Observation of Pseudocapacitive Effect and Fast Ion Diffusion in Bimetallic Sulfides as an Advanced Sodium‐Ion Battery Anode

Sodium‐ion batteries (SIBs) are promising next‐generation alternatives due to the low cost and abundance of sodium sources. Yet developmental electrodes in SIBs such as transition metal sulfides have huge volume expansion, sluggish Na+ diffusion kinetics, and poor electrical conductivity. Here bimetallic sulfide (Co9S8/ZnS) nanocrystals embedded in hollow nitrogen‐doped carbon nanosheets are demonstrated with a high sodium diffusion coefficient, pseudocapacitive effect, and excellent reversibility. Such a unique composite structure is designed and synthesized via a facile sulfidation of the CoZn‐MOFs followed by calcination and is highly dependant on the reaction time and temperature. The optimized Co1Zn1‐S(600) electrode exhibits excellent sodium storage performance, including a high capacity of 542 mA h g−1 at 0.1 A g−1, good rate capability at 10 A g−1, and excellent cyclic stability up to 500 cycles for half‐cell. It also shows potential in full‐cell configuration. Such capabilities will accelerate the adoption of sodium‐ion batteries for electrical energy applications. The in situ synthesis of bimetallic sulfide (Co9S8/ZnS) nanocrystals embedded in hollow nitrogen‐doped carbon nanosheets is reported with a high sodium diffusion coefficient, pseudocapacitive effect, and excellent reversibility. Such a unique composite exhibits excellent sodium storage performance in a half‐cell, especially with a high capacity retention of over 88% after 500 cycles at 10 A g−1.