p- and n-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 spine] Li4Ti5O12 (LTO) by designing theoretically stoichiometric Li11Ti13O32 (p-type) and Li10Ti14O32 (n-type) because LTO has a nonstoichiometric (Li)(8)[Li8/3Ti40/3]O-32 formula with the Fd3F (m) over bar 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, Li(4)Ti(5)O(12-x)Hal(x) (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.