Modified tungsten oxide as a binder-free anode in lithium-ion battery for improving electrochemical stability

As the anode active substance of lithium ions battery (LIB), the low conductivity/ion diffusivity and large volume changes of tungsten oxide (WO3) lead to its serious polarization during the lithiation/delithiation process, decreasing the cycling stability. To address these challenges, a binder-free anode consisting of nitrogen-doped tungsten oxide nanosheets, encapsulated in carbon layers (N-doped WO3@CL) and entangled with carbon nanotubes macro-films (CMF), was successfully synthesized through a combination of hydrothermal and online assembly method. Compared with the pristine tungsten oxide entangled with carbon nanotubes macro-films (WO3@CMF), the synthesized N-doped WO3@CL@CMF as a binder-free LIB anode demonstrated better electrochemical performance, which could be attributed to (1) surface defects of WO3 created by N dopant providing more channels to improve Li+ diffusion, (2) the N-doped WO3@CL with a flower-like structure shortening the diffusion length of Li+ ions and further leading to high Li+ incorporation, and (3) carbon layers and carbon nanotubes synergistically alleviating the large volume change of the N-doped WO3@CL@CMF electrode during the charging and discharging process. The present study offers insights into employing nitrogen dopant and a carbon matrix to mediate the conductivity and wrapped structure in the WO3 semiconductor powder, which provides an important strategy for large-scale design of the binder-free LIB anode with high performance.