Lithium-ion batteries (LIBs) have been used in many fields, such as consumer electronics and automotive and grid storage, and its applications continue to expand. Several studies have attempted to improve the performance of LIBs. In particular, the use of high-capacity silicon and tin as anodes has been widely studied. Although anodes composed of silicone and tin have high theoretical capacities, poor electrical conductivity and considerable volume expansion of such anodes deteriorate the LIB performance. Thus, Li4Ti5O12 (LTO), a zero-strain material, has attracted much attention with high cycle stability and rate capability through improved electrical conductivity. However, LTO has the disadvantages of a low electrical conductivity (10−8 to 10−13 S cm−1) and moderate Li+ ion diffusion coefficient (10−9 to 10−16 cm2 s−1). In this study, the flexible and free-standing composite films were fabricated using only LTO and multi-walled carbon nanotube(CNT) with high electrical conductivity and ion diffusivity. The prepared LTO/CNT films showed a higher charge/discharge capacity than the theoretical capacity of the LTO electrode.
TiNi shape-memory-alloy thin films can be used as small high-speed actuators or sensors because they exhibit a rapid response rate. In recent years, the transformation temperature of these films, manufactured via a magnetron sputtering method, was found to be lower than that of the bulk alloys owing to the small size of the grain. In this study, deposition conditions (growth rate, film thickness, and substrate temperature) affecting the grain size of thin films were investigated. The grain size of the thin film alloys was found to be most responsive to the substrate temperature.
Sn is a promising candidate anode material with a high theoretical capacity (994 mAh/g). However, the drastic structural changes of Sn particles caused by their pulverization and aggregation during charge–discharge cycling reduce their capacity over time. To overcome this, a TiNi shape memory alloy (SMA) was introduced as a buffer matrix. Sn/TiNi SMA multilayer thin films were deposited on Cu foil using a DC magnetron sputtering system. When the TiNi alloy was employed at the bottom of a Sn thin film, it did not adequately buffer the volume changes and internal stress of Sn, and stress absorption was not evident. However, an electrode with an additional top layer of room-temperature-deposition TiNi (TiNi(RT)) lost capacity much more slowly than the Sn or Sn/TiNi electrodes, retaining 50% capacity up to 40 cycles. Moreover, the charge-transfer resistance decreased from 318.1 Ω after one cycle to 246.1 Ω after twenty. The improved cycle performance indicates that the TiNi(RT) and TiNi-alloy thin films overall held the Sn thin film. The structure was changed so that Li and Sn reacted well; the stress-absorption effect was observed in the TiNi SMA thin films.
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