One of the longstanding problems in engineering has been in finding a long-lasting battery that will provide storage capacity for energy, while reducing safety risks and costs. Researchers from the Harvard School of Engineering and Applied Sciences believe they have done just that.
The new flow battery stores energy in organic molecules dissolved in neutral pH water, allowing for a non-toxic, non-corrosive battery with an exceptionally long lifetime, with the potential to significantly decrease the cost of production.
The research was led by Michael Aziz and Roy Gordon. Flow batteries store energy in liquid solutions in external tanks. The bigger the tanks, the more energy they store. They are promising power storage solutions for renewable, intermittent energy like wind and solar, but today's flow batteries often see degraded energy storage capacity after many charge-discharge cycles, with their capacity restored only after periodic maintenance of the electrolyte.
The researchers found they could modify the structures of the molecules used in the positive and negative electrolyte solutions, in order to make them water soluble. In so doing, they can engineer a battery that only loses one percent of its capacity every 1000 cycles. To put this into context, this is better performance than lithium ion batteries.
Unlike conventional batteries, the liquid used to dissolve the electrolytes is neutral, minimising the corrosive nature of the medium. This allows the use of cheaper materials for other components, like the ion-selective membrane that separates the positive and negative sides of the batteries, as well as the tanks and the pumps.
This reduced cost is important, as cost-effective energy storage is a key piece of the puzzle that would make stored wind and solar energy competitive to traditional fossil fuel produced energy, and allow the integration of batteries in a lot more applications.
The researchers started by finding out why previous flow battery electrolyte molecules were degrading quickly in neutral solutions. They looked at the molecule viologen, which is used in the negative electrolyte, then modified its molecular structure to make it more resilient in neutral solutions.
They then investigated a similar approach for the positive electrolyte, turning to ferrocene. Ferrocene is well known for its electrochemical properties, but is normally insoluble in water. They modified the molecule to make it highly soluble.