Ajayi, O.S and Covenant University, Theses (2021) SYNTHESES AND ELECTROCHEMICAL PERFORMANCE OF COMPOSITE AND CORE-SHELL LITHIUM-RICH OXIDES CATHODE FOR LITHIUM-ION BATTERY. ["eprint_fieldopt_thesis_type_phd" not defined] thesis, COVENANT UNIVERSITY.
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Abstract
The layered lithium-rich oxide (LLO) cathode delivers higher capacity and excellent thermal stability compared to the conventional cathode materials but they demonstrate several performance limitations that affect their practical applications. The aim of this research work is to optimise the electrochemical performance of LLOs using different synthetic routes, LLO architecture (composite/core-shell), and stoichiometries. The effects of the nature of fuel [citric acid (CA) and ammonium acetate (AA)] in different proportions and annealing temperature on the structural properties and electrochemical performance of Li1.2Mn0.52Ni0.2Co0.08O2 composite material synthesised by the solution combustion synthesis (SCS) were determined. The samples were analysed with TG-DSC, ICP-OES, powder XRD, Raman Spectrometer, and SEM/EDX. The 75%CA:25%AA fuel mixture samples had the largest particle size compared with 50%CA:50%AA and 100%CA samples. The electrochemical result revealed that 50%CA:50%AA samples gave the highest initial discharge capacities of 196 mAh/g and 215 mAh/g and a capacity retention of 99.9% and 86.7% after 30 cycles, for the sample annealed at 1000oC/10 hr (5050-T1) and 900oC/3 hr (5050-T2), respectively. The 75%CA:25%AA fuel mixture sample pre-annealed at 500oC/3 hr and further annealed at 1000oC/3 hr (7525-T3) gave the highest capacity retention of 121.4% after 30 cycles. A core-shell (CS) structure can be used to improve the electrochemical performance of LLO materials. Therefore, CS 0.5Li2MnO3·0.5LiNi0.5Mn0.3Co0.2O2 (Li1.2Mn0.52Ni0.2Co0.08O2) were synthesised through different synthetic routes (sol-gel and wet chemical synthesis). The sol gel synthesised sample gave an overall better electrochemical performance compared to the wet chemical synthesised sample. The effects of coating solvent and annealing temperature on the sol-gel synthesised CS sample were further examined. The initial discharge capacity and coulombic efficiency of the CS sample coated in distilled water and annealed at 1000oC (CS-SG-W-1000) were 240 mAh/g and 76%, respectively while the same sample coated in aqueous ethanol (CS-SG-A-1000) gave 175 mAh/g and 28.2%, respectively. After 30 cycles, the discharge capacity and capacity retention of CS-SG-W-1000 sample was 215 mAh/g and 89.4%, while that of CS-SG-A-1000 was 138 mAh/g and 79.0%, respectively. The better overall electrochemical performance observed for CS-SG-W-1000 compared to CS-SG-A-1000 was attributed to the better dispersion in the water and the presence of better-layered and crystalline structure obtained at the highest annealing temperature. Finally, different LLO stoichiometric quantities of xLi1.2Mn0.6Ni0.2O2(LMO)∙(1-x)LiNi0.5Mn0.3Co0.2O2(NCM) (x = 0.7, 0.5, 0.3) composite cathode materials were synthesised using solution combustion-mechanochemical synthesis. The initial discharge capacity and coulombic efficiency of the 0.7LMO-0.3NCM sample was 239 mAh/g and 67.9%, 0.5LMO-0.5NCM sample was 171.5 mAh/g and 63.2%, while the 0.3LMO-0.7NCM sample gave 213.1 mAh/g and 74.2%, respectively. After 30 cycles, the discharge capacity and capacity retention of 0.7LMO-0.3NCM were 209 mAh/g and 87.2%, 0.5LMO-0.5NCM sample were 155 mAh/g and 91.0%, while 0.3LMO-0.7NCM were 149.1 mAh/g and 70.0%, respectively. This study shows that the composite powders synthesised with only citric acid fuel gave the best electrochemical performance compared with those produced using the fuel mixtures. Also, the core-shell architecture improved the first coulombic efficiency of LLO material compared with the composite architecture.
| Item Type: | Thesis (["eprint_fieldopt_thesis_type_phd" not defined]) |
|---|---|
| Uncontrolled Keywords: | Li1.2Mn0.52Ni0.2Co0.08O2, Composite, Core-shell, Coulombic efficiency, Electrochemical performance, Solution combustion synthesis |
| Subjects: | Q Science > Q Science (General) Q Science > QD Chemistry |
| Divisions: | Faculty of Engineering, Science and Mathematics > School of Chemistry |
| Depositing User: | AKINWUMI |
| Date Deposited: | 16 Feb 2022 08:56 |
| Last Modified: | 08 Mar 2023 08:12 |
| URI: | http://eprints.covenantuniversity.edu.ng/id/eprint/15626 |
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