Dual-function ethyl 4,4,4-trifluorobutyrate additive for high-performance Ni-rich cathodes and stable graphite anodes

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Journal of Power Sources, ISSN: 0378-7753, Vol: 396, Page: 276-287

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Kim, Koeun; Kim, Yeonkyoung; Park, Sewon; Yang, Hyun Ji; Park, Sung Ji; Shin, Kyomin; Woo, Jung-Je; Kim, Saheum; Hong, Sung You; Choi, Nam-Soon
Energy; Chemistry; Engineering; Lithium-ion batteries; Ni-rich layered cathodes; Graphite anodes; Ethyl 4,4,4-trifluorobutyrate; Solid electrolyte interphase
article description
An ethyl 4,4,4-trifluorobutyrate (ETFB) additive, with ester and partially fluorinated alkyl moieties, is employed to stabilize the interface structure of Ni-rich layered LiNi 0.7 Co 0.15 Mn 0.15 O 2 (NCM) cathodes and graphite anodes. The analysis of the surface chemistry of the electrodes shows that ETFB serves as a bifunctional additive for constructing protective layers on both electrodes in a full cell. Cycling tests reveal that the addition of 1% ETFB leads to excellent capacity retention (84.8%) for the NCM/graphite full cell, which also delivers a superior discharge capacity of 167 mAh g −1 and a high Coulombic efficiency of over 99.8% after 300 cycles at 45 °C. The ETFB-derived protective layer effectively reduces intergranular cracking in secondary NCM cathode particles upon repeated charge-discharge cycling and limits the dissolution of transition metal ions from the cathode at high temperatures. In addition, after ETFB reduction, the graphite anode develops a thermally stable interface structure, which suppresses the self-discharge of graphite coupled with the NCM cathode at 60 °C.