Guangdong Key Laboratory of New and Renewable Energy Research and Development, Key Laboratory of Renewable Energy, Chinese Academy of Sciences, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, P. R. China
Nitrile-modified 2, 5-di-tert-butyl-hydroquinones were synthesized and investigated as redox shuttle overcharge additives for LiFePO4/Li cells. The cyanoethylation reaction was utilized to synthesize the target molecules 2, 5-di-tert-butyl-1, 4-di(β-cyanoethoxyl)benzene (RS-DCN) and 2, 5-di-tert-butyl-1-(β-cyanoethoxyl)-4-methoxybenzene (RS-MCN) in high efficiency from 2, 5-di-tert-butyl-hydroquinone and acrylonitrile. The solubility, cyclic voltammetric measurements, 5 V overcharge test, 100% overcharge test, high rate performance under 100% overcharge conditions, and cycle performance under normal conditions were studied in detail for the electrolyte with the addition of RS-DCN or RS-MCN. The RS-MCN compounds with the asymmetric structure delivered better solubility (with max. 0.3 mol·L-1 in 1.0 mol·L-1 LiPF6/EC+DEC+EMC, 1 : 1 : 1, in vol.), higher overcharge protection life (over 1200 h for the 5 V overcharge test), and excellent rate performance under 100% overcharge conditions (specific discharge capacity reached 153.5 mAh·g-1 at 2.5C). The addition of RS-MCN also improved the cycling performance of the LiFePO4/Li cell under the charge-discharge voltage range of 2.5-3.8 V.
Fund: the Program of Guangdong Provincial Project for Science & Technology, China(2014A050503050/2015B010135008);Guangzhou Municipal Project for Science & Technology, China(2014Y2-00012/201509010018);Dongguan Municipal Project for Science & Technology, China(2013509104210);K. C. Wang Education Foundation, China