Oxygen-ion Battery for Large-scale Grid Storage

Lithium-ion batteries have proven the best current choice for electric vehicles (EVs), cell phones, and personal electronic devices. This is largely due to their relatively lightweight and high energy density, which makes them optimum for things that move. Lithium-ion batteries are also finding growing applications in battery energy storage systems (BESS), but their advantage of lighter weight isn’t as clear, and their high cost and limited lifetime mean that other battery concepts may provide benefits.

 

Image used courtesy of Advanced Energy Materials, Volume: 13, Issue: 11, First published: 25 January 2023, DOI: (10.1002/aenm.202203789)

 

Battery Storage for Renewables

Battery storage is a requirement for intermittent renewable energy sources like wind and solar. The batteries are charged when the wind is blowing or the sun is shining, providing power back to the grid at night or when it is calm. A variety of energy storage concepts are currently in use, including pumped hydro storage using water reservoirs and battery designs such as flow batteries and a variety of traditional battery designs using materials that cost less than those used in lithium-ion batteries.

 

Charge Carriers (Ions)

As a review, a typical battery has a cathode (positive electrode) and an anode (negative electrode) that are separated by an electrolyte that allows ions to flow freely between the two electrodes. When the battery is charged, electrons are absorbed as the charge-carrying ions move from the cathode to the anode. When the battery is discharged, the electrons are released as the charge carriers move back from the anode to the cathode. A lithium-ion battery is called that not because it contains a lot of lithium (around 2 percent by weight) but because lithium ions carry the charge between the electrodes.

Other ions, such as sodium, magnesium, and aluminum, can be used as charge carriers. Batteries using such materials are under study but have yet to provide all the benefits the lithium-ion combination can provide.

 

Lithium-ion batteries. Image used courtesy of Pixabay

 

Oxygen as Charge Carrier

For stationary applications, the Vienna University of Technology (TU Wien) is working on a new ceramic-based battery system that uses oxygen as the charge carrier. The research team had experience working with ceramic materials for fuel cells and decided to apply their knowledge to making a ceramic-based battery. Because oxygen can release two electrons and is readily available from the atmosphere, it makes an effective charge carrier. Electrical energy is stored chemically in the electrode by changing its oxygen content. The oxygen ions travel from one ceramic material to the other during charging and discharging, allowing an electric current to flow. 

 

Ceramic-based Battery

The ceramic single-crystal electrolyte used in the model cells in the UT Wien study was composed of yttria-stabilized zirconia (YSZ) with thin film electrodes. Although the test battery was made using rare-earth yttria, the researchers are confident that with more research, the use of rare-earth materials will not be required. The batteries also pose less fire risk than traditional lithium-ion cells. The energy density of the oxygen ceramic cells is not as high as that of a lithium-ion battery; however, its storage capacity does not degrade over time, providing a potential for long service life. What’s more, if oxygen is lost from the cell, it can be regenerated using oxygen from the atmosphere. 

Because the new battery operates at temperatures between 200 and 400 °C and has only about a third of the energy density of a lithium-ion battery, it is not suitable for cell phones, portable electronics, or EVs. But the long service life, the potential for a relatively low cost of materials, and enhanced fire safety make them a viable contender for the rapidly growing large-scale energy storage market. 

 

Featured image used courtesy of Adobe Stock