SnO2 nanoparticles composited with biomass N-doped carbon microspheres as low cost, environmentally friendly and high-performance anode material for sodium-ion and lithium-ion batteries

The oxygen vacancy-riched tin dioxide (SnO2) nanoparticles composites with biomass nitrogen-doped carbon microspheres (SNC composite materials) were fabricated to enhance the electrochemical performance of SnO2 as anode materials for sodium-ion batteries (SIBs) and lithium-ion batteries (LIBs). The optimal SNC-2 electrode not only shows excellent electrochemical performance (reversible capacity of 557.1 mAh g−1 after 50 cycles at 0.05 A g−1, high-rate capability of 329.5 mAh g−1 and reversible capacity of 320 mAh g−1 after 1000 cycles even at a high current density of 1.0 A g−1) in SIBs, but also exhibits superior electrochemical performance in LIBs. Furthermore, ex-situ solid-state nuclear magnetic resonance (NMR) results (23Na, 19F and 119Sn MAS NMR spectra) reveal that the reversibility of the alloy NaxSn and SnO2, as well as the formation of NaF during the electrode reaction of SNC-2. The sodium peroxide (Na2O2) is probed by ex-situ solid-state NMR and ex-situ electron paramagnetic resonance (EPR) tests during the electrochemical process of SNC-2 electrodes for SIBs. An optimized reaction mechanism characterized by the formation of Na2O2 in SnO2 anodes for SIBs is proposed according to our work.