What options we have to make sustainable batteries of the future? Can we make sustainable Li-ion batteries, do we have enough materials for them, or should we find new solutions? The answer is very clear. There is no single chemistry that can solve all problems, and which would be suitable for all energy storage applications. Especially, we have to develop and use several chemistries in parallel in order to guarantee materials sufficiency.
In part 1, we gave an overview on the topic of future batteries, focusing on the sustainability aspect and the importance of energy storage to reach the climate neutrality goals. In this second part, we will introduce some promising battery chemistries and tools, which can help to guarantee materials sufficiency and sustainable production of future batteries. There are several material options available and under investigation, and it is not possible to list them all here. Instead, we will focus on a few chemistries and methods, which we consider to be relevant and interesting for us.
The definition of a sustainable battery is not very simple as it is a combination of many different aspects. Of course, we need to use materials, which are mined under environmentally safe conditions. Or even better, we can produce several battery materials from renewable or recycled sources, or from industrial waste streams. However, increasing the battery lifetime and performance is also important as we need less new batteries if the existing ones will last longer and are more efficient. Battery 2030+, a large scale research initiative led by Uppsala University, is focusing on such chemistry-neutral methods to create sustainable batteries of the future. Both VTT and Aalto University are actively involved in the initiative, together with more than 100 research and industrial partners around Europe. This joint action is a reassuring example of the willingness of the European community to work together in order to find solutions to the urgent energy storage need.
Regarding the battery chemistries, examples of novel materials for batteries include e.g. nickel-rich layered oxides (to minimize use of cobalt), solid state electrolytes, sodium instead of lithium, and organic or even bio-based materials.
As for the positive electrode materials, steps toward utilizing less critical raw materials containing nickel-rich layered oxides have already been taken (LiNi1-x-yCoxMnyO2 family) adopting these materials in small scale batteries. Replacing the cobalt-rich predecessor also in large-scale batteries enables manufacturing vehicles and stationary storage units with higher energy storage capacity alongside more sustainable positive electrode production. Other high-voltage materials such as Li-rich layered manganese oxides (Li1+xM1-xO2) are under development but they suffer from poor high-power performance and have instability issues. On the other hand, high voltage polyanion based compounds, with ability to store more than one lithium ion per molecular unit, are of great interest. Opposite to the other next-generation positive materials, they have good stability but suffer from low volumetric energy density. These issues address the need for further material development. Finland has already strong expertise in battery material and processing field, giving us an excellent opportunity to reach the forefront of the next-generation electrode material development.
The above-mentioned high-voltage positive electrode materials require more stable next-generation electrolytes to satisfy the durability and ambitious performance target values of 400 Wh/g set by EU. Solid state electrolytes offer such benefits as enhanced safety because of their non-flammable nature and higher energy density, i.e. they can offer with the same size of a battery longer operation time thanks to their improved electrochemical and mechanical stability. However, to adopt solid state electrolytes, new innovations are needed in facile preparation of the cells paying attention to such issues as connectivity in the solid electrolyte to offer lithium transport pathways and electrochemical and mechanical contacts at electrolyte electrode interphases. Currently, solutions for that are looked for using hybrid materials and new processing fabrication methods.
It is also possible to produce batteries, which utilize e.g. sodium instead of lithium as the charge carrier. Sodium is a low-cost, more abundant material, which does not suffer from supply risk. On the contrary to Li-ion batteries, Na-ion batteries can also use aluminum as the current collector instead of copper, which will help to reduce the pressure on Cu demand. There are several types of Na-based batteries, which have different maturity levels and performance: Na-ion batteries are the most advanced technology, which could be a more sustainable partner for Li-ion batteries already in near future. Other Na-based options, like Na/S and Na/O2 batteries, have very promising performance, safety and cost predictions, but require more research to become commercially available.
Finally, also organic or even bio-based and renewable materials can be used to store energy. Bio-based materials can be used in all parts of the battery: as electrodes, binders, separators and electrolytes. And in addition of being more sustainable, e.g. organic radical batteries can provide other benefits like fast charging, safe and non-toxic materials and flexibility. Their energy density might not be comparable with the traditional high-performance batteries but they could be very well suitable for applications where lower energy density would be sufficient.
In order to have working solutions for clean energy storage, development of novel materials is crucial. In parallel, it is very important to develop manufacturing solutions for the new material types. Industrialization is a huge effort, which requires efficient collaboration between different players in the field. There already is a common understanding that this is a battle we cannot afford to lose. We also know that promising solutions do exist. Due to the urgency, we just need to make sure that all actions are taken to accelerate this process at different levels, starting from education, continuing with material and process development, and ending up to industrial production and market acceptance.