Stabilizing the structure and suppressing the voltage decay of Li[Li0.2Mn0.54Co0.13Ni0.13]O2 cathode materials for Li-ion batteries via multifunctional Pr oxide surface modification

Abstract

The development of Li-rich layer cathode materials has been limited by poor cycle, rate performance, phase transformation and voltage decay. To improve these properties, a facile and low-cost wet method is employed to fabricate Pr6O11 coating layer on Li[Li0.2Mn0.54Co0.13Ni0.13]O2 nanoparticles. The 3–6nm Pr6O11 coating layer is observed on the surface of Li[Li0.2Mn0.54Co0.13Ni0.13]O2 by HRTEM. Interestingly, HAADF-STEM and EDS analyses show that the transition metal ions and the praseodymium ions mutually infiltrate in the Pr6O11 coating layer and Li[Li0.2Mn0.54Co0.13Ni0.13]O2 nanoparticles during calcination. A combination of HAADF-STEM with EDS and XPS studies reveals that Pr6O11 coating layer is bridged to Li[Li0.2Mn0.54Co0.13Ni0.13]O2 nanoparticles by the chemical bonds of transition phase Li1.2MXPr1−xO2. XRD patterns show that all samples are indexed to the layered structure α-NaFeO2, but the lattice parameters are influenced lightly after Pr6O11 coating. HRTEM and SAED analyses elucidate that the super large Pr ions surface-doping and the Pr6O11 coating are verified to suppress the transformation of layer to spinel structure in the bulk nanoparticles after cycles. The sample coated with 3wt% Pr6O11 exhibits wonderful electrochemical performance with the first coulomb efficiency of 85.6%, the capacity retention ratio of 97.9% after 50 cycles and the discharge capacity of 162.2mAhg−1 at 5C. The resistant of charge transfer and the electrodes polarization are reduced by Pr6O11 coating according to EIS. Therefore, Pr6O11, which contains the super large Pr ions, plays two roles: the first one, it is coated on the Li[Li0.2Mn0.54Co0.13Ni0.13]O2 nanoparticles to optimize the environment of the interface reaction between electrodes and electrolyte; the other one, its Pr ions surface-doping stabilizes the structure in the superficial region of Li[Li0.2Mn0.54Co0.13Ni0.13]O2 nanoparticles and suppresses the voltage decay. The multifunctional Pr6O11 can play a significant role in accelerating development of new materials with excellent stabilization and high capacity.