As we are again starting a new year, it is good to look back, have a break, learn from the past, and make plans for the coming months. I did it by thinking about energy and power. Maintaining high energy and power levels is equally important for batteries and people.

There is a difference between energy and power. So, let’s first clarify what energy and power density mean in the context of batteries.

Definition of energy and power density

Energy density means that how much energy can be stored per unit mass or volume. Its unit is Wh/kg or Wh/l. If I want to drive for a longer time without charging my electric vehicle, I either need a heavier battery with the same energy density, or a higher energy density battery.

Power density means that how fast a battery, or another energy storage component, can deliver energy. It has a unit of W/kg or W/l. Supercapacitors are an example of a device with high power density. They can provide energy quickly for short times, having a response time of milliseconds. Their charging is also much faster than for batteries.

It is common to use a “Ragone plot” to visualize energy and power densities of different types of energy storage components, and/or the energy-power characteristics of a single energy storage device. Simply said, the plot is a graph showing the relationship of energy and power density. But there are different ways of drawing the graph and it might be difficult, and in the worst case, misleading, to compare different graphs if they are not prepared similarly. Some graphs show single (nominal/average) points, some a range, and some a curve. Some show values for battery materials, some for a cell and some for a battery pack.

I encourage you to read a recent review about the topic. The review also lists best practises and guidelines for preparing Ragone plots.

How to maintain high level of energy

If you look at a typical Ragone plot, you notice that it is not possible to have high energy and power density at the same time. When energy is consumed fast, there are always losses, and the fast pace cannot be maintained for a long time.

It is good to remember this also as individuals. Sometimes we need to push and work hard, but if we continue it for too long, we run out of energy. Fast charging might help for a while, but eventually it damages both the battery and the people. This might lead to a complete breakdown, and it will be more challenging to get the energy levels back again.

Optimizing the energy and power density

Batteries are optimised to have either high energy or power density. Typically, a Li-ion battery has an energy density of 150-300 Wh/kg, or 300-700 Wh/l. The energy density of a Li-ion battery can be fine-tuned by modifying the cathode material: lithium iron phosphate (LFP) has lower energy density than for example lithium nickel manganese cobalt oxide (NMC).

A more substantial increase can be achieved by changing the porous graphite anode to silicon, metallic lithium, or ultimately, to a so called “zero excess lithium” anode – sometimes referred to as an anode-free structure. At the same time, the electrolyte is usually changed to a solid one. This is since metallic lithium is not stable enough when a liquid electrolyte is used (unless some special self-healing methods are used, like the piezoelectric separator, which we are developing in the HIDDEN project).

On the other hand, high power density can be achieved for example by adding more conductive additives, such as carbon black or carbon nanotubes, into the electrode layers. This will increase the electronic conductivity and allow higher currents to flow in the electrodes. Using thinner electrodes helps as well as the electrons and ions will need to travel a shorter distance, which is faster. As both methods increase the mass of inactive materials (carbon black or current collector) vs. active materials, they decrease the energy density of the cell.

Again, the same applies for people. A professional marathon runner typically has a different body type as a sprinter.

My professional goals for 2024

My goals for year 2024 are clear. I want to ensure that we can make batteries with high energy density – of course not forgetting the sustainability.

This means that I will do my best to create batteries that are able to utilise the metallic lithium anode. Our HIDDEN project will end soon, and we are just finalising the work to develop self-healing methods to prevent dendrite growth, which is a common problem with the lithium anode. The results are (finally!) looking amazing, and I can’t wait to tell you more about those. You can join our final dissemination event in Brussels on January 31st to hear the latest news, or otherwise you need to wait until we get the results published 😉 The event is arranged jointly with the BAT4EVER project and Battery 2030+ and I can guarantee that the program is super good!

In addition, we have also the SOLiD project ongoing. There we have just made the first cathodes by solvent-free methods. During 2024, we will continue the work to optimize and combine them with the polymeric electrolyte and the metallic lithium anode, targeting eventually energy densities of 900 Wh/l.

Sustainability is a must. And there are several ways to handle that. We aim at minimising the energy consumption in battery manufacturing, e.g., by the solvent-free coating methods in the SOLiD project, which I described in my previous blog text. In addition, increased lifetime, which is a target both in HIDDEN and SOLiD, will help to utilize the battery materials in the best possible way.

On the other hand, we also look for and develop alternative and more abundant materials and their processing methods, such as Na-ion battery materials and biobased carbon materials. With my work at BEPA, being the research chair of the Raw Materials and Recycling group, I also aim at preparing the best possible conditions and calls for researchers around Europe to be able to develop recycling methods and sustainable raw materials for the current and future battery chemistries.

My personal goals for 2024

Then, regarding myself, I need to increase my power density – and at the same time reserve enough time for charging and recovery. I realized this as I managed to get a stress injury from running before Christmas. A physiotherapist just told me that I should get more power into my running muscles to prevent injuries. And he reminded me about the balance between work, training, and life in general. If there are too many things going on at the same time, the body and mind do not have time to recover. Easy to understand but so hard to remember in practice.

In any case, I’m happy that I finally asked for help from a professional. I now know what to do at the gym, and can hopefully balance my training, work, and rest better. The same approach, asking for advice, applies to research. We are never experts in everything, it is challenging to solve problems alone, and it is ok to ask for help.

And in the end, about sustainability. A few weeks ago, I joined a training at VTT, called “Sustainable pace at knowledge work”. The trainer told many tips, and he also said that he has a habit of doing a short yoga practice each morning. I have been “dreaming” about this for a long time but never actually done it on a regular basis (as I like to sleep late 😊). But now I decided that I will take this habit as a priority. I will give it a try as it will help me to avoid/cope with both physical and mental stress. And if I promise that here in public, it will help me to keep up with the habit.