Stable, hierarchical MWCNT/δ&γ-MnO2 composite cathode for high-performance solid-state Li-CO2 batteries

Abstract

Li-CO2 batteries (LCBs) hold great promise for energy storage and CO2 utilization, yet their practical use is hindered by limited reversibility, high polarization, and safety concerns associated with liquid electrolytes. To address these issues, we introduced an all-solid-state LCB incorporating a NASICON-type lithium aluminum titanium phosphate (LATP) solid electrolyte and a novel MWCNT/S &gamma-MnO2 composite cathode, where the distinct roles of the MnO2 phases were systematically investigated, with S-MnO2 enhancing CO2 adsorption and gamma-MnO2 improving Li-ion diffusion. The developed cell exhibits remarkable electrochemical performance, achieving a high full-depth discharge capacity of 35,502 mAh g-1, stable cycling for over 1000 hat 100 mA g-1, and substantially reduced polarization. These results are attributed to the synergistic interactions of the cathode components, with the S-MnO2 facilitating the CO2 adsorption, gamma-MnO2 promoting the Li-ion diffusion, and the conductive MWCNT network boosting the electronic conductivity. Additionally, the high density and robust microstructure of the LATP electrolyte ensures reliable long-term operation and contributes to the high capacity by enabling a wider stable electrochemical window compared to liquid electrolytes. Comprehensive post-cycle analyses confirmed the improved performance, effective Li2CO3 formation/decomposition, and catalyst structural integrity. These findings offer a viable strategy, rooted in a well-defined synergistic catalytic mechanism, to overcome critical challenges, enabling safer and more efficient LCBs.