First-Principle Insights Into Molecular Design for High-Voltage Organic Electrode Materials for Mg Based Batteries

Abstract

Low cost, scalability, potentially high energy density, and sustainability make organic magnesium (ion) battery (OMB) technologies a promising alternative to other rechargeable metal-ion battery solutions such as secondary lithium ion batteries (LIB). However, most reported OMB cathode materials have limited performance due to, in particular, low voltages often smaller than 2 V vs. Mg 2+ /Mg and/or low specific capacities compared to other competing battery technologies, e.g., LIB or sodium ion batteries. While the structural diversity of organic compounds and the large amount of possible chemical modifications potentially allow designing high voltage/capacity OMB electrode materials, the large search space requires efficient exploration of potential molecular-based electrode materials by rational design strategies on an atomistic scale. By means of density functional theory (DFT) calculations, we provide insights into possible strategies to increase the voltage by changes in electronic states via functionalization, by strain, and by coordination environment of Mg cations. A systematic analysis of these effects is performed on explanatory systems derived from selected prototypical building blocks: five-and six-membered rings with redox-active groups. We demonstrate that voltage increase by direct bandstructure modulation is limited, that strain on the molecular scale can in principle be used to modulate the voltage curve and that the coordination/chemical environment can play an important role to increase the voltage in OMB. We propose molecular structures that could provide voltages for Mg insertion in excess of 3 V.

Use of a Porous Phenanthrenequinone Polymer-Based Cathode in Mg-Ion Batteries

“…Furthermore, the AIM results show that there is negligible force of attraction (ρ = 0.00001 au and ρ∇ 2 = 0.000009 au) between the Mg ion and neighbor CO sites of phenanthrenequinone groups after storage, providing evidence that there will be one Mg ion stored successfully at each phenanthrenequinone group and 2e reduction will occur, which is in agreement with the EA value. The above outcomes are in good agreement with the previously reported battery findings, ,, where CO sites show similar behaviors for ion storage compared to other sites.…”

“…The charge-transfer analysis validates that there is 0.182e (Table 1) transferred to PMCP after Mg ion storage. Thus, the structural information and binding energies evince that the storage of Mg ions at site A is energetically more favorable, which are in good agreement with the experimental and computational results reported earlier, 36,59,62 and that the C�O sites are the most active sites for the ion storage in quinone-type organic cathodes. This large charge shifting after Mg 2+ storage in site A exhibit the stronger electrostatic interactions between the Mg ion and the electrode material.…”

Molecular modeling of organic redox‐active battery materials

“…Considering the vastness of the chemical space resulting from the possible molecular design strategies as well as the complexity of the physicochemical processes in OEMs, atomic‐scale simulations have been widely used to gain detailed mechanistic insights and accelerate the design of novel materials 90–92 . As in most functional materials, the basic properties of OEMs result from an interplay between the microscopic morphology and the electronic structure.…”

Linear Polymer Comprising Dual Functionalities with Hierarchical Pores for Lithium Ion Batteries

“…In lithium‐ion batteries, the LUMO of the organic molecule impacts the discharge voltage. Therefore, there is a handle to modulate the battery voltage while using organic molecules [10–12] . Organic molecules with carbonyl, nitrile, azo, and imine moieties have been explored as lithium‐ion battery electrodes [13–18] .…”