High-EnergyNa-Ion Batteries Using Single-CrystallineCathode

Owing to the high theoretical capacity, O3-type Ni–Fe–Mn-based layered oxides are one of the cathodes with the greatest potential for high-energy Na-ion batteries (NIBs). However, their poor cycling life and air stability greatly limit their practical application. Herein, we synthesized single-crystalline O3–Na_0.95Ni_0.4Fe_0.2Mn_0.4O₂ (SC-NFM424) with a preferred orientation of the (003) facet by a simple resintering method, which delivered a high capacity of 172.3 mA h g^–1 and stable cycling stability (80.0% after 450 cycles at 1 C). The various characterizations confirm that SC-NFM424 can effectively suppress the side reactions and structural degradation during the charge/discharge process. Moreover, the assembled 18650 cylindrical-type SC-NFM424||HC cell shows a capacity of 1726 mA h and an energy density of 172.2 W h kg^–1 with a prominent cycling retention over 91.6% after 300 cycles at 0.5 C, which represents record values for high-energy and cycling stability of NIBs among the various cathode-based Ah-level cells.