二价金属元素掺杂对LiCoO2体系电子输运性质的影响

为了解释Ca掺杂与Mg掺杂在影响锂离子二次电池正极材料LiCoO₂体系电子输运性质方面的不同效应，采用基于密度泛函理论的第一性原理方法研究了该体系的电子结构.计算结果表明，虽然在LiCoO₂体系中用Ca或Mg替代Co都会在费米能级附近产生部分占据的受主带，但两者对应的电子态都具有明显的局域化特征；此外，与Mg掺杂体系明显不同的是，Ca掺杂体系的受主带与价带之间存在清晰的带隙.这一带隙的存在正是Ca掺杂不能明显提高LiCoO₂体系电导率的主要原因.此外，Ca²⁺与Mg²⁺离子半径的较大差别也是造成这两个掺杂体系的电导率存在明显差异的一个重要因素.

Effect of bivalent metal element doping on the electronic transport properties of LiCoO2

In order to understand the different effects of Ca and Mg doping on the electronic transport properties of LiCoO₂，which is the primary cathode material in Li-ion secondary batteries，the electronic structures of the relevant systems are studied with the ab initio method based on the density-functional theory. It is found that both Ca and Mg partial substitution for Co in LiCoO₂ crystal will give rise to partially occupied acceptor band near the Fermi level，but these bands are substantially localized. Moreover，Ca-doped system has a clear energy gap between the acceptor band and the valence band，whereas for the Mg-doped system there isn't such a gap. It's believed that the existence of this gap is the main factor resulting in the non-significant increase of the electronic conductivity in the Ca-doped LiCoO₂. In addition，the remarkable distinction in the ionic radii of Ca²⁺ and Mg²⁺ can also induce noticeably different effects on the electronic conductivities.