Carbon composites for Li-ion and Na-ion batteries

Abstract

Due to the high demand for power supply in hybrid vehicle and renewable energy storage, Li-ion battery (LIB) and Na-ion battery (NIB) technologies have developed rapidly in the past few years. LIB industry has bloomed for portable devices and hybrid electric vehicles, while NIB techniques have been revived for large-scale energy storage. In this dissertation, novel anode materials, including Si-graphene, Si-carbon nanotubes composites for LIB anodes, and expanded graphite for NIB anodes, were studied. In LIB technology, Si is one of the most promising anode materials for next generation batteries because of its high theoretical capacity(~3598 mAh g-1). However, the rapid capacity decay caused by the substantial volume change during the lithation/delithiation process limits the practical application of Si anode. In this dissertation, grahene and carbon nanotubes were used as frameworks to maintain the integration and the electrical connection of Si during charge/discharge cycles. Both graphene-Si and CNT-Si species show superior performance and would be potentially beneficial for Si anode commercialization. As for Na-ion battery, graphite, the most commonly used anode in Li-ion batteries, is not suitable for NIB due to its limit of interlayer distance. In this dissertation, expanded graphite (EG) with similar long-term-ordered layer structure as graphite and larger interlayer distance was synthesized for NIB anode. EG is expected to allow reversible Na+ insertion to occur and accommodate Na+ mostly by intercalation, which is similar to how graphite stores Li+ in LIB. The atomic observation by in situ TEM study and linear scanning voltammetry analysis confirm the storage mechanism.