Homogeneous Fluorine Doping toward Highly Conductive and Stable Li<sub>10</sub>GeP<sub>2</sub>S<sub>12</sub> Solid Electrolyte for All‐Solid‐State Lithium Batteries
Nini Zhang, Qinsheng He, Lu Zhang, Jing Zhang, Liang‐Feng Huang, Xiayin Yao
Abstract
Abstract The unique structure and exceptionally high lithium ion conductivity over 10 mS cm −1 of Li 10 GeP 2 S 12 have gained extensive attention in all‐solid‐state lithium batteries. However, its poor resistivity to moisture and chemical/electrochemical incompatibility with lithium metal severely impede its practical application. Herein, a fluorine functionalized Li 10 GeP 2 S 12 is synthesized by stannous fluoride doping and employed as a monolayer solid electrolyte to realize stable all‐solid‐state lithium batteries. The atomic‐scale mechanism underlying the impact of fluorine doping on both moisture and electrochemical stability of Li 10 GeP 2 S 12 is revealed by density functional theory calculations. Fluorine surface doping significantly reduces surface hydrophilicity by electronic regulation, thereby retarding the hydrolysis reaction of Li 10 GeP 2 S 12 . After exposed to a relative humidity of 35%–40% for 20 min, the ionic conductivity of Li 9.98 Ge 0.99 Sn 0.01 P 2 S 11.98 F 0.02 maintains as high as 2.21 mS cm −1 , nearly one order of magnitude higher than that of Li 10 GeP 2 S 12 with 0.31 mS cm −1 . Meanwhile, bulk doping of highly electronegative fluorine promotes the formation of lithium vacancies in the Li 10 GeP 2 S 12 system, thus allowing stable lithium plating/stripping in Li | Li symmetric batteries, boosting a critical current density reaching 2.1 mA cm −2 . The LiCoO 2 | lithium all‐solid‐state batteries display improved cycling stability and rate capability, showing 80.1% retention after 600 cycles at 1C.