Going Beyond Sweep Voltammetry: Alternative Approaches in Search of the Elusive Electrochemical Stability of Polymer Electrolytes

Abstract

Solid polymer electrolytes (SPEs) are promising candidates for solid-state lithium-ion batteries. Potentially, they can be used with lithium metal anodes and high-voltage cathodes, provided that their electrochemical stability is sufficient. Thus far, the oxidative stability has largely been asserted based on results obtained with sweep voltammetry, which are often determined and reliant on arbitrary assessments that are highly dependent on the experimental conditions and do not take the interaction between the electrolyte and the electrode material into account. In this study, alternative techniques are introduced to address the pitfalls of sweep voltammetry for determining the oxidative stability of SPEs. Staircase voltammetry involves static conditions and eliminates the kinetic aspects of sweep voltammetry, and coupled with impedance spectroscopy provides information of changes in resistance and interphase layer formation. Synthetic charge–discharge profile voltammetry applies the real voltage profile of the active material of interest. The added effect of the electrode active material is investigated with a cut-off increase cell cycling method where the upper cut-off voltage during galvanostatic cycling is gradually increased. The feasibility of these techniques has been tested with both poly(ethylene oxide) and poly(trimethylene carbonate) combined with LiTFSI, thereby showing the applicability for several categories of SPEs.

Are Polymer‐Based Electrolytes Ready for High‐Voltage Lithium Battery Applications? An Overview of Degradation Mechanisms and Battery Performance

“…Thus, each technique offers its own merits and limits. The cell setup and experimental conditions impact the stability [319] Copyright 2021, The Authors, published by IOP Publishing.…”

“…Although the tangent methods (ii and iii) are less affected by the scan rate and mass transport limitations, the selection of the intercept and the determination of the regions for linear fitting (for tangents construction) remain as arbitrary parameters (Figure 11c,d). [ 319 ] Following Mousavi et al, [ 320 ] the linear fitting of I versus E profiles should be performed in the LSV regions in which the differential profile d I /d E approaches zero. Generally, the potential respective to the steep increase of the current was selected, corresponding to the final breakdown of the electrolyte.…”

“…Reproduced under the terms of Creative Commons Attribution 4.0 License. [ 319 ] Copyright 2021, The Authors, published by IOP Publishing.…”

Fluorine‐Free Electrolytes for Lithium and Sodium Batteries

“…This is important because only focusing on the solubility, conductivity or even the electrochemical stability window determined with inert electrodes does not provide a good overview of their application in real devices, as the conditions of such experiments do not necessarily correlate to good electrochemical performance in real cells. [122,126] In the end, cheap and environmentally friendly electrolytes are very important not least for Na-ion batteries, that are typically posed as cheaper and more sustainable alternatives to their lithium counterparts, and to this end it is somewhat surprising how little has been done in this field thus far. Many of the results presented here provide a very good starting point for further studies and trials in batteries.…”

“…Therefore, we urge the community to continue exploring different anions and testing them in relevant devices in order to assess their true potential for use in Li‐ and Na‐ion batteries. This is important because only focusing on the solubility, conductivity or even the electrochemical stability window determined with inert electrodes does not provide a good overview of their application in real devices, as the conditions of such experiments do not necessarily correlate to good electrochemical performance in real cells [122,126] …”