A high-safety, flame-retardant lithium-ion battery electrolyte with a low reactive coordination structure

Abstract

This invention provides a high-safety, flame-retardant lithium-ion battery electrolyte with a low-reactivity coordination structure, relating to the field of energy storage battery technology. By employing a highly stable bis(fluorosulfonyl)imide lithium salt as the lithium salt, an ether solvent with weak solvation capability as a secondary solvent, and adding additives, the high-safety, flame-retardant lithium-ion battery electrolyte with a low-reactivity coordination structure is constructed by replacing the highly reactive components in traditional electrolytes with a low-reactivity solvent and a high-stability salt, and by controlling the ratio of lithium salt, solvent, and additives. This significantly improves the thermal safety of the battery. The electrolyte effectively suppresses the self-generating heat reaction rate and combustible gas generation at the electrolyte-electrode interface, increases the battery's thermal failure initiation temperature and trigger temperature, reduces the maximum thermal runaway temperature, and substantially improves the intrinsic thermal safety of high-energy-density lithium-ion batteries, making it suitable for high-energy-density lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of energy storage battery technology, and specifically to a high-safety, flame-retardant lithium-ion battery electrolyte with a low-reactivity coordination structure. Background Technology

[0002] Lithium-ion batteries are widely used in portable devices, electric vehicles, and energy storage stations due to their high energy density, long cycle life, and environmental friendliness. However, the thermal safety issues of high-energy-density lithium-ion batteries pose a significant challenge to their further application. Thermal runaway events caused by the failure of internal materials in lithium-ion batteries are the core cause of thermal safety problems. High-energy-density lithium-ion batteries using traditional electrolytes are prone to thermal runaway, combustion, and even explosion.

[0003] Electrolytes play a crucial role in ion transfer, significantly impacting the cost, specific energy, safety, cycle performance, and rate performance of lithium-ion batteries. Currently used electrolytes consist of lithium salts and organic solvents. Traditional lithium hexafluorophosphate (LiPF6) / ethylene carbonate (EC) based electrolytes are unsuitable for high-energy-density power batteries. During thermal runaway, the reaction between the negative electrode and the electrolyte leads to initial heat accumulation. The EC solvent is first reduced by the negative electrode, generating highly flammable and explosive reducing gases such as H2, C2H4, and CH4. Simultaneously, the decomposition of LiPF6 releases a large amount of heat. Furthermore, after the phase transition of the positive electrode material releases a large amount of oxygen, the EC is oxidized by the oxygen released from the positive electrode, releasing a significant amount of heat. This reaction is the triggering reaction for thermal runaway in high-nickel batteries.

[0004] The electrolyte plays an indispensable role in the entire thermal runaway process, becoming the trigger for thermal runaway in lithium-ion batteries. In traditional electrolytes, the solvation structure dominated by solvent molecule coordination in the first electrolyte shell preferentially decomposes on the negative electrode surface. Compared with solvent coordination, the solvation structure involving anion coordination significantly increases the lowest unoccupied molecular orbital (LUMO) energy, indicating that anion coordination enhances the reducing stability of the electrolyte.

[0005] Therefore, by rationally designing the coordination and concentration of the electrolyte, the exothermic reaction between the highly reactive negative electrode and the electrolyte can be suppressed, thereby improving the safety of high-energy-density lithium-ion batteries. Summary of the Invention

[0006] This invention addresses the technical problems of high-energy-density lithium-ion batteries in traditional electrolytes by providing a high-safety, flame-retardant lithium-ion battery electrolyte with a low-reactivity coordination structure, aiming to improve the thermal safety performance of high-energy-density lithium-ion batteries.

[0007] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0008] The present invention first provides a high-safety flame-retardant lithium-ion battery electrolyte with a low-reactivity coordination structure. The low-reactivity high-safety flame-retardant electrolyte uses a high thermal stability salt as the lithium salt, a low-activity ester solvent as the main solvent, an ether solvent with weak solvation ability as the secondary solvent, and adds additives.

[0009] Furthermore, the high thermal stability lithium salt is lithium bisfluorosulfonylimide (LiFSI). Since the decomposition temperature of LiFSI is above 300℃, while the decomposition temperature of the traditional lithium salt LiPF6 is around 100℃, the addition of LiFSI can improve the stability of the electrolyte.

[0010] Furthermore, the low-activity ester solvent is selected from one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), or a mixture of several in any proportion.

[0011] Furthermore, the ether solvent with weak solvation capability is one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE), which have higher lowest unoccupied molecular orbital (LUMO) energies. These ether solvents effectively block electron transport and exhibit strong resistance to reduction.

[0012] Furthermore, the additive is selected from one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC), and lithium hexafluorophosphate (LiPF6).

[0013] Furthermore, the concentration of the lithium salt in the low-reactivity, high-safety, flame-retardant electrolyte is 1.0–2.0 mol / L, and the volume ratio of the ester solvent to the ether solvent in the electrolyte is (3–6): (4–7). Since the ether solvent hardly participates in the solvation structure and mainly acts as a dilution agent, this concentration ratio can ensure the advantages of contact ion pairs and ion aggregate structures (i.e., constructing anion-derived interfaces and improving interface stability), while avoiding the disadvantages of high viscosity and slow ion transport. Among the additives, if the fluoroethylene carbonate is added, its mass accounts for 2%–10% of the low-reactivity, high-safety, flame-retardant electrolyte; if the vinylene carbonate additive is added, its mass accounts for 2%–10% of the total mass of the high-safety, low-reactivity electrolyte; if the lithium hexafluorophosphate is added, its mass accounts for 1%–2% of the total mass of the high-safety, low-reactivity electrolyte.

[0014] Furthermore, the low-reactivity chain coordination structure, compared to the cyclic coordination structure of traditional electrolytes, has a higher minimum unoccupied molecular orbital (LUMO), resulting in stronger electron transport blocking ability and greater resistance to reduction. Since the EC solvent in traditional electrolytes is cyclic, the cyclic unsaturated bonds are easily broken. Compared to traditional Li... + The cyclic unsaturated bonds in the -EC coordination structure make the low-reactivity coordination structure of this invention less prone to bond breakage, generating reducing gases such as C2H4 and H2.

[0015] Furthermore, the preparation method of the electrolyte of the present invention is as follows: in an argon-protected glove box, the lithium salt is weighed first, and then the main solvent, the auxiliary solvent and the additive are added in sequence according to the proportion, and the mixture is stirred evenly to form a mixed solution, thereby obtaining the high safety flame-retardant lithium-ion battery electrolyte with a low reactive coordination structure.

[0016] Furthermore, the ion coordination number ratio of lithium ions, anions, and the main solvent in the weakly solvated structure is 1:(2~3):(2~3). The ion coordination number refers to the ratio of the number of lithium ions to the number of molecules in the main solvent and the secondary solvent in the electrolyte solvation structure. This ratio helps to form anion-rich (FSI) electrolyte. - The interface is more stable and can improve battery safety.

[0017] The present invention also provides a lithium-ion battery, comprising a positive electrode active material, a negative electrode active material, an electrolyte, and a separator, wherein the electrolyte is the aforementioned low-reactivity, high-safety, flame-retardant electrolyte.

[0018] Furthermore, the positive electrode active material is LiNi. x Co y Mn z O2, where x≥0.8, 0.1≥y≥0.05, 0.1≥z≥0.05.

[0019] Furthermore, the negative electrode active material is selected from one or more of natural graphite, artificial graphite, and silicon-carbon composite materials.

[0020] Furthermore, the diaphragm is selected from any one of polypropylene film (PP), polyethylene film (PE), and PP / PE composite film.

[0021] Furthermore, the battery energy density is ≥250Wh kg. -1 .

[0022] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0023] The electrolyte in this invention has a weak solvation structure. Through theoretical calculations, compared with traditional electrolytes, the high-safety, low-reactivity electrolyte has a higher least unoccupied molecular orbital (LUMO) and lower electrophilicity and anti-reduction ability, thereby effectively mitigating the side reactions between the electrolyte and the negative electrode and improving the thermal stability of the negative electrode side.

[0024] The electrolyte in this invention uses a lithium salt with higher thermal stability and an inert solvent with low reactivity to replace the highly reactive materials in traditional electrolytes, which can effectively improve the thermal safety of a single battery cell. Specifically, this manifests as a higher thermal failure initiation temperature and trigger temperature, and a lower maximum thermal runaway temperature during thermal runaway.

[0025] The electrolyte in this invention uses one or more of the flame-retardant solvents 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE), which can effectively suppress the generation of reducing gases in high-energy-density lithium-ion batteries and further reduce the combustion and explosion hazards after battery thermal runaway. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a diagram of the lowest unoccupied molecular orbitals for different electrolyte components;

[0028] Figure 2 The graphs are the adiabatic thermal runaway curves corresponding to Example 1 and Comparative Example 1.

[0029] Figure 3 These are the thermal flow curves of the materials corresponding to Example 1 and Comparative Example 1;

[0030] Figure 4 The graphs show the reducing gas curves of the materials corresponding to Example 1 and Comparative Example 1, representing the thermal failure of the materials. Detailed Implementation

[0031] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0032] Example 1

[0033] This embodiment provides a high-safety, low-reactivity lithium-ion battery electrolyte based on ester-based solvents with localized weak solvation, as detailed below:

[0034] The positive electrode active material of lithium-ion batteries is LiNi 0.9 Co 0.05 Mn 0.05 O2, the negative electrode active material is silicon-carbon (90%Gr@10%SiO), and the separator is a PP separator with ceramic single-sided coating.

[0035] Electrolyte preparation: The raw materials consist of lithium salt, ester-based main solvent, ether-based secondary solvent, and additives. The volume fractions of the ester-based main solvent and ether-based secondary solvent are: dimethyl carbonate: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether = 3:7. The lithium salt is lithium difluorosulfonylimide, and its concentration in the electrolyte is 1.2 mol / L. The electrolyte additive is vinylene carbonate, which accounts for 4% of the total mass of the electrolyte. The electrolyte preparation is carried out in an argon-protected glove box (H2O ≤ 0.1 ppm, O2 ≤ 0.1 ppm). During preparation, the heavy lithium salt is weighed first, and then the ester solvent and ether solvent are added in sequence according to the proportion. Then the additive is added, and the mixture is stirred evenly to form a mixed solution, thus obtaining a high-energy-density lithium-ion battery with localized weak solvation, high safety, and low reactive activity electrolyte.

[0036] Example 2

[0037] This embodiment provides a high-safety, low-reactivity lithium-ion battery electrolyte based on ester-based solvents with localized weak solvation, as detailed below:

[0038] The positive electrode active material of lithium-ion batteries is LiNi 0.9 Co 0.05 Mn 0.05 O2, the negative electrode active material is graphite (Gr), and the separator is a PP separator with ceramic single-sided coating.

[0039] Electrolyte preparation: The raw materials consist of lithium salt, ester-based main solvent, ether-based secondary solvent, and additives. The volume fractions of the ester-based main solvent and ether-based secondary solvent are: dimethyl carbonate: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether = 4:6. The lithium salt is lithium difluorosulfonylimide, and its concentration in the electrolyte is 1.5 mol / L. The electrolyte additives are vinylene carbonate and fluoroethylene carbonate, with a mass percentage of 2% and 3% of the total electrolyte mass, respectively. The electrolyte preparation is carried out in an argon-protected glove box (H2O ≤ 0.1 ppm, O2 ≤ 0.1 ppm). During preparation, the heavy lithium salt is weighed first, and then the ester solvent and ether solvent are added sequentially according to the proportions. Then, the additives are added, and the mixture is stirred evenly to form a mixed solution, thus obtaining a high-energy-density lithium-ion battery with localized weak solvation, high-safety, low-reactivity electrolyte.

[0040] Example 3

[0041] This embodiment provides a high-safety, low-reactivity lithium-ion battery electrolyte based on ester-based solvents with localized weak solvation, as detailed below:

[0042] The positive electrode active material of lithium-ion batteries is LiNi 0.8 Co 0.1 Mn 0.1 O2, the negative electrode active material is graphite (Gr), and the separator is a PP separator with ceramic single-sided coating.

[0043] Electrolyte preparation: The raw materials consist of lithium salt, ester-based main solvent, ether-based secondary solvent, and additives. The volume fractions of the ester-based main solvent and ether-based secondary solvent are: dimethyl carbonate: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether = 6:4. The lithium salt is lithium difluorosulfonylimide, and its concentration in the electrolyte is 1.1 mol / L. The electrolyte additive is lithium hexafluorophosphate, which accounts for 2% of the total mass of the electrolyte. The electrolyte preparation is carried out in an argon-protected glove box (H2O ≤ 0.1 ppm, O2 ≤ 0.1 ppm). During preparation, the heavy lithium salt is weighed first, and then the ester solvent and ether solvent are added in sequence according to the proportion. Then the additive is added, and the mixture is stirred evenly to form a mixed solution, thus obtaining a high-energy-density lithium-ion battery with localized weak solvation, high safety, and low reactive activity electrolyte.

[0044] Example 4

[0045] This embodiment provides a high-safety, low-reactivity lithium-ion battery electrolyte based on ester-based solvents with localized weak solvation, as detailed below:

[0046] The positive electrode active material of lithium-ion batteries is LiNi 0.8 Co 0.1 Mn 0.1 O2, the negative electrode active material is silicon-carbon (Gr), and the separator is a PP separator with ceramic single-sided coating.

[0047] Electrolyte preparation: The raw materials consist of lithium salt, ester-based main solvent, ether-based secondary solvent, and additives. The volume fractions of the ester-based main solvent and ether-based secondary solvent are: dimethyl carbonate: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether: 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE) = 3:4:3. The lithium salt is lithium difluorosulfonylimide, and its concentration in the electrolyte is 1.2 mol / L. The electrolyte is prepared in an argon-protected glove box (H2O≤0.1ppm, O2≤0.1ppm). During preparation, the heavy lithium salt is weighed first, and then the ester solvent and ether solvent are added sequentially according to the ratio. Then, the additives are added, and the mixture is stirred until homogeneous to form a mixed solution, thus obtaining a high-energy-density lithium-ion battery with locally weak solvation, high-safety, low-reactivity electrolyte.

[0048] Comparative Example 1

[0049] This comparative example provides a traditional electrolyte based on ester solvents as the main solvent, as detailed below:

[0050] The positive electrode active material of lithium-ion batteries is LiNi 0.9 Co 0.05 Mn 0.05 O2, the negative electrode active material is graphite (Gr), and the separator is a PP separator with ceramic single-sided coating.

[0051] Electrolyte preparation: The raw materials consist of lithium salt, ester solvent, and additives. The volume fraction of the ester solvent is ethylene carbonate: methyl ethyl carbonate = 3:7. The lithium salt is lithium hexafluorophosphate, and its concentration in the electrolyte is 1 mol / L. The additive is fluoroethylene carbonate, and its mass percentage is 1% of the total electrolyte mass. The electrolyte preparation is carried out in an argon-protected glove box (H2O ≤ 0.1 ppm, O2 ≤ 0.1 ppm). During preparation, the heavy lithium salt is weighed first, and then the ester solvent and ether solvent are added in sequence according to the proportion. Then the additive is added, and the mixture is stirred evenly to form a mixed solution, thus obtaining a high-energy-density lithium-ion battery with localized weak solvation, high safety, and low reactive activity electrolyte.

[0052] Comparative Example 2

[0053] This comparative example provides a traditional electrolyte based on ester solvents as the main solvent, as detailed below:

[0054] The positive electrode active material of lithium-ion batteries is LiNi 0.9 Co 0.05 Mn 0.05 O2, the negative electrode active material is silicon-carbon (90%Gr@10%SiO), and the separator is a PP separator with ceramic single-sided coating.

[0055] Electrolyte preparation: The raw materials consist of lithium salt, ester solvent, and additives. The volume fraction of the ester solvent is ethylene carbonate: methyl ethyl carbonate = 3:7. The lithium salt is lithium hexafluorophosphate, and its concentration in the electrolyte is 1 mol / L. The additive is fluoroethylene carbonate, and its mass percentage is 1% of the total electrolyte mass. The electrolyte preparation is carried out in an argon-protected glove box (H2O ≤ 0.1 ppm, O2 ≤ 0.1 ppm). During preparation, the heavy lithium salt is weighed first, and then the ester solvent and ether solvent are added in sequence according to the proportion. Then the additive is added, and the mixture is stirred evenly to form a mixed solution, thus obtaining a high-energy-density lithium-ion battery with localized weak solvation, high safety, and low reactive activity electrolyte.

[0056] Comparative Example 3

[0057] This comparative example provides a traditional electrolyte based on ester solvents as the main solvent, as detailed below:

[0058] The positive electrode active material of lithium-ion batteries is LiNi 0.8 Co 0.1 Mn 0.1 O2, the negative electrode active material is graphite (Gr), and the separator is a PP separator with ceramic single-sided coating.

[0059] Electrolyte preparation: The raw materials consist of lithium salt, ester solvent, and additives. The volume fraction of the ester solvent is ethylene carbonate: methyl ethyl carbonate = 3:7. The lithium salt is lithium hexafluorophosphate, and its concentration in the electrolyte is 1 mol / L. The additive is fluoroethylene carbonate, and its mass percentage is 1% of the total electrolyte mass. The electrolyte preparation is carried out in an argon-protected glove box (H2O ≤ 0.1 ppm, O2 ≤ 0.1 ppm). During preparation, the heavy lithium salt is weighed first, and then the ester solvent and ether solvent are added in sequence according to the proportion. Then the additive is added, and the mixture is stirred evenly to form a mixed solution, thus obtaining a high-energy-density lithium-ion battery with localized weak solvation, high safety, and low reactive activity electrolyte.

[0060] The characteristic temperatures of thermal runaway of single cells in Examples 1-4 and Comparative Examples 1-3, the material thermal failure initiation temperatures, and the heat flows are as follows:

[0061] 1. Battery charge / discharge test conditions: Constant current and constant voltage charging and constant current discharging, with a voltage range of 2.8-4.2V. Examples 1-4 and Comparative Examples 1-3 were charged to 4.2V at 30°C, reaching 100% SOC, and their safety performance was then tested. The single-cell thermal runaway test conditions were as follows: Thermal safety of the fully charged single-cell was determined using an adiabatic calorimeter, with an initial heating temperature of 50°C, a termination heating temperature of 300°C, a temperature step of 10°C, and a waiting time of 25 minutes. The onset of thermal runaway heat generation, T1, was defined as a temperature rise rate greater than 0.02°C / min. -1 Thermal runaway trigger temperature T2 is defined as the temperature rise rate greater than 1°C s. -1 The thermal stability test conditions for the battery materials were as follows: Differential scanning calorimetry was used to test the thermal stability of the fully charged battery materials. The heating temperature range was 50-550°C, and the temperature rise rate was 10°C / min. -1 The measured characteristic temperatures of thermal runaway in a single cell, along with the material's thermal failure initiation temperature and heat flux, are shown in Table 1.

[0062] Table 1

[0063]

[0064] Table 1 shows that, under adiabatic thermal runaway test conditions, the fully charged battery assembled with the electrolyte in Example 1 had a thermal runaway self-generated heat initiation temperature of 152.9°C, a thermal runaway trigger temperature of 260.2°C, and a maximum thermal runaway temperature of 809.2°C. Compared with Comparative Example 1, its thermal runaway initiation temperature increased by 38°C, the trigger temperature increased by 77°C, and the maximum temperature decreased by 284°C. The thermal failure test results of the entire component of the fully charged battery material (positive electrode + negative electrode + electrolyte) show that the thermal failure initiation temperature of the material in Example 1 is 102.4°C, which is 19°C higher than that of Comparative Example 1, and the heat flux of Example 1 is 786 J / g. -1 The comparison ratio 1 decreased by 510 J g -1 This indicates that the high-safety flame-retardant electrolyte with low reactive coordination can effectively delay the failure temperature of battery materials, suppress interfacial side reactions, further reduce heat release, and effectively improve the safety performance of the battery.

[0065] Figure 1 This is a diagram of the lowest unoccupied molecular orbitals (LUMOs) of the electrolyte components used in Examples 1-3 and Comparative Examples 1-3 of the present invention. A comparison shows that the LUMO energy of the electrolyte solvent component in the examples is higher than that of the solvent EC in the comparative examples. The LUMO energy of the solvated structure of the electrolyte in Example 1 is also higher than that of the solvated structure in Comparative Example 4. This indicates that the electrolytes in the examples have lower electrophilicity and higher resistance to reduction, effectively mitigating the exothermic side reactions between the electrolyte and the negative electrode, and improving the thermal stability of the negative electrode side.

[0066] Figure 2 The figures show the adiabatic thermal runaway curves for Example 1 and Comparative Example 2. As can be seen from the figures, the battery in Example 1 also exhibits a higher self-generated heat initiation temperature and thermal runaway trigger temperature, as well as a lower maximum thermal runaway temperature. Its thermal runaway initiation temperature increased by 38°C, the trigger temperature increased by 77°C, and the maximum temperature decreased by 284°C, indicating that the thermal safety performance of the battery obtained in Example 1 is effectively improved.

[0067] Figure 3 The figures show the heat flow curves for material thermal failure in Example 1 and Comparative Example 1. The thermal failure initiation temperature of the material in Example 1 was 102.4°C, which was 19°C higher than that in Comparative Example 1. The heat flow rate of Example 1 was 786 J / g. -1 The comparison ratio 1 decreased by 510 J g -1 This demonstrates that the electrolyte in Example 1 can effectively delay the failure temperature of battery materials, suppress interfacial side reactions, further reduce heat release, and improve battery safety performance.

[0068] Figure 4The figures show the reducing gas profiles after thermal failure of the materials in Example 1 and Comparative Example 1. The comparison shows that the proportion of reducing gas after thermal runaway in the battery of Example 1 is much lower than that in the battery of Comparative Example 1. This indicates that the electrolyte in Example 1 has a coordination structure with lower reactivity, and the bond-breaking ability of the chain-like CO bonds in this coordination structure is weaker than that of the conventional Li in Comparative Example 1. + The ability to break CO bonds in the -EC cyclic chain can effectively reduce the generation of reducing gases such as C2H4 and H2.

[0069] As can be seen from the above, the present invention provides a high-safety flame-retardant electrolyte with low reactive coordination. It uses a high thermal stability lithium salt as the lithium salt, a low-activity ester solvent as the main solvent, an ether solvent with weak solvation ability as a secondary solvent and an inert diluent, and adds additives to produce a lithium-ion battery with excellent thermal safety performance. The selected solvent combines the advantages of multiple solvents: high LUMO energy level and good resistance to reduction, effectively suppressing redox reactions on the negative electrode side and in the electrolyte, reducing heat accumulation; the high-safety flame-retardant electrolyte has a low reactive coordination structure, effectively suppressing the generation of reducing gases and reducing external combustion hazards; the selected lithium salt is a high-stability lithium salt with good thermal stability; and the optimized ratio of solvent to lithium salt effectively improves the solvation structure of the electrolyte, further enhancing battery safety. Simultaneously, the additives used can help construct an electrolyte interface rich in inorganic matter, improving interface stability.

[0070] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A lithium-ion battery, comprising a positive electrode active material, a negative electrode active material, an electrolyte, and a separator, characterized in that, The electrolyte is a high-safety flame-retardant lithium-ion battery electrolyte with a low reactive coordination structure. The electrolyte uses a high thermal stability salt as the lithium salt, a low-activity ester solvent as the main solvent, an ether solvent with weak solvation ability as the secondary solvent, and additives are added. The volume ratio of the ester solvent to the ether solvent in the electrolyte is (3~6):(4~7); The lithium salt is lithium bis(fluorosulfonyl)imide (LiFSI), and the concentration of the lithium salt in the electrolyte is 1.0–2.0 mol / L; The low-activity ester solvent is selected from one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC); The ether solvent with weak solvation ability is a combination of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE). The additive includes lithium hexafluorophosphate (LiPF6), and the mass of lithium hexafluorophosphate accounts for 1% to 2% of the total mass of the electrolyte; The positive electrode active material is LiNi. x Co y Mn z O2, where x≥0.8, 0.1≥y≥0.05, 0.1≥z≥0.

05.

2. The lithium-ion battery according to claim 1, characterized in that, The additives include one or more of fluoroethylene carbonate (FEC) and vinylene carbonate (VC).

3. The lithium-ion battery according to claim 2, characterized in that, If the fluoroethylene carbonate is added, the mass of the fluoroethylene carbonate accounts for 2% to 10% of the total mass of the electrolyte; if the vinylene carbonate is added, the mass of the vinylene carbonate accounts for 2% to 10% of the total mass of the electrolyte.

4. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, The preparation method of the electrolyte includes: weighing lithium salt in an argon-protected glove box, then adding the main solvent, secondary solvent and additives in sequence according to the proportion, stirring evenly to form a mixed solution, thereby obtaining the electrolyte.

5. The lithium-ion battery according to claim 1, characterized in that, The negative electrode active material is selected from one or more of natural graphite, artificial graphite, and silicon-carbon composite materials; The diaphragm is selected from any one of polypropylene film (PP), polyethylene film (PE), and PP / PE composite film. The energy density of the lithium-ion battery is ≥250Wh / kg. -1 .

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