The overall energy density of the Li-ion batteries depends on the operation voltage and the theoretical capacity of the electrodes. Theoretical capacity of layered lithium cobalt oxide (Li_1-xCoO₂) cathode is 274 mAh/g, which is higher than the many other commercially available cathode materials, including lithium manganese oxide (148 mAh/g) and lithium iron phosphate (170 mAh/g). However, the irreversible chemo-mechanical deformations at deep charge condition (x>0.5) at high voltages (>4.2V) presents harvesting its full theoretical capacity. Previous XRD and NMR studies demonstrated the structural collapse of the material at deep charge condition [1]. A various material-based strategies such as doping and surface coating have been utilized to improve the stability of the LCO cathodes at deep charge conditions [2]. However, the governing forces behind the chemo-mechanical instabilities in LCO cathodes at high voltages are still poorly understood.

In this study, our goal is to elucidate the electrochemically-driven mechanical deformations in the LCO cathode during Li-ion intercalation. To achieve it, we performed in situ curvature measurement and digital image correlation measurements to probe stress and strain evolution in the electrode while cycling the battery. The combination of these techniques previously provided information about the interfacial and structural deformations in LiFePO₄ and LiMn₂O₄ [3,4]. Here, free-standing composite LCO electrodes were fabricated for strain measurements. Thin film LCO electrode was prepared using chemical vapor deposition method on a silicon wafer for stress measurements. The electrodes were cycled in 1 M LiClO₄ in 1:1 EC:DMC electrolyte against Li counter electrode. The upper limit of the charge voltage were varied from 4.2 to 4.5V periodically in order to investigate the deformations at deep charge state. Strain and stress derivatives were calculated with respect to applied potential in order to understand the potential-dependent mechanical deformations in the LCO electrode. In this talk, we will present the impact of the structural and interfacial deformations on the chemo-mechanical instabilities of LCO cathodes.

Acknowledgment: This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (Award number DE-SC0021251). We are also grateful for Dr. Gabriel Veith for fabricating thin film LCO cathodes.

References

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[2] L. Wang, B. Chen, J. Ma, G. Cui, L. Chen, Reviving lithium cobalt oxide-based lithium secondary batteries-toward a higher energy density, Chem. Soc. Rev. 47 (2018) 6505–6602. https://doi.org/10.1039/c8cs00322j.

[3] Ö.Ö. Çapraz, K.L. Bassett, A.A. Gewirth, N.R. Sottos, Electrochemical Stiffness Changes in Lithium Manganese Oxide Electrodes, Adv. Energy Mater. 7 (2017). https://doi.org/10.1002/aenm.201601778.

[4] K.L. Bassett, Ö. Özgür Çapraz, B. Özdogru, A.A. Gewirth, N.R. Sottos, Cathode/Electrolyte Interface-Dependent Changes in Stress and Strain in Lithium Iron Phosphate Composite Cathodes, J. Electrochem. Soc. 166 (2019) A2707–A2714. https://doi.org/10.1149/2.1391912jes.