First-principle Studies Of WO₃ As Anode Material For Lithium Ion Batteries

With the development of modern science and technology,lithium ion batteries are playing an important role in people's life.Lithium ion batteries have many advantages such as high energy density,high operating voltage,wide operating temperature range,good cycle performance and less environmental pollution which lead them been widely used in many fields like portable electronic products,electric vehicle,large power source,rechargeable energy storage device,aerospace,national defense and military.Graphite has been used as an anode material in commercial lithium ion batteries for many years.However,developing novel anode materials becomes more and more significant as graphite has some disadvantages such as low energy density,secondary reactions and poor structural stability.The tungsten trioxide?WO₃?was investigated based on the first principles calculation as a novel lithium ion battery anode.Firstly,the adsorption mechanism of lithium ions was studied according to the WO₃ crystal structure.The calculation results show that the adsorption sites of lithium ions are existed between W-O planes and which can form a Li-O plane with the O atoms.With the structural optimization and energy calculation theory,three stable adsorption sites of lithium ions were found in the WO₃ crystal structure.They are all in the Li-O plane,corresponding to the center of O triangle,the center of O hexagon,and the O site which is in the W-O plane with an approximately 0.78 ? offset toward the center of O hexagon.The total energy of LixWO₃ was calculated based on the first principles energy calculation theory.The results show that the maximum number of lithium ions adsorption in the WO₃ primitive cell is six while the structure will become unstable when more lithium ions were intercalated.The voltage curve and the relationship between the voltage and the number of lithium ions were obtained combining the voltage formula and the calculation results.The cNEB method was used to study the diffusion mechanism of lithium ions in the WO₃ system.It was shown that lithium ions were more likely diffused within the Li-O plane compared with passing through layers because of the smaller energy barrier.As well the results show that lithium ions were easily diffused along the short pathway which parallels to the edge of O hexagon rather than any other diffusion pathway within the Li-O plane.In summary,the absorption and diffusion mechanism of lithium ions in WO₃ system were investigated using the first principles calculation theory.The results show that WO₃ has excellent properties for lithium ions absorption and diffusion as a promising novel anode material of lithium ion batteries.