Development of safe Li-ion batteries with high operating voltages and enhanced capacities is the keystone for the development of high energy density demand in emerging technologies such as the electric car. Current Li-ion batteries involve the use of flammable organic solvents as liquid electrolytes for Li-ions diffusion between the electrodes. These organic solvents present several safety concerns thereby limiting their operating voltage due to potential decomposition. The replacement of these liquid electrolytes with a solid-state electrolyte would overcome not only the safety concerns but the voltage window limit at which the battery could operate. A major requirement in the design of solid-state electrolyte materials is therefore high electrochemical stability and high ionic conductivity.

Here we present the synthesis and electrochemical study of Li₆Hf₂O₇ as a candidate for solid-state electrolyte for next generation Li-ion batteries. Phase pure material was synthesized via a new microwave-assisted solid-state approach.¹ In the crystal structure, Hf⁴⁺ ions are coordinated with 6 surrounding O^2- ions in a octahedral fashion, whereas Li⁺ ions are located on square-pyramidal interstitial sites.² Scanning Electron Microscopy images show inhomogeneous sized microparticles without a particular morphology.

Li-ion conductivity has been analysed by electrochemical impedance spectroscopy, with ionic conductivities of 1.42 × 10^-2 S cm^-1 achieved at 324 ^oC and a modest activation energy of 0.97 eV, comparable with the isostructural Li₆Zr₂O₇ material.³ Also presented will be our further attempts to substitute on the Hf position to introduce Li-ions on interstitial sites to facilitate the Li hoping diffusion mechanism.⁴

1. M. Amores, T. E. Ashton, P. J. Baker, E. J. Cussen and S. A. Corr, J. Mater. Chem. A, 2016. DOI: 10.1039/C5TA08107F
2. R. Czekalla, W. Jcitschko, Z. anorg. allg. Chcm. 619, 1993, 2038
3. R. Prasada Rao, M.V. Reddy, S. Adams, B.V.R. Chowdari, Mater. Sci. Eng. B, 177, 2012, 100
4. Y. Liao, P. Singh, K. Park, W. Li, J. B. Goodenough, Electrochim. Acta 102, 2013, 446