Improvement of charge/discharge performance for lithium ion batteries with tungsten trioxide electrodes

• Increasing conductivity of electrode improved performance of lithium ion battery.
• N2 annealing can change monoclinic WO3 into a cubiclike structure.
• N2 annealing can decrease electrode-reaction resistance and improve reversibility.

Although a large amount of research on Li ion transportation has been carried out with the aim of improving the properties of lithium ion batteries, there has been little detailed research on electron conduction. Hence, we have been focusing on improving the charge/discharge performance of lithium ion batteries by increasing the electron conductivity of the electrodes. The electron conductivity of crystalline tungsten trioxide (WO3) was found to be increased by N2 annealing owing to the generation of oxygen vacancies. It was clarified that increasing the conductivity of the electrodes can improve the performance of lithium ion batteries, particularly their charge/discharge speed and reversibility. Additionally, the best performance was observed in a sample subjected to high-temperature annealing at 700 °C in N2 ambient, which decreased the resistivity of the WO3 electrode by five orders of magnitude and simultaneously changed the monoclinic crystalline structure into a cubiclike structure into which Li ions are more easily intercalated. Therefore, to enhance the charge/discharge performance of lithium ion batteries, electron conduction should be a focus of research. Crystalline WO3 was also demonstrated to be a promising material for electrodes since oxygen vacancy generation can be induced by a simple annealing treatment, improving the electron conduction and Li ion transportation.