Non-aqueous electrolyte and non-aqueous electrolyte secondary battery

Abstract

The application discloses a nonaqueous electrolyte and a nonaqueous electrolyte secondary battery. The nonaqueous electrolyte comprises a lithium salt, a nonaqueous organic solvent and an additive, and the additive is a compound shown in structural formula 1: wherein R1-R2 are each independently selected from hydrogen, halogen, substituted or unsubstituted C1-C6 alkyl, and substituted or unsubstituted C1-C6 unsaturated bond, and M is one of Li, Na, K, Rb and Cs. The application forms a stable interface film at the interface by means of ring-opening polymerization of the nitrogen-containing heterocycle of the additive. The film has a good lithium ion conduction channel, and is beneficial to improving the cycle and high-temperature performance of a ternary high-voltage battery. Fluoroborane forms a strong B-O bond with oxygen on the surface of the positive electrode, passivates the positive electrode and prevents the electrolyte from being oxidized and decomposed, and is beneficial to improving the high-voltage cycle performance of the ternary high-voltage battery. Meanwhile, the structure can form a low-impedance SEI film on the negative electrode, reduces the charge transfer impedance of the negative electrode, and further improves the low-temperature performance of the ternary high-voltage lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery. Background Technology

[0002] Traditional carbonate electrolytes have a narrow electrochemical window, typically below 4.3V. As the voltage increases, solvent decomposition occurs, and more importantly, the solvent reacts with the high-voltage cathode, causing the transition metals in the ternary material to dissolve and generating large amounts of gas. This significantly reduces battery capacity and can even compromise battery safety. For ternary cathodes, Ni, Co, and Mn have oxidation states of +2, +3, and +4, respectively. During charging, lithium ions are extracted from the cathode, causing Ni to change from +2 to +3 or even +4. Simultaneously, the cathode reacts with the electrolyte to form a solid electrolyte interphase (CEI) layer. The CEI layer protects the cathode (similar to the SEI film on the anode), hindering further reactions between the cathode and electrolyte and improving the cathode's stability under delithiation conditions. However, the formation of the CEI film also causes increased battery impedance, rate decay, capacity decay, and gas generation. Therefore, optimizing the electrolyte composition to form the optimal cathode CEI film is crucial.

[0003] Positive electrode film-forming additives are an important component of electrolytes. Although their addition amount is often only about 1% by mass, they can significantly improve certain aspects of battery performance. Therefore, it is the most economical and easily industrialized method. In high-voltage electrolyte positive electrode film formation, boron-containing lithium salt additives such as LiBOB and LiDFOB are frequently used in commercial high-voltage electrolyte formulations. Their film-forming mechanism with the positive electrode is as follows: the additive oxidizes and forms stable acyl radicals. These radicals recombine at the oxide-electrolyte interface to generate difluoroborane dimers. These difluoroborane dimers form strong B-O bonds with oxygen on the positive electrode surface, thereby passivating the positive electrode and preventing electrolyte oxidation. However, these boron-containing salts contain oxalic acid groups, which easily generate gas during formation and cycling, leading to performance degradation at high temperatures.

[0004] Therefore, there is an urgent need to develop an electrolyte that can withstand high voltages in ternary lithium batteries, so as to achieve excellent performance of lithium-ion batteries and solve the shortcomings of existing technologies. Summary of the Invention

[0005] The purpose of this invention is to provide a non-aqueous electrolyte in which special additives are used to passivate the positive electrode and prevent the electrolyte from oxidizing and decomposing, which is beneficial to improving the high-voltage cycle performance of ternary high-voltage batteries.

[0006] Another objective of this invention is to provide a non-aqueous electrolyte secondary battery that uses the aforementioned electrolyte. This lithium-ion battery exhibits good cycle performance, low-temperature performance, and high-temperature performance at a high voltage of 4.4V.

[0007] To achieve the above objectives, the present invention provides a non-aqueous electrolyte comprising a lithium salt, a non-aqueous organic solvent, and an additive, wherein the additive is a compound represented by structural formula 1:

[0008]

[0009] R1 to R2 are each independently selected from hydrogen, halogen, substituted or unsubstituted C1 to C6 alkyl groups, substituted or unsubstituted C1 to C6 unsaturated bonds, and M is at least one of Li, Na, K, Rb, Cs, Mg, Ca, Ba, Al, Fe, Cu, and Ni.

[0010] Compared with the prior art, in the non-aqueous electrolyte of the present invention, the additive adopts the compound shown in structural formula 1. The nitrogen-containing heterocyclic ring of the additive can form a stable interfacial film at the interface through ring-opening polymerization. This film has a good lithium-ion conduction channel, which is beneficial to improving the cycle and high-temperature performance of ternary high-voltage batteries. Moreover, this structure contains a fluorinated boron salt structure. In this type of structure, fluorinated boronane forms a strong B-O bond with oxygen on the positive electrode surface, thereby passivating the positive electrode and preventing electrolyte oxidation and decomposition, which is beneficial to improving the high-voltage cycle performance of ternary high-voltage batteries. At the same time, this type of structure can form a low-impedance SEI film at the negative electrode, reducing the charge transfer impedance of the negative electrode, thereby further improving the low-temperature performance of ternary high-voltage lithium-ion batteries.

[0011] Wherein, C1 to C6 alkyl means alkyl or silane with 1 to 6 carbon atoms. The alkyl can be a chain alkyl or a cycloalkyl. The hydrogen on the ring of the cycloalkyl can be replaced by the alkyl group. For example, the alkyl can be, but is not limited to, methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, pentyl and cyclohexyl.

[0012] In this context, the C1-C6 unsaturated bonds represent hydrocarbon groups with 1-6 carbon atoms, which can be cyclic alkenyl groups or chain alkenyl groups. Further, the hydrocarbon group can be, but is not limited to, alkenyl, alkynyl, nitrile, etc. As examples, alkenyl groups include, but are not limited to, vinyl, propenyl, 1-propenyl, isopropenyl, 2-butenyl, 1,3-butadienyl, etc. As examples, alkynyl groups include, but are not limited to, ethynyl, 2-propynyl, and 1,1-dimethyl-2-propynyl, etc.

[0013] Wherein, M is one or more of Li, Na, K, Rb, Cs, Mg, Ca, Ba, Al, Fe, Cu and Ni. For example, M includes, but is not limited to, Li, Na, K, Rb, Cs, etc.

[0014] In some embodiments, the additive is selected from at least one of compounds 1 to 6:

[0015]

[0016] In some embodiments, the additive accounts for 0.1% to 3% of the total mass of the electrolyte by mass percentage; more specifically, the additive accounts for 0.5% to 3% of the total mass of the electrolyte. For example, the additive accounts for 0.1%, 0.3%, 0.5%, 0.8%, 1.2%, 1.5%, 2%, 2.5%, and 3% of the total mass of the electrolyte, but is not limited to the listed values; other unlisted values ​​within this range also apply.

[0017] In some embodiments, the organic solvent is selected from at least one of carbonates, carboxylic acid esters, ethers, and heterocyclic compounds. For example, the non-aqueous organic solvent is selected from at least one of cyclic carbonates, chain carbonates, cyclic esters, chain esters, cyclic ethers, chain ethers, sulfone compounds, sulfoxide compounds, and ionic liquids. Further, the carbonates may be, but are not limited to, chain carbonates and cyclic carbonates. As examples, cyclic carbonates include: ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), amyl carbonate, vinylene carbonate (VC), or derivatives thereof. In some embodiments, the organic solvent is at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and propylene carbonate (PC). In some embodiments, the organic solvent is a carboxylic acid ester solvent, which includes cyclic carboxylic acid esters and / or chain carbonates. Specifically, cyclic carboxylic acid esters may include, but are not limited to, at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. As for chain carbonates, they may include, but are not limited to, at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate. In some embodiments, the organic solvent is an ether solvent, including cyclic ethers or chain ethers. The cyclic ether may specifically include, but is not limited to, at least one of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF). The chain ether may specifically include, but is not limited to, at least one of dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether.

[0018] In some embodiments, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium dioxolaneborate (LiBOB), lithium difluorooxolaneborate (LiDFOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxolane)phosphate (LiDFBP), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium fluorosulfonate (LiSO2F), lithium diphosphate (LiPO2F2), and lower aliphatic carboxylic acids. As an example, the lithium salt is lithium hexafluorophosphate or lithium tetrafluoroborate.

[0019] In some embodiments, the lithium salt accounts for 6-20% of the total mass of the electrolyte by mass percentage, preferably 7-20%. As examples, the lithium salt accounts for 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and 20% of the total mass of the electrolyte, but is not limited to these listed values; other unlisted values ​​within this range also apply.

[0020] In some embodiments, the electrolyte of the present invention further includes an additive selected from vinylene carbonate (VC), vinylene carbonate (VEC), fluoroethylene carbonate (FEC), vinyl sulfite (ES), 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PES), 1,4-butanesulfonate lactone (BS), vinyl sulfate (DTD), succinic anhydride (SA), maleic anhydride, 2-methylmaleic anhydride, methyl carbonate-2-propynyl ester, tetraethylenesilane, and triallyl isocyanurate. At least one of the following: hexamethylene diisocyanate, o-phenanthroline, terephthalic diisocyanate, 2,4-toluene diisocyanate, N-phenylbis(trifluoromethanesulfonyl)imide, vinyl disulfate, phenyl methanesulfonate, vinyl disulfate, dispironyl propylene sulfate, hydroquinone difluorosulfonate, triallyl phosphate, triargyl phosphate, 2,4-butanesulfonyl lactone, isocyanoethyl methacrylate, methylene disulfonate, tris(trimethylsilane)borate, tris(trimethylsilane) phosphate, and tris(vinyldimethylsilane) phosphate. As an example, the adjuvant is 1,4-butyrolactone or fluoroethylene carbonate.

[0021] In some embodiments, the mass percentage of the additive is 0.5% to 10.0% of the total mass of the electrolyte; more specifically, the mass percentage of the additive is 2% to 8% of the total mass of the electrolyte; preferably, the mass percentage of the additive is 3% to 8% of the total mass of the electrolyte. As examples, the mass percentage of the additive is 0.5%, 1.5%, 2%, 2.5%, 3%, 4%, 4.5%, 5%, 5.5%, 6.0%, or 8% of the total mass of the electrolyte, but this is not limited to the listed values; other unlisted values ​​within this range also apply.

[0022] Accordingly, the present invention also provides a non-aqueous electrolyte secondary battery, comprising a positive electrode, a negative electrode, a separator, and the aforementioned non-aqueous electrolyte. Non-aqueous electrolyte secondary batteries include, but are not limited to, lithium-ion batteries. Using the aforementioned non-aqueous electrolyte in a non-aqueous electrolyte secondary battery, good cycle performance, low-temperature performance, and high-temperature performance can still be achieved even at a maximum charging voltage of 4.4V.

[0023] In some embodiments, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (structures such as LiNi). x Co y Mn (1-x-y) M z O2, where 0.6≤x<0.9, x+y<1, 0≤z<0.08, and M is at least one of Al, Mg, Zr, and Ti. Examples of lithium phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0024] In some embodiments, the negative electrode active material includes at least one of carbon-based, silicon-based, tin-based, and lithium-based negative electrodes. Carbon-based negative electrodes may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, etc.; silicon-based negative electrodes may include silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials, etc.; tin-based negative electrodes may include tin, tin-carbon, tin oxide, and tin metal compounds; lithium-based negative electrodes may include metallic lithium or lithium alloys. Specifically, the lithium alloy may be at least one of lithium-silicon alloys, lithium-sodium alloys, lithium-potassium alloys, lithium-aluminum alloys, lithium-tin alloys, and lithium-indium alloys.

[0025] In some embodiments, the separator is located between the positive and negative electrodes. The separator can be a conventional separator, such as a ceramic separator, a polymer separator, a non-woven fabric separator, or an inorganic-organic composite separator. The polymer separator is selected from at least one of polyolefins, polyamides, polysulfones, polyphosphazenes, polyethersulfones, polyetheretherketones, polyetheramides, and polyacrylonitriles, including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP separators. Detailed Implementation

[0026] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0027] Example 1

[0028] (1) Preparation of electrolyte:

[0029] Ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a mass ratio of EC:DEC:EMC = 2:1:1 to obtain 83.5 g of organic solvent. After mixing, 13 g of lithium hexafluorophosphate (LiPF6) was added. After the lithium salt was completely dissolved, 3 g of 1,4-butyrosulactone (BS) and 0.5 g of additive compound 1 were added.

[0030] (2) Preparation of the positive electrode:

[0031] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.09 Al 0.01 A positive electrode slurry is prepared in N-methylpyrrolidone (NMP) using O2, conductive agent Super P, and binder polyvinylidene fluoride (PVDF). The solid content of the positive electrode slurry is 50 wt%, and the solid component is LiNi. 0.8 Co 0.1 Mn 0.09 Al0.01 The mass ratio of O2, Super P, and PVDF is 8:1:1. The positive electrode slurry is coated on the upper and lower surfaces of the current collector aluminum foil and dried at 85°C. After cold pressing, the foil is trimmed, cut into sheets, and slit. Then, it is dried under vacuum at 85°C for 4 hours to produce the positive electrode sheet.

[0032] (3) Preparation of negative electrode:

[0033] Graphite, conductive agent Super P, thickener carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are mixed evenly in deionized water to prepare a negative electrode slurry. The solid content of the negative electrode slurry is 30 wt%, and the mass ratio of graphite, Super P, CMC, and binder styrene-butadiene rubber (SBR) in the solid components is 88:7:3:2. The negative electrode slurry is coated on the upper and lower surfaces of the current collector copper foil and dried at 85°C. Then, it is cold-pressed, trimmed, cut into sheets, and slit. Finally, it is dried under vacuum at 120°C for 12 hours to prepare the negative electrode sheet.

[0034] (4) Use a 16μm polyethylene film as the isolation film.

[0035] (5) Preparation of lithium-ion batteries:

[0036] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to isolate them. The cells are then wound to obtain a bare cell. The tabs are welded on, and the bare cell is placed in an outer package. The electrolyte prepared above is injected into the dried cell. The cells are then encapsulated, left to stand, formed, shaped, and have their capacity tested to complete the preparation of a 1000mAh lithium-ion battery.

[0037] The electrolyte composition of Examples 2-8 and Comparative Example 1 is shown in Table 1. The steps for preparing the non-aqueous electrolyte and lithium-ion battery are the same as in Example 1.

[0038] Table 1. Electrolyte composition of the examples and comparative examples

[0039] Example 1 <![CDATA[LiPF6(13g)]]> EC / DEC / EMC = 2:1:1 (83.5g) Compound 1 (0.5g) BS (3.0g) Example 2 <![CDATA[LiPF6(13g)]]> EC / DEC / EMC = 2:1:1 (83.5g) Compound 2 (0.5g) BS (3.0g) Example 3 <![CDATA[LiPF6(13g)]]> EC / DEC / EMC = 2:1:1 (83.5g) Compound 3 (0.5g) BS 3.0g) Example 4 <![CDATA[LiPF6(13g)]]> EC / DEC / EMC = 2:1:1 (83.5g) Compound 4 (0.5g) BS (3.0g) Example 5 <![CDATA[LiPF6(13g)]]> EC / DEC / EMC = 2:1:1 (83.5g) Compound 5 (0.5g) BS (3.0g) Example 6 <![CDATA[LiPF6(13g)]]> EC / DEC / EMC = 2:1:1 (83.5g) Compound 6 (0.5g) BS (3.0g) Example 7 <![CDATA[LiPF6(14g)]]> EC / DEC / EMC = 1:1:1 (80g) Compound 4 (1g) BS (5g) Example 8 <![CDATA[LiPF6(12.5g)]]> EC / DEC / EMC = 1:1:1 (79.5g) Compound 4 (2g) BS(6g) Comparative Example 1 <![CDATA[LiPF6(13g)]]> EC / DEC / EMC = 2:1:1 (82.5g) - BS (4.5g)

[0040] The lithium-ion batteries prepared in Examples 1-8 and Comparative Example 1 were subjected to room temperature cycling test, high temperature cycling test, high temperature storage test, and low temperature discharge test under the following test conditions. The test results are shown in Table 2.

[0041] ambient temperature cycling test :

[0042] Under normal temperature (25℃) conditions, the lithium-ion battery is charged and discharged once at 1.0C / 1.0C (battery discharge capacity is C0), with an upper limit voltage of 4.4V. Then, it is charged and discharged for 500 cycles at 1.0C / 1.0C under normal temperature conditions (battery discharge capacity is C1).

[0043] Capacity retention rate = (C1 / C0) * 100%

[0044] High temperature cycling test :

[0045] Under high temperature (45℃) conditions, the lithium-ion battery is charged and discharged once at 1.0C / 1.0C (battery discharge capacity is C0), with an upper limit voltage of 4.4V, and then charged and discharged for 300 cycles at 1.0C / 1.0C under normal temperature conditions (battery discharge capacity is C1).

[0046] Capacity retention rate = (C1 / C0) * 100%

[0047] High-temperature storage test :

[0048] Under normal temperature (25℃) conditions, the lithium-ion battery was subjected to one 0.3C / 0.3C charge and discharge cycle (the battery discharge capacity is recorded as C0), with an upper limit voltage of 4.4V; the battery was placed in a 60℃ oven for 15 days, then removed and placed in a 25℃ environment for 0.3C discharge, with the discharge capacity recorded as C1; then the lithium-ion battery was subjected to one 0.3C / 0.3C charge and discharge cycle (the battery discharge capacity is recorded as C2);

[0049] Capacity retention rate = (C1 / C0) * 100%

[0050] Capacity recovery rate = (C2 / C0) * 100%

[0051] Low temperature discharge test :

[0052] At room temperature (25℃), a lithium-ion battery was subjected to a single 0.3C / 0.3C charge and discharge cycle (the battery discharge capacity is recorded as C0), with an upper limit voltage of 4.4V. The battery was then placed in a -20℃ oven for 4 hours, followed by a 0.3C discharge, with the discharge capacity recorded as C1 and a cutoff voltage of 3.0V.

[0053] Capacity retention rate = (C1 / C0) * 100%

[0054] Table 2. Performance test results of lithium-ion batteries in the examples and comparative examples.

[0055]

[0056] As shown in Table 2, the electrolyte of Comparative Example 1, which does not use the additives of this invention, exhibits unsatisfactory high-temperature storage performance, high-temperature cycling performance, and low-temperature discharge performance. In contrast, the lithium-ion batteries prepared with the electrolytes of Examples 1-8 demonstrate excellent high-temperature storage performance, cycling performance, and low-temperature discharge performance. This is because the electrolyte additives utilize compounds shown in Structural Formula 1, which can form a stable interfacial film at the interface through ring-opening polymerization of nitrogen-containing heterocyclic rings. This film provides excellent lithium-ion conduction channels, which is beneficial for improving the cycling and high-temperature performance of ternary high-voltage batteries. Furthermore, this structure contains a fluoroboron salt structure, in which fluoroborane forms a strong B-O bond with oxygen on the positive electrode surface, thereby passivating the positive electrode and preventing electrolyte oxidative decomposition, which is beneficial for improving the high-voltage cycling performance of ternary high-voltage batteries. Simultaneously, this structure can form a low-impedance SEI film at the negative electrode, reducing the charge transfer impedance of the negative electrode, thereby further improving the low-temperature performance of ternary high-voltage lithium-ion batteries.

[0057] A comparison of Examples 1-4 reveals that, compared to Compounds 3 and 4, Compounds 1 and 2 exhibit thicker films due to the enhanced positive and negative electrode film-forming polymerization via double bonds. Therefore, their high-temperature cycling and high-temperature storage performance are significantly improved, but their low-temperature discharge performance is noticeably worse.

[0058] As can be seen from the comparison of Examples 4-6, the overall performance of Compound 5 is significantly better than that of Compound 4 and Compound 6. This is because, compared with sodium ions and lithium ions, CS cesium ions can form an electrostatic protective layer on the surface of the negative electrode active material, reduce or inhibit the formation of dendrites, and improve the room temperature and high temperature cycle performance and low temperature discharge performance of the battery cell. Its overall performance is significantly better than that of lithium ions and sodium ions.

[0059] As can be seen from the comparison between Examples 7 and 8 and Example 1, the optimal dosage of compound 4 is around 1%. When the content is low, the film is relatively thin, which is not conducive to the overall performance. When the content is high, the overall performance is slightly reduced due to the excessive film impedance.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A non-aqueous electrolyte, comprising lithium salt, non-aqueous organic solvent, and additives, characterized in that, The additive is a compound represented by structural formula 1: Structural Formula 1 R1 to R2 are each independently selected from hydrogen, halogen, substituted or unsubstituted C1 to C6 alkyl groups, substituted or unsubstituted C1 to C6 unsaturated bonds, and M is at least one of Li, Na, K, Rb, Cs, Mg, Ca, Ba, Al, Fe, Cu, and Ni.

2. The non-aqueous electrolyte as described in claim 1, characterized in that, The alkyl group is selected from at least one of methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, pentyl, and cyclohexyl.

3. The non-aqueous electrolyte as described in claim 1, characterized in that, The unsaturated bond is selected from at least one of alkenyl, alkynyl, and nitrile groups.

4. The non-aqueous electrolyte as described in claim 1, characterized in that, The additive is selected from at least one of compounds 1 to 6: Compound 1 Compound 2 Compound 3 Compound 4, Compound 5, Compound 6.

5. The non-aqueous electrolyte as described in claim 1, characterized in that, The additive accounts for 0.1% to 3% of the total mass of the electrolyte.

6. The non-aqueous electrolyte as described in claim 1, characterized in that, The non-aqueous organic solvent is selected from at least one of cyclic esters, chain esters, cyclic ethers, chain ethers, sulfone compounds, sulfoxide compounds, and ionic liquids.

7. The non-aqueous electrolyte as described in claim 1, characterized in that, The non-aqueous organic solvent is selected from at least one of cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, sulfone compounds, sulfoxide compounds, and ionic liquids.

8. The non-aqueous electrolyte as described in claim 1, characterized in that, It also includes additives selected from vinylene carbonate, vinylene ethylene carbonate, fluorovinyl carbonate, vinyl sulfite, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, succinic anhydride, maleic anhydride, 2-methylmaleic anhydride, methyl carbonate-2-propynyl ester, tetraethylenesilane, triallyl isocyanurate, hexamethylene diisocyanate, o-phenanthroline, and terephthalic diisocyanate. At least one of the following: ester, 2,4-toluene diisocyanate, N-phenylbis(trifluoromethanesulfonyl)imide, phenyl methanesulfonate, vinyl disulfate, propylene dispiron sulfate, hydroquinone difluorosulfonate, triallyl phosphate, triargyl phosphate, 2,4-butane sulpholol, isocyanate ethyl methacrylate, methylene disulfonate, tri(trimethylsilane)borate, tri(trimethylsilane) phosphate, and tri(vinyl dimethylsilane) phosphate.

9. The non-aqueous electrolyte as described in claim 1, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium methanesulfonate, lithium trifluoromethanesulfonate, lithium dioxalate borate, lithium difluorooxalate borate, lithium difluorophosphate, lithium difluorobis(oxalate) phosphate, lithium difluorosulfonylimide and lithium di(trifluoromethanesulfonylimide), lithium fluorosulfonate, lithium diphosphate and lithium lower aliphatic carboxylic acids.

10. A non-aqueous electrolyte secondary battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that, It also includes the non-aqueous electrolyte as described in any one of claims 1 to 9.

11. The non-aqueous electrolyte secondary battery as described in claim 10, characterized in that, The positive electrode active material includes at least one of the following: lithium phosphate with olivine structure, lithium transition metal oxide, and their respective modified compounds.

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