Synthesis of 2D Li₄Ti₅O₁₂ Nanosheets via the "insertion-Exfoliation-Lithiation" Process

Plenty of research efforts have been devoted to developing the anisotropic 2D architectures with intriguing electrochemical and optoelectronic properties. However, the scalable production of nonlayered binary metal oxides with a 2D structure still remains a great challenge. Here, we develop an "insertion-exfoliation-lithiation" process to delaminate the spinel Li₄Ti₅O₁₂ (LTO) into the thickness of ?4 nm. After the intercalation of methylamine (MA) into the H₂Ti₃O₇ interlayers, the MA intercalated titanic acid (MA/Ti₃O₇) exhibits the volume expansion along the stacking direction with the interlayer spacing increasing from an original 7.9 to 10.1 Å. Driven by the acid-base equilibrium and osmotic pressure balance, this crucial step significantly enhances the exfoliation yield of MA/Ti₃O₇ nanosheets upon the mechanical peeling process. First-principles calculation validates that 1.1 unit of MA has been inserted per mole of H₂Ti₃O₇ described as MA_1.1H_0.9Ti₃O₇. In addition, the transmission-mode in situ X-ray diffraction records the real-time phase transition of the as-developed synthetic process, enabling the precise control over the reaction temperature, phase purity, crystallinity of each intermediate, and prevention of the restacking of the LTO nanosheets into the cubic-spinel bulk material. The as-fabricated LTO nanosheets with an appealing ultrathin structure exhibit a reversible specific capacity of 210 mA h g^-1 at 0.25 C, which far surpasses the theoretical capacity limit of bulk counterparts due to the pseudocapacitive contribution from the reduced dimensionality.