Ecologue

Human dependence on fossil fuels is a major contributor to the greenhouse gas emissions that are damaging Earth’s atmosphere and contributing to climate change across the globe. Fortunately, advances in renewable energy extraction, such as wind and solar energy, are bringing us closer to breaking free from fossil fuels and the negative externalities that they place on the environment. Securing sustainable energy sources is absolutely vital for maintaining a lifestyle similar to the one which we are currently living, not to mention advancing technologically, culturally, and economically. The difficulty of storing energy generated by renewable extraction methods is the main factor preventing the feasibility of switching to one-hundred percent renewable energy. Currently, we do not have powerful enough batteries to store sufficient energy generated from solar arrays or wind turbines. That is why students like Lynza Sprowl are working hard to develop batteries that have a higher energy density; energy density is the amount of energy that a battery can store relative to its size.

Lynza Sprowl is a fifth-year Ph.D. student in chemical engineering, studying lithium-ion batteries. She utilizes computer modeling of atomic-scale reactions to see how different atoms interact with each other, what reactions are happening, which products are formed, and the amount of charge transferred between different atoms.

How do lithium-ion batteries work?

“The anode and cathode are two electrodes in the battery. The anode is the negative electrode, which holds lithium with more energy, whereas the cathode is the positive electrode and binds lithium with a lower energy. And so you charge a battery, you’re putting high-energy electrons into the anode to meet up with the positive lithium ions to store that lithium atom in a high-energy state in the anode.”

-Lynza Sprowl

How do you make better batteries?

According to Sprowl, in order to increase a battery’s energy density one must be able to store more lithium in the battery and be able to move more lithium back and forth between the cathode and the anode. In order to move more lithium between the cathode and the anode, one must change the material used; the stronger the bond between the lithium and the anode, the more energy that can be stored. For example, lithium-ion batteries currently have a graphite anode, but silicon can store ten times more lithium. The reason that silicon anodes are not yet being implemented is that the electrolyte breaks down on the anode surface and consumes some lithium; this breakdown forms a solid barrier which inhibits lithium ions from reaching the anode. When lithium ions can’t reach the anode, the battery can’t be charged fully.

So it seems that if we can prevent the electrolyte from breaking down and forming a barrier, then we can implement silicon anodes, resulting in a more energy-dense battery. According to Sprowl, though, it is not so simple, because you can’t stop the electrolyte from breaking down. What you can do is add different organic solvents that break down differently, so that you can control which products go into the barrier formed by the electrolyte breakdown. According to this methodology, researchers like Sprowl can create barriers that are ionically conductive, so that the lithium ions can diffuse through and reach the anode, resulting in a fully chargeable, more energy-dense battery.

So, where do we go from here?

Sprowl says that we do not have lithium-ion batteries with silicon anodes yet, but hopefully we will in the near future. After lithium-ion batteries with silicon anodes, the next step is lithium-sulfur batteries with a sulfur cathode, because sulfur cathodes are far less expensive than transition-metal oxide cathodes. So far, data shows that batteries improve about seven percent per year, whether the improvements are in energy-density or cost-reduction, but when we are able to fundamentally change the battery technology by using different materials for anodes and cathodes, battery improvements will take drastic jumps. Engineering batteries might not seem like particularly groundbreaking work, because we all already use batteries in our daily lives, but the race for a better battery is exhilarating when you realize that it is the key to independence from fossil fuels and thus a future for humans and the rest of the environment.