 Enhanced thermal decomposition of carbonates is developed to improve the traditional solid state reaction for the synthesis of ultrafine LiNi1/3Co1/3Mn1/3O2 powders. Controllable activation is obtained by optimizing the mechano-chemical treatment time, which is found to affect lattice structure, morphology and electrochemical properties of the as-synthesized ultrafine LiNi1/3Co1/3Mn1/3O2 powders. The optimal mechano-chemical activation time of 10 h results in more stable and integrated structured ultrafine LiNi1/3Co1/3Mn1/3O2 powders with average diameter of 200–500 nm, leading to a high reversible capacity of 114.3 and 140.9 mAh g−1 at 6 C (1620 mA g−1) in the voltage range of 2.5–4.3 and 2.5–4.5 V, respectively. Moreover, the particles exhibit capacity retentions of 80.8% (2.5–4.3 V) and 83.3% (2.5–4.5 V) at 270 mA g−1 after 200 cycles. Importantly, it is revealed that ball-milling has a positive impact on the calcination process, and the decomposition efficiency is about 35.7% higher compared to ball-milling-free process.