Study on Surface Modification of Carbon Anode for Lithium-ion Batteries
Date Issued
2016
Date
2016
Author(s)
Yang, Nai-Hsuan
Abstract
In this work, the reversible capacity, cycle life stability and rate performance can be improved by using different surface modification process. As we know, disordered carbon reveal good cycle life stability. However, despite of the favorable features, the large initial irreversible capacity and low specific capacity still are big problems and needed to be solved. Surface modification method was used to solve the weak points. The results showed that the first-cycle irreversible capacity of the disordered carbon anode and its specific surface area has a strong positive correlation. And the result was also proved by using different kinds of pitch coating process. From electrochemical test, the initial irreversibiluty can be lower than 20% by using polymer coating and the electrodes still remain good cycle stability. Small amount of Si nanoparticles was used for further improvement of the charge capacity. The Si nanoparticles can be well distribute on the disordered carbon surface by combining polymer and pitch coating. The charge capacity retention is around 75% when cycle at 1C rate after 70 cycles. Secondly, a Si oxide-coated graphite composite anode for Li-ion batteries (LIBs) was synthesized using a microwave-assisted coating method. In this synthesis, a solution comprising liquid polysiloxanes is used as the Si-containing precursor. For conventional synthesis process, people usually use chemical vapor deposition and toxic Si-containing vapor precursors, such as SinHm or SiHxCly. On the contrary, microwave-assisted coating method is safe, saving energy, and selective when doing the process. Here, carbon nano tube, graphite flake and graphite sphere were used as the microwave absorbent. Heating the graphite or carbon with microwave induces the deposition of a Si-containing conformal layer on the particle surfaces. Because the deposited layer is not microwave absorbent, it is also not good heat conductor. When the coating grew to certain thickness the reaction will stop (the thickness of the coating is around nano-scale). The resulting sample was subsequently calcined to produce SiOx/graphite composite. When tested as a LIB anode, the resulting composites exhibited an improvement in reversible specific capacity, good rate performance and excellent cyclability. When cycle at high C rate, all the composite electrodes showed the average coulombic efficiency higher than 99.9% after 100 cycles and the charge capacity retention were around 95% after 500 cycles. In this work, several polymer were chose to do surface modification. The reversible capacity, cycle life stability and rate performance of carbon anode can be improved by using different surface modification process. The results suggest new strategies for both designing and synthesizing high-performance anode materials for LIB applications.
Subjects
Li-ion battery
anode
graphite
disordered carbon
silicon
microwave synthesis
surface modification
SDGs
Type
thesis