Hollow Na0.62K0.05Mn0.7Ni0.2Co0.1O2 polyhedra with exposed stable {001} facets and K riveting for sodium-ion batteries

Recently, there has been an increased interest in sodium-ion batteries (SIBs), in which cathodes that directly determine the performance of batteries play a critical role. Among the cathode materials, layered oxide cathodes are the most fascinating electrode materials for SIBs. However, irreversible phase transition, low capacity, poor air stability, and inferior cycling stability limit the application of layered oxides. In this study, hollow P2-Na0.62K0.05Mn0.7Ni0.2Co0.1O2 polyhedra consisting of nanosheets with exposed stable {001} facets and a small amount of large-size K+ ions partly replacing Na+ ions were successfully obtained. By virtue of the high redox potential of Ni2+/4+, it can be stored in air for several days. It also exhibits a high discharge capacity of 115.0 mA h g−1 after 100 cycles at 100 mA g−1. A preeminent discharge capacity of 104.1 mA h g−1 can be achieved even at 500 mA g−1. Results showed that such performances are related to the block of phase transition from P2 to O2 and to the riveting of K+ ions, which expands the interlayer space (d(O—Na—O)) and accelerates the transfer of sodium. Thus, the P2-Na0.62K0.05Mn0.7Ni0.2Co0.1O2 cathode is one of the promising cathode materials for SIBs.