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DopingBatteryTMOs.pdf (2.81 MB)

Can Doping of Transition Metal Oxide Cathode Materials Increase Achievable Voltages with Multivalent Metals?

preprint
submitted on 25.10.2019, 16:03 and posted on 29.10.2019, 16:51 by Daniel Koch, Sergei Manzhos
We investigate from first principles the use of substitutional p-doping as a means to enhance the insertion energies of multivalent metals in transition metal oxides, and therefore the resulting voltages in an electrochemical cell, due to bandstructure modulation. Multivalent and earth-abundant metals such as magnesium or aluminium are attractive candidates to replace lithium in future high-performance secondary batteries with intercalation-type electrodes. Unfortunately, the achievable voltages obtained with this kind of elements still remain uncompetitively low. We study and compare the changes in insertion energetics (voltages) of single- and multivalent metals in semiconducting and insulating transition metal oxides upon substitutional p-doping with different metals, introducing different numbers of hole states. We use a single vanadium pentoxide monolayer as model system to study the effect of p-doping on achievable voltages and deduce general trends for transition metal oxides. Our investigations reveal the formation of n-hole polarons (with n>1) in form of oxygen dimers in p-doped vanadia caused by localized p holes on oxide ions in agreement with previous findings. We find that the oxygen dimer formation has an adverse effect on adsorption energetics compared to the single-hole case without dimerization. We find an analogous oxygen dimerization in other TMOs with oxygen-dominated valence bands like molybdenum trioxide and titanium dioxide, while strained systems like trigonal nickel- or titanium dioxide, or Mott-type systems like monoclinic vanadium dioxide with qualitatively different valence band composition do not exhibit oxygen dimerization with multi-hole doping. Our results demonstrate the advantages and limitations of TMO electrode p-doping and show a path to possible strategies to overcome detrimental effects.

Funding

This work was supported by the Ministry of Education of Singapore (Grant No. MOE2015-T2-1-011).

History

Email Address of Submitting Author

koch.danielm@gmail.com

Institution

National University of Singapore

Country

Singapore

ORCID For Submitting Author

0000-0003-4775-6879

Declaration of Conflict of Interest

There are no conflicts to declare.

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