Liquid-Like Li-Ion Conduction in Oxides Enabling Anomalously Stable Charge Transport across the Li/Electrolyte Interface in All-Solid-State Batteries

The softness of sulfur sublattice and rotational PS4 tetrahedra in thiophosphates result in liquid-like ionic conduction, leading to enhanced ionic conductivities and stable electrode/thiophosphate interfacial ionic transport. However, the existence of liquid-like ionic conduction in rigid oxides remains unclear, and modifications are deemed necessary to achieve stable Li/oxide solid electrolyte interfacial charge transport. In this study, by combining the neutron diffraction survey, geometrical analysis, bond valence site energy analysis, and ab initio molecular dynamics simulation, 1D liquid-like Li-ion conduction is discovered in LiTa2PO8 and its derivatives, wherein Li-ion migration channels are connected by four- or five-fold oxygen-coordinated interstitial sites. This conduction features a low activation energy (0.2 eV) and short mean residence time (<1 ps) of Li ions on the interstitial sites, originating from the Li-O polyhedral distortion and Li-ion correlation, which are controlled by doping strategies. The liquid-like conduction enables a high ionic conductivity (1.2 mS cm(-1) at 30 & DEG;C), and a 700 h anomalously stable cycling under 0.2 mA cm(-2) for Li/LiTa2PO8/Li cells without interfacial modifications. These findings provide principles for the future discovery and design of improved solid electrolytes that do not require modifications to the Li/solid electrolyte interface to achieve stable ionic transport.

Automated summary

The softness of sulfur sublattice and rotational PS4 tetrahedra in thiophosphates lead to liquid-like ionic conduction, while the existence of such conduction in rigid oxides remains unclear. This study discovers 1D liquid-like Li-ion conduction in LiTa2PO8 and its derivatives, enabled by doping strategies, with low activation energy and short mean residence time of Li ions on interstitial sites. The findings provide principles for the future design of improved solid electrolytes without modifications to achieve stable ionic transport.