On the use of organic ionic plastic crystals in all solid-state lithium metal batteries

We show that a previously observed low current, pre-conditioning behavior which allows increased lithium flux through a solid state, symmetric lithium cell containing a pyrrolidinium bis(trifluoromethyl)sulfonamide electrolyte is a more general phenomenon for organic ionic plastic crystal electrolytes. Furthermore, the mechanism of the preconditioning behavior has been highlighted via a post-mortem characterisation of the cells. Differential scanning calorimetry (DSC) indicated a decrease in the melting point by 1.9 °C after 35 h of 0.01 mA cm− 2 cycling and scanning electron microscopy (SEM) images revealed that substantial changes to the OIPC microstructure, in particular grain size, had occurred. Both of these phenomena would lead to an enhancement of lithium ion transport near the Li/electrolyte interface. In a preliminary experiment incorporating a LiFePO4 cathode, similar preconditioning behavior was observed. Furthermore, good battery performance can be achieved, between 129 and 110 mAh g− 1 during 50 cycles at 0.2 C, denoting the promise of these plastic crystal electrolytes in highly stable, all solid-state lithium metal batteries.