Potapenko A. Spinels of Li[LiхMn2-х]O4 and LiNi0.5Mn1.5O4 composition obtained from citric acid precursors as electrode materials for high rate lithium-ion batteries

The thesis deals with the citric acid aided routes of obtaining nanosized lithium manganese spinels of Li[LiхMn2-х]O4 and LiNi0.5Mn1.5O4 composition suitable to using as cathode materials in high-rate lithium ion batteries (LIB), as well as with disclosing the influence of spinel morphology (size of crystals and crystallites, their perfection and aggregation ability) on the capacity and high-rate properties of spinels. By means of pyrolysis and annealing of the citrate precursors, spinels Li[LixMn2-x]O4 and LiNi0.5Mn1.5O4 are obtained; the schemes of decomposition of precursors are found; the morphology of the materials is characterized. The spinels of Li[LixMn2-x]O4 composition have the maximal specific capacity of 117 mAh g-1. The best high-rate properties are characteristic of LiMn2O4: Sample Li||LiMn2O4 cells can be discharged with the currents of 6660 mA g-1 (45C). The spinel of LiNi0.5Mn1.5O4 composition has the specific capacity of 103 mAh g-1. Sample Li||LiNi0.5Mn1.5O4 cells can be discharged with the currents of 5870 mA g-1 (40C). Capacity retention at current loads of materials obtained from citrate precursors is superior against commercial samples recommended for high-rate LIB. The method of tuning the particle size of lithium-manganese spinels based on the prevention of manganese oxidation at the stage of pyrolysis of precursors by using an inert atmosphere has been offered. This method ensures a decrease in the particle size by a half if compared to the method of pyrolysis and annealing in air, and allows for a substantial increase in the ability of the materials to the discharge with the large currents. It is concluded that a decrease in the specific capacity of cathode materials compared to theoretical values is caused by the aggregation of particles, and the ability to sustain high current loads is governed not only by the particle size, but also by the perfection of the crystals.