Electrochemical performance of a garnet solid electrolyte based lithium metal battery with interface modification

Abstract

Garnet-type Li₇La₃Zr₂O₁₂ solid electrolyte is a promising candidate for all-solid-state batteries owing to its high lithium ion conductivity (up to 10⁻³ S cm⁻¹) and chemical stability when in contact with the lithium metal with a wide electrochemical window of 6 V. However, the realization still remains elusive mainly due to the high resistance of the electrode/electrolyte interface at room temperature. Although significant improvements have been made toward accomplishing an effective Li metal||garnet solid electrolyte interface, the cathode||garnet solid electrolyte interface is challenging due to the rigid morphology of the garnet solid electrolyte, and poor conductivity and chemical instability of the cathode materials. Herein we report an effective strategy of lowering the interfacial resistance between LiNi_0.33Mn_0.33Co_0.33O₂ (NMC) and Li_6.28La₃Zr₂Al_0.24O₁₂ (LLZA) solid electrolytes with a Li₂SiO₃ (LS) interlayer. The investigation of the NMC||LS-LLZA interface by SEM, adherence test and electrochemical symmetric cell measurement (NMC||LS-LLZA-LS||NMC) revealed that a liquid phase derived Li₂SiO₃ buffer layer, not only improves the wettability, but also assists the lithium ion conduction to the active material. On the basis of this improved interface, a bulk type all-solid-state and a quasi-solid-state (using a gel polymer electrolyte at the Li||LLZA interface) lithium metal batteries were fabricated with initial discharge capacities of 138 mA h g⁻¹ (100 °C) and 165 mA h g⁻¹ (25 °C) at 10 μA cm⁻² and 100 μA cm⁻², respectively. The quasi-solid-state battery (NMC||LS-LLZA||GPE||Li) at room temperature displays a capacity retention of 87% over 50 cycles at a higher current density of 100 μA cm⁻².