Interstitial versus substitutional metal insertion in V 2 O 5 as post-lithium ion battery cathode: a comparative GGA/GGA
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Research Letter
Interstitial versus substitutional metal insertion in V2O5 as post-lithium ion battery cathode: a comparative GGA/GGA + U study with localized bases Daniel Koch, Department of Mechanical Engineering, National University of Singapore, Block EA #07-08, 9 Engineering Drive 1, Singapore 117576, Singapore Sergei Manzhos , Centre Énergie Matériaux Télécommunications, Institut National de la Recherche Scientifique, 1650 boulevard Lionel-Boulet, Varennes, QC J3X1S2, Canada Address all correspondence to Daniel Koch at [email protected] and Sergei Manzhos at [email protected] (Received 18 February 2020; accepted 11 May 2020)
Abstract The generalized gradient approximation (GGA) often fails to correctly describe the electronic structure and thermochemistry of transition metal oxides and is commonly improved using an inexpensive correction term with a scaling parameter U. The authors tune U to reproduce experimental vanadium oxide redox energetics with a localized basis and a GGA functional. The value for U is found to be significantly lower than what is generally reported with plane-wave bases, with the uncorrected GGA results being already in reasonable agreement with experiments. This computational set-up is used to calculate interstitial and substitutional insertion energies of main group metals in vanadium pentoxide and interstitial doping is found to be thermodynamically favored.
Introduction Layered Pmmn vanadium pentoxide (α-V2O5) is a frequently investigated intercalation-type cathode material for secondary batteries reported to be electrochemically active with a variety of working metals beyond the currently prevalent lithium (Li), like sodium (Na), magnesium (Mg), calcium (Ca), or aluminum (Al).[1–5] The appreciable performance of this material is commonly explained by its accommodative structure with large stable intercalation sites between the stacked V2O5 monolayers and small changes in coordination numbers during ionic hopping enabling fast ionic diffusion. However, the weak, mostly dispersive, interlayer cohesion bears disadvantageous stability issues due to easy monolayer puckering and interlayer shear distortions,[2] while the semiconducting electronic structure (experimental band gap 2.2–2.8 eV[6,7]) potentially impedes ionic motion by large electron-polaron hopping barriers.[8] Interstitial doping has been shown to improve the cycling stability of α-V2O5 by an anchoring of the neighboring layers via the pre-intercalated ions, while electron donation to the vanadium pentoxide host creates mid-gap states close to the conduction band minimum increasing electrical conductivity and hence ionic mobility.[9,10] On the other hand, achievable voltages with multivalent metals (e.g., Mg, Ca, Al) remain uncompetitively low compared to commonly observed voltages with Li, a common drawback of cells with multivalent metals.[11] The substitutional p-doping of semiconducting cathode materials has been suggested as a way to improve insertion potentials due to band structure modulations and loweri
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