Electrolyte and battery containing the same

Abstract

This invention relates to the field of lithium-ion battery technology, specifically providing an electrolyte and a battery containing the same, comprising a solvent, a diluent, a lithium salt, and a metal-ion negative electrode additive with the structure shown in Formula I. Through the reaction of metal ions on the lithium metal surface, a compact-loose bilayer SEI film is formed. The compact layer is a metal-Li alloy interface with low interfacial energy, which enhances the adhesion between the SEI film and lithium, thereby reducing interfacial resistance. Furthermore, the loose layer is a lithium-rich layer, which alleviates the mechanical stress caused by the compact layer, enhances the flexibility of the SEI film, increases the conductivity between the electrolyte and the lithium metal surface, and improves the cycle performance of the lithium metal battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically to an electrolyte and a battery containing the electrolyte. Background Technology

[0002] With the development of human life, the demand for various high-tech electronic products is increasing, which has stimulated extensive research on next-generation energy storage materials and chemicals, such as lithium metal batteries, Li / ternary batteries, Li / oxygen batteries, Li / sulfur batteries, and solid-state Li batteries. However, the low coulombic efficiency and Li dendrite growth seriously hinder the development of lithium metal batteries.

[0003] Currently, the following strategies are used to solve the above problems: 1. Optimization of electrolyte and additives; 2. Research on modification of negative electrode lithium metal foil; 3. Artificial construction of SEI film.

[0004] Research focuses on electrolytes and additives, aiming to optimize locally high-concentration electrolytes to improve the cycle performance and safety of lithium metal batteries. Much of the research revolves around organic (flexible) SEI films and inorganic (rigid) SEI films. Inorganic SEI films offer the advantage of higher mechanical strength, which helps improve the performance of Li-metal batteries. + Diffusion, uniform lithium deposition, and effective suppression of lithium dendrites; organic SEI films can effectively improve Li-terminal diffusion, uniform lithium deposition, and effective suppression of lithium dendrites through covalent bonding. + The diffusion effect is good. However, its lithium-phobicity will disrupt the contact surface between Li and the separator, eventually causing the SEI film to become loose and porous with uneven current density distribution, thereby triggering the formation of lithium dendrites and resulting in poor cycle performance of the metal battery. Summary of the Invention

[0005] In view of the problems existing in the background art, the purpose of this invention is to provide a metal ion anode additive for constructing a double-layer SEI film to improve the cycle performance of lithium metal batteries.

[0006] This invention provides an electrolyte comprising a solvent, a diluent, a lithium salt, and a metal ion anode additive with the structure shown in Formula I:

[0007]

[0008] Among them, R1 and R2 are independently selected from C. n F 2n+1 n is an integer ≥ 0; R1 and R2 can be the same or different; M is a metal ion, and q is the valence of M.

[0009] Further, M is selected from magnesium ions, aluminum ions, potassium ions, sodium ions, copper ions, calcium ions, manganese ions, cobalt ions, zinc ions, nickel ions, or cesium ions, preferably magnesium ions, zinc ions, calcium ions, or potassium ions.

[0010] Furthermore, q is 1 or 2; n is an integer from 1 to 5, preferably 1.

[0011] Furthermore, the mass percentage of the metal ion negative electrode additive in the total mass of the electrolyte is 0.01–3%, preferably 0.05–1%.

[0012] Furthermore, the metal ion anode additive is selected from one or more of bis(trifluoromethanesulfonyl)imide magnesium, bis(trifluoromethanesulfonyl)imide zinc, bis(trifluoromethanesulfonyl)imide zinc, and bis(trifluoromethanesulfonyl)imide potassium.

[0013] Furthermore, the electrolyte also includes a synergistic additive having the structure shown in Formula II:

[0014]

[0015] Among them, R3 and R4 are independently selected from H and C. m F 2m+1 m is an integer ≥ 0; R3 and R4 are not both H.

[0016] Furthermore, m is an integer from 0 to 5, preferably 0 or 1.

[0017] Furthermore, the mass ratio of the metal ion anode additive to the synergistic additive is 1:2 to 200; preferably 1:10-20.

[0018] Furthermore, the synergistic additive is selected from one or more of fluoroethylene carbonate and 3,3,3-trifluoropropylene carbonate.

[0019] Furthermore, the metal ion anode additive is magnesium bis(trifluoromethanesulfonyl)imide, and the synergistic additive is fluoroethylene carbonate.

[0020] Further, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium metaphosphate, lithium bis(nonafluorobutylsulfonyl)imide, lithium hexafluorostannate, dilithium ethylenediaminetetraacetic acid, lithium hexafluoroarsenate, lithium dibutyl(isopropyl)magnesium, lithium 2,2-di-n-propylacetate, dilithium sulfonypyruvate, 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonylimide, lithium tri(1,2-dimethoxyethyl)tetraphenylborate, lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imino, and lithium bis(pentafluoroethylsulfonyl)imino. Preferably, the mass ratio of the lithium salt to the total volume of the solvent and diluent is 0.5M to 4M.

[0021] Further, the solvent is an ether solvent, preferably ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol dimethyl ether, phthalic acid dimethyl ether, isosorbide dimethyl ether, pinoresinol dimethyl ether, phthalic acid dimethyl ether, ethylene glycol butyl ether, boron trifluoride dimethyl ether, ethylene glycol phenyl ether, ethylene glycol propyl ether, ethylene glycol butyl ether, ethylene glycol dibutyl ether, ethylene glycol monohexyl ether, tri(ethylene glycol)diethylene ether, tetraethylene glycol monomethyl ether, ethylene glycol monododecyl ether, ethylene glycol tert-butyl ether, triethylene glycol butyl methyl ether, ethylene glycol methyl ether, tetraethylene glycol monododecyl ether, hexaethylene glycol monododecyl ether, ethylene glycol... One or more of phenyl alcohol ether, ethylene glycol monopentyl ether, and isosorbide dimethyl ether; the diluent is a fluorinated ether compound, preferably bis(2,2,2-trifluoroethyl) ether, fluoromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether, eicosfluoro-15-crown-5-ether, phenyltrifluoromethyl sulfide, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, pentafluorophenyl sulfide, ethyltrifluoromethyl ether, ethoxysulfuron, trifluorocarboxysulfuron, 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, heptafluoroisopropylmethyl 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-hexafluoropropyl ether, methyl 2,2,3,3,3-pentafluoropropyl ether, polyperfluoromethyl 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, olefin One or more of the following: propyl 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-octafluoropentane 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, and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether.

[0022] Furthermore, the volume ratio of the solvent to the diluent is 1:9 to 4:6.

[0023] The present invention also provides a lithium metal battery, comprising any of the electrolytes described above, and further comprising a positive electrode and a negative electrode.

[0024] The technical solution of this invention has the following advantages:

[0025] 1. The electrolyte provided by this invention comprises a metal ion negative electrode additive having the structure shown in Formula I. Through the reaction of metal ions on the lithium metal surface, a compact-loose bilayer SEI film is formed. The compact layer is a metal ion-Li alloy interface, which has low interfacial energy, enhancing the adhesion between the SEI film and lithium, thereby reducing interfacial resistance. Furthermore, the loose layer is a lithium-rich layer, which can alleviate the mechanical stress caused by the compact layer, enhance the flexibility of the SEI film, increase the conductivity between the electrolyte and the lithium metal surface, and improve the cycle performance of the lithium metal battery.

[0026] 2. The electrolyte additive provided by the present invention has CFC or CO bonds in the synergistic additive that can assist the metal ion additive in forming an optimal double-layer SEI film on the lithium metal surface, thereby further improving the cycle performance of the lithium metal battery. In particular, when the mass ratio of the metal ion anode additive to the synergistic additive is controlled to be 1:2 to 200, the cycle performance is optimal when the mass ratio is 1:10-20. Detailed Implementation

[0027] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0028] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0029] Examples 1-7 and Comparative Examples 1-2 respectively provide an electrolyte and a lithium-ion battery containing the electrolyte. The composition of the electrolyte and the concentration or content of each component are shown in Table 1. The concentration of lithium salt refers to the molar concentration (M, i.e., mol / L), which is equal to the molar amount of lithium salt (mol) divided by the total volume (L) of solvent and diluent.

[0030] The preparation method of the electrolyte is as follows: Lithium salt is dissolved in a mixed solvent composed of solvent and diluent. The type and concentration of lithium salt, the type of solvent and diluent and their volume ratio are shown in Table 1. Then, according to Table 1, 0-10 wt% of synergistic additives and 0-0.5 wt% of metal ion anode additives are added and stirred evenly to obtain the electrolyte.

[0031] Table 1. Composition of the electrolyte and concentration or content of each component.

[0032]

[0033]

[0034] Lithium metal batteries were assembled using the electrolytes provided in the respective examples and comparative examples. The preparation methods and battery performance testing methods are as follows:

[0035] Fabrication of the positive electrode: A lithium-ion battery positive electrode slurry is prepared by uniformly mixing lithium nickel cobalt manganese oxide ternary material LiNi8Co1Mn1O2, conductive agent SuperP, binder PVDF, and carbon nanotubes (CNT) at a mass ratio of 97:1.2:0.8:1.0. This slurry is then coated onto aluminum foil used for current collectors, with a coating weight of 324 g / m². 2 After drying at 85℃, the material is cold-pressed; then trimmed, cut, and slit, and dried at 85℃ for 8 hours under vacuum to produce the positive electrode sheet for lithium metal batteries; the negative electrode uses 8μm thick copper foil purchased from the market, and a copper-lithium composite strip with lithium on both sides (lithium thickness is 20μm); after trimming, cutting, and slitting, the negative electrode sheet for lithium metal batteries is produced; the positive electrode sheet, negative electrode sheet, and separator prepared according to the above process are stacked to form a three-positive-four-negative lithium metal battery with a capacity of 1400mAh, and each group of electrolytes is injected to complete the battery manufacturing.

[0036] Battery performance test

[0037] 1. Room temperature formation test: At 25℃, charge the battery to 3.7V with a constant current of 0.1C, charge it to 4.2V with a constant current of 0.2C, charge it to 4.2V with a constant voltage of 4.2V until the cutoff current is 0.05C, and then discharge the battery to 2.8V with a constant current of 0.1C. Record the discharge capacity and charge capacity, and calculate the first efficiency.

[0038] 2. Room temperature cycle test: At 25℃, the battery was charged to 4.2V at a constant current of 0.3C, then charged to the cutoff current of 0.05C at a constant voltage of 4.2V, and then discharged to 2.8V at a constant current of 0.5C. The discharge capacity was recorded as C1. The charge and discharge cycle was repeated for 300 cycles to obtain the discharge capacity CN of the Nth cycle. The capacity retention rate was CN / C1*100%. The results are shown in Tables 2 and 3.

[0039] Table 2 Performance results of high-energy-density lithium metal batteries

[0040]

[0041]

[0042] Table 3 Number of test cycles to stop

[0043]

[0044] Note: If the capacity retention rate of a pouch lithium metal battery is below 80% or the coulombic efficiency is below 90% during cycle testing, the battery test should be stopped, and the number of test cycles, as well as the capacity retention rate and coulombic efficiency of the last cycle, should be recorded.

[0045] As shown in the table above, the electrolyte with added metal ion anode additive has a significantly improved cycle life. Moreover, the metal ion anode additive and the synergistic additive of the present invention work together to achieve a synergistic effect, greatly increasing the number of cycles.

[0046] Furthermore, a comparison between Example 1 and Examples 6-7 shows that the cycle life can be further improved by limiting the mass ratio of metal ion anode additive to synergistic additive within a preferred range.

[0047] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An electrolyte, characterized in that, The product includes a solvent, a diluent, a lithium salt, a metal ion anode additive, and a synergistic additive; the metal ion anode additive is magnesium bis(trifluoromethanesulfonyl)imide, the synergistic additive is fluoroethylene carbonate, and the lithium salt is selected from lithium bisfluorosulfonylimide; the mass ratio of the metal ion anode additive to the synergistic additive is 1:10-20. The mass percentage of the metal ion negative electrode additive in the total mass of the electrolyte is 0.01-3%. The molar amount of the lithium salt is in the ratio of the total volume of the solvent and diluent to 0.5M to 4M. The solvent is an ether solvent; The diluent is a fluorinated ether compound.

2. The electrolyte according to claim 1, characterized in that, The mass percentage of the metal ion negative electrode additive to the total mass of the electrolyte is 0.05% to 1%.

3. The electrolyte according to claim 1, characterized in that, The solvent is one or more selected from ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol dimethyl ether, phthalic acid dimethyl ether, isosorbide dimethyl ether, pinoresinol dimethyl ether, phthalic acid dimethyl ether, ethylene glycol butyl ether, boron trifluoride dimethyl ether, ethylene glycol phenyl ether, ethylene glycol propyl ether, ethylene glycol butyl ether, ethylene glycol dibutyl ether, ethylene glycol monohexyl ether, tri(ethylene glycol)divinyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monododecyl ether, ethylene glycol tert-butyl ether, triethylene glycol butyl methyl ether, ethylene glycol methyl ether, tetraethylene glycol monododecyl ether, hexaethylene glycol monododecyl ether, ethylene glycol phenyl ether, ethylene glycol monopentyl ether, and isosorbide dimethyl ether. The diluent is bis(2,2,2-trifluoroethyl) ether, fluoromethyl-1,1,1,3,3,3-hexafluoroisopropyl ether, eicosfluoro-15-crown-5-ether, phenyltrifluoromethyl sulfide, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, pentafluorophenyl sulfide, ethyltrifluoromethyl ether, ethoxysulfuron, trifluorocarboxysulfuron, difluoromethyl 2,2,3,3,3-pentafluoropropyl ether, allyl... Heptafluoropropyl 1,2,2,2-tetrafluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, heptafluoroisopropylmethyl ether, 2-fluorophenyl allyl ether, bis-(1,2,2,2-tetrafluoroethyl) ether, 2-iodotetrafluoroethyl trifluoromethyl ether, 1,1,2,2-tetrafluoroethyl ether, ethyl 1,1,2,3,3,3-hexafluoropropyl ether, methyl 2,2,3,3,3-pentafluoropropyl Fiber ethers, 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 One or more of the following: 3-tetrafluoropropyl ether, 2-fluorophenyl-2-nitrophenyl ether, allyl 2,2,3,3,4,4,5,5-octafluoropentane 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, and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether.

4. A battery, characterized in that, The electrolyte includes any one of claims 1-3, and further includes a positive electrode and a negative electrode.

Images