Promoting the performances of P2-type sodium layered cathode by inducing Na site rearrangement

Abstract

The electrochemical performance and structural stability of sodium-ion battery is substantially dependent on the occupancy and distribution of Na+ in cathode materials. However, it is challenging to simultaneously regulate the occupancy and optimize the distribution of Na+ in cathodes for higher capacity and superior cyclability. Here we attempt to adjust the arrangement of Na+ in layered cathode materials by applying a combination approach, including enhancing the Na content, disrupting transition metal ordering and strengthening Na+-TMn+ electrostatic force. Through detailed structural characterizations on cathodes, it is revealed that the rearrangement of Na+ at two distinct Wyckoff positions can be realized in Li/Ti-codoped Na2/3Ni1/3Mn2/3O2 cathodes, contributing to outstanding rate performance and smooth kinetic process. In addition, the inhibited P2-O2 phase transition and intact lattice structure is closely related to the rearranged Na layer and strengthened transition metal slab, jointly resulting in excellent long cycling performance with 90.2% capacity retention after 200 cycles at 1 C (150 mA/g). This work sheds new light on the role of different Na sites and provides a universal and practical approach to adjusting the Na+ distribution in P2-type cathode materials.