An electrolyte and its preparation method, and a lithium metal battery containing the same

Abstract

The present invention provides an electrolyte, a preparation method thereof, and a lithium metal battery containing the same. The electrolyte includes a lithium salt, an organic solvent, a diluent, and an additive. The additive includes a pyridine ring containing one lone pair of electrons and one nitrogen as shown in Formula 1, wherein at least one of the substituents R1 to R4 contains C n F 2n+1 , n≥0; the diluent includes a fluoroether, and the organic solvent includes a phosphate ester solvent. The electrolyte prepared by the present invention has high safety performance and electrochemical performance when applied to a lithium metal battery.

Description

Technical Field

[0001] The present invention relates to the field of lithium metal batteries, and relates to an electrolyte, and particularly relates to an electrolyte, a preparation method thereof, and a lithium metal battery containing the same. Background Art

[0002] In today's society, lithium-ion batteries have become an essential part of our lives. Whether it is a mobile phone, a Bluetooth headset, a laptop computer, or a new energy vehicle, they all rely on lithium-ion batteries for power supply. With the improvement of people's living standards, in order to meet the energy density requirements of products for lithium-ion batteries, in addition to using materials with a relatively high theoretical capacity for the positive electrode, materials such as silicon, copper-lithium composite tape, and lithium metal with a relatively large specific capacity are also being used synchronously for the negative electrode. However, as the theoretical capacity of the positive and negative electrode materials increases, the problems that the electrolyte needs to challenge become greater.

[0003] CN111769325A discloses a lithium-ion battery electrolyte and a lithium-ion battery for improving high and low temperature cycle performance. The electrolyte contains a sulfur-containing polyfunctional electrolyte additive, that is, lithium dithioglycolate borate or lithium dithioglycolate phosphate, which has a lower film-forming impedance, and the obtained battery has higher cycle performance.

[0004] CN105206875A discloses an electrolyte for improving the cycle performance of a lithium-ion battery negative electrode material. The organic solvent includes a cyclic carbonate and a linear carbonate, and the electrolyte additive includes tris(2,2,2-trifluoroethyl) borate, which effectively improves the cycle performance, charge and discharge efficiency, and rate performance of the negative electrode material.

[0005] The above electrolytes all use carbonate-based electrolytes, which are flammable under safety tests (such as short circuit, puncture, collision, overcharge, high temperature, etc.), and there are potential safety hazards. Therefore, it is urgent to find new solvents, additives, solvent-solute systems, etc.

[0006] How to prepare an electrolyte with high safety performance and high electrochemical performance is an important research direction in this field. Summary of the Invention

[0007] The purpose of the present invention is to provide an electrolyte with high safety performance and electrochemical performance, a preparation method thereof, and a lithium metal battery containing the same.

[0008] To achieve the purpose of this invention, the following technical solutions are adopted:

[0009] One of the purposes of the present invention is to provide an electrolyte, the electrolyte includes a lithium salt, an organic solvent, a diluent, and an additive, and the additive includes a pyridine ring with one lone pair of electrons containing one nitrogen, wherein at least one of the substituents R1 to R4 contains Cn F 2n+1 , n ≥ 0, where the value of n can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable. The diluent includes fluoroether, and the organic solvent includes phosphate solvents.

[0010] The present invention selects fluoroether with a low dielectric constant as the diluent, effectively reducing the overall viscosity of the electrolyte, improving the wettability of the electrolyte to the electrode sheet and the separator, and alleviating polarization. The present invention selects a pyridine ring containing one lone pair of electrons of nitrogen as the additive, and R1 - R4 are perfluorinated molecular chains (both polyfluoro and monofluoro are acceptable, —C n F 2n+1 , n ≥ 0), and at least one of R1 - R4 is connected with a perfluorinated molecular chain, and it is not necessary for all of them to have it simultaneously. If there are two or more perfluorinated molecular chains, the number of fluorine-containing molecules can be the same or different.

[0011] The additive selected by the present invention has the following advantages: The additive decomposes on the surface of Li, participates in the construction of SEI, enables Li to be evenly deposited on the surface of lithium metal, and effectively inhibits the side reaction between lithium metal and the electrolyte; the additive decomposes on the surface of lithium metal to generate relatively dense LiF and pyridine rings, enhancing the conductivity between the electrolyte and the surface of lithium metal; the pyridine ring has a lone pair of electrons acting as a Lewis base, and the uniform deposition of lithium can be guided to the empty orbital of Li + through acid-base interaction, thereby forming a flat and dense film on the surface of lithium metal; the flat and relatively dense SEI film covers the surface of lithium metal, which can effectively prevent the generation of holes, reduce the loss of the electrolyte and active lithium, and improve the cycling performance of the base electrolyte.

[0012] The present invention selects phosphate solvents, and selects non-flammable phosphates as solvents, increasing the safety performance of the battery. The phosphate solvents have a lower LUMO, can enhance the overall reducibility of the electrolyte, and the cycling performance of the phosphate solvents is superior to that of carbonate electrolytes.

[0013] As a preferred technical solution of the present invention, the additive includes any one or a combination of at least two of pentafluoropyridine, 2-fluoropyridine, 3-fluoropyridine, 2,3,6-trifluoropyridine, 2,5-difluoropyridine, 3,5-difluoropyridine, 2,3,5-trifluoropyridine, 2,4-difluoropyridine, 2,6-difluoropyridine, 2,3-difluoropyridine or 2,3,5,6-tetrafluoropyridine. Typical but non-limiting examples of the combination include: the combination of pentafluoropyridine and 2-fluoropyridine, the combination of 2,3,6-trifluoropyridine and 2,5-difluoropyridine, the combination of 3,5-difluoropyridine and 2,3,5-trifluoropyridine, the combination of 2,4-difluoropyridine and 2,6-difluoropyridine, or the combination of 2,3-difluoropyridine and 2,3,5,6-tetrafluoropyridine, etc.

[0014] Preferably, based on the mass of the electrolyte being 100%, the mass fraction of the additive in the electrolyte is 0.1-10%. The mass fraction can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably 0.2-5.5%.

[0015] As a preferred technical solution of the present invention, the fluoroether includes any one or a combination of at least two of bis(2,2,2-trifluoroethyl) ether, fluoromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether, eicosadecafluoro-15-crown-5-ether, phenyl trifluoromethyl sulfide, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, pentafluorophenyl sulfide, ethyl trifluoromethyl ether, oxyfluorfen, acifluorfen, difluoromethyl 2,2,3,3,3-pentafluoropropyl ether, allyl pentafluorophenyl ether, heptafluoropropyl 1,2,2,2-tetrafluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, heptafluoroisopropyl methyl ether, 2-fluorophenyl allyl ether, bis-(1,2,2,2-tetrafluoroethyl) ether, 2-iodotetrafluoroethyl trifluoromethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, ethyl 1,1,2,3,3,3-hexafluoropropylether, methyl 2,2,3,3,3-pentafluoropropyl ether, perfluoromethyl isopropyl ether, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, 1-chloro-2,2,2-trifluoroethyl difluoromethyl ether, 3-bromo-4'-fluorodiphenyl ether, 2H-hexafluoropropyl allyl ether, allyl 2,2,2-trifluoroethyl ether, allyl 1,1,2,2-tetrafluoroethyl ether, allyl 2,2,3,3,3-pentafluoropropyl ether, allyl 2,2,3,3-tetrafluoropropyl ether, 2-fluorophenyl 2-nitrophenyl ether, allyl 2,2,3,3,4,4,5,5-octafluoropentyl ether, octyl [2-(trifluoromethyl)phenyl] ether, allyl 1H,1H-heptafluorobutyl ether, perfluorobutyl methyl ether, 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether or 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether. Typical but non-limiting examples of the combination include: the combination of bis(2,2,2-trifluoroethyl) ether and fluoromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether; the combination of eicosadecafluoro-15-crown-5-ether and phenyl trifluoromethyl sulfide; the combination of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether and pentafluorophenyl sulfide; the combination of ethyl trifluoromethyl ether, oxyfluorfen and acifluorfen; the combination of difluoromethyl 2,2,3,3,3-pentafluoropropyl ether, allyl pentafluorophenyl ether, heptafluoropropyl 1,2,2,2-tetrafluoroethyl ether and difluoromethyl 2,2,3,3-tetrafluoropropyl ether; the combination of heptafluoroisopropyl methyl ether and 2-fluorophenyl allyl ether; the combination of bis-(1,2,2,2-tetrafluoroethyl) ether and 2-iodotetrafluoroethyl trifluoromethyl ether; the combination of 1,1,2,2-tetrafluoroethyl ethyl ether and ethyl 1,1,2,3,3,3-hexafluoropropylether; the combination of methyl 2,2,3,3,3-pentafluoropropyl ether and perfluoromethyl isopropyl ether; the combination of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether and 1-chloro-2,2,Combinations such as 2-trifluoroethyl difluoromethyl ether, combination of 3-bromo-4'-fluorodiphenyl ether and 2H-hexafluoropropyl allyl ether, combination of allyl 2,2,2-trifluoroethyl ether and allyl 1,1,2,2-tetrafluoroethyl ether, combination of allyl 2,2,3,3,3-pentafluoropropyl ether and allyl 2,2,3,3-tetrafluoropropyl ether, combination of 2-fluorophenyl 2-nitrophenyl ether and allyl 2,2,3,3,4,4,5,5-octafluoropentyl ether, combination of octyl [2-(trifluoromethyl)phenyl] ether and allyl 1H, combination of 1H-heptafluorobutyl ether and perfluorobutyl methyl ether, or combination of 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, etc.

[0016] Preferably, taking the volume of the electrolyte as 100%, the volume fraction of the diluent in the electrolyte is 51-90%, where the volume fraction can be 51%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0017] As a preferred technical solution of the present invention, the phosphate ester solvents include any one or a combination of at least two of triethyl phosphate, trimethyl phosphate, tris(trifluoroethyl) phosphate, tripropargyl phosphate or triphenyl phosphite, and typical but non-limiting examples of the combination are: combination of triethyl phosphate and trimethyl phosphate, combination of trimethyl phosphate and tris(trifluoroethyl) phosphate, combination of tris(trifluoroethyl) phosphate and tripropargyl phosphate, or combination of tripropargyl phosphate and triphenyl phosphite, etc.

[0018] Preferably, the organic solvent further includes any one or a combination of at least two of ether solvents, sulfone solvents or nitrile solvents, and typical but non-limiting examples of the combination are: combination of ether solvents and sulfone solvents, combination of sulfone solvents and nitrile solvents, or combination of ether solvents and nitrile solvents, etc.

[0019] Preferably, the ether solvent includes any one or a combination of at least two of ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol dimethyl ether, o-dimethoxybenzene, m-dimethoxybenzene, isosorbide dimethyl ether, pinitol dimethyl ether, o-dimethoxybenzene, ethylene glycol butyl ether, boron trifluoride dimethyl ether, ethylene glycol propyl ether, ethylene glycol dibutyl ether, ethylene glycol monohexyl ether, tris(ethylene glycol) divinyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monolauryl ether, ethylene glycol tert-butyl ether, triethylene glycol butyl methyl ether, ethylene glycol methyl ether, tetraethylene glycol monolauryl ether, hexaethylene glycol monododecyl ether, ethylene glycol monopentyl ether or isosorbide dimethyl ether. Typical but non-limiting examples of the combination include: a combination of ethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether, a combination of triethylene glycol dimethyl ether and diethylene glycol dimethyl ether, a combination of o-dimethoxybenzene and m-dimethoxybenzene, a combination of isosorbide dimethyl ether and pinitol dimethyl ether, a combination of ethylene glycol and ethylene glycol methyl ether, a combination of ethylene glycol methyl ether and o-dimethoxybenzene, a combination of ethylene glycol butyl ether and boron trifluoride dimethyl ether, a combination of ethylene glycol phenyl ether and ethylene glycol propyl ether, a combination of ethylene glycol butyl ether and ethylene glycol dibutyl ether, a combination of ethylene glycol monohexyl ether and tris(ethylene glycol) divinyl ether, a combination of tetraethylene glycol monomethyl ether and ethylene glycol monolauryl ether, a combination of ethylene glycol tert-butyl ether and triethylene glycol butyl methyl ether, a combination of ethylene glycol methyl ether and tetraethylene glycol monolauryl ether, a combination of hexaethylene glycol monododecyl ether and ethylene glycol phenyl ether, or a combination of ethylene glycol monopentyl ether and isosorbide dimethyl ether.

[0020] Preferably, the sulfone solvent includes any one or a combination of at least two of tetramethylene sulfoxide, sulfolane, ethyl methyl sulfone, bis(4-fluorophenyl) sulfone, phenyl trifluoromethyl sulfone, 4-fluorophenyl methyl sulfone, 4-chlorophenyl phenyl sulfone, bis(3-aminophenyl) sulfone, phenyl vinyl sulfone, nitromethyl phenyl sulfone, dimethyl sulfone, phenyl p-tolyl sulfone, 3-bromophenyl methyl sulfone, dimethyl sulfoxide or bromodifluoromethyl phenyl sulfone. Typical but non-limiting examples of the combination include: a combination of tetramethylene sulfoxide and sulfolane, a combination of sulfolane and ethyl methyl sulfone, a combination of ethyl methyl sulfone and bis(4-fluorophenyl) sulfone, a combination of phenyl trifluoromethyl sulfone and 4-fluorophenyl methyl sulfone, a combination of 4-fluorophenyl methyl sulfone and 4-chlorophenyl phenyl sulfone, a combination of 4-chlorophenyl phenyl sulfone and bis(3-aminophenyl) sulfone, a combination of phenyl vinyl sulfone and nitromethyl phenyl sulfone, a combination of dimethyl sulfone and phenyl p-tolyl sulfone, a combination of 3-bromophenyl methyl sulfone and dimethyl sulfoxide, or a combination of dimethyl sulfoxide and bromodifluoromethyl phenyl sulfone, etc.

[0021] Preferably, the nitrile solvent includes any one or a combination of at least two of ethoxy (pentafluoro) cyclotriphosphazene, fumaronitrile, 3,4,5,6-tetrafluorophthalonitrile, 2-butenenitrile, diaminomaleic dinitrile, 2-methyl-3-butenenitrile or 2-methyl-2-butenenitrile, wherein typical but non-limiting examples of the combination include: a combination of ethoxy (pentafluoro) cyclotriphosphazene and fumaronitrile, a combination of fumaronitrile and 3,4,5,6-tetrafluorophthalonitrile, a combination of 2-butenenitrile and diaminomaleic dinitrile, or a combination of 2-methyl-3-butenenitrile and 2-methyl-2-butenenitrile, etc.

[0022] As a preferred technical solution of the present invention, taking the volume of the electrolyte as 100%, the volume fraction of the organic solvent in the electrolyte is 10 to 49%, wherein the volume fraction can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 49%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are also applicable, preferably 15 to 45%.

[0023] Preferably, with the volume of the organic solvent being 100%, the volume fraction of the phosphate ester solvent in the organic solvent is 50-95%, wherein the volume fraction can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95%, etc., but is not limited to the listed values. Other values not listed within this numerical range are also applicable, preferably 25-75%.

[0024] Preferably, with the volume of the organic solvent being 100%, the volume fraction of the ether solvent in the organic solvent is 5 to 50%, wherein the volume fraction can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc., but is not limited to the listed values. Other values not listed within this numerical range are also applicable, preferably 10 to 40%.

[0025] Preferably, with the volume of the organic solvent as 100%, the volume fraction of the sulfone solvent in the electrolyte is 5 to 50%, wherein the volume fraction can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc., but is not limited to the listed values. Other values not listed within this numerical range are also applicable, preferably 10 to 40%.

[0026] Preferably, taking the volume of the organic solvent as 100%, the volume fraction of the nitrile solvent in the electrolyte is 5-50%, where the volume fraction can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable, preferably 10-40%.

[0027] As a preferred technical solution of the present invention, the lithium salt includes any one or a combination of at least two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium metaphosphate, lithium iodate, lithium bis(ethylenedioxy)borate, lithium trifluoroacetate, lithium difluoroacetate, lithium hexafluorosilicate, lithium tri-n-butylmagnesate, lithium hexafluoroantimonate, lithium bis(trimethylsilyl)amide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(nonafluorobutanesulfonyl)imide, lithium hexafluorostannate, lithium ethylenediaminetetraacetate, lithium hexafluoroarsenate, lithium diisopropylbutylmagnesium, lithium 2,2-dipropylacetate, lithium sulfopyruvate, lithium 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide, lithium tris(1,2-dimethoxyethyl)tetraphenylborate, lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide or lithium bis(pentafluoroethylsulfonyl)imide. Typical but non-limiting examples of the combination include: the combination of lithium hexafluorophosphate and lithium tetrafluoroborate, the combination of lithium bis(oxalato)borate and lithium difluoro(oxalato)borate, the combination of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide and lithium trifluoromethanesulfonate, the combination of lithium metaphosphate and lithium iodate, the combination of lithium bis(ethylenedioxy)borate and lithium trifluoroacetate, the combination of lithium difluoroacetate and lithium hexafluorosilicate, the combination of lithium tri-n-butylmagnesate and lithium hexafluoroantimonate, the combination of lithium bis(trimethylsilyl)amide and lithium bis(trifluoromethanesulfonyl)imide, the combination of lithium bis(nonafluorobutanesulfonyl)imide and lithium hexafluorostannate, the combination of lithium ethylenediaminetetraacetate and lithium hexafluoroarsenate, the combination of lithium diisopropylbutylmagnesium and lithium 2,2-dipropylacetate, the combination of lithium sulfopyruvate and lithium 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide, the combination of lithium tris(1,2-dimethoxyethyl)tetraphenylborate and lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide or the combination of lithium bis(pentafluoroethylsulfonyl)imide and lithium metaphosphate.

[0028] Preferably, the concentration of the lithium salt in the electrolyte is 0.5 - 6 M, where the concentration can be 0.5 M, 1.0 M, 1.2 M, 1.5 M, 1.6 M, 1.7 M, 1.8 M, 1.9 M, 2.0 M, 2.1 M, 2.2 M, 2.3 M, 2.4 M, 2.5 M, 2.6 M, 2.7 M, 2.8 M, 2.9 M, 3 M, 3.1 M, 3.2 M, 3.3 M, 3.4 M, 3.5 M, 3.6 M, 3.7 M, 3.8 M, 3.9 M, 4.0 M, 4.1 M, 4.2 M, 4.3 M, 4.4 M, 4.5 M, 4.6 M, 4.7 M, 4.8 M, 4.9 M, 5.0 M, 5.1 M, 5.2 M, 5.3 M, 5.4 M, 5.6 M, 5.7 M, 5.8 M, 5.9 M or 6.0 M, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0029] A second object of the present invention is to provide a method for preparing an electrolyte as described in the first object, and the preparation method includes:

[0030] Dissolve the lithium salt in an organic solvent, and then sequentially add a diluent and an additive for mixing to obtain the electrolyte.

[0031] As a preferred technical solution of the present invention, the temperature of the mixing is 25 - 50 °C, where the temperature can be 25 °C, 28 °C, 30 °C, 32 °C, 34 °C, 36 °C, 38 °C, 40 °C, 42 °C, 44 °C, 46 °C, 48 °C or 50 °C, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0032] A third object of the present invention is to provide a lithium metal battery, which is characterized in that the lithium metal battery includes the electrolyte as described in the first object, and the lithium metal battery further includes a positive electrode plate and a negative electrode plate.

[0033] As a preferred technical solution of the present invention, the active material of the positive electrode plate includes any one or a combination of at least two of lithium cobaltate, lithium iron phosphate, nickel cobalt manganese ternary positive electrode material, lithium manganate or lithium iron phosphate.

[0034] Preferably, the active material of the negative electrode plate includes a copper-lithium composite tape or a lithium foil.

[0035] Preferably, the thickness of copper in the copper-lithium composite tape is 4 - 12 μm, where the thickness can be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm or 12 μm, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0036] Preferably, lithium layers are attached to both sides of the copper in the copper-lithium composite strip, and the thickness of each lithium layer is 5-50 μm. The thickness can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0037] Preferably, the thickness of the lithium foil is 10-2000 μm. The thickness can be 10 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1000 μm, 1200 μm, 1400 μm, 1600 μm, 1800 μm or 2000 μm, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0038] The numerical ranges described in the present invention include not only the point values listed above, but also any point values between the above-mentioned numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the ranges.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] The electrolyte prepared by the present invention is applied to a lithium metal battery, has high safety performance and electrochemical performance. The capacity retention rate at the 40th cycle can reach more than 94%, and the Coulomb efficiency can reach more than 99%. Compared with a soft-pack battery with a capacity retention rate lower than 80% and a Coulomb efficiency lower than 90%, it has a high capacity retention rate and Coulomb efficiency. Description of the Drawings

[0041] Figure 1 It is a qualitative analysis diagram of the electrolyte in Example 1 of the present invention.

[0042] Figure 2 It is a qualitative analysis diagram of the electrolyte in Comparative Example 1 of the present invention. Detailed Description of the Invention

[0043] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0044] Example 1

[0045] This example provides an electrolyte:

[0046] The electrolyte includes an organic solvent, a diluent, an additive, and a lithium salt.

[0047] The organic solvent includes: based on the volume of the organic solvent being 100%, the volume fraction of triethyl phosphate in the organic solvent is 75%, and the volume fraction of ethylene glycol dimethyl ether in the organic solvent is 25%;

[0048] The diluent includes: 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether;

[0049] The additive includes: 2-fluoropyridine;

[0050] The lithium salt: lithium bis(fluorosulfonyl)imide with a concentration of 1.5 M in the electrolyte;

[0051] Based on the mass of the electrolyte being 100%, by mass fraction, the organic solvent, diluent, and lithium salt account for 99.5% of the electrolyte, and the additive accounts for 0.5% of the electrolyte. By volume fraction, the diluent accounts for 60% of the electrolyte.

[0052] The qualitative analysis diagram of the electrolyte prepared in this example is as Figure 1 shown. Among them, solvent impurity 1 and solvent impurity 2 in the figure are impurities in acetone introduced by the test method, and butyl butyrate is the internal standard for testing the 2-fluoropyridine additive; however, 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether has a low boiling point, so the peak cannot be detected by this test method.

[0053] Example 2

[0054] This example provides an electrolyte:

[0055] The electrolyte includes an organic solvent, a diluent, an additive, and a lithium salt.

[0056] The organic solvent includes: based on the volume of the organic solvent being 100%, the volume fraction of tris(trifluoroethyl) phosphate in the organic solvent is 70%, and the volume fraction of diaminomaleonitrile in the organic solvent is 30%;

[0057] The diluent includes: bis-(1,2,2,2-tetrafluoroethyl) ether;

[0058] The additive includes: 2,3-difluoropyridine;

[0059] The lithium salt: lithium tributylmagnesate with a concentration of 1 M in the electrolyte;

[0060] Based on the mass of the electrolyte being 100%, by mass fraction, the organic solvent, diluent, and lithium salt account for 99.25% of the electrolyte, and the additive accounts for 0.75% of the electrolyte. By volume fraction, the diluent accounts for 55% of the electrolyte.

[0061] Example 3

[0062] This example provides an electrolyte:

[0063] The electrolyte includes an organic solvent, a diluent, an additive, and a lithium salt.

[0064] The organic solvent includes: based on the volume of the organic solvent being 100%, tris(trifluoroethyl) phosphate accounts for 66.66% of the volume of the organic solvent, and dicyanomaleonitrile accounts for 33.33% of the volume of the organic solvent;

[0065] The diluent includes: bis-(1,2,2,2-tetrafluoroethyl) ether;

[0066] The additive includes: 2,3-difluoropyridine;

[0067] The lithium salt: tributylmagnesium lithium with a concentration of 3M in the electrolyte;

[0068] Based on the mass of the electrolyte being 100%, by mass fraction, the organic solvent, the diluent, and the lithium salt account for 99% of the mass of the electrolyte, and the additive accounts for 1.0% of the mass of the electrolyte. By volume fraction, the diluent accounts for 75% of the volume of the electrolyte.

[0069] Example 4

[0070] This example provides an electrolyte:

[0071] The electrolyte includes an organic solvent, a diluent, an additive, and a lithium salt.

[0072] The organic solvent includes: based on the volume of the organic solvent being 100%, triethyl phosphate accounts for 75% of the volume of the organic solvent, and ethylene glycol dimethyl ether accounts for 25% of the volume of the organic solvent;

[0073] The diluent includes: 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether;

[0074] The additive includes: 2-fluoropyridine;

[0075] The lithium salt: lithium bis(fluorosulfonyl)imide with a concentration of 0.5M in the electrolyte;

[0076] Based on the mass of the electrolyte being 100%, by mass fraction, the organic solvent, the diluent, and the lithium salt account for 95% of the mass of the electrolyte, and the additive accounts for 5.0% of the mass of the electrolyte. By volume fraction, the diluent accounts for 80% of the volume of the electrolyte.

[0077] Example 5

[0078] This example provides an electrolyte:

[0079] The electrolyte includes an organic solvent, a diluent, an additive, and a lithium salt.

[0080] The organic solvent includes: based on the volume of the organic solvent being 100%, trimethyl phosphate accounts for 60% by volume of the organic solvent, and dimethyl sulfone accounts for 40% by volume of the organic solvent;

[0081] The diluent includes: fluoromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether;

[0082] The additive includes: trifluoropyridine;

[0083] The lithium salt: lithium hexafluorophosphate with a concentration of 1.2 M in the electrolyte;

[0084] Based on the mass of the electrolyte being 100%, by mass fraction, the organic solvent, the diluent, and the lithium salt account for 98% of the mass of the electrolyte, and the additive accounts for 2.0% of the mass of the electrolyte. By volume fraction, the diluent accounts for 85% of the volume of the electrolyte.

[0085] Example 6

[0086] This example provides an electrolyte:

[0087] The electrolyte includes an organic solvent, a diluent, an additive, and a lithium salt.

[0088] The organic solvent includes: based on the volume of the organic solvent being 100%, trimethyl phosphate accounts for 95% by volume of the organic solvent, and fumarodinitrile accounts for 5% by volume of the organic solvent;

[0089] The diluent includes: 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether;

[0090] The additive includes: 2,3,5,6-tetrafluoropyridine;

[0091] The lithium salt: lithium bis(oxalato)borate with a concentration of 0.5 M in the electrolyte;

[0092] Based on the mass of the electrolyte being 100%, by mass fraction, the organic solvent, the diluent, and the lithium salt account for 97.5% of the mass of the electrolyte, and the additive accounts for 2.5% of the mass of the electrolyte. By volume fraction, the diluent accounts for 90% of the volume of the electrolyte.

[0093] Example 7

[0094] In this example, except that ethylene glycol dimethyl ether is not added to the organic solvent, that is, the organic solvent is only triethyl phosphate, other conditions are the same as in Example 1.

[0095] Example 8

[0096] In this example, except that the mass fraction of the additive in the electrolyte is replaced from 0.5% to 10%, and the mass fraction of the organic solvent, diluent and lithium salt in the electrolyte is 90%, other conditions are the same as those in Example 1.

[0097] Example 9

[0098] In this example, except that the mass fraction of the additive in the electrolyte is replaced from 0.5% to 12%, and the mass fraction of the organic solvent, diluent and lithium salt in the electrolyte is 88%, other conditions are the same as those in Example 1.

[0099] Comparative Example 1

[0100] In this comparative example, except that 2-fluoropyridine is not added and the electrolyte is made up with an organic solvent, other conditions are the same as those in Example 1.

[0101] The qualitative analysis diagram of the electrolyte in this comparative example is as Figure 2 shown.

[0102] Comparative Example 2

[0103] In this comparative example, except that triethyl phosphate is replaced by ethylene carbonate and ethylene glycol dimethyl ether is replaced by ethyl methyl carbonate, other conditions are the same as those in Example 1.

[0104] Comparative Example 3

[0105] In this comparative example, except that triethyl phosphate is replaced by ethylene carbonate, ethylene glycol dimethyl ether is replaced by ethyl methyl carbonate, and 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether is replaced by dimethyl carbonate, other conditions are the same as those in Example 1.

[0106] The electrolytes in Examples 1-9 and Comparative Examples 1-3 were prepared into lithium metal batteries. The preparation method of the lithium metal battery includes:

[0107] Preparation method of the positive electrode sheet: Mix the ternary material of lithium nickel cobalt manganese oxide LiNi8Co1Mn1O2, conductive agent SuperP, binder PVDF and carbon nanotubes (CNT) evenly according to the mass ratio of 97:1.2:0.8:1.0 to make a lithium metal battery positive electrode paste with a certain viscosity, coat it on the current collector made of aluminum foil, and the coating amount is 324 g / m [[ID=NO-BREAK SPACE]] 2 2, and after drying at 85 °C, perform cold pressing; then perform trimming, slicing, and slitting, and then dry at 85 °C for 8 hours under vacuum conditions to make a lithium metal battery positive electrode sheet that meets the requirements.

[0108] The negative electrode uses a copper foil with a thickness of 8 μm purchased on the market, a copper-lithium composite tape with lithium coated on both sides (the thickness of lithium is 20 μm); through trimming, slicing, and slitting, a lithium metal battery negative electrode sheet meeting the requirements is made.

[0109] Preparation of the lithium metal battery: The positive electrode sheet, negative electrode sheet, and separator prepared according to the above process are made into a lithium metal battery with three positives and four negatives through the stacking process, with a capacity of 1400 mAh, and the above electrolyte is injected to complete the battery production.

[0110] Perform room-temperature formation and room-temperature cycling tests on the lithium metal batteries corresponding to Examples 1-9 and Comparative Examples 1-3, and the test results are shown in Table 1.

[0111] Among them, room-temperature formation is as follows: at 25°C, constant current charge at 0.1C to 3.7V, constant current charge at 0.2C to 4.2V, constant voltage charge at 4.2V until the cut-off current is 0.05C, and then discharge the battery at 0.1C constant current to 2.8V; room-temperature cycling test: at 25°C, constant current charge at 0.3C to 4.2V, constant voltage charge at 4.2V until the cut-off current is 0.05C, and then discharge the battery at 0.5C constant current to 2.8V. The discharge capacity is recorded as C1, repeat the charge and discharge steps 300 cycles, and obtain the discharge capacity CN in the Nth cycle. The capacity retention rate = CN / C1×100%.

[0112] Table 1

[0113]

[0114] It can be obtained from the above table that Examples 1-5 have good cycling performance. In Example 6, the volume fraction of the diluent in the electrolyte is 90%, and the volume fraction of the phosphate ester solvent in the organic solvent is 95%. Excessive addition of the diluent and phosphate ester solvent slightly reduces the electrochemical performance of the battery. Comparing Example 1 and Example 7, it can be seen that when only triethyl phosphate is added to the organic solvent, the cycling performance of the battery decreases. The organic solvent in the electrolyte needs to be used in combination with ether solvents, sulfone solvents, or nitrile solvents to achieve better cycling performance. Comparing Example 1 with Examples 8 and 9, it can be seen that when the addition amount of the additive is excessive, the electrochemical performance of the battery decreases, and when the content of the additive is higher than 10%, the electrochemical performance of the battery further decreases.

[0115] Comparing Example 1 and Comparative Example 1, it can be seen that the additive significantly improves the cycling performance of the basic electrolyte. Comparing Example 1 with Comparative Examples 2-3, it can be seen that using fluoroether as the diluent and phosphate ester as the solvent can enhance the overall reducibility of the electrolyte.

[0116] The applicant declares that the above description is only a specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A lithium metal battery, characterized in that, The lithium metal battery includes an electrolyte, a positive electrode sheet, and a negative electrode sheet; The electrolyte is composed of a lithium salt, an organic solvent, a diluent, and an additive, and the additive is selected from any one or a combination of at least two of pentafluoropyridine, 2-fluoropyridine, 3-fluoropyridine, 2,3,6-trifluoropyridine, 2,5-difluoropyridine, 3,5-difluoropyridine, 2,3,5-trifluoropyridine, 2,4-difluoropyridine, 2,6-difluoropyridine, 2,3-difluoropyridine, or 2,3,5,6-tetrafluoropyridine; The diluent is a fluoroether, and the organic solvent includes a phosphate ester solvent; Based on the volume of the electrolyte being 100%, the volume fraction of the diluent in the electrolyte is 51-90%; Based on the volume of the electrolyte being 100%, the volume fraction of the organic solvent in the electrolyte is 10-49%; Based on the volume of the organic solvent being 100%, the volume fraction of the phosphate ester solvent in the organic solvent is 50-95%; The phosphate ester solvent includes any one or a combination of at least two of triethyl phosphate, trimethyl phosphate, tris(trifluoroethyl) phosphate, tripropargyl phosphate, or triphenyl phosphite; Based on the mass of the electrolyte being 100%, the mass fraction of the additive in the electrolyte is 0.1-10%.

2. The lithium metal battery according to claim 1, wherein, Based on the mass of the electrolyte being 100%, the mass fraction of the additive in the electrolyte is 0.2-5.5%.

3. The lithium metal battery according to claim 1, wherein The fluoroethers include any one or a combination of at least two of bis(2,2,2-trifluoroethyl) ether, fluoromethyl 1,1,1,3,3,3-hexafluoroisopropyl ether, 20-fluoro-15-crown-5-ether, phenyl trifluoromethyl sulfide, 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether, pentafluorophenyl sulfide, ethyl trifluoromethyl ether, oxyfluorfen, acifluorfen, difluoromethyl 2,2,3,3,3-pentafluoropropyl ether, allyl pentafluorophenyl ether, heptafluoropropyl 1,2,2,2-tetrafluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, heptafluoroisopropyl methyl ether, 2-fluorophenyl allyl ether, bis-(1,2,2,2-tetrafluoroethyl) ether, 2-iodotetrafluoroethyl trifluoromethyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, ethyl 1,1,2,3,3,3-hexafluoropropylether, methyl 2,2,3,3,3-pentafluoropropyl ether, perfluoromethyl isopropyl ether, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, 1-chloro-2,2,2-trifluoroethyl difluoromethyl ether, 3-bromo-4'-fluorodiphenyl ether, 2H-hexafluoropropyl allyl ether, allyl 2,2,2-trifluoroethyl ether, allyl 1,1,2,2-tetrafluoroethyl ether, allyl 2,2,3,3,3-pentafluoropropyl ether, allyl 2,2,3,3-tetrafluoropropyl ether, 2-fluorophenyl 2-nitrophenyl ether, allyl 2,2,3,3,4,4,5,5-octafluoropentyl ether, octyl [2-(trifluoromethyl)phenyl] ether, allyl 1H,1H-heptafluorobutyl ether, perfluorobutyl methyl ether, 1,1,2,3,3,3-pentafluoropropyl 2,2,2-trifluoroethyl ether or 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether.

4. The lithium metal battery according to claim 1, wherein The organic solvent further includes any one or a combination of at least two of ether solvents, sulfone solvents or nitrile solvents.

5. The lithium metal battery according to claim 4, characterized in that, The ether solvents include any one or a combination of at least two of ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol dimethyl ether, o-xylene, m-xylene, isosorbide dimethyl ether, pinoresinol dimethyl ether, ethylene glycol butyl ether, boron trifluoride dimethyl ether, ethylene glycol propyl ether, ethylene glycol dibutyl ether, ethylene glycol monohexyl ether, tris(ethylene glycol) divinyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monolauryl ether, ethylene glycol tert-butyl ether, triethylene glycol butyl methyl ether, ethylene glycol methyl ether, tetraethylene glycol monolauryl ether, hexaethylene glycol monolauryl ether, ethylene glycol monopentyl ether or isosorbide dimethyl ether.

6. The lithium metal battery according to claim 4, wherein The sulfone solvents include any one or a combination of at least two of tetramethylene sulfoxide, sulfolane, ethyl methyl sulfone, bis(4-fluorophenyl) sulfone, phenyl trifluoromethyl sulfone, 4-fluorophenyl methyl sulfone, 4-chlorophenyl phenyl sulfone, bis(3-aminophenyl) sulfone, phenyl vinyl sulfone, nitromethyl phenyl sulfone, dimethyl sulfone, phenyl p-tolyl sulfone, 3-bromophenyl methyl sulfone, dimethyl sulfoxide or bromodifluoromethyl phenyl sulfone.

7. The lithium metal battery according to claim 4, wherein, The nitrile solvents include any one or a combination of at least two of ethoxy(pentafluoro)cyclotriphosphazene, fumaronitrile, 3,4,5,6-tetrafluorophthalonitrile, 2-butenenitrile, diaminofumaronitrile, 2-methyl-3-butenenitrile, or 2-methyl-2-butenenitrile.

8. The lithium metal battery according to claim 1, wherein, Based on the volume of the electrolyte being 100%, the volume fraction of the organic solvent in the electrolyte is 15 - 45%.

9. The lithium metal battery according to claim 1, wherein, Based on the volume of the organic solvent being 100%, the volume fraction of the phosphate ester solvent in the organic solvent is 50 - 75%.

10. The lithium metal battery according to claim 4, wherein, Based on the volume of the organic solvent being 100%, the volume fraction of the ether solvent in the organic solvent is 5 - 50%.

11. The lithium metal battery according to claim 10, wherein, Based on the volume of the organic solvent being 100%, the volume fraction of the ether solvent in the organic solvent is 10 - 40%.

12. The lithium metal battery according to claim 4, wherein, Based on the volume of the organic solvent being 100%, the volume fraction of the sulfone solvent in the electrolyte is 5 - 50%.

13. The lithium metal battery according to claim 12, wherein, Based on the volume of the organic solvent being 100%, the volume fraction of the sulfone solvent in the electrolyte is 10 - 40%.

14. The lithium metal battery according to claim 4, wherein, Based on the volume of the organic solvent being 100%, the volume fraction of the nitrile solvent in the electrolyte is 5 - 50%.

15. The lithium metal battery according to claim 14, wherein, Based on the volume of the organic solvent being 100%, the volume fraction of the nitrile solvent in the electrolyte is 10 - 40%.

16. The lithium metal battery according to claim 1, characterized in that, The lithium salts include any one or a combination of at least two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium metaphosphate, lithium iodate, lithium bis(ethylenedioxy)borate, lithium trifluoroacetate, lithium difluoroacetate, lithium hexafluorosilicate, lithium tri-n-butylmagnesate, lithium hexafluoroantimonate, lithium bis(trimethylsilyl)amide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(nonafluorobutanesulfonyl)imide, lithium hexafluorostannate, lithium disodium ethylenediaminetetraacetate, lithium hexafluoroarsenate, lithium diisopropylbutylmagnesate, lithium 2,2-dipropylacetate, lithium disulfopyruvate, lithium 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide, lithium tris(1,2-dimethoxyethyl)tetraphenylborate, (fluorosulfonyl)(trifluoromethanesulfonyl)imino lithium, or lithium bis(pentafluoroethylsulfonyl)imide.

17. The lithium metal battery according to claim 1, characterized in that, The concentration of the lithium salt in the electrolyte is 0.5 - 6M.

18. The lithium metal battery according to claim 1, characterized in that, The preparation method of the electrolyte includes: Dissolving the lithium salt in the organic solvent, and then successively adding a diluent and an additive for mixing to obtain the electrolyte.

19. The lithium metal battery according to claim 18, wherein, The temperature of the mixing is 25 - 50°C.

20. The lithium metal battery according to claim 1, characterized in that, The active material of the positive electrode sheet includes any one or a combination of at least two of lithium cobaltate, lithium iron phosphate, nickel cobalt manganese ternary cathode material, lithium manganate, or lithium iron(II) phosphate.

21. The lithium metal battery according to claim 1, wherein The active material of the negative electrode sheet includes a copper-lithium composite tape or a lithium foil.

22. The lithium metal battery according to claim 21, wherein, The thickness of the copper in the copper-lithium composite tape is 4 - 12μm.

23. The lithium metal battery according to claim 21, wherein, Both sides of the copper in the copper-lithium composite tape are attached with lithium layers, and the thickness of each lithium layer is 5 - 50μm.

24. The lithium metal battery according to claim 21, wherein, The thickness of the lithium foil is 10 - 2000μm.

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