Investigation of potential in-situ polymerization reactions for use in lithium-ion batteries
- Authors: Dube, Tafara
- Date: 2024-12
- Subjects: Lithium ion batteries , Lithium cells , Electrochemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/68851 , vital:77127
- Description: With the rise in popularity of electric vehicles and portable electronic devices, having a reliable, lightweight, and long-lasting battery is crucial. This has led to the mass commercialisation of lithium-ion batteries (LIB’s) because they offer several advantages over other battery technologies. Over the years, one of the concerns was with the ease with which the batteries can burn or explode when subjected to certain extreme conditions. In order to build trust in these products and to expand the technology into more diverse applications, safety aspects of the batteries has become of widespread concern resulting in a key area of research. One aspect of improving the safety is by reducing the flammability of the battery by the addition of certain chemicals that stop or suppress the thermal runaway effect. However, this in-turn reduces the battery’s capacity and life-cycle performance. Researchers have used the idea of encapsulating these chemicals thereby physically separating them within the lithium-ion battery (LIB) electrolyte system with a minimum effect on performance. This research aims to explore use of R-diols and R-amines as additives that upon a thermal trigger would react with the lithium-ion battery electrolyte to stop the effect of the thermal runaway by forming carbamate derivatives which are gel-like or form solid aggregates. The R-diols or R-amines can react with electrolyte at higher temperatures with the lithium-hexafluorophosphate acting as a catalyst. This change in the physical state of the electrolyte increases the resistance inside the battery which then hinders ion movement and forms a physical barrier to reduce the effect of short circuiting when the separator or other components are damaged due to higher temperatures. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
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- Date Issued: 2024-12
Development of high capacity lithium-manganese-rich cathode materials xLi2MnO3•(1-x)LiMn0.5Ni0.5O2 for lithium ion batteries
- Authors: Rapulenyane, Nomasonto
- Date: 2018
- Subjects: Lithium ion batteries , Electrochemistry Lithium cells
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/34766 , vital:33442
- Description: In this study, a facile synthesis method was developed to produce layered-layered cathode materials with the formula xLi2MnO3•(1-x)LiMO2 (M= Ni and Mn) referred to as lithium-manganese-rich materials for lithium ion batteries. The prepared materials displayed high capacity ≥200 mAh/g at a current density of 20 mA/g in the voltage range of 2.0 V to 4.8 V. In particular the cathode material prepared at pH 10.0 delivered a high initial discharge capacity of 266 mAh/g at 20 mA/g current density and maintained a discharge capacity ≥220 mAh/g at 50 mA/g after 50 cycles. The synthesis method was used to further investigate the effect of lithium ratio in the layered-layered material. Li1+xMn0.6Ni0.2O2, x= 0.2, 0.25, 0.3 and 0.4 cathode materials were produced respectively. The BET surface area analysis results showed that Li1.3Mn0.6Ni0.2O2 material had comparatively higher surface area to the other cathode materials and also delivered good electrochemical results. XPS showed that the cation distribution is affected by the increase in lithium ratio, the Mn4+ percentages decreased significantly with an increase in lithium ratio. All materials peaks deconvoluted into two peaks namely Mn4+ and Mn3+, Li1.3Mn0.6Ni0.2O2 had the highest percentages of the stable Mn4+ 70.8%. Further investigation focused on the effect of the sintering temperature on the structure and the electrochemical performance of Li1+xMn0.6Ni0.2O2, x= 0.25, 0.3 and 0.4 cathode materials. X-ray diffraction showed the same patterns for all cathode materials sintered at 700˚C, 800˚C and 900˚C. Rietveld refined results however, showed that the increase in the sintering temperature, results in a decrease in the Li2MnO3 component percentage in the layered structures. Scanning electron microscopy images further proved that the particle size increases with increasing temperature. The charge–discharge tests of coin cells demonstrated that the materials sintered at 800˚C delivered higher discharge capacities above 200 mAh/g at 20 mA/g current density when compared to the materials made at the lower temperatures. Lastly the cathode material prepared at pH 10.0 was further evaluated in a cell using lithium titanate oxide Li4Ti5O12 as anode material. The cells delivered an initial discharge capacity of 213 mAh/g at 20 mA/g within a voltage range 3.3V-0.5V. The coin cells developed in this work delivered good cycling performance.
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- Date Issued: 2018