High safety and long life high-energy lithium battery local high concentration electrolyte and application thereof

Abstract

This invention belongs to the field of lithium battery electrolyte technology, specifically relating to a high-safety, long-life, high-energy lithium battery locally high-concentration electrolyte and its application. The locally high-concentration electrolyte of this invention comprises lithium salt, solvent, and diluent, providing a battery-grade, highly safe lithium salt-solvent-diluent combination system. Adding additives further enhances the specific capacity and improves long-term cycle performance of the lithium battery. This locally high-concentration electrolyte not only significantly improves the overall safety performance of the lithium battery but also enables high-energy-density lithium-ion batteries to maintain high capacity and long lifespan under high-voltage (greater than 4.2V) charging cutoff voltage, making it highly valuable for applications in flame-retardant lithium batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery electrolyte technology. More specifically, it relates to a high-safety, long-life, high-energy lithium battery locally high-concentration electrolyte and its application. Background Technology

[0002] Traditional commercial lithium-ion batteries typically use electrolytes that dissolve lithium hexafluorophosphate in linear carbonates such as ethylene carbonate and methyl ethyl carbonate, and dimethyl carbonate. Due to the use of large amounts of organic solvents, conventional electrolyte systems are highly flammable. Furthermore, conventional electrolytes can undergo violent exothermic reactions with battery electrode materials under abnormal operating conditions (such as puncture, overheating, and overcharging), leading to battery thermal runaway. The flammability and high reactivity of conventional electrolytes are significant factors affecting the overall safety performance of batteries. Initially, to improve the safety performance of lithium-ion batteries, researchers introduced phosphorus-containing flame retardants to suppress battery flammability. However, while controlling battery flammability, the introduction of phosphorus-containing flame retardants also hindered the formation of the solid electrolyte interphase (SEI) at the graphite anode interface, resulting in a significant decrease in battery performance. Moreover, considering comprehensive battery-level safety performance, the reactivity between the electrolyte and electrode materials should be considered while achieving flame retardancy. To better achieve safety performance at high energy densities, it is necessary to develop a new and effective lithium-ion battery electrolyte system.

[0003] The emergence of locally high-concentration electrolytes (LHCEs) has solved the incompatibility problem between flame retardants and graphite anodes, making it possible to use flame retardants as the main solvent in electrolytes. Researchers have designed various flame retardant-based LHCEs, which not only achieve flame retardancy but also exhibit significantly better cycle life in lithium-ion batteries than conventional electrolytes. However, existing flame-retardant LHCEs mainly use lithium bis(fluorosulfonyl)imide and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether as lithium salts and diluents. Lithium bis(fluorosulfonyl)imide has been shown to undergo severe exothermic reactions with the electrodes, leading to battery thermal runaway. The exothermic reaction between the electrolyte and electrode materials at high temperatures is a more dangerous factor than the flammability of the electrolyte itself. For example, in their previous research (Jia H, Yang Z, Xu Y, et al. Is nonflammability of electrolyte overrated in the overall safety performance of lithium ion batteries? A sobering revelation from a completely nonflammable electrolyte[J]. Advanced Energy Materials, 2023, 13(4): 2203144.), the inventors prepared a dual flame retardant (DFR) electrolyte. Using lithium bis(fluorosulfonyl)imide as the lithium salt, trimethyl phosphate (TMPa) as the solvent, tris(2,2,2-trifluoroethyl) phosphite (TTFEPi) as the diluent, and ethylene carbonate (EC) as the additive, they achieved not only complete nonflammability of LHCE (its liquid and vapor phases are flame retardant) but also a solvated structure. Although this DFR electrolyte exhibits strict nonflammability, penetration and overheating tests indicate that, at the battery level, this DFR electrolyte is not as safe as traditional lithium battery electrolytes and cannot achieve battery-level safety performance. In other words, simply reducing the flammability of the electrolyte is far from enough to improve the safety performance of the battery; it is also necessary to consider reducing the reactivity between the electrolyte and the charging electrodes.

[0004] Therefore, it is necessary to explore and establish a richer lithium salt-solvent-diluent system to further expand the spectrum of LHCE and better achieve the organic combination of high energy density, long cycle life and high safety performance of lithium-ion batteries. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of existing flame-retardant LHCE, which, although achieving complete non-flammability, still undergo violent exothermic reactions with battery electrode materials under abnormal operating conditions (such as puncture, overheating, overcharging, etc.), leading to battery thermal runaway. The present invention provides a local high-concentration electrolyte for lithium batteries, which, while retaining the structural advantages of LHCE, reduces the reaction heat of LHCE and improves the safety performance at the battery level.

[0006] Another object of the present invention is to provide the application of the high-concentration electrolyte in the preparation of lithium-ion batteries.

[0007] Another object of the present invention is to provide a lithium-ion battery.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution:

[0009] This invention protects a locally high-concentration electrolyte for lithium batteries, the locally high-concentration electrolyte for lithium batteries comprising lithium salt, solvent, and diluent;

[0010] The solvent includes at least one of the following reagents: sulfolane, dimethyl sulfone, dimethyl sulfoxide, ethyl methyl sulfone, 3-methyl sulfolane, ethylene sulfite, ethyl isopropyl sulfone, trimethyl phosphate, tributyl phosphate, dimethyl methyl phosphate, ethylene ethyl phosphate, and trifluoroethyl methanesulfonate.

[0011] The diluent comprises at least one of the following reagents: tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) ethyl phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate, triphenyl phosphate, hexafluorocyclotriphosphazene, (trifluoroethoxy)pentafluorocyclotriphosphazene, (phenoxy)pentafluorocyclotriphosphazene, pentafluorophenyl diphenyl phosphate, and tris(pentafluorophenyl)phosphine;

[0012] The lithium salt does not include lithium bis(fluorosulfonyl)imide;

[0013] The diluent accounts for 30% to 80% of the mass of the locally high-concentration electrolyte in the lithium battery; the additive accounts for 0% to 20% of the mass of the locally high-concentration electrolyte in the lithium battery.

[0014] While existing flame-retardant lithium-ion batteries (LHCEs) achieve complete non-flammability, they still exhibit violent exothermic reactions with battery electrode materials under abnormal operating conditions (such as puncture, overheating, and overcharging), leading to battery thermal runaway. This invention develops a flame-retardant LHCE with low heat of reaction. It replaces lithium bisfluorosulfonylimide (LiFSI) with a low-heat lithium salt and explores compatible, safe, and stable solvents and diluents. These components synergistically produce an electrolyte with excellent electrochemical performance and high safety. The highly polar solvent and the low-heat lithium salt constitute a solvent sheath structure, promoting the formation of an effective SEI and improving the anodic stability of the electrolyte, thus achieving a long cycle life for high-energy lithium batteries. The diluent reduces electrolyte viscosity, facilitating electrolyte wetting of the separator and enhancing the flame-retardant properties of the electrolyte without interfering with the battery's long-cycle performance. Additives are only used to improve the formation of an effective SEI, further enhancing the battery's long-cycle performance; their addition or absence does not affect the solvent sheath structure or flame-retardant properties of the resulting electrolyte.

[0015] Preferably, the additive includes at least one of the following reagents: fluoroethylene carbonate, difluoroethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, ethylene ethylene carbonate, propylene carbonate, ethylene sulfate, and ethylene sulfite.

[0016] Preferably, the additive accounts for 0% to 20% of the mass of the locally high-concentration electrolyte in the lithium battery.

[0017] More preferably, the additive accounts for 1% to 10% of the mass of the locally high-concentration electrolyte in the lithium battery.

[0018] Preferably, the lithium salt comprises at least one of the following reagents: lithium tetrafluoroborate, lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(trifluoromethane)sulfonylimide, lithium difluorododecanoate, lithium tetra(trifluoromethyl)borate, lithium tetra(pentafluorophenyl)borate, lithium tetracyanoborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium trifluoromethanesulfonate, lithium methane disulfonate difluoroborate, lithium (2-fluoromalonate) difluoroborate, lithium dimalonate borate, lithium difluorophosphoroxytrifluoroborate, lithium bis(difluorophosphoroxy)difluoroborate, lithium tetra(difluorophosphoroxy)borate, lithium tetrafluorooxalate phosphate, and lithium tetrafluorodioxalate phosphate.

[0019] Preferably, the diluent accounts for 40% to 70% of the mass of the locally high-concentration electrolyte in the lithium battery.

[0020] Preferably, the solvent accounts for 20% to 70% of the mass of the high-concentration electrolyte in the lithium battery.

[0021] More preferably, the solvent accounts for 20% to 50% of the mass of the locally high-concentration electrolyte in the lithium battery.

[0022] Preferably, the lithium salt accounts for 5% to 20% of the mass of the locally high-concentration electrolyte in the lithium battery.

[0023] More preferably, the lithium salt accounts for 8% to 20% of the mass of the locally high-concentration electrolyte in the lithium battery.

[0024] Preferably, the concentration of lithium ions in the lithium salt in the high-concentration electrolyte of the lithium battery is 1-3 mol / L (M).

[0025] Furthermore, the molar ratio of the lithium salt, solvent, diluent, and additive is 1:(1-3):(1-3):(0-1).

[0026] Preferably, the molar ratio of the lithium salt, solvent, diluent, and additive is 1:(1-2.5):(1-2.5):(0-0.5).

[0027] This invention also protects the application of the locally high-concentration electrolyte in the preparation of lithium-ion batteries.

[0028] This invention also protects a lithium-ion battery, including a positive electrode, a negative electrode, and a locally high-concentration electrolyte of the lithium battery.

[0029] Compared with existing technologies, the present invention has the following beneficial effects: The locally high-concentration electrolyte for lithium batteries described in this invention comprises lithium salt, solvent, and diluent, providing a battery-grade, highly safe lithium salt-solvent-diluent combination system. Adding additives further enhances the specific capacity and long-term cycle performance of the lithium battery. This electrolyte not only significantly improves the overall safety performance of the lithium battery but also enables high-energy-density lithium-ion batteries to maintain high capacity and long lifespan under high-voltage (greater than 4.2V) charging cutoff voltage, making it widely applicable in flame-retardant lithium batteries. Attached Figure Description

[0030] Figure 1 The specific capacity performance curves of the batteries using the electrolyte prepared in Example 1 of this invention (referred to as E-SE-F), the electrolyte prepared in Example 3 (referred to as E-SE), and the conventional commercial electrolyte prepared in Comparative Example 1 (referred to as E-Baseline) as electrolytes for graphite||NMC lithium-ion batteries were obtained after 500 charge-discharge cycles at a charging rate of 0.33C and a discharging rate of 1C.

[0031] Figure 2This is a schematic diagram of the microscopic solvent sheath structure of Example 3 (Figure (a)) and Example 1 (Figure (b)) under molecular dynamics simulations of the present invention. Different atoms are distinguished by different colors: gray represents C; red represents O; green represents Li; pink represents B; cyan represents F; purple represents P; yellow represents S; and white represents H. For clearer observation, the diluent is simplified and shown as lines.

[0032] Figure 3 The figures show a comparison of the flammability of the conventional commercial electrolyte prepared in Comparative Example 1 (Figure (a)), the electrolyte prepared in Example 3 (Figure (b)), and the electrolyte prepared in Example 1 (Figure (c)), as well as a comparison of the combustion phenomena of the conventional commercial electrolyte (Figure (d)), the electrolyte prepared in Example 3 (Figure (e)), and the electrolyte prepared in Example 1 (Figure (f)) after the fire source was removed.

[0033] Figure 4 The diagram shows the needle penetration test phenomena of the electrolyte (E-SE-F) prepared in Example 1 of this invention in the application of battery-grade graphite||NMC soft-pack batteries, as well as the temperature and voltage change curves during the needle penetration test.

[0034] Figure 5 The needle penetration test phenomena of the conventional commercial electrolyte (E-Baseline) prepared for Comparative Example 1 in the application of battery-grade graphite||NMC pouch cells, and the temperature and voltage change curves in the needle penetration test. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0036] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0037] Electrolyte preparation was carried out in an argon-filled glove box at room temperature. The oxygen and water content in the glove box was maintained below 0.01 ppm.

[0038] Example 1: Preparation of locally high-concentration electrolyte for lithium batteries

[0039] Battery electrolyte preparation: Lithium tetrafluoroborate was dissolved in sulfolane at a lithium salt:solvent molar ratio of 1:2. After stirring overnight, tris(2,2,2-trifluoroethyl) phosphate, a diluent in an equal molar amount to lithium tetrafluoroborate, was added. Then, fluoroethylene carbonate, an additive in an amount equal to one-fifth the molar amount of lithium tetrafluoroborate, was added to form a safe electrolyte.

[0040] Of these, the lithium tetrafluoroborate comprises 13.4% (the concentration of lithium salt in the electrolyte is 2 mol / L) by mass percentage, sulfolane comprises 34.4%, tri(2,2,2-trifluoroethyl) phosphate comprises 49.2%, and fluoroethylene carbonate comprises 3.0%.

[0041] Example 2: Preparation of locally high-concentration electrolyte for lithium batteries

[0042] The difference from Example 1 lies in the different mass ratios of lithium salt, solvent, diluent, and additives. The specific preparation includes the following steps:

[0043] Battery electrolyte preparation: Lithium tetrafluoroborate was dissolved in sulfolane at a lithium salt:solvent molar ratio of 1:2. After stirring overnight, tris(2,2,2-trifluoroethyl) phosphate, a diluent in an equal molar amount to sulfolane, was added. Then, fluoroethylene carbonate, an additive in a molar amount equal to that of lithium tetrafluoroborate, was added to form a safe electrolyte.

[0044] Of these, the lithium tetrafluoroborate comprises 9.0% (2 mol / L lithium salt concentration in the electrolyte), sulfolane comprises 23.0%, tri(2,2,2-trifluoroethyl) phosphate comprises 66.0%, and fluoroethylene carbonate comprises 2.0% by mass percentage of the electrolyte.

[0045] Example 3: Preparation of Lithium-ion Battery Electrolyte

[0046] The difference from Example 1 is the absence of additives. The specific preparation includes the following steps:

[0047] Battery electrolyte preparation: Lithium tetrafluoroborate was dissolved in sulfolane at a lithium salt:solvent molar ratio of 1:2. After stirring overnight, an equimolar amount of tris(2,2,2-trifluoroethyl) phosphate was added to form a safe electrolyte. The electrolyte composition, by mass percentage, is as follows: lithium tetrafluoroborate 13.8% (lithium salt concentration in the electrolyte is 2 mol / L), sulfolane 35.5%, and tris(2,2,2-trifluoroethyl) phosphate 50.7%.

[0048] Comparative Example 1: Preparation of Conventional Lithium-ion Battery Electrolyte

[0049] Battery electrolyte preparation: Ethylene carbonate and ethyl methyl carbonate were mixed uniformly at a mass ratio of 3:7. The mixed solvent was added to a quantitative amount of lithium hexafluorophosphate and fully dissolved to form a conventional commercial electrolyte with a lithium salt concentration of 1 mol / L as a control group.

[0050] The preparation of the above-mentioned conventional commercial electrolyte, taking a 25mL specification as an example, is as follows:

[0051] Preparation of S1.EC / EMC solution: Ethyl carbonate and methyl ethyl carbonate are mixed uniformly at a mass ratio of 3:7 to obtain EC / EMC solution;

[0052] S2. Weigh 3.7978g of LiPF6, add a small amount of the EC / EMC solution obtained in step S1 to dissolve it, transfer it to a 25mL volumetric flask, and then add EC / EMC solution to make up to 25mL, thus forming a conventional commercial electrolyte with a lithium salt concentration of 1mol / L.

[0053] The electrolyte components and the proportion of each component in the electrolyte in the embodiments and comparative examples provided by the present invention are shown in Table 1.

[0054] Table 1 shows the electrolyte components and their mass percentage in the electrolyte in the embodiments provided by the present invention.

[0055]

[0056] Experiment 1: Preparation and Performance Testing of Lithium-ion Batteries

[0057] (1) Battery cycle performance test

[0058] The electrolytes obtained in Examples 1 and 3 were used as representative locally high-concentration electrolytes to further prepare lithium batteries for cycle performance testing.

[0059] Lithium-ion battery fabrication: 14mm diameter graphite electrodes and 12mm diameter NMC811 electrodes were vacuum-dried at 110°C for 12 hours, then transferred to an argon-filled glove box. Each coin cell was assembled from an NMC811 electrode, a 19mm diameter polypropylene separator, a graphite electrode, a gasket, a spring, and 50μL of electrolyte (the electrolytes prepared in Examples 1, 3, and Comparative Example 1). To prevent anodic corrosion of the stainless steel under high pressure, all coin cells used an aluminum-plated positive electrode shell and an additional 19mm diameter aluminum foil placed on top of the aluminum-plated positive electrode shell.

[0060] The button cells prepared above were placed in a temperature-controlled chamber (LONGYUE LBI-250) connected to a LAND battery testing system (CT2001A) and left to stand for 12 hours. After standing, the cells were subjected to one charge-discharge cycle at 0.05C, followed by two charge-discharge cycles at 0.1C to promote SEI formation. After SEI formation, the graphite||NMC811 cells were evaluated for long-term cycle performance by charging at 0.33C and discharging at 1C for 500 cycles, with the charge / discharge cutoff voltage controlled between 2.5V and 4.4V. The battery cycle life is as follows. Figure 1 As shown, in the long-term battery cycle test, after 500 cycles, the specific capacity and capacity retention of the battery in Example 3 (115.5 mAh / g, 66.2%) were the same as those of the lithium battery in Comparative Example 1 (116.0 mAh / g, 67.5%), since no additives were added. However, after adding a small amount of additives to Example 1, it was observed that the specific capacity and capacity retention of the battery (127.5 mAh / g, 70.1%) were significantly improved compared to Comparative Example 1 and Example 3.

[0061] The lithium battery prepared using the electrolyte obtained in Example 2 has a better specific capacity and capacity retention rate than Comparative Example 1, and has similar cycle performance as the lithium battery obtained in Example 1. These details will not be repeated here.

[0062] (2) Molecular dynamics calculations

[0063] Lithium salt, solvent, diluent, and additive molecules from Example 1 or Example 3 (without additives) were randomly inserted into a molecular dynamics simulation chamber according to experimental proportions and densities to construct the original structural model of the lithium salt / solvent / diluent / additive mixture system. All systems were pre-equilibrated for 5 ps and simulated for 50 ps with a time step of 1 fs. The results are illustrated in the diagram below. Figure 2 As shown, the lithium salt and solvent molecules in Example 3 of this invention have a tendency to form a solvation structure in the electrolyte, thereby forming a solvent sheath structure. Figure 2 (a) A locally high-concentration electrolyte, and after the introduction of a small amount of additives (Example 1), the solvent sheath structure of the locally high-concentration electrolyte can still remain intact. Figure 2 (b)).

[0064] (3) Flammability test

[0065] The electrolytes obtained in Examples 1 and 3 were used as representative high-concentration electrolytes for flammability testing.

[0066] The flammability of the electrolyte was determined by an ignition test. A 200 μL sample of electrolyte was dropped onto non-combustible glass fiber filter paper (Whatman, GF / D), and the sample was ignited with a butane flame for 1 second. The ignition and combustion phenomena of the electrolyte were continuously recorded using a digital camera. The flammability test results are as follows: Figure 3As shown in the figure, (a), (b), and (c) represent the flammability tests of Comparative Example 1, Example 3, and Example 1, respectively, while (d), (e), and (f) represent the phenomena of Comparative Example 1, Example 3, and Example 1 after the fire source was removed at the end of the test. It can be seen from the figure that the glass fiber paper with the electrolyte obtained from Comparative Example 1 was immediately ignited and continued to burn in the air, while the glass fiber paper with the electrolytes from Examples 1 and 3 could not be ignited by an external heat source, exhibiting a significant flame-retardant effect. Therefore, the additive is only used to improve the formation of the effective solid electrolyte interphase (SEI), enhancing the initial specific capacity and cycle performance of the battery, and is not related to the electrolyte solvent sheath structure or flame-retardant properties. Other properties of Example 3 are basically the same as those of Example 1.

[0067] (4) Needle penetration test of soft-pack battery

[0068] Using the electrolyte obtained in Example 1 as a representative locally high-concentration electrolyte, a needle penetration test was conducted on a soft-pack battery.

[0069] The electrolyte obtained in Example 1 or Comparative Example 1 was injected into a commercial graphite-NMC721 pouch cell (1.8Ah), charged to 4.3V using CCCV, and placed in a test chamber. A 3mm diameter steel nail was driven into the geometric center of the cell and held for at least 1 minute. During this time, the cell temperature and voltage were monitored by an electrochemical workstation and a temperature sensor, respectively. Real-time changes in temperature and voltage were continuously recorded for 10–20 minutes after penetration. The results of the pouch cell nail penetration experiment are as follows: Figure 4 , 5 As shown, the pouch battery of Example 1 passed the nail penetration test safely, while the pouch battery prepared in Comparative Example 1 immediately caught fire after being punctured. After puncture, the temperature change of the pouch battery of Example 1 was very small, remaining stable after rising from 32°C to 35°C, and the voltage value was also very stable. Except for some voltage fluctuations in the early stage of the test, the voltage value was consistently higher than 4.1V thereafter. Figure 4 In contrast, the temperature of the pouch cell prepared in Comparative Example 1 rapidly rose to a maximum of 514.3°C. After puncture, the cell short-circuited, and the voltage experienced a precipitous drop, immediately falling to 0V. Figure 5 ).

[0070] In their previous research (Jia H, Yang Z, Xu Y, et al. Is nonflammability of electrolyte overrated in the overall safety performance of lithium ion batteries? As a revelation from a completely nonflammable electrolyte [J]. Advanced Energy Materials, 2023, 13(4): 2203144.), the inventors' team prepared a dual flame retardant (DFR) electrolyte. They used lithium bis(fluorosulfonyl)imide as the lithium salt, trimethyl phosphate (TMPa) as the solvent, tris(2,2,2-trifluoroethyl) phosphite (TTFEPi) as the diluent, and ethylene carbonate (EC) as the additive. This not only achieved the complete nonflammability of LHCE (its liquid and vapor phases are flame retardant), but also achieved a solvated structure. Although the DFR electrolyte exhibits strict non-flammability, both penetration and overheating tests show that, at the battery level, it is less safe than conventional lithium-ion battery electrolytes (i.e., the electrolyte in Comparative Example 1) and fails to achieve battery-level safety performance. In contrast, the electrolyte of this application not only possesses excellent flame-retardant properties but also achieves battery-level safety performance, representing a significant advancement.

[0071] The pouch cell injected with the electrolyte obtained in Example 2 had essentially the same needle penetration test results as the pouch cell obtained in Example 1, and exhibited excellent battery-level safety performance, which will not be elaborated further here.

[0072] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A locally high-concentration electrolyte for lithium batteries, characterized in that, The high-concentration electrolyte in the lithium battery comprises lithium salt, solvent, diluent, and additives; The solvent is selected from at least one of the following reagents: sulfolane, dimethyl sulfone, dimethyl sulfoxide, ethyl methyl sulfone, and 3-methylsulfolane; The diluent is selected from at least one of the following reagents: tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) ethyl phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate, triphenyl phosphate, pentafluorophenyl diphenyl phosphate, and tris(pentafluorophenyl)phosphine. The lithium salt does not include lithium bis(fluorosulfonyl)imide; The lithium salt is selected from at least one of the following reagents: lithium tetrafluoroborate, lithium hexafluorophosphate, lithium difluorophosphate, dilithium fluorododecanoate, lithium tetra(trifluoromethyl)borate, lithium tetra(pentafluorophenyl)borate, lithium tetracyanoborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium trifluoromethanesulfonate, lithium methanedisulfonate difluoroborate, lithium (2-fluoromalonate) difluoroborate, lithium dimalonate borate, lithium difluorophosphoroxytrifluoroborate, lithium di(difluorophosphoroxy)difluoroborate, lithium tetra(difluorophosphoroxy)borate, lithium tetrafluorooxalate phosphate, lithium tetrafluorodioxalate phosphate. The additive is selected from at least one of the following reagents: fluoroethylene carbonate, difluoroethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, ethylene ethylene carbonate, propylene carbonate, ethylene sulfate, and ethylene sulfite. The diluent accounts for 40% to 70% of the mass of the high-concentration electrolyte in the lithium battery; the additive accounts for 0% to 20% of the mass of the high-concentration electrolyte in the lithium battery; the lithium salt accounts for 5% to 20% of the mass of the high-concentration electrolyte in the lithium battery; and the solvent accounts for 20% to 50% of the mass of the high-concentration electrolyte in the lithium battery.

2. The locally high-concentration electrolyte for a lithium battery according to claim 1, characterized in that, The concentration of lithium ions in the lithium salt in the high-concentration electrolyte of the lithium battery is 1~3 mol / L.

3. The locally high-concentration electrolyte for a lithium battery according to claim 1, characterized in that, The molar ratio of the lithium salt, solvent, diluent, and additive is 1:(1~3):(1~3):(0~1).

4. The application of the high-concentration electrolyte in the lithium battery as described in any one of claims 1 to 3 in the preparation of lithium-ion batteries.

5. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and a locally high-concentration electrolyte of the lithium battery as described in any one of claims 1 to 3.

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