Ether electrolyte for lithium-rich manganese-based positive electrode material and high-voltage lithium metal battery based on ether electrolyte

Abstract

The invention discloses an ether electrolyte for a lithium-rich manganese-based positive electrode material and a high-voltage lithium metal battery based on the ether electrolyte. The electrolyte consists of a lithium salt, an organic ether solvent and a fluorine-containing ether compound serving as a diluent. The ether electrolyte provided by the invention has relatively good oxidation stability, can stably circulate in a wide voltage window of 2-4.7 V, also has relatively good stability of a lithium metal negative electrode, improves the coulombic efficiency of the lithium metal negative electrode, prolongs the cycle life of the lithium metal negative electrode, solves the problem of lithium dendrites faced by the lithium metal negative electrode, and has a wide application prospect.

Description

Technical Field

[0001] The present invention belongs to the field of lithium metal batteries, and particularly relates to an ether-based electrolyte for a lithium-rich manganese-based cathode material, as well as a preparation method thereof and a lithium metal battery based thereon. Background Art

[0002] Due to characteristics such as safety and cleanliness, lithium-ion batteries have been widely used in fields such as portable electronic devices, electric vehicles, and renewable energy storage. However, the energy density of the current most advanced lithium-ion batteries is still lower than 300 Wh / kg, which cannot meet the urgent demand for higher energy density batteries (>400 Wh / kg) in the trend of social electrification. A lithium metal battery with a lithium metal anode and a high-voltage layered cathode can easily meet this demand. Therefore, lithium metal batteries, as a battery system with high energy density and long cycle life, have received increasing attention.

[0003] Lithium-rich manganese-based layered oxides are regarded as the next-generation key cathode materials for improving the energy density of batteries due to their high theoretical specific capacity (>250 mAh / g) and high charging cut-off voltage (>4.6 V). However, in lithium metal batteries, the formation of an unstable solid electrolyte interface film (SEI) and the uneven deposition and stripping process of lithium metal lead to a decrease in the Coulombic efficiency (CE) of the lithium metal anode and a shortening of the cycle life. The electrolyte of a lithium metal battery prepared with an ether solvent has good compatibility with lithium metal, can inhibit the formation of lithium dendrites, and is beneficial to the cycle stability of the lithium metal anode. However, the oxidation stability of the ether-based electrolyte is limited (<4.0 V), and it often causes violent oxidation decomposition of the electrolyte at high voltages, reducing the stability and life of the lithium metal battery. In addition, at high voltages, it may also cause side reactions between the electrolyte and the cathode surface, generating harmful gases and solid products, which have an adverse impact on the battery performance. Therefore, in order to achieve a high-voltage lithium metal battery with high performance and reliability, it is necessary to solve the challenges of ether-based electrolytes at high voltages. Summary of the Invention

[0004] In order to solve the challenges faced by the current electrolyte in matching a high-voltage lithium-rich manganese-based cathode material, the present invention provides an ether-based electrolyte for a lithium-rich manganese-based cathode material, which improves the oxidation stability of the ether-based electrolyte, so that it can still obtain good electrochemical performance of the lithium-rich manganese-based cathode and the lithium metal battery at a high voltage of 4.7 V.

[0005] The present invention adopts the following technical solutions to achieve the purpose:

[0006] An ether-based electrolyte for a lithium-rich manganese-based cathode material, the electrolyte comprising a lithium salt, an organic ether solvent, and a diluent; the lithium salt comprising at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium difluoro(oxalato)borate, the lithium salt being insoluble in the diluent; the organic ether solvent comprising at least one of diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, and ethylene glycol dimethyl ether; the diluent being a fluorinated ether compound, specifically comprising at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, and tris(trifluoroethoxy)methane.

[0007] As a preferred embodiment, in the electrolyte, the concentration of the lithium salt is 1 to 3 mol / L, more preferably 1 to 2 mol / L.

[0008] As a preferred embodiment, in the electrolyte, the molar ratio of the organic ether solvent to the diluent is 0.2 to 0.6:1, more preferably 0.3 to 0.4:1.

[0009] In the ether-based electrolyte of the present invention: a chain-like ether reagent with a shorter chain segment is used as the solvent of the electrolyte. On the one hand, it can increase the interaction between the solvent molecules and lithium ions and reduce the free solvent molecular weight; on the other hand, the solvent molecules with shorter chain segments have better oxidation stability, improving the electrochemical performance of the high-voltage lithium-rich manganese-based cathode lithium metal battery using this electrolyte. Increasing the concentration of the lithium salt in the ether solvent can not only reduce the content of free ether solvent in the electrolyte, but also form a special solvation structure, resulting in improved oxidation stability of the obtained electrolyte and improving the high-voltage performance of the ether-based electrolyte to a certain extent. In addition, the introduction of the diluent can reduce the viscosity of the electrolyte while maintaining the solvation structure, improve the electrolyte kinetics, reduce the cost of the electrolyte, and further improve the application of the ether-based electrolyte in the lithium metal battery with a lithium-rich manganese-based cathode material.

[0010] As a preferred embodiment, lithium bis(fluorosulfonyl)imide is used as the lithium salt, diethylene glycol dimethyl ether is used as the organic ether solvent, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is used as the diluent.

[0011] The ether-based electrolyte of the present invention is suitable for matching a lithium-rich manganese-based cathode material (such as Li 1.19 Mn 0.55 Ni 0.22 Co 0.04 O2). Based on this, the present invention also provides a lithium metal battery, comprising a lithium metal anode, an electrolyte, a cathode, and a separator. Among them, the electrolyte is the above-mentioned ether-based electrolyte, and the cathode uses a lithium-rich manganese-based cathode material.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0013] 1. The ether-based electrolyte of the present invention has multiple advantages, including the characteristics of withstanding high voltages and the ability to inhibit the corrosion of aluminum foil by sulfonylimide-based electrolytes. At the same time, it also solves the problems of high viscosity, low conductivity, and poor wettability with the separator brought about by high-concentration electrolytes. These advantages significantly improve the cycling performance of lithium metal batteries at high voltages.

[0014] 2. The special solvation structure formed in the ether-based electrolyte of the present invention induces the formation of an inorganic-rich interfacial layer, improving the Coulombic efficiency and cycle life of the lithium metal anode, solving the problem of lithium dendrites faced by the lithium metal anode, and having broad application prospects.

[0015] 3. The preparation method of the ether-based electrolyte of the present invention is simple and the cost is low, which is suitable for industrial production. Description of the Drawings

[0016] Figure 1 are the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels of diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and diethylene glycol dibutyl ether obtained by theoretical calculation.

[0017] Figure 2 is the linear sweep voltammetry (LSV) diagram of the lithium-aluminum batteries assembled with the electrolytes prepared in Comparative Examples 1, 2, and Example 1 from 3V positive sweep to 8V at a sweep rate of 1mV / s.

[0018] Figure 3 is the Raman spectrum diagram Figure 3 ((a) in Figure 3 ) and the relative content diagram of the solvation structure

[0019] Figure 4 is the nuclear magnetic resonance lithium spectrum diagram 7 (Li NMR) of the electrolytes prepared in Comparative Examples 1, 2, and Example 1, where the internal standard for the nuclear magnetic test is a D2O solution (0ppm) of 1mol / L LiCl.

[0020] Figure 5 is the comparison of the long-term cycling performance of the lithium-copper half-cells assembled with the electrolytes prepared in Comparative Examples 1, 2, and Example 1 at a deposition capacity of 3mAh / cm 2 at a current density of 2 and stripping to 1V at a current density of 1mA / cm 2 .

[0021] Figure 6For the lithium-copper half-cells assembled with the electrolytes prepared in Comparative Examples 1, 2 and Example 1, at a current density of 1 mA / cm 2 for a deposition capacity of 3 mAh / cm 2 and then stripping to 1 V at a current density of 1 mA / cm 2 for the capacity-voltage curve.

[0022] Figure 7 For the lithium-copper half-cells assembled with the electrolytes prepared in Comparative Examples 1, 2 and Example 1, after depositing a capacity of 3 mAh / cm 2 at a current density of 1 mA / cm 2 the top-view SEM morphology and cross-sectional morphology of lithium deposited on the copper electrode, where (a) and (b) correspond to Example 1, (c) and (d) correspond to Comparative Example 1, and (e) and (f) correspond to Comparative Example 2.

[0023] Figure 8 For the lithium-rich manganese-based cathode lithium-metal batteries assembled with the electrolytes prepared in Comparative Examples 1, 2 and Example 1, after charging and discharging three cycles at a rate of 0.1 C at room temperature, then charging at a rate of 0.2 C and discharging at a rate of 0.33 C, the long-term cycling performance and Coulomb efficiency graphs with a charge-discharge voltage window of 2 - 4.7 V, where 1 C = 3 mA / cm 2 .

[0024] Figure 9 For the lithium-rich manganese-based cathode lithium-metal batteries assembled with the electrolytes prepared in Comparative Examples 1, 2 and Example 1, after charging and discharging three cycles at a rate of 0.1 C at room temperature, then charging at a rate of 0.2 C and discharging at a rate of 0.33 C, the first-cycle charge-discharge curve graphs, where 1 C = 3 mA / cm 2 .

[0025] Figure 10 For the Raman spectra of the electrolytes prepared in Comparative Examples 3, 4 and Example 1 ( Figure 10 (a) in Figure 10 ) and the relative content graphs of the solvation structures ( (b) in

[0026] Figure 11 For the lithium-copper half-cells assembled with the electrolytes prepared in Comparative Examples 3, 4 and Example 1, at a current density of 1 mA / cm 2 for a deposition capacity of 3 mAh / cm 2 and then stripping to 1 V at a current density of 1 mA / cm 2 for the comparison of long-term cycling performance.

[0027] Figure 12 For the lithium-copper half-cells assembled with the electrolytes prepared in Comparative Examples 3, 4 and Example 1, at a current density of 1 mA / cm 2 for a deposition capacity of 3 mAh / cm2 The deposition capacity, at a current density of 1 mA / cm 2 The capacity-voltage curve of stripping to 1 V at the current density.

[0028] Figure 13 Figure showing the long-term cycling performance and Coulomb efficiency of a lithium-rich manganese-based cathode lithium-metal battery assembled with the electrolytes prepared in Comparative Examples 3 and 4 and Example 1 at room temperature, after three charge-discharge cycles at a rate of 0.1C, then charging at a rate of 0.2C and discharging at a rate of 0.33C, with a charge-discharge voltage window of 2 - 4.7V, where 1C = 3 mA / cm 2 .

[0029] Figure 14 Figure showing the first charge-discharge curve of a lithium-rich manganese-based cathode lithium-metal battery assembled with the electrolytes prepared in Comparative Examples 3 and 4 and Example 1 at room temperature, after three charge-discharge cycles at a rate of 0.1C, then charging at a rate of 0.2C and discharging at a rate of 0.33C, where 1C = 3 mA / cm 2 . Detailed Embodiments

[0030] To further understand the present invention, the preferred embodiments of the present invention will be described below in conjunction with examples. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0031] In an embodiment of the present invention, a lithium-copper half-cell is provided, which includes a lithium metal negative electrode, an electrolyte, a copper current collector, and a polyethylene separator. The lithium metal negative electrode, the copper current collector, and the polyethylene separator are well-known to those skilled in the art, and the electrolyte is an ether-based electrolyte prepared in the example.

[0032] In an embodiment of the present invention, a lithium-rich manganese-based cathode lithium-metal battery is also provided, which includes a lithium metal negative electrode, a lithium-rich manganese-based cathode, an electrolyte, and a polyethylene separator. The lithium metal negative electrode and the polyethylene separator are well-known to those skilled in the art, and the electrolyte is an ether-based electrolyte prepared in the example. The manufacturing process of the lithium-rich manganese-based cathode is as follows: The lithium-rich manganese-based cathode material (Li 1.19 Mn 0.55 Ni 0.22 Co 0.04O2), Super P and polyvinylidene fluoride were weighed and mixed in a mass ratio of 85:7.5:7.5, wherein the polyvinylidene fluoride was a 5wt% polyvinylidene fluoride-N-methylpyrrolidone (NMP) solution prepared in advance. The above solid-liquid mixture was calculated based on a total mass of 1g, 1mL of NMP and 10 zirconium oxide rotors were added, and stirred at 1500rpm in a homogenizer for 15min, and degassed for 40s to obtain a uniform positive electrode slurry. The positive electrode slurry was evenly coated on a carbon-coated aluminum foil to obtain a positive electrode sheet. The positive electrode sheet was placed in a vacuum drying oven and dried at 50°C for 12 hours, and then dried at 110°C for 12 hours. After the sheet was dried, the positive electrode sheet was punched into a disc with a diameter of 12mm using a tablet press and stored in a glove box (moisture content less than 0.01ppm, oxygen content less than 0.01ppm) for later use.

[0033] All potential values in the present invention are relative to Li + / Li redox couple (vs.Li + / Li).

[0034] 1. Effect of solvent type on the performance of ether electrolyte

[0035] Example 1

[0036] The ether electrolyte of this embodiment uses lithium bis(fluorosulfonyl)imide as the lithium salt, diethylene glycol dimethyl ether as the solvent, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether as the diluent. The preparation method is as follows: weigh 187 mg of lithium bis(fluorosulfonyl)imide, add it to 170 mL of diethylene glycol dimethyl ether, and stir the mixed solution thoroughly to dissolve the lithium salt. Subsequently, 454 mL of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is added and stirred thoroughly to make the solution clear and transparent to obtain an ether electrolyte. Wherein, the molar ratio of lithium salt, solvent and diluent is 1:1.2:3.

[0037] Comparative Example 1

[0038] The ether electrolyte of this comparative example uses lithium bis(fluorosulfonyl)imide as the lithium salt, diethylene glycol diethyl ether as the solvent, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether as the diluent. The preparation method is as follows: weigh 187 mg of lithium bis(fluorosulfonyl)imide, add it to 214 mL of diethylene glycol diethyl ether, and stir the mixed solution thoroughly to dissolve the lithium salt. Subsequently, 454 mL of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is added and stirred thoroughly to make the solution clear and transparent to obtain an ether electrolyte. The molar ratio of lithium salt, solvent, and diluent is 1:1.2:3.

[0039] Comparative Example 2

[0040] The ether-based electrolyte of this comparative example uses lithium bis(fluorosulfonyl)imide as the lithium salt, diethylene glycol dibutyl ether as the solvent, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether as the diluent. The preparation method is as follows: Weigh 187 mg of lithium bis(fluorosulfonyl)imide and add it to 298 mL of diethylene glycol dibutyl ether. Stir the mixed solution thoroughly to dissolve the lithium salt. Subsequently, add 454 mL of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and stir well until the solution is clear and transparent to obtain the ether-based electrolyte. Among them, the molar ratio of the lithium salt, solvent, and diluent is 1:1.2:3.

[0041] As Figure 1 shown, it is a comparison diagram of the HOMO and LUMO energy levels of the solvent molecules of diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and diethylene glycol dibutyl ether. The more negative the HOMO energy level of the solvent molecule, the better its oxidation stability; the more positive the LUMO energy level, the better its reduction stability. The results show that the HOMO energy level of diethylene glycol dimethyl ether is the most negative (-7.048 eV), indicating that its oxidation stability is the best, and the electrolyte of Example 1 prepared from it may tolerate a higher charging cut-off voltage.

[0042] Perform the following performance tests on the ether-based electrolytes prepared in Example 1 and Comparative Examples 1 and 2:

[0043] Assemble lithium-aluminum batteries using the electrolytes prepared in Comparative Examples 1 and 2 and Example 1, and test the LSV curve of the battery from 3 V to 8 V at a sweep rate of 1 mV / s at room temperature, as Figure 2 shown. The results show that when the voltage reaches 7.4 V in Comparative Examples 1 and 2, the oxidation current rises sharply, while in Example 1, the current rises at 7.5 V. This indicates that Example 1 has a wider electrochemical stability window and may have better high-voltage positive electrode cycling performance.

[0044] As Figure 3 shown, it is the Raman spectrum of the electrolytes prepared in Comparative Examples 1 and 2 and Example 1, and the coordination environment of the FSI - anion in different systems is analyzed. The vibration peak position of the S-N-S bond in the FSI - anion is between 700 - 780 cm -1 , and its specific peak position depends on the interaction strength between the anion and the solvent and lithium ions in the electrolyte. Different interaction modes form different solvation structures, including solvent-separated ion pairs (SSIP, ~720 cm -1 ), contact ion pairs (CIP, 731 cm -1 ), aggregates (AGG, 744 cm -1 ), and super aggregates (AGG+, 756 cm -1) The results show that in Comparative Example 1 and Example 1, the lithium-ion solvation structures are both dominated by CIP, AGG, and AGG+, but there are no obvious Raman signals in Comparative Example 2. Among them, the proportion of CIP in Example 1 is the highest, indicating that the - interaction between the FSI

[0045] As Figure 4 shown, it is the nuclear magnetic resonance lithium spectrum ([[]] 7 Li NMR) of the electrolytes prepared in Comparative Example 1, 2, and Example 1. The chemical shift shifting towards the high field (more negative) indicates an increase in the electron cloud density around the lithium ion and an increase in the interaction between the lithium ion and the solvent / anion. The results show that the chemical shift of Example 1 moves towards a higher field (-1.13 ppm), while the chemical shifts of Comparative Example 1 (-1.00 ppm) and Comparative Example 2 (-0.96 ppm) move towards the low field. This result indicates that the interaction between the lithium ion and the solvent / anion in Example 1 is stronger.

[0046] Lithium-copper half-cells were assembled using the electrolytes prepared in Comparative Example 1, 2, and Example 1, and the battery was tested for the deposition capacity of 3 mAh / cm 2 at a current density of 1 mA / cm 2 and the long-term cycling performance of stripping to 1 V at a current density of 1 mA / cm 2 , as Figure 5 shown. The results show that the initial Coulombic efficiency of the lithium-copper half-cell in Comparative Example 1 is 97.6%. Starting from the 74th cycle, the Coulombic efficiency suddenly drops significantly, and the average Coulombic efficiency in the first 73 cycles is 99.2%. The initial Coulombic efficiency of the lithium-copper half-cell in Comparative Example 2 is 97.9%. Starting from the 31st cycle, the Coulombic efficiency shows an obvious decline, and the average Coulombic efficiency in the first 30 cycles is 98.8%. The initial Coulombic efficiency of the lithium-copper half-cell in Example 1 is 98.7%, and it can maintain a high Coulombic efficiency and stably cycle for 125 cycles, with an average Coulombic efficiency of 99.3%. Starting from the 125th cycle, the Coulombic efficiency begins to show a slight decline. This shows that Example 1 has better cycling stability of the lithium metal anode.

[0047] Lithium-copper half-cells were assembled using the electrolytes prepared in Comparative Example 1, 2, and Example 1, and the battery was tested for the deposition capacity of 3 mAh / cm 2 at a current density of 1 mA / cm 2 and the capacity-voltage curve of stripping to 1 V at a current density of 1 mA / cm 2 , as Figure 6As shown in the figure. The results show that the nucleation overpotential and growth overpotential in Comparative Example 1 are 144 mV and 95 mV respectively, and the nucleation overpotential and growth overpotential in Comparative Example 2 are 170 mV and 135 mV respectively; the nucleation overpotential and growth overpotential in Example 1 are 129 mV and 92 mV respectively. This indicates that lithium ions are more likely to nucleate and grow in Example 1.

[0048] The lithium copper half-cells assembled with the electrolytes prepared in Comparative Examples 1 and 2 and Example 1 were deposited with a deposition capacity of 3 mAh / cm 2 at a current density of 2 . After that, the top-view SEM morphology and cross-sectional morphology of lithium deposited on the copper electrode are shown in Figure 7 the figure, where (a) and (b) correspond to Example 1, (c) and (d) correspond to Comparative Example 1, and (e) and (f) correspond to Comparative Example 2. The deposited lithium in Comparative Example 1 and Comparative Example 2 presents a round bar shape, and the deposition thicknesses are 23.52 nm and 26.355 nm respectively; the deposited lithium in Example 1 has a larger volume, also presents a round bar shape, and the deposition thickness is the smallest, which is 20.875 nm. This shows that in Example 1, the lithium metal is deposited most closely, with the smallest surface area, and the side reaction between the electrolyte and the lithium metal negative electrode is also the smallest.

[0049] The lithium-rich manganese-based cathode lithium metal batteries assembled with the electrolytes prepared in Comparative Examples 1 and 2 and Example 1 were tested for the long-term cycling performance and Coulomb efficiency at a charge-discharge voltage window of 2 - 4.7 V after being charged and discharged at a rate of 0.1C for three cycles at room temperature, and then charged at a rate of 0.2C and discharged at a rate of 0.33C, as shown in Figure 8 the figure. The results show that the highest discharge specific capacity of Comparative Example 1 at a rate of 0.1C is 248 mAh / g, the first-cycle discharge specific capacity at a rate of 0.33C is 223.7 mAh / g, the discharge specific capacity after 223 cycles is 179.0 mAh / g, the retention rate of the discharge specific capacity is 80%, and the average Coulomb efficiency is 99.6%; the highest discharge specific capacity of Comparative Example 2 at a rate of 0.1C is 232.8 mAh / g, the first-cycle discharge specific capacity at a rate of 0.33C is 208.2 mAh / g, the discharge specific capacity after 43 cycles is 168.3 mAh / g, the retention rate of the discharge specific capacity is 81%, and the average Coulomb efficiency is 98.7%; the highest discharge specific capacity of Example 1 at a rate of 0.1C is 256.7 mAh / g, the first-cycle discharge specific capacity at a rate of 0.33C is 235.5 mAh / g, the discharge specific capacity after 275 cycles is 206.2 mAh / g, the retention rate of the discharge specific capacity is 88%, and the average Coulomb efficiency is 99.2%.

[0050] Using the electrolytes formulated in Comparative Examples 1, 2 and Example 1 to assemble lithium metal batteries with a lithium-rich manganese-based cathode, the first charge-discharge curves of the batteries were tested at room temperature after three charge-discharge cycles at a rate of 0.1C, and then at a charge rate of 0.2C and a discharge rate of 0.33C, as shown in Figure 9 shown. From the first charge-discharge curves, the first-cycle Coulombic efficiencies of Comparative Examples 1, 2 and Example 1 were calculated to be 81.6%, 81.1% and 86.2% respectively. This indicates that the lithium-rich manganese-based cathode material has better stability in Example 1.

[0051] II. Influence of Lithium Salt Concentration on the Performance of Ether-Based Electrolytes

[0052] Comparative Example 3

[0053] The ether-based electrolyte of this comparative example uses lithium bis(fluorosulfonyl)imide as the lithium salt, diethylene glycol dimethyl ether as the solvent, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether as the diluent. The preparation method is as follows: Weigh 187 mg of lithium bis(fluorosulfonyl)imide and add it to 227 mL of diethylene glycol dimethyl ether. The mixed solution is stirred thoroughly to dissolve the lithium salt. Subsequently, add 454 mL of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and stir thoroughly until the solution is clear and transparent to obtain the ether-based electrolyte. Among them, the molar ratio of the lithium salt, solvent and diluent is 1:1.6:3.

[0054] Comparative Example 4

[0055] The ether-based electrolyte of this comparative example uses lithium bis(fluorosulfonyl)imide as the lithium salt, diethylene glycol dimethyl ether as the solvent, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether as the diluent. The preparation method is as follows: Weigh 187 mg of lithium bis(fluorosulfonyl)imide and add it to 114 mL of diethylene glycol dimethyl ether. The mixed solution is stirred thoroughly to dissolve the lithium salt. Subsequently, add 454 mL of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and stir thoroughly until the solution is clear and transparent to obtain the ether-based electrolyte. Among them, the molar ratio of the lithium salt, solvent and diluent is 1:0.8:3.

[0056] The following performance tests were carried out on the ether-based electrolytes formulated in Example 1 and Comparative Examples 3 and 4: As shown in Figure 10 shown, are the Raman spectra of the electrolytes formulated in Comparative Examples 3, 4 and Example 1, and the FSI in different systems was analyzed -The coordination environment of anions. The results show that the lithium-ion solvation structure of Comparative Example 4 with the highest lithium salt concentration is dominated by AGG and AGG+, and the lithium-ion solvation structures in Example 1 and Comparative Example 3 are both dominated by CIP, AGG and AGG+. The proportions of CIP in Example 1, Comparative Example 3 and Comparative Example 4 are 52%, 73% and 0% respectively, indicating that the higher the lithium salt concentration in the electrolyte, the more solvation configurations of ionic aggregates in the electrolyte.

[0057] Lithium copper half-cells were assembled using the electrolytes prepared in Comparative Examples 3 and 4 and Example 1, and the deposition capacity of the battery at a current density of 1 mA / cm 2 for 3 mAh / cm 2 was tested at room temperature, and the long cycle performance of stripping to 1 V at a current density of 1 mA / cm 2 was tested, as shown in Figure 11 The results show that the cycle lives of the lithium copper half-cells in Example 1, Comparative Example 3 and Comparative Example 4 are 125 cycles, 100 cycles and 170 cycles respectively, and the average Coulombic efficiencies are 99.3%, 99.3% and 99.4% respectively. The results show that the cycle life and average Coulombic efficiency of the lithium copper half-cell are proportional to the lithium salt concentration in the electrolyte.

[0058] Lithium copper half-cells were assembled using the electrolytes prepared in Comparative Examples 3 and 4 and Example 1, and the deposition capacity of the battery at a current density of 1 mA / cm 2 for 3 mAh / cm 2 was tested at room temperature, and the capacity-voltage curve of stripping to 1 V at a current density of 1 mA / cm 2 was tested, as shown in Figure 12 The results show that the nucleation overpotential and growth overpotential in Comparative Example 3 are 188 mV and 132 mV respectively, and the nucleation overpotential and growth overpotential in Comparative Example 4 are 132 mV and 169 mV respectively; the nucleation overpotential and growth overpotential in Example 1 are 129 mV and 92 mV respectively. This shows that lithium ions are more likely to nucleate and grow in Example 1.

[0059] Lithium-rich manganese-based cathode lithium metal batteries were assembled using the preparations in Comparative Examples 3 and 4 and Example 1, and the long cycle performance and Coulombic efficiency of the battery were tested at room temperature with a charge-discharge rate of 0.1C for three cycles and then a charge rate of 0.2C and a discharge rate of 0.33C, and a charge-discharge voltage window of 2 - 4.7V, as shown in Figure 13As shown in the figure. The results show that: for Comparative Example 3, the highest discharge specific capacity at a rate of 0.1C is 237.1 mAh / g, the first-cycle discharge specific capacity at a rate of 0.33C is 217.7 mAh / g, the discharge specific capacity after 110 cycles is 198.5 mAh / g, the retention rate of the discharge specific capacity is 90%, and the average coulombic efficiency is 99.4%; for Comparative Example 4, the highest discharge specific capacity at a rate of 0.1C is 226.2 mAh / g, the first-cycle discharge specific capacity at a rate of 0.33C is 203.4 mAh / g, the discharge specific capacity after 18 cycles is 161.5 mAh / g, the retention rate of the discharge specific capacity is 79%, and the average coulombic efficiency is 71.2%; for Example 1, the highest discharge specific capacity at a rate of 0.1C is 256.7 mAh / g, the first-cycle discharge specific capacity at a rate of 0.33C is 235.5 mAh / g, the discharge specific capacity after 275 cycles is 206.2 mAh / g, the retention rate of the discharge specific capacity is 88%, and the average coulombic efficiency is 99.2%.

[0060] Using the lithium-rich manganese-based cathode lithium metal batteries prepared and assembled in Comparative Examples 3 and 4 and Example 1, the first charge-discharge curves of the batteries at a rate of 0.2C for charging and 0.33C for discharging after three cycles of charging and discharging at a rate of 0.1C at room temperature were tested, as Figure 14 shown. From the first charge-discharge curves, it can be calculated that the first-cycle coulombic efficiencies of Comparative Examples 3 and 4 and Example 1 are 85.7%, 84.4% and 86.2% respectively. This shows that the lithium-rich manganese-based cathode material has better stability in Example 1.

[0061] From the above data, it can be seen that Example 1 provided by the present invention can perform stable long-term charge-discharge cycles in a lithium metal battery with a lithium-rich manganese-based cathode at a wide voltage window of 2-4.7V.

[0062] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0063] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An ether-based electrolyte for a lithium-rich manganese-based cathode material, characterized in that: The electrolyte includes lithium salt, organic ether solvent, and diluent; the organic ether solvent includes at least one of diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, and ethylene glycol dimethyl ether; and the diluent is a fluorine-containing ether compound.

2. The ether-based electrolyte for a lithium-rich manganese-based cathode material according to claim 1, wherein: The fluorine-containing ether compound includes at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, and tris(trifluoroethoxy)methane.

3. The ether-based electrolyte for a lithium-rich manganese-based cathode material according to claim 1, wherein: The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium difluorooxalatoborate.

4. An ether-based electrolyte for a lithium-rich manganese-based cathode material according to claim 1 or 3, characterized in that: In the electrolyte, the concentration of the lithium salt is 1 to 3 mol / L.

5. An ether-based electrolyte for a lithium-rich manganese-based cathode material according to claim 1, characterized in that: In the electrolyte, the molar ratio of the organic ether solvent to the diluent is 0.2-0.6:

1.

6. The preparation method of the ether-based electrolyte for the lithium-rich manganese-based cathode material according to any one of claims 1 to 5, characterized in that: In an argon-protected glove box, the lithium salt is completely dissolved in an organic ether solvent, and then a diluent is added and stirred thoroughly to obtain an ether electrolyte for lithium-rich manganese-based positive electrode materials.

7. Use of the ether electrolyte according to any one of claims 1 to 5 in a lithium metal battery.

8. The application according to claim 7, wherein: The ether electrolyte is suitable for matching lithium-rich manganese-based positive electrode materials.

9. A lithium metal battery, comprising a lithium metal negative electrode, an electrolyte, a positive electrode and a separator, characterized in that: The electrolyte is the ether electrolyte according to any one of claims 1 to 5.

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