Peak currents for wireless IoT labels: Thin-film solid-state batteries have the edge

Moritz Futscher: One big lesson we learned was that as scientists, we are constantly optimizing: testing new ideas, trying out improvements, sometimes taking one step forward and two steps back in order to ultimately improve.

As a start-up, however, this logic only works to a limited extent. We can't afford to constantly introduce new approaches that set us back in our schedule. Instead, we have to improve the existing product in a targeted manner – ideally using the materials and processes we already have. The focus is on scaling and optimizing, not on constantly reinventing ourselves.

This means we have many more ideas that we could implement later. But we have to actively hold back and consciously not pursue them in order to stay focused, so that we can deliver robust results quickly.

Jeronimo von Ah: Many electronics manufacturers arecurrently working on the next generation of devices, which will be better connected, more durable, and smaller than any previous ones. Such devices need a high-performance energy supply in micro format.

In addition, energy harvesting is firmly planned into many of these devices. Once energy is harvested from the environment, the system almost always needs a buffer, meaning a storage element that temporarily stores energy, absorbs load peaks, and bridges periods when no ambient energy is available. That is exactly where rechargeable solutions like our batteries are in demand.

Energy harvesting refers to the extraction of small amounts of energy from the environment (e.g., light, radio waves, temperature differences, or vibration) to partially or temporarily power systems. The most suitable method depends heavily on the location, power requirements, and system costs. Solar panels are often particularly attractive for labels because they are very thin, easy to integrate, and inexpensive.

Jeronimo von Ah: We arecurrently developing capacities of up to 10 mAh. These batteries achieve discharge rates of up to 60C, which means that pulse currents of up to 600 mA are possible.

The C-rate describes how much current a battery can deliver in relation to its nominal capacity – "C" always means per hour: 1C theoretically means discharged/charged in 1 hour, 2C in 0.5 hours, 60C in 1/60 hours (= 1 minute). The current I (amperage) is calculated as follows:

I = C-rate × capacity (in Ah)

At 10 mAh (= 0.01 Ah) and 60C, this corresponds to I = 60 × 0.01 A = 0.6 A, i.e. up to 600 mA.

These 600 mA should be understood as pulse or peak current. Pulse currents are short current spikes (for example during radio transmission) specified by pulse duration and often a duty cycle, meaning the fraction of time the pulse is active (pulse duration divided by repetition period). "Peak current" is often used synonymously for the maximum pulse current.

The cycle stability is around 1,000 cycles. We are also planning significantly higher capacities in the future.

Moritz Futscher: Time and again, we hear people in the market saying that batteries are "not a good option" and not the future in the long term – especially when compared to energy harvesting approaches, i.e., products that are powered by small solar cells, for example, and are positioned as "battery-free." Such claims are understandable because the advantages seem significant at first glance: less maintenance, less waste, a clear sustainability narrative.

At the same time, this view falls short. In practice, many applications need a storage element despite energy harvesting in order to cushion failures and fluctuations – for example, at night, indoors, or in shaded areas. This storage element can also be a capacitor, but often a capacitor is not sufficient if energy needs to be stored for a longer period of time or load peaks need to be reliably covered.

The key issue is not "battery yes/no," but rather what type of battery and for what purpose. Today, primary button cells in particular are a massive problem. They are used in very large quantities and then thrown away. This is exactly where rechargeable, very small storage solutions come in.

Thin-film solid-state batteries are relevant in this context because they are rechargeable, can be integrated in very small form factors, and depending on the design use different materials and safety profiles than classic cells. The goal is not to replace every power supply, but to replace a specific waste and replacement logic (primary cells) in suitable applications.

Jeronimo von Ah: That may be true at first glance. In reality, however, different product classes with different niches are emerging. Energy harvesting is efficient where light is reliably available from the environment and the power output is sufficient. Thin-film solid-state batteries are interesting when predictability, integration, service life, size, and rechargeability are crucial – and in areas where primary cells can realistically be replaced.

Both approaches are a real answer to a very specific problem, namely microbatteries that are thrown away en masse. Energy harvesting is a powerful approach – but not automatically a replacement for storage. In the end, there will most likely be several paths that coexist because they serve different requirements in the end product.

Jeronimo von Ah: Autoclaving is not just about "short-term heat," but about repeated cycles of temperature, pressure, and humidity. Classic batteries, especially small cells, coin cells, or Li-ion pouches, are often not designed for that.

Solid-state thin-film batteries are attractive here because they do not require liquid electrolytes and can be integrated hermetically in layers. This makes them more thermally robust and allows them to be designed to withstand such sterilization cycles – which can be a real enabler for sterile sensors, trackers, or smart medical devices.

Our battery does not contain any liquid electrolyte. This enables it to reliably supply energy at temperatures of up to 150 °C over many cycles.

Of course, as with all batteries, degradation occurs over time, and this is accelerated somewhat at very high temperatures. However, the exact performance after 100 cycles at high temperatures depends on many factors.

Moritz Futscher: Yes, in principle, a label equipped with a battery can also be combined with a display – this is particularly interesting with very thin, sometimes even flexible displays such as E-Ink. Although such displays require energy, they have a major advantage in that they consume extremely little power in sleep mode.

They can maintain a generated image without consuming a lot of energy on a continuous basis. It only becomes energy-intensive when the image is updated, as this requires short, high power or current peaks.

This is exactly where traditional batteries often hit their limits. They cannot provide those power peaks, or they need to be oversized, making the label larger, thicker, and more expensive. Thin-film solid-state batteries can address this because they provide not only the right form factor, very thin and easy to integrate, but also occupy an intermediate position between a supercapacitor and a battery when it comes to current peaks.

This allows significantly higher peak currents to be provided – in the order of 20–30× compared to conventional batteries – enabling displays such as E-Ink to be switched reliably without having to design the battery unnecessarily large.