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[摘要]：We disclose a distortion-assisted diffusion mechanism in Li(3)N and Li(2.5)Co(0.5)N by first-principles simulations. A B(2g) soft mode at the Gamma point is found in alpha - Li(3)N, and a more stable alpha' - Li(3)N (P (3) over bar m1) structure, which is 0.71 meV lower in energy, is further derived. The same soft mode is inherited into Li(2.5)Co(0.5)N and is enhanced due to Co doping. Consequently, unlike the usual Peierls spin instability along Co-N chains, large lithium-ion displacements on the Li-N plane are induced by a set of soft modes. Such a distortion is expected to offer Li atoms a route to bypass the high diffusion barrier and promote Li-ion conductivity. In addition, we further illustrate abnormal Born effective charges along Co-N chains which result from the competition between the motions of electrons and ion cores. Our results provide future opportunities in both fundamental understanding and structural modifications of Li-ion battery materials. |
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