Upgrading Cycling Stability and Capability of Hybrid Na‐CO₂ Batteries via Tailoring Reaction Environment for Efficient Conversion CO₂ to HCOOH

Abstract Rechargeable Na‐CO₂ batteries are considered to be an effective way to address the energy crisis and greenhouse effect due to their dual functions of CO₂ fixation/utilization and energy storage. However, the insolubility and irreversibility of solid discharge products lead to poor discharge capacity and poor cycle performance. Herein, a novel strategy is proposed to enhance the electrochemical performance of hybrid Na‐CO₂ batteries, using water‐in‐salt electrolyte (WiSE) to establish an optimal reaction environment, regulate the CO₂ reduction pathway, and ultimately convert the discharge product of the battery from Na₂CO₃ to formic acid (HCOOH). This strategy effectively resolves the issue of poor reversibility, allowing the battery to exhibit excellent cycle performance (over 1200 cycles at 30 °C), especially under low‐temperature conditions (2534 cycles at −20 °C). Furthermore, density functional theory (DFT) calculations and experiments indicate that by adjusting the relative concentration of H/O atoms at the electrolyte/catalyst interface, the CO₂ reduction pathway in the battery can be regulated, thus effectively enhancing CO₂ capture capability and consequently achieving an ultra‐high discharge specific capacity of 148.1 mAh cm⁻². This work effectively promotes the practical application of hybrid Na‐CO₂ batteries and shall provide a guidance for converting CO₂ into products with high‐value‐added chemicals.