Spin‐Polarized Surface Capacitance Effects Enable Fe<sub>3</sub>O<sub>4</sub> Anode Superior Wide Operation‐Temperature Sodium Storage
Zhenwei Li, Meisheng Han, Peilun Yu, Jie Yu
Abstract
Abstract Fe 3 O 4 is widely investigated as an anode for ambient sodium‐ion batteries (SIBs), but its electrochemical properties in the wide operation‐temperature range have rarely been studied. Herein, the Fe 3 O 4 nanoparticles, which are well encapsulated by carbon nanolayers, are uniformly dispersed on the graphene basal plane (named Fe 3 O 4 /C@G) to be used as the anode for SIBs. The existence of graphene can reduce the size of Fe 3 O 4 /C nanoparticles from 150 to 80 nm and greatly boost charge transport capability of electrode, resulting in an obvious size decrease of superparamagnetic Fe nanoparticles generated from the conversion reaction from 5 to 2 nm. Importantly, the ultra‐small superparamagnetic Fe nanoparticles (≈2 nm) can induce a strong spin‐polarized surface capacitance effect at operating temperatures ranging from −40 to 60 °C, thus achieving highly efficient Na‐ion transport and storage in a wide operation‐temperature range. Consequently, the Fe 3 O 4 /C@G anode shows high capacity, excellent fast‐charging capability, and cycling stability ranging from −40 to 60 °C in half/full cells. This work demonstrates the viability of Fe 3 O 4 as anode for wide operation‐temperature SIBs and reveals that spin‐polarized surface capacitance effects can promote Na‐ion storage over a wide operation temperature range.