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

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 degrees 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 x 10(-10 )cm(2) s(-1)) and local (3 x 10(-10 )cm(2) s(-1)) values for lithium diffusion coefficients (D-Li) characterized by electrochemical impedance spectroscopy and muon spin relaxation (mu SR), respectively. The similarity between both D-Li 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 (E-a = 73 meV) of lithium diffusion is also estimated from the mu SR data.