Configuring Optimal FeS2@Carbon Nanoreactor Anodes: Toward Insights into Pyrite Phase Change/Failure Mechanism in Rechargeable Ni-Fe Cells

Pyrite FeS2 has long been a research focus as the alternative anode of rechargeable Ni-Fe cells owing to its eye-catching merits of great earth-abundance, attractive electrical conductivity, and output capacity. However, its further progress is impeded by unsatisfactory cyclic behaviors due to still ill-defined phase changes. To gain insights into the pyrite working principles/failure factors, we herein design a core-shell hybrid of a FeS2@carbon nanoreactor, an optimal anode configuration approaching the practical usage state. The resultant electrodes exhibit a Max. specific capacity of similar to 272.89 mAh g(-1) (at similar to 0.81 A g(-1)), remarkably improved cyclic longevity/stability (beyond similar to 80% capacity retention after 103 cycles) and superior rate capability (similar to 146.18 mAh g(-1) is remained at similar to 20.01 A g(-1)) in contrast to bare FeS2 counterparts. The as-built Ni-Fe full cells can also output impressive specific energy/power densities of similar to 87.38 Wh kg(-1)/similar to 11.54 kW kg(-1). Moreover, a refreshed redox reaction working mechanism of FeS2OH <-> FeS2 <-> Fe-0 ((in pyrite domains)) is redefined based on real-time electrode characterizations at distinct operation stages. In a total cyclic period, the configured pyrite-based anodes would stepwise undergo three critical stages nominally named retention, phase transition/coexistence, and degradation, each of which is closely related to variations on anodic compositions/structures. Combined with optimal electrode configurations and in-depth clarifications on inherent phase conversions, this focus study may guide us to maximize the utilization efficiency of pyrite for all other aqueous electrochemical devices.