| dc.description.abstract | Lithium-ion batteries (LIBs) are currently the dominant energy storage technology, current commercial lithium ion battery utilizes graphite anode which have intercalation of lithium between the layered structure. The lithium ions are transported through the electrolyte during the charge/discharge process. LIBs have now made inroads into the electric vehicle sector and large-scale grid storage, both of which require batteries with significantly higher energy densities due to their success. Alternative anode and cathode chemistries are required to meet this demand. As a result, the electrolyte will be under a lot of strain, and it will decompose at both low and high potentials to form a passivation layer known as the solid electrolyte interphase (SEI).
Here, in this work we investigate moderately concentrated electrolytes and find that the effects of lithium bis(fluorosulfonyl)imide (LiFSI) concentration on the capacity, rate capability, and cycling stability of Si anodes in an ethylene carbonate (EC)/diethyl carbonate (DEC) mixed electrolyte are found to be opposite to those in a fluoroethylene carbonate (FEC) electrolyte in this study. The reasons for these observations are investigated using Raman spectroscopy, transmission electron microscopy, electrochemical impedance spectroscopy, and the galvanostatic intermittent titration technique. The solid electrolyte interphase chemistry is investigated in detail using an X-ray photoelectron spectroscopy investigation. Al corrosion that occurs with EC/DEC-based electrolytes can be efficiently reduced with FEC-based electrolytes if an acceptable LiFSI concentration is used.
The compatibility of a prepared ionic liquid (IL) electrolyte containing ether-side-chain pyrrolidinium, asymmetric imide, and a high Li+ fraction with a high conductivity, high dimensional stability composite anode (denoted as Si/CNT/G) as a high energy density anode material for LIBs is studied in the second study of this thesis. This is the first time this electrolyte has been used in Si-based Li-ion batteries. Organic components are formed when the ether groups decompose to form a solid electrolyte interphase (SEI). Because of the high Li+ concentration, the (fluorosulfonyl)(trifluoromethanesulfonyl)imide (FTFSI−) anions decompose, resulting in a LiF and Li3N-rich SEI. The Si/CNT/G anode′s exceptional charge-discharge characteristics are due to the organic-inorganic balanced SEI. The FTFSI− anions are non-corrosive to the Al current collector and have a high compatibility with the LiNi0.8Co0.1Mn0.1O2 (NCM-811) cathode. NCM-811 in the high-Li+-fraction N-methoxyethyl-N-methylpyrrolidinium/FTFSI IL electrolyte exhibits remarkable reversible capacity and cycle stability when charged upto 4.5 V. The interfacial exothermic interactions between the delithiated NCM-811 and various electrolytes are investigated using differential scanning calorimetry.
In the third section of this thesis, we describe a Si-rich silicon nitride (Si-SiNx) synthesized via heat treatment under gaseous nitric oxide (NO) to alleviate the main inherent difficulties of Si anodes, such as mechanical deterioration and slow Li+ diffusion. During charge/discharge, the produced Si-SiNx nanoparticles successfully change the inherent electrochemical properties of the Si anode by enhancing mechanical stability and ionic conductivity with Si3N4 and in-situ generated Li3N. Si-SiNx nanoparticles have shown enhanced battery performance, including high rate capability and cycling stability. | en_US |