Enhanced High-Rate Performance of Nanosized Single Crystal ε-VOPO₄ with Niobium Substitution for Lithium-Ion Batteries

Abstract

ε-VOPO4 has the potential to be the next high energy density cathode material for lithium-ion batteries due to its high thermal stability and its ability to reversibly intercalate two full Li+, giving a high discharge capacity of 305 mAh g−1. However, vanadyl phosphate materials typically experience poor Li+ kinetics that impedes the high-rate capability at the high voltage plateau. In this work, we applied niobium substitution to improve the high-rate performance of the 4.0 V plateau of ε-VOPO4. Elemental analysis and lattice parameter refinements determined that up to 10% Nb can be substituted into ε-VOPO4 without any impurities. TEM and Synchrotron-based EXAFS confirmed that all the substituted samples have Nb in the ε-VOPO4 structure. Electrochemical tests revealed that 1% Nb substitution can deliver a high discharge capacity of ∼300 mAh g−1 without any degradation in cycling behavior by maintaining its nanosized morphology.

Probing how Ti- and Nb-substitution affect the stability and improve the electrochemical performance of β- and ε-LiVOPO4

“…Nb has also been substituted in other cathode systems, [46][47][48] with a recent increased interest in its use as a substituent in (Li)VOPO 4 . [49][50][51] Overall, we predict Ti and Nb to have a high probability of successful substitution into LiVOPO 4 . However, due to differences in atomic size and bonding characteristics, substitution will also have an effect on the thermodynamic stability of the host material used.…”

“…Nb has also been substituted in other cathode systems, 46–48 with a recent increased interest in its use as a substituent in (Li)VOPO 4 . 49–51…”

Complex defect chemistry of hydrothermally-synthesized Nb-substituted β′-LiVOPO4

“…These efforts have been extended into (Li)VOPO 4 systems as a strategy to improve the reaction kinetics and electrochemical stability at high voltages (i.e., V 5+ /V 4+ redox). 22,[27][28][29][30][31][32][33] In our earlier study, 3.5% Cr-substituted 3-LiVOPO 4 demonstrated better cycling performance than the unsubstituted material, which was attributed to increased reaction reversibility and Li-ion diffusivity in the high-voltage regime. 27 29 In this study, the substitution of V with Nb is implemented for its larger ionic radius and higher bond dissociation energy with O in relation to V (DHf 298 (Nb-O) = 753 kJ mol −1 vs. DHf 298 (V-O) = 618 kJ mol −1 ).…”

“…22,[27][28][29][30][31][32][33] In our earlier study, 3.5% Cr-substituted 3-LiVOPO 4 demonstrated better cycling performance than the unsubstituted material, which was attributed to increased reaction reversibility and Li-ion diffusivity in the high-voltage regime. 27 29 In this study, the substitution of V with Nb is implemented for its larger ionic radius and higher bond dissociation energy with O in relation to V (DHf 298 (Nb-O) = 753 kJ mol −1 vs. DHf 298 (V-O) = 618 kJ mol −1 ). 34 It is hypothesized that Nb substitution at the V-site would enlarge the diffusion channel to facilitate faster Li-ion diffusion in the high-voltage region.…”

2D vanadium oxide inverse opal films: cycling stability exploration as an electrochromic active electrode

“…It has been proved that this heterogeneity strongly depends on the particle dimensions and geometries, the nature of the interfaces and the relative positioning of the particles within the electrode architecture. 10,11 For example, Luo et al have shown that, in contrast to its bulk counterpart, which showed an extended phase coexistence, nanosized V 2 O 5 undergoes consecutive transformations with minimal phase coexistence on discharge since it possesses higher porosity and thus faster Li-ion diffusion. 12 Therefore, the lattice-mismatched phase boundaries and the corresponding stress could be circumvented.…”