Development of the ReaxFF Reactive Force Field for Li/Mn/O Battery Technology with Application to Design a Self-Healing Cathode Electrolyte Interphase

Lithium manganese oxide (LMO) batteries, notable for their three-dimensional structure enhancing ion transport and power, are ideal for critical uses, such as implantable biomedical devices, where battery life and performance are crucial for safety. Understanding their internal chemical reactions is vital for developing advanced models with longer lifetimes and better performance. A significant reaction aspect is the formation of the solid-electrolyte interphase (SEI), crucial in determining the cycle life, capacity fade, and safety of these batteries at both the cathode and anode interfaces. Although the SEI layer's role in battery performance is well-documented, the cathode electrolyte interphase (CEI) formation and its impact on Li-ion battery performance remain unclear. Understanding the CEI formation and mechanisms is vital for improving Li-ion batteries. In this study, we propose a novel strategy for creating a self-healing CEI that effectively seals and neutralizes cracks on the cathode surface. This is achieved by attaching an ion pair to the surface, which promotes a spontaneous healing process. Once the CEI is formed, the bonded cations restrict the reactions between the cathode material and electrolyte, while the anions migrate toward the cracked surface and preferentially decompose compared to the electrolyte. The self-healing CEI significantly minimizes electrolyte depletion and decreases the loss of active materials. To investigate the formation of CEI under real experimental conditions without incurring excessive computational costs, we employed ReaxFF, a molecular dynamics simulation framework trained against ab initio reaction energies and barriers. The ReaxFF simulations enable us to predict CEI formation and study its properties. The results have confirmed that the presence of PYR13+ cations as an electrolyte additive enhances the CEI layer formation and stability on the cathode surface. Moreover, the Li+ ion transference number is higher for systems in the presence of PYR13+. These trends can be attributed to the differences in interactions between FSI– anions and PYR13+ cations. From the results, we expect that ReaxFF will be very useful for the study of medical device batteries and the development of novel regulatory protocols to aid regulators and device manufacturers in the verification of the safe operation of Li-ion batteries.