Entropy Change Characteristics for Sodium Ion Half/Full Cells Based on Na₃V₂(PO₄)₃ and Hard Carbon Materials

Abstract

Understanding the entropy change (ΔS) characteristics of hard carbon || Na3V2(PO4)3 full cell is crucial for its long cycle life and high safety. This work investigated the thermodynamic data of sodium ion half/full cells based on Na3V2(PO4)3 and hard carbon material. The results show that the trend of ΔS for Na || Na3V2(PO4)3 exhibits great change at 0-10% and 90-100% SOCs (states of charge), and remains constant (≈-14.54 J·mol-1·k-1) in 10-90% SOCs, which is consistent with the characteristics of two-phase reaction. Whereas the ΔS of Na || hard carbon (HC) remains essentially constant (≈8.30 J·mol-1·k-1) in the most Na+ concentration, fluctuating in the range of 3.17-11.71 J·mol-1·k-1. Notably, ΔS shows a negative value (-6.09 J·mol-1·k-1) at x = 0.3 (x in NaxC) and is close to 0 J·mol-1·k-1 at x = 1.0. The HC || Na3V2(PO4)3 full cell entropy change is basically constant (≈-19.56 J·mol-1·k-1) in 10-90% SOCs, and reaches a peak at 60% SOC (-10.75 J·mol-1·k-1), indicating the ΔS of full cell is mainly influenced by Na3V2(PO4)3 electrode. Based on thermodynamic entropy change characteristics, this work aims to provide a reliable reference to the storage, transportation, thermal management, and safety boundary for batteries.

Constructing p-type substitution induced by Ca2+ in defective Na3V2−xCax(PO4)3/C wrapped with conductive CNTs for high-performance sodium-ion batteries

“…33 There are two typical peaks at around 1350 cm −1 and 1600 cm −1 , representing the D band (disordered carbon) and G band (graphitic carbon), respectively. 34 The degree of graphitization is denoted as I D / I G . The values of I D / I G for NVP, Ca0.01-NVP@CNTs, Ca0.04-NVP@CNTs and Ca0.10-NVP@CNTs are 0.98, 1.17, 1.16 and 1.15, respectively, which indicate that the Ca-doped samples have a better graphitization degree of carbon, which is advantageous for carbon-containing cathode materials as it can greatly improve the electronic conductivity of the material.…”