A superior mix of big and small: Graphene is often described as an unrolled carbon nanotube. However, although nanotubes are known for their exceptional mechanical and conductivity properties, the same is not true of graphene-based fibers. Xin et al. intercalated small fragments of graphene into the gaps formed by larger graphene sheets that had been coiled into fibers. Once annealed, the large sheets provided pathways for conduction, while the smaller fragments helped reinforce the fibers. The result? Superior thermal and electrical conductivity and mechanical strength. Science , this issue p. 1083

Mechanical and chemical degradations of high-capacity anodes, resulting from lithiation-induced stress accumulation, volume expansion and pulverization, and unstable solid–electrolyte interface formation, represent major mechanisms of capacity fading, limiting the lifetime of electrodes for lithium-ion batteries. Here we report that the mechanical degradation on cycling can be deliberately controlled to finely tune mesoporous structure of the metal oxide sphere and optimize stable solid–electrolyte interface by high-rate lithiation-induced reactivation. The reactivated Co₃O₄ hollow sphere exhibits a reversible capacity above its theoretical value (924 mAh g⁻¹ at 1.12 C), enhanced rate performance and a cycling stability without capacity fading after 7,000 cycles at a high rate of 5.62 C. In contrast to the conventional approach of mitigating mechanical degradation and capacity fading of anodes using nanostructured materials, high-rate lithiation-induced reactivation offers a new perspective in designing high-performance electrodes for long-lived lithium-ion batteries.

We report a new nano-geometry based on porous nickel oxide nano-sheets for high performance pseudo-capacitance materials. The porous nickel oxide nanosheets were fabricated by synthesizing porous Ni(OH)₂ sheets by surfactant-templated wet chemistry followed by the decomposition of hydroxides to oxides upon thermal treatment. The nickel oxide nanosheets display tunable specific capacitance varying from 641 to 1025 F/g at a charge–discharge current density of 3 A g⁻¹, and from 326 to 445 F/g at 15 A/g. By optimizing the thermal annealing conditions (e.g., 300 °C for 3 h), the electrochemical performance can be achieved with a high capacitance of 993 F/g at current density of 3 A g⁻¹, and 445 F/g at 15 A g⁻¹ with an excellent cycle stability. Detailed XRD, CV, EIS, UV and XPS characterization indicated that the interplay among the surface area, morphology, pore size distribution, crystal size and defect determined the electrochemical performance of porous NiO nanosheets as pseudocapacitive materials. The unique nano-sheet geometry and intrinsically high surface area may have a great potential for designing high performance supercapacitors with simultaneous high power and energy densities, and the reported surfactant-templated wet chemistry approach may also be applicable for developing various metal oxide nano-sheet pseudo-capacitance materials for electrochemical energy storage.