Doping of active electrode materials for electrochemical batteries: an electronic structure perspective

Abstract

Abstract

Insertion of Mono- vs. Bi- vs. Trivalent Atoms in Prospective Active Electrode Materials for Electrochemical Batteries: An ab Initio Perspective

“…The demand for lithium for application in batteries recently became the dominant Li sink, and although the global reserves-to-production ratio is currently still at around 430 years [2], the breakthrough of electric vehicles into the mass market might drastically decrease this number. Also, further competition for Li resources might eventually arise in the future by the deployment of novel technologies, e.g., in the form of nuclear fusion reactors likely depending on 6 Li (and potentially 7 Li) as a tritium precursor nuclide. A replacement of lithium in future high-performance electrochemical energy storage applications is therefore desirable.…”

“…Among these, ab initio methods play a critical role, because the phenomena providing the functionality of an active electrode material involve changes in electronic level occupancies and energies, and changes in charge states. This is conspicuous in materials with redox centers, such as oxides, in which changes in the oxidation and charge state are the origin of capacity, but also in materials without such redox centers, such as monoelemental semiconductors like Si where electronic interactions and bandstructure play a critical role [7]. Methods that in principle do not provide electronic properties, such as force field molecular dynamics, therefore, cannot in principle model the mechanism of charge-discharge, although they can assist in finding structures and in modeling ionic transport related to the cycling rate.…”

“…Over the last several years, our group has performed a series of comparative ab initio studies of the Li, Na, K, Mg, and Al interactions with several phases of several potential electrode materials which have been extensively studied in experimental labs, and some also computationally [7,, including amorphous phases. These studies were the first truly comparative, i.e., using the same approximations and computational parameters, studies permitting comparisons among different phases and types of ions.…”

“…Different functionals, basis sets, and software were used which were deemed most suitable for a specific system. The reader is referred to the original papers for details of calculation setups [7,. Here, we only introduce key computed quantities which are important for a material's performance as an active electrode material and which are discussed in Sections 2 and 3.…”

“…The lowest energy state is achieved when the number of electrons donated by the interstitial dopants equals the number of hole states created by substitutional dopants, allowing all electrons donated by the interstitials to occupy lower-lying states in the valence band rather than higher-energy states in the conduction band. We dubbed this effect "self-doping" [7]. …”