Letter abstract
Nature Materials 3, 147 - 152 (2004)
Published online: 22 February 2004 | doi:10.1038/nmat1063
Subject Categories: Materials for energy | Nanoscale materials
Nano-network electronic conduction in iron and nickel olivine phosphates
P. Subramanya Herle1, B. Ellis1, N. Coombs1 & L. F. Nazar1
The provision of efficient electron and ion transport is a critical issue in an exciting new group of materials based on lithium metal phosphates that are important as cathodes for lithium-ion batteries. Much interest centres on olivine-type LiFePO4, the most prominent member of this family1. Whereas the one-dimensional lithium-ion mobility in this framework is high2, the electronically insulating phosphate groups that benefit the voltage also isolate the redox centres within the lattice. The pristine compound is a very poor conductor (
10-9 S cm-1), thus limiting its electrochemical response. One approach to overcome this is to include conductive phases, increasing its capacity to near-theoretical values3, 4, 5, 6. There have also been attempts to alter the inherent conductivity of the lattice by doping it with a supervalent ion. Compositions were reported to be black p-type semiconductors with conductivities of 10-2 S cm-1 arising from minority Fe3+ hole carriers7. Our results for doped (and undoped) LiMPO4 (M = Fe, Ni) show that a percolating nano-network of metal-rich phosphides are responsible for the enhanced conductivity. We believe our demonstration of non-carbonaceous-network grain-boundary conduction to be the first in these materials, and that it holds promise for other insulating phosphates.
- University of Waterloo, Department of Chemistry, 200 University Ave. West, Waterloo Ontario Canada N2L 3G1
Correspondence to: L. F. Nazar1 e-mail: lfnazar@uwaterloo.ca
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