Organic Cathode for Lithium Batteries, Enabled by Solid-State LLZO Separator

Abstract

Small organic molecule quinones are promising as cathode active materials for Li batteries. They have high theoretical capacity (up to ~500 mAh/g) at moderate voltage (2 to 3V vs. Li/Li+). However, in conventional Li-ion batteries with liquid electrolyte, they dissolve and cross through the membrane, leading to reaction with the Li anode. To solve this issue, we employ a dense lithium garnet solid electrolyte (LLZO) as the separator to block transport of the organic cathode material. This work demonstrates solid electrolyte/liquid catholyte hybrid battery cells with metallic Li alloy as the anode and lawsone, a biologically-derived quinone, as the cathode. LLZO is used as a separator and effectively prevents dissolved cathode material from meeting the anode. Lawsone LLZO hybrid cells reached cathode utilization of up to 67% based on lithiation of both carbonyl groups, and had little self-discharge compared to liquid cells. A side-reaction at low voltage is identified as the main source of capacity fade. Nevertheless, use of a solid electrolyte is shown to be a promising approach to enable use of soluble organic cathode active materials.