On the high and low temperature performances of Na-ion battery materials: Hard carbon as a case study

• Carbon coating of hard carbon allows improving first cycle coulombic efficiency.
• Hard carbon was cycled in Na cells at temperatures ranging from − 15 °C to 75 °C.
• High capacities are recorded at 75 °C (450 mAh/g) and − 15 °C (265 mAh/g).
• Very good power performance (340 mAh/g at 2C) is achieved at 75 °C.
• Decreasing IR drop was determinant to attain high capacity at high rate.

Electrochemical performance of hard carbon (HC) prepared from sugar pyrolysis was investigated against sodium anodes at temperatures ranging from − 15 °C up to 75 °C. Carbon coating was performed on HC decreasing its surface area and allowing significant improvement in terms of the first cycle coulombic efficiency and thus, irreversible capacity loss. Electrochemical performances of HC at various temperatures pointed at the IR drop of the cell being determinant for achieving the highest reversible capacity (450 mAh/g at C/10, 75 °C) and rate capability (340 mAh/g at 2C, 75 °C) ever reported. Stable cycling was also achieved at − 15 °C with reversible capacity of ca. 265 mAh/g.

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