| Carbon nanotubes（CNTs）are gradually replacing carbon black to play an important role in lithium ion batteries（LIBs）owing to its unique mechanical,electrical and thermal properties.The state-of-the-art CNT conductive additive in LIBs has two challenges:first,the metal catalyst residue in CNT conductive additive causes the inner short circuit in the electrochemical process of LIBs;second,the built conductive network of CNTs could not sustain the volume variation of electroactive materials in the high rate charge-discharge process for the long cyclicity.To solve these two problems,the ultra-high-purity carbon nanotubes and the hybrid carbon nanotubes（H-CNTs）were introduced for the conductive additive to improve the cycle performance and rate performance of LIBs.The main research contents are summarized as follows:（1）A water-assisted chemical vapor deposition（CVD）device was built to realize the scale preparation of the vertically aligned carbon nanotubes（VACNTs）with the ultra-high purity（>99.99%）.Based on the optimized catalytic system,VACNT with uniform diameter and controllable structure performance was obtained,and the daily output of over 1 gram was achieved.（2）The CNT dispersion parameters were optimized in the ultrasonic and ball milling methods for the conductive additive preparation,the as-prepared sample was used in the LiFePO4 LIBs.The electrochemical performance（5 C:140 mAh/g,10 C:109 mAh/g）is better than the conventional ones（5 C:100 mAh/g,10 C:0 mAh/g）.（3）The H-CNTs were synthesized by a fluidized bed process in the assistance of a designed Ni-Mn-Al catalyst.The small diameter（10 nm）and large diameter（50 nm）CNTs were used in the conductive additive for the SnO2 LIBs to testify the idea.The H-CNTs battery exhibits an excellent cycling performance（1 A/g 1000 cycles:710 mAh/g）and rate capability（10 A/g:400 mAh/g）.The conventional CNTs battery is much lower（10A/g:200 mAh/g）.The characterization results show the H-CNTs conductive network remained stable after the tests. |
