(Student Battery Slam Best Presentation Award Winner) Enhancing the Stability of the Electrode/Electrolyte Interface in Solid State Li-Ion Batteries

Abstract

All-solid-state Lithium-ion batteries (LIBs) based on solid ceramic electrolytes are a promising next-generation energy storage technology for high energy density and enhanced cycle life. A key requirement for such batteries is packing high energy in low form factor (i.e. in thin-film form) to increase both the gravimetric and volumetric energy densities. Lithium superionic conducting (LISICON) solid electrolytes are prominent candidates among liquid, gel, polymer and solid electrolytes that can enable safety and optimum performance in a high energy density battery with thin-film cell components. One particular LISICON material, lithium aluminum germanium phosphate (LAGP), is a promising solid-electrolyte due to its high ionic conductivity (~ 5 mS/cm at 23 °C), high electrochemical stability window (> 5V), and single Li+ ion conduction (high transference number, low porosity mitigating dendrite propagation), enabling a high energy battery and mitigating safety and packaging issues of conventional LIBs. However, most solid electrolytes, suffer from low chemical stability with the lithium (Li) anode. This is especially true for LAGP, with such chemical instability invariably leading to the formation of a highly resistive electrode/electrolyte interface which is detrimental for high power and cell longevity. Therefore, despite the promise of solid ceramic electrolytes for next-generation solid-state LIBs, if they are to be practical for use in solid-state LIBs with Li metal anodes, it is very important to design a chemically stable interface with kinetically efficient charge transport processes (i.e. Li+ transport). In order to enhance the chemical stability of the electrode/electrolyte interface, we identified lithium compatible materials (such as thin film of lithium phosphorus oxynitride (LIPON), gold (Au), carbon nanotube (CNT) layer, aluminium oxide (Al2O3) and suitable methods to apply them at the Li metal/LAGP interface. The evolution of the interfacial resistance as a function of time was monitored using Electrochemical Impedance Spectroscopy (EIS). We will present data showing that the application of the lithium-compatible, thin film interfacial layer, results in enhanced stability and a significant reduction in resistance compared with the unmodified Li metal/LAGP interface, offering an interfacial engineering approach for improved performance of an all-solid-state LIB.