Self-templating construction of hollow microspheres assembled by nanosheets with exposed active planes for sodium ion storage

P2-type layered metal oxides have been considered as one of the promising cathode candidates for high-performance Na-ion batteries (SIBs). However, it is still challenging to balance the contradiction of high energy density and long cycle life due to the structural degradation and sluggish ion diffusion dynamics. Here, the hierarchical P2-Na_2/3Ni_1/3Mn_2/3O₂ hollow microspheres assembled by nanosheets are constructed via a self-template approach. The obtained nanosheets with more exposed electrochemical active planes serving as desodiation/sodiation reactors can provide substantial Na⁺ channels, shorten the diffusion pathways, and accommodate the volume changes during charge/discharge process. Benefiting from the facile Na⁺ diffusion paths and optimal architecture modulation, the cathode delivers a high initial Coulombic efficiency of 96.0% with a high energy density of 299.7 Wh·kg⁻¹. The highly reversible structural evolutions processes are verified by galvanostatic intermittent titration technique (GITT) and operando electrochemical impedance spectroscopy (EIS) measurement, which would significantly improve the cycle stability (83.3% capacity retention at 1.0 C over 500 loops). Furthermore, the full cell assembled by hard carbon presents a high reversible capacity of 71 mAh·g⁻¹ at 0.2 C and promising capacity retention (91.5% after 50 cycles). The designing concept of morphological configuration in this work paves an accessible route for building high-performance electrode materials.