is inevitable in Li-CO 2 batteries, [11,12] Li-CO 2 /O 2 batteries, [8,13] and even Li-air batteries. [14] Exception is that the discharge products could be different without the generation of Li 2 CO 3 under specific conditions including protected anodes and effective electrolytes. [15,16] Li 2 CO 3 decomposes to CO 2 when the potential is higher than 3.8 V versus Li/Li + . Notably, O 2 evolution is not detected, as is expected according to the decomposition reaction 2Li 2 CO 3 → 4Li + + 4 e -+ 2CO 2 + O 2 . Instead, superoxide radicals or "nascent oxygen" form during the self-decomposition of Li 2 CO 3 . [12,17] More accurate verification was performed through chemical probes, which qualitatively detected the existence of singlet oxygen ( 1 O 2 ). [18] Parasitic reactions of electrolytes and catalyst degradation were then induced by Li 2 CO 3 oxidation. [12,18] Therefore, efficient air cathodes are expected to change this situation.The introduction of metal nanoparticles could limit side reactions and promote the interaction between Li 2 CO 3 and C. [11,[19][20][21] Beyond this, metal-organic frameworks or surface modified carbon materials also brought unexpected electrochemical performance. [22,23] Therefore, catalysts play important roles in Li-CO 2 batteries. [24][25][26][27][28][29] As mentioned above, self-decomposition of Li 2 CO 3 induced a series of parasitic reactions, and further influenced the stability of catalysts during the operation of Li-CO 2 batteries. Only by clarifying the changes of catalysts in this process can we design more stable Li-CO 2 batteries. In previous reports, mono metal catalysts (Ru, Cu, Au, and Ni) exhibited outstanding activity toward Li-CO 2 batteries and revealed some changes in electrochemical processes. [19][20][21] Nevertheless, there exist shortcomings with mono metal catalysts from materials preparation to electrochemical processes. First, for example, the preparation for monodispersed Ru nanoparticles was often achieved under mild experimental conditions without the generation of stable crystal surfaces, further affecting catalytic activity in Li-CO 2 batteries. [21,30] Second, the incompatibility between the discharge products and mono metal nanomaterials might lead to severe agglomeration and dropping during long cycles. [20,31] In this work, we designed a composite of ruthenium-copper nanoparticles highly co-dispersed on graphene (Ru-Cu-G), and this composite cathode endows Li-CO 2 batteries with low overpotential and excellent cyclability through their synergistic Li-CO 2 batteries are attractive electrical energy storage devices; however, they still suffer from unsatisfactory electrochemical performance, and the kinetics of CO 2 reduction and evolution reactions must be improved significantly. Herein, a composite of ruthenium-copper nanoparticles highly co-dispersed on graphene (Ru-Cu-G) as efficient air cathodes for Li-CO 2 batteries is designed. The Li-CO 2 batteries with Ru-Cu-G cathodes exhibit ultra-low overpotential and can be operated for 100 cycles with ...

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As an attractive cathode candidate for sodium-ion batteries, P2-type Na 2/3 Ni 1/3 Mn 2/3 O 2 is famous for its high stability in humid air, attractive capacity, and high operating voltage. However, the low Na + transport kinetics, oxygen-redox reactions, and irreversible structural evolution at high-voltage areas hinder its practical application. Herein, a comprehensive study of a microbar P2-type Ni 2/3 Ni 1/4 Mg 1/12 Mn 2/3 O 2 material with {010} facets is presented, which exhibits high reversibility of structural evolution and anionic redox activity, leading to outstanding rate capability and cyclability. The notable rate performance (53 mA h g −1 at 20 C, 2.0− 4.3 V) contributed to the high exposure of {010} facets via controlling the growth orientation of the precursor, which is certified by density functional theory calculation and lattice structural analysis. Mg substitution strengthens the reversibility of anionic oxygen redox and structural evolution in high-voltage areas that was confirmed by the in situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy tests, leading to outstanding cyclic reversibility (68.9% after 1000 cycles at 5 C) and slowing down the voltage fading. This work provides new insights into constructing electrochemically active planes combined with heteroatom substitution to improve the Na + transport kinetics and structural stability of layered oxide cathodes for sodium storage.

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