Non-aqueous electrolyte and secondary battery

Abstract

In order to solve the problem that a negative electrode SEI membrane structure is damaged due to dissolution of transition metal ions in an existing high-voltage lithium ion battery, the invention provides a non-aqueous electrolyte and a secondary battery, and the non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte salt and an additive, the additive comprises a sulfur-containing additive as shown in a structural formula 1 and a phosphine-containing additive as shown in a structural formula 2: # imgabs 0 # structural formula 1 and # imgabs 1 # structural formula 2. The non-aqueous electrolyte provided by the invention is used for improving the high-temperature safety performance of the battery and improving the high-temperature cycle performance and rate discharge performance of the battery.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a non-aqueous electrolyte and a secondary battery. Background Art

[0002] Lithium-ion batteries have made great progress in the field of portable electronic products due to their high operating voltage, high safety, long life, and no memory effect. Consumer electronics, as the starting point of the development of lithium-ion batteries, has been widely used in the market for more than 30 years since 1991. Lithium cobalt oxide cathodes are the most commonly used negative electrodes in consumer batteries. In order to meet the increasingly high requirements of terminals for energy density, the positive electrode cutoff voltage has developed from the initial 4.2V to the current 4.5V and above. However, with the increase of the upper limit voltage of the positive electrode, the structural instability of the positive electrode material increases, making it more prone to structural collapse, and the dissolution of transition metal ions will destroy the structure of the negative electrode SEI film (solid electrolyte interface film), triggering large-scale side reactions and causing battery performance failure. Summary of the invention

[0003] In view of the problem that the dissolution of transition metal ions in existing high-voltage lithium-ion batteries leads to the destruction of the negative electrode SEI film structure, the present invention provides a non-aqueous electrolyte and a secondary battery.

[0004] The technical solution adopted by the present invention to solve the above technical problems is as follows: In one aspect, the present invention provides a non-aqueous electrolyte, comprising a non-aqueous organic solvent, an electrolyte salt and an additive, wherein the additive comprises a sulfur-containing additive as shown in Structural Formula 1 and a phosphine-containing additive as shown in Structural Formula 2: ; Wherein n is 0 or 1, A is selected from C or O, and X is selected from or , R 1 , R 2 Each independently selected from H, or , R 1 and R 2 are not selected from H at the same time, and X, R 1 and R 2 Contains at least one sulfur atom; ; Among them, R 3 , R 4 , R 5 , R 6 Each independently selected from H, C1~C4 hydrocarbon group or -OPF 2 , R 7Selected from O or C1~C4 hydrocarbon group, m=0~10, z=0~10.

[0005] Optionally, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage X% of the sulfur-containing additive represented by the structural formula 1 is 0.1% to 3%; and / or, Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content Y% of the phosphine-containing additive represented by the structural formula 2 is 0.01% to 0.5%.

[0006] Optionally, the mass percentage X% of the sulfur-containing additive shown in structural formula 1 in the non-aqueous electrolyte and the mass percentage Y% of the phosphine-containing additive shown in structural formula 2 in the non-aqueous electrolyte satisfy: 0.3≤X+Y≤3, 10≤X / Y≤100.

[0007] Optionally, in the sulfur-containing additive shown in the structural formula 1, R 1 , R 2 Each independently selected or , and X, R 1 and R 2 Contains at least one sulfur atom.

[0008] Optionally, in the sulfur-containing additive shown in the structural formula 1, X, R 1 and R 2 It does not contain sulfur atoms at the same time.

[0009] Optionally, in the sulfur-containing additive shown in the structural formula 1, R 1 Selected from H, X selected from , R 2 Selected from ,or, R 1 Selected from H, X selected from , R 2 Selected from or .

[0010] Optionally, the sulfur-containing additive shown in the structural formula 1 is selected from at least one of the following compounds: ; And / or, the phosphine-containing additive represented by structural formula 2 is selected from at least one of the following compounds: .

[0011] Optionally, the non-aqueous electrolyte contains 10-500 ppm of cobalt ions.

[0012] Optionally, the additive further includes a nitrile compound, and the nitrile compound includes at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile, and sebacononitrile; Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage Z% of the nitrile compound is 1% to 4%.

[0013] The mass percentage of the phosphine-containing additive Y% shown in the structural formula 2 and the mass percentage of the nitrile compound Z% satisfy: 10≤Z / Y≤80.

[0014] In another aspect, the present invention provides a secondary battery comprising a positive electrode, a negative electrode, and the nonaqueous electrolyte as described above.

[0015] Optionally, the content of cobalt ions in the non-aqueous electrolyte is 10-500 ppm.

[0016] According to the non-aqueous electrolyte provided by the present invention, a sulfur-containing additive shown in structural formula 1 and a phosphine-containing additive shown in structural formula 2 are added, wherein the sulfur-containing additive shown in structural formula 1 has a sulfur-containing multi-ring structure, and the film-forming activity (LUMO potential) of the characteristic structure is relatively high. After the sulfur-containing structure is cyclized, the lone electron on O is more exposed and easy to coordinate and complex with Li ions, occupying the lithium ion solvation sheath, and migrating to the negative electrode interface under the action of the electric field to preferentially form a film to form a sulfur-containing component, while the phosphine-containing additive shown in structural formula 2 can also decompose on the negative electrode surface to form a phosphorus-containing component. The inventors have found that the phosphine-containing additive shown in structural formula 1 The negative electrode solid electrolyte interface film formed by the decomposition of the sulfur additive and the phosphine-containing additive shown in structural formula 2 has sulfur phosphide, so that the negative electrode solid electrolyte interface film has a strong complexing effect on Co ions, avoiding the destructive effect of Co ions on the negative electrode solid electrolyte interface film and the negative electrode active material, and improving the high temperature safety performance of the battery. At the same time, the Co ions complexed with the negative electrode solid electrolyte interface film are reduced on the negative electrode surface to form a negative electrode solid electrolyte interface film containing Co, which can improve the conductivity of the negative electrode solid electrolyte interface film, thereby improving the high temperature cycle performance and rate discharge performance of the battery. DETAILED DESCRIPTION

[0017] 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 used to limit the present invention.

[0018] The embodiment of the present invention provides a non-aqueous electrolyte, including a non-aqueous organic solvent, an electrolyte salt and an additive, wherein the additive includes a sulfur-containing additive shown in Structural Formula 1 and a phosphine-containing additive shown in Structural Formula 2: ; Wherein n is 0 or 1, A is selected from C or O, and X is selected from or , R 1 , R 2 Each independently selected from H, or , R 1 and R 2 are not selected from H at the same time, and X, R 1 and R 2 Contains at least one sulfur atom; ; Among them, R 3 , R 4 , R 5 , R 6 Each independently selected from H, C1~C4 hydrocarbon group or -OPF 2 , R 7 Selected from O or C1~C4 hydrocarbon group, m=0~10, z=0~10.

[0019] Among them, the sulfur-containing additive shown in structural formula 1 has a sulfur-containing multi-ring structure, and the film-forming activity (LUMO potential) of this characteristic structure is relatively high. After the sulfur-containing structure is cyclized, the lonely electrons on O are more exposed and easy to coordinate and complex with Li ions, occupy the lithium ion solvation sheath, and migrate to the negative electrode interface under the action of the electric field to preferentially form a film to form a sulfur-containing component, and the phosphine-containing additive shown in structural formula 2 can also decompose on the negative electrode surface to form a phosphorus-containing component. The inventors found that the negative electrode solid electrolyte interface film formed by the decomposition of the sulfur-containing additive shown in structural formula 1 and the phosphine-containing additive shown in structural formula 2 has sulfur phosphide, so that the negative electrode solid electrolyte interface film has a strong complexing effect on Co ions, avoiding the destructive effect of Co ions on the negative electrode solid electrolyte interface film and the negative electrode active material, and improving the high temperature safety performance of the battery. At the same time, the Co ions complexed with the negative electrode solid electrolyte interface film are reduced on the negative electrode surface to form a negative electrode solid electrolyte interface film containing Co, which can improve the conductivity of the negative electrode solid electrolyte interface film, thereby improving the high temperature cycle performance and rate discharge performance of the battery.

[0020] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage X% of the sulfur-containing additive represented by the structural formula 1 is 0.1% to 3%.

[0021] In a specific embodiment, based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage X% of the sulfur-containing additive shown in Structural Formula 1 can be 0.1%, 0.2%, 0.4%, 0.5%, 0.7%, 0.9%, 1.0%, 1.1%, 1.3%, 1.5%, 1.8%, 2.0%, 2.3%, 2.7%, 3.0% or a range therebetween.

[0022] In a preferred embodiment, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage X% of the sulfur-containing additive represented by the structural formula 1 is 0.1%-2%.

[0023] The sulfur-containing additive shown in the structural formula 1 participates in the formation of the negative electrode solid electrolyte interface film. The content of the sulfur-containing additive shown in the structural formula 1 in the non-aqueous electrolyte has a great influence on the sulfur-containing components in the negative electrode solid electrolyte interface film, thereby affecting the complexation of Co ions. If the content of the sulfur-containing additive shown in the structural formula 1 is too low, it is difficult to improve the complexation of the negative electrode solid electrolyte interface film for Co ions, and the effect on improving battery performance is limited; if the content of the sulfur-containing additive shown in the structural formula 1 is too high, the film thickness of the negative electrode solid electrolyte interface film will increase, thereby increasing the battery impedance, which is not conducive to the performance of the battery rate discharge performance.

[0024] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage Y% of the phosphine-containing additive represented by the structural formula 2 is 0.01% to 0.5%.

[0025] In a specific embodiment, based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage Y% of the phosphine-containing additive shown in Structural Formula 2 can be 0.01%, 0.02%, 0.03%, 0.05%, 0.06%, 0.08%, 0.1%, 0.13%, 0.15%, 0.18%, 0.2%, 0.23%, 0.25%, 0.28%, 0.3%, 0.33%, 0.35%, 0.38%, 0.4%, 0.43%, 0.45%, 0.48%, 0.5% or a range therebetween.

[0026] In a preferred embodiment, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage Y% of the phosphine-containing additive represented by the structural formula 2 is 0.05% to 0.3%.

[0027] The phosphine-containing additive shown in the structural formula 2 is used to cooperate with the film-forming effect of the sulfur-containing additive shown in the structural formula 1 to construct a negative electrode solid electrolyte interface film containing sulfur phosphide. If the content of the phosphine-containing additive shown in the structural formula 2 is too low, it is difficult to improve the complexing effect of the negative electrode solid electrolyte interface film on Co ions, and the effect on improving battery performance is limited; if the content of the phosphine-containing additive shown in the structural formula 2 is too high, the conductivity of the negative electrode solid electrolyte interface film is affected.

[0028] In some embodiments, the mass percentage X% of the sulfur-containing additive shown in Structural Formula 1 in the non-aqueous electrolyte and the mass percentage Y% of the phosphine-containing additive shown in Structural Formula 2 in the non-aqueous electrolyte satisfy: 0.3≤X+Y≤3, 10≤X / Y≤100.

[0029] The contents of the sulfur-containing additive shown in structural formula 1 and the phosphine-containing additive shown in structural formula 2 in the non-aqueous electrolyte are related to the film-forming quality on the negative electrode surface. When the total content of X+Y is too small, it is difficult to form a continuous and complete solid electrolyte interface film on the negative electrode surface. Under high temperature conditions, the non-aqueous electrolyte is easy to decompose and consume active lithium on the positive and negative electrode surfaces, resulting in problems such as decreased battery capacity and gas production. When the total content of X+Y is too large, the film thickness on the negative electrode surface will be too large, which will in turn increase the battery impedance.

[0030] At the same time, based on the synergistic relationship between the sulfur-containing additive shown in Structural Formula 1 and the phosphine-containing additive shown in Structural Formula 2 in film formation on the negative electrode surface, when the contents of the sulfur-containing additive shown in Structural Formula 1 and the phosphine-containing additive shown in Structural Formula 2 satisfy the condition 10≤X / Y≤100, the formed negative electrode solid electrolyte interface film has a more suitable sulfur and phosphorus ratio, making it more conducive to combining with free Co ions in the non-aqueous electrolyte, forming a stable solid electrolyte interface film on the common negative electrode, and ensuring the improvement of the high temperature performance and rate performance of the lithium-ion battery.

[0031] In some embodiments, in the sulfur-containing additive shown in the structural formula 1, R 1 , R 2 Each independently selected or , and X, R 1 and R 2 Contains at least one sulfur atom.

[0032] When the sulfur-containing additive shown in Structural Formula 1 meets the above conditions, the sulfur-containing additive shown in Structural Formula 1 has a three-ring structure. Compared with the two-ring structure, the three-ring structure each opens to participate in the formation of the interface film on the electrode surface, which has the effect of improving the strength of the interface film structure, and thus helps to improve its high temperature stability.

[0033] As an example, the sulfur-containing additive shown in the structural formula 1 is selected from one or more of the following compounds: .

[0034] In some embodiments, in the sulfur-containing additive represented by the structural formula 1, X, R 1 and R 2 It does not contain sulfur atoms at the same time.

[0035] When the sulfur-containing additive shown in the structural formula 1 satisfies the above conditions, the sulfur-containing additive shown in the structural formula 1 has a tricyclic structure, and the sulfur-containing additive shown in the structural formula 1 includes both a sulfur-containing cyclic structure and a carbonate-containing cyclic structure, wherein the carbonate cyclic structure is conducive to the formation of a lithium carbonate component in the electrode interface film, and compared with simple sulfur-containing decomposition products, the interface film component formed by the carbonate cyclic structure and the sulfur-containing cyclic structure is more stable and dense.

[0036] In some embodiments, in the sulfur-containing additive shown in the structural formula 1, R 1 Selected from H, X selected from R 2 Selected from ;or, R 1 Selected from H, X selected from , R 2 Selected from or .

[0037] When the sulfur-containing additive shown in the structural formula 1 satisfies the above conditions, the sulfur-containing additive shown in the structural formula 1 has a double-ring structure, and the sulfur-containing additive shown in the structural formula 1 includes both a sulfur-containing cyclic structure and a carbonate-containing cyclic structure. Compared with simple sulfur-containing decomposition products, the interface film component formed by the carbonate cyclic structure and the sulfur-containing cyclic structure is more stable and dense.

[0038] In some embodiments, the sulfur-containing additive represented by Structural Formula 1 is selected from at least one of the following compounds: .

[0039] In some embodiments, the phosphine-containing additive represented by structural formula 2 is selected from at least one of the following compounds: .

[0040] In some embodiments, the additive further comprises a nitrile compound, and the nitrile compound comprises at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile, and sebacononitrile; Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage Z% of the nitrile compound is 1% to 4%.

[0041] In a specific embodiment, based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of the nitrile compound can be 1.0%, 1.1%, 1.3%, 1.5%, 1.8%, 2.0%, 2.3%, 2.7%, 3.0%, 3.3%, 3.7%, 4.0% or a range therebetween.

[0042] By further adding nitrile compounds to the non-aqueous electrolyte, the cyanide group in the molecular structure of the nitrile compound has a strong coordination ability and can combine with high-valent metal ions (such as cobalt, etc.) on the surface of the positive electrode to mask these active ions and reduce the decomposition effect of the electrode on the electrolyte. At the same time, the carbon-nitrogen triple bond in the cyanide group has a high bond energy, and it has good stability and oxidation resistance on the positive electrode. It is not easy to be oxidized, which can enhance the resistance of the electrolyte to positive electrode oxidation and inhibit the side reactions accompanied by metal ion reduction and electrolyte oxidation decomposition, thereby improving the cycle life of the electrolyte at high voltage and reducing gas generation and the increase of positive electrode resistance.

[0043] In some preferred embodiments, the mass percentage of the phosphine-containing additive Y% shown in the structural formula 2 and the mass percentage of the nitrile compound Z% satisfy: 10≤Z / Y≤80.

[0044] Although the addition of nitrile compounds is beneficial to improving the complexation of cobalt ions on the positive electrode and improving the stability of the non-aqueous electrolyte, nitrile compounds will also deteriorate the solid electrolyte interface film on the surface of the negative electrode. The improvement of the solid electrolyte interface film on the surface of the negative electrode by the phosphine-containing additive can effectively offset the deterioration of the solid electrolyte interface film on the surface of the negative electrode by the nitrile compounds. When the phosphine-containing additive Y% shown in Structural Formula 2 and the mass percentage Z% of the nitrile compound meet the condition 10≤Z / Y≤80, the coordination effect between the nitrile compound and the phosphine-containing additive can be fully coordinated to achieve the effect of synergistically improving the high-temperature electrochemical performance and safety performance of lithium-ion batteries.

[0045] 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 content of the additive is 0.01% to 30%.

[0046] In some embodiments, the cyclic sulfate ester 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-propylene 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 formula 3.

[0047] In the structural formula 3, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 Each is independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group; The phosphate compound is selected from the compound shown in structural formula 4:

[0048] In the structural formula 4, R 31 , R 32 , R 33 Each independently selected from a C1-C5 saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group, -Si(C m H 2m+1 ) 3 , m is a natural number from 1 to 3; In a preferred embodiment, the compound shown in the structural formula 4 may be at least one of tris(trimethylsilane)phosphate, tris(trimethylsilane)phosphite, 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.

[0049] In other embodiments, the additives may also include other additives that can improve battery performance: for example, additives that enhance battery safety performance, such as flame retardant additives such as fluorophosphates and cyclophosphazenes, or overcharge prevention additives such as tert-amylbenzene and tert-butylbenzene.

[0050] It should be noted that, unless otherwise specified, in general, the content of any one of the optional substances in the additives in the non-aqueous electrolyte is less than 10%, preferably, the content is 0.1%-5%, and more preferably, the content is 0.1%~2%. Specifically, the content of any one of the optional substances in the additives can be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, 10%.

[0051] In some embodiments, when the additive is selected from fluoroethylene carbonate, the content of the fluoroethylene carbonate is 0.05% to 30% based on the total mass of the non-aqueous electrolyte as 100%.

[0052] In some embodiments, the electrolyte salt is selected from a lithium salt, and the lithium salt is selected from LiPF 6 、LiBOB、LiDFOB、LiPO 2 F 2 , LiBF 4 、LiSbF 6 、LiAsF 6 、LiN(SO 2 CF 3 ) 2 、LiN(SO 2 C 2 F 5 ) 2 、LiC(SO 2 CF 3 ) 3 、LiN(SO 2 F) 2 、LiClO 4 、LiAlCl 4 、LiCF 3 SO 3 , Li 2 B 10 Cl 10 、LiSO2 F. at least one of LiTOP (lithium trioxalate phosphate), LiDODFP (lithium difluorodioxalate phosphate), LiOTFP (lithium tetrafluorooxalate phosphate) and lower aliphatic carboxylic acid lithium salts.

[0053] 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 may be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, or 2.5 mol / L.

[0054] In some embodiments, the non-aqueous organic solvent includes at least one of an ether solvent, a carbonate solvent, and a carboxylate solvent.

[0055] In some embodiments, the ether solvent includes a cyclic ether or a chain ether and a fluorinated product thereof, preferably a chain ether having 3 to 10 carbon atoms and a cyclic ether having 3 to 6 carbon atoms. The cyclic ether may be, but is not limited to, 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH 3 -THF), 2-trifluoromethyltetrahydrofuran (2-CF 3 -THF); the chain ether may specifically be, but is not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Since the chain ether has a high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which have low viscosity and can impart high ionic conductivity, are particularly preferred. The ether compound can be used alone or in any combination and ratio. The content of the ether compound is not particularly limited, and is arbitrary within the range that does not significantly damage the effect of the high-density lithium-ion battery of the present invention. In the non-aqueous solvent volume ratio of 100%, the volume ratio is usually 1% or more, preferably 2% or more, and more preferably 3% or more. In addition, the volume ratio is usually 30% or less, preferably 25% or less, and more preferably 20% or less. When two or more ether compounds are used in combination, the total amount of the ether compounds can be within the above range. When the content of the ether compound is within the above preferred range, it is easy to ensure the improvement of ion conductivity brought about by the increase in 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.

[0056] In some embodiments, the carbonate solvent includes a cyclic carbonate or a chain carbonate, and the cyclic carbonate may be, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); the chain carbonate may be, but is not limited to, at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). The content of the cyclic carbonate is not particularly limited, and is arbitrary within the range that does not significantly damage the effect of the lithium ion battery of the present invention, but when one is used alone, the lower limit of its content is usually 3% or more by volume, preferably 5% or more by volume, relative to the total amount of solvent in the non-aqueous electrolyte. By setting this range, the conductivity can be reduced due to the reduction in the dielectric constant of the non-aqueous electrolyte, and it is easy to make the large current discharge characteristics, stability relative to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery reach a good range. In addition, the upper limit is usually 90% or less by volume, preferably 85% or less by volume, and more preferably 80% or less by volume. By setting this scope, the oxidation / reduction tolerance of nonaqueous electrolyte can be improved, thus contribute to the stability during high temperature storage. The content of linear carbonate is not particularly limited, and relative to the total amount of solvent of nonaqueous electrolyte, it is usually more than 15% by volume, preferably more than 20% by volume, and more preferably more than 25% by volume. In addition, usually the volume ratio is less than 90%, preferably less than 85% by volume, and more preferably less than 80% by volume. By making the content of linear carbonate in the above-mentioned scope, it is easy to make the viscosity of nonaqueous electrolyte reach appropriate range, suppress the reduction of ionic conductivity, and then contribute to make the output characteristics of nonaqueous electrolyte battery reach good scope. When two or more linear carbonates are used in combination, the total amount of linear carbonate is made to meet the above-mentioned scope.

[0057] In certain embodiments, it is also possible to preferably use chain carbonates with fluorine atoms (hereinafter referred to as "fluorinated chain carbonates"). The number of fluorine atoms possessed by the fluorinated chain carbonate is not particularly limited as long as it is more than 1, but is generally less than 6, preferably less than 4. When the fluorinated chain carbonate has a plurality of fluorine atoms, these fluorine atoms can be bonded to the same carbon or to different carbons. As the fluorinated chain carbonate, fluorinated dimethyl carbonate derivatives, fluorinated ethyl methyl carbonate derivatives, fluorinated diethyl carbonate derivatives, etc. can be listed.

[0058] The carboxylate solvent includes cyclic carboxylate and / or chain carbonate. Examples of cyclic carboxylate include at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of chain carbonate include at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), butyl propionate, and ethyl fluoroacetate.

[0059] In some embodiments, the sulfone solvent includes a cyclic sulfone and a chain sulfone. Preferably, in the case of a cyclic sulfone, it is usually a compound with 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms, and in the case of a chain sulfone, it is usually a compound with 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms. The content of the sulfone solvent is not particularly limited, and 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 of the non-aqueous electrolyte, the volume ratio is usually 0.3% or more, preferably 0.5% or more, and more preferably 1% or more. In addition, the volume ratio is usually 40% or less, preferably 35% or less, and more preferably 30% or less. In the case of using two or more sulfone solvents in combination, the total amount of the sulfone solvent is sufficient to meet the above range. When the content of the sulfone solvent is within the above range, a non-aqueous electrolyte with excellent high temperature storage stability tends to be obtained.

[0060] In a preferred embodiment, the non-aqueous organic solvent is a mixture of cyclic carbonate and chain carbonate.

[0061] Another embodiment of the present invention provides a secondary battery including a positive electrode, a negative electrode, and the non-aqueous electrolyte as described above.

[0062] The positive electrode includes a positive electrode material layer containing a positive electrode active material, and the positive electrode active material includes a cobalt-containing material. More specifically, the cobalt-containing material includes LiCoO 2 , Lithium cobalt oxide modified by doping and / or coating with any one or more elements selected from Ni, Mn, Mg, Al, Zr, W, F, B, Cr, Mo and rare earth elements, with 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 which is provided with a coating layer of Li q Ni x Co y M 1-x-y O 2-g R gAt 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.

[0063] In some embodiments, the non-aqueous electrolyte contains 10-500 ppm of cobalt ions.

[0064] In a specific embodiment, the mass content of cobalt ions in the non-aqueous electrolyte can be 10 ppm, 35 ppm, 47 ppm, 68 ppm, 92 ppm, 115 ppm, 137 ppm, 160 ppm, 184 ppm, 210 ppm, 235 ppm, 260 ppm, 285 ppm, 310 ppm, 335 ppm, 360 ppm, 385 ppm, 410 ppm, 435 ppm, 500 ppm or a range between any two of the above.

[0065] Since the sulfur-containing additive shown in Structural Formula 1 and the phosphine-containing additive shown in Structural Formula 2 decompose together to form a negative electrode solid electrolyte interface film having the characteristic of complexing Co ions, and can further cooperate with the complexed Co ions to enhance the conductivity of the negative electrode solid electrolyte interface film, therefore, when a certain amount of cobalt ions is contained in the non-aqueous electrolyte, it is beneficial to improve the conductivity of the negative electrode solid electrolyte interface film, and then it is beneficial to improve the rate discharge performance.

[0066] The present invention is further described below by way of examples.

[0067] Table 1

[0068] Example 1 This embodiment is used to illustrate the lithium ion battery and the preparation method thereof disclosed in the present invention, and includes the following steps: 1) Preparation of non-aqueous electrolyte Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP) and ethyl propionate (EP) were mixed in a mass ratio of EC:PC:DEC:PP:EP=10:15:20:40:15, and then lithium hexafluorophosphate (LiPF 6 ) to a molar concentration of 1 mol / L, as shown in Table 1, and additives calculated based on the total mass of the electrolyte are added.

[0069] 2) Preparation of positive electrode The positive electrode active material LiCoO was mixed in a mass ratio of 93:4:3 2 , conductive carbon black Super-P and binder polyvinylidene fluoride (PVDF), and then disperse them in N-methyl-2-pyrrolidone (NMP) to obtain positive electrode slurry. The slurry is evenly coated on both sides of the aluminum foil, dried, rolled and vacuum dried, and welded with aluminum lead wires using an ultrasonic welder to obtain a positive electrode plate with a thickness of 120-150μm.

[0070] 3) Preparation of negative electrode The negative electrode active material artificial graphite, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) are mixed in a mass ratio of 94:1:2.5:2.5, and then dispersed in deionized water to obtain negative electrode slurry. The slurry is coated on both sides of the copper foil, dried, rolled and vacuum dried, and the nickel lead wire is welded with an ultrasonic welder to obtain the negative electrode plate, and the thickness of the plate is 120-150μm.

[0071] 4) Preparation of battery cells A three-layer separator with a thickness of 20 μm was placed between the positive plate and the negative plate, and then the sandwich structure consisting of the positive plate, the negative plate and the separator was wound. The wound body was flattened and placed in an aluminum foil packaging bag, and vacuum-baked at 75 ° C for 48 h to obtain a battery cell to be injected with liquid.

[0072] 5) Battery filling and formation In a glove box with a dew point controlled below -40°C, the non-aqueous electrolyte prepared above was injected into the battery cell, vacuum packaged, and left to stand for 24 h.

[0073] Then, the first charge was performed by hot pressing at 80 degrees according to the following steps: 0.1 C constant current charging for 4 minutes, pressure 12.51 kg / cc; 0.3 C constant current charging for 15 minutes, pressure 12.51 kg / cc; 1 C constant current charging for 45 minutes, pressure 12.51 kg / cc; secondary vacuum sealing, and then further charging at 0.2 C constant current to 4.5 V, after being placed at room temperature for 24 hours, it was discharged at 0.2 C constant current to 3.0 V.

[0074] Embodiments 2 to 23 Examples 2 to 23 are used to illustrate the lithium ion battery and the preparation method thereof disclosed in the present invention, and include most of the operation steps in Example 1, except that: The types and mass percentages of additives in the non-aqueous electrolytes used in Examples 2 to 23 are shown in Table 1.

[0075] Comparative Examples 1 to 27 Comparative Examples 1 to 27 are used to compare and illustrate the lithium ion battery and the preparation method thereof disclosed in the present invention, and include most of the operation steps in Example 1, except that: The types and mass percentages of additives in the non-aqueous electrolytes used in Comparative Examples 1 to 27 are shown in Table 1.

[0076] Performance Testing The lithium-ion battery prepared above was subjected to the following performance tests: 1. High temperature cycle performance test The prepared lithium-ion battery was placed in an oven at a constant temperature of 45°C and charged at a constant current of 1C to 4.5VLiCoO 2 / artificial graphite battery, then charge at constant voltage until the current drops to 0.02 C, then discharge at a constant current of 1 C to 3.0V, and repeat this cycle, recording the first discharge capacity and the last discharge capacity.

[0077] The capacity retention rate of high temperature cycle is calculated as follows: Capacity retention rate (%) = last discharge capacity / first discharge capacity × 100%.

[0078] 2. Maximum non-lithium precipitation rate performance test The formed lithium-ion battery was charged to 4.5V LiCoO at room temperature using different rates from 1C to 5C (0.5C gradient) at constant current and constant voltage. 2 / Artificial graphite battery, each group has 3 batteries. After fully charged, the battery cells are disassembled to observe whether there is lithium deposition on the surface of the negative electrode. If there is no lithium deposition at 3C, there will be no lithium deposition at 3.5C for all 3 batteries. The highest rate of no lithium deposition is 3.5C.

[0079] 3. Hot box performance test At 25°C, the formed battery was charged to 4.5V LiCoO with 1 C constant current and constant voltage. 2 / Artificial graphite battery, place 3 fully charged batteries in a constant temperature explosion-proof oven for 30 minutes, set the temperature to 130℃, if all three batteries do not catch fire or explode, it is considered that the 130℃ 30min hot box test has been passed; place another 3 batteries in a constant temperature explosion-proof oven for 30 minutes, set the temperature to 131℃, if all three batteries do not catch fire or explode, it is considered that the 131℃ 30min hot box test has been passed; and so on, increase the temperature by 1℃ each time until the highest hot box passing temperature of the battery is tested. If the 130℃ 30min hot box test is not passed for the first time, reduce the temperature by 1℃ each time until the highest hot box passing temperature of the battery is tested.

[0080] 4. Cobalt ion detection The lithium-ion battery is discharged and centrifuged, and the liquid obtained after centrifugation is tested by inductively coupled plasma spectroscopy (ICP) to obtain the content of cobalt ions in the electrolyte.

[0081] (1) The test results obtained in Examples 1 to 11 and Comparative Examples 1 to 8 and 16 to 24 are entered in Table 2.

[0082] Table 2

[0083] It can be seen from the test results of Examples 1 to 11 and Comparative Examples 1 to 8, 16 to 24 that, compared with adding only the sulfur-containing additive shown in Structural Formula 1 or only adding the phosphine-containing additive shown in Structural Formula 2, adding both additives in Examples 1 to 11 significantly improves the rate performance, high-temperature cycle performance and hot box safety of the lithium-ion battery. In particular, this combination shows an unexpected effect on inhibiting the dissolution of positive electrode cobalt ions, indicating that the negative electrode solid electrolyte interface film formed by the decomposition of the sulfur-containing additive of Structural Formula 1 and the phosphine-containing additive of Structural Formula 2 has a strong complexing effect on Co ions, preventing Co ions from damaging the negative electrode solid electrolyte interface film and the negative electrode active material, thereby improving the high temperature safety of the battery. In addition, the Co ions complexed on the negative electrode solid electrolyte interface film are reduced on the negative electrode surface to form a negative electrode solid electrolyte interface film containing Co, further enhancing the conductivity of the film.

[0084] (2) The test results obtained in Examples 12 to 16 are entered in Table 3.

[0085] Table 3

[0086] By comparing the test results of Examples 1 to 11 and Examples 12 to 16, it can be seen that when the sulfur-containing additive shown in Structural Formula 1 and the phosphine-containing additive shown in Structural Formula 2 further meet the conditions of 0.3≤X+Y≤3, 10≤X / Y≤100 (Examples 1 to 11), the obtained lithium-ion lithium battery has a significant improvement in inhibiting the dissolution of positive electrode Co ions. At the same time, based on this effect, the rate performance, high temperature cycle performance and safety performance of the lithium-ion battery are improved to a certain extent; while Examples 12 to 16 that do not meet this condition show the deterioration of the electrochemical performance of the lithium-ion battery and the aggravation of the dissolution of positive electrode Co ions, indicating that the sulfur-containing additive shown in Structural Formula 1 and the phosphine-containing additive shown in Structural Formula 2 have a synergistic effect. When the contents of the two are controlled in a balanced state, the cooperation of the two can be fully exerted to achieve the improvement of the lithium-ion battery.

[0087] (3) The test results of Examples 1, 17 to 23 and Comparative Examples 9 to 15, 25 to 27 are entered in Table 4.

[0088] Table 4

[0089] From the comparison of the test results of Examples 17 to 23 and Comparative Examples 9 to 15 and 25 to 27, it can be seen that in the electrolyte system provided by the present invention, the combination of different sulfur-containing additives shown in Structural Formula 1 and different phosphine-containing additives shown in Structural Formula 2 has a significant effect on the inhibition of Co ion dissolution, rate performance, high temperature performance and safety performance of lithium-ion batteries, indicating that the coordination effect between the sulfur-containing additive shown in Structural Formula 1 and the phosphine-containing additive shown in Structural Formula 2 is mainly reflected in the coordination of the common structure of the sulfur-containing additives shown in different Structural Formulas 1 and the common structure of the phosphine-containing additives shown in different Structural Formulas 2. In particular, when the sulfur-containing additive shown in the structural formula 1 is selected from compound 1-1, compound 1-3, compound 1-7, compound 1-8, and compound 1-10, the sulfur-containing additive shown in the structural formula 1 includes a sulfur-containing cyclic structure and a carbonate-containing cyclic structure, wherein the carbonate cyclic structure is conducive to the formation of a lithium carbonate component in the electrode interface film. Compared with simple sulfur-containing decomposition products, the interface film component formed by the carbonate cyclic structure and the sulfur-containing cyclic structure is more stable and dense, and has a better improvement effect on the rate performance, high-temperature cycle performance and hot box safety of lithium-ion batteries.

[0090] Table 5

[0091] Embodiments 24 to 36 Examples 24 to 36 are used to illustrate the lithium ion battery and the preparation method thereof disclosed in the present invention, and include most of the operation steps in Example 1, except that: The non-aqueous electrolytes used in Examples 24 to 36 additionally contain nitrile compounds. The types of additives in the non-aqueous electrolytes and their mass percentages are shown in Table 5.

[0092] Performance Testing The lithium-ion battery prepared above was subjected to the following performance tests: 1. High temperature cycle performance test The prepared lithium-ion battery was placed in an oven at a constant temperature of 45°C and charged at a constant current of 1C to 4.5VLiCoO 2 / artificial graphite battery, then charge at constant voltage until the current drops to 0.02 C, then discharge at a constant current of 1 C to 3.0V, and repeat this cycle, recording the first discharge capacity and the last discharge capacity.

[0093] The capacity retention rate of high temperature cycle is calculated as follows: Capacity retention rate = last discharge capacity / first discharge capacity × 100%.

[0094] 2. Maximum non-lithium precipitation rate performance test The formed lithium-ion battery was charged to 4.5V LiCoO at room temperature using different rates from 1C to 5C (0.5C gradient) at constant current and constant voltage. 2 / Artificial graphite battery, each group has 3 batteries. After fully charged, the battery cells are disassembled to observe whether there is lithium deposition on the surface of the negative electrode. If there is no lithium deposition at 3C, there will be no lithium deposition at 3.5C for all 3 batteries. The highest rate of no lithium deposition is 3.5C.

[0095] 3. Hot box performance test At 25°C, the formed battery was charged to 4.5V LiCoO with 1 C constant current and constant voltage. 2 / Artificial graphite battery, place 3 fully charged batteries in a constant temperature explosion-proof oven for 30 minutes, set the temperature to 130℃, if none of the three batteries catch fire or explode, it is considered that the 130℃ 30min hot box test has passed. Place another 3 batteries in a constant temperature explosion-proof oven for 30 minutes, set the temperature to 132℃, if none of the three batteries catch fire or explode, it is considered that the 132℃ 30min hot box test has passed. And so on, increase 1℃ each time until the highest hot box passing temperature of the battery is tested.

[0096] 4. Cobalt ion detection The lithium-ion battery is discharged and centrifuged, and the liquid obtained after centrifugation is tested by inductively coupled plasma spectroscopy (ICP) to obtain the content of cobalt ions in the electrolyte.

[0097] The test results of Examples 1, 24 to 36 are entered in Table 6.

[0098] Table 6

[0099] From the comparison of the test results of Examples 1 and 24 to 36, it can be seen that when a nitrile compound is further added to the electrolyte system provided by the present invention, and the mass percentage content Z% of the phosphine-containing additive Y% shown in Structural Formula 2 and the nitrile compound is controlled to satisfy the condition 10≤Z / Y≤80, the coordination effect between the nitrile compound and the phosphine-containing additive can be fully coordinated, and the complexation of the cobalt ions of the positive electrode can be strengthened by the nitrile compound. At the same time, the improvement effect of the phosphine-containing additive on the solid electrolyte interface film on the surface of the negative electrode can effectively offset the deterioration effect of the nitrile compound on the solid electrolyte interface film on the surface of the negative electrode, thereby achieving the effect of synergistically improving the high temperature electrochemical performance and safety performance of the lithium ion battery.

[0100] 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 protection scope of the present invention.

Claims

1. A non-aqueous electrolyte, characterized in that: It includes a non-aqueous organic solvent, an electrolyte salt and an additive, wherein the additive includes a sulfur-containing additive shown in structural formula 1 and a phosphine-containing additive shown in structural formula 2: ； Wherein n is 0 or 1, A is selected from C or O, and X is selected from or , R1, R2 are each independently selected from H, or , R1 and R2 are not simultaneously selected from H, and X, R1 and R2 contain at least one sulfur atom; ； Wherein, R3, R4, R5, and R6 are each independently selected from H, a C1~C4 hydrocarbon group or -OPF2, R7 is selected from O or a C1~C4 hydrocarbon group, m=0~10, z=0~10.

2. The non-aqueous electrolyte according to claim 1, characterized in that Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage X% of the sulfur-containing additive represented by the structural formula 1 is 0.1% to 3%; and / or, Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content Y% of the phosphine-containing additive represented by the structural formula 2 is 0.01% to 0.5%.

3. The non-aqueous electrolyte according to claim 1, characterized in that The mass percentage X% of the sulfur-containing additive represented by structural formula 1 in the non-aqueous electrolyte and the mass percentage Y% of the phosphine-containing additive represented by structural formula 2 in the non-aqueous electrolyte satisfy: 0.3≤X+Y≤3, 10≤X / Y≤100.

4. The non-aqueous electrolyte according to claim 1, characterized in that In the sulfur-containing additive shown in the structural formula 1, R1 and R2 are each independently selected from or , and X, R1 and R2 contain at least one sulfur atom.

5. The non-aqueous electrolyte according to claim 1 or 4, characterized in that: In the sulfur-containing additive shown in the structural formula 1, X, R1 and R2 do not contain sulfur atoms at the same time.

6. The non-aqueous electrolyte according to claim 1, characterized in that In the sulfur-containing additive shown in the structural formula 1, R1 is selected from H, X is selected from , R2 is selected from ,or, R1 is selected from H, X is selected from , R2 is selected from or .

7. The non-aqueous electrolyte according to claim 1, characterized in that The sulfur-containing additive shown in structural formula 1 is selected from at least one of the following compounds: ； And / or, the phosphine-containing additive represented by structural formula 2 is selected from at least one of the following compounds: 。 8. The non-aqueous electrolyte according to claim 1, characterized in that The additive further comprises a nitrile compound, wherein the nitrile compound comprises at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebaconitrile; Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage Z% of the nitrile compound is 1% to 4%; The mass percentage of the phosphine-containing additive Y% shown in the structural formula 2 and the mass percentage of the nitrile compound Z% satisfy: 10≤Z / Y≤80.

9. A secondary battery, characterized in that: It comprises a positive electrode, a negative electrode and the non-aqueous electrolyte as claimed in any one of claims 1 to 8.

10. The secondary battery according to claim 9, characterized in that: The content of cobalt ions in the non-aqueous electrolyte is 10-500 ppm.

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