Enhanced cyclic stability of Co-free and Ni-rich LiNi0.95Mn0.05O2 cathodes by coating flexible and electronically conductive PPy layer

Abstract

Co-free and Ni-rich LiNi0.95Mn0.05O2 (NM95) cathodes are expected to be widely employed in power batteries due to their high capacity and low cost. However, the loss of Co and increase in Ni compromise cyclic stability and high-rate performance. Herein, PPy coating layer with excellent flexibility and conductivity is introduced on NM95 surface to enhance the structural stability and charge transfer properties. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry are utilized to elaborate on positive influence of PPy on electrochemical performance. PPy coating alleviates volumetric changes of cathode caused by charge/discharge process, suppressing mechanical fragmentation. Moreover, PPy provides protective layer to suppress side reactions and isolate the corrosion of electrolytes. Besides, PPy is widely recognized excellent electronic conductor that can promote electronic conduction. It is revealed that PPy-coated NM95 cathode exhibits excellent capacity retention of 90.1 % (4.3 V) and 84.4 % (4.5 V) after 100 charge/discharge cycles at 1 C. Moreover, capacity retention is 91.1 % after 100 cycles and initial capacity is as high as 153.4 mAh/g at 5 C. These results indicate that flexible and electronically conductive coating is effective strategy to enhance cyclic stability of NM95 cathodes.