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Sodium chromium oxide, NaCrO2, exhibits promising features as a cathode electrode in Na-ion batteries, yet it encounters challenges with its capacity fading and poor cycle life. NaCrO2 undergoes multiple phase transitions during Na ion intercalation, eventually leading to chemical instabilities and mechanical deformations. Here, we employed the digital image correlation (DIC) technique to probe electrochemical strain generation in the cathode during cycling via cyclic voltammetry and galvanostatic cycling. The electrode undergoes significant irreversible mechanical deformations in the initial cycle, and irreversibility decreases in the subsequent cycles. During desodiation and sodiation, the electrode initially undergoes volume contraction at lower state-of-(dis)charge followed by expansions at a higher state-of-(dis)charge. The similar progression between strain and capacitive derivatives points out the phase-transition-induced deformations in the electrode. The evolution of cumulative irreversible strains with cycling time indicates the irreversibility rising from the formation of cathode-electrolyte interphase layers. The study demonstrates valuable insights into mechanical deformations in NaCrO2 electrodes during battery cycling, which is critical to engineer mechanically robust cathodes for Na-ion batteries. 

The battery chemistry must be diversified to achieve a sustainable energy landscape by effectively utilizing renewable energy sources. Alkali metal-ion, all-solid-state, metal-air batteries, and multivalent batteries offer unique cost, safety, raw material abundance, energy, and power density solutions. However, realizing these “Beyond Li-ion batteries” must uncover their working principles and performance & property relationship. In this aspect, mitigating chemo-mechanical instabilities in the structure and surface of the electrodes plays a crucial role in their performance. Unfortunately, the coupling between electrochemical and mechanical interactions is often poorly understood due to a lack of operando characterization. This review article explains the working principles of curvature measurement and digital image correlation for measuring stress and strain generations in battery materials. We provided specific examples of how these operando mechanical measurements shed light on instabilities in alkali-metal ion electrodes, solid electrolytes, Li-O2 batteries, and aqueous Zn-ion batteries. Operando mechanical measurements offer an effective way to map changes in the physical fingerprint of the battery materials, therefore providing crucial information to elucidate instabilities in battery materials.