Halogenated Functional Electrolyte Additive for Li-CO2 Batteries

In recent years, functional electrolyte additives have been widely studied during the CO2 evolution reaction (CO2ER) and CO2 reduction reaction (CO2RR) processes for Li-CO2 batteries. Owing to different concerns, functions of these additives are also multiple and limited. In this work, the multiple impacts of functional electrolyte additives for Li-CO2 batteries are discussed. N-phenylpyrrolidine (PPD) and 1-(3-bromophenyl) pyrrole (Br-PPD) are investigated as additives successively. First, the corresponding charging potential during the CO2ER process can be reduced to 3.65 V with PPD; then the Li||Li symmetric cells with Br-PPD possess a superior long-term cycling of 800 h benefited from a stable solid electrolyte interphase (SEI) on the surface of a Li metal by using a Li anode protected with bromine functional groups. In Br-PPD-based Li-CO2 cells, the charging potential can be maintained at 3.70 V for 120 cycles even with a Super P cathode. In this work, the relationship between the structural properties of organic molecules and their electrochemical applications is discussed and investigated. This is essential for the targeted design and preparation of additives in rechargeable batteries.

Unveiling the mysteries of operating voltages of lithium-carbon dioxide batteries

Lithium-carbon dioxide (Li-CO₂) batteries are regarded as a promising electrochemical system owing to their energy storage capability and CO₂ utilization. However, the reported operating voltage of ~2.6 V is increasingly questioned as seemingly beyond the capability of the electrochemical carbon dioxide reduction reaction to carbon. Herein, the real operating voltage of a Li-CO₂ battery is reacquainted, and the operating voltage and the equilibrium potential are clarified to be ~1.1 V and ~2.82 V, respectively. The products formed at low voltage are identified to be crystalline Li₂CO₃, amorphous C, and explicitly amorphous Li₂CO₃. Moreover, by decoupling small currents, 1% O₂, and 500 ppm H₂O, the operating voltage plateaus are stimulated to ~2.0 V. An ever-increasing plateau can be achieved up to the reported level of ~2.6 V activated by a minor air leak or residue in test environments. Conclusively, the operating voltages of Li-CO₂ batteries are proposed to be deceptive and extremely sensitive to the surrounding environments. This work unveils the real operating voltage and provides the voltage regulation rules to advance next-generation Li-CO₂ batteries.

Boosting the reaction kinetics in aprotic lithium-carbon dioxide batteries with unconventional phase metal nanomaterials

Given the high energy density and eco-friendly characteristics, lithium-carbon dioxide (Li-CO₂) batteries have been considered to be a next-generation energy technology to promote carbon neutral and space exploration. However, Li-CO₂ batteries suffer from sluggish reaction kinetics, causing large overpotential and poor energy efficiency. Here, we observe enhanced reaction kinetics in aprotic Li-CO₂ batteries with unconventional phase 4H/face-centered cubic (fcc) iridium (Ir) nanostructures grown on gold template. Significantly, 4H/fcc Ir exhibits superior electrochemical performance over fcc Ir in facilitating the round-trip reaction kinetics of Li⁺-mediated CO₂ reduction and evolution, achieving a low charge plateau below 3.61 V and high energy efficiency of 83.8%. Ex situ/in situ studies and theoretical calculations reveal that the boosted reaction kinetics arises from the highly reversible generation of amorphous/low-crystalline discharge products on 4H/fcc Ir via the Ir-O coupling. The demonstration of flexible Li-CO₂ pouch cells with 4H/fcc Ir suggests the feasibility of using unconventional phase nanomaterials in practical scenarios.