Preparation And Lithium - Storage Properties Of Tungsten Oxide - Based Cathode Materials With Multistage Structure

By using a simple solvothermal method, three kinds of hierarchical structured WO₃ nanosmaterials were successfully prepared, including hollow spherical WO₃ constructed by nanoplates, high conductive carbon evenly coated WO₃/C hollow spherical composites and one-dimensional tubular WO₃. The morphology, microstructure,stability and lithium storage performance of the above materials were studied in detail.The results are as follows:（1） Using tungsten hexachloride as tungsten source, WO₃ hollow spheres with hierarchical structure were prepared through a template free solvothermal method with acetic acid as the solvent. The hollow spheres are constructed by the nanoplates with a average thickness of 40 nm. The shell of the spheres is loose and porous with a thickness of about 200 nm. Such hollow spheres showed excellent performance of lithium ion storage: under the current density of 100 mA g-1, the first discharge capacity was 1701 mAh g-1 and charge capacity was 1228 mAh g-1, the coulombic efficiency was72%. After 100 cycles, the reversible specific capacity was kept at 700 mAh g-1, close to theoretical lithium ion storage capacity of the WO₃. Under the current density of 1600 mA g-1, the discharge specific capacity was about 214 mAh g-1after 500 cycles.（2） Hollow spherical WO₃/C composites were obtained by hydrothermal reaction with WO₃ hollow microspheres and glucose as carbon source. Compared with the pure phase of WO₃ hollow sphere, the WO₃/C composites had a certain improvement in the first Kulun efficiency and the rate performance. At the current density of 100 mA g-1,the first Kulun efficiency reached 84%. When the current density was 1600 mA g-1, the discharge specific capacity reached 379 mAh g-1 after 50 cycles, which was much higher than that of the pure phase of WO₃ hollow spheres（234 mAh g-1） under the same conditions.（3） A novel tubular WO₃ assembled by nanoparticles was prepared by the ethanol solvothermal method with six tungsten chloride as the tungsten source under the assistance of urea. Such WO₃ tubes also exhibited excellent performance of lithium ion storage: at a current density of 400 mA g-1, the first discharge specific capacity was 491 mAh g-1, and still reached to 456 mAh g-1 after 50 cycles. The capacity retention rate was 93%, the capacity attenuation per cycle was only 0.14%. When the current density was increased to 1600 mA g-1, the discharge capacity was still as high as 342 mAh g-1,which indicated excellent rate performance of such WO₃ tubes.