Study On Li~+ Extra Transition Metal Oxide Cathode Materials For Lithium Ion Cell

The layered cathode material of LixNi1/3Co1/3Mn1/3O2 (0.95≤x<1.20) has been prepared by using the co-precipitated (Ni1/3Co1/3Mn1/3)(OH)2 and Li2CO3 through solid reaction, ICP-OES and AAS were applied to analyze their compositions; XRD, Rietveld refinement, SEM, DSC and charge-discharge test were employed to characterize LixNi1/3Co1/3Mn1/3O2's structure and performances. The results show that the ratio of I003/I104, the first discharge capacity and the highest peak temperature of DSC curves were all increasing first and then decreasing when 1.00≤x<1.20 and got their maximal value around x=1.05. Rietveld refinement shows that the ratio of cation mixing decreased firstly and then increased as 1.00≤x<1.20, and possessed the minimal value around x=1.08. Therefore, the cation mixing is a key factor which will affect the electrochemical performance, crystal cell parameter and thermal stability of the LixNi1/3Co1/3Mn1/3O2 cathode material.Most of Li1+x[Ni0.4Co0.2Mn0.4]O2(x>0)materials have firstly been found could absorb microwave. Thus, Li1.05Ni1/3Co1/3Mn1/3O2 was firstly prepared by a new simple microwave heating method using Li1.19Ni0.4Co0.2Mn0.4O2 as microwave absorber. The sample has excellent electrochemical properties and thermal stability.Li1.2+x[Ni0.25Mn0.75]0.8-xO2 (0≤x≤4/55) was firstly prepared by a new simple microwave heating method and the effect of extra Li+ content on electrochemistry of Li1.2Ni0.2Mn0.6O2 (x=0) was firstly revealed. X-ray diffraction identified that they had layered a-NaFeO2 structure (space group R-3m). Linear variation of lattice constant as a function of x value supported the formation of solid solution, that is, extra Li+ is possibly incorporated in structure of layered Li1.2Ni0.2Mn0.6O2 (x=0), accompanying oxidization of Ni2+to Ni3+ to form Li1.2+x[Ni0.25Mn0.75]0.8-xO2 (0≤x≤4/55). This was confirmed by X-ray photoelectron spectroscopy that Ni3+ appeared and increased in content with increasing x value. Charge-discharge tests showed that Li1.2+x[Ni0.25Mn0.75]0.8-xO2 (0≤x≤4/55) truly displayed different electrochemical properties (different initial charge-discharge plots, capacities and cycleability). Li1.2Ni0.2Mn0.6O2 (x=0) in this work delivered the highest discharge capacity of 219mAh/g between 4.8 and 2.0 V. Increasing Li content (x value in Li1.2+x[Ni0.25Mn0.75]0.8-xO2 reduced charge-discharge capacities, but significantly enhancing cycleability.