The present work demonstrates that lithium ions can be stepwise substituted by protons from spinel Li4Ti5O12 crystalline particles though simple ion-exchange in aqueous HCl solution with the aid of heat treatment. This enables us to continuously tune the Li-to-Ti stoichiometric ratios from 0.80 to 0.59, 0.41, 0.21, 0.15, and 0.09, thus transforming Li4Ti5O12 to Li4−xTi5O12 nanocrystals. The resulting nanocrystals maintain the spinel crystal structure when x becomes smaller than 3. Among as-prepared the Li4−xTi5O12 crystalline particles, Li1Ti5O12 shows the highest capacity of 193 mAh g−1 at 1C and 148 mAh g−1 at 20C, lower current impedance (47 Ω), significantly improved rate capability and fairly long cycle life. This excellent electrochemical performance makes spinel Li4−xTi5O12 particles as a promising anode candidate for lithium ion batteries superior.