Abstract

Abstract Transition metal selenides have been attracting significant attention owing to their high conductivity and theoretical capacity. In this article, the N‐doped carbon (NDC)‐coated Ni 1.8 Co 1.2 Se 4 nanoparticles encapsulated in NDC nanoboxes are prepared from the bi‐metal organic framework (Ni 3 [Co(CN) 6 ] 2 ·6H 2 O, Ni‐Co BMOF) after the selenization reaction and carbon coating. When used as an anode material for sodium‐ion batteries, the prepared anode material delivers excellent rate performance (211 and 153 mA h g −1 at ultrahigh current densities of 30 and 50 A g −1 , respectively) and good cycling performance (379.3 mA h g −1 at 0.5 A g −1 after 100 cycles). More importantly, it also exhibits superior sodium‐ion full cell (SIFC) performance when coupled with a high‐voltage Na 3 V 2 (PO 4 ) 2 O 2 F cathode recently self‐made by the authors. The fabricated SIFC gives an energy density up to 227 W h kg −1 and the capacity retention of above 97.6% even after 60 cycles at 0.4 A g −1 in a voltage range of 1.2–4.3 V at 25 °C. Moreover, the low‐temperature (from 25 to −25 °C) Na‐storage performance of the fabricated SIFC is also studied.