Preparation method of nitrogen-doped negative electrode material for sodium battery

The invention discloses a preparation method of a nitrogen-doped negative electrode material for a sodium battery, which comprises the following steps: preparing graphite-phase carbon nitride from melamine, pretreating, mixing with sodium triacetoxyborohydride, and calcining to obtain the nitrogen-doped negative electrode material. Oxalic acid is adopted to etch graphite-phase carbon nitride, so that a graphite-like interlayer structure is damaged, oxygen-containing groups are introduced, the electrochemical performance is improved, the interlayer spacing is increased, and sodium ions are easier to embed; graphite phase carbon nitride is subjected to denitrification reduction by adopting sodium triacetoxyborohydride, and the nitrogen content is reduced to a proper level to improve the sodium storage capacity, so that relatively high nitrogen content is ensured, and meanwhile, huge first irreversible capacity loss caused by too high nitrogen content is also avoided; meanwhile, the boron element is doped into t