RESUMO
The inherent flexibility of redox-active organic polymers and carbon-based fillers, combined with flexible current collectors (CCs) is ideal for the fabrication of flexible batteries. Herein, a one-step electrophoretic deposition of polyviologen (PV)/graphene-oxide (GO) aqueous composites onto a flexible mesh of 60 µm thick wires, 100 µm apart, is described. Notably, during electrodeposition, GO is transformed into conductive reduced GO (rGO), and nanoscopic pores are formed by self-assembly allowing charge/discharge of the redox sites over dozens of micrometers. Typically, electrodeposition of PV alone on a flat CC (FCC) is limited by its electrically insulating structure to ≈0.15 mAh cm-2 , but the presence of rGO allows thicker active layers without loss in (dis-)charging kinetics and reaching areal capacities of ≈2 mAh cm-2 . Remarkably, when the FCC is replaced by a mesh, the deposition of significantly more anode materials (≈5 mAh cm-2 ) is possible, while the (dis-)charging kinetics is considerably improved. It exhibits high capacity retention at an ultrafast rate of 100 C (<3%) and excellent bending stabilities. This represents the first combination of a microscopic-CC (mesh wires) with a molecular-electronic and -ionic conductor (rGO with its pores), i.e., a hierarchical-CC system with maximized polymer thickness and minimized wire thickness. The stacking of such modified grids paves the road to further increase the areal capacity.
RESUMO
The first all-metallocene rechargeable battery consisting of poly-cobaltocenium/- and poly-ferrocene/reduced graphene oxide composites as anode and cathode was prepared. The intrinsically fast ET self-exchange rate of metallocenes was successfully combined with an efficient ion-percolation achieved by molecular self-assembly. The resulting battery materials show ideal Nernstian behavior, is thickness scalable up to >1.2â C cm-2 , and exhibit high coulombic efficiency at ultrafast rates (200â A g-1 ). Using aqueous LiClO4 , the charge is carried exclusively by the anion. The ClO4 - intercalation is accompanied by a reciprocal height change of the active layers. Principally, volume changes in organic battery materials during charging/discharging are not desirable and represent a major safety issue. However, here, the individual height changes-due to ion breathing-are reciprocal and thus prohibiting any internal pressure build-up in the closed-cell, leading to excellent cycling stability.
RESUMO
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.
