Lithium ion battery electrolyte additive, preparation method and application thereof

Abstract

This invention relates to the fields of organic chemistry and organic optoelectronic functional materials, specifically to a lithium-ion battery electrolyte additive, its preparation method, and its application. The invention provides a lithium-ion battery electrolyte additive, characterized in that the chemical formula of the additive is as shown in formula (D): wherein R1 and R2 are each independently H, a C1-C4 alkyl group, a fluoroalkane, a benzene ring, or a fluorobenzene ring. The compounds included in the lithium-ion battery electrolyte additive provided by this invention, by introducing electron-donating N atoms, facilitate reduction at the negative electrode and can polymerize on the electrode to form a polymer film. These characteristics allow the additive to form a dense and stable solid electrolyte interface film on the surface of the positive and negative electrode active materials after application to the battery electrolyte, thereby blocking direct contact between the electrolyte and the active materials, avoiding side reactions, and improving the cycle performance of the lithium-ion battery.

Description

Technical Field

[0001] This invention relates to the fields of organic chemistry and lithium battery technology, specifically to a lithium-ion battery electrolyte additive, its preparation method, and its application. Background Technology

[0002] In recent years, lithium-ion batteries have been widely used in 3C portable electronic devices, electric vehicles, and energy storage systems, and consumers' demands for the energy density of lithium-ion batteries are also increasing. Energy density can be improved by selecting high-capacity and high-voltage positive and negative electrode materials. Compared to graphite anodes, lithium metal has a capacity of 3860 mAh / g. -1 With its ultra-high theoretical specific capacity and low redox potential of -3.04V, the pure silicon anode has a capacity of up to 4200mAh g / L. -1 With its theoretical specific capacity, lithium metal is an ideal high-capacity anode material for lithium-ion secondary batteries. Matching it with a high-voltage cathode, such as a nickel-rich layered cathode, can further improve the battery's energy density. However, unstable electrolyte-electrode interfaces (EEIs) limit the development of high-energy-density batteries. For example, for lithium metal anodes, an unstable solid electrolyte interphase (SEI) leads to electrolyte consumption, poor battery cycle stability, low coulombic efficiency, and lithium dendrite growth, which can cause short circuits and safety issues. For high-voltage cathodes, the electrolyte continuously undergoes oxidative decomposition on the cathode surface, generating a cathode interphase (CEI). An unstable CEI accelerates electrolyte decomposition, increases impedance, and accelerates capacity decay.

[0003] Therefore, constructing stable EEIs is crucial for improving the cycle stability of high-energy-density batteries. Adding functionalized film-forming additives to the electrolyte is the most effective and economical method to improve EEIs and enhance battery cycle performance. Ethyl carbonate (VC) is a typical anode film-forming additive. Its double-bond structure gives it a lower LUMO energy level, making it easily reduced at the anode and capable of polymerizing on the electrode surface to form a polymer film. Due to its good film-forming properties, it is widely used in graphite and silicon anodes. However, while there are many additives for high-voltage cathodes, additives that can simultaneously form films on both positive and negative electrodes are rarely reported. Therefore, it is necessary to explore and develop multifunctional film-forming additives that can simultaneously form stable and effective protective layers on both positive and negative electrode sides to improve battery performance. Summary of the Invention

[0004] This invention is made to solve the above-mentioned problems, and aims to provide a lithium-ion battery electrolyte additive that can simultaneously form a stable and effective protective layer on both the positive and negative electrode sides, thereby improving battery performance, as well as its preparation method and application.

[0005] A first aspect of the present invention provides a lithium-ion battery electrolyte additive, characterized in that the chemical formula of the lithium-ion battery electrolyte additive is as shown in formula (D):

[0006]

[0007] R1 and R2 are each independently H, C1 to C4 alkyl, fluoroalkane, benzene ring, or fluorobenzene ring.

[0008] The lithium-ion battery electrolyte additive provided by this invention includes compounds that, by introducing electron-donating nitrogen atoms, increase the negative charge distribution in the carbonyl group, weaken oxidizing properties, and facilitate oxidative decomposition at the high-voltage positive electrode. Simultaneously, the retention of double bonds promotes reduction at the negative electrode, and polymerization can occur on the electrode to form a polymer film. These characteristics allow the additive to form a dense and stable solid electrolyte interface film on the surface of the positive and negative electrode active materials after application in the battery electrolyte, thus blocking direct contact between the electrolyte and the active materials, avoiding side reactions, and improving the cycle performance of the lithium-ion battery. Furthermore, the presence of nitrogen in the additive helps to generate lithium-ion batteries rich in Li3N and LiN. x O y The SEI component enhances the electrochemical performance and mechanical strength of the SEI.

[0009] In some embodiments of the present invention, the following compounds are included:

[0010]

[0011] In this invention, considering that the introduction of F element helps to generate a solid electrolyte interface film rich in LiF, F-substituted alkanes were designed.

[0012] A second aspect of the present invention provides a method for preparing a lithium-ion battery electrolyte additive as described in the first aspect, characterized in that compound (D) is obtained by oxidizing compound (c).

[0013]

[0014] R1 and R2 are each independently H, C1 to C4 alkyl, fluoroalkane, benzene ring, or fluorobenzene ring.

[0015] In some embodiments of the present invention, the following steps are included: reacting compound (a) with compound (b) to obtain intermediate (c);

[0016]

[0017] Wherein, R1 and R2 are each independently any one of C1 to C4 alkyl, fluoroalkane, benzene ring, or fluorobenzene ring; X is a halogen or p-toluenesulfonyl group.

[0018] A third aspect of the present invention provides a lithium-ion battery electrolyte, characterized in that it includes the lithium-ion battery electrolyte additives described in the first aspect.

[0019] In some embodiments of the present invention, the volume ratio of the lithium-ion battery electrolyte additive is 0.1% to 10%.

[0020] The inventors' experiments revealed that within this range, the additives can significantly improve the cycle performance of the battery. However, the proportion of additives needs to be adjusted within this range according to different battery types.

[0021] In some embodiments of the present invention, the volume ratio of the lithium-ion battery electrolyte additive is 0.1% to 0.5%.

[0022] In some embodiments of the present invention, the lithium-ion battery electrolyte includes the following preparation steps: adding the lithium-ion battery electrolyte additive to the electrolyte mother liquor according to the addition volume ratio, and mixing evenly.

[0023] In some embodiments of the present invention, the electrolyte mother liquor includes an electrolyte, which is lithium hexafluorophosphate, lithium bis(trifluorosulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium perchlorate, or lithium nitrate.

[0024] In some embodiments of the present invention, the electrolyte stock solution is a commercial electrolyte such as KELOD 0116 (1.0M LiPF6 in EC:DEC:EMC = (1:1:1) vol%) or KELOD 0516 (1.0M LiPF6 in EC:DEC = (1:1) vol%).

[0025] A fourth aspect of the present invention provides a lithium-ion battery, characterized in that it comprises a lithium-ion battery electrolyte as described in the third aspect.

[0026] By implementing the above technical solution, the present invention has the following beneficial effects:

[0027] The lithium-ion battery electrolyte additive provided by this invention includes compounds that introduce electron-donating nitrogen atoms, thereby increasing the negative charge distribution in the carbonyl group, weakening its oxidative stability, and making it easier to undergo oxidative decomposition at the high-voltage positive electrode. At the same time, it retains double bonds, which is beneficial for reduction at the negative electrode, and can also polymerize on the electrode to form a polymer film. These characteristics are beneficial for the additive to form a dense and stable solid electrolyte interface film on the surface of the positive and negative electrode active materials after being applied to the battery electrolyte, so as to block the direct contact between the electrolyte and the active materials, avoid the occurrence of side reactions, and improve the cycle performance of lithium-ion batteries.

[0028] The lithium-ion battery electrolyte additive provided by this invention contains nitrogen (N) element, which helps to generate lithium-ion battery electrolytes rich in Li3N and LiN. x O y The SEI component enhances the electrochemical performance and mechanical strength of the SEI.

[0029] The lithium-ion battery electrolyte additive provided by this invention incorporates F-substituted alkanes, which helps to generate a solid electrolyte interface film rich in LiF.

[0030] The lithium-ion battery electrolyte provided by this invention can significantly improve the battery's capacity retention rate, increasing the coulombic efficiency from 77.3% to 95.1%. Attached Figure Description

[0031] Figure 1 This is the proton NMR spectrum of compound D1 in Example 1 of this invention;

[0032] Figure 2 This is the proton NMR spectrum of compound D4 in Example 2 of this invention;

[0033] Figure 3 This is the proton NMR spectrum of compound D6 in Example 3 of this invention;

[0034] Figure 4 This is the fluorine spectrum of compound D6 in Example 3 of the present invention;

[0035] Figure 5 This is the proton NMR spectrum of compound D9 in Example 4 of this invention;

[0036] Figure 6 This is the fluorine spectrum of compound D9 in Example 4 of this invention;

[0037] Figure 7 This is a comparison chart of the cycle performance of the NCM622||Li battery in Example 6 of the present invention in blank electrolyte and electrolyte with additives;

[0038] Figure 8 This is a comparison chart of the cycle performance of the NCM||C battery in Example 7 of the present invention in blank electrolyte and electrolyte with additives;

[0039] Figure 9 This is a comparison chart of the cycle performance of the NCM||C battery in Example 8 of the present invention in blank electrolyte and electrolyte with additives;

[0040] Figure 10 This describes the effect of different additive contents on the coulombic efficiency of Li||Cu batteries in Example 9 of this invention. Detailed Implementation

[0041] To make the technical means, creative features, objectives and effects of this invention easy to understand, the invention will be specifically described below in conjunction with embodiments and accompanying drawings.

[0042] Example 1: Preparation of compound D1

[0043]

[0044] (1) Preparation of imidazole salt: In a single-necked round-bottom flask, 20 g of 1-methylimidazolium was added to 100 mL of dichloromethane and stirred. Then, 34.6 g of iodomethane was added. After stirring at room temperature for 5 hours, the solvent was removed by rotary evaporation to obtain the intermediate product 1,3-dimethylimidazolium iodide (DMImI).

[0045] (2) Imidazole salt oxidation: 1 g of prepared DMImI, 1.2 g of K2CO3 and 1.2 g of iodine molecules were added to 50 mL of a methanol-water mixture (volume ratio 9:1). The reaction was carried out at 40 °C for 0.5–1 h until the raw materials were completely consumed. After removing the solvent by rotary evaporation, the mixture was extracted multiple times with ethyl acetate. The organic phase was washed three times each with deionized water, 1 M sodium sulfite solution and saturated brine. The organic phase was dried with anhydrous sodium sulfate and then rotary evaporated to obtain the crude product. The crude product was purified by silica gel column chromatography to obtain the desired compound D1. The synthesized compound D1 was stored at 0–4 °C before use. Before preparing the electrolyte, compound D1 was vacuum-treated at room temperature to remove trace amounts of water.

[0046] Example 2: Preparation of compound D4

[0047]

[0048] (1) Preparation of imidazole salt: In a single-necked round-bottom flask, add 30 g of 1-butylimidazolium and 100 mL of dichloromethane, stir, and then add 34.6 g of iodomethane. After stirring at room temperature for 5 hours, remove the solvent by rotary evaporation to obtain the intermediate product 1-dimethyl-3-butylimidazolium iodide (MBuImI);

[0049] (2) Imidazole salt oxidation: 1g of prepared MBuImI, 1g of K2CO3, and 1g of iodine molecules were added to 50mL of a methanol-water mixture (volume ratio 9:1). The reaction was carried out at 40℃ for 0.5-1h until the raw materials were completely consumed. After removing the solvent by rotary evaporation, the mixture was extracted multiple times with ethyl acetate. The organic phase was washed three times each with deionized water, 1M sodium sulfite solution, and saturated brine. The organic phase was dried with anhydrous sodium sulfate and then rotary evaporated to obtain the crude product. The crude product was purified by silica gel column chromatography to obtain the desired compound D4. The synthesized compound D4 was stored at 0-4℃ before use. Before preparing the electrolyte, compound D4 was vacuum-treated at room temperature to remove trace amounts of water.

[0050] Compounds D2, D3, and D5 were synthesized using the method described above in this embodiment.

[0051] Example 3: Preparation of compound D6

[0052]

[0053] (1) Preparation of imidazole salt: 20g of 1-methylimidazolium and 30g of trifluoroethyl p-toluenesulfonate (TFETos) were added to a high-pressure reaction flask, sealed, and reacted at 120℃ for 12h. After cooling to room temperature, the product was precipitated with diethyl ether to obtain the intermediate product 1-methyl-3-trifluoroethylimidazolium p-toluenesulfonate (MTFEImTos).

[0054] Imidazole salt oxidation: 1 g of prepared MTFEImTos, 0.8 g of K2CO3, and 0.76 g of iodine molecules were added to 40 mL of a methanol-water mixture (9:1, v / v). The reaction was carried out at 40 °C for 0.5–1 h until the starting material was completely consumed. After removing the solvent by rotary evaporation, the mixture was extracted multiple times with ethyl acetate. The organic phase was washed three times each with deionized water, 1 M sodium sulfite solution, and saturated brine. The organic phase was dried with anhydrous sodium sulfate and then rotary evaporated to obtain the crude product. The crude product was purified by silica gel column chromatography to obtain the desired compound D6. The synthesized compound D6 was stored at 0–4 °C before use. Before preparing the electrolyte, compound D6 was vacuum-treated at room temperature to remove trace amounts of water.

[0055] Compounds D7 and D8 were synthesized using the method described in this embodiment.

[0056] Example 4: Preparation of compound D9

[0057]

[0058] (1) Preparation of fluorinated imidazole: 10 g imidazole and 20 g trifluoroethyl p-toluenesulfonate were added to a high-pressure reaction flask, sealed, and reacted at 120 °C for 12 h. The mixture was then added to 100 mL of 2 M potassium hydroxide solution, stirred, and extracted multiple times with ethyl acetate. The extracted organic phase was washed three times each with 2 M potassium hydroxide solution, deionized water, and saturated brine. After drying the organic phase with anhydrous sodium sulfate, rotary evaporation was performed to obtain the crude product. The crude product was purified by silica gel column chromatography to obtain the desired compound, 1-trifluoroethyl imidazole.

[0059] (2) Preparation of imidazole salt: 30g of 1-trifluoroethyl imidazole and 25g of trifluoroethyl p-toluenesulfonate were added to a high-pressure reaction flask, sealed, and reacted at 150℃ for 12h. After cooling to room temperature, the product was precipitated with diethyl ether to obtain the intermediate product 1,3-bis(trifluoroethyl)imidazole p-toluenesulfonate (DTFEImTos).

[0060] (3) Imidazole salt oxidation: 1 g of the prepared DTFEImTos, 1.36 g of K2CO3 and 0.62 g of iodine molecules were added to 40 mL of a methanol-water mixture (volume ratio 9:1). The reaction was carried out at 40 °C for 0.5–1 h until the raw materials were completely consumed. After removing the solvent by rotary evaporation, the mixture was extracted multiple times with ethyl acetate. The organic phase was washed three times each with deionized water, 1 M sodium sulfite solution and saturated brine. The organic phase was dried with anhydrous sodium sulfate and then rotary evaporated to obtain the crude product. The crude product was purified by silica gel column chromatography to obtain the desired compound D9. The synthesized compound D9 was stored at 0–4 °C before use. Before preparing the electrolyte, compound D9 was vacuum-sealed at room temperature to remove trace amounts of water.

[0061] Compounds D10 and D11 were synthesized according to the method described in this embodiment.

[0062] Example 5: Preparation of lithium-ion battery electrolyte

[0063] In this embodiment, lithium-ion battery electrolytes with different volume ratios of lithium-ion battery electrolyte additives were prepared. The specific preparation steps are as follows: The synthesized additives were added to the electrolyte mother liquor according to the set volume ratio. The electrolyte mother liquors were KELOD 0116 (1.0M LiPF6 in EC:DEC:EMC = (1:1:1) Vol%) and KELOD 0516 (1.0M LiPF6 in EC:DEC = (1:1) Vol%). The specific parameters are shown in the table below.

[0064] Table 1. Parameters of Lithium-ion Battery Electrolytes

[0065]

[0066]

[0067] As shown in Table 1, different additives have different effects on efficiency improvement in different battery types depending on the volume ratio of the additives. When the volume ratio of the additives is 0.1% to 10%, the effect of improving cycle efficiency can be basically achieved. Within this range, the selected additives and the volume ratio of the additives need to be adjusted according to different battery types.

[0068] Example 6: Performance Testing

[0069] This embodiment further demonstrates the cycling test of the lithium-ion battery electrolyte prepared in Example 5 in a coin cell composed of a lithium metal anode and a ternary nickel-cobalt-manganese 622 cathode. The test results are as follows: Figure 7 As shown.

[0070] like Figure 7As shown, adding 0.1 vol%, 0.2 vol%, and 0.2 vol% D1 and D6 additives to commercial electrolytes effectively improves the cycle performance of NCM||Li batteries. However, when the D1 additive content exceeds 0.5 vol%, the battery efficiency decreases. High concentrations of D1 additives lead to efficiency reduction due to their reaction with the additives.

[0071] Example 7: Performance Testing

[0072] This embodiment further demonstrates the cycling test of the lithium-ion battery electrolyte prepared in Example 5 in a coin cell composed of a graphite anode and a ternary nickel-cobalt-manganese 622 cathode. The test results are as follows: Figure 8 As shown.

[0073] like Figure 8 As shown, adding 0.2 vol% of D1 and D6 additives to commercial electrolytes can effectively improve the cycle performance of NCM||C batteries.

[0074] Example 8: Performance Testing

[0075] This embodiment further demonstrates the cycling test of the lithium-ion battery electrolyte prepared in Example 5 in a coin cell composed of a graphite anode and a ternary nickel-cobalt-manganese 622 cathode. The test results are as follows: Figure 9 As shown.

[0076] like Figure 9 As shown, adding 0.2 vol% of D6 additive to a commercial electrolyte can effectively improve the cycle performance of high-load NCM||C batteries.

[0077] Example 9: Performance Testing

[0078] This embodiment further demonstrates the cycling test of the lithium-ion battery electrolyte prepared in Example 5 in a Li||Cu battery. The test results are as follows: Figure 10 As shown.

[0079] like Figure 10 As shown, adding 0.1-0.5 vol% of D1 or 0.1-10 vol% of D6 additives to commercial electrolytes can effectively improve the cycle performance of Li||Cu batteries, increasing the coulombic efficiency from 77.3% to 95.1%.

[0080] The above embodiments are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention.

Claims

1. A lithium-ion battery electrolyte, characterized in that, This includes lithium-ion battery electrolyte additives, the chemical structural formula of which is: or .

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The volume ratio of the lithium-ion battery electrolyte additive is 0.1% to 10%.

3. The lithium-ion battery electrolyte according to claim 2, characterized in that, The lithium-ion battery electrolyte includes the following preparation steps: adding the lithium-ion battery electrolyte additive to the electrolyte mother liquor according to the addition volume ratio, and mixing evenly.

4. The lithium-ion battery electrolyte according to claim 3, characterized in that, The electrolyte mother liquor includes an electrolyte, which is lithium hexafluorophosphate, lithium bis(trifluorosulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium perchlorate, or lithium nitrate.

5. A lithium-ion battery, characterized in that, Includes the lithium-ion battery electrolyte as described in claim 1.

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