Microscopic Elucidation of Solid‐Electrolyte Interphase (SEI) Film Formation via Atomistic Reaction Simulations: Importance of Functional Groups of Electrolyte and Intact Additive Molecules

Abstract

Secondary batteries such as Li‐ion battery are expected to be utilized as not only ubiquitous electric power sources such as mobile phones but also large‐scale electricity storage devices. Therefore, it is urgent to develop the higher performance secondary batteries. Their lifetime and stability are found to be strongly dependent on the nature of passivation film called solid electrolyte interphase (SEI) film formed on the anode surface in the initial charge‐discharge cycle. However, since it is difficult to directly observe the film formation processes in experiment, its microscopic mechanism is still not found. On the other hand, although the theoretical methods are useful complement to the experiment, some new methodologies are necessary to understand the long‐term processes of SEI film, which is produced as a result of that a lot of chemical reactions proceed simultaneously. Under the circumstances, we have developed Red Moon method that can simulate such complex chemical reaction systems, and were able to analyze for the first time the SEI film formation processes on the anode surface at the atomistic level. Then, we clarified theoretically the microscopic mechanism of the additive effect which is essential to improve the Na‐ion battery performance so as to enhance the SEI film formation. This new microscopic insight must provide an important guiding principle for use in designing the most suitable electrolytes for developing high‐performance secondary batteries.

Development of advanced electrolytes in Na-ion batteries: application of the Red Moon method for molecular structure design of the SEI layer

“…Also, the RM method has shown great applicability in simulating the dynamic effect on SEI lm formation, such as the aggregation and the dissolution of the reduction reaction products. [59][60][61][62][63][64][65] In addition, the RM method has recently shown a high efficiency to treat the dynamic processes of catalytic polymerization reactions. 66,67 In fact, it can be applicable also to more complicated electrolyte systems such as polymer electrolytes or ionic liquids.…”

“…More recently, we have theoretically observed that, on a similar structural basis, the cis-versus trans-conguration difference of butylene carbonate (BC) molecule brings about a similar stabilization difference during the microscopic SEI formation processes in LIBs. 65 In this way, the RM method has fruitfully bridged the gap between the computational investigations and experimental ones from the viewpoint of SEI lm formation. It can clarify the mystery of the conventional LIBs performance affected by the slight difference between EC and PC or BC, which is the presence or absence of a methyl group 62 or even just the difference between the cis-and trans-isomeric congurations of a unique molecule.…”

“…Then, many application works have demonstrated that this method is predictive enough and, therefore, quite helpful to understand the microscopic mechanism concerning the SEI lm formation in secondary batteries. [59][60][61][62][63][64][65] Consequently, this review aims to shed light on the modeling progress of SEI formation using a new theoretical chemistry approach and correlate some predicted SEI properties with battery performance and degradation for the development of advanced secondary batteries electrolyte in NIBs.…”

Frontiers in Theoretical Analysis of Solid Electrolyte Interphase Formation Mechanism

“…In particular, the recently developed RM method [ 77 ] has greatly advanced the analysis of unexplored subjects that link elementary electrolyte reduction reactions to the morphological features of SEI layers. [ 62–69 ] In this regard, this review focuses on the aggregation process of electrolyte reduction products that ultimately leads to the formation of a stable SEI layer to ensure a longer lifetime and faster kinetics. Notably, the formation of SEI was found to proceed in a bottom‐up manner (Figures 4 and 8), which dominates the overall morphology of the SEI, such as the inorganic–organic bilayer structure in conventional electrolytes and the anion‐derived nature in concentrated electrolytes.…”

“…Although the compositional and morphological evolution during SEI growth has been studied by in situ experiments, [28,58,59] there is only a limited understanding of how the SEI structure is formed and what reactions dominate at each stage. Recently, theoretical studies using multiscale simulation methods, such as kinetic Monte Carlo (MC) [60,61] and Red Moon (RM) methods, [62][63][64][65][66][67][68][69] have emerged to bridge the gap between the conventional theoretical results (e.g., initial reduction reactions of electrolytes) and experimental ones (e.g., morphologies of the formed SEI layers). Elucidating these poorly understood intermediate steps will enable us to establish a new interphaseoriented electrolyte design that may realize next-generation batteries.…”