Tuning the microstructures of uniform carbon spheres by controlling the annealing conditions for high-performance lithium-ion full batteries and lithium-ion capacitors

Abstract

Microstructures include graphited microcrystal structures, micro-pores, specific areas, and pore volume of hard carbon spheres (CSs), have been tuned to optimize their Li+ storage performance by annealing at different temperature. The sample annealed at 650 °C (CS-650) exhibits the best performance for Li+ storage with high specific capacity, stable cycling stability, and superior rate performance. The CS-650 displays an initial capacity of 284 mAh g–1 at a specific current of 0.3 A g–1 with 277 mAh g–1 can be retained after 400 cycles, and a specific capacity of 180 mAh g–1 can be achieved at a high specific current of 2.0 A g–1. More significantly, the CS-650 exhibits a high capacitive contribution ratio from 62.2% to 76.0% as the scan rate increases from 0.3 to 1.0 mV s−1 due to its high specific area and large pore volume. The capacitive behaviour of CS-650 enhances the reaction kinetics for high energy and high-power applications in both full battery and Li-ion capacitor (LIC), which are assembled with LiNi0.5Co0.2Mn0.3O2 cathode and activated carbon positive electrode, respectively. The CS-650-based full battery shows a specific capacity of 66.1 mAh g−1 at 0.1 A g−1 combined with high cycling stability. The LIC displays a specific energy of 115 Wh kg−1 at 242 W kg−1 with a specific energy of 48 Wh kg−1 at 2364 W kg−1. Our work indicates that the Li+ storage performance of hard carbon can be tuned by the microstructure and both high energy and high power performances can be achieved.