<i>p</i>- and <i>n</i>‑type Doping Effects on the Electrical and Ionic Conductivities of Li₄Ti₅O₁₂ Anode Materials

Abstract

We systematically investigated p- and n-type doping effects on the electrical conductivity of spinel Li₄Ti₅O₁₂ (LTO) by designing theoretically stoichiometric Li₁₁Ti₁₃O₃₂ (p-type) and Li₁₀Ti₁₄O₃₂ (n-type) because LTO has a nonstoichiometric (Li)₈[Li_8/3Ti_40/3]­O₃₂ formula with the <i>Fd</i>3<i>m̅</i> space group. In this work, we present evidence that the electronic modification plays a fundamental role in the electrical conductivity of LTO, especially, n-type Li₁₀Ti₁₄O₃₂, which has superior electrical conductivity compared to p-type Li₁₁Ti₁₃O₃₂. We proposed a way to improve the electrical conductivity of pristine LTO by halogen ion doping, Li₄Ti₅O_{12–<i>x</i>}Hal_<i>x</i> (Hal: F, Cl, and Br), for an n-type doping effect. However, the substitution of halogen ions can enhance the electrical conductivity by mixing Ti⁴⁺/Ti³⁺ and impede the Li ion diffusion in the lattice. The larger size of Cl and Br increases the Li ion diffusion energy barrier with van der Waals repulsion. Therefore, our theoretical investigations of the effects of halogen doping on the electrical and ionic conductivities anticipate that the smaller-sized F may be the most promising dopant for improving the performance of LTO