A High‐Performance Solid‐State Secondary Battery Using a Triple‐Phase‐Interface Anode Displaying Excellent Capacity and Electrochemical Kinetics

ABSTRACT Solid‐state sodium‐ion batteries (SSSIBs) combining with good safety and appropriate cost are considered as a promising emerging energy‐storage system. However, poor electrochemical reversibility and sluggish kinetics of anodes remain critical bottlenecks. Here, we develop a CoS/Co ₉ S ₈ /SnS composite coated with nitrogen‐doped carbon (named as CoS/Co ₉ S ₈ /SnS@NC), where a triple‐phase‐interface heterostructure is constructed among CoS, Co ₉ S ₈ and SnS, which enables synergistically amplifying of electric field network and thus improving electron/ion transport kinetics. The CoS/Co ₉ S ₈ /SnS@NC as SSSIB anode exhibits excellent compatibility with conventional Na ₃ PS ₄ solid‐electrolyte, and delivers a large capacity of 441 mAh g ^{− 1} after 120 cycles at 0.5 A g ^{− 1} , and superior rate‐performance of 348.7 mAh g ^{− 1} at 5.0 A g ^{− 1} . Stable high‐temperature tolerance (capacity keeps 502 mAh g ^{− 1} after 50 cycles), and solid‐state full‐cells paring with Na ₃ V ₂ (PO ₄ ) ₃ cathode, are also achievable. Synergistic enhancement effect of the heterostructure is demonstrated via ex situ characterizations and in situ electrochemical impedance spectroscopy, which verifies that the triple‐phase‐interface efficiently reduces the charge transfer resistance and promotes ion diffusion. These findings provide a general strategy for engineering triple‐phase‐interface heterostructures for energy‐storage with optimal interfaces, and sheds light on the fundamental understanding of interface‐enhanced solid‐state batteries.