Electrolyte for lithium battery, lithium battery and method for improving performance of high-temperature lithium battery

Abstract

The application provides a kind of electrolyte for lithium battery, it includes lithium salt and non-water organic solvent, wherein the lithium ion concentration in the electrolyte is 0.005-0.3mol / L.The application also provides a kind of lithium battery, it includes the electrolyte described in the application.The application also provides a kind of method for improving the performance of high temperature lithium battery, it includes the following steps: lithium salt and optional functional additives are added into non-water organic solvent, and electrolyte is prepared;Then, the lithium battery comprising the electrolyte is used in high temperature environment of 60-120 DEG C;Wherein, the lithium ion concentration in the electrolyte is 0.005-0.3mol / L.The lithium battery comprising the electrolyte of the application still has excellent performance such as high safety, high stability, high voltage, high rate, high specific energy and long cycle when it is operated in high temperature environment such as 60-120 DEG C.Meanwhile, the content of lithium ion in the lithium battery of the application is low, which can greatly reduce the economic cost.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials. Specifically, this invention relates to electrolytes for lithium batteries, lithium batteries, and methods for improving the performance of high-temperature lithium batteries. Background Technology

[0002] Lithium-ion batteries boast the highest energy density among all commercially available batteries and are widely used in consumer electronics, electric vehicles, and large-scale energy storage. In recent years, the rapid development of various industries has placed higher demands on battery lifespan, energy density, rate performance, and safety. The electrolyte plays a crucial role in lithium-ion batteries, serving as the carrier for ion transport and ensuring the batteries achieve their advantages of high safety, high voltage, high rate capability, high specific energy, and low cost.

[0003] Regarding battery safety: Safety is a fundamental need for human society. Lithium batteries inevitably experience thermal runaway during operation due to various reasons. Due to its chemical composition and battery configuration, the electrolyte is usually the first to decompose during thermal runaway, and it is also a key factor in inducing and amplifying the continued occurrence of thermal runaway. Therefore, researching safer electrolytes is of great significance.

[0004] Regarding battery costs: Battery costs directly determine consumers' willingness to buy, and the ongoing research and development costs of batteries also stem from consumer demand. The electrolyte is an essential component of a battery, and its cost accounts for the second largest proportion of the total battery cost, after the positive electrode active material. Therefore, developing lower-cost electrolytes is of great significance.

[0005] Regarding battery rate performance: Currently, the charging and discharging speed of lithium batteries in electric vehicles and consumer electronics is a major pain point for consumers. The rate corresponds to the charge and discharge rate of the battery, determining the time efficiency of production and daily life. Battery rate is affected by multiple factors, among which the electrolyte is a key factor. The conductivity of the electrolyte and the interface layer it forms are ways in which it affects rate performance.

[0006] Regarding battery voltage: The electrolyte acts as a bridge connecting the positive and negative electrodes. During charging and discharging, the electrolyte undergoes chemical or electrochemical decomposition on the surfaces of the positive and negative electrodes, generating a so-called solid electrolyte interphase (SEI) interface layer. The electrolyte's voltage window and the stability of the SEI interface determine the battery's voltage level, with the construction of the SEI interface largely depending on the selection of the electrolyte.

[0007] Regarding battery specific energy: A battery's energy density determines the amount of energy carried per unit mass or volume, which is another important consumer requirement. The choice and content of the electrolyte are crucial factors in determining battery energy density. Using an electrolyte with a wider voltage window and higher load density per unit volume, and reducing the total amount of electrolyte used, can effectively improve the overall energy density of the battery.

[0008] Currently, non-aqueous liquid electrolytes (NALEs) dominate the market and are the most widely used in commercially available lithium batteries. NLEs are typically composed of organic solvents and lithium salts, and to achieve functions such as good SEI (Sediment Injection), improved conductivity, overcharge protection, prevention of electrolyte combustion, and improved wettability, additives are often added.

[0009] Common organic solvents in non-aqueous liquid electrolytes include several major categories such as carbonates (cyclic and chain), carboxylic acid esters, and ethers. Lithium salts include inorganic and organic lithium salts. Additives also include inorganic and organic additives, and can be classified according to function as film-forming additives, conductive additives, flame-retardant additives, voltage-limiting additives (overcharge protection additives), and multifunctional additives. Electrolyte concentration is also an important parameter.

[0010] Suo Liumin et al. developed an electrolyte with a high salt concentration (up to 21 mol / L). However, high-salt-concentration electrolytes are prone to a phenomenon where, with increasing lithium salt concentration, the electrolyte conductivity initially increases and then decreases, while the viscosity continuously increases, leading to increased battery polarization and performance degradation. Furthermore, increasing the lithium salt ratio also results in a significant increase in cost.

[0011] The lithium-ion concentration in the electrolyte of currently commercially available lithium batteries is approximately 1 mol / L. Current lithium batteries exhibit poor performance at high temperatures (60-120℃), including issues with cycle life, rate capability, and stability. Current methods to improve the high-temperature performance of lithium-ion batteries focus on the selection of electrolyte components, such as finding solvents with high melting points, lithium salts with high thermal stability, or high-temperature additives.

[0012] There is an urgent need for a lithium-ion battery that can perform well at high temperatures (60-120℃), such as high safety, high voltage, high rate and high specific energy, while also being low in cost. Summary of the Invention

[0013] The purpose of this invention is to provide an electrolyte for lithium batteries, a lithium battery, and a method for improving the performance of high-temperature lithium batteries. The lithium battery of this invention can reduce economic costs while exhibiting excellent performance at high temperatures, such as high safety, high voltage, high rate capability, and high specific energy.

[0014] The above-mentioned objective of the present invention is achieved through the following technical solution.

[0015] In the context of this invention, the term "lithium battery" includes lithium metal batteries and lithium-ion batteries.

[0016] During their research, the inventors unexpectedly discovered that high lithium-ion concentrations, such as 1 mol / L, not only resulted in insufficient electrolyte costs but also led to poor performance at high temperatures (60-120°C), particularly in terms of cycle life, rate capability, and stability. Lithium batteries with such high lithium-ion concentrations (1 mol / L and above) typically operate within a narrow temperature range (-20 to 55°C) and are not suitable for high-temperature conditions. Conversely, the inventors also unexpectedly discovered that reducing the lithium-ion concentration to below 0.3 mol / L improved the performance of lithium batteries at high temperatures, resulting in higher safety, higher energy density, and higher rate capability.

[0017] In a first aspect, the present invention provides an electrolyte for lithium batteries, comprising a lithium salt and a non-aqueous organic solvent, wherein the lithium ion concentration in the electrolyte is 0.005-0.3 mol / L.

[0018] Preferably, in the electrolyte for lithium batteries of the present invention, the lithium ion concentration is 0.005-0.2 mol / L, more preferably 0.005-0.1 mol / L.

[0019] Preferably, in the electrolyte for lithium batteries of the present invention, the lithium salt is selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluorotantalate (LiTaF6), lithium hexafluorostannate (LiSnF6), lithium hexafluorogermanate (LiGeF6), lithium sulfate (Li2SO4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium nitrate (LiNO3), lithium tetraaluminohalate LiAlX4 (X is a halogen), lithium tri(catechol)phosphate (LTBP), Li(C2O4)3P (LiTOP), Li(CO2)2PF4 (LiTFOP), Li(C3F7)PF3, and bis(trimethylsilylamine). Lithium (LiHMDS), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate (LiCF3SO3), tri(trifluoromethanesulfonyl)methyl lithium (LiC(SO2CF3)3), lithium bis(perfluoroethylsulfonyl)imide (LiBETI), lithium (trifluoromethanesulfonyl)(n-perfluorobutylsulfonyl)imide (LiTNFSI), lithium (trifluoromethanesulfonyl)(fluorosulfonyl)imide (LiFTFSI), LiC2F6(SO2)N (LiFPFSI), lithium (sulfonamide)(n-perfluorobutylsulfonyl)imide (LiFNFSI), lithium thiocyanate (LiSCN), LiC8F 18(SO2)2N(LiFHFSI), LiBF3(CF2CF3)3(LiFAB), Lithium tri(pentafluoroethyl)trifluorophosphate (LiPF3(CF2CF3)3, LiFAP), Lithium bis(oxalate)borate (LiBOB), Lithium difluorooxalate borate (LiDFOB), Lithium dimalonate borate (LiBMB), Lithium bis(catechol)borate (LBBB), Lithium bis(3-fluorocatechol)borate (3-FLBBB), Lithium bis(2,3,4,5-tetrafluorocatechol)borate (TFLBBB), Lithium bis(salicylic acid)borate (LBSB), Lithium bis(2,3-naphthyldiol)borate (LBNB), Lithium bis(2,2'-biphenyl)borate (LBBPB), Lithium bis(2,3-pyridinyldioxy)borate (LBPB), Li(C6F 12 At least one of O2)2B (LBPFPB), LiC7H2O3Cl2B (DCLBSB), Li(C8H6O3)2B (3-MLBSB) and Li(C7HO3Cl3)2B (TCLBSB).

[0020] Preferably, in the electrolyte for lithium batteries of the present invention, the non-aqueous organic solvent is a carbonate; more preferably, the non-aqueous organic solvent is at least two kinds of carbonates.

[0021] Preferably, in the electrolyte for lithium batteries described in this invention, the non-aqueous organic solvent is selected from dialkyl carbonate, tributyl carbonate, ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BC), vinylene carbonate (VC), ethylene sulfite (ES), dimethyl sulfite (DMS), diethyl sulfite (DES), dibutyl carbonate (DBC), dibutyl carbonate (GBL), methyl butyl carbonate (BMC), dipropyl carbonate (DPC), methyl ester (PA), propylene sulfite (PS), γ-butyrolactone (γBL), γ-valerolactone (γVL), ethylene ethylene carbonate (VEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), fluoroethylene carbonate (FEC), dimethyl pyrocarbonate (DMPC), dioxolane (DOL), ethylene glycol dimethyl ether (DME), dimethoxymethane (DMM), ethylene glycol diethyl ether (DEE), tetraethylene glycol diethyl ether, etc. Dimethyl alcohol ether (TEGDME), methyl propyl carbonate (MPC), isopropyl methyl carbonate (MiPC), methyl formate (MF), ethyl formate (EF), methyl acetate (MA), ethyl acetate (EA), methyl propionate (MP), ethyl propionate (EP), ethyl butyrate (EB), fluorobenzene (FB), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2Me-THF), tetrahydropyran (THP), diethylene glycol dimethyl ether / diethylene glycol dimethyl ether (DGDME) At least one of the following: acetonitrile (AN), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), sulfolane (SL), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), 3,3,3-trifluoropropylmethyl sulfone (FPMS), 1,3-dioxolane (1,3-DL), 4-methyl-1,3-dioxolane (4-Me-1,3-DL), 2-methyl-1,3-dioxolane (2Me-1,3-DL), and acetone.

[0022] Preferably, in the lithium battery electrolyte of the present invention, the electrolyte further includes functional additives. In the present invention, functional additives can improve the electrochemical performance of the electrolyte, such as increasing the wettability of the electrodes, separator, and electrolyte, providing overcharge protection, and improving the cycle performance or safety performance of the battery.

[0023] Preferably, in the electrolyte for lithium batteries described in this invention, the functional additive is selected from vinyl sulfate (DTD), propylene sulfate (TMS), butene sulfite (BS), 4-methylethylene sulfate, 4-methylethylene sulfite, 4-methylethylene sulfite, 1,3-propanesulfonate lactone (1,3-PS), 1,4-butanesulfonate lactone (1,4-BS), 1,3-(1-propene)sulfonate lactone (PTS), diethyl(cyanomethyl)phosphonate (DECP), methanedisulfonate methylene (CDE), cyclohexylbenzene (C HB), hydrogenated biphenyl oxide, tris(trimethylsilane)phosphonite (TMSPi), tris(trimethylsilane)borate (TMSB), N,N'-dimethyltrifluoroacetamide (DTA), tert-butylbenzene, adiponitrile (ADN), succinic anion (SN), 3-hexenedionitrile (DCB), 1,2-bis(2-cyanoethoxy)ethane (BCN), 1,3-phenyleneacetonitrile (PEN), sulfur dioxide (SO2), carbon dioxide (CO2), lithium fluoride (LiF), lithium carbonate (Li2CO3), lithium nitrate (LiNO3), high chlorine Potassium perchlorate (KClO4), sodium perchlorate (NaClO4), propenyl-1,3-sulfonyl lactone (PRS), lithium sulfide (Li2S), lithium sulfite (Li2SO3), lithium sulfate (Li2SO4), dihexyl borate (BEG), trimethoxyborane, trimethylborane, TEG, biphenyl (BP), phenylacetone, anisole, 4-methyl-o-dimethoxybenzene, 4-fluorosubstituted o-dimethoxybenzene, 2,3,5,6-tetramethyl-p-dimethoxybenzene, 2,6-di-tert-butyl-1,4-benzoquinone, o-diphenylbenzene (OTP), N 2,5-Methylpyrrole (MPL), 1,2-diphenylethane (DBZ), diphenyl ether (DPE), 2,5-di-tert-butyl-1,4-benzoquinone (DDB), 4-tert-butyl-o-dimethoxybenzene (TDB), trimethyl phosphate (TMP), triethyl phosphate (TEP), triphenyl phosphate (TPP), tributyl phosphate (TBP), tris(2,2,2-trifluoroethyl) phosphate (TFP), (2,2,2-trifluoroethyl)diethyl phosphate (TDP), 3-(2,2,2-trifluoro)ethoxyphosphide (TTFP), di(2,2,2-trifluoro)ethoxyphosphide, ...2-Trifluoroethyl)methyl phosphate (BMP), hexamethylphosphonon (HMPN), methyl difluoroacetate (MFA), ethyl difluoroacetate (EFA), methyl fluorobutyl ether (MFE), potassium perfluorobutyl sulfonate (PNB), trifluoromethyl phosphorous acid (TTFP), methyl chloroformate, fluoromethyl vinyl carbonate, difluoromethyl vinyl carbonate, trifluoromethyl vinyl carbonate, fluoroacetoethane, bromobutyrolactone (Br-BL), N-methyl-2-pyrrolidine The following are included: at least one of the following: ketone (NMP), fluorinated carbamate, hexamethylphosphoramide (HMPA), pyridine, ethanolamine, tributylamine, 4-phenylbutylamine, thiocyanate, vinyl acetate (VA), divinyl adipate (ADV), allyl methyl carbonate (AMC), 4-(N,N-dimethylamino)pyridine (DMAP), 12-crown-4-ether, 18-crown-6-ether, heptamethyldisilazane, fluorinated ether, silane compound, trialkyl phosphate, and trioctyl phosphate.

[0024] In a preferred embodiment of the present invention, the electrolyte has the following composition: the solvent is ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), and the lithium salt is LiFSI; meanwhile, the lithium ion concentration is controlled at 0.005-0.1 mol / L. This electrolyte composition exhibits excellent performance, particularly at high temperatures such as 60-120°C, including high safety, high stability, high voltage, high rate capability, high specific energy, and long cycling performance.

[0025] In a second aspect, the present invention also provides a lithium battery comprising a positive current collector, a positive active material, a negative current collector, a negative active material, a separator, and an electrolyte as described in any one of claims 1-7.

[0026] Preferably, in the lithium battery of the present invention, the positive electrode active material is a lithium-containing positive electrode active material and / or a lithium-free positive electrode active material;

[0027] Preferably, in the lithium battery of the present invention, the positive electrode active material is a lithium-containing positive electrode active material and / or a lithium-free positive electrode active material.

[0028] Preferably, in the lithium battery of the present invention, the lithium-containing positive electrode active material is selected from one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich layered oxide, lithium nickel manganese oxide, and lithium titanate.

[0029] Preferably, in the lithium battery of the present invention, the lithium-free positive electrode active material is selected from one or more of fluorinated graphite, manganese dioxide (MnO2), ferrous disulfide (FeS2), ferric fluoride (FeF3), sulfur (S), water (H2O), carbon dioxide (CO2), and oxygen (O2).

[0030] Preferably, in the lithium battery of the present invention, the negative electrode active material is selected from lithium titanate (Li4Ti5O4). 12 One or more of the following: highly definite pyrolytic graphite, artificial graphite, natural graphite, graphitized carbon fiber, graphitized mesophase carbon microspheres, hard carbon, soft carbon, carbon nanotubes, graphene and graphene composites, silicon, silicon suboxide, silicon-carbon composites, lithium metal, lithium alloys, composite lithium metal, tin-based compounds, tin oxides and molybdenum disulfide (MoS2).

[0031] Preferably, in the lithium battery of the present invention, the separator is selected from one or more of polyethylene (PE) separator, polypropylene (PP) separator, double-layer or multi-layer polyethylene and polypropylene composite separator, polyaramid separator, cellulose separator, polyvinylidene fluoride (PVDF) separator and polyimide (PI) separator.

[0032] Thirdly, the present invention provides a method for improving the performance of high-temperature lithium batteries, comprising the following steps:

[0033] An electrolyte is prepared by adding lithium salt and optional functional additives to a non-aqueous organic solvent; then, a lithium battery containing the electrolyte is used in a high-temperature environment of 60-120°C; wherein the lithium ion concentration in the electrolyte is 0.005-0.3 mol / L.

[0034] The present invention has the following beneficial effects:

[0035] Lithium batteries containing the electrolyte of this invention maintain excellent performance, such as high safety, high stability, high voltage, high rate capability, high specific energy, and long cycle life, even when operating in high-temperature environments such as 60-120°C. Furthermore, the lithium-ion content of the lithium batteries of this invention is low, which can significantly reduce economic costs.

[0036] Lithium batteries containing the electrolyte of this invention still exhibit good interface stability, excellent rate performance, and high conductivity over a wide temperature range, even in high-temperature environments such as 60-120°C, and have good wettability to the electrodes. Attached Figure Description

[0037] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0038] Figure 1 The temperature-dependent conductivity curve of the electrolyte in Example 1 of the present invention;

[0039] Figure 2 This is a graph showing the cycle capacity decay of the lithium battery in Example 3 of the present invention at a high temperature of 90°C.

[0040] Figure 3This is a rate test diagram of the lithium battery in Example 3 of the present invention at a high temperature of 90°C. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0042] Example 1

[0043] An electrolyte for high-temperature use comprises ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) as solvents, and LiTFSI as the lithium salt. EC, DMC, and DEC are mixed in a volume ratio of 1:1:1, and then LiTFSI is added to achieve a lithium ion concentration of 0.1 mol / L. The conductivity of the electrolyte is then measured at different temperatures using a conductivity meter with a fixed area and distance, yielding temperature-varying conductivity curves as shown below. Figure 1 As shown.

[0044] Example 2

[0045] An electrolyte for high-temperature use is disclosed, comprising ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) as solvents, and LiTFSI as the lithium salt. EC, DMC, and EMC are mixed in a 1:1:1 volume ratio, and then LiTFSI is added to achieve a lithium-ion concentration of 0.2 mol / L. This electrolyte is then matched with graphite and LiCoO2 electrodes to assemble a lithium-ion battery. Cycling at 60°C and a 0.5C rate reveals good cycle performance, with 72% of the initial capacity retained after 550 cycles.

[0046] Example 3

[0047] An electrolyte for high-temperature use comprises ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) as solvents, and LiFSI as the lithium salt. EC, DMC, and DEC are mixed in a volume ratio of 1:1:1, and then LiFSI is added to achieve a lithium-ion concentration of 0.1 mol / L. This electrolyte is then matched with Li₄Ti₅O₂. 12 Electrodes are assembled into a lithium-ion battery. Good cycle performance was observed when cycling at 90°C with an initial rate of 0.2C followed by 1C. Figure 2 As shown, the capacity remains at 80% after 170 cycles. Rate testing of the lithium battery revealed good performance from 0.1C to 5C, as shown in the results. Figure 3 As shown.

[0048] Example 4

[0049] An electrolyte for high-temperature use employs ethylene carbonate (EC) and diethyl carbonate (DEC) as solvents, with LiFSI as the lithium salt. EC and DEC are mixed in a 1:1 volume ratio, and then LiFSI is added to achieve a lithium-ion concentration of 0.1 mol / L. This electrolyte is matched with a silicon-carbon composite anode and a LiFePO4 cathode to assemble a lithium-ion battery. Cycling at 80°C at a rate of 0.2C for the first cycle and then 0.5C for the next cycle showed good cycle performance, retaining 80% of the capacity after 630 cycles.

[0050] Example 5

[0051] An electrolyte for high-temperature use is disclosed. The solvents used are dimethyl ethylene glycol (DME) and dioxolane (DOL), with LiFSI and LiTFSI as lithium salts and LiNO3 as an additive. DOL and DME are mixed at a volume ratio of 1:1, followed by the addition of LiFSI, LiTFSI, and LiNO3. The concentrations of LiFSI and LiTFSI are each 0.1 mol / L, and the concentration of LiNO3 is 0.01 mol / L, resulting in a final overall lithium-ion concentration of 0.21 mol / L in the electrolyte. This electrolyte is then matched with a sulfur-carbon composite positive electrode and a lithium metal negative electrode to assemble a lithium-sulfur battery. Cycling at 60°C at a rate of 0.1C for the first cycle and then 0.2C for the next cycle showed good cycle performance, retaining 72% of the capacity after 350 cycles.

[0052] Example 6

[0053] An electrolyte for high-temperature use is disclosed. The solvents used are dimethyl carbonate (DMC) and dioxolane (DOL), the lithium salts are LiDFOB and LiTFSI, and the additives are FEC and VC. DOL and DMC are mixed at a volume ratio of 1:1, then LiDFOB, LiTFSI, FEC, and VC are added. The volume ratio of FEC and VC to the solvent is 1:50. The concentrations of LiDFOB and LiTFSI are each 0.1 mol / L, resulting in a final overall lithium-ion concentration of 0.2 mol / L in the electrolyte. This electrolyte is matched with a positive electrode using LiCoO2 and a negative electrode using metallic lithium to assemble a lithium metal battery. Cycling at 70°C at a rate of 0.1C for the first cycle and then 0.5C for the next cycle shows good cycle performance, retaining 77% of the capacity after 650 cycles.

[0054] Example 7

[0055] An electrolyte for high-temperature use is disclosed. The solvents used are dimethyl carbonate (DMC) and dioxolane (DOL), the lithium salts are LiBOB and LiTFSI, and the additives are ES and CHB. DOL and DMC are mixed at a volume ratio of 1:1, then LiBOB, LiTFSI, ES, and CHB are added. The volume ratio of ES and CHB to the solvent is 1:50. The concentrations of LiBOB and LiTFSI are each 0.8 mol / L, resulting in an overall lithium-ion concentration of 0.2 mol / L in the electrolyte. This electrolyte is matched with a positive electrode using LiCoO2 and a negative electrode using metallic lithium to assemble a lithium metal battery. Cycling at 90°C at a rate of 0.1C for the first cycle and then 1C for the next cycle shows good cycle performance, retaining 82% of the capacity after 500 cycles.

[0056] Example 8

[0057] An electrolyte for high-temperature use is disclosed, comprising ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) as solvents, and LiFNFSI as the lithium salt. EC, DMC, and EMC are mixed in a volume ratio of 0.35:0.3:0.35, and then LiFNFSI is added to achieve a lithium-ion concentration of 0.5 mol / L. This electrolyte is then matched with graphite and LiCoO2 electrodes to assemble a lithium-ion battery. Cycling at 0.5C at room temperature reveals good cycle performance, with 85% of the initial capacity retained after 550 cycles.

[0058] Example 9

[0059] An electrolyte for high-temperature use is disclosed. The solvents used are propylene carbonate (PC) and ethylene carbonate (EC), with LiPF6 as the lithium salt and BP as the additive. EC and PC are mixed at a volume ratio of 1:1, and then LiPF6 is added to achieve a lithium-ion concentration of 0.1 mol / L. This electrolyte is then matched with graphite and LiCoO2 electrodes to assemble a lithium-ion battery. Cycling at 60°C and a 0.5C rate revealed good cycle performance, with the capacity retaining 81% of the initial capacity after 750 cycles.

[0060] Example 10

[0061] An electrolyte for high-temperature use is disclosed. The solvents used are propylene carbonate (PC) and ethylene carbonate (EC), with LiAlCl4 as the lithium salt and CHB as the additive. EC and PC are mixed in a 1:1 volume ratio, and then LiAlCl4 is added to achieve a lithium-ion concentration of 0.3 mol / L. This electrolyte is then matched with graphite and LiNi. 1 / 3 Mn 1 / 3 Co1 / 3 An O2 electrode was used to assemble a lithium-ion battery. It exhibited good cycle performance at 80°C and a 2C rate, retaining 80% of its initial capacity after 450 cycles.

[0062] Example 11

[0063] An electrolyte for high-temperature use is disclosed. The solvents used are diethyl carbonate (DEC) and ethylene carbonate (EC), with LiBF4 as the lithium salt and CHB as the additive. EC and DEC are mixed in a 1:1 volume ratio, and then LiBF4 is added to achieve a lithium-ion concentration of 0.2 mol / L. This electrolyte is then matched with metallic lithium and LiNi. 1 / 3 Mn 1 / 3 Co 1 / 3 The O2 electrode is assembled into a lithium battery. After formation at 70°C and a 0.2C rate, it retains 80% of its initial capacity after 450 cycles at room temperature.

[0064] Example 12

[0065] An electrolyte for high-temperature use is disclosed. The solvents used are diethyl carbonate (DEC) and ethylene carbonate (EC), with LiFSI as the lithium salt and ADN as the additive. EC and DEC are mixed at a volume ratio of 1:1, and then LiFSI is added to achieve a lithium-ion concentration of 0.1 mol / L. This electrolyte is then matched with lithium metal and LiFePO4 electrodes to assemble a lithium battery. After formation at 70°C and a 0.1C rate, the battery retains 75% of its initial capacity after 480 cycles at 90°C.

[0066] Example 13

[0067] An electrolyte for high-temperature use is disclosed. The solvents used are ethyl methyl carbonate (EMC) and ethylene carbonate (EC), with LiTFSI as the lithium salt and VA as the additive. EC and EMC are mixed at a 1:1 volume ratio, and then LiTFSI is added to achieve a lithium-ion concentration of 0.05 mol / L. This electrolyte is then matched with metallic lithium and LiNi. 1 / 2 Mn 1 / 2 An O2 electrode is used to assemble a lithium battery. After 380 cycles at 90°C, the battery retains 75% of its initial capacity.

[0068] Example 14

[0069] An electrolyte for high-temperature use is disclosed. The solvents used are ethyl methyl carbonate (EMC) and ethylene carbonate (EC), with LiClO4 as the lithium salt and PS and LiF as additives. EC and EMC are mixed at a volume ratio of 1:1, and then LiClO4 is added to achieve a lithium-ion concentration of 0.6 mol / L. This electrolyte is then matched with metallic lithium and LiNi. 1 / 2 Mn 1 / 2 An O2 electrode is used to assemble a lithium battery. After 395 cycles at 60°C, the battery retains 81% of its initial capacity.

[0070] Example 15

[0071] An electrolyte for high-temperature use is disclosed. The solvents used are dimethyl carbonate (DMC) and ethylene carbonate (EC), with LiFAP selected as the lithium salt and PRS as the additive. EC and DMC are mixed at a volume ratio of 1:1, and then LiFAP is added to achieve a lithium-ion concentration of 0.3 mol / L. This electrolyte is then matched with metallic lithium and LiNi. 0.8 Mn 0.1 Co 0.1 An O2 electrode is used to assemble a lithium battery. After cycling at 100°C for 428 cycles, the battery retains 85% of its initial capacity.

[0072] Example 16

[0073] An electrolyte for high-temperature use is disclosed. The solvents used are tetraethylene glycol dimethyl ether (TEGDME) and dioxolane (DOL). LiFNFSI and LiTFSI are selected as lithium salts, and LiBOB is selected as the additive. DOL and DME are mixed at a volume ratio of 1:1, and then LiFNFSI, LiTFSI, and LiBOB are added. The concentrations of LiFNFSI and LiTFSI are each 0.1 mol / L, and the concentration of LiBOB is 0.01 mol / L, resulting in a final overall lithium-ion concentration of 0.21 mol / L in the electrolyte. This electrolyte is matched with a positive electrode using LiCoO2 as the positive active material and a negative electrode using metallic lithium as the negative active material to assemble a lithium battery. Cycling at 85°C at a rate of 0.1C for the first cycle and then 1C for the next cycle showed good cycle performance, retaining 82% of the capacity after 550 cycles.

[0074] Example 17

[0075] An electrolyte for high-temperature use is disclosed. The solvents used are dimethyl carbonate (DMC) and vinylene carbonate (VC), the lithium salt is lithium hexafluorophosphate (LiPF6), and the additive is FEC. VC and DMC are mixed at a volume ratio of 1:1, and then lithium hexafluorophosphate (LiPF6) is added to achieve a lithium-ion concentration of 0.02 mol / L. This electrolyte is then matched with metallic lithium and LiNi. 0.8 Mn 0.1 Co 0.1 An O2 electrode is used to assemble a lithium battery. After formation at a high temperature of 90°C, the battery retains 81% of its initial capacity after 453 cycles.

[0076] Example 18

[0077] An electrolyte for high-temperature use is disclosed. The solvents used are tetraethylene glycol dimethyl ether (TEGDME) and dioxolane (DEE). LiBETI and LiTFSI are selected as lithium salts, and LiDFOB is selected as the additive. DOL and DME are mixed at a volume ratio of 1:1, and then LiBETI, LiTFSI, and LiDFOB are added. The concentrations of LiBETI and LiTFSI are each 0.05 mol / L, and the concentration of LiDFOB is 0.02 mol / L, resulting in a final overall lithium ion concentration of 0.12 mol / L in the electrolyte. This electrolyte is matched with a positive electrode using LiMn₂O₄ as the positive electrode active material and a negative electrode using metallic lithium as the negative electrode active material to assemble a lithium battery. Cycling at 75°C at a rate of 0.2C for the first cycle and then 1C for the next cycle shows good cycle performance, retaining 80% of the capacity after 500 cycles.

[0078] Comparative Example 1

[0079] This comparative example is compared with Example 3.

[0080] The electrolyte uses three solvents: ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), with LiFSI selected as the lithium salt. EC, DMC, and DEC are mixed in a 1:1:1 volume ratio, and then LiFSI is added to achieve a lithium ion concentration of 1 mol / L. This electrolyte is then matched with Li₄Ti₅O₂. 12 Electrodes were assembled into lithium-ion batteries. Cycling at 90°C with an initial rate of 0.2C followed by 1C revealed poor cycle performance; after 50 cycles, the capacity was less than 40%. When LiFSI was added to 5 mol / L, the same battery system showed a capacity decay to 22.5% after 25 cycles. Electrolytes of 1 mol / L and 5 mol / L concentrations were then assembled into Li₄Ti₅O₂ batteries. 12After conducting rate tests on the battery, it was found that the capacity decay was significant from 0.1C to 5C. In particular, the capacity of the 5 mol / L electrolyte decreased to half that of the 0.1 mol / L electrolyte at the 5C rate.

[0081] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above description is only a specific embodiment of this application and is not intended to limit the scope of protection of this invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for improving the performance of high-temperature lithium batteries, comprising the following steps: An electrolyte is prepared by adding lithium salt and functional additives to a non-aqueous organic solvent. Then, the lithium battery containing the electrolyte is used in a high-temperature environment of 90-120°C; wherein, The lithium ion concentration in the electrolyte is 0.005-0.3 mol / L; The non-aqueous organic solvent is a mixture of dimethyl carbonate and ethylene carbonate; The lithium salt is lithium tri(pentafluoroethyl) trifluorophosphate; The functional additive is propylene-1,3-sulfonyl lactone.

2. The method for improving the performance of high-temperature lithium batteries according to claim 1, wherein, The lithium ion concentration is 0.005-0.2 mol / L.

3. The method for improving the performance of high-temperature lithium batteries according to claim 2, wherein, The lithium ion concentration is 0.005-0.1 mol / L.

4. The method for improving the performance of high-temperature lithium batteries according to claim 1, wherein, The lithium battery includes a positive current collector, a positive active material, a negative current collector, a negative active material, a separator, and the electrolyte.

5. The method for improving the performance of high-temperature lithium batteries according to claim 4, wherein, The positive electrode active material is a lithium-containing positive electrode active material and / or a lithium-free positive electrode active material.

6. The method for improving the performance of high-temperature lithium batteries according to claim 5, wherein, The lithium-containing positive electrode active material is selected from one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich layered oxide, lithium nickel manganese oxide, and lithium titanate.

7. The method for improving the performance of high-temperature lithium batteries according to claim 5, wherein, The lithium-free positive electrode active material is selected from one or more of fluorinated graphite, manganese dioxide, ferrous disulfide, ferric fluoride, sulfur, water vapor, carbon dioxide, and oxygen.

8. The method for improving the performance of high-temperature lithium batteries according to claim 4, wherein, The negative electrode active material is selected from one or more of lithium titanate, highly stabilized pyrolytic graphite, artificial graphite, natural graphite, graphitized carbon fiber, graphitized mesophase carbon microspheres, hard carbon, soft carbon, carbon nanotubes, graphene and graphene composite materials, silicon, silicon suboxide, silicon-carbon composite materials, lithium metal, lithium alloys, composite lithium metal, tin-based compounds, tin oxides, and molybdenum disulfide.

9. The method for improving the performance of high-temperature lithium batteries according to claim 4, wherein, The diaphragm is selected from one or more of polyethylene diaphragms, polypropylene diaphragms, double-layer or multi-layer polyethylene and polypropylene composite diaphragms, polyaramid diaphragms, cellulose diaphragms, polyvinylidene fluoride diaphragms, and polyimide diaphragms.

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