Secondary battery

Abstract

In order to solve the problem that an existing lithium ion battery cannot give consideration to safety, low impedance performance and high-temperature storage performance, the invention provides a secondary battery which comprises a positive electrode, a diaphragm, a negative electrode and a non-aqueous electrolyte, and the non-aqueous electrolyte comprises a non-aqueous organic solvent, electrolyte salt and an additive, the additives comprise a first additive, a second additive and a third additive, the first additive comprises at least one of the following compounds: # imgabs 0 #, the second additive comprises a compound shown as a structural formula 1: # imgabs 1 #, and the third additive comprises fluoroethylene carbonate; the secondary battery satisfies the following conditions: 0.2 < = (a * 10 + b + c) / e < = 1.5, 0.01 < = a < = 3, 0.1 < = b < = 10, 6 < = c < = 20, 32 < = e < = 55. The secondary battery provided by the invention has excellent safety performance on the premise of relatively low impedance and excellent high-temperature storage performance.

Description

Technical Field

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

[0002] Compared to other secondary batteries, lithium-ion batteries have a number of advantages, including high operating voltage, high energy density, no memory effect, and low self-discharge. Since their commercialization, they have been widely used in various fields such as electric vehicles and electronic devices. However, in recent years, there have been a number of car battery fires, causing people to worry about the safety of lithium-ion batteries. How to improve the stability of lithium-ion batteries at high temperatures and ensure that they do not catch fire or explode under harsh working conditions is a research topic that has attracted much attention. The existing solution is generally to add flame retardants to the non-aqueous electrolyte. This method of adding flame retardants will increase the battery impedance and degrade the battery's storage performance at high temperatures, resulting in a decrease in the battery's electrochemical performance. Summary of the Invention

[0003] In view of the problem that existing lithium-ion batteries cannot provide a balance between safety, low impedance performance and high-temperature storage performance, the present invention provides a secondary battery.

[0004] The technical solutions adopted by the present invention to solve the above technical problems are as follows: The present invention provides a secondary battery comprising a positive electrode, a separator, a negative electrode, and a non-aqueous electrolyte. The non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte salt, and an additive. The additive comprises a first additive, a second additive, and a third additive. The first additive comprises at least one of the following compounds: The second additive includes a compound shown in structural formula 1: Structural formula 1 Wherein, R1 is selected from F or , R2 is selected from an alkyl group having 1 to 4 carbon atoms, a haloalkyl group having 1 to 4 carbon atoms, or a phenyl group; The third additive includes fluoroethylene carbonate; The secondary battery meets the following conditions: 0.2≤(a*10+b+c) / e≤1.5, and 0.01≤a≤3, 0.1≤b≤10, 6≤c≤20, 32≤e≤55; Wherein, a is the mass percentage of the first additive in the non-aqueous electrolyte, and the unit is %; b is the mass percentage of the second additive in the non-aqueous electrolyte, unit is %; c is the mass percentage of the third additive in the non-aqueous electrolyte, in %; e is the porosity of the diaphragm, in %.

[0005] Optionally, the secondary battery meets the following conditions: 0.4≤(a*10+b+c) / e≤1.

[0006] Optionally, the mass percentage a% of the first additive in the non-aqueous electrolyte is 0.05% to 2%.

[0007] Optionally, the mass percentage b% of the second additive in the non-aqueous electrolyte is 1% to 5%.

[0008] Optionally, the mass percentage c% of the third additive in the non-aqueous electrolyte is 8%-10%.

[0009] Optionally, the porosity e% of the diaphragm is 32%~45%.

[0010] Optionally, the second additive includes one or more of the following compounds:

[0011] Optionally, the non-aqueous organic solvent includes a long-chain carboxylate, the long-chain carboxylate includes propyl propionate and / or ethyl propionate, and the mass percentage d% of the long-chain carboxylate in the non-aqueous electrolyte is 20% to 56%; The non-aqueous electrolyte satisfies the following conditions: 0.15≤(a*10+b+c) / d≤2.

[0012] Optionally, the diaphragm includes an organic base layer and an inorganic coating layer provided on at least one surface of the organic base layer, and the thickness f of the inorganic coating layer is 2 to 6 μm; The secondary battery meets the following conditions: 8≤a*10+c+b / f≤40.

[0013] Optionally, the electrolyte salt is selected from lithium salts.

[0014] According to the secondary battery provided by the present invention, a tricyclic sulfuric acid ester compound is used as a first additive, a compound represented by structural formula 1 is used as a second additive, fluoroethylene carbonate is used as a third additive, and a separator with a porosity of 32% to 55% is used. The inventors have found through extensive research that when the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive in the non-aqueous electrolyte, the mass percentage c of the third additive in the non-aqueous electrolyte, and the porosity e of the separator are controlled to meet the conditions of 0.2≤(a*10+b+c) / e≤1.5, and 0.01≤a≤3, 0.1≤b≤10, 6≤ When c≤20, 32≤e≤55, the resulting secondary battery has excellent safety performance while having low impedance and excellent high-temperature storage performance. This is presumably because: the combination of the second additive and the third additive in the non-aqueous electrolyte can release fluorine-containing free radicals and phosphorus-containing free radicals to capture hydrogen free radicals when the internal temperature of the battery rises sharply, blocking the chain reaction of combustion and improving the safety of the battery under thermal runaway. However, the second additive and the third additive will react with active lithium during the battery formation process, consuming a large amount of the solid electrolyte interface film formed on the electrode surface, thereby reducing the retention of the second additive and the third additive in the non-aqueous electrolyte after the battery is formed. The addition of the first additive can reduce the consumption of the second and third additives in the electrode surface, thereby improving the battery's flame retardancy and enhancing its performance. The thickness of the solid electrolyte interface membrane is relatively high, which affects the ion conduction efficiency and leads to an increase in the battery impedance. However, by adding the first additive, since the first additive has a lower redox potential, in the formation stage, it can take precedence over the second and third additives in forming a dense and thin organic protective membrane on the electrode surface through a ring-opening polymerization reaction to form a flexible organic protective membrane. The organic protective membrane serves as the bottom layer of the solid electrolyte interface membrane, which can reduce the consumption of the second and third additives in the formation stage, and at the same time reduce the thickness of the solid electrolyte interface membrane, thereby improving its high-temperature stability, and having the effect of reducing the internal resistance of the battery, improving the high-temperature storage and safety of the battery. The overall performance has a significant gain effect. Furthermore, the inventors found that the porosity of the diaphragm will affect the transmission efficiency, concentration gradient and concentration overpotential of lithium ions, the first additive, the second additive and the third additive on both sides of the positive and negative electrodes in the non-aqueous electrolyte during the formation stage, and thus has a greater impact on the uniformity of the solid electrolyte interface film formed by the active lithium, the first additive, the second additive and the third additive, and is correlated with the impedance of the battery. Therefore, by comprehensively considering the effects of the first additive, the second additive, the third additive and the porosity of the diaphragm, the four are in a synergistic state, which is conducive to obtaining a secondary battery with excellent comprehensive electrochemical performance and safety performance. DETAILED DESCRIPTION

[0015] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0016] An embodiment of the present invention provides a secondary battery including a positive electrode, a separator, a negative electrode, and a non-aqueous electrolyte. The non-aqueous electrolyte includes a non-aqueous organic solvent, an electrolyte salt, and an additive. The additive includes a first additive, a second additive, and a third additive. The first additive includes at least one of the following compounds: The second additive includes a compound shown in structural formula 1: Structural formula 1 Wherein, R1 is selected from F or , R2 is selected from an alkyl group having 1 to 4 carbon atoms, a haloalkyl group having 1 to 4 carbon atoms, or a phenyl group; The third additive includes fluoroethylene carbonate; The secondary battery meets the following conditions: 0.2≤(a*10+b+c) / e≤1.5, and 0.01≤a≤3, 0.1≤b≤10, 6≤c≤20, 32≤e≤55; Wherein, a is the mass percentage of the first additive in the non-aqueous electrolyte, and the unit is %; b is the mass percentage of the second additive in the non-aqueous electrolyte, unit is %; c is the mass percentage of the third additive in the non-aqueous electrolyte, in %; e is the porosity of the diaphragm, in %.

[0017] When the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive in the non-aqueous electrolyte, the mass percentage c of the third additive in the non-aqueous electrolyte and the porosity e of the diaphragm are controlled to meet the conditions of 0.2≤(a*10+b+c) / e≤1.5, and 0.01≤a≤3, 0.1≤b≤10, 6≤c≤20, 32≤e≤55, the obtained secondary battery has excellent safety performance under the premise of having low impedance and excellent high temperature storage performance, which is presumably because: the second additive and the third additive in the non-aqueous electrolyte are added to the electrolyte. The combination of the three additives can release fluorine-containing free radicals and phosphorus-containing free radicals to capture hydrogen free radicals when the internal temperature of the battery rises sharply, blocking the chain reaction of combustion and improving the safety of the battery under thermal runaway. However, the second additive and the third additive will react with the active lithium during the battery formation process, consuming a large amount of solid electrolyte interface film formed on the electrode surface, thereby reducing the retention of the two in the non-aqueous electrolyte after the battery is formed, affecting its flame retardant performance, and the thickness of the solid electrolyte interface film is relatively high, affecting the ion conduction efficiency, resulting in an increase in battery impedance, and the first additive The addition of the first additive, due to its lower redox potential, can take precedence over the second and third additives in the formation stage to form a dense and thin organic protective film with certain flexibility on the electrode surface through a ring-opening polymerization reaction. The organic protective film, as the bottom layer of the solid electrolyte interface membrane, can reduce the consumption of the second and third additives in the formation stage, while reducing the thickness of the solid electrolyte interface membrane and improving its high-temperature stability, which has a significant benefit effect on reducing the internal resistance of the battery and improving the high-temperature storage and safety of the battery. Furthermore, the inventors found that the porosity of the diaphragm affects the transmission efficiency, concentration gradient and concentration overpotential of lithium ions, the first additive, the second additive and the third additive on both sides of the positive and negative electrodes in the non-aqueous electrolyte in the formation stage, thereby having a greater impact on the uniformity of the solid electrolyte interface membrane formed by the active lithium, the first additive, the second additive and the third additive, and is correlated with the impedance of the battery. Therefore, by comprehensively considering the effects of the first additive, the second additive, the third additive and the porosity of the diaphragm, the four are in a synergistic state, which is conducive to obtaining a secondary battery with excellent comprehensive electrochemical performance and safety performance.

[0018] In a preferred embodiment, the secondary battery meets the following conditions: 0.4≤(a*10+b+c) / e≤1.

[0019] When the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive in the non-aqueous electrolyte, the mass percentage c of the third additive in the non-aqueous electrolyte and the porosity e of the diaphragm further meet the above conditions, it is beneficial to further reduce the battery impedance and improve the capacity retention rate and needle puncture safety of high-temperature storage.

[0020] In a specific embodiment, the mass percentage a% of the first additive in the non-aqueous electrolyte can be 0.01%, 0.23%, 0.46%, 0.67%, 0.89%, 1.12%, 1.34%, 1.56%, 1.78%, 1.91%, 2.13%, 2.25%, 2.37%, 2.49%, 2.61%, 2.73%, 2.85%, 2.90%, 2.97%, 3% or a range between any two of them.

[0021] In a preferred embodiment, the mass percentage a% of the first additive in the non-aqueous electrolyte is 0.05%-2%.

[0022] When batteries are stored in high-temperature environments, the solid electrolyte interface membrane between the non-aqueous electrolyte and the electrodes is easily destroyed, causing various side reactions at the interface between the components of the non-aqueous electrolyte. The continuous destruction and regeneration of the interface membrane consumes active lithium ions in the electrolyte, resulting in a decrease in battery capacity. These side reactions also cause gas production and swelling within the battery. The first additive, with the second and third additives, is used in combination with the above-mentioned mass content. During the battery formation process, redox reactions occur on the positive and negative electrode surfaces. The first additive forms a dense and thin organic protective film with a certain degree of flexibility through ring-opening polymerization, which reduces the consumption of the second and third additives and reduces the thickness of the solid electrolyte interface membrane. Simultaneously, the third additive introduces an inorganic salt substance, such as LiF, with high ion conductivity and strong thermal stability, into the solid electrolyte interface membrane. This solid electrolyte interface membrane suppresses side reactions, optimizes the battery's high-temperature storage performance, and also has low interfacial internal resistance.

[0023] In a specific embodiment, the mass percentage b% of the second additive in the non-aqueous electrolyte can be 0.1%, 0.6%, 1.2%, 1.8%, 2.3%, 3.1%, 3.7%, 4.4%, 5.0%, 5.6%, 6.2%, 6.8%, 7.3%, 7.9%, 8.5%, 9.0%, 9.3%, 9.5%, 9.7%, 10% or a range between any two of them.

[0024] In a preferred embodiment, the mass percentage b% of the second additive in the non-aqueous electrolyte is 1%-5%.

[0025] In a specific embodiment, the mass percentage c% of the third additive in the non-aqueous electrolyte can be 6%, 6.7%, 7.9%, 8.4%, 9.2%, 10.5%, 11.3%, 12.6%, 13.1%, 14.7%, 15.4%, 16.2%, 17.5%, 18.3%, 18.9%, 19.1%, 19.3%, 19.5%, 19.7%, 20% or a range between any two of them.

[0026] In a preferred embodiment, the mass percentage c% of the third additive in the non-aqueous electrolyte is 8%-10%.

[0027] When the battery is punctured during a needle penetration test, the positive and negative electrodes will contact and cause an internal short circuit, releasing a large amount of heat and causing thermal runaway of the battery. The second additive and the third additive used in the present invention will decompose when the internal temperature of the battery rises sharply, releasing fluorine and phosphorus-containing free radicals to capture hydrogen free radicals, which can block the chain reaction of combustion and significantly reduce the probability of fire in the battery needle penetration test. The second additive has a high viscosity and a high content, which leads to an increase in the internal resistance of the battery. Among them, the flame retardant effect of the second additive is better than that of the third additive, but the second additive has the disadvantage of high viscosity, which will affect the ion conduction efficiency of the non-aqueous electrolyte. The viscosity of the third additive is lower than that of the second additive, and the content can be set higher. It can also form a protective film with lower interfacial internal resistance together with the first additive. Therefore, when the second additive and the third additive are within the above range, it is beneficial to combine the advantages of the second additive and the third additive, and improve the pass rate of the secondary battery in the needle penetration test while reducing the impact on ion conduction, thereby improving the safety of the secondary battery.

[0028] In the present invention, porosity is the ratio of the volume of the pores to the volume of the diaphragm. The porosity e of the diaphragm can be measured by the following method: The weighed diaphragm (W d ) was soaked in n-butanol for a certain period of time (e.g. 2 h) and then taken out, the liquid on its surface was gently absorbed with filter paper and then weighed (W w ), the mass W of n-butanol absorbed in the diaphragm can be obtained b =W w -W d The pore volume of the membrane can be calculated from the mass of n-butanol (W b ) and the density of n-butanol (ρ b ) is divided by the volume of the dry film (V p ) is the porosity of the diaphragm e% = (W w -W d ) / (ρ b ·V p ).

[0029] In a specific embodiment, the porosity e% of the diaphragm can be 32%, 33.6%, 35.2%, 37.1%, 38.8%, 40.3%, 41.9%, 43.2%, 44.6%, 46.1%, 47.5%, 48.8%, 50.2%, 51.6%, 52.7%, 53.4%, 54.1%, 54.4%, 54.7%, 55% or a range between any two of them.

[0030] In a preferred embodiment, the porosity e% of the diaphragm is 32% to 45%.

[0031] The porosity of the diaphragm has a certain influence on the formation quality of the solid electrolyte interface film on the electrode surface. If the porosity of the diaphragm is too small, lithium ions cannot shuttle smoothly between the diaphragms, which will reduce the kinetic performance of the lithium-ion battery and increase the battery impedance. It not only causes the heat generation rate to accelerate and the temperature rise to increase when the battery is discharged with a large current, but also causes uneven film formation of the solid electrolyte interface film, resulting in large local impedance and uneven lithium deposition; if the porosity of the diaphragm is too large, the diaphragm cannot effectively prevent harmful impurities from shuttling between the positive and negative electrodes, deteriorating the electrochemical performance of the battery. In severe cases, the positive and negative electrodes will be in direct contact or easily pierced by lithium dendrites, causing a short circuit.

[0032] In some embodiments, the second additive includes one or more of the following compounds:

[0033] In some embodiments, the non-aqueous organic solvent includes a long-chain carboxylate, the long-chain carboxylate includes propyl propionate and / or ethyl propionate, and the mass percentage d% of the long-chain carboxylate in the non-aqueous electrolyte is 20% to 56%; The non-aqueous electrolyte satisfies the following conditions: 0.2≤(a*10+b+c) / d≤1.

[0034] Adding long-chain carboxylates to non-aqueous electrolytes can reduce the viscosity of the electrolyte, thereby reducing the resistance to lithium ion movement, further reducing the internal resistance of the battery, and compensating for the impedance increase caused by the increase in the viscosity of the non-aqueous electrolyte due to the second additive. The disadvantage of long-chain carboxylates is that they have poor electrochemical stability and are prone to side reactions with the negative electrode in a highly lithium-intercalated state at high temperatures, resulting in deterioration of high-temperature storage performance. The positive and negative electrode protective films formed by the first additive, the second additive, and the third additive can inhibit the occurrence of such side reactions, thereby preventing the long-chain carboxylates from degrading the high-temperature performance of the battery. When the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive in the non-aqueous electrolyte, the mass percentage c of the third additive in the non-aqueous electrolyte, and the mass percentage d of the long-chain carboxylates in the non-aqueous electrolyte meet the above conditions, the combined effects of the four on the secondary battery can be balanced to obtain a secondary battery with low impedance and excellent high-temperature performance.

[0035] In a specific embodiment, the mass percentage d% of the long-chain carboxylic acid ester in the non-aqueous electrolyte can be 20%, 21.8%, 23.6%, 25.4%, 27.2%, 29%, 30.8%, 32.6%, 34.4%, 36.2%, 38%, 39.8%, 41.6%, 43.4%, 45.2%, 47%, 48.8%, 50.6%, 52.4%, 54.2%, 56% or a range between any two of them.

[0036] In some embodiments, the membrane includes an organic base layer and an inorganic coating layer disposed on at least one surface of the organic base layer, and the thickness f of the inorganic coating layer is 2 to 6 μm; The secondary battery meets the following conditions: 8≤a*10+c+b / f≤40.

[0037] Setting an appropriate thickness of inorganic coating can give the separator good chemical stability, thermal stability, and mechanical strength. It also inhibits deformation and shrinkage of the organic substrate during high-temperature storage, preventing side reactions and degradation. When the separator is punctured in a needle puncture test, the inorganic coating decomposes and absorbs heat during thermal runaway, reducing the probability of fire. However, as the thickness of the inorganic coating increases, the internal resistance of the secondary battery also increases. When a secondary battery meets the above conditions, it is beneficial to combine the effects of the inorganic coating, the first additive, the second additive, and the third additive on the internal resistance and safety performance of the secondary battery, achieving a synergistic state.

[0038] In some embodiments, the organic base layer includes one or more layers of a PE layer and a PP layer, and the inorganic coating layer includes one or more of aluminum oxide, aluminum hydroxide, and boehmite.

[0039] In some embodiments, the electrolyte salt is selected from lithium salts.

[0040] In some embodiments, the lithium salt is selected from LiPF6, LiBOB, LiDFOB, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN(SO2F)2, LiClO4, LiAlCl4, LiCF3SO3, Li2B 10 Cl 10 , LiSO2F, LiTOP (lithium trioxalatophosphate), LiDODFP (lithium difluorodioxalatophosphate), LiOTFP (lithium tetrafluorooxalatophosphate) and at least one of a lower aliphatic carboxylic acid lithium salt.

[0041] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol / L to 8 mol / L. In a preferred embodiment, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 mol / L to 2.5 mol / L. Specifically, the concentration of the lithium salt in the non-aqueous electrolyte can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, or any range therebetween.

[0042] In some embodiments, the additive further comprises at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, a phosphate compound, and a borate compound; Preferably, based on the total mass of the non-aqueous electrolyte being 100%, the amount of the additive added is 0.01% to 30%.

[0043] In some embodiments, the cyclic sulfate compound is selected from vinyl sulfate, propylene sulfate, methyl vinyl sulfate, 、 At least one of; The sultone compound is selected from at least one of 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone; The cyclic carbonate compound is selected from at least one of vinylene carbonate, ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethylethylene carbonate, bisfluoroethylene carbonate or the compound shown in structural formula 2. Structural Formula 2 In the structural formula 2, R 21 、R 22 、R 23 、R 24 、R 25 、R26 Each is independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group; The phosphate compound includes a compound shown in structural formula 3: Structural formula 3 In the structural formula 3, R 31 、R 32 、R 33 Each independently selected from C1-C5 saturated hydrocarbon group, unsaturated hydrocarbon group, halogenated hydrocarbon group, -Si(C m H 2m+1 )3, m is a natural number from 1 to 3; In a preferred embodiment, the phosphate compound shown in the structural formula 3 may be at least one of tris(trimethylsilane)phosphate, tris(triethylsilane)phosphate, tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl-2,2,2-trifluoroethyl phosphate, dipropargyl-3,3,3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate; The borate compound is selected from at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate.

[0044] In other embodiments, the additives may also include other additives that can improve battery performance: for example, additives that enhance battery safety, such as flame retardant additives such as fluorophosphate, or overcharge prevention additives such as tert-amylbenzene and tert-butylbenzene.

[0045] It should be noted that, unless otherwise specified, under normal circumstances, the amount of any one of the optional substances in the additives added to the non-aqueous electrolyte is less than 10%, preferably, the amount added is 0.1%-5%, and more preferably, the amount added is 0.1%-2%. Specifically, the amount of any one of the optional substances in the additives can be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, 10%, or any range therebetween.

[0046] In some embodiments, the non-aqueous organic solvent further comprises at least one of an ether solvent, a carbonate solvent, and a sulfone solvent.

[0047] In some embodiments, the ether solvent includes cyclic ethers or chain ethers and their fluorinated derivatives, preferably chain ethers with 3 to 10 carbon atoms and cyclic ethers with 3 to 6 carbon atoms. The cyclic ethers may be, but are not limited to, at least one of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF). The chain ethers may be, but are not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Because chain ethers have high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are particularly preferred due to their low viscosity and high ionic conductivity. The ether compound can be used alone or in any combination and ratio. There is no special restriction on the amount of ether compound added, and it is arbitrary within the range that does not significantly damage the effect of the high-density lithium-ion battery of the present invention. The volume ratio is usually 1% or more, preferably 2% or more, and more preferably 3% or more in the non-aqueous solvent volume ratio of 100%. In addition, the volume ratio is usually 30% or less, preferably 25% or less, and more preferably 20% or less. When two or more ether compounds are used in combination, the total amount of the ether compound can be made to meet the above range. When the amount of ether compound added is within the above-mentioned preferred range, it is easy to ensure the improvement effect of ionic conductivity brought about by the increase in the lithium ion dissociation degree of the chain ether and the decrease in viscosity. In addition, when the negative electrode active material is a carbon-based material, the phenomenon of co-embedding of the chain ether and lithium ions can be suppressed, so that the input-output characteristics and the charge-discharge rate characteristics can reach an appropriate range.

[0048] In some embodiments, the carbonate solvent includes a cyclic carbonate or a chain carbonate. The cyclic carbonate may be, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); the chain carbonate may be, but is not limited to, at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). The amount of the cyclic carbonate is not particularly limited and may be any amount that does not significantly impair the performance of the lithium-ion battery of the present invention. However, when a single carbonate is used, the lower limit of its content is generally 3% by volume or greater, preferably 5% by volume or greater, relative to the total volume of the non-aqueous electrolyte solvent. This range avoids a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte, facilitating the achievement of excellent high-current discharge characteristics, stability relative to the negative electrode, and cycling characteristics of the non-aqueous electrolyte battery. The upper limit is generally 90% by volume or less, preferably 85% by volume or less, and more preferably 80% by volume or less. By setting this scope, the oxidation / reduction tolerance of nonaqueous electrolytic solution can be improved, thus the stability during helping to improve high temperature storage.The content of linear carbonate is not particularly limited, and relative to the total amount of solvent of nonaqueous electrolytic solution, is usually more than 15% by volume, preferably more than 20% by volume, more preferably more than 25% by volume. In addition, usually volume ratio is below 90%, preferably below 85% by volume, more preferably below 80% by volume. By making the content of linear carbonate in above-mentioned scope, easily make the viscosity of nonaqueous electrolytic solution reach appropriate range, suppress the reduction of ionic conductivity, and then help make the output characteristics of nonaqueous electrolyte battery reach good scope. When using two or more linear carbonates in combination, make the total amount of linear carbonate meet above-mentioned scope.

[0049] In some embodiments, the sulfone solvent includes a cyclic sulfone and a chain sulfone. Preferably, in the case of a cyclic sulfone, it is generally a compound having 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms; in the case of a chain sulfone, it is generally a compound having 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms. There is no particular limitation on the amount of sulfone solvent added, and it is arbitrary within the range that does not significantly damage the effect of the lithium-ion battery of the present invention. Relative to the total amount of solvent in the non-aqueous electrolyte, the volume ratio is generally 0.3% or more, preferably 0.5% or more, more preferably 1% or more. In addition, the volume ratio is generally 40% or less, preferably 35% or less, more preferably 30% or less. When two or more sulfone solvents are used in combination, the total amount of the sulfone solvent is sufficient to meet the above range. When the amount of sulfone solvent added is within the above range, a non-aqueous electrolyte with excellent high-temperature storage stability tends to be obtained.

[0050] In some embodiments, the positive electrode includes a positive electrode material layer.

[0051] In some embodiments, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material includes at least one of a ternary material, a phosphate material, a lithium cobalt oxide material, a lithium manganese-rich material, or a lithium nickel manganese oxide material.

[0052] In some preferred embodiments, the ternary material comprises a chemical formula of Li q Ni x Co y M 1-x-y O 2-g R g The material or the surface of the Li q Ni x Co y M 1-x-y O 2-g R g At least one of the materials, wherein 0.9≤q≤1.2, 0.01≤x≤0.96, y>0, 1-xy>0, 0≤g≤1, M includes one or two of Mn and Al, and zero, one or more of Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe, B, Ga, Cr, W, V, Nb, and Ce, and R includes one or more of N, F, S, and Cl.

[0053] In some preferred embodiments, the phosphate material includes a molecular formula of Li r Mn α Fe β A 1-α-β PO 4-n G n The material or the surface of the Li r Mn α Fe β A 1-α-β PO 4-n G n At least one of the materials, wherein 0.9≤r≤1.1, 0≤α≤0.8, 0.2≤β≤1, 0≤n≤0.1, A is selected from one or more of Ti, Mg, V, Cr, Zr, Nb, Zn, Al, Na, K, Mo, W, Ni, Co, Ga, Sn, Sb, Ge and W, and G includes one or more of N, F, S and Cl.

[0054] In some preferred embodiments, the lithium cobalt oxide material includes LiCoO2, or lithium cobalt oxide modified by doping and / or coating with any one or more elements of Ni, Mn, Mg, Al, Zr, W, F, B, Cr, Mo and rare earth elements.

[0055] In some preferred embodiments, the lithium nickel manganese oxide material includes a molecular formula of LiNi x' L' y’ Mn （2-x'-y'） O4, or LiNi with a coating layer on the surface x' L' y’ Mn （2-x'-y'） At least one of the O4 materials, 0.3≤x'≤0.6, 0.01≤y'≤0.2, and L' is selected from one or more of Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si and Fe.

[0056] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductor, and the positive electrode active material, the positive electrode binder and the positive electrode conductor are blended to obtain the positive electrode material layer.

[0057] The positive electrode binder includes polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, a thermoplastic resin such as polyethylene and polypropylene; an acrylic resin; and at least one of styrene butadiene rubber.

[0058] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0059] In some embodiments, the positive electrode current collector includes a metal material that can conduct electrons. Preferably, the positive electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive electrode current collector is selected from aluminum foil.

[0060] In some embodiments, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes at least one of a carbon-based negative electrode, a silicon-based negative electrode, a tin-based negative electrode, and a lithium negative electrode.

[0061] Carbon-based anodes may include graphite, hard carbon, soft carbon, graphene, mesocarbon microbeads, and the like. Silicon-based anodes may include one or more of silicon materials, silicon oxides, silicon-carbon composites, and silicon alloys. Tin-based anodes may include tin, tin-carbon, tin oxide, or tin metal compounds. Lithium anodes may include metallic lithium or a lithium alloy. Specifically, the lithium alloy may be at least one of lithium-silicon alloy, lithium-sodium alloy, lithium-potassium alloy, lithium-aluminum alloy, lithium-tin alloy, and lithium-indium alloy.

[0062] In some embodiments, the silicon material is one or more of silicon nanoparticles, silicon nanowires, silicon nanotubes, silicon thin films, 3D porous silicon, and hollow porous silicon.

[0063] In some embodiments, the negative electrode further comprises a negative electrode current collector, and the negative electrode material layer covers the surface of the negative electrode current collector. The negative electrode current collector comprises an electron-conducting metal material, preferably comprising at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0064] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductor, and the negative electrode active material, the negative electrode binder and the negative electrode conductor are blended to obtain the negative electrode material layer.

[0065] The negative electrode binder includes polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, a thermoplastic resin such as polyethylene and polypropylene; an acrylic resin; and at least one of styrene butadiene rubber.

[0066] The negative electrode conductive agent includes at least one of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0067] The present invention is further described below with reference to the following examples.

[0068] Table 1 Example 1 This embodiment is used to illustrate the lithium ion battery and its preparation method disclosed in the present invention, including the following operations: 1) Preparation of non-aqueous electrolyte: Ethylene carbonate (EC), propylene carbonate (PC) and a long-chain carboxylate are mixed, and then lithium hexafluorophosphate (LiPF6) is added, wherein the long-chain carboxylate is selected from propyl propionate. The mass percentage of the long-chain carboxylate in the non-aqueous electrolyte is shown in Table 1. At the same time, based on the total weight of the non-aqueous electrolyte being 100%, the non-aqueous electrolyte contains a first additive, a second additive and a third additive as shown in Table 1.

[0069] 2) Preparation of positive electrode: The cathode active material, lithium cobalt oxide (LCO), the conductive carbon black Super-P, and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97:1.5:1.5 and then dispersed in N-methyl-2-pyrrolidone (NMP) to create a cathode slurry. The slurry is evenly coated on both sides of the aluminum foil current collector. After drying, rolling, and vacuum drying, aluminum lead wires are welded using an ultrasonic welder to obtain the cathode sheet, which is 120-150μm thick.

[0070] 3) Preparation of negative electrode sheet: The negative electrode active material, artificial graphite, conductive carbon black Super-P, and binders styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC), are mixed in a mass ratio of 95:1:1.5:2.5. These are then dispersed in deionized water to create a negative electrode slurry. The slurry is then coated on both sides of a copper foil, dried, rolled, and vacuum-dried. Nickel lead wires are then ultrasonically welded to form the negative electrode sheet, which is 120-150μm thick.

[0071] 4) Preparation of battery cells: A separator was placed between the positive plate and the negative plate. The separator included a PE layer and an alumina coating provided on both sides of the PE layer. The porosity and thickness of the alumina coating of the separator were tested. The porosity and thickness of the alumina coating are recorded in Table 1. The sandwich structure consisting of the positive plate, negative plate, and separator was then wound. The wound body was flattened and placed in an aluminum foil packaging bag. The battery cell was vacuum-baked at 85°C for 48 hours to obtain a battery cell ready for liquid injection.

[0072] 5) Battery filling and formation: In a glove box with moisture and oxygen levels controlled below 10 ppm, the prepared non-aqueous electrolyte was injected into the battery cell, vacuum-sealed, and allowed to rest at 45°C for 48 hours. The cells were then subjected to conventional initial charge formation as follows: 0.1C constant current charging for 45 minutes, 0.2C constant current charging for 30 minutes, and 0.5C constant current charging for 75 minutes.

[0073] 6) Cell capacity division: The battery cell was left at rest at 45°C for 48 hours, then vacuum sealed for a second time to remove the generated gas, and then charged to 4.5V at a constant current of 0.2C, and then charged at a constant voltage until the current dropped to 0.05C. After being left for 5 minutes, the battery cell was discharged to 3.0V at a constant current of 0.2C to obtain a lithium cobalt oxide positive electrode / graphite lithium ion battery.

[0074] Examples 2 to 37 Examples 2 to 37 are used to illustrate the lithium-ion batteries and preparation methods disclosed in the present invention, and include most of the operating steps in Example 1, except that: In the non-aqueous electrolyte, the mass percentages of the long-chain carboxylic acid ester, the first additive, the second additive, and the third additive are shown in Table 1.

[0075] The porosity of the membrane and the thickness of the alumina coating are shown in Table 1.

[0076] In Examples 25 to 27, propyl propionate was replaced by ethyl acetate, methyl acetate, and propyl acetate.

[0077] Comparative Examples 1-12 Comparative Examples 1 to 12 are used to illustrate the lithium-ion batteries and preparation methods disclosed in the present invention, and include most of the operating steps in Example 1, except that: In the non-aqueous electrolyte, the mass percentages of the long-chain carboxylic acid ester, the first additive, the second additive, and the third additive are shown in Table 1.

[0078] The porosity of the membrane and the thickness of the alumina coating are shown in Table 1.

[0079] Performance Testing The lithium-ion battery prepared above was subjected to the following performance tests: 1) Normal temperature discharge DC internal resistance test At 25°C, the divided battery was adjusted to 50% SOC, discharged at a constant current rate of 2C for 10s, and the voltage before and after discharge was recorded.

[0080] Discharge DC internal resistance = (voltage before discharge - voltage after discharge) / discharge current.

[0081] 2) High temperature storage performance test At 25°C, charge the battery to 4.5V (cut-off current 0.05C) at 1C constant current and constant voltage, then discharge it to 3.0V at 1C constant current. Record the discharge capacity. Then charge the battery to 4.5V (cut-off current 0.05C) at 1C constant current and constant voltage, then place it in a 60°C oven for 15 days. After cooling, discharge it to 3.0V at 1C constant current at 25°C, and record the discharge capacity.

[0082] High temperature storage capacity retention rate = discharge capacity after 15 days of storage at 60°C / discharge capacity before storage × 100% 3) Acupuncture test The battery is charged to 4.5V with a constant current and constant voltage of 0.2C (cut-off current 0.05C), placed in a needle penetration test explosion-proof box, and a 4mm diameter steel needle is vertically pierced through the center of the flat battery at a speed of 100mm / s and maintained for 60s. If the battery does not catch fire or explode during this period, it passes the test.

[0083] (1) The test results obtained in Examples 1 to 18 and Comparative Examples 1 to 12 are shown in Table 2.

[0084] Table 2 The test results of Examples 1 to 18 and Comparative Examples 1 to 12 show that in the lithium ion battery system provided by the present invention, a separator having a porosity of 32% to 55% is used, and a tricyclic sulfuric acid ester compound, a compound represented by Structural Formula 1, and fluoroethylene carbonate are used as additives in the non-aqueous electrolyte. When the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive in the non-aqueous electrolyte, the mass percentage c of the third additive in the non-aqueous electrolyte, and the porosity e of the separator are controlled so as to satisfy the conditions 0.2 ≤ (a*10+b+c) / e ≤ 1.5, and 0.01 ≤ a ≤ 3, 0.1 ≤ b ≤ 10, 6 ≤ c ≤ 20, and 32 ≤ e ≤ 55, the prepared lithium ion battery has a low discharge DC internal resistance, a high high-temperature storage capacity retention rate, and a high needle penetration test safety. The hypothesis is that the addition of the second and third additives to the non-aqueous electrolyte can release fluorine- and phosphorus-containing free radicals when the internal battery temperature rises sharply. These free radicals capture hydrogen radicals, interrupt the combustion chain reaction, and improve battery safety in the event of thermal runaway. However, these additives react with active lithium during the battery formation process, significantly consuming the solid electrolyte interface film (SEL) on the electrode surface, resulting in a decrease in post-formation retention and affecting flame retardancy. Furthermore, this SEL is thick, which impairs ion conduction efficiency and increases battery impedance. By introducing the first additive, which has a lower redox potential, a flexible, thin organic protective film is preferentially formed on the electrode surface via ring-opening polymerization during the formation phase. This serves as a base layer for the SEL, reducing the consumption of the second and third additives, reducing the thickness of the SEL, and improving its high-temperature stability. This significantly reduces the battery's internal resistance, enhancing high-temperature storage and safety. The study also found that the separator's porosity affects the transport efficiency, concentration gradient, and concentration overpotential of lithium ions and additives in the non-aqueous electrolyte during the formation phase, which in turn affects the uniformity of the SEL, which is correlated with battery impedance. Therefore, comprehensive consideration of the effects of the first, second, and third additives and the porosity of the separator, and their synergistic effect, contributes to the production of a secondary battery with excellent electrochemical and safety performance.

[0085] From the comparison of the test results of Examples 1 to 18, it can be seen that when the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive in the non-aqueous electrolyte, the mass percentage c of the third additive in the non-aqueous electrolyte and the porosity e of the separator further satisfy the conditions 0.4≤(a*10+b+c) / e≤1, and 0.05≤a≤2, 1≤b≤5, 8≤c≤10, 32≤e≤45, the impedance of the lithium-ion battery can be further reduced, and the high-temperature storage performance and needle puncture safety of the lithium-ion battery can be improved.

[0086] The test results of Comparative Examples 1-8 show that if the mass percentage a of the first additive, the mass percentage b of the second additive, the mass percentage c of the third additive, and the porosity e of the separator in the non-aqueous electrolyte are not within their respective specified ranges, even if the condition of 0.2 ≤ (a*10+b+c) / e ≤ 1.5 is met, the impedance performance, high-temperature performance, and safety performance of the prepared lithium-ion batteries will still be significantly insufficient. This indicates that whether the values a, b, c, or e are too high or too low, it is not conducive to improving the electrochemical performance of lithium-ion batteries.

[0087] The test results of Comparative Examples 9-12 show that when the values of a, b, c, and e do not satisfy the condition of 0.2 ≤ (a*10+b+c) / e ≤ 1.5, even if they are within their respective ranges, the impedance of the lithium-ion battery still increases, and the high-temperature storage performance and needle puncture pass rate are low. This indicates that the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive, the mass percentage c of the third additive, and the porosity e of the separator are mutually influenced. Only when these four factors are well balanced can the performance of the lithium-ion battery be significantly improved.

[0088] (2) The test results obtained in Examples 19 to 27 are entered in Table 3.

[0089] Table 3 A comparison of the test results of Examples 19 to 24 with those of Examples 1 to 18 in Table 2 shows that in the lithium-ion battery system provided by the present invention, when the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive in the non-aqueous electrolyte, the mass percentage c of the third additive in the non-aqueous electrolyte, and the mass percentage d of the long-chain carboxylate in the non-aqueous electrolyte meet the condition 0.2 ≤ (a*10+b+c) / d ≤ 1 (Examples 1 to 18), lithium-ion batteries with low impedance and excellent high-temperature performance are obtained. However, Examples 19 to 24, which do not meet the above conditions, exhibit significant battery performance degradation. This indicates that the addition of a certain amount of long-chain carboxylate can reduce the viscosity of the electrolyte, thereby reducing the resistance to lithium ion movement, further reducing the internal resistance of the battery, and compensating for the impedance increase caused by the increased viscosity of the non-aqueous electrolyte due to the second additive.

[0090] From the comparison of the test results of Examples 25 to 27 and Examples 1 to 18 in Table 2, it can be seen that when short-chain carboxylates are used instead of long-chain carboxylates, they cannot replace the long-chain carboxylates, indicating that in the lithium-ion battery system of the present invention, it is more suitable to add long-chain carboxylates rather than short-chain carboxylates. It is speculated that this is because long-chain carboxylates have higher electrochemical stability than short-chain carboxylates, and when used in the lithium-ion battery provided by the present invention, the problem of non-aqueous electrolyte degradation caused by decomposition of non-aqueous organic solvents can be reduced.

[0091] (3) The test results obtained in Examples 28 to 32 are entered in Table 4.

[0092] Table 4 From the comparison of the test results of Examples 28 to 32 and Examples 1 to 18 in Table 2, it can be seen that in the lithium-ion battery system provided by the present invention, when the mass percentage a of the first additive in the non-aqueous electrolyte, the mass percentage b of the second additive in the non-aqueous electrolyte, the mass percentage c of the third additive in the non-aqueous electrolyte, and the thickness f of the inorganic coating satisfy the condition 8≤a*10+c+b / f≤40 (Examples 1 to 18), it is beneficial to comprehensively consider the effects of the inorganic coating, the first additive, the second additive, and the third additive on the internal resistance and safety performance of the secondary battery, thereby improving the acupuncture safety of the lithium-ion battery while reducing the impedance.

[0093] (4) The test results obtained in Examples 1 and 33 to 37 are entered in Table 5.

[0094] Table 5 From the comparison of the test results of Examples 1 and 33 to 37, it can be seen that in the battery system provided by the present invention, under the premise of satisfying the conditions 0.2≤(a*10+b+c) / e≤1.5, and 0.01≤a≤3, 0.1≤b≤10, 6≤c≤20, 32≤e≤55, the use of different first additives and different second additives has a certain degree of improvement effect on the low impedance performance, high temperature storage performance and safety performance of the lithium-ion battery, indicating that the battery system provided by the present invention is suitable for different first additives and different second additives.

[0095] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A secondary battery, characterized in that: The invention comprises a positive electrode, a separator, a negative electrode and a non-aqueous electrolyte, wherein the non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte salt and an additive, wherein the additive comprises a first additive, a second additive and a third additive, wherein the first additive comprises at least one of the following compounds: The second additive includes a compound shown in structural formula 1: Structural formula 1 Wherein, R1 is selected from F or , R2 is selected from an alkyl group having 1 to 4 carbon atoms, a haloalkyl group having 1 to 4 carbon atoms, or a phenyl group; The third additive includes fluoroethylene carbonate; The secondary battery meets the following conditions: 0.2≤(a*10+b+c) / e≤1.5, and 0.01≤a≤3, 0.1≤b≤10, 6≤c≤20, 32≤e≤55; Wherein, a is the mass percentage of the first additive in the non-aqueous electrolyte, and the unit is %; b is the mass percentage of the second additive in the non-aqueous electrolyte, unit is %; c is the mass percentage of the third additive in the non-aqueous electrolyte, unit is %; e is the porosity of the diaphragm, in %.

2. The secondary battery according to claim 1, wherein The secondary battery meets the following conditions: 0.4≤(a*10+b+c) / e≤1.

3. The secondary battery according to claim 1, wherein The mass percentage a% of the first additive in the non-aqueous electrolyte is 0.05% to 2%.

4. The secondary battery according to claim 1, wherein The mass percentage b% of the second additive in the non-aqueous electrolyte is 1% to 5%.

5. The secondary battery according to claim 1, wherein The mass percentage c% of the third additive in the non-aqueous electrolyte is 8% to 10%.

6. The secondary battery according to claim 1, wherein The porosity e% of the diaphragm is 32% to 45%.

7. The secondary battery according to claim 1, wherein The second additive includes one or more of the following compounds: 。 8. The secondary battery according to claim 1, wherein The non-aqueous organic solvent includes a long-chain carboxylate, the long-chain carboxylate includes propyl propionate and / or ethyl propionate, and the mass percentage d% of the long-chain carboxylate in the non-aqueous electrolyte is 20% to 56%; The non-aqueous electrolyte satisfies the following conditions: 0.15≤(a*10+b+c) / d≤2.

9. The secondary battery according to claim 1, wherein The diaphragm includes an organic base layer and an inorganic coating layer provided on at least one surface of the organic base layer, wherein the thickness f of the inorganic coating layer is 2 to 6 μm; The secondary battery meets the following conditions: 8≤a*10+c+b / f≤40.

10. The secondary battery according to claim 9, wherein The electrolyte salt is selected from lithium salts.

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