Enhanced cyclic stability and discharge capacity of NCM811 cathode by coating ferroelectric-type LiNbO3 ionically conductive layer

High nickel LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode is widely employed in power batteries. However, discharge capacity and cyclic stability are significantly influenced by the operating temperature. Surface coating is an effective way of improving the electrochemical properties of NCM811. Herein, a stable LiNbO3 coating layer, with excellent ferroelectricity, is introduced on the NCM811 surface. Several material and electrochemical characterization techniques, such as XRD, SEM, EDS, TEM, XPS, CV and EIS, are utilized to discuss the positive influence of LiNbO3 on electrochemical performance. On the one hand, LiNbO3 provides a protective layer to suppress side reactions and isolate the corrosion of electrolyte. On the other hand, ferroelectric LiNbO3 generates polarization under the influence of electric field to promote Li+ (de)intercalation during the charge/discharge process. Besides, LiNbO3 is a widely recognized fast ionic conductor that can promote the rapid diffusion of Li+. It is revealed that the LiNbO3-coated NCM811 exhibits excellent capacity retention of 91.7%, 93.5% and 88.4% at 0 ℃, 25 ℃ and 50 ℃ after 100 charge/discharge cycles at 1 C, respectively. Moreover, the initial discharge capacity of LiNbO3-coated NCM811 cathode is as high as 152.4 mAh/g at 0 ℃. These results indicate that a ferroelectric ionic conductor coating is an effective strategy to enhance the cyclic stability and specific capacity of NCM811 cathode.