A lithium-ion battery electrolyte, its preparation method and its application

Abstract

This invention provides a lithium-ion battery electrolyte, its preparation method, and its application. The electrolyte comprises lithium salt, organic solvent, and additives, wherein, by mass percentage, lithium salt is 10%-20%, organic solvent is 75%-89%, and additives are 1%-5%. The additives include cyclic carbon-containing additives, cyclic sulfur-containing additives, and boron-containing additives. The electrolyte of this invention can be applied to lithium-ion batteries using lithium manganese iron phosphate cathode materials, improving the stability of the electrode-electrolyte interface and solving the problem of manganese leaching during cycling in existing lithium manganese iron phosphate cathode materials, resulting in poor high-temperature cycling stability of the prepared lithium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a lithium-ion battery electrolyte, its preparation method, and its application. Background Technology

[0002] Currently, in the field of power batteries, lithium iron phosphate (LFP) and ternary materials (NCM) are developing in parallel as mainstream cathode materials. LFP has advantages such as high safety, low cost, and long cycle life, making it the preferred choice for power battery companies. However, its voltage platform is relatively low, making it difficult to meet higher energy density requirements. Lithium manganese iron phosphate (LMFP) is an olivine-type phosphate cathode material obtained by doping LFP with manganese (Mn), exhibiting high safety and stability. Furthermore, the high voltage characteristic of manganese gives LMFP a higher voltage platform (4.1V), with an energy density approximately 15% higher than LFP. Therefore, LMFP can balance high safety and high energy density, showing great application potential. Currently, LMFP cathode materials are still in the early stages of industrialization and have not yet achieved large-scale commercial use, mainly due to the presence of manganese (Mn) in LMFP. 3+ It is prone to disproportionation reaction, 2Mn 3+ →Mn 2+ +Mn 4+ Mn 2+ It can dissolve in the electrolyte and then undergo a reduction reaction on the electrode surface to generate Mn, which is deposited on the negative electrode surface. This leads to increased contact resistance and film resistance, increased battery polarization, and consequently, severe capacity loss and deterioration of cycle performance. Especially under high-temperature conditions, the above-mentioned disproportionation reaction is more severe, resulting in even worse battery performance.

[0003] Currently, to improve the cycle performance of LMFPs, modifications such as elemental doping and surface coating are commonly used to prevent the dissolution of Mn and thus improve the structural stability of LMFP materials. While elemental doping and coating modifications can partially improve the electrochemical performance of LMFPs, their effect on improving cycle stability at high temperatures is not ideal. Furthermore, the existing electrolytes have poor compatibility with LMFP cathode materials; therefore, optimizing the electrolyte to improve the high-temperature cycle stability of LMFP batteries remains a critical challenge.

[0004] CN115360412A discloses an electrolyte for lithium manganese iron phosphate batteries, comprising a lithium salt, a solvent, and additives; the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluoromethanesulfonylimide, lithium difluorooxalate borate, and lithium difluorophosphate; the solvent includes at least one of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate; the additives include at least one of vinylene carbonate, ethylene sulfate, and N,N-dimethylacrylamide (DMAA); the lithium salt accounts for 10%-20% of the total mass of the electrolyte, the solvent accounts for 60%-85% of the total mass of the electrolyte, and the additives account for 1.7%-5% of the total mass of the electrolyte; however, when the above electrolyte is applied to lithium manganese iron phosphate batteries, there is a problem of gas generation during high-temperature storage / high-temperature cycling, which affects the high-temperature cycling stability of the battery. Summary of the Invention

[0005] To address the shortcomings and defects of existing technologies, this invention aims to provide a lithium-ion battery electrolyte, its preparation method, and its application. The electrolyte of this invention can be applied to lithium-ion batteries using lithium manganese iron phosphate cathode materials, improving the stability of the electrode-electrolyte interface and solving the problem of manganese leaching during cycling of existing lithium manganese iron phosphate cathode materials, resulting in poor high-temperature cycling stability of the prepared lithium-ion batteries.

[0006] To achieve the above objectives, the first aspect of the present invention provides a lithium-ion battery electrolyte, which adopts the following technical solution:

[0007] A lithium-ion battery electrolyte comprises: lithium salt, organic solvent, and additives, wherein, by mass percentage, lithium salt is 10%-20% (e.g., 11%, 12%, 13%, 15%, 17%, 18%, 19%), organic solvent is 75%-89% (e.g., 76%, 78%, 80%, 82%, 85%, 87%, 88%), and additives are 1%-5% (e.g., 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%); wherein the additives include: cyclic carbon-containing additives, cyclic sulfur-containing additives, and boron-containing additives.

[0008] In the above-mentioned lithium-ion battery electrolyte, as a preferred embodiment, the mass ratio of the cyclic carbon-containing additive to the cyclic sulfur-containing additive and the boron-containing additive is 1:(0.1-1):(0.1-1) (e.g., 1:0.2:0.2, 1:0.2:0.5, 1:0.2:0.9, 1:0.5:0.2, 1:0.9:0.2).

[0009] The electrolyte in this invention is suitable for lithium-ion batteries using lithium manganese iron phosphate (LFP) as the cathode material. By adding cyclic carbon-containing additives, cyclic sulfur-containing additives, and boron-containing additives to the electrolyte, the cycle stability of the LFP cathode material during high-temperature cycling is improved. Specifically, the cyclic carbon-containing additive undergoes a polymerization reaction on the negative electrode surface in the lithium-ion battery, forming a dense SEI film, thereby preventing further reduction and decomposition of the electrolyte on the negative electrode surface. The cyclic sulfur-containing additive, due to its high reduction potential, also has a good passivation effect on the graphite surface, and can inhibit electrolyte oxidation and gas formation on the cathode surface during cycling or storage. The boron-containing additive can significantly improve the battery's initial charge-discharge coulombic efficiency, cycle life, and high-temperature cycling performance. During cycling, it is preferentially oxidized compared to the electrolyte solvent, forming a protective film covering the cathode surface. This protective film has good ionic conductivity, inhibiting the oxidative decomposition of the electrolyte and the destruction of the cathode material structure in subsequent cycles, stabilizing the electrode / electrolyte interface.

[0010] The reason for limiting the mass ratio of cyclic carbon-containing additives to cyclic sulfur-containing additives and boron-containing additives to 1:(0.1-1):(0.1-1) in this invention is that within this range, lithium manganese iron phosphate batteries exhibit excellent high-temperature storage and high-temperature cycling performance within the 2.5-4.2V voltage range. If too little cyclic sulfur-containing additive is added, the improvement on CEI film formation is minimal; if too much cyclic sulfur-containing additive is added, it is prone to crystallization and deposition in the electrolyte, and due to its poor high-temperature stability, excessive addition can easily degrade battery performance. If too little boron-containing additive is added, the improvement on high-temperature cycling performance of the battery is not significant; if too much boron-containing additive is added, it can easily promote lithium salt decomposition and increase interfacial impedance.

[0011] In the above-mentioned lithium-ion battery electrolyte, as a preferred embodiment, the cyclic carbon-containing additive is selected from one or more of vinylene carbonate (VC), ethylene ethylene carbonate (VEC), and fluoroethylene carbonate (FEC).

[0012] In the above-mentioned lithium-ion battery electrolyte, as a preferred embodiment, the cyclic sulfur-containing additive is selected from one or two of methylene disulfonate (MMDS) and propane-1,3-disulfonic anhydride (ODTO, molecular formula C3H6O5S2).

[0013] The reason why the cyclic sulfur-containing additive in this invention is selected from one or both of methylene methane disulfonate and propane-1,3-disulfonic anhydride is that the addition of methylene methane disulfonate can prevent the transition metal dissolved at high temperature from adsorbing on the negative electrode surface, thereby suppressing the impedance rise and reducing the interfacial impedance; the addition of propane-1,3-disulfonic anhydride can reduce the impedance at 1.4V vs. Li / Li + At a certain potential, an SEI film is formed on the graphite surface, and a CEI film can also be formed on the positive electrode, thereby significantly improving the cycle performance of the battery.

[0014] In the above-mentioned lithium-ion battery electrolyte, as a preferred embodiment, the boron-containing additive is selected from one or more of lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiFOB), tetramethylborate (TMB), trimethyl borate (TB), and trimethylcyclotriboroxane.

[0015] In the above-mentioned lithium-ion battery electrolyte, as a preferred embodiment, the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium fluorocarbonyl sulfonate, lithium difluorooxalate borate (LiODFB), and lithium difluorosulfonate imine; the lithium fluorocarbonyl sulfonate is preferably lithium trifluoromethyl sulfonate (LiCF3SO3). In the above-mentioned lithium-ion battery electrolyte, as a preferred embodiment, the organic solvent includes cyclic carbonates and chain carbonates; the mass ratio of the cyclic carbonates to the chain carbonates is (25-35):(65-75) (e.g., 28:72, 30:70, 32:68, 34:66).

[0016] In the above-mentioned lithium-ion battery electrolyte, as a preferred embodiment, the cyclic carbonate is selected from at least one of ethylene carbonate (EC) and propylene carbonate (PC); preferably, the chain carbonate is selected from at least two of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0017] A second aspect of the present invention provides a method for preparing the above-mentioned lithium-ion battery electrolyte, comprising:

[0018] S1. Dissolve lithium salt in an organic solvent and stir to obtain a mixed solution;

[0019] S2. Add the additive to the mixed solution and stir to obtain the lithium-ion battery electrolyte.

[0020] A third aspect of the present invention provides the application of the above-mentioned lithium-ion battery electrolyte in a lithium-ion battery using lithium manganese iron phosphate as the cathode material.

[0021] Compared with existing technologies, the present invention has the following advantages:

[0022] (1) The present invention provides a lithium-ion battery electrolyte that matches lithium manganese iron phosphate cathode material. By adding cyclic carbon additives, cyclic sulfur additives and boron additives to the electrolyte, the cycle stability of lithium manganese iron phosphate cathode material during high-temperature cycling is improved. Cyclic carbon-containing additives polymerize on the negative electrode surface in lithium-ion batteries, forming a dense SEI film that prevents further reduction and decomposition of the electrolyte on the negative electrode surface. Cyclic sulfur-containing additives, due to their high reduction potential, also provide excellent passivation for graphite surfaces and inhibit electrolyte oxidation and gas formation on the positive electrode surface during cycling or storage. Boron-containing additives significantly improve the initial charge-discharge coulombic efficiency, cycle life, and high-temperature cycling performance. During cycling, they are preferentially oxidized compared to the electrolyte solvent, forming a protective film that covers the positive electrode surface. This protective film has good ionic conductivity, inhibiting oxidative decomposition of the electrolyte and damage to the positive electrode material structure in subsequent cycles, stabilizing the electrode / electrolyte interface. Furthermore, the cyclic carbon-containing, cyclic sulfur-containing, and boron-containing additives of this invention work synergistically, resulting in excellent high-temperature storage and high-temperature cycling performance of lithium manganese iron phosphate batteries within a voltage range of 2.5-4.2V.

[0023] (2) The preparation method of the present invention is simple to operate, controllable, and easy to be mass-produced in industry. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0026] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0027] In this invention, unless otherwise specified and / or stated, all values ​​relating to component amounts are in "parts by weight" throughout. Process parameters in the following examples, unless otherwise specified, are generally performed under conventional conditions. The raw materials described in the following examples are all available from publicly available commercial sources.

[0028] Example 1: A lithium-ion battery electrolyte and its preparation method

[0029] The content of each component in the electrolyte, by mass percentage, is as follows:

[0030] Organic solvents: ethylene carbonate 23.5%, dimethyl carbonate 16.5%, diethyl carbonate 16%, methyl ethyl carbonate 20%;

[0031] Lithium salts: lithium hexafluorophosphate 13.5%, lithium trifluoromethanesulfonate 3.5%, lithium difluorooxalate borate 2%;

[0032] additive:

[0033] Cyclic carbon-containing additives: 1.5% vinylene carbonate and 1% ethylene ethylene carbonate;

[0034] Cyclic sulfur-containing additive: 1% methylene disulfonate;

[0035] Boron-containing additive: 1.5% lithium bis(oxalato)borate.

[0036] Methods for preparing electrolytes include:

[0037] S1. Dissolve lithium salt in an organic solvent and stir to obtain a mixed solution;

[0038] S2. Add the additive to the mixed solution and stir to obtain the lithium-ion battery electrolyte.

[0039] Example 2

[0040] The difference between Example 2 and Example 1 is that the cyclic carbon-containing additives are: 1.5% ethylene carbonate and 1% ethylene ethylene carbonate; the cyclic sulfur-containing additives are: 2% methane disulfonate; and the boron-containing additives are: 0.5% trimethyl borate. The rest are the same as in Example 1.

[0041] Example 3

[0042] The difference between Example 3 and Example 1 is that the cyclic carbon-containing additives are: 1.5% ethylene carbonate and 1% ethylene ethylene carbonate; the cyclic sulfur-containing additives are: 0.5% propane-1,3-disulfonic anhydride; and the boron-containing additives are: 2% lithium bis(oxalato)borate. The rest are the same as in Example 1.

[0043] Example 4

[0044] The difference between Example 4 and Example 1 is that the methane disulfonate in Example 1 is replaced with propane-1,3-disulfonic anhydride, while the rest is the same as in Example 1.

[0045] Example 5

[0046] The difference between Example 5 and Example 1 is that the cyclic sulfur-containing additive is 2% methylene disulfonate; the boron-containing additive is 0.5% lithium bis(oxalato)borate, and the rest are the same as in Example 1.

[0047] Example 6

[0048] The difference between Example 6 and Example 1 is that the cyclic sulfur-containing additive is 0.5% methanedisulfonate; the boron-containing additive is 2% lithium bis(oxalato)borate, and the rest are the same as in Example 1.

[0049] Example 7

[0050] The difference between Example 7 and Example 1 is that the cyclic sulfur-containing additives are: 0.5% methane disulfonate and 0.5% propane-1,3-disulfonic anhydride, while the rest are the same as in Example 1.

[0051] Comparative Example 1: A lithium-ion battery electrolyte and its preparation method

[0052] The content of each component in the electrolyte, by mass percentage, is as follows:

[0053] Organic solvents: ethylene carbonate 23.5%, dimethyl carbonate 16.5%, diethyl carbonate 16%, methyl ethyl carbonate 20%;

[0054] Lithium salts: lithium hexafluorophosphate 13.5%, lithium trifluoromethanesulfonate 3.5%, lithium difluorooxalate borate 2%;

[0055] additive:

[0056] Cyclic carbon-containing additives: 3% vinylene carbonate, 2% ethylene ethylene carbonate;

[0057] The electrolyte was prepared using the same method as in Example 1.

[0058] Comparative Example 2: A lithium-ion battery electrolyte and its preparation method

[0059] The content of each component in the electrolyte, by mass percentage, is as follows:

[0060] Organic solvents: ethylene carbonate 23.5%, dimethyl carbonate 16.5%, diethyl carbonate 16%, methyl ethyl carbonate 20%;

[0061] Lithium salts: lithium hexafluorophosphate 13.5%, lithium trifluoromethanesulfonate 3.5%, lithium difluorooxalate borate 2%;

[0062] additive:

[0063] Cyclic carbon-containing additives: 1.5% vinylene carbonate and 1% ethylene ethylene carbonate;

[0064] Cyclic sulfur-containing additive: Methylene methane disulfonate 2.5%;

[0065] The electrolyte was prepared using the same method as in Example 1.

[0066] Comparative Example 3: A lithium-ion battery electrolyte and its preparation method

[0067] The content of each component in the electrolyte, by mass percentage, is as follows:

[0068] Organic solvents: ethylene carbonate 23.5%, dimethyl carbonate 16.5%, diethyl carbonate 16%, methyl ethyl carbonate 20%;

[0069] Lithium salts: lithium hexafluorophosphate 13.5%, lithium trifluoromethanesulfonate 3.5%, lithium difluorooxalate borate 2%;

[0070] additive:

[0071] Cyclic carbon-containing additives: 1.5% vinylene carbonate and 1% ethylene ethylene carbonate;

[0072] Boron-containing additive: Lithium bis(oxalate)borate 2.5%;

[0073] The electrolyte was prepared using the same method as in Example 1.

[0074] Comparative Example 4: A lithium-ion battery electrolyte and its preparation method

[0075] The content of each component in the electrolyte, by mass percentage, is as follows:

[0076] Organic solvents: ethylene carbonate 23.5%, dimethyl carbonate 16.5%, diethyl carbonate 16%, methyl ethyl carbonate 20%;

[0077] Lithium salts: lithium hexafluorophosphate 13.5%, lithium trifluoromethanesulfonate 3.5%, lithium difluorooxalate borate 2%;

[0078] additive:

[0079] Cyclic carbon-containing additives: 1.5% vinylene carbonate and 1% ethylene ethylene carbonate;

[0080] Cyclic sulfur-containing additive: 1% 1-3 propane sulfonyl lactone;

[0081] Boron-containing additive: 1.5% lithium bis(oxalato)borate;

[0082] The electrolyte was prepared using the same method as in Example 1.

[0083] Performance testing

[0084] The positive electrode active material (LiMn) 0.6 Fe 0.4 PO4), conductive carbon black (Super-P), carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone solvent (NMP) at a mass ratio of 96:0.5:1.5:2. The mixture was mechanically stirred for 3 hours to form a stable slurry. This slurry was then uniformly coated onto aluminum foil and vacuum dried at 80°C for 2 hours. The final product was 2.4 g / cm³. 3 The material is compacted and rolled, then die-cut to the specified size. Using graphite as the negative electrode, Super-P as the conductive agent, and CMC and SBR as the binders, it is added to deionized water at a mass ratio of 96.5:1:1:1.5 for the active material:CMC:SBR:Super-P. The mixture is mechanically stirred for 3 hours to form a stable slurry. This slurry is then evenly coated onto aluminum foil and vacuum dried at 80℃ for 2 hours. The electrode is then dried and its density is 1.5 g / cm³. 3 The material is rolled under compaction and finally die-cut to the specified size. Using a polyethylene (PE) base film with double-sided alumina ceramic as the separator, the above-mentioned positive electrode, separator, and negative electrode are stacked to prepare a battery electrode assembly with 12 positive electrode pieces and 13 negative electrode pieces. After hot pressing and tab welding, the battery electrode assembly is placed in an aluminum-plastic film and injected with the lithium-ion battery electrolyte from the above examples and comparative examples. After electrolyte injection, the battery undergoes processes such as encapsulation, resting, formation, aging, secondary sealing, and capacity testing to obtain a soft-pack battery with a capacity of 1.5Ah. A series of electrochemical tests were performed on the prepared battery, and the test results are shown in Table 1.

[0085] Initial Coulombic Efficiency Test: The battery was charged to 4.2V at 0.1C constant current and constant voltage at 25℃±2℃, with a cutoff current of 0.05C. The charging capacity C1 was recorded. After resting for 10 minutes, the battery was discharged to 2.5V at 0.1C constant current, and the discharge capacity C2 was recorded. After resting for 10 minutes, the initial Coulombic efficiency was calculated as C2 / C1*100%.

[0086] Battery thickness expansion and capacity retention test at 60℃: The battery was charged at 25℃±2℃ using a 1C constant current / constant voltage method to 4.2V, with a cutoff current of 0.05C. After resting for 10 minutes, it was discharged at a 1C constant current method to 2.5V, and rested for another 10 minutes. This process was repeated three times, and the discharge capacity C1 of the last cycle was recorded. The battery was then charged at a 1C constant current / constant voltage method to 4.2V, with a cutoff current of 0.05C, and rested for 2 hours. The initial battery thickness T1 was measured. After storing the battery at 60℃±2℃ for 30 days, the battery was removed, and the battery thickness T2 was immediately measured. After resting at 25℃±2℃ for 5 hours, it was discharged at a 1C constant current method to 2.5V, and the remaining capacity C2 was recorded. The battery thickness expansion rate after 30 days of storage at 60℃ = (T2-T1) / T1*100%; the capacity retention rate after 30 days of storage at 60℃ = C2 / C1*100%.

[0087] Cyclic test: At 45℃±2, charge to 4.2V with 1C constant current and constant voltage, let stand for 10 minutes, discharge to 2.5V with 1C constant current, let stand for 10 minutes, repeat the above charge and discharge steps, and cycle 1000 times. The capacity retention rate refers to the percentage of the discharge capacity after 1000 cycles at 45℃ to the initial discharge capacity at 45℃.

[0088]

[0089] Compared with Examples 1-7 and Comparative Examples 1-4, the addition of cyclic carbon-containing additives, cyclic sulfur-containing additives, and boron-containing additives to the electrolyte of the present invention can jointly improve the high-temperature storage performance and high-temperature cycle performance of batteries made with lithium manganese iron phosphate as the cathode material; and the volume expansion of the battery during high-temperature storage is significantly and effectively suppressed, thanks to the synergistic effect of the cyclic carbon-containing additives, cyclic sulfur-containing additives, and boron-containing additives.

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be within the scope of protection of the pending claims of the present invention.

Claims

1. A lithium-ion battery electrolyte, characterized in that, include: The lithium salt, organic solvent, and additives, by mass percentage, are: lithium salt 10%-20%, organic solvent 75%-89%, and additives 1%-5%; wherein the additives consist of cyclic carbon-containing additives, cyclic sulfur-containing additives, and boron-containing additives. The lithium-ion battery uses lithium manganese iron phosphate as the positive electrode material. The cyclic sulfur-containing additive is methylene methane disulfonate and propane-1,3-disulfonic anhydride, and the mass of methylene methane disulfonate and propane-1,3-disulfonic anhydride each accounts for 0.5% of the total mass of the electrolyte. The boron-containing additive is selected from one or two of lithium bis(oxalato)borate and lithium difluorooxalato)borate. The mass ratio of the cyclic carbon-containing additive to the cyclic sulfur-containing additive and the boron-containing additive is 1:(0.1-1):(0.1-1).

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The cyclic carbon-containing additive is selected from one or more of vinylene carbonate, ethylene ethylene carbonate, and fluoroethylene carbonate.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium fluoroalkyl sulfonate, lithium difluorooxalate borate, and lithium difluorosulfonate imine.

4. The lithium-ion battery electrolyte according to claim 3, characterized in that, The fluoroalkyl sulfonate lithium is lithium trifluoromethyl sulfonate.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that, The organic solvent includes cyclic carbonates and chain carbonates; the mass ratio of the cyclic carbonates to the chain carbonates is (25-35):(65-75).

6. The lithium-ion battery electrolyte according to claim 5, characterized in that, The cyclic carbonate is selected from at least one of ethylene carbonate and propylene carbonate; And / or, the chain carbonate is selected from at least two of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

7. A method for preparing a lithium-ion battery electrolyte as described in any one of claims 1-6, characterized in that, include: S1. Dissolve lithium salt in an organic solvent and stir to obtain a mixed solution; S2. Add the additive to the mixed solution and stir to obtain the lithium-ion battery electrolyte.

8. The application of a lithium-ion battery electrolyte as described in any one of claims 1-6 in a lithium-ion battery using lithium manganese iron phosphate as the cathode material.

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