High voltage lithium ion battery electrolyte

Abstract

The application discloses a high-voltage lithium ion battery electrolyte, which comprises a main solvent, a lithium salt and a functional additive, wherein the main solvent comprises functionalized dimethyl carbonate and a cyclic carbonate; the functionalized dimethyl carbonate is a monosubstituted modified dimethyl carbonate obtained by covalently grafting a strong electron-withdrawing functional group on a dimethyl carbonate molecular skeleton, and the strong electron-withdrawing functional group is at least one selected from a nitrile group, a sulfonic acid group and a sulfonyl group; and the chemical structure formula is R-CH2-O-CO-OCH3, wherein R is -CN or -SO2R' or -SO3R', and R' is C1-C3 alkyl; and the functional additive comprises a film forming agent, an antioxidant and a hydrolysis inhibition stabilizer. The electrolyte has strong ion conduction capacity, good oxidation resistance, can inhibit transition metal dissolution and can improve the cycle life and rate performance of a lithium ion battery.

Description

Technical Field

[0001] This invention relates to a high-voltage lithium-ion battery electrolyte, belonging to the field of new energy lithium-ion battery material technology. Background Technology

[0002] Existing lithium-ion battery electrolytes typically consist of lithium salts, organic solvents, and additives. Commonly used solvent systems include combinations of EC with DMC, EMC, and DEC. These conventional electrolytes are suitable for 4.2V traditional ternary battery systems, but cannot meet the development needs of high-voltage lithium-ion batteries of 4.7V and above.

[0003] Conventional electrolyte solvents such as EC, DMC, and EMC are linear carbonates. DMC, in particular, has a high electron cloud density at the carbonyl oxygen group, resulting in insufficient oxidation resistance. It is prone to continuous oxidative decomposition at high-potential cathode surfaces, generating gas and causing battery swelling. Simultaneously, conventional electrolytes struggle to construct a stable and dense CEI passivation film on the high-voltage cathode surface, allowing transition metals to easily dissolve. These dissolved metal ions migrate to the anode, damaging the SEI film. Furthermore, in the lithium-ion solvation sheath formed by conventional solvents, DMC exhibits strong coordination with lithium ions, resulting in a high desolvation energy barrier and limited electrolyte ion conductivity. These multiple side reactions combine to cause a continuous increase in internal resistance, rapid capacity decay, and insufficient cycle life in high-voltage batteries, hindering the practical application of high-voltage cathode materials. Summary of the Invention

[0004] The technical problem this invention aims to solve is addressing the stability issue of conventional electrolytes under high-voltage conditions. This is achieved by functionalizing dimethyl carbonate (DMC) using molecular modification techniques, covalently introducing strong electron-withdrawing functional groups such as nitrile and sulfonic acid groups into the DMC molecular structure. The electron-withdrawing inductive effect is utilized to regulate the coordination between DMC and lithium ions, reconstructing the lithium-ion solvation structure, promoting lithium salt dissociation, lowering the lithium-ion desolvation energy barrier, and effectively improving the electrolyte's ion conductivity. Simultaneously, the modified solvent preferentially participates in the electrode interface reaction, constructing an SEI / CEI passivation film with both high ion conductivity and chemical stability. This inhibits continuous electrolyte decomposition and transition metal dissolution, maintains the stability of the positive and negative electrode crystal structures during charge-discharge cycles, and improves the cycle life and rate performance of lithium-ion batteries.

[0005] The beneficial effects of this invention are as follows: 1. It introduces strong electron-withdrawing groups and enhances the antioxidant properties of the solvent itself; 2. It weakens Li⁺ coordination, optimizes the solvation structure, and improves ion conduction; 3. It continuously participates in interfacial film formation during the charge and discharge process, constructing a stable N / S-containing CEI / SEI; 4. It inhibits the dissolution of transition metals and alleviates the damage to the electrode structure.

[0006] The present invention relates to a high-voltage lithium-ion battery electrolyte, comprising: a main solvent, a lithium salt, and functional additives.

[0007] Furthermore, the main solvent comprises functionalized dimethyl carbonate and cyclic carbonate, wherein the functionalized dimethyl carbonate is a monosubstituted modified dimethyl carbonate obtained by covalently grafting a strong electron-withdrawing functional group onto the molecular skeleton of dimethyl carbonate, and the strong electron-withdrawing functional group is selected from at least one of nitrile group, sulfonic acid group, and sulfonyl group; its chemical structure is R-CH2-O-CO-OCH3, wherein R is -CN or -SO2R' or -SO3R', and R' is C1-C3 alkyl.

[0008] Furthermore, the cyclic carbonate is at least one of ethylene carbonate (EC) or propylene carbonate (PC).

[0009] Optionally, the volume ratio of cyclic carbonate to functionalized dimethyl carbonate is 2:8 to 4:6.

[0010] Furthermore, the lithium salt is at least one of LiPF6, LiFSI, and LiDFOB.

[0011] Optionally, the lithium salt concentration is 1.0–1.2 mol / L.

[0012] Furthermore, the film-forming agent is fluoroethylene carbonate (FEC) or vinylene carbonate (VC).

[0013] Optionally, the amount of film-forming agent added is 3 to 8 vol%.

[0014] Furthermore, the antioxidant is trimethylsilyl phosphate (TMSP) or a boron compound.

[0015] Optionally, the amount of antioxidant added is 0.2 to 1.0 vol%.

[0016] Furthermore, the hydrolysis-inhibiting stabilizer is hexamethyldisilazane (HMDS).

[0017] Optionally, the amount of hydrolysis inhibitor added is 0.1 to 0.8 vol%. Detailed Implementation

[0018] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternatives, improvements, and equivalents that may be included within the scope of the claims.

[0019] I. Electrolyte Preparation

[0020] Example 1

[0021] This embodiment relates to a high-voltage lithium-ion battery electrolyte:

[0022] Cyclic ethylene carbonate (EC) and nitrile-modified dimethyl carbonate (DMC) were mixed in a ratio of 30%:70%, and then a lithium hexafluorophosphate (LiPF6) solution with a concentration of 1.2 mol / L was added. Subsequently, 5 vol% fluoroethylene carbonate (FEC), 2 vol% vinylene carbonate (VC), 0.5 vol% hexamethyldisilazane (HMDS), and 1 wt% lithium difluorooxalate borate (LiDFOB) were added sequentially.

[0023] Example 2

[0024] Cyclic ethylene carbonate (EC) and sulfonyl-modified dimethyl carbonate (DMC) were mixed in a ratio of 30%:70%, and then a lithium hexafluorophosphate (LiPF6) solution with a concentration of 1.2 mol / L was added. Subsequently, 5 vol% fluoroethylene carbonate (FEC), 2 vol% vinylene carbonate (VC), 0.5 vol% hexamethyldisilazane (HMDS), and 1 wt% lithium difluorooxalate borate (LiDFOB) were added sequentially.

[0025] Example 3

[0026] Cyclic ethylene carbonate (EC), sulfonyl-modified dimethyl carbonate (DMC), and nitrile-modified dimethyl carbonate (DMC) were mixed in a ratio of 30%:35%:35%, and then a 1.2 mol / L lithium hexafluorophosphate (LiPF6) solution was added. Subsequently, 6 vol% fluoroethylene carbonate (FEC), 1.5 vol% vinylene carbonate (VC), 0.6 vol% hexamethyldisilazane (HMDS) (1.5 wt%), lithium difluorooxalate borate (LiDFOB), and 0.5 wt% trimethylsilyl phosphate (TMSP) were added sequentially.

[0027] Example 4

[0028] Cyclic ethylene carbonate (EC), ordinary dimethyl carbonate (DMC), and nitrile-modified dimethyl carbonate (DMC) were mixed in a ratio of 30%:35%:35%, and then a 1.2 mol / L lithium hexafluorophosphate (LiPF6) solution was added. Subsequently, 6 vol% fluoroethylene carbonate (FEC), 1.5 vol% vinylene carbonate (VC), 0.6 vol% hexamethyldisilazane (HMDS) 1.5 wt%, lithium difluorooxalate borate (LiDFOB), and 0.5 wt% trimethylsilyl phosphate (TMSP) were added sequentially.

[0029] Comparative Example 1

[0030] Ordinary ethylene carbonate EC and ordinary dimethyl carbonate DMC were mixed in a ratio of 30%:70%, and then a lithium hexafluorophosphate (LiPF6) solution with a concentration of 1.2 mol / L was added. Subsequently, 5 vol% fluoroethylene carbonate (FEC) and 2 vol% vinylene carbonate (VC) were added in sequence.

[0031] Comparative Example 2

[0032] Ordinary ethylene carbonate EC, ordinary dimethyl carbonate DMC, and propionitrile were mixed in a ratio of 30%:67%:3%, and then a lithium hexafluorophosphate (LiPF6) solution with a concentration of 1.2 mol / L was added. Subsequently, 5 vol% fluoroethylene carbonate (FEC) and 2 vol% vinylene carbonate (VC) were added sequentially.

[0033] Comparative Example 3

[0034] Ordinary ethylene carbonate EC, ordinary dimethyl carbonate DMC, and 1,3-propanesulfonate lactone were mixed in a ratio of 30%:67%:3%, and then a lithium hexafluorophosphate (LiPF6) solution with a concentration of 1.2 mol / L was added. Subsequently, 5 vol% fluoroethylene carbonate FEC and 2 vol% vinylene carbonate VC were added sequentially.

[0035] II. Electrochemical Performance Testing

[0036] The electrolytes provided in Examples 1-4 and Comparative Examples 1-3 were loaded into lithium-ion half-cells, and their electrochemical performance was tested. Lithium nickel manganese oxide (LiNiO) was used with a lithium sheet as the negative electrode and had a high operating voltage (4.7V). 0.5 Mn 1.5 O4) is used as the positive electrode active material (wherein, LiNi) 0.5 Mn 1.5 The mass ratio of O4 to conductive carbon black to PVDF binder is 8:1:1. The diaphragm is a porous polypropylene membrane. Finally, 100 μL of electrolyte is added to each membrane, and they are assembled together to form LiNi. 0.5 Mn 1.5 O4 / L half-cell.

[0037] The cycle performance of the assembled experimental battery was tested. The test conditions were as follows: at 25℃, room temperature cycle tests were conducted within the 3.5-4.9V voltage range at charge / discharge rates of 0.2C / 0.2C and 1C / 1C, respectively. Then, at 45℃, high-temperature high-rate cycle tests were conducted within the 3.5-4.9V voltage range at charge / discharge rates of 3C / 3C.

[0038] Example 1 84.5 93.7 88.6 Example 2 84.1 93.5 88.9 Example 3 85.2 94.6 90.1 Example 4 83.6 92.9 87.2 Comparative Example 1 81.8 90.3 85.3 Comparative Example 2 82.3 91.1 85.9 Comparative Example 3 82.1 90.8 85.7

[0039] Example 1 (nitrile-modified DMC) demonstrates advantages in ion conductivity and oxidation resistance. Example 2 (sulfonyl-modified DMC) is more conducive to forming a highly stable interfacial film, inhibiting transition metal dissolution, and exhibits slightly better long-cycle stability than Example 1. Example 3 uses a combination of nitrile-modified DMC and sulfonyl-modified DMC, balancing high ion conductivity with excellent interfacial stability, resulting in superior overall performance compared to single-modified solvent formulations. Comparative Example 1 uses a traditional EC / DMC electrolyte, and its electrocycling performance is somewhat inferior to that of the modified DMC in Examples 1-4. Comparative Examples 2 and 3 involve the external addition of propionitrile and propane sulfonate small molecule additives, showing some improvement in electrocycling performance compared to Comparative Example 1, but the effect is not as good as that of functional group-modified DMC.

[0040] 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.

Claims

1. A high-voltage lithium-ion battery electrolyte, characterized in that, It includes a main solvent, a lithium salt, and functional additives. The main solvent comprises functionalized dimethyl carbonate and cyclic carbonates. The functional additives include film-forming agents, antioxidants, and hydrolysis-inhibiting stabilizers.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The functionalized dimethyl carbonate is a monosubstituted modified dimethyl carbonate obtained by covalently grafting a strong electron-withdrawing functional group onto the molecular skeleton of dimethyl carbonate. The strong electron-withdrawing functional group is selected from at least one of nitrile group, sulfonic acid group, and sulfonyl group. Its chemical structure is R-CH2-O-CO-OCH3, where R is -CN or -SO2R' or -SO3R', and R' is a C1-C3 alkyl group.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that, The cyclic carbonate is at least one of ethylene carbonate (EC) or propylene carbonate (PC).

4. The content according to claims 1-3, characterized in that, The volume ratio of cyclic carbonate to functionalized dimethyl carbonate is 2:8 to 4:

6.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt is at least one of LiPF6, LiFSI, and LiDFOB.

6. According to claim 5, the lithium salt concentration is 1.0–1.2 mol / L.

7. The lithium-ion battery electrolyte according to claim 1, characterized in that, The film-forming agent is fluoroethylene carbonate (FEC) or vinylene carbonate (VC), and its addition amount is 3-8 vol.

8. The lithium-ion battery electrolyte according to claim 1, characterized in that, The antioxidant is trimethylsilyl phosphate (TMSP) or a boron compound, and its addition amount is 0.2–1.0 vol.

9. The lithium-ion battery electrolyte according to claim 1, characterized in that, The hydrolysis inhibitor is hexamethyldisilazane (HMDS), and its addition amount is 0.1–0.8 vol.