Rhombohedral Li1-xZr2-xSbx(PO4)3 electrolytes with improved Li+ conductivity for high-performance solid-state Li-metal battery

Recent studies on solid electrolytes have promoted the development of solid-state Li-metal batteries (SSLBs). The NASICON-type LiZr2(PO4)(3) (LZP) electrolyte has received less attention due to its low conductivity and the existence of several crystal forms, which have impeded the development of LZP-based materials for SSLBs. Herein, Li1-xZr2-xSbx(PO4)(3) (LZSP) ceramics were synthesized by solid-state method, and the cycle performances of symmetrical cell and Li-metal battery using LZSP electrolyte were characterized for the first time. The Sb5+ doping stabilizes the rhombohedral phase at room temperature and results in distortions in the ZrO6 octahedron and PO4 tetrahedron, which lead to variations of bond length and bond angle. The room temperature total conductivity of Li0.94Zr1.94Sb0.06(PO4)(3) (LZSP-0.06) increased to 6.53 x 10(-5) S<middle dot>cm(-1). This rise can be attributed to a reduction of the Li+ ions transport barrier originated from variations of bond length, bond angle and Raman vibrations mode. The Li/LZSP-0.06/Li symmetrical cell maintains a stable cycle duration of 670 h at a current density of 0.12 mA cm(-2). The specific capacity of Li/LZSP-0.06/LiFePO4 battery reaches 140.1 mAh g(-1) at 0.5C and the coulombic efficiency is 99.8 %. This battery maintains 80 % capacity after 105 cycles. These results provide reference significance for the research on SSLBs using LZP-based electrolytes. In general, the Li0.94Zr1.94Sb0.06(PO4)(3) ceramic appears to be a promising solid electrolyte for SSLBs.