Understanding Electrochemical Stability and Lithium Ion‐Dominant Transport in Concentrated Poly(ethylene carbonate) Electrolyte

Abstract

Ion‐conductive solid polymer electrolytes (SPEs) are important materials for implementing safer energy storage. In the present study we show that a concentrated SPE composed of poly(ethylene carbonate) (PEC) and lithium bis(fluorosulfonyl)imide (LiFSI) has high oxidation tolerance and prevents aluminum corrosion. These properties enable cycling of a LiMn2O4 cell charged above 4 V. Battery operation above 4 V is difficult for conventional polyether electrolytes because of their poor electrochemical stability. Mechanistic studies imply that an aggregated solvation structure, in which a large portion of the carbonyl groups interact with Li ions, is correlated with the enhanced electrochemical stability. The studies suggest that relatively rigid structure of PEC induces an increase in conductivity with increasing salt concentration. The increase in conductivity enables concentrated electrolyte with reasonable conductivity and high Li transference number. The present study reveals the clear potential of concentrated SPEs based on unexplored polymers having relatively high glass transition temperature for use in high‐voltage Li batteries.

Intermolecular Chemistry in Solid Polymer Electrolytes for High‐Energy‐Density Lithium Batteries

“…In “polymer in salt” electrolytes, the enhanced oxidation stability and interface stability with Al foil are also reported by Y. Tominaga et al In concentrated PEC‐LiFSI electrolytes, they demonstrated the nearly saturated CO···Li + interaction and the aggregate FSI ions at high concentrations above 50 mol% through FTIR and Raman spectroscopy, respectively (Figure b) . Furthermore, to investigate the effect of concentration on the oxidation stability of PEC‐based electrolyte, they compared the linear sweep voltammograms of PEC‐LiFSI 10 and 120 mol% electrolytes, as shown in Figure c.…”

“…The HOMO energy of LiTFSI (−10.19 eV) is much lower than that of LiFSI (about −7.5 eV) . The experimental results also demonstrate that the poly(trimethylene carbonate) (PTMC)‐LiTFSI has better antioxidant ability than that of PEC‐LiFSI . Nevertheless, due to the different measurement conditions between research groups, it is difficult to strictly compare the influence of salt type and concentration on stability.…”

“…c) Linear sweep voltammograms of PEC/LiFSI 10 and 120 mol% electrolytes at 40 °C and a potential scan rate of 0.5 mV s −1 (working electrode: stainless steel). Reproduced with permission . Copyright 2018, Wiley‐VCH.…”

Stable Cycling of Sodium Metal All-Solid-State Batteries with Polycarbonate-Based Polymer Electrolytes

“…This is indicative of formation of salt agglomerates as previously reported by Tominaga et al for high-concentration poly(ethylene carbonate):LiFSI electrolytes. 31 This initially subtle shift in peak position undergoes a sudden jump between n = 3 and n = 2, i.e., at the previously suggested percolation threshold.…”

Solid Polymer Electrolytes with High Conductivity and Transference Number of Li Ions for Li‐Based Rechargeable Batteries

“…Tominaga and coworkers demonstrated that Li salt concentration and polymer structure have a significant influence on LITN of SPEs. [ 173–175 ] For example, more than 50 mol% lithium bis(fluorosulfonyl)imide (LiFSI) in PEC gives a high LITN of up to 0.6. This is because FSI anions tend to form aggregates, which have strong bonding with the CO group in PEC.…”