Enhanced Electrochemical Performance of LiNi0.5Mn1.5O4 by a Dual Modification of Ti Doping and in Situ Coating Using Metal–organic Frameworks As Precursors

During the charging and discharging process of LiNi0.5Mn1.5O4(LNMO) battery, Ni2+ and Mn2+ dissolve into the electrolyte and cause oxidation decomposition, which seriously affects the cycle life of the battery. In addition, the impurity phase in the material can also make the structure unstable, causing poor cycle and rate performance. In this paper, LNMO and LiNi0.5-xTi4xMn1.5-3xO4 ((x)Ti-LNMO, x = 0.02, 0.03, 0.04, 0.06) with spinel structure are synthesized by hydrothermal and high-temperature calcination using metal–organic frameworks (MOFs) as precursors. The obtained LNMO and Ti-LNMOs are further analyzed by a series of characterization and electrochemical performance tests. The XRD results and the Rietveld refinements show that the impurity phases gradually disappear and the lattice parameters of the materials increase with the doping of Ti4+. From the TEM and XPS results, we have observed the Ti-LNMO surface has a uniform Li2CO3 coating layer, which can isolate the direct contact between the electrolyte and the cathode material. The rate and cyclic performance of LNMO are simultaneously improved by a dual modification of Ti doping and in situ coating. When x(Ti) = 0.03, discharge specific capacity is 91.2 mAh/g at 15 C, while the undoped LNMO is only 72.1 mAh/g. Besides, the capacity retention rates of LNMO and 0.03 Ti-LNMO after 200 cycles are 83.2% and 93.8%, respectively. These excellent electrochemical properties are mainly attributed to the more stable crystal structure of the material after titanium doping, the generation of in situ coating layers, the reduction of impurity phases, the suitable particle size, and the stable chemical interface.