Preparation of Si/CNFs Composite Anode by Electrophoretic Deposition (EPD)

摘要

Recently, lithium ion batteries (LIBs) have been widely used in the field of portable electronic devices and electric vehicles due to high adaptability, high working voltage and low toxicity. However, traditional electrode materials have greatly limited the future of LIBs because of their low theoretical specific capacities; meanwhile, new electrode materials always need to be prepared by complicated and expensive methods, indicating the small probability of large-scale promotion. In this study, the Si/CNFs composite film anode without any binder by a simple and effective method - electrophoretic deposition (EPD) - is developed, which exhibits improved electrochemical properties.;This thesis is firstly focused on building a metastable/stable system for the multi-component (Si/CNFs) EPD. It's observed that in the basic condition (pH9 -- 10) or acidic condition (pH0.5), a suspension in ethanol consisting of surface-modified Si and CNFs can approximately keep stable for at least 0.5h, which can meet the minimum requirements for a successful deposition. Based on the dynamics analysis, a new "three-step growth theory" on the deposition process is proposed.;Then, this thesis is focused on preparing different composite films by EPD and improving their electrochemical performance via optimizing the component and microstructures. Three kinds of Si nanoparticles are used: Si, Si with hydroxyl groups (Si-OH) and Si with amino groups (Si-NH2), while only one carbonaceous material is investigated: CNFs with carboxyl groups (CNFs-COOH). The possible factors on the film density, thickness and the microstructure have been studied, including the applied voltage, concentration, additives and after-treatment procedures. The results show that each dense composite film exhibits better performance than the tradition graphite anode. To be specific, the Si/CNFs-COOH film is obtained in ethanol by EPD at pH10, which has the specific capacity of 610 mAh/g after 100 cycles at 400 mA/g. The Si-OH/CNFs- COOH film with honeycomb structure is obtained in ethanol by EPD at pH10, which has the specific capacity of 510 mAh/g at 400 mA/g after 300 cycles. The Si-NH2 /CNFs-COOH film is obtained by EPD at pH0.5, which has the specific capacity of 1020 mAh/g at 400 mA/g after 100 cycles.