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

• The Li⁺ and Br⁻ ions are firstly co-doped in LiNi 0.5 Mn 1.5 O 4 via a solid-state method. • Significant increase of Li⁺ diffusivity and decrease of Mn³⁺ion contents can be observed in the Li⁺ and Br⁻ co-doped LiNi 0.5 Mn 1.5 O 4. • Rate performance and cycling capability have been improved by the Li⁺ and Br⁻ co-doping. • 4. The surface resistance, especially the charge transfer resistance, can effectively reduce by the Li⁺ and Br⁻ co-doping in spinel LiNi 0.5 Mn 1.5 O 4. Few studies have reported the effects of cation and anion co-doping in LNMO. Pristine LiNi 0.5 Mn 1.5 O 4 and Li 1+ x Ni 0.5 Mn 1.5 O 4- x Br x (0 ≤ x ≤ 0.04, mol%) were synthesized using a facile solid-state ball-milling process. The structural characterization results suggested that Li⁺ and Br⁻ co-doping effectively decreased the Mn³⁺content and Li x Ni 1- x O impurity phases, and enhanced chemical and structural stability by forming stronger Mn Br bonds rather than Mn O bonds. Electrochemical performance tests indicated that the Li⁺ and Br⁻ co-doped Li 1.02 Ni 0.5 Mn 1.5 O 3.98 Br 0.02 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 LiNi 0.5 Mn 1.5 O 4 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. (a) Schematic illustration of Li 1+x Ni 0.5 Mn 1.5 O 4-x Br x structure; (b) Rate capacities of all the samples at different C-rates. [Display omitted] [ABSTRACT FROM AUTHOR]