Effect of Sb3+ doping on the electrochemical performance of a LATP solid electrolyte

Abstract

NASICON-type solid electrolyte Li_1.3Al_0.3Ti_1.7P₃O₁₂ (LATP) is attractive because of its cheap raw materials, excellent air stability, and high ionic conductivity. However, due to the poor sintering performance and the easy reduction of Ti⁴⁺ by lithium metal, the grain boundary resistance is high and the interface between the solid electrolyte and lithium anode is unstable. In this paper, the LATP solid electrolyte was synthesized by doping Sb³⁺ with a larger ion radius and stronger electronegativity instead of Ti⁴⁺ by a solid-state method. The effects of different doping amounts of Sb³⁺ on the electrochemical performance of the solid electrolyte were systematically studied. It was found that a small amount of Sb³⁺ doping not only increases the concentration of oxygen vacancies, thereby facilitating Li⁺ ion transfer, but also induces the segregation of the secondary phase, LiTiPO₅, at the grain boundaries, which promotes grain growth and increases density. Excessive Sb³⁺ doping, however, shifts the secondary phase from the orthorhombic to the triclinic system, which is less favorable for Li⁺ ion transfer, and leads to abnormal grain growth. The optimal total ionic conductivity of 0.56 mS cm⁻¹ was achieved with a 0.5 wt% addition of Sb₂O₃, significantly enhancing the bulk density to 2.83 g cm⁻³. In addition, the Sb³⁺-doped LATP solid-state electrolyte-assembled full cell provides 152.30 mA h g⁻¹ high discharge specific capacity, and can operate stably for 100 cycles, with an average coulomb efficiency of 98.5%.