Nanosized Design And Electrochemical Lithium Storage Performance Of Transition Metal Oxide Anode Materials For Lithium-Ion Batteries

Transition metal oxides have attracted considerable interests as one of the most promising energy storage devices, because of high specific capacity and abundant resources. However, their large-scale commercial application is still subject to many limitations, due to the fact that most metal oxides are semiconductor materials with poor conductivity, which is not conducive to rapid electrochemical reaction. Another problem is that severe volume expansion could happen during charge-discharge cycles, which leads to the destruction of material structure or pulverization of electrode. As a result, the cycle stability and high rate characteristics can not meet practical application needs. In this paper, basing on the design of materials microstructures through nano and combination methods. Nanocrystals-constructed mesoporous Co3O4nanobelts, the CoO/graphene sheet-rod composite materials and MnO/C nanomaterial are successfully synthesized. The electrochemical performances of the as-synthesized materials have been improved significantly. The main results are listed as follows:(1) Hydroxide precursor is prepared by hydrothermal method with Co(NO3)2·6H2O, NH4F, CO(NH2)2as raw materials. The morphology and microstructure of the precursor are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM). It is found that the precursor consists of uniform1D nanobelt-like structures, and their typical size are100-300nm in width and several micrometer in longth. The one-dimensional porous CO3O4nanobelt is obtained by calcination of the precursor at400℃for4h in air. Microstructural analysis results show that the Co3O4nanobelts are constructed from numerous nanocrystals with a size in the range of20-30nm. The BET surface area of Co3O4nanobelts is determined to be about36.5m2g-1with dominant pore diameter of29.2nm. As an anode material for Li-ion batteries, the mesoporous Co3O4nanobelt exhibits excellent electrochemical performance. The reversible capacity could remains over614mAh g-1after60cycles at a current density of1A g-1. Even at a high current density of3A g-1, these Co3O4nanobelts still could deliver a remarkable discharge capacity of605mAh g-1.(2) Graphite oxides (GO) are directely prepared from graphite flakes by a modified Hummers method. CoO NRs/rGO composite is synthesized by a facile hydrothermal method followed by calcination treatment in an Ar2atmosphere (450℃,4h) with GO, Co(NO3)2-6H2O, NH4F, CO(NH2)2as raw materials. The capacities of the composite could keep960and513mAh g-1after50cycles at current densities of0.1and1A g-1, respectively, which are much higher than pure CoO (only285and9mAh g-1) under the same conditions. The result indicates that graphene could effectively improve the cycling performance and rate capability, due to the facts that graphene could greatly improve the conductivity of CoO material and effectively suppress the volume expansion during charge-discharge cycles.(3) The MnO/C composite is synthesized by chemical plating followed by calcination treatment, using KMnO4, NaNO3as raw materials and natural lotus pollen as carbon sources and biotemplate. The electrochemical test results exhibit that the MnO/C composite has good cycling performance and excellent rate performance. The capacity could remain about730mAh g-1after50cycles at a current density of0.1A g-1, even at a high rate of3A g-1,the reversible capacity could deliver445mAh g-1.