Flexible sodium-ion battery anodes using indium sulfide-based nanohybrid paper electrodes

Flexible nanohybrid paper electrode (termed as C-I) consisting of multi-walled carbon nanotubes (MWCNTs) and indium sulfide (In ₂ S ₃ ) nanoplates is formed via a simple vacuum-assisted assembly and used as an anode for sodium-ion batteries (SIBs). In ₂ S ₃ nanoplates which are well distributed on and bound to the MWCNTs provide a high Na storage capacity of the nanohybrid electrode as high as 410 mAh g ⁻¹ at a specific current of 50 mA g ⁻¹ over 100 charge/discharge cycles and ∼97% of rate-retention capability over the specific currents of 50 mA g ⁻¹ to 1 A g ⁻¹ for at least 50 charge/discharge cycles. Particularly, when In ₂ S ₃ in the form of nanoplates was added to MWCNTs, the electrochemical performances are considerable as compared to those of bulk In ₂ S ₃ or MWCNTs film electrodes. This highlights the importance of nanohybrid approach in overcoming the intrinsic complication of In ₂ S ₃ , i.e., the agglomeration of In ₂ S ₃ into bulk form during assembly, followed by annealing. For C-I nanohybrid electrode, capacitive contribution (∼95%) rather than insertion contribution (∼5%) is predominant during charge/discharge process. The nanohybrid paper electrode is robust and thus retains capacity even under repeated mechanical deformation (flat-bent-flat cycles), demonstrating the potential of the electrode being used for flexible and wearable energy storage.