Since renewable energy sources, such as solar and wind power, are intermittent in nature, there is a need to store the energy produced by these sources. Lithium-ion batteries (LIBs) have emerged as a leading energy storage technology due to their portability and high energy density. However, the raw materials for the LIBs are not spread over the globe uniformly, leading to the exploration of alternative energy storage technologies like sodium-ion, potassium-ion, magnesium-ion, and calcium-ion batteries (NIBs, KIBs, MIBs, and CIBs, respectively). To achieve the maximum performance, optimization of anode, cathode, electrolyte, and solid electrolyte interface (SEI) for each of these technologies is necessary. In this thesis, we explored alternate anode materials for LIBs, NIBs, and KIBs. Using density functional theory (DFT) simulations, we calculated various electrochemical properties, such as specific charge capacity, voltage, and metal-ion diffusion energy barrier, for the newly discovered 2D materials, namely, cobalt anti-MXenes.1 Among the six cobalt anti-MXenes we studied (CoX; X=As, B, P, S, Se, Si), we found that CoP is a promising anode material for alkali metal-ion batteries.2,3

Also, in the context of CIBs, we explored the stability of various salts and solvents, and studied the formation and evolution of SEI at the calcium anode surface. It should be noted that calcium has several advantages, such as its abundance on the earth’s crust, high electropositive nature (E0Ca2+/Ca = -2.87 V vs. SHE, 170 mV lower than Li), and so on. However, due to the high reduction potential of Ca, the majority of the salts and solvents decompose spontaneously at the Ca surface and form SEI that prohibits the reversible deposition of Ca.4,5 Interestingly, recent experiments showed the reversible shuttling of Ca ion through SEIs at high temperatures,6,7 highlighting the potential for optimizing SEI composition to enhance calcium ion conductivity at lower temperatures. To this end, we investigated the formation and evolution of SEI on the Ca(001) surface when it is in contact with 0.45 M Ca(TFSI)2 or Ca(BF4)2 salt in a 1:1 wt% ethylene carbonate and propylene carbonate solvent mixture. Our ab initio molecular dynamics (AIMD) simulations show that the SEI is majorly composed of inorganic and organic fragments of the decomposed salt and solvent molecules, and the interaction between these fragments and the Ca surface is governed by the radius and charge on the fragments. We also explained the microscopic understanding of the electrolyte decomposition. Interestingly, we find that the stability of the salt can be increased by pre-passivating the Ca surface with the decomposed products of the solvent, and thereby improving the reversible deposition. Additionally, we identified the Ca-ion migration path through the SEIs and computed the corresponding migration energy barriers. These findings help us to tune the nature of SEI and further improve the performance of CIBs.

References
(1) Gu, J.; Zhao, Z.; Huang, J.; Sumpter, B. G.; Chen, Z. MX Anti-MXenes from Non-van Der Waals Bulks for Electrochemical Applications: The Merit of Metallicity and Active Basal Plane. ACS Nano 2021, 15 (4), 6233–6242.
(2) Banerjee, S.; Ghosh, K.; Reddy, S. K.; Yamijala, S. S. R. K. C. Cobalt Anti-MXenes as Promising Anode Materials for Sodium-Ion Batteries. J. Phys. Chem. C 2022, 126 (25), 10298–10308.
(3) Banerjee, S.; Narwal, A.; Reddy, S. K.; Yamijala, S. S. R. K. C. Promising Anode Materials for Alkali Metal Ion Batteries: A Case Study on Cobalt Anti-MXenes. Phys. Chem. Chem. Phys. 2023, 25 (16), 11789–11804.
(4) Yamijala, S. S. R. K. C.; Kwon, H.; Guo, J.; Wong, B. M. Stability of Calcium Ion Battery Electrolytes: Predictions from Ab Initio Molecular Dynamics Simulations. ACS Appl. Mater. Interfaces 2021, 13 (11), 13114–13122.
(5) Aurbach, D.; Skaletsky, R.; Gofer, Y. The Electrochemical Behavior of Calcium Electrodes in a Few Organic Electrolytes. J. Electrochem. Soc. 1991, 138 (12), 3536–3545.
(6) Ponrouch, A.; Frontera, C.; Barde, F.; Palacin, M. R. Towards a Calcium-Based Rechargeable Battery. Nat. Mater. 2016, 15 (2), 169–172.
(7) Forero-Saboya, J.; Davoisne, C.; Dedryvere, R.; Yousef, I.; Canepa, P.; Ponrouch, A. Understanding the Nature of the Passivation Layer Enabling Reversible Calcium Plating. Energy Environ. Sci. 2020, 13, 3423-3431.