The Effects Of Conductive Polymer/Sodium Alginate On Volume Expansion Of Anode Materials For Lithium-ion Batteries

A variety of novel anode materials for the lithium-ion battery,such as Sn and metal oxides,are expected to be the alternatives to traditional graphite because of their high theoretical capacity.However,these materials suffer from the mechanical instability associated with the lithium alloy and large volume expansion during Li⁺insertion/extraction process,causing rapid capacity fading.Conductive polymers have been used as the coating layer for inorganic anode materials to alleviate their volume change during cycling.However,the composition,structure and mechanical strength of the conductive polymer coating haven't been investigated deeply.Therefore,the study of conductive polymer with 3D structure has important implications for alleviating the volume expansion of anode materials.In this paper,we designed the three-dimensionalpolyaniline/sodium alginate?PANI/SA?and polypyrrole/sodium alginate?PPy/SA?composites via the situ polymerization of aniline and pyrrole in an aqueous solution of SA,respectively.Then the PANI/SA and PPy/SA were separately used as the coating layer of Sn and ZnCo₂O₄ in order to obtain the Sn@PANI/SA and ZnCo₂O₄@PPy/SA composite.The composition,structure,morphology,mechanical properties,conductivity and the electrochemical performance of the samples were explored comprehensively.The results suggested that the SA can enhance the mechanical strength of PANI and PPy.Meanwhile,the PANI/SA and PPy/SA coating can mitigate the volume change of Sn and ZnCo₂O₄ during cycling and improve their electrochemical performance.The experimental results show that the Sn@PANI/SA electrode remains a reversible capacity of 616 mAh g^-1 at the current density of 100 mA g^-1 after 100 cycles,which is much higher than that of Sn@PANI.And the ZnCo₂O₄@PPy/SA electrode exhibits a high capacity of 604 mAh g^-1 at the current density of 100 mA g^-1 after 150 cycles,indicating its excellent cycling stability.Besides,the electrochemical impedance spectra?EIS?suggest thatthe ZnCo₂O₄@PPy/SA composite shows lower SEI resistance and charge transfer resistance compared with ZnCo₂O₄@PPy and ZnCo₂O₄electrodes,demonstrating its superior electrochemical performance.