Infoscience

Thesis

Mesoscopic manganese based cathode materials for high voltage lithium ion batteries

Alternative cathode materials were investigated for application to high voltage lithium ion batteries. Manganese based materials were considered due to the low cost and environmentally sustainable impact. Layer-structured oxide and phospho-olivine materials were prepared by a sol-gel method to obtain mesoscopic particles. The particle size of the layered Li1.15Mn0.545Ni0.245Al0.06O2 material was 200 nm. A ball-milling process reduced the particle size to 60 nm. Doping with Ni and Al in the layered Li1.15Mn0.545Ni0.245Al0.06O2 material provided a redox potential at 4.1 V vs. Li+/Li. The specific capacities of 60 and 200 nm particle sized materials were 150 and 125 mAh/g, respectively at C/10. The 60 nm sized material showed a higher lithium intercalation rate than the 200 nm sized material. Particularly, at high charge-discharge rates (1C and 5C), 127 and 85 mAh/g, respectively compared to 95 and 10 mAh/g at 1C and 5C, respectively of 200 nm material. However, the 60 nm sized material degraded faster upon cycling after 80 cycles. The increased impedance indicates a large resistance associated with the interface reaction in the cycled 60 nm particlels. Two types of electrolytes were investigated in the same cathode material. 3-methoxypropionitrile (MPN) with 1M LiN(SO2CF3)2 electrolyte showed faster Li intercalation than ethylene carbonate/dimethyl carbonate (EC/DMC) with 1M LiPF6 at 1C and 5C in complete cells. LiMnPO4 was synthesized by a sol-gel method using glycolic acid. The decomposition temperature was lower in the dried gel prepared under strong acid conditions. Finally, highly ordered crystallites were formed between 520 and 570°C with particle sizes in the range of 140 to 160 nm. Subsequent dry ballmilling reduced the diameter to 130 ± 10 nm and also improved the carbon coating on the active material. LiMnPO4 material provided a redox potential of 4.1 V vs. Li+/Li. Reversible capacities of 156 mAh/g at C/100 and 134 mAh/g at C/10 were measured. At 92 and 79 % of the theoretical value, respectively, these are the highest values reported to date for this material. At faster charging rates, the electrochemical performance was found to be improved when smaller LiMnPO4 particles were used. The LiMnPO4 material showed an excellent capacity retention upon cycling as phosphate framwork is chemically and thermodynamically stable.

Fulltext

Related material