Lithium solvated electrons solution anode for rechargeable lithium batteries
Tan, Kim Seng
Date of Issue2015
School of Materials Science and Engineering
Energy Research Institute @ NTU (ERI@N)
At present, most of the research in lithium-air and lithium-ion batteries focused on solid state electrode materials such as metallic lithium, lithium alloys and oxides of lithium (i.e Li4Ti5O12). The concept of a room temperature rechargeable Li-Air cell that utilizes liquid-based electrodes, classified as anolyte and catholyte, allows for the cell to be either refuelled or recharged. This project studied the synthesis and characterization of poly-aromatic hydrocarbon (PAH)-based (biphenyl and naphthalene) lithium solvated electrons solution (LiSES) which can be used as a liquid anode defined as anolyte. Complementing this study, iodine/methanol solution has been investigated as an alternative cathode, defined as catholyte, in place of air/oxygen for LiSES//Air cell. Possible reaction mechanisms of different Li concentrations with PAH in THF are formulated. LiSES has been observed to demonstrate a metallic behaviour based on conductivity-temperature studies. The relationship of the half-cell OCV of LiSES versus temperature has been obtained and thermodynamics data (∆G, ∆S and ∆H) were determined. In a LiSES//Iodine full cell setup, LiSES & iodine/methanol have both shown promising results as liquid electrodes and their charge/discharge electrochemical reactions have been identified. Successful electrosynthesis of LiSES in the anolyte from the charge process of an uncharged cell with LiI in both liquid electrodes and with initial 0 V open circuit voltage (OCV) has been observed. The oxidative formation of I2 catholyte from LiI in methanol also occurred concomitantly during the same charge process. This demonstrates that the LiSES//Iodine cell can be initially prepared either chemically (charged or partially charged depending on user’s requirements) or electrochemically (uncharged). Lithium Phosphorus Oxynitride’s (LIPON) effectiveness as a protective coating on Lithium Titanium Aluminium Phosphate (LTAP) solid electrolyte membrane against LiSES viii corrosion has also been shown. Finally, the unexpected effect of the LIPON layer upon LiSES, causing higher OCVs for LiSES cells, has been observed. The causes of this effect are still under investigation. There are two main technological implications from the results of this thesis. Firstly, by having both electrodes in the liquid state, the LiSES cell can be refuelled by replenishing the discharged electrodes with fresh ones in several minutes as compared to the minimum 30 min fast-charging time for conventional lithium ion batteries (LIB). Secondly, the option of preparing an initial 0 V OCV uncharged cell for LiSES//I2 configuration that can be charged up to electrochemically synthesise LiSES and I2 allows for safe storage and transportation of both anolyte and the catholyte.