High-entropy flame-retardant electrolyte and preparation method and application thereof

Abstract

The invention discloses a high-entropy flame-retardant electrolyte as well as a preparation method and application thereof, and belongs to the field of battery electrolytes. The high-entropy flame-retardant electrolyte comprises 20%-60% of an organic solvent; the organic solvent comprises a phosphate ester solvent and an ether solvent in a volume ratio of (0.5-5): (0.5-5), and the number of the solvents is not less than five. According to the high-entropy flame-retardant electrolyte, the phosphate solvent and the ether solvent are used as the mixed solvent, so that the diversity of components of the electrolyte can be increased, the disorder degree of a system can be improved, interaction of Li < + > and anions can be promoted, a solvation structure can be adjusted, and deposition and stripping of Li < + > at an electrochemical window and a uniform interface of the electrolyte are improved; and a solid electrolyte interface film (SEI) rich in inorganic components is generated on the surface of the negative electrode, so that the electrochemical performance and the safety performance of the lithium metal battery are improved. When the high-entropy flame-retardant electrolyte is applied to the lithium metal battery, the safety performance and electrochemical performance requirements of the lithium metal battery can be met.

Description

Technical Field

[0001] The present invention relates to the field of battery electrolytes, and in particular to a high entropy flame retardant electrolyte and a preparation method and application thereof. Background Art

[0002] With the rapid development of new energy technologies and electric vehicles, the market has higher demands for the safety and energy density of lithium-ion batteries. Lithium metal batteries use lithium metal as the negative electrode, and the theoretical specific capacity can reach 3860mAh / g, which has significant advantages over graphite negative electrodes (372mAh / g). In addition, the standard electrode potential of metallic lithium is lower (-3.040V vs standard hydrogen electrode), which can output higher voltage. Therefore, lithium metal batteries have potential advantages in energy density.

[0003] Currently, the commonly used electrolytes for lithium metal batteries cannot provide both battery safety and electrochemical performance.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The object of the present invention is to provide a high entropy flame retardant electrolyte and a preparation method and application thereof, so as to solve or improve the above technical problems.

[0006] The present invention can be implemented like this:

[0007] In a first aspect, the present invention provides a high entropy flame retardant electrolyte, wherein the high entropy flame retardant electrolyte comprises 20% to 60% of an organic solvent by volume percentage;

[0008] The organic solvent includes a phosphate solvent and an ether solvent in a volume ratio of (0.5-5):(0.5-5).

[0009] In an optional embodiment, the phosphate ester solvent includes at least two of trimethyl phosphate, triethyl phosphate, dimethyl methylphosphonate, diethyl ethylphosphonate, triphenyl phosphate, triphenyl phosphite, triallyl phosphate, tris(hexafluoroisopropyl) phosphate, tris(trimethylsilyl) phosphite, tris(trimethylsilyl) phosphate and tris(2,2,2-trifluoroethyl) phosphate;

[0010] In an alternative embodiment, each phosphate ester solvent accounts for at least 10% of the total volume of the organic solvent.

[0011] In an optional embodiment, the ether solvent includes at least two of ethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxypropane, diethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and 1,4-dioxane.

[0012] In an alternative embodiment, each ether solvent accounts for at least 10% of the total volume of the organic solvent.

[0013] In an optional embodiment, the organic solvent contains at least five types of phosphate ester solvents and ether solvents.

[0014] In an optional embodiment, the high entropy flame retardant electrolyte further includes a lithium salt.

[0015] In an optional embodiment, the lithium salt includes at least two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium bistrifluoromethanesulfonyl imide, lithium bisfluorosulfonyl imide, lithium difluorophosphate, lithium difluorobisoxalatephosphate, and lithium tetrafluorooxalatephosphate.

[0016] In an alternative embodiment, each lithium salt accounts for at least 25% of the total mass of the lithium salts.

[0017] In an optional embodiment, the total concentration of lithium ions in the high entropy flame retardant electrolyte is 0.2 mol / L to 2 mol / L.

[0018] In an optional embodiment, the high entropy flame retardant electrolyte further includes a diluent.

[0019] In an alternative embodiment, the diluent includes at least two of ethoxypentafluorocyclotriphosphazene, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, and 2,2,2-trifluoroethyl-1,1,2,2-tetrafluoroethyl ether.

[0020] In an alternative embodiment, each diluent comprises at least 20% of the total volume of the diluents.

[0021] In an optional embodiment, the volume content of the diluent in the high entropy flame retardant electrolyte is 40% to 80%.

[0022] In an optional embodiment, the high entropy flame retardant electrolyte further includes an additive.

[0023] In an alternative embodiment, the additive includes at least one of fluoroethylene carbonate, vinylene carbonate, vinylethylene carbonate, and 1,3-propane sultone.

[0024] In an optional embodiment, the mass fraction of the additive in the high entropy flame retardant electrolyte is 0.2% to 10%.

[0025] In an optional embodiment, the high entropy flame retardant electrolyte includes an organic solvent, a lithium salt, a diluent and an additive;

[0026] Among them, the organic solvent is composed of triethyl phosphate, dimethyl methylphosphonate, tri(2,2,2-trifluoroethyl) phosphate, ethylene glycol dimethyl ether and 1,3-dioxolane; the lithium salt is composed of lithium bis(fluorosulfonyl)imide and lithium difluorooxalatoborate; the diluent is composed of ethoxypentafluorocyclotriphosphazene and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; and the additive is fluoroethylene carbonate.

[0027] In a second aspect, the present invention provides a method for preparing a high entropy flame retardant electrolyte as described in any of the aforementioned embodiments, comprising the following steps: mixing the components of the high entropy flame retardant electrolyte according to a ratio.

[0028] In an optional embodiment, when the high entropy flame retardant electrolyte contains an organic solvent, a lithium salt, a diluent and an additive, the preparation of the high entropy flame retardant electrolyte includes: first mixing a phosphate solvent and an ether solvent to obtain an organic solvent; dissolving the lithium salt in the organic solvent, and then adding the diluent and the additive, and the entire electrolyte preparation process is carried out in a glove box filled with argon, and the water and oxygen content in the glove box is kept less than 0.01 ppm.

[0029] In a third aspect, the present invention provides a lithium metal battery, wherein the lithium metal battery contains the high entropy flame retardant electrolyte of any one of the aforementioned embodiments.

[0030] The beneficial effects of the present invention include:

[0031] The high entropy flame retardant electrolyte provided by the present invention can increase the diversity of electrolyte components and improve the disorder of the system by using phosphate ester solvent and ether solvent as mixed solvent, which can promote Li + Interaction with anions, regulating the solvation structure, improving the electrochemical window of the electrolyte, and uniformly treating Li + Deposition and stripping form a solid electrolyte interface (SEI) rich in inorganic components on the negative electrode surface, improving the electrochemical performance and safety performance of lithium metal batteries. The use of this high entropy flame retardant electrolyte in lithium metal batteries can take into account both the safety performance and electrochemical performance requirements of lithium metal batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 The electrochemical window test curves of Example 2 and Comparative Example 2;

[0034] Figure 2 The first cycle charge and discharge curve of the nickel cobalt manganese oxide lithium metal battery assembled in Example 2;

[0035] Figure 3 The charge and discharge curves of the Li-Li symmetrical battery assembled in Example 3;

[0036] Figure 4 The AC impedance spectra of the Li-Li symmetrical batteries assembled in Example 3 and Comparative Example 3;

[0037] Figure 5 The first cycle charge and discharge curves of the lithium iron phosphate lithium metal batteries assembled in Example 4 and Comparative Example 4;

[0038] Figure 6 The first cycle charge and discharge curves of the nickel cobalt manganese oxide lithium metal battery assembled in Example 5 and Comparative Example 5;

[0039] Figure 7 The charge and discharge curves of the Li-Cu batteries assembled from Example 1, Comparative Examples 11 and 12. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0041] The high entropy flame retardant electrolyte provided by the present invention and its preparation method and application are described in detail below.

[0042] In terms of volume percentage, the high entropy flame retardant electrolyte provided by the present invention comprises 20% to 60% of an organic solvent; the organic solvent comprises a phosphate solvent and an ether solvent in a volume ratio of (0.5 to 5):(0.5 to 5).

[0043] In some optional embodiments, the amount of organic solvent contained in the high entropy flame retardant electrolyte can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% or 60%, etc., or other values ​​within the range of 20% to 60%.

[0044] If the volume percentage of organic solvents in the high-entropy flame-retardant electrolyte is lower than 20%, the viscosity of the electrolyte will increase significantly, reducing the ionic conductivity of the electrolyte and causing a decline in the electrochemical performance of the battery; if the volume percentage of organic solvents in the high-entropy flame-retardant electrolyte is higher than 60%, some organic solvents will interact with lithium ions, aggravating the decomposition side reaction of the solvent at the interface and affecting the electrochemical window of the electrolyte and the cycle stability of the battery.

[0045] In some optional embodiments, the volume ratio of the phosphate solvent to the ether solvent can be 0.5:0.5, 0.5:1, 0.5:2, 0.5:3, 0.5:4, 0.5:5, 1:0.5, 1:3, 1:5, 2:0.5, 2:1, 2:3, 2:5, 3:0.5, 3:1, 3:2, 3:4, 3:5, 4:0.5, 4:1, 4:3, 4:5, 5:0.5, 5:1, 5:2, 5:3 or 5:4, etc., or it can be other values ​​within the range of (0.5-5):(0.5-5).

[0046] If the volume ratio of phosphate ester solvents to ether solvents is lower than 0.5:5 (such as 0.5:10), it is easy to cause the flame retardant properties of the electrolyte to decrease and affect the safety performance; if the volume ratio of phosphate ester solvents to ether solvents exceeds 5:0.5 (such as 10:0.5), it is easy to cause the interface compatibility between the electrolyte and the lithium metal negative electrode to decrease, which is not conducive to the cycle stability of the battery.

[0047] It should be noted that the interface between the ether solvent and the lithium metal negative electrode in the above-mentioned high entropy flame retardant electrolyte is stable and can maintain a stable electrochemical cycle. However, the electrochemical window of ether electrolytes is limited, and it is difficult to be compatible with high-voltage positive electrode materials. In addition, ether electrolytes usually have low flash points and boiling points, and have high flammability, which can easily cause thermal runaway or even fire and explosion during battery use. Phosphate solvents have rich P-containing flame retardant groups, which can capture combustion free radicals, prevent electrolyte combustion reactions, and improve safety performance. However, phosphate solvents are unstable at the interface of lithium metal negative electrodes, and the battery cannot be stably cycled, which affects the electrochemical performance.

[0048] The present invention creatively combines phosphate solvents and ether solvents in the above-mentioned specific ratio as a mixed solvent, which can increase the diversity of electrolyte components, improve the disorder of the system, and promote Li + Interaction with anions, regulating the solvation structure, improving the electrochemical window of the electrolyte, and uniformly treating Li + Deposition and stripping form a solid electrolyte interface film (SEI) rich in inorganic components on the surface of the negative electrode, improving the electrochemical performance and safety performance of lithium metal batteries.

[0049] In some optional embodiments, the phosphate ester solvent may illustratively but not limitatively include at least two of trimethyl phosphate (TMP), triethyl phosphate (TEP), dimethyl methylphosphonate (DMMP), diethyl ethylphosphonate (DEEP), triphenyl phosphate (TPP), triphenyl phosphite (TPPi), triallyl phosphate (TAP), tris(hexafluoroisopropyl) phosphate (HFiP), tris(trimethylsilyl) phosphite (TMSPi), tris(trimethylsilyl) phosphate (TMSP) and tris(2,2,2-trifluoroethyl) phosphate (TFEP).

[0050] Each of the above phosphate ester solvents accounts for at least 10% of the total volume of the organic solvent.

[0051] In some optional embodiments, the ether solvent may illustratively but not limitatively include at least two of ethylene glycol dimethyl ether (DME), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane (DOL), dimethoxymethane (DMM), 1,2-dimethoxypropane (DMP), diethylene glycol dimethyl ether (DG), diethylene glycol dimethyl ether (DGM), triethylene glycol dimethyl ether (T3GM), tetraethylene glycol dimethyl ether (T4GM) and 1,4-dioxane (DXA).

[0052] Each of the above ether solvents accounts for at least 10% of the total volume of the organic solvent.

[0053] In some preferred embodiments, the number of phosphate ester solvents and ether solvents contained in the organic solvent is at least 5. If the number of solvent types contained in the organic solvent is less than 5, the solvation structure in the electrolyte is relatively single, the ion transport path is limited, and the electrochemical stability of the solvation structure in the electrolyte is insufficient, and the battery performance is greatly reduced.

[0054] In the present invention, the high entropy flame retardant electrolyte further comprises a lithium salt.

[0055] In some optional embodiments, the lithium salt may illustratively but not limitedly include lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), at least two of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiDFP), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0056] Each of the above lithium salts accounts for at least 25% of the total mass of the lithium salts.

[0057] The total concentration of all lithium ions in the high entropy flame retardant electrolyte can be, for example, 0.2 mol / L to 2 mol / L, such as 0.2 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L or 2 mol / L, or other values ​​within the range of 0.2 mol / L to 2 mol / L.

[0058] If the total concentration of all lithium ions in the high entropy flame retardant electrolyte is lower than 0.2 mol / L, the number of lithium ions in the electrolyte will be small, the electrolyte ion conductivity will be reduced, and the concentration polarization will be greater, increasing the risk of lithium dendrites, and the electrochemical performance, interface stability, and safety performance of the battery will be affected; if the total concentration of all lithium ions in the high entropy flame retardant electrolyte is higher than 2 mol / L, the viscosity of the electrolyte will increase, hindering the infiltration of the electrolyte and the electrode interface, increasing the internal resistance of the battery, and the lithium salt concentration is too high, which will affect the ion transport in the electrolyte and the charge transfer kinetics will be slow. In the present invention, the high entropy flame retardant electrolyte also includes a diluent.

[0059] In some optional embodiments, the diluent may illustratively but not limitatively include at least two of ethoxypentafluorocyclotriphosphazene (PFPN), 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether (BTFE) and 2,2,2-trifluoroethyl-1,1,2,2-tetrafluoroethyl ether (HFE).

[0060] Each of the above diluents accounts for at least 20% of the total volume of the diluent.

[0061] The volume content of all diluents in the high entropy flame retardant electrolyte can be 40% to 80%, such as 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%, etc., or other values ​​within the range of 40% to 80%.

[0062] The main functions of the diluent include reducing the viscosity of the electrolyte, optimizing the ion transfer performance, enhancing the interaction between lithium ions and anions, and adjusting the solvation structure of lithium ions. If the volume content of the diluent in the high-entropy flame-retardant electrolyte is less than 40%, the viscosity of the electrolyte will increase significantly, resulting in poor wettability of the electrolyte and reduced ion transfer efficiency in the electrolyte; if the volume content of the diluent in the high-entropy flame-retardant electrolyte is higher than 80%, the solvation structure in the electrolyte will be destroyed, resulting in instability of the solvation sheath of lithium ions and reduced interface stability.

[0063] In the present invention, the high entropy flame retardant electrolyte also includes additives. The functions of the additives include: preferential reduction or oxidation on the electrode surface, forming a stable solid electrolyte interface film or positive electrode interface film, effectively reducing interface side reactions, and improving the electrochemical performance of the battery. In some optional embodiments, the additives may exemplarily but not limitatively include at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl carbonate (VEC) and 1,3-propane sultone (1,3-PS).

[0064] The total mass fraction of all additives in the high entropy flame retardant electrolyte can be 0.2% to 10%, such as 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc., or other values ​​within the range of 0.2% to 10%.

[0065] If the total mass fraction of the additives in the high-entropy flame-retardant electrolyte is lower than 0.2%, it is not conducive to the function of the electrolyte additives, resulting in incomplete formation of the interface film and affecting the cycle stability of the battery; if the total mass fraction of the additives in the high-entropy flame-retardant electrolyte is higher than 10%, it will cause the interface film to be too thick, increase the internal resistance of the battery, and reduce the specific capacity and coulombic efficiency of the battery.

[0066] In some typical embodiments, the high entropy flame retardant electrolyte includes an organic solvent, a lithium salt, a diluent and an additive. Among them, the organic solvent is composed of triethyl phosphate, dimethyl methylphosphonate, tris (2,2,2-trifluoroethyl) phosphate, ethylene glycol dimethyl ether and 1,3-dioxolane, and the volume ratio of triethyl phosphate, dimethyl methylphosphonate, tris (2,2,2-trifluoroethyl) phosphate, ethylene glycol dimethyl ether and 1,3-dioxolane can be (1-2): 1: (1-2): (1-2): (1-2). The lithium salt is composed of lithium bis(fluorosulfonyl)imide and lithium difluorooxalate borate, and the concentration of lithium bis(fluorosulfonyl)imide in the high entropy flame retardant electrolyte can be 0.6 mol / L-0.8 mol / L, and the concentration of lithium difluorooxalate borate in the high entropy flame retardant electrolyte can be 0.4 mol / L-0.7 mol / L. The diluent is composed of ethoxy pentafluorocyclotriphosphazene and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and the volume ratio of ethoxy pentafluorocyclotriphosphazene and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether can be (5-9):(5-8). The additive is fluoroethylene carbonate, and the concentration of fluoroethylene carbonate in the high entropy flame retardant electrolyte can be 5wt%.

[0067] As mentioned above, the high entropy flame-retardant electrolyte provided by the present invention has good interface stability with the lithium metal negative electrode. By increasing the types of electrolyte components and the degree of system disorder, the solvation structure and interface behavior of the electrolyte are optimized, and the electrochemical window of the electrolyte is improved, which is beneficial to promote the efficient deposition and stripping of the lithium metal negative electrode. By introducing phosphate flame-retardant solvents, the safety performance of the electrolyte is improved, which is beneficial to the construction of a high-safety and high-performance lithium metal battery.

[0068] Correspondingly, the present invention also provides a method for preparing the above-mentioned high entropy flame retardant electrolyte, comprising the following steps: mixing the components of the high entropy flame retardant electrolyte according to a proportion.

[0069] When the high entropy flame retardant electrolyte contains an organic solvent, a lithium salt, a diluent and an additive, the preparation of the high entropy flame retardant electrolyte includes: first mixing a phosphate solvent and an ether solvent to obtain an organic solvent; dissolving the lithium salt in the organic solvent, and then adding the diluent and the additive, and the entire electrolyte preparation process is carried out in a glove box filled with argon, and the water oxygen content in the glove box is kept less than 0.01 ppm.

[0070] In addition, the present invention also provides a lithium metal battery, which contains the above-mentioned high-entropy flame-retardant electrolyte.

[0071] Illustratively, a lithium metal battery is composed of a positive electrode, a separator, a negative electrode, and a high-entropy flame-retardant electrolyte, and can be assembled into, for example, a button cell or a soft-pack cell.

[0072] In some optional embodiments, the positive electrode active material used in the positive electrode may include lithium nickel cobalt manganese oxide (NCM), lithium iron phosphate (LFP) or lithium cobalt oxide (LCO). A uniform positive electrode slurry is prepared by mixing the positive electrode active material with a conductive agent and a binder and adding an appropriate amount of N-methylpyrrolidone (NMP), and then coating it on a positive electrode current collector (such as aluminum foil) and drying to obtain a positive electrode. The negative electrode used in a lithium metal battery can be a metal lithium sheet or lithium foil.

[0073] The above-mentioned lithium metal battery can maintain a wide electrochemical window and good interface stability, taking into account both safety performance and electrochemical performance.

[0074] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0075] Example 1

[0076] This embodiment provides a high entropy flame retardant electrolyte, which has the following composition:

[0077] ①. Organic solvent: triethyl phosphate (TEP), dimethyl methylphosphonate (DMMP), tri(2,2,2-trifluoroethyl) phosphate (TFEP), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a volume ratio of 1:1:2:1:1; the volume percentage of the organic solvent in the high entropy flame retardant electrolyte is 37.5%.

[0078] ②. Lithium salt: lithium bis(fluorosulfonyl)imide (LiFSI) and lithium difluorooxalatoborate (LiDFOB). The concentration of lithium bis(fluorosulfonyl)imide in the high entropy flame retardant electrolyte is 0.6 mol / L, and the concentration of lithium difluorooxalatoborate in the high entropy flame retardant electrolyte is 0.6 mol / L.

[0079] ③. Diluent: ethoxypentafluorocyclotriphosphazene (PFPN) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a volume ratio of 5:5; the volume percentage of the diluent in the high entropy flame retardant electrolyte is 62.5%.

[0080] ④. Additive: fluoroethylene carbonate (FEC), the concentration of fluoroethylene carbonate in the high entropy flame retardant electrolyte is 5wt%.

[0081] The preparation process of the high entropy flame retardant electrolyte is as follows: The high entropy flame retardant electrolyte is prepared in a glove box filled with argon gas, and the water and oxygen content in the glove box is kept less than 0.01ppm. According to the set dosage, the components of the organic solvent are first mixed evenly, and then the lithium salt is dissolved in the organic solvent, and the diluent and additives are added and mixed evenly.

[0082] Example 2

[0083] The difference between this embodiment and embodiment 1 is that:

[0084] The organic solvent is composed of triethyl phosphate (TEP), dimethyl methylphosphonate (DMMP), tri(2,2,2-trifluoroethyl) phosphate (TFEP), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a volume ratio of 2:1:2:1:1; the volume percentage of the organic solvent in the high entropy flame retardant electrolyte is about 30.4%.

[0085] Among the lithium salts, the concentration of lithium bis(fluorosulfonyl)imide in the high entropy flame retardant electrolyte is 0.6 mol / L, and the concentration of lithium difluorooxalatoborate in the high entropy flame retardant electrolyte is 0.5 mol / L.

[0086] The diluent is composed of ethoxy pentafluorocyclotriphosphazene (PFPN) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a volume ratio of 8:8; the volume percentage of the diluent in the high entropy flame retardant electrolyte is about 69.6%.

[0087] The remaining conditions are the same as in Example 1.

[0088] Example 3

[0089] The difference between this embodiment and embodiment 1 is that:

[0090] The organic solvent is composed of triethyl phosphate (TEP), dimethyl methylphosphonate (DMMP), tri(2,2,2-trifluoroethyl) phosphate (TFEP), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a volume ratio of 1:1:1:2:2; the volume percentage of the organic solvent in the high entropy flame retardant electrolyte is about 30.4%.

[0091] Among the lithium salts, the concentration of lithium bis(fluorosulfonyl)imide in the high entropy flame retardant electrolyte is 0.8 mol / L, and the concentration of lithium difluorooxalatoborate in the high entropy flame retardant electrolyte is 0.4 mol / L.

[0092] The diluent is composed of ethoxy pentafluorocyclotriphosphazene (PFPN) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a volume ratio of 9:7; the volume percentage of the diluent in the high entropy flame retardant electrolyte is about 69.6%.

[0093] The remaining conditions are the same as in Example 1.

[0094] Example 4

[0095] The difference between this embodiment and embodiment 1 is that:

[0096] The organic solvent is composed of triethyl phosphate (TEP), dimethyl methylphosphonate (DMMP), tri(2,2,2-trifluoroethyl) phosphate (TFEP), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a volume ratio of 2:1:1:1:1; the volume percentage of the organic solvent in the high entropy flame retardant electrolyte is about 33.3%.

[0097] The diluent is composed of ethoxy pentafluorocyclotriphosphazene (PFPN) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a volume ratio of 6:6; the volume percentage of the diluent in the high entropy flame retardant electrolyte is about 66.7%.

[0098] The remaining conditions are the same as in Example 1.

[0099] Example 5

[0100] The difference between this embodiment and embodiment 1 is that:

[0101] The organic solvent is composed of triethyl phosphate (TEP), dimethyl methylphosphonate (DMMP), tri(2,2,2-trifluoroethyl) phosphate (TFEP), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a volume ratio of 1:1:1:1:1; the volume percentage of the organic solvent in the high entropy flame retardant electrolyte is about 33.3%.

[0102] Among the lithium salts, the concentration of lithium bis(fluorosulfonyl)imide in the high entropy flame retardant electrolyte is 0.7 mol / L, and the concentration of lithium difluorooxalatoborate in the high entropy flame retardant electrolyte is 0.7 mol / L.

[0103] The remaining conditions are the same as in Example 1.

[0104] Example 6

[0105] This embodiment provides a high entropy flame retardant electrolyte, which has the following composition:

[0106] ①. Organic solvent: trimethyl phosphate (TMP), triethyl phosphate (TEP), dimethyl methylphosphonate (DMMP), tri(2,2,2-trifluoroethyl) phosphate (TFEP), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a volume ratio of 1:1:1:1:1:1; the volume percentage of the organic solvent in the high entropy flame retardant electrolyte is 60%.

[0107] ② Lithium salt: lithium borate oxalate (LiBOB) and lithium tetrafluorooxalate phosphate (LiTFOP), the concentration of lithium borate oxalate in the high entropy flame retardant electrolyte is 1.5 mol / L, and the concentration of lithium tetrafluorooxalate phosphate in the high entropy flame retardant electrolyte is 0.5 mol / L;

[0108] ③. Diluent: ethoxypentafluorocyclotriphosphazene (PFPN), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and bis(2,2,2-trifluoroethyl) ether (BTFE) in a volume ratio of 1:2:1; the volume percentage of the diluent in the high entropy flame retardant electrolyte is 40%.

[0109] ④. Additive: 1,3-propane sultone (1,3-PS), the concentration of 1,3-propane sultone in the high entropy flame retardant electrolyte is 10wt%.

[0110] Comparative Example 1

[0111] The electrolyte provided in this comparative example is formed by an organic solvent and a lithium salt, wherein the organic solvent is ethylene glycol dimethyl ether (DME), and the lithium salt is lithium bis(fluorosulfonyl)imide (the concentration of lithium bis(fluorosulfonyl)imide in the high entropy flame retardant electrolyte is 1.2 mol / L).

[0112] Comparative Example 2

[0113] The electrolyte provided in this comparative example is composed of an organic solvent, a lithium salt and an additive, wherein the organic solvent is composed of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a volume ratio of 1:1, and the lithium salt is composed of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium difluorooxalate borate (LiDFOB) (the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.6 mol / L, and the concentration of lithium difluorooxalate borate in the electrolyte is 0.5 mol / L). The additive is fluoroethylene carbonate (FEC), and the concentration of fluoroethylene carbonate in the high entropy flame retardant electrolyte is 5wt%.

[0114] Comparative Example 3

[0115] The electrolyte provided in this comparative example consists of an organic solvent and a lithium salt, wherein the organic solvent is triethyl phosphate (TEP) and the lithium salt is lithium bis(fluorosulfonyl)imide (the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 1.2 mol / L).

[0116] Comparative Example 4

[0117] The electrolyte provided in this comparative example consists of an organic solvent, a lithium salt and an additive, wherein the organic solvent consists of triethyl phosphate (TEP), dimethyl methylphosphonate (DMMP), tri(2,2,2-trifluoroethyl) phosphate (TFEP), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a volume ratio of 2:1:1:1:1; the lithium salt consists of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium difluorooxalatoborate (LiDFOB), the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.6 mol / L, and the concentration of lithium difluorooxalatoborate in the electrolyte is 0.6 mol / L; the additive is fluoroethylene carbonate (FEC), and the concentration of fluoroethylene carbonate in the electrolyte is 5wt%.

[0118] Comparative Example 5

[0119] The electrolyte provided in this comparative example is formed by a lithium salt, an organic solvent, a diluent and an additive, wherein the organic solvent is composed of triethyl phosphate (TEP) and ethylene glycol dimethyl ether (DME) in a volume ratio of 1:1; the lithium salt is composed of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium difluorooxalate borate (LiDFOB), the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.7 mol / L, and the concentration of lithium difluorooxalate borate in the electrolyte is 0.7 mol / L; the diluent is ethoxypentafluorocyclotriphosphazene (PFPN), and the volume ratio of PFPN to TEP is 5:1; the additive is fluoroethylene carbonate (FEC), and the concentration of fluoroethylene carbonate in the electrolyte is 5wt%.

[0120] Comparative Example 6

[0121] The difference between this comparative example and Example 1 is that the volume ratio of triethyl phosphate (TEP), dimethyl methylphosphonate (DMMP), tri(2,2,2-trifluoroethyl) phosphate (TFEP), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) is 0.2:0.2:0.1:2.5:3.

[0122] The rest is the same as in Example 1.

[0123] Comparative Example 7

[0124] The difference between this comparative example and Example 1 is that the volume percentage of the organic solvent in the electrolyte is 10%, and the volume percentage of the diluent is 90%.

[0125] The rest is the same as in Example 1.

[0126] Comparative Example 8

[0127] The difference between this comparative example and Example 1 is that the volume percentage of the organic solvent in the electrolyte is 70%, and the volume percentage of the diluent is 30%.

[0128] The rest is the same as in Example 1.

[0129] Comparative Example 9

[0130] The difference between this comparative example and Example 1 is that the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.05 mol / L, and the concentration of lithium difluorooxalatoborate in the electrolyte is 0.05 mol / L.

[0131] The rest is the same as in Example 1.

[0132] Comparative Example 10

[0133] The difference between this comparative example and Example 1 is that the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 2 mol / L, and the concentration of lithium difluorooxalatoborate in the electrolyte is 2 mol / L.

[0134] The rest is the same as in Example 1.

[0135] Comparative Example 11

[0136] The difference between this comparative example and Example 1 is that the mass fraction of the additive in the electrolyte is 0.1%.

[0137] The rest is the same as in Example 1.

[0138] Comparative Example 12

[0139] The difference between this comparative example and Example 1 is that the mass fraction of the additive in the electrolyte is 15%.

[0140] The rest is the same as in Example 1.

[0141] Furthermore, for the convenience of comparison, the components and dosages of the high entropy flame retardant electrolytes of Examples 1 to 5 and Comparative Examples 1 to 6 are statistically shown in Table 1.

[0142] Table 1 Statistics of high entropy flame retardant electrolyte composition and dosage

[0143]

[0144]

[0145] Test example

[0146] (1) A certain amount of the electrolytes obtained in Example 1, Comparative Example 1 and Comparative Example 6 were placed in containers respectively, and the self-extinguishing time of the electrolytes was recorded after ignition. The results were as follows: the high entropy flame-retardant electrolyte of Example 1 could not be ignited, the self-extinguishing time of the electrolyte of Comparative Example 1 after ignition was 50 s / g, and the self-extinguishing time of the electrolyte of Comparative Example 6 after ignition was 15 s / g.

[0147] Table 2, Table 3 and Table 4 respectively record the test results of the limiting oxygen index of the high entropy flame retardant electrolyte of Example 1, Comparative Example 1 and Comparative Example 6.

[0148] Table 2 Test results of limiting oxygen index of high entropy flame retardant electrolyte of Example 1

[0149] Oxygen concentration (volume fraction) / % 25.0 27.0 30.0 40.0 35.0 32.0 33.0 Burning time / s non-flammable non-flammable non-flammable >60 >60 non-flammable >60

[0150] Table 3 Test results of limiting oxygen index of electrolyte of comparative example 1

[0151] Oxygen concentration (volume fraction) / % 18.0 17.0 16.0 (Instrument limit) Burning time / s >60 >60 >60

[0152] Table 4 Test results of limiting oxygen index of electrolyte of comparative example 6

[0153] Oxygen concentration (volume fraction) / % 20.0 22.0 24.0 26.0 25.0 24.5 Burning time / s non-flammable non-flammable non-flammable >60 >60 non-flammable

[0154] It can be seen from Table 2 that the test result of the limiting oxygen index of Example 1 is 33%. The high entropy flame retardant electrolyte of Example 1 has a flame retardant characteristic and good safety performance.

[0155] It can be seen from Table 3 that the electrolyte limiting oxygen index of Comparative Example 1 is below 16%, which is flammable.

[0156] It can be seen from Table 4 that the electrolyte limiting oxygen index of Comparative Example 6 is 25%, which has flammable characteristics.

[0157] (2) The electrolytes prepared in Example 2 and Comparative Example 2 were respectively used to assemble Li-Al button cells, and the electrochemical window of the electrolyte was analyzed. The button cell preparation process includes the following steps: The assembly process of the CR2025 button cell was carried out in a glove box filled with argon gas, and the water oxygen content in the glove box was kept less than 0.01ppm. A lithium sheet with a diameter of 15.6mm was used for the negative electrode, an aluminum sheet with a diameter of 14mm was used for the positive electrode, and a double-layer polypropylene (PP) diaphragm was used for the diaphragm. The positive electrode shell, positive electrode, diaphragm, negative electrode, stainless steel sheet, spring sheet, and negative electrode shell were placed in order, and 60μL of electrolyte was injected. The button cell was sealed with a battery sealer and taken out of the glove box for testing.

[0158] The lithium-aluminum battery was tested by linear sweep voltammetry (LSV) using an electrochemical workstation at a scan rate of 0.5 mV / s. Figure 1 As shown by Figure 1 It can be seen that the high entropy flame retardant electrolyte prepared in Example 2 begins to decompose at about 5V and has a wide electrochemical window. The electrochemical window of the electrolyte prepared in Comparative Example 2 is only about 4V, which cannot match the high voltage positive electrode material.

[0159] (3) The electrolytes prepared in Example 2 and Comparative Example 2 were respectively used to assemble lithium metal batteries, and the electrochemical properties of the electrolytes were analyzed. The preparation process of the lithium metal battery was referred to the above-mentioned Li-Al button battery assembly process, except that the positive electrode used lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1 O 2 , NCM811) pole piece. The preparation process of NCM811 pole piece includes the following steps: NCM811 main material, conductive graphite, and binder are mixed in a mass ratio of 8:1:1, and an appropriate amount of N-methylpyrrolidone (NMP) is added and stirred evenly. The prepared slurry is evenly coated on the metal aluminum foil, and the slurry thickness is controlled to 100μm. After drying in a vacuum oven at 120℃ for more than 12 hours, a positive pole piece with a diameter of 14mm is obtained.

[0160] The first cycle charge and discharge curve of the Li-NCM battery of Example 2 at a rate of 0.1C is as follows: Figure 2 As shown by Figure 2 It can be seen that the charge and discharge voltage range is 3.0-4.3 V, and the first cycle discharge capacity of NCM811 is 198 mAh / g. The Li-NCM battery of Comparative Example 2 cannot be charged and discharged normally.

[0161] (4) Li-Li symmetrical batteries were assembled using the high entropy flame-retardant electrolytes prepared in Example 3 and Comparative Example 3, respectively. The preparation process was similar to the above-mentioned Li-Al button battery assembly process, except that both the positive and negative electrodes of the Li-Li symmetrical battery used metal lithium sheets with a diameter of 15.6 mm.

[0162] The Li-Li symmetric battery of Example 3 is 0.5 mA / cm 2 The cycle curve under current density is as follows Figure 3 As shown by Figure 3 It can be seen that the overpotential is within 60mV and can be stably cycled for 500 hours.

[0163] The AC impedance spectra of the Li-Li symmetrical batteries assembled in Example 3 and Comparative Example 3 are shown in Figure 4 As shown by Figure 4 It can be seen that the interface impedance between Example 3 and the lithium metal negative electrode is about 500Ω. However, the Li-Li battery of Comparative Example 3 cannot be stably cycled, which is due to the poor interface compatibility between TEP and the lithium metal negative electrode, and the interface impedance between Comparative Example 3 and the lithium metal negative electrode is as high as 1000Ω.

[0164] (5) Li-LFP batteries were assembled from Example 4 and Comparative Example 4 respectively. The preparation process was similar to the preparation process of the Li-NCM811 battery, except that the positive electrode used lithium iron phosphate material and the charge and discharge voltage range was 2.5V to 4.2V. Figure 5 As shown, the first cycle capacity of the Li-LFP battery of Example 4 is 159 mAh / g at 0.1C, and the capacity retention rate is 96% after 100 cycles. The first cycle capacity of the Li-LFP battery of Comparative Example 4 is 114 mAh / g at 0.1C, and the capacity retention rate is 82% after 60 cycles.

[0165] (6) Example 5 and Comparative Example 5 were assembled into Li-NCM811 batteries respectively. Figure 6 As shown, the discharge capacity of the Li-NCM811 battery of Example 5 is 181 mAh / g at 0.1C, and the capacity retention rate is 93% after 100 cycles. The discharge capacity of the Li-NCM811 battery of Comparative Example 5 is 147 mAh / g at 0.1C, and the capacity retention rate is 72% after 100 cycles.

[0166] (7) A conductivity meter was used to test Example 1, Comparative Example 7, Comparative Example 8, Comparative Example 9, and Comparative Example 10. According to the test results, the conductivity of Example 1 was 8.2 mS / cm; the lithium salt in Comparative Example 7 was not completely dissolved, and the electrolyte was turbid; the conductivity of Comparative Example 8 was 2.3 mS / cm; the conductivity of Comparative Example 9 was 0.96 mS / cm; and the conductivity of Comparative Example 10 was 4.1 mS / cm.

[0167] (8) Li-Cu batteries were assembled from Example 1, Comparative Examples 11 and 12 respectively. The preparation process was similar to the preparation process of the Li-Al battery, except that the Li-Cu battery used a copper foil with a diameter of 14 mm as the positive electrode. The coulombic efficiency of the electrolyte was tested using the Li-Cu battery. Figure 7 As shown, the coulombic efficiency of Example 1 is 97.6%, the coulombic efficiency of Comparative Example 11 is 96.6%, and the coulombic efficiency of Comparative Example 12 is 95.4%.

[0168] In summary, the high entropy flame retardant electrolyte provided by the present invention has at least the following advantages:

[0169] (1) The high entropy flame retardant electrolyte proposed in the present invention can utilize the good reduction stability of ether solvents to improve coulombic efficiency; at the same time, the high entropy flame retardant electrolyte increases the diversity of components, improves the disorder of the electrolyte, adjusts the solvation structure, and generates a stable and inorganic-rich SEI film at the lithium negative electrode interface, thereby improving the electrochemical performance.

[0170] (2) The high entropy flame retardant electrolyte proposed in the present invention significantly improves the safety performance of ether solvents through the flame retardant properties of phosphate solvents. At the same time, the entropy increase of the electrolyte can improve the electrolyte solvation structure, reduce the content of free solvent in the electrolyte, and widen the electrochemical window.

[0171] (3) The high entropy flame-retardant electrolyte proposed in the present invention is used for lithium metal batteries, which can take into account the safety performance and electrochemical performance requirements of lithium metal batteries. When used with NCM, LFP, and LCO positive electrodes, it can provide good electrochemical performance and safety performance.

[0172] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high entropy flame retardant electrolyte, characterized in that: The high entropy flame retardant electrolyte comprises 20% to 60% of an organic solvent in terms of volume percentage; The organic solvent comprises a phosphate solvent and an ether solvent in a volume ratio of (0.5-5):(0.5-5).

2. The high entropy flame retardant electrolyte according to claim 1, characterized in that: The phosphate ester solvent includes at least two of trimethyl phosphate, triethyl phosphate, dimethyl methylphosphonate, diethyl ethylphosphonate, triphenyl phosphate, triphenyl phosphite, triallyl phosphate, tris(hexafluoroisopropyl) phosphate, tris(trimethylsilyl) phosphite, tris(trimethylsilyl) phosphate and tris(2,2,2-trifluoroethyl) phosphate; Preferably, each phosphate ester solvent accounts for at least 10% of the total volume of the organic solvent.

3. The high entropy flame retardant electrolyte according to claim 1, characterized in that: The ether solvent includes at least two of ethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxypropane, diethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and 1,4-dioxane; Preferably, each ether solvent accounts for at least 10% of the total volume of the organic solvent.

4. The high entropy flame retardant electrolyte according to any one of claims 1 to 3, characterized in that: The organic solvent contains at least five types of phosphate ester solvents and ether solvents.

5. The high entropy flame retardant electrolyte according to any one of claims 1 to 3, characterized in that: The high entropy flame retardant electrolyte also includes a lithium salt; Preferably, the lithium salt includes at least two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(trifluoromethanesulfonylimide), lithium bis(fluorosulfonylimide), lithium difluorophosphate, lithium difluorobis(oxalatophosphate) and lithium tetrafluorooxalatophosphate; Preferably, each lithium salt accounts for at least 25% of the total mass of the lithium salts; Preferably, the total concentration of lithium ions in the high entropy flame retardant electrolyte is 0.2 mol / L to 2 mol / L.

6. The high entropy flame retardant electrolyte according to any one of claims 1 to 3, characterized in that: The high entropy flame retardant electrolyte also includes a diluent; Preferably, the diluent comprises at least two of ethoxypentafluorocyclotriphosphazene, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether and 2,2,2-trifluoroethyl-1,1,2,2-tetrafluoroethyl ether; Preferably, each diluent comprises at least 20% of the total volume of the diluent; Preferably, the volume content of the diluent in the high entropy flame retardant electrolyte is 40% to 80%.

7. The high entropy flame retardant electrolyte according to any one of claims 1 to 3, characterized in that: The high entropy flame retardant electrolyte further includes an additive; Preferably, the additive includes at least one of fluoroethylene carbonate, vinylene carbonate, vinyl carbonate and 1,3-propane sultone; Preferably, the mass fraction of the additive in the high entropy flame retardant electrolyte is 0.2% to 10%.

8. The high entropy flame retardant electrolyte according to claim 1, characterized in that: The high entropy flame retardant electrolyte comprises an organic solvent, a lithium salt, a diluent and an additive; The organic solvent is composed of triethyl phosphate, dimethyl methylphosphonate, tri(2,2,2-trifluoroethyl) phosphate, ethylene glycol dimethyl ether and 1,3-dioxolane; the lithium salt is composed of lithium bis(fluorosulfonyl)imide and lithium difluorooxalatoborate; the diluent is composed of ethoxypentafluorocyclotriphosphazene and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; and the additive is fluoroethylene carbonate.

9. A method for preparing a high entropy flame retardant electrolyte according to any one of claims 1 to 8, characterized in that: The following steps are involved: Mixing various components of the high entropy flame retardant electrolyte according to a proportion; Preferably, when the high entropy flame retardant electrolyte contains an organic solvent, a lithium salt, a diluent and an additive, the preparation of the high entropy flame retardant electrolyte comprises: firstly mixing a phosphate ester solvent and an ether solvent to obtain an organic solvent; The lithium salt is dissolved in the organic solvent, and then the diluent and the additive are added. The electrolyte preparation is performed in a glove box filled with argon gas throughout the process, and the water and oxygen content in the glove box is maintained at less than 0.01 ppm.

10. A lithium metal battery, characterized in that: The lithium metal battery contains the high entropy flame retardant electrolyte according to any one of claims 1 to 8.

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