High and low temperature resistant electrolyte and lithium metal battery

Abstract

In order to solve the problems that the high-temperature cycle life and the low-temperature cycle life of the battery are short due to the fact that an electrolyte used by an existing lithium metal battery contains a strong-strong solvent pair or a strong-anti-solvent pair in LHCE, the invention provides a high and low temperature resistant electrolyte and a lithium metal battery. The high and low temperature resistant electrolyte comprises an organic solvent, the organic solvent comprises a strong solvating solvent and a weak solvating solvent, the weak solvating solvent is 4-methyl-1, 3-dioxane, and the strong solvating solvent is ethylene glycol dimethyl ether. At low temperature, due to the dipole interaction of MeDX-DME, a layered solvation structure is formed, and the interaction of Li < + >-DME is weakened, so that the Li < + > desolvation energy is reduced, the Li < + > transmission kinetics is increased, and the low-temperature cycle life of the battery is prolonged; and at high temperature, due to the dipole interaction of MeDX-DME, a layered solvation structure is formed, so that the ring-opening reaction of MeDX is slowed down, the generation of side reactions is reduced, the high-temperature stability of the electrolyte is improved, and the high-temperature cycle life of the battery is prolonged.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more particularly to a high and low temperature resistant electrolyte and a lithium metal battery. Background Technology

[0002] With the rise of the electric vehicle industry, the demand for advanced battery technology is constantly increasing, requiring batteries with higher energy density, faster charging speeds, and longer cycle life. While lithium-ion batteries currently dominate the market, they face limitations in meeting the growing performance demands of electric vehicles. Among various alternative technologies, lithium metal batteries (LMBs) are considered ideal for next-generation batteries due to the high theoretical specific capacity of lithium metal anodes (3860 mA hg⁻¹) and low electrochemical potential (-3.04 V compared to standard hydrogen electrodes).

[0003] Traditional lithium metal batteries use electrolytes with strong-solvent pairs and strong-antisolvent pairs in LHCE. Strong solvent pairs, such as EC / DMC mixed systems, have high reactivity with lithium metal and easily form a loose and porous solid electrolyte interface (SEI) on the negative electrode surface, leading to continuous electrolyte decomposition and loss of active lithium. The repeated rupture and regeneration process of the SEI film further consumes lithium source, exacerbates capacity decay, and reduces the battery's high-temperature and low-temperature cycle life. Although the synergistic effect of strong-antisolvent pairs can increase the local lithium-ion concentration, the low viscosity of the antisolvent may cause uneven distribution of the electrolyte during cycling, causing local "dead zone" deposition of lithium metal, ultimately leading to rapid capacity decay and similarly reducing the battery's high-temperature and low-temperature cycle life. Summary of the Invention

[0004] The electrolytes used in existing lithium metal batteries contain strong-strong solvent pairs or strong-anti-solvent pairs in LHCE, which result in low high-temperature cycle life and low-temperature cycle life. This application provides a high- and low-temperature resistant electrolyte and a lithium metal battery.

[0005] On one hand, the present invention provides a high and low temperature resistant electrolyte, comprising an organic solvent, wherein the organic solvent comprises a strong solvating solvent and a weak solvating solvent, wherein the weak solvating solvent is 4-methyl-1,3-dioxane, and the strong solvating solvent is ethylene glycol dimethyl ether.

[0006] Preferably, in the organic solvent, the volume ratio of the strong solvating solvent to the weak solvating solvent is (9~1):(1~9).

[0007] Preferably, in the organic solvent, the volume ratio of the strong solvating solvent to the weak solvating solvent is (4~6):(6~4).

[0008] Preferably, the organic solvent is composed of 4-methyl-1,3-dioxane and ethylene glycol dimethyl ether.

[0009] Preferably, the electrolyte further includes a lithium salt, which includes one or more of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium bis(trifluoromethanesulfonyl)imide.

[0010] Preferably, the molar concentration of the lithium salt in the electrolyte is 1~2 mol / L.

[0011] Secondly, this application provides a lithium metal battery, including the high and low temperature resistant electrolyte described above.

[0012] Preferably, the lithium metal battery includes a positive electrode, the positive electrode includes a positive electrode active material, and the positive electrode active material includes any one of lithium cobalt oxide, lithium nickel oxide, nickel cobalt manganese ternary material, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based material, lithium manganese oxide, or lithium nickel manganese oxide.

[0013] Preferably, the lithium metal battery includes a lithium anode, which comprises lithium metal or a lithium metal composite.

[0014] The high and low temperature resistant electrolyte provided in this application has the following effects: (1) The high and low temperature resistant electrolyte provided in this application constructs a mixed solvated electrolyte (HSEs), including a mixture of strong solvated solvent (DME) and weak solvated solvent (MeDX), which can react with Li + Synergistic effects lead to the formation of a layered solvated structure, with the inner layer being Li. + -DME, with an outer layer of DME-MeDX, and correspondingly achieves fine-tuning of solvation capability. Compared with strong-strong solvent pairs in traditional dilute electrolytes and strong-antisolvent pairs in LHCE, HSEs have a larger material design space and can explore different ratios of strong and weak solvent pairs. The weak solvation solvent can determine the redox stability and cyclic polarization, while the strong solvation solvent can gradually adjust the conductivity, redox stability and cyclic polarization of the electrolyte. (2) At low temperature, due to the dipole interaction of MeDX-DME, a layered solvation structure is formed, which weakens the Li + The interaction of -DME makes Li + The desolvation energy decreases, increasing the Li +Transport kinetics, extending the low-temperature cycle life of the battery. (3) At high temperature, due to the dipole interaction of MeDX-DME, a layered solvation structure is formed, which slows down the ring-opening reaction of MeDX and reduces the generation of side reactions to a certain extent, thereby improving the high-temperature stability of the electrolyte and improving the high-temperature cycle life of the battery. (4) Under high pressure, due to the presence of more anions in the layered solvation structure, more anions are reduced at the electrode interface, forming a high-mechanical-strength SEI film rich in inorganic components (such as LiF, which is a good inorganic component with high mechanical strength, which can inhibit dendrite growth and make Li uniformly deposited), which can make lithium metal uniformly deposited, inhibit lithium dendrite formation, and improve high-pressure stability. Attached Figure Description

[0015] Figure 1 The constant current charge-discharge curves of batteries in Example 1, Comparative Examples 3 and 4 at 30°C are shown. Figure 2 The constant current charge-discharge curves of batteries in Example 1, Comparative Examples 3 and 4 at -20°C are shown. Figure 3 The constant current charge-discharge curves of batteries in Example 1, Comparative Examples 3 and 4 at 60°C are shown. Figure 4 The lithium copper Aurbach test results for batteries in Example 1, Comparative Examples 3 and 4 at -20°C, 30°C, and 60°C are shown. Figure 5 The lithium metal deposition morphology of the negative electrode after cycle life testing of batteries in Example 1, Comparative Examples 3 and 4 at -20°C; Figure 6 The lithium metal deposition morphology of the negative electrode after cycle life test of the batteries in Example 1, Comparative Examples 3 and 4 at 30°C; Figure 7 The lithium metal deposition morphology of the negative electrode after cycle life test of batteries in Example 1, Comparative Examples 3 and 4 at 60°C; Figure 8 This is a comparison chart of the cycle efficiency of batteries in Example 1, Comparative Examples 3 and 4 during the cycle life test at -20°C. Figure 9 This is a comparison chart of the cycle efficiency of batteries in Example 1, Comparative Examples 3 and 4 during the cycle life test at 30°C. Figure 10 This is a comparison chart of the cycle efficiency of batteries in Example 1, Comparative Examples 3 and 4 during the cycle life test at 60°C. Figure 11 The activation energy test graphs are for batteries in Example 1, Comparative Examples 3 and 4. Figure 12 These are XPS test images of the SEI film on the surface of the lithium anode in Example 1 and Comparative Examples 3 and 4. Figure 13 These are electrolyte conductivity diagrams for Examples 1, 2, 4, 6, 8 and Comparative Example 1; Figure 14 This is a graph showing the solvation-distribution function of the electrolyte layered structure as a function of distance in Example 1; Figure 15 These are the Tafel curves for the batteries in Example 1 and Comparative Examples 3 and 4.

[0016] Figure 16 This is a diagram of the layered solvation structure formed by MeDX and DME. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] To illustrate the technical solution of the present invention, specific embodiments are described below.

[0019] In one embodiment of the present invention, a high and low temperature resistant electrolyte includes an organic solvent, wherein the organic solvent includes a strong solvating solvent and a weak solvating solvent, wherein the weak solvating solvent is 4-methyl-1,3-dioxane, and the strong solvating solvent is ethylene glycol dimethyl ether.

[0020] Specifically, the organic solvents include strong and weak solvating solvents. The weak solvating solvent is 4-methyl-1,3-dioxane (MeDX), and the strong solvating solvent is dimethyl glycol ether (DME). Due to the dipole interaction between 4-methyl-1,3-dioxane and dimethyl glycol ether, the electrolyte forms a layered solvation structure. This solvation structure not only weakens the Li... + -DME interaction and resulting in more anion FSI - It participates in the solvation sheath, thereby constructing an SEI layer rich in inorganic components, reducing desolvation energy, and improving the battery's wide temperature range (-20~60℃) performance.

[0021] like Figure 16 As shown, Figure 16 The left side shows the coordination strength relationship between THF, 1,3-DOX, MeDX and lithium ions. From left to right, the coordination ability with lithium ions gradually weakens. Figure 16 On the right is a layered solvation structure formed by lithium ions, DME, and MeDX, with the inner layer being Li. + -DME, with an outer layer of DME-MeDX, and the positive ions in the diagram represent lithium ions.

[0022] Compared to fluorinated ether molecules, fluorine-free cyclic solvent molecules offer advantages such as lower material cost, lower mass density, and higher ionic conductivity. Compared to linear ether DME, cyclic ether MeDX has greater steric hindrance, making it easier to form a weak solvation structure, which is beneficial for the composition of the interfacial film and desolvation at low temperatures. To address the above issues, the high- and low-temperature resistant electrolyte provided in this application includes MeDX and DME as organic solvents. MeDX is methylated DOX, which can enhance the dipole interaction between cyclic ether molecules and linear ether molecules, forming a layered solvation structure with lithium ions to improve the high-voltage stability and high- and low-temperature performance of the battery.

[0023] The high and low temperature resistant electrolyte provided in this application has the following effects: (1) The high and low temperature resistant electrolyte provided in this application constructs a mixed solvated electrolyte (HSEs), including a mixture of strong solvated solvent (DME) and weak solvated solvent (MeDX), which can react with Li + Synergistic effects lead to the formation of a layered solvated structure, with the inner layer being Li. + -DME, with an outer layer of DME-MeDX, and correspondingly achieves fine-tuning of solvation capability. Compared with strong-strong solvent pairs in traditional dilute electrolytes and strong-antisolvent pairs in LHCE, HSEs have a larger material design space and can explore different ratios of strong and weak solvent pairs. The weak solvation solvent can determine the redox stability and cyclic polarization, while the strong solvation solvent can gradually adjust the conductivity, redox stability and cyclic polarization of the electrolyte. (2) At low temperature, due to the dipole interaction of MeDX-DME, a layered solvation structure is formed, which weakens the Li + The interaction of -DME makes Li + The desolvation energy decreases, increasing the Li + Transport kinetics, extending the low-temperature cycle life of the battery. (3) At high temperature, due to the dipole interaction of MeDX-DME, a layered solvation structure is formed, which slows down the ring-opening reaction of MeDX and reduces the generation of side reactions to a certain extent, thereby improving the high-temperature stability of the electrolyte and improving the high-temperature cycle life of the battery. (4) Under high pressure, due to the presence of more anions in the layered solvation structure, more anions are reduced at the electrode interface, forming a high-mechanical-strength SEI film rich in inorganic components (such as LiF, which is a good inorganic component with high mechanical strength, which can inhibit dendrite growth and make Li uniformly deposited), which can make lithium metal uniformly deposited, inhibit lithium dendrite formation, and improve high-pressure stability.

[0024] The explanation of strong-antisolvent pairs in LHCE is as follows: LHCE refers to the effect of reducing overall viscosity and maintaining local high concentration by introducing a diluent (antisolvent) into a traditional high-concentration electrolyte (HCE); antisolvents are inert solvents with low solubility for lithium salts but partially miscible with the main solvent, such as 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and bis(2,2,2-trifluoroethyl) ether (BTFE), etc., and strong solvents such as commonly used ethylene carbonate (EC) and dimethyl carbonate (DMC); strong-antisolvent pairs include EC-TTE combinations and DMC-TTE combinations.

[0025] In some embodiments, the volume ratio of the strong solvating solvent to the weak solvating solvent in the organic solvent is (9~1):(1~9).

[0026] Specifically, the volume ratio of the strong solvating solvent to the weak solvating solvent can be 9:1, 8:2, 7:3, 6:4, 75:5, 4:6, 3:7, 2:8, 1:9, etc., as long as the volume ratio of the strong solvating solvent to the weak solvating solvent is within the range of (9~1):(1~9).

[0027] A volume ratio of strong solvating solvent to weak solvating solvent in the range of (9~1):(1~9) is beneficial to improve the conductivity of the electrolyte, improve the redox stability and cycle polarization of the battery, improve the low-temperature cycle life and high-temperature cycle life of the battery, and improve the high and low temperature resistance of the electrolyte.

[0028] In some preferred embodiments, the volume ratio of the strong solvating solvent to the weak solvating solvent in the organic solvent is (4~6):(6~4).

[0029] Specifically, when the volume ratio of strong solvating solvent to weak solvating solvent is within the range of (4~6):(6~4), the electrolyte has higher conductivity, smaller cycle polarization, higher low-temperature cycle capacity retention rate, and higher high-temperature cycle capacity retention rate, which is more conducive to improving the high-temperature and low-temperature performance of the electrolyte.

[0030] In some embodiments, the organic solvent is composed of 4-methyl-1,3-dioxane and ethylene glycol dimethyl ether.

[0031] Specifically, the organic solvent consists of MeDX and DME, without other solvents, and forms a mixed solvated electrolyte (HSEs) with the lithium electrolyte salt. The organic solvent and lithium ions work together to form a layered solvation structure, which results in a lower desolvation energy for lithium ions at low temperatures, making it easier for lithium ions to desolvate. This is more conducive to improving the lithium ion transport kinetics of the electrolyte at low temperatures and improving the low-temperature cycle life of the electrolyte. At high temperatures, the side reactions of MeDX are reduced, the stability of the electrolyte is increased, and the high-temperature cycle life and high-voltage stability of the battery are improved.

[0032] In some embodiments, the electrolyte further includes a lithium salt, which includes one or more of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium bis(trifluoromethanesulfonyl)imide.

[0033] Specifically, the lithium salts are selected from the above types. The mixed solvated electrolytes (HSEs) constructed by combining lithium salts with strong solvating solvents and weak solvating solvents are more conducive to improving the high temperature resistance and low temperature resistance of the electrolyte, improving the conductivity of the electrolyte, improving the low temperature cycle life and high temperature cycle life of the battery, and improving high voltage stability.

[0034] In some embodiments, the molar concentration of the lithium salt in the electrolyte is 1~2 mol / L.

[0035] Specifically, lithium salt molar concentrations in the range of 1–2 mol / L, combined with strong and weak solvating solvents to construct mixed solvated electrolytes (HSEs), exhibit high lithium ion transport kinetics and electrolyte conductivity at low temperatures due to the ease of lithium ion desolvation. The molar concentrations of lithium salts can be 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, etc., as long as the lithium salt molar concentration is within the range of 1–2 mol / L.

[0036] More preferably, the molar concentration of lithium salt in the electrolyte is 1.5 mol / L.

[0037] Secondly, this application provides a lithium metal battery, including the high and low temperature resistant electrolyte described above.

[0038] The lithium metal battery provided in this application uses the aforementioned high and low temperature resistant electrolyte. Due to the dipole interaction of MeDX-DME, a layered solvation structure is formed, which facilitates the desolvation of lithium ions at low temperatures, improves lithium ion transport kinetics, increases the conductivity of the electrolyte, and enhances the low-temperature cycle life of the battery. At high temperatures, it reduces the ring-opening reaction of MeDX and side reactions, improving the high-temperature cycle capacity retention rate and enhancing the high-temperature performance of the battery. Under high voltage, it has more anions, forming a high-mechanical-strength SEI film on the lithium metal anode, which can suppress lithium dendrite formation and improve the high-voltage stability of the battery.

[0039] In some embodiments, the lithium metal battery includes a positive electrode, the positive electrode including a positive electrode active material, the positive electrode active material including any one of lithium cobalt oxide, lithium nickel oxide, nickel cobalt manganese ternary material, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based material, lithium manganese oxide, or lithium nickel manganese oxide.

[0040] The positive electrode includes a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer includes positive electrode active material.

[0041] The positive electrode active material layer also includes a conductive agent and a binder. This application does not impose specific restrictions on the types of conductive agents and binders. For example, the conductive agent may be one or more of graphite, acetylene black, carbon black, Ketjen black, carbon nanotubes, or graphite; the binder may be one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA), and polyvinyl alcohol (PVA).

[0042] The positive current collector can be made of metal foil or metal plate, such as copper foil or aluminum foil.

[0043] In some embodiments, the lithium metal battery includes a lithium anode, which comprises lithium metal or a lithium metal composite.

[0044] Specifically, lithium anodes can be lithium metal anodes or lithium metal composite anodes, such as lithium alloy anodes or lithium carbon composite materials.

[0045] The lithium anode may also include a negative electrode current collector and a lithium metal sheet or lithium alloy sheet disposed on the surface of the negative electrode current collector. The negative electrode current collector may be made of metal foil or metal plate, such as copper foil or aluminum foil.

[0046] Lithium metal batteries also include a separator, which is placed between the positive and negative electrodes. The separator is a porous material with electrochemical and chemical stability, such as polyethylene, polypropylene, polyvinylidene fluoride, or nonwoven fabric.

[0047] The present application will be further illustrated by the following examples.

[0048] Example 1 Preparation of S1 electrolyte: The organic solvents are 4-methyl-1,3-dioxane (MeDX) and dimethyl ethylene glycol (DME), with a volume ratio of MeDX to DME of 5:5. The lithium salt is lithium bis(fluorosulfonyl)imide. The organic solvent and lithium salt are mixed uniformly to obtain the electrolyte, in which the molar concentration of the lithium salt is 1.5 mol / L.

[0049] Preparation of S2 cathode: The positive electrode active material is NCM811, a nickel-cobalt-manganese ternary material; the conductive agent is carbon black; and the binder is polyvinylidene fluoride (PVDF).

[0050] NCM811, carbon black, PVDF and NMP (N-methylpyrrolidone) are mixed evenly in a mass ratio of 96:2:2 to obtain a positive electrode slurry. The positive electrode slurry is coated on the surface of aluminum foil and then rolled and die-cut to obtain a positive electrode sheet.

[0051] S3 is the lithium metal anode.

[0052] S4 combines an electrolyte, a positive electrode, and a negative electrode to form a lithium metal battery.

[0053] Examples 2-9 Examples 2-9 are largely the same as Example 1, except that the volume ratio of MeDX to DME differs in Examples 2-9, as detailed in Table 1. The rest is the same as Example 1.

[0054] Comparative Example 1 This comparative example is the same as Example 1 in most steps, except that in step S1, the organic solvent is MeDX. The rest is the same as in Example 1.

[0055] Comparative Example 2 This comparative example is the same as Example 1 in most steps, except that in step S1, the organic solvent is DME. The rest is the same as in Example 1.

[0056] Comparative Example 3 This comparative example is the same as Example 1 in most steps, except that in step S1, the organic solvents are THF (tetrahydrofuran) and DME, with a volume ratio of THF to DME of 5:5. The rest is the same as in Example 1.

[0057] Comparative Example 4 This comparative example is the same as Example 1 in most steps, except that in step S1, the organic solvents are 1,3-DOX (1,3-dioxane) and DME, and the volume ratio of 1,3-DOX to DME is 5:5. The rest is the same as in Example 1.

[0058] Performance testing The lithium metal batteries prepared in the above embodiments and comparative examples were subjected to the following performance tests.

[0059] 1) Cycle life at -20℃, 30℃, and 60℃ At -20℃, the charging cutoff voltage is 4.3V and the discharging cutoff voltage is 3.0V. The lithium metal battery was subjected to 0.2C / 0.5C charge-discharge cycle tests, and the capacity retention rate was 80%. The number of cycles was recorded.

[0060] Similarly, the above cycle test was performed at 30℃ and 60℃, and the number of cycles was recorded respectively.

[0061] The test results are shown in Table 1.

[0062] Comparison of cycle efficiency of batteries in Example 1, Comparative Example 3, and Comparative Example 4 during cycling. Figure 8-10 .

[0063] 2) High voltage resistance and stability test against lithium metal at different temperatures The batteries prepared in Example 1, Comparative Example 3, and Comparative Example 4 were subjected to constant current charge-discharge tests at -20°C, 30°C, and 60°C, respectively, with a current of 0.5C. Specific test results are shown below. Figure 1-3 .

[0064] The batteries prepared in Example 1, Comparative Example 3, and Comparative Example 4 were subjected to a lithium-copper Aurbach test at 30°C to test the stability of the three electrolytes for lithium metal at different temperatures. Specific test results are shown below. Figure 4 .

[0065] 3) Lithium metal deposition morphology testing The batteries prepared in Examples 1, 3, and 4 were subjected to 20 cycles of charge-discharge testing at -20°C, 30°C, and 60°C, as described above. The lithium metal deposition morphology on the lithium metal anode surface was then measured using SEM. See details in the original text. Figure 5-7 .

[0066] 4) Activation energy test The batteries of Example 1 and Comparative Examples 3 and 4 were subjected to EIS tests at different temperatures. The obtained data were fitted and calculated to obtain the activation energy test chart. Specific test results can be found in [link to specific test results]. Figure 11 .

[0067] 5) The conductivity of the electrolyte in Examples 1, 2, 4, 6, and 8, and Comparative Example 1, was tested. The test results are shown in [the table below]. Figure 13 .

[0068] 6) XPS tests were performed on the SEI film on the surface of the lithium anode in Example 1 and Comparative Examples 3 and 4 lithium metal batteries. The test results are shown in […]. Figure 12 .

[0069] 7) The layered solvation structure of lithium salt and organic solvent in the electrolyte of Example 1 was tested. Simulation calculations were performed on the solvation structure of Example 1 at temperatures of -20℃, 30℃, and 60℃ to obtain curves showing the distribution function as a function of distance. The test results are shown in […]. Figure 14 .

[0070] 8) Tafel curves were tested on the batteries of Example 1 and Comparative Examples 3 and 4. The Tafel curves were obtained by measuring the current density of the electrodes at different voltages. The test results are shown in [Figure number missing]. Figure 15 .

[0071] Table 1 As shown in Table 1, compared with Comparative Examples 1 and 2, when the organic solvent is DME, the electrolyte is in a solidified state at -20℃, resulting in poor low-temperature cycle life of the battery. When the organic solvent is MeDX, both the low-temperature and high-temperature cycle life of the battery are poor. The weak solvating solvent in the organic solvent is MeDX, and the strong solvating solvent is DME. Due to the synergistic effect of MeDX-DME and the dipole interaction, a layered solvation structure is formed, which is beneficial to improving the low-temperature and high-temperature cycle life of the battery.

[0072] Comparing Examples 1-5 with Comparative Examples 3 and 4, Comparative Example 3 used a combination of THF and DME as the organic solvent, resulting in poor low-temperature and high-temperature cycle life of the battery. Comparative Example 4 used a combination of 1,3-DOX and DME as the organic solvent, resulting in poor low-temperature performance of the battery. This indicates that the addition of MeDX and DME to the organic solvent forms a layered solvation structure, which is beneficial to improving the low-temperature and high-temperature cycle life of the battery.

[0073] Comparing Examples 1-9 with Comparative Examples 1-2, it is shown that when the volume ratio of MeDX to DME added to the organic solvent is in the range of (9~1):(1~9), the battery has a longer low-temperature cycle life and a longer high-temperature cycle life; when the volume ratio of MeDX to DME added to the organic solvent is (6~4):(4~6), the battery has an even longer low-temperature cycle life and a even longer high-temperature cycle life.

[0074] In Comparative Example 2, the organic solvent was DME. The high content of DME has several drawbacks. Firstly, DME is prone to solidification at low temperatures, which reduces the low-temperature performance of the battery. Secondly, excessive use of DME causes the solvation structure to no longer be layered, but rather dominated by a strong solvation structure, which affects the battery interface structure and kinetics. Therefore, it is detrimental to the operation of wide-temperature batteries.

[0075] In Example 4, the volume ratio of MeDX to DME is 7:3. In Comparative Example 1, the organic solvent is MeDX. The higher amount of MeDX solvent results in lower electrolyte conductivity, which leads to severe battery polarization and affects battery performance.

[0076] Comparative Examples 3-4 show that the dipole interactions of the solvents THF-DME and 1,3-DOX-DME are not as strong as those of MeDX-DME, resulting in a less pronounced "stratification" of the solvation structure in the electrolyte. Therefore, this is less effective in reducing the Li... + The insufficient contribution of -DME interaction results in slightly poorer overall battery cycle performance.

[0077] Figure 1 In the first image on the far left, TD stands for THF and DME, respectively. Figure 1 The first figure in the diagram shows the constant current charge-discharge curve of the battery corresponding to Scale 3. Figure 1 In the second image, from left to right, DD stands for the abbreviation of solvent 1,3-DOX and solvent DME. Figure 1 The second figure in the diagram is the constant current charge-discharge curve of the battery corresponding to Scale 4. Figure 1 In the third image from left to right, MD stands for MeDOX and DME, respectively. Figure 1 The second figure shows the constant current charge-discharge curve of the battery corresponding to Example 1. Similarly... Figure 2 , Figure 3 Which image corresponds to Comparative Example 3, Comparative Example 4, or Example 1? The explanation is the same. Figure 1 .

[0078] pass Figure 1-3 The comparison shows that, through Figure 1-3 It can be concluded that Figure 2 , Figure 3 The battery corresponding to Example 1 has a flat discharge voltage plateau and good voltage stability, indicating that compared with Comparative Examples 3 and 4, the combination of weak solvation solvent MeDX and strong solvation solvent DME in Example 1 results in a battery with good voltage stability under high and low temperature conditions.

[0079] pass Figure 4 It can be seen that the coulombic efficiency of Example 1 is 99.42% at room temperature (30℃), 98.67% at low temperature (-20℃), and 98.98% at high temperature (60℃). The coulombic efficiency of Example 1 is the highest at all three different temperatures. The higher the efficiency, the stronger the stability to lithium metal. This indicates that the solvents MeDX and DME provide the best stability to lithium metal.

[0080] Figure 5-7The lithium metal deposition morphology was measured after electrical cycle life tests in Examples 1, 3, and 4 at -20℃, 30℃, and 60℃. Figure 5-7 It can be seen that the lithium metal deposition thickness in Example 1 is relatively thin, and the lithium layer in the electron microscope image on the left side of the figure has no obvious dendrites or pores; this indicates that in the lithium metal battery of Example 1, lithium metal can be uniformly deposited on the surface of the lithium anode during battery cycling. This shows that the high and low temperature resistant electrolyte provided in this application has more anions in its layered solvation structure, which allows more anions to be reduced at the electrode interface, forming a high-mechanical-strength SEI film rich in inorganic components. This enables uniform lithium metal deposition, inhibits lithium dendrite formation, and improves high-voltage stability.

[0081] Figures 8-10 This is a comparison chart of cycle efficiency. The left vertical axis corresponds to capacity, and the right vertical axis corresponds to cycle efficiency. To distinguish between capacity and cycle efficiency, one chart uses a solid sphere, and the other uses a hollow sphere. The hollow sphere represents the cycle efficiency on the right.

[0082] Figure 8-10 The graph shows a comparison of cycle efficiency during the electrical cycle life test of Example 1, Comparative Example 3, and Comparative Example 4 under conditions of -20℃, 30℃, and 60℃. Figure 8-10 It can be seen that at different temperatures, the cycle life of Example 1 is longer than that of Comparative Examples 3 and 4, indicating that the high-voltage stability and low-temperature kinetics of Example 1 are optimal. This shows that the solvent combination of weak solvation solvent MeDX and strong solvation solvent DME results in a battery with good voltage stability under high and low temperature conditions.

[0083] Figure 11 The graph shows the activation energy test results of Example 1 and Comparative Examples 3 and 4 at different temperatures. Figure 11 It can be seen that the lithium-ion transport activation energy in Example 1 is low and the energy barrier overcome is low, indicating that the electrolyte provided in this application can improve the lithium-ion transport kinetics and improve the low-temperature and high-temperature performance of the battery.

[0084] Figure 13 The figures show a comparison of the conductivity of the electrolytes in Examples 1, 2, 4, 6, and 8, and Comparative Example 1. It can be seen from the figures that when the volume ratio of MeDX to DME is (6~4):(4~6), the conductivity of the electrolyte is relatively high.

[0085] Figure 12 XPS tests were performed on the SEI film on the surface of the lithium anode in the lithium metal batteries of Examples 1 and Comparative Examples 3 and 4. Figure 12As can be seen, the characteristic peaks of lithium fluoride gradually increase over time, indicating that the content of lithium fluoride rich in inorganic components inside the SEI film increases with time, which is beneficial to the transport of lithium ions. It can be seen from the figure that the content is the highest in Example 1; indicating that the electrolyte provided in this application can form a dense SEI film rich in inorganic components at the lithium metal anode interface.

[0086] Figure 14 The simulation calculations for the solvation structure of Example 1 at three temperatures are shown, where g(r) represents the probability of coordination between the two substances. Figure 14 From left to right, the corresponding temperatures are -20℃, 30℃, and 60℃, respectively. Figure 14 As you can see, the gray curve represents FSI. - The peak value of the lithium-ion coordination is the largest, proving that the layered solvation structure weakens the binding between DME and lithium ions, which is beneficial to battery kinetics and forms an inorganic-rich SEI interface. The blue curve represents the coordination between lithium ions and O atoms on DME, and its large peak value indicates that lithium ions are more closely bound to DME. Furthermore, the comparison of the dashed lines shows that the inner solvation layer (around 0.2 on the horizontal axis) contains the most DME, while MeDX is located in the outer solvation structure (around 0.6 on the horizontal axis). Figure 14 It can be concluded that the weak solvating solvent is 4-methyl-1,3-dioxane (MeDX), and the strong solvating solvent is ethylene glycol dimethyl ether (DME). Due to the dipole interaction of 4-methyl-1,3-dioxane, the electrolyte forms a layered solvation structure. This solvation structure not only weakens the Li... + -DME interaction and resulting in more anion FSI - It participates in the solvation sheath, thereby constructing an SEI layer rich in inorganic components, reducing desolvation energy, improving the battery's wide temperature range (-20~60℃), and the battery exhibits good cycle performance and high-voltage stability within the range of -20~60℃.

[0087] Figure 15 The figure shows the Tafel curve, with the vertical axis representing the exchange current density. A higher exchange current density indicates faster electrode reaction kinetics and lower polarization. The Tafel curve shows that the exchange current density j0 of MeDX:DME=1:1 is higher than that of DOX+DME and THF+DME, indicating that the battery in Example 1 has lower polarization, faster electrolyte kinetics, and higher electrolyte conductivity. In contrast, the batteries in Comparative Examples 3 and 4 have slower electrolyte kinetics, greater polarization, and lower electrolyte conductivity.

[0088] This description is intended to illustrate the technical solutions of the present invention, and not to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A high and low temperature resistant electrolyte, characterized in that, It includes organic solvents, which include strong solvating solvents and weak solvating solvents, wherein the weak solvating solvent is 4-methyl-1,3-dioxane and the strong solvating solvent is ethylene glycol dimethyl ether.

2. The high and low temperature resistant electrolyte according to claim 1, characterized in that, In the organic solvent, the volume ratio of the strong solvating solvent to the weak solvating solvent is (9~1):(1~9).

3. The high and low temperature resistant electrolyte according to claim 2, characterized in that, In the organic solvent, the volume ratio of the strong solvating solvent to the weak solvating solvent is (4~6):(6~4).

4. The high and low temperature resistant electrolyte according to claim 1, characterized in that, The organic solvent is composed of 4-methyl-1,3-dioxane and ethylene glycol dimethyl ether.

5. The high and low temperature resistant electrolyte according to claim 1, characterized in that, The electrolyte also includes lithium salts, including one or more of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium bis(trifluoromethanesulfonyl)imide.

6. The high and low temperature resistant electrolyte according to claim 5, characterized in that, In the electrolyte, the molar concentration of the lithium salt is 1~2 mol / L.

7. A lithium metal battery, characterized in that, Includes the high and low temperature resistant electrolyte as described in any one of claims 1 to 6.

8. The lithium metal battery according to claim 7, characterized in that, The lithium metal battery includes a positive electrode, which includes a positive electrode active material, and the positive electrode active material includes any one of lithium cobalt oxide, lithium nickel oxide, nickel cobalt manganese ternary material, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based material, lithium manganese oxide, or lithium nickel manganese oxide.

9. The lithium metal battery according to claim 8, characterized in that, The lithium metal battery includes a lithium anode, which comprises lithium metal or a lithium metal composite.

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