Development of supercapacitors with high-energy density and high-power density is a tremendous challenge. Although the use of conductive carbon materials is promising, other methods are needed to reach high cyclability, which cannot be achieved by fully utilizing the surface-oxygen redox reactions of carbon. Here we introduce an effective strategy that utilizes Cu 2 þ reduction with carbon-oxygen surface groups of the binder-free electrode in a new redox-active electrolyte. We report a 10-fold increase in the voltammetric capacitance (4,700 F g À 1 ) compared with conventional electrolyte. We measured galvanostatic capacitances of 1,335 F g À 1 with a retention of 99.4% after 5,000 cycles at 60 A g À 1 in a threeelectrode cell and 1,010 F g À 1 in a two-electrode cell. This improvement is attributed to the synergistic effects between surface-oxygen molecules and electrolyte ions as well as the low charge transfer resistance (0.04 O) of the binder-free porous electrode. Our strategy provides a versatile method for designing new energy storage devices and is promising for the development of high-performance supercapacitors for large-scale applications.

Lithium-ion batteries have attracted enormous attention for large-scale and sustainable energy storage applications. Here we present a design of hierarchical Li3V2(PO4)3/C mesoporous nanowires via one-pot synthesis process. The mesoporous structure is directly in situ carbonized from the surfactants (CTAB and oxalic acid) along with the crystallization of Li3V2(PO4)3 without using any hard templates. As a cathode for lithium-ion battery, the Li3V2(PO4)3/C mesoporous nanowires exhibit outstanding high-rate and ultralong-life performance with capacity retention of 80.0% after 3000 cycles at 5 C in 3-4.3 V. Even at 10 C, it still delivers 88.0% of its theoretical capacity. The ability to provide this level of performance is attributed to the hierarchical mesoporous nanowires with bicontinuous electron/ion pathways, large electrode-electrolyte contact area, low charge transfer resistance, and robust structure stability upon prolonged cycling. Our work demonstrates that the unique mesoporous nanowires structure is favorable for improving the cyclability and rate capability in energy storage applications.

Inspired by the Archimedean spiral, a new integrated design of micropseudocapacitors is presented. The fabricated micropseudocapacitors deliver an energy density of 34.9 mW h cm(-3) and a power density of 193.4 W cm(-3). Meanwhile, this spiral design can be engineered into arbitrary microshapes and unconventional series/parallel combinations with symmetrical electrodes.

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