silicon element in the negative electrode material layer are shown in Table 1.

[0088] Comparative Examples 1 to 17 Comparative Examples 1 to 17 are used to illustrate the non-aqueous electrolyte of the lithium-ion battery and its preparation method disclosed in the present invention, including most of the operation steps in Example 1. The differences are as follows: The mass percentage content 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 content of silicon element in the negative electrode material layer are shown in Table 1.

[0089] Performance test (1) Thermal shock test At 25°C, the lithium-ion battery is left standing for 5 minutes, charged at a constant current of 1C to 4.53V, then charged at a constant voltage until the current is less than or equal to 0.05C, and then left standing for 5 minutes. Then the battery is placed in a high-temperature oven, and the temperature of the high-temperature oven is set to rise from 25°C to 133°C at a rate of 2°C / min and kept warm for 1 hour. During the heating process and the heat preservation process, monitor the battery surface temperature and the battery state of the battery. If the battery does not have a thermal runaway problem after the test, it is considered to pass.

[0090] (2) High-temperature cycle performance test At 45 °C, the lithium-ion secondary battery is left standing for 5 minutes, charged at a constant current of 1C to 4.53V, then charged at a constant voltage until the current is less than or equal to 0.05C. After that, it is left standing for 5 minutes, and then discharged at a constant current of 1C to 3.0V. The 800-cycle charge-discharge test is carried out in this way, and the discharge capacity of each cycle is recorded. The calculation method of the capacity retention rate after 800 cycles is as follows: The capacity retention rate (%) after 800 cycles = the discharge capacity of the 800th cycle / the discharge capacity of the 1st cycle × 100%.

[0091] 1. The test results of Examples 1 to 11 and Comparative Examples 1 to 17 are filled in Table 2 Table 2

[0092] It can be seen from the test results of Examples 1 to 11 and Comparative Examples 1 to 17 that in the battery system using lithium cobaltate as the positive electrode, by regulating the mass percentage content a of the first additive, the mass percentage content b of the second additive, the mass percentage content c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, the thickness d of the ceramic coating, and the mass percentage content e of silicon element in the negative electrode material layer, so that it satisfies the condition 0.2 ≤ ≤ 33, and 0.1 ≤ a ≤ 3, 0.5 ≤ b ≤ 5, 1 ≤ c ≤ 40, 0.2 ≤ d ≤ 7, 5 ≤ e ≤ 30, the obtained lithium-ion battery has excellent high-temperature cycle performance and safety performance, indicating that in lithium-ion batteries, the thickness of the ceramic coating on the surface of the separator has an improving effect on battery safety, but an increase in its thickness will lead to a decrease in ion conduction efficiency. During the battery formation stage, the first additive, the second additive and 2,2-difluoroethyl acetate jointly participate in the formation process of the solid electrolyte interface film (SEI film) on the positive and negative electrodes. By precisely regulating the contents of these three components, an SEI film with both low impedance, high ion conduction efficiency and excellent high-temperature stability can be constructed. Further, by optimizing the compatibility between the SEI film and the ceramic coating, it is possible to simultaneously improve the high-temperature stability and safety of the battery on the premise of avoiding a significant increase in battery impedance. In addition, the content of silicon element in the negative electrode material layer will directly affect the volume change amplitude of the negative electrode during charge and discharge, and excessive volume change may cause the SEI film to rupture. Therefore, it is necessary to adjust the relative proportions of the above three additives according to the silicon content characteristics of the negative electrode material to prepare an SEI film that matches a specific silicon-containing negative electrode. Finally, through this cooperative regulation strategy, a lithium-ion battery with both high energy density, excellent high-temperature cycle performance and excellent high-temperature safety performance can be obtained.

[0093] From the test results of Examples 1 to 11, it can be seen that when the mass percentage content a of the first additive in the non-aqueous electrolyte, the mass percentage content b of the second additive in the non-aqueous electrolyte, the mass percentage content c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, the thickness d of the ceramic coating, and the mass percentage content e of silicon element 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 the lithium-ion battery.

[0094] From the test results of Comparative Examples 1 to 11, it can be seen that when the mass percentage content a of the first additive in the non-aqueous electrolyte, the mass percentage content b of the second additive in the non-aqueous electrolyte, the mass percentage content c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, the thickness d of the ceramic coating, and the mass percentage content e of silicon element in the negative electrode material layer are not within their respective defined ranges, even if the condition 0.2 ≤ ≤ 33 is satisfied, it still cannot be obtained. This indicates that there is a close correlation among the values of a, b, c, and d in terms of affecting the ion conduction efficiency between the solid electrolyte interface film and the ceramic coating. Any change in any one of these values will affect the high-temperature cycle performance and safety performance of the battery.

[0095] Similarly, according to the test results of Comparative Examples 12 to 17, when the values of a, b, c, and d are all within the defined ranges, but the value does not meet the above preset conditions, the safety performance and high-temperature cycle performance of the lithium-ion battery cannot be improved either. This further shows that only when the values of a, b, c, and d are in a state of coordinated cooperation can the safety performance and high-temperature cycle performance of the lithium-ion battery be effectively improved.

[0096] 2. Fill the test results of Examples 12 to 24 into Table 3 Table 3

[0097] 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, further adding non-fluorinated carboxylic acid ester is beneficial to reducing the viscosity of the non-aqueous electrolyte. At the same time, when the mass percentage content c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte and the mass percentage content f of 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 non-fluorinated carboxylic acid ester and 2,2-difluoroethyl acetate on the battery impedance and high-temperature stability, and improve the discharge performance and high-temperature performance of the lithium-ion battery.

[0098] 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, when the total mass of the non-fluorinated carboxylic acid ester and 2,2-difluoroethyl acetate is further limited to be within the range of 13 ≤ c + f ≤ 45, it is beneficial to ensure the improvement of the performance of the non-aqueous electrolyte by the non-fluorinated carboxylic acid ester and 2,2-difluoroethyl acetate, and at the same time avoid affecting the high-temperature stability of the non-aqueous electrolyte due to the excessive addition of the non-fluorinated carboxylic acid ester or 2,2-difluoroethyl acetate, and ensure the high-temperature cycling performance of the lithium-ion battery.

[0099] Examples 25 to 34 Examples 25 to 34 are used to illustrate the non-aqueous electrolyte for lithium-ion batteries and its preparation method disclosed by the present invention, including most of the operation steps in Example 1, and the differences are as follows: 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.

[0100] The thermal shock test and the high-temperature cycling performance test are carried out by the above method, and the obtained test results are filled into Table 4.

[0101] Table 4

[0102] From the test results of Examples 1, 25 to 34, it can be seen that in the battery system provided by the present invention, when the mass percentage content a of the first additive in the non-aqueous electrolyte, the mass percentage content b of the second additive in the non-aqueous electrolyte, the mass percentage content c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, the thickness d of the ceramic coating and the mass percentage content e of silicon element in the negative electrode material layer satisfy the conditions 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 combinations of the first additive, the second additive and the non-fluorinated carboxylic acid ester are used, the high-temperature cycling performance and safety performance of the lithium-ion battery can still be improved to a certain extent, which indicates that the battery system provided by the present invention has good applicability to different first additives, second additives and non-fluorinated carboxylic acid esters.

[0103] Examples 35 to 38 Examples 35 to 38 are used to illustrate the non-aqueous electrolyte for lithium-ion batteries and its preparation method disclosed by the present invention, including most of the operation steps in Example 1, and the differences are as follows: The types of the positive electrode active materials are shown in Table 5.

[0104] The thermal shock test and the high-temperature cycling performance test are carried out by the above method, and the obtained test results are filled into Table 5.

[0105] Table 5

[0106] From the test results of Examples 1, 35 to 38, it can be seen that in the battery system provided by the present invention, the mass percentage content a of the first additive in the non-aqueous electrolyte, the mass percentage content b of the second additive in the non-aqueous electrolyte, the mass percentage content c of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, the thickness d of the ceramic coating, and the mass percentage content e of silicon element in the negative electrode material layer satisfy the condition 0.2 ≤ ≤ 33, and on the premise that 0.1 ≤ a ≤ 3, 0.5 ≤ b ≤ 5, 1 ≤ c ≤ 40, 0.2 ≤ d ≤ 7, 5 ≤ e ≤ 30, even if different combinations of lithium cobaltate positive electrode 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. This shows that the battery system provided by the present invention has good applicability to lithium cobaltate materials.

[0107] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope 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 disposed 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, and the first additive comprises a sulfur-containing additive shown in 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, in units of %; b is the mass percentage of the second additive in the non-aqueous electrolyte, in %; 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, characterized in that 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, characterized in that 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, characterized in that 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, characterized in that: The non-aqueous organic solvent also includes a non-fluorinated carboxylic acid ester; The non-aqueous electrolyte meets the following conditions: 0.5≤c / f≤2; Wherein, c is the mass percentage of 2,2-difluoroethyl acetate in the non-aqueous electrolyte, in units of %; 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, characterized in that 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, fluoroapatite, fluorophlogopite, mullite, aluminum titanate, copper oxide, titanium dioxide, and zinc oxide.

9. The lithium-ion battery according to claim 1, characterized in that: The silicon-based material includes one or more of silicon alone, silicon oxide, silicon-carbon composite material and silicon alloy material.

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

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