Plane-Selective Coating of LiCoO2 Powders for Li-Ion Batteries

Abstract

LiCoO2 is one of the most widely commercialized cathode materials for Li-ion batteries. Recently, LiCoO2 has been revisited to improve its reversible capacity by increasing the upper cut-off voltage to 4.55 V (vs. Li/Li+). However, LiCoO2 suffers from determental Co-dissolution and electrolyte decomposition at high voltages and high temperatures, resulting in poor electrochemical performance.[1,2] In this connection, various coated LiCoO2 powders have been investigated to reduce these irreversible surface reactions.[3] Coated LiCoO2 powders 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 LiCoO2 powders. However, the full coverage of coating layers interrupts the charge-transfer of Li+ ions, resulting in the poor rate capability of LiCoO2. This implies that we can improve the rate performance of LiCoO2, if we are able to coat specific facets of LiCoO2 powders except for the charge-transfer planes. In this presentation, we introduce, for the first time, a new plane-selective coating of LiCoO2. For example, we demonstrate that metal oxides coating layers are grown plane-selectively on the LiCoO2(001) surface. We show synthesis details for the plane-selective coating of LiCoO2. Scanning transmission electron microscopy (STEM) analysis was carried out with a high-angle annual dark field (HAADF) mode to observe the plane-selective coatings. The electrochemical performance of the plane-selectively coated LiCoO2 was better than that of the conventionally coated LiCoO2. Moreover, we discuss the origin of the plane-selective coating of LiCoO2.