Uniform Na3V2(PO4)2O2F microcubes enhanced by ionic liquid-modified multi-walled carbon nanotubes as a superior cathode for Sodium-Ion Batteries

Na3V2(PO4)2O2F with a typical Na+ superionic conductor (NASICON) structure is a promising cathode material for sodium-ion batteries (SIBs) due to its unique layered structure, high energy density and fast ionic conduc-tivity. However, the low intrinsic electronic conductivity seriously hinders the practical application of Na3V2(-PO4)2O2F. In this work, ionic liquid-modified multi-walled carbon nanotubes (MWCNT-IL) were applied as a conductive network to form Na3V2(PO4)2O2F-based cathode. The highly dispersed MWCNT-IL can hinder the agglomeration growth of Na3V2(PO4)2O2F crystal and can result in the formation of uniform Na3V2(PO4)2O2F cubes of-1 mu m which are covered evenly by conductive MWCNT-IL through C-O-P/V bonds (denoted as NVOPF@MWCNT-IL). Relying on the synergistic effect of conductive MWCNT-IL and uniform Na3V2(PO4)2O2F cubes, NVOPF@MWCNT-IL cathode for SIBs can exhibit improved cycling stability and superior rate perfor-mance. The specific capacity of NVOPF@MWCNT-IL can reach 107 mA h g-1 with high retention of 96.7% after 900 cycles at a current density of 1C (1C=130 mA h g-1). At a high current density of 30C, NVOPF@MWCNT-IL maintains a high discharge capacity of 79 mA h g-1 after 1500 cycles. The above results provide an effective and simple method to construct advanced NASICON cathodes for SIBs.

Automated summary

In this study, ionic liquid-modified multi-walled carbon nanotubes (MWCNT-IL) were used as a conductive network to form a Na3V2(PO4)2O2F-based cathode (NVOPF@MWCNT-IL). The use of MWCNT-IL allowed for the dispersion of Na3V2(PO4)2O2F crystals and the formation of uniform Na3V2(PO4)2O2F cubes. The NVOPF@MWCNT-IL cathode exhibited improved cycling stability and superior rate performance.