Achieving High Pseudocapacitance Anode By An In Situ Nanocrystallization Strategy For Ultrastable Sodium-Ion Batteries

Conversion/alloying type anodes have shown great promise for sodium-ion batteries (SIBs) because of their high theoretical capacity. However, the poor structural stability derived from the large volume expansion and short lifetime impedes their further practical applications. Herein, we report a novel anode with a pomegranate-like nanostructure of SnP2O7 particles homogeneously dispersed in the robust N-doped carbon matrix. For the first time, we make use of in situ self-nanocrystallization to generate ultrafine SnP2O7 particles with a short pathway of ions and electrons to promote the reaction kinetics. Ex situ transmission electron microscope (TEM) shows that the average particle size of SnP2O7 decreases from 66 to 20 nm successfully based on this unique nanoscale-engineering method. Therefore, the nanoparticles together with the N-doped carbon contribute a high pseudocapacitance contribution. Moreover, the N-doped carbon matrix forms strong interaction with the self-nanocrystallization ultrafine SnP2O7 particles, leading to a stable nanostructure without any particle aggregation under a long-cycle operation. Benefiting from these synergistic merits, the SnP2O7@C anode shows a high specific capacity of 403 mAh g(-1) at 200 mA g(-1) and excellent cycling stability (185 mAh g(-1) after 4000 cycles at 1000 mA g(-1)). This work presents a new route for the effective fabrication of advanced conversion/alloying anodes materials for SIBs.