Study on titanium foil coated with partial reduction titanium dioxide as bipolar lead-acid battery's substrate

Pure titanium foil cannot be directly as the substrate for the bipolar lead-acid battery due to its surface oxidized into titanium dioxide in the cell cycle. The poor electronic conductivity of titanium dioxide will increase substrate's ohmic resistance and can affect the cell's electrochemical performances. In this paper, titanium foil's surface is coated with a lay of partial reduction titanium dioxide (TiO2−x) which has excellent chemical stability and high electronic conductivity by means of sol-gel method. Through XRD, SEM and four-probe test, it shows that the modified titanium's surface has the most superior crystal structure and morphology and the highest electronic conductivity in the sintering temperature of 800 °C. We subsequently assemble bipolar lead-acid batteries with Ti coated by TiO2−x as the substrate material. The batteries are discovered that when charged and discharged in 3.5 V-4.84 V at 0.5C the voltage between the charge and discharge voltage platform is 0.3 V, and the initial discharge specific capacity can reach 80 mAh g−1. When the current rate is up to 1C and 2C, the initial discharge specific capacity is 70 mAh g−1and 60 mAh g−1. After 100 cycles, the initial specific capacity only decreases 12.5%.