Phase Evolution and Li Diffusion in LATP Solid-State Electrolyte Synthesized via a Direct Heat-Cycling Method

Abstract

Herein, the direct synthesis of phase-pure lithium aluminum titanium phosphate (Li1.3Al0.3Ti1.7(PO4)3, LATP) solid-electrolyte powder in 220 min and relatively low temperatures (850 °C) is achieved via a new (cyclic) fast heat treatment (c-FHT) route. The complex structural evolution highlights rate-limited lithium incorporation of intermediate metal phosphates formed prior to the final phase-pure LATP. The prepared LATP product powder displays similar bulk (2 × 10−10cm2 s−1) and local (3 × 10−10cm2 s−1) values for lithium diffusion coefficients (DLi) characterized by electrochemical impedance spectroscopy and muon spin relaxation (μSR), respectively. The similarity between both DLi values suggests excellent retention of inter- and intraparticle lithium diffusion, which is attributed to the absence of deleterious surface impurities such as AlPO4. A low-energy barrier (Ea = 73 meV) of lithium diffusion is also estimated from the μSR data.