Hierarchical Porous Carbon As Anode Material For Super Lithium Ion Capacitor

Super lithium ion capacitor (SLIC) is a new kind of energy storage device possessing high energy density as well as high power density. It is very important to develop a new anode material for SLIC. Aiming at obtaining the carbon materials of appropriate pore structure, high reversible capacity and high quality capacitance, in this paper, hierarchical porous carbon was innovatively fabricated as SLIC anode material. A series of hierarchical porous carbon (HPC) were prepared by templating method, and their physical or electrochemical properties were analyzed. Then physical activation-templating method was used to prepare local graphitization hierarchical porous carbon materials (HPGC) with high specific capacitance and high reversible capacity. Finally, in consideration of the large initial irreversible capacity of HPGC materials, CHPGC materials, which are consist of HPGC materials as shells, and CMS (carbonaceous mesophase spherule) as the core were designed and prepared as the anode materials for SLIC, their electrochemical and electrode dynamic properties were also studied intensively. The relative conclusions are as follows:(1) It can be found that HPC-600 (activation temperature is 600℃, alkali/C ratio is 2) exhibits the best electrochemical performance. The specific surface area and average aperture of HPC-600 are 276.2 m2/g and 7.25 nm respectively. It has large initial discharge capacity of 1062 mAh/g and reversible charge capacity of 410 mAh/g, specific quality capacitance of 65 F/g and better circulation performance, however, it's inevitable to emerge large diffusion resistance and contact resistance.(2) The results indicate that proper porous structure and specific surface area are beneficial to form anode material with higher reversible capacity, better rate performance and higher capacitance. HPGC-800 prepared at 800℃has the highest specific surface area (524.2m2/g) and average aperture of 5.57 nm, but HPGC-600 has the optimal electrochemical performance. The initial discharge capacity of HPGC-600 is 2031.2 mAh/g, and charging capacity is 611.2 mAh/g. After 50 times cycles, the rate of capacity retention is 74%. The reversible capacity at 6C is 225 mAh/g. The specific capacitance is up to 143 F/g and the capacitance rate performance is also great.(3) The capacitance features of CHPGC show that when CMS increases, the capacitance, contact resistance, and the diffusion resistance of CHPGC materials decrease. CHPGC-1 (mass ratio of CMS and phenolic resin is 1) material has the most reasonable shell/core structure and the highest specific capacitance (36 F/g). The battery features show that the initial discharge capacity and charge capacity of CHPGC-1 are 1049 mAh/g and 524 mAh/g respectively. The rate of capacity retention is 90.3% after 50 times cycles.(4) The results of kinetics show that the exchange current density increases, while the lithium ion diffusion coefficient decreases as lithium ion is intercalated into carbon electrode. Among these materials, the minimum exchange current density is HPGC-600, while the maximum is CHPGC-1. Comparing HPGC-600, CHPGC-1, and CMS, lithium ion diffusion coefficient decreases gradually.