Rational Lithium Salt Molecule Tuning for Fast Charging/Discharging Lithium Metal Battery
Pan Zhou, Haiyu Zhou, Yingchun Xia, Qingqing Feng, Xian Kong, Wenhui Hou, Yu Ou, Xuan Song, Hangyu Zhou, Weili Zhang, Yang Lu, Fengxiang Liu, Qingbin Cao, Hao Liu, Shuaishuai Yan, Kai Liu
Abstract
Abstract The electrolytes for lithium metal batteries (LMBs) are plagued by a low Li + transference number (T + ) of conventional lithium salts and inability to form a stable solid electrolyte interphase (SEI). Here, we synthesized a self‐folded lithium salt, lithium 2‐[2‐(2‐methoxy ethoxy)ethoxy]ethanesulfonyl(trifluoromethanesulfonyl) imide (LiETFSI), and comparatively studied with its structure analogue, lithium 1,1,1‐trifluoro‐N‐[2‐[2‐(2‐methoxyethoxy)ethoxy)]ethyl]methanesulfonamide (LiFEA). The special anion chemistry imparts the following new characteristics: i) In both LiFEA and LiETFSI, the ethylene oxide moiety efficiently captures Li + , resulting in a self‐folded structure and high T + around 0.8. ii) For LiFEA, a Li−N bond (2.069 Å) is revealed by single crystal X‐ray diffraction, indicating that the FEA anion possesses a high donor number (DN) and thus an intensive interphase “self‐cleaning” function for an ultra‐thin and compact SEI. iii) Starting from LiFEA, an electron‐withdrawing sulfone group is introduced near the N atom. The distance of Li−N is tuned from 2.069 Å in LiFEA to 4.367 Å in LiETFSI. This alteration enhances ionic separation, achieves a more balanced DN, and tunes the self‐cleaning intensity for a reinforced SEI. Consequently, the fast charging/discharging capability of LMBs is progressively improved. This rationally tuned anion chemistry reshapes the interactions among Li + , anions, and solvents, presenting new prospects for advanced LMBs.