No abstract

The lattice constants of thin-film Li 1Ϫx CoO 2 cathodes at the 4.2 V charged states were influenced by various deposition conditions. Li 1Ϫx CoO 2 thin films ͓yielding a strong ͑003͒ texture͔ on a Pt or Au current collector, which were unheated during sputtering deposition and ex situ annealed, showed negligible lattice expansion at 4.2 V during the first charge. This is in contrast to the Li 1Ϫx CoO 2 powders exhibiting ϳ3% c axis expansion at x Х 0.5 ͑from ϳ14.05 to ϳ14.45 Å͒. The total energy of the constrained Li 0.5 CoO 2 lattice ͑0% c axis expansion͒ obtained by a pseudopotential total-energy calculation was slightly higher than that of the relaxed one by ϳ1.0 eV per 12 Li 0.5 CoO 2 ͑or ϳ80 meV/Li 0.5 CoO 2), indicating no difficulty of limited lattice expansion during the first cycle. However, splitting of the ͑009͒ diffraction peak was observed at 4.2 V as cycling proceeded: one has a lattice constant c of 14.01 Ϯ 0.05 Å as LiCoO 2 before charging, and the other has a lattice parameter of 14.40 Ϯ 0.05 Å, which is similar to the Li 0.5 CoO 2 powders. In contrast, the lattice constants c of the Li 1Ϫx CoO 2 thin films deposited at different conditions ͓yielding a weak ͑003͒ texture͔ expanded when first charged to 4.2 V, which is similar to that observed in the powder geometry.

Herein, we propose an ionic liquid-polymer dielectric layer for flexible electronics reinforced by a chemical interaction between the polymer matrix (PVP) and the ionic liquid. Due to the robust structures of the cross-linked PVP matrix and hydrogen bonding between the ionic liquid and PVP, the ionic liquid-PVP (IL-PVP) layer exhibited a good mechanical strength when bending up to 1000 times and a stable thermal behaviour up to 300 8C. Furthermore, the IL-PVP dielectric layer showed a high capacitance value of B2 lF cm À2 and was operated well as a gate insulator for flexible ZnO thin film transistors with a linear field-effect mobility of B3.3 cm 2 V À1 s À1 at a gate bias of 3 V.Suwon-si, Gyeonggi-do 443-270, Republic of Korea † Electronic supplementary information (ESI) available: Experimental process for fabricating the IL-PVP dielectric layer and TFT devices and experimental results including detailed ATR FT-IR peak analysis, impedance analysis, surface roughness analysis of each film and hysteresis of TFTs. See