Li Storage Properties of (1-x-y)Li[Li1/3Mn2/3]O2-xLiFeO2-yLiNiO2 Solid Solution Cathode Materials

Abstract

In view of cost and safety, some Fe-Mn based cathode materials such as LiFeO2-Li2MnO3 solid solution [1], Li(Li0.15Ni0.21Fe0.21Mn0.45)O2 [2] and Li1.2(Mn0.32Ni0.32Fe0.16)O2 [3] etc., were investigated in recent years. Our research group also developed a new cobalt free LiFeO2-Li2MnO3 based solid solution with a composition of Li(Li0.23Mn0.47Fe0.2Ni0.1)O2 to obtain high capacity of 277.4 mAh/g and better cycling stability [4]. In order to further optimize the solid solution composition to obtain the best electrochemical performance, the effects of solid solution composition on Li storage properties should be investigated thoroughly.In this paper, a series of materials with the composition of (1-x-y)Li[Li1/3Mn2/3]O2-xLiFeO2-yLiNiO2(x+y£0.5)were prepared by sol-gel method, and the effect of annealing condition on the structural and electrochemical properties of as-prepared materials were investigated. The results reveal that all of materials prepared at 600 oC ~800 oC show pure layered a-NaFeO2 phase. However, the electrochemical performance varies with the solid solution composition. As shown in Fig.1, as-prepared materials with x+y=0.3~0.4 exhibit better cycling performance, indicating that suitable amounts of composited LiFeO2 and LiNiO2 in the solid solution is benefit for reducing the transformation of layered Li[Li1/3Mn2/3]O2 to spinel phase, and suitable amounts of composited Li[Li1/3Mn2/3]O2 can also restrain cubic LiFeO2 formation. Obvious cooperative effects are observed. In addition, as-prepared samples with high capacity of >210 mAh/g also distribute in this composition range, as shown in shadow area of Fig.1. However, high capacity of above 240 mAh/g can only be obtained while the material with composition of x/y<0.6 and x/y>2 in the shadow range. Further detailed discussion will be presented in the meeting.