X-ray photoelectron spectroscopic investigation of atomic-layer-deposited spinel Li4Ti5O12: Calcination under reducing atmosphere

Across all material candidates used as anodes in lithium-ion batteries, lithium titanate (Li4Ti5O12) (LTO) is an excellent replacement for conventional electrode materials, such as graphite or silicon. Compares to commercial graphite anodes, LTO offers a higher charging rate and safer operation, and compares to silicon, it undergoes almost no volume expansion during intercalation of lithium ions into the crystal lattice, so-called zero-strain material. However, the LTO performance still suffers from low conductivity due to the oxidation of titanium (Ti) in spinel-LTO and low ionic kinetics diffusion while cycling, which largely limits its application in solid-state batteries. Modifying the LTO lattice or crystal structure is one way to mitigate this problem. This study shows the coexistence of two main components, Ti4+ and Ti3+, in the crystal structure of LTO developed with a modified atomic layer deposition. The X-ray photoelectron spectroscopy analysis shows calcination under reducing gas, introduces Ti3+ and oxygen vacancies into the Li4Ti5O12 crystal, which can affect the electronic conductivity of LTO. Furthermore, we show how different substrates acting as diffusion barriers affect the film properties.