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As a new environmental-friendly gas insulating medium, perfluoroisobutyronitrile (C 4 F 7 N) has been widely concerned in recent years due to its relatively low global warming potential and excellent dielectric strength, which has the potential to replace the most greenhouse gas, sulfur hexafluoride(SF 6). However, there are a few systematic studies on the influence of gas pressure and mixing ratio on the dielectric strength of C 4 F 7 N/CO 2 gas mixture at present. In this paper, the power frequency breakdown characteristics of C 4 F 7 N/CO 2 gas mixture under different pressure and mixing ratio conditions were tested using the gas insulation performance test platform. The optimal mixing ratio and pressure range of C 4 F 7 N/CO 2 gas mixture for engineering application were also discussed. It is found that the breakdown voltages of C 4 F 7 N/CO 2 gas mixture show a saturated growth trend with gas pressure and mixing ratio. The breakdown voltage of the gas mixture with 10% C 4 F 7 N can reach 80% of pure SF 6 under the same condition. The insulation performance of the gas mixture with 20% C 4 F 7 N can reach more than 95% of pure SF 6. Relevant results indicate that the gas mixture with 4%-12% C 4 F 7 N has the potential to be applied to high-voltage gas-insulated equipment. INDEX TERMS C 4 F 7 N/CO 2 , SF 6 alternative gas, quasi-homogeneous electric field, power frequency breakdown characteristics.

Improving the specific capacity and electronic conductivity of TiO2 can boost its practical application as a promising anode material for lithium ion batteries. In this work, a three-dimensional networking oxygen-deficient nano TiO2-x/carbon fibre membrane was achieved by combining the electrospinning process with a hot-press sintering method and directly used as a self-standing anode. With the synergistic effects of three-dimensional conductive networks, surface oxygen deficiency, high specific surface area and high porosity, binder-free and self-standing structure, etc., the nano TiO2-x/carbon fibre membrane electrode displays a high electrochemical reaction kinetics and a high specific capacity. The reversible capacity could be jointly generated from porous carbon, full-lithiation of TiO2 and interfacial lithium storage. At a current density of 100 mA g−1, the reversible discharge capacity can reach 464 mA h g−1. Even at 500 mA g−1, the discharge capacity still remains at 312 mA h g−1. Compared with pure carbon fibre and TiO2 powder, the TiO2-x/C fibre membrane electrode also exhibits an excellent cycle performance with a discharge capacity of 209 mA h g−1 after 700 cycles at the current density of 300 mA g−1, and the coulombic efficiency always remains at approximately 100%.

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