Ionic conductivity in LixTaOy thin films grown by atomic layer deposition

Yang Hu, Ville Miikkulainen, Kenichiro Mizohata, Truls Norby, Ola Nilsen, Helmer Fjellvåg
2020 Electrochimica Acta  
The material system Li-Ta-O is a promising candidate for thin-film solid-state electrolytes in Li-ion batteries. In the present study, we have varied the Li content x in Li x TaO y thin films grown by atomic layer deposition (ALD) with the aim of improving the Li-ion conductivity. The amorphous films were grown at 225 °C on insulating sapphire and on conductive Ti substrates using tantalum ethoxide (Ta(OEt) 5 ), lithium tert-butoxide (LiO t Bu) and water as reactants. The film composition was
more » ... m composition was determined by time-offlight elastic recoil detection analysis (TOF-ERDA), displaying an almost linear relationship between the pulsed and deposited Li content. The ionic conductivities were determined by in-plane and cross-plane AC measurements, exhibiting an Arrhenius-type behaviour and comparatively weak thickness-dependence. Increasing Li content x from 0.32 to 0.98 increases the film conductivity by two orders of magnitude while higher Li content x = 1.73 results in decreased conductivity. A room-temperature conductivity σ RT of ~10 −8 S cm −1 is obtained for a 169 nm thick Li 0.98 TaO y film. The evolution of conductivity and activation energy suggests a competing effect between the concentration and the mobility of mobile Li ions when more Li are incorporated. The compositional dependence of Li transport mechanism is discussed. .no (Y. Hu). ies is to deposit a conformal and pinhole-free electrolyte thin film. Atomic layer deposition (ALD) has already demonstrated its potential for Li-containing materials and holds promise for enabling such 3D microbatteries. ALD is based on sequential self-limiting gassolid surface reactions, and it offers high-aspect-ratio conformity, precise thickness control at the angstrom level, tunable composition and freedom in the degree of crystallinity. Additionally, ALD processes are easy to scale up for industry-level applications [ 6 , 7 ]. Since the first report on the deposition of Li-containing films [8] , ALD has developed rapidly and become an effective method to synthesize active electrode materials of Li-ion batteries and to engineer the electrode-electrolyte interface for improving the electrode stability and battery cyclability [9] [10] [11] [12] . More significantly, ALD has progressively demonstrated its potential to fabricate solidstate electrolytes, which hold the key for the advancement of solidstate batteries and 3D microbatteries. Aaltonen et al. [13] firstly suggested ALD grown [(Li, La) x Ti y O z , LLT] amorphous thin films for the application of solid electrolytes. Thereafter, successful depositions of ALD thin-film electrolytes have been reported for various material systems including Li 2 O-Al 2 O 3 [ 9 , 14 , 15 ], Li
doi:10.1016/j.electacta.2020.137019 fatcat:g5ue4kxchjebrosyshsbjphap4