Environmentally friendly energy storage Carbon batteries store renewable energy and help protect the climate

Related Vendors

Oak Ridge National Laboratory

Taiwan Machine Tool & Accessory Builders' Association (TMBA)

Wuxi InfiMotion Technology Co., Ltd.

Researchers at Oak Ridge National Laboratory are pioneering a groundbreaking battery technology that not only stores renewable energy but also captures carbon dioxide directly from the air, offering a dual solution to two of the most pressing environmental challenges.

Researchers at Oak Ridge National Laboratory (ORNL) are developing battery technologies to combat climate change in two ways: by increasing the use of renewable energy and by capturing carbon dioxide from the air.

This type of battery stores the renewable energy generated by solar panels or wind turbines. To use this energy when wind and sunlight are not available, an electrochemical reaction is required that captures carbon dioxide from industrial emissions and converts it into value-added products in ORNL's new battery formula.

ORNL researchers have recently developed and tested two different battery concepts that convert carbon dioxide gas (CO₂) into a solid form that can be used for other products. One of these new battery types maintained its capacity for 600 hours of operation and could store electricity for up to ten hours. The researchers also identified, investigated and overcame the main obstacle, deactivation caused by chemical deposits, which was an obstacle for the other battery concept.

"ORNL's Transformation Energy Science and Technology (TEST) initiative is exactly the kind of effort we need to combat climate change. We're excited that ORNL is investing in innovative ideas and approaches that can transform the way we think about storing energy beyond lithium-ion batteries and other conventional electrochemical energy storage systems," said Ilias Belharouak, an ORNL Corporate Fellow and leader of the initiative.

It's a fantastic scenario: using free electrons to store CO₂ and convert it into profitable products is a concept I could never have imagined ten years ago, but this is just the beginning.

Ilias Belharouak, ORNL Corporate Fellow and leader of the initiative

Stationary and open

Batteries work through electrochemical reactions in which ions are moved between two electrodes through an electrolyte. Unlike cell phone or car batteries, batteries designed to store energy on the grid do not have to function as a portable, closed system. This has enabled ORNL researchers to develop and test two types of batteries that can convert CO₂ from stationary industrial sources.

For example, the carbon dioxide produced in a power plant could be pumped through a pipe into the liquid electrolyte, creating bubbles similar to those in a carbonated soft drink. During battery operation, the gas bubbles turn into a solid powder.

How does it work?

Each component of a battery can consist of different elements or connections. This selection determines the life of the battery, how much energy it can store, how large or heavy it is and how quickly it charges or releases energy. In one of the new ORNL battery concepts, CO₂ is combined with sodium from salt water using an inexpensive iron-nickel catalyst. In the second, the gas is combined with aluminum. Each approach uses abundant materials and a liquid electrolyte in the form of salt water, sometimes mixed with other chemicals. The batteries are safer than existing technologies because their electrodes are stable in water, according to lead researcher Ruhul Amin.

Very little research has been carried out into CO₂ batteries to date. The approach tested so far is based on a reversible metal-CO₂ reaction that regenerates carbon dioxide, which continues to release greenhouse gases into the atmosphere. In addition, solid discharge products tend to clog the surface of the electrode, which impairs the performance of the battery.

However, the CO₂ batteries developed at ORNL do not release carbon dioxide. Instead, the carbonate by-product dissolves in the liquid electrolyte. The by-product either continuously enriches the liquid to improve battery performance or it can be filtered from the bottom of the container without interrupting battery operation.

The battery design can even be adapted to produce more of these by-products for use in the pharmaceutical or cement industries. The only gases released are oxygen and hydrogen, which do not contribute to climate change and can even be captured for energy or fuel production. The ORNL researchers used an almost entirely new combination of materials for these CO₂ batteries. The few similar earlier designs only worked for a short time or contained expensive metals.

Advantages, disadvantages and challenges overcome

The sodium-carbon dioxide or Na-CO₂ battery was the first to be developed and encountered a number of obstacles. For this system to work, the electrodes must be separated into wet and dry chambers with a solid ionic conductor in between. The barrier slows down the movement of the ions, which in turn slows down the operation of the battery and reduces its efficiency.

A major challenge for this Na-CO₂ battery is that a film forms on the electrode surface after prolonged use, which eventually leads to the battery being deactivated. Amin's research team used highly specialized microscopes and X-ray techniques to examine the battery cell at various stages of operation and then when it failed.

Studying the film formation helped the researchers to understand how to degrade it again. They were intrigued when they realized that the battery could be reactivated or prevented from deactivating by changing the charge/discharge cycle. Uneven charging and discharging pulses prevented the formation of a film on the electrode.

"We are reporting for the first time that the deactivated cell can be reactivated," says Amin. "And we have found the cause of deactivation and activation. If you charge and discharge the battery symmetrically for too long, it is dead at one stage. If you use the protocol we developed for our cell, the probability of failure is very low."

A second design for long-term storage

Next, the researchers focused on the design of the aluminum-carbon dioxide or Al-CO₂ battery. The team experimented with different electrolyte solutions and three different synthesis processes to find the best combination. The result was a battery that offers a storage capacity of more than ten hours of electricity for later use. "This is very important for long-term storage," said Amin. "This is the first Al-CO₂ battery that could run stably over a long period of time, which is the goal. Storing only a few hours of stored energy is not helpful."

The tests showed that the ORNL battery can operate for more than 600 hours without losing capacity, Amin said—far more than the only previously reported Al-CO₂ battery, which was only tested for eight hours. The icing on the cake is that this battery captures almost twice as much carbon dioxide as the Na-CO₂ battery. The system can be designed to operate in a single chamber, with both electrodes in the same liquid solution, so there is no impediment to ion movement.

The challenge for the Al-CO₂ battery is to improve its scalability, says Amin. Nevertheless, the team will continue to systematically investigate the battery's properties in order to extend the operating time and capture CO₂ more efficiently. To make the Na-CO₂ battery competitive, the team will focus on developing a very fine, dense and mechanically stable ceramic membrane to separate the battery chambers.

This research project was funded by ORNL's Laboratory Directed Research and Development (LDRD) program. The Center for Nanophase Materials Sciences, a DOE user facility at ORNL, was used for the sodium CO₂ battery research. (sb)

This article was first published on our sister website www.ElektronikPraxis.de (German language), Vogel Communications Group