Synthesis and electrochemical properties of Li[Ni0.45Co0.1Mn045-xZrx]O2 (x=0, 0.02) via co-precipitation

Abstract

Introduction Recently, a lot of attention has been paid to layered Li[Ni0.5Mn0.5]O2 as an alternative to LiCoO2 and LiNiO2-based cathode materials for Lithium battery system. [1] Due to its small amount of active nickel Ni2+ and a unique role of Mn4+ in stabilizing the structure during cycling, Li[Ni0.5Mn0.5]O2 could be cheaper cathode material with longer cycle life and thermal stability. However, one of problems is its low electronic conductivity that affects poor rate capability and low capacity in the normal operating voltage range. So, Co-doping in Li[Ni0.5Mn0.5]O2 studied to get a good rate capability and a higher capacity. [2] Various kinds of metal doping also investigated to improve electrochemical properties. [3] In this study, we report the synthesis of Li[Ni0.45Co0.1Mn0.45-xZrx]O2 (x=0, 0.02) via co-precipitation and electrochemical properties.

Experimental The [Ni0.45Co0.1Mn0.45-xZrx](OH)2 (x=0,0.02) compounds were synthesized by co-precipitation. An aqueous solution of NiSO4·6H2O, CoSO4·7H2O, MnSO4·H2O and Zr(SO4)2·4H2O were used as the starting materials and NaOH solution and desired amount of NH4OH solution (aq) as a chelating agent were also used. The obtained [Ni0.45Co0.1Mn0.45-xZrx](OH)2 (x=0,0.02) powders were dried in 110oC for 12hr to remove adsorbed water. Finally, powders were simply mixed with lithium sources, and then the mixed powders were calcined at 950oC in a box furnace. The morphology of the powders was observed using a scanning microscope (SEM, JSM 6400, JEOL, Japan). Powder X-ray diffraction (Rigaku, Rint-2000) using Cu Kα radiation was used to identify crystalline phase of the prepared powders at each stage. Cell tests were done using the 2032 coin-type cell with Li-metal as the negative electrode. The cells were charged and discharged between 3.0 and 4.6 V by applying a constant current of 40mA g-1 at 25oC.

Results and discussion SEM images of [Ni0.45Co0.1Mn0.43Zr0.02](OH)2 and Li[Ni0.45Co0.1Mn0.43Zr0.02]O2 powder shown in Figure 1 which have spherical morphology. The average particle size estimated was almost 5-8μm in diameter. Figure 2a shows the XRD patterns of Li[Ni0.45Co0.1Mn0.45]O2 and Li[Ni0.45Co0.1Mn0.43Zr0.02]O2 that exhibits Zr-doped Li[Ni0.45Co0.1Mn0.43Zr0.02]O2 has a good crystallinity. Cycling performance in the voltage rage of 3.0-4.6V shown in Figure 2b which exhibits the Zr-doped material have a lower capacity but shows a superior cyclability.