A Polymer-in-Salt Electrolyte with Enhanced Oxidative Stability for Lithium Metal Polymer Batteries
Haiping Wu, Peiyuan Gao, Hao Jia, Lianfeng Zou, Linchao Zhang, Xia Cao, Mark Engelhard, Mark Bowden, Michael S. Ding, Jiangtao Hu, Dehong Hu, Sarah Burton, Kang Xu, Chongmin Wang, Ji‐Guang Zhang, Wu Xu
Abstract
The lithium (Li) metal polymer battery (LMPB) is a promising candidate for solid-state batteries with high safety. However, high voltage stability of such a battery has been hindered by the use of polyethylene oxide (PEO), which oxidizes at a potential lower than 4 V versus Li. Herein, we adopt the polymer-in-salt electrolyte (PISE) strategy to circumvent the disadvantage of the PEO–lithium bis(fluorosulfonyl)imide (LiFSI) system with EO/Li ≤ 8 through a dry ball-milling process to avoid the contamination of the residual solvent. The obtained solid-state PISEs exhibit distinctly different morphologies and coordination structures which lead to significant improvement in oxidative stability. P(EO)1LiFSI has a low melting temperature, a high ionic conductivity at 60 °C, and an oxidative stability of ∼4.5 V versus Li/Li+. With an effective interphase rich in inorganic species and a good stability of the hybrid polymer electrolyte toward Li metal, the LMPB constructed with Li||LiNi1/3Co1/3Mn1/3O2 can retain 74.4% of capacity after 186 cycles at 60 °C under the cutoff charge voltage of 4.3 V. The findings offer a promising pathway toward high-voltage stable polymer electrolytes for high-energy-density and safe LMPBs.