Reversible Li plus Storage in CFx-Based Cathodes through Transition Metal Decomposition

Graphite fluorides (CFx) have been commercially applied in primary lithium batteries for decades with high specific capacity and low self -discharge rate, but the electrode reaction of CF with Li+ is basically irreversible compared to that of transition metal fluorides (MFx, M = Co, Ni, Fe, Cu, etc.). In this work, rechargeable CFx-based cathodes are fabricated by introducing transition metals, which reduces the Rct of the CFx electrode during the primary discharge process and participates in the re-conversion process of LiF under high voltage, which generates MFx (confirmed by ex situ X-ray diffraction measurements) for subsequent Li+ storage. A CF-Cu (F/Cu = 2/1 by mol) electrode, for example, delivers a primary capacity as high as 898 mAh g(CF0.56)-1 (similar to 2.35 V vs Li/Li+) and a reversible capacity of 383 mAh g(CF0.56)-1 (similar to 3.35 V vs Li/Li+) in the second cycle. Furthermore, excessive transition metal decomposition during the charge process is harmful to electrode structure stability. Methods such as building a compact counter electrolyte interface (CEI) and obstructing the electron transport of transition metal atoms will contribute to finite and local transition metal oxidation that benefits cathode reversibility.

Automated summary

In this work, rechargeable CFx-based cathodes with high specific capacity and low self-discharge rate are developed by introducing transition metals, which reduces the irreversible electrode reaction of CF with Li+ and enhances cathode reversibility. Methods such as building a compact counter electrolyte interface (CEI) and obstructing the electron transport of transition metal atoms are proposed to mitigate the harmful effects of excessive transition metal decomposition during the charge process.