Cathode active material for lithium-ion secondary battery and preparation method thereof, cathode pole piece for lithium-ion secondary battery, and lithium-ion secondary battery

Abstract

Embodiments of the present disclosure provide a cathode active material for a lithium-ion secondary battery, where the cathode active material for a lithium-ion secondary battery includes a silicon-based active substance and a nitrogen-doped carbon material. The silicon-based active substance is encased in the interior of the nitrogen-doped carbon material, and the silicon-based active substance is one or more of a nanoparticle and a nanowire; a micropore is arranged on at least one of the exterior and the interior of the nitrogen-doped carbon material; and a material of the nitrogen-doped carbon material is a nitrogen-doped carbon network. The cathode active material for a lithium-ion secondary battery solves a problem in the prior art that a silicon material, when used as a cathode active material, easily falls from a current collector due to a great volume change and has a low conductivity.

What is claimed is: 
     
         1 . A cathode active material for a lithium-ion secondary battery, the cathode active material comprising:
 one or more of a nanoparticle and a nanowire comprising a silicon-based active substance;   a nitrogen-doped carbon material, wherein the silicon-based active substance is encased in an interior of the nitrogen-doped carbon material, wherein the nitrogen-doped carbon material comprises a plurality of interlinked branches formed by the nitrogen-doped carbon network;   micropores arranged on at least one of the exterior and the interior of the plurality of interlinked branches of the nitrogen-doped carbon material; and   a material of the nitrogen-doped carbon material is a nitrogen-doped carbon network, wherein a nitrogen atom and a carbon atom in the nitrogen-doped carbon network are bonded in at least one form of pyridinic nitrogen, graphite nitrogen and pyrrolic nitrogen.   
     
     
         2 . The cathode active material for a lithium-ion secondary battery according to  claim 1 , wherein a particle diameter of the silicon-based active substance nanoparticle is 1 nm-1 μm, and the nanowire is 1-200 nm in diameter and 1-10 μm long 
     
     
         3 . The cathode active material for a lithium-ion secondary battery according to  claim 1 , wherein an aperture of the micropore ranges between 0.5-500 nm. 
     
     
         4 . The cathode active material for a lithium-ion secondary battery according to  claim 1 , wherein a mass ratio of the silicon-based active substance to the cathode active material is 0.1%-80%. 
     
     
         5 . The cathode active material for a lithium-ion secondary battery according to  claim 1 , wherein a ratio of the particle diameter of the silicon-based active substance nanoparticle to the aperture of the micropore is 1-10:1. 
     
     
         6 . The cathode active material for a lithium-ion secondary battery according to  claim 1 , wherein the nitrogen-doped carbon material is in a shape of a three-dimensional network and the nitrogen-doped carbon material comprises a plurality of interlinked branches, and the branches are 1 nm-10 μm in diameter. 
     
     
         7 . The cathode active material for a lithium-ion secondary battery according to  claim 1 , wherein the nitrogen-doped carbon network comprises pyrrolic nitrogen. 
     
     
         8 . The cathode active material for a lithium-ion secondary battery according to  claim 1 , wherein the material of the silicon-based active substance is selected from one or more of simple substance silicon, silicon oxide and silicon alloy. 
     
     
         9 . A method of preparing a cathode active material for a lithium-ion battery, the method comprising:
 dispersing, by using a dispersant, a silicon-based active substance with a particle diameter of 1 nm-1 μm in solution to obtain a mixed solution; adding an oxidizer into the mixed solution and then adding an organic molecular monomer, wherein the organic molecular monomer is selected from one or more of a pyridine monomer, a pyrrole monomer, an aniline monomer, and a derivative of the pyridine monomer, the pyrrole monomer, or the aniline monomer, and the silicon-based active substance reacts with the organic molecular monomer to form a black precipitate;   filtering the black precipitate and taking a filter residue; and then encasing the exterior of the silicon-based active substance in a nitrogen-doped carbon material by using a pyrolysis method, so as to obtain the cathode active material for a lithium-ion secondary battery;   placing a silicon-based active substance with a particle diameter of 1 nm-1 μm in a tubular furnace; bringing in, by protective gas, a gasified organic molecular monomer, wherein the organic molecular monomer is selected from one or more of a pyridine monomer, a pyrrole monomer, an aniline monomer, and a derivative of the pyridine monomer, the pyrrole monomer, or the aniline monomer; and encasing the exterior of the silicon-based active substance in a nitrogen-doped carbon material by using a chemical vapor deposition method, so as to obtain the cathode active material for a lithium-ion secondary battery; and   mixing one or more organic molecules of the ionic liquid 3-methyl-1-butylpyridine dicyanamide or 1-ethyl-3-methylimidazole dicyanamide and a derivative of the 3-methyl-1-butylpyridine dicyanamide or the 1-ethyl-3-methylimidazole dicyanamide, with a silicon-based active substance with a particle diameter of 1 nm-1 μm to obtain a mixed solution and then encasing the exterior of the silicon-based active substance in a nitrogen-doped carbon material by using an ionic liquid pyrolysis method, so as to obtain the cathode active material for a lithium-ion secondary battery, wherein:
 the cathode active material for a lithium-ion secondary battery comprises a silicon-based active substance and a nitrogen-doped carbon material; the silicon-based active substance is encased in the interior of the nitrogen-doped carbon material, and the silicon-based active substance is one or more of a nanoparticle and a nanowire, 
 a particle diameter of the silicon-based active substance nanoparticle is 1 nm-1 μm, and the nanowire is 1-200 nm in diameter and 1-10 μm long; 
 a micropore is arranged on at least one of the exterior and the interior of the nitrogen-doped carbon material, 
 an aperture of the micropore ranges between 0.5-500 nm, and 
 a material of the nitrogen-doped carbon material is a nitrogen-doped carbon network, wherein a nitrogen atom and a carbon atom in the nitrogen-doped carbon network are bonded in at least one form of pyridinic nitrogen, graphite nitrogen and pyrrolic nitrogen. 
   
     
     
         10 . The preparation method of the cathode active material for a lithium-ion secondary battery according to  claim 9 , wherein the encasing the exterior of the silicon-based active substance in a nitrogen-doped carbon material by using a pyrolysis method includes: drying the filter residue at 60-100° C. for 12-36 hours; placing the dried filter residue in a tubular furnace; introducing protective gas; and sintering the dried filter residue at 500-1300° C. for 1-6 hours; 
     
     
         11 . The method of  claim 9  wherein the encasing the exterior of the silicon-based active substance in a nitrogen-doped carbon material by using a chemical vapor deposition method is: setting a mass ratio of the silicon-based active substance to the organic molecular monomer to 1:1-10; controlling the amount of gas flow of the protective gas to be 10-100 ml/min; heating the tubular furnace to 500-1300° C. inside at a heating rate of 10-50° C./min and preserving a temperature for 1-12 hours; and then cooling the tubular furnace to be in a room temperature. 
     
     
         12 . The method of  claim 9  wherein the encasing the exterior of the silicon-based active substance in a nitrogen-doped carbon material by using an ionic liquid pyrolysis method includes placing the mixed solution in a tubular furnace; evacuating the tubular furnace; introducing protective gas and controlling the amount of gas flow of the protective gas to be 10-100 ml/min; heating the tubular furnace to 500-1300° C. inside at a heating rate of 1-10° C./min and preserving a temperature for 1-6 hours; and then cooling the tubular furnace to be in a room temperature. 
     
     
         13 . A cathode pole piece for a lithium-ion secondary battery, the cathode pole piece comprising:
 a current collector;   a cathode active material coated on the current collector and comprising a silicon-based active substance and a nitrogen-doped carbon material, wherein the silicon-based active substance is encased in the interior of the nitrogen-doped carbon material, and the silicon-based active substance is one or more of a nanoparticle and a nanowire;   micropores arranged on at least one of the exterior and the interior of the nitrogen-doped carbon material; and   a material of the nitrogen-doped carbon material is a nitrogen-doped carbon network, wherein the nitrogen-doped carbon material comprises a plurality of interlinked branches formed by the nitrogen-doped carbon network, the silicon-based active substance is encased in an interior of the nitrogen-doped carbon material, wherein the micropores are arranged on at least one of the exterior and the interior of the plurality of interlinked branches of the nitrogen-doped carbon material, wherein a nitrogen atom and a carbon atom in the nitrogen-doped carbon network are bonded in at least one form of pyridinic nitrogen, graphite nitrogen and pyrrolic nitrogen.   
     
     
         14 . The cathode pole piece for a lithium-ion secondary battery according to  claim 13 , wherein a particle diameter of the silicon-based active substance nanoparticle is 1 nm-1 μm, and the nanowire is 1-200 nm in diameter and 1-10 μm long 
     
     
         15 . The cathode pole piece for a lithium-ion secondary battery according to  claim 13 , wherein an aperture of the micropore ranges between 0.5-500 nm. 
     
     
         16 . A lithium-ion secondary battery comprising a cathode pole piece, an anode pole piece, a membrane, a non-aqueous electrolyte and a casing, wherein the cathode pole piece comprises:
 a current collector;   a cathode active material coated on the current collector and comprising a silicon-based active substance and a nitrogen-doped carbon material, wherein the silicon-based active substance is encased in the interior of the nitrogen-doped carbon material, and the silicon-based active substance is one or more of a nanoparticle and a nanowire, and wherein a particle diameter of the silicon-based active substance nanoparticle is 1 nm-1 μm, and the nanowire is 1-200 nm in diameter and 1-10 μm long;   a micropore arranged on at least one of the exterior and the interior of the nitrogen-doped carbon material, and wherein an aperture of the micropore ranges between 0.5-500 nm; and   a material of the nitrogen-doped carbon material is a nitrogen-doped carbon network, wherein a nitrogen atom and a carbon atom in the nitrogen-doped carbon network are bonded in at least one form of pyridinic nitrogen, graphite nitrogen and pyrrolic nitrogen.