A high-voltage ether gel electrolyte and its preparation method and application

Abstract

The present invention belongs to the field of lithium / sodium metal battery materials and relates to a high-voltage ether gel electrolyte comprising a copolymer, a lithium / sodium salt, an organic solvent, and an additive. The copolymer is formed by polymerizing a polymerizable crosslinker monomer material; the lithium salt is one or more of LiPF6, LiTFSI, and LiFSI; the sodium salt is one or more of NaPF6, NaTFSI, and NaFSI; the organic solvent is composed of an ether solvent and a fluorinated solvent in a mass ratio of 0.05 to 1:1; and the additive is composed of a lithium / sodium ion salt and a phosphate compound mixed in any proportion. The ether electrolyte of the present invention facilitates the formation of a stable CEI / SEI film on the surfaces of high-voltage positive electrode materials and metallic lithium / sodium negative electrode materials, and exhibits a high electrochemical window (>5.6V), achieving the highest voltage ever achieved for an ether electrolyte, while also enabling lithium / sodium metal batteries to exhibit good cycling stability.

Description

Technical Field

[0001] The present invention belongs to the field of lithium / sodium metal battery materials, and more particularly relates to a high-voltage ether gel electrolyte and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries (LIBs) have become the preferred energy storage technology for electric vehicles, hybrid electric vehicles, and portable energy storage devices due to their high energy density, long cycle life, and lack of memory effect. Sodium-ion batteries (Na-ion Batteries) have attracted significant attention from the industry due to their low cost and electrochemical performance comparable to that of LIBs.

[0003] Electrolyte is a key material in lithium batteries. However, at high voltage, the lithium metal anode will continuously react with the electrolyte to form a chemically unstable and mechanically fragile solid electrolyte interface (SEI), resulting in continuous electrolyte consumption and low Coulombic efficiency (CE). In addition, the electrolyte decomposes under high voltage and produces harmful HF acid, which severely corrodes the cathode and causes structural degradation during cycling. Moreover, the decomposition and interfacial side reactions of ether electrolytes at high voltage are more serious, which seriously affects the capacity and cycle life of the battery. Currently, ester electrolytes are usually improved by optimizing the electrolyte solvent components and regulating additives to improve the voltage stability of the electrolyte, but there is no countermeasure for the design of high-voltage ether electrolytes.

[0004] Therefore, how to provide a high-voltage ether gel electrolyte is a problem that those skilled in the art urgently need to solve. Summary of the Invention

[0005] To overcome the shortcomings and deficiencies of the existing technology, the present invention provides an ether-based gel polymer electrolyte with a high oxidative decomposition voltage, nearly 1V higher than that of corresponding liquid ether electrolytes. This electrolyte is compatible with high-voltage cathode materials for use in lithium / sodium metal batteries. The present invention also provides a method for preparing the polymer electrolyte and its application in preparing lithium / sodium metal batteries.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A high-voltage ether gel electrolyte is composed of a copolymer, a lithium / sodium salt, an organic solvent and an additive. The copolymer is formed by polymerizing a polymerizable crosslinker monomer material; the lithium salt is one or more of LiPF6, LiTFSI, and LiFSI; the sodium salt is one or more of NaPF6, NaTFSI, and NaFSI; the organic solvent is composed of an ether solvent and a fluorinated solvent in a mass ratio of 0.05 to 1:1; and the additive is composed of a mixture of lithium / sodium ion salts and phosphate compounds in any proportion.

[0008] Preferably, the cross-linking agent monomer material is an amide-based cross-linking agent monomer material.

[0009] Preferably, the amide-based cross-linking agent monomer material is selected from one or more of N,N-methylenebisacrylamide, methacrylamide, N-ethylacrylamide, and cyclic acrylamide.

[0010] Preferably, the ether solvent is selected from one or more of cyclic ether tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, chain ether dimethoxymethane, 1,2-dimethoxyethane, 1,2-dimethoxypropane, and diethylene glycol dimethyl ether; the fluorinated solvent is selected from one or more of fluoroethylene carbonate and hydrofluoroether.

[0011] Preferably, the lithium ion salt is selected from one or more of lithium tetrafluoroborate, lithium bisoxalatoborate, lithium difluorooxalatoborate, and lithium nitrate; the sodium ion salt is selected from one or more of sodium tetrafluoroborate, sodium bisoxalatoborate, sodium difluorooxalatoborate, and sodium nitrate; and the phosphate ester compound is selected from one or more of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, and di(trimethylsilyl)difluorophosphate.

[0012] Preferably, the high voltage ether gel electrolyte is composed of the following components calculated by mass percentage: 1% to 15% copolymer, 10% to 20% lithium / sodium salt, 60% to 85% organic solvent, and 0.1% to 10% additives.

[0013] The method for preparing the high-voltage ether gel electrolyte specifically comprises the following steps:

[0014] (1) After mixing the organic solvent, add lithium / sodium salt, stir until no solid remains, then add additives, mix well, and obtain an electrolyte solution;

[0015] (2) adding a crosslinker monomer material to the electrolyte solution, mixing uniformly, then adding AIBN, wherein the AIBN accounts for 0.1% to 5% of the mass of the crosslinker monomer material, and stirring uniformly to obtain a gel electrolyte precursor solution;

[0016] (3) Add the gel electrolyte precursor solution to the battery, let it stand for 1-20 hours, and polymerize it at 45-70°C for 2-10 hours to obtain a high-voltage ether gel electrolyte.

[0017] A high-voltage ether gel electrolyte is used in lithium / sodium metal batteries. The lithium / sodium metal battery includes a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte and a shell. The electrolyte adopts the above-mentioned high-voltage ether gel electrolyte; the positive electrode sheet is formed by mixing active material, conductive agent carbon black, and binder polyvinylidene fluoride in a weight ratio to form a positive electrode slurry, which is coated on the positive electrode current collector Al foil; the active material is selected from one of a high-voltage lithium-rich positive electrode, a high-voltage lithium manganate positive electrode, a high-voltage sodium battery P2 positive electrode, and a high-voltage O3 positive electrode; the negative electrode sheet is a metal lithium sheet or a metal sodium sheet; the separator is selected from one of a PP film, a PE film, and a cellulose separator.

[0018] The electrolyte of the present invention is different from ordinary ether electrolytes. Its oxidative decomposition potential exceeds 5.6V, and its charging cut-off voltage exceeds 4.6V in button batteries and soft-pack batteries and can be stably cycled. It can pass the needle penetration test when applied to lithium / sodium metal batteries.

[0019] It can be seen from the above technical solutions that, compared with the prior art, the present invention provides a high-voltage ether gel electrolyte and its preparation method and application, which have the following beneficial effects:

[0020] 1. The present invention is an ether electrolyte, which has better affinity for lithium / sodium metal negative electrodes than liquid ester electrolytes and gel ester electrolytes, and can form a uniform CEI / SEI film on the positive and negative electrodes, thereby improving the service life of lithium / sodium metal batteries.

[0021] 2. Compared with liquid ether electrolytes, this product has a higher oxidative decomposition potential. The oxidative decomposition potential of ordinary ether electrolytes is only 4.65V, while the oxidative decomposition potential of the ether gel electrolyte after gelation of the present invention is as high as 5.65V, which can significantly improve the energy density of the battery.

[0022] 3. Existing research has not yet proposed an ether electrolyte with a charging voltage exceeding 4.6V. This invention proposes a strategy to surpass existing high-voltage ester electrolytes, broadening the categories and applications of high-voltage electrolytes and enabling the application of high-energy-density lithium metal batteries.

[0023] 4. The application of the electrolyte of the present invention enables lithium / sodium metal batteries to pass the needle penetration test. The preparation process is simple and can be quickly mass-produced, which has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0025] Figure 1 1 is the LSV curve of Example 1 and Comparative Example 1.

[0026] Figure 2 The performance comparison curve of Example 1 and Comparative Example 1 at 2-65V is shown. DETAILED DESCRIPTION

[0027] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0028] Example 1

[0029] Preparation of lithium metal batteries:

[0030] A lithium sheet with a thickness of 0.6 to 1.5 mm is used as the negative electrode, and a PP film is used as the separator;

[0031] (1) Preparation of positive electrode sheet: high voltage lithium-rich positive electrode active material Li[Li 0.2 Mn 0.53 Ni 0.27 ]O2, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an appropriate amount of n-methylpyrrolidone (NMP) solvent in a weight ratio of 8:1:1 to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector Al foil, and the positive electrode sheet is obtained after drying and rolling;

[0032] (2) Preparation of gel electrolyte precursor solution: In a dry argon atmosphere glove box, fluoroethylene carbonate (FEC), hydrofluoroether (HFE), and 1,2-dimethoxyethane (DME) were mixed in a mass ratio of FEC:HFE:DME=3:5:2. After complete clarification, 1M lithium salt LiPF6 was added, dissolved and stirred thoroughly, and then additives 2wt% tris(trimethylsilyl) phosphate (TMSP), 2wt% lithium difluorooxalatoborate (LiDFOB), and 0.1wt% lithium nitrate (LiNO3) were added to obtain a liquid ether electrolyte; then 3% N,N-methylenebisacrylamide and 3% azobisisobutyronitrile (AIBN) of the mass of N,N-methylenebisacrylamide were added to obtain a gel electrolyte precursor solution;

[0033] (3) Preparation of lithium-ion batteries: button-type batteries were assembled in a glove box with a moisture content of <0.5 ppm. The battery shell model was a 2016-type battery shell. The positive battery shell, positive electrode sheet, separator, negative electrode sheet, and negative battery shell were stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation. 35 μl of gel electrolyte precursor solution was dripped onto both sides of the separator, and the button-type battery was obtained after packaging.

[0034] (4) The battery was allowed to stand for 2 hours and then heated in a 60°C oven for 5 hours to obtain a lithium metal battery using a high-voltage ether gel electrolyte. The high-voltage ether gel electrolyte comprises, by mass percentage, 12% copolymer, 13.9% lithium salt, 70% organic solvent, and 4.1% additive.

[0035] Depend on Figure 1 and Figure 2 It can be seen that the oxidation decomposition potential of Example 1 is 5.65 V, and the capacity retention rate after 100 cycles at a high voltage of 2-4.65 V is 92%.

[0036] Example 2

[0037] The preparation method was essentially the same as that of Example 1, except that the additives used were 2 wt% tris(trimethylsilyl)phosphite (TMSPi), 2 wt% lithium difluorooxalatoborate (LiDFOB), and 0.1 wt% lithium nitrate (LiNO3), based on the total weight of the electrolyte. The resulting high-voltage ether-based gel electrolyte had a composition, calculated by mass percentage, of 12% copolymer, 13.9% lithium salt, 70% organic solvent, and 4.1% additives.

[0038] Example 3

[0039] The preparation method was essentially the same as that of Example 1, except that the additives used were 1 wt% tris(trimethylsilyl)phosphite (TMSPi), 3 wt% lithium tetrafluoroborate (LiBF4), and 0.1 wt% lithium nitrate (LiNO3), based on the total weight of the electrolyte. The resulting high-voltage ether-based gel electrolyte had a composition, calculated by mass percentage, of 12% copolymer, 13.9% lithium salt, 70% organic solvent, and 4.1% additives.

[0040] Example 4

[0041] The preparation method was essentially the same as that of Example 1, except that the additives used were 1 wt% tris(trimethylsilyl)phosphite (TMSPi), 3 wt% lithium difluorooxalatoborate (LiDFOB), and 1 wt% lithium bis(oxalatoborate) (LiBOB), based on the total weight of the electrolyte. The resulting high-voltage ether-based gel electrolyte had a composition, calculated by mass percentage, of 12% copolymer, 70% organic solvent, 5% additives, and 13% lithium salt.

[0042] Example 5

[0043] The preparation method was essentially the same as that of Example 1, except that the organic solvent used was a mixture of fluoroethylene carbonate (FEC), fluoroether (HFE), and 1,3-dioxolane (DOL) in a volume ratio of 3:4:3. The resulting high-voltage ether gel electrolyte had a composition, calculated by mass percentage, of 12% copolymer, 13.9% lithium salt, 70% organic solvent, and 4.1% additives.

[0044] Example 6

[0045] The preparation method was essentially the same as that of Example 1, except that the organic solvent used was a mixed solvent consisting of fluoroethylene carbonate (FEC), 1,2-dimethoxypropane (DMP), and 1,3-dioxolane (DOL) in a volume ratio of 4:3:3. The resulting high-voltage ether gel electrolyte had a composition, calculated by mass percentage, of 12% copolymer, 13.9% lithium salt, 70% organic solvent, and 4.1% additives.

[0046] Example 7

[0047] The preparation method was essentially the same as that of Example 1, except that the amide-based crosslinker monomer used was methacrylamide at a content of 4%. The resulting high-voltage ether gel electrolyte had a composition, calculated by mass percentage, of 13% copolymer, 70% organic solvent, 4.1% additive, and 12.9% lithium salt.

[0048] Example 8

[0049] The preparation method is basically the same as that of Example 1, except that the active material of the positive electrode plate is a high-voltage lithium manganese oxide positive electrode.

[0050] Example 9

[0051] The preparation method is basically the same as that of Example 1, except that the active material of the positive electrode plate is a high-voltage P2 sodium-based positive electrode material, and the lithium salt compound used is replaced by a corresponding sodium salt compound.

[0052] Comparative Example 1

[0053] The preparation method is basically the same as that of Example 1, except that a liquid ether electrolyte without a crosslinking agent monomer and an AIBN initiator is used instead of a high voltage ether gel electrolyte to obtain the battery of Comparative Example 1. The LSV curve of the battery obtained under the same test conditions is as follows: Figure 1 As shown. Figure 1 It can be seen that the oxidation decomposition potential of Comparative Example 1 is 4.75 V, which is much lower than that of Example 1, and its capacity retention rate after 100 cycles at a high voltage of 2-4.65 V is 70%.

[0054] Comparative Example 2

[0055] The preparation method is basically the same as that of Example 1, except that a liquid ester electrolyte is used, and the composition is as follows: the organic solvent (EC, EMC, and DMC are mixed in a mass ratio of 1:2:2) accounts for 80.8% of the total mass of the electrolyte, the lithium salt LiPF6 accounts for 15.1wt% of the total mass of the electrolyte, and the additives are 2wt% tris(trimethylsilyl) phosphate (TMSP), 2wt% lithium difluorooxalatoborate (LiDFOB), and 0.1wt% lithium nitrate (LiNO3).

[0056] Comparative Example 3

[0057] The preparation method is basically the same as that of Example 1, except that a gel ester electrolyte is used, which is composed of: an organic solvent (EC, EMC, and DMC are mixed in a mass ratio of 1:2:2) accounting for 77% of the total mass of the electrolyte, a lithium salt LiPF6 accounting for 15.1wt% of the total mass of the electrolyte, and additives such as 2wt% tris(trimethylsilyl) phosphate (TMSP), 2wt% lithium difluorooxalatoborate (LiDFOB), and 0.1wt% lithium nitrate (LiNO3). Then, 3% N,N-methylenebisacrylamide and 0.8% azobisisobutyronitrile (AIBN) are added, the electrolyte is loaded into the battery, the battery is allowed to stand for 2 hours, and then placed in an oven at 60°C and heated for 5 hours to obtain a lithium metal battery using an ether gel electrolyte.

[0058] Comparative Example 4

[0059] The preparation method is basically the same as that of Example 8, except that a liquid ether electrolyte is used. Fluoroethylene carbonate (FEC), hydrofluoroether (HFE), and 1,2-dimethoxyethane (DME) are mixed in a mass ratio of FEC:HFE:DME = 3:5:2. After complete clarification, 1M lithium salt LiPF6 is added, dissolved, and stirred thoroughly. Then, additives 2wt% tris(trimethylsilyl) phosphate (TMSP), 2wt% lithium difluorooxalatoborate (LiDFOB), and 0.1wt% lithium nitrate (LiNO3) are added.

[0060] Comparative Example 5

[0061] The preparation method is basically the same as that of Comparative Example 1, except that a high-voltage P2 sodium cathode material is used, and the lithium salt compound in the liquid ether electrolyte is replaced by a sodium salt compound.

[0062] The test results of the embodiments and comparative examples of the present invention are shown in Table 1 and Table 2:

[0063] Table 1 Capacity retention and oxidation decomposition potential results of lithium metal batteries

[0064]

[0065]

[0066] Table 2 Capacity retention and oxidation decomposition potential results of sodium metal batteries

[0067]

[0068] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An ether gel electrolyte, consisting of a copolymer, a lithium salt or a sodium salt, an organic solvent and an additive, characterized in that: The copolymer is formed by polymerizing a polymerizable crosslinking agent monomer material; the lithium salt is one or more of LiPF6, LiTFSI, and LiFSI; the sodium salt is one or more of NaPF6, NaTFSI, and NaFSI; the organic solvent is composed of an ether solvent and a fluorinated solvent in a mass ratio of 0.05 to 1:1; the additive is composed of a mixture of a lithium ion salt or a sodium ion salt and a phosphate compound in any proportion; The ether gel electrolyte is composed of 1% to 15% copolymer, 10% to 20% lithium salt or sodium salt, 60% to 85% organic solvent, and 0.1% to 10% additives, calculated by mass percentage. The ether gel electrolyte has an oxidative decomposition potential exceeding 5.6 V; The cross-linking agent monomer material is an amide-based cross-linking agent monomer material.

2. The ether gel electrolyte according to claim 1, characterized in that: The amide-based cross-linking agent monomer material is selected from one or more of N,N-methylenebisacrylamide, methacrylamide, N-ethylacrylamide, and cyclic acrylamide.

3. The ether gel electrolyte according to claim 1, characterized in that: The ether solvent is selected from one or more of cyclic ether tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, chain ether dimethoxymethane, 1,2-dimethoxyethane, 1,2-dimethoxypropane, and diethylene glycol dimethyl ether; the fluorinated solvent is selected from one or more of fluoroethylene carbonate and hydrofluoroether.

4. The ether gel electrolyte according to claim 1, characterized in that: The lithium ion salt is selected from one or more of lithium tetrafluoroborate, lithium bisoxalatoborate, lithium difluorooxalatoborate, and lithium nitrate; the sodium ion salt is selected from one or more of sodium tetrafluoroborate, sodium bisoxalatoborate, sodium difluorooxalatoborate, and sodium nitrate; and the phosphate compound is selected from one or more of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, and di(trimethylsilyl)difluorophosphate.

5. The method for preparing an ether gel electrolyte according to any one of claims 1 to 4, characterized in that: The specific steps include: (1) After mixing the organic solvent, add lithium salt or sodium salt, stir until no solid remains, then add additives, mix well, and obtain an electrolyte solution; (2) adding a crosslinker monomer material to the electrolyte solution, mixing uniformly, then adding AIBN, wherein the AIBN accounts for 0.1% to 5% of the mass of the crosslinker monomer material, and stirring uniformly to obtain a gel electrolyte precursor solution; (3) Add the gel electrolyte precursor solution to the battery, let it stand for 1-20 hours, and polymerize it at 45-70°C for 2-10 hours to obtain an ether gel electrolyte.

6. An application of an ether gel electrolyte in a lithium metal battery or a sodium metal battery, wherein the lithium metal battery or the sodium metal battery comprises a positive electrode sheet, a negative electrode sheet, a separator, an electrolyte and a casing, characterized in that: The electrolyte adopts the ether gel electrolyte as described in any one of claims 1 to 4; the positive electrode plate is formed by mixing the active material, the conductive agent carbon black, and the binder polyvinylidene fluoride in a weight ratio of 8:1:1 to form a positive electrode slurry, which is coated on the positive electrode current collector Al foil; the active material is selected from one of the lithium-rich positive electrode, the lithium manganate positive electrode, the P2 type positive electrode, and the O3 type positive electrode; the negative electrode plate is a metal lithium sheet or a metal sodium sheet; the separator is selected from one of the PP film, the PE film, and the cellulose separator.

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