Tin Nanodots Derived From Sn2+ /Graphene Quantum Dot Complex as Pillars into Graphene Blocks for Ultrafast and Ultrastable Sodium-Ion Storage.

Tin (Sn) is considered to be an ideal candidate for the anode of sodium ion batteries. However, the design of Sn-based electrodes with maintained long-term stability still remains challenging due to their huge volume expansion (≈420%) and easy pulverization during cycling. Herein, a facile and versatile strategy for the synthesis of nitrogen-doped graphene quantum dot (GQD) edge-anchored Sn nanodots as the pillars into reduced graphene oxide blocks (NGQD/Sn-NG) for ultrafast and ultrastable sodium-ion storage is reported. Sn nanodots (2-5 nm) anchored at the edges of "octopus-like" GQDs via covalent SnOC/SnNC bonds function as the pillars that ensure fast Na-ion/electron transport across the graphene blocks. Moreover, the chemical and spatial (layered structure) confinements not only suppress Sn aggregation, but also function as physical barriers for buffering volume change upon sodiation/desodiation. Consequently, the NGQD/Sn-NG with high structural stability exhibits excellent rate performance (555 mAh g-1 at 0.1 A g-1 and 198 mAh g-1 at 10 A g-1 ) and ultra-long cycling stability (184 mAh g-1 remaining even after 2000 cycles at 5 A g-1 ). The confinement-induced synthesis together with remarkable electrochemical performances should shed light on the practical application of highly attractive tin-based anodes for next generation rechargeable sodium batteries.