Electrochemical and thermal properties of hard carbon-type anodes for Na-ion batteries

The hard carbon C1600 was studied as an anode material for Na-ion batteries. The electrochemical performance of the C1600 electrode was investigated in four kinds of typical electrolytes: 1 mol dm−3 NaClO4/EC–DMC, 1 mol dm−3 NaClO4/PC, 1 mol dm−3 NaPF6/EC–DMC, and 1 mol dm−3 NaPF6/PC. The C1600 electrodes showed excellent electrochemical properties in NaClO4-containing electrolytes. An initial Na insertion/extraction capacity of 413/321 mAh g−1 was obtained in the NaClO4/EC–DMC electrolyte, followed by a good capacity retention of 90% over 50 cycles. These are the best electrochemical properties reported thus far for carbonaceous anode materials in Na-ion batteries. The safety risk of C1600 anodes for Na-ion batteries was evaluated by using a TG–DSC system. Based on the results of DSC analysis for simple electrolytes, the thermal behaviors of mixtures of the sodiated/lithiated C1600 and the associated electrolyte in a temperature range from room temperature to 400 °C were investigated and compared. The C1600 anodes showed better thermal stability in EC–DMC-based electrolytes than in PC-based ones. Moreover, although Na metal is much more unstable than Li metal, the anode and electrolyte mixture of Na-ion batteries showed similar or better thermal stability than that of Li-ion batteries. •Hard carbon C1600 was applied as an anode active material for Na-ion batteries.•A high reversible capacity of ∼290 mAh g−1 was maintained over 50 cycles.•The dependence of the electrochemical properties of C1600 on electrolytes was studied.•Sodiated C1600 was more thermally stable than lithiated C1600 in electrolytes.•Na-ion batteries seem to be more thermally stable than Li-ion batteries.