Chemical degradation and capacity fading is one of challenge in LIBs due to the loss of active cathode material from interaction at the interface of the cathode and electrolyte.¹ The use of coatings based on a non-active oxide, e.g. Al₂O₃, is a prevailing strategy to decrease such degradation based on their role as electronic insulator between cathode and electrolyte.^2,3 Although many strategies have been reported using different synthetic methods, the surface coating is not well controlled owing to random deposition of precursor on powders of complex morphology, which results in inhomogeneities that leave active surfaces without proper passivation.  Therefore, the synthesis of uniform thin films based on aluminum oxides with controlled thickness, coated on each nanocrystal of an active oxide is an important prerequisite to improve the durability of cathode materials.

Herein, LiCoO₂ (LCO) nanoplates were directly synthesized by a hydrothermal process and subsequent coating of aluminum oxide by precursor decomposition and thermal treatment. Figure 1(a) and (b) show TEM images of as-prepared bare LCO nanoplates and coated LCO nanoplates. The edge length and thickness of hexagonal nanoplates is about 50nm and 10~20nm. The exposed surfaces are (001) and (010). 1~2nm thick alumina were uniformly coated on LCO nanoplates. EDX mapping and line scan has confirmed the LCO core and alumina shell structure. The thermal treatments were performed at 400~600^oC for 3hours. The size of LCO didn’t change after coating. The electrochemical properties have demonstrated the enhanced effect of alumina coating. The balance of capacity and cycling ability is dependent on different temperature and loading of alumina.

References:

1. Jonathon L. Tebbe, Aaron M. Holder, and Charles B. Musgrave. ACS Appl. Mater. Interfaces, 24265-24278, 7(2015). Mechanisms of LiCoO₂ Cathode Degradation by Reaction with HF and Protection by Thin Oxide Coatings

2. Seung-Taek Myung, Kentarou Izumi, Shinichi Komaba, Hitoshi Yashiro, Hyun Joo Bang, Yang-Kook Sun, and Naoaki Kumagai J. Phys. Chem. C 2007, 111, 4061-4067, 111(2007). Functionality of Oxide Coating for Li[Li_0.05Ni_0.4Co_0.15Mn _0.4]O₂ as Positive Electrode Materials for Lithium-Ion Secondary Batteries

3. Jun Liu and Arumugam Manthiram. Chem. Mater. 1695-1707, 21 (2009). Understanding the Improvement in the Electrochemical Properties of Surface Modified 5 V LiMn_1.42Ni _0.42Co_0.16O₄ Spinel Cathodes in Lithium-ion Cells