Li4+XTi5O12 (X > 0) negative active material has been successfully synthesized by anew chemical method for Li-doping with the catalytic function of naphthalene in Li-organic complex solution of butylmethylether (BME) or dimethoxyethane (DME) solvent. The Li-doping reaction rate constant in BME was found to be greater than that of the case of DME and its value was 5.10 and 2.78 x 10(-4) S-1/2, respectively, by the calculation from the slope of distinct straight line in the relationship between ln(1/1 - Y) and root t, where Y is molar fraction of Li-doping materials of Li7Ti5O12. (c) 2605 Elsevier B.V. All rights reserved.