Increasing ionic conductivity in Li0.33La0.56TiO3 thin-films via optimization of processing atmosphere and temperature

As a promising solid electrolyte for thin-film lithium batteries, the amorphous Li0.33La0.56TiO3 (LLTO) thin film has gained great interest. However, enhancing ionic conductivity remains challenging in the field. Here, a systematical study was performed to improve the ionic conductivity of sputter-deposited LLTO thin films via the optimization of processing atmosphere and temperature. By combining the optimized oxygen partial pressure (30%), annealing temperature (300 °C), and annealing atmosphere (air), an amorphous LLTO thin film with an ionic conductivity of 5.32 × 10−5 S·cm−1 at room temperature and activation energy of 0.26 eV was achieved. The results showed that, first, the oxygen partial pressure should be high enough to compensate for the oxygen loss, but low enough to avoid the abusive oxygen scattering effect on lithium precursors that results in a lithium-poor composition. The oxygen partial pressure needs to achieve a balance between lithium loss and oxygen defects to improve the ionic conductivity. Second, a proper annealing temperature reduces the oxygen defects of LLTO thin films while maintaining its amorphous state, which improves the ionic conductivity. Third, the highest ionic conductivity for the LLTO thin films that were annealed in air (a static space without a gas stream) occurs because of the decreased lithium loss and oxygen defects during annealing. These findings show that the lithium-ion concentration and oxygen defects affect the ionic conductivity for amorphous LLTO thin films, which provides insight into the optimization of LLTO thin-film solid electrolytes, and generates new opportunities for their application in thin-film lithium batteries.