Na + /Vacancy Disordered P2-Na 0.67 Co 1– x Ti x O 2 : High-Energy and High-Power Cathode Materials for Sodium Ion Batteries

Although sodium ion batteries (NIBs) have gained wide interest, their poor energy density poses a serious challenge for their practical applications. Therefore, high-energy-density cathode materials are required for NIBs to enable the utilization of a large amount of reversible Na ions. This study presents a P2-type Na 0.67 Co 1– x Ti x O 2 ( x < 0.2) cathode with an extended potential range higher than 4.4 V to present a high specific capacity of 166 mAh g –1 . A group of P2-type cathodes containing various amounts of Ti is prepared using a facile synthetic method. These cathodes show different behaviors of the Na + /vacancy ordering. Na 0.67 CoO 2 suffers severe capacity loss at high voltages due to irreversible structure changes causing serious polarization, while the Ti-substituted cathodes have long credible cycleability as well as high energy. In particular, Na 0.67 Co 0.90 Ti 0.10…