Josef Máca

Elimination of irreversible effects during first charging of lithium battery anodes

The irreversible capacity of negative electrode in a lithium-ion cell is a widely described the phenomenon. Irreversible capacity losses are connected with formation of a solid electrolyte interface layer. This layer is growing on the electrode-electrolyte interface during first several charging cycles. The layer is indispensable for proper functioning of a lithium-ion cell. However, during this layer formation, the atoms of lithium are consumed in a range from 18 to 45% of the total amount of lithium atoms presented in cell. Demonstration of possibilities to suppress this phenomenon that occurs on a negative electrode interface is the main aim of this paper.

Effect of UV radiation on the electrical properties of modified oligobutadienes

Oligobutadienes are viscous liquid polymers of butadiene with low relative molecular mass representing the raw material for polyurethanes production, which are widely used not only in the electrical engineering. The article describes the properties and accelerated degradation processes of variously modified oligobutadienes (LB 3000, LB 5000, LBH 3000 and LBM 32) due to effects of UV radiation. The behavior of materials in the course of UV degradation is observed in the AC electric field using the method of dielectric relaxation spectroscopy in the frequency range 20 Hz - 2 MHz and in the temperature interval 20 °C to -30 °C. Dielectric properties are measured using precision LRC meter Agilent E4980 including dielectric liquid test fixture Agilent 16452A immersed in to the water bath thermostat Medingen KT40. Frequency dependencies of the parts of complex permittivity are approximated by a mathematical function describing the position and shape of the relaxation maximum and information about the activation energy of relaxation process are added. The dielectric spectra changes of individual samples during the acceleration ageing by UV radiation are evaluated with respect to different molecular chain length and terminating functional group.