Mechanism of the interfacial reaction between cation-deficient La0.56Li0.33TiO3 and metallic lithium at room temperature

We used x-ray diffractometry (XRD), x-ray photoelectron spectrometry (XPS), and secondary-ion mass spectrometry (SIMS) to investigate the mechanism of the interfacial room-temperature (RT) chemical reaction between cation-deficient La 0.56 Li 0.33 TiO 3 solid electrolytes and metallic lithium anodes in all-solid-state lithium batteries. A stoichiometric mixture of La 2 O 3 , Li 2 CO 3 , and TiO 2 powders was calcined at 1250 °C for 8 h to obtain a single perovskite structure of La 0.56 Li 0.33 TiO 3 . When this La 0.56 Li 0.33 TiO 3 sample and lithium were placed in contact at room temperature for 24 h, the phase of the La 0.56 Li 0.33 TiO 3 remained unchanged. The XPS results indicate that 12% of the tetravalent Ti 4+ ions were converted into trivalent Ti 3+ ions. The valence conversion and degree of conversion were limited by the structural rigidity of the host crystal. Our SIMS analysis suggests the existence of a local electric field near the contact surface and indicates that the 6 Li + isotope ions were inserted into the specimen through the effect of this field. The change in the electrical properties of La 0.56 Li 0.33 TiO 3 supports this mechanism for the interfacial reaction. The ionic conductivities of the grain and total grain boundary decreased and increased, respectively, after the insertion of Li + , and the total electronic conductivity increased as a result of the presence of intervalence electron hopping between mixed Ti 3+ /Ti 4+ states. The mechanism of the lithium-activated RT interfacial reaction is associated with the reduction of Ti 4+ transition metal ions from tetravalent to trivalent states and the local-electric-field-induced Li + insertion into La 3+ /Li + -site vacancies of La 0.56 Li 0.33 TiO 3 .