Biphasic layered transition metal oxides as positive electrode materials for sodium-ion battery: An emerging strategy for enhancement of electrochemical performance

The necessity and development of sodium-ion batteries are increasing exponentially owing to the higher abundance and wide uniform distribution of sodium on Earth's crust. The improvement in the electrochemical performance of positive electrode materials is essential to upgrade the sodium-ion batteries for commercialization. The layered transition metal oxides (LTMOs) are one of the potential candidates for commercialization due to their high capacity and facile synthesis methods. Moreover, different strategies are employed to further increase the performance of layered cathodes. Among the various methods, structural integration of different layered phases is one of the promising strategies in which the synergistic effect of phases was effectively explored for sodium intercalation/de-intercalation. In this review, a comprehensive report of the different biphasic layered materials reported in the literature as positive electrode materials for SIBs is provided. The different synthesis strategies for grafting structures and its effect on the formation of phase fractions are extensively discussed. This review provides a summary of research developments in the field of structurally integrated layered materials and prospects for the development of layered transition metal oxides in new research directions as potential positive cathode materials for sodium-ion batteries.