| Lithium-ion battery, as a kind of efficient and clear energy storage and transferdevices, has been considered as one of the most effective methods to solve the energycrisis and environmental pollution. Thanks to the increasing development of theportable electric devices, the coming of4G communication time and applications ofelectric vehicle (EVs) and grid energy storage, there is rapid increasing demand forhigh energy and power density, long cycle life and safety of lithium-ion battery.Currently, novel Li-excess manganese-based cathode is regarded as the mostpromising cathode material for the EVs application. However, some disadvantages,such as the option of anode materials, the matching technology between the voltageand energy, and some safety issues related with the wide range of working potentials,strongly restrict its commercial application. Our work constructed three kinds offull-cell systems by employing Li-excess manganese-based compounds as the cathodeand graphite, Li4Ti5O12and nano SixO/C as the anodes, respectively. And theelectrochemical properties have been studied comprehensively. Our results providethe insights into the design of novel lithium-ion battery. The main research results aregiven as following:Firstly, we obtained the relationship between capacity and voltage of the full cellsystem by evaluating the charge and discharge curves of the cathode and anode in thehalf-cell system, which provided the fundamental suggestions for constructing fullcell lithium ion system. Li-excess manganese-based cathode Li1.18Co0.15Ni0.15Mn0.52O2 was prepared by sol-gel method. Then high-performance Li-ion full cell wasassembled using Li-excess compound as the cathode and commercial graphite asanode. The full cell delivered a high discharge capacity of243mAh g-1with anaverage voltage of3.5V, comparable with that of Li-rich compound in the half cellsystem. Further, we studied the electrochemical performance under different voltageranges (1.75V-4.78V and2.5V-4.5V), and the full cell shows a better cycle and rateperformance between2.5and4.5V.Secondly, we assembled a novel full cell system by combining Li-excess cathodeand Li4Ti5O12anode. Based on the proposed principle, a reasonable working voltagebetween1.5V and3.3V was employed. By adjusting the mass ratio between cathodeand anode, we found that, at the low current density, the full cell showed goodperformance when the ratio equaled to1:1.8; while under the high current density of2A g-1, a better performance was acquired when the ratio increased to1:2. The reasonwas possibly related to the need of more anode materials for the charge compensationunder high current density. In addition, by comparing the two different full-cellsystems (Li-excess/graphite and Li-excess/Li4Ti5O12), it could be found thatLi-excess/Li4Ti5O12full cell exhibited a better rate capability and safety property.However, the energy density of Li-excess/Li4Ti5O12full cell is much lower than thatof Li-rich/graphite due to the lower working voltage of Li-rich/Li4Ti5O12full cellcompared with Li-rich/graphite.Finally, SixO/C nano-composite was prepared by carbon thermal reductionmethod. SEM and TEM images showed that the well-crystallized SixO particles wereinserted into the amorphous carbon matrix, which was considered to play a key role inbuffering the volume expansion and enhancing the electronic conductivity. The initialdischarge capacity of SixO/C nano-composite reached560mAh g-1with the capacityretention of95.6%after50cycles in the Li ions half cell. In addition, the full cell wasalso assembled by using Li-excess compound and SixO/C nano-composite as cathodeand anode, respectively, and its electrochemical properties were studied. Li-excess/SixO/C full cell delivered118mAh g-1after150cycles and the cycle retentionequaled to74.6%. Both severe polarization and low initial columbic efficiency of64% of SixO/C nano-composite strongly affect the electrochemical performance. Hence itis highly expected that Li-excess/SixO/C full cell would demonstrate a superior Li-ionstorage performance in future by improving the cycle stability of SixO/Cnano-composite and its initial columbic efficiency. |
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