Synthesis of LiCoO2 and LiNi1/3Mn1/3Co1/3O2 2D Nanosheets By Osmotic Swelling for High Performance Lithium-Ion Batteries

2D materials have attracted a great deal of attention for their unique electrical and magnetic properties, but may also play important roles in energy storage applications. Lithium-ion batteries and supercapacitors are widely used to power mobile devices, but the energy and power densities of the electrode materials still need improvement. Many conventional battery materials have layered structures, and hence can be readily exfoliated into 2D nanosheet materials.  The high surface area and short ionic diffusion distances in the 2D nanosheets may improve the charging/discharging rates and result in more lithium insertion or surface adsorption. Furthermore, hybrid electrode materials composed layers of different cathode materials may be possible by reassembling different nanosheets. These sandwich structures could potentially result in unique synergistic effects and novel redox behavior due to the interactions from different sheets. Finally, we can obtain better understanding of the structure of complex layered cathode materials through exfoliation and high resolution ex-situ microscopy studies.

Here we present our synthesis of 2D nanosheets of two common lithium-ion battery materials, LiCoO₂ (LCO) and LiNi_1/3Mn_1/3Co_1/3O₂ (NMC). Nanosheets were obtained by exfoliation of LCO and NMC particles using traditional osmotic swelling with tetraethylammonium (TEA). TEM, SEM and AFM analysis showed that the particles were successfully exfoliated nanosheets with around 2 nm thickness. XRD and SADP[CKC1]  analysis showed that these materials had hexagonal structures with good crystallization. A reassembly process was developed and applied to obtain LCO, NMC, and LCO/NMC hybrid particles. Electrochemical evaluation of the particles as electrodes for lithium-ion batteries and supercapacitors were performed. Our work is a firm step forward on improving understanding of osmotic swelling processes for the synthesis of nanosheets from complex metal oxides as well as the design and fabrication of high performance hybrid electrodes for energy storage applications.