Talking about sustainability is good form - but it often remains superficial. Because at its core, it is about securing minimum conditions for a dignified life on this planet in the long term.¹ Our energy supply, the use of battery storage, technological innovations and entrepreneurial actions must be aligned with this guiding principle. We feel committed to this: as development pioneers, enthusiastic entrepreneurs and as inhabitants of this earth.

More than just an empty phrase

Sustainable development is the ambitious attempt to think together two central challenges of our time: the protection of the natural basis of life on the one hand, and economic development for humane living conditions on the other.² For one cannot exist without the other: Poverty and hunger lead to environmental destruction, destroyed livelihoods to miserable living conditions. With this in mind, the world community committed itself at the Rio Conference in 1992 to "sustainable development", a global guiding principle that should guide political, civil-society and corporate action.³

The sustainability model is basically optimistic: it is possible to preserve the natural foundations of life and at the same time create humane living conditions for all. However, we are still a long way from achieving this.⁴ The watering down of the guiding principle in the social debate also contributes to this. Not everything that is vaguely "related" to the environment, economy and society is relevant to sustainability. Not every economic development is sustainable just because it creates jobs or economic growth. What seems useful in the short term may turn out to be a sustainability problem in the longer term. What is convincing at first glance may disappoint on closer inspection.

Orienting oneself towards sustainability therefore means: acting in such a way that the natural foundations of life and humane living conditions can be secured at the same time. If the options for action are not sufficient: to look for better options. Solving serious problems without creating new ones. And to maintain a critical spirit in all of this.

The energy transition towards sustainability

Our energy supply is accompanied by serious sustainability problems: finite fossil resources, formed over millions of years, are exploited and irretrievably consumed within decades. Their extraction and use threaten natural ecosystems, especially the climate system and biodiversity. And the social consequences, although not the focus of the debate, are also considerable. Therefore, an energy transition towards sustainability is one of the most important projects of current politics.⁵ The switch from fossil to renewable energy sources, from a centralised to a decentralised energy supply, from combustion engines to electric engines marks not only cornerstones of this project, but also the magnitude of the challenge ahead.

This is because the sun and wind, the most important renewable energy sources, do not supply electricity steadily, but rather depending on weather conditions. It is true that sunny and windy periods complement each other in the annual cycle, and phases with low total electricity generation from renewable sources are short. Nevertheless, the challenge remains to mediate between fluctuating electricity generation on the one hand and electricity consumption in industry, households and transport on the other.

Battery storage for the energy transition

This is where battery storage comes into play. They can store electricity when it is produced in surplus and make it available again when production weakens. And they can make electrical energy available for mobile applications that - unlike rail transport, for example - cannot be connected to the power grid. In addition, battery storage systems are easily scalable, have high energy efficiency and short response times, and have a wide range of applications ↗, some of which are less well-known, that can contribute to a sustainable energy supply in many ways. Therefore, they are considered a central element for the success of the energy transition.⁶

It must be kept in mind that batteries also consume energy and raw materials - to a considerable extent with today's technology. Although only small amounts of electricity are lost when batteries are used, the energy and resources required for battery production are considerable. In addition, the batteries have to be disposed of in an environmentally friendly way at the end of their life. All of this represents a major technological, political and economic challenge, because the storage volumes required for the energy transition are immense: the battery capacity alone required for the extensive electrification of the German passenger car fleet ↗  with its 47 million vehicles is likely to be well over 1,000 GWh.

Today's mass battery production may thus turn out to be tomorrow's gigantic resource and disposal problem: To solve one sustainability problem, a new one would have been created. Instead, battery storage systems must also meet strict sustainability criteria. Only in this way can a real energy transition succeed.

The sustainability trap of battery ageing

Sustainability has many facets - also in the field of battery storage. In many cases, critical raw materials (e.g. cobalt) are used that are extracted under unacceptable conditions and whose availability is not guaranteed in the long term. The lynchpin of battery sustainability, however, is battery ageing. Today's lithium-ion batteries reach the end of their useful life after a few thousand charging cycles at the latest. The old battery has to be replaced by a new one, which in turn has to be produced at a considerable cost in terms of energy and resources.

However, the importance of battery ageing for sustainability goes beyond the obvious. How quickly batteries age depends to a large extent on the charging speed: slow charging protects the battery, while fast charging drives its ageing. However, since fast charging is also crucial for user comfort, in practice people try to solve the dilemma by oversizing the battery. After all, fast charging that is easy on the battery is certainly possible - but only within a narrow corridor of charge levels. If the battery is enlarged, the capacity of the charge level corridor also increases, which can then be charged quickly and comfortably.

This relationship can be called the sustainability trap of battery ageing: Battery ageing is the root not only of short life, but also of the oversizing of conventional batteries, as can currently be observed in the field of electromobility. It decisively determines how much battery is actually needed per application.

Life cycle assessment: A must for battery storage systems

The energy transition towards sustainability needs battery storage systems that also meet the sustainability guiding principle. The following applies: The required assessment of batteries is not easy, since - as always with sustainability assessments - it involves various points of view and sometimes not obvious consequences. However, there are methods that help to carry out comprehensive and at the same time transparent assessments.

The life cycle assessment method plays a central role here. It analyses all material and energy flows associated with the production, use and disposal of a product - over its entire life cycle.⁷ In this way, raw material requirements and environmental impacts that are easily overlooked at first glance also become transparent and quantifiable. Using the example of the product "battery storage": Not only the use of the battery is associated with relevant consequences (e.g. energy losses), but also production and disposal. Not only the material and energy requirements in the actual battery cell production are important, but also in upstream processes such as raw material extraction and transport.

The linchpin of any LCA is the functional unit to which its statements are related. In order to enable comparisons between different battery technologies as well as between different storage approaches (e.g. hydroelectric power), the effectively stored kilowatt hour (kWh_eff) can be used as a reference value. This is the total amount of energy that the storage system can temporarily store for actual use - over its entire lifetime. Up to now, life cycle assessments of battery storage systems have not been standard. This must change, because it is the only way to determine the optimal mix of storage technologies for the energy transition on a holistic basis.

Sustainable batteries are also an economic gain

The sustainability trap of battery ageing also has an important economic consequence. If one compares a conventional battery with a technologically advanced, genuinely fast-charging storage system, the former must be dimensioned significantly larger than the latter for the same convenience of use. Common price comparisons based on "euros per kWh capacity" do not do justice to this context. The conventional battery may seem cheaper in terms of kWh - but in terms of the actual storage size required, new technologies are already competitive in terms of acquisition costs due to the lower quantity of kWh required. In addition, of course, there is the economic advantage that the longevity of a battery storage system already brings in itself.

It shows that ecological and price advantages coincide when the sustainability trap of battery ageing is avoided. And the widespread opinion that sustainability and economic efficiency are opposites is removed.

The Green Solid State Battery. Our contribution to the energy transition