Controlled Interfacial Stress Platform for Electrochemical‐Mechanical Coupling Measurements

ABSTRACT There are few direct measurements of the coupling of electrochemical processes with mechanical stresses, especially when the applied stress is an independent control variable, and the stress is nearly uniform and on a planar interface. In this paper, we demonstrate a novel controlled interfacial stress platform for electrochemical‐mechanical (CISP‐ECM) coupling measurements at a single electrode/electrolyte interface. We realize this platform using a nanoindentation system and a sample composed of a thin‐film Li x V 2 O 5 electrode in a lateral configuration on a solid‐electrolyte substrate, and we report the coupling of applied stress and open‐circuit voltage (OCV). These measurements provide estimates of the partial molar volume of Li in the Li x V 2 O 5 thin‐film electrode at various lithiation states; the resulting mean volume expansion of 1.5% for x = 0.32 to 0.73 in Li x V 2 O 5 is consistent with literature crystallographic values. Our methods provide a means to measure the partial molar volume of lithium as a function of lithium content in electrode materials for both crystalline and amorphous electrode materials. In addition to solid‐state batteries, the CISP‐ECM platform is relevant to other areas where mechanical stresses can couple with variable‐composition electrode materials, such as wearable electronics, actuators, and iontronics.