Exploring the potential of natural pyrrhotite mineral for electrochemical energy storage

Natural mineral is an attractive class of materials showing inherent electrical, magnetic, and electrochemical properties, while in most cases, they were smelted into refined chemicals for synthesizing functional materials. The direct utilization of natural minerals as electrode materials for energy storage reduces chemical footprint and energy consumption in industrial production, yet remains rare due to redox inactivity or cycling instability. Here, we explore the direct utilization of an electrochemically active natural mineral, pyrrhotite (Fe1-xS), as an electrode material for energy storage. We discover the cycling instability mechanism of pyrrhotite as irreversible phase segregation of discharged products (Li2S and Fe) and Fen+ leaching into the electrolyte. To improve the cycling stability, we control carbon addition and voltage window without introducing chemical synthesis, eventually overcoming the rapid capacity fading and extending the stability from 3 cycles to 100 cycles. The optimized pyrrhotite/C electrode shows 519 mAh g(-1) initial capacity when cycled between 1 and 3 V under 1 A g(-1), retaining 80% of the 2nd cycle capacity after 100 cycles. Our study is a proof-of-concept demonstrating the potential of directly utilizing natural minerals as eco-friendly and low-cost electrode materials for electrochemical energy storage.