锂离子电池负极材料NiSi2嵌锂性质的第一性原理研究

First-principle study of Li-insertion properties of NiSi_2 as anode materials for lithium-ion batteries

采用基于密度泛函理论的第一性原理方法研究锂离子电池负极材料NiSi_2的嵌锂路径。首先计算Li嵌入NiSi_2各反应的嵌锂形成能、理论质量比容量和体积膨胀率,然后研究Li_xNi_8Si_4(x=0,1,4)的电子结构,计算其能带结构、态密度和差分电荷密度。研究结果表明:Li嵌入NiSi_2最有可能的3步反应路径为12Li^++12e^-+7NiSi_2→Li_(12)Si_7+7Ni Si,13Li^++13~e-+8NiSi→Li_(13)Si_4+4δ-Ni_2Si和Li^++e^-+δ-Ni_2Si→Li Ni_2Si;Li_xNi_8Si_4呈现出金属特性,Ni-Si之间形成较强的共价键,能够有效缓解嵌锂过程中的体积膨胀,稳定基体骨架,从而提高材料的循环性能。

First-principle calculation based on the density functional theory was employed to investigate the reaction pathway of NiSi2 with Li. Li-intercalation formation energy, specific capacity and volume expansion ratio of NiSi2 as well as its lithiated products were calculated. Then, the energy band structure, density of states and deformation charge density of LixNi8Si4 （x=0, 1, 4） phases were discussed to study their electronic structures. The results show that the most possible reaction pathway for Li-insertion into NiSi2 is as follows： firstly, Li reacts with NiSi2 to form Li12Si7 and NiSi, then Li reacts with NiSi to produce Li13Si4 and δ-Ni2Si, and finally ternary compound LiNi2Si is formed by further lithiation of δ-Ni2Si. LixNi8Si4 reveals metallic feature, and there exists strong covalent bond between Ni and Si. Moreover, the strong Ni-Si covalent bond can provide a stable framework during Li intercalation process, which benefits the cyclic stability.