A Ca‐substituted air‐stable layered oxide cathode material with facilitated phase transitions for high‐performance Na‐ion batteries

Abstract Cost‐efficient and high‐performance cathodes play a crucial role in the advancement of grid‐scale sodium‐ion batteries (SIBs). As promising high‐capacity cathode materials for SIBs, O 3 ‐type Na‐based layered transition metal oxides constantly experience inadequate air stability and complex phase transitions. Herein, a comprehensive investigation was conducted to explore the impact of Ca substitution on both the electrochemical performance and structural stability of O 3 –Na 1−2 x Ca x Ni 0.25 Fe 0.5 Mn 0.25 O 2 ( x = 0, 0.02 and 0.05) that is proposed. With proper Ca content, O 3 ‐type Na 0.96 Ca 0.02 Ni 0.25 Fe 0.5 Mn 0.25 O 2 can deliver a reversible capacity of 122.1 mAh·g −1 at 10 mA·g −1 , with capacity retention of 83.4% after 200 cycles at 50 mA·g −1 and good rate capability. Its air sensitivity is investigated, and its potential as the Na host in full cells has been studied. In situ X‐ray diffraction reveals the facilitated O 3 –P 3 –O 3 phase transitions of such cathode during the whole electrochemical reaction. Such a simple and effective strategy may reveal a new avenue for high‐stable O 3 ‐type cathodes and promote the practical applications of SIBs.