Enhanced high-rate and cyclic performance of Co-free and Ni-rich LiNi_0.95Mn_0.05O₂ cathodes by coating electronic/Li⁺ conductive PANI-PEG layer

Co-free and Ni-rich LiNi_0.95Mn_0.05O₂ (NM95) cathodes are expected to be widely employed in power batteries due to their high charge storage capacity and cost-effectiveness. However, the loss of Co and increase in Ni contents result in highly active surfaces and unstable structures, compromising rate capability and cyclic stability. Herein, polyaniline-polyethylene glycol (PANI-PEG) coating layer, with excellent electronic and Li-ion conductivity, is introduced on NM95 surface to enhance charge transfer properties and cyclic stability. Several material and electrochemical characterization techniques, such as XRD, SEM, EDS, TEM, XPS, 4-point probe, CV and EIS, are utilized to unveil the positive influence of PANI-PEG on electrochemical performance. The results reveal that PANI-PEG layer can promote electron and Li⁺ conduction of NM95 due to the excellent electronic and Li⁺ conductivities. Besides, PANI-PEG acts as protective layer to hinder the corrosion of electrolyte and suppress side reactions. It is revealed that NM95 cathode coated with PANI-PEG with a mass ratio of 4/6, exhibits excellent initial capacity, as high as 219.4 and 163.1 mAh/g at 1 C and 5 C, respectively, and maintains capacity retention of 94.7% (1 C, 100th cycle) and 79.0% (5 C, 200th) under cut-off voltage of 4.3 V (vs. Li/Li⁺). Moreover, NM95 exhibits capacity retention of 70.7% after 100 charge/discharge cycles at 1 C within voltage range of 2.7 to 4.5 V (vs. Li/Li⁺). These results indicate that coating electronic/Li⁺ conductor is effective strategy to enhance rate performance and cyclic stability of Co-free and Ni-rich cathodes.