Non-aqueous electrolyte and secondary battery

Abstract

The application belongs to the field of secondary batteries, and particularly relates to a non-aqueous electrolyte and a secondary battery. The non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte salt and a compound shown in structural formula I: wherein X is selected from any one of, * is a bonding position; R is selected from an alkyl group or a halogenated alkyl group with 1-4 carbon atoms; A is selected from a lithium atom or a sodium atom; the lithium salt and the sodium salt structure of the compound shown in structural formula I can be electrochemically reacted with current moving to an electrode surface; when the cyclic structure of the compound shown in structural formula I is electrochemically reacted, it is empirically speculated that the carbon-oxygen bond is opened, the oxygen-containing end is reacted with a lithium salt or a sodium salt in an electrolyte to form a corresponding organic lithium salt and an organic sodium salt respectively; and the other end free radical is polymerized with an organic matter in the battery or itself to form a double lithium salt or a double sodium salt organic thin film with good ion permeability, so that the battery impedance is reduced and the high-temperature performance of the battery is improved.

Description

Technical Field

[0001] This invention belongs to the field of secondary batteries, specifically relating to a non-aqueous electrolyte and a secondary battery. Background Technology

[0002] With the development of science and technology and the improvement of people's quality of life, green environmental protection is receiving more and more attention, and the application range of secondary batteries is becoming wider and wider. For example, lithium-ion batteries have seen significant acceleration in research progress due to their high energy density and power density, good safety characteristics, excellent cycle performance and wide range of temperature applications. Higher energy density, excellent cycle performance and good safety have led to their widespread use in 3C products, electric vehicles and hybrid vehicles and other devices.

[0003] Secondary batteries consist of a positive electrode, a negative electrode, a separator, and an electrolyte, each component significantly impacting performance. The solid electrolyte interphase (SEI) film on the electrode surface has been extensively studied and discussed. The performance of the SEI layer between the electrode material and the electrolyte depends on its ionic conductivity, ion transfer number, and stability to the electrolyte, among other factors. Film-forming additives can form an SEI film on the negative electrode, slowing down the chemical reaction between the electrode material and the electrolyte, increasing metal ion permeability, and reducing electronic conductivity. However, currently available additives such as VC, FEC, and ES derivatives, while improving certain battery performance aspects, offer limited improvement, particularly in high-temperature storage and cycling performance, which still fail to meet market demands. Developing an additive that further enhances the high-temperature performance of batteries is a pressing issue. Summary of the Invention

[0004] To address the problems of low ionic conductivity, high impedance, and insufficient high-temperature performance of existing electrode surface passivation films, this application provides a non-aqueous electrolyte and battery.

[0005] The following technical solution is adopted in this application:

[0006] On the one hand, this application provides a non-aqueous electrolyte, comprising a non-aqueous organic solvent, an electrolyte salt, and a compound represented by structural formula I:

[0007]

[0008] Where X is selected from In any of the following, * indicates the bonding position;

[0009] R is selected from alkyl or haloalkyl groups having 1 to 4 carbon atoms;

[0010] A is selected from lithium atoms or sodium atoms.

[0011] Preferably, the compound represented by structural formula I is selected from one or more of the following compounds:

[0012]

[0013]

[0014] Those skilled in the art, knowing the structural formula of the compound shown in structural formula I, can understand the preparation method of the above compound based on common knowledge in the field of chemical synthesis. For example, compound 1 can be prepared by reacting 2,2-dioxide-1,2,3-oxathiazoline with chlorosulfonic acid at low temperature for several hours, recrystallizing and purifying, and then reacting it with lithium hydroxide in a solvent to obtain compound 1.

[0015] Specifically, based on the total mass of the non-aqueous electrolyte as 100%, the content of the compound represented by structural formula I is 0.05-10 wt%; in a preferred embodiment, based on the total mass of the non-aqueous electrolyte as 100%, the content of the compound represented by structural formula I is 0.1-5 wt%.

[0016] Specifically, the content of the compound represented by structural formula I can be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, or 10%.

[0017] When the content of the compound shown in Structural Formula I is within the above range, it can effectively maintain the stability of the film formed on the electrode surface and improve battery performance. If the content of the compound shown in Structural Formula I is too low, it will be difficult to significantly improve the performance of the battery. If the content of the compound shown in Structural Formula I is too high, it may affect the function of other substances in the electrolyte due to the excessive decomposition products.

[0018] In a specific embodiment, the electrolyte salt is selected from one or more lithium salts and sodium salts.

[0019] In non-aqueous electrolytes, alkali metal ions formed by the dissociation of electrolyte salts undergo intercalation and deintercalation between the positive and negative electrodes to complete charge-discharge cycles. The concentration of the electrolyte salt directly affects the transfer rate of alkali metal ions, which in turn affects the potential change at the negative electrode. During fast charging, it is necessary to maximize the movement speed of alkali metal ions to prevent the negative electrode potential from dropping too quickly, which could lead to the formation of lithium dendrites and pose a safety hazard to the battery. This also helps prevent the battery's cycle capacity from decaying too rapidly. If the electrolyte salt content is too low, the intercalation and deintercalation efficiency of alkali metal ions between the positive and negative electrodes will be reduced, failing to meet the requirements of fast charging. Conversely, if the electrolyte salt content is too high, the viscosity of the non-aqueous electrolyte will increase, which is also detrimental to improving the intercalation and deintercalation efficiency of alkali metal ions and increases the battery's internal resistance.

[0020] In specific embodiments, the concentration of the lithium salt is 0.1 mol / L to 8 mol / L; in preferred embodiments, the concentration of the lithium salt is 0.5 mol / L to 2.5 mol / L. Specifically, the concentration of the lithium salt can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, or 2.5 mol / L.

[0021] In a preferred embodiment, the lithium salt is selected from LiPF6, LiBOB, LiDFOB, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN(SO2F)2, LiClO4, LiAlCl4, LiCF3SO3, and Li2B. 10 Cl 10 At least one of the following: lithium salts of lower aliphatic carboxylic acids.

[0022] In a specific embodiment, the concentration of the sodium salt is 0.1 mol / L to 2 mol / L. In a preferred embodiment, the concentration of the sodium salt is 0.4 mol / L to 1.5 mol / L. Specifically, the concentration of the sodium salt can be 0.1 mol / L, 0.4 mol / L, 0.5 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, or 2 mol / L.

[0023] In a preferred embodiment, the sodium salt is selected from at least one of sodium perchlorate (NaClO4), sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium bis(fluorosulfonyl)imide (NaFSI), sodium trifluoromethanesulfonate (NaOTf), and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI).

[0024] In a specific embodiment, the non-aqueous electrolyte further includes auxiliary additives, which are selected from at least one of cyclic carbonate compounds, sulfonyl lactone compounds, cyclic sulfate compounds, phosphate compounds, borate ester compounds, and nitrile compounds.

[0025] In some preferred embodiments, the cyclic carbonate compound is selected from at least one of vinylene carbonate (VC), ethylene ethylene carbonate (VEC), ethylene methylene carbonate, fluoroethylene carbonate (FEC), trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and compounds represented by structural formula II below:

[0026]

[0027] In the structural formula II shown, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of hydrogen atoms, halogen atoms, and C1-C5 groups; more preferably, the compound shown in structural formula II includes at least one of the compounds shown in compounds 2-1 to 2-6 below:

[0028]

[0029]

[0030] The cyclic sulfate compounds are selected from vinyl sulfate, 4-methylvinyl sulfate, propylene sulfate, etc. At least one of them;

[0031] The sulfonyl lactone compounds are selected from 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, propenyl-1,3-sulfonyl lactone, and others. At least one of them;

[0032] The phosphate ester compound is selected from at least one of saturated phosphate ester compounds and unsaturated phosphate ester compounds; wherein the saturated phosphate ester compound includes tris(trimethylsilane) phosphate; and the unsaturated phosphate ester compound includes at least one of the compounds represented by structural formula III below:

[0033]

[0034] Among them, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H2m+1 )3, m is a natural number from 1 to 3, and R 31 R 32 R 33 At least one of them is an unsaturated hydrocarbon group; more preferably, the compound represented by structural formula III includes at least one of the following: triargyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.

[0035] The borate ester compound is selected from at least one of tris(trimethylsilane)borate ester and tris(triethylsilane)borate ester;

[0036] The nitrile compound is selected from at least one of butadionitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octadionitrile, nonadionitrile, and sebaconitrile.

[0037] It should be noted that, unless otherwise specified, the content of any one of the optional substances in the auxiliary additives in the non-aqueous electrolyte is generally less than 10%, preferably 0.1-5%, and more preferably 0.1% to 3%. Specifically, the content of any one of the optional substances in the auxiliary additives can be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, or 10%.

[0038] In a specific embodiment, when the auxiliary additive is selected from fluoroethylene carbonate, the content of fluoroethylene carbonate is 0.05% to 30% based on the total mass of the non-aqueous electrolyte as 100%.

[0039] In the non-aqueous electrolyte, compared with single addition or combination of other existing additives, the compound shown in structural formula I, when added together with the auxiliary additive, exhibits a significant synergistic effect in improving battery performance. This indicates that the compound shown in structural formula I and the auxiliary additive can form a film together on the electrode surface, which can compensate for the film formation defects of single addition and obtain a more stable passivation film.

[0040] In specific embodiments, the non-aqueous organic solvent includes at least one of ether solvents, nitrile solvents, carbonate solvents, carboxylic acid ester solvents, and sulfone solvents.

[0041] In preferred embodiments, the ether solvent includes cyclic ethers or chain ethers. Specifically, the cyclic ether may be, 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 be, but is not limited to, at least one of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), and diethylene glycol dimethyl ether (TEGDME). The nitrile solvent may be, but is not limited to, at least one of acetonitrile, glutaronitrile, and malononitrile. Carbonate solvents include cyclic carbonates or chain carbonates. Cyclic carbonates may specifically include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC). Chain carbonates may specifically include, but are not limited to, at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). Carboxylic acid ester solvents may specifically 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.

[0042] On the other hand, this application also provides a secondary battery comprising a positive electrode, a negative electrode, and the aforementioned non-aqueous electrolyte.

[0043] Because the secondary battery uses the non-aqueous electrolyte as described above, Structure I can form a high-performance passivation film on the positive and negative electrodes, thereby effectively improving the battery's high-temperature storage performance and high-temperature cycle performance, and enhancing the battery's power characteristics.

[0044] In a specific embodiment, the secondary battery is a lithium-ion battery, a lithium metal battery, or a sodium-ion battery.

[0045] In some embodiments, the positive electrode includes a positive electrode material layer, and the positive electrode material layer includes a positive electrode active material. The type and content of the positive electrode active material are not particularly limited and can be selected according to actual needs. It can be any positive electrode active material or conversion type positive electrode material that can reversibly insert / deintercalate metal ions (such as lithium ions and sodium ions).

[0046] In a preferred embodiment, the secondary battery is a lithium-ion battery, and its positive electrode active material can be selected from LiFe. 1-x’ M' x’ PO4, LiMn 2-y’ My’ O4 and LiNi x Co y Mn z M 1-x-y-z At least one of O2, wherein M' is selected from at least one of Mn, Mg, Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, or Ti, and M is selected from at least one of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, or Ti, and 0≤x'<1, 0≤y'≤1, 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1. The positive electrode active material may also be selected from at least one of sulfides, selenides, and halides. More preferably, the positive electrode active material may be selected from LiCoO2, LiFePO4, or LiFe... 0.8 Mn 0.2 PO4, LiMn2O4, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.5 Co 0.2 Mn 0.2 Al 0.1 O2, LiNi 0.5 Co 0.2 Al 0.3 At least one of O2.

[0047] In a preferred embodiment, the secondary battery is a sodium-ion battery, and its positive electrode active material includes, but is not limited to, at least one of transition metal oxides, Prussian-type materials, phosphates, sulfates, and titanates. The chemical formula of the transition metal oxide may be Na. z M x O y M can be selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V. More preferably, the transition metal oxide is NaNi. m Fe n Mn p O2 (m+n+p=1, 0≤m≤1, 0≤n≤1, 0≤p≤1) or NaNi m Co n Mn p O2 (m+n+p=1, 0≤m≤1, 0≤n≤1, 0≤p≤1); the molecular formula of the Prussian-like material is Na. xM[M′(CN)6] y ·zH2O, where M is a transition metal, M′ is a transition metal, 0 < x ≤ 2, 0.8 ≤ y < 1, 0 < z ≤ 20. More preferably, the Prussian material is Na x Mn[Fe(CN)6] y ·nH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 10) or Na x Fe[Fe(CN)6] y ·nH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 10); The chemical formula of the phosphate is Na3(MO 1-x PO4)2F 1+2x , 0 ≤ x ≤ 1, M is selected from at least one of Al, V, Ge, Fe, Ga. More preferably, the phosphate is Na3(VPO4)2F3 or Na3(VOPO4)2F; The chemical formula of the phosphate is Na2MPO4F, M is selected from at least one of Fe, Mn. More preferably, the phosphate is Na2FePO4F or Na2MnPO4F; The titanate material can be selected from at least one of Na2Ti3O7, Na2Ti6O 13 , Na4Ti5O 12 , Li4Ti5O 12 , NaTi2(PO4)3; The chemical formula of the sulfate is Na2M(SO4)2·2H2O, M can be selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, V.

[0048] In some embodiments, the positive electrode further includes a positive electrode current collector, and the positive electrode material layer is disposed on the surface of the positive electrode current collector.

[0049] The positive electrode current collector is selected from metal materials that can conduct electrons. Preferably, the positive electrode current collector includes at least one of Al, Ni, tin, copper, stainless steel. In a more preferred embodiment, the positive electrode current collector is selected from aluminum foil.

[0050] In some embodiments, the positive electrode active material layer further includes a positive electrode binder and a positive electrode conductive agent, and the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent are blended to obtain the positive electrode material layer.

[0051] The positive electrode binder includes at least one of the following: polyvinylidene fluoride (PVDF), copolymers of PVDF, polytetrafluoroethylene (PTFE), copolymers of PVDF-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of PVDF-tetrafluoroethylene, copolymers of PVDF-trifluoroethylene, copolymers of PVDF-trichloroethylene, copolymers of PVDF-fluorinated vinylidene, copolymers of PVDF-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0052] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0053] In some embodiments, the negative electrode includes a negative electrode material layer, and the negative electrode material layer includes a negative electrode active material. The type and content of the negative electrode active material are not particularly limited and can be selected according to actual needs.

[0054] In a preferred embodiment, the secondary battery is a lithium-ion battery, and its negative electrode active material includes at least one of carbon-based, silicon-based, tin-based, and lithium-based negative electrodes. The carbon-based negative electrode may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, etc.; the silicon-based negative electrode may include silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials, etc.; the tin-based negative electrode may include tin, tin-carbon, tin-oxygen, and tin metal compounds; and the lithium-based negative electrode 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.

[0055] In a preferred embodiment, the secondary battery is a sodium-ion battery, and its negative electrode active material includes at least one of metallic sodium, graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with sodium. The alloy material may also be selected from at least one of Si, Ge, Sn, Pb, and Sb combined with C; the graphite may be selected from at least one of artificial graphite, natural graphite, and modified graphite; the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.

[0056] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode material layer is disposed on the surface of the negative electrode current collector. The material of the negative electrode current collector may be the same as that of the positive electrode current collector, and will not be described in detail here.

[0057] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder, and the negative electrode conductive agent are blended to obtain the negative electrode material layer. The negative electrode binder and the negative electrode conductive agent can be the same as the positive electrode binder and the positive electrode conductive agent, respectively, and will not be described in detail here.

[0058] In some embodiments, the secondary battery further includes a separator located between the positive electrode and the negative electrode.

[0059] The diaphragm can be a conventional diaphragm, such as a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, or an inorganic-organic composite diaphragm, 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 diaphragms.

[0060] The non-aqueous electrolyte described in this invention can effectively reduce battery impedance and improve battery cycle life. In lithium-ion and sodium-ion batteries, the lithium and sodium salt structures of the compound shown in Formula I can move to the electrode surface with the current and undergo electrochemical reactions. When the cyclic structure of the compound shown in Formula I undergoes an electrochemical reaction, it is empirically inferred that its carbon-oxygen bonds open, and the oxygen-containing end reacts with the lithium or sodium salt in the electrolyte to form corresponding organic lithium salts and organic sodium salts, respectively. The free radical at the other end polymerizes with organic matter in the battery or itself to form a double lithium salt or double sodium salt organic film with good ion permeability, thereby reducing battery impedance and improving battery cycle performance. Detailed Implementation

[0061] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0062] The present invention will be further illustrated by the following examples.

[0063] Table 1

[0064]

[0065]

[0066] Note: The compounds used in the following examples and comparative examples are selected from Table 1.

[0067] Examples 1-20

[0068] This embodiment illustrates the preparation method of the non-aqueous electrolyte and lithium-ion battery disclosed in this invention. The preparation method is identical except for the additives used in the non-aqueous electrolyte. The specific preparation method is as follows:

[0069] 1) Preparation of non-aqueous electrolyte:

[0070] Ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a mass ratio of EC:DEC:EMC = 1:1:1. Then, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol / L. Additives were added based on the total weight of the non-aqueous electrolyte as 100%. The types and contents of each additive are shown in Table 2.

[0071] 2) Preparation of the positive electrode:

[0072] The positive electrode active material, lithium nickel cobalt manganese oxide (LiNiO), was mixed in a mass ratio of 93:4:3. 0.5 Co 0.2 Mn 0.3 O2, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) are mixed and dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The slurry is uniformly coated on both sides of an aluminum foil, dried, calendered, and vacuum dried, and then aluminum leads are welded on using an ultrasonic welder to obtain a positive electrode sheet with a thickness between 120-150 μm.

[0073] 3) Preparation of the negative electrode:

[0074] Artificial graphite, conductive carbon black Super-P, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:1:2.5:2.5 and then dispersed in deionized water to obtain a negative electrode slurry. The slurry was coated on both sides of a copper foil, dried, calendered, and vacuum dried, and then nickel leads were welded on using an ultrasonic welder to obtain a negative electrode plate with a thickness between 120-150 μm.

[0075] 4) Cell fabrication:

[0076] A three-layer separator with a thickness of 20 μm is placed between the positive and negative plates. Then, the sandwich structure composed of the positive plate, negative plate and separator is wound up. The wound body is flattened and placed in an aluminum foil packaging bag. It is then vacuum baked at 75°C for 48 hours to obtain the cell to be injected with electrolyte.

[0077] 5) Electrolyte injection and formation of the battery cell:

[0078] In a glove box where the dew point is controlled below -40°C, the electrolyte prepared above is injected into the battery cell, vacuum sealed, and left to stand for 24 hours.

[0079] The initial formation was then performed as follows: constant current charging at 0.05C for 180 minutes, constant current charging at 0.2C to 3.95V, followed by a second vacuum sealing. Then, it was further charged at a constant current of 0.2C to 4.2V, left to stand at room temperature for 24 hours, and finally discharged at a constant current of 0.2C to 3.0V to obtain a LiNi alloy. 0.5 Co 0.2 Mn 0.3 O2 / artificial graphite lithium-ion battery.

[0080] Comparative Examples 1-5

[0081] This comparative example is used to compare and illustrate the non-aqueous electrolyte and battery method disclosed in this invention, including most of the operation steps in the above embodiments. The difference is that in the preparation of the non-aqueous electrolyte, the components with the mass percentage shown in Comparative Examples 1-5 in Table 2 are added as additives based on the total weight of the non-aqueous electrolyte as 100%, and the test results are filled in Table 2.

[0082] Performance testing

[0083] The lithium-ion batteries prepared in Examples 1-20 and Comparative Examples 1-5 were subjected to the following performance tests:

[0084] High-temperature storage performance test

[0085] The formed lithium-ion battery was charged at room temperature with a constant current of 1C to 4.2V, then charged with a constant current and constant voltage until the current dropped to 0.05C. It was then discharged at a constant current of 1C to 3.0V. The initial discharge capacity D1, initial battery volume V1, and initial impedance F1 were measured. After being fully charged, the battery was stored at 60℃ for 30 days, then discharged at 1C to 3V. The retention capacity D2, recovery capacity D3, impedance after storage F2, and battery volume V2 after storage were measured. The calculation formulas are as follows:

[0086] Battery capacity retention rate (%) = Retained capacity D2 / Initial capacity D1 × 100%;

[0087] Volume expansion rate (%) = (Battery volume after storage V2 - Initial battery volume V1) / Initial battery volume V1 × 100%;

[0088] Internal resistance growth rate (%) = Impedance after storage F2 / Initial impedance F1 × 100%.

[0089] The test results are shown in Table 2.

[0090] Table 2

[0091]

[0092]

[0093] Comparing the test results of Examples 1-10, it can be seen that as the amount of compound shown in Structural Formula I increases, the volume expansion rate and internal resistance growth rate of lithium-ion batteries first decrease and then increase, while the capacity remains stable, first increasing and then decreasing. This indicates that too much or too little addition will affect the high-temperature cycle performance of lithium-ion batteries and reduce their internal resistance growth. In particular, when the amount of compound shown in Structural Formula I is between 0.1% and 5%, the lithium-ion battery has the best impedance reduction and high-temperature cycle performance.

[0094] Comparing the test results of Examples 1-10 and Comparative Examples 1-4, it can be seen that, compared with traditional vinylene carbonate (VC), vinyl sulfate (DTD), and 1,3-propanesulfonate lactone (PS), using the compound shown in Structural Formula I provided in this application as an additive can more significantly improve the cycle performance of lithium-ion batteries at high temperatures, indicating that the passivation film formed by the compound shown in Structural Formula I has superior low impedance and lithium-ion permeability.

[0095] Comparing the test results of Examples 4, 11-17 and Comparative Examples 1-4, it can be seen that, compared with lithium-ion batteries without additives or with existing additives, lithium-ion batteries using the compound shown in Structural Formula I provided by this invention as an additive have better high-temperature cycle performance.

[0096] Comparing the test results of Examples 18-20 and Comparative Example 5, it can be seen that when the compound of structural formula I provided in this application is used in conjunction with conventional additives, the cycle performance of lithium-ion batteries at high temperatures can be further improved.

[0097] Examples 21-38

[0098] Examples 21-38 illustrate the preparation method of the non-aqueous electrolyte and sodium-ion battery described in this invention. The preparation methods are identical except for the additives used in the non-aqueous electrolyte; the specific preparation methods are as follows:

[0099] (1) Preparation of non-aqueous electrolyte

[0100] Ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a mass ratio of EC:DEC:EMC = 1:1:1. Then, sodium hexafluorophosphate (NaPF6) was added to a molar concentration of 1 mol / L. Based on the total weight of the non-aqueous electrolyte being 100%, the types and amounts of additives shown in Table 3 were added.

[0101] (2) Preparation of positive electrode plate

[0102] The positive electrode active material Na3V2(PO4)3, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 94:3:3, and then dispersed in N-methyl-2-pyrrolidone (NMP) to obtain the positive electrode slurry. The slurry is uniformly coated on both sides of an aluminum foil, dried, calendered, and vacuum dried, and then aluminum or nickel leads are welded on using an ultrasonic welder to obtain the positive electrode sheet with a thickness between 80-200 μm.

[0103] (3) Preparation of negative electrode plate

[0104] The negative electrode active materials, spherical hard carbon, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) are mixed in a mass ratio of 97:1:1:1, and then dispersed in deionized water to obtain a negative electrode slurry. The slurry is coated on both sides of an aluminum foil, dried, calendered, and vacuum dried, and then aluminum or nickel leads are welded on using an ultrasonic welder to obtain a negative electrode sheet with a thickness between 80-300 μm.

[0105] 4) The positive electrode, separator, and negative electrode are stacked in sequence, and then packaged with aluminum-plastic film, baked, injected with electrolyte, left to stand, formed, shaped with fixtures, resealed, and tested for capacity to complete the preparation of sodium-ion batteries.

[0106] Comparative Examples 6-7

[0107] This comparative example is used to illustrate the non-aqueous electrolyte and battery method disclosed in this invention. It includes most of the operation steps in the above embodiments. The difference is that in the preparation of the non-aqueous electrolyte, the components with the mass percentage shown in Comparative Examples 6-7 in Table 3 are added as additives based on the total weight of the non-aqueous electrolyte as 100%, as shown in Table 3.

[0108] Performance testing

[0109] The sodium-ion batteries prepared in the examples and comparative examples were subjected to the following performance tests:

[0110] I. High-Temperature Storage Performance Test

[0111] The sodium-ion battery, after formation, was charged at a constant current of 0.5C to 4.0V at room temperature, then charged at a constant voltage until the current dropped to 0.03C. It was then discharged at a constant current of 1C to 1.5V. The initial discharge capacity D3, initial battery volume V4, and initial impedance F3 were measured. After being fully charged, the battery was stored at 60℃ for 30 days, then discharged at 1C to 3V. The retention capacity D4, recovery capacity D5, impedance F4 after storage, and battery volume V4 after storage were measured. The calculation formulas are as follows:

[0112] Battery capacity retention rate (%) = (retained capacity D4 / initial capacity D3) × 100%;

[0113] Battery capacity recovery rate (%) = (recovered capacity D5 / initial capacity D3) × 100%;

[0114] Volume expansion rate (%) = [(Battery volume after storage V4 - Initial battery volume V3) / Initial battery volume V3] × 100%;

[0115] Internal resistance growth rate (%) = Impedance after storage F4 / Initial impedance F3 × 100%.

[0116] II. High-Temperature Cycling Performance Test

[0117] After formation, the battery was left to stand at 45°C for 2 hours, then charged at a constant current rate of 0.5C to 4.0V, then charged at a constant voltage rate to 0.03C, and then discharged at a constant current rate of 1C to 1.5V, for 500 cycles.

[0118] Measure the battery's initial discharge capacity D6, discharge capacity D7 after 500 cycles, and battery coulombic efficiency E.

[0119] Battery capacity retention rate (%) after 500 cycles = (Capacity D7 / Initial capacity D6) × 100%.

[0120] The test results are shown in Table 3.

[0121] Table 3

[0122]

[0123]

[0124] Comparing the test results of Examples 21-30, it can be seen that as the amount of compound shown in Structural Formula I increases, the volume expansion rate and internal resistance growth rate of sodium-ion batteries first decrease and then increase, while the capacity remains stable, first increasing and then decreasing. This indicates that both excessive and insufficient addition will improve the high-temperature cycle performance of sodium-ion batteries and reduce their internal resistance growth. In particular, when the amount of compound shown in Structural Formula I is between 0.1% and 5%, sodium-ion batteries exhibit optimal impedance reduction and high-temperature cycle performance.

[0125] Comparing the test results of Examples 21-30 and Comparative Examples 6-7, it can be seen that, compared with traditional vinyl fluoride (FEC), using the compound shown in Structural Formula I provided in this application as an additive can more significantly improve the high-temperature performance of sodium-ion batteries, indicating that the passivation film formed by the compound shown in Structural Formula I has superior low impedance and sodium ion permeability.

[0126] Comparing the test results of Examples 24, 31-37 and Comparative Examples 6-7, it can be seen that, compared with sodium-ion batteries without additives or with existing additives, sodium-ion batteries using the compound of structural formula I provided by the present invention as an additive have better high-temperature performance.

[0127] Comparing the test results of Examples 25 and 38, it can be seen that using the compound shown in Structural Formula I provided in this application with vinyl fluoride (FEC) as an additive can further improve the high-temperature performance of sodium-ion batteries.

[0128] In summary, the compound represented by structural formula I of this application, when used as an additive for non-aqueous electrolytes in secondary batteries, can effectively reduce battery impedance and improve battery cycle life; the passivation film formed has superior low impedance and metal ion permeability; compared with traditional electrolyte additives, it has a better effect on improving the functionality of secondary batteries and has great industrial value.

[0129] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. A nonaqueous electrolyte, characterized by comprising: Including non-aqueous organic solvents, electrolyte salts, and compounds represented by structural formula I: Structural Formula I wherein X is selected from , , any one of, * is a bonding position; R is selected from alkyl or haloalkyl groups having 1 to 4 carbon atoms; A is selected from lithium atoms or sodium atoms.

2. The nonaqueous electrolyte according to claim 1, characterized by The compound represented by structural formula I is selected from one or more of the following compounds:

3. The nonaqueous electrolyte according to claim 1, characterized by Based on the total mass of the non-aqueous electrolyte as 100%, the content of the compound represented by structural formula I is 0.05-10 wt%.

4. The nonaqueous electrolyte according to claim 1, characterized by Based on the total mass of the non-aqueous electrolyte being 100%, the content of the compound represented by structural formula I is 0.1-5 wt%.

5. The nonaqueous electrolyte according to claim 1, wherein The electrolyte salt is selected from one or more lithium salts and sodium salts.

6. The non-aqueous electrolyte according to claim 5, characterized in that, The lithium salt is selected from LiPF6, LiBOB, LiDFOB, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN(SO2F)2, LiClO4, LiAlCl4, LiCF3SO3, and Li2B. 10 Cl 10 At least one of the following: lower aliphatic lithium carboxylate salts; The sodium salt is selected from at least one of NaClO4, NaPF6, NaBF4, NaFSI, NaOTf, and NaTFSI.

7. The nonaqueous electrolyte according to claim 5, wherein The concentration of the lithium salt is 0.1 mol / L to 8 mol / L; the concentration of the sodium salt is 0.1 mol / L to 2 mol / L.

8. The nonaqueous electrolyte according to claim 5, wherein The concentration of the lithium salt is 0.5 mol / L to 2.5 mol / L; the concentration of the sodium salt is 0.4 mol / L to 1.5 mol / L.

9. The nonaqueous electrolyte according to claim 1, wherein The non-aqueous electrolyte also includes auxiliary additives, which are selected from at least one of cyclic carbonate compounds, sulfonyl lactone compounds, cyclic sulfate compounds, phosphate compounds, borate ester compounds, and nitrile compounds.

10. The nonaqueous electrolyte according to claim 9, wherein The cyclic carbonate compound is selected from at least one of vinylene carbonate, ethylene ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate, and the compound shown in structural formula II below: Structural Form II In the structural formula II shown, R 21 R 22 R 23 R 24 R 25 R 26 Each is independently selected from one of the following: hydrogen atom, halogen atom, or C1-C5 group.

11. The non-aqueous electrolyte according to claim 10, characterized in that, the cyclic sulfate compound is selected from at least one of ethylene sulfate, 4-methyl ethylene sulfate, propylene sulfate, , , , The sulfonyl lactones are selected from 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone. At least one of them; The phosphate ester compound is selected from at least one of saturated phosphate ester compounds and unsaturated phosphate ester compounds; wherein the saturated phosphate ester compound includes tris(trimethylsilane) phosphate; and the unsaturated phosphate ester compound includes at least one of the compounds represented by structural formula III below: Structural Form III Among them, R 31 R 32 R 33 Each is independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halohydrocarbon groups, and -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 R 32 R 33 At least one of them is an unsaturated hydrocarbon group; The borate ester compound is selected from at least one of tris(trimethylsilane)borate ester and tris(triethylsilane)borate ester; The nitrile compound is selected from at least one of butadionitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, heptanonitrile, octadionitrile, nonadionitrile, and sebaconitrile.

12. The nonaqueous electrolyte according to claim 1, wherein The non-aqueous organic solvent includes at least one of ether solvents, nitrile solvents, carbonate solvents, carboxylic acid ester solvents, and sulfone solvents.

13. A secondary battery characterized by comprising: It includes a positive electrode, a negative electrode, and the non-aqueous electrolyte as described in any one of claims 1-12.

14. The secondary battery according to claim 13, characterized by The secondary battery is a lithium-ion battery, a lithium metal battery, or a sodium-ion battery.

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