Enhancing the interfacial stability of P2-type cathodes by polydopamine-derived carbon coating for achieving performance improvement

P2-type sodium nickel manganese oxides are considered as promising high-energy-density cathode materials for sodium-ion batteries. However, the interface of P2-type sodium nickel manganese oxides is susceptible to moisture during electrode fabrication process, leading to the occurrence of adverse effects. Herein, we demonstrate that the polydopamine-derived carbon coating is an effective strategy to enhance the interfacial stability of P2-type Na0.80Ni0.22Zn0.06Mn0.66O2. The continuous and uniform carbonized PDA (C-PDA) layers with a thickness of similar to 5 nm can effectively prevent the sodium extraction from the surface of P2-type Na0.80Ni0.22Zn0.06Mn0.66O2 particles during electrode fabrication process and the formation of electrochemically harmful Na2CO3/NaOH species. It is found that an excess of Na2CO3/NaOH species covering on Na0.80Ni0.22Zn0.06Mn0.66O2 particles leads to the formation of an unfavorably thick cathode electrolyte interphase (CEI) layer, which hinders electrochemical sodium extraction from the P2-type phase. As a result, the C-PDA-coated Na0.80Ni0.22Zn0.06Mn0.66O2 exhibits a higher discharge capacity (124 m Ah g(-1) at 12 mA g(-1)), better rate capability (62 mAh g(-1) at 1536 mA g(-1)) and better cycling stability (90.7% capacity retention over 100 cycles) than the uncoated sample. These results suggest that appropriate surface protection to avoid the formation of by-products is critical to the performance improvement of P2-type cathode materials. (C) 2019 Elsevier Ltd. All rights reserved.