A Practical Polymer Electrolyte for Lithium and Sodium Batteries: Poly(pentyl malonate)

The rate at which rechargeable batteries can be charged and discharged depends primarily on ion transport between the electrodes. This is governed by the limiting current and electrochemical stability of the electrolyte. To our knowledge, the limiting current values of all dry polymer electrolytes in the literature are either not reported or lower than that of the benchmark polymer electrolyte comprising poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). We describe the synthesis and characterization of a new polymer electrolyte, poly(pentyl malonate) (PPM). The length-normalized limiting current of PPM/LiTFSI in lithium-polymer-lithium symmetric cells is about a factor of 2.8 higher than that of PEO/LiTFSI at the same salt concentration and temperature. This polymer also exhibits increased electrochemical stability at high potentials (up to 5 V against Li+/Li) relative to PEO. Promising preliminary data obtained in sodium-polymer-sodium symmetric cells is also presented.