Muon spin relaxation and powder neutron diffraction have been combined to study three lithium cobalt nitride battery materials. Neutron diffraction shows that these retain the P6/mmm space group of Li3N with Co located only on Li(1) sites. The lattice parameters vary smoothly with the degree of metal substitution, such that the [Li2N] layers expand while the layer separation contracts, as observed previously for similar series of Cu- and Ni-substituted materials. However, in contrast to the latter, the Li 3-x-yCoxN phases exhibit Curie-Weiss paramagnetism and this prevents the use of nuclear magnetic resonance to measure Li+ transport parameters. Therefore, muon spin relaxation has been employed here as an alternative technique to obtain quantitative information about Li+ diffusion. Muon spin relaxation shows that Li+ diffusion in Li 3-x-yCoxN is anisotropic with transport confined to the [Li2N] plane at low temperature and exchange between Li(1) and Li(2) sites dominant at high temperature. By a comparison with previous studies some general trends have been established across a range of Cu-, Ni- and Co-substituted materials. For intra-layer diffusion Ea decreases as metal substitution increases and the corresponding expansion of the layers results in a more open pathway for Li+ diffusion. However, an optimal value of x is found with a ≈ 3.69 Å after which the concomitant contraction in layer spacing reduces the polarizability of the lattice framework.
|ジャーナル||Physical Chemistry Chemical Physics|
|出版ステータス||出版済み - 1月 21 2013|
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