Molecular Design of a Highly Stable Single-Ion Conducting Polymer Gel Electrolyte

Abstract

Single-ion conducting (SIC) polymer electrolytes with a high Li transference number (t Li + ) have shown the capability to enable enhanced battery performance and safety by avoiding liquid−electrolyte leakage and suppressing Li dendrite formation. However, issues of insufficient ionic conductivity, low electrochemical stability, and poor polymer/electrode interfacial contact have greatly hindered their commercial use. Here, a Li-containing boroncentered fluorinated SIC polymer gel electrolyte (LiBFSIE) was rationally designed to achieve a high t Li + and high electrochemical stability. Owing to the low dissociation energy of the boroncentered anion and Li + , the as-prepared LiBFSIE exhibited an ionic conductivity of 2 × 10 −4 S/ cm at 35 °C, which is exclusively contributed by Li ions owing to a high t Li + of 0.93. Both simulation and experimental approaches were applied to investigate the ion diffusion and concentration gradient in the LiBFSIE and non-cross-linked dual-ion systems. Typical rectangular Li stripping/plating voltage profiles demonstrated the uniform Li deposition assisted by LiBFSIE. The interfacial contact and electrolyte infiltration were further optimized with an in situ UV−vis-initiated polymerization method together with the electrode materials. By virtue of the high electrochemical stability of LiBFSIE, the cells achieved a promising average Coulombic efficiency of 99.95% over 200 cycles, which is higher than that of liquid−electrolyte-based cells. No obvious capacity fading was observed, indicating the long-term stability of LiBFSIE for lithium metal batteries.

Organoboron‐Containing Polymer Electrolytes for High‐Performance Lithium Batteries

“…fabricated a lithium‐containing boron‐center fluorinated single‐ion conductive polymer gel electrolyte (LiBFSIE) (Figure 2h) by in situ method (Figure 4e), with a Li + transference number of 0.93 and an ionic conductivity of 2 × 10 −4 S cm −1 at 35 °C. [ 65 ] The average Coulombic efficiency of LiBFSI‐based cells reached 99.95% after 200 cycles, which was higher than that of LE based cells, with no significant capacity decay observed (Figure 4f). These benefits may be derived from in situ UV‐induced polymerization methods, which can optimize the interface contact.…”

Single‐Ion Conducting Polymer Electrolytes for Solid‐State Lithium–Metal Batteries: Design, Performance, and Challenges

“…So far, extensive computational studies have been carried out to examine the structure‐ionic conductivity/transference number‐electrochemical performance relationships in SICPEs. [ 126–136 ] For example, McCloskey and co‐workers demonstrated that increasing the t Li + of the electrolyte could enable high power densities and fast charging of the cells. [ 62 ] Besides, the polymer electrolyte with high t Li + s could potentially suppress the concentration gradients and minimize the Li dendrite growth.…”

Recent Developments of Nanomaterials and Nanostructures for High‐Rate Lithium Ion Batteries

“…Secondly, the kinetics of the electrochemical reaction is also affected by the dissociation of lithium ions in the electrolyte . Because the ionic radius of the lithium ion is small, coulombic interactions between the solvent molecules and lithium ions are strong and the activation energy for ion dissociation is high (about 50 kJ mol −1 ).…”

“…Secondly, the kinetics of the electrochemical reaction is also affected by the dissociation of lithium ions in the electrolyte. [364] Because the ionic radius of the lithium ion is small, coulombic interactions between the solvent molecules and lithium ions are strong and the activation energy for ion dissociation is high (about 50 kJ mol À 1 ). Surface functionalisation of the active materials (such as lithium manganese oxide and cobalt oxide) with functional groups enriched with electrons is recommended in order to decrease the energy barrier by enhancing the attractive interaction between lithium ions and active materials.…”