Particle size-dependent bulk and grain-boundary contributions in Li2O–B2O3–Al2O3 solid electrolytes

Abstract

Solid oxide electrolytes are promising for next-generation all-solid-state batteries due to their intrinsic stability and safety. Yet, bulk and grain-boundary transport in oxide glass electrolytes remains unclear, particularly regarding particle-size effects. Here, we show that particle size governs densification, microstructural evolution, and ionic conduction in Li₂O–B₂O₃–Al₂O₃ (LBA) electrolytes. Fine particles (1.5 µm) achieve higher densification with reduced porosity, yielding lower total resistance than coarser powders. Impedance and distribution of relaxation times analyses indicate that bulk resistance is minimal, whereas GB resistance dominates overall transport. Temperature-dependent measurements corroborate this trend, with Arrhenius analysis revealing a higher activation energy for GB conduction (0.446 eV) than for bulk transport (0.293 eV). Beyond fundamentals, LBA was applied as a low-temperature-processed protective coating on Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) pellets via drop casting and annealing at 525 °C. The LBA coated LATP shows stabilized voltage profiles during cycling at 0.1 mA cm⁻² and suppressed impedance, demonstrating effective interfacial stabilization against Li metal. Overall, LBA is established as an ionically conductive glass electrolyte and a scalable interfacial engineering material.