Conductivity Enhancement and Thin-Film Processing of Li4Ti5O12(LTO) Spinel for Li Battery Applications

Lithium titanium oxide spinel Li₄Ti₅O₁₂ has been reported to be a zero-strain lithium insertion host material because it exhibits extremely small variations of the lattice parameters during the charge and discharge processes. In general, Poor adhesion between thin-film electrode and substrates is the common cause for performance degradation of thin-film electrode during repeated charge/discharge tests. Thus, Li₄Ti₅O₁₂ spinel may be the ideal candidate for the anode of thin-film Li ion battery for long cycle applications. 

However, unmodified Li₄Ti₅O₁₂ usually exhibits poor rate performance, which mainly results from its low electronic conductivity (ca. 10^-13 S·cm^-1) and moderate Li+ diffusion coefficient (10^-8cm²·s^-1). 

In addition, different electrochemical behaviors will be expected when Li₄Ti₅O₁₂ spinel is prepared in thin-film compared to that in power forms. Therefore, the objective of this work is (1) to enhance the conductivity of  Li₄Ti₅O₁₂ spinel by substitution of aliovalent dopants for Ti ions, (2) to fabricate thin film of Li₄Ti₅O₁₂spinel by using RF-sputtering technique, (2) to investigate the effect of annealing temperature/atmospheres on the electrical/electrochemical properties of thin film Li₄Ti₅O₁₂, (3) to evaluate the feasibility of using thin film of Li₄Ti₅O₁₂ as anode for Li microbattery applications.

In this study, the Li4Ti5O12 thin film was deposited on either the Si substrate or glass substrate by sputtering technique. The crystallization of deposited Li4Ti5O12 thin film will be enhanced by annealing at various atmospheres and temperatures. The single phase Li4Ti5O12 was finally obtained after co-sputtering of Li-containg and Ti-containing targets. The crystal structure and crystallization will be examined by glancing XRD. The resistivity of Li₄Ti₅O₁₂ thin film will be evaluated by four probe technique and our novel micromeaurement system. The capacity of Li₄Ti₅O₁₂ thin film will be evaluated from charge/discharge tests.