Triggering Reversible Intercalation-Conversion Combined Chemistry for High-Energy-Density Lithium Battery Cathodes

Abstract

Combining intercalation and conversion reactions maximizes the utilization of redox-active elements in electrodes, providing a means for overcoming the current capacity ceiling. However, integrating both mechanisms within a single electrode material presents significant challenges owing to their contrasting structural requirements. Intercalation requires a well-defined host structure for efficient lithium-ion diffusion, whereas conversion reactions entail structural reorganization, which can undermine intercalation capabilities. Based on the previous study that successfully demonstrated reversible intercalation-conversion chemistry in amorphous LiFeSO4F, this study aims to provide an in-depth understanding on how this can be enabled. Experimental and theoretical investigations of a model system based on tavorite-structured LiFeSO4F revealed that amorphization governs the activation and reversibility of the combined reactions. Enhanced reversibility is achieved through the facile migration of transition metals within the amorphous matrix. Unexpectedly, it is found that amorphization also narrowed the voltage gap between the intercalation and conversion reactions. This voltage-gap reduction is explained by the thermodynamic metastability of the amorphous phase. The applicability of the approach to other intercalation hosts is further demonstrated, showing that amorphization enables reversible intercalation and conversion. These findings suggest a new strategy that leverages the full potential of intercalation and conversion reactions, introducing new avenues for cathode design. Utilizing both intercalation and conversion mechanisms within a single phase represents an optimal approach for achieving high energy density in cathode materials. For the purposes of reversible operation and achieving a high redox voltage, the amorphization process is proposed as a strategic design method for cathode materials. The influence of amorphization on electrode materials is meticulously confirmed in thermodynamics and kinetics. image