Sodium-Ion Batteries

4Polyanion‐Type Cathodes for Sodium‐Ion Batteries

4.1 Introduction

In stark contrast to the transition metal (TM) oxide cathodes, polyanionic compounds are more stable in structure and display good cycling stability. NaFePO₄ in olivine structure is highly pursued and optimized as a sodium‐ion battery (SIB) cathode to duplicate the success of its counterpart LiFePO₄ in lithium‐ion batteries (LIBs). The most appealing feature of NaFePO₄ lies in its high theoretical capacity of 154 mAh g⁻¹ and working voltage plateau of 2.9 V (vs. Na⁺/Na), along with rigid lattice framework that guarantees facile sodium‐ion migration within the host structure. Moreover, as compared to low‐dimensional sodium‐ion transport pathways in NaFePO₄, the three‐dimensional ...