To improve the reversible capacity of TiO 2 (B) negative electrode close to the theoretical one, some preparation and experimental conditions such as the precursor (Na 2 Ti 3 O 7 , K 2 Ti 4 O 9 and Cs 2 Ti 5 O 11 ), the co-solvent in ethylene carbonate-based electrolyte solutions, and homogeneity of the composite electrode were optimized. TiO 2 (B) powder samples were successfully prepared from K 2 Ti 4 O 9 and Cs 2 Ti 5 O 11 precursors, but not from Na 2 Ti 3 O 7 . The sample prepared from Cs 2 Ti 5 O 11 gave a higher discharge capacity (185.5 mAh g −1 ) than that prepared from K 2 Ti 4 O 9 (156.6 mAh g −1 ). The reversible capacity of TiO 2 (B) was significantly influenced by the kind of co-solvent in the electrolyte solutions. The presence of dimethyl carbonate (DMC) as a co-solvent drastically improved the capacity, and the highest discharge capacity of 235.3 mAh g −1 was obtained in 1 M LiPF 6 dissolved EC+DMC (1:2 by volume). Furthermore, improvement of the homogeneity of the composite electrode by premixing the TiO 2 (B) and Ketjen Black conductor was effective to improve the discharge capacity. The optimized electrode gave an initial discharge capacity of 314.4 mAh g −1 , which reached 93.9% of the theoretical capacity (335 mAh g −1 ). It also exhibited a good cycleability (287.9 mAh g −1 after 50 cycles) and a high rate capability (118.5 mAh g −1 at 10 C rate).

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Surface fluorination of TiO2(B) powder was conducted by pure F2 gas at room temperature for 1 h and the effect on the charge/discharge properties was examined as a negative electrode of Li-ion batteries (LIBs). X-ray diffraction (XRD) pattern was not changed before and after the surface fluorination though the peak intensities became weaker than that of the pristine sample, indicating the etching of the surface of SF-TiO2(B) power. This was supported by scanning electron microscopy (SEM) observation. However, X-ray photoelectron spectroscopy (XPS) analysis clearly revealed that F atoms exist on the surface of TiO2(B) particles and probably were covalently bonded with Ti atoms near the surface. From the charge/discharge tests at a C/6 rate, the SF-TiO2(B) exhibited a higher 1st discharge (203 mAh g-1) than the pristine sample (181 mAh g-1) with a good cycleability. Impedance analysis revealed that both resistances of solid electrolyte interphase (SEI) film and charge transfer at the SEI /active material interface were reduced by surface fluorination, implying the improvement of SEI film and permeability of the electrolyte solution to the interphase. The rate capability was improved by the surface fluorination up to 1C rate, at which the SF-TiO2(B) exhibited a high discharge capacity of around 150 mAh g-1.

The shape and size of TiO2(B) particles were controlled by ball-milling K2Ti4O9, H2Ti4O9 and TiO2(B) powders to improve the tap density of TiO2(B). It was found that only K2Ti4O9 endured the ball-milling process and provided a fine TiO2(B) powder after the ion-exchange and dehydration processes. In contrast, ball-milling of H2Ti4O9 and TiO2(B) powders resulted in a formation of a large amount of the rutile and anatase phase, respectively. In addition, a reduction of the spinning rate to 600 rpm suppressed the formation of the minor impurity of the anatase phase in the TiO2(B) sample prepared from the milled K2Ti4O9 powder. The resulting TiO2(B) (M1-600) powder exhibited a high tap density of 0.71 g cm-3 and a high electrode density of 1.25 g cm-3, which were 2.37 and 1.29 times, respectively, higher than those of the pristine TiO2(B). In charge/discharge tests, M1-600 exhibited a discharge of 213.1 mAh g-1, which is higher than that of the pristine TiO2(B), with a good cycleability. It gave a discharge capacity of 80.1 mAh g-1 even at a high rate of 10 C.