Controlling the geometric morphology and distributive location of discharge products play an important role in the reversibility and efficiency of Li–O2 batteries. This work presents novel Co2CrO4 nanospheres (CCO) prepared via a facile method, which are applied as the electrocatalysts for Li–O2 batteries. The as-prepared CCO was characterized by XRD, XPS, SEM, TEM, BET, and TG measurements. The CCO exhibited a yolk–shell microstructure, which could facilitate fast Li+ and O2 diffusion as well as possessing enough space for the discharge product deposition. In comparison to the performance of the cell without catalyst, the overpotential of the cell with CCO was apparently reduced and the cyclability significantly enhanced. Based on the experimental results and DFT calculations, direct evidence of the CCO employment being linked to the Li2O2 morphology was provided. In addition, a catalytic mechanism was proposed. Furthermore, fundamental information about the key factors and steps involved in the Li2O2 formation and decomposition was revealed. We expect that this study gives insight into the development of electrocatalysts, the selection of O2 electrode materials, and the design of O2 electrodes for Li–O2 batteries, as well as advancing our understanding of the catalytic mechanism.

•LiNi1/3Co1/3Mn1/3O2 layered structure is doped with (PO4)3− polyanions.•Results confirm that (PO4)3− influences MO6 octahedral environment in LiNi1/3Co1/3Mn1/3O2 lattice.•Charge–discharge properties are investigated under high voltage battery operation.•Cycling and rate performance of the doped materials is markedly enhanced.•Pre-cycling treatment inhibits microcracks at the grain boundaries at 4.7–2.8 V.Layered compounds LiNi1/3Co1/3Mn1/3O2 have recently received much attention as they have been regarded as a promising cathode materials for industrial application. However, its fast energy density decay and poor rate performance which originate from structure disruption especially at high rate and high cut-off voltage limit its large-scale application. Here, a novel designed concept and facile method were firstly used to fabricate (PO4)3− polyanions doped layered LiNi1/3Co1/3Mn1/3O2 (LNMC-(PO4) 0.015-O1.94) structure, which could offer more stable high-voltage cycling performance and high rate capability. We attribute this improved performance to the robust Ptet-O covalence, which will stabilize the oxygen close-packed structure during repeated cycling. Moreover, our stepwise pre-cycling treatments could effectively restrain the formation of micro-cracks and non-crystallization defects, and significantly improve cyclic durability with high charge voltage of 4.7V. The LNMC-(PO4) 0.015-O1.94 electrode can still delivers capacity retention of 81% after 200 cycles at a current density of 300mA g−1. The preliminary results reported here manifest that this novel-designed LNMC-(PO4) 0.015-O1.94 material represents an attractive alternative to ultrafast-rate, long-life and high-voltage electrode material for lithium ion batteries.Download high-res image (132KB)Download full-size image

•MnO2 coated LiNi1/3Co1/3Mn1/3O2 cathode material is synthesized for the first time.•MnO2 offers available sites for insertion of extracted lithium.•The preserved surface and crystal structures results in the improved kinetics.LiNi1/3Co1/3Mn1/3O2 is successfully coated with MnO2 by a chemical deposition method. The X-ray diffraction (XRD), scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM) results demonstrate that MnO2 forms a thin layer on the surface of LiNi1/3Co1/3Mn1/3O2 without destroying the crystal structure of the core material. Compared with pristine LiNi1/3Co1/3Mn1/3O2, the MnO2-coated sample shows enhanced electrochemical performance especially the rate capability. Even at a current density of 750 mA g−1, the discharge capacity of MnO2-coated LiNi1/3Co1/3Mn1/3O2 is 155.15 mAh g−1, while that of the pristine electrode is only 132.84 mAh g−1 in the range of 2.5–4.5 V. The cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) curves show that the MnO2 coating layer reacts with Li+ during cycling, which is responsible for the higher discharge capacity of MnO2-coated LiNi1/3Co1/3Mn1/3O2. Electrochemical impedance spectroscopy (EIS) results confirmed that the MnO2 coating layer plays an important role in reducing the charge transfer resistance on the electrolyte–electrode interfaces.

Li[Li0.2Mn0.54Ni0.13Co0.13]O2 was prepared using a coprecipitation method and modified with Li4Ti5O12. The sample coated with 3 wt% Li4Ti5O12 exhibited the best cyclability and mean coulombic efficiency in the voltage range of 2.0–4.75 V. These improvements are attributed to the effective Li4Ti5O12 coating layer, which stabilizes the host structure, protects the electrode surface from electrolyte attack, and prevents the formation of a thick passive film on the electrode surface. The initial irreversible capacity loss was eliminated by blending with 10 wt% Li4Ti5O12, in the larger potential window of 1.5–4.75 V. It was confirmed that the irreversible capacity loss decreased with increasing Li4Ti5O12 content; this is because Li4Ti5O12 offers a larger number of available sites for insertion of extracted lithium.

Controlling the geometric morphology and distributive location of discharge products play an important role in the reversibility and efficiency of Li–O2 batteries. This work presents novel Co2CrO4 nanospheres (CCO) prepared via a facile method, which are applied as the electrocatalysts for Li–O2 batteries. The as-prepared CCO was characterized by XRD, XPS, SEM, TEM, BET, and TG measurements. The CCO exhibited a yolk–shell microstructure, which could facilitate fast Li+ and O2 diffusion as well as possessing enough space for the discharge product deposition. In comparison to the performance of the cell without catalyst, the overpotential of the cell with CCO was apparently reduced and the cyclability significantly enhanced. Based on the experimental results and DFT calculations, direct evidence of the CCO employment being linked to the Li2O2 morphology was provided. In addition, a catalytic mechanism was proposed. Furthermore, fundamental information about the key factors and steps involved in the Li2O2 formation and decomposition was revealed. We expect that this study gives insight into the development of electrocatalysts, the selection of O2 electrode materials, and the design of O2 electrodes for Li–O2 batteries, as well as advancing our understanding of the catalytic mechanism.