High-voltage-resistant flame-retardant lithium metal battery electrolyte and battery application

Abstract

The invention belongs to the technical field of new energy materials and devices, and relates to a high-voltage-resistant flame-retardant lithium metal battery electrolyte and battery application, the electrolyte comprises a carbonic ester solvent, a diluent and a lithium salt, and the diluent is 1H, 1H, 5H-octafluoropentyl 1, 1, 2, 2-tetrafluoroethyl ether (OTE). According to the invention, a common carbonic ester solvent is used as a main component of an organic solvent of the electrolyte and is matched with a high-voltage lithium salt and a proper amount of diluent OTE, and the use amount of the high-voltage lithium salt is equivalent to 70-200vol.% of the carbonic ester solvent. By regulating and controlling the diluent proportion and the solution composition proportion, the oxidation resistance of the conventional carbonate electrolyte can be improved to 6.7 V or above, the problems of gas release and cycle capacity fading caused by side reaction between the electrolyte and the positive and negative electrode sides are remarkably inhibited, and the preparation method has a good application prospect.

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 fields of power batteries / grid energy storage, it is urgent to improve the volumetric capacity and mass capacity of positive and negative electrode materials. Based on this, a lithium-rich manganese-based positive electrode has been developed, which has a high voltage window and high specific capacity, while the negative electrode tends to the ultimate goal of lithium metal, which has the highest specific capacity and the most negative potential, and can effectively exert the battery capacity.

[0003] But with it comes a series of adaptation problems. Traditional lithium-ion batteries are composed of graphite negative electrodes and medium-voltage positive electrodes (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 graphite negative electrodes without much optimization. As an alkali metal negative electrode, although the extremely negative potential of lithium metal gives it a higher capacity range, 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. The ether electrolyte adapted to the lithium metal negative electrode is difficult to withstand high voltages above 4V, which limits its 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 requirements on the electrolyte. Transition metals Ni, Co and Mn will catalyze and induce the decomposition of the electrolyte, further reducing the voltage window for the use of traditional ester electrolytes, making the decomposition of traditional ester electrolytes more severe. Due to the energy storage characteristics of lithium-rich manganese-based materials during use, some active oxygen (singlet oxygen, superoxide, etc.) is released. Its reaction with the electrolyte generates a large number of organic species and gases, which increases the interface impedance and accelerates the dissolution of transition metal elements on the positive electrode surface, causing the positive electrode particles to break, the capacity to decrease, and the material to fail. The reaction in turn further promotes the escape of active oxygen.

[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 and cause a fire that is difficult to extinguish by traditional means, endangering human life and causing serious property losses.

[0006] Therefore, developing 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 needs to be urgently addressed before the actual 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 prior art 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 volume of the carbonate solvent.

[0010] The diluent OTE introduced in the present invention has an optimal electrochemical window to match the requirements of interface film formation, so as to decompose and form an inorganic layer on the negative electrode side. At the same time, the diluent changes the solvation shell layer, increases the coordination of cyclic carbonate and lithium ions to reduce its reactivity to active oxygen. The formation of anion-rich solvation shell plays a role in decomposing into an inorganic-rich interface film on the positive electrode side. The outer layer of diluent surrounds and isolates the reactivity of solvent molecules and active components in the battery, greatly improving the cycle stability of the battery. The fluorine free radicals of the diluent combine with the hydrogen free radicals formed in the early stage of combustion, thereby inhibiting and indirectly blocking the occurrence of combustion. By precisely controlling the ratio of high-solubility cyclic carbonate, high-co-solubility chain carbonate and diluent in the electrolyte, the effective control of the electrolyte solvation structure, electrochemical window, ionic conductivity and density is achieved. The high-voltage lithium metal battery electrolyte after the optimized ratio has both positive and negative electrode interface stability, high voltage resistance of all components, effective side reaction inhibition ability and non-flammability, and has high cycle 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 can effectively reduce its reactivity with the positive and negative electrodes of the battery. Using a relatively high content of linear carbonate can effectively reduce the viscosity of the electrolyte and increase the ionic conductivity. The preferred diluent addition ratio can be adjusted according to the characteristics of the matching high-voltage positive electrode. When the diluent is added in a small amount, the problem of reduced ionic conductivity caused by the addition of diluent is reduced. When the amount is appropriate or excessive, the electrochemical window is greatly improved, the content of diluent decomposition products at the interface is increased, the interface stability is enhanced, the side reactions are reduced, and flame retardancy is achieved.

[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 the 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 first, 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 dehydration, at least one of anhydrous magnesium sulfate, anhydrous calcium chloride and sodium hydride is preferably used, and for impurity removal, a diameter of Molecular sieve.

[0027] The third aspect of the present invention provides 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 adopts common carbonate solvents as the main component of the organic solvent of the electrolyte, and is matched with high-pressure lithium salt LiPF6 and an appropriate amount of diluent 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether, the amount of which is equivalent to 70-200vol.% of the carbonate solvent. By adjusting the diluent ratio and the solution composition ratio, the antioxidant capacity of the conventional carbonate electrolyte can be increased to above 6.7V, and the gas release and cycle capacity attenuation caused by the side reaction between the electrolyte and the positive and negative electrode sides can be significantly inhibited, which has good application prospects.

[0030] 2. The present invention achieves the effect of balancing the salt dissolving ability and ion conductivity by precisely changing the solvent ratio and regulating the ratio of cyclic carbonate and chain carbonate within an appropriate range, and uses the regulating effect of the diluent on the electrolyte solvation shell to fix the easily reactive cyclic carbonate in the first solvation shell of lithium ions, reduce its reactivity with the positive and negative electrodes of the battery, and achieve effective retention of the electrolyte components. The diluent further blocks the harmful components in the battery such as active oxygen and active proton groups from the reaction damage of the solvent and lithium salt through the outer layer wrapping, and forms a good interface layer of the positive and negative electrodes by constructing anion-rich solvation shell and its own better reaction film-forming ability on the negative electrode side, further preventing the occurrence of side reactions. The fluorine free radicals of the diluent also play a role in combining with the hydrogen free radicals formed in the early stage of electrolyte combustion to block the further progress of combustion. The optimized overall electrolyte ratio effectively guarantees the ionic conductivity and lithium ion migration 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 2The leakage current diagram of the diluent series ratio of the high voltage lithium metal battery electrolyte in Example 2;

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

[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 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 The cyclic coulombic efficiency diagram of the high-voltage lithium metal battery electrolyte in Test Example 1;

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

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

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

[0041] Fig.11 The cycle 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] Fig.12 The cycle 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 Test Example 6;

[0043] Fig.13 The cycle 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 Test Example 7;

[0044] Fig.14 The cycle 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 Test Example 8;

[0045] Fig.15 The gas phase differential electrochemical mass spectrometer 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] Fig.16 The gas phase differential electrochemical mass spectrometer 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] Fig.17 The combustion condition of the high-voltage lithium metal battery electrolyte in Test Example 11 under air atmosphere;

[0048] Fig.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 solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with 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), and 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 the mixture was evenly mixed under magnetic stirring, 1 mL was quantitatively weighed using a calibrated pipette.

[0052] 151.92 mg of lithium salt LiPF6 was slowly added to the EDO-37x solution and stirred for 12 hours. The stirring speed was 500 rpm and the heating temperature was 45° C. A uniformly mixed EDO-37x (x=0, 3, 7, 10, 15, 20) high-voltage lithium metal battery electrolyte was obtained.

[0053] The high-voltage-resistant lithium metal battery electrolyte is used for battery assembly, wherein 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 not added, the electrolyte is prone to decomposition at <4V, and the current rises rapidly, indicating the poor high-voltage tolerance of the system without adding electrolyte; when the amount of diluent added is EDO-373, the electrolyte window is significantly improved due to the effect of the diluent, but the high dielectric constant solvent component ethylene carbonate is not fully combined, causing the electrolyte to decompose at around 4.5V. The above two ratios cannot meet the 4.8V voltage window of lithium-rich manganese-based materials and cannot match high-voltage lithium-rich manganese-based lithium metal batteries. When the electrolyte ratio is EDO-377 and above, the electrolyte has an extremely high electrochemical stability window. The stability windows of EDO-377 and EDO-3710 both reach 6.7V, while the stability windows of EDO-3715 and EDO-3720 exceed 7V, indicating that the above electrolytes have strong electrochemical stability. Excessive diluent addition will cause the viscosity and density of the electrolyte to increase, so the preferred EDO-377 electrolyte has a suitable high-voltage matching capability.

[0056] Example 2

[0057] 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 homogenizer is used to evenly mix for 3 hours at a speed of 3000r / min. The obtained slurry is cast on aluminum foil and scraped to prepare the positive electrode. The obtained pole piece is vacuum dried in an oven at 120°C for 24 hours, and the pole piece is punched and cut into a circular piece with a diameter of 10mm. The surface loading of the active material of the pole piece 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 for leakage current in the range of 0.1V / 2h step-up condition, with an initial voltage of 4.6V and a final voltage of 5.0V. Figure 2 As shown, 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 the amount of diluent added, 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 ratio of EDO-377 to EDO-377 gradually increases, which 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, which makes it the main solvent in the commonly used carbonate electrolyte. However, it is easy to induce side reactions due to its high chemical reaction activity and low electrochemical stability. The Raman spectrum comparison results show that when the electrolyte ratio reaches EDO-377, the free ethylene carbonate solvent in the electrolyte is basically combined, and the subsequent addition of diluent no longer plays a significant role in the reduction of ethylene carbonate, which is mainly reflected in the gradual enhancement of the dimethyl carbonate peak. As a stable co-solvent, dimethyl carbonate is less involved in the 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 the figure, the commercial electrolyte LB-012 (formula is 1.15M LiPF6in DMC:EC:EMC=2:1:2Vol%, DMC: dimethyl carbonate, EC: ethylene carbonate, EMC: ethyl methyl carbonate) and EDO-370 have higher ionic conductivity because they are pure carbonate solvent electrolytes, among which the ionic conductivity of EDO-370 is 1.819mS 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 transport 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 transport component diluent adjusts the internal solvation structure of the electrolyte, causing agglomeration 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 innovative points 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 limited battery ion transport due to excessive addition of diluents, indicating the special value of the preferred 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 belong to the same ester electrolyte and have similar densities. However, with the addition of 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 soft-pack battery assembly electrolyte density requirements, so it has good application potential.

[0069] Table 1 shows the ratio of diluent series of high voltage lithium metal battery electrolyte and the density of 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 claims of this article are not limited to the high-voltage lithium metal battery electrolyte resistant to the specific ratio of EDO-377.

[0073] Example 6

[0074] The battery is 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 is a CR-2032 assembled battery. The positive electrode is a copper foil with a diameter of 16 mm and a thickness of 12 μm. 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.

[0075] The amount of electrolyte added was controlled by pipette injection. The order of assembling lithium-copper button cells 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 cell. 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 times of 0.5mAcm -2 , 1mAh cm -2 The battery was cycled and 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 the battery charge capacity / 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 coulomb efficiency, reaching 97.44%, and the coulomb 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, the reaction between OTE and the lithium metal on the negative electrode side will be aggravated, causing a certain loss of lithium metal. Therefore, the amount of OTE added needs to be kept within a certain proportion range, which is also one of the core innovations of the present invention, that is, by accurately controlling the electrolyte solvent and diluent and the ratio between them, good electrochemical performance and electrolyte physicochemical parameters such as density, electrochemical window, etc. are achieved, thereby achieving better comprehensive performance and matching conditions for lithium-rich manganese-based lithium metal batteries.

[0077] Comparative Example 1

[0078] An untreated commercial electrolyte having 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 preferred EDO-377 high-voltage lithium metal battery electrolyte in Example 6 was used to assemble lithium-copper button batteries, and the coulombic efficiency was tested by charge and discharge cycles.

[0083] The amount of electrolyte added was controlled by pipette injection. The order of assembling lithium-copper button cells 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 9.5 MPa was applied to press the button cell. After standing for 10 hours 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 after 100 cycles reaches 96.93%, 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 a lithium-copper button cell. Except that the electrolyte was a commercial electrolyte, the assembly sequence was the same as that of the above-mentioned Test Example 1. The cyclic coulomb efficiency test was also performed. Figure 8 As shown. The average coulombic efficiency of commercial electrolyte is extremely low, only about 31.33%, which is difficult to support 100 cycles of lithium-copper batteries. The battery was forced to terminate the test at the 30th cycle due to lithium depletion. This shows that the adaptability of commercial electrolyte to lithium metal negative electrodes is low, and it is difficult to adapt to lithium metal negative electrodes under actual working conditions, and it cannot support the long-term stable cycle of lithium metal batteries.

[0086] Test Example 3

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

[0088] The amount of electrolyte was controlled by pipette injection, and lithium-lithium symmetrical button cells were assembled in the order of positive electrode shell-lithium metal sheet-electrolyte-polypropylene diaphragm-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 cells. After standing at room temperature for 10 hours, the battery was heated to 0.5 mA / cm 2 , 0.5mAh / cm 2 The constant current charge and discharge cycle test was carried out under the condition of Fig. 9 As shown, the symmetrical battery still maintains a low overvoltage and stable cycling performance after 2500 h of cycling, demonstrating the long-term cycling stability of lithium ion insertion / deinsertion and the 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 a lithium-lithium symmetrical button cell. Except that the electrolyte was a commercial electrolyte, the assembly sequence was the same as that of the above-mentioned Test Example 3. The constant current charge and discharge cycle test was also performed, and the test conditions were the same as those in Test Example 3, such as Fig.10 The symmetric battery failed after about 320 hours of cycling due to excessive overpotential, indicating that the commercial electrolyte has poor film-forming ability and compatibility on the lithium metal surface.

[0091] The test results of lithium-lithium symmetrical batteries show that 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] 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 homogenizer is used to evenly mix for 3 hours at a speed of 3000r / min. The obtained slurry is cast on aluminum foil and scraped to prepare the positive electrode. The obtained pole piece is vacuum dried in an oven at 120°C for 24 hours, and the pole piece is punched and cut into a circular piece with a diameter of 10mm. The surface loading of the active material of the pole piece 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] Select the preferred EDO-377 lithium metal battery high-voltage electrolyte in Example 6, assemble the homemade LRMO positive electrode sheet, liquid electrolyte and lithium metal negative electrode with a thickness of 500μm into a CR2032 button battery, the order is 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, apply 9.5MPa pressure to seal the half-cell, and let it stand at room temperature for 12h. First, perform 0.1C charge and discharge cycles three times, and then cycle at a charge and discharge rate of 0.2C. The test results are as follows Fig.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 a commercial electrolyte, the assembly sequence and test conditions were consistent with those of the above-mentioned Test Example 5. The test results are shown in FIG. Fig.12 As shown in the figure, the battery's first discharge specific capacity at 0.1C has poor cycle performance. The battery fails quickly due to poor coulombic efficiency. The capacity retention rate after 300 cycles is only 13.8%, and the average coulombic efficiency is 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 sequence 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. Cycling was performed at a charge and discharge rate of 0.1C. The test results are as follows: Fig.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 Case 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 the above-mentioned Test Example 7. The test results are shown in Fig.14As shown in the figure, the battery's first discharge capacity at 0.1C has poor cycle 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] The full battery test results show that under actual application conditions, i.e. full battery limited lithium metal negative electrode conditions, commercial electrolytes cause rapid battery failure due to poor lithium compatibility and continuous side reactions with the positive electrode, indicating that commercial electrolytes are difficult to apply in the field of lithium metal batteries. The preferred high-voltage lithium metal battery electrolyte has a high average coulombic efficiency and good stability to both the lithium metal negative electrode and the LRMO positive electrode. It can be used for stable long-term battery cycling under actual working conditions, showing better 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. Fig.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 of active oxygen generated by the positive electrode material with the electrolyte is significantly reduced, which is expected to greatly improve the battery's cycle capacity.

[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 Fig.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 the side reaction of active oxygen with the electrolyte. This shows that during the battery cycle, the electrolyte does not match the positive and negative electrodes, and a large amount of side reaction substances are produced, which may cause the battery to fail quickly, and cause battery bulging and explosion, posing a greater 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 preferred 1000 μL pipette was used to quantitatively weigh 1 g of the high-voltage lithium metal battery electrolyte into the positive electrode shell of a CR2032 battery on a weighing balance, and a flame spray gun was used to continuously burn for 5 seconds. Fig.17 As shown, after the flame spray gun was removed, the electrolyte did not burn, indicating that the electrolyte was non-flammable and had good application value.

[0108] Test Example 12

[0109] The commercial electrolyte described in Comparative Example 1 was used for the electrolyte self-extinguishing time. Except that the electrolyte was a commercial electrolyte, the assembly sequence and test conditions were the same as those of the above-mentioned Test Example 11. Fig.18 As shown, after the flame spray gun was removed, the electrolyte continued to burn and maintained for about 73.2 seconds. It can be known that the commercial electrolyte is flammable and the self-extinguishing time is 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 potential. 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 description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications should also be regarded as within 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 a carbonate solvent, a diluent and a lithium salt, wherein the diluent is 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether.

2. The electrolyte according to claim 1, wherein the amount of the diluent is 70 to 200% of the volume of the carbonate solvent.

3. The electrolyte according to claim 1, characterized in that The carbonate solvent consists of cyclic carbonate and chain carbonate, and the volume ratio of the cyclic carbonate to the chain carbonate is 3:7-10.

4. The electrolyte according to claim 3, characterized in that The cyclic carbonate is one or both of ethylene carbonate and propylene carbonate.

5. The electrolyte according to claim 3, characterized in that The chain carbonate is one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and methyl propyl carbonate.

6. The electrolyte according to claim 3, characterized in that The cyclic carbonate is ethylene carbonate, the chain carbonate is dimethyl carbonate, and the volume ratio of ethylene carbonate to dimethyl carbonate to the diluent is 3:7:7-20.

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

8. A lithium metal battery, characterized in that: The invention comprises the electrolyte described in any one of claims 1 to 8.

9. The lithium metal battery according to claim 8, 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.

10. Use of the electrolyte according to any one of claims 1 to 8 in a lithium metal battery.

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