Ti-Doped Na₃V₂(PO₄)₃ Activates Additional Ti³⁺/Ti⁴⁺ and V⁴⁺/V⁵⁺ Redox Pairs for Superior Sodium Ion Storage

Abstract

Na3V2(PO4)3 (NVP) is considered as a potential cathode material for next-generation sodium ion batteries (SIBs) because of its open Na+ diffusion channels and high operating voltage. In this paper, we design a Na3V1.9Ti0.1(PO4)3/C (Ti0.1-NVP/C) composite as a cathode for SIBs. Using Ti4+ to replace V3+ can not only stabilize the crystal structure of NVP, but also generate Na vacancies to promote Na+ diffusion and improve the intrinsic electronic conductivity of NVP. Meanwhile, the coated carbon layer provides a surface channel for the electron transport of NVP. More importantly, Ti-doped NVP activates additional Ti3+/Ti4+ and V4+/V5+ redox pairs. The synergistic effect of the two redox pairs makes the capacity of the Ti0.1-NVP/C electrode (123.3 mAh g–1 at 0.1 C) higher than the theoretical specific capacity of NVP. Ti0.1-NVP/C cathode also exhibits excellent rate capability (89.5 mAh g–1 at 30 C) and long cycle performance (retention of 62.3% at 20 C after 8000 cycles). Furthermore, the symmetric full cell of the Ti0.1-NVP/C electrode exhibits superior competitiveness. The reaction mechanism of the Ti0.1-NVP/C electrode is elucidated by ex-situ XRD and GITT measurements.

Exceeding Three-Electron Reactions in Polyanionic Cathode To Achieve High-Energy Density for Sodium-Ion Batteries

“…Figure a shows the X-ray diffraction (XRD) patterns of NVTP-0, NVTP-0.5, and NVTP-1 samples, which can be indexed to the trigonal crystal phase with the space group R 3̅ c (PDF#00-062-0345). The great similarity of XRD patterns indicates the full solubility of V and Ti in the framework. − The enlarged image shows a progressive shift of the diffraction peak toward higher angles as the content of Ti increases. This phenomenon is attributed to the alteration of the TM type and the corresponding adjustment of the sodium content.…”

Internal Vanadium Doping and External Modification Design of P2‐Type Layered Mn‐Based Oxides as Competitive Cathodes toward Sodium‐Ion Batteries

“…The two peaks of 516.8 and 524.0 eV represent V 2p 3/2 and V 2p 1/2 , respectively, indicating that V ions appear at a high valence of + 5 on the surface of V-doped oxides. [44] With the increase in the amount of V element doping, Mn ions will gradually be replaced by V ions. An overabundance of V 5 + doping will infiltrate the octahedral space, occupy the Na + diffusion channels, induce lattice defects, ultimately resulting in a decline in the electrochemical performance of P2 oxide cathodes.…”

“…Figure 4c shows the V 2p XPS spectral analysis of NNMVO@NVPOF. The two peaks of 516.8 and 524.0 eV represent V 2p 3/2 and V 2p 1/2 , respectively, indicating that V ions appear at a high valence of +5 on the surface of V‐doped oxides [44] . With the increase in the amount of V element doping, Mn ions will gradually be replaced by V ions.…”

Tremella-like Zn–Al–Zr-Layered Double-Hydroxide/Graphene Oxide Nanocomposites for Enhanced Phosphorus Recovery

“…Until now, the applications of phosphorus (P) and its derivates are present everywhere in our life; they have been widely used in the fields of agriculture, food, pharmacy, electronics, new energy, and daily chemical products. , With enjoying the benefits from P, its discharge will also inevitably lead to increased contamination to the ecological environment. If the concentration of total P (TP) exceeds 0.02 mg/L in the aquatic environment, it can cause water eutrophication and trigger the burst of algal blooms, which seriously threatens the safety of our drinking water .…”