Preparation of Zn_0.76Co_0.24S@C yolk-shell sphere with phenonic resin derived carbon layer and its high electrochemical performance for sodium-ion batteries

Drastic volume expansion and low intrinsic conductivity have limited the practical implementation of transition metal sulfides in Sodium-ion batteries (SIBs). Herein, Zn_0.76Co_0.24S@C yolk-shell sphere was prepared by a hydrothermal method, following an in-situ polymerization of phenolic resin and carbonization process. The yolk-shell structure of Zn_0.76Co_0.24S@C with carbon protective layer provides sufficient buffer zones for the release of mechanical stresses and large volume changes associated with intercalation and extraction process of Na⁺. Meanwhile, the conductivity of the electrode material is also improved due to the design of the carbon protective layer. It delivers a capacity of 392.1 mA h g⁻¹ at a current density of 2 A g⁻¹ after 1000 cycle, attenuates only 0.0178% per cycle, and a great rate performance of 279.5 mA h g⁻¹ at 5 A g⁻¹. This experiment provides a creative idea for the design and synthesis of electrode materials for SIBs.