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Fast Charging of Chlorine Doped Amorphous TiO2 Reaching 1 Li per TiO2 for Sub-Micron Thick Films

Wednesday, 4 October 2017: 17:20
Maryland D (Gaylord National Resort and Convention Center)
S. Moitzheim (KU Leuven, imec), E. Balder, P. Poodt, S. Unnikrishnan (TNO), S. De Gendt, and P. M. Vereecken (KU Leuven, imec)
Negative electrodes from TiO2 remains an intriguing choice for lithium-ion batteries, as it could offer a high theoretical capacity (336 mAh/g) and excellent cycling stability. Unfortunately, due to its low electronic and ionic conductivity, state-of-the-art nanosized (< 20 nm) TiO2 electrodes still only achieve about 75% of this capacity at 1 C (or 336 mA/g). From submicron sizes on, TiO2 almost no accessible capacity is left at practical C-rates. In this work, submicron thick chlorine doped amorphous TiO2 (TiO2-xClx) films are investigated as a high-performance Li+-ion insertion electrode material. The TiO2-xClx films were fabricated by Spatial Atomic Layer Deposition (S-ALD), by which the chlorine content was controlled by varying the deposition temperature and gas precursor exposure time, as determined by Rutherford Backscatter Spectroscopy (RBS) and X-Ray Photoelectron Spectroscopy (XPS). Electrochemical tests revealed a maximum reversible Li+-ion insertion/extraction capacity of 362 mAh/g at 0.25 C for the TiO1.912Cl0.088 film (see Fig. 1), which is above the theoretical maximum and suggests that reduction of Ti(III) to Ti(II) is accessible in Cl-doped amorphous TiO2. At a rate of 1 C, still 90% (301 mAh/g) of the theoretical TiO2 capacity is achieved and even 27% (92 mAh/g) at 50 C (see Fig. 1). In addition, TiO2-xClx films deposited by S-ALD are demonstrated as three-dimensional (3D) thin-film electrodes for 3D solid-state batteries. Using 3D structuring, the footprint capacity increased 24 times, while the excellent rate-performance of the planar TiO2-xClx films is retained. The cycling stability of the 3D TiO1.912Cl0.088 electrode was tested for 1000 cycles at 10 C, and no degradation in capacity is observed. Finally, benchmarking our 3D thin-film TiO1.912Cl0.088 electrode shows that it outperforms all other 3D thin-film TiO2 electrodes previously reported.