Exploring the synergistic effect of Li+ and Br− co-doping on improving the microstructural and electrochemical performances of LiNi0.5Mn1.5O4 cathode materials

Abstract

BackgroundFew studies have reported the effects of cation and anion co-doping in LNMO. MethodsPristine LiNi0.5Mn1.5O4 and Li1+xNi0.5Mn1.5O4-xBrx (0 ≤ x ≤ 0.04, mol%) were synthesized using a facile solid-state ball-milling process. Significant findingsThe structural characterization results suggested that Li+ and Br− co-doping effectively decreased the Mn3+content and LixNi1-xO impurity phases, and enhanced chemical and structural stability by forming stronger MnBr bonds rather than MnO bonds. Electrochemical performance tests indicated that the Li+ and Br− co-doped Li1.02Ni0.5Mn1.5O3.98Br0.02 sample (LNMO-Br0.02) possessed an excellent rate capability. The corresponding discharge capacity at 0.2 C, 0.5 C, 1 C, 2 C, 3 C, 5 C, 7 C, and 10 C were around 134.6, 132.8, 132.0, 127.4, 122.1, 112.9, 102.9, and 82.5 mAh/g, respectively. Under similar conditions, pristine LiNi0.5Mn1.5O4 yielded only 125.7, 124.8, 121.8, 117.0, 111.1, 95.2, 73.0, and 27.6 mAh/g. In addition, LNMO-Br0.02 delivered favorable cycling performance at room temperature (25 °C), and about 95.3% of the initial capacity (120.5 mAh/g) could be obtained after 270 cycles at 3 C. Post-cycling Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analyses revealed that LNMO-Br0.02 possessed the thinner cathode-electrolyte interphase (CEI) film than the other materials.