Probing Lithium Carbonate Formation in Trace-O₂-Assisted Aprotic Li-CO₂ Batteries Using in Situ Surface-Enhanced Raman Spectroscopy

Abstract

A trace-O2-assisted aprotic Li-CO2 battery represents a promising approach for CO2 recycling. However, cathode passivation and large overpotential are frequently observed for current Li-CO2 batteries because of the insolubility and nonconductivity of the discharge product of lithium carbonate (Li2CO3). Toward maximizing the energy capabilities of the Li-CO2 electrochemistry, it is crucially important to have a fundamental understanding of the Li2CO3 formation mechanism in Li-CO2 batteries. In this report, the discharge reaction of a trace-O2-assisted Li-CO2 battery has been interrogated with in situ surface-enhanced Raman spectroscopy. It was found that in high-donor-number (DN) solvents Li2CO3 formation proceeds primarily via an “electrochemical solution route”, with peroxodicarbonate (C2O6 2–) as the key intermediate, whereas in low-DN solvents Li2CO3 forms via a chemical reaction of Li2O2 and CO2 on the cathode surface, namely, a “chemical surface route”. It is notable that during discharge the trace-O2 acts as a “pseudo-catalyst” to activate CO2 in high-DN solvents but not in low-DN solvents. The mechanistic study presented here will assist us in tailor-designing better electrolyte systems and enable more energetic electrochemistry operation far away from the poison of Li2CO3.

A molten carbonate shell modified perovskite redox catalyst for anaerobic oxidative dehydrogenation of ethane

“…As reported and characterized by Devynck and co-workers (35), molten carbonate salts can react with gaseous oxygen to form peroxide. Peng and co-workers (36) reported that CO 2 can react with lithium peroxide to form to lithium carbonate. Therefore, formation of peroxide species from carbonate is a reversible reaction, and peroxide formation will be inhibited by excess CO 2 .…”

Recent Advances in Lithium–Carbon Dioxide Batteries

“…Reproduced with permission. [ 27 ] Copyright 2019, American Chemical Society. d) Left: schematic illustration of the electrolyte structure in dilute LiTFSI/DMSO‐based Li–O 2 /CO 2 .…”

“…Recently, Zhao et al investigated the reaction pathways in Li–O 2 /CO 2 batteries with two electrolytes that were prepared with two solvents of acetonitrile (CH 3 CN (ACN)) and DMSO. [ 27 ] These two solvents exhibit different donor numbers but show similar dielectric strengths. From the results obtained by surface‐enhanced Raman spectroscopy, they concluded that the formation of Li 2 CO 3 was dependent on the donor number of electrolyte solvents.…”

“…From the results obtained by surface‐enhanced Raman spectroscopy, they concluded that the formation of Li 2 CO 3 was dependent on the donor number of electrolyte solvents. [ 27 ] In high‐donor‐number solvents (such as DMSO), C 2 O 6 2− was a key intermediate for the formation of Li 2 CO 3 [via reaction (6)]. The formation of C 2 O 6 2− was via a reaction shown in reaction (9).…”

Nano Polymorphism‐Enabled Redox Electrodes for Rechargeable Batteries

“…Conversely, in low‐DN solvents, Li 2 CO 3 was formed when Li 2 O 2 and CO 2 reacted via a “chemical surface method”. [ 215 ] Furthermore, O 2 could act as a “pseudocatalyst” to activate CO 2 in high‐DN systems but not in low‐DN electrolytes upon discharging. This mechanistic study offered guidance for improving the performance of Li–CO 2 batteries by optimizing the electrolyte system design.…”