In-situ interface reinforcement for 3D printed fiber electrodes

The growing demand for wearable electronics has boosted research on flexible fiber batteries. 3D printing has been applied to fiber battery manufacturing, in which tremendous amount of polymer binders with low conductivity are required. Replacing polymer by conducting skeleton such as graphene can offer long-range conductivity and high active material ratio. However, poor interaction and vast voids between active materials and skeletons result in fragile structure with inferior stabilities. Herein, a facile in-situ interface reinforcement method is proposed to print stable binder-free fiber electrodes. Electrode inks consisting of common LiFePO4 (LFP) particles and graphene oxide (GO) are directly printed in a solution containing dopamine and calcium ions. Catalyzed by Ca2+, dopamine that permeated into the fiber could rapidly polymerize and synchronously establish crosslinks during printing. Subsequently, polydopamine-derived carbon (PDC) networks efficiently reinforce the interface. The PDC at interfaces enriches the electron-transfer pathways and ensures a tight connection through covalent and π-π bonding. The reinforcement enables the printed binder-free electrodes to possess remarkably higher stability, flexibility, and durability under deformation. Additionally, the proposed method has remarkable application potential both for individual fiber batteries and directly printed battery textiles, thereby enabling new possibilities for future wearable energy-storage fabrics.