From Li₂CO₃ to Li₂C₂O₄: Understanding Discharge Product Decomposition in Li-CO₂ Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Rechargeable lithium-carbon dioxide (Li-CO2) batteries offer dual functionality for CO2 capture and energy storage.
• The practical application of Li-CO2 batteries is hindered by the high decomposition potential and slow kinetics of the Li2CO3 discharge product.
• Lithium oxalate (Li2C2O4) has emerged as a promising alternative discharge product with superior electrochemical decomposition properties.

Purpose of the Study:

• To comprehensively investigate and compare the physical and chemical differences between Li2CO3 and Li2C2O4.
• To elucidate the decomposition mechanism of Li2C2O4 in Li-CO2 batteries.
• To provide mechanistic insights for enhancing Li-CO2 battery performance.

Main Methods:

• Density Functional Theory (DFT) calculations, including climbing image nudged elastic band (CI-NEB) calculations.
• Ab initio molecular dynamics (AIMD) simulations.
• Analysis of electronic structures and bonding characteristics.

Main Results:

• Both Li2CO3 and Li2C2O4 are electronic insulators, but exhibit rapid lithium diffusion when lithium vacancies are present.
• The presence of C-C covalent bonds in the C2O4 group of Li2C2O4 facilitates its lower decomposition potential and barrier-free release of CO2 upon delithiation.
• Decomposition of Li2CO3 involves slow, cooperative dissociation of CO3 groups, whereas Li2C2O4 undergoes simultaneous dissociation of C2O4 with delithiation, enabling fast and continuous decomposition.

Conclusions:

• The C-C bond in Li2C2O4 is crucial for its facile decomposition, offering a significant advantage over Li2CO3.
• Understanding the distinct decomposition mechanisms of Li2CO3 and Li2C2O4 provides a pathway for designing advanced Li-CO2 batteries.
• This research offers fundamental insights to guide the development of high-performance CO2 capture and energy storage systems based on Li-CO2 batteries.