Dilithium phthalocyanine - A Single Ion Transport Interfacial layer for Solid-State Lithium Batteries

All-solid-state batteries possess several advantages including high safety, flexibility to use high-capacity metal anodes and are projected to be the next generation energy storage devices. Garnet-type cubic Li7La3Zr2O12 (LLZO) solid electrolyte is of particular interest due to its high ionic conductivity under ambient conditions and compatibility with Li metal. However, large electrode/electrolyte interfacial resistance constraints their development. Herein, the use of a highly lithium ion conducting dilithium phthalocyanine (Li2Pc) as an interlayer is proposed to effectively suppress the high impedance at the interface thus improving the electrode-electrolyte contact. Fast Li+ mobility and high dielectric constant of dilithium phthalocyanine enhance the kinetics of Li+ transport across the interface. A significant reduction in overpotential and very stable stripping/plating cycling are observed in lithium symmetric cells upon introducing Li2Pc interlayer as compared to the use of bare tantalum doped lithium lanthanum zirconium oxide (LLZTO) electrolyte. Cells comprising interlayer-modified Li|LLZTO|LiFePO4 show high capacity with excellent cycling and rate capability. The performance of full cells using lithiated graphite and lithium titanate anodes has also been evaluated. This study presents a promising application of garnet electrolytes towards the advancement of solid-state lithium batteries.