Effects of amorphous V2O5 coating on the electrochemical properties of Li[Li0.2Mn0.54Ni0.13Co0.13]O-2 as cathode material for Li-ion batteries

摘要

Lithium-rich layered oxide Li[Li0.2Mn0.54Ni0.13Co0.13]O-2 coated with V2O5 layers (labeled as LMNCO@V2O5) has been synthesized and its electrochemical properties as cathode material for lithium ion batteries have been measured and compared with pristine Li[Li0.2Mn0.54Ni0.13Co0.13]O-2 (labeled as LMNCO) and LMNCO-V2O5 composite. As a lithium ions insertion host material, both the V2O5 in the LMNCO@V2O5 and the LMNCO-V2O5 can reduce the irreversible capacity losses and improve the Coulombic efficiencies of the cathode in the first charge-discharge cycle. However, for improving the cycling stabilities and the high-rate capabilities of the LMNCO, the effects of the V2O5 coating layers in the LMNCO@V2O5 are far beyond the effects of the V2O5 nanoparticles in the LMNCO-V2O5. When charge-discharged galvanostatically at 25 mA g(-1) between 2.0 and 4.8 V (vs. Li+/Li), the LMNCO@V2O5 with 3 wt.% V2O5 exhibits a discharge capacity of 279.5 mAh g(-1) in the first cycle and maintains a discharge capacity of 269.1 mAh g(-1) after 50 cycles, with capacity retention of 96.3%. In contrast, the discharge capacity of the pristine LMNCO changes from 251.2 mAh g(-1) in the initial cycle to 202.2 mAh g(-1) in the 50th cycle, with capacity retention of 80.2%; and the LMNCO-V2O5 shows the same capacity fading trend as the pristine LMNCO, with no obvious improvement in the capacity retention. At high rate of 1250 mA g(-1), the discharge capacity of the LMNCO@V2O5 can reach 113.6 mAh g(-1), which is much higher than the capacities that the pristine LMNCO and the LMNCO-V2O5 can reach. Different effects of V2O5 are due to their different roles in the cathode materials. While the V2O5 coating layer in the LMNCO@V2O5 can reduce the charge transfer resistance at the electrode-electrolyte interfaces and improve the transportation of lithium ions among the LMNCO particles, the V2O5 nanoparticles in the LMNCO-V2O5 can only work as a Li+ ions insertion host material. (C) 2016 Elsevier B.V. All rights reserved.