F127-assisted synthesis of LiNi0.5Co0.2Mn0.3O1.99F0.01 as a high rate and long lifespan cathode material for lithium-ion batteries

Modification method with various modus combined has become a hot spot for studying cathode materials for lithium-ion batteries. In this work, F127-assisted synthetic LiNi0.5Co0.2Mn0.3O1.99F0.01 (F127-NCMF) was prepared by a simple carbonate co-precipitation method. The use of F127 surfactant resulted in a changed precursor morphology which confirmed by SEM results, making LiNi0.5Co0.2Mn0.3O2 product with more complete crystal structure and higher crystallinity. F-doping further stabilizes the structure, enlarges the layer spacing, and thereby greatly increases the rate capability and cycle stability of materials. The modified F127-NCMF shows super-high capacity retention of 79.04% at 10C after 500 repeated cycles, while that of pristine NCM remains only 2.93%. From cycle results, we can draw that F127 modification can only delay but cannot reduce capacity attenuation during long-term cycling due to the unchanged intrinsic material structural stability. In addition, F doping can suppress the occurrence of side reactions between electrode and electrolyte at high voltages, thereby reducing the increase in impedance during cycling. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results of the cycled electrodes prove that F127-NCMF has a very stable structure, which well explains the excellent cycling performance of F127-NCMF.