Based on the considerations in environmental and economic benefits, Cr2O72 as the major chromium pollutant is employed for applications in energy storage. A novel Cr2O3 ultrasmall nanoparticles (NPs) (<5 nm) filled carbon nanocapsule configuration is achieved through a surfactant-free solvothermal route with renewable furfural as the carbon source. The confinement effect that Cr2O3 NPs are restrained in the outer robust carbon shell and the plenty space among Cr-2 O-3 NPs result in substantially enhanced Li-storage performances, such as stable capacity of 568 mAh g(-1) at 100 mA g(-1) after more than 200 cycles and high capacity retention at large current density. (C) 2018 Elsevier B.V. All rights reserved.