Solid‐State Lithium Conductors for Lithium Metal Batteries Based on Electrospun Nanofiber/Plastic Crystal Composites

Abstract

Organic ionic plastic crystals (OIPCs) are a class of solid-state electrolytes with good thermal stability, non-flammability, non-volatility, and good electrochemical stability. When prepared in a composite with electrospun polyvinylidene fluoride (PVdF) nanofibers, a 1:1 mixture of the OIPC N-ethyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide ([C mpyr][FSI]) and lithium bis(fluorosulfonyl)imide (LiFSI) produced a free-standing, robust solid-state electrolyte. These high-concentration Li-containing electrolyte membranes had a transference number of 0.37(±0.02) and supported stable lithium symmetric-cell cycling at a current density of 0.13 mA cm . The effect of incorporating PVdF in the Li-containing plastic crystal was investigated for different ratios of PVdF and [Li][FSI]/[C mpyr][FSI]. In addition, Li|LiNi Co Mn O cells were prepared and cycled at ambient temperature and displayed a good rate performance and stability.

Synthesis and Characteristics of Pyrrolidinium‐Based Organic Ionic Plastic Crystals with Various Sulfonylamide Anions

“…The ionic conductivity of [C 2 epyr][FSA] is higher than that of N-ethyl-N-methylpyrrolidinium bis(fluorosulfonyl)amide (1.23 × 10 À 6 S cm À 1 at 25°C), [13] which has been successfully used in Li batteries. [39,40]…”

Toward High‐Energy‐Density Lithium Metal Batteries: Opportunities and Challenges for Solid Organic Electrolytes

“…Although OIPCs have demonstrated respectable properties in terms of the ionic conductivity and good electrochemical stability (e.g., 5.6 V vs Li + /Li), several aspects still need to be further improved for future battery applications. For example, some OIPCs with “rigid” anions (e.g., BF 4 , PF 6 ) normally show high thermal stability which can keep their solid‐state at high temperature up to 200 °C, however the low temperature conductivity is not suitable for battery applications.…”

“…The right‐hand side y‐axis is columbic efficiency. d) Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

“…By incorporation of PVDF fibers into this material, a free‐standing OIPC composite electrolyte can be easily prepared even when 50 mol% Li salt is mixed with the [C 2 mpyr][FSI]. As a result, the composite electrolyte, 50Li‐[C 2 mpyr][FSI]/PVDF, shows an electrochemical stability window up to 5.6 V and a t Li + of 0.37 . The assembled solid‐state Li∣NMC111 cell demonstrates a promising capacity retention of 71% after 50 cycles (initial specific capacity 120 mAh g −1 vs 86 mAh g −1 at 50 cycles) at high cut‐off voltage of 4.6 V, ambient temperature (Figure d).…”

“…Li + transference number is another important parameter to evaluate OIPC‐based electrolytes. For the [C 2 mpyr][FSI]‐based electrolytes with different LiFSI concentrations, the PVDF fiber composite electrolytes containing 10 mol% LiFSI (10Li‐[C 2 mpyr][FSI]/PVDF fiber composite), 50 mol% LIFSI (50Li‐[C 2 mpyr][FSI]/PVDF fiber composite) show transference numbers of 0.1 and 0.37 at 50 °C, respectively . Interestingly, when PVDF nanoparticles were used, the 50Li‐[C 2 mpyr][FSI]/PVDF nanoparticle composite shows a transference number of 0.44, which is higher than the PVDF fiber composite containing the same LiFSI doped OIPC .…”