Synthesis And Performance Study Of Fe^ⅡLi_1.2Ni_0.13Co_0.13Mn_0.54O₂Cathode Material For Li-ion Battery

Compared with conventional cathode materials for lithium ion batteries, thelayered Li1.2Ni0.13Co0.13Mn0.54O2has many merits, such as higher capacity, lowertoxicity, and lower cost, and so on.Also, the material can deliver an initial dischargecapacity as high as250mAh/g when the cut-off voltage is over4.5V. However, thematerial has an irreversible capacity loss on the initial cycle and bad cycling stability,particularly at higher current rates.In this paper, Li1.2Ni0.13Co0.13Mn0.54O2with high capacity was parpared bycarbonate co-precipitation methode and solid state reaction methods. The facts such asconcentration of ammonia, agitation speed, concentration of [M2+](M=Ni, Co, Mn),pH and reaction time in co-precipitation and the calcining way, calcining temperatureand the Li content were optimized to obtain the layered lithium rich oxides withexcellent performance. The perfect spherical precursor (TD is1.8g/cm3)with highpahse purity was synthesized by controlling the facts in co-precipitation process, andthe nickel-cobalt-manganese ratio of the precursor closed to the theoretical value(0.13:0.13:0.54). The Li1.2Ni0.13Co0.13Mn0.54O2synthesized at the best conditiondelivered an initial discharge capacity of230.96mAh/g with initial coulombicefficiency of76.5%.Acapacity retention of about98.46%was obtained after40cycles between2.0~4.8V at0.1C rate.And then, the Li1.2Ni0.13Co0.13Mn0.54O2samples coated with AlF3have beenprepared and investigated. The2%AlF3-coated Li1.2Ni0.13Co0.13Mn0.54O2powdersexhibited superior electrochemical performance in comparison with the pristinesample at room temperature (25℃), including highest initial discharge capacity of240.3mAh/g, lowest initial irreversible capacity loss, better cyclic performance.Meanwhile, the low-temperature performance of material was also improved afterAlF3coating. CV and EIS results showed that the improvement of low-temperatureperformance of theAlF3-coated Li1.2Ni0.13Co0.13Mn0.54O2is determined primarily byRctand DLi+(SEI). The decrease of Rctis mainly due to the formation of Spinel structure and the LiAlO2on the surface of the material, while the increase of DLi+isdue to the suppression of undesired SEI layers.At last, porous Li1.2Ni0.13Co0.13Mn0.54O2cathode material is prepared bycolloidal crystal template assembled by the poly (methyl methacrylate)(PMMA)beads. SEM and TEM results show that the nanoplates of porous solid solutioncathodes are conposed of nanoparticles with a range of30nm, which interweavetogether forming an open porous structure. Electrochemical tests show that porousLi1.2Ni0.13Co0.13Mn0.54O2cathode could deliver higher discharge capacity than that ofbulk Li1.2Ni0.13Co0.13Mn0.54O2cathode at all C-rates. The enhanced structure stabilityreflected by high ratios of integrated Intensity I(003)/I(104) and lattice parameters c/a,high specific surface area, a fast reaction and ionic diffusion kinetics of the nanoplatesare considered attributable to the improved electrochemical properties.