Effects of chelating agents on the performance of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ as cathode material for Li-ion battery prepared by sol–gel method

In this study, Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ as lithium-ion battery cathode active material was prepared by a sol–gel method. The effects of chelating agents including three different kinds of chelating agents (citric acid, glycolic acid, and polyvinyl pyrrolidone) on its performance were studied. X-ray diffraction tests were carried out to explore the samples’ structure, showing α-NaFeO₂ structure with \(R - \bar 3m\) space group for all the samples. After various kinds of tests, the sample prepared with citric acid showed the worst properties among the three samples. The sample prepared with polyvinyl pyrrolidone has the smallest size (200–350 nm), with uniform distribution and smooth surfaces. Electrochemical tests show that it has the highest initial discharge capacity (231 mAh g⁻¹) and initial charge/discharge efficiency (70.9%). Electrical impedance spectroscopy confirms that its low charge-transfer resistance is responsible for the superior discharge capacity and rate performance. Furthermore, the sample prepared with polyvinyl pyrrolidone could improve its cycle performance after coating with 3% graphene; its capacity retention is up to 89.8% after 100 cycles at 1 C rate. The sample prepared with glycolic acid achieved the best cycling stability. The discharge capacity was decreased from 150 to 138 mAh g⁻¹, and the capacity retention rate was as high as 91.7% after 100th cycle under a current of 1 C.