Electrochemical investigation of Sn-Co alloys as anode for Na-ion batteries

The effect of Co amount on the sodium storage properties of Sn_1-xCo_x (x = 0.2–0.5) alloys is systematically investigated. The trade-off between the cycle stability and the reversible capacity is identified. It is found that the reduced capacity with increased amount of Co is not only due to its inactive nature towards reaction with Na, but also because of its poor Na⁺ diffusion rate, which hinders the accessibility of “Sn” in Sn_1-xCo_x (x = 0.2–0.5) alloys. The optimal sample, Sn_0.7Co_0.3, delivers a reasonably high reversible capacity and shows a good cycle stability (i.e., delivers ∼200 mAh/g over 80 cycles and ∼300 mAh/g over 60 cycles at room temperature and 40 °C, respectively).