Rotatable Methylene Ether Bridge Units Enabling High Chain Flexibility and Rapid Ionic Transport in a New Universal Aqueous Conductive Binder

Binders play an essential role in maintaining the mechanical integrity and stability of electrodes. Herein, a novel aqueous and conductive binder (OXP/CNT-1.5) consisting of carbon nanotubes (CNTs) interwoven with a flexible nano-film of oxidized pullulan (OXP) is designed. The rotatable methylene ether bridge units within OXP chain endow the binder with high chain flexibility, facilitate rapid ion transport, and buffer severe volumetric expansion during charge-discharge cycling. Furthermore, its tight intertwining with CNTs forms continuously conductive and flexible skeletons, which can firmly grasp active nanoparticles through a face-to-point bonding type, guaranteeing the electrodes high conductivity and outstanding mechanical integrity. More importantly, these conductive binders are applicable to the Si/C anode as well as the LiFePO4 cathode. The as-fabricated Si/C anode delivers a 88.2% capacity retention after 100 cycles and 80.2% capacity retention at 0.5 A g(-1) (vs 0.05 A g(-1)), far surpassing the electrode fabricated by conventional polyvinylidene fluoride binder and carbon black mixtures. The LiFePO4/Si/C full cells based on OXP/CNT-1.5 demonstrate excellent electrochemical behavior and stability (97.4% capacity retention after 100 cycles). This work highlights the key role of rotatable methylene ether bridge units to enhance the flexibility, ion conductivity, and stability, which is inspiring in the context of designing novel binders for high-performance batteries.

Automated summary

In this study, a novel aqueous and conductive binder (OXP/CNT-1.5) composed of carbon nanotubes (CNTs) interwoven with a flexible nano-film of oxidized pullulan (OXP) is designed. The binder exhibits high flexibility, rapid ion transport, and excellent mechanical integrity, thanks to the rotatable methylene ether bridge units within the OXP chain. The binder also forms continuously conductive and flexible skeletons with CNTs, ensuring high conductivity and stability of the electrodes.