Efficient electrocatalysts for Li2CO3 decomposition play an important role in Li–CO2 batteries. In this paper, carbon nanotubes (CNTs) decorated with RuO2 is firstly introduced as cathode materials for Li–CO2 batteries. The CNT@RuO2 composite can not only deliver a high specific capacity but also a lower charge voltage. With the CNT@RuO2 cathodes, the Coulombic efficiency still remains around 100% until the 15th cycle. The charge voltage of early 30 cycles at a current of 50 mA·g–1 with a capacity limit of 500 mAh·g–1 can be fully lowered under 4.0 V. Particularly, the CNT@RuO2 cathode can realize most decomposition of prefilled Li2CO3 and show a platform at around 3.9 V. This catalytic activity toward both in situ formed and preloaded Li2CO3 is more feasible for practical application in complex environment.
Lithium carbonate, the primary discharge product in Li–CO 2 batteries with high thermodynamic stability and a wide band gap, leads to significant electrochemical inertness, limiting efficiency and cycle life. The strongly delocalized p z orbital at a lower-energy HOMO level in Li 2 CO 3 causes weak coupling with the O-p z orbitals, increasing decomposition resistance owing to d-orbital degeneracy in high-local-symmetry catalysts. This study introduces metastable tetragonal-pyramidal nickel sulfide (tp-NiS) with low-symmetry NiS 5 coordination, breaking d-orbital degeneracy and bringing d z 2 , d xz , and d yz orbitals closer to the Fermi level. Enhanced orbital overlap with Li 2 CO 3 O-p z orbitals facilitates robust Ni–O bond formation. In situ spectroscopy confirms reversible Ni–O bond formation during cycling, ensuring electron transfer and complete Li 2 CO 3 decomposition. Conversely, weak interfacial interactions in octahedral NiS with highly symmetric local coordination only allow decomposition-resistant Li 2 CO 3 and interface passivation. Consequently, tp-NiS exhibits superior electrochemical performance, with the best reported reversibility and stability, a charge potential below 4.0 V, and 92.03% capacity retention after 1800 h. This metal redox-driven mechanism establishes a reversible geometric conversion pathway, emphasizing the critical role of symmetry-engineered Ni–O interactions in bifunctional catalysts.
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