Unraveling the Significance of Li⁺/e⁻/O₂ Phase Boundaries with a 3D‐Patterned Cu Electrode for Li–O₂ Batteries

Abstract

The reaction kinetics at a triple‐phase boundary (TPB) involving Li+, e−, and O2 dominate their electrochemical performances in Li–O2 batteries. Early studies on catalytic activities at Li+/e−/O2 interfaces have enabled great progress in energy efficiency; however, localized TPBs within the cathode hamper innovations in battery performance toward commercialization. Here, the effects of homogenized TPBs on the reaction kinetics in air cathodes with structurally designed pore networks in terms of pore size, interconnectivity, and orderliness are explored. The diffusion fluxes of reactants are visualized by modeling, and the simulated map reveals evenly distributed reaction areas within the periodic open structure. The 3D air cathode provides highly active, homogeneous TPBs over a real electrode scale, thus simultaneously achieving large discharge capacity, unprecedented energy efficiency, and long cyclability via mechanical/electrochemical stress relaxation. Homogeneous TPBs by cathode structural engineering provide a new strategy for improving the reaction kinetics beyond controlling the intrinsic properties of the materials.

Modulating the Configuration of Air Cathodes toward the Extended Triple-Phase Boundaries of Li-O2 Batteries

“…The cell with electrode B presented the largest discharge capacity among all the electrodes, at 16.0 mAh cm –2 . The increased discharge capacity of electrode B indicates an increased amount of Li 2 O 2 produced by an electrochemical reaction that requires a confluence of electrons, oxygen, and lithium ions at the same time . Even though electrode C has a slightly higher SSA than electrode B, the discharge capacity of electrode C is lower than that of electrode B, confirming that the SSA itself is not proportional to the TPB of the LOB system.…”

“…The increased discharge capacity of electrode B indicates an increased amount of Li 2 O 2 produced by an electrochemical reaction that requires a confluence of electrons, oxygen, and lithium ions at the same time. 44 Even though electrode C has a slightly higher SSA than electrode B, the discharge capacity of electrode C is lower than that of electrode B, confirming that the SSA itself is not proportional to the TPB of the LOB system. Figure 5b shows the X-ray diffraction (XRD) patterns of electrodes that underwent a galvanostatic discharge test at various capacity points.…”

“…The increased volume of air pockets in electrode B indicates that more gas phase is available within the electrode, which helps to enhance the mass transfer of oxygen , and thereby alleviates the limited capacity caused by sluggish oxygen transfer accompanying lower TPB. ,, …”

“…43 The increased volume of air pockets in electrode B indicates that more gas phase is available within the electrode, which helps to enhance the mass transfer of oxygen 14,41 and thereby alleviates the limited capacity caused by sluggish oxygen transfer accompanying lower TPB. 13,44,45 In LOBs, the diffusion coefficient is particularly informative, as it reflects the combination of mass transfer of oxygen and lithium-ion transport. The transport properties of oxygen and lithium ions are determined through CV at various scan rates (Figure S4).…”

Nanoengineering of Cathode Catalysts for Li–O2 Batteries

“…13,33−38 Another difference from LIBs is that Li−O 2 batteries exhibit high charging overpotentials, resulting in lower energy efficiency (Figure 1b). 12,39,40 The reasons for the high overpotentials will be discussed in more detail in the subsequent challenges section. In Li−O 2 batteries, the ORR process involves a series of chemical and electrochemical processes.…”