Several strategies for efficient energy storage

The development of high-performance energy storage devices needs continuing efforts. To increase the energy/power density and flexibility of energy storage devices, we have developed several approaches. (1) A hierarchical pore structure was proposed, in which different pores have different functions in supercapacitors (SCs). Then hierarchical porous carbon with facilitated ion transport and good capacitive performance was synthesized for SCs. (2) A common problem in SCs is that the specific capacity of electrode materials and the voltage window of electrolytes cannot be fully used. By using electrochemical charge injection, electrode potential can be optimized to fully use the working voltage of electrolyte, consequently the energy density of SCs has significantly improved. Based on this method, we also designed a smart device which can monitor safety and self-regenerate its power during use. (3) Graphene materials are widely used in oxide/graphene composite electrodes to improve the electrochemical properties, such as high capacity, high rate capability and excellent cycling stability, of energy storage devices. The roles of graphene in LIBs are found to form a conductive network, increase electron and lithium ion conductivity, and anchor and trap electrode materials, and their effectiveness is dependent upon how strong the interaction between graphene and electrode materials is. (4) By using a commercially-available graphene material with high electrical conductivity, simple graphene membrane-sulfur integrated cathode configurations were developed for Li-S batteries that show excellent performance. (5) A template-directed CVD was used to synthesize a 3D interconnected graphene framework (GF) that is flexible and has outstanding electrical and mechanical properties. By using the GF as a current collector on which Li4Ti5O12 and LiFePO4 were loaded as anode and cathode, a lightweight and flexible full lithium ion battery was fabricated. It has high-rate performance and energy density, and can be repeatedly bent without structural failure and performance loss. Similarly, a high sulfur loading flexible electrode was fabricated, and it shows excellent electrochemical performance as a cathode for Li-S batteries.