In-situ Ni-oxidation-assisted coupling reduction of NiO and CO2 to synthesize core-shell Ni@octahedral carbon with energy storage properties

A bi-directional electrolysis method for synthesizing metal-carbon core-shell structure was reported, wherein a nickel-encapsulated octahedral carbon (Ni@OC) was synthesized in molten salt via the coupled electroreduction of CO2 and NiO formed by in-situ electrochemical oxidation of Ni. An in-situ generated NiO directs the self -template formation of Ni@OC. By etching the nickel core from Ni@OC with hydrochloric acid, difficult-to -prepare hollow octahedral carbon (HOC) is obtained. The plausible formation mechanism of Ni@OC was unraveled by a series of control experiments. When used as negative materials for lithium-ion batteries (LIBs), Ni@OC exhibits enhanced specific capacitance (433.6 mAh g-1 at 25 mA g-1) and stability (83.3% capacity retention after 4800 cycles at 2000 mA g-1) relative to HOC. The performance improvement can be attributed to the Ni core, which helps to improve the capacity and alleviates the structural collapse during the lithiation/ delithiation process. This study not only develops new structures but also presents a unique technological pathway for the sustainable synthesis of functional metal-encapsulated carbons.

Automated summary

A bi-directional electrolysis method was used to synthesize metal-carbon core-shell structure, and a nickel-encapsulated octahedral carbon (Ni@OC) was obtained via the electroreduction of CO2 and NiO in molten salt. By etching the nickel core, difficult-to-prepare hollow octahedral carbon (HOC) was achieved. Ni@OC exhibited improved specific capacitance and stability compared to HOC as negative materials for lithium-ion batteries, due to the presence of the Ni core.