For eight years, Prof. Jean-François Gohy, a researcher at UCLouvain's Institute of Condensed Matter and Nanosciences, has studied the use of polymers in batteries. Today, thanks to his work, more powerful batteries that recharge at the speed of light exist. And in addition, they respond to several ecological issues, such as those related to the electric car.
Batteries still have a long way to go: they charge too slow, they’re weak, they’re made with heavy metals, their liquid electrolytes are flammable, etc. Not only to respond to these deficiencies, but also to explore all the capabilities of polymers – his favorited subject – Prof. Jean-François Gohy has managed to make these plastics (polymers) functional in batteries.
How does a classic battery work?
To understand his team’s work, let's go back to chemistry basics: how does a conventional lithium ion battery work? It consists of three superimposed layers: two layers of electrodes containing lithium compounds (anode and cathode), separated by a membrane impregnated with a liquid called electrolyte. When the battery discharges, a chemical reaction at the anode generates lithium ions and electrons. Lithium ions diffuse into the electrolyte to reach the cathode where they recover electrons to be stored in a chemical compound different from that of the anode. The electrons thus circulate from the anode to the cathode by generating an electric current characterised by a potential difference related to the chemical structure and the reactions taking place at the anode and at the cathode (generally of the order of 3.6 volts). Today, most Li-ion batteries work this way.
Storing energy in polymers
In this type of battery, energy is currently stored in electrodes composed of inorganic materials (generally crystalline materials that contain heavy metals such as cobalt or nickel). These materials pose problems today not only when it comes to obtaining them (extraction in third world countries, limited resources, etc.) but also recycling them. This is why the UCLouvain team led by Prof. Gohy has been trying for several years to develop polymers (organic materials) capable of storing electrons in their structure and releasing them by means of reversible oxidation-reduction (or redox) reactions (to recharge batteries after discharge).
New polymer materials
Until now, polymers used in batteries had no functional role. Prof. Gohy and his team have therefore developed polymer materials for the reversible storage of electrons. These materials with completely new properties are based on conductive polymer gels swollen by the electrolyte.
Definite advantages, one disadvantage
This discovery has several advantages. First, the batteries consist of organic matter (carbon, hydrogen, nitrogen, oxygen) and not heavy metals. Note that at this stage, the polymers used are from petrochemicals, but in the future, the idea is to produce them from molecules extracted from biomass. Second, the close contact between the polymer and the electrolyte in the gels makes it possible to obtain extremely fast redox reactions and immediate diffusion of the ions in the electrolyte. Thanks to this, charging a battery is extremely fast (it takes five minutes instead of a few hours). During discharge, the polymer offers greater power. When you want to accelerate with an electric car or drill effectively, this power is very useful. The team calls this polymer the ‘power booster’.
The main disadvantage is its low storage capacity. However, for batteries, what the scientific community is constantly looking for is to store a maximum of energy in a minimum of volume and battery weight. Hence the interest at this stage in considering hybrid materials in which the polymeric materials for charging and/or power are mixed with inorganic materials with high storage capacity, thus combining the best of both worlds.
Powerful, safe electric cars
Why conduct this research? Why is it important to concentrate on energy storage? Because it’s a central problem that concerns the energy transition and the many markets associated with it, among them, that of the electric car, our transport of tomorrow. With a battery containing the ‘power booster’ polymer as an additive, power is significantly improved and charging is faster. As for safety, polymers have an important role to play. Polymeric electrolytes are seen as substitutes for flammable liquid electrolytes. When the battery is degraded, heated or short-circuited, a liquid electrolyte can lead to an explosion or fire. That's why Jean-François Gohy's team is also working on the replacement of liquid electrolytes with solid electrolytes based on polymers, for greater safety.
Storing your home’s renewable energy
Home energy storage, particularly that produced by renewable resources (photovoltaic panels, in particular), is the second reason this research is important. Currently, in Belgium, the interface between the producers of electric currents (photovoltaic panel owners) and the electricity grid is poorly managed. And two questions arise: How to manage the flow of electricity production? And how to store energy produced during the day and not used immediately? The batteries developed by Prof. Gohy solve this problem. He also talks about the long-term application of his research to the ‘Internet of things’ or medical devices sector. These devices indeed require lighter, flexible and often miniaturised energy sources. Polymers could fit the bill.
Ecological transition prospects
These new polymer materials are of great ecological interest, thanks to their application in the electric car sector and in the management of electricity produced by renewable sources. In their production, green chemistry predominates and ecology is always considered: the starting materials are preferably biobased and the synthesis and battery manufacturing processes are environmentally friendly, taking care to reduce considerably the use of solvents, and, in order to make polymer solid electrolytes to replace liquid electrolytes, CO2 is used as a reagent and therefore immobilised in a solid material instead of persisting in a gaseous state in the atmosphere.
Going even further tomorrow
Today, the UCLouvain team has developed the use of polymers. They were the first to mix them as additives with conventional inorganic materials to improve battery power and charge. They have improved polymer structure to get the best of its properties. Now the challenge is to develop other polymers for the central battery compartment (electrolyte), especially for the automotive sector. Research must continue to achieve at room temperature lithium ion diffusion that is as fast in a solid polymer material as it is in a liquid electrolyte.
A glance at Jean-François Gohy's bio
Jean-François Gohy is a full professor at the UCLouvain School of Chemistry and the Institute of Condensed Matter and Nanosciences. In 2001, he joined the Eindhoven University of Technology (Netherlands) to pursue postdoctoral research on metallo-supramolecular polymers. Since then, he has been studying functional nano-structured polymeric materials. His main research focuses on self-assembly processes in polymer systems, their use in nanotechnology and the development of polymers for energy storage. Since 1 January 2019, he has been the president of the Belgian Polymer Group (BPG).