Surface oxo-functionalized hard carbon spheres enabled superior high-rate capability and long-cycle stability for Li-ion storage

Hard carbon is emerging as a highly promising material for power-demanded energy storage devices. Recently, introducing heteroatom such as oxygen is confirmed to be available to improve the capacity. However, it remains a significant challenge to achieve simultaneously superior high-rate capability and long-term cycling stability. Here we demonstrate that the surface oxo-funcitionalized hard carbon spheres (o-HCS, 4.2m(2) g(-1)) derived from mild oxidative approach enhance pseudocapacitance lithiumion storage with improved Li-ion diffusivity and thus exhibit high-rate capacity and long cycle life in both Li-ion batteries and Li-ion capacitors. The o-HCS electrode delivers specific capacity of around 275 mAh g(-1) at 744mA g(-1) (2C) and capacity retention of above 92.0% and about 86.5% after 1100 and 1700 cycles, respectively. Impressively, it delivers above 110mAh g(-1) at extreme high current density of 14.88 A g(-1) (40C). As well, o-HCS electrode in Li-ion capacitor shows a capacitance of 34.8 F g(-1) (corresponding to 48.5 Whkg(-1) and 3.6 kW kg(-1)) at the current density of 3720 mA g(-1), and after 7000 cycles the capacity retention is 96% (similar to 0.057% decay per cycle). (c) 2017 Elsevier Ltd. All rights reserved.