Film strains enhance the reversible cycling of intercalation electrodes

• Published in: Journal of the mechanics and physics of solids 2021-10, Vol.155, p.104551, Article 104551
• Main Authors: Zhang, Delin, Sheth, Jay, Sheldon, Brian W., Renuka Balakrishna, Ananya
• Format: Article
• Language: English
• Subjects: Amorphization; Chemo-mechanical degradation; Cycles; Degradation; Electric potential; Electrodes; Intercalation; Intercalation electrodes; Microcracks; Phase transformations; Phase transitions; Strain; Stress evolution; Surface layers; Thin films; Vanadium pentoxide; Voltage
• ISSN: 0022-5096; 1873-4782
• DOI: 10.1016/j.jmps.2021.104551

A key cause of chemo-mechanical degradation in battery electrodes is that they undergo abrupt phase transformation during the charging/discharging cycle. This phase transformation is accompanied by lattice misfit strains that nucleate microcracks, induce fracture and, in extreme cases, amorphize the intercalation electrode. In this work, we propose a strategy to prevent the chemo-mechanical degradation of intercalation electrodes: we show that by engineering suitable film strains we can regulate the phase transformations in thin-film intercalation electrodes and circumvent the large volume changes. We test this strategy using a combination of theory and experiment: we first analytically derive the effect of film strain on the electrochemical response of a thin-film intercalation electrode and next apply our analytical model to a representative example (LixV2O5 with multiple phase transformations). We then test our theoretical predictions experimentally. Specifically, we electrochemically cycle thin-film V2O5 electrodes with different film strains and measure their structure, voltage, and stress responses. Our findings show that tensile film strains lower the voltage for phase transformations in thin-film V2O5 electrodes and facilitate their reversible cycling across a wider voltage window without chemo-mechanical degradation. These results suggest that film strain engineering is an alternative approach to preventing chemo-mechanical degradation in intercalation electrodes. Beyond thin-film electrodes, our findings from this study are applicable to the study of stress-induced phase transformations in particle-based electrodes and the thin surface layers forming on cathode particles. •Film strains modify the free energy landscape of phase transformation electrodes.•We engineer film strains to circumvent structural degradation in V2O5 electrodes.•Our work initiates an approach to address chemo-mechanical challenges in electrodes.