A high-voltage flame-retardant lithium metal battery electrolyte and battery applications

Abstract

The present invention belongs to the field of new energy materials and device technology, and relates to a high-voltage flame-retardant lithium metal battery electrolyte and battery application. The electrolyte includes a carbonate solvent, a diluent and a lithium salt, and the diluent is 1H, 1H, 5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE). The present invention adopts a commonly used carbonate solvent as the main component of the electrolyte organic solvent, and is matched with a high-voltage lithium salt and an appropriate diluent OTE, and its consumption is equivalent to 70 to 200 vol.% of the carbonate solvent. By regulating the diluent ratio and the solution composition ratio, the antioxidant capacity of the conventional carbonate electrolyte can be increased to more than 6.7V, and the gas release and cycle capacity attenuation problems caused by the side reactions of the electrolyte and the positive and negative electrode sides are significantly suppressed, with good application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy materials and devices, and specifically relates to a high-voltage flame-retardant lithium metal battery electrolyte and battery applications. Background Art

[0002] After decades of commercial application, lithium-ion batteries have reached their energy density limit. Considering the demand for high-energy-density batteries in the development of power batteries and grid energy storage, there is an urgent need to increase the volumetric and gravimetric capacity of positive and negative electrode materials. Based on this, lithium-rich manganese-based positive electrodes have been developed, which have a high voltage window and high specific capacity, while the ultimate target is lithium metal negative electrodes, which have the highest specific capacity and the most negative potential, effectively utilizing the battery capacity.

[0003] But with it comes a series of adaptation problems. Traditional lithium-ion batteries are composed of a graphite negative electrode and a medium-voltage positive electrode (usually lithium iron phosphate, etc.). The graphite negative electrode has good adaptability to traditional ester electrolytes. There is almost no chemical reaction between the two, and there is no embedding of small molecule solvents. This makes it easy for traditional commercial ester electrolytes to adapt to the graphite negative electrode without much optimization. As an alkali metal negative electrode, lithium metal has an extremely negative potential that gives it a higher capacity range, but it will directly react chemically with the carbonyl functional group of the ester electrolyte, resulting in continuous decomposition of the electrolyte, the occurrence of interfacial side reactions and the continuous increase of interfacial impedance, causing the battery to fail quickly after short-term use. Ether electrolytes adapted to lithium metal negative electrodes are difficult to withstand high voltages above 4V, which limits their use in high-nickel ternary positive electrodes (4.3~4.6V), let alone the next generation of positive electrode materials with higher voltage and specific capacity, lithium-rich manganese-based materials (4.8V).

[0004] The lithium-rich manganese-based positive electrode also places higher demands on the electrolyte. Transition metals Ni, Co, and Mn will catalyze and induce electrolyte decomposition, further reducing the voltage window for use of traditional ester electrolytes and exacerbating the decomposition of traditional ester electrolytes. Due to the energy storage characteristics of lithium-rich manganese-based materials during use, some reactive oxygen species (singlet oxygen, superoxide, etc.) are released. These react with the electrolyte to generate a large number of organic species and gases, increasing interfacial impedance while accelerating the dissolution of transition metal elements on the positive electrode surface, causing positive electrode particle fragmentation, capacity reduction, and material failure. The reaction in turn further promotes the escape of reactive oxygen species.

[0005] The existing commercial ester electrolytes have safety risks. When a lithium battery leaks, the highly reactive lithium metal will quickly ignite the flammable electrolyte when it comes into contact with air, causing a fire that is difficult to extinguish by traditional means, endangering human life and causing serious property damage.

[0006] Therefore, the development of a new lithium metal battery electrolyte with controllable cost that can simultaneously inhibit side reactions at the positive and negative electrodes and withstand ultra-high voltage operation has become a pain point and key issue that urgently needs to be solved before the practical application of high-power energy storage power stations and high-energy-density power batteries. Summary of the Invention

[0007] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a highly safe, high-voltage-resistant, flame-retardant lithium metal battery electrolyte that can inhibit side reactions and can be matched with a high-voltage, high-capacity positive electrode and a high-capacity negative electrode to assemble a high-energy-density lithium metal battery.

[0008] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0009] The first aspect of the present invention provides an electrolyte comprising a carbonate solvent, a diluent and a lithium salt, wherein the diluent is 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE), and the amount of the diluent is 70 to 200% of the total volume of the carbonate solvent.

[0010] The diluent OTE introduced in this invention has an optimal electrochemical window to match the requirements of interfacial film formation, allowing it to decompose and form an inorganic layer on the negative electrode side. Simultaneously, the diluent modifies the solvation shell, increasing the coordination of the cyclic carbonate with lithium ions and reducing its reactivity to active oxygen species. The formation of an anion-rich solvation shell facilitates decomposition into an inorganic-rich interfacial film on the positive electrode side. The outer layer of diluent isolates the solvent molecules from the reactivity of the active components within the battery, significantly improving the battery's cycling stability. The diluent's fluorine radicals bind to hydrogen radicals formed in the early stages of combustion, thereby inhibiting and indirectly blocking the occurrence of combustion. By precisely controlling the ratios of the highly solubilizing cyclic carbonate, the highly co-solvable linear carbonate, and the diluent in the electrolyte, effective control of the electrolyte's solvation structure, electrochemical window, ionic conductivity, and density is achieved. The optimized ratio results in a high-voltage lithium metal battery electrolyte that combines positive and negative electrode interfacial stability, high voltage resistance across all components, effective side reaction suppression, and non-flammability, resulting in high cycling stability and application value.

[0011] Furthermore, the carbonate solvent is composed of cyclic carbonate and chain carbonate, and the volume ratio of the cyclic carbonate to the chain carbonate is 3:7-10.

[0012] Limiting the amount of cyclic carbonate effectively reduces its reactivity with the battery's positive and negative electrodes. Using a relatively high content of linear carbonate effectively reduces electrolyte viscosity and increases ionic conductivity. The optimal diluent addition ratio can be adjusted based on the characteristics of the matching high-voltage positive electrode. Small amounts can reduce the reduction in ionic conductivity caused by diluent addition, while appropriate and excessive amounts significantly improve the electrochemical window, increase the content of diluent decomposition products at the interface, enhance interfacial stability, reduce side reactions, and provide flame retardancy.

[0013] Furthermore, the cyclic carbonate is one or both of ethylene carbonate and propylene carbonate.

[0014] Furthermore, the chain carbonate is one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and methyl propyl carbonate.

[0015] Furthermore, the cyclic carbonate is ethylene carbonate, the chain carbonate is dimethyl carbonate, and the volume ratio of ethylene carbonate to dimethyl carbonate to diluent is 3:7:7-20.

[0016] Preferably, the volume ratio of ethylene carbonate to dimethyl carbonate to diluent is 3:7:7.

[0017] Furthermore, the lithium salt is one or more of LiPF6, LiDFOB, LiFSI, LiTFSI, and LiBOB.

[0018] Furthermore, the positive electrode of the above-mentioned lithium metal battery adopts at least one of lithium iron phosphate, nickel manganese cobalt, lithium cobalt oxide, lithium-rich manganese-based, and high-nickel materials, and the negative electrode adopts at least one of graphite, lithium metal, silicon negative electrode, silicon-carbon negative electrode, and no negative electrode material.

[0019] The second aspect of the present invention provides a lithium metal battery comprising the above-mentioned electrolyte.

[0020] The present invention also provides a method for preparing the above electrolyte, comprising the following steps:

[0021] (1) purifying the cyclic carbonate and the chain carbonate first, and then mixing them in a volume ratio of 3:(7-10) to obtain an optimized organic mixed solvent;

[0022] (2) purifying the diluent and then adding it to the optimized organic mixed solvent in step (1), wherein the amount of the diluent is 70 to 200% of the volume ratio of the optimized organic mixed solvent to obtain an organic electrolyte solvent;

[0023] (3) dissolving the lithium salt in the organic electrolyte solvent of step (2) at a concentration of 1.0 mol / L to obtain a high-voltage lithium metal battery electrolyte.

[0024] The purification of the carbonate solvent and diluent in steps (1) and (2) refers to the removal of impurities and water.

[0025] The lithium salt described in step (3) must be added slowly under continuous stirring, the ambient temperature must be controlled below 35° C., and the ambient oxygen content and water content must be ≤0.1 ppm.

[0026] For dewatering, at least one of anhydrous magnesium sulfate, anhydrous calcium chloride and sodium hydride is preferred, and for impurity removal, a diameter of molecular sieve.

[0027] The third aspect of the present invention is to provide an application of the above-mentioned electrolyte in a lithium metal battery.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention utilizes a common carbonate solvent as the primary organic solvent component of the electrolyte, along with a high-voltage lithium salt, LiPF6, and an appropriate amount of diluent, 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether, equivalent to 70-200 vol.% of the carbonate solvent. By regulating the diluent ratio and solution composition, the antioxidant capacity of conventional carbonate electrolytes can be increased to above 6.7V, while significantly suppressing gas release and cyclic capacity decay caused by side reactions between the electrolyte and the positive and negative electrodes. This approach has promising application prospects.

[0030] 2. The present invention achieves a balance between salt solubility and ion conductivity by precisely changing the solvent ratio and regulating the ratio of cyclic carbonate and chain carbonate within an appropriate range. The diluent also regulates the electrolyte solvation shell to fix the easily reactive cyclic carbonate in the first solvation shell of lithium ions, reducing its reactivity with the positive and negative electrodes of the battery, thereby effectively retaining the electrolyte components. The diluent further blocks harmful components in the battery such as active oxygen and active proton groups from reacting with the solvent and lithium salts through the outer layer wrapping effect, and by constructing an anion-rich solvation shell and its own better reaction film-forming ability on the negative electrode side, it simultaneously forms a good interface layer between the positive and negative electrodes, further preventing the occurrence of side reactions. The fluorine radicals in the diluent also play a role in combining with the hydrogen radicals formed in the early stage of electrolyte combustion to block the further progress of combustion. The optimized overall electrolyte ratio effectively ensures ionic conductivity and lithium ion transference number, greatly improving the energy density and long cycle performance of lithium metal high-voltage batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The linear sweep voltammetry diagram of the diluent series ratio of the high voltage lithium metal battery electrolyte in Example 1;

[0032] Figure 2This is a leakage current diagram of a series of diluent ratios for the high-voltage lithium metal battery electrolyte in Example 2;

[0033] Figure 3 The Raman spectra of the solvent and diluent ratios used in the high-voltage lithium metal battery electrolyte in Example 3 are as follows;

[0034] Figure 4 The diluent series ratio of the high-voltage lithium metal battery electrolyte and the ionic conductivity of the commercial ester electrolyte in Example 4;

[0035] Figure 5 is the Aurbach coulombic efficiency of the diluent series ratio of the high-voltage lithium metal battery electrolyte in Example 6;

[0036] Figure 6 is the linear sweep voltammetry diagram of the commercial electrolyte in Comparative Example 1;

[0037] Figure 7 This is a cyclic coulombic efficiency diagram of the high-voltage lithium metal battery electrolyte in Test Example 1;

[0038] Figure 8 This is the cyclic coulombic efficiency diagram of the commercial electrolyte in Test Example 2;

[0039] Figure 9 This is a graph showing the cycling performance of a lithium symmetric battery using the high-voltage lithium metal battery electrolyte in Test Example 3;

[0040] Figure 10 This is a graph showing the cycling performance of a lithium symmetric battery using a commercial electrolyte in Test Example 4;

[0041] Figure 11 The cycling performance of the half-cell prepared by matching the high-voltage lithium metal battery electrolyte with the lithium-rich manganese-based positive electrode and the lithium metal negative electrode in Test Example 5;

[0042] Figure 12 To test the cycling performance of the half-cell prepared by matching the commercial electrolyte with the lithium-rich manganese-based positive electrode and the lithium metal negative electrode in Example 6;

[0043] Figure 13 To test the cycling performance of the full battery prepared by matching the high-voltage lithium metal battery electrolyte with the lithium-rich manganese-based positive electrode and the lithium metal negative electrode in Example 7;

[0044] Figure 14 To test the cycling performance of the full battery prepared by matching the commercial electrolyte with the lithium-rich manganese-based positive electrode and the lithium metal negative electrode in Example 8;

[0045] Figure 15 The gas phase differential electrochemical mass spectrometry of the full battery obtained by matching the high-voltage lithium metal battery electrolyte with the lithium-rich manganese-based positive electrode and the lithium metal negative electrode in Test Example 9;

[0046] Figure 16 Gas phase differential electrochemical mass spectrometry of the full battery obtained by matching the commercial electrolyte with the lithium-rich manganese-based positive electrode and the lithium metal negative electrode in Test Example 10;

[0047] Figure 17 The combustion condition of the high-voltage lithium metal battery electrolyte in Test Example 11 under air atmosphere;

[0048] Figure 18 This is the combustion condition of the commercial electrolyte in Test Example 12 under air atmosphere. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0050] Example 1

[0051] Ethylene carbonate, dimethyl carbonate, and 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE) were mixed in a volume ratio of 3:7:x (x = 0, 3, 7, 10, 15, 20). Magnetic stirring was continuously performed during the mixing process. The mixture was named EDO-37x (x refers to the volume ratio of the diluent in the corresponding solution). After magnetic stirring and mixing, 1 mL was quantitatively weighed using a calibrated pipette.

[0052] Slowly add 151.92 mg of LiPF6 to the EDO-37x solution and continue stirring for 12 hours at 500 rpm and 45°C. This yields a uniformly mixed EDO-37x (x = 0, 3, 7, 10, 15, 20) high-voltage lithium metal battery electrolyte.

[0053] The high-voltage-resistant lithium metal battery electrolyte is used for battery assembly. The battery shell is a CR2032 assembled battery, the positive electrode is a stainless steel electrode, the negative electrode is lithium metal, the electrolyte dosage is 30 μL, and the injection tool is preferably a pipette with a range of 100 μL.

[0054] The assembled battery was left to stand at room temperature for 12 h to obtain a steady-state battery.

[0055] The electrochemical window of EDO-37x electrolyte was tested by linear sweep voltammetry. Figure 1As shown, when OTE is absent, the electrolyte readily decomposes below 4V, leading to a rapid increase in current, indicating the poor high-voltage tolerance of the system without OTE. When EDO-373 is added as a diluent, the electrolyte window is significantly improved due to the diluent's action. However, due to insufficient incorporation of the high-dielectric-constant solvent component, ethylene carbonate, the electrolyte decomposes around 4.5V. These two ratios fail to meet the 4.8V voltage window required for lithium-rich manganese-based materials and are unsuitable for high-voltage lithium-manganese-based lithium metal batteries. When the electrolyte ratio is EDO-377 or higher, the electrolyte exhibits an extremely high electrochemical stability window. EDO-377 and EDO-3710 both achieve a stability window of 6.7V, while EDO-3715 and EDO-3720 exceed 7V, demonstrating the strong electrochemical stability of these electrolytes. However, excessive diluent addition increases the electrolyte viscosity and density, making the preferred EDO-377 electrolyte suitable for high-voltage applications.

[0056] Example 2

[0057] According to the mass ratio of lithium-rich manganese-based material (LRMO): conductive carbon black Super P: polyvinylidene fluoride is 94:3.5:2.5, and the solvent N-methylpyrrolidone is added at a solid content of 30%. The mixture is uniformly mixed at a speed of 3000r / min for 3 hours using a homogenizer. The obtained slurry is cast on aluminum foil and scraped to prepare the positive electrode. The obtained electrode is vacuum dried in an oven at 120°C for 24 hours. The electrode is punched and cut into circular pieces with a diameter of 10mm. The surface loading of the active material of the electrode is 7-9mg / cm 2 .

[0058] The battery is assembled using the electrolyte ratio and preparation method in Example 1. The battery shell is a CR-2032 assembled battery, the positive electrode is the prepared lithium-rich manganese-based positive electrode plate, the negative electrode is lithium metal, the electrolyte dosage is 30 μL, and the injection tool is preferably a pipette with a range of 100 μL.

[0059] The assembled battery was left to stand at room temperature for 12 h to obtain a steady-state battery.

[0060] The prepared battery was tested with a step-up condition of 0.1V / 2h, an initial voltage of 4.6V, and a final voltage of 5.0V. The leakage current of the battery was tested within the range. Figure 2 As shown in the figure, the test results are basically consistent with the electrochemical window results. The leakage current of EDO-373 is large, indicating that the electrolyte is decomposed at this voltage. EDO-37x (x = 7, 10, 15, 20) has a very small leakage current, showing the ability to operate stably at this voltage.

[0061] Example 3

[0062] Using the electrolyte ratio and preparation method in Example 1, the Raman spectrum of the electrolyte was tested. Figure 3 As shown in the figure, with the increase of diluent addition, the ethylene carbonate (893 cm -1 about) and dimethyl carbonate (914cm -1 The free solvent peak (about 903 cm) gradually disappears, and the lithium ion-ethylene carbonate peak (903 cm) combined with lithium ions -1 about) and lithium ion-dimethyl carbonate peak (932cm -1 The gradual increase in the concentration of dimethyl carbonate (about 1.5) indicates that the coordination effect of these two solvents with lithium ions in the electrolyte is enhanced. Ethylene carbonate has an extremely high dielectric constant, making it the main solvent in common carbonate electrolytes. However, due to its high chemical reactivity and low electrochemical stability, it easily induces side reactions. Raman spectroscopy comparison results show that when the electrolyte ratio reaches EDO-377, the free ethylene carbonate solvent in the electrolyte is basically bound, and the subsequent addition of diluent no longer has a significant effect on the reduction of ethylene carbonate. This is mainly reflected in the gradual increase of the dimethyl carbonate peak. As a stable co-solvent, dimethyl carbonate is less involved in side reactions with oxygen on the positive electrode side.

[0063] Example 4

[0064] The battery is assembled using the electrolyte ratio and preparation method in Example 1. The battery shell is a CR-2032 assembled battery, the positive and negative electrodes are stainless steel sheets, the electrolyte dosage is 30 μL, and the injection tool is preferably a pipette with a range of 100 μL.

[0065] The assembled battery was left to stand at room temperature for 12 h to obtain a steady-state battery.

[0066] Test the ionic conductivity of the battery, the results are as follows Figure 4 As shown in Figure 2, the commercial electrolyte LB-012 (formulation: 1.15M LiPF6 in DMC:EC:EMC = 2:1:2 Vol%), DMC: dimethyl carbonate, EC: ethylene carbonate, EMC: ethyl methyl carbonate) and EDO-370 have higher ionic conductivity due to their pure carbonate solvent electrolytes. The ionic conductivity of EDO-370 is 1.819 mS cm -1 , which is higher than the 1.228 mS cm of the commercial electrolyte LB-012. -1, indicating that the basic electrolyte with optimized ratio has higher ion transmission performance. With the addition of diluent, the ionic conductivity of EDO-37x (x = 0, 3, 7, 10, 15, 20) continues to decrease. This is because the addition of non-ionic transmission component diluent adjusts the internal solvation structure of the electrolyte, causing agglomeration to form inside the electrolyte, which plays a role in protecting the internal ester solvent. However, the addition also reduces the ionic conductivity, thus highlighting the importance of effectively regulating the amount of diluent added, which is also one of the innovations of the present invention, that is, it shows the role and influence of the regulation of the electrolyte solvent and diluent ratio on the overall performance of the electrolyte. Examples 1-3 and Figure 4 The results show that EDO-377 not only has basic properties such as a high electrochemical window, but also has high ionic conductivity, which makes its ion transport performance even better and avoids the adverse effects of excessive diluent addition that can lead to limited ion transport in batteries. This demonstrates the special value of the optimized EDO-377 ratio.

[0067] Example 5

[0068] Using the electrolyte ratio and preparation method in Example 1 and the commercial electrolyte LB-012, the electrolyte density was tested using a density meter. As shown in Table 1, the commercial electrolyte and EDO-370 are both ester electrolytes with similar densities. However, with the addition of the high-density diluent OTE, the electrolyte density gradually increased. Excessive addition of diluent will increase the electrolyte density, which is not conducive to battery assembly. Examples 1-2 have proved that EDO-377 has the ability to match lithium-rich manganese-based lithium metal batteries. At the same time, it has a relatively reasonable density and can meet the actual electrolyte density requirements of soft-pack battery assembly. Therefore, it has good application potential.

[0069] Table 1 shows the diluent series ratios of the high-voltage lithium metal battery electrolyte and the density of the commercial ester electrolyte in Example 4.

[0070] Table 1

[0071] electrolyte <![CDATA[Density (g / cm 3 )]]> Commercial electrolyte LB-012 1.221 EDO-370 1.217 EDO-373 1.286 EDO-377 1.359 EDO-3710 1.400 EDO-3715 1.427 EDO-3720 1.473

[0072] It should also be pointed out that since the addition of diluents on the basis of EDO-377 will further improve the electrochemical window of the electrolyte, it is expected to be suitable for the next generation of new positive electrode materials such as ultra-high voltage. Therefore, the invention of this article is not limited to the high-voltage lithium metal battery electrolyte resistant to the specific ratio of EDO-377.

[0073] Example 6

[0074] The battery was assembled using the electrolyte ratio and preparation method in Example 1 and the commercial electrolyte LB-012 (formula 1.15MDMC:EC:EMC=2:1:2vol.%). The battery shell was a CR-2032 assembled battery, the positive electrode was a copper foil with a diameter of 16 mm and a thickness of 12 μm, the negative electrode was lithium metal, the electrolyte dosage was 30 μL, and the injection tool was preferably a pipette with a range of 100 μL.

[0075] The amount of electrolyte added was controlled by pipette injection. The order of assembling the lithium-copper button battery was positive electrode shell-copper foil-electrolyte-polypropylene diaphragm-electrolyte-lithium metal sheet-stainless steel gasket-stainless steel spring-negative electrode shell. A pressure of 9.5MPa was applied to press the button battery. After standing for 10 hours, the Aurbach method was used to measure the Aurbach coulomb efficiency of the battery. The method is to first discharge the battery for 10 hours, charge it until the voltage reaches 1V, discharge it again for 10 hours, and then perform 10 cycles of 0.5mAcm -2 , 1mAh cm -2 The battery was cycled and finally charged until the voltage reached 1 V. The current density of all charge and discharge operations was 0.5 mA cm -2 , the Aurbach coulomb efficiency of the electrolyte is calculated by dividing the battery charge capacity by the discharge capacity × 100%. The coulomb efficiency of the electrolyte is a key performance indicator before its practical application. Low coulomb efficiency will cause the electrode (usually the negative electrode) to be quickly depleted and cause battery failure. The test results are as follows Figure 5 shown.

[0076] EDO-377 exhibits the best Aurbach Coulombic efficiency, reaching 97.44%. The coulombic efficiency of the electrolyte shows a curve that first rises, then falls, and finally remains stable. This is because OTE has a certain negative electrode decomposition ability. When OTE is added in excess, it will intensify the reaction between OTE and the lithium metal on the negative electrode side, resulting in a certain amount of lithium metal loss. Therefore, the amount of OTE added needs to be maintained within a certain proportion range. This is also one of the core innovations of the present invention, that is, by precisely controlling the electrolyte solvent and diluent and the ratio between them, good electrochemical performance and electrolyte physicochemical parameters such as density and electrochemical window are achieved, thereby achieving better overall performance and matching conditions for lithium-rich manganese-based lithium metal batteries.

[0077] Comparative Example 1

[0078] An untreated commercial electrolyte with a formula of 1.15 M DMC:EC:EMC=2:1:2 vol.% was used as a comparison.

[0079] The battery was assembled according to the steps of Example 1 and the electrochemical window of the commercial electrolyte was tested after standing at room temperature for 10 hours. Figure 6As shown, its voltage window is 4.1V, which is smaller than EDO-377. It relies on the organic interface layer produced by the decomposition of solvent molecules to maintain the operation of the battery under high voltage, and the long cycle performance will be affected.

[0080] In summary, the high-voltage lithium metal battery electrolyte of the present invention has a voltage window far exceeding that of commercial electrolytes and can match positive electrode materials with higher voltages.

[0081] Test Example 1

[0082] The EDO-377 high-voltage lithium metal battery electrolyte selected in Example 6 was used to assemble lithium-copper button cells, and the coulombic efficiency was tested by charge and discharge cycles.

[0083] The amount of electrolyte added was controlled by pipetting, and the order of assembling the lithium-copper button battery was as follows: positive electrode shell - copper foil - electrolyte - polypropylene separator - electrolyte - lithium metal sheet - stainless steel gasket - stainless steel spring - negative electrode shell. A pressure of 9.5 MPa was applied to press the button battery. After standing for 10 hours, the battery was tested at 0.5 mA / cm 2 and 0.5mAh / cm 2 The test was carried out under the cycle conditions, and the cycle coulomb efficiency of the electrolyte was calculated by the discharge specific capacity / charge specific capacity of each cycle of the battery × 100%. The test results are as follows Figure 7 As shown, the average coulombic efficiency of the battery reached 96.93% after 100 cycles, showing good lithium ion insertion / deinsertion efficiency and stability.

[0084] Test Example 2

[0085] The commercial electrolyte described in Comparative Example 1 was used to assemble lithium-copper button batteries. The assembly sequence was the same as that of Test Example 1. The cyclic coulombic efficiency test was also performed. Figure 8 As shown in Figure 2, the average coulombic efficiency of commercial electrolytes is extremely low, only around 31.33%, which is difficult to support the lithium-copper battery for 100 cycles. The battery was forced to terminate the test due to lithium depletion at the 30th cycle. This shows that commercial electrolytes have low adaptability to lithium metal anodes and are difficult to adapt to lithium metal anodes under actual operating conditions, and cannot support the long-term stable cycling of lithium metal batteries.

[0086] Test Example 3

[0087] The EDO-377 high-voltage lithium metal battery electrolyte selected in Example 6 was used to assemble a lithium-lithium symmetrical battery, and a constant current charge-discharge stable cycle test was performed.

[0088] The amount of electrolyte was controlled by pipetting, and a lithium-lithium symmetrical button cell was assembled in the following order: positive electrode shell - lithium metal sheet - electrolyte - polypropylene separator - lithium metal sheet - stainless steel gasket - stainless steel spring - negative electrode shell. A pressure of about 9.5 MPa was applied to press the button cell. After standing at room temperature for 10 hours, the battery was tested at 0.5 mA / cm 2 , 0.5mAh / cm 2 The constant current charge and discharge cycle test was carried out under the conditions of Figure 9 As shown, the symmetrical battery still maintains a low overvoltage and stable cycling performance after 2500h of cycling, demonstrating long-term cycling stability of lithium ion insertion / deinsertion and effective inhibition of lithium dendrites at the interface.

[0089] Test Example 4

[0090] The commercial electrolyte described in Comparative Example 1 was used to assemble lithium-lithium symmetrical button cells. Except that the electrolyte was commercial electrolyte, the assembly sequence was the same as that of Test Example 3. The constant current charge and discharge cycle test was also carried out. The test conditions were the same as those in Test Example 3. Figure 10 The symmetrical battery failed after about 320 h of cycling due to excessive overpotential, indicating that the commercial electrolyte has extremely poor film-forming ability and compatibility on the lithium metal surface.

[0091] The test results of lithium-lithium symmetrical batteries show that the high-voltage lithium metal battery electrolyte has good stability to lithium metal and is more suitable for the field of lithium metal batteries.

[0092] Test Example 5

[0093] According to the mass ratio of lithium-rich manganese-based material (LRMO): conductive carbon black Super P: polyvinylidene fluoride is 94:3.5:2.5, and the solvent N-methylpyrrolidone is added at a solid content of 30%. The mixture is uniformly mixed at a speed of 3000r / min for 3 hours using a homogenizer. The obtained slurry is cast on aluminum foil and scraped to prepare the positive electrode. The obtained electrode is vacuum dried in an oven at 120°C for 24 hours. The electrode is punched and cut into circular pieces with a diameter of 10mm. The surface loading of the active material of the electrode is 23-25mg / cm 2 The negative electrode uses a commercial lithium metal negative electrode sheet with a diameter of 14 mm and a thickness of 500 μm.

[0094] The preferred EDO-377 lithium metal battery high-voltage electrolyte in Example 6 was selected, and the homemade LRMO positive electrode sheet, liquid electrolyte and lithium metal negative electrode with a thickness of 500μm were assembled into a CR2032 button battery. The order was the above positive electrode sheet-high-voltage lithium metal battery electrolyte-polypropylene diaphragm-lithium metal sheet-stainless steel gasket-stainless steel spring-negative electrode shell. A pressure of 9.5MPa was applied to seal the half-cell and the battery was left standing at room temperature for 12h. First, 0.1C charge and discharge cycles were performed three times, and then cycles were performed at a charge and discharge rate of 0.2C. The test results are as follows: Figure 11 As shown: the first discharge specific capacity of the half-cell at 0.1C is 273.8mAh / g, the capacity retention rate can still reach 87.9% after 300 cycles, and the average coulombic efficiency reaches 99.52%, showing good electrochemical performance.

[0095] Test Example 6

[0096] The commercial electrolyte described in Comparative Example 1 was used to assemble button-type half-cells. Except that the electrolyte was commercial electrolyte, the assembly sequence and test conditions were consistent with those of Test Example 5. Figure 12 The battery's first discharge specific capacity at 0.1C has poor cycling performance. The battery quickly fails due to poor coulombic efficiency, with a capacity retention rate of only 13.8% after 300 cycles and an average coulombic efficiency of only 98.8%.

[0097] Test Example 7

[0098] The preferred EDO-377 lithium metal battery high-voltage electrolyte in Example 6 was selected, and the LRMO positive electrode prepared in Test Example 5 was used. The homemade LRMO positive electrode, liquid electrolyte and lithium metal negative electrode with a thickness of 50 μm were assembled into a CR2032 button-type full battery. The order was the above positive electrode - high-voltage lithium metal battery electrolyte - polypropylene diaphragm - lithium metal sheet - stainless steel gasket - stainless steel spring - negative electrode shell. A pressure of 9.5 MPa was applied to seal the full battery and it was left at room temperature for 12 hours. The cycle was carried out at a charge and discharge rate of 0.1C. The test results are as follows: Figure 13 As shown: the first discharge specific capacity of the full battery at 0.1C is 261mAh / g, the capacity retention rate can still reach 73.2% after 50 cycles, and the average coulombic efficiency reaches 98.7%, showing good electrochemical performance.

[0099] Test Example 8

[0100] The commercial electrolyte described in Comparative Example 1 was used to assemble button-type full batteries. Except that the electrolyte was commercial electrolyte, the assembly sequence and test conditions were consistent with those of Test Example 7. The test results are shown in Figure 2. Figure 14The battery's first discharge specific capacity at 0.1C has poor cycling performance. After 8 cycles, the battery quickly fails due to poor coulombic efficiency. The capacity retention rate after 30 cycles is only 1.1%, and the average coulombic efficiency is only 84.1%.

[0101] Full-cell test results show that under practical application conditions, namely full-cell limited lithium metal anode conditions, commercial electrolytes quickly fail due to poor lithium compatibility and continuous side reactions with the cathode, indicating that commercial electrolytes are difficult to apply in the lithium metal battery field. The preferred high-voltage lithium metal battery electrolyte has high average coulombic efficiency and good stability with both the lithium metal anode and the LRMO cathode, allowing stable and long-term battery cycling under practical operating conditions, demonstrating greater commercial application value.

[0102] Test Example 9

[0103] Using the preferred EDO-377 high-voltage lithium metal battery electrolyte in Example 6, a test battery was assembled in an electrochemical differential mass spectrometer test mold according to a conventional battery assembly method, i.e., LRMO positive electrode sheet - high-voltage lithium metal battery electrolyte - polypropylene diaphragm - lithium metal negative electrode - stainless steel gasket in this order, and an electrochemical differential mass spectrometry test was performed. Figure 15 As shown: There is no obvious gas release peak during the first cycle of charging, indicating that the amount of active gas released in the battery is reduced. The reduction and disappearance of CO and CO2 peaks indicate that the side reaction between the active oxygen generated by the positive electrode material and the electrolyte is significantly reduced, which is expected to greatly improve the cycle capacity of the battery.

[0104] Test Example 10

[0105] The commercial electrolyte described in Comparative Example 1 was used to assemble and test the electrochemical differential mass spectrometer. Except that the electrolyte was a commercial electrolyte, the assembly sequence and test conditions were consistent with those of the above-mentioned Test Example 9. The test results are shown in Figure 1. Figure 16 When the battery is charged above 4.65V, there are obvious O2, CO, and CO2 precipitation peaks, indicating that there is obvious active oxygen precipitation at the LRMO positive electrode and side reactions between active oxygen and the electrolyte. This shows that during the battery cycle, the electrolyte is mismatched with the positive and negative electrodes, resulting in the generation of a large amount of side reaction substances, which may lead to rapid battery failure, battery bulging and explosion, posing a great application risk.

[0106] Test Example 11

[0107] The preferred EDO-377 high-voltage lithium metal battery electrolyte in Example 6 was used. Under room temperature and air atmosphere, a pipette with a preferred range of 1000 μL was used, and 1 g of high-voltage lithium metal battery electrolyte was quantitatively weighed on a weighing balance into the positive electrode shell of a CR2032 battery. The electrolyte was then burned for 5 seconds using a flame spray gun. Figure 17 As shown in the figure, after removing the flame spray gun, the electrolyte did not burn, indicating that the electrolyte is non-flammable and has good application value.

[0108] Test Example 12

[0109] The commercial electrolyte described in Comparative Example 1 was used to measure the electrolyte self-extinguishing time. Except that the electrolyte was commercial electrolyte, the assembly sequence and test conditions were the same as those in Test Example 11. Figure 18 As shown, after the flame spray gun was removed, the electrolyte continued to burn for about 73.2 seconds, indicating that the commercial electrolyte was flammable and had a self-extinguishing time of about 73.2 seconds / g.

[0110] The comparison results of the self-extinguishing time of the preferred high-voltage lithium metal battery electrolyte and the commercial electrolyte show that the optimized preferred high-voltage lithium metal battery electrolyte has excellent non-flammability, which makes its application in future high-voltage lithium metal batteries more promising. However, the commercial electrolyte is flammable and can easily cause combustion and explosion due to leakage in high-voltage lithium metal batteries, which poses a great safety hazard.

[0111] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A high-voltage flame-retardant lithium metal battery electrolyte, characterized in that: The invention comprises ethylene carbonate, dimethyl carbonate, a diluent and a lithium salt, wherein the diluent is 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether, the volume ratio of ethylene carbonate to dimethyl carbonate to the diluent is 3:7:7~20, the electrolyte withstand voltage is above 6.7 V, and it matches a lithium-rich manganese-based positive electrode.

2. The electrolyte according to claim 1, characterized in that The lithium salt is one or more of LiPF6, LiDFOB, LiFSI, LiTFSI, and LiBOB.

3. A lithium metal battery, characterized in that: The invention comprises the electrolyte according to any one of claims 1 to 2.

4. The lithium metal battery according to claim 3, characterized in that The positive electrode adopts at least one of lithium iron phosphate, nickel manganese cobalt, lithium cobalt oxide, lithium-rich manganese-based, and high-nickel materials, and the negative electrode adopts at least one of graphite, lithium metal, silicon negative electrode, silicon-carbon negative electrode, and no negative electrode material.

5. Use of the electrolyte according to any one of claims 1 to 2 in a lithium metal battery.

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