High-voltage lithium metal batteries offer a pathway to exceed energy densities of 600 Wh kg−1, but their practical application is limited by electrolyte stability. Current high-voltage electrolytes rely on costly fluorinated solvents, which pose environmental (PFAS) and recycling challenges.
Recently, Professor Qiang Zhang’s team from the Department of Chemical Engineering at Tsinghua University proposed an "α-hydrogen removal" molecular design strategy to develop a fluorine-free, high-voltage stable electrolyte solvent, methyl trimethylacetate (MTMA). Through mechanistic studies, the team identified that conventional carboxylate ester solvents primarily degrade on high-voltage cathodes via the α-oxidation of the carbonyl group. By replacing the reactive α-hydrogens with inert methyl groups, this oxidation pathway is effectively blocked in MTMA. Experimental results show that MTMA exhibits an oxidation stability of up to 5.6 V (vs. Li/Li⁺) without the use of electron-withdrawing fluorine atoms, while a typical mixed fluorinated solvent system LB372 is only stable below 4.9 V (vs. Li/Li+).
Testing at the pouch cell level confirmed the viability of the MTMA electrolyte. A 7.2 Ah pouch cell achieved an energy density of 652.4 Wh kg−1 with a capacity retention of 94.5% after 28 cycles under stringent conditions (4.6 V charge cut-off, 1.0 g Ah−1 electrolyte). Additionally, under rapid discharge conditions simulating electric vertical takeoff and landing (eVTOL) aircraft operations, a 5.0 Ah pouch cell cycled stably for over 350 cycles, maintaining an average energy efficiency above 90%. Furthermore, the 5.0 Ah pouch cell successfully powered a quadcopter prototype through take-off, prolonged high-altitude hovering, and landing during an outdoor field test.
Figure 1. Fluorine-free, high-voltage-stable molecular design strategy. (a) Enhancing oxidative stability by blocking the optimal oxidation pathway; (b) Common oxidation mechanisms of carboxylate esters; (c) The α-oxidation mechanism of conventional carboxylate esters; (d) The blocked α-oxidation pathway of the MTMA solvent.
Figure 2. Performance of the MTMA-based 7.2 Ah pouch cell. (a) The cell shows a 94.5% capacity retention after 28 cycles; (b) Energy density reaches 652.4 Wh kg−1.
The research, titled " Blocking oxidation of α-hydrogens enables non-fluorinated solvents to achieve high-potential stability in lithium batteries", was published in Nature Chemistry on May 26, 2026. Professor Qiang Zhang and Associate Researcher Chen-Zi Zhao from the Department of Chemical Engineering are the co-corresponding authors. Yu-Xin Huang (Tsinghua University) and Yi Yang (Beijing Institute of Technology) are co-first authors. Co-authors include Pan Xu, Zi-Yue Jiang, Zi-Zhang Qiu, Xing-Yu Zhong, Zong-Yao Shuang, Xue-Yan Huang, Yong-Feng Li, Wei-Jing Kong, Yi-Fan Tan, Xiang Chen, Kaihang Zhang, Jia-Qi Huang.
This research was supported by the Discipline Breakthrough Precursor Project of the Ministry of Education of China, the National Natural Science Foundation of China, the Beijing Natural Science Foundation, the Xplorer Prize, and the Tsinghua University Initiative Scientific Research Program.
Link:
Blocking oxidation of α-hydrogens enables non-fluorinated solvents to achieve high-potential stability in lithium batteries | Nature Chemistry
https://www.nature.com/articles/s41557-026-02161-2
