High-voltage-resistant polymer-based solid electrolyte as well as preparation method and application thereof

Abstract

The embodiment of the invention relates to a high-voltage-resistant polymer-based solid electrolyte and a preparation method and application thereof, and the preparation method comprises the following steps: uniformly mixing a lithium salt, a polymer monomer, a cross-linking agent and a solvent in proportion to obtain a polymer-based solid electrolyte precursor; wherein the polymer monomer comprises a cyanoacrylate monomer; and adding an initiator into the polymer-based solid electrolyte precursor, and then carrying out thermal polymerization to obtain the polymer-based solid electrolyte with a polar functional group with a cyano group, namely the high-voltage-resistant polymer-based solid electrolyte. By using the cyanoacrylate monomer containing a cyano functional group, cyano can be effectively adsorbed and coordinated on positive transition metal to form a stable-bond positive electrode-electrolyte interface, so that the leakage of solvent molecules is reduced, the oxidation stability of the electrolyte is effectively improved, and the electrolyte can be matched with a high-voltage positive electrode material; the chemical stability of the interface is maintained.

Description

Technical Field

[0001] The present invention relates to the field of solid electrolyte materials, and particularly to a high-voltage resistant polymer-based solid electrolyte and its preparation method and application. Background Art

[0002] With the rapid development of electric vehicles, energy storage devices, etc., the urgent demand for high-energy density batteries is increasing day by day. However, at present, commercial liquid lithium batteries are not only difficult to achieve the ideal high energy density, but also have serious safety hazards due to the flammability and explosiveness of liquid electrolytes. Therefore, the development of solid-state lithium batteries has become a competitive field for researchers and important new energy companies around the world.

[0003] Solid electrolytes have the characteristics of non-volatility, flame retardancy, strong mechanical strength, and the ability to inhibit lithium dendrites. Therefore, the development of solid-state lithium batteries using solid electrolytes can effectively solve the problems of energy density and safety. At present, inorganic solid electrolytes and polymer electrolytes have been widely studied. Among them, inorganic solid electrolytes have high room temperature ionic conductivity (>10 -4 Scm -1 ) and a wide electrochemical window, but they have problems such as poor contact with the electrode interface, high sensitivity to oxygen and water, inherent brittleness, and poor interfacial expansibility, thus limiting further development. Polymer electrolytes are regarded as the most promising materials for preparing solid-state lithium batteries due to their good flexibility, close contact with the electrode, easy processing, and low cost. However, polymer electrolytes have low room temperature ionic conductivity, narrow electrochemical window, and poor electrochemical stability. Therefore, using polymer electrolytes to match high-voltage cathodes to prepare high-energy density solid-state batteries is still a huge challenge.

[0004] Therefore, there is an urgent need to design a polymer-based solid electrolyte with a wide electrochemical window and capable of forming a stable electrolyte-electrode interface at high voltages. Summary of the Invention

[0005] The purpose of the present invention is to address the deficiencies of the prior art and provide a high-voltage resistant polymer-based solid electrolyte and its preparation method and application. This high-voltage resistant polymer-based solid electrolyte exhibits good physical and chemical properties and electrochemical performance at a cut-off voltage of greater than or equal to 4.5V.

[0006] To achieve the above purpose, in the first aspect, the present invention provides a preparation method of a high-voltage resistant polymer-based solid electrolyte, and the preparation method includes:

[0007] Mixing a lithium salt, a polymer monomer, a crosslinking agent, and a solvent in proportion to obtain a polymer-based solid electrolyte precursor; wherein, the polymer monomer includes cyanoacrylate monomers.

[0008] An initiator is added to the polymer-based solid electrolyte precursor, and then thermal polymerization is carried out to obtain a polymer-based solid electrolyte with polar functional groups containing cyano groups, which is the high-voltage-resistant polymer-based solid electrolyte.

[0009] Preferably, the mass ratio of the polymer monomer to the solvent is 1:10 - 10:1; the mass of the crosslinking agent is 0.5% - 3% of the mass of the polymer monomer; the concentration of the lithium salt in the polymer-based solid electrolyte precursor is 0.5 mol / L - 2 mol / L.

[0010] Preferably, the mass of the initiator is not more than 1% of the mass of the polymer-based solid electrolyte precursor.

[0011] Preferably, the temperature of the thermal polymerization is 45°C - 80°C, and the time is 1 hour - 24 hours.

[0012] Preferably, the lithium salt includes one or more of lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorodioxalate phosphate;

[0013] The cyanoacrylate monomers include one or more of 2-cyanoethyl acrylate, acrylonitrile, 2-ethyl cyanoacrylate, 2-cyanoethoxyethyl acrylate, cyanoethyl methacrylate, ethyl cyanoacrylate, 2-cyanopropyl acrylate, 2-cyanopentyl acrylate, 3-amino-2-butenoic acid cyanoacetic acid, and ethyl 2-cyano-3-methylbutenoate;

[0014] The solvent includes carbonate compounds and / or sulfite compounds; the carbonate compounds include one or several of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate;

[0015] The sulfite compounds include one or several of dimethyl sulfite, dimethyl sulfate, diethyl sulfite, ethylene sulfite, and propylene sulfite;

[0016] The crosslinking agent is an acrylate compound, and the acrylate compounds include one or several of ethoxylated trimethylolpropane triacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, and pentaerythritol triacrylate.

[0017] Preferably, the initiator is a radical initiator; the radical initiators include one or several of azobisisobutyronitrile, azobisisoheptonitrile, and benzoyl peroxide.

[0018] In a second aspect, the present invention provides a high-voltage resistant polymer-based solid electrolyte, which is prepared by the preparation method according to any one of the first aspects above.

[0019] In a third aspect, the present invention provides a solid-state battery, which includes the high-voltage resistant polymer-based solid electrolyte according to the second aspect.

[0020] Preferably, the positive electrode active material of the solid-state battery includes one or two of layered structure oxides and polyanion-type compounds; the layered structure oxides include one or two of lithium cobaltate and lithium nickel cobalt manganate; the polyanion-type compound includes lithium iron phosphate; the negative electrode active material includes any one of graphite and metallic lithium sheets.

[0021] In a fourth aspect, the present invention provides a preparation method for the solid-state battery according to the third aspect, and the preparation method includes:

[0022] Mix lithium salt, polymer monomer, cross-linking agent, and solvent evenly in proportion to obtain a polymer-based solid electrolyte precursor; wherein, the polymer monomer includes cyanoacrylate monomers.

[0023] Add an initiator to the polymer-based solid electrolyte precursor to obtain a liquid precursor to be polymerized.

[0024] Inject the liquid precursor to be polymerized between the positive and negative electrodes inside the battery to be assembled, so that the liquid precursor to be polymerized fully infiltrates the positive electrode, negative electrode, and separator, and then complete the encapsulation of the battery; or, drop the liquid precursor to be polymerized onto the positive electrode, negative electrode, and separator of the battery to be assembled, and then complete the encapsulation of the battery.

[0025] Heat-treat the battery to obtain the solid-state battery.

[0026] A preparation method of a high-voltage-resistant polymer-based solid electrolyte provided by an embodiment of the present invention prepares a polymer-based solid electrolyte applicable to high-voltage-resistant types by screening polymer monomers and solvents and optimizing the precursor ratio using an in-situ polymerization process. By using a cyanoacrylate monomer containing a cyano functional group, the cyano group can be effectively adsorbed and coordinated on the cathode transition metal to form a stable cathode-electrolyte interface, reducing the leakage of solvent molecules and effectively improving the oxidation stability of the electrolyte; at the same time, the parasitic reaction between the solvent molecules and the electrode is reduced, enabling the solid-state battery to operate stably at a high voltage (≥4.5V); after polymerization, the cyanoacrylate monomer forms a solid electrolyte containing polar groups. Due to the high electronegativity of the polar functional groups, they can preferentially coordinate and adsorb with the transition metal on the cathode, reducing the dissolution of the transition metal on the cathode side; the unique coordination structure formed by the coordination of the polar functional groups in the cyanoacrylate monomer and the cathode reduces the decomposition of the solvent, thereby increasing the oxidation potential of the electrolyte. The high-voltage-resistant polymer-based solid electrolyte prepared by the present invention exhibits good antioxidant properties, and the electrochemical window is broadened to about 5.1V, which can match high-voltage cathode materials and maintain the chemical stability of the interface, thus showing good physical and chemical properties and electrochemical performance at a cut-off voltage of ≥4.5V and having good application prospects. Description of the Drawings

[0027] Figure 1 It is a flowchart of the preparation method of the high-voltage-resistant polymer-based solid electrolyte provided by the embodiment of the present invention;

[0028] Figure 2 It is a test curve of the electrochemical window of the high-voltage-resistant polymer-based solid electrolyte provided by Embodiment 1 of the present invention;

[0029] Figure 3 It is a test curve of the electrochemical window of the electrolyte provided by Comparative Example 1 of the present invention;

[0030] Figure 4 It is a leakage current test curve provided by Embodiment 2 and Comparative Example 1 of the present invention;

[0031] Figure 5 It is an electrochemical cycling performance diagram of a solid-state battery with lithium cobaltate as the cathode at a charging cut-off voltage of 4.5V provided by Embodiment 2 of the present invention;

[0032] Figure 6 It is an electrochemical cycling performance diagram of a solid-state battery with lithium cobaltate as the cathode at a charging cut-off voltage of 4.6V provided by Embodiment 2 of the present invention;

[0033] Figure 7 It is a battery cycling performance diagram of a solid-state battery with lithium nickel cobalt manganese oxide as the cathode at a charging cut-off voltage of 4.7V provided by Embodiment 2 of the present invention;

[0034] Figure 8 One of the XPS diagrams of the interface between the high-voltage resistant polymer-based solid electrolyte and the positive electrode provided in Example 2 of the present invention;

[0035] Figure 9 Another XPS diagram of the interface between the high-voltage resistant polymer-based solid electrolyte and the positive electrode provided in Example 2 of the present invention;

[0036] Figure 10 One of the electrochemical performance comparison diagrams of the solid-state battery provided in Example 2 of the present invention and the button cell provided in Comparative Example 1;

[0037] Figure 11 Another electrochemical performance comparison diagram of the solid-state battery provided in Example 2 of the present invention and the button cell provided in Comparative Example 1. Detailed implementation manners

[0038] The technical solutions of the present invention will be further described in detail below with reference to the drawings and examples.

[0039] The embodiment of the present invention provides a preparation method of a high-voltage resistant polymer-based solid electrolyte, and the process is as Figure 1 shown, including the following steps:

[0040] Step 110: Mix a lithium salt, a polymer monomer, a crosslinking agent, and a solvent evenly to obtain a polymer-based solid electrolyte precursor;

[0041] Among them, the lithium salt includes one or more of lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorodioxalate phosphate.

[0042] The polymer monomer includes cyanoacrylate monomers. The cyanoacrylate monomers can include one or more of 2-cyanoethyl acrylate, acrylonitrile, 2-ethyl cyanoacrylate, 2-cyanoethoxyethyl acrylate, cyanoethyl methacrylate, ethyl cyanoacrylate, 2-cyano propyl acrylate, 2-cyano pentyl acrylate, 3-amino-2-butenoic acid cyanoacetic acid, and ethyl 2-cyano-3-methylbutenoate. The cyanoacrylate monomers can provide cyano groups for the solid electrolyte, which have significant electronegativity and low highest occupied molecular orbitals, can improve the oxidation stability of the solid electrolyte, and make it suitable for positive electrodes with high voltages (greater than or equal to 4.5V).

[0043] The crosslinking agent can be an acrylate compound. Among them, the acrylate compound specifically includes one or several of ethoxylated trimethylolpropane triacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, and pentaerythritol triacrylate.

[0044] The solvent may include carbonate compounds and / or sulfite compounds. Among them, the carbonate compounds include one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. The sulfite compounds include one or more of dimethyl sulfite, dimethyl sulfate, diethyl sulfite, ethylene sulfite, and propylene sulfite. The polar groups in the solvent can improve ionic conductivity, form hydrogen bonds or other interactions with the polymer backbone, enhance the mechanical strength of the solid electrolyte, and also form channels for ion transport to improve ion mobility, etc. In particular, the sulfur-oxygen double bond in the sulfite compound has high chemical activity and can react with other substances to form a new interfacial layer. For example, during the decomposition of the electrolyte, the sulfur-oxygen double bond can break to generate various products (sulfides), and these products can further react with the electrode surface to form a stable passivation layer, thereby enhancing the stability and functionality of the interface.

[0045] Specifically, first, a single solvent can be used, or two solvents can be mixed. When the two solvents are carbonate compounds and sulfite compounds, the mass ratio of the carbonate compound to the sulfite compound can be 1:4.

[0046] Then, a polymer monomer and a crosslinking agent are added to the solvent, and they are mixed by mechanical stirring at a temperature of 30°C for 2 hours to obtain a mixed solution.

[0047] Finally, a lithium salt is added to the mixed solution, and they are mixed by mechanical stirring at a temperature of 30°C for 2 hours to obtain an electrolyte precursor.

[0048] Among them, the mass ratio of the polymer monomer to the solvent can be 1:10 - 10:1, preferably 3:20 - 1:1. The mass of the crosslinking agent can be 0.5% - 3% of the mass of the polymer monomer, preferably 1% - 2%. The concentration of the lithium salt in the polymer-based solid electrolyte precursor can be 0.5 mol / L - 2 mol / L, preferably 1 mol / L - 2 mol / L.

[0049] Step 120: Add an initiator to the polymer-based solid electrolyte precursor, and then perform thermal polymerization to obtain a polymer-based solid electrolyte with polar functional groups having cyano groups, which is a high-voltage-resistant polymer-based solid electrolyte.

[0050] Specifically, this step can be carried out in a glove box with the water and oxygen contents both less than 0.1 ppm.

[0051] The initiator includes free radical initiators. The mass of the initiator is not more than 1% of the mass of the polymer-based solid electrolyte precursor, preferably 0.2%-1%. The free radical initiator can include one or more of azobisisobutyronitrile, azobisisoheptonitrile, and benzoyl peroxide.

[0052] The conditions for thermal polymerization are specifically: temperature 45°C - 80°C, time 1 hour - 24 hours, preferably 60°C, 2 hours. During the thermal polymerization process, the initiator decomposes to generate free radicals, causing the cyanoacrylate monomers to polymerize to form cyanoacrylate polymer chains, and the cross-linking agent connects different cyanoacrylate polymer chains to form a network structure, obtaining a polymer-based solid electrolyte with polar functional groups, that is, a high-voltage-resistant polymer-based solid electrolyte. Among them, the polar functional groups are cyano groups and fluorinated groups.

[0053] A preparation method of a high-voltage-resistant polymer-based solid electrolyte provided by an embodiment of the present invention prepares a polymer-based solid electrolyte applicable to high-voltage types by screening polymer monomers and solvents and optimizing the precursor ratio using an in-situ polymerization process.

[0054] By using cyanoacrylate monomers containing cyano functional groups, the cyano groups can be effectively adsorbed and coordinated on the cathode transition metal to form a stable cathode-electrolyte interface, reducing the leakage of solvent molecules, effectively improving the oxidation stability of the electrolyte; at the same time, reducing the parasitic reaction between solvent molecules and the electrode, enabling the solid-state battery to work stably at high voltages (≥4.5V); after the cyanoacrylate monomers polymerize to form a solid electrolyte containing polar groups, due to the polar functional groups having high electronegativity, they can preferentially coordinate and adsorb with the transition metal on the cathode, reducing the dissolution of the transition metal on the cathode side; due to the unique coordination structure formed by the coordination of the polar functional groups in the cyanoacrylate monomers with the cathode, the decomposition of the solvent is reduced, thereby increasing the oxidation potential of the electrolyte. The high-voltage-resistant polymer-based solid electrolyte prepared by the present invention exhibits good antioxidant properties, the electrochemical window is broadened to about 5.1V, it can match high-voltage cathode materials, maintain the chemical stability of the interface, and thus exhibit good physical and chemical properties and electrochemical performance at a cut-off voltage higher than 4.5V, having good application prospects.

[0055] The high-voltage-resistant polymer-based solid electrolyte provided by an embodiment of the present invention can be applied to solid-state lithium metal batteries.

[0056] When applying it to a solid-state lithium metal battery, the solid-state battery can be prepared in the following manner:

[0057] Step 210, uniformly mix a lithium salt, a polymer monomer, a cross-linking agent, and a solvent in proportion to obtain a polymer-based solid electrolyte precursor;

[0058] Among them, the polymer monomer includes cyanoacrylate monomers;

[0059] Step 220: Add an initiator to the polymer-based solid electrolyte precursor to obtain a liquid precursor to be polymerized.

[0060] It should be noted that the various materials in Step 210 and Step 220 are the same as those used in the preparation of the above high-voltage-resistant polymer-based solid electrolyte, and the mixing methods and conditions are also the same, which will not be elaborated here.

[0061] Step 230: Inject the liquid precursor to be polymerized between the positive and negative electrodes inside the battery to be assembled, so that the liquid precursor to be polymerized fully infiltrates the positive electrode, negative electrode and separator, and then complete the encapsulation of the battery; or, drop the liquid precursor to be polymerized onto the positive electrode, negative electrode and separator of the battery to be assembled, and then complete the encapsulation of the battery.

[0062] Step 240: Heat-treat the battery to obtain a solid-state battery.

[0063] Those skilled in the art can select the positive and negative electrode materials of the solid-state battery according to the needs with reference to the following materials.

[0064] The positive electrode active material of the solid-state battery includes one or two of layered structure oxides and polyanion-type compounds; the layered structure oxides include: one or two of lithium cobaltate and lithium nickel cobalt manganate; the polyanion-type compounds include: lithium iron phosphate; the negative electrode active material includes: any one of graphite and metallic lithium flakes.

[0065] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0066] Example 1

[0067] In this example, a high-voltage-resistant polymer-based solid electrolyte was prepared.

[0068] Preparation of electrolyte precursor: Mix the solvent fluoroethylene carbonate (FEC) and dimethyl sulfite (DMS) in a mass ratio of 1:4; then add 2-cyanoethyl acrylate (CA) as a polymer monomer with a mass ratio of 3:20 to the solvent and ethoxylated trimethylolpropane triacrylate as a crosslinking agent accounting for 2% of the mass of the polymer monomer, and stir at 30 °C for about 2 hours to obtain a mixed solution; then add lithium salt lithium difluoro(oxalato)borate (LiDFOB) to the mixed solution in an amount of 1 mol / L and stir at 30 °C for about 2 hours until completely dissolved, finally obtaining a uniformly mixed polymer-based solid electrolyte precursor.

[0069] Preparation of polymer-based solid electrolyte: Add 1% by mass of initiator azobisisobutyronitrile (AIBN) to the polymer-based solid electrolyte precursor obtained above, and heat at 60 °C for 2 hours to fully polymerize CA, thus obtaining a polymer-based solid electrolyte with high voltage resistance.

[0070] Use the prepared polymer-based solid electrolyte with high voltage resistance to assemble a half-blocking battery for electrochemical window testing. The specific process is as follows: Use a stainless steel gasket as the working electrode and lithium metal as the reference electrode to assemble a half-blocking battery, and conduct linear sweep voltammetry (LSV) testing. The test is carried out at a scan rate of 1 mV / s from the open circuit voltage to the termination voltage of 7 V. The test equipment is a Gamry electrochemical workstation Interface 1000, and the results are as Figure 2 shown below.

[0071] Example 2

[0072] In this example, a solid-state battery containing a polymer-based solid electrolyte with high voltage resistance was prepared.

[0073] Preparation of electrolyte precursor: Mix the solvent fluoroethylene carbonate (FEC) and dimethyl sulfite (DMS) in a mass ratio of 1:4; then add 2-cyanoethyl acrylate (CA) as a polymer monomer with a mass ratio of 3:20 to the solvent and ethoxylated trimethylolpropane triacrylate as a crosslinking agent accounting for 2% of the mass of the polymer monomer, and stir at 30 °C for about 2 hours to obtain a mixed solution; then add lithium salt lithium difluoro(oxalato)borate (LiDFOB) to the mixed solution in an amount of 1 mol / L and stir at 30 °C for about 2 hours until completely dissolved, finally obtaining a uniformly mixed polymer-based solid electrolyte precursor.

[0074] Use the polymer-based solid electrolyte precursor prepared above to carry out the preparation and related tests of a solid-state battery. The specific process is as follows:

[0075] Add 1% by mass of the initiator azobisisobutyronitrile (AIBN) to the obtained polymer-based solid electrolyte precursor to form a liquid precursor to be polymerized. Take 15 μL of the liquid precursor to be polymerized, drop it on the lithium cobalt oxide (LCO) positive electrode, then cover it with a polypropylene separator, and drop another 15 μL of the liquid precursor to be polymerized to soak the separator. Then stack the negative lithium metal sheet, gasket, and shrapnel; finally, move the assembled battery above to a heating device and heat it at 60 °C for 2 hours to cause the CA to undergo a polymerization reaction to form a high-voltage-resistant polymer-based solid electrolyte, and simultaneously in-situ form an integrated stack including a positive electrode, electrolyte, separator, and negative electrode. Finally, encapsulate the battery with a casing to obtain a solid-state battery, namely a Li||LCO battery.

[0076] First, use a CT2001A battery test system to perform a timed current method to test the leakage current of the solid-state battery (Li||LCO battery) with the above-mentioned lithium cobalt oxide (LCO) positive electrode: Charge the battery to 4.2 V, 4.3 V, 4.4 V, 4.5 V, 4.6 V, 4.7 V, 4.8 V, 4.9 V, and 5.0 V and hold for 3 hours at each voltage, and observe the leakage current of the battery to evaluate the actual oxidation stability of the electrolyte. The results are as Figure 4 shown.

[0077] Second, use a CT-4008Tn-mA battery test system to characterize the electrochemical performance of the solid-state battery (Li||LCO battery) with the above-mentioned lithium cobalt oxide (LCO) positive electrode: The results are as Figure 5 shown. At a charging cut-off voltage of 4.5 V and a charge-discharge rate of 1 C, the capacity retention rate after 400 cycles is 89.5%, and the discharge capacity is about 157.2 mAh / g. As Figure 6 shown. At a charging cut-off voltage of 4.6 V and a charge-discharge rate of 1 C, the capacity retention rate after 600 cycles is 84%, and the discharge capacity is about 168.9 mAh / g. This shows that the polymer-based solid electrolyte can withstand high voltages.

[0078] Third, replace the above positive electrode with lithium nickel 0.8 Co 0.1 Mn 0.1 O2 (NCM811), assemble a solid-state battery according to the above steps, namely a Li||NCM811 battery, and use a CT2001A battery test system to characterize the electrochemical performance. The results are as Figure 7 shown. At a charging cut-off voltage of 4.7 V and a charge-discharge rate of 1 C, the capacity retention rate after 200 cycles is 79.3%, and the discharge capacity is about 153.9 mAh / g.

[0079] In summary, the solid-state battery prepared in this embodiment can maintain a good capacity retention rate during long-term charge and discharge at a cut-off voltage greater than or equal to 4.5 V, indicating that the polymer-based solid electrolyte is resistant to high voltages.

[0080] Fourth, the solid-state battery with lithium cobaltate (LCO) as the positive electrode (Li||LCO battery) was charged and discharged 10 cycles, and then the positive electrode of the battery was tested by X-ray photoelectron spectroscopy (XPS).

[0081] Among them, the X-ray photoelectron spectroscopy (XPS) test instrument is the AXI S Ul traDLD-600W instrument of Shimadzu Corporation, Japan, and the voltage and beam current are 15 kV and 15 mA respectively.

[0082] The test results are as Figures 8 - 9 shown. Figure 8 The peak splitting of N in [the figure] indicates that the -CN group in the polymer monomer used does coordinate with Co in the positive electrode, and this coordination can form a stable positive electrode-electrolyte interface. 3+ This coordination can form a stable positive electrode-electrolyte interface. Figure 9 The peak splitting of F in [the figure] indicates that the formed positive electrode-electrolyte interface contains LiF, and LiF has high mechanical properties and chemical stability, which can well protect the positive electrode side and reduce side reactions caused by solvent decomposition.

[0083] Fifth, the cycle capacity retention rate of the solid-state battery with lithium cobaltate (LCO) as the positive electrode (Li||LCO battery) was tested. At a voltage of 3 - 4.5 V and a charge-discharge rate of 0.5 C, the cycle capacity retention rate was tested for 500 cycles, and the results are as Figure 10 shown. At a voltage of 3 - 4.6 V and a charge-discharge rate of 0.5 C, the cycle capacity retention rate was tested for 300 cycles, and the results are as Figure 11 shown.

[0084] Example 3

[0085] In this example, a solid-state battery containing a polymer-based solid electrolyte resistant to high voltages was prepared.

[0086] Preparation of the electrolyte precursor: Mix the solvent fluoroethylene carbonate (FEC) and dimethyl sulfite (DMS) in a mass ratio of 1:4; then add to the solvent the polymer monomer 2-cyanoethyl acrylate (CA) with a mass ratio to the solvent of 1:4 and 2% by mass of the polymer monomer of the cross-linking agent ethoxylated trimethylolpropane triacrylate, and stir at 30 °C for about 2 hours to obtain a mixed solution; then add the lithium salt lithium difluorooxalate borate (LiDFOB) to the mixed solution in an amount of 2 mol / L and stir at 30 °C for about 2 hours until completely dissolved, finally obtaining a uniformly mixed polymer-based solid electrolyte precursor.

[0087] Preparation of Polymer - based Solid Electrolyte and Assembly of Solid - state Battery: Add 1% by mass of initiator azobisisobutyronitrile (AIBN) to the obtained electrolyte precursor above to form a liquid precursor to be polymerized. Take 15 μL of the liquid precursor to be polymerized, drop it on the lithium cobaltate (LCO) positive electrode, then cover it with a polypropylene separator, and drop another 15 μL of the liquid precursor to be polymerized to soak the separator. Then stack the negative lithium metal sheet, gasket, and spring piece; finally, move the assembled battery above to a heating device and heat it at 60 °C for 2 hours to cause the polymerization of CA to form a high - voltage - resistant polymer - based solid electrolyte, and simultaneously in - situ form an integrated stack including the positive electrode, electrolyte, separator, and negative electrode. Finally, encapsulate the battery with a casing to obtain a solid - state battery.

[0088] Electrochemical performance characterization was carried out using a CT - 4008Tn - mA battery test system. The results were as follows: For this solid - state battery, at a charging cut - off voltage of 4.6 V and a charge - discharge rate of 1 C, the capacity retention rate was 88% after 600 cycles, and the discharge capacity was approximately 171.9 mAh / g.

[0089] Example 4

[0090] In this example, a solid - state battery containing a polymer - based solid electrolyte was prepared.

[0091] Preparation of Electrolyte Precursor: Mix the solvent fluoroethylene carbonate (FEC) and dimethyl sulfite (DMS) in a mass ratio of 1:4; then add 2 - cyanoethyl acrylate (CA) as a polymer monomer with a mass ratio of 7:20 to the solvent mass and 2% by mass of the cross - linker ethoxylated trimethylolpropane triacrylate to the polymer monomer to the solvent, and stir at 30 °C for about 2 hours to obtain a mixed solution; then add lithium salt lithium difluoro(oxalato)borate (LiDFOB) to the mixed solution in an amount of 2 mol / L and stir at 30 °C for about 2 hours until completely dissolved to finally obtain a uniformly mixed polymer - based solid electrolyte precursor.

[0092] Preparation of Polymer - based Solid Electrolyte and Assembly of Solid - state Battery: Add 1% by mass of initiator azobisisobutyronitrile (AIBN) to the obtained electrolyte precursor above to form a liquid precursor to be polymerized. Take 15 μL of the liquid precursor to be polymerized, drop it on the lithium cobaltate (LCO) positive electrode, then cover it with a polypropylene separator, and drop another 15 μL of the liquid precursor to be polymerized to soak the separator. Then stack the negative lithium metal sheet, gasket, and spring piece; finally, move the assembled battery above to a heating device and heat it at 60 °C for 2 hours to cause the polymerization of CA to form a high - voltage - resistant polymer - based solid electrolyte, and simultaneously in - situ form an integrated stack including the positive electrode, electrolyte, separator, and negative electrode. Finally, encapsulate the battery with a casing to obtain a solid - state battery.

[0093] The electrochemical performance was characterized using a CT-4008 Tn-mA battery test system, and the results were as follows: for this solid-state battery, at a charging cut-off voltage of 4.7 V and a charge-discharge rate of 1 C, the capacity retention rate was 85% after 200 cycles, and the discharge capacity was approximately 170.3 mAh / g.

[0094] Example 5

[0095] In this example, a solid-state battery containing a polymer-based solid electrolyte was prepared.

[0096] Preparation of the electrolyte precursor: The solvent fluoroethylene carbonate (FEC) and diethyl sulfite were mixed in a mass ratio of 1:4; then, a polymer monomer 2-cyanoethyl acrylate and 2% by mass of the polymer monomer of the cross-linking agent trimethylolpropane triacrylate were added to the solvent, and the mixture was stirred at 30 °C for about 2 hours to obtain a mixed solution; then, the lithium salt lithium bis(fluorosulfonyl)imide was added to the mixed solution in an amount of 2 mol / L, and the mixture was stirred at 30 °C for about 2 hours until completely dissolved, finally obtaining a uniformly mixed polymer-based solid electrolyte precursor.

[0097] Preparation of the polymer-based solid electrolyte and assembly of the solid-state battery: An initiator azobisisobutyronitrile (AIBN) with a mass fraction of 0.5% was added to the above-obtained electrolyte precursor to form a liquid precursor to be polymerized. Take 15 μL of the liquid precursor to be polymerized and drop it on the lithium nickel cobalt manganese oxide LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) cathode, then cover it with a polypropylene separator, and add another 15 μL of the liquid precursor to be polymerized to infiltrate the separator, and then stack a negative lithium metal sheet, a gasket, and a shrapnel; finally, move the assembled battery to a heating device and heat it at 45 °C for 8 hours to cause the polymerization reaction of 2-cyanoethyl acrylate to form a high-voltage-resistant polymer-based solid electrolyte, and simultaneously in-situ form an integrated stack including a cathode, an electrolyte, a separator, and a negative electrode, and finally encapsulate the battery with a casing to obtain a solid-state battery.

[0098] Example 6

[0099] In this example, a solid-state battery containing a polymer-based solid electrolyte was prepared.

[0100] Preparation of electrolyte precursor: Mix the solvent fluoroethylene carbonate (FEC) and propylene carbonate in a mass ratio of 1:4; then add the polymer monomer propyl 2-cyanoacrylate with a mass ratio to the solvent of 1:10 and pentaerythritol tetraacrylate with a mass of 1% of the polymer monomer mass to the solvent, and stir at 30 °C for about 2 hours to obtain a mixed solution; then add lithium bis(fluorosulfonyl)imide lithium salt to the mixed solution in an amount of 0.5 mol / L, and stir at 30 °C for about 2 hours until completely dissolved, finally obtaining a uniformly mixed polymer-based solid electrolyte precursor.

[0101] Preparation of polymer-based solid electrolyte and assembly of solid-state battery: Add 0.2% by mass of the initiator azobisisobutyronitrile (AIBN) to the electrolyte precursor obtained above to form a liquid precursor to be polymerized. Take 15 μL of the liquid precursor to be polymerized, drop it on the lithium nickel cobalt manganese oxide LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) cathode, then cover it with a polypropylene separator, and drop another 15 μL of the liquid precursor to be polymerized to soak the separator, and then stack a negative lithium metal sheet, a spacer, and a shrapnel; finally, move the assembled battery above to a heating device and heat it at 50 °C for 5 hours to cause the polymerization reaction of propyl 2-cyanoacrylate to form a high-voltage-resistant polymer-based solid electrolyte, and at the same time in-situ form an integrated stack including a cathode, an electrolyte, a separator, and a negative electrode, and finally encapsulate the battery with a casing to obtain a solid-state battery.

[0102] Comparative Example 1

[0103] In this comparative example, an electrolyte solution without polymer monomers was prepared.

[0104] Preparation of electrolyte solution: Mix the solvent fluoroethylene carbonate (FEC) and dimethyl sulfite (DMS) in a mass ratio of 1:4, and stir at 30 °C for about 2 hours; then add lithium difluoro(oxalato)borate (LiDFOB) to the solvent in an amount of 1 mol / L and stir at 30 °C for about 2 hours until completely dissolved, finally obtaining a uniformly mixed electrolyte solution.

[0105] After that, relevant tests were carried out using the electrolyte solution prepared above:

[0106] First, assemble a semi-blocking battery for testing the electrochemical window:

[0107] Use a stainless steel gasket as the working electrode and a lithium metal as the reference electrode to assemble a semi-blocking battery, and perform linear sweep voltammetry (LSV) test, and test from the open-circuit voltage to the termination voltage of 7 V at a sweep rate of 1 mV / s. The test equipment is a Gamry electrochemical workstation Interface 1000, and the results are as Figure 3 shown below.

[0108] Second, assemble the coin cell for relevant tests:

[0109] Add 1% by mass of the initiator azobisisobutyronitrile (AIBN) to the above-obtained electrolyte to form a liquid precursor to be polymerized. Take 15 μL of the liquid precursor to be polymerized, drop it on the lithium cobalt oxide (LCO) cathode, then cover it with a polypropylene separator, and drop another 15 μL of the liquid precursor to be polymerized to soak the separator. Then stack the negative lithium metal sheet, gasket, and shrapnel; finally, move the assembled battery to a heating device and heat it at 60 °C for 2 hours to form a coin cell including a cathode, electrolyte, separator, and anode.

[0110] First, test the leakage current of the coin cell by the constant current method: Charge the battery to 4.2V, 4.3V, 4.4V, 4.5V, 4.6V, 4.7V, 4.8V, 4.9V, and 5.0V and hold it at each voltage for 3 h, and observe the leakage current of the battery to evaluate the actual oxidation stability of the electrolyte. The results are as Figure 4 shown.

[0111] Second, test the cycle capacity retention rate of the coin cell. At a voltage of 3 - 4.5V and a charge-discharge rate of 0.5C, the cycle capacity retention rate was tested for 500 cycles. The results are as Figure 10 shown. At a voltage of 3 - 4.6V and a charge-discharge rate of 0.5C, the cycle capacity retention rate was tested for 300 cycles. The results are as Figure 11 shown.

[0112] Analyze the test results of Example 2 and Comparative Example 1 as follows:

[0113] Compare Figure 2 and Figure 3 It can be seen that the electrochemical window of the high-voltage resistant polymer-based solid electrolyte in this Example 1 reaches 5.1V, while the electrochemical window of the electrolyte in Comparative Example 1 is 4.6V, which is lower than that of the polymer-based solid electrolyte in Example 1 of this application. It shows that the high-voltage resistant polymer-based solid electrolyte in Example 1 of this application has a wider electrochemical window because the polymer-based solid electrolyte contains polar functional groups such as cyano and fluorinated groups, which increases the oxidation potential of the electrolyte.

[0114] According to Figure 4As can be seen from the comparison, for the solid-state battery of Example 1 of the present invention, even when charged to 5V (total time in the figure is 27 hours), the leakage current of the battery is 33.3 μA, indicating that the polymer-based solid electrolyte has good oxidation stability. For the coin cell of Comparative Example 1, when charged to 4.7V, the leakage current of the battery has reached 70.5 μA, indicating that the oxidation stability of this electrolyte is average. In short, the oxidation stability of the electrolyte of Comparative Example 1 is much lower than that of the high-voltage-resistant polymer-based solid electrolyte of Example 2 of the present invention. It should be noted that in Example 2, the polymer-based solid electrolyte precursor in Example 1 was polymerized in a battery system to obtain a polymer-based solid electrolyte, and then relevant tests were carried out on the solid-state battery. The compositions and properties of the polymer-based solid electrolytes in Example 2 and Example 1 are the same.

[0115] According to Figure 10 As shown, after 500 cycles, the capacity retention rate of the solid-state battery of Example 2 of the present invention is 98.4%, while after 350 cycles, the capacity retention rate of the semi-blocking battery of Comparative Example 1 has dropped to 67.3%. According to Figure 11 As shown, after 300 cycles, the capacity retention rate of the solid-state battery of Example 2 of the present invention is 80.91%, while for the coin cell of Comparative Example 1, the capacity retention rate has started to decline after 120 cycles and drops to 67.3% at 175 cycles. The above shows that the solid-state battery of the present application still has a high capacity retention rate during long-term charge and discharge cycling at a high voltage (greater than or equal to 4.5V).

[0116] The present invention prepares a high-voltage-resistant polymer-based solid electrolyte applicable by screening polymer monomers and solvents, optimizing the precursor ratio, and using an in-situ polymerization process.

[0117] The high-voltage-resistant polymer-based solid electrolyte prepared by the present invention exhibits good physical and chemical properties and electrochemical performance under the condition of a charging cut-off voltage of ≥4.5V, can be applied to lithium batteries, and has good application prospects.

[0118] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a high-voltage resistant polymer-based solid electrolyte, characterized in that, The preparation method includes: Mixing a lithium salt, a polymer monomer, a crosslinking agent, and a solvent uniformly in proportion to obtain a polymer-based solid electrolyte precursor; wherein, the polymer monomer includes a cyanoacrylate monomer; Adding an initiator to the polymer-based solid electrolyte precursor, and then performing thermal polymerization to obtain a polymer-based solid electrolyte with a polar functional group containing cyano, which is the high-voltage-resistant polymer-based solid electrolyte.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the polymer monomer to the solvent is 1:10 - 10:1; the mass of the crosslinking agent is 0.5% - 3% of the mass of the polymer monomer; the concentration of the lithium salt in the polymer-based solid electrolyte precursor is 0.5 mol / L - 2 mol / L.

3. The preparation method according to claim 1, characterized in that, The mass of the initiator is not more than 1% of the mass of the polymer-based solid electrolyte precursor.

4. The preparation method according to claim 1, characterized in that The temperature of the thermal polymerization is 45°C - 80°C, and the time is 1 hour - 24 hours.

5. The preparation method according to claim 1, characterized in that, The lithium salt includes one or more of lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorodioxalate phosphate; The cyanoacrylate monomers include one or more of 2-cyanoethyl acrylate, acrylonitrile, 2-ethyl cyanoacrylate, 2-cyanoethoxyethyl acrylate, cyanoethyl methacrylate, ethyl cyanoacrylate, 2-cyano-n-propyl acrylate, 2-cyano-n-pentyl acrylate, 3-amino-2-butenoic acid cyanoacetic acid, and ethyl 2-cyano-3-methylbutenoate; The solvent includes a carbonate compound and / or a sulfite compound; the carbonate compound includes one or several of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, and fluorinated ethylene carbonate; The sulfite compound includes one or several of dimethyl sulfite, dimethyl sulfate, diethyl sulfite, ethylene sulfite, and propylene sulfite; The crosslinking agent is an acrylate compound, and the acrylate compound includes one or several of ethoxylated trimethylolpropane triacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, and pentaerythritol triacrylate.

6. The preparation method according to claim 1, wherein, The initiator is a radical initiator; the radical initiator includes one or several of azobisisobutyronitrile, azobisisoheptonitrile, and benzoyl peroxide.

7. A high-voltage resistant polymer-based solid electrolyte, characterized in that, The high-voltage-resistant polymer-based solid electrolyte is prepared by the preparation method described in any one of claims 1 - 6 above.

8. A solid-state battery, characterized in that, The solid-state battery includes the high-voltage-resistant polymer-based solid electrolyte described in claim 7.

9. The solid-state battery according to claim 8, wherein, The positive electrode active material of the solid-state battery includes one or two of a layered structure oxide and a polyanion-type compound; the layered structure oxide includes one or two of lithium cobaltate and lithium nickel cobalt manganese oxide; the polyanion-type compound includes lithium iron phosphate; the negative electrode active material includes any one of graphite and metallic lithium foil.

10. A method for preparing the solid-state battery according to claim 8, characterized in that, The preparation method includes: Mixing a lithium salt, a polymer monomer, a crosslinking agent, and a solvent uniformly in proportion to obtain a polymer-based solid electrolyte precursor; wherein, the polymer monomer includes a cyanoacrylate monomer; An initiator is added to the polymer-based solid electrolyte precursor to obtain a liquid precursor to be polymerized. The liquid precursor to be polymerized is injected between the positive and negative electrodes inside the battery to be assembled, so that the liquid precursor to be polymerized fully infiltrates the positive electrode, negative electrode and separator, and then the battery is encapsulated; or, the liquid precursor to be polymerized is dropped onto the positive electrode, negative electrode and separator of the battery to be assembled, and then the battery is encapsulated. The battery is heat-treated to obtain the solid-state battery.

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