High Performance Poly(viologen)-Graphene Nanocomposite Battery Materials with Puff Paste Architecture

Abstract

Four linear poly(viologens) (PV1, PV2: phenylic, PV3: benzylic, and PV4: aliphatic) in tight molecular contact with reduced graphene oxide (rGO), that is, PV@rGO, were prepared and used as anodic battery materials. These composites show exceptionally high, areal, volumetric, and current densities, for example, PV1@rGO composites (with 15 wt % rGO, corresponding to 137 mAh g^-1) show 13.3 mAh cm^-2 at 460 μm and 288 mAh cm^-3 with 98% Coulombic efficiency at current densities up to 1000 A g^-1, better than any reported organic materials. These remarkable performances are based on (i) molecular self-assembling of PVs on individual GO sheets yielding colloidal PV@GO and (ii) efficient GO/rGO transformation electrocatalyzed by PVs. Ion breathing during charging/discharging was studied by electrochemical quartz crystal microbalance and electrochemical atomic force microscopy revealing an absolute reversible and strongly anisotropic thickness oscillation of PV1@rGO at a right angle to the macroscopic current collector. It is proposed that such stress-free breathing is the key property for good cyclability of the battery material. The anisotropy is related to a puff paste architecture of rGO sheets parallel to the macroscopic current collector. A thin graphite sheet electrode with an areal capacity of 1.23 mAh cm^-2 is stable over 200 bending cycles, making the material applicable for wearable electronics. The polymer acts as a lubricant between the rGO layers if shearing forces are active.

Keywords: battery; composites; eQCM; electrochemical AFM; graphene; graphene oxide; viologen.