Sun Nan, Zhang Yali, Xu Shiguan, Sun Wei, Huang Yuhao
Key Laboratory of Laser Technology and Optoelectronic Functional Materials of Hainan Province, Key Laboratory of Functional Materials and Photoelectrochemistry of Haikou, College of Chemistry and Chemical Engineering, Hainan Normal University, 99 South Longkun Road, Haikou 571158, China.
Langmuir. 2023 Mar 28;39(12):4257-4264. doi: 10.1021/acs.langmuir.2c03205. Epub 2023 Mar 13.
Graphite fluorides (CF) 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 (MF, M = Co, Ni, Fe, Cu, etc.). In this work, rechargeable CF-based cathodes are fabricated by introducing transition metals, which reduces the of the CF electrode during the primary discharge process and participates in the re-conversion process of LiF under high voltage, which generates MF (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 (∼2.35 V vs Li/Li) and a reversible capacity of 383 mAh g (∼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.
几十年来，石墨氟化物（CF）因其高比容量和低自放电率已在一次锂电池中得到商业应用，但与过渡金属氟化物（MF，M = Co、Ni、Fe、Cu等）相比，CF与Li的电极反应基本上是不可逆的。在这项工作中，通过引入过渡金属制备了可充电的CF基阴极，这减少了CF电极在初次放电过程中的 ，并在高压下参与LiF的再转化过程，生成MF（通过非原位X射线衍射测量证实）用于后续的Li存储。例如，CF-Cu（摩尔比F/Cu = 2/1）电极在第一个循环中提供高达898 mAh g的初次容量（相对于Li/Li约为2.35 V），在第二个循环中提供383 mAh g的可逆容量（相对于Li/Li约为3.35 V）。此外，充电过程中过度的过渡金属分解对电极结构稳定性有害。构建致密的反电解质界面（CEI）和阻碍过渡金属原子的电子传输等方法将有助于有限和局部的过渡金属氧化，这有利于阴极的可逆性。
