Sodium-Rich Vanadium-Based Polyanion Cathode Material for High Energy Density Sodium Ion Storage

Abstract

A promising cathode material has been developed for sodium ion batteries (SIBs) is NASICON-type Na3V2(PO4)3 (NVP). However, replacing V with a low-cost, environmentally friendly metal ion is an immediate priority for NVP industrialisation. In this paper, we synthesize a sodium-rich vanadium-based polyanion cathode material by mechanochemical method. Na3.5V1.5Mn0.5(PO4)3/C (NVMP/C-0.5) shows excellent electrochemical performance and has almost no Jahn-Teller effect. NVMP/C-0.5 has an initial discharge capacity of 136.2 mAh g-1 at 0.1 C, and a plateau voltage of 3.5 V. As well as exhibiting excellent rate performance (96.4 mAh g-1 at 20 C), the NVMP/C-0.5 exhibits long cycle capability (64.7% of the capacity is retained after 8000 cycles at 20 C). Ex-situ X-ray photoelectron spectroscopy (XPS) tests demonstrate that V3+/V4+, V4+/V5+ and Mn2+/Mn3+ redox pairs are all involved in redox reactions. Ex-situ X-ray diffraction (XRD) tests reveal that NVMP/C-0.5 has high structural reversibility and small volume change in charge-discharge reaction. With its high energy density, NVMP/C-0.5/hard carbon full cells have potential for use in a wide range of applications.

Keywords: NVMP/C-0.5, Ex-situ XRD, NVMP/C-0.5//hard carbon full cell, High energy density, Ex-situ XPS