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 a 2-thiophenesulfonyl compound as shown in a structural formula I and a 3-cyanopyridine compound as shown in a structural formula II. Wherein R1, R2 and R3 are respectively and independently selected from a hydrogen group, a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted oxygen-containing heterocyclic group, a substituted or unsubstituted sulfur-containing heterocyclic group and a substituted or unsubstituted nitrogen-containing heterocyclic group. And R4, R5, R6 and R7 are independently selected from a hydrogen group, a substituted or unsubstituted C1-C6 alkyl group, a nitrile group, a substituted or unsubstituted amino group and a substituted or unsubstituted aldehyde group. According to the non-aqueous electrolyte, the high-temperature performance of a battery under high pressure can be improved through the synergistic effect of the 3-cyanopyridine compound and the 2-thiophenesulfonyl fluoride compound, and the non-aqueous electrolyte is particularly suitable for a lithium ion battery of a high-nickel ternary material system under high pressure. Structural formula I and structural formula II

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy batteries, and in particular 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, and environmental friendliness. They have been widely used in electronic products such as mobile phones, laptops, digital cameras, and are also widely used as power batteries in electric bicycles, model aircraft, and electric vehicles.

[0003] As a key component of lithium-ion batteries, cathode materials play a decisive role in their overall capacity and have become a focus of research, development, industrialization, and large-scale application in the field of new energy materials. As the new energy vehicle industry continues to demand ever-increasing energy density in power batteries, high-nickel ternary cathode materials have become a key approach to improving battery energy density. Increasing the charge cutoff voltage (≥4.5V) can further unlock the capacity potential of ternary materials. However, the insufficient oxidative stability and poor interfacial compatibility of traditional carbonate-based electrolytes (such as EC / DMC+LiPF6) at high voltages severely restrict their practical application.

[0004] Specifically, under high voltage conditions, high nickel ternary cathode materials face multiple challenges: (1) the electrolyte on the cathode surface undergoes severe oxidation and decomposition (e.g., the EC oxidation potential is only 4.45 V, which is easily oxidized), producing gases such as CO2 and H2, which accelerate capacity decay; (2) high valence Ni 4+ Dissolution can easily destroy the CEI layer structure, causing lattice oxygen precipitation and phase change; (3) The dissolved transition metal ions migrate to the graphite negative electrode, destroying the SEI and intensifying the growth of lithium dendrites; (4) LiPF6 decomposes at high temperature to produce HF, which corrodes the electrode interface and increases the impedance.

[0005] Although the use of some additives (such as adding VC, FEC, etc.) can partially alleviate the problem, it still faces new bottlenecks such as high-voltage film failure (such as decomposition under a high voltage of 4.5V), low-temperature performance deterioration or increased gas production (additives release new gases). Therefore, there is an urgent need to develop a new electrolyte system that has high-voltage anti-oxidation, interface passivation and low side reaction activity. Summary of the Invention

[0006] To address the above challenges, the present invention provides a non-aqueous electrolyte and lithium-ion battery comprising a 3-cyanopyridine compound and a 2-thiophenesulfonyl fluoride compound. The 3-cyanopyridine and 2-thiophenesulfonyl fluoride compounds synergistically improve the high-temperature performance of batteries under high voltage conditions, and are particularly suitable for high-voltage, high-nickel ternary lithium-ion batteries.

[0007] To achieve the above objectives, the present invention provides a non-aqueous electrolyte in one aspect. The non-aqueous electrolyte comprises a lithium salt, a non-aqueous organic solvent, and an additive. The additive comprises a 2-thiophene fluorosulfonyl compound represented by Structural Formula I and a 3-cyanopyridine compound represented by Structural Formula II. In which, R1, R2, and R3 are each independently selected from a hydrogen group, a substituted or unsubstituted C1-C6 hydrocarbon group, a substituted or unsubstituted oxygen-containing heterocyclic group, a substituted or unsubstituted sulfur-containing heterocyclic group, or a substituted or unsubstituted nitrogen-containing heterocyclic group. R4, R5, R6, and R7 are each independently selected from a hydrogen group, a substituted or unsubstituted C1-C6 hydrocarbon group, a nitrile group, a substituted or unsubstituted amine group, or a substituted or unsubstituted aldehyde group.

[0008]

[0009] Structural Formula I Structural Formula II The electrolyte additive of the present invention contains a 2-thiophene fluorosulfonyl compound as shown in structural formula I and a 3-cyanopyridine compound as shown in structural formula II. The fluorosulfonyl group of the 2-thiophene fluorosulfonyl compound decomposes to produce a solid electrolyte interface film rich in S and F, and the Li2S and LiF inorganic components formed therefrom have high Li + Conductivity. Thiophene undergoes reductive polymerization to form polythiophene CEI, which exhibits high-voltage durability and reduces physical contact between the cathode surface and the electrolyte, stabilizing the cathode-electrolyte interface. Polythiophene CEI exhibits high mechanical strength and toughness, enabling it to withstand repeated volume changes during high-voltage cycling. However, the fluorosulfonyl group readily hydrolyzes to form HF and thiophenesulfonic acid, which not only consumes the active ingredient in the additive but also increases the acidity of the electrolyte. Furthermore, it has a weak binding capacity for transition metal ions, both of which can reduce battery cycling performance. 3-Cyanopyridine compounds can neutralize the acidic byproducts of 2-thiophene fluorosulfonyl compounds, capture HF generated by lithium salt decomposition, and reduce its corrosion on the positive and negative electrode materials. Furthermore, the cyano group can complex with transition metal ions, inhibiting their dissolution. Furthermore, 3-Cyanopyridine compounds can undergo electrochemical polymerization under high voltage to form a nitrogen-containing polymer CEI layer, which inhibits oxidative decomposition of the electrolyte. Therefore, the CEI layer formed by the 2-thiophene fluorosulfonyl compound and the 3-cyanopyridine compound can improve the high-temperature storage and high-temperature cycling performance of the battery under high voltage.

[0010] As a technical solution of the present invention, R1, R2, and R3 are each independently selected from hydrogen, substituted or unsubstituted C1-C3 alkyl, substituted or unsubstituted dioxolanyl, or substituted or unsubstituted thiazolyl; and R4, R5, R6, and R7 are each independently selected from hydrogen, substituted or unsubstituted C1-C3 alkyl, nitrile, amino, or aldehyde.

[0011] As a technical solution of the present invention, the 2-thiophene fluorosulfonyl compound is selected from at least one of Compounds 1 to 4.

[0012]

[0013] Compound 1 Compound 2

[0014] Compound 3 Compound 4 As a technical solution of the present invention, the 3-cyanopyridine compound is at least one selected from Compound 5 to Compound 8.

[0015]

[0016] Compound 5 Compound 6

[0017] Compound 7 Compound 8 As a technical solution of the present invention, the mass proportion of the 2-thiophene fluorosulfonyl compound in the non-aqueous electrolyte is 0.05-5.00%, and the mass proportion of the 3-cyanopyridine compound in the non-aqueous electrolyte is 0.05-5.00%.

[0018] 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 bistrifluoromethanesulfonyl imide, lithium bisoxalatoborate, lithium difluorophosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium lower aliphatic carboxylate, lithium difluorobisoxalatophosphate and lithium bisfluorosulfonyl imide.

[0019] As a technical solution of the present invention, the non-aqueous organic solvent is selected from at least one of sulfolane, dimethyl sulfoxide, methyl acetate, ethyl acetate, ethyl propionate, butyl acetate, propyl propionate, butyl propionate, ethylene carbonate, propylene carbonate, butylene carbonate, pentylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl n-propyl carbonate, ethyl n-propyl carbonate, propylene carbonate, acetonitrile, 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.

[0020] Another 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.

[0021] As a technical solution of the present invention, the positive electrode material includes a lithium nickel cobalt manganese oxide material or a lithium nickel cobalt aluminum oxide material.

[0022] As a technical solution of the present invention, the negative electrode material is selected from at least one of carbon-based negative electrode materials, silicon-based negative electrode materials, titanium-based oxide negative electrode materials and alloy negative electrode materials. DETAILED DESCRIPTION

[0023] The non-aqueous electrolyte of this invention improves the high-temperature cycling and storage performance of lithium-ion batteries under high voltage. At a high voltage of 4.45V and a high temperature of 45°C, the battery maintains a capacity retention rate of over 78% after 1,000 cycles. After 30 days of storage at 60°C, the capacity retention rate remains above 75%, and the capacity recovery rate reaches over 80%.

[0024] The lithium-ion battery of the present invention may include a positive electrode material, a negative electrode material, and a non-aqueous electrolyte.

[0025] Among them, the positive electrode material can be a lithium cobalt oxide material, a lithium iron phosphate material, a nickel cobalt manganese oxide material or a nickel cobalt aluminum oxide material. The lithium cobalt oxide material can be lithium cobalt oxide or lithium cobalt oxide modified by doping or coating, the lithium iron phosphate material can be lithium iron phosphate or lithium iron phosphate modified by doping or coating, the nickel cobalt manganese oxide material can be nickel cobalt manganese oxide or nickel cobalt manganese oxide modified by doping or coating, and the nickel cobalt aluminum oxide material can be nickel cobalt aluminum oxide or nickel cobalt aluminum oxide modified by doping or coating. In particular, the positive electrode material is a nickel cobalt manganese oxide material or a nickel cobalt aluminum oxide material. The chemical formula of the nickel cobalt manganese oxide material is LiNi x Co y Mn z M (1-x-y-z) O2, the chemical formula of lithium nickel cobalt aluminum oxide material is LiNi o Co p Al q N (1-o-p-q)O2, where M is selected from at least one of Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, N is selected from at least one of Mn, Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V, and Ti, 0.5 ≤ x < 1.0, 0 < y < 1.0, 0 < z < 1.0, x + y + z ≤ 1.0, 0.5 ≤ o < 1.0, 0 < p < 1.0, 0 < q < 1.0, o + p + q ≤ 1.0. 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. Further, 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.

[0026] The non-aqueous electrolyte includes a lithium salt, a non-aqueous organic solvent, and an additive.

[0027] 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, account 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(trifluoromethylsulfonyl)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), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0028] The non-aqueous organic solvent may account for 65-90% of the mass of the non-aqueous electrolyte. Preferably, the non-aqueous organic solvent may account for 75-89% of the mass of the non-aqueous electrolyte. More preferably, the non-aqueous organic solvent may account for 78-88% of the mass of the non-aqueous electrolyte. By way of example, the non-aqueous organic solvent may account for, but is not limited to, 65%, 70%, 80%, 85%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, or 90% of the mass of the non-aqueous electrolyte. The non-aqueous organic solvent is at least one of a carboxylate, a carbonate, and an ether compound. Furthermore, the non-aqueous organic solvent is selected from sulfolane, dimethyl sulfoxide, 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), pentylene carbonate, vinylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl n-propyl carbonate (MPC), ethyl n-propyl carbonate The present invention can be selected from at least one of propylene carbonate (PC), acetonitrile, 1,3-dioxolane, 1,4-dioxolane, 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).

[0029] The additives include a 2-thiophene fluorosulfonyl compound represented by structural formula I and a 3-cyanopyridine compound represented by structural formula II. The mass proportion of the 2-thiophene fluorosulfonyl compound in the non-aqueous electrolyte is 0.05-5.00%, and the mass proportion of the 3-cyanopyridine compound in the non-aqueous electrolyte is 0.05-5.00%. More preferably, the mass proportion of the 2-thiophene fluorosulfonyl compound in the non-aqueous electrolyte is 0.10-2.00%, and the mass proportion of the 3-cyanopyridine compound in the non-aqueous electrolyte is 0.10-4.00%. Further preferably, the mass proportion of the 2-thiophene fluorosulfonyl compound in the non-aqueous electrolyte is 0.10-1.00%, and the mass proportion of the 3-cyanopyridine compound in the non-aqueous electrolyte is 0.50-2.00%. For example, the mass percentage of the 2-thiophene fluorosulfonyl compound in the non-aqueous electrolyte may 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%, or 5.00%. The mass percentage of the 3-cyanopyridine compound in the non-aqueous electrolyte may 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%, or 5.00%.

[0030]

[0031] Structural Formula I Structural Formula II Wherein, R1, R2, and R3 are each independently selected from a hydrogen group, a substituted or unsubstituted C1-C6 hydrocarbon group, a substituted or unsubstituted oxygen-containing heterocyclic group, a substituted or unsubstituted sulfur-containing heterocyclic group, or a substituted or unsubstituted nitrogen-containing heterocyclic group. Further, R1, R2, and R3 are each independently selected from a hydrogen group, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted dioxolanyl group, or a substituted or unsubstituted thiazolyl group. Furthermore, R1, R2, and R3 are each independently selected from hydrogen, methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, vinyl, propenyl, isopropenyl, butenyl, pentenyl, hexenyl, ethynyl, propynyl, isopropynyl, butynyl, pentynyl, hexynyl, a fluoromethyl, a fluoroethyl, a fluoropropyl, a fluoroisopropyl, a fluorobutyl, a fluoropentyl, a fluorohexyl, a fluorovinyl, a fluoropropenyl, a fluoroisopropenyl, a fluorobutenyl, a fluoropentenyl, a fluorohexenyl, a fluoroethynyl, a fluoropropynyl, a fluoroisopropynyl, a fluorobutynyl, a fluoropentynyl, a fluorohexynyl, a polyfluoromethyl, a polyfluoroethyl, a polyfluoropropyl, a polyfluoroisopropyl, a polyfluorobutyl, polyfluoropentyl, polyfluorohexyl, polyfluorovinyl, polyfluoropropenyl, polyfluoroisopropenyl, polyfluorobutenyl, polyfluoropentenyl, polyfluorohexenyl, polyfluoroethynyl, polyfluoropropynyl, polyfluoroisopropynyl, polyfluorobutynyl, polyfluoropentynyl, polyfluorohexynyl, 1,3-dioxolanyl, 4-methyl-1,3-dioxolanyl, 4-ethyl-1,3-dioxolanyl, 4,5-dimethyl-1,3-dioxolanyl, 4,5-diethyl-1,3-dioxolanyl, 4-methyl-5-ethyl-1,3-dioxolanyl, 4-ethyl-5-methyl-1,3-dioxolanyl, 1,4-thiazolyl, 5-methyl-1,4-thiazolyl, 5-ethyl-1,4-thiazolyl, pyrrolyl, pyridinyl.

[0032] R4, R5, R6, and R7 are each independently selected from hydrogen, a substituted or unsubstituted C1-C6 hydrocarbon group, a nitrile group, a substituted or unsubstituted amine group, or a substituted or unsubstituted aldehyde group. Furthermore, R4, R5, R6, and R7 are each independently selected from hydrogen, a substituted or unsubstituted C1-C3 alkyl group, a nitrile group, an amine group, or an aldehyde group. Furthermore, R4, R5, R6, and R7 are each independently selected from hydrogen, 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, nitrile, amino, methylamino, formaldehyde, methylformaldehyde, ethylformaldehyde.

[0033] Furthermore, the 2-thiophene fluorosulfonyl compound is selected from at least one of Compounds 1 to 4.

[0034]

[0035] Compound 1 Compound 2 CAS:1934686-00-6CAS:1936662-66-6

[0036] Compound 3 Compound 4 CAS:2648966-50-9CAS:1955505-66-4 The 3-cyanopyridine compound is at least one compound selected from compound five to compound eight.

[0037]

[0038] Compound 5 Compound 6 CAS:100-54-9CAS:1195-58-0

[0039] Compound 7 Compound 8 CAS:13600-47-0CAS:70416-53-4 In order to better illustrate the purpose, technical solutions 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.

[0040] If no specific conditions are specified in the Examples and Comparative Examples, the experiments may be carried out under conventional conditions or those recommended by the manufacturer. Reagents or instruments used without specifying the manufacturer are all conventional products available on the market.

[0041] Example 1 (1) Preparation of non-aqueous electrolyte In an argon-filled glove box (O2 <1ppm, H2O <1ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a weight ratio of EC:EMC = 3:7 (86.0g) to obtain a non-aqueous organic solvent. Subsequently, 0.2g of compound 1 and 0.5g of compound 5 were added, dissolved, and thoroughly stirred. After that, 13.3g of lithium hexafluorophosphate was added and mixed uniformly to obtain a non-aqueous electrolyte.

[0042] (2) Preparation of positive electrode LiNi 0.8 Co 0.1 Mn 0.1 , adhesive PVDF and conductive agent SuperP are evenly mixed in a mass ratio of 96:2.5:1.5 to form a lithium secondary battery positive electrode slurry with a certain viscosity. The mixed slurry is coated on both sides of an aluminum foil, dried, and rolled to obtain a positive electrode sheet.

[0043] (3) Preparation of negative electrode Artificial graphite, adhesive PVDF and conductive agent SuperP are evenly mixed in a mass ratio of 90:2:8 to prepare a lithium secondary battery negative electrode slurry with a certain viscosity. The mixed slurry is coated on both sides of a copper foil, dried and rolled to obtain a negative electrode sheet.

[0044] (4) Preparation of lithium-ion batteries The positive electrode sheet, separator, and negative electrode sheet are stacked in order and then stacked as needed. After the tabs are welded, they are placed in the aluminum-plastic film outer packaging of the battery. The prepared non-aqueous electrolyte is injected into the dried bare cell. The cells are then vacuum packaged, allowed to stand, formed (charged at a constant current of 0.05C to 3.0V, then at a constant current of 0.1C to 3.95V), shaped, and tested for capacity, resulting in a 1Ah lithium secondary battery.

[0045] The components and contents of the non-aqueous electrolytes of Examples 1 to 10 and Comparative Examples 1 to 3 are shown in Table 1. The preparation processes of the non-aqueous electrolytes, positive electrode sheets, negative electrode sheets, and lithium-ion batteries of Examples 2 to 10 and Comparative Examples 1 to 3 are the same as those of Example 1.

[0046] Table 1 Non-aqueous electrolyte components of Examples and Comparative Examples

[0047] The lithium ion batteries prepared in Examples 1 to 10 and Comparative Examples 1 to 3 were subjected to high temperature storage performance tests and high temperature cycle performance tests, respectively. The specific test conditions are as follows. The performance test results are shown in Table 2.

[0048] (1) High temperature storage performance test At room temperature (25°C), the lithium-ion battery is charged and discharged at 0.3C / 0.3C (the battery discharge capacity is recorded as C0), with an upper voltage of 4.45V. The lithium-ion battery is placed in a 60°C oven for 30 days, the battery is removed, and the battery is placed in a 25°C environment and discharged at 0.3C. The discharge capacity is recorded as C1. The lithium-ion battery is then charged and discharged at 0.3C / 0.3C (the battery discharge capacity is recorded as C2). The capacity retention rate and capacity recovery rate of the lithium-ion battery are calculated using the following formula.

[0049] Capacity retention rate = C1 / C0×100% Capacity recovery rate = C2 / C0×100% (2) High temperature cycle performance test Place the lithium-ion battery in a 45°C constant temperature box and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Then charge it at a constant current of 4C to a voltage of 4.45V, then charge it at a constant voltage of 4.45V to a current of 0.05C. Then discharge it at a constant current of 1C to a voltage of 3.0V. Record the first discharge capacity of the battery as C0. This is one charge and discharge cycle. Then, charge and discharge it at 1C / 1C for 1000 cycles at 45°C. Record the discharge capacity as C1. Use the following formula to calculate the capacity retention rate of the lithium-ion battery.

[0050] Capacity retention rate = C1 / C0×100% Table 2 Performance test results of lithium ion batteries prepared in Examples 1 to 10 and Comparative Examples 1 to 3

[0051] As shown in Table 2, the lithium-ion batteries of Examples 1 to 10 have good high-temperature storage performance and high-temperature cycling performance. This is because the additives of the lithium-ion batteries of Examples 1 to 10 include 3-cyanopyridine compounds and 2-thiophene fluorosulfonyl compounds. The 3-cyanopyridine compounds and 2-thiophene fluorosulfonyl compounds synergistically improve high-temperature cycling and high-temperature storage performance under high pressure. However, Comparative Example 2 contains only Compound 2. The fluorosulfonyl group is easily hydrolyzed to form HF and thiophenesulfonic acid, which not only consumes the active ingredients of the additive but also may increase the acidity of the electrolyte. In addition, the binding ability to transition metal ions is weak, so the performance of Comparative Example 2 is poor. Comparative Example 3 contains only Compound 5. Although the nitrile group can effectively inhibit the dissolution of transition metal ions, its film-forming ability is weak and cannot meet the long-cycle performance requirements. Therefore, the performance of Comparative Example 3 is poor.

[0052] Comparison of Examples 1-4 with Examples 5-8 reveals that Compound 2, a 2-thiophene fluorosulfonyl compound, or Compound 6, a 3-cyanopyridine compound, exhibits superior high-temperature performance. This is due to Compound 2 having two methyl groups, which are electron-donating groups, increasing the overall electron cloud density of the molecule and reducing the LUMO value. Compound 6, with its two nitrile groups, effectively complexes transition metal ions and removes water and acid.

[0053] 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 scope of protection of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents 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 a 2-thiophene fluorosulfonyl compound as shown in structural formula I and a 3-cyanopyridine compound as shown in structural formula II, wherein: R1, R2, and R3 are each independently selected from a hydrogen group, a substituted or unsubstituted C1-C6 hydrocarbon group, a substituted or unsubstituted oxygen-containing heterocyclic group, a substituted or unsubstituted sulfur-containing heterocyclic group, or a substituted or unsubstituted nitrogen-containing heterocyclic group; R4, R5, R6, and R7 are each independently selected from a hydrogen group, a substituted or unsubstituted C1-C6 hydrocarbon group, a nitrile group, a substituted or unsubstituted amino group, or a substituted or unsubstituted aldehyde group; Structural Formula I Structural Formula II 2. The non-aqueous electrolyte according to claim 1, wherein R1, R2, and R3 are each independently selected from hydrogen, substituted or unsubstituted C1-C3 alkyl, substituted or unsubstituted dioxolanyl, or substituted or unsubstituted thiazolyl; R4, R5, R6, and R7 are each independently selected from hydrogen, substituted or unsubstituted C1-C3 alkyl, nitrile, amino, or aldehyde.

3. The non-aqueous electrolyte according to claim 1, wherein The 2-thiophene fluorosulfonyl compound is selected from at least one of Compounds 1 to 4, Compound 1 Compound 2 Compound three and compound four.

4. The non-aqueous electrolyte according to claim 1, wherein The 3-cyanopyridine compound is selected from at least one of Compounds 5 to 8, Compound 5 Compound 6 Compound 7 Compound 8 5. The non-aqueous electrolyte according to claim 1, characterized in that The mass proportion of the 2-thiophene fluorosulfonyl compound in the non-aqueous electrolyte is 0.05-5.00%, and the mass proportion of the 3-cyanopyridine compound in the non-aqueous electrolyte is 0.05-5.00%.

6. The non-aqueous 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 and lithium bisfluorosulfonyl imide.

7. The non-aqueous electrolyte according to claim 1, characterized in that The non-aqueous organic solvent is selected from at least one of sulfolane, dimethyl sulfoxide, methyl acetate, ethyl acetate, ethyl propionate, butyl acetate, propyl propionate, butyl propionate, ethylene carbonate, propylene carbonate, butylene carbonate, pentylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl n-propyl carbonate, ethyl n-propyl carbonate, propylene carbonate, acetonitrile, 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.

8. 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 7.

9. The lithium-ion battery according to claim 8, characterized in that The positive electrode material includes a lithium nickel cobalt manganate material or a lithium nickel cobalt aluminum material.

10. The lithium-ion battery according to claim 8, characterized in that The negative electrode material is selected from 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.

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