Doping of active electrode materials for electrochemical batteries: an electronic structure perspective
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Prospective Article
Doping of active electrode materials for electrochemical batteries: an electronic structure perspective Johann Lüder, Fleur Legrain†, Yingqian Chen, and Sergei Manzhos, Department of Mechanical Engineering, National University of Singapore, Block EA #07-08, 9 Engineering Drive 1, Singapore 117576, Singapore Address all correspondence to Sergei Manzhos at [email protected] (Received 9 June 2017; accepted 1 August 2017)
Abstract Doping is a potent and often used strategy to modify properties of active electrode materials in advanced electrochemical batteries. There are several factors by which doping changes properties critically affecting battery performance, most notably the voltage, capacity, rate capability, and stability. These factors have to do specifically with changes in structure, band gap and band structure, and structural instability induced by doping. We review our recent modeling works on the effects of doping of active electrode materials, notably for prospective materials for organic and post-lithium (Na ion, Mg ion) batteries, as well as present new results, to build a coherent view on the use of n- and p-doping to modulate Li, Na, and Mg storage properties, most notably voltage. Specifically, we clearly point out effects due to electronic structure and those due to strain (structural instability), which clears some confusion about the effects of n- versus p-doping and facilitates rational rather than ad hoc design of doped materials.
Introduction Metal ion batteries have enjoyed an ever increasing use and have the potential to be in widespread use not only in mobile electronic devices but also in electric vehicles and in stationary storage serving to palliate supply-demand misbalance characteristic of wind and solar powered plants.[1–4] Much has been written about the necessity on one hand to develop post-lithium batteries based on much more abundant and cheap Na, Mg, Al etc. and on the other hand to develop active electrode materials, which themselves rely on abundant and cheap inputs and processes, to result in sustainable and scalable metal ion batteries.[5–7] It is also understood that it is more difficult to achieve high performance (high rate, energy and power density) with post-lithium ion batteries than with Li ion batteries. These issues follow from a higher electrochemical potential, which is believed to lead to a lower battery voltage and energy density,[8] from a large ionic radius of Na+ or multivalence of Mg and Al, which lead to high diffusion barriers (resulting in low rate capability and low-power density) in many widely studied materials[9–12] and to thermodynamically inhibited Na, Mg, Al, etc. insertion, which implies difficulties in obtaining high voltage cathodes or even outright lack of electrochemical activity. Specifically this last point highlights the idiosyncrasies of material design for post-lithium batteries, whereby some high-performance materials well suited for Li
† Present address: CEA, LITEN, 17 Rue des Martyrs, 38054 Grenoble, France.
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