Covalent and polyfluorinated lithium salt for stable LiCoO2 batteries at high temperature and high voltage
Qi Xiong, Ruijie Wang, Dedi Li, Ruhong Li, Shuo‐Qing Zhang, Zhiquan Wei, Shimei Li, Dechao Zhang, Shixun Wang, Hu Hong, Li Song, Qi Liu, Xiulin Fan, Chunyi Zhi
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. LiCoO2 faces challenges at high voltages due to structural instability and poor thermal/hydrolytic performance of traditional lithium salts. Here, authors show stable LiCoO2 batteries at 4.7 V using covalent fluorine-rich lithium salt, exhibiting good heat and water tolerance.