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 Li6.8Al0.2La3Zr2O11.80F0.20 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 Li6.8Al0.2La3Zr2O11.80F0.20-t electrolyte in order to supply a stable contact; as a result, the interface resistance of Li|Li6.8Al0.2La3Zr2O11.80F0.20-t decreases to 12.8 Ω cm2. The Li|Li6.8Al0.2La3Zr2O11.80F0.20-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|LiNi0.8Co0.1Mn0.1O2 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.