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Nano-network electronic conduction in iron and nickel olivine phosphates

Nature Materials volume 3, pages 147–152 (2004)Cite this article

Abstract

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 (σ ∼ 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.

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Figure 1: X-ray diffraction patterns of various powders and sintered pellets of Li1–xZryFePO4 compositions.
Figure 2: Conductivity of Li1–xZryMPO4 (M = Fe, Ni) samples.
Figure 3: Elemental mapping of Li0.90Zr0.01FePO4.
Figure 4: Representation of the Li1–xZr0.01FePO4 composite.

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Acknowledgements

We gratefully acknowledge funding from the National Sciences and Engineering Research Council of Canada (NSERC) through its Discovery Grant Program. We also thank R. A. Dunlap (Physics, University of Dalhousie) for providing the Mössbauer data. We gratefully acknowledge the help of Ian Swainson (Chalk River Neutron Beam Laboratory) in acquiring neutron diffraction data on substoichiometric LixFePO4.

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  1. Department of Chemistry, University of Waterloo, 200 University Ave. West, Waterloo, N2L 3G1, Ontario, Canada

    P. Subramanya Herle, B. Ellis, N. Coombs & L. F. Nazar

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  1. P. Subramanya Herle
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Correspondence to L. F. Nazar.

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Herle, P., Ellis, B., Coombs, N. et al. Nano-network electronic conduction in iron and nickel olivine phosphates. Nature Mater 3, 147–152 (2004). https://doi.org/10.1038/nmat1063

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