Lithium metal battery electrolyte suitable for fast charging and low temperature, battery and preparation method thereof

Abstract

The present application relates to a kind of lithium metal battery electrolyte suitable for fast charging and low temperature, battery and its preparation method, belong to lithium metal battery technical field.The method includes the following steps: A.lithium salt is dissolved in ether solvent, mixed uniformly, and the basic electrolyte is prepared;B.trifluoromethanesulfonic acid tert-butyl diphenyl silyl ester is added to the basic electrolyte for at least 2 hours;Wherein, the addition amount of trifluoromethanesulfonic acid tert-butyl diphenyl silyl ester is 1%~9% of the total mass of basic electrolyte.The present application realizes the synergistic effect of "solvation optimization-interface barrier-ion conduction";The product of the present application has excellent electrochemical performance, including high ion transference number, effectively inhibits the growth of lithium dendrite, excellent fast charging and cycle performance, excellent low temperature performance.The preparation process of the present application is simple, easy to industrial production and popularization.

Description

Technical Field

[0001] This invention relates to a lithium metal battery electrolyte, battery, and preparation method suitable for fast charging and low temperature, belonging to the field of lithium metal battery technology. Background Technology

[0002] Lithium metal batteries have an extremely high theoretical specific capacity (3860 mAh g) due to the lithium metal anode. -1 With its extremely low redox potential (-3.04 V vs. standard hydrogen electrode), lithium metal is considered a core candidate technology for next-generation high-energy-density energy storage devices. Among them, 2M LiFSI-DME electrolyte, due to the high dissociation degree of LiFSI salt and the good solubility of lithium salt in DME solvent, shows potential in improving ionic conductivity and suppressing some side reactions, and has become one of the important research directions for lithium metal battery electrolytes.

[0003] However, 2M LiFSI-DME electrolytes still face the critical problem of poor lithium metal interface stability in practical applications: 1) DME molecules have strong lithium affinity and easily undergo reduction reactions with the lithium metal surface, generating a loose and uneven solid electrolyte interphase (SEI) layer. This SEI layer has low mechanical strength and uneven ion conduction, and cannot effectively block the penetration of subsequent solvent molecules, leading to continuous side reactions; 2) The loose SEI layer cannot effectively guide the lithium metal deposition process, and lithium metal easily grows into dendrites along SEI defects, which not only consumes electrolyte and lithium metal, but may also puncture the separator and cause a battery short circuit, seriously threatening battery safety; 3) The above interface problems lead to rapid capacity decay of Li|| cathode (such as NCM, LFP) full cells during cycling, especially at medium and high current densities, where the cycle stability is even more difficult to meet practical requirements; 4) In addition, at low temperatures, the desolvation process of lithium ions is slow, and the interfacial impedance increases sharply, further aggravating the degradation of battery performance.

[0004] Currently, the interface optimization strategies for 2M LiFSI-DME electrolytes mainly include: 1) adding SEI film-forming additives (such as LiNO3 and fluorocarbonates). Although this can improve the SEI composition, some additives have poor compatibility with DME, and the SEI can only be optimized through "passive film formation," failing to fundamentally reduce the direct contact between DME and lithium metal; 2) constructing an artificial SEI layer, pre-preparing a protective layer on the lithium metal surface using physical or chemical methods. However, the uniformity of the artificial layer's thickness is difficult to control, and interfacial compatibility with the electrolyte is prone to problems; 3) introducing diluents. Although this can reduce the electrolyte viscosity, it may weaken the Li... + The solvation of DME leads to a decrease in ionic conductivity and fails to resolve the inherent reactivity of DME with lithium metal.

[0005] Existing improvement strategies often focus on optimizing a single dimension (such as improving only the SEI component or physical barrier), making it difficult to achieve synergy between "reducing contact with harmful solvents", "stabilizing the SEI structure" and "promoting rapid lithium-ion transport", resulting in an inability to simultaneously improve battery cycle life, fast charging capability and low-temperature performance.

[0006] Therefore, there is an urgent need in this field for a novel electrolyte solution that can regulate interfacial chemistry and ion transport dynamics at the source. Summary of the Invention

[0007] The first objective of this invention is to provide a method for preparing a lithium metal battery electrolyte suitable for fast charging and low temperatures.

[0008] To achieve the first objective of this invention, the method includes the following steps:

[0009] A. Dissolve lithium salt in an ether solvent, mix thoroughly, and prepare a basic electrolyte;

[0010] B. Add tert-butyl diphenylsilyl trifluoromethanesulfonate to the basic electrolyte and react for at least 2 hours;

[0011] The amount of tert-butyldiphenylsilyl trifluoromethanesulfonate added is 1% to 9% of the total mass of the base electrolyte.

[0012] The preferred addition amount of tert-butyldiphenylsilyl trifluoromethanesulfonate is 7% of the total mass of the base electrolyte—this addition amount ensures TB and FSI. - The reaction generates sufficient TB-FSI, forming a crack-free adsorption layer at the anode. When the addition amount is 1%–6 wt%, the continuity of the adsorption layer weakens as the addition amount decreases, but it is still superior to the reference electrolyte. When the addition amount is 8%–9 wt%, the electrolyte viscosity increases compared to 7 wt%, and Li… + The transmission efficiency has decreased slightly, but the cycle performance still meets the requirements for fast charging and low temperature.

[0013] In one specific embodiment, the lithium salt is lithium bis(fluorosulfonyl)imide.

[0014] In one specific embodiment, the ether solvent is at least one selected from ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), tetrahydrofuran (THF), or dimethoxypropane (DMP). DME is preferred as the ether solvent because it allows the electrolyte to possess both high ionic conductivity and low viscosity.

[0015] In one specific embodiment, the concentration of lithium bis(fluorosulfonyl)imide in the base electrolyte is 2M.

[0016] In one specific embodiment, the temperature of the reaction in step B is 25°C to 30°C.

[0017] In one specific embodiment, the amount of tert-butyldiphenylsilyl trifluoromethanesulfonate added is 7% of the total mass of the base electrolyte.

[0018] The second objective of this invention is to provide a lithium metal battery electrolyte suitable for fast charging and low temperatures.

[0019] To achieve the second objective of this invention, the lithium metal battery electrolyte suitable for fast charging and low temperature is prepared using the method described above.

[0020] In one specific embodiment, the electrolyte has a lithium-ion transference number of not less than 0.6 at 25°C.

[0021] The third objective of this invention is to provide a lithium metal battery suitable for fast charging and low temperatures.

[0022] To achieve the third objective of the present invention, the lithium metal battery suitable for fast charging and low temperature includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the electrolyte described above.

[0023] In one specific embodiment, the negative electrode is a lithium foil or a lithium alloy.

[0024] Beneficial effects:

[0025] 1. Synergistic Regulation: The silicon atoms in the TB molecule of this invention and FSI - The anion undergoes a nucleophilic substitution reaction, passing through a five-coordinate transition state to form the TB-FSI complex. In the TB-FSI complex, the FSI⁻ component preferentially and directionally adsorbs onto the lithium metal anode surface, while the leaving group (trifluoromethanesulfonate group) of TB can modulate the adsorption of Li. + Solvation of the sheath layer reduces DME and Li + The coordination ratio significantly reduced Li + Desolvation energy barrier; in addition, the hydrophobic groups such as phenyl and tert-butyl groups in TB-FSI are oriented by van der Waals forces to form a dense yet porous adsorption layer. This adsorption layer can both physically block the direct contact between DME and lithium metal and protect Li through its porous structure. + Rapid transport enables the synergistic effect of "solventization optimization - interface barrier - ion conduction".

[0026] 2. Excellent electrochemical performance:

[0027] High ion mobility number: The lithium ion mobility number of the electrolyte can reach above 0.6, preferably up to 0.731, which is much higher than the reference electrolyte 0.454, which is beneficial for achieving rapid charge and discharge.

[0028] Suppressing lithium dendrites: The Li||Li symmetric cells and Li||Cu half-cells using this electrolyte exhibited uniform and dense lithium deposition morphology, effectively suppressing the growth of lithium dendrites.

[0029] Excellent fast charging and cycle performance: The assembled Li||NCM811 full battery retains 80% of its capacity after 400 cycles at a high rate of 5C.

[0030] Excellent low-temperature performance: After 300 cycles at 1C rate in a low-temperature environment of -20℃, the capacity retention rate is still as high as 76.8%.

[0031] 3. Simple preparation process: The preparation process only requires simple mixing and reaction, without the need for complex equipment or harsh conditions, making it easy to industrialize and promote. Attached Figure Description

[0032] Figure 1 Example 1: Electrolyte vs. Reference Electrolyte 7 Li NMR comparison spectrum.

[0033] Figure 2 Raman spectra of the electrolyte and the reference electrolyte in Example 1, where a is Example 1 and b is the reference electrolyte.

[0034] Figure 3 Example 1: Lithium-ion transport number test graphs of electrolyte and reference electrolyte. a is the reference electrolyte, and b is Example 1.

[0035] Figure 4 XPS spectrum of lithium metal anode after cycling.

[0036] Figure 5 SEM images of lithium metal anodes after cycling with the reference electrolyte and the electrolyte of Example 1, a for Example 1 and b for the reference electrolyte.

[0037] Figure 6 Example 1: A Li||Cu half-cell assembled with an electrolyte and a reference electrolyte at 4 mA cm⁻¹ -2 Comparison of coulombic efficiency at high current density.

[0038] Figure 7 Example 1: Comparison of ionic conductivity between electrolyte and reference electrolyte.

[0039] Figure 8 Example 1: Cycling performance of a Li||NCM811 full cell assembled with electrolyte and reference electrolyte at 5C.

[0040] Figure 9 Example 1: Cycling performance of a Li||NCM811 full cell assembled with electrolyte and reference electrolyte at -20°C.

[0041] Figure 10 Comparison of ionic conductivity of electrolytes in Examples 2-5 Detailed Implementation

[0042] To achieve the first objective of this invention, the method includes the following steps:

[0043] A. Dissolve lithium salt in an ether solvent, mix thoroughly, and prepare a basic electrolyte;

[0044] B. Add tert-butyl diphenylsilyl trifluoromethanesulfonate to the basic electrolyte and react for at least 2 hours;

[0045] The amount of tert-butyldiphenylsilyl trifluoromethanesulfonate added is 1% to 9% of the total mass of the base electrolyte.

[0046] In one specific embodiment, the lithium salt is lithium bis(fluorosulfonyl)imide.

[0047] In one specific embodiment, the ether solvent includes at least one selected from ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), tetrahydrofuran (THF), or dimethoxypropane (DMP). DME is preferred as the ether solvent because it allows the electrolyte to possess both high ionic conductivity and low viscosity.

[0048] In one specific embodiment, the concentration of lithium bis(fluorosulfonyl)imide in the base electrolyte is 2M.

[0049] In one specific embodiment, the temperature of the reaction in step B is 25°C to 30°C.

[0050] In one specific embodiment, the amount of tert-butyldiphenylsilyl trifluoromethanesulfonate added is 7% of the total mass of the base electrolyte.

[0051] To achieve the second objective of this invention, the lithium metal battery electrolyte suitable for fast charging and low temperature is prepared using the method described above.

[0052] In one specific embodiment, the electrolyte has a lithium-ion transference number of not less than 0.6 at 25°C.

[0053] To achieve the third objective of the present invention, the lithium metal battery suitable for fast charging and low temperature includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the electrolyte described above.

[0054] In one specific embodiment, the negative electrode is a lithium foil or a lithium alloy.

[0055] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0056] Example 1

[0057] Take tert-butyl diphenylsilyl trifluoromethanesulfonate (TB); ethylene glycol dimethyl ether (DME); and lithium bis(fluorosulfonyl)imide (LiFSI).

[0058] Step 1: Obtain LiFSI in DME reference electrolyte by dissolving LiFSI in DME. The concentration of LiFSI in the reference electrolyte is 2M.

[0059] Step 2: Add 7wt% TB to 1mL of 2M LiFSI in DME standard electrolyte and stir thoroughly at 25°C for 2h to obtain an electrolyte suitable for fast charging and low temperature.

[0060] The electrolyte prepared in Example 1, suitable for fast charging and low temperature operation, is characterized below:

[0061] Depend on Figure 1 As shown, Figure 1 The NMR spectrum of Li showed that upon the addition of TB, the peak position of the Li spectrum shifted from approximately -1.61 ppm to -1.69 ppm at a higher field. This result can be attributed to the addition of TB causing the Li peak to shift to a higher field. + The binding with DME weakens.

[0062] Figure 2 The images show the Raman spectra of the fast-charging and low-temperature electrolyte prepared in Example 1 of this invention and the LiFSI in DME reference electrolyte at room temperature; where a is the Raman spectrum of the fast-charging and low-temperature electrolyte and b is the Raman spectrum of the reference electrolyte. The proportion of ion aggregates (27%) in the fast-charging and low-temperature electrolyte is higher than that in the reference electrolyte (7%). This increased aggregate content is related to LiFSI in DME. + The reduction of the desolvation energy barrier is related.

[0063] Depend on Figure 3 The chronoampere curves and AC impedance spectra before and after polarization of the Li||Li symmetric battery (illustrated) show that b is suitable for fast charging and low-temperature electrolytes with lithium-ion transfer numbers (t). Li + =0.731) is significantly higher than that of the reference electrolyte (t) Li + =0.454) High. This significant enhancement can be attributed to the anion-rich solvation structure of the electrolyte, suitable for fast charging and low temperatures, modulating rapid Li... + Conduction, multiple Li + The presence of ligands accelerates the Li +The migration of electrolyte ions further confirms the improved ion transport performance suitable for fast charging and low temperatures.

[0064] Figure 4 The X-ray photoelectron spectra of the lithium metal anode interface after 50 cycles of the reference electrolyte and the electrolyte suitable for fast charging and low temperature are shown. The presence of Si-N composition at the interface of the electrolyte suitable for fast charging and low temperature indicates that TB-FSI has formed a stable SEI layer at the anode interface.

[0065] Figure 5 Li||Li batteries assembled with a reference electrolyte and an electrolyte suitable for fast charging and low temperatures, respectively, at 1 mA cm⁻¹. -2 The lithium deposition morphology under the reference electrolyte shows that the lithium deposited on the surface of the lithium metal electrode is more uniform and dense, while the lithium deposited on the reference electrolyte exhibits loose and rough dendrites.

[0066] Figure 6 Li||Cu half-cells assembled using the electrolyte prepared in Example 1, suitable for fast charging and low temperatures, as the electrolyte for lithium metal batteries and the reference electrolyte, were tested at 4 mA cm⁻¹. -2 The half-cell with high current density electrolyte assembly, suitable for fast charging and low temperature, has an average coulombic efficiency of 96.86% after 250 cycles, compared to the reference electrolyte which fails after 175 cycles with an average coulombic efficiency of only 83.26%.

[0067] Depend on Figure 7 The comparison chart of ionic conductivity shows that, at 25℃, the electrolyte suitable for fast charging and low temperature achieves 2.8 mS / cm. -1 High ionic conductivity, compared to the reference electrolyte 2.4 mS / cm. -1 In comparison, this indicates that electrolytes suitable for fast charging and low temperatures have excellent ionic conductivity.

[0068] Figure 8 The cycling performance of Li||NCM811 full cells assembled using the electrolyte suitable for fast charging and low temperature prepared in Example 1 as the electrolyte for lithium metal batteries and the reference electrolyte is compared with that of the reference electrolyte at a high current density of 5C. The full cell assembled with the electrolyte suitable for fast charging and low temperature still has 80% capacity retention after 400 cycles, while the reference electrolyte only has 75% capacity retention after 170 cycles.

[0069] Figure 9The cycling performance of Li||NCM811 full cells assembled using the electrolyte suitable for fast charging and low temperature prepared in Example 1 as the electrolyte for lithium metal batteries and the reference electrolyte was tested at a current density of 1C under a low temperature condition of -20°C. The full cell assembled with the electrolyte suitable for fast charging and low temperature still had a capacity retention of 76.8% after 300 cycles, while the capacity retention of the reference electrolyte was only 44% of the original after 300 cycles.

[0070] The performance improvements mentioned above can all be attributed to the modification of the anode interface by electrolytes suitable for fast charging and low temperatures.

[0071] Example 2

[0072] The electrolyte suitable for fast charging and low temperature is prepared according to the steps of Example 1, with the only difference being that: the ether solvent is still ethylene glycol dimethyl ether (DME), and the "add 7 wt% TB" in step 2 is changed to "add 5 wt% TB"; the other steps remain unchanged.

[0073] Example 3

[0074] The electrolyte suitable for fast charging and low temperature is prepared according to the steps of Example 1, with the only difference being that: the ether solvent is still ethylene glycol dimethyl ether (DME), and the "add 7 wt% TB" in step 2 is changed to "add 3 wt% TB"; the other steps remain unchanged.

[0075] Example 4

[0076] The electrolyte suitable for fast charging and low temperature is prepared according to the steps of Example 1, with the only difference being that: the ether solvent is still ethylene glycol dimethyl ether (DME), and the "add 7 wt% TB" in step 2 is changed to "add 1 wt% TB"; the other steps remain unchanged.

[0077] Example 5

[0078] The electrolyte suitable for fast charging and low temperature is prepared according to the steps of Example 1, with the only difference being that: the ether solvent is still ethylene glycol dimethyl ether (DME), and the "add 7 wt% TB" in step 2 is changed to "add 9 wt% TB"; the other steps remain unchanged.

[0079] like Figure 10 As shown, the conductivity of Examples 2-5 is 2.7 mS / cm. -1 2.6 mS cm -1 2.5 mS cm -1 2.4 mS cm -1In contrast, the ionic conductivity in Example 1 was the highest among all examples, indicating that the 7 wt% TB addition in Example 1 was the optimal ratio. The ionic conductivity in Examples 2-5 decreased as the TB addition deviated from 7 wt% (2.7 → 2.4 mS / cm). -1 The corresponding Li||NCM811 full cell cycle performance (5C / low temperature) also decreased slightly with decreasing conductivity, but was still better than the reference electrolyte, further confirming the feasibility of the technical solution of the present invention within the range of 1% to 9% TB addition.

Claims

1. A method for preparing a lithium metal battery electrolyte suitable for fast charging and low temperature, characterized in that, The method includes the following steps: A. Dissolve lithium salt in an ether solvent, mix thoroughly, and prepare a basic electrolyte; B. Add tert-butyl diphenylsilyl trifluoromethanesulfonate to the basic electrolyte and react for at least 2 hours; The amount of tert-butyl diphenylsilyl trifluoromethanesulfonate added is 1% to 9% of the total mass of the basic electrolyte, and the ether solvent is at least one of ethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, or dimethoxypropane. The lithium salt is lithium difluorosulfonylimide.

2. The method for preparing a lithium metal battery electrolyte suitable for fast charging and low temperature according to claim 1, characterized in that, The concentration of lithium difluorosulfonylimide in the basic electrolyte is 2M.

3. The method for preparing a lithium metal battery electrolyte suitable for fast charging and low temperature according to claim 1, characterized in that, The reaction temperature in step B is 25℃~30℃.

4. The method for preparing a lithium metal battery electrolyte suitable for fast charging and low temperature according to claim 1, characterized in that, The amount of tert-butyl diphenylsilyl trifluoromethanesulfonate added is 7% of the total mass of the base electrolyte.

5. A lithium metal battery electrolyte suitable for fast charging and low temperatures, characterized in that, The lithium metal battery electrolyte suitable for fast charging and low temperature is prepared by the method described in any one of claims 1 to 4.

6. The lithium metal battery electrolyte suitable for fast charging and low temperature as described in claim 5, characterized in that, The electrolyte has a lithium-ion transference number of not less than 0.6 at 25°C.

7. A lithium metal battery suitable for fast charging and low temperature operation, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte is the electrolyte described in claim 5 or 6.

8. The lithium metal battery suitable for fast charging and low temperature as described in claim 7, characterized in that, The negative electrode is a metallic lithium foil or lithium alloy.

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