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Rechargeable Li–CO2 batteries are promising energy storage systems for reducing fossil fuel consumption and mitigating the “greenhouse effect” due to the reversible reaction between lithium ions and carbon dioxide. The addition of metal nanoparticles with high catalytic activities can accelerate the reaction between Li2CO3 and carbon during the charge process, but more work is required to accurately describe how metal nanoparticles work in Li–CO2 batteries. In this study, a gel-like film synthesis mechanism method is presented for the preparation of a composite of Cu nanoparticles that are highly dispersed on N-doped graphene (Cu-NG), which acts as an efficient cathode for Li–CO2 batteries. Additionally, Cu-NG can achieve a low overpotential of 0.77 V and has excellent cyclability (50 cycles). It is speculated that superoxide radicals generated from the self-decomposition of Li2CO3 unavoidably corrode electrodes during the charge process. Nevertheless, the surface of the Cu nanoparticles forms a 3–5 nm thick CuO film that protects and stabilizes the cathode during later cycles. This study may open up new directions and strategies for developing highly efficient cathodes and provide a better understanding of the electrochemical processes of Li–CO2 batteries. [ABSTRACT FROM AUTHOR]

Lithium sulfide (Li2S), which has a high theoretical specific capacity of 1166 mA h g−1, has potential application in cathode materials because of its high safety and compatibility with lithium-free anodes for Li–S batteries. However, its low electron conductivity and lithium transfer cause significant polarization in Li2S electrodes. Here, we demonstrate the use of ultrasmall Li2S nanocrystals encapsulated in N-rich carbon (NRC) as a cathode material for Li–S batteries. By evaporating a mixture of polyacrylonitrile (PAN) and Li2S in dimethylformamide (DMF) solution and then subjecting the mixture to carbonization, a nano-Li2S@NRC composite with ultrasmall Li2S well dispersed in its carbon matrix was successfully synthesized. The obviously lower potential barriers and excellent cycling performance of nano-Li2S@NRC electrodes confirm their improved polarization because of the size effect of Li2S nanocrystals and the good electron transfer between Li2S and N-doped carbon. The nano-Li2S@NRC cathode delivers a high initial specific capacity of 1046 mA h g−1 of Li2S (∼1503 mA h g−1 of S) at 0.25C and 958 mA h g−1 of Li2S (∼1376 mA h g−1 of S) at 0.5C with a favorable cycling performance with an ∼0.041% decay rate per cycle over 1000 cycles. [ABSTRACT FROM AUTHOR]