Abstract

Significance To enhance the reversibility and kinetics of Li-CO₂ batteries， this paper summarizes the history， structure，working principle， and key scientific challenges of Li-CO₂batteries. It reviews the composition， morphology， microstructure，and other characteristics of transition metal and alloy catalysts used in Li-CO₂ batteries and analyzes their impact on battery performance. Furthermore， the catalytic mechanisms and evolutionary behaviors of these catalysts during the reaction process are examined.

Progress Transition metals exhibit incomplete d orbitals， abundant and adjustable valence states， and ease of processing，allowing them for broad applications in Li-CO₂batteries. 3 d transition metals such as Ni， Co， Fe， Cu， and Zn，4 d transitionmetals such as Ru， Pd， and Ag， and 5d transition metals such as Ir and Au， all promote reactant adsorption and activation， as well as the deposition and decomposition of discharge products. Single-metal and bimetallic cathode catalysts constructed based on these elements show different catalytic activities， mechanisms， and evolutionary behaviors during catalytic process in Li-CO₂ batteries. Ni and Co undergo no redox reactions during catalysis. Cu tends to oxidize during charging and cannot effectively catalyze the co-decomposition of Li₂CO₃and elemental C， while CuO formed through oxidation during charging and discharging can significantly enhance the reversibility of battery reactions. Fe undergoes redox reactions between Fe—O—C and Fe in Li-CO₂ batteries. Zn can catalyze CO₂ reduction to generate Li₂CO₃ and CO products in proton-based Li-CO2 batteries. The electron configuration of Pd facilitates the weakening of Li-O bonds and the activation of Li₂CO3， exhibiting smaller charge-discharge polarization compared to other precious metals such as Ru， Ag， Ir， and Au. Intermetallic compounds possess unique chemical microenvironments significantly different from those of solid solution alloys， monodisperse bimetals， and single metals in atomic configurations， electronic structures， and chemical bonding， thus demonstrating distinctive advantages in promoting reactant adsorption and activation and product decomposition.

Conclusions and Prospects The study proposes several research directions for transition metals and alloy catalysts. Regulating the macroscopic morphology and surface microstructure of catalysts， as an important means to improve the density and intrinsic activity of active sites， modulate the adsorption and activation of species during reactions， and change the battery reaction pathway. Monitoring the evolution of catalyst structure and composition during the catalytic process， as well as the deposition and decomposition behaviors of discharge products， to summarize the internal relationships between catalyst composition，structure， and performance. This can provide theoretical support for catalyst design， failure analysis， and re-optimization. Establishing key “descriptors” of catalysts suitable for Li-CO₂ batteries to reduce trial-and-error processes and promote the development of high-performance catalysts. Developing cost-effective catalyst mass production techniques to select low-cost catalysts that can be applied in practical engineering， thereby guiding scientific research efforts and facilitating the practical development of Li-CO₂ batteries.

Keywords：Li-CO₂ battery； transition metal； alloy catalyst