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

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 degrees 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.

Automated summary

Microstructures of hard carbon spheres have been tuned by annealing at different temperatures to optimize their Li+ storage performance. The sample annealed at 650 degrees C shows the best performance for Li+ storage with high specific capacity, stable cycling stability, and superior rate performance.