Scalable nanomanufacturing of millimetre-length 2D NaxCoO2 nanosheets

Abstract

A novel, scalable nanomanufacturing technique is reported for batch fabrication of nanoscale-thick Na_0.7CoO₂ nanosheets. The nanomanufacturing technique is a high-yield, bottom-up process that is capable of producing tens of thousands of nanosheets stacked into a macro-scale pellet. The nanosheets are uniform in length and shape with very high crystal anisotropy. The nanosheet thicknesses can be 10–100 nm while their lengths can measure up to 1.8 mm long. The typical dimension ratios are highly anisotropic, at 10⁻⁵:1 : 1 (thickness:length:width). X-ray synchrotron studies indicate that the 2D crystals are stacked in a turbostratic arrangement with rotational misalignment with respect to the stacking axis. The stacked nanosheets are readily delaminated into very large (350 μm × 150 μm × 100 nm) free-standing 2D crystals. The novel nanomanufacturing technique is based on sol–gel and electric-field induced kinetic-demixing followed by a brief high temperature treatment, thus providing an efficient means of large scale crystal growth requiring only a simple furnace and power supply. Evidence shows that the demixing process increases the concentration of Na ions and that demixing is necessary to produce the millimetre-length nanosheets. Electric field induced kinetic-demixing is successfully performed at low temperatures (<300 °C), which is more than three times lower than past kinetic-demixing temperatures.