Electrolyte, lithium-ion secondary battery, battery module, battery pack, and electronic device

Abstract

The present application provides an electrolyte, a lithium-ion secondary battery, a battery module, a battery pack, and an electronic device. The electrolyte comprises a first component and a second component. The first component comprises ethyl methyl carbonate and ethylene carbonate; and on the basis of the mass of the electrolyte, the mass percentage content of ethyl methyl carbonate is W1%, the mass percentage content of ethylene carbonate is W2%, and the mass percentage content of the first component is W%, wherein 60≤W≤88, and 1.14≤W1 / W2≤1.93. The second component comprises lithium tetrafluoroborate and lithium difluorophosphate; and on the basis of the mass of the electrolyte, the mass percentage content of lithium tetrafluoroborate is m1%, the mass percentage content of lithium difluorophosphate is m2%, and the mass percentage content of the second component is m%, wherein 0.03≤m≤1.5, and 0.1≤m1 / m2≤25. By means of the configuration, an electrolyte system can have relatively good kinetic performance and improve the interfacial stability of positive electrodes and negative electrodes, thereby improving the safety performance and high-temperature cycle performance of lithium-ion secondary batteries.

Description

Electrolyte, lithium-ion secondary battery, battery module, battery pack and electronic device

[0001] This application claims priority to the Chinese patent application filed with the Patent Office of China on March 28, 2024, with application number 202410369752.9 and invention name “An electrolyte, lithium-ion secondary battery, battery module, battery pack and electronic device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of electrochemical technology, and in particular to an electrolyte, a lithium-ion secondary battery, a battery module, a battery pack, and an electronic device. Background Art

[0003] Lithium-ion batteries are widely used in electric vehicles and consumer electronics due to their high energy density, high output power, long cycle life, and low environmental pollution. As the scope of use of lithium-ion batteries continues to expand and their use scenarios become more diverse, the market has placed higher demands on the electrochemical performance of lithium-ion batteries. Lithium-ion batteries currently widely use non-aqueous electrolyte systems with lithium hexafluorophosphate as the conductive lithium salt. However, these non-aqueous electrolytes still have many shortcomings. For example, in high-voltage systems, the safety performance of these non-aqueous electrolytes needs to be improved, which affects the safety performance and high-temperature cycle performance of secondary batteries. Summary of the Invention

[0004] The purpose of this application is to provide an electrolyte, a lithium-ion secondary battery, a battery module, a battery pack, and an electronic device to improve the safety and high-temperature cycle performance of lithium-ion secondary batteries. The specific technical solution is as follows:

[0005] The first aspect of the present application provides an electrolyte comprising a first component and a second component. The first component comprises ethyl methyl carbonate and ethylene carbonate. Based on the mass of the electrolyte, the mass percentage of ethyl methyl carbonate is W1%, the mass percentage of ethylene carbonate is W2%, the mass percentage of the first component is W%, 60≤W≤88, 1.14≤W1 / W2≤1.93. The second component comprises lithium tetrafluoroborate and lithium difluorophosphate. Based on the mass of the electrolyte, the mass percentage of lithium tetrafluoroborate is m1%, the mass percentage of lithium difluorophosphate is m2%, and the mass percentage of the second component is m%, 0.03≤m≤1.5, 0.1≤m1 / m2≤25. By regulating the mass percentage W% of the first component and the ratio of W1 / W2 within the scope of the present application, the electrolyte system can have better kinetic performance and reduce side reactions at the negative electrode interface, thereby improving the stability of the negative electrode interface and improving the safety performance and high-temperature cycle performance of lithium-ion secondary batteries. By regulating the mass percentage m% and the value of m1 / m2 of the second component within the scope of this application, the interface stability of the positive and negative electrodes can be further improved, thereby further improving the safety performance and high-temperature cycle performance of the lithium-ion secondary battery.

[0006] In some embodiments of the present application, 75 ≤ W ≤ 88. By regulating the mass percentage W% of the first component within the above range, it is possible to improve the kinetic performance of the electrolyte system, reduce side reactions at the negative electrode interface, improve the stability of the negative electrode interface, and improve the safety performance and high-temperature cycle performance of the lithium-ion secondary battery.

[0007] In some embodiments of the present application, 32≤W1≤58, 0.01≤m1≤1.4. By regulating the mass percentage of ethyl methyl carbonate W1% and the mass percentage of lithium tetrafluoroborate m1% within the above ranges, the safety performance and high-temperature cycle performance of the lithium-ion secondary battery can be further improved.

[0008] In some embodiments of the present application, the electrolyte further includes a third component, the third component including at least one of diethyl sulfate or triphenyl phosphate, and the mass percentage of the third component is a ppm based on the mass of the electrolyte, where 10≤a≤1000. The electrolyte includes the third component within the above range and regulates the mass percentage of the third component a ppm within the above range, which can further enrich the components of the solid electrolyte interface film (SEI film) at the negative electrode interface, enhance the stability of the negative electrode interface, and further improve the safety performance and high-temperature cycle performance of the lithium-ion secondary battery.

[0009] In some embodiments of the present application, the electrolyte further includes a fourth component, the fourth component including at least one of triphenyl phosphite, triethyl phosphate, trimethyl phosphate, or vinyl sulfate, and the mass percentage of the fourth component is b%, based on the mass of the electrolyte, 0.1≤b≤1.1. The electrolyte includes the fourth component within the above range and regulates the mass percentage b% of the fourth component within the above range. The fourth component can form a stable interface at the positive electrode, increase the proportion of sulfide and / or phosphide in the positive electrode electrolyte interface film (CEI film), enhance the oxidation resistance of the positive electrode interface, and further improve the safety performance and high temperature cycle performance of the lithium-ion secondary battery.

[0010] In some embodiments of the present application, the electrolyte further includes a fifth component comprising a fluorine-containing inorganic salt; based on the mass of the electrolyte, the mass percentage of the fifth component is c ppm, where 2≤c≤500. Including the fifth component within the aforementioned range and regulating the mass percentage of the fifth component, c ppm, within the aforementioned range facilitates timely repair of damaged SEI films, reduces the probability of thermal runaway, and further improves the safety and high-temperature cycling performance of lithium-ion secondary batteries.

[0011] In some embodiments of the present application, the fifth component includes at least one of magnesium fluoride, potassium fluoride, calcium fluoride, lithium fluoride, sodium fluoride, silicon fluoride, iron fluoride, or zirconium fluoride. The electrolyte including the fifth component within the above range facilitates timely repair of damaged SEI films, reduces the probability of thermal runaway, and further improves the safety and high-temperature cycling performance of lithium-ion secondary batteries.

[0012] In some embodiments of the present application, the electrolyte further includes at least one of a third component, a fourth component, or a fifth component, the third component including at least one of diethyl sulfate or triphenyl phosphate, and the mass percentage of the third component based on the mass of the electrolyte is a ppm, the fourth component including at least one of triphenyl phosphite, triethyl phosphate, trimethyl phosphate, or vinyl sulfate, and the mass percentage of the fourth component based on the mass of the electrolyte is b%, the fifth component including at least one of magnesium fluoride, potassium fluoride, calcium fluoride, lithium fluoride, sodium fluoride, silicon fluoride, iron fluoride, or zirconium fluoride, and the mass percentage of the fifth component based on the mass of the electrolyte is c ppm, and the electrolyte satisfies at least one of the following characteristics: (1) 50≤a≤500; (2) 0.21≤b≤0.55; (3) 5≤c≤300. The electrolyte meeting at least one of the above characteristics can further improve the safety performance and high temperature cycle performance of the lithium ion secondary battery.

[0013] The second aspect of the present application provides a lithium-ion secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and the electrolyte provided by the first aspect of the present application. The positive electrode comprises a lithium-cobalt composite oxide, wherein the lithium-cobalt composite oxide includes at least three doping elements selected from aluminum, magnesium, titanium, zirconium, lanthanum, iridium, cerium, tungsten, zinc, nickel, manganese, boron, phosphorus, silicon, gallium, indium, and cesium; and the mass percentage of any one of the doping elements is 0.01% to 1% based on the mass of the lithium-cobalt composite oxide. The positive electrode comprising the lithium-cobalt composite oxide within the aforementioned range and regulating the mass percentage of any one of the doping elements within the aforementioned range is beneficial for improving the structural stability of the lithium-cobalt composite oxide in a highly delithiated state.

[0014] A third aspect of the present application provides a battery module, which includes the lithium-ion secondary battery provided in the second aspect of the present application.

[0015] A fourth aspect of the present application provides a battery pack, which includes the battery module provided in the third aspect of the present application.

[0016] The fifth aspect of the present application provides an electronic device, which includes the lithium-ion secondary battery provided by the second aspect of the present application, the battery module provided by the third aspect of the present application, or the battery pack provided by the fourth aspect of the present application.

[0017] Beneficial effects of this application:

[0018] The present application provides an electrolyte, a lithium-ion secondary battery, a battery module, a battery pack and an electronic device. The electrolyte includes a first component and a second component. The first component includes ethyl methyl carbonate and ethylene carbonate. Based on the mass of the electrolyte, the mass percentage of ethyl methyl carbonate is W1%, the mass percentage of ethylene carbonate is W2%, and the mass percentage of the first component is W%, 60≤W≤88, 1.14≤W1 / W2≤1.93. The second component includes lithium tetrafluoroborate and lithium difluorophosphate. Based on the mass of the electrolyte, the mass percentage of lithium tetrafluoroborate is m1%, the mass percentage of lithium difluorophosphate is m2%, and the mass percentage of the second component is m%, 0.03≤m≤1.5, 0.1≤m1 / m2≤25. The electrolyte with the above characteristics is applied to lithium-ion secondary batteries, which can make the electrolyte system have better kinetic performance and improve the interface stability of the positive and negative electrodes, thereby improving the safety performance and high-temperature cycle performance of the lithium-ion secondary battery.

[0019] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. All other embodiments obtained by those skilled in the art based on the present application are within the scope of protection of the present application.

[0021] The present application provides an electrolyte comprising a first component and a second component. The first component comprises ethyl methyl carbonate and ethylene carbonate. Based on the mass of the electrolyte, the mass percentage of ethyl methyl carbonate is W1%, the mass percentage of ethylene carbonate is W2%, and the mass percentage of the first component is W%, 60≤W≤88, 1.14≤W1 / W2≤1.93. In some embodiments of the present application, 75≤W≤88. For example, the mass percentage W% of the first component can be 60%, 63%, 65%, 68%, 70%, 73%, 75%, 78%, 80%, 83%, 85%, 88% or a range consisting of any two of the values ​​therein. The value of W1 / W2 can be 1.14, 1.20, 1.30, 1.40, 1.50, 1.60, 1.70, 1.80, 1.90, 1.93 or a range consisting of any two of the values ​​therein. The second component includes lithium tetrafluoroborate and lithium difluorophosphate. Based on the mass of the electrolyte, the mass percentage of lithium tetrafluoroborate is m1%, the mass percentage of lithium difluorophosphate is m2%, and the mass percentage of the second component is m%, 0.03≤m≤1.5, and 0.1≤m1 / m2≤25. For example, the mass percentage of the second component m% can be 0.03%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, or a range consisting of any two of these values. The value of m1 / m2 can be 0.1, 1, 3, 5, 8, 10, 13, 15, 18, 20, 23, 25, or a range consisting of any two of these values.

[0022] The inventors have found that the electrolyte includes a first component, ethyl methyl carbonate and ethylene carbonate. On the one hand, the electrolyte system can have better kinetic properties; on the other hand, ethyl methyl carbonate, which has better reduction resistance at the negative electrode, is used as the main solvent, and ethylene carbonate, which has better negative electrode film-forming effect, is used as the auxiliary solvent. Controlling the ratio W1 / W2 of the two within the scope of this application can reduce the side reactions of the negative electrode and improve the stability of the negative electrode interface. When the external temperature rises, the highly stable negative electrode interface can inhibit the reaction of the electrolyte at the negative electrode, reduce the temperature rise inside the lithium-ion secondary battery, delay the failure time of the lithium-ion secondary battery, and improve the safety performance of the lithium-ion secondary battery. In addition, by simultaneously introducing lithium tetrafluoroborate and lithium difluorophosphate into the electrolyte, lithium tetrafluoroborate can be reduced at the positive and negative electrode interfaces before the solvent, further improving the stability of the positive and negative electrode interfaces. However, lithium tetrafluoroborate can increase the interfacial impedance. The introduction of lithium difluorophosphate can weaken the effect of lithium tetrafluoroborate on the interfacial impedance of the positive and negative electrodes. The two work synergistically to further improve the interfacial stability of the positive and negative electrodes while also reducing the effect of lithium tetrafluoroborate on the interfacial impedance, thereby further improving the safety and high-temperature cycling performance of the lithium-ion secondary battery. When the mass percentage W% of the first component is too low, for example, less than 60%, the content of ethyl methyl carbonate and ethylene carbonate is low, and the negative electrode interface stability cannot be effectively improved. When the mass percentage W% of the first component is too high, for example, greater than 88%, the mass percentage of the lithium salt is too low, affecting the cycling performance of the lithium-ion secondary battery. When the value of W1 / W2 is too small, for example, less than 1.14, the ethylene carbonate content is too high, and the excess ethylene carbonate will be oxidized at the positive electrode, resulting in a drop in the safety temperature; when the value of W1 / W2 is too large, for example, greater than 1.93, the ethylene carbonate content is too low, and the negative electrode film formation stability decreases, resulting in a drop in the safety temperature. When the value of m1 / m2 is too small, for example, less than 0.1, the film formation reaction of lithium tetrafluoroborate on the interface is too weak, and the interface stability cannot be effectively improved; and when the value of m1 / m2 is too large, for example, greater than 25, the content of lithium difluorophosphate is too small, and the high interface impedance problem caused by lithium tetrafluoroborate cannot be effectively alleviated, affecting the cycle performance of the lithium ion secondary battery. When the electrolyte includes a first component of ethyl methyl carbonate and ethylene carbonate, and a second component of lithium tetrafluoroborate and lithium difluorophosphate, and the mass percentage W of the first component, the value of W1 / W2, the mass percentage m of the second component, and the value of m1 / m2 are regulated within the scope of this application, the safety performance and high-temperature cycle performance of the lithium ion secondary battery can be improved. In this application, high temperature generally refers to a temperature greater than or equal to 30°C.

[0023] In some embodiments of the present application, 32≤W1≤58, 0.01≤m1≤1.4. For example, the mass percentage content W1% of ethyl methyl carbonate can be 32%, 35%, 38%, 40%, 43%, 45%, 48%, 50%, 53%, 55%, 58% or a range consisting of any two of the values, and the mass percentage content m1% of lithium tetrafluoroborate can be 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.8%, 1%, 1.2%, 1.4% or a range consisting of any two of the values. By regulating the mass percentage content W1% of ethyl methyl carbonate and the mass percentage content of lithium tetrafluoroborate to be m1% within the above range, the safety performance and high temperature cycle performance of the lithium ion secondary battery can be further improved.

[0024] In some embodiments of the present application, 21≤W2≤41. For example, the mass percentage content W2% of ethylene carbonate can be 21%, 25%, 28%, 30%, 32%, 35%, 38%, 41%, or a range consisting of any two of these values. By regulating the mass percentage content W2% of ethylene carbonate within the above range, the safety performance and high-temperature cycle performance of the lithium-ion secondary battery can be further improved.

[0025] In some embodiments of the present application, 0.01≤m2≤1.3. For example, the mass percentage m2 of lithium difluorophosphate can be 0.01, 0.05, 0.1, 0.5, 0.8, 1, 1.3, or a range consisting of any two of these values. By regulating the mass percentage m2 of lithium difluorophosphate within the above range, the safety performance and high-temperature cycle performance of the lithium-ion secondary battery can be further improved.

[0026] In some embodiments of the present application, the electrolyte further comprises a third component, the third component comprising at least one of diethyl sulfate or triphenyl phosphate, and the mass percentage of the third component is a ppm based on the mass of the electrolyte, 10≤a≤1000. In some embodiments of the present application, 50≤a≤500. For example, the mass percentage content a ppm of the third component can be 10ppm, 50ppm, 100ppm, 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm or a range consisting of any two values ​​thereof. The electrolyte comprises a third component within the above range and regulates the mass percentage content a ppm of the third component within the above range, which can further enrich the components of the solid electrolyte interface film (SEI film) at the negative electrode interface, enhance the stability of the negative electrode interface, and further improve the safety performance and high temperature cycle performance of the lithium ion secondary battery.

[0027] In some embodiments of the present application, the electrolyte further includes a fourth component, the fourth component including at least one of triphenyl phosphite, triethyl phosphate, trimethyl phosphate or vinyl sulfate, and the mass percentage of the fourth component is b%, 0.1≤b≤1.1 based on the mass of the electrolyte. In some embodiments of the present application, 0.21≤b≤0.55. For example, the mass percentage b% of the fourth component can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.1% or a range consisting of any two values ​​therein. The electrolyte includes the fourth component within the above range and regulates the mass percentage b% of the fourth component within the above range. The fourth component can form a stable interface at the positive electrode, increase the proportion of sulfide and / or phosphide in the positive electrode electrolyte interface film (CEI film), enhance the oxidation resistance of the positive electrode interface, and further improve the safety performance and high temperature cycle performance of the lithium-ion secondary battery.

[0028] In some embodiments of the present application, the electrolyte further comprises a fifth component, the fifth component comprising a fluorine-containing inorganic salt; based on the mass of the electrolyte, the mass percentage of the fifth component is c ppm, 2≤c≤500. In some embodiments of the present application, 5≤c≤300. For example, the mass percentage of the fifth component c ppm can be 2ppm, 5ppm, 10ppm, 50ppm, 100ppm, 150ppm, 200ppm, 250ppm, 300ppm, 350ppm, 400ppm, 450ppm, 500ppm or a range consisting of any two values ​​therein. The electrolyte comprises the fifth component within the above range and regulates the mass percentage of the fifth component c ppm within the above range, which is conducive to timely repairing the damaged SEI film, reducing the probability of thermal runaway, and further improving the safety performance and high temperature cycle performance of the lithium-ion secondary battery.

[0029] In some embodiments of the present application, the fifth component includes at least one of magnesium fluoride, potassium fluoride, calcium fluoride, lithium fluoride, sodium fluoride, silicon fluoride, iron fluoride, or zirconium fluoride. The electrolyte including the fifth component within the above range facilitates timely repair of damaged SEI films, reduces the probability of thermal runaway, and further improves the safety and high-temperature cycling performance of lithium-ion secondary batteries.

[0030] In some embodiments of the present application, the electrolyte of the present application further includes an electrolyte salt. The electrolyte salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the electrolyte salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), bistrifluoromethanesulfonyl imide lithium LiN(CF3SO2)2(LiTFSI), bis(fluorosulfonyl)imide lithium Li(N(SO2F)2)(LiFSI), lithium hexafluorocesium oxide (LiCsF6), lithium perchlorate (LiClO4) or lithium trifluoromethanesulfonate (LiCF3SO3). The present application has no particular restrictions on the content of the electrolyte salt, as long as the purpose of the present application can be achieved. For example, based on the mass of the electrolyte, the mass percentage of the electrolyte salt is 10% to 15%.

[0031] In some embodiments of the present application, the electrolyte may further include a non-aqueous organic solvent. For example, the non-aqueous solvent may include, but is not limited to, at least one of a carbonate compound, a carboxylate compound, an ether compound, or other organic solvents.

[0032] Above-mentioned carbonate compound can include but not limited to at least one in linear carbonate compound, cyclic carbonate compound or fluorinated carbonate compound.Above-mentioned linear carbonate compound can include but not limited to at least one in dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC) or ethyl propyl carbonate (EPC).Above-mentioned cyclic carbonate can include but not limited to at least one in propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound may include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The above-mentioned carboxylate compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerolactone, or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile or trioctyl phosphate. The present application does not particularly limit the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved. For example, based on the mass of the electrolyte, the mass percentage of the non-aqueous organic solvent is 0% to 25%.

[0033] In some embodiments of the present application, the electrolyte includes a first component, a second component, and at least one of a third component, a fourth component, and a fifth component. By regulating the mass percentages of the first component, the second component, and at least one of the third component, the fourth component, and the fifth component within the scope of the present application, the safety performance and high-temperature cycle performance of the lithium-ion secondary battery can be further improved.

[0034] The second aspect of the present application provides a lithium-ion secondary battery comprising a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and the electrolyte provided by the first aspect of the present application, wherein the positive electrode comprises a positive electrode active material, the positive electrode active material comprises a lithium cobalt composite oxide, the lithium cobalt composite oxide comprises at least three doping elements selected from aluminum, magnesium, titanium, zirconium, lanthanum, iridium, cerium, tungsten, zinc, nickel, manganese, boron, phosphorus, silicon, gallium, indium, and cesium; based on the mass of the lithium cobalt composite oxide, the mass percentage of any one of the doping elements is 0.01% to 1%. For example, the mass percentage of any one of the doping elements can be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, or a range consisting of any two of these values. The positive electrode comprises a lithium cobalt composite oxide within the above range and the mass percentage of any one of the doping elements is regulated within the above range, which is beneficial for improving the structural stability of the lithium cobalt composite oxide in a highly delithiated state.

[0035] The present application does not particularly limit the preparation method of the above-mentioned lithium cobalt composite oxide positive electrode active material containing doping elements, as long as the purpose of the present application can be achieved. For example, the preparation method of the lithium cobalt composite oxide positive electrode active material containing doping elements may include but is not limited to the following steps: the lithium cobalt composite oxide is mixed with the compound containing the doping element and then heat-treated in an oxygen atmosphere or an air atmosphere to obtain a lithium cobalt composite oxide containing the doping element. The lithium cobalt composite oxide may include but is not limited to at least one of lithium nickel cobalt manganese oxide (NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide or lithium cobalt oxide (LiCoO2). When the doping element is aluminum, magnesium, titanium, zirconium, lanthanum, iridium, cerium, tungsten, zinc, nickel, manganese, boron, phosphorus, silicon, gallium, indium, and cesium, an oxide containing the doping element, a hydroxide containing the doping element, and a carbonate compound containing the doping element may be added accordingly, and can be selected according to actual needs, as long as the purpose of the present application can be achieved. The present application does not particularly limit the heat treatment temperature or time, as long as the purpose of the present application can be achieved. For example, the heat treatment temperature is 650°C to 1100°C and the time is 22 hours to 26 hours. The mass percentage of the doping element in the lithium cobalt composite oxide positive electrode active material including the doping element can be controlled by adjusting the amount of the compound containing the doping element added.

[0036] The positive electrode of the present application includes a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector, and the positive electrode material layer includes the above-mentioned positive electrode active material. The present application has no special restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector), etc. In the present application, there is no special restriction on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5μm to 20μm. The thickness of the single-sided positive electrode material layer is 30μm to 120μm. In the present application, the positive electrode material layer can be arranged on one surface in the thickness direction of the positive electrode current collector, or on two surfaces in the thickness direction of the positive electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the positive electrode current collector or a partial area of ​​the positive electrode current collector. The present application has no special restrictions, as long as the purpose of the present application can be achieved. In the present application, the positive electrode material may also include other positive electrode active materials, such as lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, etc.

[0037] The cathode material layer of the present application may further include a conductive agent and a binder. The present application has no particular restrictions on the types of the conductive agent and the binder, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metallic materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metallic materials may include but are not limited to metal powder and / or metal fibers, and specifically, the metal may include but are not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. For example, the binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamideimide, styrene-butadiene rubber, or polyvinylidene fluoride.

[0038] There is no particular limitation on the negative electrode in this application, as long as the object of this application can be achieved. For example, the negative electrode includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. In this application, the negative electrode material layer can be provided on one surface in the thickness direction of the negative electrode current collector, or can be provided on both surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of the negative electrode current collector or a partial area of the negative electrode current collector. There is no particular limitation in this application, as long as the object of this application can be achieved. There is no particular limitation on the negative electrode current collector in this application, as long as the object of this application can be achieved. For example, the negative electrode current collector can include, but is not limited to, copper foil, copper alloy foil, nickel foil, titanium foil, nickel foam, copper foam, or composite current collector, etc. The negative electrode material layer of this application contains a negative electrode active material. There is no particular limitation on the type of the negative electrode active material in this application, as long as the object of this application can be achieved. For example, the negative electrode active material can include, but is not limited to, natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0 < x ≤ 2), or metallic lithium, etc., at least one of them. In this application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode material layer, as long as the object of this application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm, and the thickness of the single-sided negative electrode material layer is 30 μm to 130 μm. The negative electrode material layer of this application can also contain a conductive agent and a binder. There is no particular limitation on the conductive agent and the binder in this application, as long as the object of this application can be achieved. For example, the binder and the conductive agent can include, but are not limited to, at least one of the above-mentioned conductive agents and the above-mentioned binders.

[0039] The present application has no particular restrictions on the isolation membrane, as long as the purpose of the present application can be achieved. For example, the material of the isolation membrane may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (such as polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of isolation membrane may include at least one of a woven membrane, a non-woven membrane (non-woven fabric), a microporous membrane, a composite membrane, a rolled membrane or a spun membrane. The diaphragm of the present application may have a porous structure, and the porous layer is provided on at least one surface of the diaphragm, and the porous layer includes inorganic particles and a binder. The inorganic particles may include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The binder may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The present application does not particularly limit the size of the pore size of the porous structure, as long as the purpose of the present application can be achieved. For example, the pore size can be 0.01 μm to 1 μm. In the present application, the thickness of the diaphragm is not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickness can be 3 μm to 30 μm.

[0040] The lithium-ion secondary battery of the present application further includes a housing, which may be a hard shell or a flexible shell. The hard shell may be made of a metal. The present application does not limit the type of metal; any metal hard shell known in the art may be used as long as the purpose of the present application is achieved. The flexible shell may be a metal plastic film, such as an aluminum plastic film or a steel plastic film.

[0041] The preparation process of the lithium-ion secondary battery of the present application is well known to those skilled in the art and is not particularly limited in the present application. For example, the preparation process of the lithium-ion secondary battery may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a lithium-ion secondary battery. Alternatively, stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a lithium-ion secondary battery. In addition, as needed, overcurrent protection elements, guide plates, etc. may be placed in the shell to prevent pressure rise and overcharge and discharge inside the lithium-ion secondary battery.

[0042] A third aspect of the present application provides a battery module comprising the lithium-ion secondary battery provided in the second aspect of the present application. The lithium-ion secondary batteries can be assembled into a battery module, and the number of lithium-ion secondary batteries contained in the battery module can be one or more, with those skilled in the art selecting the specific number based on the application and capacity of the battery module.

[0043] A fourth aspect of the present application provides a battery pack comprising the battery modules provided in the third aspect of the present application. The battery modules can be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, with those skilled in the art selecting the specific number based on the application and capacity of the battery pack.

[0044] A fifth aspect of the present application provides an electronic device comprising at least one of the lithium-ion secondary battery provided in the second aspect of the present application, the battery module provided in the third aspect, or the battery pack provided in the fourth aspect. The lithium-ion secondary battery, battery module, or battery pack can be used as a power source for the electronic device or as an energy storage unit for the electronic device. The electronic device can select a lithium-ion secondary battery, battery module, or battery pack based on its usage requirements.

[0045] The present application does not particularly limit the electronic device, and it can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery or a lithium-ion capacitor, etc.

[0046] Example

[0047] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0048] Test methods and equipment:

[0049] Safety performance testing

[0050] A lithium-ion battery was placed in a 25°C environment and charged to 4.3V at a constant current of 0.5C. It was then charged to 0.025C at a constant voltage of 4.3V. A temperature-sensing wire was attached to the surface of the lithium-ion battery near the positive electrode tab. The lithium-ion battery was then placed in an oven with an initial temperature of 25°C. The oven was heated at a rate of 1°C / second. When the oven temperature reached a certain temperature, the lithium-ion battery would experience thermal runaway. If the surface temperature of the lithium-ion battery increased by 30°C within 3 seconds, the lithium-ion battery was considered to have experienced thermal runaway. The temperature T0 in the oven before thermal runaway occurred was recorded. T0 is the safety temperature of the lithium-ion battery. Five lithium-ion batteries were tested for each set of examples or comparative examples, and the average value was taken as the safety temperature of that example or comparative example. The higher the safety temperature, the better the safety performance of the lithium-ion secondary battery.

[0051] High temperature cycle performance test

[0052] Place the lithium-ion battery in a 45°C environment, charge it to 4.3V at a constant current of 0.5C, let it stand for 30 minutes, and then discharge it to 3.0V at a constant current of 0.5C. Record the initial discharge capacity of the lithium-ion battery as C1. Cycle it 200 times under this charge and discharge condition, and record the discharge capacity of the lithium-ion battery after 200 cycles as C. 200 , calculate the capacity retention rate of lithium-ion batteries.

[0053] Capacity retention rate = C 200 / C1×100%, the capacity retention rate is used to characterize the high-temperature cycle performance of the lithium-ion battery. The higher the capacity retention rate, the better the high-temperature cycle performance of the lithium-ion secondary battery.

[0054] Testing of doping element content in positive electrode active materials

[0055] Lithium-ion batteries were disassembled, the positive electrode plates were separated, and a solid powder sample was scraped off the positive electrode plates using a knife. 0.2 g of the solid powder sample was weighed and dissolved in a 42% nitric acid solution. The nitric acid solution was then analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES) to determine the type and mass percentage of the doping element.

[0056] Example 1-1

[0057] <Preparation of Electrolyte>

[0058] In an argon atmosphere glove box with a water content of less than 10 ppm, ethyl methyl carbonate and ethylene carbonate were added in a mass ratio W1 / W2 of 1.14, and then an organic solvent, sulfolane, as well as lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium difluorophosphate were added, and stirred uniformly to obtain an electrolyte. The electrolyte solution comprises, based on the mass of the electrolyte, ethyl methyl carbonate (W1%), 32% by mass; ethylene carbonate (W2%), 28% by mass; lithium tetrafluoroborate (m1%), 0.1% by mass; lithium difluorophosphate (m2%), 0.1% by mass; lithium hexafluorophosphate (11.5%) by mass; and the balance being the organic solvent.

[0059] <Preparation of Separator>

[0060] Aluminum oxide, a thickener (sodium carboxymethyl cellulose), and a wetting agent (dimethylsiloxane) were mixed in a mass ratio of 95:0.5:4.5, deionized water was added, and the mixture was stirred evenly in a vacuum mixer to obtain a porous coating slurry with a viscosity of 40 mPa·s and a solid content of 5%. The porous coating slurry was evenly coated on one surface of a 10 μm thick polyethylene porous substrate and dried in an 85°C oven for 4 hours to obtain a single-sided porous coating separator with a coating weight of 1 mg / 1000 mm. 2 The above coating process was repeated on the other surface of the polyethylene porous substrate to obtain a separator coated with a porous coating on both sides.

[0061] <Preparation of positive electrode sheet>

[0062] The positive electrode active material is lithium nickel cobalt manganese oxide LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), positive electrode binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black are mixed in a mass ratio of 96:2:2, N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 70wt%. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 14μm, and baked at 120°C for 1 hour to obtain a positive electrode sheet with a single-sided positive electrode material layer coated with a coating thickness of 110μm. Repeat the above steps on the other surface of the positive electrode current collector aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode material layer coated. Then, after drying under vacuum conditions at 120°C for 1 hour, a positive electrode sheet with a specification of 74mm×867mm is obtained by cold pressing, cutting, slitting, and welding the pole ears. Among them, the compaction density of the positive electrode material layer is 3.4g / cm 3 .

[0063] <Preparation of negative electrode sheet>

[0064] The negative electrode active material artificial graphite, sodium carboxymethyl cellulose (CMC), and the negative electrode binder styrene-butadiene rubber are mixed in a mass ratio of 85:2:13, deionized water is added, and the mixture is stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry with a solid content of 28wt%. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 12μm, and baked at 120°C for 1 hour to obtain a negative electrode sheet with a single-sided coating of a negative electrode material layer with a coating thickness of 100μm. The above steps are repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode sheet with a double-sided coating of a negative electrode material layer. Then, after drying under vacuum conditions at 120°C for 1 hour, a negative electrode sheet with a specification of 76mm×875mm is obtained by cold pressing, cutting, slitting, and welding the pole ears. Among them, the compaction density of the negative electrode material layer is 1.6g / cm 3 .

[0065] <Preparation of Lithium Ion Secondary Battery>

[0066] The separator, positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrode sheets, and then wound to form an electrode assembly. The electrode assembly is placed in an aluminum foil bag, and the positive and negative tabs are led out of the bag's interior. After baking at 80°C for 12 hours to remove moisture, electrolyte is injected. The battery undergoes vacuum packaging, resting, formation, degassing, trimming, and shaping to produce a lithium-ion secondary battery. The upper formation voltage is 4.15V, the formation temperature is 70°C, and the formation rest time is 2 hours.

[0067] Example 1-2 to Example 1-16

[0068] The preparation of the electrolyte was the same as in Example 1-1 except that the mass percentages of ethyl methyl carbonate, ethylene carbonate, lithium tetrafluoroborate, and lithium difluorophosphate were adjusted according to Table 1, the mass percentages of the organic solvent were changed accordingly, and the mass percentage of lithium hexafluorophosphate remained unchanged.

[0069] Example 2-1 to Example 2-11

[0070] The preparation of the electrolyte was the same as in Example 1-11, except that the third component was added and the mass percentage of the third component was adjusted as shown in Table 2, wherein the mass percentage of the organic solvent was changed accordingly, and the mass percentages of the first component, the second component, and the lithium salt lithium hexafluorophosphate remained unchanged.

[0071] Example 3-1 to Example 3-14

[0072] The preparation of the electrolyte was the same as in Example 2-5, except that the fourth component was added and the mass percentage of the fourth component was adjusted as shown in Table 3, wherein the mass percentage of the organic solvent was changed accordingly, and the mass percentages of the first component, the second component, the third component and the lithium salt lithium hexafluorophosphate remained unchanged.

[0073] Example 4-1 to Example 4-11

[0074] The preparation of the electrolyte was the same as in Examples 3-6, except that the fifth component was added and the mass percentage of the fifth component was adjusted as shown in Table 4, wherein the mass percentage of the organic solvent was changed accordingly, and the mass percentages of the first component, the second component, the third component, the fourth component and the lithium salt lithium hexafluorophosphate remained unchanged.

[0075] Example 5-1 to Example 5-4

[0076] The preparation of the electrolyte was the same as in Example 1-11 except that the relevant parameters were adjusted as shown in Table 5, wherein the mass percentage of the organic solvent changed after the third component, the fourth component, and the fifth component were added, and the mass percentage of the first component, the second component, and the lithium salt lithium hexafluorophosphate remained unchanged.

[0077] Example 6-1

[0078] <Preparation of positive electrode active material>

[0079] Lithium nickel cobalt manganese oxide (NCM811), Al2O3, MgO, and TiO2 were uniformly mixed in a mass ratio of 19700:1:100:200 and calcined at 800°C in an oxygen atmosphere to obtain a lithium cobalt composite oxide positive electrode active material doped with aluminum, magnesium, and titanium. The mass percentage of aluminum, magnesium, and titanium, based on the mass of the positive electrode active material, was 0.01%, 0.5%, and 1%, respectively.

[0080] Except that the preparation of the positive electrode active material was carried out according to the above steps, the rest was the same as that of Example 1-11.

[0081] Example 6-2

[0082] Except for adjusting the mass ratio of lithium nickel cobalt manganese oxide NCM811, Al2O3, MgO, and TiO2 in <Preparation of positive electrode active material> so that the mass percentage of doping elements of aluminum, magnesium, and titanium is as shown in Table 6, the rest is the same as Example 6-1.

[0083] Example 6-3, Example 6-4

[0084] The preparation method was the same as Example 6-1, except that the type of doping element and the mass ratio of lithium nickel cobalt manganese oxide NCM811 to the compound containing the doping element were adjusted in the "Preparation of Positive Electrode Active Material" so that the type and mass percentage of the doping element were as shown in Table 6. The zinc-containing compound was zinc oxide, the boron-containing compound was boron oxide, the phosphorus-containing compound was lithium phosphate, the gallium-containing compound was gallium oxide, and the indium-containing compound was indium oxide.

[0085] Comparative Examples 1 to 7

[0086] The preparation of the electrolyte was the same as in Examples 1-2, except that the mass percentages of ethyl methyl carbonate, ethylene carbonate, lithium tetrafluoroborate, and lithium difluorophosphate were adjusted according to Table 1. The mass percentages of the organic solvents in Comparative Examples 1, 3, 4, 5, 6, 7, and 8 were changed accordingly, while the mass percentage of the lithium hexafluorophosphate remained unchanged. In Comparative Example 2, the mass percentage of the organic solvent sulfolane was 0, and the mass percentage of the lithium hexafluorophosphate was 10.8%. The preparation was the same as in Examples 1-2.

[0087] Comparative Example 8

[0088] The preparation of the electrolyte was the same as in Example 1-9 except that lithium tetrafluoroborate and lithium difluorophosphate were not added, the mass percentages of ethyl methyl carbonate and ethylene carbonate remained unchanged, the mass percentage of lithium salt lithium hexafluorophosphate remained unchanged, and the mass percentage of the organic solvent was changed accordingly.

[0089] Comparative Example 9

[0090] The preparation of the electrolyte was the same as in Example 1-9 except that lithium difluorophosphate was not added, the mass percentages of ethyl methyl carbonate and ethylene carbonate remained unchanged, the mass percentage of lithium salt lithium hexafluorophosphate remained unchanged, and the mass percentage of the organic solvent was changed accordingly.

[0091] Comparative Example 10

[0092] The preparation of the electrolyte was the same as in Example 1-9 except that lithium tetrafluoroborate was not added, the mass percentages of ethyl methyl carbonate and ethylene carbonate remained unchanged, the mass percentage of lithium hexafluorophosphate remained unchanged, and the mass percentage of the organic solvent was changed accordingly.

[0093] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 6.

[0094] Table 1 Note: “ / ” in Table 1 indicates no relevant parameters.

[0095] It can be seen from Examples 1-1 to 1-16 and Comparative Examples 1 to 10 that the electrolyte of the lithium-ion secondary battery in each embodiment of the present application includes first components ethyl methyl carbonate and ethylene carbonate, and second components lithium tetrafluoroborate and lithium difluorophosphate, and the mass percentage W and W1 / W2 values ​​of the first component, and the mass percentage m and m1 / m2 values ​​of the second component are regulated within the scope of the present application, while the lithium-ion secondary battery in the comparative example does not meet the above characteristics at the same time. The lithium-ion battery in each embodiment has a higher safety temperature and a higher capacity retention rate, indicating that the safety performance and high-temperature cycle performance of the lithium-ion secondary battery are improved.

[0096] The mass percentage W1% of ethyl methyl carbonate usually affects the safety performance and high-temperature cycle performance of lithium-ion secondary batteries. It can be seen from Examples 1-1 to 1-8 that by adjusting the value of W1% within the scope of this application, the lithium-ion secondary battery can have a higher safety temperature and a higher capacity retention rate, indicating that the lithium-ion secondary battery has good safety performance and high-temperature cycle performance.

[0097] The mass percentage content m1% of lithium tetrafluoroborate usually affects the safety performance and high-temperature cycle performance of lithium-ion secondary batteries. It can be seen from Examples 1-9 to 1-16 that by regulating the value of m1% within the scope of this application, the lithium-ion secondary battery can have a higher safety temperature and a higher capacity retention rate, indicating that the lithium-ion secondary battery has good safety performance and high-temperature cycle performance.

[0098] Table 2 Note: “ / ” in Table 2 indicates no relevant parameters.

[0099] It can be seen from Examples 1-11 and 2-1 to 2-11 that, by further introducing a third component into the electrolyte comprising the first component ethyl methyl carbonate and ethylene carbonate and the second component lithium tetrafluoroborate and lithium difluorophosphate, the safe temperature and capacity retention rate of the lithium-ion secondary battery can be further improved, indicating that the safety performance and high-temperature cycle performance of the lithium-ion secondary battery are further improved.

[0100] The type of the third component usually affects the safety performance and high-temperature cycle performance of the lithium-ion secondary battery. It can be seen from Examples 2-7, 2-10, and 2-11 that when the type of the third component is within the scope of this application, the lithium-ion secondary battery can have a higher safety temperature and a higher capacity retention rate, indicating that the lithium-ion secondary battery has good safety performance and high-temperature cycle performance.

[0101] The mass percentage content a ppm of the third component usually affects the safety performance and high-temperature cycle performance of the lithium-ion secondary battery. It can be seen from Examples 2-1 to 2-9 that when the mass percentage content a ppm of the third component is within the range of this application, the lithium-ion secondary battery can have a higher safety temperature and a higher capacity retention rate, indicating that the lithium-ion secondary battery has good safety performance and high-temperature cycle performance.

[0102] Table 3 Note: “ / ” in Table 3 indicates no relevant parameters.

[0103] It can be seen from Examples 2-5 and 3-1 to 3-14 that, by further introducing a fourth component into the electrolyte comprising a first component of ethyl methyl carbonate and ethylene carbonate, a second component of lithium tetrafluoroborate and lithium difluorophosphate, and a third component, the safe temperature and capacity retention rate of the lithium-ion secondary battery can be further improved, indicating that the safety performance and high-temperature cycle performance of the lithium-ion secondary battery are further improved.

[0104] The type of the fourth component usually affects the safety performance and high-temperature cycle performance of the lithium-ion secondary battery. It can be seen from Examples 3-2, 3-13, and 3-14 that when the type of the fourth component is within the scope of this application, the lithium-ion secondary battery can have a higher safety temperature and a higher capacity retention rate, indicating that the lithium-ion secondary battery has good safety performance and high-temperature cycle performance.

[0105] The mass percentage b% of the fourth component usually affects the safety performance and high-temperature cycle performance of the lithium-ion secondary battery. It can be seen from Examples 3-1 to 3-11 that when the mass percentage b% of the fourth component is within the range of this application, the lithium-ion secondary battery can have a higher safety temperature and a higher capacity retention rate, indicating that the lithium-ion secondary battery has good safety performance and high-temperature cycle performance.

[0106] Table 4 Note: “ / ” in Table 4 indicates no relevant parameters.

[0107] It can be seen from Examples 3-6 and 4-1 to 4-11 that, by further introducing a fifth component into the electrolyte comprising a first component of ethyl methyl carbonate and ethylene carbonate, a second component of lithium tetrafluoroborate and lithium difluorophosphate, a third component, and a fourth component, the safe temperature and capacity retention rate of the lithium-ion secondary battery can be further improved, indicating that the safety performance and high-temperature cycle performance of the lithium-ion secondary battery are further improved.

[0108] The researchers of this application found that the type of the fifth component usually affects the safety performance and high-temperature cycle performance of the lithium-ion secondary battery. It can be seen from Examples 4-6 and 4-11 that when the type of the fifth component is within the scope of this application, the lithium-ion secondary battery can have a higher safety temperature and a higher capacity retention rate, indicating that the lithium-ion secondary battery has good safety performance and high-temperature cycle performance.

[0109] The researchers of this application found that the mass percentage content c ppm of the fifth component usually affects the safety performance and high-temperature cycle performance of the lithium-ion secondary battery. It can be seen from Examples 4-1 to 4-10 that when the mass percentage content c ppm of the fifth component is within the range of this application, the lithium-ion secondary battery can have a higher safety temperature and a higher capacity retention rate, indicating that the lithium-ion secondary battery has good safety performance and high-temperature cycle performance.

[0110] Table 5 Note: “ / ” in Table 5 indicates no relevant parameters.

[0111] It can be seen from Examples 1-11, 2-5, 3-6, 4-5, and 5-1 to 5-4 that the first component, the second component, and at least one of the third component, the fourth component, and the fifth component all have good superposition properties. When the electrolyte further includes at least one of the third component, the fourth component, and the fifth component on the basis of the first component and the second component, the safe temperature and capacity retention rate of the lithium-ion secondary battery are further improved, indicating that the safety performance and high-temperature cycle performance of the lithium-ion secondary battery are further improved.

[0112] Table 6 Note: “ / ” in Table 6 indicates no relevant parameters.

[0113] The type of positive electrode active material usually affects the safety performance and high-temperature cycle performance of lithium-ion secondary batteries. It can be seen from Examples 1-11 and Examples 6-1 to 6-4 that when the type and mass percentage of the doping elements in the positive electrode active material are within the scope of this application, the lithium-ion secondary battery can have a higher safety temperature and a higher capacity retention rate, indicating that the lithium-ion secondary battery has good safety performance and high-temperature cycle performance.

[0114] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrolyte for a lithium ion secondary battery, comprising a first component and a second component, wherein the first component comprises ethyl methyl carbonate and ethylene carbonate, wherein, based on the mass of the electrolyte, the mass percentage of the ethyl methyl carbonate is W1%, the mass percentage of the ethylene carbonate is W2%, and the mass percentage of the first component is W%, 60≤W≤88, and 1.14≤W1 / W2≤1.93; The second component includes lithium tetrafluoroborate and lithium difluorophosphate. Based on the mass of the electrolyte, the mass percentage of the lithium tetrafluoroborate is m1%, the mass percentage of the lithium difluorophosphate is m2%, and the mass percentage of the second component is m%, 0.03≤m≤1.5, 0.1≤m1 / m2≤25.

2. The electrolyte according to claim 1, wherein 75≤W≤88。 3. The electrolyte according to claim 1, wherein 32≤W1≤58, 0.01≤m1≤1.

4.

4. The electrolyte according to any one of claims 1 to 3, wherein The electrolyte further includes a third component, which includes at least one of diethyl sulfate and triphenyl phosphate. Based on the mass of the electrolyte, the mass percentage of the third component is a ppm, 10≤a≤1000.

5. The electrolyte according to any one of claims 1 to 3, wherein The electrolyte also includes a fourth component, which includes at least one of triphenyl phosphite, triethyl phosphate, trimethyl phosphate or vinyl sulfate; based on the mass of the electrolyte, the mass percentage of the fourth component is b%, and 0.1≤b≤1.

1.

6. The electrolyte according to any one of claims 1 to 3, wherein The electrolyte further includes a fifth component, which includes a fluorine-containing inorganic salt; based on the mass of the electrolyte, the mass percentage content of the fifth component is c ppm, 2≤c≤500.

7. The electrolyte according to claim 6, wherein The fifth component includes at least one of magnesium fluoride, potassium fluoride, calcium fluoride, lithium fluoride, sodium fluoride, silicon fluoride, iron fluoride or zirconium fluoride.

8. The electrolyte according to any one of claims 1 to 3, further comprising at least one of a third component, a fourth component, or a fifth component; the third component comprising at least one of diethyl sulfate or triphenyl phosphate, and the mass percentage of the third component based on the mass of the electrolyte is a ppm; the fourth component comprising at least one of triphenyl phosphite, triethyl phosphate, trimethyl phosphate, or vinyl sulfate, and the mass percentage of the fourth component based on the mass of the electrolyte is b%; the fifth component comprising at least one of magnesium fluoride, potassium fluoride, calcium fluoride, lithium fluoride, sodium fluoride, silicon fluoride, iron fluoride, or zirconium fluoride, and the mass percentage of the fifth component based on the mass of the electrolyte is c ppm; the electrolyte satisfies at least one of the following characteristics: (1)50≤a≤500； (2)0.21≤b≤0.55； (3)5≤c≤300。 9. A lithium-ion secondary battery comprising a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte according to any one of claims 1 to 8, wherein the positive electrode comprises a lithium cobalt composite oxide, the lithium cobalt composite oxide comprising at least three doping elements selected from the group consisting of aluminum, magnesium, titanium, zirconium, lanthanum, iridium, cerium, tungsten, zinc, nickel, manganese, boron, phosphorus, silicon, gallium, indium, and cesium; and the mass percentage of any one of the doping elements is 0.01% to 1% based on the mass of the lithium cobalt composite oxide. 10 . A battery module comprising the lithium-ion secondary battery according to claim 9 . A battery pack comprising the battery module according to claim 10 . 12 . An electronic device comprising the lithium-ion secondary battery according to claim 9 , the battery module according to claim 10 , or the battery pack according to claim 11 .

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