Preparation And Electrochemical Of Li-Rich Li_1.2Co_0.4Mn_0.4O₂ Cathode Materials

Li-rich layered cathode materials have been considered as very promising cathode materials due to their advantageous physical-chemical properties, such as high operational voltage, high theoretical capacity and good thermal stability However, lithium-rich composites simultaneously suffer from high initial irreversibility, intrinsic inferior rate capability and modest cycling performance. The progresses for lithium-rich composites are predominantly focused on the problems in recent years.Morphological designs of spherical architecture, composed by nanosheet taken as secondary nanomaterials, have been successfully realised by solvothermal methods. Li_1.2Co_0.4Mn_0.4O₂ particles are typically of micrometer dimensions but internally consist of nanometre-sized domains or bars, which could not only reduce sidereactions with the electrolyte, but also can provide shorter diffusion length, faster Li+ transport pathway and effective interfacial area. The hierarchical microspheres（H-LCM） shows better electronical performances than the porous microspheres（P-LCM）, expecially at the high current density. For the sample H-LCM, the specific discharge capacity is 173.38 mA h g^-1 for the first cycle and the capacity retention is 76.55%（132.73 mA h/g） after 100 cycles at a current density of 200 mA g^-1. The GITT results shows that the higher DLi+ value of H-LCM than that of P-LCM is indicative of a better kinetic potential window, which confirms that the H-LCM has a better hierarchy configuration.Carbon coated Li_1.2Co_0.4Mn_0.4O₂ cathode material has been successfully synthesized by a self-combustion reaction（SCR）. The sintering temperature and time were optimized to 900℃ and 15 h. Moreover, sucrose is the best source of sugar and the amount of sucrose should be appropriate. The samples prepared at optimum conditions exhibited a high discharge capacity and excellent rate capability. Compared with the material produced by solid state method（SSM）, the one from self-combustion reaction（SCR） exhibits both better rate capability and cycling performance. For the sample SC-LCM, the specific discharge capacity is 166.01 mA h g^-1 for the first cycle and the capacity retention is 85.98%(142.74 mA h g^-1) after 50 cycles at a current density of 200 mA g^-1. It should be noted that carbon layer is of significance to improve the electrochemistry performance. The carbon layer is confirmed by the EDX, TEM and XPS measurements, and the layer slows down the transformation rate of layered to spinel structure. In addition, the layer acts as a fast electron conduction path to increase the Li+ diffusion coefficient, which was further confirmed by the EIS.