Covalent and polyfluorinated lithium salt for stable LiCoO₂ batteries at high temperature and high voltage.

Abstract

Elevating the charge cut-off voltage of the LiCoO₂ positive electrode beyond 4.5 V has already been the focus to unlock its energy for portable electronics, whereas the severe phase transitions during the delithiation of LiCoO₂ from 4.5 V to 4.7 V can ruin the electrode structure. Besides, the poor thermal and hydrolytic stabilities of traditional lithium salt (LiPF₆) prevent batteries from working at high temperatures and increase production costs and environmental pollution. Here, we show that using covalent lithium nonafluoro-n-butanesulfonate as a fluorine-rich lithium salt to create a robust LiF-rich cathode electrolyte interphase, which effectively impedes the surface destruction, we successfully realize a stable LiCoO₂ battery at a high voltage of 4.7 V and demonstrate a 2.14 Ah Li|| LiCoO₂ pouch cell with a stack-level specific energy of 518 Wh kg^-1 (without packaging). Furthermore, its satisfactory thermal stability empowers LiCoO₂ to work at a harsh condition of 60 °C and 4.6 V. Even more, its antihydrolytic stability enables the LiCoO₂ battery to work with the electrolyte with 200 or even 1000 ppm water contamination. Lithium nonafluoro-n-butanesulfonate presents itself as a potentially viable lithium salt for advanced lithium batteries, offering the prospect of high voltage, improved thermal stability and eco-friendliness.