Formation of Solid Electrolyte Interphase in Lithium Batteries: A Reactive Force Field Molecular Dynamics Study

Lithium battery (LB) is one of the most promising candidates for replacement of petrol/diesel to achieve environmentally friendly targets in electric vehicles (EVs). However, the performance of lithium batteries is strongly affected by degradation and thermal effects. The solid electrolyte interphase (SEI) forms between anode and electrolyte in the LB and is considered to be the main contributor to LB degradation. Understanding the mechanisms of SEI formation and the associated electrolyte reduction could be beneficial in the design of high-performance lithium batteries for a wide range of applications in energy and power industry. In order to study the degradation and SEI formation, reactive force field (ReaxFF) molecular dynamics simulations are employed in this research to gain detailed atomic-level insights into the key phenomena. Firstly, the fundamental decomposition mechanism of ethylene carbonate (EC) electrolytes with active lithium atoms is investigated. Secondly, the effect of different reaction temperatures on SEI formation on the lithium metal anode surface in contact with pure EC electrolyte is studied. The structural variations of SEI are observed, and the results indicate that temperature elevation boosts SEI formation. Thirdly, the effect of the composition of electrolytes on SEI structure is studied, and the addition of lithium salts with different concentrations is investigated. The findings of this research provide important insights into the nature and structural variations of the lithium metal electrode and SEI at the molecular level. The results demonstrate that reactive molecular dynamics simulation is an efficient and effective tool for predicting the performance and degradation of lithium batteries. The research and the atomistic simulation tool can contribute to the design and optimisation of future novel battery materials