A siloxane electrolyte, a preparation method thereof, and application in low-temperature lithium metal batteries

Abstract

The present invention belongs to the technical field of lithium metal batteries, and specifically relates to a siloxane electrolyte, a preparation method thereof, and an application in low-temperature lithium metal batteries. The siloxane electrolyte comprises a lithium salt and dimethoxydimethylsilane, and the mass ratio of the lithium salt to the dimethoxydimethylsilane is 0.16-0.48:0.5-1.5. The siloxane electrolyte composition provided by the present invention comprises a lithium salt and dimethoxydimethylsilane, and the silicon atom and the adjacent oxygen atom in the dimethoxydimethylsilane have a d-p conjugated effect, which effectively increases the high-voltage resistance of the electrolyte and is conducive to weakening the Li + -Solvent interaction promotes the release of lithium ions during the desolvation process; combined with the low-temperature formation method, it can significantly improve the electrochemical performance of lithium batteries in the low-temperature range, can match the ternary positive electrode and operate stably at 4.7V, and has excellent low-temperature capacity retention rate, and has broad application prospects in low-temperature lithium metal batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium metal batteries, and in particular relates to a siloxane electrolyte, a preparation method thereof, and an application thereof in low-temperature lithium metal batteries. Background Art

[0002] Lithium-ion batteries with graphite negative electrodes are difficult to achieve high reversible charge and discharge performance at low temperatures, especially below -40°C. Under such working conditions, the lithium insertion potential of graphite is easily reduced to a value relative to Li / Li. + When the voltage drops below 0.0V, lithium deposition occurs, which limits the reversibility of lithium-ion batteries. In contrast, the lithium metal negative electrode contains excess lithium, which effectively prevents the rapid decrease in capacity caused by lithium loss. In addition, the lithium metal negative electrode has a high theoretical specific capacity (3860mAh g -1 ) and the lowest electrode potential (-3.04V relative to the standard hydrogen electrode), is expected to significantly increase the energy density of lithium batteries. These characteristics make lithium metal anode the first choice for achieving high energy density low-temperature batteries.

[0003] However, the high desolvation energy under low temperature conditions poses a huge challenge to the performance of low-temperature lithium metal batteries. To this end, researchers have developed weakly solvated ether electrolytes and fluorinated electrolytes in recent years, which have significantly accelerated the desolvation of Li metal batteries at low temperatures. + The desolvation kinetics of lithium metal batteries provide a new approach to the difficulty of low-temperature charging and discharging of lithium metal batteries. However, ether electrolytes generally exhibit a narrow electrochemical stability window (<4.0V), which limits their use with current high-capacity ternary cathode materials. The complexity of the synthesis process and the limitation of output of fluorinated electrolytes have led to a significant increase in their cost. More importantly, the abnormal stability of the CF bond makes them highly resistant to degradation, raising concerns about their potential environmental hazards. Therefore, it is difficult for existing low-temperature electrolytes to have the characteristics of weak solvation, high voltage resistance, low cost and environmental friendliness. Summary of the Invention

[0004] To address the above issues, the present invention provides a siloxane electrolyte, a preparation method thereof, and its application in low-temperature lithium metal batteries. This invention aims to address the technical issues that existing low-temperature electrolytes struggle to combine weak solvation, high-voltage resistance, low cost, and environmental friendliness.

[0005] The present invention solves the above technical problems through the following technical solutions.

[0006] One of the purposes of the present invention is to provide a siloxane electrolyte, which comprises a lithium salt and dimethoxydimethylsilane, wherein the mass ratio of the lithium salt to the dimethoxydimethylsilane is 0.16-0.48:0.5-1.5.

[0007] Furthermore, the mass ratio of lithium salt to dimethoxydimethylsilane is 0.26-0.38:0.8-1.2.

[0008] Furthermore, the mass ratio of lithium salt to dimethoxydimethylsilane is 0.3-0.35:1-1.2.

[0009] Furthermore, the mass ratio of lithium salt to dimethoxydimethylsilane is 0.32:1.

[0010] Furthermore, the lithium salt is lithium bis(fluorosulfonyl)imide.

[0011] A second object of the present invention is to provide a method for preparing the above-mentioned siloxane electrolyte, comprising the following steps:

[0012] Add lithium salt to dimethoxydimethylsilane and stir at room temperature for 10 to 15 hours to obtain a siloxane electrolyte.

[0013] A third object of the present invention is to provide an application of the above-mentioned siloxane electrolyte in a low-temperature lithium metal battery, wherein the low-temperature lithium metal battery comprises a positive electrode, a negative electrode and the above-mentioned siloxane electrolyte, wherein the positive electrode and the negative electrode are arranged opposite to each other, and the siloxane electrolyte is formed between the positive electrode and the negative electrode.

[0014] Furthermore, the formation method of the siloxane electrolyte in the low-temperature lithium metal battery includes the following steps:

[0015] The siloxane electrolyte is injected between the positive and negative electrodes of the low-temperature lithium metal battery, and then allowed to stand at -35°C to -40°C to form the electrolyte.

[0016] Furthermore, the standing time is 10 hours and the formation temperature is -40°C.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The siloxane electrolyte composition provided by the present invention comprises lithium salt and dimethoxydimethylsilane. By controlling the ratio of lithium salt and dimethoxydimethylsilane, a uniform and transparent solution can be formed, which can maintain good fluidity and high chemical stability under low temperature conditions. Compared with fluorinated electrolytes, it has the characteristics of low cost and environmental friendliness. Among them, lithium salt has strong electron-withdrawing property, which weakens the coordination effect between anions and cations in lithium salt, making lithium ions more active, thereby improving the ionic conductivity of the electrolyte. The silicon atoms and adjacent oxygen atoms in the dimethoxydimethylsilane solvent have dp conjugation effect, which effectively increases the high voltage resistance of the electrolyte and is conducive to weakening the Li + -solvent interactions promote Li +It is released during the desolvation process; in addition, the siloxane electrolyte can synergistically optimize the low-temperature bulk transport, interfacial chemistry and interfacial mass transfer kinetics in lithium metal batteries, giving them excellent electrochemical performance.

[0019] (2) The lithium salt of the present invention adopts lithium bis(fluorosulfonyl)imide. On the one hand, the fluoride ions in lithium bis(fluorosulfonyl)imide have strong electron-withdrawing properties, which weakens the coordination effect between anions and cations in the lithium salt, making the lithium ions more active, thereby improving the ionic conductivity of the electrolyte; on the other hand, lithium bis(fluorosulfonyl)imide has excellent electrochemical stability and can support the battery to operate in a wider operating temperature range, especially in low temperature environments, where its performance is even better. In addition, lithium bis(fluorosulfonyl)imide can also effectively passivate the positive and negative electrode interfaces, inhibit the formation of lithium dendrites at the negative electrode, and improve the high-voltage resistance of the electrolyte at the positive electrode. Due to these characteristics of lithium bis(fluorosulfonyl)imide, it can improve the discharge capacity and charge and discharge times of low-temperature lithium metal batteries, thereby extending the service life of the battery.

[0020] (3) The siloxane electrolyte composition provided by the present invention, combined with a special low-temperature formation method, can further improve the Li + Desolvation kinetics and Li-ion ions in the solid electrolyte interface (SEI) + Transport dynamics.

[0021] (4) The present invention provides a siloxane electrolyte that can match the ternary positive electrode in a low-temperature lithium metal battery and operate stably at 4.7V. After the button battery is cycled 180 times at -40°C, the capacity retention rate is 95.2%; after the 1.2Ah soft-pack battery is cycled 50 times under low temperature and poor electrolyte conditions at -20°C, the capacity retention rate is 92.1%. It has excellent low-temperature capacity retention and has broad application prospects in low-temperature lithium metal batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Graph showing the results of ionic conductivity tests on the electrolytes of Examples 1 to 6 of the present invention.

[0023] Figure 2 Graph showing the results of ionic conductivity tests on the electrolytes of Example 1 and Comparative Examples 2 to 5 of the present invention.

[0024] Figure 3 Graph showing the results of ionic conductivity tests of the electrolytes of Example 1 and Comparative Example 6 of the present invention.

[0025] Figure 4 The long cycle capacity diagram of the button battery with lithium metal and NCM811 positive electrode matched at -40°C for the electrolyte prepared in Example 1 of the present invention and Comparative Example 6.

[0026] Figure 5 This is a long cycle capacity diagram of a button cell with lithium metal matched with an NCM811 positive electrode at -40°C for the electrolytes of Example 1 of the present invention and Comparative Example 1.

[0027] Figure 6 The charge and discharge curves of button batteries with lithium metal and NCM811 positive electrodes at -40°C are shown for the electrolytes of Example 1 and Comparative Example 1 of the present invention.

[0028] Figure 7 The lithium metal of the button cell matched with the NCM811 positive electrode in Example 1 and Comparative Example 1 of the present invention is + Desolvation energy test diagram.

[0029] Figure 8 The lithium metal of the button cell matched with the NCM811 positive electrode in Example 1 and Comparative Example 1 of the present invention is + Diagram of activation energy transfer within the SEI.

[0030] Figure 9 This is a long cycle capacity diagram of a soft-pack battery with lithium metal and NCM811 positive electrode matched at -20°C using the siloxane electrolyte prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0032] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Certain words are used in the present invention to refer to specific components. Those skilled in the art should understand that technicians will use different nouns to refer to the same component. The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms of "a" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates otherwise.

[0033] In recent years, researchers have developed weakly solvated ether electrolytes and fluorinated electrolytes, which have significantly accelerated the development of Li +The desolvation kinetics of fluorinated electrolytes provide new ideas for solving the low-temperature charging and discharging difficulties of lithium metal batteries. However, ether electrolytes generally exhibit a narrow electrochemical stability window (<4.0V), which limits their use with current high-capacity ternary cathode materials. The cost of fluorinated electrolytes has increased significantly due to the complexity of the synthesis process and the limitation of production output. More importantly, the abnormal stability of the CF bond makes them highly resistant to degradation, raising concerns about their potential environmental hazards.

[0034] Based on the above problems, it is of great significance to develop low-temperature electrolytes that have the characteristics of weak solvation, high voltage resistance, low cost and environmental friendliness.

[0035] Based on this, on the one hand, the present invention provides a siloxane electrolyte, which includes lithium salt and dimethoxydimethylsilane, and the mass ratio of lithium salt to dimethoxydimethylsilane is 0.16-0.48:0.5-1.5.

[0036] The siloxane electrolyte composition provided by the present invention comprises a lithium salt and a dimethoxydimethylsilane solvent. On the one hand, the silicon atoms and adjacent oxygen atoms in the dimethoxydimethylsilane solvent have a dp conjugated effect, which effectively increases the high-voltage resistance of the electrolyte and is conducive to weakening the Li + -solvent interactions promote Li + Released during the desolventizing process; on the other hand, siloxane electrolytes are low-cost and environmentally friendly compared to fluorinated electrolytes. The present invention provides a siloxane electrolyte that can synergistically optimize low-temperature bulk phase transport, interface chemistry, and interface mass transfer kinetics in lithium metal batteries, resulting in excellent electrochemical performance; and combined with a special low-temperature formation method, it can further improve the Li-ion battery performance of siloxane electrolytes. + Desolvation kinetics and Li-ion ions in the solid electrolyte interface (SEI) + Transport dynamics.

[0037] In some specific embodiments, the mass ratio of lithium salt to dimethoxydimethylsilane is 0.26-0.38:0.8-1.2. Preferably, the mass ratio of lithium salt to dimethoxydimethylsilane is 0.3-0.35:1-1.2. More preferably, the mass ratio of lithium salt to dimethoxydimethylsilane is 0.32:1. By controlling the ratio of lithium salt to dimethoxydimethylsilane, the present invention can form a uniform and transparent solution, maintaining good fluidity and high chemical stability even under low temperature conditions.

[0038] In some specific embodiments, the lithium salt is lithium bis(fluorosulfonyl)imide. The fluoride ions in lithium bis(fluorosulfonyl)imide have strong electron-withdrawing properties, which weaken the coordination effect between anions and cations in the lithium salt, making the lithium ions more active, thereby improving the ionic conductivity of the electrolyte. In addition, lithium bis(fluorosulfonyl)imide has excellent electrochemical stability and can support the battery to operate in a wider operating temperature range, especially in low temperature environments, where its performance is even better. In addition, lithium bis(fluorosulfonyl)imide can also effectively passivate the positive and negative electrode interfaces, inhibit the formation of lithium dendrites at the negative electrode, and improve the high-voltage resistance of the electrolyte at the positive electrode. Due to these characteristics of lithium bis(fluorosulfonyl)imide, it can improve the discharge capacity and charge and discharge times of low-temperature lithium metal batteries, thereby extending the service life of the battery.

[0039] In another aspect, the present invention provides a method for preparing the above-mentioned siloxane electrolyte, comprising the following steps:

[0040] Add lithium salt to dimethoxydimethylsilane and stir at room temperature for 10 to 15 hours to obtain a siloxane electrolyte.

[0041] It should be noted that the siloxane electrolyte provided by the present invention has the following characteristics: (1) high transparency, with the electrolyte salt being completely soluble in the electrolyte solvent; (2) good voltage resistance and stability, capable of matching the ternary cathode and operating stably at 4.7V; (3) high ionic conductivity, maintaining good fluidity even at -40°C and matching various commercial cathodes; (4) low cost and environmental friendliness, with the cost being much lower than that of fluorinated electrolytes, and being easily degradable, with no risk of environmental pollution; and (5) long-term stability during low-temperature operation, capable of supporting stable high-capacity operation of lithium metal batteries matching the NCM811 cathode at -20°C.

[0042] In addition, the present invention provides an application of the above-mentioned siloxane electrolyte in a low-temperature lithium metal battery. The low-temperature lithium metal battery includes a positive electrode, a negative electrode and the above-mentioned siloxane electrolyte. The positive electrode and the negative electrode are arranged opposite to each other, and the siloxane electrolyte is formed between the positive electrode and the negative electrode.

[0043] It should be noted that the siloxane electrolyte provided by the present invention can synergistically optimize low-temperature bulk phase transport, interfacial chemistry and interfacial mass transfer kinetics in low-temperature lithium metal batteries, so that they have excellent electrochemical performance.

[0044] In some specific embodiments, the formation of the siloxane electrolyte in a low-temperature lithium metal battery comprises the following steps:

[0045] The siloxane electrolyte is injected between the positive and negative electrodes of the low-temperature lithium metal battery, and then allowed to stand at -35°C to -40°C to form the electrolyte.

[0046] In a specific embodiment, the standing time is 10 hours and the formation temperature is -40°C.

[0047] It should be noted that the formation method described in the present invention is specifically to complete a charge-discharge-charge at a small rate. The rate used is not specified, and it is sufficient to ensure that the battery is charged and discharged normally. Among them, the temperature of room temperature formation is generally 30°C, and the SEI formed therein has more inorganic components, while the -35°C to -40°C formation method adopted in the present invention represents low-temperature formation, and the SEI formed therein has more organic components. In the siloxane electrolyte, the result of the complex interaction of multiple components in the interface region is that the lithium metal full battery matching the rich organic SEI has faster Li+ desolvation kinetics and Li in SEI than the inorganic SEI. + Transport kinetics. Fast Li + The desolvation kinetics is attributed to the more anion-rich solvation structure in the interfacial region. + The transport kinetics is attributed to the gel-like electrolyte transport in the organic-rich SEI.

[0048] The present invention is based on the excellent properties of the siloxane electrolyte, such as high transparency, high electrochemical stability, high ionic conductivity, and low-temperature cycling stability, at a low cost. It can enable lithium-ion batteries to operate stably at high capacity at temperatures between -40°C and 30°C, and has broad application prospects. The siloxane electrolyte can be used with a ternary cathode in low-temperature lithium metal batteries and operate stably at 4.7V. After 180 cycles at -40°C, a button cell maintained a capacity retention of 95.2%. After 50 cycles at -20°C, a 1.2Ah soft-pack cell maintained a capacity retention of 92.1% under low-temperature, lean electrolyte conditions. These excellent low-temperature capacity retention rates hold great promise for application in low-temperature lithium metal batteries.

[0049] The following is further described through specific examples.

[0050] Example 1

[0051] This embodiment provides a siloxane electrolyte, which includes lithium bis(fluorosulfonyl)imide (LiFSI) and dimethoxydimethylsilane, and the mass ratio of LiFSI to dimethoxydimethylsilane is 0.32:1.

[0052] The preparation method of the above-mentioned siloxane electrolyte comprises the following steps:

[0053] 0.282 g of LiFSI was added to 1 mL of dimethoxydimethylsilane and stirred at room temperature for 12 h to obtain a siloxane electrolyte.

[0054] The formation method of siloxane electrolyte in low-temperature lithium metal batteries includes the following steps:

[0055] The siloxane electrolyte is injected between the positive and negative electrodes of the lithium metal battery, and then formed at -40°C after standing.

[0056] Example 2

[0057] This embodiment provides a siloxane electrolyte, which includes LiFSI and dimethoxydimethylsilane, and the mass ratio of LiFSI to dimethoxydimethylsilane is 0.96:1.

[0058] The preparation method of the above-mentioned siloxane electrolyte comprises the following steps:

[0059] 0.917 g of LiFSI was added to 1 mL of dimethoxydimethylsilane and stirred at room temperature for 12 h to obtain a siloxane electrolyte.

[0060] The formation method of siloxane electrolyte in low-temperature lithium metal batteries includes the following steps:

[0061] The siloxane electrolyte is injected between the positive and negative electrodes of the lithium metal battery, and then formed at -40°C after standing.

[0062] Example 3

[0063] This embodiment provides a siloxane electrolyte, which includes LiFSI and dimethoxydimethylsilane, and the mass ratio of LiFSI to dimethoxydimethylsilane is 0.7:1.

[0064] The preparation method of the above-mentioned siloxane electrolyte comprises the following steps:

[0065] 0.616 g of LiFSI was added to 1 mL of dimethoxydimethylsilane and stirred at room temperature for 12 h to obtain a siloxane electrolyte.

[0066] The formation method of siloxane electrolyte in low-temperature lithium metal batteries includes the following steps:

[0067] The siloxane electrolyte is injected between the positive and negative electrodes of the lithium metal battery, and then formed at -40°C after standing.

[0068] Example 4

[0069] This embodiment provides a siloxane electrolyte, which includes LiFSI and dimethoxydimethylsilane, and the mass ratio of LiFSI to dimethoxydimethylsilane is 0.5:1.

[0070] The preparation method of the above-mentioned siloxane electrolyte comprises the following steps:

[0071] 0.440 g of LiFSI was added to 1 mL of dimethoxydimethylsilane and stirred at room temperature for 12 h to obtain a siloxane electrolyte.

[0072] The formation method of siloxane electrolyte in low-temperature lithium metal batteries includes the following steps:

[0073] The siloxane electrolyte was injected between the positive and negative electrodes of the lithium metal battery, and then allowed to stand at -40°C for formation.

[0074] Example 5

[0075] This embodiment provides a siloxane electrolyte, which includes LiFSI and dimethoxydimethylsilane, and the mass ratio of LiFSI to dimethoxydimethylsilane is 0.2:1.

[0076] The preparation method of the above-mentioned siloxane electrolyte comprises the following steps:

[0077] 0.176 g of LiFSI was added to 1 mL of dimethoxydimethylsilane and stirred at room temperature for 12 h to obtain a siloxane electrolyte.

[0078] The formation method of siloxane electrolyte in low-temperature lithium metal batteries includes the following steps:

[0079] The siloxane electrolyte was injected between the positive and negative electrodes of the lithium metal battery, and then allowed to stand at -40°C for formation.

[0080] Example 6

[0081] This embodiment provides a siloxane electrolyte, which includes LiFSI and dimethoxydimethylsilane, and the mass ratio of LiFSI to dimethoxydimethylsilane is 0.11:1.

[0082] The preparation method of the above-mentioned siloxane electrolyte comprises the following steps:

[0083] 0.097 g of LiFSI was added to 1 mL of dimethoxydimethylsilane and stirred at room temperature for 12 h to obtain a siloxane electrolyte.

[0084] The formation method of siloxane electrolyte in low-temperature lithium metal batteries includes the following steps:

[0085] The siloxane electrolyte was injected between the positive and negative electrodes of the lithium metal battery, and then allowed to stand at -40°C for formation.

[0086] Comparative Example 1

[0087] This comparative example provides a siloxane electrolyte, which includes LiFSI and dimethoxydimethylsilane, and the mass ratio of LiFSI to dimethoxydimethylsilane is 0.32:1.

[0088] The preparation method of the above-mentioned siloxane electrolyte comprises the following steps:

[0089] 0.282 g of LiFSI was added to 1 mL of dimethoxydimethylsilane and stirred at room temperature for 12 h to obtain a siloxane electrolyte.

[0090] The formation method of siloxane electrolyte in low-temperature lithium metal batteries includes the following steps:

[0091] The siloxane electrolyte was injected between the positive and negative electrodes of the lithium metal battery and allowed to stand at 30°C for formation.

[0092] Comparative Example 2

[0093] This comparative example provides an electrolyte, which is different from Example 1 in that ethyl silicate is selected as the electrolyte solvent. The siloxane electrolyte includes LiFSI and ethyl silicate, and the mass ratio of LiFSI to ethyl silicate is 0.30:1.

[0094] The preparation method of the above electrolyte comprises the following steps:

[0095] 0.282 g of LiFSI was added to 1 mL of ethyl silicate and stirred at room temperature for 12 h to obtain an electrolyte solution.

[0096] The formation method of the electrolyte in the low-temperature lithium metal battery includes the following steps:

[0097] The electrolyte is injected between the positive and negative electrodes of the lithium metal battery, and then allowed to stand at -40°C to form the electrolyte.

[0098] Comparative Example 3

[0099] This comparative example provides a siloxane electrolyte, which differs from Example 1 in that trimethylethoxysilane is selected as the electrolyte solvent. The siloxane electrolyte includes LiFSI and trimethylethoxysilane, and the mass ratio of LiFSI to trimethylethoxysilane is 0.37:1.

[0100] The preparation method of the above-mentioned siloxane electrolyte comprises the following steps:

[0101] 0.282 g of LiFSI was added to 1 mL of trimethylethoxysilane and stirred at room temperature for 12 h to obtain a siloxane electrolyte.

[0102] The formation method of siloxane electrolyte in low-temperature lithium metal batteries includes the following steps:

[0103] The siloxane electrolyte was injected between the positive and negative electrodes of the lithium metal battery, and then allowed to stand at -40°C for formation.

[0104] Comparative Example 4

[0105] This comparative example provides a siloxane electrolyte, which differs from Example 1 in that methyltriethoxysilane is used as the electrolyte solvent. The siloxane electrolyte includes LiFSI and methyltriethoxysilane, and the mass ratio of LiFSI to methyltriethoxysilane is 0.32:1.

[0106] The preparation method of the above-mentioned siloxane electrolyte comprises the following steps:

[0107] 0.282 g of LiFSI was added to 1 mL of methyltriethoxysilane and stirred at room temperature for 12 h to obtain a siloxane electrolyte.

[0108] The formation method of siloxane electrolyte in low-temperature lithium metal batteries includes the following steps:

[0109] The siloxane electrolyte was injected between the positive and negative electrodes of the lithium metal battery, and then allowed to stand at -40°C for formation.

[0110] Comparative Example 5

[0111] This comparative example provides a siloxane electrolyte, which differs from Example 1 in that dimethyldiethoxysilane is used as the electrolyte solvent. The siloxane electrolyte includes LiFSI and dimethyldiethoxysilane, and the mass ratio of LiFSI to dimethyldiethoxysilane is 0.33:1.

[0112] The preparation method of the above-mentioned siloxane electrolyte comprises the following steps:

[0113] 0.282 g of LiFSI was added to 1 mL of dimethyldiethoxysilane and stirred at room temperature for 12 h to obtain a siloxane electrolyte.

[0114] The formation method of siloxane electrolyte in low-temperature lithium metal batteries includes the following steps:

[0115] The siloxane electrolyte was injected between the positive and negative electrodes of the lithium metal battery, and then allowed to stand at -40°C for formation.

[0116] Comparative Example 6

[0117] This comparative example provides an ether electrolyte, which is different from Example 1 in that ethylene glycol dimethyl ether is used as the electrolyte solvent. The siloxane electrolyte includes LiFSI and ethylene glycol dimethyl ether, and the mass ratio of LiFSI to ethylene glycol dimethyl ether is 0.33:1.

[0118] The preparation method of the above-mentioned siloxane electrolyte comprises the following steps:

[0119] 0.282 g of LiFSI was added to 1 mL of ethylene glycol dimethyl ether and stirred at room temperature for 12 h to obtain an ether electrolyte.

[0120] The formation method of siloxane electrolyte in low-temperature lithium metal batteries includes the following steps:

[0121] The siloxane electrolyte was injected between the positive and negative electrodes of the lithium metal battery, and then allowed to stand at -40°C for formation.

[0122] The electrolytes prepared in Examples 1 to 6 and Comparative Examples 1 to 6 were subjected to an ion conductivity test. The ion conductivity test included the following steps:

[0123] Conductivity test method: Stainless steel is used as the positive and negative electrodes, separated by a polytetrafluoroethylene gasket, and the electrolytes of Examples 1 to 6 and Comparative Examples 1 to 6 are added to assemble stainless steel|stainless steel batteries. The ohmic impedance of the battery is tested, and the ionic conductivity of the electrolyte is estimated by the ohmic impedance results. The results are as follows Figures 1 to 3 shown.

[0124] Figure 1 The results of the ionic conductivity test of the electrolytes of Examples 1 to 6 of the present invention are shown in FIG. Figure 1 As shown, the ionic conductivity of the siloxane electrolyte used in Examples 2 to 6 is lower than that in Example 1. This shows that within the range of the mass ratio of LiFSI to dimethoxydimethylsilane of 0.16 to 0.48:0.5 to 1.5, the electrolyte with a mass ratio of LiFSI to dimethoxydimethylsilane of 0.32:1 has the highest ionic conductivity. The lithium salt concentration of the electrolyte corresponding to this mass ratio is 1.5M. High electrolyte ionic conductivity is beneficial to reducing the internal resistance of low-temperature lithium metal batteries, reducing battery polarization, and is beneficial to improving the battery discharge capacity and cycle life. Therefore, Example 1 is the most preferred siloxane electrolyte formula.

[0125] Based on this, the present invention further studies the electrolyte prepared with a mass ratio of LiFSI and dimethoxydimethylsilane of 0.32:1 in Example 1, and the results are as follows.

[0126] Figure 2 The results of the ionic conductivity test of the electrolytes of Example 1 and Comparative Examples 2 to 5 of the present invention are shown in FIG. Figure 2 As shown, at the same electrolyte concentration, the ionic conductivity of the siloxane electrolyte used in Comparative Examples 2 to 5 is lower than that of Example 1. Example 1 can maintain a conductivity greater than 10 -4 S cm -1 This ensures that the electrolyte has sufficient ion transport capacity at low temperatures, ensuring that lithium metal batteries can operate normally under low temperature conditions.

[0127] Figure 3The results of the ionic conductivity test of the electrolytes of Example 1 and Comparative Example 6 are shown in FIG. Figure 3 As shown, the conductivity of the traditional ether electrolyte used in Example 1 is lower than that in Comparative Example 6.

[0128] To verify the improved low-temperature performance of Example 1, the electrolytes from Example 1, Comparative Example 1, and Comparative Example 6 were used to assemble a lithium metal full cell. In this lithium metal full cell, a lithium sheet served as the negative electrode and NCM811 served as the positive electrode. The NCM811 electrode sheet was prepared by knife coating a mixture of NCM811 active material, conductive carbon black, and polyvinylidene fluoride (PVDF) in a mass ratio of 80:10:10 onto carbon-coated aluminum foil. The film was then dried in a 120°C vacuum oven and cut into 12mm diameter pieces to produce the NCM811 electrode sheet. The electrolytes prepared in Example 1, Comparative Example 1, and Comparative Example 6 were then injected into the cells, forming button-style full cells with lithium metal and NCM811 positive electrodes.

[0129] Figure 4 The long cycle capacity diagram of the button cell with lithium metal and NCM811 positive electrode matched at -40°C for the electrolyte prepared in Example 1 of the present invention and Comparative Example 6. Figure 4 As shown, the lithium metal full battery matching Example 1 shows excellent long cycle stability and high discharge capacity characteristics under low temperature conditions. After 180 cycles at -40°C and 4.7V, the capacity retention rate is 95.2%. However, the capacity of the lithium metal full battery matching the ether electrolyte of Comparative Example 6 decays rapidly under low temperature conditions, and the charge and discharge efficiency is also very low. This is mainly due to the poor Li + Desolvation kinetics. However, the siloxane electrolyte in Example 1 has dp conjugation between silicon atoms and adjacent oxygen atoms, which makes Li + -solvent interaction is weakened, accelerating the Li + Desolvation kinetics.

[0130] In order to verify the effect of the formation method on the low-temperature performance of the siloxane electrolyte, Example 1 and Comparative Example 1 were subjected to low-temperature charge and discharge cycle tests of a low-temperature lithium metal full battery. Figure 5 The long cycle capacity diagram of the button cell with lithium metal and NCM811 positive electrode matched at -40°C for the electrolyte of Example 1 of the present invention and Comparative Example 1 is shown. Figure 5 As shown in Figure 1, despite matching the same electrolyte, the capacity of the lithium metal full battery formed at low temperature in Example 1 is higher than that of the sample formed at low temperature in Comparative Example 1. This indicates that low temperature formation can form an interface layer with faster interface transport kinetics.

[0131] Figure 6 The charge and discharge curves of the button cell with lithium metal and NCM811 positive electrode matched at -40°C for the electrolyte of Example 1 and Comparative Example 1 of the present invention are shown in FIG. Figure 6As shown, the charge and discharge proves that the comparative example 1 has a higher polarization than the example 1, which indicates that the sample formed at room temperature will have a larger interface impedance.

[0132] Figure 7 The lithium metal of the button cell matched with the NCM811 positive electrode in Example 1 and Comparative Example 1 of the present invention is + Desolvation energy test diagram. Figure 8 The lithium metal of the button cell matched with the NCM811 positive electrode in Example 1 and Comparative Example 1 of the present invention is + Transmission activation energy test diagram within SEI. Figures 7 and 8 As shown, the Li of Comparative Example 1 and Example 1 were tested respectively. + Desolvation energy and Li in SEI + The results show that the samples formed at low temperature have lower desolvation energy and SEI transport activation energy, which once again confirms that low temperature formation can form an interfacial layer with faster interfacial transport kinetics.

[0133] The present invention conducts comprehensive performance tests on the electrolyte prepared in Example 1. Figure 9 This is the long cycle capacity diagram of the soft pack battery with lithium metal and NCM811 positive electrode matched at -20°C using the siloxane electrolyte prepared in Example 1 of the present invention. Figure 9 The 1.2Ah soft-pack battery with lithium metal and NCM811 positive electrode matched with the electrolyte used in Example 1 at -20°C showed excellent long-cycle stability and high discharge capacity characteristics under low-temperature and lean electrolyte conditions. It maintained a capacity of 92.1% within the low-temperature test range of 50 cycles, and the average charge and discharge efficiency was as high as 99.7%.

[0134] As can be seen from the above, the siloxane electrolyte provided by the present invention includes lithium bis(fluorosulfonyl)imide and dimethoxydimethylsilane. By controlling the ratio of lithium bis(fluorosulfonyl)imide and dimethoxydimethylsilane, a uniform and transparent solution can be formed, which can maintain good fluidity and high chemical stability under low temperature conditions. The silicon atoms and adjacent oxygen atoms in the dimethoxydimethylsilane have a dp conjugated effect, which effectively increases the high voltage resistance of the electrolyte and is conducive to weakening the Li + -Solvent interaction promotes the release of lithium ions during the desolvation process; combined with the low-temperature formation method, it can significantly improve the electrochemical performance of lithium batteries in the low-temperature range, can match the ternary positive electrode and operate stably under 4.7V conditions, and has excellent low-temperature capacity retention rate (after 180 cycles of button batteries at -40°C, the capacity retention rate is 95.2%; after 50 cycles of 1.2Ah soft-pack batteries at -20°C under low-temperature and lean electrolyte conditions, the capacity retention rate is 92.1%), and has broad application prospects in low-temperature lithium metal batteries.

[0135] It should be noted that when numerical ranges are mentioned in the present invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints may be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes preferred embodiments. Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they understand the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0136] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A formation method for a low-temperature lithium metal battery, characterized in that: The low-temperature lithium metal battery includes a positive electrode, a negative electrode and a siloxane electrolyte. The positive electrode and the negative electrode are arranged opposite to each other. The siloxane electrolyte is composed of lithium bis(fluorosulfonyl)imide and dimethoxydimethylsilane. The mass ratio of lithium bis(fluorosulfonyl)imide to dimethoxydimethylsilane is 0.16-0.48:0.5-1.

5. The siloxane electrolyte is injected between the positive electrode and the negative electrode of the low-temperature lithium metal battery, and after standing, it is formed at -35°C to -40°C.

2. The formation method of a low-temperature lithium metal battery according to claim 1, characterized in that: The mass ratio of lithium salt to dimethoxydimethylsilane is 0.26-0.38:0.8-1.

2.

3. The formation method of a low-temperature lithium metal battery according to claim 1, characterized in that: The mass ratio of lithium salt to dimethoxydimethylsilane is 0.3-0.35:1-1.

2.

4. The formation method of a low-temperature lithium metal battery according to claim 1, characterized in that: The mass ratio of lithium salt to dimethoxydimethylsilane is 0.32:

1.

5. The formation method of a low-temperature lithium metal battery according to claim 1, characterized in that: The preparation method of the siloxane electrolyte comprises the following steps: Add lithium salt to dimethoxydimethylsilane and stir at room temperature for 10 h to 15 h to obtain a siloxane electrolyte.

6. The formation method of a low-temperature lithium metal battery according to claim 1, characterized in that: The standing time is 10 h, and the formation temperature is -40°C.

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