Preparation method and application of solid-state battery electrode

Abstract

The invention discloses a preparation method and application of a solid-state battery electrode and belongs to the technical field of chemical power sources. The method specifically comprises the following steps: distributing a solid cross-linking agent in an electrode material in a gradient manner to prepare a pole piece, injecting an electrolyte precursor solution containing a polymerizable monomer into the pole piece, and copolymerizing the polymerizable monomer with the solid cross-linking agent distributed in the gradient manner under the action of an initiator or electron beam irradiation, the gradient change of the polymerization degree of the polymer electrolyte in the electrode is realized, the gradient polymerized solid-state battery electrode is obtained, and the additive amount gradient of the solid cross-linking agent is increased in the direction from the near current collector to the far away from the current collector. The invention provides an innovative electrode scheme for the realization of a high-power and high-cycle-stability solid-state battery.

Description

Technical Field

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

[0002] Solid-state batteries, especially those prepared by the in-situ polymerization method of electrolytes, can significantly improve the safety of batteries 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, there are significant gradient changes in the electrochemical reaction kinetics of the positive and negative electrodes of alkali metal ion secondary batteries based on liquid electrolytes in the longitudinal direction, that is, the reaction kinetics of the active material layer near the current collector is poor, while the reaction kinetics of the active material layer far from the current collector is high. This characteristic will significantly affect the utilization rate of active materials, rate performance, and cycle stability of secondary batteries. Moreover, the polymer electrolytes prepared by the in-situ polymerization method often have the characteristics of high degree of polymerization and relatively low ionic conductivity, and the uniformity of the electrochemical reaction kinetics of the solid-state battery electrode in the longitudinal direction will further decrease. In view of the electrode reaction kinetic characteristics of solid-state batteries, constructing a polymer electrolyte system with a gradient change in the degree of polymerization inside the electrode is of great significance for improving the utilization rate of active materials, 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 utilization rate of active materials, poor rate performance, and poor cycle stability of in-situ polymerization solid-state batteries under high-rate conditions (≥1C), the present invention provides a preparation method and application of a solid-state battery electrode with gradient polymerization characteristics. By using the gradient distribution of a solid cross-linking agent, the cross-linking polymerization degree of polymerizable monomers in the electrode is regulated, the gradient control of the degree of polymerization of the polymer electrolyte is realized, the utilization rate of active materials of the solid-state battery under high-rate working conditions is improved, the concentration polarization inside the solid electrode is reduced, the interface stability between the electrode and the electrode / electrolyte is enhanced, and the electrochemical performance of the solid-state battery is comprehensively improved.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A preparation method of a solid-state battery electrode, comprising the following steps: preparing a pole piece by distributing a solid cross-linking agent in a gradient manner in an electrode material, injecting an electrolyte precursor solution containing polymerizable monomers into the pole piece, and the polymerizable monomers copolymerize with the gradient-distributed solid cross-linking agent under the action of an initiator or electron beam irradiation to realize the gradient change of the degree of polymerization of the polymer electrolyte in the electrode, thereby obtaining a solid-state battery electrode with gradient polymerization, wherein the addition amount of the solid cross-linking agent increases in a gradient manner from the direction close to the current collector to the direction far from the current collector.

[0006] The mass range of the gradient distribution of the solid cross-linking agent in the electrode material from near the current collector to away from the current collector is 0.1 wt%-2 wt%.

[0007] The solid cross-linking agent is micro-nano particles with surface vinyl functionalization or epoxy functionalization, vinyl-capped or cyclic ether-capped cage-like polyhedral oligomeric silsesquioxanes.

[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%-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 methods are thermal initiation method, photoinitiation method and salt initiation method respectively.

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

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

[0013] Preferably, the method for preparing the electrode sheet: Different mass fractions of the solid cross-linking agent are incorporated into the electrode material to prepare several slurries, and then the several slurries are coated on the current collector layer by layer, so that the addition amount of the solid cross-linking agent increases in a gradient from near the current collector to away from the current collector, and then dried, rolled and slit to obtain the electrode sheet.

[0014] An application of a solid-state battery electrode prepared by the described preparation method, and 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 beneficial effects of the present invention are:

[0016] Compared with the solid-state battery prepared by the traditional in-situ polymerization method, the polymer electrolyte in the novel solid-state battery electrode shows a change in the degree of polymerization gradient longitudinally. From the surface of the current collector to the direction away from the current collector, the degree of polymerization of the polymer electrolyte increases in a gradient, 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 during the high-rate charge and discharge process of the solid-state battery electrode, improve the ion transport kinetics inside the electrode, realize the full utilization of deep active materials, and significantly improve the interface stability, rate performance and cycle stability of the solid-state battery; In summary, the present invention provides an innovative electrode solution for the realization of high-power and high-cycle stability solid-state batteries. Detailed implementation mode

[0017] The technical solutions in the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0018] Embodiment 1:

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

[0020] Step 1: Uniformly mix 96 parts of the positive electrode active material sodium vanadium phosphate Na 3 V 2 (PO 4 ) 3 , 2 parts of the conductive agent Super P, and 2 parts of the binder polyvinylidene fluoride PVDF to form a positive electrode material, and divide it into 4 equal parts. Add octavinylcage polyhedral oligomeric silsesquioxane (OV-POSS) with a mass fraction of 0.1%, 0.3%, 0.6%, and 1.0% of the positive electrode material to the 4 parts of the positive electrode material respectively, and perform wet mixing to obtain 4 liquid slurries with different solid cross-linker contents;

[0021] Step 2: Coat the 4 liquid slurries prepared in Step 1 layer by layer on the surface of the current collector, so that the addition amount of the solid cross-linker increases in a gradient from the direction close to the current collector to the direction far from the current collector, and then dry, roll, and slit to obtain a positive electrode sheet with a gradient distribution of the solid cross-linker;

[0022] Step 3: Mix sodium perchlorate NaClO 4 , the film-forming additive fluoroethylene carbonate FEC (accounting for 1 wt% of the total mass of the electrolyte precursor solution), the solvent ethylene glycol dimethyl ether DME and 1,3-dioxolane DOL (the volume ratio of DME to DOL is 1:1), the polymerizable monomer pentaerythritol tetraacrylate (PETEA, accounting for 15 wt% of the total mass of the electrolyte precursor solution), and the thermal initiator azobisisobutyronitrile (AIBN, accounting for 0.5 wt% of the mass of the polymerizable monomer) uniformly to prepare an electrolyte precursor solution with a concentration of 1 mol / L of sodium salt NaClO 4 ;

[0023] Step 4: Inject the electrolyte precursor solution prepared in Step 3 onto the positive electrode sheet with a gradient distribution of the solid cross-linker prepared in Step 2 under a vacuum state;

[0024] Step 5: Leave it standing for 12 h at 70 °C. The solid crosslinker with a gradient distribution undergoes crosslinking copolymerization with PETEA under the initiation of the thermal initiator AIBN, realizing the gradient polymerization of PETEA monomers in the electrode, and obtaining a solid-state sodium-ion battery positive electrode with gradient polymerization characteristics.

[0025] Example 2:

[0026] A preparation method of a solid-state sodium-ion battery negative electrode includes the following steps:

[0027] Step 1: Uniformly mix 90 parts of negative electrode active material hard carbon, 5 parts of conductive agent Super P, and 5 parts of binder carboxymethyl cellulose sodium CMC to form a negative electrode material and divide it into 4 equal parts. Add solid crosslinker OV-POSS with a mass fraction of 0.5%, 1.0%, 1.5%, and 2.0% of the negative electrode material to the 4 parts of negative electrode materials respectively, and perform wet mixing to obtain 4 liquid slurries with different solid crosslinker contents;

[0028] Step 2: Coat the 4 liquid slurries prepared in Step 1 layer by layer on the surface of the current collector, so that the addition amount of the solid crosslinker increases in a gradient from the direction close to the current collector to the direction far from the current collector, and then dry, roll, and slit to obtain a negative electrode sheet with a gradient distribution of the solid crosslinker;

[0029] Step 3: Mix sodium perchlorate NaClO 4 , film-forming additive fluoroethylene carbonate FEC (accounting for 1 wt% 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 to DOL is 1:1), polymerizable monomer pentaerythritol tetraacrylate (PETEA, accounting for 15 wt% of the total mass of the electrolyte precursor solution), and thermal initiator azobisisobutyronitrile (AIBN, accounting for 0.5 wt% of the mass of the polymerizable monomer) uniformly to prepare an electrolyte precursor solution with a concentration of 1 mol / L of sodium salt NaClO 4 ;

[0030] Step 4: Inject the electrolyte precursor solution prepared in Step 3 onto the negative electrode sheet with a gradient distribution of the solid crosslinker prepared in Step 2 under a vacuum state;

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

[0032] Example 3:

[0033] The positive electrode sheet with a gradient distribution of OV-POSS prepared in the second step of Example 1, a separator, and sodium metal are assembled into a coin-type half-cell, and the electrolyte precursor solution prepared in the third step of Example 1 is dropped. It is left standing for 12 h at 70 °C. The polymerizable monomer PETEA undergoes crosslinking copolymerization with OV-POSS under the action of the thermal initiator AIBN, realizing the gradient polymerization of PETEA monomers 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 rate of 1C in the voltage range of 2.5 - 3.8 V, 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 negative electrode sheet with a gradient distribution of OV-POSS prepared in the second step of Example 2, a separator, and sodium metal are assembled into a coin-type half-cell, and the electrolyte precursor solution prepared in the third step of Example 2 is dropped. It is left standing for 12 h at 70 °C. The polymerizable monomer PETEA undergoes crosslinking copolymerization with OV-POSS under the action of the thermal initiator AIBN, realizing the gradient polymerization of PETEA monomers 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 rate of 1C in the voltage range of 0.1 - 1.5 V, 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 sheet with a gradient distribution of OV-POSS prepared in the second step of Example 1 and the negative electrode sheet with a gradient distribution of OV-POSS prepared in the second step of Example 2 are assembled into a coin-type full-cell, and the electrolyte precursor solution prepared in the third step of Example 1 is dropped. It is left standing for 12 h at 70 °C. The polymerizable monomer PETEA undergoes crosslinking copolymerization with OV-POSS under the action of the thermal initiator AIBN, obtaining a solid-state sodium-ion full-cell with gradient polymerization characteristics. The battery has a capacity retention rate of 94.5% after 1000 cycles at a rate of 1C in the voltage range of 2.5 - 3.8 V, the initial reversible capacity at a rate of 1C reaches 95.5% of the reversible capacity at a rate of 0.1C, and the initial reversible capacity at a rate of 5C reaches 91% of the reversible capacity at a rate of 0.1C.

[0038] Example 6:

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

[0040] Step 1. 96 parts of the positive electrode active material lithium iron phosphate LiFePO 4, 2 parts of conductive agent Super P and 2 parts of binder polyvinylidene fluoride PVDF are uniformly mixed to form the cathode material, which is evenly divided into 4 parts. 0.2%, 0.4%, 0.6% and 0.8% of the solid crosslinking agent (silica nanoparticles modified with surface silane coupling agent KH560: KH560@SiO 2 ) based on the mass of the cathode material are added to the 4 parts of the cathode material respectively, and wet mixing is carried out to obtain 4 parts of liquid slurries with different contents of KH560@SiO 2 ;

[0041] Step 2: The 4 parts of liquid slurries prepared in Step 1 are coated layer by layer on the surface of the current collector, so that the addition amount of the solid crosslinking agent increases in a gradient from the direction close to the current collector to the direction far from the current collector, and then dried, rolled and slit to obtain a cathode electrode with a gradient distribution of the solid crosslinking agent;

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

[0043] Step 4: The electrolyte precursor solution prepared in Step 3 is injected onto the cathode electrode with a gradient distribution of the solid crosslinking agent prepared in Step 2 under a vacuum state;

[0044] Step 5: Stand still for 12 h at room temperature. The cyclic ether monomer DOL undergoes crosslinking copolymerization with KH560@SiO 2 under the action of the initiator LiODFB to realize the gradient polymerization of the DOL monomer in the electrode, and a solid-state lithium-ion battery cathode with gradient polymerization characteristics is obtained.

[0045] Example 7:

[0046] A method for preparing a negative electrode of a solid-state lithium-ion battery, comprising 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 the negative electrode material, which is evenly divided into 4 parts. 0.5%, 1.0%, 1.5% and 2.0% of the solid crosslinking agent KH560@SiO 2 are added to the 4 parts of the negative electrode material respectively, and wet mixing is carried out to obtain 4 parts of liquid slurries with different contents of KH560@SiO 2 ;

[0048] Step 2: Coat the 4 portions of liquid slurry prepared in Step 1 layer by layer on the surface of the current collector, so that the addition amount of the solid crosslinking agent increases in a gradient manner from the direction near the current collector to the direction far from the current collector, and then obtain a negative electrode sheet with a gradient distribution of the solid crosslinking agent after drying, rolling, and slitting;

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

[0050] Step 4: Inject the electrolyte precursor solution prepared in Step 3 onto the negative electrode sheet with a gradient distribution of the solid crosslinking agent prepared in Step 2 under a vacuum state;

[0051] Step 5: Stand still for 12 h at room temperature. The cyclic ether monomer DOL undergoes crosslinking copolymerization with KH560@SiO 2 under the action of the initiator LiODFB, realizing the gradient polymerization of the DOL monomer in the electrode, and obtaining a negative electrode of a solid-state lithium-ion battery with gradient polymerization characteristics.

[0052] Example 8:

[0053] Assemble a coin-type half-cell with the positive electrode sheet with a gradient distribution of KH560@SiO 2 prepared in Step 2 of Example 6, a separator, and lithium metal, and drop the electrolyte precursor solution prepared in Step 3 of Example 6. Stand still for 12 h at room temperature. The cyclic ether monomer DOL undergoes crosslinking copolymerization with KH560@SiO 2 under the action of the initiator LiODFB, realizing the gradient polymerization of the DOL monomer in the electrode, and obtaining a solid-state lithium-ion positive electrode half-cell with gradient polymerization characteristics. The battery has a capacity retention rate of 99% after 2000 cycles at a rate of 1C in the voltage range of 2.5 - 4.0V, and the initial reversible capacity at a rate of 1C reaches 96% of the reversible capacity at a rate of 0.1C.

[0054] Example 9:

[0055] Assemble a coin-type half-cell with the negative electrode sheet with a gradient distribution of KH560@SiO 2 prepared in Step 2 of Example 7, a separator, and lithium metal, and drop the electrolyte precursor solution prepared in Step 3 of Example 7. Stand still for 12 h at room temperature. The cyclic ether monomer DOL undergoes crosslinking copolymerization with KH560@SiO 2Crosslinking copolymerization occurs to achieve gradient polymerization of DOL monomers in the electrode, resulting in a solid-state lithium-ion negative electrode half-cell with gradient polymerization characteristics. The battery has a capacity retention rate of 98% 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 reaches 96% of the reversible capacity at a rate of 0.1C.

[0056] Example 10:

[0057] The KH560@SiO prepared in Step 2 of Example 6 2 The positive electrode sheet with a gradient distribution, the separator, and the KH560@SiO prepared in Step 2 of Example 7 2 The button-type full cell is assembled with the negative electrode sheet with a gradient distribution, and the electrolyte precursor solution prepared in Step 3 of Example 6 is dropped. It is left standing at room temperature for 12 h. The cyclic ether monomer DOL reacts with KH560@SiO under the action of the initiator LiODFB 2 Crosslinking copolymerization occurs to achieve gradient polymerization of DOL monomers in the electrode, resulting in a solid-state lithium-ion full cell with gradient polymerization characteristics. The battery has a capacity retention rate of 94% 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 reaches 95% of the reversible capacity at a rate of 0.1C, and the initial reversible capacity at a rate of 5C reaches 80% of the reversible capacity at a rate of 0.1C.

[0058] Comparative Example 1:

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

[0060] Step 1: 96 parts of the positive electrode active material sodium vanadium phosphate Na 3 V 2 (PO 4 ) 3 , 2 parts of the conductive agent Super P, and 2 parts of the binder polyvinylidene fluoride PVDF are wet-mixed to obtain a positive electrode slurry;

[0061] Step 2: The positive electrode slurry prepared in Step 1 is coated on the surface of the current collector, and then dried, rolled, and slit to obtain a positive electrode sheet;

[0062] Step 3: Sodium perchlorate NaClO 4 , the film-forming additive fluoroethylene carbonate FEC (accounting for 1 wt% of the total mass of the electrolyte precursor solution), the solvents ethylene glycol dimethyl ether DME and 1,3-dioxolane DOL (the volume ratio of DME to DOL is 1:1), the polymerizable monomer pentaerythritol tetraacrylate (PETEA, accounting for 15 wt% of the total mass of the electrolyte precursor solution), and the thermal initiator azobisisobutyronitrile (AIBN, accounting for 0.5 wt% of the mass of the polymerizable monomer) are mixed evenly to prepare the sodium salt NaClO4 An electrolyte precursor solution with a concentration of 1 mol / L;

[0063] Step 4: Inject the electrolyte precursor solution prepared in Step 3 onto the positive electrode sheet prepared in Step 2 under a vacuum state;

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

[0065] Comparative Example 2:

[0066] A preparation method of a negative electrode of a solid-state sodium-ion battery, comprising 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: Coat the negative electrode slurry prepared in Step 1 on the surface of the current collector, and then dry, roll, and slit to obtain a negative electrode sheet;

[0069] Step 3: Mix sodium perchlorate NaClO 4 , film-forming additive fluoroethylene carbonate FEC (accounting for 1 wt% 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 to DOL is 1:1), polymerizable monomer pentaerythritol tetraacrylate (PETEA, accounting for 15 wt% of the total mass of the electrolyte precursor solution), and thermal initiator azobisisobutyronitrile (AIBN, accounting for 0.5 wt% of the monomer mass) evenly to prepare sodium salt NaClO 4 An electrolyte precursor solution with a concentration of 1 mol / L;

[0070] Step 4: Inject the electrolyte precursor solution prepared in Step 3 onto the negative electrode sheet prepared in Step 2 under a vacuum state;

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

[0072] Comparative Example 3:

[0073] The positive electrode sheet, separator, and sodium metal prepared in Comparative Example 1 were assembled into a coin-type half-cell, and the electrolyte precursor solution prepared in Step 3 of Comparative Example 1 was dropped. It was left standing at 70 °C for 12 h to obtain a solid-state sodium-ion positive electrode half-cell. The battery had a capacity retention rate of 45% 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 coin-type half-cell, and the electrolyte precursor solution prepared in Step 3 of Comparative Example 2 was dropped. It was left standing at 70 °C for 12 h to obtain a solid-state sodium-ion negative electrode half-cell. The battery had a capacity retention rate of 50% after 1000 cycles at a rate of 1C in the voltage range of 0.1 - 1.5V, and 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 prepared in Comparative Example 1, separator, and negative electrode sheet prepared in Comparative Example 2 were assembled into a coin-type full-cell, and the electrolyte precursor solution prepared in Step 3 of Comparative Example 1 was dropped. It was left standing at 70 °C for 12 h to obtain a solid-state sodium-ion full-cell. The battery had a capacity retention rate of 47% after 1000 cycles at a rate of 1C in the voltage range of 2.5 - 3.8V, the initial reversible capacity at a rate of 1C was only 60% of the reversible capacity at a rate of 0.1C, and the initial reversible capacity at a rate of 5C was only 25% of the reversible capacity at a rate of 0.1C.

[0078] Comparative Example 6:

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

[0080] Step 1: Wet-mix 96 parts of the positive electrode active material lithium iron phosphate LiFePO 4 , 2 parts of the conductive agent Super P, and 2 parts of the binder polyvinylidene fluoride PVDF to obtain a positive electrode slurry;

[0081] Step 2: Coat the positive electrode slurry prepared in Step 1 on the surface of the current collector, and then obtain a positive electrode sheet after drying, rolling, and slitting;

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

[0083] Step 4: Inject the electrolyte precursor solution prepared in Step 3 onto the positive electrode sheet prepared in Step 2 under a vacuum state.

[0084] Step 5: Let it stand at room temperature for 12 h. The cyclic ether monomer DOL polymerizes 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 negative electrode of a solid-state lithium-ion battery, comprising 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: Coat the negative electrode slurry prepared in Step 1 on the surface of the current collector, and then dry, roll, and slit to obtain a negative electrode sheet.

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

[0090] Step 4: Inject the electrolyte precursor solution prepared in Step 3 onto the negative electrode sheet prepared in Step 2 under a vacuum state.

[0091] Step 5: Let it stand at room temperature for 12 h. The cyclic ether monomer DOL polymerizes 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 coin-type half-cell, and the electrolyte precursor solution prepared in Step 3 of Comparative Example 6 was dropped. It was left standing at room temperature for 12 h to obtain a solid-state lithium-ion positive electrode half-cell. The battery was cycled 2000 times at a rate of 1C in the voltage range of 2.5 - 4.0V, and the capacity retention rate was 56%. 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 coin-type half-cell, and the electrolyte precursor solution prepared in Step 3 of Comparative Example 7 was dropped. It was left standing at room temperature for 12 h to obtain a solid-state lithium-ion negative electrode half-cell. The battery was cycled 2000 times at a rate of 1C in the voltage range of 0.05 - 1.5V, and the capacity retention rate was 45%. 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 prepared in Comparative Example 6, the separator, and the negative electrode sheet prepared in Comparative Example 7 were assembled into a coin-type full-cell, and the electrolyte precursor solution prepared in Step 3 of Comparative Example 6 was dropped. It was left standing at room temperature for 12 h to obtain a solid-state lithium-ion full-cell. The battery was cycled 2000 times at a rate of 1C in the voltage range of 2.5 - 4.0V, and the capacity retention rate was 37%. The initial reversible capacity at a rate of 1C was only 52% of the reversible capacity at a rate of 0.1C, and the initial reversible capacity at a rate of 5C was only 15% of the reversible capacity at a rate of 0.1C.

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

[0099] In addition, it should be understood that although this specification is described according to the embodiments, not each embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments 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: A solid cross-linking agent is distributed in an electrode material in a gradient manner to prepare an electrode sheet, and an electrolyte precursor solution containing a polymerizable monomer is injected into the electrode sheet. The polymerizable monomer copolymerizes 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, wherein the amount of the solid cross-linking agent added increases gradually from the direction close to the current collector to the direction away from the current collector.

2. The preparation method according to claim 1, characterized in that: 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, characterized in that: The solid crosslinking agent is micro-nano particles with vinyl functionalization or epoxy functionalization on the surface, vinyl-terminated or cyclic ether-terminated cage-type polysilsesquioxane.

4. The preparation method according to claim 1, characterized in that: The polymerizable monomer is an ester monomer containing an unsaturated carbon-carbon double bond or an ether monomer containing an epoxy functional group.

5. The preparation method according to claim 1, characterized in that: The polymerizable monomer accounts for 5% to 85% of the mass of the electrolyte precursor solution.

6. The preparation method according to claim 1, characterized in that: 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.

7. The preparation method according to claim 1, characterized in that: The electrode material comprises an active material, a conductive agent and a binder which are uniformly mixed.

8. The preparation method according to claim 1, characterized in that: 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.

9. The preparation method according to claim 1, characterized in that: The method for preparing pole pieces is as follows: adding different mass fractions of solid cross-linking agent into the electrode material to prepare several slurries, and then coating the several slurries 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 drying, rolling and cutting to obtain pole pieces.

10. An application of a solid-state battery electrode prepared by the preparation method according to any one of claims 1 to 9, 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.