Non-aqueous electrolyte and lithium ion battery

Abstract

The invention provides a non-aqueous electrolyte and a lithium ion battery. The non-aqueous electrolyte comprises a lithium salt, a non-aqueous organic solvent and an additive. The additive comprises vinylene carbonate and a compound A shown as a structural formula I; wherein R1 and R2 are respectively and independently selected from a substituted or unsubstituted alkyl group of C1-C6, a substituted or unsubstituted alkenyl group of C2-C6, a substituted or unsubstituted alkynyl group of C2-C6, and a substituted or unsubstituted aryl group. And R3 is selected from a substituted or unsubstituted alkyl group of C1-C6, a substituted or unsubstituted alkenyl group of C2-C6, a substituted or unsubstituted alkynyl group of C2-C6, a substituted or unsubstituted aryl group, a substituted or unsubstituted silyl group, and a substituted or unsubstituted siloxane group. The non-aqueous electrolyte contains the compound A and the vinylene carbonate, the unique structure of the compound A and the vinylene carbonate cooperate to improve the fast charging and high-temperature performance of the electrolyte, and the non-aqueous electrolyte is especially suitable for a lithium iron phosphate battery. The structural formula I of the # imgabs0 # is shown in the specification.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy batteries, and particularly relates to a non-aqueous electrolyte and a lithium-ion battery. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, long life, environmental friendliness, etc., and have been widely used in electronic products such as mobile phones, laptop computers, digital cameras, etc., and have also been widely used as power batteries in electric bicycles, model airplanes, and electric vehicles.

[0003] As one of the key materials of lithium-ion batteries, the cathode material plays a decisive role in the capacity of the entire lithium-ion battery, and has also become the focus of research, industrialization, and large-scale application in the field of new energy materials. Among the current relatively many studies on cathode materials, lithium cobaltate and lithium nickelate have safety problems due to unstable structures, and environmental problems are not suitable for large-scale applications. The lithium manganate material has a serious problem of capacity decay during high-temperature cycling, which restricts its further application in the field of power batteries. Although the NCM ternary material has relatively outstanding comprehensive performance, there are still problems of toxic elements and strategic resource element Co, and this material can only be used as a transitional product. For the lithium iron phosphate material, due to its excellent cycling performance, high safety performance, environmental friendliness, and moderate cost, it has been widely used in the fields of energy storage and new energy vehicles. With the continuous prosperity of the new energy industry, especially the gradually increasing share of pure electric vehicles in the global automotive market, the installation volume of lithium iron phosphate batteries has continued to rise. With the development demand of power batteries, higher requirements are put forward for the fast charging performance of lithium iron phosphate batteries.

[0004] In lithium-ion batteries, film-forming additives such as VC, PS, DTD, etc. undergo redox reactions prior to carbonate solvents such as EC, and form a solid electrolyte film with a thickness of about 100 nm on the surface of the positive or negative electrode, which contains inorganic components such as Li2O, LiF, Li2CO3 and organic components such as LiOCO2R, LiOSO2R. Its function can prevent the contact between the electrolyte and the positive and negative electrodes during the charge and discharge of the lithium-ion battery, and reduce the side reactions between the electrolyte and the positive and negative electrodes. However, the SEI film formed by the current film-forming additives is not dense, has uneven thickness, poor ionic conductivity, decomposition of the electrolyte at high temperature and failure of the SEI film, which affect the high-temperature storage and fast charging performance of lithium iron phosphate batteries.

[0005] Therefore, there is an urgent need for a non-aqueous electrolyte and its lithium-ion battery to solve the above problems. Summary of the Invention

[0006] Based on the above problems, the object of the present invention is to provide a non-aqueous electrolyte and a lithium-ion battery. The non-aqueous electrolyte contains compound A and vinylene carbonate. The unique structure of compound A and vinylene carbonate can synergistically improve the fast charging and high-temperature performance of the electrolyte, and is particularly suitable for lithium iron phosphate batteries.

[0007] To achieve the above object, on the one hand, the present invention provides a non-aqueous electrolyte. The non-aqueous electrolyte includes a lithium salt, a non-aqueous organic solvent, and an additive. The additive includes vinylene carbonate and compound A shown in structural formula I. Among them, R1 and R2 are each independently selected from a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted C2-C6 alkenyl group, a substituted or unsubstituted C2-C6 alkynyl group, a substituted or unsubstituted aryl group, and R3 is selected from a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted C2-C6 alkenyl group, a substituted or unsubstituted C2-C6 alkynyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted silyl group, a substituted or unsubstituted siloxanyl group.

[0008] Structural formula I The non-aqueous electrolyte of the present invention has at least the following technical effects.

[0009] (1) The additive includes vinylene carbonate and compound A containing a phosphonamide structure (-N=P-O-) shown in structural formula I. The strong polar P-O bond in the N=P-O group can preferentially combine with active oxygen (such as O - radicals) in the electrolyte to inhibit the oxidative decomposition of the electrolyte at high voltage (>4.3 V); the compound containing N=P-O is preferentially reduced on the surface of the positive electrode to form a dense CEI film, inhibiting the dissolution of transition metals (such as Mn, Co) and the continuous decomposition of the electrolyte; the P-O group can decompose to generate phosphate substances at high temperature, achieving flame retardancy through a dual mechanism of gas-phase radical quenching and condensed-phase carbonization; the strong electron-withdrawing effect of the N=P-O group can weaken the association between Li + and anions (such as PF6 - ), and enhance Li +The transference number. Therefore, using Compound A in a lithium-ion battery can promote the formation of the SEI, which can allow lithium ions to pass through quickly, enhancing the fast-charging ability. At the same time, it can also inhibit the reduction of the electrolyte, reduce the increase in high-temperature storage impedance, and improve the high-temperature storage performance of the lithium-ion battery. The trimethylsilyl group can, on the one hand, inhibit the increase in acid value, relieve gas generation, reduce the erosion of HF on the SEI, and improve the growth of DCIR. On the other hand, it can improve the positive electrode CEI, inhibit the dissolution of metal ions, and improve the high-temperature performance. Therefore, using Compound A in a lithium-ion battery can promote the formation of the SEI, which can allow lithium ions to pass through quickly, enhancing the fast-charging ability. At the same time, it can also inhibit the reduction of the electrolyte, reduce the increase in high-temperature storage impedance, and improve the high-temperature storage performance of the lithium-ion battery.

[0010] (2)In the phosphonamide structure, P can, on the one hand, capture some oxygen free radicals in the electrolyte. On the other hand, its structure allows for the connection of more other effective functional groups. Therefore, it can be connected to the carbon-carbon double bond structure inside the ring of vinylene carbonate (VC). The strong polarity of the P-O group enables it to preferentially adsorb on the electrode surface, guiding the directional arrangement of VC molecules, promoting the uniform decomposition and polymerization of VC, avoiding the increase in lithium-ion transport impedance caused by local over-thickness of the SEI film, and further enhancing the effective action of the additive on the lithium-ion battery and its electrolyte.

[0011] (3)N in the phosphonamide structure can have a weak coordination interaction with iron ions to regulate the dissolution behavior of iron ions, and at the same time generate an inorganic SEI component with a smaller impedance. Therefore, the electrolyte of the present invention is particularly suitable for use in lithium iron phosphate batteries.

[0012] As a technical solution of the present invention, R1 and R2 are each independently selected from substituted or unsubstituted C1-C3 alkyl groups, substituted or unsubstituted C2-C3 alkenyl groups, substituted or unsubstituted C2-C3 alkynyl groups, and substituted or unsubstituted phenyl groups, and R3 is selected from substituted or unsubstituted C1-C3 alkyl groups, substituted or unsubstituted C2-C3 alkenyl groups, substituted or unsubstituted C2-C3 alkynyl groups, substituted or unsubstituted phenyl groups, and substituted or unsubstituted silyl groups.

[0013] As a technical solution of the present invention, Compound A is selected from at least one of Compound One to Compound Three.

[0014]

[0015] As a technical solution of the present invention, the mass ratio of vinylene carbonate in the non-aqueous electrolyte is 1.00-5.00%, and the mass ratio of Compound A in the non-aqueous electrolyte is 0.05-5.00%.

[0016] As a technical solution of the present invention, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate, lithium difluorophosphate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium lower aliphatic carboxylate, lithium difluorodioxalate phosphate, lithium bis(fluorosulfonyl)imide, lithium chloroborane, and lithium tetraphenylborate.

[0017] As a technical solution of the present invention, the non-aqueous organic solvent is selected from at least one of γ-butyrolactone, γ-valerolactone, δ-valerolactone, methyl acetate, ethyl acetate, ethyl propionate, butyl acetate, propyl propionate, butyl propionate, ethylene carbonate, propylene carbonate, butylene carbonate, methyl pentyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, propylene carbonate, 1,3-dioxolane, 1,4-dioxane, crown ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2-trifluoromethyltetrahydrofuran, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether.

[0018] The second aspect of the present invention provides a lithium ion battery, comprising a positive electrode material, a negative electrode material, and the aforementioned non-aqueous electrolyte.

[0019] As a technical solution of the present invention, the positive electrode material is a lithium iron phosphate-based material, and the chemical general formula of the lithium iron phosphate-based material is Li m Fe α M β PO4 or Li 1-x A x Fe 1-y B y PO4 / C, where 0.85 ≤ m ≤ 1.0, 0.8 ≤ α ≤ 1.0, 0 ≤ β ≤ 0.2, 0 ≤ x ≤ 0.15, 0 ≤ y ≤ 0.15, M is at least one of Ti, Mg, V, Mn, W, Al, Nb, Mo, Zr, Cr, Ni, and Co, A and B are different and are respectively at least one of Ag, Mg, Zn, Cu, Al, In, Ti, Nb, Mo, V, Zr, Mn, Cr, Ni, and Co, and C accounts for 1-20 wt.% of Li 1-x A x Fe 1-y B y PO4 / C.

[0020] As a technical solution of the present invention, the negative electrode material includes at least one of a carbon-based negative electrode material, a silicon-based negative electrode material, a titanium-based oxide negative electrode material, and an alloy-based negative electrode material.

[0021] As a technical solution of the present invention, the negative electrode material includes soft carbon, hard carbon, artificial graphite, natural graphite, silicon-carbon composite material, silicon-oxygen composite material, lithium titanate, FeS x , Cu x O, MoS2, Sn x O, CoS x , Fe2O3, Fe3O4, ZnS and at least one of SbSn. Specific Embodiments

[0022] The non-aqueous electrolyte of the present invention can improve the high-temperature and fast-charging performance of lithium-ion batteries. At a high rate of 4C and a high temperature of 45°C, after 1000 cycles, it still has a capacity retention rate of more than 95%. After storing at 60°C for 30 days, the DCR growth rate is less than 110%. In particular, it is used to improve the performance of lithium iron phosphate batteries.

[0023] The lithium-ion battery of the present invention may include a positive electrode material, a negative electrode material, and a non-aqueous electrolyte.

[0024] Among them, the positive electrode material may be a lithium cobalt oxide-based material, a lithium iron phosphate-based material, a nickel cobalt manganese-based oxide, or a nickel cobalt aluminum-based oxide. The lithium cobalt oxide-based material may be lithium cobalt oxide or lithium cobalt oxide doped or coated and modified. The lithium iron phosphate-based material may be lithium iron phosphate or lithium iron phosphate doped or coated and modified. The nickel cobalt manganese-based oxide may be nickel cobalt manganese oxide or nickel cobalt manganese oxide doped or coated and modified. The nickel cobalt aluminum-based oxide may be nickel cobalt aluminum oxide or nickel cobalt aluminum oxide doped or coated and modified. In particular, the positive electrode material is a lithium iron phosphate-based material, and the chemical general formula of the lithium iron phosphate-based material is Li m Fe α M β PO4 or Li 1-x A x Fe 1-y B y PO4 / C, where 0.85 ≤ m ≤ 1.0, 0.8 ≤ α ≤ 1.0, 0 ≤ β ≤ 0.2, 0 ≤ x ≤ 0.15, 0 ≤ y ≤ 0.15, M is at least one of Ti, Mg, V, Mn, W, Al, Nb, Mo, Zr, Cr, Ni, and Co, A and B are different and are respectively at least one of Ag, Mg, Zn, Cu, Al, In, Ti, Nb, Mo, V, Zr, Mn, Cr, Ni, and Co, and C accounts for Li 1-x A x Fe 1-y B yThe content of PO4 / C is 1-20 wt.%. The negative electrode material includes at least one of carbon-based negative electrode materials, silicon-based negative electrode materials, titanium-based oxide negative electrode materials, and alloy-based negative electrode materials. Further, the negative electrode material includes soft carbon, hard carbon, artificial graphite, natural graphite, silicon-carbon composite materials, silicon-oxygen composite materials, lithium titanate, FeS x , Cu x O, MoS2, Sn x O, CoS x , Fe2O3, Fe3O4, ZnS, and at least one of SbSn.

[0025] The non-aqueous electrolyte includes a lithium salt, a non-aqueous organic solvent, and an additive.

[0026] The lithium salt can account for 5-25% of the mass of the non-aqueous electrolyte. Further, the lithium salt accounts for 8-20% of the mass of the non-aqueous electrolyte. More preferably, the lithium salt accounts for 10-15% of the mass of the non-aqueous electrolyte. By way of example, the lithium salt can but is not limited to accounting for 5%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 20%, 25% of the mass of the non-aqueous electrolyte. The lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium lower aliphatic carboxylate, lithium difluorodioxalate phosphate (LiDFBP), lithium bis(fluorosulfonyl)imide (LiFSI), lithium chloroborane, and lithium tetraphenylborate.

[0027] The non-aqueous organic solvent may account for 65 to 90% by mass of the non-aqueous electrolyte. Preferably, the non-aqueous organic solvent may account for 75 to 89% by mass of the non-aqueous electrolyte. More preferably, the non-aqueous organic solvent may account for 78 to 88% by mass of the non-aqueous electrolyte. By way of example, the non-aqueous organic solvent may, but is not limited to, account for 65%, 70%, 80%, 85%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 90% by mass of the non-aqueous electrolyte. The non-aqueous organic solvent is selected from at least one of γ-butyrolactone (GBL), γ-valerolactone (GVL), δ-valerolactone (DVL), methyl acetate (MA), ethyl acetate (EA), ethyl propionate (EP), butyl acetate (BAC), propyl propionate (PP), butyl propionate (PRB), ethylene carbonate (EC), propylene carbonate (PCA), butylene carbonate (BC), methyl pentyl carbonate (MPC), vinylene carbonate (VEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), propylene carbonate (PC), 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), 2-trifluoromethyltetrahydrofuran (2-CF3-THF), dimethoxymethane (DMM), diethoxymethane (DEM), ethoxymethoxymethane (DCE), ethylene glycol di-n-propyl ether (EDP), ethylene glycol di-n-butyl ether (EDB), and diethylene glycol dimethyl ether (DEGME).

[0028] The additives include vinylene carbonate and Compound A shown in Structural Formula I. Compound A connects the carbon-carbon double bond structure inside the ring of vinylene carbonate through the contained phosphonamide structure. Due to the strong polarity of the P-O group through their synergistic effect, it preferentially adsorbs on the electrode surface, guides the directional arrangement of VC molecules, promotes the uniform decomposition and polymerization of VC, and avoids the increase in lithium-ion transport impedance caused by the local excessive thickness of the SEI film. The mass ratio of vinylene carbonate in the non-aqueous electrolyte is 1.00 - 5.00%, and the mass ratio of Compound A in the non-aqueous electrolyte is 0.05 - 5.00%. More preferably, the mass ratio of vinylene carbonate in the non-aqueous electrolyte is 2.00 - 4.00%, and the mass ratio of Compound A in the non-aqueous electrolyte is 0.10 - 4.00%. Further preferably, the mass ratio of vinylene carbonate in the non-aqueous electrolyte is 2.00 - 3.00%, and the mass ratio of Compound A in the non-aqueous electrolyte is 0.50 - 2.00%. By way of example, the mass ratio of vinylene carbonate in the non-aqueous electrolyte can be, but is not limited to, 1.00%, 1.50%, 2.00%, 2.50%, 3.00%, 3.50%, 4.00%, 4.50%, 5.00%. The mass ratio of Compound A in the non-aqueous electrolyte can be, but is not limited to, 0.05%, 0.10%, 0.50%, 1.00%, 1.50%, 2.00%, 2.50%, 3.00%, 3.50%, 4.00%, 4.50%, 5.00%.

[0029]

[0030] Structural Formula I R1 and R2 are each independently selected from substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C2-C6 alkynyl, substituted or unsubstituted aryl; R3 is selected from substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C2-C6 alkynyl, substituted or unsubstituted aryl, substituted or unsubstituted silyl, substituted or unsubstituted siloxanyl. Further, R1 and R2 are each independently selected from substituted or unsubstituted C1-C3 alkyl, substituted or unsubstituted C2-C3 alkenyl, substituted or unsubstituted C2-C3 alkynyl, substituted or unsubstituted phenyl; R3 is selected from substituted or unsubstituted C1-C3 alkyl, substituted or unsubstituted C2-C3 alkenyl, substituted or unsubstituted C2-C3 alkynyl, substituted or unsubstituted phenyl, substituted or unsubstituted silyl. Still further, R1 and R2 are each independently selected from methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, vinyl, propenyl, isopropenyl, butenyl, pentenyl, hexenyl, ethynyl, propynyl, isopropynyl, butynyl, pentynyl, hexynyl, monofluoromethyl, monofluoroethyl, monofluoropropyl, monofluoroisopropyl, monofluorobutyl, monofluoropentyl, monofluorohexyl, monofluoro vinyl, monofluoropropenyl, monofluoroisopropenyl, monofluorobutenyl, monofluoropentenyl, monofluorohexenyl, monofluoroethynyl, monofluoropropynyl, monofluoroisopropynyl, monofluorobutynyl, monofluoropentynyl, monofluorohexynyl, polyfluoromethyl, polyfluoroethyl, polyfluoropropyl, polyfluoroisopropyl, polyfluorobutyl, polyfluoropentyl, polyfluorohexyl, polyfluoro vinyl, polyfluoropropenyl, polyfluoroisopropenyl, polyfluorobutenyl, polyfluoropentenyl, polyfluorohexenyl, polyfluoroethynyl, polyfluoropropynyl, polyfluoroisopropynyl, polyfluorobutynyl, polyfluoropentynyl, polyfluorohexynyl, phenyl, tolyl, ethylphenyl, monofluorophenyl, monofluorotolyl, monofluoroethylphenyl, polyfluorophenyl, polyfluorotolyl, polyfluoroethylphenyl.R3 is selected from methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, vinyl, propenyl, isopropenyl, butenyl, pentenyl, hexenyl, ethynyl, propynyl, isopropynyl, butynyl, pentynyl, hexynyl, monofluoromethyl, monofluoroethyl, monofluoropropyl, monofluoroisopropyl, monofluorobutyl, monofluoropentyl, monofluorohexyl, monofluorovinyl, monofluoropropenyl, monofluoroisopropenyl, monofluorobutenyl, monofluoropentenyl, monofluorohexenyl, monofluoroethynyl, monofluoropropynyl, monofluoroisopropynyl, monofluorobutynyl, monofluoropentynyl, monofluorohexynyl, polyfluoromethyl, polyfluoroethyl, polyfluoropropyl, polyfluoroisopropyl, polyfluorobutyl, polyfluoropentyl, polyfluorohexyl, polyfluorovinyl, polyfluoropropenyl, polyfluoroisopropenyl, polyfluorobutenyl, polyfluoropentenyl, polyfluorohexenyl, polyfluoroethynyl, polyfluoropropynyl, polyfluoroisopropynyl, polyfluorobutynyl, polyfluoropentynyl, polyfluorohexynyl, phenyl, tolyl, ethylphenyl, monofluorophenyl, monofluorotolyl, monofluoroethylphenyl, polyfluorophenyl, polyfluorotolyl, polyfluoroethylphenyl, trimethylsilyl, triethylsilyl, monofluorotrimethylsilyl, monofluorotriethylsilyl, difluorotrimethylsilyl, difluorotriethylsilyl, trifluorotrimethylsilyl, trifluorotriethylsilyl, trimethylsilyloxy, triethylsilyloxy, monofluorotrimethylsilyloxy, monofluorotriethylsilyloxy, difluorotrimethylsilyloxy, difluorotriethylsilyloxy, trifluorotrimethylsilyloxy, trifluorotriethylsilyloxy.

[0031] Furthermore, compound A is at least one selected from compound 1 to compound 3. Preferably, compound A is compound 1, and the bistrimethylsilyl group contained therein can effectively improve the formation of SEI and reduce the corrosion of water and acid on SEI.

[0032]

[0033] In order to better illustrate the purpose, technical scheme and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following implementation method is a further explanation of the present invention and should not be used as a limitation of the present invention.

[0034] If no specific conditions are specified in the examples and comparative examples, the experiments may be carried out under conventional conditions or conditions recommended by the manufacturer. If no manufacturer is specified for the reagents or instruments used, they are all conventional products available on the market.

[0035] Example 1 (1) Preparation of non-aqueous electrolyte In a glove box filled with argon (O2 < 1 ppm, H2O < 1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a weight ratio of EC:EMC = 3:7 (84.0 g) to obtain a non-aqueous organic solvent. Then, 0.5 g of Compound I and 3.0 g of vinylene carbonate were added, dissolved, and stirred well. After that, 12.5 g of lithium hexafluorophosphate was added and mixed evenly to obtain a non-aqueous electrolyte.

[0036] (2)Preparation of the positive electrode The lithium iron phosphate material LiFePO4, binder PVDF, and conductive agent SuperP were mixed evenly in a mass ratio of 95:1:4 to prepare a lithium secondary battery positive electrode paste with a certain viscosity. After the prepared paste was coated on both sides of the aluminum foil, it was dried and roll-pressed to obtain the positive electrode sheet.

[0037] (3)Preparation of the negative electrode Artificial graphite, binder PVDF, and conductive agent SuperP were mixed evenly in a mass ratio of 90:2:8 to prepare a lithium secondary battery negative electrode paste with a certain viscosity. After the prepared paste was coated on both sides of the copper foil, it was dried and roll-pressed to obtain the negative electrode sheet.

[0038] (4)Preparation of the lithium-ion battery The positive electrode sheet, separator, and negative electrode sheet were stacked in sequence and then stacked as needed. After the tabs were welded, they were placed in the aluminum-plastic film of the battery outer package. The prepared non-aqueous electrolyte was injected into the dried bare battery cell, and then vacuum packaging, standing, formation (constant current charging at 0.05C to 3.0V, and then constant current charging at 0.1C to 3.3V), shaping, capacity testing and other processes were carried out. Finally, a 1Ah lithium secondary battery was obtained.

[0039] The composition and content of the non-aqueous electrolytes of Examples 1 to 11 and Comparative Examples 1 to 5 are shown in Table 1. Among them, the preparation processes of the non-aqueous electrolytes, positive electrode sheets, negative electrode sheets, and lithium-ion batteries of Examples 2 to 11 and Comparative Examples 1 to 5 are the same as those of Example 1.

[0040] Table 1 Non-aqueous electrolyte components of Examples and Comparative Examples

[0041] Among them, the structural formula of Compound IV is as follows.

[0042]

[0043] Compound IV The lithium-ion batteries prepared in Examples 1 to 11 and Comparative Examples 1 to 5 were respectively subjected to high-temperature fast charging performance testing, high-temperature storage performance testing, and internal resistance growth rate testing. The specific testing conditions are as follows, and the performance test results are shown in Table 2.

[0044] (1)High-temperature fast charging performance test Place the lithium-ion battery in an incubator at 45°C and let it stand for 30 min to reach a constant temperature. Charge the battery at a constant current of 4C until the voltage reaches 3.65V, then charge it at a constant voltage of 3.65V until the current reaches 0.05C. Then discharge it at a constant current of 4C until the voltage reaches 2.5V. Record the first-cycle discharge capacity of the battery as C0, which is one charge-discharge cycle. Then, after 1000 cycles of 4C / 4C charging and discharging at 45°C, record the discharge capacity as C1, and calculate the capacity retention rate of the lithium-ion battery using the following formula.

[0045]

[0046] (2)High-temperature storage performance test At a constant temperature of 25°C, charge the lithium-ion battery at a constant current of 1C until the voltage reaches 3.65V, then charge it at a constant voltage of 3.65V until the current reaches 0.05C. Then discharge it at a constant current of 1C until the voltage reaches 2.5V. Record the first-cycle discharge capacity of the battery as C0. Then place the lithium-ion battery in an incubator at 60°C and let it stand for 30 min to reach a constant temperature. After storing it at 60°C for 15 days, discharge it at a constant current and voltage of 1C / 1C to 2.5V at a constant temperature of 25°C, and record the discharge capacity as C1. Then, at a constant temperature of 25°C again, charge the lithium-ion battery at a constant current of 1C until the voltage reaches 3.65V, then charge it at a constant voltage of 3.65V until the current reaches 0.05C. After storing it at 60°C for another 15 days, discharge it at a constant current and voltage of 1C / 1C to 2.5V at a constant temperature of 25°C, and record the discharge capacity as C2. Calculate the capacity retention rates of the lithium-ion battery after storing it for 15 days and 30 days respectively using the following formula.

[0047]

[0048]

[0049] (3)Internal resistance growth rate test For the battery after 30 days of storage in the high-temperature storage performance test, charge it at a constant current and voltage of 0.5C to the cut-off voltage of 3.65V at room temperature, and then discharge it at a constant current and voltage until the capacity drops to 50% SOC to measure the internal resistance of the battery. Internal resistance growth rate = (Internal resistance of the battery after 30 days of storage - Internal resistance of the battery after the first full charge) / Internal resistance of the battery after the first full charge × 100% Table 2 Test results of lithium-ion battery performance

[0050] As can be seen from the results in Table 2, the lithium-ion batteries of Examples 1 to 11 have good high-temperature storage performance and high-temperature fast-charging performance. This is because the additives of the lithium-ion batteries of Examples 1 to 11 contain Compound A and vinylene carbonate, and the unique structure of Compound A and vinylene carbonate can synergistically improve the fast-charging and high-temperature performance of the electrolyte.

[0051] Combined with the comparison of Examples 1 to 3, it can be seen that the performance of the lithium-ion battery of Example 1 is better. This may be because the bis(trimethylsilyl) group contained in Compound 1 can more effectively improve the SEI structure and reduce the erosion of water and acid on SEI. Compounds 2 and 3 contain phenyl groups, which will form a dense CEI layer on the positive electrode at high potentials, affecting the lithium-ion transport efficiency, reducing the fast charge-discharge ability, and resulting in an increase in internal resistance.

[0052] By comparing Examples 1 and Examples 4 to 6, it can be seen that the high-temperature storage retention rate and high-temperature fast-charging retention rate performance of the battery of Example 4 are the best, and the effect is the best when the content of Compound 1 is 1.0%. This may be because when the content is too high, a too thick SEI is formed, which cannot quickly transport lithium ions, resulting in a decline in cycle performance and an increase in internal resistance.

[0053] By comparing Examples 7 to 9, it can be seen that the high-temperature storage retention rate and high-temperature fast-charging retention rate performance of the battery of Example 8 are the best, and the effect is the best when the content of vinylene carbonate is 3%. This may be because when vinylene carbonate and Compound 2 act together, Compound 2 is preferentially reduced to form a dense inorganic SEI, allowing lithium ions to pass quickly; at the same time, the relatively strong polar P-O structure in Compound 2 promotes the reduction of vinylene carbonate to form a cross-linked and ordered organic SEI. When the content of vinylene carbonate is low, the inorganic SEI formed only by Compound 2 decomposes at high temperatures, and the improvement of battery performance is not obvious. When the content is high, the organic SEI formed by the reduction of vinylene carbonate is too thick, seriously increasing the impedance and sharply deteriorating the high-temperature storage and cycle performance of the lithium-ion battery.

[0054] In Comparative Examples 4 and 5, although the electrolyte also contains Compound 4 similar to Compound A, which contains a phosphonamide structure (-N=P-O-) and a trimethylsilyl group, it contains a pyrrole structure. When 0.5% of Compound 4 is added, it forms a dense inorganic SEI film on the negative electrode and a dense organic CEI framework on the positive electrode. The high-temperature performance of the lithium-ion battery in Comparative Example 1 is improved, but the impedance of the positive CEI containing a pyrrole structure formed is relatively large, and the performance of Comparative Example 4 is weaker than that of Comparative Example 3. Even when used in combination with vinylene carbonate in Comparative Example 5, it can improve the organic CEI structure of the positive electrode, but its impedance increase is still greater than that of Comparative Example 3, and the 4C cycle retention rate performance is slightly worse.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it is not limited to the embodiments listed. Those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A non-aqueous electrolyte comprising a lithium salt, a non-aqueous organic solvent and an additive, wherein the additive comprises vinylene carbonate and a compound A as shown in structural formula I, wherein: R1 and R2 are each independently selected from substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C2-C6 alkynyl, substituted or unsubstituted aryl, R3 is selected from substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C2-C6 alkynyl, substituted or unsubstituted aryl, substituted or unsubstituted silanyl, substituted or unsubstituted siloxane, Structural formula Ⅰ.

2. The non-aqueous electrolyte according to claim 1, characterized in that R1 and R2 are each independently selected from substituted or unsubstituted C1~C3 alkyl, substituted or unsubstituted C2~C3 alkenyl, substituted or unsubstituted C2~C3 alkynyl, substituted or unsubstituted phenyl, and R3 is selected from substituted or unsubstituted C1~C3 alkyl, substituted or unsubstituted C2~C3 alkenyl, substituted or unsubstituted C2~C3 alkynyl, substituted or unsubstituted phenyl, and substituted or unsubstituted silanyl.

3. The non-aqueous electrolyte according to claim 1, characterized in that The compound A is selected from at least one of compound 1 to compound 3, 。 4. The non-aqueous electrolyte according to claim 1, characterized in that The mass proportion of the vinylene carbonate in the non-aqueous electrolyte is 1.00-5.00%, and the mass proportion of the compound A in the non-aqueous electrolyte is 0.05-5.00%.

5. The nonaqueous electrolyte according to claim 1, characterized in that The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bistrifluoromethanesulfonyl imide, lithium bisoxalatoborate, lithium difluorophosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium lower aliphatic carboxylate, lithium difluorobisoxalatophosphate, lithium bisfluorosulfonyl imide, lithium chloroborane and lithium tetraphenylborate.

6. The nonaqueous electrolyte according to claim 1, characterized in that The non-aqueous organic solvent is selected from at least one of γ-butyrolactone, γ-valerolactone, δ-valerolactone, methyl acetate, ethyl acetate, ethyl propionate, butyl acetate, propyl propionate, butyl propionate, ethylene carbonate, propylene carbonate, butylene carbonate, methyl pentyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, propylene carbonate, 1,3-dioxolane, 1,4-dioxane, crown ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2-trifluoromethyltetrahydrofuran, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether and diethylene glycol dimethyl ether.

7. A lithium ion battery, characterized in that: The invention comprises a positive electrode material, a negative electrode material and the non-aqueous electrolyte according to any one of claims 1 to 6.

8. The lithium-ion battery according to claim 7, characterized in that: The positive electrode material is a lithium iron phosphate material, and the general chemical formula of the lithium iron phosphate material is Li m Fe α M β PO4 or Li 1-x A x Fe 1-y B y PO4 / C, wherein 0.85≤m≤1.0, 0.8≤α≤1.0, 0≤β≤0.2, 0≤x≤0.15, 0≤y≤0.15, M is at least one of Ti, Mg, V, Mn, W, Al, Nb, Mo, Zr, Cr, Ni and Co, A and B are different and are at least one of Ag, Mg, Zn, Cu, Al, In, Ti, Nb, Mo, V, Zr, Mn, Cr, Ni and Co, respectively, and C accounts for Li in terms of mass percentage. 1-x A x Fe 1-y B y The content of PO4 / C is 1~20wt.%.

9. The lithium-ion battery according to claim 7, characterized in that: The negative electrode material includes at least one of a carbon-based negative electrode material, a silicon-based negative electrode material, a titanium-based oxide negative electrode material and an alloy negative electrode material.

10. The lithium ion battery according to claim 7, characterized in that: The negative electrode material includes soft carbon, hard carbon, artificial graphite, natural graphite, silicon-carbon composite material, silicon-oxygen composite material, lithium titanate, FeS x , Cu x O, MoS2, Sn x O. CoS x , Fe2O3, Fe3O4, ZnS and SbSn.

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