Lithium ion battery electrolyte, preparation method thereof and lithium ion battery

Abstract

The invention provides a lithium ion battery electrolyte, a preparation method thereof and a lithium ion battery, the lithium ion battery electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, and the additive comprises a film-forming additive and an organic compound as shown in a structural formula I. A benzene ring in the additive can improve the battery voltage and prevent continuous side reaction between an electrolyte and a positive electrode material under the high voltage of 4.5 V or above, a sulfonate group can be reduced into an interfacial film containing a sulfur-oxygen structure on the surface of a negative electrode, the Li < + > diffusion resistance is reduced, the cycle performance is improved, cyano groups can be oxidized and polymerized on the surface of the positive electrode to form a compact protective layer, and the battery performance is improved. According to the present invention, the silicon oxygen group can effectively inhibit the oxidation decomposition of the electrolyte and the dissolution of the transition metal under the high voltage, can improve the boiling point of the electrolyte, can reduce the gas production risk at the high temperature, can capture the adverse substances in the electrolyte, and particularly can inhibit the influence of HF on the positive electrode and the negative electrode, such that the high-temperature stability is improved, and the high-temperature storage and cycle performance of the battery is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a lithium-ion battery electrolyte, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] With the wide use of energy storage, society's expectations for the performance of lithium-ion batteries are constantly rising, especially for their volumetric energy density, which puts forward more stringent requirements.

[0003] Among many cathode materials of lithium-ion batteries, lithium iron manganese phosphate (LiMn x Fe 1-x PO4, 0 < x < 1) with an olivine structure has characteristics such as high energy density and high working voltage, and is a promising new cathode material for the next generation. However, there are also new challenges in its use process. Under high voltage conditions, the oxidation reaction between the lithium iron manganese phosphate cathode material and the electrolyte is likely to intensify. In addition, metal ions in high valence states will also migrate under the action of an electric field, resulting in a reduction reaction at the negative electrode, leading to metal precipitation and irreversible capacity loss, which will have a serious impact on the high-temperature storage and cycling of the battery.

[0004] As an important component of lithium-ion batteries, the electrolyte has become one of the most important factors affecting the electrical performance of lithium iron manganese phosphate batteries. Through electrolyte optimization, the problems of poor high-temperature storage and cycling performance of lithium iron manganese phosphate batteries can be effectively solved. For example, Patent CN109473721A discloses a high-voltage electrolyte additive, which is a heterocyclic nitrile compound grafted with a nitrile group on an unsaturated five-membered heterocycle. It can form a dense and stable interfacial film on the surface of the cathode material, effectively inhibiting the oxidation decomposition of the electrolyte. The lithium-ion battery prepared with the high-voltage electrolyte containing this additive has effectively improved cycling performance and high-temperature shelf performance under high voltage; Patent CN104979589A discloses a high-voltage electrolyte and a lithium-ion battery using this electrolyte, including a non-aqueous solvent, a lithium salt, and an additive. The non-aqueous organic solvent is a carboxylic acid ester compound with a mass percentage content of 1-40% in the high-voltage electrolyte; the additive is any one or more of lithium bis(oxalato)borate (Li-BOB), fluoroethylene carbonate (FEC), and ethylene glycol bis(propionitrile) ether. The high-voltage electrolyte contains a carboxylic acid ester solvent that improves the electrode / electrolyte interface. Through the optimized combination of various additives such as Li-BOB, fluoroethylene carbonate, and ethylene glycol bis(propionitrile) ether, it ensures that the high-voltage battery obtains excellent cycling performance, and at the same time effectively improves the high-temperature storage performance of the high-voltage battery, and significantly inhibits the gas generation of the battery under high-voltage high-temperature storage.

[0005] However, the above-mentioned existing technologies have the problem of large film formation impedance, and there is still great room for improvement in the cycling and storage performance of the prepared batteries.

[0006] Therefore, there is an urgent need to provide an optimized lithium-ion battery electrolyte to effectively improve the cycling performance and high-temperature storage performance of lithium-ion batteries. Summary of the Invention

[0007] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a lithium-ion battery electrolyte, its preparation method and a lithium-ion battery. By introducing an organic compound shown in Structural Formula I as an additive into the lithium-ion battery electrolyte, the benzene ring in this additive can increase the battery voltage and prevent continuous side reactions between the electrolyte and the positive electrode material at high voltages above 4.5V. The sulfonate group can be reduced to an interfacial film containing a sulfur-oxygen structure on the surface of the negative electrode, reducing the Li + diffusion resistance and enhancing the cycling performance. The cyano group with high electronegativity can preferentially oxidize and polymerize on the surface of the positive electrode, thereby forming a dense protective layer, inhibiting the oxidation decomposition of the electrolyte and the dissolution of transition metals at high voltages, and at the same time increasing the boiling point of the electrolyte and reducing the risk of gas generation at high temperatures. The Si-O group can capture trace amounts of water, PF5, HF and other adverse substances in the electrolyte, especially effectively inhibiting the influence of HF on the positive and negative electrodes, thereby enhancing the high-temperature stability and further improving the high-temperature storage and cycling performance. Therefore, the cooperation between various functional groups can synergistically improve the cycling performance and high-temperature storage performance of lithium iron phosphate manganese batteries, greatly promoting the application of lithium iron phosphate manganese batteries in different environments.

[0008] To achieve the purpose of this invention, the following technical solutions are adopted:

[0009] In the first aspect, the present invention provides a lithium-ion battery electrolyte, which includes a non-aqueous organic solvent, a lithium salt and an additive, and the additive includes a film-forming additive and an organic compound shown in Structural Formula I:

[0010]

[0011] Wherein, R1, R2 and R3 are each independently selected from a hydrogen group, a siloxy group, a substituted or unsubstituted C1-C5 alkyl group, and at least one of R1, R2 and R3 is a siloxy group.

[0012] By introducing an organic compound shown in Structural Formula I as an additive into the lithium-ion battery electrolyte, the benzene ring in this additive can increase the battery voltage and prevent continuous side reactions between the electrolyte and the positive electrode material at high voltages above 4.5V. The sulfonate group can be reduced to an interfacial film containing a sulfur-oxygen structure on the surface of the negative electrode, reducing the Li +Diffusion resistance, improve cycle performance. The cyano group with high electronegativity can preferentially oxidize and polymerize on the surface of the positive electrode, thus forming a dense protective layer, inhibiting the oxidative decomposition of the electrolyte and the dissolution of transition metals under high voltage. At the same time, it can also increase the boiling point of the electrolyte and reduce the gas generation risk at high temperature. The siloxy group can capture trace amounts of water, PF5, HF and other harmful substances in the electrolyte, especially can effectively inhibit the influence of HF on the positive and negative electrodes, thereby improving the high-temperature stability, and further improving the high-temperature storage and cycle performance. Therefore, the cooperation between various functional groups can synergistically improve the cycle performance and high-temperature storage performance of lithium iron phosphate manganese batteries, greatly promoting the application of lithium iron phosphate manganese batteries in different environments.

[0013] Preferably, the R2 and / or R3 is a siloxy group.

[0014] It should be noted that for the organic compound shown in Structural Formula I, when the siloxy group undergoes a nucleophilic substitution reaction, it tends to attack the position on the benzene ring with relatively low electron cloud density. The cyano group in Structural Formula I is a strong electron-withdrawing group, which will reduce the electron cloud density of the carbon atoms adjacent to and para to the cyano group on the benzene ring, making them more vulnerable to attack by nucleophiles. Considering the steric hindrance and electronic effects comprehensively, the siloxy group may replace the hydrogen atom on the carbon atom para to the cyano group on the benzene ring. However, since the carbon atom of the benzene ring connected to the sulfonate group has no hydrogen atom available for substitution, if the siloxy group is to undergo a nucleophilic substitution reaction, on the premise of retaining the cyano group and the sulfonate group, based on the electron cloud density distribution on the benzene ring and the rules of nucleophilic substitution reactions, it will preferentially consider the hydrogen atom on the carbon atom adjacent to the cyano group on the benzene ring. The cyano group, as a strong electron-withdrawing group, reduces the electron cloud density of the adjacent position, making it more easily attacked by nucleophiles, and the siloxy group will replace the adjacent hydrogen atom to achieve the modification of this compound.

[0015] Preferably, the siloxy group is selected from any one of alkoxysiloxy groups, alkylsiloxy groups, hydroxylsiloxy groups, aminosiloxy groups or mercaptosiloxy groups.

[0016] Preferably, the R1 is a halomethyl group.

[0017] In the present invention, the halomethylene group contains halogen, which can promote the formation of a solid electrolyte interface film (SEI film) rich in lithium halide (such as LiF). Lithium halide (such as LiF) can improve the stability, mechanical strength and ionic conductivity of the SEI film, inhibit the further decomposition of the electrolyte, reduce the irreversible capacity loss, and improve the battery cycle performance. In addition, halogen has strong electronegativity and an electron-withdrawing inductive effect, which can change the molecular electron cloud distribution, reduce the interfacial impedance, and improve the battery charge-discharge efficiency and rate performance.

[0018] Preferably, the organic compound is selected from any one or a combination of at least two of the compounds shown in the following structural formulas:

[0019]

[0020] It should be noted that the present invention does not limit the synthesis method of organic compounds. Exemplarily, The synthesis method of includes: 1) Dissolve 4-cyanophenyl trifluoromethanesulfonate (CAS No.: 66107-32-3) in N,N-dimethylformamide, then dropwise add a reagent containing trimethylsilyloxy group (such as sodium trimethylsilyloxide), react at 5 °C for 1 h first, and then react at 40 °C for 4 h. After the reaction, perform extraction and separation, washing and drying to obtain the organic compound.

[0021] Preferably, based on the mass of the lithium-ion battery electrolyte being 100%, the mass ratio of the organic compound is 1.5 - 4%, for example, it can be 1.5%, 2%, 2.5%, 3%, 3.5% or 4%, etc.

[0022] In the present invention, adding an appropriate content of the organic compound to the lithium-ion battery electrolyte helps to form a dense and uniform-thickness film, which can effectively inhibit the dissolution of manganese ions and improve the storage and cycling performance of the battery.

[0023] Preferably, the film-forming additive includes any one or a combination of at least two of vinylene carbonate, ethylene sulfate or fluoroethylene carbonate.

[0024] Preferably, based on the mass of the lithium-ion battery electrolyte being 100%, the mass ratio of the film-forming additive is 1 - 3%, for example, it can be 1%, 1.5%, 2%, 2.5% or 3%, etc.

[0025] Preferably, the mass ratio of the organic compound shown in Structural Formula I to the film-forming additive is (1.5 - 3.5):(1.5 - 2.5). Among them, the selection range of the organic compound shown in Structural Formula I "1.5 - 3.5" can be, for example, 1.5, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.1, 3.2, 3.3, 3.4 or 3.5, etc., and the selection range of the film-forming additive "1.5 - 2.5" can be, for example, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4 or 2.5, etc.

[0026] In the present invention, using the above-mentioned appropriate mass ratio to organically combine the organic compound shown in Structural Formula I with the film-forming additive helps to form a dense film while efficiently inhibiting the dissolution of manganese ions. The two cooperate synergistically to jointly improve the storage and cycling performance of the battery.

[0027] Preferably, the non-aqueous organic solvent includes any one or a combination of at least two of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, or dimethyl carbonate, and is preferably a combination of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0028] Preferably, the mass ratio of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate is (15 - 30):(5 - 15):(35 - 65):(15 - 20). Among them, the selection range of "15 - 30" for ethylene carbonate can be, for example, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30, etc.; the selection range of "5 - 15" for diethyl carbonate can be, for example, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15, etc.; the selection range of "35 - 65" for ethyl methyl carbonate can be, for example, 35, 40, 45, 50, 55, 60, or 65, etc.; the selection range of "15 - 20" for dimethyl carbonate can be, for example, 15, 16, 17, 18, 19, or 20, etc.

[0029] In the present invention, using the combination of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate with the above mass ratio as the non-aqueous organic solvent in the electrolyte helps to obtain an electrolyte with an appropriate viscosity, thereby maintaining a high ionic conductivity.

[0030] Preferably, based on the mass of the lithium-ion battery electrolyte being 100%, the mass proportion of the non-aqueous organic solvent is 78 - 87.5%, and can be, for example, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, or 87.5%, etc.

[0031] Preferably, the lithium salt includes any one or a combination of at least two of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, or lithium bis(oxalato)borate.

[0032] Preferably, based on the mass of the lithium-ion battery electrolyte being 100%, the mass proportion of the lithium salt is 10 - 15%, and can be, for example, 10%, 11%, 12%, 13%, 14%, or 15%, etc.

[0033] In a second aspect, the present invention provides a method for preparing a lithium-ion battery electrolyte as described in the first aspect. The preparation method includes the following steps:

[0034] Mix an additive, a lithium salt, and a non-aqueous organic solvent to obtain the lithium-ion battery electrolyte.

[0035] Among them, the additive includes a film-forming additive and an organic compound as shown in Structural Formula I:

[0036]

[0037] Among them, R1, R2 and R3 are each independently selected from a hydrogen group, a siloxy group, a substituted or unsubstituted C1-C5 alkyl group, and at least one of the R1, R2 and R3 is a siloxy group.

[0038] Preferably, the mixing method includes:

[0039] Adding the lithium salt to the non-aqueous organic solvent, and then adding the film-forming additive and the organic compound.

[0040] Preferably, stirring is accompanied during the mixing process.

[0041] Preferably, the mixing temperature is 25-35°C, for example, it can be 25°C, 30°C or 35°C, etc.

[0042] In the present invention, the appropriate mixing temperature helps the lithium salt, the film-forming additive and the organic compound to be fully dissolved in the non-aqueous organic solvent.

[0043] Preferably, the mixing process is carried out in an inert atmosphere. Exemplarily, for example, it can be a nitrogen atmosphere, etc.

[0044] In a third aspect, the present invention provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and the lithium-ion battery electrolyte as described in the first aspect.

[0045] Preferably, the structural formula of the positive electrode active material in the positive electrode sheet is LiMn x Fe 1-x PO4, where 0 < x < 1, for example, it can be 0.2, 0.4, 0.6 or 0.8, etc.

[0046] In a fourth aspect, the present invention provides an electrical device, which includes the lithium-ion battery as described in the second aspect.

[0047] The numerical ranges described in the present invention not only include the above-listed point values, but also include any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the ranges.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] In the present invention, an organic compound as shown in structural formula I is introduced as an additive into the lithium-ion battery electrolyte. The benzene ring in the additive can increase the battery voltage and prevent the continuous side reaction between the electrolyte and the positive electrode material at high voltages above 4.5V. The sulfonate group can be reduced to an interface film containing a sulfur-oxygen structure on the surface of the negative electrode, reducing Li+ Diffusion resistance, improving cycle performance. The cyano group with high electronegativity can preferentially oxidize and polymerize on the surface of the positive electrode, thereby forming a dense protective layer, inhibiting the oxidation decomposition of the electrolyte and the dissolution of excessive metals under high voltage. At the same time, it can also increase the boiling point of the electrolyte and reduce the gas generation risk at high temperature. The siloxy group can capture trace amounts of water, PF5, HF and other adverse substances in the electrolyte, especially effectively inhibit the influence of HF on the positive and negative electrodes, thereby improving the high-temperature stability and further improving the high-temperature storage and cycle performance. Therefore, the cooperation among various functional groups can synergistically improve the cycle performance and high-temperature storage performance of lithium iron phosphate manganese batteries, greatly promoting the application of lithium iron phosphate manganese batteries in different environments. Specific embodiments

[0050] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0051] Example 1

[0052] This example provides a lithium-ion battery electrolyte. The lithium-ion battery electrolyte includes a non-aqueous organic solvent, a lithium salt, and an additive. The additive includes a film-forming additive and an organic compound shown in Structural Formula I:

[0053]

[0054] Among them, based on the mass of the lithium-ion battery electrolyte, the mass ratio of the organic compound is 1.5%; the film-forming additive is vinylene carbonate, and based on the mass of the lithium-ion battery electrolyte, the mass ratio of the film-forming additive is 2.5%; the mass ratio of the organic compound shown in Structural Formula I to the film-forming additive is 1.5:2.5; the non-aqueous organic solvent is a combination of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate, and the mass ratio of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate is 20:10:55:15. Based on the mass of the lithium-ion battery electrolyte, the mass ratio of the non-aqueous organic solvent is 84%; the lithium salt is lithium hexafluorophosphate, and based on the mass of the lithium-ion battery electrolyte, the mass ratio of the lithium salt is 12%.

[0055] This example also provides a preparation method for the above lithium-ion battery electrolyte. The preparation method includes the following steps:

[0056] (1) In a glove box filled with argon, first mix ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate according to a mass ratio of 20:10:55:15 to obtain a non-aqueous organic solvent.

[0057] (2) Under the condition of 30 °C, lithium hexafluorophosphate is added to the non-aqueous organic solvent, and then vinylene carbonate and the organic compound shown in Structural Formula I are added. After stirring evenly, a lithium-ion battery electrolyte is obtained; in the lithium-ion battery electrolyte, the mass ratio of lithium hexafluorophosphate is 12%, the mass ratio of vinylene carbonate is 2.5%, and the mass ratio of the organic compound is 1.5%.

[0058] Example 2

[0059] This example provides a lithium-ion battery electrolyte. The lithium-ion battery electrolyte includes a non-aqueous organic solvent, a lithium salt, and an additive. The additive includes a film-forming additive and the organic compound shown in Structural Formula I:

[0060]

[0061] Among them, based on the mass of the lithium-ion battery electrolyte, the mass ratio of the organic compound is 1.5%; the film-forming additive is ethylene sulfate. Based on the mass of the lithium-ion battery electrolyte, the mass ratio of the film-forming additive is 2.5%; the mass ratio of the organic compound shown in Structural Formula I to the film-forming additive is 1.5:2.5; the non-aqueous organic solvent is a combination of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate. The mass ratio of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate is 15:15:35:20. Based on the mass of the lithium-ion battery electrolyte, the mass ratio of the non-aqueous organic solvent is 86%; the lithium salt is lithium bis(fluorosulfonyl)imide. Based on the mass of the lithium-ion battery electrolyte, the mass ratio of the lithium salt is 10%.

[0062] This example also provides a preparation method for the above lithium-ion battery electrolyte. The preparation method includes the following steps:

[0063] (1) In a glove box filled with argon, ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate are first mixed according to a mass ratio of 15:15:35:20 to obtain a non-aqueous organic solvent.

[0064] (2) Under the condition of 30 °C, lithium bis(fluorosulfonyl)imide is added to the non-aqueous organic solvent, and then ethylene sulfate and the organic compound shown in Structural Formula I are added. After stirring evenly, a lithium-ion battery electrolyte is obtained; in the lithium-ion battery electrolyte, the mass ratio of lithium bis(fluorosulfonyl)imide is 10%, the mass ratio of ethylene sulfate is 2.5%, and the mass ratio of the organic compound is 1.5%.

[0065] Example 3

[0066] This embodiment provides a lithium-ion battery electrolyte. The lithium-ion battery electrolyte includes a non-aqueous organic solvent, a lithium salt, and an additive. The additive includes a film-forming additive and an organic compound represented by Structural Formula I:

[0067]

[0068] Among them, based on the mass of the lithium-ion battery electrolyte, the mass ratio of the organic compound is 3.5%; the film-forming additive is fluoroethylene carbonate, and based on the mass of the lithium-ion battery electrolyte, the mass ratio of the film-forming additive is 1.5%; the mass ratio of the organic compound represented by Structural Formula I to the film-forming additive is 3.5:1.5; the non-aqueous organic solvent is a combination of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate, and the mass ratio of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate is 30:5:35:20. Based on the mass of the lithium-ion battery electrolyte, the mass ratio of the non-aqueous organic solvent is 80%; the lithium salt is lithium bis(oxalato)borate, and based on the mass of the lithium-ion battery electrolyte, the mass ratio of the lithium salt is 15%.

[0069] This embodiment also provides a preparation method for the above lithium-ion battery electrolyte. The preparation method includes the following steps:

[0070] (1) In a glove box filled with argon, first mix ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate according to a mass ratio of 30:5:35:20 to obtain a non-aqueous organic solvent.

[0071] (2) Under the condition of 30 °C, add lithium bis(oxalato)borate to the non-aqueous organic solvent, and then add fluoroethylene carbonate and the organic compound represented by Structural Formula I. After stirring evenly, a lithium-ion battery electrolyte is obtained; in the lithium-ion battery electrolyte, the mass ratio of lithium bis(oxalato)borate is 15%, the mass ratio of fluoroethylene carbonate is 1.5%, and the mass ratio of the organic compound is 3.5%.

[0072] Example 4

[0073] The difference between this embodiment and Example 1 is that the mass ratio of the organic compound is 2.5%, and at the same time, the mass ratio of the non-aqueous organic solvent is adaptively adjusted.

[0074] The remaining preparation methods and parameters are the same as those in Example 1.

[0075] Example 5

[0076] The difference between this embodiment and Example 1 is that the mass ratio of the organic compound is 3.5%, and at the same time, the mass ratio of the non-aqueous organic solvent is adaptively adjusted.

[0077] The remaining preparation methods and parameters are the same as those in Example 1.

[0078] Example 6

[0079] The difference between this example and Example 4 is that the mass ratio of vinylene carbonate is 1.5%, and at the same time, the mass ratio of the non-aqueous organic solvent is adjusted accordingly.

[0080] The remaining preparation methods and parameters are the same as those in Example 4.

[0081] Example 7

[0082] The difference between this example and Example 1 is that the mass ratio of the organic compound is 5.5%, and at the same time, the mass ratio of the non-aqueous organic solvent is adjusted accordingly.

[0083] The remaining preparation methods and parameters are the same as those in Example 1.

[0084] Example 8

[0085] The difference between this example and Example 1 is that the mass ratio of the organic compound is 0.5%, and at the same time, the mass ratio of the non-aqueous organic solvent is adjusted accordingly.

[0086] The remaining preparation methods and parameters are the same as those in Example 1.

[0087] Example 9

[0088] The difference between this example and Example 1 is that the mass ratio of vinylene carbonate is 3.5%, and at the same time, the mass ratio of the non-aqueous organic solvent is adjusted accordingly.

[0089] The remaining preparation methods and parameters are the same as those in Example 1.

[0090] Example 10

[0091] The difference between this example and Example 1 is that the mass ratio of vinylene carbonate is 0.5%, and at the same time, the mass ratio of the non-aqueous organic solvent is adjusted accordingly.

[0092] The remaining preparation methods and parameters are the same as those in Example 1.

[0093] Comparative Example 1

[0094] The difference between this comparative example and Example 1 is that in step (2), the organic compound shown in structural formula I is not added, and the mass ratio of vinylene carbonate is ensured to be 4%.

[0095] The remaining preparation methods and parameters are the same as those in Example 1.

[0096] Comparative Example 2

[0097] The difference between this comparative example and Example 1 is that vinylene carbonate is not added in step (2).

[0098] The remaining preparation methods and parameters are the same as those in Example 1.

[0099] Comparative Example 3

[0100] The difference between this comparative example and Example 1 is that the organic compound described in step (2) is replaced with 4-cyanophenyl trifluoromethanesulfonate.

[0101] The remaining preparation methods and parameters are the same as those in Example 1.

[0102] Performance Test

[0103] Lithium-ion batteries are made from the lithium-ion battery electrolytes provided in the above examples and comparative examples. The specific steps include:

[0104] 1) Preparation of the positive electrode sheet: LiMn 0.5 Fe 0.5 PO4 positive electrode active material, polyvinylidene fluoride, acetylene black and carbon nanotubes are added to N-methylpyrrolidone in a weight ratio of 96:2:1.5:0.5, and stirred and mixed to obtain a positive electrode slurry; then the positive electrode slurry is coated on an aluminum foil and dried in a vacuum oven at 100 °C for 12 h, and after rolling and slitting, a positive electrode sheet is obtained.

[0105] 2) Preparation of the negative electrode sheet: artificial graphite, polyacrylic acid, sodium carboxymethyl cellulose, styrene-butadiene rubber and acetylene black are mixed and added to deionized water in a mass ratio of 96:1.5:0.5:1:1, and stirred and mixed to obtain a negative electrode slurry; then the negative electrode slurry is coated on a copper foil and dried in a vacuum oven at 100 °C for 12 h, and after rolling and slitting, a negative electrode sheet is obtained.

[0106] 3) Assembly of the battery: The prepared positive electrode sheet, negative electrode sheet and polypropylene separator are assembled into a soft-pack battery cell, and then transferred to a glove box to inject the lithium-ion battery electrolytes provided in the above examples and comparative examples; the battery cells after injection are left standing, formed, aged, shaped and sorted to obtain lithium-ion batteries.

[0107] The above lithium-ion batteries are subjected to high-temperature storage performance tests and cycle performance tests. Among them, the test steps for high-temperature storage performance include:

[0108] The lithium-ion battery is charged at a constant current and constant voltage of 1.0C to 4.5V at 25°C, left standing for 5 min, then discharged at 0.1C to 2.5V. The discharged capacity is recorded as the initial capacity. Then it is charged at a constant current and constant voltage of 1.0C to 4.5V again, and the initial thickness and initial internal resistance are measured. The lithium-ion battery is stored under the condition of 60°C ± 2°C, and after open-circuit storage for 30 days, the battery is taken out, the hot-state thickness is tested, the internal resistance is tested after standing at room temperature for 2 h, then the battery core is charged and discharged at 1.0C, the remaining capacity and recovery capacity are tested, and then the thermal thickness change rate, internal resistance change rate, capacity retention rate and capacity recovery rate are calculated.

[0109] The test steps for the cycle performance test include:

[0110] Charge and discharge at 1C at 25°C, the voltage range is 2.5 - 4.5V, the number of cycles is 1000 cycles, and calculate the capacity retention rate.

[0111] The above test results are shown in Table 1.

[0112] Table 1

[0113]

[0114]

[0115] Analysis:

[0116] As can be seen from Table 1, by comparing Example 1, Example 2, Example 3, Example 4, Example 5, Example 7, Example 8 and Comparative Example 1, it can be known that when the organic compound provided by the present invention is synergistically combined with the film-forming additive, the high-temperature storage and cycle performance can be effectively improved, and when the addition amount of the organic compound is 2.5%, the performance is optimal.

[0117] By comparing Example 4, Example 6, Example 9, Example 10 and Comparative Example 2, it can be known that when the film-forming additive vinylene carbonate is synergistically combined with the organic compound, and when the addition amount of the film-forming additive vinylene carbonate is 2.5%, the improvement effect on the high-temperature storage and cycle performance of the battery is optimal.

[0118] By comparing Example 1 and Comparative Example 3, it can be known that the synergistic effect among the sulfonate group, the cyano group and the siloxy group is excellent, and the organic compound having the above groups can more significantly improve the high-temperature storage performance and cycle performance of the battery.

[0119] It should be noted that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of the raw materials selected for the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A lithium-ion battery electrolyte, characterized in that, The lithium-ion battery electrolyte includes a non-aqueous organic solvent, a lithium salt, and an additive, and the additive includes a film-forming additive and an organic compound represented by Structural Formula I: Wherein, R1, R2, and R3 are each independently selected from a hydrogen group, a siloxy group, a substituted or unsubstituted C1-C5 alkyl group, and at least one of the R1, R2, and R3 is a siloxy group.

2. The lithium-ion battery electrolyte according to claim 1, wherein The R2 and / or R3 is a siloxy group; Preferably, the siloxy group is selected from any one of an alkoxysiloxy group, an alkylsiloxy group, a hydroxylsiloxy group, an aminosiloxy group, or a mercaptosiloxy group; Preferably, the R1 is a halomethyl group.

3. The lithium-ion battery electrolyte according to claim 1 or 2, characterized in that, The organic compound is selected from any one or a combination of at least two of the compounds represented by the following structural formulas:

4. The lithium-ion battery electrolyte according to any one of claims 1-3, characterized in that, Based on the mass of the lithium-ion battery electrolyte being 100%, the mass ratio of the organic compound is 1.5-4%.

5. The electrolyte for a lithium-ion battery according to any one of claims 1-4, characterized in that, The film-forming additive includes any one or a combination of at least two of vinylene carbonate, ethylene sulfate, or fluoroethylene carbonate; Preferably, based on the mass of the lithium-ion battery electrolyte being 100%, the mass ratio of the film-forming additive is 1-3%; Preferably, the mass ratio of the organic compound represented by Structural Formula I to the film-forming additive is (1.5-3.5):(1.5-2.5).

6. The electrolyte for a lithium-ion battery according to any one of claims 1-5, characterized in that, The non-aqueous organic solvent includes any one or a combination of at least two of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, or dimethyl carbonate, and is preferably a combination of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate; Preferably, the mass ratio of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate is (15-30):(5-15):(35-65):(15-20); Preferably, based on the mass of the lithium-ion battery electrolyte being 100%, the mass ratio of the non-aqueous organic solvent is 78-87.5%; Preferably, the lithium salt includes any one or a combination of at least two of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, or lithium bis(oxalato)borate; Preferably, based on the mass of the lithium-ion battery electrolyte being 100%, the mass ratio of the lithium salt is 10-15%.

7. A method for preparing an electrolyte of a lithium-ion battery according to any one of claims 1-6, characterized in that, The preparation method includes the following steps: Mix the additive, the lithium salt, and the non-aqueous organic solvent to obtain the lithium-ion battery electrolyte; Wherein, the additive includes a film-forming additive and an organic compound represented by Structural Formula I: Wherein, R1, R2, and R3 are each independently selected from a hydrogen group, a siloxy group, a substituted or unsubstituted C1-C5 alkyl group, and at least one of the R1, R2, and R3 is a siloxy group.

8. The preparation method according to claim 7, characterized in that, The mixing method includes: Add the lithium salt to the non-aqueous organic solvent, and then add the film-forming additive and the organic compound; Preferably, stirring is accompanied during the mixing process; Preferably, the mixing temperature is 25-35°C; Preferably, the mixing process is carried out in an inert atmosphere.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, a separator, and the lithium-ion battery electrolyte according to any one of claims 1-6.

10. The lithium-ion battery according to claim 9, characterized in that, The structural formula of the positive active material in the positive electrode sheet is LiMn x Fe 1-x PO4, where 0 < x < 1.

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