Investigation of the reaction mechanisms during Li uptake and release of spinel oxide nanoparticles MIIMIIIFeO4 (MII = Mn, Mg, Co, Ni; MIII = Mn, Fe) for application as anode materials in Lithium ion batteries
Lithium ion batteries (LIBs) have achieved great success as portable power supply for consumer electronic devices. New applications for LIBs in the near future are electric vehicles and stationary energy storage systems. Therefore, higher energy density and simultaneously cost reduction is needed. Materials should also be earth abundant and environmental friendly. Actually commercialized materials exhibit a capacity limit due to the fact that just a limited number of Li+ ions can be intercalated/deintercalated per formula unit. Alternative materials were investigated during the past decades. Conversion materials exhibit 2 - 5 times larger capacities because more Li per formula unit can be stored. Intensively investigated materials are e.g. spinel oxides MIIMIII2O4 (MII = Co, Cu, Mn, Mg, Co, Ni; MIII = Mn, Fe, Co). The reactions occurring during electrochemical cycling are complex affecting both the crystal structure and the electronic properties, which were not investigated in detail. In the thesis the synthesis of several spinel oxide nanoparticles MnFe2O4, MgFe2O4, CoFe2O4, CoMnFeO4 and NiMnFeO4 are reported. In addition, composites were synthesized including NiFe2O4 interconnected with a network made of carbon nanotubes and CoFe2O4 deposited on reduced graphite oxide. The materials were intensively characterized and processed as electrodes for testing their electrochemical performance applying galvanostatic cycling and cyclic voltammetry (CV).
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