Electrolyte containing hexamethylenedisulfuric urea additive, its preparation method and application

Abstract

This invention discloses a lithium-ion battery electrolyte, its preparation method, and its application. The electrolyte comprises a lithium salt, a non-aqueous organic solvent, and an additive, wherein the additive is hexamethyldisilazane. This additive contains two trimethylsilyl groups, two N-H bonds, and one carbonyl group within a single symmetrical molecule. It can preferentially react with trace amounts of HF and H₂O in the electrolyte through multi-site synergy to inhibit LiPF₆ hydrolysis. Furthermore, it forms an in-situ film at the interface between the positive and negative electrodes, preceding the carbonate solvent. The resulting interfacial film possesses both high lithium-ion conductivity and electronic insulation, thereby stabilizing the lithium negative electrode deposition / stripping interface while inhibiting the oxidative decomposition, transition metal dissolution, and structural degradation of the high-nickel positive electrode. This electrolyte is simple to prepare, compatible with existing processes, and can improve the cycle life, rate performance, and high-temperature stability of lithium-ion batteries.

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and large-scale energy storage due to their advantages such as high energy density, long cycle life, and low self-discharge rate. The electrolyte plays a crucial role in the transport of lithium ions between the positive and negative electrodes, and its composition and properties directly determine the battery's rate performance, cycle stability, safety performance, and lifespan.

[0003] As cathode materials continue to evolve towards higher nickel content and higher voltage, conventional electrolytes face challenges such as intensified oxidation and decomposition, increased interfacial side reactions, and severe dissolution of transition metal ions under high voltage and high nickel conditions. Simultaneously, LiPF6-based electrolytes readily hydrolyze to generate HF in the presence of trace amounts of water. HF corrodes the cathode material surface and triggers the dissolution of transition metal ions, thereby damaging the cathode crystal structure and accelerating performance degradation. Furthermore, lithium anodes, which are compatible with high-nickel cathodes, exhibit interfacial instability during deposition and stripping, easily generating dendrites and persistent side reactions, further shortening battery life.

[0004] Therefore, single-function additives cannot meet all the above requirements. Developing a multifunctional electrolyte additive that can simultaneously achieve acid and water removal, positive electrode interfacial film formation, and lithium anode interfacial stabilization is of great significance for improving the overall performance of high-voltage, high-nickel lithium-ion batteries. Summary of the Invention

[0005] To address the technical problems of existing lithium-ion battery electrolytes, such as limited additive functionality, poor interface stability at high-nickel and high-voltage cathodes, transition metal dissolution caused by trace amounts of HF and H2O, severe gas expansion during high-temperature storage, and unstable lithium anode interface, this invention provides a lithium-ion battery electrolyte comprising a lithium salt, a non-aqueous organic solvent, and an additive, wherein the additive is hexamethyldisilazine, with the molecular formula C7H. 20 N2OSi2 (molecular weight 204.42, abbreviated as BSU below).

[0006] Preferably, the hexamethyldisilure is added to the electrolyte at a mass percentage of 0.5% to 3%, and most preferably 1%.

[0007] Preferably, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide; and the non-aqueous organic solvent is selected from at least two of ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0008] The present invention also provides a method for preparing the above-mentioned electrolyte: dissolving a lithium salt in a non-aqueous organic solvent and stirring until completely dissolved, then adding hexamethyldisilure and stirring until completely dissolved, thus obtaining the electrolyte. The present invention also provides a lithium-ion battery, comprising a positive electrode, a lithium negative electrode, and the above-mentioned electrolyte; preferably, the positive electrode is at least one of a high-nickel ternary material, lithium cobalt oxide, or a lithium-rich manganese-based material.

[0009] The key to this invention lies in the fact that hexamethyldisilazane is a small and symmetrical molecule that integrates two trimethylsilyl groups (TMS, providing two Si-N bonds), two NH bonds, and one carbonyl group (C=O) within a single molecule, thereby providing multiple synergistic active sites. On one hand, the Si-N and NH bonds preferentially react with trace amounts of H2O in the electrolyte and HF generated from the hydrolysis of LiPF6 (generating Si-F bonds, which are then coordinated via NH and C=O), inhibiting LiPF6 hydrolysis at its source and reducing the corrosion of the positive electrode by HF. On the other hand, the TMS groups and urea groups can decompose and polymerize into a film at the interface between the positive and lithium negative electrodes before the carbonate solvent. Unlike additives containing only a single type of functional group, the multi-site synergy of the above-mentioned "double Si-N + double N-H + carbonyl" allows this additive to simultaneously construct an interface protective film with both high lithium-ion conductivity and electronic insulation on both the positive and lithium negative electrodes, achieving "dual-interface" synergistic protection.

[0010] Compared to the blank electrolyte without this additive, the electrolyte containing this additive significantly extends the stable cycle time from 105 h to 650 h in lithium (metal) symmetric batteries and reduces its polarization overpotential, demonstrating a significant and unexpected stabilizing effect on the lithium anode interface. In the high-nickel NCM811 system, it significantly reduces interfacial charge transfer impedance, improves the discharge specific capacity at various rates, and enhances the capacity retention rate during long 1 C cycles. This additive is directly soluble in conventional electrolytes without requiring changes to existing formulation processes, making it low-cost and easy to industrialize. Attached Figure Description

[0011] Figure 1 The lithium metal symmetric battery of Example 1 of the present invention, consisting of an electrolyte containing hexamethyldisilazane additive and a blank electrolyte, was tested at 0.5 mA cm⁻¹. -2 A comparison chart of constant current circulation.

[0012] Figure 2 This is a comparison of the cyclic voltammetry (CV) curves of the two electrolytes in the NCM811 cathode system.

[0013] Figure 3 The graph shows a comparison of the discharge specific capacity of the two electrolytes in the NCM811 cathode system at different discharge rates.

[0014] Figure 4 The above are comparison diagrams of electrochemical impedance spectroscopy (EIS) after the two electrolytes were cycled in the NCM811 cathode system.

[0015] Figure 5 This is a comparison chart of the long-cycle performance of the two electrolytes in the NCM811 cathode system at a 1 C rate. Detailed Implementation

[0016] The hexamethyldisilazane (BSU) described in this invention has the molecular formula C7H. 20 N2OSi2, with a molecular weight of 204.42, contains two trimethylsilyl groups, two NH bonds, and one carbonyl group. It was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with a purity of ≥97%. Unless otherwise specified, all raw materials are commercially available products well-known in the art.

[0017] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the protection scope of this invention. Example 1

[0018] In an argon-protected glove box (water and oxygen content both below 0.1 ppm), LiPF6 was dissolved in an organic solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a 1:1:1 volume ratio to prepare a basic electrolyte with a lithium salt concentration of 1.0 M. Then, hexamethyldisilamide was added to the basic electrolyte at 1% of its total mass, and stirred at room temperature until completely dissolved to obtain an electrolyte containing hexamethyldisilamide additive. The blank electrolyte was identical except for the absence of BSU. Example 2

[0019] The only difference from Example 1 is that the amount of BSU added is 0.5% of the total mass of the electrolyte; the rest of the preparation methods and parameters are the same as in Example 1. Example 3

[0020] The only difference from Example 1 is that the amount of BSU added is 3% of the total mass of the electrolyte; the rest of the preparation methods and parameters are the same as in Example 1. Comparative Example 1

[0021] The reference is “F. Xian, J. Li, Z. Hu, Q. Zhou, C. Wang, C. Lu, Z. Zhang, S. Dong, C. Mou, G. Cui, Chem. Commun. 2020, 56, 4998.” Comparative Example 2

[0022] Document "S. Li, W. Zhang, Q. Wu, L. Fan, X. Wang, X. Wang, Z. Shen, Y.He, Y. Lu, Angew. Chem. Int. Ed. 2020, 59, 14935." Comparative Example 3

[0023] The reference is “X. Yang, M. Lin, G. Zheng, J. Wu, X. Wang, F. Ren, W. Zhang, Y. Liao, W. Zhao, Z. Zhang, N. Xu, W. Yang, Y. Yang, Adv. Funct. Mater. 2020, 30, 2004664.” Experimental Example

[0024] Figure 1 This image shows the long-cycle results of a lithium metal symmetric battery constructed using the electrolyte containing BSU additive and a blank electrolyte, as provided in Example 1 of this invention. Figure 1 It was found that the blank electrolyte exhibited a sharp increase in polarization and short-circuit failure after 105 h; while the electrolyte containing 1% BSU could cycle stably for over 650 h. This result directly demonstrates that BSU has a significant stabilizing effect on the lithium metal anode deposition and stripping interface. This substantial stabilization on the anode side is difficult to anticipate with similar additives aimed solely at cathode film formation or HF removal, constituting the outstanding technical effect of this invention on the lithium anode interface.

[0025] Figure 2 This is a comparison of cyclic voltammetry (CV) curves in the NCM811 cathode system for batteries using the BSU-added electrolyte and a blank electrolyte, as provided in Example 1 of this invention. Figure 2 It can be seen that, compared with the blank electrolyte system, the peak potential difference of the electrolyte system containing BSU is significantly reduced, indicating that the additive reduces the polarization of the redox process at the positive electrode interface and improves the reversibility of the reaction.

[0026] Figure 3This is a comparison chart of the discharge specific capacity of batteries with BSU additive-containing electrolyte and blank electrolyte provided in Example 1 of the present invention at different rates in the NCM811 cathode system. Figure 3 It can be seen that the discharge specific capacity of the electrolyte containing BSU additive is significantly higher than that of the blank electrolyte at all rates. This result indicates that the interfacial protective film formed by BSU additive has excellent lithium-ion conductivity, significantly reduces concentration polarization, and thus greatly improves the rate performance of the battery.

[0027] Figure 4 This is a comparison of the electrochemical impedance spectroscopy (EIS) spectra of the battery with BSU additive and the battery with blank electrolyte provided in Example 1 of this invention after cycling in the NCM811 cathode system. Figure 4 It is known that BSU additives can form an interface film with high ionic conductivity on the electrode surface, effectively reducing the interfacial charge transfer resistance and promoting the rapid transport of lithium ions at the electrode / electrolyte interface.

[0028] Figure 5 This is a comparison chart of the long-cycle performance of the battery with BSU additive and blank electrolyte provided in Example 1 of the present invention at 1 C rate in an NCM811 cathode system. Figure 5 It can be seen that the blank electrolyte exhibits rapid capacity decay during cycling, while the electrolyte containing BSU additive shows a significant improvement in capacity retention. This indicates that an appropriate amount of BSU additive can effectively stabilize the electrode interface, inhibit cathode structure degradation and side reaction accumulation, thereby significantly extending the battery's cycle life.

Claims

1. A lithium-ion battery electrolyte, characterized in that, The lithium salt, non-aqueous organic solvent and additive, the additive is hexamethyl disilicon urea; the hexamethyl disilicon urea contains two trimethyl silicon groups, two N-H bonds and one carbonyl in the molecule, the molecular formula is C7H 20 N2OSi2, the molecular weight is 204.

42.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The hexamethyldisilamide is added to the electrolyte at a mass percentage of 0.5% to 3%.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

4. The lithium-ion battery electrolyte according to claim 1, characterized in that, The non-aqueous organic solvent is selected from at least two of ethylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate.

5. A method for preparing a lithium-ion battery electrolyte as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Lithium salt is dissolved in a non-aqueous organic solvent and stirred until completely dissolved to obtain a lithium salt solution; Hexamethyldisilamide was then added to the lithium salt solution and stirred until completely dissolved to obtain the lithium-ion battery electrolyte.

6. A lithium-ion battery, characterized in that, It includes a positive electrode, a lithium negative electrode, and a lithium-ion battery electrolyte as described in any one of claims 1 to 5.

7. The lithium-ion battery according to claim 6, characterized in that, The material of the positive electrode is selected from at least one of high-nickel ternary materials, lithium cobalt oxide, or lithium-rich manganese-based materials.

8. The lithium-ion battery according to claim 7, characterized in that, The high-nickel ternary material is LiNi. x Co y Mn z O2, where x≥0.8 and x+y+z=1.

9. The application of hexamethyldisilure as an additive in lithium-ion battery electrolytes, characterized in that, The hexamethyldisilamide is used to remove HF and H2O from the electrolyte and to form a film in situ at the interface between the positive electrode and the lithium negative electrode, so as to improve the deposition and stripping stability of the lithium negative electrode and inhibit the dissolution of the transition metal from the positive electrode.

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