A hybrid cell may be defined as a galvanic electro-technical generator in which one of the active reagents is in the gaseous state i.e. the oxygen of the air. Such cells take advantage of both battery and fuel cell technology. Examples of such cells are:
1. Metal-air cells such as iron oxygen and zinc oxygen cells:
The Zn/O2 cell has an open-circuit voltage of 1.65 V and a theoretical energy density of 1090 Wh/kg. The Fe/O2 cell has an OCV of 1.27 V and energy density of 970 Wh/kg.
2. Metal-halogen cells such as zinc-chlorine and zinc-bromine cells:
The zinc-chlorine cell has an OCV of 2.12 V at 25°C and a theoretical energy density of 100 Wh/ kg. Such batteries are being developed for EV and load leveling applications. The zinc-bromine cell has an OCV of 1.83 V at 25°C and energy density of 400 Wh/kg.
3. Metal-hydrogen cells such as nickel-hydrogen cell:
Such cells have an OCV of 1.4 V and a specific energy of about 65 Wh/kg. Nickel-hydrogen batteries have captured large share of the space battery market in recent years and are rapidly replacing Nickel/cadmium batteries as the energy storage system of choice. They are acceptable for geosynchronous orbit applications where not many cycles are required over the life of the system (1000 cycles, 10 years).
The impetus for research and development of metal-air cells has arisen from possible EV applications where energy density is a critical parameter. An interesting application suggested for a secondary zinc-oxygen battery is for energy storage on-board space craft where the cell could be installed inside one of the oxygen tanks thereby eliminating need for gas supply pipes and valves etc. These cells could be recharged using solar converters.
Some of the likely future developments for nickel-hydrogen batteries are
(1) Increase in cycle life for low earth orbit applications up to 40,000 cycles (7 years)
(2) Increase in the specific energy up to 100 W/kg for geosynchronous orbit applications and
(3) Development of a bipolar nickel-hydrogen battery for high pulse power applications.
1. Metal-air cells such as iron oxygen and zinc oxygen cells:
The Zn/O2 cell has an open-circuit voltage of 1.65 V and a theoretical energy density of 1090 Wh/kg. The Fe/O2 cell has an OCV of 1.27 V and energy density of 970 Wh/kg.
2. Metal-halogen cells such as zinc-chlorine and zinc-bromine cells:
The zinc-chlorine cell has an OCV of 2.12 V at 25°C and a theoretical energy density of 100 Wh/ kg. Such batteries are being developed for EV and load leveling applications. The zinc-bromine cell has an OCV of 1.83 V at 25°C and energy density of 400 Wh/kg.
3. Metal-hydrogen cells such as nickel-hydrogen cell:
Such cells have an OCV of 1.4 V and a specific energy of about 65 Wh/kg. Nickel-hydrogen batteries have captured large share of the space battery market in recent years and are rapidly replacing Nickel/cadmium batteries as the energy storage system of choice. They are acceptable for geosynchronous orbit applications where not many cycles are required over the life of the system (1000 cycles, 10 years).
The impetus for research and development of metal-air cells has arisen from possible EV applications where energy density is a critical parameter. An interesting application suggested for a secondary zinc-oxygen battery is for energy storage on-board space craft where the cell could be installed inside one of the oxygen tanks thereby eliminating need for gas supply pipes and valves etc. These cells could be recharged using solar converters.
Some of the likely future developments for nickel-hydrogen batteries are
(1) Increase in cycle life for low earth orbit applications up to 40,000 cycles (7 years)
(2) Increase in the specific energy up to 100 W/kg for geosynchronous orbit applications and
(3) Development of a bipolar nickel-hydrogen battery for high pulse power applications.