Increasing the storage capacity is a crucial goal of battery research. Li-ion battery cathodes have severe capacity limitations; while Li-O2 batteries promise much higher theoretical capacity, they are plagued by several key challenges. Li-O2 batteries generally exhibit high overpotentials and form Li2O2 which may lead to electrolyte decomposition. In this talk, we explore hybrid materials that are a combination of the two – Li-transition metal-oxides that embody both Li-ion and Li-O2 reactions,1 with smaller-than-typical overpotentials and without forming Li2O2. The prototype hybrid Li-ion/Li-O2 material is Li5FeO4, which when used as an electrocatalyst in Li-O2 cells, reduces overpotentials and demonstrates a capacity of ~500 mAh/g unrelated to Li2O2 formation.2 Using first principles density functional theory (DFT) calculations, we performed a high-throughput search for similar hybrid materials with high capacities and suitable properties.3 While hybrid materials exhibit promising capacities of up to 1000 mAh/g, their reaction mechanisms remain unknown. We performed DFT investigations of the reaction mechanisms in several of these materials, including Li5FeO4, Li6MnO4, Li6CoO4, and Li8IrO6. DFT calculations are performed to investigate the thermodynamics of Li and Li-O removal from these materials, in order to establish the details of the charge reaction. Atomistic and electronic structural changes in the materials are tracked during the reactions. Results on the energetics indicate a cross-over between pure lithium removal and concomitant oxygen loss, which is electronically shown to be correlated with development of the peroxide-like character of oxygen. Acknowledgement This research was supported as part of the Center for Electrochemical Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (Award Number DE-AC02-750 06CH11357). Use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. References (1) M. M. Thackeray, M. K. Y. Chan, L. Trahey, S. Kirklin, and C. Wolverton, JPCL, 2013, 4, 3607. (2) L. Trahey, C. S. Johnson, J. T. Vaughey, S.-H. Kang, L. J. Hardwick, S. A. Freunberger, P. G. Bruce, M. M. Thackeray, ESSL, 2011, 14, A64. (3) S. Kirklin, M. K. Y. Chan, L. Trahey, M. M. Thackeray, and C. Wolverton, PCCP, 2014, 16, 22073.

Li-ion and Li-O2: exploring hybrid electrode/electrocatalyst materials

249th National Meeting (2015)

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