Synthesis and Lithiation Mechanisms of Dirutile and Rutile LiMnF₄: Two New Conversion Cathode Materials

Abstract

Driven by the need for new cathode battery materials with high energy density, fluorides have emerged as promising candidates due to their high voltages. From high throughput computations, dirutile LiMnF 4 was identified as a promising cathode with a high conversion voltage and a theoretical specific capacity of 584 mAh/g. In this work, we study the formation of dirutile LiMnF 4 through a new, low-temperature synthesis route and report its electrochemical properties. We also report the discovery of a new rutile polymorph of LiMnF 4 which has Li-Mn disorder on the cation site. Electron diffraction confirmed both dirutile and rutile LiMnF 4 to convert upon lithiation with different reaction paths. As seen with other fluoride materials, specific capacity is strongly linked with synthesis and processing conditions. With LiMnF 4 , there was a tradeoff in maintaining phase-pure samples and optimizing samples for high specific capacity. Still, even with very simple synthesis and electrode preparation methods, both rutile and dirutile polymorphs of LiMnF 4 show electrochemical activity. Further optimization of particle morphology may enhance reaction kinetics and improve specific capacity.