The Preparation, Performance And Energy Storage Mechanism Of Mn-and Ti-based Oxide Nano-arrays For Lithium Ion Battery Application

In recent years, with the development of power sources for clean/renewable energy systems, multifunctional portable electronic devices, and nano-/micro-electromechanical systems (NEMS/MEMS), many efforts have been made in developing better energy storage devices. Lithium ion batteries (LIBs)show a most promising property for energy storage due to the fact that they have high energy density, long lifetime and low pollution. Although LIBs have gained current commercial success, they still suffer some restrictions such as low power density and security issues. Considerable attention has been focused on the design of new type of electrode materials and modification of those electrode materials in recent decades. In this thesis we will design and fabricate the nano-arrayed Ti-based anode and Mn-based cathode of LIBs and use them to assemble full cells. The anode and cathode electrodes will be tested in half cell and full cell respectively. We expect to provide some strategies to improve the performance of LIBs. EIS is a very important method to analyze the property of LIB electrodes, but the traditional method has some limitations. In this thesis we will further make every effort to develop more accurate analysis route of EIS by amending some parameters. The main research content of this thesis is as follows:(1) Using RTO nanowire array as the template, the LTO-RTO hybrid nanowire array was synthesized by a solid-state reaction. We studied some samples with different mLTo:mRTo ratios to choose the optimized ratio-3:1electrode to conduct the following study.3:1electrode displays perfect performance in half and full cell measurements. The half cell assembled using optimized3:1LTO-RTO electrode as the cathode and Li-metal circular foil as anode exhibits high capacity (among the highest:～181mAh g-1at～1C rate), excellent cycleablity and good rate capability. A lithium ion full cell assembled using LTO-RTO hybrid array as the anode and commercial LCO film as the cathode further manifests outstanding performance with ultralong lifetime (3000times at even～2.5C). Based on the experimental results, we proposed the synergistic energy storage mechanism of the LTO-RTO hybrid electrode.(2) We synthesized MO nano-array directly on current collector by a new facile hydrothermal method in this thesis. This MO nano-array is uniform, ordered and having robust adhesion with Ti substrate. Using MO nanowire array as the template, the LMO nano-array was synthesized by a solid-state reaction. Without any further modification, the LMO electrode exhibits good performance in half and full cell measurements. The capacity can still be retained about66%after400cycles at current rate of5C in half cell measurements. The capacity can still be retained about70%after200cycles at current density of500mA g-1in full cell measurements. It is believed that the elegant integration of the advantages of ordered nano-array and the porous structure of the LMO nanorods plays an important role in enhancing the electrochemical performance.(3) For the limitations of conventional EIS analysis method, via amending analysis method of some parameters in EIS spectrum such as electric double layer, charge transfer resistance and Warburg factor, we obtained a more accurate method for EIS analysis. By comparing the results obtained using our new method and conventional method to analyze experimental data, the precision of our method was verified.