Interactive Multiscale Modeling to Bridge Atomic Properties and Electrochemical Performance in Li-CO$_2$ Battery Design
Li-CO$_2$ batteries are promising energy storage systems due to their high theoretical energy density and CO$_2$ fixation capability, relying on reversible Li$_2$CO$_3$/C formation during discharge/charge cycles. We present a multiscale modeling framework integrating Density Functional Theory (DFT), Ab-Initio Molecular Dynamics (AIMD), classical Molecular Dynamics (MD), and Finite Element Analysis (FEA) to investigate atomic and cell-level properties. The considered Li-CO$_2$ battery consists of a lithium metal anode, an ionic liquid electrolyte, and a carbon cloth cathode with Sb$_{0.67}$Bi$_{1.33}$Te$_3$ catalyst. DFT and AIMD determined the electrical conductivities of Sb$_{0.67}$Bi$_{1.33}$Te$_3$ and Li$_2$CO$_3$ using the Kubo-Greenwood formalism and studied the CO$_2$ reduction mechanism on the cathode catalyst. MD simulations calculated the CO$_2$ diffusion coefficient, Li$^+$ transference number, ionic conductivity, and Li$^+$ solvation structure. The FEA model, parameterized with atomistic simulations data, reproduced the available experimental voltage-capacity profile at 1 mA/cm$^2$ and revealed spatio-temporal variations in Li$_2$CO$_3$/C deposition, porosity, and CO$_2$ concentration dependence on discharge rates in the cathode. Accordingly, Li$_2$CO$_3$ can form large and thin film deposits, leading to dispersed and local porosity changes at 0.1 mA/cm$^2$ and 1 mA/cm$^2$, respectively. The capacity decreases exponentially from 81,570 mAh/g at 0.1 mA/cm$^2$ to 6,200 mAh/g at 1 mA/cm$^2$, due to pore clogging from excessive discharge product deposition that limits CO$_2$ transport to the cathode interior. Therefore, the performance of Li-CO$_2$ batteries can be improved by enhancing CO$_2$ transport, regulating Li$_2$CO$_3$ deposition, and optimizing cathode architecture.