Electrochemical properties of Li1−z (Ni1−y Fe y )1+z O2 synthesized by the combustion method in an air atmosphere

For the syntheses of LiNi1-y Fe y O2 (0.000 < = y < = 0.300), mixtures of the starting materials with the desired compositions were preheated in an air atmosphere at 400 deg C for 30 min and calcined in air at 700 deg C for 48 h. The phases appearing in the intermediate reaction steps for the formation of lithium nickel oxide are deduced from the DTA analysis. XRD analysis, FE-SEM observation, FTIR analysis and electrochemical measurement were performed for the synthesized Li1-z (Ni1-y Fe y )1+z O2 (0.000 < = y < = 0.300) samples. The samples of Li1-z (Ni1-y Fe y )1+z O2 with y = 0.025 and 0.050 have higher first discharge capacities than Li1-z (Ni1-y Fe y )1+z O2 with y = 0.000 and better or similar cycling performance at the 0.1 C rate in the voltage range of 2.7-4.2 V. Similar results have not previously been reported except for Co-substituted LiNiO2. The sample Li1-z (Ni0.975Fe0.025)1+z O2 has the highest first discharge capacity (176.5 mAh g). Rietveld refinement of the XRD patterns of LiNi1-y Fe y O2 (0.000 < y < = 0.100) from a starting structure model [Li,Ni]3b[Li,Ni,Fe]3a[O2]6c showed that cation disordering occurred in the samples.