The Application Exploration Of Porous LiFePO₄and Silicon Thin Film In3D Lithium-ion Batteries

Since the invention of the lithium-ion battery, the advantages of high-security, high-capacity, high operating voltage, no memory effect and low self-discharge rate got more and more attention. The enthusiasm in research of Lithium-ion battery technology is higher than ever before. In this article we did some exploration in the anode and cathode materials for lithium-ion electrodes.First, the LiFePO4, as anode materials for lithium-ion battery, were studied. The LiFePO4material with high purity and good crystallinity was fabricated by the sol-gol method. The Ammonium bicarbonate and the LiFePO4was sufficiently mixed using a ball mill, and pressed into thin slices, and sintered under the protection of argon with the decomposition of the Ammonium bicarbonate. This method realized the porous structure of the LiFePO4material. Under the Charge-discharge test potential from2.5to4.3V, and0.1C magnification, the attenuation ratio of the capacity after50cycles is82%of the initial. The most important thing is that the cycle coulomb efficiency was close to100%in each cycle of charging and discharging, and the potential platform was maintained a good consistency.After that, the Si-MCPs/Graphite composite electrode was studied. The composite electrode was fabricated through two steps. The first step mainly involves in the silicon processing of4inch<100> crystallographic orientation of the P-type. After cleaning, oxidation, photolithography, developing and electrochemical etching, the P-type silicon was made into a kind of microstructures with a pore size of5μm, depth up to180μm. The second step primarily was filling graphite into the Si-MCP channels with the method of centrifugation. The Si-MCP/Graphite composite electrode packaged with the lithium foil as the pair electrode composed of half-cell lithium-ion battery. We set the test current40mA/g and the test voltage between0.05-1.5V to study our half-cell lithium-ion battery. The discharge capacity of the fifth cycle is still reach2388mAh/g, more than three times higher than ordinary Si-MCP electrode (vs. Li/Li+), which showing a better capacity retention ability than normal silicon material.In the latter part of the article, we focus on the applications of composite thin film filled into the three-dimensional channel as the lithium ion battery electrode. The microcrystalline Si/Ni/Si-MCP electrode was fabricated through the electroless nickel plating and PECVD on Si-MCP with large specific surface ratio and three-dimensional structure. The fabricate process is reported by the first time in the field of lithium ion battery. The electrode was packaged in a vacuum glove box as a half-cell lithium battery (vs. Li/Li+). We tested the half-cell lithium battery in1C charge and discharge rate by the constant current charge-discharge with the voltage range from0.05V to1.5V. The first cycle discharge capacity reached3780mAh/g, and the discharge capacity of3591mAh/g. The discharge capacity of the30th cycle is reach to2452mAh/g as well as the charge capacity of2442mAh/g. Compared with the thin film microcrystalline Si/steel electrode (vs. Li/Li+), the microcrystalline Si/Ni/Si-MCP electrode has a relatively less capacity and cycle performance. However, in the case of the same electrode area, the microcrystalline Si/Ni/Si-MCP electrode has a120times greater than metal plane electrode due to the large specific surface area of the three-dimensional structure which could greatly improve the capacity of silicon lithium ion battery.