Improvement of cycling performance in Ti substituted 0.5Li2MnO3-0.5LiNi0.5Mn0.5O2 through suppressing metal dissolution

Ti substituted 0.5Li2MnO3-0.5LiNi0.5Mn0.5O2 cathode material with the composition of Li1.5Ni0.25Mn0.75−xTixO2.5 has been synthesized by spray pyrolysis method. A great variety of characterization methods have been applied to study the influence of Ti substitution for Mn on the structural, morphological and electrochemical performances of Li1.5Ni0.25Mn0.75−xTixO2.5. X-ray diffraction (XRD) results of Li1.5Ni0.25Mn0.75−xTixO2.5 show that they exhibit similar XRD patterns as those of lithium-excess manganese metal oxide based cathode materials. It is confirmed from energy dispersive x-ray spectroscopy (EDX) data that Ti was homogenously substituted for Mn and well distributed in the host structure. X-ray absorption near edge structure (XANES) spectra analysis reveals that oxidation state of Mn in Li1.5Ni0.25Mn0.75−xTixO2.5 remains +4 while that of Ni changes from +2 to +4 during the initial activation process. Further investigation of the local structure of transition metal (TM) ions indicates that Ti has same coordination environment as that of Mn. Drastic capacity fade occurred in full cells with Li1.5Ni0.25Mn0.75O2.5 cathode and graphite anode, while full cell with Ti substituted cathode shows high capacity retention after 100 cycles. Further examination of the amount of dissolved transition metal (TM) ions after long cycling test enable us to demonstrate that substitution of Mn with Ti in Li1.5Ni0.25Mn0.75O2.5 has a significant impact on suppressing the TM ions dissolution and its deposition on both separator and anode thus leads to improved cycleability.