Green Synthesis And Surface Coating Modification Of Li-rich Mn-based Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ As Cathode Material For Li-ion Batteries

The Li-excess Mn-based cathode materials xLi2MnO₃·?1-x?LiMO2?M = Mn, Ni and Co? are considered to be the ideal cathode materials of lithium ion batteries for electric vehicles?EV?and hybrid electric vehicles?HEV? due to their high specific capacity and stability at high working voltage. In the work, the M?OH?2 precursor was synthesized via co-precipitation using NaOH and C3H5NaO₃ as the precipitation and complexing agents,then the mixtures of M?OH?2 precursor and LiOH·H2O were calcined at high temperature to form the Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂. The effect of co-precipitation temperature and Li/?Ni+Mn+Co? molar ratio on the microstructure and electrochemical properties of Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂?LMNCO? positive electrode are studied in detail. And then the pristine Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ is modified by ?-MoO₃ and P?VDF-Tr FE? coating layer, respectively, to improve the electrochemical properties.When the co-precipitation temperature is 50 oC and the Li/?Ni+Mn+Co? molar ratio is 1.25:1, the synthesized Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ shows the better layer structure and lower cation mixing degree. The charge/discharge specific capacities of the sample are 355.2/289.4 mAh g-1, as well as 81.5% of the initial coulombic efficiency. In addition, the sample shows a capacity retention of 91.2% and a difference value of discharger mid-point voltage??V? with 0.18 V after 100 cycles at 0.5C rate.The MoO₃ coated Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ cathode materials are synthesized successfully via wet coating process. The MoO₃ coating Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ materials show the better layer structure and lower cation mixing degree. Besides, the electrochemical properties are improved after coated with MoO₃ thin films and the 3wt.%MoO₃@LMNCO sample delivers the best electrochemical properties. The 3 wt.% MoO₃@LMNCO demonstrates the capacities of 179.9mAh g-1 at 1C rate and remains 194.7 mAh g-1 after 100 cycles at 0.5 C rate. However, when further improve the MoO₃ coating content as 5wt.%, the electrochemical properties have declined on the contrary.The P?VDF-TrFE? coated Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ cathode materials are synthesized successfully by using NMP as solvent to dissolve P?VDF-Tr FE?. Subsequently, the a-P?VDF-TrFE?@LMNCO sample undergoes heat treatment at 140 oC to obtain the c-P?VDF-TrFE?@LMNCO sample. Among these cathode materials, the c-P?VDF-TrFE?@LMNCO sample shows the best electrochemical properties. The initial coulombic efficiency is improved from 69.2% to 73.8% at 0.1C rate. And after 100 cycles at 0.5 C rate, the discharge specific capacities remains 190.5 mAh g-1 and a capacity retention of 90.8%.