Doped graphene encapsulated SnP2O7 with enhanced conversion reactions from polyanions as a versatile anode material for sodium dual-ion battery

Tin-based ternary oxides have obtained much attention for energy storage systems due to high capacity based on alloying/dealloying reactions and improved cycling performance resulted from the inactive buffer matrix. Herein, SnP2O7 particles are encapsulated into N/P dual-doped graphene (SnP2O7/NPG), which is served as an universal anode material for sodium-ion batteries (SIBs) and sodium-based dual-ion batteries (SDIBs). Benefiting from the unique structure of tin-based ternary oxides and synergy effect of multicomponent, the obtained SnP2O7/NPG delivers a good reversible capacity of 412.9 mAh g(-1) at 0.05 A g(-1), superior cycling performance of 86.2 mAh g(-1) at 2 A g(-1) after 100 0 cycles, and exceptional rate performance of 182.3 mAh g(-1) at 2 A g(-1) in Na+ half cells. Especially, assembly of SnP2O7/NPG with the graphite cathode could yield a SnP2O7/NPG-graphite SDIBs, which shows high rate performance (up to 2 A g(-1)) and good cycling stability over 100 cycles with a capacity retention of 63.2%. Furthermore, the Na+ insertion/extraction mechanism is systematically investigated using the extensive kinetics investigation. This work provides inspirations as to extending the wider application prospect of tin-based ternary oxides in energy storage systems. (C) 2020 Elsevier Ltd. All rights reserved.