Since one of the failure modes of Li-ion batteries is irreversible surface reactions, surface chemistry plays an important role in determining the electrochemical performance of Li-ion batteries.[1,2] For example, transition metal dissolution and electrolyte decomposition on the cathode surface at high voltages and temperatures cause poor electrochemical performance. In this connection, many research groups investigated various coated cathode materials, such as metal oxides, metal fluorides, and carbon-coated cathode materials.[3] These surface modifications reduced the irreversible surface reactions, leading to the improved electrochemical performance.

Surface-modified cathode materials are usually obtained via sol-gel synthesis, dry coating, and atomic layer deposition. These coating techniques are pursuing to uniform coating covering the whole surface of cathode powders. However, the full coverage of coating layers interrupts the charge-transfer of Li⁺ ions, resulting in poor rate capability. Therefore, if we are able to coat specific facets of cathode powders except for the charge-transfer planes, we can improve the rate performance of cathode materials.

In this presentation, we introduce a plane-selective coating of layered oxide cathode materials as a new coating technique. For example, we demonstrate that metal oxide coating layers are grown plane-selectively on the LiCoO₂(001) surface. We carried out scanning transmission electron microscopy (STEM) analysis with a high-angle annual dark field (HAADF) mode to observe the plane-selective coatings. We also performed the theoretical calculations to understand the origin of the plane-selective coatings. The plane-selectively coated LiCoO₂ showed better electrochemical performance than did the conventionally coated LiCoO₂. Moreover, we demonstrate that the plane-selective coating can be extended to various layered oxide cathode materials for Li-ion batteries.

References:

[1] B. Xu, D. Qian, Z. Wang, Y. S. Meng, Materials Science and Engineering: R: Reports 2012, 73, 51

[2] W. Li, A. Dolocan, P. Oh, H. Celio, S. Park, J. Cho, A. Manthiram, Nat Commun 2017, 8, 14589

[3] Y.-K. Sun, C. S. Yoon, S.-T. Myung, I. Belharouak, K. Amine, Journal of The Electrochemical Society 2009, 156, A1005