| 초록 |
High-performance lithium manganese iron phosphate (LMFP) was synthesized with modified carbon nanotubes (CNTs) and carbon blacks (CBs). The CNTs functionalized with carboxylic groups exhibited better affinity toward cathode materials than did pristine nanotubes. The electrochemical performance of the LMFP cathode materials was also improved by using CNTs shortened by lithiation process, compared with pristine long CNT samples. The CNTs can be uncapped by lithiation, without further ball milling or sonication. The modified LMFP (m-LMFP) with shortened and functionalized CNTs showed excellent rate capability, with discharge capacities of 162 mAh g-1 at 0.1C and 147 mAh g-1 at 1C, the highest values reported to date for this type of electrode, because the shortened CNTs seemed to be favorable for lithium ion diffusion with small resistance. The capacity retention of the m-LMFP was 94% after 50 cycles, whereas that of the pristine sample was only 82%. Transmission electron microscopy and AC-impedance results confirmed that the addition of CNTs to the cathode materials improved their networking and electrical properties. However, excessive substitution of CNTs for CBs was not favorable for maximizing electrochemical performance because of increased internal resistance. |
