| Recently, the new type of Li-rich materials xLi2MnO3·(1-x)LiMO2(M=Ni,Co or Mn),which attract much attention, has been considered as one of the most promising commercialcathode materials of Li-ion battery in the next new generation due to its advantages of highamount of Li, the low proportion of transition metals, and extraordinarily high capacity. Inthis paper, we chose the cathode material Li[Li0.2Ni0.15Mn0.55Co0.1]O2as substrate, thencation/anion doping and co-doping were used to modify it. The electrochemical performancewas characterized by TG, XRD, SEM, CV, EDS and the charge-discharge performance test.The cathode material Li[Li0.2Ni0.15Mn0.55Co0.1]O2was successfully synthesized by thesol-gel method. The effects of different calcination temperatures and time on the morphology,crystal structure and electrochemical performance were extensively studied, and the resultsshow the sample sintering at900℃for12h owns the best electrochemical performance.When using Cr3+, Al3+, Mg2+to substitute Co3+, we found that the doping has no effect onstructure and morphology, but the particle sizes were greatly changed, Cr3+-doped andAl3+-doped materials show the smaller particles compared with undopedLi[Li0.2Ni0.15Mn0.55Co0.1]O2, while the primary particles grow bigger by doping with Mg2+.Charge-discharge performance tests show that the discharge capacity is reduced in someextent with cation Cr3+and Al3+doping, but the cycling performance is improved. When thedoping amount of Cr3+and Al3+was0.05and0.03, the initial discharge capacity was230.6and224.2mAh·g-1with the first coulombic efficiency of80.1and83.2%, respectively at20℃，2.0~4.8V. When the temperature rise to55℃, the initial discharge capacity was293.1and274.8mAh·g-1with the first coulombic efficiency of90.1and90.4%respectively.In addition, the capacity retention after30cycles at0.1C was97.9and94.7%at55℃,respectively. While doping with Mg2+, the primary particles of the sample was seriousagglomeration, and the material shows lower discharge specific capacity, poor cyclingperformance than the bare material.The XRD test indicates that anion F-and Cl--doped materials possess more typicallayered structure than the pristine one. When the doping amount of F-or Cl-is0.05, the initialdischarge capacity increases from235.4mAh·g-1to230.6mAh/g and224.2mAh·g-1, with acapacity retention of87.8and88.9%after50cycles, respectively at20℃; when cycled at55℃，the F-and Cl--doped materials possess the initial discharge capacity of318.0mAh·g-1and302.9mAh·g-1, with a capacity retention of88.3or90.0%respectively.We also investigated the Al3+/Cl-and Cr3+/Cl-co-doped materials, and the results revealthat Li[Li0.2Ni0.15Mn0.55Co0.07Al0.03]O1.95Cl0.05and Li[Li0.2Ni0.15Mn0.55Co0.05Cr0.05]O1.95Cl0.05show the remarkable electrochemical performance, which show an initial discharge capacityof242.6mAh·g-1and239.8mAh·g-1at room temperature, respectively, and an initialdischarge capacity of303.5mAh·g-1and308.3mAh·g-1at elevated temperature, respectively.In comparison, the Cr3+/Cl-co-doped material Li[Li0.2Ni0.15Mn0.55Co0.05Cr0.05]O1.95Cl0.05exhibits more excellent performance than Li[Li0.2Ni0.15Mn0.55Co0.07Al0.03]O1.95Cl0.05Whencycled at1C, the material also possess a high discharge capacity of184.6and207.7mAh·g-1 at room and elevated temperature, respectively after50cycles. CV test shows that thedoped material exhibits the increased redox peak intensity and smaller redox interval,implying the polarization is decreased and the stability is enhanced. |
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