The sluggish decomposition kinetics of insulating discharge products impose large charging overpotentials and limit the practical application of Li–CO₂ batteries. While constant-voltage charging has shown promise in overcoming kinetic barriers, the optimal charging voltage and its evolution with depth of discharge remain unclear. Here we establish, for the first time, a kinetic-window framework that identifies the depth of discharge (DOD) as the master variable governing the feasible voltage range for reversible operation in a model Ru@rGO cathode with 1 M LiTFSI/TEGDME electrolyte. The lower bound of this window rises progressively with increasing depth of discharge, driven by continuous accumulation of crystalline Li₂CO₃ and carbon that thickens the passivation layer, whereas Li₂C₂O₄ persists at a quasi-steady level through a dynamic cycle of formation, disproportionation, and regeneration. Guided by this framework, we demonstrate that the shallow-optimized 4.0 V protocol fails at deeper discharge, while 4.2 V supports 87 stable cycles at 500 μAh cm^–2. At 1000 μAh cm^–2, even 4.4 V fails to sustain long-term operation, as the required driving force exceeds the electrolyte stability limit. This work establishes DOD as the master variable for protocol design and offers a universal, boundary-governed principle that can be extended to other metal–gas batteries facing similar polarization-accumulation challenges.

Li-CO₂ batteries are among the most intriguing techniques for balancing the carbon cycle, but are challenged by the annoyed thermodynamic barrier of the Li₂CO₃ decomposition reaction. Herein, we demonstrate the electrocatalytic performances of two-dimensional (2D) CoAl-layer double hydroxide (LDH) nanosheets can be significantly improved by trans-dimensional crosslinking with three-dimensional (3D) multilevel nanoporous (MP)-RuCoAl alloy (MP-RuCoAl alloy⊥CoAl-LDH). The MP-RuCoAl alloy⊥CoAl-LDH with multiscale pore channels and abundant nano-heterointerface is directly prepared by controllable etching Al from a Ru-Co-Al master alloy along with simultaneous partial oxidization of Al and Co atoms. The MP-RuCoAl is composed of various intermetallic compounds and Ru with abundant grain boundaries, and forms numerous heterointerface with 2D CoAl-LDH nanosheets. The multiscale porous metallic network benefits mass and electron transportation as well as discharge product storage and enables a rich multiphase reaction interface. In situ differential electrochemical mass spectrometry shows that the mass-to-charge ratio in the charging process is ~ 0.733 which is consistent with the theoretical value of 3/4, stating that the reversible co-decomposition of Li₂CO₃ and C can be achieved with the MP-RuCoAl alloy⊥CoAl-LDH. The Ketjen black (KB)/MP-RuCoAl⊥CoAl-LDH battery demonstrates a high cyclability for over 2270 h (227 cycles) with a lower voltage gap stabilized at ~ 1.3 V at 200 mA·g⁻¹. Our findings here provide useful guidelines for developing high efficiency transition metal based electrocatalysts by coupling with conductive porous substrate for impelling the development of practical Li-CO₂ battery systems.