Electrolyte and preparation method and application thereof

Abstract

The invention provides an electrolyte as well as 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 disultone compound; the boric acid disultone compound has a structure as shown in a formula I; according to the electrolyte, the interface additive with a specific structure and the fluorine-containing diluent are compounded, so that the electrolyte is high in conductivity, a unique high-voltage-resistant fast-charging electrolyte system is formed, the high-voltage-resistant performance and the cycle performance of the battery are improved, and under the same condition, the charging capacity is higher, and the battery has good fast-charging performance.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries and relates to an electrolyte and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have the characteristics of high energy density, long cycle life, and environmental friendliness, and are widely used in 3C digital products, electric vehicles, military aerospace, etc. With the popularization of consumer digital products and the widespread application of new energy vehicles, people's requirements for shortening the charging time of such products have further increased. Therefore, the development of lithium-ion batteries that can be charged quickly has become a research hotspot in recent years.

[0003] At present, the market has always been pursuing a lithium-ion battery that can be charged quickly, has high safety and long life. Research has found that the development of fast-charging electrolytes is the key to meeting the above requirements. During the fast charging process of the battery, lithium ions quickly escape from the positive electrode into the electrolyte, then pass through the diaphragm and enter the negative electrode for lithium insertion. The rapid migration of a large number of lithium ions requires the electrolyte to have higher kinetic properties and smaller mass transfer resistance during the mass transfer process. Therefore, the electrolyte needs to meet better wettability, lower viscosity, and lower lithium ion transmission resistance. The traditional electrolyte system is mainly composed of lithium salt lithium hexafluorophosphate dissolved in a carbonate-based mixed solvent. The kinetic performance is not high enough. Under fast charging conditions, ohmic polarization and concentration polarization will occur. The increase in battery polarization will lead to the occurrence of lithium precipitation, and further problems such as low capacity, rapid capacity decay, short cycle life, and low safety will occur.

[0004] In the prior art, most fast-charge electrolytes reduce the viscosity of the electrolyte by reducing the lithium salt concentration, increasing the proportion of low-viscosity linear carbonates, or adding carboxylates, thereby improving the kinetic performance of the electrolyte. Generally speaking, this type of electrolyte with a low lithium salt concentration has a low viscosity and high conductivity, but slightly poor electrochemical stability. In addition, low-viscosity solvents such as carboxylates often have a low boiling point, which will cause challenges to the high-temperature performance and safety performance of the battery. High-concentration electrolytes have a high viscosity and low conductivity, which is not conducive to the battery's performance. + The combination forms a solvated shell structure, so the electrochemical stability is high, but the high viscosity and low ion mobility caused by high concentration will lead to the decline of 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] In view of the shortcomings of the prior art, the purpose of the present invention is to provide an electrolyte and a preparation method and application thereof. The electrolyte overcomes the limitations of current low-concentration and high-concentration electrolytes, has excellent electrochemical stability, low viscosity, high ion permeability, improves the high-voltage resistance and cycle performance of the battery, has high charging capacity, and has good fast charging performance.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides an electrolyte, the electrolyte comprising an organic solvent, a lithium salt, an interface additive and a fluorine-containing diluent; the interface additive comprises a boric acid bissultone compound; the boric acid bissultone compound has a structure shown in Formula I:

[0009]

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

[0011] In the present invention, the interface additive can participate in the film formation of the positive and negative electrodes at the same time, and the low impedance film formation characteristics can be achieved through the regulation of different functional groups. In terms of the positive electrode, it can be decomposed into a thin surface film at the positive electrode under high voltage to obtain a sulfonate structure, improve the interface lithium conductivity, and inhibit the decomposition of lithium salts and electrolytes on the positive electrode surface, reducing the film formation impedance of the positive electrode material; in terms of the negative electrode, this interface additive contains double or triple bond functional groups, which can be gradually reduced and decomposed at the negative electrode to form a thinner but denser SEI film. Under the synergistic effect of the borate functional group, the LiF in the negative electrode SEI may be dissolved to a certain extent, resulting in the SEI having the advantages of many holes, good permeability, and low internal resistance, which is conducive to further reducing the impedance of lithium-ion batteries and can effectively improve the performance of battery fast charging.

[0012] The electrolyte is compounded by an interface additive with a specific structure and a fluorine-containing diluent, so that the electrolyte forms a unique high-voltage fast-charging electrolyte system, which not only retains the excellent properties of a high-concentration electrolyte, but also obtains the advantages of low viscosity and high ionic conductivity of a low-concentration electrolyte; it not only changes the solvation structure of lithium ions in the electrolyte, reduces the desolvation ability of lithium ions, improves the battery reaction kinetics, but also improves the high-voltage resistance of the battery; at the same time, the addition of a fluorine-containing diluent and an interface additive with a specific structure can also promote the lithium salt anions to participate in the solvation structure, thereby forming a stable, dense and low-impedance SEI layer, further improving the battery's cycle performance.

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

[0014] Preferably, in the boric acid bissulfone lactone compound, R1 is selected from any one of a substituted or unsubstituted C2-C6 straight chain or branched alkenyl group, a substituted or unsubstituted C2-C6 straight chain or branched alkynyl group, and / or R2 and R3 are each independently selected from F.

[0015] Preferably, the boric acid bissulfone compound is selected from at least one of the compounds having the following structures:

[0016]

[0017] Preferably, the mass percentage of the interfacial additive in the electrolyte is 0.5-3%, 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% and the like.

[0018] Preferably, the fluorine-containing diluent includes 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, based on the total volume of the organic solvent and the fluorine-containing diluent as 100%, the volume percentage of the fluorine-containing diluent is 40-60%, 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% and the like.

[0020] In the present invention, on the one hand, by adding a fluorinated diluent that cannot dissolve lithium salts but can be miscible with carbonate electrolytes into a high-concentration electrolyte, a local dilution electrolyte is formed, which not only retains the characteristics of the high-concentration electrolyte, but also obtains the advantages of low viscosity, good wettability, and high ion conductivity of the low-concentration electrolyte, which is conducive to the transmission of lithium ions; on the other hand, the fluorinated diluent used in the present invention has low viscosity, high boiling point and flash point, and O in the compound is affected by the F element with strong electronegativity and reacts with Li + The binding capacity is weak, which enhances the anion and Li + The interaction between them enables more anions to participate in the formation of a SEI film with the characteristics of high mechanical strength, high ionic conductivity, and fast ion diffusion; through the mutual cooperation of fluorine-containing diluents and interfacial additives, lithium salt anions can be encouraged to participate in the solvation structure, thereby forming a stable, dense and low-impedance SEI layer, further improving the battery's cycle performance.

[0021] Preferably, the organic solvent comprises a carbonate organic solvent.

[0022] In the present invention, carbonate solvents are used as the basic solvents, which are consistent with the current commercial electrolytes and have the advantages of a wide electrochemical window and strong high-voltage resistance, and are more conducive to practical promotion and 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 includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate), lithium tetrafluoroborate or lithium difluorooxalatoborate.

[0025] Preferably, the concentration of lithium salt in the electrolyte is 0.8-1.5 mol / L, for example, 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 preparation method comprising:

[0027] The organic solvent, lithium salt, fluorine-containing diluent and interface additive are mixed to obtain the electrolyte.

[0028] Preferably, the mixing comprises mixing a lithium salt, an organic solvent and a fluorine-containing diluent, and then mixing the obtained mixed solution with an interface additive to obtain the electrolyte.

[0029] In a third aspect, the present invention provides a lithium ion battery, wherein the lithium ion battery comprises the electrolyte as described in the first aspect.

[0030] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes 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 no longer exhaustively lists the specific point values ​​included in the range.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The electrolyte provided by the present invention is added with an interface additive of a specific structure and a fluorine-containing diluent, which cooperate with each other to improve the conductivity of the electrolyte, form a unique high-voltage fast-charging electrolyte system, improve the high-voltage resistance and cycle performance of the battery, and under the same conditions, have a higher charging capacity and good fast-charging performance. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0034] Example 1

[0035] This embodiment provides an electrolyte solution, which includes 1.2M lithium hexafluorophosphate (LiPF6), 1% interface additive (ethynyl boric acid bissulfone, ), ethylene carbonate, ethyl methyl carbonate and tris(2,2,2-trifluoroethyl)orthoformate (TTFO); the volume percentages of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and tris(2,2,2-trifluoroethyl)orthoformate are 25:35:40.

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

[0037] The conductive lithium salt lithium hexafluorophosphate is added to a mixed solvent of ethylene carbonate, ethyl methyl carbonate and fluorine-containing diluent tris(2,2,2-trifluoroethyl)orthoformate to form a solution after being fully dissolved, and then ethynyl boric acid bissulfone is added thereto and mixed evenly to obtain the electrolyte.

[0038] Example 2

[0039] This embodiment provides an electrolyte solution, which includes 1.2M lithium hexafluorophosphate (LiPF6), 1% interface additive (ethynyl boric acid bissulfone, ), ethylene carbonate, ethyl methyl carbonate and tris(2,2,2-trifluoroethyl)orthoformate (TTFO); the volume percentages of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and tris(2,2,2-trifluoroethyl)orthoformate are 25:25:50.

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

[0041] Example 3

[0042] This embodiment provides an electrolyte solution, which includes 1.2M lithium hexafluorophosphate (LiPF6), 1% interface additive (ethynyl boric acid bissulfone, ), ethylene carbonate, ethyl methyl carbonate and tris(2,2,2-trifluoroethyl)orthoformate (TTFO); the volume percentages of ethylene carbonate (EC), ethyl methyl 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 those in Embodiment 1.

[0044] Example 4

[0045] This embodiment provides an electrolyte solution, which includes 1.2M lithium bis(fluorosulfonyl)imide, 1.5% interface additive Ethylene carbonate, ethyl methyl carbonate and tris(2,2,3,3-tetrafluoropropyl)orthoformate; the volume percentages of ethylene carbonate, ethyl methyl carbonate and tris(2,2,3,3-tetrafluoropropyl)orthoformate are 25:35:40.

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

[0047] Example 5

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

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

[0050] Comparative Example 1

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

[0052] Comparative Example 2

[0053] This comparative example provides an electrolyte, which differs from Example 1 only in that the interface additive is replaced by a disulfonate compound of equal mass. The other components, dosage and preparation method are the same as those in Example 1.

[0054] Comparative Example 3

[0055] This comparative example provides an electrolyte, which is different from Example 1 only in that the electrolyte does not contain fluorine-containing diluent and interface additive, the volume ratio of ethylene carbonate to ethyl methyl carbonate is 25:75, and other components, dosages and preparation methods are the same as those in Example 1.

[0056] Performance Testing

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

[0058] (2) The electrolytes provided in Examples 1 to 5 and Comparative Examples 1 to 3 were injected into a 2000mAh soft-pack battery, the positive electrode material of which was single crystal ternary and the negative electrode material was graphite. The battery was activated after formation, and a rate charge test and a cycle test were performed, with a voltage range of 2.8-4.35V.

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

[0060] Table 1

[0061]

[0062] It can be seen from the above table that the electrolyte provided by the present invention is compounded with a fluorine-containing diluent and an interface additive so that the electrolyte retains the advantages of both a high-concentration electrolyte and a low-concentration electrolyte, forming a unique high-voltage fast-charge resistant electrolyte system, thereby improving the high-voltage resistance and cycle performance of the battery. Under the same conditions, the charging capacity is higher and has good fast-charging performance; the conductivity of the electrolyte reaches 8.83-9.88 mS / cm, the 4C charging capacity is 1729.4-1905.2 mAh, the charging capacity accounts for 86.47-95.26% of the rated capacity, and the capacity retention rate after 500 cycles at 45°C is 78.9-89.8%.

[0063] By comparing the embodiments with the comparative examples, it can be seen that the electrolyte provided by the present invention can charge significantly more electricity at a high rate of 4C, and the 4C fast charging capacity can reach 86.47% or more, while the 4C fast charging capacity in the comparative example is lower, indicating that the electrolyte of the present invention has good internal conductivity, can better withstand high-rate lithium ion migration, and has good fast charging performance. The addition of interface additives with specific structures can achieve low-impedance film-forming characteristics at the positive and negative electrode interfaces by regulating different functional groups, which is beneficial to further reduce the impedance of lithium-ion batteries and effectively improve the fast charging performance of batteries.

[0064] Compared with Comparative Example 1, the capacity retention rate of Example 1 is further improved after 500 cycles at 45°C. This is because the addition of fluorinated compounds promotes more anions to participate in the solvation configuration coordination, and the formed 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.

[0065] Comparing Example 1 with the comparative example, it can be seen that the cycle performance is significantly improved. On the one hand, because the addition of fluorinated compounds promotes more anions to participate in the solvation configuration coordination, the formed 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 additive can participate in the film formation of the positive and negative electrodes at the same time, and the generated low-impedance interface film can further inhibit the decomposition of lithium salts and electrolytes on the surfaces of the positive and negative electrodes, reduce the occurrence of electrolyte / electrode interface side reactions under high voltage, and help to further improve the 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 objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific 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 should be included in the protection scope of the present invention.

[0067] The applicant declares that the above is only a specific implementation mode 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 thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

[0068] The applicant declares that the present invention illustrates the detailed method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed method, that is, it does not mean that the present invention must rely on the above-mentioned detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various 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 comprises an organic solvent, a lithium salt, an interface additive and a fluorine-containing diluent; The interface additive includes boric acid bissulfone compounds; The boric acid bissulfone compound has a structure shown in Formula I: Wherein, R1 is selected from any one of substituted or unsubstituted C2-C6 straight chain or branched alkenyl, substituted or unsubstituted C2-C6 straight chain or branched alkynyl; R2 and R3 are each independently selected from any one of H, F, substituted or unsubstituted C1-C6 straight chain or branched alkyl; The substituted substituent includes any one of a C1-C6 straight chain or branched chain alkyl group and a halogen.

2. The electrolyte according to claim 1, characterized in that In the boric acid bissulfone lactone compound, R1 is selected from any one of a substituted or unsubstituted C2-C6 straight chain or branched alkenyl group, a substituted or unsubstituted C2-C6 straight chain or branched alkynyl group, and / or R2 and R3 are each independently selected from F.

3. The electrolyte according to claim 1 or 2, characterized in that The boric acid bissulfone compound is selected from at least one of the compounds having the following structures:

4. The electrolyte according to any one of claims 1 to 3, characterized in that The mass percentage of the interface additive in the electrolyte is 0.5-3%.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The fluorine-containing diluent includes 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; Preferably, based on the total volume of the organic solvent and the fluorine-containing diluent being 100%, the volume percentage of the fluorine-containing diluent is 40-60%.

6. The electrolyte according to any one of claims 1 to 5, characterized in that The organic solvent includes a carbonate organic solvent; Preferably, the carbonate organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate or fluoroethylene carbonate.

7. The electrolyte according to any one of claims 1 to 6, characterized in that The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate), lithium tetrafluoroborate or lithium difluorooxalatoborate; Preferably, the concentration of lithium salt in the electrolyte is 0.8-1.5 mol / L.

8. A method for preparing an electrolyte according to any one of claims 1 to 7, characterized in that: The preparation method comprises: The organic solvent, lithium salt, fluorine-containing diluent and interface additive are mixed to obtain the electrolyte.

9. The preparation method according to claim 8, characterized in that: The mixing includes mixing a lithium salt, an organic solvent and a fluorine-containing diluent, and then mixing the obtained mixed solution with an interface additive to obtain the electrolyte.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the electrolyte according to any one of claims 1 to 7.

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