A passivation layer called the solid electrolyte interphase (SEI) is formed on electrode surfaces from decomposition products of electrolytes. The SEI allows Li⁺ transport and blocks electrons in order to prevent further electrolyte decomposition and ensure continued electrochemical reactions. The formation and growth mechanism of the nanometer thick SEI films are yet to be completely understood owing to their complex structure and lack of reliable in situ experimental techniques. Significant advances in computational methods have made it possible to predictively model the fundamentals of SEI. This review aims to give an overview of state-of-the-art modeling progress in the investigation of SEI films on the anodes, ranging from electronic structure calculations to mesoscale modeling, covering the thermodynamics and kinetics of electrolyte reduction reactions, SEI formation, modification through electrolyte design, correlation of SEI properties with battery performance, and the artificial SEI design. Multi-scale simulations have been summarized and compared with each other as well as with experiments. Computational details of the fundamental properties of SEI, such as electron tunneling, Li-ion transport, chemical/mechanical stability of the bulk SEI and electrode/(SEI/) electrolyte interfaces have been discussed. This review shows the potential of computational approaches in the deconvolution of SEI properties and design of artificial SEI. We believe that computational modeling can be integrated with experiments to complement each other and lead to a better understanding of the complex SEI for the development of a highly efficient battery in the future.

Cracking the problem of cracking cathodes: Polycrystalline cathode materials that contain a combination of nickel, manganese, and cobalt have been used for advanced lithium batteries. These materials fracture at high voltage, which increases surface area and leads to more side reactions and shorter cycle life. Using single-crystalline samples as model materials, Bi et al. observed changes in nickel-rich cathodes to study the fracture behavior under well-characterized conditions. As the material is charged and lithium is removed, specific planes glide over one another and microcracks are observed. However, this process is reversed on discharge, removing all traces of the microcracking. The authors developed a diffusion-induced stress model to understand the origin of the planar gliding and propose ways to stabilize these nickel-rich cathodes in working batteries. Science , this issue p. 1313

Tougher solar cell interfaces: The low formation energies of the active layers in perovskite solar cells lead to low-toughness materials that are compliant and soft, which limits their interface stability and long-term reliability. Dai et al. show that treatment with iodine-terminated self-assembled monolayers that react with surface hydroxyl groups (which ultimately creates unwanted charge traps and voids) leads to a 50% increase of adhesion toughness between the electron transport layer and a mixed-composition perovskite thin film. The projected point at which 80% of the operating efficiency in perovskite solar cells was still retained increased from ∼700 to 4000 hours for 1-sun exposure with continuous maximum power point tracking. Science , this issue p. 618