Loss-free pulverization by confining copper oxide inside hierarchical nitrogen-doped carbon nanocages toward superb potassium-ion batteries.

Taking the advantages of hierarchical nitrogen-doped carbon nanocages (hNCNCs) with nanocavities for encapsulation and multiscale micro-meso-macropores/high conductivity for mass/electron synergistic transportation, a conversion-type CuO anode material is confined inside hNCNCs for potassium storage. The so-obtained yolk-shelled CuO@hNCNC hybrids have tunable CuO contents in the range of 11.7-63.7 wt%. The unique architecture leads to the loss-free pulverization of the active components during charge/discharge, which increases the surface-controlled charge storage, shortens the K+ solid diffusion lengths with an enlarged K+ diffusion coefficient, and meanwhile enhances the rate capability and durability. Consequently, the optimized CuO@hNCNC delivers a high specific capacity of 498 mA h g-1 at 0.1 A g-1 and 194 mA h g-1 at 10.0 A g-1 based on the total mass of CuO@hNCNC, and a long-term stability. The capacity based on the CuO active component reaches a record-high 522 mA h g-1 at 1.0 A g-1 after 2000 cycles, which is ca. 2.5 times the state-of-the-art value in the literature. The evolution of the cycling performance with CuO loading is well understood based on the loss-free pulverization. This study demonstrates a new strategy to turn the generally harmful pulverization of active components into a beneficial factor for K+ storage, which paves the way for exploring high-performance anodes for rechargeable batteries.