Preparation method and application of solid-state battery electrode

Abstract

A method for preparing and applying a solid-state battery electrode belongs to the field of chemical power source technology. Specifically, the method comprises the following steps: distributing a solid crosslinker in a gradient pattern in an electrode material to prepare an electrode plate; injecting an electrolyte precursor solution containing a polymerizable monomer into the electrode plate; and copolymerizing the polymerizable monomer with the gradient-distributed solid crosslinker under the action of an initiator or electron beam irradiation to achieve a gradient change in the degree of polymerization of the polymer electrolyte in the electrode, thereby obtaining a gradient-polymerized solid-state battery electrode. The amount of the solid crosslinker added increases gradually from near the current collector to away from the current collector. The present invention provides an innovative electrode solution for the realization of high-power, high-cycle stability solid-state batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical power sources, and in particular relates to a preparation method and application of a solid-state battery electrode. Background Art

[0002] Solid-state batteries, especially those prepared based on the in-situ polymerization method of electrolytes, can significantly improve battery safety and are an important direction for the development of next-generation secondary batteries. Generally, during the charge and discharge process, especially under high-rate conditions, the electrochemical reaction kinetics of the positive and negative electrodes of alkali metal ion secondary batteries based on liquid electrolytes have large gradient changes in the longitudinal direction. That is, the reaction kinetics of the active material layer close to the current collector are poor, while the reaction kinetics of the active material layer far from the current collector are high. This characteristic will significantly affect the active material utilization rate, rate performance and cycle stability of the secondary battery. Polymer electrolytes prepared based on the in-situ polymerization method often have the characteristics of high polymerization degree and relatively low ionic conductivity. The uniformity of the electrochemical reaction kinetics of the solid-state battery electrode in the longitudinal direction will be further reduced. In view of the electrode reaction kinetics characteristics of solid-state batteries, constructing a polymer electrolyte system with a gradient change in polymerization degree inside the electrode is of great significance to improving the active material utilization rate, interface stability, rate performance and cycle stability of solid-state batteries. Summary of the Invention

[0003] In order to solve the technical problems of poor electrode electrochemical reaction kinetics, low active material utilization, poor rate performance and cycle stability in in-situ polymerization solid-state batteries under high-rate conditions (≥1C), the present invention provides a preparation method and application of solid-state battery electrodes with gradient polymerization characteristics. The gradient distribution of the solid cross-linking agent is utilized to regulate the cross-linking polymerization degree of the polymerizable monomers in the electrode, thereby realizing gradient control of the polymerization degree of the polymer electrolyte, improving the active material utilization of the solid-state battery under high-rate working conditions, reducing the concentration polarization inside the solid-state electrode, improving the stability of the electrode and the electrode / electrolyte interface, and comprehensively improving the electrochemical performance of the solid-state battery.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for preparing a solid-state battery electrode comprises the following steps: distributing a solid cross-linking agent in a gradient manner in an electrode material to prepare an electrode piece, injecting an electrolyte precursor solution containing a polymerizable monomer into the electrode piece, copolymerizing the polymerizable monomer with the gradient-distributed solid cross-linking agent under the action of an initiator or electron beam irradiation, achieving a gradient change in the degree of polymerization of the polymer electrolyte in the electrode, and obtaining a gradient-polymerized solid-state battery electrode, wherein the amount of the solid cross-linking agent added increases gradually from near the current collector to far away from the current collector.

[0006] The solid cross-linking agent has a gradient distribution in the electrode material in a direction from close to the current collector to far away from the current collector and a mass range of 0.1 wt % to 2 wt %.

[0007] The solid crosslinking agent is micro-nano particles with vinyl functionalization or epoxy functionalization on the surface, and vinyl-terminated or cyclic ether-terminated cage-type polysilsesquioxane.

[0008] The polymerizable monomer is an ester monomer containing an unsaturated carbon-carbon double bond or an ether monomer containing an epoxy functional group.

[0009] The polymerizable monomer accounts for 5% to 85% of the mass of the electrolyte precursor solution.

[0010] The initiator includes a thermal initiator, a photoinitiator or a salt initiator, and the corresponding initiation modes are thermal initiation mode, photoinitiation mode and salt initiation mode respectively.

[0011] The electrode material includes an active material, a conductive agent and a binder that are uniformly mixed.

[0012] The electrolyte precursor solution further comprises a solvent, an alkali metal ion salt and an additive, wherein the alkali metal ion salt comprises a lithium salt, a sodium salt or a potassium salt.

[0013] Preferably, the method for preparing the electrode sheet is as follows: different mass fractions of solid cross-linking agent are added to the electrode material to prepare several slurries, and then the several slurries are coated on the current collector layer by layer, so that the amount of solid cross-linking agent added increases gradually from the current collector to the direction away from the current collector, and then dried, rolled, and cut to obtain the electrode sheet.

[0014] An application of a solid-state battery electrode prepared by the preparation method, wherein the solid-state battery electrode is applied to the positive electrode and / or negative electrode of a lithium-ion battery, the positive electrode and / or negative electrode of a sodium-ion battery, or the positive electrode and / or negative electrode of a potassium-ion battery.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] Compared with solid-state batteries prepared based on traditional in-situ polymerization methods, the polymer electrolyte in the new solid-state battery electrode of the present invention presents a change in polymerization degree gradient in the longitudinal direction. The polymerization degree of the polymer electrolyte increases gradiently from the surface of the current collector to the direction away from the current collector, and the ionic conductivity of the polymer electrolyte inside the electrode gradually increases from the electrode surface to the current collector surface. This characteristic can reduce the concentration polarization generated by the solid-state battery electrode during high-rate charge and discharge, improve the ion transfer kinetics inside the electrode, realize the full utilization of deep-layer active substances, and significantly improve the interface stability, rate characteristics and cycle stability of the solid-state battery. In summary, the present invention provides an innovative electrode solution for the realization of high-power, high-cycle stability solid-state batteries. DETAILED DESCRIPTION

[0017] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0018] Example 1:

[0019] A method for preparing a solid-state sodium ion battery positive electrode comprises the following steps:

[0020] Step 1, 96 parts of positive electrode active material sodium vanadium phosphate Na3V2(PO4)3, 2 parts of conductive agent Super P, and 2 parts of binder polyvinylidene fluoride PVDF are uniformly mixed to form a positive electrode material and divided into 4 parts, and 0.1%, 0.3%, 0.6% and 1.0% of the solid crosslinker octavinyl cage polysilsesquioxane (OV-POSS) accounting for the mass fraction of the positive electrode material are added to the 4 parts of positive electrode material, respectively, and wet mixed to obtain 4 parts of liquid slurries with different solid crosslinker contents;

[0021] Step 2: Apply the four portions of liquid slurry prepared in step 1 layer by layer on the surface of the current collector, so that the amount of solid crosslinker added increases gradually from the direction close to the current collector to the direction away from the current collector, and then dry, roll-press, and cut to obtain a positive electrode sheet with a gradient distribution of solid crosslinker;

[0022] Step 3, sodium salt sodium perchlorate NaClO4, film-forming additive fluoroethylene carbonate FEC (accounting for 1wt% of the total mass of the electrolyte precursor solution), solvent ethylene glycol dimethyl ether DME and 1,3-dioxolane DOL (the volume ratio of DME and DOL is 1:1), polymerizable monomer pentaerythritol tetraacrylate (PETEA, accounting for 15wt% of the total mass of the electrolyte precursor solution), thermal initiator azobisisobutyronitrile (AIBN, accounting for 0.5wt% of the mass of the polymerizable monomer) are mixed uniformly to prepare an electrolyte precursor solution with a sodium salt NaClO4 concentration of 1 mol / L;

[0023] Step 4: injecting the electrolyte precursor solution prepared in step 3 into the positive electrode sheet with the gradient distribution of the solid cross-linking agent prepared in step 2 under vacuum;

[0024] Step 5: Standing at 70°C for 12 hours, the gradient-distributed solid crosslinker undergoes crosslinking copolymerization with PETEA under the initiation of the thermal initiator AIBN, realizing the gradient polymerization of the PETEA monomer in the electrode, and obtaining a solid-state sodium ion battery positive electrode with gradient polymerization characteristics.

[0025] Example 2:

[0026] A method for preparing a solid-state sodium ion battery negative electrode comprises the following steps:

[0027] Step 1: 90 parts of negative electrode active material hard carbon, 5 parts of conductive agent Super P, and 5 parts of binder sodium carboxymethyl cellulose CMC are uniformly mixed to form a negative electrode material and divided into 4 parts. Solid crosslinking agent OV-POSS accounting for 0.5%, 1.0%, 1.5% and 2.0% of the mass fraction of the negative electrode material are added to the 4 parts of negative electrode material, respectively, and wet mixed to obtain 4 parts of liquid slurries with different solid crosslinking agent contents;

[0028] Step 2: Apply the four portions of liquid slurry prepared in step 1 layer by layer on the surface of the current collector, so that the amount of solid crosslinker added increases gradually from the direction close to the current collector to the direction away from the current collector, and then dry, roll-press, and cut to obtain a negative electrode sheet with a gradient distribution of solid crosslinker;

[0029] Step 3, sodium salt sodium perchlorate NaClO4, film-forming additive fluoroethylene carbonate FEC (accounting for 1wt% of the total mass of the electrolyte precursor solution), solvent ethylene glycol dimethyl ether DME and 1,3-dioxolane DOL (the volume ratio of DME and DOL is 1:1), polymerizable monomer pentaerythritol tetraacrylate (PETEA, accounting for 15wt% of the total mass of the electrolyte precursor solution), thermal initiator azobisisobutyronitrile (AIBN, accounting for 0.5wt% of the mass of the polymerizable monomer) are mixed uniformly to prepare an electrolyte precursor solution with a sodium salt NaClO4 concentration of 1 mol / L;

[0030] Step 4: injecting the electrolyte precursor solution prepared in step 3 into the negative electrode sheet with the gradient distribution of the solid cross-linking agent prepared in step 2 under vacuum;

[0031] Step 5: Standing at 70°C for 12 hours, the polymerizable monomer PETEA undergoes cross-linking copolymerization with OV-POSS under the action of the thermal initiator AIBN, realizing gradient polymerization of the PETEA monomer in the electrode, and obtaining a solid-state sodium ion battery negative electrode with gradient polymerization characteristics.

[0032] Example 3:

[0033] The OV-POSS prepared in step 2 of Example 1 is assembled into a button half-cell with a gradient distribution of the positive electrode sheet, a separator and sodium metal, and the electrolyte precursor solution prepared in step 3 of Example 1 is added dropwise. The mixture is allowed to stand at 70°C for 12 hours. The polymerizable monomer PETEA undergoes cross-linking copolymerization with the OV-POSS under the action of the thermal initiator AIBN, thereby achieving gradient polymerization of the PETEA monomer in the positive electrode, and obtaining a solid-state sodium ion positive electrode half-cell with gradient polymerization characteristics. The battery has a capacity retention rate of 98.5% after 1000 cycles at a voltage range of 2.5-3.8V and a rate of 1C, and the initial reversible capacity at a rate of 1C reaches 94.5% of the reversible capacity at a rate of 0.1C.

[0034] Example 4:

[0035] The OV-POSS prepared in step 2 of Example 2 is assembled into a button half-cell with a gradient distribution of the negative electrode, a separator and sodium metal, and the electrolyte precursor solution prepared in step 3 of Example 2 is added dropwise. The mixture is allowed to stand at 70°C for 12 hours. The polymerizable monomer PETEA undergoes cross-linking copolymerization with the OV-POSS under the action of the thermal initiator AIBN, thereby achieving gradient polymerization of the PETEA monomer in the negative electrode, and obtaining a solid-state sodium ion negative electrode half-cell with gradient polymerization characteristics. The battery has a capacity retention rate of 97.5% after 1000 cycles at a voltage range of 0.1-1.5V and a rate of 1C, and the initial reversible capacity at a rate of 1C reaches 96.5% of the reversible capacity at a rate of 0.1C.

[0036] Example 5:

[0037] The positive electrode piece and diaphragm with a gradient distribution of OV-POSS prepared in step 2 of Example 1 and the negative electrode piece with a gradient distribution of OV-POSS prepared in step 2 of Example 2 were assembled into a button-type full battery, and the electrolyte precursor solution prepared in step 3 of Example 1 was added dropwise, and the mixture was allowed to stand at 70°C for 12 hours. The polymerizable monomer PETEA was cross-linked and copolymerized with OV-POSS under the action of the thermal initiator AIBN to obtain a solid-state sodium ion full battery with gradient polymerization characteristics. The battery had a capacity retention rate of 94.5% after 1000 cycles at a 1C rate in the voltage range of 2.5-3.8V, the initial reversible capacity at 1C rate reached 95.5% of the reversible capacity at a 0.1C rate, and the initial reversible capacity at a 5C rate reached 91% of the reversible capacity at a 0.1C rate.

[0038] Example 6:

[0039] A method for preparing a positive electrode of a solid-state lithium-ion battery comprises the following steps:

[0040] Step 1: 96 parts of positive electrode active material lithium iron phosphate LiFePO4, 2 parts of conductive agent Super P, and 2 parts of binder polyvinylidene fluoride PVDF are uniformly mixed to form a positive electrode material and divided into 4 parts, and a solid crosslinking agent (silica nanoparticles modified with surface silane coupling agent KH560: KH560@SiO2) accounting for 0.2%, 0.4%, 0.6% and 0.8% of the mass fraction of the positive electrode material are added to the 4 parts of positive electrode material, respectively, and wet mixed to obtain 4 parts of liquid slurries with different KH560@SiO2 contents;

[0041] Step 2: Apply the four portions of liquid slurry prepared in step 1 layer by layer on the surface of the current collector, so that the amount of solid crosslinker added increases gradually from the direction close to the current collector to the direction away from the current collector, and then dry, roll-press, and cut to obtain a positive electrode sheet with a gradient distribution of solid crosslinker;

[0042] Step 3: The lithium salt lithium bis(trifluoromethylsulfonyl)imide LiTFSI, the film-forming additive fluoroethylene carbonate FEC (accounting for 2% of the total mass of the electrolyte precursor solution), the initiator lithium difluorooxalatoborate LiODFB (concentration of 0.5 mol / L), the solvent ethylene glycol dimethyl ether DME and the cyclic ether monomer 1,3,-dioxolane DOL (the volume ratio of DOL to DME is 1:1) are mixed to prepare an electrolyte precursor solution with a lithium salt LiTFSI concentration of 1 mol / L;

[0043] Step 4: injecting the electrolyte precursor solution prepared in step 3 into the positive electrode sheet with the gradient distribution of the solid cross-linking agent prepared in step 2 under vacuum;

[0044] Step 5. After standing at room temperature for 12 hours, the cyclic ether monomer DOL undergoes cross-linking copolymerization with KH560@SiO2 under the action of the initiator LiODFB, realizing gradient polymerization of the DOL monomer in the electrode, and obtaining a solid-state lithium-ion battery positive electrode with gradient polymerization characteristics.

[0045] Example 7:

[0046] A method for preparing a solid-state lithium-ion battery negative electrode comprises the following steps:

[0047] Step 1: 90 parts of negative electrode active material graphite, 5 parts of conductive agent Super P, and 5 parts of binder sodium carboxymethyl cellulose CMC are uniformly mixed to form a negative electrode material and divided into 4 parts. Solid crosslinking agent KH560@SiO2 is added to the 4 parts of negative electrode material at a mass fraction of 0.5%, 1.0%, 1.5% and 2.0% respectively, and wet mixing is performed to obtain 4 parts of liquid slurries with different KH560@SiO2 contents;

[0048] Step 2: Apply the four portions of liquid slurry prepared in step 1 layer by layer on the surface of the current collector, so that the amount of solid crosslinker added increases gradually from the direction close to the current collector to the direction away from the current collector, and then dry, roll-press, and cut to obtain a negative electrode sheet with a gradient distribution of solid crosslinker;

[0049] Step 3: The lithium salt lithium bis(trifluoromethylsulfonyl)imide LiTFSI, the film-forming additive fluoroethylene carbonate FEC (accounting for 2% of the total mass of the electrolyte precursor solution), the initiator lithium difluorooxalatoborate LiODFB (concentration of 0.5 mol / L), the solvent ethylene glycol dimethyl ether DME and the cyclic ether monomer 1,3,-dioxolane DOL (the volume ratio of DOL to DME is 1:1) are mixed to prepare an electrolyte precursor solution with a lithium salt LiTFSI concentration of 1 mol / L;

[0050] Step 4: injecting the electrolyte precursor solution prepared in step 3 into the negative electrode sheet with the gradient distribution of the solid cross-linking agent prepared in step 2 under vacuum;

[0051] Step 5. After standing at room temperature for 12 hours, the cyclic ether monomer DOL undergoes cross-linking copolymerization with KH560@SiO2 under the action of the initiator LiODFB, achieving gradient polymerization of the DOL monomer in the electrode, and obtaining a solid-state lithium-ion battery negative electrode with gradient polymerization characteristics.

[0052] Example 8:

[0053] A button-type half-cell was assembled with a positive electrode sheet, a separator, and lithium metal having a gradient distribution of KH560@SiO2 prepared in step 2 of Example 6, and the electrolyte precursor solution prepared in step 3 of Example 6 was added dropwise. The cells were allowed to stand at room temperature for 12 hours. The cyclic ether monomer DOL cross-linked and copolymerized with KH560@SiO2 under the action of the initiator LiODFB, thereby achieving gradient polymerization of the DOL monomer in the electrode, thereby obtaining a solid-state lithium-ion positive electrode half-cell with gradient polymerization characteristics. The battery had a capacity retention rate of 99% after 2000 cycles at a 1C rate in the voltage range of 2.5-4.0 V, and the initial reversible capacity at a 1C rate reached 96% of the reversible capacity at a 0.1C rate.

[0054] Example 9:

[0055] A button-type half-cell was assembled with the negative electrode sheet, separator, and lithium metal having a gradient distribution of KH560@SiO2 prepared in step 2 of Example 7, and the electrolyte precursor solution prepared in step 3 of Example 7 was added dropwise. The cells were allowed to stand at room temperature for 12 hours. The cyclic ether monomer DOL cross-linked and copolymerized with KH560@SiO2 under the action of the initiator LiODFB, achieving gradient polymerization of the DOL monomer in the electrode, thereby obtaining a solid-state lithium-ion negative electrode half-cell with gradient polymerization characteristics. The battery had a capacity retention rate of 98% after 2000 cycles at a voltage range of 0.05-1.5V and a rate of 1C, and the initial reversible capacity at a rate of 1C reached 96% of the reversible capacity at a rate of 0.1C.

[0056] Example 10:

[0057] The positive electrode sheet and diaphragm with a gradient distribution of KH560@SiO2 prepared in step 2 of Example 6 and the negative electrode sheet with a gradient distribution of KH560@SiO2 prepared in step 2 of Example 7 were assembled into a button-type full battery, and the electrolyte precursor solution prepared in step 3 of Example 6 was added dropwise. The mixture was allowed to stand at room temperature for 12 hours. The cyclic ether monomer DOL was cross-linked and copolymerized with KH560@SiO2 under the action of the initiator LiODFB, thereby achieving gradient polymerization of the DOL monomer in the electrode, and obtaining a solid-state lithium-ion full battery with gradient polymerization characteristics. The battery had a capacity retention rate of 94% after 2000 cycles at a 1C rate in the voltage range of 2.5-4.0V, the initial reversible capacity at a 1C rate reached 95% of the reversible capacity at a 0.1C rate, and the initial reversible capacity at a 5C rate reached 80% of the reversible capacity at a 0.1C rate.

[0058] Comparative Example 1:

[0059] A method for preparing a solid-state sodium ion battery positive electrode comprises the following steps:

[0060] Step 1: Wet-mix 96 parts of positive electrode active material sodium vanadium phosphate Na3V2(PO4)3, 2 parts of conductive agent Super P, and 2 parts of binder polyvinylidene fluoride PVDF to obtain a positive electrode slurry;

[0061] Step 2: coating the positive electrode slurry prepared in step 1 on the surface of the current collector, and then drying, rolling, and cutting to obtain positive electrode sheets;

[0062] Step 3, sodium salt sodium perchlorate NaClO4, film-forming additive fluoroethylene carbonate FEC (accounting for 1wt% of the total mass of the electrolyte precursor solution), solvent ethylene glycol dimethyl ether DME and 1,3-dioxolane DOL (the volume ratio of DME and DOL is 1:1), polymerizable monomer pentaerythritol tetraacrylate (PETEA, accounting for 15wt% of the total mass of the electrolyte precursor solution), thermal initiator azobisisobutyronitrile (AIBN, accounting for 0.5wt% of the mass of the polymerizable monomer) are mixed uniformly to prepare an electrolyte precursor solution with a sodium salt NaClO4 concentration of 1 mol / L;

[0063] Step 4: injecting the electrolyte precursor solution prepared in step 3 into the positive electrode sheet prepared in step 2 under vacuum;

[0064] Step 5: Standing at 70°C for 12 hours, the polymerizable monomer PETEA polymerizes under the action of the thermal initiator AIBN to obtain a solid-state sodium ion battery positive electrode.

[0065] Comparative Example 2:

[0066] A method for preparing a solid-state sodium ion battery negative electrode comprises the following steps:

[0067] Step 1: Wet-mix 90 parts of negative electrode active material hard carbon, 5 parts of conductive agent Super P, and 5 parts of binder sodium carboxymethyl cellulose CMC to obtain a negative electrode slurry;

[0068] Step 2: coating the negative electrode slurry prepared in step 1 on the surface of the current collector, and then drying, rolling, and cutting to obtain negative electrode sheets;

[0069] Step 3, sodium salt sodium perchlorate NaClO4, film-forming additive fluoroethylene carbonate FEC (accounting for 1wt% of the total mass of the electrolyte precursor solution), solvent ethylene glycol dimethyl ether DME and 1,3-dioxolane DOL (the volume ratio of DME and DOL is 1:1), polymerizable monomer pentaerythritol tetraacrylate (PETEA, accounting for 15wt% of the total mass of the electrolyte precursor solution), thermal initiator azobisisobutyronitrile (AIBN, accounting for 0.5wt% of the monomer mass) are mixed uniformly to prepare an electrolyte precursor solution with a sodium salt NaClO4 concentration of 1 mol / L;

[0070] Step 4: injecting the electrolyte precursor solution prepared in step 3 into the negative electrode sheet prepared in step 2 under vacuum;

[0071] Step 5: Standing at 70°C for 12 hours, the polymerizable monomer PETEA polymerizes under the action of the thermal initiator AIBN to obtain a solid-state sodium ion battery negative electrode.

[0072] Comparative Example 3:

[0073] The positive electrode sheet, separator, and sodium metal prepared in Comparative Example 1 were assembled into a button half-cell, and the electrolyte precursor solution prepared in step 3 of Comparative Example 1 was added dropwise. The cells were allowed to stand at 70°C for 12 hours to obtain a solid-state sodium ion positive electrode half-cell. The battery retained 45% of its capacity after 1000 cycles at a rate of 1C in the voltage range of 2.5-3.8V, and the initial reversible capacity at a rate of 1C was only 65% ​​of the reversible capacity at a rate of 0.1C.

[0074] Comparative Example 4:

[0075] The negative electrode sheet, separator, and sodium metal prepared in Comparative Example 2 were assembled into a button half-cell, and the electrolyte precursor solution prepared in step 3 of Comparative Example 2 was added dropwise. The cells were allowed to stand at 70°C for 12 hours to obtain a solid-state sodium ion negative electrode half-cell. The battery retained 50% of its capacity after 1000 cycles at a voltage range of 0.1-1.5V and a rate of 1C. The initial reversible capacity at a rate of 1C was only 70% of the reversible capacity at a rate of 0.1C.

[0076] Comparative Example 5:

[0077] The positive electrode sheet and separator prepared in Comparative Example 1 and the negative electrode sheet prepared in Comparative Example 2 were assembled into a button-type full battery, and the electrolyte precursor solution prepared in step 3 of Comparative Example 1 was added dropwise. The battery was allowed to stand at 70°C for 12 hours to obtain a solid-state sodium ion full battery. The battery had a capacity retention rate of 47% after 1000 cycles at a 1C rate in the voltage range of 2.5-3.8V. The initial reversible capacity at a 1C rate was only 60% of the reversible capacity at a 0.1C rate, and the initial reversible capacity at a 5C rate was only 25% of the reversible capacity at a 0.1C rate.

[0078] Comparative Example 6:

[0079] A method for preparing a positive electrode of a solid-state lithium-ion battery comprises the following steps:

[0080] Step 1: Wet-mix 96 parts of positive electrode active material lithium iron phosphate LiFePO4, 2 parts of conductive agent Super P, and 2 parts of binder polyvinylidene fluoride PVDF to obtain a positive electrode slurry;

[0081] Step 2: coating the positive electrode slurry prepared in step 1 on the surface of the current collector, and then drying, rolling, and cutting to obtain positive electrode sheets;

[0082] Step 3: The lithium salt lithium bis(trifluoromethylsulfonyl)imide LiTFSI, the film-forming additive fluoroethylene carbonate FEC (accounting for 2% of the total mass of the electrolyte precursor solution), the initiator lithium difluorooxalatoborate LiODFB (concentration of 0.5 mol / L), the solvent ethylene glycol dimethyl ether DME and the cyclic ether monomer 1,3,-dioxolane DOL (the volume ratio of DOL to DME is 1:1) are mixed to prepare an electrolyte precursor solution with a lithium salt LiTFSI concentration of 1 mol / L;

[0083] Step 4: injecting the electrolyte precursor solution prepared in step 3 into the positive electrode sheet prepared in step 2 under vacuum;

[0084] Step 5: The mixture was allowed to stand at room temperature for 12 hours, and the cyclic ether monomer DOL was polymerized under the action of the initiator LiODFB to obtain a solid-state lithium-ion battery positive electrode.

[0085] Comparative Example 7:

[0086] A method for preparing a solid-state lithium-ion battery negative electrode comprises the following steps:

[0087] Step 1: Wet-mix 90 parts of negative electrode active material graphite, 5 parts of conductive agent Super P, and 5 parts of binder sodium carboxymethyl cellulose CMC to obtain a negative electrode slurry;

[0088] Step 2: coating the negative electrode slurry prepared in step 1 on the surface of the current collector, and then drying, rolling, and cutting to obtain negative electrode sheets;

[0089] Step 3: The lithium salt lithium bis(trifluoromethylsulfonyl)imide LiTFSI, the film-forming additive fluoroethylene carbonate FEC (accounting for 2% of the total mass of the electrolyte precursor solution), the initiator lithium difluorooxalatoborate LiODFB (concentration of 0.5 mol / L), the solvent ethylene glycol dimethyl ether DME and the cyclic ether monomer 1,3,-dioxolane DOL (the volume ratio of DOL to DME is 1:1) are mixed to prepare an electrolyte precursor solution with a lithium salt LiTFSI concentration of 1 mol / L;

[0090] Step 4: injecting the electrolyte precursor solution prepared in step 3 into the negative electrode sheet prepared in step 2 under vacuum;

[0091] Step 5: Standing at room temperature for 12 hours, the cyclic ether monomer DOL is polymerized under the action of the initiator LiODFB to obtain a solid-state lithium-ion battery negative electrode.

[0092] Comparative Example 8:

[0093] The positive electrode sheet, separator and lithium metal prepared in Comparative Example 6 were assembled into a button half-cell, and the electrolyte precursor solution prepared in step 3 of Comparative Example 6 was added dropwise. The cells were allowed to stand at room temperature for 12 hours to obtain a solid-state lithium-ion positive electrode half-cell. The cell retained 56% of its capacity after 2000 cycles at a rate of 1C in the voltage range of 2.5-4.0V. The initial reversible capacity at a rate of 1C was only 61% of the reversible capacity at a rate of 0.1C.

[0094] Comparative Example 9:

[0095] The negative electrode sheet, separator and lithium metal prepared in Comparative Example 7 were assembled into a button half-cell, and the electrolyte precursor solution prepared in step 3 of Comparative Example 7 was added dropwise. The cells were allowed to stand at room temperature for 12 hours to obtain a solid-state lithium-ion negative electrode half-cell. The cell retained 45% of its capacity after 2000 cycles at a rate of 1C in the voltage range of 0.05-1.5V, and the initial reversible capacity at a rate of 1C was only 55% of the reversible capacity at a rate of 0.1C.

[0096] Comparative Example 10:

[0097] The positive electrode sheet and separator prepared in Comparative Example 6 and the negative electrode sheet prepared in Comparative Example 7 are assembled into a button-type full battery, and the electrolyte precursor solution prepared in step 3 of Comparative Example 6 is added dropwise. The battery is allowed to stand at room temperature for 12 hours to obtain a solid-state lithium-ion full battery. The battery has a capacity retention rate of 37% after 2000 cycles at a 1C rate in the voltage range of 2.5-4.0V. The initial reversible capacity at a 1C rate is only 52% of the reversible capacity at a 0.1C rate, and the initial reversible capacity at a 5C rate is only 15% of the reversible capacity at a 0.1C rate.

[0098] In summary, compared with the traditional solid-state batteries prepared in Comparative Examples 5 and 10, the solid-state batteries with gradient polymerization characteristics prepared in Examples 5 and 10 show excellent electrochemical performance, and the discharge specific capacity and cycle stability at the same rate are significantly improved, which fully demonstrates the superiority of the gradient polymerization solid-state battery.

[0099] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing a solid-state battery electrode, characterized in that: The following steps are involved: Solid cross-linking agents of different mass fractions are added to the electrode material to prepare several slurries, and then several slurries are coated on the current collector layer by layer, so that the amount of solid cross-linking agent added increases gradually from the current collector to the direction away from the current collector. Then, the slurry is dried, rolled, and cut to obtain pole pieces. An electrolyte precursor solution containing polymerizable monomers is injected into the pole pieces. The polymerizable monomers copolymerize with the gradient-distributed solid cross-linking agent under the action of an initiator or electron beam irradiation to achieve a gradient change in the degree of polymerization of the polymer electrolyte in the electrode, thereby obtaining a gradient-polymerized solid-state battery electrode. The solid cross-linking agent is a surface vinyl-functionalized or epoxy-functionalized micro-nanoparticle, a vinyl-terminated or cyclic ether-terminated cage-type polysilsesquioxane, and the polymerizable monomer is an ester monomer containing an unsaturated carbon-carbon double bond or an ether monomer containing an epoxy functional group.

2. The preparation method according to claim 1, wherein: The solid cross-linking agent has a gradient distribution in the electrode material in a direction from close to the current collector to far away from the current collector and a mass range of 0.1 wt % to 2 wt %.

3. The preparation method according to claim 1, wherein: The polymerizable monomer accounts for 5%-85% of the mass of the electrolyte precursor solution.

4. The preparation method according to claim 1, wherein: The initiator includes a thermal initiator, a photoinitiator or a salt initiator, and the corresponding initiation modes are thermal initiation mode, photoinitiation mode and salt initiation mode respectively.

5. The preparation method according to claim 1, wherein: The electrode material includes an active material, a conductive agent and a binder that are uniformly mixed.

6. The preparation method according to claim 1, wherein: The electrolyte precursor solution further comprises a solvent, an alkali metal ion salt and an additive, wherein the alkali metal ion salt comprises a lithium salt, a sodium salt or a potassium salt.

7. An application of a solid-state battery electrode prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The solid-state battery electrode is applied to the positive electrode and / or negative electrode of a lithium-ion battery, the positive electrode and / or negative electrode of a sodium-ion battery, or the positive electrode and / or negative electrode of a potassium-ion battery.