# What are properties of interest for energy storage materials?

In the field of simulation for energy storage materials, there is always a gap between theoretical calculations and demand for experimentalists. What could be directly calculated from ab initio calculations (e.g. SCF energy, electron density, optimized geometry, etc.) cannot be instantly interpreted into the properties of the materials. Here the question is: What are the major properties that are relevant when material scientists are designing a novel battery? Among them, what are the properties that can be predicted by theoretical calculations of those materials?

Properties that seem experimentally relevant and computationally accessible would include, naïvely:

• Density of States at the Fermi level, relation with conductivity
• Density of States above and below the Fermi level, relation with how much negative/positive charge the system will accept, and at what voltage
• Density (in g/cm$$^3$$ trivially obtained from unit cell mass/volume)
• Kinetics of the desired electrochemical reactions, related with charging time

Phenomena that would also be interesting experimentally but which would require more detailed theoretical studies could be those related to materials fatigue, e.g.:

• Formation and propagation of defects
• Irreversible redox reactions
• Structure and chemical reactions at the grain boundaries

I have personally worked on many of these projects, and I consider the following paper as the most simplistic benchmark (as well as the Holy Grail) to better understand the properties of interest that need to be computed for energy storage materials, with necessary proof on why each of such properties are significant: High capacity reversible hydrogen storage in titanium doped 2D carbon allotrope Ψ-graphene: Density Functional Theory investigations

From the computational point of view, involving methodologies like DFT (Density Functional Theory), the following properties would be of prime interest:

• Density of States at the Fermi level, relation with magnetic nature and conductivity
• Density of States above and below the Fermi level, relation with details on the charge transfer occurring within the constituent atoms
• Density (in g/cm3 trivially obtained from unit cell mass/volume)
• Kinetics of the desired electrochemical reactions, related with charging time
• MD Simulations are to be run to check for stability at higher operating temperatures.
• Diffusion Energy Barrier Calculations need to be performed and illustrated