High‐Energy‐Density Cathode Achieved via the Activation of a Three‐Electron Reaction in Sodium Manganese Vanadium Phosphate for Sodium‐Ion Batteries

Abstract

Sodium superionic conductor (NASICON)‐type Na3V2(PO4)3 has attracted considerable interest owing to its stable three‐dimensional framework and high operating voltage; however, it suffers from a low‐energy density due to the poor intrinsic electronic conductivity and limited redox couples. Herein, the partial substitution of Mn3+ for V3+ in Na3V2(PO4)3 is proposed to activate V4+/V5+ redox couple for boosting energy density of the cathodes (Na3V2‒xMnx(PO4)3). With the introduction of Mn3+ into Na3V2(PO4)3, the band gap is significantly reduced by 1.406 eV and thus the electronic conductivity is greatly enhanced. The successive conversions of four stable oxidation states (V2+/V3+, V3+/V4+, and V4+/V5+) are also successfully achieved in the voltage window of 1.4–4.0 V, corresponding to three electrons involved in the reversible reaction. Consequently, the cathode with x = 0.5 exhibits a high reversible discharge capacity of 170.9 mAh g−1 at 0.5 C with an ultrahigh energy density of 577 Wh kg−1. Ex‐situ x‐ray diffraction (XRD) analysis reveals that the sodium‐storage mechanism for Mn‐doped Na3V2(PO4)3 consists of single‐phase and bi‐phase reactions. This work deepens the understanding of the activation of reversible three‐electron reaction in NASICON‐structured polyanionic phosphates and provides a feasible strategy to develop high‐energy‐density cathodes for sodium‐ion batteries.

Mixed-Dimensional (2D/3D/3D) Heterostructured Vanadium Oxide with Rich Oxygen Vacancies for Aqueous Zinc Ion Batteries with High Capacity and Long Cycling Life

“…These observations indicated that the multielectron redox reaction of V 3+ ⇋ V 4+ ⇋ V 5+ is achieved during the electrochemical reaction process in the Zn//VO x battery. 48 Moreover, vanadium can be restored to a mixed valence state of V 5+ /V 4+ when charged to 1.6 V, indicating that the VO x electrode has outstanding electrochemical reversibility. The XPS spectrum of the spectrum of the spectrum of the O 1s is shown in Figure 5g.…”

H2O‐Mg2+ Waltz‐Like Shuttle Enables High‐Capacity and Ultralong‐Life Magnesium‐Ion Batteries

“…[ 17 ] The co‐existence of V 5+ and V 4+ in MVOH provides opportunities for the 3 d electrons to hop from occupied 3 d orbitals of V 4+ to empty 3 d orbitals of V 5+ , which increases the electronic conductivity of MVOH and thus its capacity. [ 18 , 19 , 20 ] Furthermore, three distinct components can be observed in the O 1 s core level, which are attributed to the O atoms in V─O (530.2 eV), Mg‐O (531.4 eV), and H 2 O (533.2 eV), respectively (Figure S1D , Supporting Information). [ 21 ] The Raman spectrum and Fourier‐transformed infrared (FT‐IR) spectra of MVOH further verify its lamellar structure constituted by V─O skeleton layers (Figures S4 and S5 , Supporting Information).…”

A Nonstoichiometric Pure-Phase Na3.4Fe2.4(PO4)1.4P2O7 Cathode for High-Performance Sodium-Ion Batteries

“…Figure c illustrates the GITT curves of 1.0-NFPP/C and 1.4-NFPP/C at 0.1 C. Although the GITT curves of the two materials show minimal differences during charging, 1.4-NFPP/C demonstrates a smaller overpotential than 1.0-NFPP/C during the discharge process, indicating faster redox kinetics. Furthermore, the Na + diffusion coefficients of 1.0-NFPP/C and 1.4-NFPP/C at different potentials were calculated using eqs and , , with the findings depicted in Figure d. D normalN a + = 4 π true( m V m normalM normalA true) 2 true( normalΔ E s τ ( d E τ / d τ ) true) 2 ( τ ≤ L 2 D normalN a + ) D normalN a + = 4 π true( m V m normalM normalA true) 2 true( normalΔ E s normalΔ E τ true) 2 During the electrochemical reaction, the Na + diffusion coefficient of 1.4-NFPP/C consistently exceeds that of 1.0-NFPP/C, aligning with the results of the rate performance tests. Additionally, electrochemical impedance spectroscopy (EIS) was performed on x -NFPP/C samples, with the results presented in…”

“…Figure5cillustrates the GITT curves of 1.0-NFPP/C and 1.4-NFPP/C at 0.1 C. Although the GITT curves of the two materials show minimal differences during charging, 1.4-NFPP/C demonstrates a smaller overpotential than 1.0-NFPP/C during the discharge process, indicating faster redox kinetics. Furthermore, the Na + diffusion coefficients of 1.0-NFPP/C and 1.4-NFPP/C at different potentials were calculated using eqs 2 and 3,37,38 with the findings depicted in Figure 5d. reaction, the Na + diffusion coefficient of 1.4-NFPP/C consistently exceeds that of 1.0-NFPP/C, aligning with the results of the rate performance tests.…”