| Large-scale electrical energy storage (EES) is becoming more and more important, with the development of smart grid and the incorporation of clean reproducible energy. EES is an established, valuable approach for improving the reliability and overall use of the entire power system. Moreover, EES can be employed for providing many grid services, including a set of ancillary services such as frequency regulation, load following, cold start services, contingency reserves and energy services that shift generation from peak to off-peak periods. In addition, it can provide services to solve more localized power quality issues and reactive power support. Aqueous sodium-ion battery is a promising candidate for large-scale electric energy storage, due to its environmental benignity, safety, low cost and natural abundance of Na resource.Binessite-type manganite oxides with a interlayer spacing of-7A,2D layered structure consisted with edge-sharing MnO6octahedral, allows fast migration of cations in the interlayer and accelerates the dynamics of the ions between the electrolyte and the electrodes. Therefore, Manganite Oxides with typical layered structure can serve as an attractive cathode material for aqueous sodium-ion battery. As we know, the crystallinity, morphology and structure of the electrode materials have great effect on the electrochemical performances. In this dissertation, the electrochemical performances of manganite oxides were improved by designing unique morphology and structure. The main contents and results are summarized as follows:Ko.27MnO2microflowers with hierarchical structure were synthesized via a facile and efficient route based on a topochemical reaction process. The effects of heat treatment temperature on morphology and structure of the products are investigated via XRD, FE-SEM, TEM and so on. The result shows that the layered structure can be maintained well even at a high temperature of700℃. However, the flower-like morphology were destroyed at700℃. The KMO-500product shows the best performances according to three-electrode test results. Furthermore, the performances of KMO-500were further investigated in the KMO-500/AC full cell. Exhilaratingly, the full cell shows excellent cycling and rate performance. For example, a high energy density of41.8W h kg’is obtained at a power density of180.0W kg-1. In addition, the morphology and structure of KMO-500electrodes maintained well after1000cycles. These results demonstrated that K0.27MnO2owns stable layered structure and it is suitable for application in large-scale EES devices.Hierarchical K0.27MnO2microflowers with a typical layered structure can be used as cathode material for aqueous NIB, which was synthesized via a topochemical reaction method after heat treatment at500℃for2h. Aqueous NIB full cell using NaTi2(PO4)3as anode and K0.27Mn02as cathode exhibits high rate performance and cycling stability. After100cycles, a reversible capacity of68.5mA h g-1was obtained at a current density of0.2A g-1. Additionally, the sodium-ion insertion mechanism of K0.27MnO2was proposed by analyzing the evolution of structure and surface electronic states during the charge/discharge process. The K+ions can be extracted in the first charge process and the main reaction includes the insertion and extraction of Na+ions in the subsequent charge/discharge cycles. We believe that such a low-cost, environment-friendly electrode material can offer great promise for sodium-ion battery in large-scale energy storage applications.The monodispersed PS colloid spheres as template were synthesized via a microemulsion polymerization. After then, the flower-like PS@K-8-MnO2spheres were prepared via a hydrothermal method. Finally, K0.27MnO2with hollow structure was obtained after heat treatment in air and removal of the PS core. The electrochemical performance were evaluated via three-electrode systems. At a current density of200mA g-1,the specific discharge capacity retains about40.6mA h g-1after100cycles, exhibiting a superior cycling stability with almost100%capacity retention. To further estimate the potential application of the hollow K0.27Mn02as cathode in Na-ion energy storage device, full cell performances were investigated using NaTi2(PO4)3as anode within the cut-off voltage window of0-1.8V. At a current density of600mA g-1, the reversible capacity maintains above50mA h g-1after10cycles. The excellent performances of hollow-structured Ko.27Mn02can attributed to the larger electrode-electrolyte contact areas, shorter electron and ion transport length and faster insertion/extraction of Na+ions.Layered8-MnO2nanostructures containing different alkaline-metal (A-δ-MnO2, A:K, Na) were synthesized via a hydrothermal method and ion exchange reaction. The electrochemical performances of the products were evaluated via a full cell using A-8-MnO2as cathode and NaTi2(PO4)3as anode. The effects of morphology, structure and chemical composition on the performances were also investigated. Compared with the irregular particles, the samples with flower-like morphology show better performances. Among the three samples, the K, Na-δ-MnO2sample shows the best cycling and rate performance. It not only exhibited a highly reversible capability of-59.6mA h g-1over200cycles at a current density of200mA g-1, but also maintained an excellent performance as the current density increased to600mA g-1(-46.6mA h g-1). The chemical composition and surface electronic states of the electrodes after one cycle were determined to reveal the electrochemical reaction process. In addition, the microstructure and morphology of K, Na-8-MnO2electrode after200cycles were characterized, this result demonstrates that the structure of the material is stable. |
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