טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentHillel Tomer
SubjectCopper Vanadate Cathodes for Li Thermal Batteries
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Yair Ein-Eli
Full Thesis textFull thesis text - English Version


Abstract

Thermal batteries have been left behind in the rapid progress of battery science and technology. Pyrite has been the leading cathode in use. Its discharge potential at low current density is 2.05V vs. Li. In the last few years new cathode materials have been studied. However, a breakthrough in Li-thermal batteries cathode discharge potential has not been achieved.

In this research, a series of CuO-V2O5 oxides, such as CuV2O6, Cu2V2O7 and Cu5V2O10 have been synthesized. The structure and morphology have been determined and the electrochemical properties at room temperature and elevated temperatures (5250C) vs. Li metal alloy have been investigated. At room temperature, an increase in copper content in the vanadate has been found to provoke a gradual negative shift of the operating voltage plateau vs. Li metal. With discharge at elevated temperatures, a voltage plateau of 3.4V at a current density of 100 mA/cm2 was achieved and a voltage plateau of 2.5V was recorded with a higher current density. At higher synthesis temperatures, the CuV2O6 material presented a significantly higher capacity at a potential of 2.8 V.

X-ray analysis revealed a meta-stable phase material along with equilibrium phases. This was explained by the meta-stable β → α CuV2O6 phase transformation at 625ºC. The influence of the metastable equilibrium phase, Cu2V2O7, V2O5, and β CuxV2O5, on CuV2O6 was studied by isolating the phase or by increasing its quantity. CuxV2O5, β CuxV2O5 discharge mechanisms were uncovered and the influence of each phase on CuV2O6 electrochemical discharge behavior was obtained.

While researching the abnormal morphology of β CuxV2O5, a form of elongated particles with a size difference of two orders was seen. This abnormal morphology was studied by conducting HRSEM, XRD and EDS analysis. The study revealed a growth mechanism that decreases the grain thickness. This mechanism increases the surface area along with growth in preferred plains, reducing the total energy of the material.

This research set the foundations to the use of CVO cathodes in thermal batteries. Those cathodes yield high voltage and high capacity at both high and low current densities. The current study also enables the design of discharge curves at elevated temperature by specifying the type and quantity of each phase in the cathode. An additional research achievement is the obtainment of a desired phase composition through the understanding and control of the metastable α → β CuV2O6 phase transformation.