How Does Mg Transport in MgCr2O4 - a Cathode Active Material?

Abstract

Conventionally, we expect the transport of intercalated species in battery active particles is limited by diffusion. MgCr2O4 has been identified as a candidate active material for the Mg batteries based on its theoretical Mg-storing capacity, high open circuit potential, and acceptable diffusion barrier for Mg-ion transport (1,2). However, when operated electrochemically, its performance does not match the promised potential (3). Motivated by these observations, we examine charge transport in dense MgCr2O4 pellets in an electrolyte-free setup to conclusively probe bulk Mg transport. We find that the ion transport in this material cannot be explained by using the conventional understanding. We propose a new theory that extends the conventional picture and accounts for the unusual behavior in MgCr2O4 (4). We further discuss the implications of this understanding for engineering active material particles in MgCr2O4 porous electrodes. References Canepa, P.; Sai Gautam, G.; Hannah, D. C.; Malik, R.; Liu, M.; Gallagher, K. G.; Persson, K. A.; Ceder, G. (2017) "Odyssey of Multivalent Cathode Materials: Open Questions and Future Challenges." Chem. Rev., 117 (5), 4287–4341. DOI: 10.1021/acs.chemrev.6b00614.Bayliss, R. D.; Key, B.; Sai Gautam, G.; Canepa, P.; Kwon, B. J.; Lapidus, S. H.; Dogan, F.; Adil, A. A.; Lipton, A. S.; Baker, P. J.; Ceder, G.; Vaughey, J. T.; Cabana, J. (2020) "Probing Mg Migration in Spinel Oxides." Chem. Mater., 32 (2), 663–670. DOI: 10.1021/acs.chemmater.9b02450. Hu, L.; Johnson, I. D.; Kim, S.; Nolis, G. M.; Freeland, J. W.; Yoo, H. D.; Fister, T. T.; McCafferty, L.; Ashton, T. E.; Darr, J. A.; Cabana, J. (2019) "Tailoring the Electrochemical Activity of Magnesium Chromium Oxide towards Mg Batteries through Control of Size and Crystal Structure." Nanoscale, 11 (2), 639–646. DOI: 10.1039/C8NR08347A. Johnson, I.D.; Mistry, A.; Yin, L.; Murphy, M.; Wolfman, M.; Fister, T. T.; Lapidus, S. H.; Cabana, J.; Srinivasan, V.; Ingram, B. J. (2022) "Investigating Charge Transport in MgCr2O4 Extends the Understanding of Battery Intercalation Hosts.", under review