Ultrafast Charge‐Discharge Capable and Long‐Life Na_3.9Mn_0.95Zr_0.05V(PO₄)₃/C Cathode Material for Advanced Sodium‐Ion Batteries

Abstract

Na4MnV(PO4)3/C (NMVP) has been considered an attractive cathode for sodium‐ion batteries with higher working voltage and lower cost than Na3V2(PO4)3/C. However, the poor intrinsic electronic conductivity and Jahn–Teller distortion caused by Mn3+ inhibit its practical application. In this work, the remarkable effects of Zr‐substitution on prompting electronic and Na‐ion conductivity and also structural stabilization are reported. The optimized Na3.9Mn0.95Zr0.05V(PO4)3/C sample shows ultrafast charge‐discharge capability with discharge capacities of 108.8, 103.1, 99.1, and 88.0 mAh g−1 at 0.2, 1, 20, and 50 C, respectively, which is the best result for cation substituted NMVP samples reported so far. This sample also shows excellent cycling stability with a capacity retention of 81.2% at 1 C after 500 cycles. XRD analyses confirm the introduction of Zr into the lattice structure which expands the lattice volume and facilitates the Na+ diffusion. First‐principle calculation indicates that Zr modification reduces the band gap energy and leads to increased electronic conductivity. In situ XRD analyses confirm the same structure evolution mechanism of the Zr‐modified sample as pristine NMVP, however the strong ZrO bond obviously stabilizes the structure framework that ensures long‐term cycling stability.

Tailoring High-Performance Ternary Transition Metal-Based NASICON-Na(9–2x–3y–4z)MnxVyZrz(PO4)3 Cathodes via Combinatorial Chemical Substitutions

“…More significantly, upon doubling the areal mass loading of the ①⓪ cathode (i.e., 10 mg cm –2 ), it still displays good rate performances (62 and 55 mAh g –1 at 2C and 5C, respectively) and capacity retention (82.2% after 200 cycles at 1C) (Figure S23). The enhanced cycling stability of the ①⓪ cathode can be ascribed to its optimal Zr 4+ content, which forms a strong Zr–O bond and stabilizes the host structure . In contrast, ⑧ and ⑨ show inferior capacity retention (74–80% after 200 cycles at 1C rate), which can be attributed to the presence of a higher concentration of the Jahn–Teller active Mn 3+ in these cathodes .…”

“…Further, we computed the electronic density of states of the 5 – 11 cathodes to assess the role of Mn 2+ , V 3+ , and Zr 4+ cations and observed a stronger covalent interaction between Zr 4+ and the oxygen sublattice in 5 . , Upon decreasing the Zr 4+ and Mn 2+ (and increasing the V 3+ ) contents in the NASICON framework along the 5 – 11 series, the bonding e g bands of both Mn and V 3d orbitals are raised in energy near the Fermi level and the antibonding states (σ*) comprised majorly of the e g * bands of Mn and V are lowered, resulting in enhanced electronic conduction (Figure S16). It can also be realized from the charge density isosurfaces, which display the delocalization of the electronic cloud around transition metal centers as we move from 5 to 11 cathodes (Figure S16).…”

“…The enhanced cycling stability of the 10 cathode can be ascribed to its optimal Zr 4+ content, which forms a strong Zr−O bond and stabilizes the host structure. 39 In contrast, 8 and 9 show inferior capacity retention (74−80% after 200 cycles at 1C rate), which can be attributed to the presence of a higher concentration of the Jahn−Teller active Mn 3+ in these cathodes. 38 Moreover, both cathodes show a rapid capacity decline at higher C-rates (40 and 45 mAh g −1 for 8 and 9 at 5C, respectively) (Figure S24).…”

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

“…[19,[22][23][24][25][26] Among the strategies, element doping has attracted considerable attention due to its strong ability to intrinsically improve the electrochemical properties of NVP-based materials, especially the doping of V-site (Figure 1b). [11,27] Recently, diverse NVPbased cathodes have been developed by partially substituting V 3+ at V sites by transition metal ions based on the redox turnability of V element, [28,29] such as Mo-doped Na 3 V 2 (PO 4 ) 3 @C, [30] Na 3 VAl 0.2 Cr 0.2 Fe 0.2 In 0.2 Ga 0.2 (PO 4 ) 3 , [31] Na 4 V 0.8 Al 0.2 Mn(PO 4 ) 3 , [32] Na 3.9 Mn 0.95 Zr 0.05 V(PO 4 ) 3 /C, [33] Na 3 V 1.6 Cr 0.4 (PO 4 ) 3 , [34] and [19,[22][23][24][25][26] b) Advantages of element doping at V sites in NVP. [11,27] Na 3.75 V 1.25 Mn 0.75 (PO 4 ) 3 .…”

A zero-strain Na-deficient NASICON-type Na2.8Mn0.4V1.0Ti0.6(PO4)3 cathode for wide-temperature rechargeable Na-ion batteries

“…For example, the introduction of Mg 2+ not only helps increase the electrochemically active Na + content but also stabilizes the crystal structure, which facilitates surface reaction during the charging/discharging process. 19–22 Zr 4+ -substitution exhibits the function of expanding the migration pathway and stabilizing the lattice framework, 23–25 while doping with Al 3+ also benefits the robust crystal structure and the effective activation of Mn 3+ /Mn 4+ and V 4+ /V 5+ redox. 20,26–28 However, the inactive elements involved in the cathode are bound to sacrifice a portion of the capacity, leading to reduced energy density.…”