The effects of ball-milling on Li insertion into multi-walled carbon nanotubes (MWNTs) are presented. The MWNTs are synthesized on supported catalysts by thermal chemical vapour deposition, purified, and mechanically ball-milled by the high energy ball-milling. The purified MWNTs and the ball-milled MWNTs were electrochemically inserted with Li. Structural and chemical modifications in the ball-milled MWNTs change the insertion-extraction properties of Li ions into/from the ball-milled MWNTs. The reversible capacity (C-rev) increases with increasing ball-milling time, namely, from 351mAhg(-1) (Li0.9C6) for the purified MWNTs to 641mAhg(-1) (Li1.7C6) for the ball-milled MWNTs. The undesirable irreversible capacity (C-irr) decreases continuously with increase in the ball-milling time, namely, from 1012 mAh g(-1) (Li2.7C6) for the purified MWNTs to 518 mAh g(-1) (Li1.4C6) for the ball-milled MWNTs. The decrease in C-irr of the ball-milled samples results in an increase in the coulombic efficiency from 25% for the purified samples to 50% for the ball-milled samples. In addition, the ball-milled samples maintain a more stable capacity than the purified samples during charge-discharge cycling. (c) 2005 Elsevier B.V All rights reserved.