External ligand-free nickel-catalyzed synthesis of polypyrazines towards stable, high-capacity and low-potential sodium ion storage

Sodium ion batteries (SIBs) have been regarded as a promising alternative to lithium-ion battery owing to low cost and good sustainability, but its competitiveness in energy storage is still limited largely by the development of suitable electrode materials. Traditional inorganic anode materials for SIBs face the problems of sluggish electrochemical kinetics and large volume strain due to the insertion/extraction of large size Na + . By comparison, organic anodes have the advantages of abundance resources, renewability, and designability, but suffer from the lack of stable electrode materials with both high specific capacity and low redox potential. Here, a class of pyrazine rings-rich organic polymers (polypyrazines) were designed and synthesized through external ligand-free nickel-catalyzed carbon–carbon coupling reactions. Among them, poly(2,6-pyrazine) shows the lowest synthetic cost, the highest porosity and the best conductivity. Consequently, as the anode of SIBs, poly(2,6-pyrazine) delivers a low redox potential (about 1 V, vs Na + /Na), high-specific-capacity (617.2 mA h/g at 0.1 A/g), excellent rate-capability (300 mA h/g at 10 A/g) and long-term cycling stability (81 % after 1000 cycles at 1.0 A/g). The low preparation cost and outstanding electrochemical performance of poly(2,6-pyrazine) make it a promising anode candidate for further boosting the energy density of SIBs.