Silicon Microchannel Plate Based Three-dimensional Lithium-ion Battery Anodes

Owing to the high theoretical insertion capacity, silicon is one of the promising anode materials. However, the large volume changes during the lithium insertion/extraction process can lead to cracking and disintegration of the Si electrode as well as severe capacity fading.To overcome the large volume changes, a series of exploration and researches on3-D lithium-ion batteries based on Si-MCPs were carried out in this paper.1. During the initial cycle, the bare Si-MCP anode has a charge capacity of above3520mAh g-1and a discharge capacity close to2659mAh g-1, corresponding to a coulombic efficiency of75.5%. Compared with the bulk-Si electrode whose capacity decreased to200mAh g-1after10cycles, the current rate and cycle performance for the Si-MCP anode were be promoted.2. A three-dimensional anode using boron-doped Si microchannel plate as matrix and active material was also proposed. Compared with the anode made by untreated Si-MCP, the boron-doped Si-MCP anode exhibited a better behavior in the galvanostatic half-cell measurements. It can be attributed to thatthe increasing of electrical conductivity leaded to the promoting of the charge transfer.3. Compared to the anode without the Ni coating, the Ni/Si-MCP anode exhibits better cycle performance in the galvanostatic half-cell measurements. The initial charge capacity of the anode with the Ni coating is3016mAh g-1, but the discharge capacity is close to2890mAh g-1with a coulombic efficiency of95.8%. Even in the second cycle, the coulombic efficiency is still above97%.The excellent performance is ascribed to the existence of the Ni coating which greatly improves the conductivity and promotes charge transfer especially in the early stage of lithation.4. To further improve the cycle performance of the Ni/Si-MCP anode, galvanostatic C-D cycle tests under designated charge capacities of1000mA g-1were employed. It can be found that decreasing the Li insertion/extraction levels to1000mAh g-1would enhance the cyclic performance of the Ni/Si-MCP electrodes. However, the degree of the cyclic performance enhancement is not directly proportional to the decrease in the Li insertion/extraction level.In order to observe the morphology of Ni/Si-MCPs after a certain cycles, the electrodes were taken out from the cells. From the results of scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), the largest contributor to the fading of the Ni/Si-MCP electrode is the loss of Ni.5. Moreover, three-dimensional anode using a silver-coated Si microchannel plate as active materials was prepared by photo-assisted electrochemical etching followed by electroless deposition. In galvanostatic charge-discharge measurements at25mA g-1between0.02and1.5V, our anode exhibited a charge capacity of3484.7mAh g-1with a coulombic efficiency close to95.97%in the initial cycle. Because the silver coating was also counted in the weight of whole anode, the actual specific capacity of silicon would be close to its theoretical insertion capacity.6. By sol-gel method, one PVDF-HFP polypropylene separator was prepared based on Si microchannel plate. The galvanostatic C-D cycle test was carried out at10mA g-1between0.05and1.5V was carried out. Not only the difficult for the electrode prepare but also the charge capacity, the results of our sample would be better than the other previous results of Si-MCP electrode.