Preparation and characterization of Li1.167-xKxMn0.583Ni0·25O2 (x=0, 0.025, 0.05 and 0.075) as cathode materials for highly reversible lithium-ion batteries

Abstract Lithium-rich cathode materials have the potential for applications in high energy lithium-ion batteries, but they suffer from a low rate performance and an inferior cycling stability. In this work, Li1.167-xKxMn0.583Ni0·25O2 (x = 0, 0.025, 0.05 and 0.075) samples are synthesized and characterized. In addition, K+ doping results in small perturbations in the crystal structure of Li1.167-xKxMn0.583Ni0·25O2, such as the Li–O bond lengths, lattice parameters and the oxidation states of manganese, which effectively improves the lithium diffusion ability and hinders the detrimental interphase growth of the spinel phase during cycling. In a half-cell, Li1·117K0·05Mn0·583Ni0·25O2 (LK2MNO) with an optimized doping quantity of K+ delivers the best capacities of 152.0 mAh g−1 after 100 cycles at a 1C rate and 82.9 mAh g−1 after 300 cycles at a 10C rate, in comparison with Li1·167Mn0·583Ni0·25O2, which has a capacity of only 126.0 and 33.3 mAh g−1. In the full-cell with graphite as the negative electrode, LK2MNO delivers an initial capacity of 249.9 mAh g−1 at a 0.1C rate and retains 90.8% of its initial capacity after 100 cycles. The surface chemical states of the positive electrode and negative electrodes after 100 cycles is studied by ex situ SEM and XPS measurements, and the results reveal that an appropriate K+ doping amount effectively hinders the dissolution of Mn2+ from the cathode material and decreases the decomposition of electrolytes to some degree.