A fluoroether and its application and electrolyte for sodium-ion batteries

Abstract

The present invention discloses a fluoroether compound, and the molecular formula of the fluoroether compound is: F x C n H 2n+1‑x OC m H 2m+1 , where x / (2n + 1) < 80%, n ≥ 5, and m + n ≤ 9. Among them, the fluoroether compound is selected from at least one of hexafluoropentyl methyl ether, hexafluoropentyl ethyl ether, heptafluoropentyl methyl ether, heptafluoropentyl ethyl ether, octafluoropentyl methyl ether, octafluoropentyl ethyl ether, nonafluorohexyl methyl ether, nonafluorohexyl ethyl ether, decafluoroheptyl methyl ether, or decafluoroheptyl ethyl ether. The fluoroether compound of the present invention can be applied to the electrolyte of a sodium-ion battery, effectively improving the film-forming stability on the positive and negative electrodes, inhibiting side reactions, increasing the transmission rate of sodium ions, and significantly improving the cycle stability and rate discharge capacity of the sodium-ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrolytes, and particularly relates to a fluoroether and its application. In particular, it also relates to a sodium-ion battery electrolyte. Background Art

[0002] Sodium-ion batteries are similar in principle and structure to lithium-ion batteries. However, compared with lithium batteries, sodium-ion batteries have the characteristics of wide resources, low cost and small fluctuations, and have the performance of a wide temperature range and high safety. These characteristics endow sodium-ion batteries with the potential to replace lithium-ion batteries. With the continuous progress of sodium-ion battery technology, sodium-ion batteries will occupy an important position in China's energy system, especially in the energy storage field, where there is broad room for growth.

[0003] Developing high-performance and low-cost sodium-ion batteries is a decisive factor in determining whether they can be industrialized. At present, due to poor film-forming quality, existing sodium-ion batteries have problems such as insufficient cycle performance and poor rate discharge ability of sodium-ion batteries. Therefore, it is necessary to research and improve sodium-ion batteries. Summary of the Invention

[0004] The present invention is made based on the inventor's discovery and recognition of the following facts and problems: Currently, sodium-ion batteries generally have problems of insufficient cycle performance and poor rate discharge ability. Therefore, it is necessary to conduct in-depth research on sodium-ion batteries to improve the rate performance and cycle performance of sodium-ion batteries.

[0005] The present invention aims to solve at least one of the technical problems in the related art to some extent. For this purpose, the present invention provides a fluoroether compound, and the molecular formula of the fluoroether compound is: F x C n H 2n+1-x OC m H 2m+1 , where x / (2n + 1) < 80%, n ≥ 5, and m + n ≤ 9.

[0006] Optionally, the fluoroether compound is selected from at least one of hexafluoropentyl methyl ether, hexafluoropentyl ethyl ether, heptafluoropentyl methyl ether, heptafluoropentyl ethyl ether, octafluoropentyl methyl ether, octafluoropentyl ethyl ether, nonafluorohexyl methyl ether, nonafluorohexyl ethyl ether, decafluoroheptyl methyl ether or decafluoroheptyl ethyl ether; preferably, the fluoroether compound is selected from at least one of 3,4,4,5,5,5-hexafluoropentyl methyl ether, 3,4,4,5,5,5-hexafluoropentyl ethyl ether, 2,2,3,3,4,4,5-heptafluoropentyl methyl ether, 2,2,3,4,4,5,5-heptafluoropentyl ethyl ether, 2,2,3,3,4,4,5,5-octafluoropentyl methyl ether, 2,2,3,3,4,4,5,5-octafluoropentyl ethyl ether, 1,2,2,3,3,4,4,5,5-nonafluorohexyl methyl ether, 1,1,2,2,3,3,4,4,5,5-decafluoroheptyl methyl ether.

[0007] The present invention also provides an application of a fluoroether compound in a sodium ion battery.

[0008] The present invention also provides a sodium ion battery electrolyte, comprising an electrolyte salt and a solvent, and the solvent comprises the fluoroether compound of the present invention.

[0009] Optionally, the mass percentage content of the fluoroether compound in the electrolyte is 5-40%, preferably 8-30%.

[0010] Optionally, the electrolyte salt comprises at least one of sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium hexafluorophosphate (NaPF6), sodium trifluoroacetate (CF3COONa), sodium tetraphenylborate (NaB(C6H5)4), sodium trifluoromethanesulfonate (NaSO3CF3), sodium bis(fluorosulfonyl)imide (Na[(FSO2)2N]) or sodium bis(trifluoromethylsulfonyl)imide (Na[(CF3SO2)2N]).

[0011] Optionally, the solvent further comprises at least one of a C3-C5 carbonate, a C2-C6 carboxylate, and a C4-C10 ether, wherein

[0012] the C3-C7 carbonate comprises a cyclic carbonate or a linear carbonate having 3 to 5 carbon atoms. Preferably, the cyclic carbonate comprises at least one of ethylene carbonate (EC), vinylene carbonate, ethylene vinylene carbonate, propylene carbonate (PC), γ-butyrolactone, and butylene carbonate; the linear carbonate comprises at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate;

[0013] The carboxylic acid esters of C2-C6 include at least one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and propyl propionate.

[0014] The ethers of C4-C10 include cyclic ethers or chain ethers having 4 to 10 carbon atoms; preferably, the cyclic ethers include at least one of 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, and 2-trifluoromethyltetrahydrofuran; the chain ethers include at least one of dimethoxymethane, 1,2-dimethoxyethane, and diglyme.

[0015] And / or, in the sodium-ion battery electrolyte, the mass percentage of the solvent is 70-92%.

[0016] Optionally, the electrolyte further includes an additive, the additive includes a fluorinated carbonate, and the mass percentage of the fluorinated carbonate in the sodium-ion battery electrolyte is 1-5%. Preferably, the fluorinated carbonate includes at least one of fluoroethylene carbonate (FEC) or difluoroethylene carbonate (DFEC).

[0017] The present invention also provides a sodium-ion battery, including a positive electrode, a negative electrode, and the sodium-ion battery electrolyte of the present invention.

[0018] Optionally, the positive electrode includes a positive electrode active material, and the positive electrode active material is selected from at least one of layered metal oxides, polyanion compounds, Prussian compounds, phosphate compounds, and sulfate compounds. Among them,

[0019] The chemical formula of the layered metal oxide is Na x M y O z , 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2, and M is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V; preferably, the layered metal oxide is NaNi m Fe n Mn p O2 (m + n + p = 1, 0 ≤ m ≤ 1, 0 ≤ n ≤ 1, 0 ≤ p ≤ 1) or NaNi m Co n Mn p O2 (m + n + p = 1, 0 ≤ m ≤ 1, 0 ≤ n ≤ 1, 0 ≤ p ≤ 1) or at least one of them;

[0020] The chemical formula of the Prussian compound is Na x M[M′(CN)6] y ·zH2O, M and M′ are transition metals, 0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20; preferably, the Prussian compound is Nax Mn[Fe(CN)6] y ·zH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20) or Na x Fe[Fe(CN)6] y ·zH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20), at least one of;

[0021] The chemical formula of the phosphate compound is Na3(MO 1-x PO4)2F 1+2x where 0 ≤ x ≤ 1, M is selected from at least one of Al, V, Ge, Fe, Ga; preferably, the phosphate compound is at least one of Na3(VPO4)2F3 or Na3(VOPO4)2F; or, the chemical formula of the phosphate compound is Na2MPO4F, M is selected from at least one of Fe, Mn; preferably, the phosphate compound is at least one of Na2FePO4F or Na2MnPO4F;

[0022] The chemical formula of the sulfate compound is Na2M(SO4)2·2H2O, M is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, V;

[0023] And / or, the negative electrode includes a negative electrode active material, and the negative electrode active material includes at least one of hard carbon or soft carbon.

[0024] According to the fluoroether compound provided by the present invention, the molecular formula structure of the fluoroether is defined. The inventors found through a large number of experiments that when X / (2n + 1) ≥ 80%, using the fluoroether in the sodium-ion battery electrolyte will cause a decrease in the solubility of the electrolyte salt, resulting in a decrease in the conductivity of the electrolyte and a serious decline in the low-temperature discharge performance. At the same time, in the present invention, n ≥ 5 is controlled, and m + n ≤ 9. If n is less than 5, it will lead to an increase in the molecular chain rigidity, resulting in poor fluidity and increased viscosity of the electrolyte, deteriorating the battery rate performance. If m + n > 9, the dipole moment decreases, the solubility of the sodium salt decreases, and the battery rate performance declines seriously. Adding the fluoroether compound of the present invention as a co-solvent in the sodium-ion electrolyte, the fluoroether compound will participate in the solvation structure of the ions, affect the formation of SEI and CEI, and improve the interfacial stability between the electrode material and the electrolyte, thereby improving the cycle performance of the battery; at the same time, in the fluoroether compound, by controlling the content of the F element in the fluoroether, it is possible to regulate the solvation structure of sodium ions to make it have a weaker solvation effect, so that sodium ions can quickly desolvate when passing through the interfacial film, improving the transport rate of sodium ions and significantly improving the rate performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 1H NMR spectrum of 2,2,3,3,4,4,5,5-octafluoropentyl ethyl ether;

[0026] Figure 2 IR spectrum of 2,2,3,3,4,4,5,5-octafluoropentyl ethyl ether;

[0027] Figure 3 1H NMR spectrum of 2,2,3,3,4,4,5-heptafluoropentyl methyl ether;

[0028] Figure 4 IR spectrum of 2,2,3,3,4,4,5-heptafluoropentyl methyl ether;

[0029] Figure 5 1H NMR spectrum of 2,2,3,4,4,5,5-heptafluoropentyl ethyl ether;

[0030] Figure 6 IR spectrum of 2,2,3,4,4,5,5-heptafluoropentyl ethyl ether;

[0031] Figure 7 1H NMR spectrum of 2,2,3,3,4,4,5,5-octafluoropentyl methyl ether;

[0032] Figure 8 IR spectrum of 2,2,3,3,4,4,5,5-octafluoropentyl methyl ether;

[0033] Figure 9 1H NMR spectrum of 1,2,2,3,3,4,4,5,5-nonafluorohexyl methyl ether;

[0034] Figure 10 IR spectrum of 1,2,2,3,3,4,4,5,5-nonafluorohexyl methyl ether;

[0035] Figure 11 1H NMR spectrum of 1,1,2,2,3,3,4,4,5,5-decafluoroheptyl methyl ether;

[0036] Figure 12 IR spectrum of 1,1,2,2,3,3,4,4,5,5-decafluoroheptyl methyl ether;

[0037] Figure 13 1H NMR spectrum of 3,4,4,5,5,5-hexafluoropentyl methyl ether;

[0038] Figure 14Infrared spectrum (IR) of 3,4,4,5,5,5-hexafluoropentyl methyl ether;

[0039] Figure 15 Nuclear magnetic resonance spectrum (NMR) of 3,4,4,5,5,5-hexafluoropentyl ethyl ether;

[0040] Figure 16 Infrared spectrum (IR) of 3,4,4,5,5,5-hexafluoropentyl ethyl ether. Detailed implementation manners

[0041] The embodiments of the present invention will be described in detail below. The embodiments are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0042] A fluoroether compound according to an embodiment of the present invention, the molecular formula of the fluoroether compound being: F x C n H 2n+1- x OC m H 2m+1 , where x / (2n + 1) < 80%, n ≥ 5, and m + n ≤ 9.

[0043] In a specific embodiment, the fluoroether compound is selected from at least one of hexafluoropentyl methyl ether, hexafluoropentyl ethyl ether, heptafluoropentyl methyl ether, heptafluoropentyl ethyl ether, octafluoropentyl methyl ether, octafluoropentyl ethyl ether, nonafluorohexyl methyl ether, nonafluorohexyl ethyl ether, decafluoroheptyl methyl ether, or decafluoroheptyl ethyl ether;

[0044] In a preferred embodiment, the fluoroether compound is selected from at least one of 3,4,4,5,5,5-hexafluoropentyl methyl ether, 3,4,4,5,5,5-hexafluoropentyl ethyl ether, 2,2,3,3,4,4,5-heptafluoropentyl methyl ether, 2,2,3,4,4,5-heptafluoropentyl ethyl ether, 2,2,3,3,4,4,5,5-octafluoropentyl methyl ether, 2,2,3,3,4,4,5,5-octafluoropentyl ethyl ether, 1,2,2,3,3,4,4,5,5-nonafluorohexyl methyl ether, 1,1,2,2,3,3,4,4,5,5-decafluoroheptyl methyl ether;

[0045] The structure of the fluoroether compound can be represented as:

[0046]

[0047]

[0048] A sodium-ion battery electrolyte according to an embodiment of the present invention includes an electrolyte salt and a solvent, and the solvent includes the fluoroether compound of the present invention.

[0049] In a specific embodiment, the mass percentage of the fluoroether compound in the electrolyte is 5-40%.

[0050] In a specific embodiment, the mass percentage of the fluoroether compound in the electrolyte can be 5%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%.

[0051] In a preferred embodiment, the mass percentage of the fluoroether compound in the electrolyte is 8-30%.

[0052] Adding the fluoroether compound of the present invention as a solvent to the electrolyte, the fluoroether compound can partially replace conventional electrolyte solvents such as EMC, and form a co-solvent with other solvents. The fluoroether compound of the present invention will participate in the solvation structure of ions, affect the composition of SEI and CEI, and improve the interfacial stability between the electrode material and the electrolyte. By controlling the usage ratio of the fluoroether compound in the electrolyte, the electrolyte can obtain an appropriate viscosity, which is beneficial to further improving the rate and cycle performance of sodium-ion batteries. When the mass percentage of the fluoroether compound in the electrolyte is too high, the fluoroether will excessively participate in the formation of CEI and SEI films, resulting in an overly thick and uneven interfacial film. During the cycling process, the interfacial film dissolves severely, and the impedance increases significantly, seriously deteriorating the cycle performance of the battery; when the mass percentage of the fluoroether compound in the electrolyte is too low, it cannot effectively participate in film formation and cannot effectively regulate the interfacial film, resulting in poor cycle stability.

[0053] In a specific embodiment, the electrolyte salt includes at least one of sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium hexafluorophosphate (NaPF6), sodium trifluoroacetate (CF3COONa), sodium tetraphenylborate (NaB(C6H5)4), sodium trifluoromethanesulfonate (NaSO3CF3), sodium bis(fluorosulfonyl)imide (Na[(FSO2)2N]) or sodium bis(trifluoromethylsulfonyl)imide (Na[(CF3SO2)2N]).

[0054] In the embodiments of the present invention, there is no particular limitation on the electrolyte salt, and the electrolyte salts commonly used in sodium-ion batteries can all be applicable to the present invention.

[0055] In a specific embodiment, the solvent further includes at least one of C3-C5 carbonates, C2-C6 carboxylates, and C4-C10 ethers; in the sodium-ion battery electrolyte, the mass percentage of the solvent is 70-92%.

[0056] In a preferred embodiment, the C3-C7 carbonates include cyclic carbonates or chain carbonates having 3 to 5 carbon atoms. Further preferably, the cyclic carbonates include at least one of ethylene carbonate (EC), vinylene carbonate, ethylene ethylene carbonate, propylene carbonate (PC), γ-butyrolactone, and butylene carbonate; the chain carbonates include at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate.

[0057] In a preferred embodiment, the C2-C6 carboxylates include at least one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and propyl propionate.

[0058] In a preferred embodiment, the C4-C10 ethers include cyclic ethers or chain ethers having 4 to 10 carbon atoms; further preferably, the cyclic ethers include at least one of 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, and 2-trifluoromethyltetrahydrofuran; the chain ethers include at least one of dimethoxymethane, 1,2-dimethoxyethane, and diethylene glycol dimethyl ether.

[0059] In the embodiments of the present invention, there is no particular limitation on the solvents other than fluoroether compounds, and the solvents commonly used in sodium-ion batteries can all be applied to the present invention.

[0060] In a specific embodiment, the electrolyte further includes an additive, the additive includes a fluorinated carbonate, and the mass percentage content of the fluorinated carbonate in the sodium-ion battery electrolyte is 1-5%. Preferably, the fluorinated carbonate includes at least one of fluorinated ethylene carbonate (FEC) or difluorinated ethylene carbonate (DFEC). In the embodiments of the present invention, the electrolyte may further include an additive fluorinated carbonate, which can further improve the film-forming quality and is beneficial to improving the battery performance.

[0061] The present invention also provides a sodium-ion battery, including a positive electrode, a negative electrode, and the sodium-ion battery electrolyte of the embodiments of the present invention.

[0062] In a specific embodiment, the positive electrode includes a positive electrode active material, and the positive electrode active material is selected from at least one of layered metal oxides, polyanion compounds, Prussian compounds, phosphate compounds, and sulfate compounds.

[0063] In a preferred embodiment, the chemical formula of the layered metal oxide is Na x M y O z, 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2, M is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, V; more preferably, the layered metal oxide is NaNi m Fe n Mn p O2 (m + n + p = 1, 0 ≤ m ≤ 1, 0 ≤ n ≤ 1, 0 ≤ p ≤ 1) or NaNi m Co n Mn p O2 (m + n + p = 1, 0 ≤ m ≤ 1, 0 ≤ n ≤ 1, 0 ≤ p ≤ 1) or at least one of them.

[0064] In a preferred embodiment, the molecular formula of the Prussian compound is Na x M[M′(CN)6] y ·zH2O, M and M′ are transition metals, 0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20; more preferably, the Prussian compound is Na x Mn[Fe(CN)6] y ·zH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20) or Na x Fe[Fe(CN)6] y ·zH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20) or at least one of them.

[0065] In a preferred embodiment, the chemical formula of the phosphate compound is Na3(MO 1-x PO4)2F 1+2x , 0 ≤ x ≤ 1, M is selected from at least one of Al, V, Ge, Fe, Ga; more preferably, the phosphate compound is at least one of Na3(VPO4)2F3 or Na3(VOPO4)2F; or, the chemical formula of the phosphate compound is Na2MPO4F, M is selected from at least one of Fe, Mn; more preferably, the phosphate compound is at least one of Na2FePO4F or Na2MnPO4F;

[0066] In a preferred embodiment, the chemical formula of the sulfate compound is Na2M(SO4)2·2H2O, M is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, V.

[0067] In the embodiments of the present invention, the cathode active material in the cathode is preferably selected, which can cooperate with the additives adopted in the present invention to form a film synergistically, improve the film-forming quality, and is beneficial to further improving the performance of the battery.

[0068] In a specific embodiment, the negative electrode includes a negative electrode active material, and the negative electrode active material includes at least one of hard carbon or soft carbon.

[0069] In the embodiments of the present invention, there is no particular limitation on the negative electrode active material, and any negative electrode active material that can be used in a sodium ion battery in the prior art can be applicable to the present invention.

[0070] The present invention will be described in detail below with reference to embodiments and the accompanying drawings.

[0071] Example 1

[0072] Preparation of the fluoroether compound:

[0073] In the synthesis method of the fluoroether of the present invention, the corresponding ether can be produced by reacting the corresponding alcohol with an alcohol reagent or other alkylating reagent in an NMP solvent under the catalysis of NaOH. The reaction product can be analyzed by nuclear magnetic resonance (NMR) (400 MHz, Bruker) for 1 H and 19 F NMR spectroscopic tests, and the IR spectrum is carried out on a THERMO-NICOLET, Avatar370 Fourier transform infrared (FTIR) spectrophotometer.

[0074] Example 2

[0075] (1) Preparation of 2,2,3,3,4,4,5,5-octafluoropentyl ethyl ether: In an NMP solvent, 2,2,3,3,4,4,5,5-octafluoro-1-pentanol reacts with ethanol under the catalysis of NaOH to form 2,2,3,3,4,4,5,5-octafluoropentyl ethyl ether.

[0076] According to the nuclear magnetic resonance hydrogen spectrum, there are a total of 4 chemical shifts. The first peak is 1.05, which is a triplet; the chemical shift of 3.46 corresponds to a quartet, 3.67 corresponds to a triplet, and 6.46 corresponds to a nonet. The relevant spectra are measured as Figure 1 shown, Figure 2 and is its infrared spectrum.

[0077] (2) Preparation of the electrolyte: 8.5 wt% of the electrolyte salt sodium hexafluorophosphate, 14 wt% of the fluoroether compound 2,2,3,3,4,4,5,5-octafluoropentyl ethyl ether (prepared in Example 1), 76 wt% of the solvent (ethyl methyl carbonate EMC: ethylene carbonate EC = 1:1, mass ratio), and 1.5 wt% of the additive fluoroethylene carbonate FEC are mixed uniformly to obtain the electrolyte.

[0078] (3) Preparation of the positive electrode: The positive electrode active material NaNi0.7Co0.15Mn0.15O2, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) were taken in a mass ratio of 93:4:3 and mixed, and then they were dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The positive electrode slurry was coated on a current collector and processed through coating, drying, and rolling processes to obtain a positive electrode sheet.

[0079] (4) Preparation of the negative electrode: The negative electrode active material hard carbon with a specific surface area of 5 m2 / g, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were taken in a mass ratio of 94:1:2.5:2.5 and mixed, and then they were dispersed in an appropriate amount of deionized water to obtain a negative electrode slurry. The negative electrode slurry was coated on a current collector and processed through coating, drying, and rolling processes to obtain a negative electrode sheet.

[0080] (5) Battery assembly

[0081] A separator was placed between the prepared positive electrode sheet and negative electrode sheet, and then the sandwich structure composed of the positive electrode sheet, negative electrode sheet, and separator was wound. After that, the wound body was flattened and placed in an aluminum foil packaging bag, and vacuum baked at 75 °C for 48 h to obtain an electrode core to be filled with electrolyte. The prepared electrolyte was injected into the electrode core through an injection hole, and the amount of the electrolyte should ensure that the voids in the electrode core were filled.

[0082] Examples 3 to 19

[0083] Examples 3 to 19 are used to illustrate the sodium ion battery electrolyte and battery disclosed in the present invention, including most of the operation steps in Example 2. The differences are as follows:

[0084] The fluoroether compounds and their contents used in Examples 3 to 19 are shown in Table 1.

[0085] The nuclear magnetic resonance spectrum of the fluoroether compound 2,2,3,3,4,4,5-heptafluoropentyl methyl ether prepared in Example 13 is shown in Figure 3 , and the infrared spectrum is shown in Figure 4 ;

[0086] The nuclear magnetic resonance spectrum of the fluoroether compound 2,2,3,4,4,5,5-heptafluoropentyl ethyl ether prepared in Example 14 is shown in Figure 5 , and the infrared spectrum is shown in Figure 6 ;

[0087] The nuclear magnetic resonance spectrum of the fluoroether compound 2,2,3,3,4,4,5,5-octafluoropentyl methyl ether prepared in Example 15 is shown in Figure 7 , and the infrared spectrum is shown in Figure 8 ;

[0088] The nuclear magnetic resonance spectrum of the fluoroether compound 1,2,2,3,3,4,4,5,5-nonafluorohexyl methyl ether prepared in Example 16 is shown in Figure 9 , and the infrared spectrum is shown in Figure 10 ;

[0089] The nuclear magnetic resonance spectrum of the fluoroether compound 1,1,2,2,3,3,4,4,5,5-decafluoroheptyl methyl ether prepared in Example 17 is shown in Figure 11 , and the infrared spectrum is shown in Figure 12 ;

[0090] The nuclear magnetic resonance spectrum of the fluoroether compound 3,4,4,5,5,5-hexafluoropentyl methyl ether prepared in Example 18 is shown in Figure 13 , and the infrared spectrum is shown in Figure 14 ;

[0091] The nuclear magnetic resonance spectrum of the fluoroether compound 3,4,4,5,5,5-hexafluoropentyl ethyl ether prepared in Example 19 is shown in Figure 15 , and the infrared spectrum is shown in Figure 16 .

[0092] Comparative Examples 1 - 6

[0093] Comparative Examples 1 - 6 are used to compare and illustrate the sodium-ion battery electrolyte and battery disclosed in the present invention, including most of the operating steps in Example 2. The differences are as follows:

[0094] The fluoroether compounds and their contents used in Comparative Examples 1 - 6 are shown in Table 1.

[0095] Performance Test

[0096] For the sodium-ion batteries prepared above, initial efficiency and cyclic charge-discharge tests were carried out in the voltage range of 1.5 - 3.95 V, and the charge-discharge capacities of the first cycle formation and grading of the batteries and the capacity retention rate after 200 cycles were recorded. Specifically as follows:

[0097] (1) 4C rate discharge capacity ratio

[0098] Measure the capacity C2 released when the sodium-ion battery discharges from 3.95 V to 1.5 V at a rate of 4C and the capacity C1 released when the battery discharges from 3.95 V to 1.5 V at a rate of 0.2C during the first activation stage. The calculation formula is as follows:

[0099] 4C rate discharge capacity ratio = C2 / C1.

[0100] (2) Room temperature cyclic performance test

[0101] The sodium-ion battery is placed in a constant-temperature environment at 25°C and charged at a constant current of 0.7C to 3.9V, then charged at a constant voltage until the current drops to 0.05C, and then discharged at a constant current of 1C to 1.5V. This cycle is repeated, and the discharge capacities of the 1st - 3rd cycles and the 200th cycle are recorded.

[0102] Calculate the capacity retention rate of the cycle at 25°C according to the following formula:

[0103] Capacity retention rate of the 200th cycle (%) = Discharge capacity of the 200th cycle / Average discharge capacity of the 1st - 3rd cycles × 100%.

[0104] (3) High-temperature cycle capacity retention rate

[0105] The sodium-ion battery is placed in a constant-temperature environment at 45°C and charged at a constant current of 0.7C to 3.9V, then charged at a constant voltage until the current drops to 0.02C, and then discharged at a constant current of 1C to 1.5V. This cycle is repeated, and the discharge capacity of the 1st cycle, the battery volume, and the discharge capacity of the 200th cycle are recorded.

[0106] Calculate the capacity retention rate of the cycle at 45°C according to the following formula:

[0107] Capacity retention rate of the 200th cycle (%) = Discharge capacity of the 200th cycle / Discharge capacity of the 1st cycle × 100%.

[0108] The battery parameters and electrical performance data of Examples 2 - 19 and Comparative Examples 1 - 6 are shown in Tables 1 and 2.

[0109] Table 1

[0110]

[0111] Note: The preparation method of the fluoroether compound used in Examples 13 - 19 and Comparative Examples 4 - 6 refers to Example 1.

[0112] Table 2

[0113]

[0114] It can be seen from Tables 1 and 2 that for the sodium-ion batteries prepared in Examples 2 - 19, using the electrolyte containing the fluoroether compound of the present invention, the film-forming stability on the positive and negative electrode sides is good, which can effectively inhibit the occurrence of side reactions, improve the sodium-ion transmission rate, significantly improve the cycle stability of the sodium-ion battery, and the capacity retention rate can reach more than 87% after 200 high-temperature cycles. Moreover, the rate discharge capacity is increased, the rate performance of the sodium-ion battery is improved, and the 4C rate discharge capacity ratio can reach more than 79%, with excellent performance.

[0115] In Comparative Example 1, the fluorinated ether compound of the present invention was not added to the electrolyte solvent, and the stability of the CEI and SEI films formed on the positive and negative electrode sides was poor. During the cycling process, side reactions continuously occurred in the electrolyte, resulting in continuous consumption of the electrolyte and the active material, causing deterioration of the battery performance. The discharge capacity ratio at 4C rate was only 69.2%. At the same time, both the room temperature cycling and high temperature cycling performances decreased significantly. After 200 cycles at high temperature, the capacity retention rate dropped to 77.5%.

[0116] In Comparative Example 2, too little fluorinated ether compound was added to the electrolyte. The fluorinated ether could not effectively participate in film formation and could not effectively regulate the interfacial film, resulting in poor cycling stability. The rate performance and cycling performance were only slightly better than those of Comparative Example 1.

[0117] In Comparative Example 3, too much fluorinated ether compound was added to the electrolyte, causing excessive participation of the fluorinated ether in the formation of the CEI and SEI films, making the interfacial film too thick and uneven. As a result, during the cycling process, the interfacial film dissolved severely, leading to a significant increase in impedance and seriously deteriorating the cycling performance of the battery. After 200 cycles at high temperature, the capacity retention rate was only 76.8%.

[0118] In Comparative Example 4, the fluorinated ether compound added to the electrolyte was 2,2,3,3,3-pentafluoropropyl methyl ether. Since the n value was only 3, the fluorinated ether compound had high rigidity, resulting in poor fluidity and high viscosity of the electrolyte, deteriorating the rate performance of the battery.

[0119] In Comparative Example 5, the fluorinated ether compound added to the electrolyte was perfluorohexyl methyl ether. Although both n and m met the requirements of the present invention for the fluorinated ether compound, there were too many F atoms, and x / (2n + 1) = 100%, which was greater than 80%. This would reduce the solubility of the fluorinated ether in the salt, resulting in a decrease in the conductivity of the electrolyte and a serious decline in the low-temperature discharge performance.

[0120] In Comparative Example 6, the fluorinated ether compound used in the electrolyte was hexadecafluorononyl ether. Due to the large n value, resulting in n + m = 10, the fluorinated ether compound with a large n value would increase the viscosity of the electrolyte and could not effectively participate in ion solvation, deteriorating the battery performance.

[0121] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0122] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. Application of a fluoroether compound in a sodium-ion battery, characterized in that, The molecular formula of the fluoroether compound is: F x C n H 2n+1-x OC m H 2m+1 , where x / (2n + 1) < 80%, n ≥ 5, and m + n ≤ 9.

2. Use of the fluoroether compound according to claim 1 in a sodium ion battery, characterized in that, The fluoroether compound is selected from at least one of hexafluoropentyl methyl ether, hexafluoropentyl ethyl ether, heptafluoropentyl methyl ether, heptafluoropentyl ethyl ether, octafluoropentyl methyl ether, octafluoropentyl ethyl ether, nonafluorohexyl methyl ether, nonafluorohexyl ethyl ether, decafluoroheptyl methyl ether, or decafluoroheptyl ethyl ether.

3. Use of the fluoroether compound according to claim 2 in a sodium ion battery, characterized in that, The fluoroether compound is selected from at least one of 3,4,4,5,5,5 - hexafluoropentyl methyl ether, 3,4,4,5,5,5 - hexafluoropentyl ethyl ether, 2,2,3,3,4,4,5 - heptafluoropentyl methyl ether, 2,2,3,4,4,5,5 - heptafluoropentyl ethyl ether, 2,2,3,3,4,4,5,5 - octafluoropentyl methyl ether, 2,2,3,3,4,4,5,5 - octafluoropentyl ethyl ether, 1,2,2,3,3,4,4,5,5 - nonafluorohexyl methyl ether, 1,1,2,2,3,3,4,4,5,5 - decafluoroheptyl - methyl ether.

4. A sodium-ion battery electrolyte, characterized in that, It includes an electrolyte salt and a solvent, the solvent includes a fluoroether compound, and the molecular formula of the fluoroether compound is: F x C n H 2n+1-x OC m H 2m+1 , where x / (2n + 1) < 80%, n ≥ 5, and m + n ≤ 9.

5. The sodium ion battery electrolyte according to claim 4, characterized in that, The fluoroether compound is selected from at least one of hexafluoropentyl methyl ether, hexafluoropentyl ethyl ether, heptafluoropentyl methyl ether, heptafluoropentyl ethyl ether, octafluoropentyl methyl ether, octafluoropentyl ethyl ether, nonafluorohexyl methyl ether, nonafluorohexyl ethyl ether, decafluoroheptyl methyl ether, or decafluoroheptyl ethyl ether.

6. The sodium-ion battery electrolyte according to claim 5, wherein The fluoroether compound is selected from at least one of 3,4,4,5,5,5 - hexafluoropentyl methyl ether, 3,4,4,5,5,5 - hexafluoropentyl ethyl ether, 2,2,3,3,4,4,5 - heptafluoropentyl methyl ether, 2,2,3,4,4,5,5 - heptafluoropentyl ethyl ether, 2,2,3,3,4,4,5,5 - octafluoropentyl methyl ether, 2,2,3,3,4,4,5,5 - octafluoropentyl ethyl ether, 1,2,2,3,3,4,4,5,5 - nonafluorohexyl methyl ether, 1,1,2,2,3,3,4,4,5,5 - decafluoroheptyl - methyl ether.

7. The sodium ion battery electrolyte according to claim 4, wherein, The mass percentage content of the fluoroether compound in the electrolyte solution is 5 - 40%.

8. The sodium-ion battery electrolyte according to claim 7, wherein The mass percentage content of the fluoroether compound in the electrolyte solution is 8 - 30%.

9. The sodium-ion battery electrolyte according to claim 4, characterized in that, The electrolyte salt includes at least one of sodium perchlorate, sodium tetrafluoroborate, sodium hexafluorophosphate, sodium trifluoroacetate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, or sodium bis(trifluoromethylsulfonyl)imide.

10. The sodium ion battery electrolyte according to claim 4, wherein, The solvent further includes at least one of C3 - C5 carbonates, C2 - C6 carboxylates, C4 - C10 ethers, where the C3 - C7 carbonates include cyclic carbonates or linear carbonates with 3 - 5 carbon atoms; the C2 - C6 carboxylates include at least one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, or propyl propionate; the C4 - C10 ethers include cyclic ethers or linear ethers with 4 - 10 carbon atoms; and / or, in the sodium ion battery electrolyte solution, the mass percentage content of the solvent is 70 - 92%.

11. The sodium-ion battery electrolyte according to claim 10, characterized in that, The cyclic carbonate includes at least one of ethylene carbonate, vinylene carbonate, ethylene vinylene carbonate, propylene carbonate, γ-butyrolactone, and butylene carbonate; the linear carbonate includes at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and dipropyl carbonate.

12. The sodium ion battery electrolyte according to claim 10, characterized in that, The cyclic ether includes at least one of 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, and 2-trifluoromethyltetrahydrofuran; the linear ether includes at least one of dimethoxymethane, 1,2-dimethoxyethane, and diethylene glycol dimethyl ether.

13. The sodium-ion battery electrolyte according to claim 4, wherein The electrolyte further includes an additive, and the additive includes a fluorinated carbonate.

14. The sodium ion battery electrolyte according to claim 13, characterized in that, The fluorinated carbonate includes at least one of fluorinated ethylene carbonate or difluorinated ethylene carbonate, and the mass percentage content of the fluorinated carbonate in the sodium-ion battery electrolyte is 1-5%.

15. A sodium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and the sodium-ion battery electrolyte according to any one of claims 4-14.

16. The sodium-ion battery according to claim 15, wherein, The positive electrode includes a positive electrode active material, and the positive electrode active material is selected from at least one of layered metal oxides, polyanion compounds, Prussian compounds, phosphate compounds, and sulfate compounds, wherein The chemical formula of the layered metal oxide is Na x M y O z , where 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2, and M is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V; The molecular formula of the Prussian compound is Na x M[M′(CN)6] y ·zH2O, where M and M′ are transition metals, 0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20; The chemical formula of the phosphate compound is Na3(MO 1-x PO4)2F 1+2x , where 0 ≤ x ≤ 1 and M is selected from at least one of Al, V, Ge, Fe, and Ga; alternatively, the chemical formula of the phosphate compound is Na2MPO4F, and M is selected from at least one of Fe and Mn; the chemical formula of the sulfate compound is Na2M(SO4)2·2H2O, and M is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V; and / or, the negative electrode includes a negative electrode active material, and the negative electrode active material includes at least one of hard carbon and soft carbon.

17. The sodium ion battery according to claim 16, characterized in that, The layered metal oxide is NaNi m Fe n Mn p O2 (m + n + p = 1, 0 ≤ m ≤ 1, 0 ≤ n ≤ 1, 0 ≤ p ≤ 1) or NaNi m Co n Mn p O2 (m + n + p = 1, 0 ≤ m ≤ 1, 0 ≤ n ≤ 1, 0 ≤ p ≤ 1), or at least one of them.

18. The sodium-ion battery according to claim 16, characterized in that, The Prussian compound is Na x Mn[Fe(CN)6] y ·zH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20) or Na x Fe[Fe(CN)6] y ·zH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20), or at least one of them.

19. The sodium ion battery according to claim 16, characterized in that, The phosphate compound is at least one of Na3(VPO4)2F3 or Na3(VOPO4)2F.

20. The sodium ion battery according to claim 16, characterized in that, The phosphate compound is at least one of Na2FePO4F or Na2MnPO4F.

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