Energy storage for the future
Renewable energy sources like wind and solar provide power output that depends largely on environmental conditions. Efficient, affordable energy storage systems are essential for the viability of renewable energy. Join us as we work on an ambitious, multi-disciplinary project in the design and construction of a sustainable microgrid system on campus using rechargeable redox flow batteries.
The flow cell project began at UBC in 2016 as a research project, intended to research the viability of using a flow-assisted Zinc - Nickel oxide battery as a means of energy storage. Essentially, the flow cell is a rechargeable battery, with some different properties that make it an interesting research topic.Conventional rechargeable batteries use stationary (i.e. non-flowing) solutions, with environmentally harmful materials, such as those in lead-acid or lithium-ion batteries. These batteries are used for a certain number of charge-discharge cycles with a certain efficiency. When applying a flowing electrolytic solution to a normal battery, the energy efficiency of it is greatly increased, due to the electrodes' increased exposure to the ions in solution. This is the main benefit of using flow cells instead of conventional rechargeable batteries. In addition, the materials used in making conventional batteries are normally quite toxic or environmentally harmful. Our flow cell uses Zinc and Nickel oxide with KOH and ZnO solutions, which are all non-toxic, giving us another reason to look into the viability of these cells. Our goal in this project is to vary the parameters of the cell, such as cell geometry and electrolyte flow, in order to optimize cell performance. We will also be researching how to tackle the issue of dendritic growth (see "Technology" section below for details). Eventually, we would like to build a microgrid of flow batteries on campus.
As mentioned before, our flow cell uses Zinc and Nickel oxide, with a flowing solution of ZnO in aqueous KOH. This operates as a normal electrochemical cell, with the zinc dissolving and depositing onto a copper substrate. (Note: the reactions are summarized below) When charging, the electron surplus at the copper anode will cause the Zn(OH)2- ions to form solid Zn and 4 OH- groups. The Zn deposits are said to be dendritic, due to their growth pattern. Dendritic growth is random and very difficult to control, meaning that any unusual growth can come into contact with other cell components and cause an internal short, which is a large obstacle for advancements in flow cell technology.
Not surprisingly, the mechanics of the flow cell are all about the flow of solution through the cell.The electrolyte is caustic and cannot be flown through an ordinary pump, as it would cause corrosion. We therefore use a peristaltic pump with chemical resistant tubing to induce flow in the sytem. The solution’s flowrate will affect dendritic growth and the cell’s efficiency, which is why we are also using a variable power supply. The benefit of this is we can change the voltage going to the pump, which will change the flowrate of solution.
Our cell is made of laser-cut acrylic sheets glued together using acrylic adhesives, which allows us to see what’s going on with the electrodes during operation. This helps us develop our methods of dendrite suppression, and keeps the cell relatively light.
Since this project is focused on energy storage, there is huge potential to include microelectronic technology, such as Arduino boards and printed circuit boards. We haven’t integrated this technology into the project just yet, but we will! Some examples of what we can do include using an Arduino to control the pump’s flow direction, using circuits to display the voltage available in the battery in real-time, or even automating the flow cell’s charge-discharge cycles.
As we’re trying to optimize the cell’s performance, the shape of the cell itself will have an impact on the cell’s electrochemistry. At the moment, our cell is box-shaped, with an inlet and outlet on opposite sides of the cell. Design is one of the most important aspects of engineering, and so we will be incorporating design processes and prototyping technology into the project, to give team members a valuable experience. —
