Electrolyte, preparation method and application thereof

Abstract

The application provides an electrolyte, a preparation method and application thereof, the electrolyte comprises an organic solvent, a lithium salt, an interface additive and a fluorine-containing diluent; the interface additive comprises a boric acid bis-sulfolactone compound; the boric acid bis-sulfolactone compound has a structure shown in formula I; in the application, the electrolyte is compounded by selecting a specific structure of the interface additive and the fluorine-containing diluent, so that the electrolyte has high conductivity, forms a unique high-voltage-resistant fast-charging electrolyte system, improves the high-voltage resistance and cycle performance of the battery, has higher charging capacity under the same condition, and has good fast-charging performance.

Description

Technical Field

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

[0002] Lithium-ion batteries are characterized by high energy density, long cycle life, and environmental friendliness, and are widely used in 3C digital products, electric vehicles, military and aerospace fields. With the popularization of consumer digital products and the widespread application of new energy vehicles, the demand for shortening the charging time of these products has further increased. Therefore, the development of fast-charging lithium-ion batteries has become a research hotspot in recent years.

[0003] Currently, the market is constantly seeking a lithium-ion battery that can charge quickly, while also possessing high safety and long lifespan. Research has found that developing fast-charging electrolytes is key to meeting these requirements. During fast charging, lithium ions rapidly escape from the positive electrode into the electrolyte, then pass through the separator and enter the negative electrode for lithium intercalation. This rapid migration of a large number of lithium ions necessitates electrolytes with high kinetic performance and low mass transfer resistance. Therefore, the electrolyte needs to have good wettability, low viscosity, and low lithium-ion transport resistance. However, traditional electrolyte systems mainly consist of lithium hexafluorophosphate dissolved in a carbonate-based mixed solvent. Their kinetic performance is insufficient, leading to ohmic polarization and concentration polarization under fast charging conditions. Increased battery polarization results in lithium plating, further causing problems such as low capacity, rapid capacity decay, short cycle life, and low safety.

[0004] In existing technologies, fast-charging electrolytes mostly improve their kinetic performance by reducing the lithium salt concentration, increasing the proportion of low-viscosity linear carbonates, or adding carboxylic acid esters to lower the electrolyte viscosity. Generally, these low-lithium-salt-concentration electrolytes have lower viscosity and higher conductivity, but slightly poorer electrochemical stability. Furthermore, low-viscosity solvents like carboxylic acid esters often have low boiling points, which can challenge the battery's high-temperature performance and safety. High-concentration electrolytes, on the other hand, have most solvent molecules that bind to Li... + The electrolyte combines to form a solvated shell structure, resulting in high electrochemical stability. However, the high viscosity and low ion mobility caused by high concentration lead to a decrease in the electrical performance of the electrolyte.

[0005] Therefore, developing an electrolyte that is resistant to high voltage, has good safety, good cycle performance, high ionic conductivity, and can achieve fast charging is an urgent problem to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an electrolyte, its preparation method, and its applications. This electrolyte overcomes the limitations of current low-concentration and high-concentration electrolytes, exhibiting excellent electrochemical stability, low viscosity, high ion permeability, improved high-voltage resistance and cycle performance of batteries, high charging capacity, and good fast-charging performance.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides an electrolyte comprising an organic solvent, a lithium salt, an interfacial additive, and a fluorinated diluent; the interfacial additive comprising a borate disulfonate lactone compound; the borate disulfonate lactone compound having the structure shown in Formula I:

[0009]

[0010] Wherein, R1 is selected from any one of the following: substituted or unsubstituted C2-C6 (e.g., C2, C3, C4, C5, C6) straight-chain or branched alkenyl groups; substituted or unsubstituted C2-C6 (e.g., C2, C3, C4, C5, C6) straight-chain or branched alkynyl groups; R2 and R3 are each independently selected from any one of the following: H, F, substituted or unsubstituted C1-C6 (e.g., C1, C2, C3, C4, C5, C6) straight-chain or branched alkyl groups; the substituted substituents include any one of the following: C1-C6 (e.g., C1, C2, C3, C4, C5, C6) straight-chain or branched alkyl groups; and halogens.

[0011] In this invention, the interface additive can participate in the film formation of both the positive and negative electrodes, achieving low-resistance film formation characteristics through the regulation of different functional groups. On the positive electrode side, under high voltage, it can decompose into a thin surface film, yielding a sulfonate structure, improving interfacial lithium conductivity, while simultaneously inhibiting the decomposition of lithium salt and electrolyte on the positive electrode surface, reducing the film formation impedance of the positive electrode material. On the negative electrode side, this interface additive contains double or triple bond functional groups, which can gradually reduce and decompose on the negative electrode, forming a thinner but denser SEI film. Under the synergistic effect of borate ester functional groups, LiF in the negative electrode SEI may dissolve to a certain extent, resulting in an SEI with numerous pores, good permeability, and low internal resistance, which is beneficial for further reducing the impedance of lithium-ion batteries and effectively improving battery fast-charging performance.

[0012] The electrolyte, formulated with a specific structure of interfacial additives and a fluorinated diluent, forms a unique high-voltage fast-charging electrolyte system. This system retains the excellent properties of high-concentration electrolytes while also achieving the advantages of low-concentration electrolytes, such as low viscosity and high ionic conductivity. It not only alters the solvation structure of lithium ions in the electrolyte, reducing their desolvation ability and improving battery reaction kinetics, but also enhances the battery's high-voltage performance. Furthermore, the addition of the fluorinated diluent and the specific structure of the interfacial additives promotes the participation of lithium salt anions in the solvation structure, thereby forming a stable, dense, and low-impedance SEI layer, further improving the battery's cycle performance.

[0013] In this invention, the high voltage refers to a voltage of 2.8-4.35V, and high voltage resistance means that the electrolyte still has excellent fast charging performance and cycle performance at 2.8-4.35V.

[0014] Preferably, in the borate disulfonate lactone compound, R1 is selected from any one of substituted or unsubstituted C2-C6 straight-chain or branched alkenyl groups, and / or R2 and R3 are each independently selected from F.

[0015] Preferably, the borate disulfonate lactone compound is selected from at least one of compounds having the following structures:

[0016]

[0017] Preferably, the mass percentage of the interfacial additive in the electrolyte is 0.5% to 3%, for example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, etc.

[0018] Preferably, the fluorinated diluent comprises at least one of tris(2,2,2-trifluoroethyl) orthoformate, tris(2,2,3,3-tetrafluoropropyl) orthoformate, or tris(2,2,3,3,3-pentafluoropropyl) orthoformate.

[0019] Preferably, the volume percentage of the fluorinated diluent is 40-60% based on the total volume of the organic solvent and the fluorinated diluent as 100%, for example, it can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, etc.

[0020] In this invention, on the one hand, by adding a fluorinated diluent that cannot dissolve lithium salts but is miscible with carbonate electrolytes to a high-concentration electrolyte, a locally diluted electrolyte is formed. This retains the characteristics of a high-concentration electrolyte while also achieving the advantages of a low-concentration electrolyte, such as low viscosity, good wettability, and high ionic conductivity, which is beneficial for lithium-ion transport. On the other hand, the fluorinated diluent used in this invention has low viscosity, high boiling point and flash point, and the O in the compound is affected by the highly electronegative F element, which interacts with Li. + The binding ability is weak, which enhances the binding between anions and Li. + The interaction between them allows more anions to participate in the formation of an SEI film with high mechanical strength, high ionic conductivity and fast ion diffusion. Through the cooperation of fluorinated diluents and interface additives, lithium salt anions can participate in the solvation structure, thereby forming a stable, dense SEI layer with low impedance, which further improves the cycle performance of the battery.

[0021] Preferably, the organic solvent includes carbonate organic solvents.

[0022] In this invention, carbonate solvents are used as the base solvent, which is consistent with currently commercial electrolytes. This has the advantages of a wide electrochemical window and strong high-voltage resistance, making it more conducive to practical application.

[0023] Preferably, the carbonate organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, or fluoroethylene carbonate.

[0024] Preferably, the lithium salt comprises at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium di(oxalato)borate, lithium tetrafluoroborate, or lithium di(oxalato)borate.

[0025] Preferably, the concentration of lithium salt in the electrolyte is 0.8 to 1.5 mol / L, for example, it can be 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, etc.

[0026] In a second aspect, the present invention provides a method for preparing the electrolyte according to the first aspect, the method comprising:

[0027] The electrolyte is obtained by mixing an organic solvent, a lithium salt, a fluorinated diluent, and an interfacial additive.

[0028] Preferably, the mixing process includes mixing lithium salt, organic solvent and fluorine-containing diluent, and then mixing the resulting mixture with an interface additive to obtain the electrolyte.

[0029] Thirdly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the electrolyte as described in the first aspect.

[0030] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] The electrolyte provided by this invention incorporates interface additives with specific structures and fluorinated diluents. The two work together to improve the conductivity of the electrolyte, forming a unique high-voltage fast-charging electrolyte system. This improves the battery's high-voltage resistance and cycle performance, resulting in higher charging capacity and excellent fast-charging performance under the same conditions. Detailed Implementation

[0033] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0034] Example 1

[0035] This embodiment provides an electrolyte comprising 1.2M lithium hexafluorophosphate (LiPF6) and 1% interfacial additive (acetylenyl borate disulfonate lactone). ), ethylene carbonate, methyl ethyl carbonate and tris(2,2,2-trifluoroethyl) orthoformate (TTFO); wherein the volume percentage of ethylene carbonate (EC), methyl ethyl carbonate (EMC) and tris(2,2,2-trifluoroethyl) orthoformate is 25:35:40.

[0036] This embodiment provides a method for preparing an electrolyte, the method comprising the following steps:

[0037] Lithium hexafluorophosphate, a conductive lithium salt, is added to a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and tri(2,2,2-trifluoroethyl) orthoformate, and the solution is fully dissolved to form a solution. Then, ethynyl borate disulfonate lactone is added to the solution and mixed evenly to obtain the electrolyte.

[0038] Example 2

[0039] This embodiment provides an electrolyte comprising 1.2M lithium hexafluorophosphate (LiPF6) and 1% interfacial additive (acetylenyl borate disulfonate lactone). ), ethylene carbonate, methyl ethyl carbonate and tris(2,2,2-trifluoroethyl) orthoformate (TTFO); wherein the volume percentage of ethylene carbonate (EC), methyl ethyl carbonate (EMC) and tris(2,2,2-trifluoroethyl) orthoformate is 25:25:50.

[0040] This embodiment provides a method for preparing an electrolyte, and the specific steps are the same as in Embodiment 1.

[0041] Example 3

[0042] This embodiment provides an electrolyte comprising 1.2M lithium hexafluorophosphate (LiPF6) and 1% interfacial additive (acetylenyl borate disulfonate lactone). The mixture comprises ethylene carbonate, methyl ethyl carbonate, and tris(2,2,2-trifluoroethyl) orthoformate (TTFO); wherein the volume percentages of ethylene carbonate (EC), methyl ethyl carbonate (EMC), and tris(2,2,2-trifluoroethyl) orthoformate are 25:15:60.

[0043] This embodiment provides a method for preparing an electrolyte, and the specific steps are the same as in Embodiment 1.

[0044] Example 4

[0045] This embodiment provides an electrolyte comprising 1.2M lithium bis(fluorosulfonyl)imide and 1.5% interfacial additives. Ethylene carbonate, methyl ethyl carbonate, and tris(2,2,3,3-tetrafluoropropyl)orthoformate; wherein the volume percentage of ethylene carbonate, methyl ethyl carbonate, and tris(2,2,3,3-tetrafluoropropyl)orthoformate is 25:35:40.

[0046] This embodiment provides a method for preparing an electrolyte, and the specific steps are the same as in Embodiment 1.

[0047] Example 5

[0048] This embodiment provides an electrolyte comprising 1.2M lithium hexafluorophosphate and 2.5% interfacial additives. Ethylene carbonate, methyl ethyl carbonate, and tris(2,2,3,3,3-pentafluoropropyl) orthoformate; wherein the volume percentage of ethylene carbonate, methyl ethyl carbonate, and tris(2,2,3,3,3-pentafluoropropyl) orthoformate is 25:35:40.

[0049] This embodiment provides a method for preparing an electrolyte, and the specific steps are the same as in Embodiment 1.

[0050] Comparative Example 1

[0051] This comparative example provides an electrolyte that differs from Example 1 only in that the electrolyte does not contain a fluorinated diluent, and the volume ratio of ethylene carbonate to methyl ethyl carbonate is 25:75. All other components, amounts, and preparation methods are the same as in Example 1.

[0052] Comparative Example 2

[0053] This comparative example provides an electrolyte that differs from Example 1 only in that the interfacial additive is replaced with an equal mass of disulfonate compound. The other components, dosages, and preparation methods are the same as in Example 1.

[0054] Comparative Example 3

[0055] This comparative example provides an electrolyte that differs from Example 1 only in that the electrolyte does not contain fluorinated diluents or interface additives, and the volume ratio of ethylene carbonate to methyl ethyl carbonate is 25:75. All other components, amounts, and preparation methods are the same as in Example 1.

[0056] Performance testing

[0057] (1) Conductivity: The conductivity of the electrolytes provided in Examples 1-5 and Comparative Examples 1-3 was tested using a conductivity meter at 25°C.

[0058] (2) The electrolytes provided in Examples 1-5 and Comparative Examples 1-3 were injected into 2000mAh pouch cells. The positive electrode material of the pouch cells was a single-crystal ternary electrode, and the negative electrode material was graphite. After formation, the cells were activated and subjected to rate charging and cycle tests, with a voltage range of 2.8-4.35V.

[0059] The specific test results are shown in Table 1:

[0060] Table 1

[0061]

[0062] As shown in the table above, the electrolyte provided by this invention, through the compounding of a fluorinated diluent and an interface additive, retains the advantages of both high-concentration and low-concentration electrolytes, forming a unique high-voltage fast-charging electrolyte system. This improves the battery's high-voltage resistance and cycle performance, resulting in higher charging capacity under the same conditions and excellent fast-charging performance. The electrolyte has a conductivity of 8.83–9.88 mS / cm, a 4C charging capacity of 1729.4–1905.2 mAh, a charging capacity percentage of 86.47–95.26% of the rated capacity, and a capacity retention rate of 78.9–89.8% after 500 cycles at 45°C.

[0063] As can be seen from the comparison between the examples and the comparative examples, the electrolyte provided by the present invention can charge significantly more electricity at a high 4C rate, with a 4C fast charging capacity of 86.47% or higher, while the 4C fast charging capacity in the comparative examples is lower. This indicates that the electrolyte of the present invention has good internal conductivity and can better withstand high-rate lithium-ion migration, thus exhibiting excellent fast charging performance. Furthermore, the addition of interface additives with specific structures can achieve low-resistance film formation at the positive and negative electrode interfaces by regulating different functional groups, which is beneficial for further reducing the impedance of lithium-ion batteries and effectively improving the fast charging performance of the batteries.

[0064] Compared with Comparative Example 1, Example 1 showed a further improvement in capacity retention after 500 cycles at 45°C. This was due to the addition of fluorinated compounds, which promoted the participation of more anions in solvation configuration coordination. The resulting SEI contained more LiF, which could effectively alleviate the volume expansion effect of silicon, thereby stabilizing the silicon particles and the silicon electrode, and further improving the cycle performance of the battery.

[0065] As can be seen from the comparison of Example 1 and the comparative example, the cycle performance is significantly improved. On the one hand, the addition of fluorinated compounds promotes the participation of more anions in solvation configuration coordination, and the resulting SEI contains more LiF, which can effectively alleviate the volume expansion effect of silicon, thereby stabilizing the stability of silicon particles and silicon electrodes, and further improving the cycle performance of the battery. On the other hand, the interface additives can participate in the film formation of both positive and negative electrodes. The low-resistance interface film generated can further inhibit the decomposition of lithium salt and electrolyte on the surface of positive and negative electrodes, reduce the occurrence of side reactions at the electrolyte / electrode interface under high voltage, and help to further improve cycle performance. The two work together to further improve the battery's high voltage resistance, cycle performance, and fast charging performance.

[0066] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0067] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

[0068] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte includes an organic solvent, a lithium salt, an interfacial additive, and a fluorinated diluent; The interface additives include borate disulfonate lactone compounds. The borate disulfonate lactone compound has the structure shown in Formula I: Equation I; R1 is selected from any one of substituted or unsubstituted C2-C6 straight-chain or branched alkenyl groups or substituted or unsubstituted C2-C6 straight-chain or branched alkynyl groups. R2 and R3 are each independently selected from any one of H, F, substituted or unsubstituted C1~C6 straight-chain or branched alkyl groups; The substituents include any one of C1-C6 straight-chain or branched alkyl groups and halogens; The fluorinated diluent includes at least one of tris(2,2,2-trifluoroethyl) orthocarbamate, tris(2,2,3,3-tetrafluoropropyl) orthocarbamate, or tris(2,2,3,3,3-pentafluoropropyl) orthocarbamate; The volume percentage of the fluorinated diluent is 40-60%, based on the total volume of the organic solvent and the fluorinated diluent as 100%.

2. The electrolyte according to claim 1, characterized in that, In the borate disulfonate lactone compounds, R1 is selected from any one of substituted or unsubstituted C2-C6 straight-chain or branched alkenyl groups, and / or R2 and R3 are each independently selected from F.

3. The electrolyte according to claim 1, characterized in that, The borate disulfonate lactone compound is selected from at least one of compounds having the following structures: 。 4. The electrolyte according to claim 1, characterized in that, The electrolyte contains 0.5% to 3% by mass of the interfacial additive.

5. The electrolyte according to claim 1, characterized in that, The organic solvents include carbonate organic solvents.

6. The electrolyte according to claim 5, characterized in that, The carbonate organic solvents include at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, or fluoroethylene carbonate.

7. The electrolyte according to claim 1, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium di(oxalato)borate, lithium tetrafluoroborate, or lithium di(oxalato)borate.

8. The electrolyte according to claim 1, characterized in that, The concentration of lithium salt in the electrolyte is 0.8~1.5 mol / L.

9. A method for preparing an electrolyte according to any one of claims 1 to 8, characterized in that, The preparation method includes: The electrolyte is obtained by mixing an organic solvent, a lithium salt, a fluorinated diluent, and an interfacial additive.

10. The preparation method according to claim 9, characterized in that, The mixing process involves mixing lithium salt, organic solvent, and fluorinated diluent, followed by mixing the resulting mixture with an interfacial additive to obtain the electrolyte.

11. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte as described in any one of claims 1 to 8.

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