Electrochemical Performance Enhancement of Na0.7MnO2 for Sodium-Ion Batteries By Doping and Conformal Surface Coating

Abstract

Sodium-ion batteries (SIBs), which have similar working mechanism to that of Li-ion batteries (LIBs), have attracted great attention as new power sources for large-scale energy storage because of the abundant of Na reserves. However, there is still a huge challenge for the development of SIBs due to the low rate capacity and poor cycle stability of cathode materials. Different approaches of element doping and surface modifications have been widely applied to improve the electrochemical performance of those cathode materials. Herein, doping of Ti4+ and Zr4+ and coating of TiO2 and ZrO2 have been achieved by atomic layer deposition (ALD). The rate capability and cycling stability of the modified material were improved and the enhancement mechanism was studied. The TiO2 and ZrO2 coatings act as a stable interfacial layer to enhance the cycle stability of NMO by suppressing side reactions between the electrode and electrolyte. The doping of transition metal ions reduces the bond length of Mn-O and increases its bond energy, which further enhances the stability of the layered structure. In addition, the doping of transition metal ions can also enhance the intrinsic electronic conductivity by enlarging the Na-O bond length and lowering the Na+ migration barrier, thereby increasing the rate capacity.