Improving cycle stability of Si anode through partially carbonized polydopamine coating

In this study, we report the first investigation of the effectiveness of the partially converted carbon coating from polydopamine (PODA) to improve the cycle stability of Si anode for Li-ion batteries. It is hypothesized that by converting PODA to a partial carbonization condition, the resulting coating could have a higher electrical conductivity than PODA without carbonization, and at the same time may still contain some organic bonds and thus mechanical flexibility to accommodate the volume expansion of Si during lithiation. The results show that such a partial carbonization state can be obtained by carbonization of PODA at 400 degrees C. Furthermore, the partially converted carbon coating can offer sufficient electrical conductivity for lithiation and delithiation of Si anode while drastically reducing the charge transfer resistance for the redox reactions. In addition, the partially-converted-carbon coated hollow Si nano-spheres exhibit excellent cycle stability when the volume expansion of Si anode is not very large (similar to 88%) even though this volume expansion is significantly larger than the engineered void space (47% of the Si volume) available inside the partially-converted-carbon coated hollow Si nanospheres, unambiguously confirming the good tolerance of the partially converted carbon coating in withstanding some tensile strain without fracture. This study offers a new direction for systematic studies in the future as a means to provide a coating on Si material with sufficient electrical conductivity along with capability to withstand some tensile strain during the volume expansion of Si, thereby improving the cycle stability of Si anodes.