Na3V2(PO4)3/C in Symmetric Cells: Evaluating Anode and Cathode Performance

Abstract

Renewable energy sources necessitate efficient energy storage, highlighting the critical challenge and importance of electrochemical storage devices, such as sodium-ion batteries. Na₃V₂(PO₄)₃ (NVP), as a typical NASICON structure, is a promising electrode material exhibiting fast Na⁺ ion conductivity due to its 3D framework. In this report, we present the synthesis of NVP/C (Na₃V₂(PO₄)₃/Carbon composite) via the sol–gel method and investigate its electrochemical behavior in both the anodic and cathodic ranges, as well as its assessment in a symmetric cell followed by a detailed postcycling analysis. Increased overpotential has impacted the capacity retention of NVP-C (NVP as a cathode), delivering only 74.61% with an initial specific capacity of 120.20 mAh/g, whereas NVP-A (NVP as an anode) showed better cyclic stability, exhibiting 142.11 mAh/g at the 12th cycle with a capacity retention of 93.03%. NVP-C showed specific capacities of 99.17, 84.74, and 53.20 mAh/g at 25, 0, and −5 °C, respectively, while NVP-A exhibited 191.42, 153.33, and 91.37 mAh/g under the same conditions, at 0.2C over 60 cycles. NVP was studied in a symmetric full cell, exhibiting an average energy density of 92.94 Wh/kg over 50 cycles. Postcycling investigations, including ToF-SIMS, XPS, and XANES, revealed that products of parasitic reactions, such as Na₂CO₃, NaF₂, and Na_xPF_yO_z along with structural distortion on the anode side, significantly impact the lifecycle of NVP. Our findings provide new insights into the performance, which will results in the improvement of NVP symmetric full-cell configurations.