NOVELTY - A nonstoichiometric titanium compound contains lithium-titanium oxide (I).    USE - Nonstoichiometric titanium compound is used for manufacturing carbon composite for negative electrode active material used for lithium ion secondary battery (all claimed). Uses include but are not limited to mobile telephone, notebook personal computer, digital camera, handheld game machine, hybrid vehicle and electric vehicle.    ADVANTAGE - The nonstoichiometric titanium compound has high crystalline single phase. The lithium ion secondary battery formed using the nonstoichiometric titanium compound has excellent heat resistance and charging/discharging characteristics, and high safety.    DETAILED DESCRIPTION - A nonstoichiometric titanium compound contains lithium-titanium oxide of formula: Li4+xTi5-xO12 (I).    x=greater than 0 and less than 0.3.    INDEPENDENT CLAIMS are included for the following:    (1) carbon composite, which is obtained by subjecting nonstoichiometric titanium compound containing lithium-titanium oxide (I) as a carbon source to carbon conjugation process using 4C or more dicarboxylic acid;    (2) manufacture of nonstoichiometric titanium compound, which involves adding and stirring predetermined amount of oxalic acid, lithium salt and titanium alkoxide in water, spray-drying solution using a spray dryer to obtain a precursor and baking the precursor at 700-900 degrees C for predetermined time in a furnace;    (3) negative electrode active material, which includes nonstoichiometric titanium compound containing lithium-titanium oxide (I); and    (4) lithium ion secondary battery (1), which has a positive electrode collector layer (14), a positive electrode active material layer, an electrolyte layer, a negative electrode active material layer (16) containing negative electrode active material comprising nonstoichiometric titanium compound of lithium-titanium oxide (I) and a negative electrode collector layer (13).    DESCRIPTION OF DRAWING(S) - The drawing shows the sectional view of the lithium ion secondary battery.    Lithium ion secondary battery (1)    Negative electrode collector layer (13)    Positive electrode collector layer (14)    Negative electrode active material layer (16)    Gasket (18)