Carbon encapsulation and chlorine doping enable Na3V2(PO4)3 superior sodium ion storage properties as cathode material for sodium ion battery

Abstract

NASICON-structured Na3V2(PO4)3 possessing three-dimensional channel for sodium ion migration demonstrates promising prospect as cathode for sodium ion battery due to good thermal stability and large theoretical capacity. Herein, carbon encapsulation and chlorine doping are employed to improve sodium storage performances of Na3V2(PO4)3 through sol-gel method. Carbon-encapsulated chlorine-doped Na3V2(PO4)3 composites reveal raised electrochemical performance. Among composites, Na3V2(PO4)2.9Cl0.3@C (NVP@C/Cl-30) with proper chlorine exhibits the best performance. NVP@C/Cl-30 delivers the discharge capacity of 104.2, 86.4, 52.2 mAh g−1 at 40, 1000, 4000 mA g−1, severally, much higher than those of chlorine-undoped composite (NVP@C, 74.2, 46.4, 21.1 mAh g−1). Moreover, NVP@C/Cl-30 demonstrates excellent cycling performance (capacity retention: 93.0%, 500 cycles, 800 mA g−1). Outstanding performances is attributed to nanostructure from sol-gel route and synergetic effect of carbon encapsulation and chlorine doping for Na3V2(PO4)3. Nanostructure can shorten migration pathway of sodium ion. Carbon encapsulation and chlorine doping raise electrical and ionic conductivity, respectively.