INTER-TANGLED NETWORK OF POLYMERS FOR ULTRAFAST RECHARGEABLE BATTERIES

Abstract

Metal oxides such as LiCoO2 and LiMn2O4 have been widely used as cathode materials of lithium ion batteries. The inorganic compounds provide practically high capacity based on the redox activity of d orbital transition metals with structural stability leading to cycle retention. As a logical alternative to the conventional cathode materials, also, organic cathode materials have attracted academic attentions from the viewpoint of (1) unlimited elemental resources and (2) elastic properties guaranteeing flexibility in case of polymeric materials. In this work, poly (vinyl carbazole) (PVK) was studied as an electro-active material for cathode materials of lithium ion batteries. PVK showed binder and conductive agent-dependent performances probably because of its volumetric change during oxidation. More elastic polymer binder and use of carbon nanotubes as a conductive agent guaranteed higher capacity (~120 mAh g-1 at 0.1C) and enhanced rate capability (up to several hundreds of C-rate). Optimized condition for making electrode composites would allow practical application of PVK to cathode materials for rechargeable batteries. Moreover, A 1D organic redox-active material is composited with another 1D conductive material for rechargeable batteries. Poly (vinyl carbazole) (or PVK) and Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (or PEDOT:PSS) are used as the redoxactive and conductive 1D materials, respectively. Due to their extreme anisotropic geometry, the two polymers are expected to be inter-tangled with each other, showing an kinetically ideal model system in which each redox-active moiety of PVK is supposed to be directly connected with the conducting pathways of PEDOT:PSS. In addition to the role of conductive agents providing kinetic benefits, PEDOT:PSS works as an efficient binder that guarantees enhanced electrochemical performances with only a tenth of the amount of a conventional binder (polyvinylidene fluoride or PVdF). The benefit of gravimetric energy density gain obtained with the conductive binder comes mainly from efficient spatial coverage of binding volume due to the low density of PEDOT:PSS. Towards realizing flexible allpolymer batteries, a quasi-all-polymer battery half-cell is designed with the PVK/ PEDOT:PSS composite with a polymer gel electrolyte.