Synthesis and Electrochemical Properties of F-doped Li[NixCo1-2xMnx-yMgy]O2 materials via Coprecipitation.

Abstract

Introduction The Li[Ni1/3Co1/3Mn1/3]O2 positive electrode material was studied for use in Li-ion battery to replace the presently popular LiCoO2. Ohzuku and Makimura reported the electrochemical performance of the layered compound Li[Ni1/3Co1/3Mn1/3]O2. Li[Ni1/3Co1/3Mn1/3]O2’s unstable cycling performance results in a gradual capacity fade, especially when charged to higher voltage (~4.5, 4.6V) [1]. Li[Ni1/3Co1/3Mn1/3]O2 consists of Ni2+, Co3+, and Mn4+ in its formal charge; the solid-state redox of Li[Ni1/3Co1/3Mn1/3]O2 shows that the tetravalent manganese ions do not participate in the redox reaction between 2.7 and 4.8 V. One way to improve the electrochemical performances is to substitute metal ions for Ni, Co, Mn to stabilize the layered structure during cycling. One of the best candidate for the substitution would be Mg, because the Mg2+ ions do not participate in the redox process, making it possible to maintain the inter-slab space during repetitive Li+ de-/intercalation [2]. Anion doping also resulted in the good cycling performances. Amatucci et al. observed that the formation of oxyfluoride, LiAl0.2Mn1.8O3.8F0.2, resulted in improvements in capacity and its retention during 300 cycles [3]. Therefore, doping the Li[Ni1/3Co1/3Mn1/3]O2 oxide with Mg and F may provide a synergistic effect in improving the electrochemical performance. The synergistic effect of doping the Li[Ni1/3Co1/3Mn(1/3- x)Mgx]O2-yFy cathode (x = 0-0.04, y = 0-0.04) is presented in this paper.