Ordered mesoporous materials for lithium-ion batteries

This article reviews the synthesis and applications of ordered mesoporous materials (excluding carbon or carbon-based nanocomposites) for lithium-ion batteries. Mesoporosity of electroactive materials is usually seen as an opportunity for increasing the specific surface area, but it can have a stronger impact on the electrochemical behavior of inorganic materials because the lattice networks are significantly altered. This alteration is, of course, more severe for microporous materials, but micropores are not electrochemically accessible. In the case of mesoporous materials, the electrochemical accessibility is strongly dependent on the pore physical and chemical structure. In other words, mesoporosity should be specifically designed for specific electrochemical systems. Here, the syntheses of mesoporous electroactive materials (mostly metal oxides) are reviewed by inspecting their electrochemical performance in lithium-ion batteries. The purpose is not just to have an ordered arrangement of mesopores, but also uniform pore walls with a thickness in the meso-size range. The applicability of mesoporous electroactive materials has been somehow overshadowed by the popularity of mesoporous carbon, but there are significant differences. While the wall thickness in the latter mainly controls the specific surface area, this defines the ratio or pathway of the solid-state diffusion in the former, which is the rate-determining step in lithium-ion batteries. The ultimate goal is to highlight the potential for designing the lattice network to make more edge units ready to participate in the electrochemical reactions. It is believed that the mechanism of Li intercalation into the side lattice units is different from the conventional solid-state diffusion throughout the compact lattice network of a bulk material. It is clarified that the role of uniform thin pore walls is more important than that of pore size, though, the latter is usually the point of attention in the literature. (C) 2017 Elsevier Inc. All rights reserved.