Calcination-driven enhancement of LAGP for high-performance solid-state lithium metal batteries

Abstract

NASICON-type Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) solid electrolyte is a promising candidate for next-generation lithium-ion batteries due to its high air stability and excellent Li-ion conductivity. Here, we systematically examine the effect of calcination temperature (500, 600, and 700 °C) on physical properties of LAGP to enhance its suitability for solid state lithium metal batteries. Rietveld refinement confirmed a single phase (Rc) for all sintered pellets, with unit cell parameters decreasing at higher calcination temperatures. Li-ion conductivity, with negligible electronic conduction, increased with calcination temperature due to improved relative density and cell contraction. The sample calcined at 700 °C exhibits the highest Li-ion conductivity of 1.63 × 10⁻⁴ S cm⁻¹ and a low activation energy of ∼0.33 eV, alongside superior mechanical hardness of ∼9.2 GPa. The fabricated symmetric cell demonstrated low interfacial area specific resistance (∼40 Ω cm²) and high critical current density (1 mA cm⁻²). Consequently, it exhibited excellent cycling stability for over 500 h with low overpotential at 0.2 mA cm⁻² and 25 °C. The full cell with LFP as cathode shows initial discharge capacity ∼142.1 mA h g⁻¹ at 0.1C, with excellent capacity retention. Thus, our study offers valuable insights into optimizing the calcination temperature to enhance the performance of LAGP-based all-solid-state batteries.