Due to high voltage and theoretical capacity over 300 mAh/g, LiCoSiO is a promising compound of polyoxyanion cathode materials for lithium ion batteries. However, LiCoSiO presents obscuring complex polymorphism and unusual difficulty to realize a practical electrochemistry. Here, we report first-principles computations in coupling with simulated Xrd to characterize structures and electrochemical properties of LiCoSiO (x=2, 1.5, 1) with symmetries Pmn2, Pbn2 and P2/n. The calculated Xrd spectra and voltage profiles agree well with available experimental results. We show that the CoO tetrahedra, as the key units, present their fingerprint in the Xrd spectra and determine electrochemical behaviors of LiCoSiO polymorphs. Spin ordering and Xrd spectra of bonding characteristic associated with the oxidation of CoO tetrahedra are predicted for further experimental investigation. Delithiated phases are intrinsic Mott insulators. The swapping of insulating gap states during delithiation correlates with the contraction of the oxidized CoO units, demonstrating the occurring of Peierls distortions. The resulting electron localization is responsible for capacity quality degrading. Our results provide guidance for further realization of high performance polymorphs suitable for applications.
Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences
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