Efficient Anion Fluoride-Doping Strategy to Enhance the Performance in Garnet-Type Solid Electrolyte Li₇La₃Zr₂O₁₂

Garnet-type solid-state electrolyte Li₇La₃Zr₂O₁₂ (LLZO) is expected to realize the next generation of high-energy-density lithium-ion batteries. However, the severe dendrite penetration at the pores and grain boundaries inside the solid electrolyte hinders the practical application of LLZO. Here, it is reported that the desirable quality and dense garnet Li_6.8Al_0.2La₃Zr₂O_11.80F_0.20 can be obtained by fluoride anion doping, which can effectively facilitate grain nucleation and refine the grain; thereby, the ionic conductivity increased to 7.45 × 10^-4 at 30 °C and the relative density reached to 95.4%. At the same time, we introduced a transition layer to build the Li_6.8Al_0.2La₃Zr₂O_11.80F_0.20-t electrolyte in order to supply a stable contact; as a result, the interface resistance of Li|Li_6.8Al_0.2La₃Zr₂O_11.80F_0.20-t decreases to 12.8 Ω cm². The Li|Li_6.8Al_0.2La₃Zr₂O_11.80F_0.20-t|Li symmetric cell achieved a critical current density of 1.0 mA cm^-2 at 25 °C, which could run stably for 1000 h without a short circuit at 0.3 mA cm^-2 and 25 °C. Moreover, the Li|LiFePO₄ battery exhibited a high Coulombic efficiency (>99.5%), an excellent rate capability, and a great capacity retention (123.7 mA h g^-1, ≈80%) over 500 cycles at 0.3C and 25 °C. The Li|LiNi_0.8Co_0.1Mn_0.1O₂ cell operated well at 0.2C and 25 °C and delivered a high initial discharge capacity of 151.4 mA h g^-1 with a good capacity retention (70%) after 195 cycles. This work demonstrates that the anion doping in LLZO is an effective method to prepare a dense garnet ceramic for the high-performance lithium batteries.