Scalable nanomanufacturing of millimetre-length 2D NaxCoO2 nanosheets

A novel, scalable nanomanufacturing technique is reported for batch fabrication of nanoscale-thick Na0.7CoO2 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 mu m x 150 mu m x 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 degrees C), which is more than three times lower than past kinetic-demixing temperatures.