Facile Mn Surface Doping of Ni-Rich Layered Cathode Materials for Lithium Ion Batteries

Abstract

As the electric vehicles (EVs) market is growing rapidly, lithium ion batteries (LIBs) have received great attention as a suitable power source owing to its high-energy density and excellent power characteristic. To extend a driving mileage of the EVs, it is crucial to further improve the energy density of LIBs. Since the specific capacity and operating voltage of cathode materials are important factors for determining the energy density of LIBs, many researches focus on the development of advanced cathode materials with high specific capacity and high operating voltage. Among various cathode materials, layered cathode materials (e.g., LiMO2, M = transition metal) have been one of the most popular cathode materials in LIBs. The electrochemical properties of these cathode materials are tunable by the choice of transition metals in the host structure; i) Mn secures structural stability, ii) Co increases power characteristic, and iii) Ni contributes to a specific capacity of the materials. In order to increase the achievable specific capacity, researchers have designed the layered cathode materials with a high Ni content (>80%) and they offer a high reversible capacity more than 190 mA h g-1. Unfortunately, Ni-rich layered cathode materials suffer from poor thermal and structural stabilities arising from the high Ni content in the structure. To overcome these limitations, therefore, structural modifications on the Ni-rich cathode materials is highly required to suppress undesirable side reactions and formations of impurities (e.g., NiO). Herein, we prepare Mn surface-doped NCM811 (Mn-NCM811) with a core-shell structure via a simple wet-coating process using lithium ethoxide and Mn acetate precursors. Various structural and electrochemical investigations support that Mn-rich shell can effectively improve the structural and thermal stabilities of Ni-rich core, leading to the significant improvement in electrochemical performance of Ni-rich layered cathode materials even at a high operating temperature of 60 °C. From the results, we emphasize the importance of material design and this study will provide practical guidelines for development of Ni-rich layered cathode materials for LIBs.