As demand for more compact, affordable and safer mobile and stationary energy storage increases, current batteries such as lithium-ion are approaching their energy storage and performance limits.
An attractive alternative is the lithium-air battery in which the redox active element is atmospheric oxygen and thus does not need to be stored within the battery. In theory, lithium-air battery technology can offer simplified design and energy densities similar to gasoline.
In current lithium-air batteries, insoluble lithium oxides accumulate in the porous cathode during use. Battery performance is reduced over time as the diffusion of oxygen from the air to the cell is gradually restricted. On charging, a high voltage is needed to disproportionate the solid carbonates compared to the voltage delivered on discharge.
The overall efficiency of the battery is reduced over time as the amounts of metal carbonates increase. Exposure of the battery to air can also degrade performance. Ingress of CO2 into the battery also results in the formation of lithium metal carbonates and bi-carbonates, which reduce performance and cyclability. Ingress of moisture can also degrade battery performance.
Scientists at Newcastle University have developed a solution to these problems by employing a sodium carbonate impregnated electrode.
The use of sodium carbonate offers some distinct advantages:
- sodium carbonates are easily converted to metal ions, CO2 and O2 on charging compared to lithium carbonates
- manufacture of the cathode impregnated with sodium carbonate creates additional pore space on first charging which maintains an optimal oxygen diffusion rate and enhances battery performance
- ingress of CO2 is not detrimental to the efficiency of the battery as it is required for carbonate formation
- faster discharge rates and higher charge rates are possible than current lithium or sodium air batteries
- safer operation as the battery is stored in the discharged state; ready for charging
- sodium is earth abundant and cheap (earth crust composition of sodium 2.6% vs 0.007% for lithium)
- sodium is environmentally benign compared to lithium
The key feature of metal-air chemistries is their potential to provide an unrivalled high energy density compared to current battery technologies. High energy density translates to compact low weight battery systems that would be ideal for a number of applications from button batteries to bulk storage.
It is envisaged that metal-air battery technology is particularly applicable to:
- Grid Scale Storage
In this context metal air batteries would be a key component to ease the integration of renewable energy sources to the grid network, storing energy generated during off peak hours and releasing it to the grid when demand is high.
- Electric Vehicles
Compact, lightweight high energy density batteries offers the possibility of electric vehicles with a mileage range comparable to petrol and diesel powered vehicles.
- Portable Electronics
The research team have produced a sodium carbonate battery demonstrator button cell ideal for this type of application. The button cell project allowed for the assessment of different materials of construction and operating conditions. It was found to perform well at ambient temperature and to be tolerant to carbon dioxide.
At present research programs are directed at determining the effectiveness of other alkali earth metals in carbonate–air systems.
The University is seeking collaborative and /or license opportunities with a suitable industrial partner who can take the next steps of scale up/commercialization of the technology.
A GB patent application has been filed for this technology.
Title: Metal-air Batteries
UK patent application no: 1314934.9
Filing date: 21/8/13
The patent has entered the national phase and applications have been filed in a number of international territories.
Dr Tim Blackburn, Science, Agriculture & Engineering Enterprise Team, Research and Enterprise Services, Devonshire Building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK