Improved capacity and stability of integrated Li and Mn rich layered-spinel Li_1.17Ni_0.25Mn_1.08O₃ cathodes for Li-ion batteries

A Li-rich layered-spinel material with a target composition Li_1.17Ni_0.25Mn_1.08O₃ (xLi[Li_1/3Mn_2/3]O₂.(1 - x)LiNi_0.5Mn_1.5O₄, (x = 0.5)) was synthesized by a self-combustion reaction (SCR), characterized by XRD, SEM, TEM, Raman spectroscopy and was studied as a cathode material for Li-ion batteries. The Rietveld refinement results indicated the presence of monoclinic (Li[Li_1/3Mn_2/3]O₂) (52%), spinel (LiNi_0.5Mn_1.5O₄) (39%) and rhombohedral LiNiO₂ (9%). The electrochemical performance of this Li-rich integrated cathode material was tested at 30 °C and compared to that of high voltage LiNi_0.5Mn_1.5O₄ spinel cathodes. Interestingly, the layered-spinel integrated cathode material exhibits a high specific capacity of about 200 mA h g^-1 at C/10 rate as compared to 180 mA h g^-1 for LiNi_0.5Mn_1.5O₄ in the potential range of 2.4-4.9 V vs. Li anodes in half cells. The layered-spinel integrated cathodes exhibited 92% capacity retention as compared to 82% for LiNi_0.5Mn_1.5O₄ spinel after 80 cycles at 30 °C. Also, the integrated cathode material can exhibit 105 mA h g^-1 at 2 C rate as compared to 78 mA h g^-1 for LiNi_0.5Mn_1.5O₄. Thus, the presence of the monoclinic phase in the composite structure helps to stabilize the spinel structure when high specific capacity is required and the electrodes have to work within a wide potential window. Consequently, the Li_1.17Ni_0.25Mn_1.08O₃ composite material described herein can be considered as a promising cathode material for Li ion batteries.