Insights into Changes of Lattice and Electronic Structure Associated with Electrochemistry of Li2CoSiO4 Polymorphs

分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-05-02

Zhang, CX [Zhang, Caixia][ 1,2 ] Chen, ZL [Chen, Zhenlian][ 2 ] Zeng, YZ [Zeng, Yongzhi][ 1 ] Zhang, ZF [Zhang, Zhifeng][ 2 ] Li, J [Li, Jun][ 2 ]

摘要： First-principles calculations combined with XRD simulations are performed to systematically study crystal structures, bonding characteristics and electronic structures of LixCoSiO4 (x = 2.0, 1.5, 1.0) polymorphs with symmetries Pmn21-DP and Pbn21. The calculated average voltages by lithium extraction agree well with available experiments. CoO4 tetrahedron is the key structural unit to track the process of delithiation. The oxidation of CoO4 tetrahedron results in a special pattern of bonding characteristic, which corresponds to spin ordering and may be observable in XRD spectra according to simulation. We find delithiated phases are intrinsic Mott insulators, electronic band gaps change from Mott− Hubbard-type to charge-transfer-type during lithium removing. The swapping of near-gap states is associated with the contraction of the oxidized CoO4 units, indicating Peierls distortions that may be the physical origin of capacity degrading of Co−silicate chemistry.

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