カーボンナノファイバーを用いたリチウム二次電池用新規Si/C複合負極材料

概要

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The electrochemical performance of a composite of nano-Si powder and a pyrolytic carbon of polyvinyl chloride (PVC) with a carbon nanofiber (CNF) was examined as an anode for lithium ion batteries. CNF was incorporated into the composite by two methods; mixing of CNF, nano-Si powder, and PVC with subsequent firing (Si/CNF/C) and direct mixing of CNF with the nano-Si coated with carbon produced by pyrolysis of PVC (Si/C@CNF). The external BET surface area of Si/C@CNF was comparable to that of Si/CNF/C. The micropore BET surface area of Si/CNF/C (73.86 m2 g-1) was extremely higher than that of Si/C@CNF (0.74 m2 g-1). The composites prepared by both methods exhibited high capacity and excellent cycling stability for lithium insertion and extraction. A capacity of more than 700 mAh g-1 was maintained after 30 cycles. The coulombic efficiency of the first cycle for Si/C@CNF was as low as 53 %, compared with the 71 % for Si/CNF/C. A composite electrode prepared by mixing Si/CNF/C and CNF exhibited a high reversible capacity at high rate, excellent cycling performance.