טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentBendikov Tatyana
SubjectNovel Aqueous Zinc-Sulfur Battery
DepartmentDepartment of Chemistry
Supervisors Professor Emeritus Chaim Yarnitzky (Deceased)
Mr. Stuart Licht


Abstract

A new aqueous Zinc-Sulfur battery system consists of a Zinc anode and a solid Sulfur/Polysulfide cathode in highly concentrated alkaline electrolyte. High energetic parameters (theoretical Faradaic capacity - 550 Ah/kg, theoretical Energy density - 572 Wh/kg), low cost and low toxicity make this system very competitive with other existing aqueous battery systems.

            In aqueous polysulfide media, zinc anodes are completely passivated because of formation of insulated semiconductor ZnS on the electrode surface during the oxidation process, blocking the surface of the electrode and preventing further electrochemical reaction. In the presence of highly concentrated alkaline solutions (more than 6 m KOH), the zinc surface can be reactivated and zinc becomes an effective anode in polysulfide media.

            The first functional new Zinc-Polysulfide battery was built in the two compartment cell configuration, with the zinc alkaline anode compartment separated from the polysulfide cathode compartment by a cation permeable membrane. Judged by its energetic parameters this configuration however, cannot compete with existing commercial and noncommercial battery systems. Further research was therefore directed at the zinc-sulfur cell with one compartment configuration.

            A wide variety of experiments were performed utilizing “thick” one compartment cell configuration. The best result (105 mA/cm2) was obtained for K2S3 3 m + KOH 14 m solution, discharged under a load of 3.3 ohm and a temperature of 50 °C. This practical Faradaic capacity is competitive with that obtained for commercial primary aqueous battery systems. On the other hand, it is only about 20% of the theoretical Faradaic capacity of the Zinc-Sulfur battery system (550 Ah/kg).

            For further enhancement of the Faradaic capacity, the thin one compartment cell was constructed. This thin configuration (total battery thickness about 0.3 mm) results in approximately doubled discharge capacity (175 Ah/kg) compared with other, thicker cell configurations.

            Button cell configuration, utilizing a solid sulfur cathode with the addition of electrocatalytic CoS, has allowed the decrease of total battery weight and further enhancement of measured discharge capacity to 280 Ah/kg, which is more than 200 Wh/kg of measured energy density.