Probing Lattice-Ion Correlations in Real-Time in Solid-State Electrolyte Li_0.5La_0.5TiO₃

Solid-state electrolytes (SSEs) could further the development of more energy-dense and safer batteries by enabling the use of Li metal anodes and replacing flammable liquid electrolytes. However, the development of SSEs is limited by an incomplete understanding of solid-state ionic conduction. Current research indicates lattice-ion coupling mediates site-to-site ion hops which occur on picosecond timescales.¹ The study of these correlated processes cannot currently be probed in real-time. As such, we developed laser-driven ultrafast impedance spectroscopy to understand how lattice-ion interactions impact superionic conduction.² With this technique, we have shown that an above-bandgap excitation in Li_0.5La_0..5TiO₃ reduces electrostatic interactions in the ion hop pathway, leading to twice the increase in ionic conductivity as compared to below-bandgap heating. We then transiently probe the population of THz rocking modes which make up the phonon-ion correlations that strongly contribute to ion hopping.³ This work advances a dynamical picture of ionic conduction, enhancing design principles to develop new SSEs.

(1) Jun, K.; et al. Nat. Rev. Mater. 2024.

(2) Pham, K. H.; et al. Rev. Sci. Instrum. 2024.

(3) Pham, K. H.; et al. https://arxiv.org/abs/2305.01632.