Intrinsically Ultrahigh-Rate Charging Capability of Conversion Reaction Cathodes and Its Origin: A Mechanism Study on FeS₂

Abstract

Conversion-type electrodes with extended Li⁺ storage and multi-electron transfer capabilities hold great promise for meeting the growing demand for high energy density. However, most of these materials suffer from inherently poor rate performance and limited capacity reversibility, primarily due to the low diffusivity of metal cations and inevitable structural changes during (de)lithiation. Herein, we report the high first-cycle capacity reversibility of FeS₂ under ultrahigh charging rates. The kinetic properties of the charging process are revealed through electrochemical measurements, and the origin of the outstanding rate performance is further investigated using advanced spectroscopic characterizations. In particular, the exceptionally high apparent diffusion coefficient observed in the electrode reflects the excellent mobility of Fe²⁺ cations, which directly accounts for the remarkable rate capability. Further investigation reveals that the S^2– anion framework of the anti-fluorite structure is well preserved during charging, providing stable channels and sites for Fe²⁺ insertion. Moreover, the high-spin state of Fe²⁺ reduces the energy barrier for its migration into the tetrahedral sites formed by S^2– anions, facilitating rapid and stable ion transport. This study elucidates the origin of the kinetic performance from a mechanistic perspective and provides guidance for the development of conversion-type electrodes in high-power energy storage devices.

Keywords

anion framework / conversion–type electrodes / FeS₂ / high rate / high–spin Fe²⁺

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