Non-aqueous electrolyte and lithium ion battery thereof

Abstract

The invention discloses a non-aqueous electrolyte and a lithium ion battery thereof. The non-aqueous electrolyte comprises a lithium salt, a non-aqueous organic solvent and an additive, wherein the additive comprises a compound A as shown in a structural formula I; r1 is selected from substituted or unsubstituted C1-C6 alkyl, and amino with substituted or unsubstituted C1-C12 linear, branched or cyclic alkyl as a substituent. The non-aqueous electrolyte contains the additive compound A, the compound A has a trifluoromethoxy structure and a thioamide structure, and the normal-temperature cycle performance, the high-temperature cycle performance and the rate capability of the lithium ion battery can be effectively improved.

Description

Technical Field

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

[0002] With the development of electric vehicles and the increasing demands for energy density, cycle life, and safety of lithium batteries in daily life, there is a need to further develop high-performance lithium battery cathode materials. Lithium manganese iron phosphate (LFP) possesses advantages such as wide availability of raw materials, low cost, environmental friendliness, high energy density and theoretical specific capacity, stable discharge voltage, good thermal stability, and good cycle performance, giving it considerable overall advantages. Major battery manufacturers such as BYD, CATL, and Tesla, as well as many emerging players in the battery industry, have all recognized the value of LFP batteries, accelerating their industrialization. With broad application prospects in electric vehicles, this material demonstrates extremely promising development potential, significant research value, and considerable development potential, and is expected to be applied to lithium-ion batteries and other energy storage devices.

[0003] Although lithium manganese iron phosphate (LFP) cathode materials possess advantages such as high energy density, good thermal stability, safety, reliability, and low cost, their cycling performance is hampered by the easy dissolution of manganese in the electrolyte during cycling and the inherent Jahn-Teller effect of manganese in manganese-based cathode materials. Furthermore, its near-insulating low conductivity and poor thermal stability also lead to suboptimal electrochemical performance. Therefore, there is an urgent need for a non-aqueous electrolyte and its lithium-ion battery to address the shortcomings of existing technologies. Summary of the Invention

[0004] The purpose of this invention is to provide a non-aqueous electrolyte and its lithium-ion battery. The non-aqueous electrolyte contains additive compound A, which can effectively improve the room temperature cycle performance, high temperature cycle performance and rate performance of the lithium-ion battery.

[0005] 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 comprises compound A as shown in structural formula one:

[0006] R1 is selected from substituted or unsubstituted C1-C6 hydrocarbon groups, or amino groups having substituted or unsubstituted C1-C12 straight-chain, branched, or cyclic hydrocarbon groups as substituents. Compared with existing technologies, the electrolyte of this invention comprises lithium salt, organic solvent, and additives. The additives include compound A with a special structure. Compound A has a trifluoromethoxy group, which preferentially undergoes oxidative decomposition before other components in the electrolyte, forming a stable solid electrolyte interphase (SEI) film on the electrode surface. This SEI film effectively blocks further side reactions between the electrolyte and the electrode, reducing electrolyte decomposition losses and thus improving the electrolyte's oxidation resistance and the battery's cycle stability. Furthermore, compound A of this invention contains a thioamide group structure. The stable SEI film formed by the amide group reduces the charge transport impedance between the electrode and the electrolyte, allowing it to maintain good stability even at high temperatures, effectively improving the rate performance of the lithium-ion battery. Furthermore, R1 is selected from substituted or unsubstituted C1-C6 alkyl groups, amino groups having substituted or unsubstituted C1-C6 straight-chain, branched, or cyclic alkyl groups as substituents, and when substituted, the substituents are selected from halogens.

[0007] Furthermore, compound A is selected from at least one of compounds 1 to 4:

[0008] CAS No.: 370-85-4 CAS No.: 443291-76-7

[0009] Compound 3 Compound 4 CAS No.: 1024224-87-0 CAS No.: 138585-88-3 Further, compound A accounts for 0.1% to 5.0% of the total mass of the lithium salt, the non-aqueous organic solvent, and the additive.

[0010] Further, the lithium salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium methanesulfonate, lithium trifluoromethanesulfonate, lithium di(oxalate)borate, lithium di(fluorooxalate)borate, lithium difluorophosphate, and lithium di(fluorobis(oxalate))phosphate.

[0011] Furthermore, the mass of the lithium salt accounts for 5% to 37.5% of the sum of the masses of the lithium salt, the non-aqueous organic solvent, and the additive.

[0012] Furthermore, the non-aqueous organic solvent is selected from at least one of carbonates, carboxylic esters, and ethers.

[0013] Furthermore, the additive also includes an auxiliary agent selected from at least one of vinylene carbonate, vinylene carbonate, fluorovinyl carbonate, vinyl sulfite, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, succinic anhydride, maleic anhydride, tetraethylenesilane, triallyl isocyanurate, hexamethylene diisocyanate, o-phenanthroline, terephthalic diisocyanate, 2,4-toluene diisocyanate, phenyl methanesulfonate, vinyl disulfate, hydroquinone difluorosulfonate, triallyl phosphate, triargyl phosphate, 2,4-butanesulfonate, isocyanoethyl methacrylate, methylene disulfonate, tri(trimethylsilane)borate, tri(trimethylsilane) phosphate, and tri(trimethylsilane) phosphite.

[0014] Furthermore, the auxiliary agent accounts for 0.1% to 5% of the total mass of the lithium salt, the non-aqueous organic solvent, and the additive.

[0015] Another aspect of the present invention provides a lithium-ion battery, including a positive electrode material and a negative electrode material, and also including the aforementioned non-aqueous electrolyte, wherein the positive electrode material is selected from lithium manganese iron phosphate. Detailed Implementation

[0016] The lithium-ion battery of the present invention includes a positive electrode material, a negative electrode material, and a non-aqueous electrolyte. The positive electrode material is selected from lithium manganese iron phosphate, and the structural formula of lithium manganese iron phosphate is LiFe. 1-x Mn x PO4, 0 < x < 1. Where x represents the manganese doping ratio, and the manganese-to-iron ratio used in this invention is any one of 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1. The negative electrode 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 alloy, lithium-sodium alloy, lithium-potassium alloy, lithium-aluminum alloy, lithium-tin alloy, and lithium-indium alloy. The non-aqueous electrolyte of this invention includes lithium salts, non-aqueous organic solvents, and additives.

[0017] The lithium salt comprises 5% to 37.5% of the total mass of the lithium salt, non-aqueous organic solvent, and additives. Preferably, the lithium salt comprises 6% to 20% of the total mass of the lithium salt, non-aqueous organic solvent, and additives; more preferably, the lithium salt comprises 8% to 18% of the total mass of the lithium salt, non-aqueous organic solvent, and additives. As examples, the lithium salt comprises 5%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 20%, 25%, 30%, 35%, and 37.5% of the total mass of the lithium salt, non-aqueous organic solvent, and additives, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Lithium salts include at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium methanesulfonate, lithium trifluoromethanesulfonate (LiCF3SO3), lithium di(oxalate)borate (LiBOB), lithium di(fluorooxalate)borate (LiBF2C2O4), lithium difluorophosphate (LiPO2F2), and lithium di(fluorobis(oxalate))phosphate (LiDFBP).

[0018] The non-aqueous organic solvent is selected from at least one of carbonates, carboxylic acid esters, and ethers. Specifically, the carbonate compounds are selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), propylene carbonate (PC), ethylene carbonate (EC), and butylene carbonate (BC), but are not limited thereto; the carboxylic acid ester compounds are selected from at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), and propyl propionate (PP). At least one of γ-butyrolactone (GBL) and γ-valerolactone (GVL) is selected, but is not limited thereto; the ether compounds are selected from at least one of 1,3-dioxolane (DOL), 1,4-dioxane (DX), tetrahydrofuran (THF), ethylene glycol di-n-butyl ether (EDB), and diethylene glycol dimethyl ether (DEGME), but the invention is not limited thereto.

[0019] The additives include auxiliaries, which constitute 0.1% to 5% of the sum of the mass of the lithium salt, the non-aqueous organic solvent, and the additives. The auxiliaries are selected from vinylene carbonate (VC), vinylene carbonate (VEC), fluorovinyl carbonate (FEC), vinyl sulfite (ES), 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PST), 1,4-butanesulfonate lactone, vinyl sulfate (DTD), succinic anhydride (SA), maleic anhydride (MA), tetraethylenesilane (TVSI), triallyl isocyanurate (TAIC), hexamethylene diisocyanate (HDI), o-phenanthroline, terephthalic diisocyanate (PPDI), and 2,4-toluene. At least one of the following: diisocyanate (2,4-TDI), phenyl methanesulfonate (DBCO), ethylene disulfate (BIDTD), hydroquinone difluorosulfonate (HBFS), triallyl phosphate (TAP), triargyl phosphate (TAP), 2,4-butane sulpholol (2,4-BS), isocyanate ethyl methacrylate (IEM), methylene disulfonate (MMDS), tris(trimethylsilane)borate (TMSB), tris(trimethylsilane) phosphate (TMSP), and tris(trimethylsilane) phosphite (TMSPi). The mass of the additive accounts for 0.1% to 5% of the sum of the mass of the lithium salt, non-aqueous organic solvent, and additive; preferably, the mass of the additive accounts for 0.2% to 2% of the sum of the mass of the lithium salt, non-aqueous organic solvent, and additive. As an example, the mass of the auxiliaries is 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.2%, 2.5%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, or 5% of the sum of the masses of the lithium salt, non-aqueous organic solvent, and additives, but is not limited to the listed values; other unlisted values ​​within this range also apply.

[0020] The additive includes compound A, as shown in structural formula 1:

[0021] R1 is selected from substituted or unsubstituted C1-C6 hydrocarbon groups, or amino groups having substituted or unsubstituted C1-C12 straight-chain, branched, or cyclic hydrocarbon groups as substituents. Preferably, R1 is selected from substituted or unsubstituted C1-C6 alkyl groups, or amino groups having substituted or unsubstituted C1-C6 straight-chain, branched, or cyclic alkyl groups as substituents, and when substituted, the substituent is selected from halogens. Specifically, the halogen is selected from at least one of F, Cl, Br, and I. As an example, compound A is selected from at least one of compounds 1 to 4, but is not limited thereto.

[0022]

[0023] CAS No.: 370-85-4 CAS No.: 443291-76-7

[0024] Compound 3 Compound 4 CAS No.: 1024224-87-0 CAS No.: 138585-88-3 Compound A comprises 0.1% to 5.0% of the total mass of the lithium salt, non-aqueous organic solvent, and additives. Preferably, compound A comprises 0.1% to 3% of the total mass of the lithium salt, non-aqueous organic solvent, and additives. As examples, compound A comprises 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.2%, 2.5%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, and 5% of the total mass of the lithium salt, non-aqueous organic solvent, and additives, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0025] 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.

[0026] Unless otherwise specified in the examples and comparative examples, the conditions may be performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the reagents or instruments used are all commercially available conventional products.

[0027] 1.1 Preparation of non-aqueous electrolyte: In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), dimethyl carbonate (DMC), ethyl acetate (EA), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed thoroughly in a mass ratio of 3:1:2:2. This mixed solvent was used as the organic solvent, and compound 1 was then added to obtain a mixed solution. The mixed solution was sealed and packaged, then frozen in a freezer (-4°C) for 2 hours. After removal, lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution in a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), and after thorough mixing, a non-aqueous electrolyte was prepared.

[0028] 1.2 Preparation of the positive electrode: LiMn manganese iron phosphate material 0.6 Fe 0.4 PO4, PVDF binder, and Super P conductive agent are mixed evenly at a mass ratio of 95:1:4 to prepare a lithium secondary battery positive electrode slurry with a certain viscosity. The mixed slurry is coated on both sides of aluminum foil, dried, and rolled to obtain the positive electrode sheet.

[0029] 1.3 Preparation of the negative electrode: Artificial graphite, conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber latex) are mixed in a mass ratio of 95:1.5:1.0:2.5 to form a slurry. The mixture is then coated on both sides of a copper foil, dried, and rolled to obtain a negative electrode sheet, thus producing a lithium-ion battery negative electrode sheet that meets the requirements.

[0030] 1.4 Preparation of lithium-ion batteries: The positive electrode, separator, and negative electrode are stacked in sequence, and then layered as needed. After the tabs are welded, the battery is placed in the aluminum-plastic film of the outer packaging. The prepared electrolyte is injected into the dried bare cell, and then vacuum sealing, standing, formation (0.05C constant current charging to 3.0V, then 0.1C constant current charging to 4.3V), capacity testing, and other processes are carried out to finally obtain a 1Ah soft-pack lithium secondary battery.

[0031] The composition and content of the electrolytes in Examples 1-16 and Comparative Examples 1-4 are shown in Table 1. The preparation processes of the lithium-ion battery electrolytes, positive electrode sheets, negative electrode sheets, and lithium-ion batteries in Examples 2-16 and Comparative Examples 1-4 are the same as those in Example 1.

[0032] Table 1. Composition of the electrolytes in the examples and comparative examples

[0033] The lithium-ion batteries prepared in Examples 1-16 and Comparative Examples 1-4 were subjected to high-temperature cycling performance tests, room-temperature cycling performance tests, safety performance tests, and rate performance tests under the following conditions, and the results are shown in Table 2.

[0034] ambient temperature cycling performance test : Under normal temperature (25℃) conditions, a lithium-ion battery is subjected to one 1.0C / 1.0C charge and discharge cycle (battery discharge capacity is C0), with an upper limit voltage of 4.1V. Then, under normal temperature conditions, it is subjected to 500 cycles of 1.0C / 1.0C charge and discharge (battery discharge capacity is C1), and the capacity retention rate is calculated.

[0035] Capacity retention rate = (C1 / C0) × 100% High temperature cycling test : Under high temperature (45℃) conditions, a lithium-ion battery is subjected to one 1.0C / 1.0C charge and discharge cycle (battery discharge capacity is C0), with an upper limit voltage of 4.1V. Then, it is subjected to 400 cycles of 1.0C / 1.0C charge and discharge at room temperature (battery discharge capacity is C1). The capacity retention rate is calculated.

[0036] Capacity retention rate = (C1 / C0) × 100% Ratio Performance Test : Under normal temperature (25℃) conditions, the battery is charged at a constant current of 0.5C to 4.1V, then charged at a constant voltage to 0.05C, and then discharged at a constant current of 0.5C to 2.5V, constituting one charge-discharge cycle. This charge-discharge cycle is repeated 3 times, with the discharge capacity of the last cycle being C0. Then, the battery is charged again at a constant current of 0.5C to 4.1V, then charged at a constant voltage to 0.05C, and finally discharged at a constant current of 3C to 2.5V, with a discharge capacity of C1. Calculate the capacity retention rate.

[0037] Capacity retention rate = (C1 / C0) × 100% Table 2 Performance test results of lithium-ion batteries

[0038] As can be seen from Table 2, compared with Comparative Examples 1 to 4, the lithium-ion batteries of Examples 1 to 8 have better room temperature cycle performance, high temperature cycle performance and rate performance because the electrolytes of Examples 1 to 8 use additives with special structures of the present invention. This may be because the additives preferentially form films at the positive and negative electrode interfaces, thereby improving the stability of the electrolyte-electrode interface.

[0039] A comparison of Examples 5 and Examples 11-14 shows that adding an additive to the basis of the additives of the present invention can further improve the cycle performance and rate performance of lithium-ion batteries. This may be because the additives participate in the film formation process of the negative electrode, making the SEI more compact and improving the electrochemical performance of lithium-ion batteries.

[0040] 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, it is not limited to those listed in the 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 nonaqueous electrolyte, characterized by comprising: The non-aqueous electrolyte comprises a lithium salt, a non-aqueous organic solvent, and an additive, wherein the additive comprises a compound A represented by a structural formula I: R1 is selected from substituted or unsubstituted C1-C6 alkyl, and amino having substituted or unsubstituted C1-C12 straight chain, branched chain or cyclic alkyl as a substituent.

2. The nonaqueous electrolyte according to claim 1, wherein R1 is selected from substituted or unsubstituted C1-C6 alkyl, and amino having substituted or unsubstituted C1-C6 straight chain, branched chain or cyclic alkyl as a substituent, and when substituted, the substituent is selected from halogen.

3. The nonaqueous electrolyte according to claim 1 or 2, wherein The compound A is selected from at least one of compounds 1-4: Compound 3 Compound 4.

4. The nonaqueous electrolyte according to claim 1 or 2, wherein The compound A accounts for 0.1%-5.0% of the sum of the mass of the lithium salt, the non-aqueous organic solvent and the additive.

5. The nonaqueous electrolyte according to claim 1 or 2, wherein The lithium salt comprises at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium methylsulfonate, lithium trifluoromethylsulfonate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium difluorophosphate and lithium difluorobisoxalate phosphate.

6. The nonaqueous electrolyte according to claim 1 or 2, wherein The mass of the lithium salt accounts for 5%-37.5% of the sum of the mass of the lithium salt, the non-aqueous organic solvent and the additive.

7. The nonaqueous electrolyte according to claim 1 or 2, wherein The non-aqueous organic solvent is selected from at least one of carbonate, carboxylic acid ester and ether compounds.

8. The nonaqueous electrolyte according to claim 1 or 2, wherein The additive further comprises an auxiliary agent selected from at least one of vinylene carbonate, vinylidene carbonate, fluoroethylene carbonate, vinyl sulfite, 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, vinyl sulfate, succinic anhydride, maleic anhydride, tetraethylenesilane, triallyl isocyanurate, hexamethylenediisocyanate, phenanthroline, p-phenylene diisocyanate, 2,4-toluene diisocyanate, methylsulfonate phenyl, bis-vinyl sulfate, hydroquinone difluorosulfonate, triallyl phosphate, tripropargyl phosphate, 2,4-butane sultone, isocyanatoethyl methacrylate, methanedisulfonate methylene, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate and tris(trimethylsilyl)phosphite.

9. The nonaqueous electrolyte according to claim 8, wherein The auxiliary agent accounts for 0.1%-5% of the sum of the mass of the lithium salt, the non-aqueous organic solvent and the additive.

10. A lithium ion battery comprising a positive electrode material and a negative electrode material, characterized in that, The non-aqueous electrolyte of any one of claims 1-9, wherein the positive electrode material is selected from a lithium manganese iron phosphate material.

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