Method for constructing metal fluoride positive pole piece with built-in lithium source

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly discloses a construction method of a metal fluoride positive plate with a built-in lithium source. A positive current collector, metal fluoride, conductive carbon and glutenin form a pole piece, then the whole pole piece is immersed in a chemical lithiation agent for a pre-lithiation reaction, after the reaction is completed, the pole piece is cleaned and dried to remove a residual solvent, and finally battery assembly is carried out. The metal fluoride positive pole piece with the built-in lithium source provided by the invention solves the problems of limited application scene of metal fluoride and pole piece failure caused by side reaction of a binder in a chemical pre-lithiation process, and provides a new idea for manufacturing a high-performance lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and specifically discloses a method for constructing a metal fluoride positive electrode with an embedded lithium source. Background Technology

[0002] In recent years, high-capacity lithium-free cathode transition metal fluorides have attracted widespread attention from researchers. Studies have found that metal fluoride cathodes possess a multi-electron conversion reaction mechanism; one mole of redox center metal atoms can store 2-3 moles of lithium ions, exhibiting a high theoretical specific capacity, far exceeding that of commercial lithium-ion batteries based on intercalation cathodes and graphite anodes. However, metal fluoride cathodes are generally paired with lithium metal anodes to form secondary battery systems, which severely limits their safety and application prospects. To achieve high-energy-density and high-safety metal fluoride-lithium-ion batteries and advance the commercialization of metal fluoride cathodes, the construction of metal fluoride cathodes with built-in lithium sources is crucial.

[0003] Literature review revealed that solution chemical pre-lithiation involves dissolving metallic lithium with aromatic hydrocarbons such as naphthalene and biphenyl in an organic solvent to form free radical anions coordinated with lithium ions. When electrons from these free radical anions are transferred to the electrode material, lithium ions are also inserted into the electrode material, achieving the chemical lithiation process. Solution chemical pre-lithiation ensures reaction uniformity and simplicity.

[0004] When using this method to chemically pre-lithiate metal fluoride electrodes, it is crucial to ensure that substances other than the metal fluoride do not react with the pre-lithiating agent, as the metal fluoride, conductive carbon, and binder in the electrode all come into contact with it. However, the currently mainstream binder is polyvinylidene fluoride (PVDF), which reacts with the pre-lithiating agent during the reaction process to generate excess LiF, leading to a decrease in electrode adhesion, detachment from the current collector, and a reduction in electrode electronic conductivity—all serious challenges.

[0005] Therefore, a new method for preparing metal fluoride electrodes needs to be developed. Summary of the Invention

[0006] To address the above problems, this invention provides a method for constructing a metal fluoride positive electrode with an embedded lithium source, comprising the following steps: (1) Provides positive current collector, metal fluoride, conductive carbon and glutenin; (2) Mix the metal fluoride, conductive carbon, and glutenin evenly, then add the mixture to an organic solvent and mix evenly to obtain the positive electrode slurry: (3) Coat the positive electrode slurry obtained in step (2) onto the surface of the positive electrode current collector, dry it, and then roll it. (4) Immerse the positive electrode obtained in step (3) in a chemical lithiumizing agent for pre-lithiation treatment; (5) Remove the pre-lithiated positive electrode from the chemical lithiating agent and clean it.

[0007] Preferably, the metal fluoride includes one or more of ferric trifluoride, copper fluoride, and cobalt fluoride.

[0008] Preferably, the conductive carbon includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, and super-p.

[0009] Preferably, the amount of glutenin in the positive electrode sheet is 1 wt.% to 25 wt.% of the sum of the mass of glutenin, metal fluoride, and conductive carbon.

[0010] Preferably, the organic solvent is selected from N-methylpyrrolidone, ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, propyl butyrate, ethylene glycol dimethyl ether, 1,3-dioxane, 1,3-dioxane, dimethyl sulfoxide, and polyethylene glycol.

[0011] Preferably, the chemical lithiating agent includes at least one of the following: lithium biphenyl-tetrahydrofuran solution (Biph-Li-THF), lithium biphenyl-ethylene glycol dimethyl ether solution (Biph-Li-DME), lithium naphthene-tetrahydrofuran solution (Naph-Li-THF), lithium naphthene-ethylene glycol dimethyl ether solution (Naph-Li-DME), lithium 9,9-dimethylfluorene-tetrahydrofuran solution (DiMF-Li-THF), and lithium 9,9-dimethylfluorene-ethylene glycol dimethyl ether solution (DiMF-Li-DME), with a concentration range of 0.1-1 mol / L.

[0012] Preferably, the cleaning is performed using tetrahydrofuran solvent (THF) or dimethyl ethylene glycol ether solvent (DME), which are used in chemical lithium-ionizing agents.

[0013] By adopting the above technical solution, the present invention mainly has the following technical effects: (1) Expanding the application scenarios of metal fluoride cathodes: By using a built-in lithium source, metal fluoride cathodes no longer have to rely on lithium metal anodes and can be applied to safer and more common lithium-ion battery systems (such as matching graphite anodes), breaking through their application limitations.

[0014] (2) Solved the problem of binder failure in the pre-lithiation process: By using glutenin as a binder, the side reaction between the binder and the lithiating agent in the chemical pre-lithiation process is effectively avoided, thereby ensuring the structural integrity and stability of the electrode.

[0015] (3) Improved battery safety performance: Since the use of highly active lithium metal anodes is no longer mandatory, the safety risks of the battery system are fundamentally reduced and the overall safety of the battery is improved.

[0016] (4) Effectively inhibits the dissolution of active materials of metal fluorides during charging and discharging: During the charging and discharging process, the reaction intermediates of metal fluorides may dissolve and redeposit, leading to loss of active materials and capacity decay. The glutenin binder used in this invention can "anchor" the active materials, thereby effectively inhibiting their dissolution in the electrolyte and helping to improve the cycle life and capacity retention of the battery. Attached Figure Description

[0017] Figure 1 (a) An optical photograph of electrode C in Example 1; (b) An optical photograph of the metal fluoride positive electrode with built-in lithium source obtained in Example 1; (c) An optical photograph of electrode D in Comparative Example 1; Figure 2 (a) XRD pattern of commercial iron trifluoride; (b) XRD pattern of the metal fluoride positive electrode with built-in lithium source obtained in Example 1; Figure 3 (a) Charge-discharge curves of the first three cycles in Example 1; (b) Charge curve of the first cycle in Comparative Example 1; Figure 4 The diagram shows the cyclic performance of Example 1 and Comparative Example 2. Detailed Implementation

[0018] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. The embodiments described below are only some embodiments of the present invention and do not represent all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1 (1) Ferric trifluoride, super-p and glutenin are ground and mixed to obtain mixed powder A; (2) Mix powder A and N-methylpyrrolidone evenly in a beaker for 12 hours to obtain slurry B; (3) The slurry is evenly coated onto the aluminum foil, dried at 85°C for 12 hours, then rolled and cut into uniform small round pieces with a diameter of 12 mm to obtain electrode C; (4) Immerse electrode C in 0.1 mol / L Naph-Li-THF lithium lithiating agent and react at room temperature for 60 min to complete electrode pre-lithiation; (5) Remove electrode C from the chemical lithium-ionizing agent and clean it in THF solvent. The resulting electrode is the metal fluoride positive electrode with built-in lithium source.

[0020] (6) Assemble the positive electrode, commercial graphite negative electrode and separator into a coin cell and perform electrochemical tests.

[0021] Example 2 (1) Ferric trifluoride, super-p and glutenin are ground and mixed to obtain mixed powder A; (2) Mix powder A and N-methylpyrrolidone evenly in a beaker for 12 hours to obtain slurry B; (3) The slurry is evenly coated onto the aluminum foil, dried at 85°C for 12 hours, then rolled and cut into uniform small round pieces with a diameter of 12 mm to obtain electrode C; (4) Immerse electrode C in 1 mol / L DiMF-Li-DME lithiation agent and react at room temperature for 10 min to complete electrode prelithiation; (5) Remove electrode C from the chemical lithium-ionizing agent and clean it in DME solvent. The resulting electrode is the metal fluoride positive electrode with built-in lithium source.

[0022] (6) Assemble the positive electrode, commercial graphite negative electrode and separator into a button cell.

[0023] Example 3 (1) Cobalt fluoride, super-p and glutenin are ground and mixed to obtain mixed powder A; (2) Mix powder A and N-methylpyrrolidone evenly in a beaker for 12 hours to obtain slurry B; (3) The slurry is evenly coated onto the aluminum foil, dried at 85°C for 12 hours, then rolled and cut into uniform small round pieces with a diameter of 12 mm to obtain electrode C; (4) Immerse electrode C in 0.1 mol / L Biph-Li-THF lithium lithiating agent and react at room temperature for 60 min to complete electrode pre-lithiation; (5) Remove electrode C from the chemical lithium-ionizing agent and clean it in THF solvent. The resulting electrode is the metal fluoride positive electrode with built-in lithium source.

[0024] (6) Assemble the positive electrode, commercial graphite negative electrode and separator into a button cell.

[0025] Example 4 (1) Copper fluoride, super-p and glutenin are ground and mixed to obtain mixed powder A; (2) Mix powder A and N-methylpyrrolidone evenly in a beaker for 12 hours to obtain slurry B; (3) The slurry is evenly coated onto the aluminum foil, dried at 85°C for 12 hours, then rolled and cut into uniform small round pieces with a diameter of 12 mm to obtain electrode C; (4) Immerse electrode C in 0.1 mol / L Naph-Li-DME lithiation agent and react at room temperature for 60 min to complete electrode prelithiation; (5) Remove electrode C from the chemical lithium-ionizing agent and clean it in DME solvent. The resulting electrode is the metal fluoride positive electrode with built-in lithium source.

[0026] (6) Assemble the positive electrode, commercial graphite negative electrode and separator into a button cell.

[0027] Comparative Example 1 (1) Ferric trifluoride, super-p and PVDF are ground and mixed to obtain mixed powder A; (2) Mix powder A and N-methylpyrrolidone evenly in a beaker for 12 hours to obtain slurry B; (3) The slurry is evenly coated onto the aluminum foil, dried at 85°C for 12 hours, then rolled and cut into uniform small round pieces with a diameter of 12 mm to obtain electrode C; (4) Immerse electrode C in 0.1 mol / L Naph-Li-THF lithium lithiating agent and react at room temperature for 60 min to complete electrode pre-lithiation; (5) Remove electrode C from the chemical lithium-ionizing agent and clean it in THF solvent to obtain electrode D.

[0028] (6) Assemble the electrode D, commercial graphite negative electrode and separator into a coin cell and perform electrochemical tests.

[0029] Optical photographs of electrode preparation in Example 1 and Comparative Example 1 are as follows: Figure 1 As shown in the figure, it can be seen that during the pre-lithiation process, the pre-lithiated electrode sample prepared using glutenin remained intact, while the pre-lithiated electrode sample prepared using PDVF suffered severe active material stripping. The XRD data of the electrode samples prepared in Example 1 are shown below. Figure 2 As shown, when in contact with a chemical pre-lithiation agent, iron trifluoride is converted into iron and lithium fluoride.

[0030] The charge-discharge curves of the electrodes prepared in Example 1 and Comparative Example 1 are as follows: Figure 3 As shown, the battery system of Example 1 charges and discharges normally, while the battery system of Comparative Example 1 fails to function properly.

[0031] Comparative Example 2 (1) Ferric trifluoride, super-p and PVDF are ground and mixed to obtain mixed powder A; (2) Mix powder A and N-methylpyrrolidone evenly in a beaker for 12 hours to obtain slurry B; (3) The slurry is evenly coated onto the aluminum foil, dried at 85°C for 12 hours, then rolled and cut into uniform small round pieces with a diameter of 12 mm to obtain electrode C.

[0032] (6) Assemble the electrode C, commercial lithium metal anode and separator into a coin cell and perform electrochemical tests.

[0033] The charge-discharge curves of the electrodes prepared in Example 1 and Comparative Example 2 are as follows: Figure 4 As shown, Example 1 outperforms Comparative Example 2 in terms of cycle stability and reversible capacity. Furthermore, the negative electrode of Example 1 is commercial graphite, and compared to Comparative Example 2, which requires the use of lithium metal, the metal fluoride electrode preparation method with an integrated lithium source provided by this invention exhibits safer performance and greater industrialization potential.

Claims

1. A method for constructing a metal fluoride positive electrode with an embedded lithium source, characterized in that, Includes the following steps: (1) Provides positive current collector, metal fluoride, conductive carbon and glutenin; (2) Mix the metal fluoride, conductive carbon, and glutenin evenly, then add the mixture to an organic solvent and mix evenly to obtain the positive electrode slurry: (3) Coat the positive electrode slurry obtained in step (2) onto the surface of the positive electrode current collector, dry it, and then roll it. (4) Immerse the positive electrode obtained in step (3) in a chemical lithiumizing agent for pre-lithiation treatment; (5) Remove the pre-lithiated positive electrode from the chemical lithiating agent and clean it.

2. The method for constructing a metal fluoride positive electrode with an embedded lithium source according to claim 1, characterized in that, The metal fluoride includes one or more of ferric trifluoride, copper fluoride, and cobalt fluoride.

3. The method for constructing a metal fluoride positive electrode with an embedded lithium source according to claim 1, characterized in that, The conductive carbon includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, and super-p.

4. The method for constructing a metal fluoride positive electrode with an embedded lithium source according to claim 1, characterized in that, The gluten content in the positive electrode sheet is 1 wt.% to 25 wt.% of the sum of the mass of glutenin, metal fluoride, and conductive carbon.

5. The method for constructing a metal fluoride positive electrode with an embedded lithium source according to claim 1, characterized in that, The organic solvent is selected from one of N-methylpyrrolidone, ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, propyl butyrate, ethylene glycol dimethyl ether, 1,3-dioxane, 1,3-dioxane, dimethyl sulfoxide, and polyethylene glycol.

6. The method for constructing a metal fluoride positive electrode with an embedded lithium source according to claim 1, characterized in that, The chemical lithium-ionizing agent includes at least one of the following: lithium biphenyl-tetrahydrofuran solution, lithium biphenyl-ethylene glycol dimethyl ether solution, lithium naphthene-tetrahydrofuran solution, lithium naphthene-ethylene glycol dimethyl ether solution, lithium 9,9-dimethylfluorene-tetrahydrofuran solution, and lithium 9,9-dimethylfluorene-ethylene glycol dimethyl ether solution, with a concentration range of 0.1-1 mol / L.

7. The method for constructing a metal fluoride positive electrode with an embedded lithium source according to claim 1, characterized in that, The cleaning process uses tetrahydrofuran solvent or ethylene glycol dimethyl ether solvent, which are used in chemical lithium-ionizing agents.

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