Surface modification of nano Na[Ni0.60Mn0.35Co0.05]O2 cathode material by dextran functionalized RGO via hydrothermal treatment for high performance sodium batteries

Abstract

Wrapping of reduced graphene oxide (RGO) over 2D layered transition metal oxide cathode material is very prevailing strategy to improve the capacity and cycling performance of cathode materials for sodium-batteries. However, poorly dispersed RGO in aqueous medium restricts the proper attachment of active-material with RGO resulting in non-uniform wrapping. Herein, graphene oxide is functionalized non-covalently through multifunctional agent dextran and reduced moderately to dextran functionalized-RGO (Dx-RGO). Further, it is attached chemically with Na[Ni0.60Mn0.35Co0.05]O2 (NMC) nano-sphere, which is synthesized by co-precipitation method. Strategically, hydrothermal-treatment is applied to empower reduction as well as attachment of Dx-RGO with NMC nano-sphere to prepare NMC-Dx-RGO composite. The successful attachment of Dx-RGO over NMC nano-sphere is confirmed by various experimental techniques and their resulting electrochemical performances are investigated. The surface-modified NMC-Dx-RGO cathode material exhibits high discharge capacity of 151 mAh g−1 at 0.1C and 55% capacity retention after 120 cycles at 0.2C. Dx-RGO layer acts as conducting network around NMC providing uniform state of charge distribution (SOC), which facilitates fast transport of electrons. The presence of protective Dx-RGO layer suppresses the growth of resistive layer at cathode-electrolyte interface (Rcei) and prevents the dissolution of transition metals cathode material to get high discharge capacity for sodium-batteries.