Preparation method of tunnel phase manganese dioxide positive electrode material with high sodium content and high capacity

The invention discloses a preparation method of a tunnel phase manganese dioxide positive electrode material with high sodium content and high capacity. The method comprises the following steps: firstly preparing alpha-phase manganese dioxide growing on carbon cloth, then soaking the alpha-phase manganese dioxide in a sodium borohydride solution containing magnesium salt, carrying out liquid-phase reduction reaction, carrying out defect introduction on the material and carrying out ion pre-embedding of sodium ions and magnesium ions to obtain sodium-magnesium co-introduced tunnel-phase manganese dioxide, and then carrying out electrochemical activation treatment to obtain the sodium-magnesium co-introduced tunnel-phase manganese dioxide. And replacing the pre-occupied magnesium ions with sodium ions in situ to prepare the high-sodium-content and high-capacity tunnel-phase manganese dioxide. The method provided by the invention can break through the structural limitation of 0.44 sodium-manganese ratio of tunne