Potassium-ion batteries (PIBs) have favorable characteristics in terms of cell voltage and cost efficiency, making them a promising technology for grid-scale energy storage. The rational design of suitable electrode materials on a theoretical basis, aiming at high power and energy density, is of paramount importance to bring this battery technology to the practical market. In this paper, a series of iron-based compounds with different non-metal anions are selectively synthesized to investigate the nature of kinetic differences induced by anionic modulation. A combination of experimental characterization and theoretical calculation reveals that iron phosphide, with its moderate adsorption energy ( E a ) and lowest diffusion barrier ( E b ), exhibits the best cycling and rate properties at low electrochemical polarization, which is related to the narrow Δ d-p band center gap that facilitates ion transfer. In addition, the optimization of the electrolyte formula results in the carbon-supported iron phosphide anode running stably over 2000 cycles at 0.5 A g −1 and exhibiting a high rate capacity of 81.1 mAh g −1 at 2 A g −1 . The superior electrochemical properties are attributed to the robust KF-rich solid electrolyte interphase formed by the highly compatible KFSI in ethylene carbonate (EC)/diethyl carbonate (DEC) configuration.
Structural design combined with crystal engineering is an external and internal modifying strategy for metal oxides and sulfides as anode materials for lithium/sodium-ion batteries (LIBs/SIBs). In this paper, the low-cost iron-based oxide of Fe 2 O 3 shaped into dendritic nanostructure is locally in situ phase converted to FeS 2 and form porous Fe 2 O 3 /FeS 2 polycrystalline texture. The Fe 2 O 3 /FeS 2 maintains the original porous, cross-linked and low-dimension structural advantages of the Fe 2 O 3 precursor for electron transport and ions exchange and alleviating volume expansion. Then, the abundant heterogeneous in the converted Fe 2 O 3 /FeS 2 dramatically enhances electron diffusion in crystal and the structural stability at phase boundary. The prepared anode achieves superior rate capability and ultra-long cycling stability with high capacity both in LIBs and SIBs. Specially, it shows 1017 and 1016 mAh g −1 at 10 A g −1 in LIBs and SIBs, separately. After 3000 cycles, the electrodes maintain 266 mAh g −1 at 10 A g −1 in LIBs and 279 mAh g −1 in SIBs. In addition, the LiFePO 4 //Fe 2 O 3 /FeS 2 and (Na 3 V 2 (PO 4 ) 3 )//Fe 2 O 3 /FeS 2 full cells are successfully packaged and also show satisfactory electrochemical performances.
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