Hard carbon negative electrode material for sodium ion battery and preparation method of hard carbon negative electrode material

The invention discloses a hard carbon negative electrode material for a sodium ion battery and a preparation method, the innermost layer is biomass hard carbon, and a biomass precursor is one or more of pine cones, bamboo shoot shells and sawdust; the second layer is a mixture of resin cracked carbon and nanocarbon, the resin is epoxy resin or phenolic resin, and the resin is used for fixing the nanocarbon and enhancing the material capacity at the same time; the outermost layer is citric acid cracked carbon, the coating amount of the citric acid cracked carbon accounts for 3-20% of the whole material, and the negative electrode material is of a spherical structure and has a porous structure. A purified biomass precursor is coated with resin with nanocarbon, biomass hard carbonization and primary coating of resin cracked carbon and nanocarbon are achieved through primary heat treatment, material spheroidization is achieved through a spray drying and heat treatment process, meanwhile, a second citric acid crac