Synthesis and electrochemical properties of layer-structured 0.5Li(Ni_(0.5)Mn_(0.5))O_2-0.5Li(Li_(1/3)Mn_(2/3))O_2 solid mixture

摘要

A 1:1 mixture of electrochemically active Li(Ni_(0.5)Mn_(0.5))O_2 and electrochemically inactive Li(Li_(1/3)Mn_(2/3))O_2, i.e. Li(Li_(0.17)Ni_(0.25)Mn_(0.58))O_2, has been synthesized by a sol-gel method. The mixture was calcined at 900 ℃ in air for 24 h and cooled at three different rates: quenched into liquid nitrogen, 2℃/min, and 0.5℃/min. It was found that the crystallographic structure and electrochemical proper-ties of Li(Li_(0.17)Ni_(0.25)Mn_(0.58))O_2 highly depend on the cooling rate. The sample quenched into liquid nitrogen exhibited a long irreversible plateau at ca. 4.5 V during the first charge, and the discharge capacity gradually increased from 170 to 210 mAh/g after 40 cycles. The samples cooled at slower rates exhibited more monoclinic character and cubic spinel phase was observed; they showed no plateaus at 4,5V during the first charge and the discharge capacities also gradually increased from 80 and 55 mAh/g to 130 and 85 mAh/g for 2 and 0.5℃/min-cooled samples, respectively.