Ultimate Specific Energy for Batteries, Ultracapacitors

A comparison of practical and theoretical specific energy limits for various battery technology. Others predict higher practical and theoretical levels.

The determination of the theoretical maximum capacity of a Lithium-air battery is complex, and there isn’t a flat statement of fact in the Handbook of Batteries , Third Edition as are many more well developed chemistries. To provide the most accurate value for the maximum capacity, BD asked Dr. Arthur Dobley to provide an expert opinion, which we quote as follows:
“Specific capacity:
* For lithium metal alone 13 kWh/kg.
* For the lithium and air, theoretical, 11,100 Wh/kg, not including the weight of oxygen, and 5,200 Wh/kg including the weight of oxygen. This was checked by calculation and agrees with K.M. Abrahams publication ,JECS 1996.
* For the Lithium air cell, practical, 3,700 Wh/kg, not including the weight of oxygen, and 1,700 Wh/kg with the weight of oxygen. These numbers are predictions and are made with the presumption that 33% of the theoretical energy will be obtained. The battery industry typically obtains 25% to 50% of the theoretical energy (Handbook of Batteries). Metal air batteries are higher in the range. Zinc-air is about 44% (Handbook of Batteries, 3rd Ed. pg 1.12 and 1.16 table and fig).

We selected a conservative 33%. You may quote these numbers above and make any comments with them. The theoretical numbers are similar to the numbers in the ECS 2004 abstract. ( The difference is due to mathematical rounding.)

PolyPlus Battery Company is developing novel lithium/air batteries with unprecedented energy density, rivaling that possible for hydrocarbon fuel cells. The technology is based on proprietary encapsulated water stable lithium metal enabling the practical realization of unique galvanic couples such as Li/Air and Li/Water batteries. The theoretical specific energy of lithium metal/aqueous couples is greater than 10,000 Wh/kg and commercial batteries are expected to exceed 1000 Wh/l and Wh/kg.

IBM is starting research on lithium air batteries as well.

Only a handful of labs around the world, including those at PolyPlus Battery, in Berkeley, CA, Japan’s AIST, and St. Andrews University, in Scotland, are currently working on lithium-air batteries. Lithium metal-air batteries can store a tremendous amount of energy–in theory, more than 5,000 watt-hours per kilogram. That’s more than ten-times as much as today’s high-performance lithium-ion batteries, and more than another class of energy-storage devices: fuel cells. Instead of containing a second reactant inside the cell, these batteries react with oxygen in the air that’s pulled in as needed, making them lightweight and compact.

Metal Air Batteries estimated specific energy:

Polyplus has approached the challenge of the Lithium metal electrode with a coating of a glass-ceramic membrane, sealing the Lithium from an aqueous catholyte. The resultant structure exhibits very small self discharge, ordinarily a large contributor to cell failure. Test cells have produced 0.5 mAh/cm2 for 230 hours exhibiting approximately 100% Coulombic efficiency.

A production oriented cell construction with double sided lithium anode, solid electrolyte and double sided air/cathode is anticipated to have 600 to 1000 Wh/kg energy density.

Carbon-air Battery are the focus of a program being performed by St. Andrews University, (UK). The free energy of carbon oxidation is 9100 Wh kg and a fuel-only specific energy of 7200 Wh/kg is possible. The final system is anticipated to have a device specific energy of 2000-3000 Wh/kg. A major consideration is to maintain the operational temperature of the electrolyte at 7000 C or greater. This limits the carry-it-around-in-your-pocket and turn-it-on-in-a-moment possibilities.

Metal-Air Battery/Fuel Cell by eVionyx have been able to overcome many limitations of self corrosion and passivation while increasing specific energy, specific power and Coulombic efficiency.

Air cathodes provide up to 10 times the current of conventional air cathodes with proprietary electrolytes and patented processes. Solid polymer electrolyte membranes have reduced the problems of electrolyte loss due to dry out. Zinc-air cells produce up to 450 Wh/kg while Aluminum-air cells can produce a specific energy of more than 550 Wh/kg, and specific energies up to 650 Wh/kg are expected. Ordinarily, Magnesium-air fuel cells utilize only up to 60%, but with the electrolyte additives, can utilize up to 94% of the alloy.

Lithium Sulfur batteries, University of Waterloo, have and energy density iof about 1200 Wh/kg, for just the positive electrode, which would put the energy density of the cell at about 500 Wh/kg or more, but this depends on the other components of the cell,” Dr. Nazar said. “That is about a factor of 3 to 5 times more than a conventional lithium-ion battery.

New Scientist covers lithium air batteries.

EEStor ultracapacitor estimates if they work.

Prototype / LightEVs Mass
Low Volume Estimate Production
Energy density (Wh/l).. 606 ......... 700 .......1513
Specific energy (Wh/kg) 273........ 450 ........682
Price ($ USD/kWh) .....$61......... n/a....... $40

Lithium battery update from 2007.

Primary Zinc-carbon batteries produce less than 100 Wh/kg, primary Alkaline less than 200 Wh/kg and Lithium-thyonyl chloride batteries 730 Wh/kg.