DESIGN AND ENGINEERING OF ADVANCED SI-BASED THIN FILM ANODE MATERIALS FOR LI-ION BATTERIES

Abstract

Lithium-ion batteries (LIBs) are a versatile way of energy conversion and storage. Thin film batteries are the next generation of Li-ion battery technology with the thickness of tens μm and aimed to power a diverse range of microdevices. In order to increase the storage possibility, i.e. capacity, of such batteries, new high capacity electrode materials should be developed. Silicon-based materials are the most promising anodes due to the highest theoretical capacity and a low potential. However, the current drawbacks of Si such as significant volume expansion, electrical contact loss, and low conductivity impede its practical application in LIBs and commercialization. In this doctoral thesis, the research has been performed in two main directions in order to improve the existing microbatteries and find a way to develop a stable Si-based thin film electrode. The first direction is an investigation of novel silicon carbide thin film (3C-SiC) with a cubic lattice as an anode for LIBs. The advanced method of "single" particle measurement for studying the electrochemical properties of an individual microparticle provided the new data which allowed suggesting the mechanisms of lithiation/delithiation in 3C-SiC film. The use of XRD, TEM, XPS, Raman spectroscopy confirmed that there was no degradation of the 3C-SiC crystal lattice. The obtained results demonstrated that there are in two possible reasons of 3C-SiC thin film electrochemical activity, an intercalation or a capacitance. The second direction is the design of the three-dimensional (3D) amorphous Si (a-Si) thin film anode. The improvement of a-Si thin film anode was achieved through studying the effects of substrate surface condition, dopants incorporation, electrolyte additive and addition of graphene (GF) underlayer. The designed n-type doped porous a-Si thin film and 3D a-Si/GF anode exhibited high electrochemical performance in the lithium cells for several hundred cycles.