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

In view of cost and safety, some Fe-Mn based cathode materials such as LiFeO₂-Li₂MnO₃ solid solution ^[1], Li(Li_0.15Ni_0.21Fe_0.21Mn_0.45)O₂ ^[2] and Li_1.2(Mn_0.32Ni_0.32Fe_0.16)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(Li_0.23Mn_0.47Fe_0.2Ni_0.1)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[Li_1/3Mn_2/3]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[Li_1/3Mn_2/3]O₂ to spinel phase, and suitable amounts of composited Li[Li_1/3Mn_2/3]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.

References

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[3]  K. Karthikeyan, S. Amaresh, G.W. Lee, V. Aravindana, H. Kim, K.S. Kang, W.S. Kim, Y.S. Lee, Electrochim. Acta 68 (2012) 246.

[4]  Jiangang Li, Li Wang, Lei Wang,et al., J. Power Sources 244 (2013) 652.

Fig.1 The investigated (1-x-y)Li[Li_1/3Mn_2/3]O₂-xLiFeO₂-yLiNiO₂ solid solution cathode materials