Multi-Yolk–Shell Sn/Cu₆Sn₅@N–C Nanospheres Facilitate Na⁺/e^– Transfer at SEI, Enabling 90.8% Capacity Retention at 10 C

Tin (Sn) anode is a prospective anode for high specific capacity sodium ion batteries (SIBs). Nevertheless, tin suffers from extensive volume expansion during the charge/discharge, which results in huge internal resistance and rapid capacity decay in SIBs. Herein, a hierarchical buffer structure of Cu 6 Sn 5 and nitrogen-doped carbon coating matrix is designed via the Oswald ripening process, CuO and PDA coating, and thermal reduction to obtain the multi-yolk–shell Sn/Cu 6 Sn 5 @N–C anode material (SCN). The hierarchical buffer structure of SCN can minimize mechanical stress, avoid agglomeration, and enhance fast Na + /e – transfer at the solid electrolyte interface (SEI), which endows the SCN anode with greatly reduced contact impedance and stable long cycle performance. Consequently, the SCN anode reveals an outstanding specific reversible capacity of 440.1 mA h g –1 after 1000 cycles at 1 A g –1 with an ultralow decay of 0.024% per cycle. Even at 10 C, the specific capacity is maintained up to 486.6 mA h g –1 having a capacity retention of 90.8%, indicating outstanding rate performance.