Preparation of intergrown P/O-type biphasic layered oxides as high-performance cathodes for sodium ion batteries

This study reports on the solid-state synthesis and characterization of novel quaternary P/O intergrown biphasic Na$_{0.8}$MnyNi$_{0.8-y}$Fe$_{0.1}$Ti$_{0.1}$O$_{2}$ (y = 0.6, 0.55, 0.5, 0.45) cathode materials. Electrochemical tests reveal superior performance of the P/O biphasic materials in a sodium ion battery compared to the single P2 or O3 phases, proving the beneficial effect of the intergrowth of P2 and O3 materials. The nature of the P/O interface was studied by transmission electron microscopy. The analysis shows a semi-coherent interface grown along the a/b and c axes with local differences in the transition metal concentration along the interface between the two phases. EDX and EELS characterization revealed a charge compensation mechanism across the phase boundary based on variation of the transition element distribution, balancing the different sodium contents in the P and O phases. The results reported in this study provide a better understanding of P/O biphasic materials.