Reversible Hybrid Aqueous Li-CO₂ Batteries with High Energy Density and Formic Acid Production

Metal-CO₂ batteries, an attractive technology for both energy storage and CO₂ utilization, are typically classified into organic Li(Na)-CO₂ batteries with a high energy density/output voltage and aqueous Zn-CO₂ batteries with flexible chemical production. However, achieving both high-efficiency energy storage and flexible chemical production is still challenging. In this study, a reversible hybrid aqueous Li-CO₂ battery is developed, integrating Li with an aqueous phase, which exhibits not only a high operating voltage and energy density but also highly selective formic acid production. Based on a Li plate as the anode, NaCl solution as the aqueous electrolyte, solid electrolyte Li_1.5 Al_0.5 Ge_1.5 P₃ O₁₂ (LAGP) as a separator and Li⁺ transporter, and a bifunctional Pd-based electrocatalyst as the cathode, the resulting battery shows a high discharge voltage of up to 2.6 V, an outstanding energy conversion efficiency of above 80 %, and remarkable selectivity of CO₂ -to-HCOOH conversion of up to 97 %. The related reaction mechanism is proposed as CO₂ +2 Li+2 H⁺ ⇌HCOOH+2 Li⁺ .