Polymer wiring of insulating electrode materials: An approach to improve energy density of lithium-ion batteries

The poor electronic conductivity of LiFePO4 has been one of the major issues impeding it from achieving high power and energy density lithium-ion batteries. In this communication, a novel polymer-wiring concept was proposed to improve the conduction of the insulating electrode material. By using a polymer with tethered "swing" redox active molecules (S) attached on a polymer chain, as the standard redox potential of S matches closely the Fermi level of LiFePO4, electronic Communication between the redox molecule and LiFePO4 is established. Upon charging, S is oxidized at the current collector to S*, which then delivers the charge (holes) to the LiFePO4 particles by intermolecular hopping assisted by a "swing" - type motion of the shuttle molecule. And Li* is extracted. Upon discharging, the above process is just reversed. Preliminary studies with redox polymer consisting of poly (4-vinylpyridine) and phenoxazine moiety tethered with a C-12 alkyl chain have shown promising result with carbon-free LiFePO4, where effective electron exchange between the shuttle molecule and LiFePO4 has been observed. In addition, as the redox polymer itself could act as binder, we anticipate that the polymer-wiring concept would provide a viable approach to conducting-additive and binder free electrode for high energy density batteries. (c) 2009 Elsevier B.V. All rights reserved.