Toward multicomponent mesoporous single-crystalline metal oxides

Mesoporous metal oxide materials have attracted significant interest due to their porous frameworks and large surface areas, finding applications in sensors, catalysis and energy storage [1]. The performance of these materials is influenced by both their porous structures and the crystal phase of the frameworks [2]. In lithium-ion storage, the utilization of bulk single-crystal electrode materials enhances ionic conductivity but may trade off diffusion distance, impacting rate capability and cycle stability. Designing a mesoporous single-crystal microparticle is crucial for achieving high-performance lithium storage by combining microstructure and nanostructure advantages [3].

The two primary synthesis routes, hard-templating and soft-templating approaches, offer distinct advantages, with the latter being more straightforward, controllable and suitable for mass production [4]. Nevertheless, challenges persist in extending the soft-template approach to the synthesis of metal oxide single crystals comprising more than three components [5]. The challenge arises due to several factors, including rapid hydrolysis and condensation rate leading to macroscopic phase separation, the decomposition of surfactants at low temperatures inducing structural collapse, and the high temperature which is often needed for the crystallization of multi-metal oxides.

In a recent study led by Prof. Li, mesoporous Li₂TiSiO₅ exhibiting a single-crystal-like structure was fabricated using soft micelles as templates [6]. Rather than merely combining commercial precursors, Li et al. synthesized stoichiometric citrate Ti⁴⁺/Li⁺ chelate precursors. The coordination of Ti⁴⁺ and Li⁺ ions by carboxyl groups in citric acid not only prevented uncontrollable hydrolysis but also facilitated stable atomic dispersion. Subsequently, the conversion of citrate and silicates into rigid carbon and SiO₂ frameworks effectively prevented structural collapse. Also, an in-depth investigation was conducted into the structural evolution of mesoporous Li₂TiSiO₅ exhibiting a single-crystal-like composition, correlating with escalating pyrolytic temperatures. As the temperature rose, the framework underwent a fascinating crystallization sequence, progressing from the Li₂TiO₃ phase, through a mixed phase of polycrystalline Li₂TiO₃ and Li₂TiSiO₅ phase, to single-crystalline Li₂TiSiO₅ phase (Fig. 1). The gradual decrease of pore size and volume provided evidence of the fabrication of a highly crystalline metal oxide.

Figure 1.

Fabrication process of single-crystal-like mesoporous Li₂TiSiO₅, utilizing a micelle-directed self-assembly strategy.

Then, to explore the impact of metal oxide shape and crystallinity on lithium storage, single-crystal-like mesoporous Li₂TiSiO₅ was employed as the anode material for lithium-ion batteries. This material exhibited outstanding electrochemical performance, surpassing its counterparts, including bulk Li₂TiSiO₅ and polycrystalline Li₂TiSiO₅. Advantages included high-capacity retention, superior rate capability and long-term cycling performance. This result was attributed to the nanosized crystal frameworks and short Li⁺ ion diffusion lengths inherent in the single-crystal-like mesoporous Li₂TiSiO₅.

This leading study provides a novel method for fabricating highly crystalline mesoporous multicomponent metal oxides. This pioneering study introduces an innovative approach that has established a new standard in the fabrication of highly crystalline mesoporous multicomponent metal oxides. With its superior performance and potential for widespread applications, this discovery represents a significant leap forward in the quest for efficient energy storage solutions.

Conflict of interest statement. None declared.