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Garnet Li7La3Zr2O12(LLZO) is considered a promising solid electrolyte for all-solid-state lithium-ion batteries due to its outstanding performance in which Ga-doped LLZO particularly exhibits excellent ionic conductivity. However, the application of Ga-doped LLZO is limited by the interfacial instability between Ga-doped LLZO and Li metal. In this study, Ga3+- and Sb5+-codoped LLZO is prepared using a conventional solid-state reaction method, and the effects of dual-doping on the crystal structure, microstructure, conductivity of LLZO, and battery cycle stability are investigated. The results demonstrate that the introduction of an appropriate amount of Sb5+into Ga3+-stabilized cubic-phase LLZO promotes grain contact and enhances the total ionic conductivity. The optimized Li6.3Ga0.2La3Zr1.9Sb0.1O12solid electrolyte exhibits the highest total ionic conductivity of 4.65 × 10–4S cm–1at room temperature. Additionally, the introduction of Sb5+suppresses the formation of the LiGaO2impurity phase, thereby improving the interface stability between Ga-doped LLZO and the Li metal. The assembled Li||Ga,Sb0.1-LLZO||Li symmetric cell demonstrates stable cycling for 500 h at room temperature under a current density of 0.13 mA cm–2. The Li||Ga,Sb0.1-LLZO||LiFePO4full cell delivers a reversible capacity of about 140 mA h g–1, exhibiting negligible decay after 50 cycles. These findings suggest that the application of Ga-doped LLZO in all-solid-state lithium-ion batteries holds great promise by simply doping Zr sites with high-valence ions.

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 ZrO6octahedron and PO4tetrahedron, 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 × 10−5 S·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/LiFePO4battery reaches 140.1 mAh g−1at 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)3ceramic appears to be a promising solid electrolyte for SSLBs.

Li7La3Zr2O12(LLZO) garnet solid electrolyte has garnered significant attention as a highly promising material owing to its exceptional electrochemical properties. Nevertheless, it encounters challenges such as low ionic conductivity and inadequate interfacial properties compared to liquid electrolytes. In this study, we employed simultaneous doping of Mg2+and Ga3+to obtain a dense LLZO material with enhanced Li+conductivity. By utilizing the conventional solid-state reaction method, garnet-structured oxides with a chemical composition of Li6.55+2xGa0.15La3Zr2-xMgxO12(x = 0, 0.05, 0.1, 0.15) were synthesized. The phase composition, morphology, and lithium-ion conductivity were characterized to investigate the synergistic effects of two dopants on solid electrolytes. The density of Ga and Mg co-doped garnet pellets reached as high as 96 % - 97 %, and the peak lithium-ion conductivity of Li6.65Ga0.15La3Zr1.95Mg0.05O12electrolyte at room temperature was obtained to be 1.13 mS cm−1. Additionally, when employed in a symmetrical Li/LLZO/Li cell, this Ga and Mg co-doped garnet electrolyte exhibited excellent electrochemical stability to lithium metal and demonstrated good performance for more than 200 h in the lithium plating/stripping cycle at a current density of 0.1 mA cm−2. The LiFePO4/Ga0.15Mg0.05/Au/Li cell delivers an initial discharge capacity of 153 mAh g−1and retains a good capacity of 143.8 mAh g−1after 30 charge-discharge cycles.