Solid-state batteries are widely seen as the future of energy storage.
They promise higher capacity, better safety, and improved performance compared with today’s lithium-ion batteries, which contain flammable liquid electrolytes.
Because solid-state batteries use solid electrolytes instead, they cannot leak or catch fire easily, making them ideal for electric vehicles and large-scale energy storage.
However, these next-generation batteries still face challenges that limit how efficiently they can charge and discharge.
A major issue is something called the space charge effect. Until now, scientists knew this effect existed, but they didn’t know exactly how big the problem was or how much it slowed down battery performance.
Researchers from the Max Planck Institute for Polymer Research in Germany, working with partners in Japan, have now taken a major step toward solving this mystery.
Their findings, published in ACS Nano, provide the first precise measurements of space charge zones inside solid-state batteries and offer clues for designing more efficient systems.
A battery works by moving charged particles—ions—back and forth between electrodes. These ions must travel through an electrolyte and across internal interfaces within the battery.
But when ions accumulate at one of these internal boundaries, they create a narrow layer of electric charge. This is the space charge layer, and it acts like a traffic jam inside the battery.
Incoming ions get pushed back or slowed down, which increases resistance and reduces overall performance.
The new study shows that this effect mostly occurs at the positive electrode. There, the space charge layer forms a barrier less than 50 nanometers thick—about the size of the thinnest part of a soap bubble.
Although small, this layer significantly affects efficiency. The team found that it accounts for roughly 7% of the total internal resistance of the battery. Depending on the materials used, this percentage could be even higher.
Another important discovery is that the space charge layer is not fixed. It changes depending on how full or empty the battery is.
This dynamic nature helps explain why previous studies often measured very different layer thicknesses. For years, researchers have struggled to capture accurate data because the layer was difficult to observe directly.
To overcome this challenge, the team built a thin-film model battery and used two advanced microscopic techniques that had not been applied together in battery research before.
Kelvin probe force microscopy allowed scientists to scan the battery’s cross-section with a tiny needle and map electrical potentials in real time.
Nuclear reaction analysis, on the other hand, detected the buildup of lithium at the interface between the electrolyte and the positive electrode.
By combining both methods, the researchers could finally pinpoint the location, thickness, and behavior of the space charge layer. Their work offers a clearer understanding of why resistance forms and how it limits performance.
With this new knowledge, researchers hope to design better materials and electrode structures that minimize the space charge effect.
Reducing this hidden barrier could lead to more powerful, faster-charging, and longer-lasting solid-state batteries—bringing us one step closer to safer and more efficient energy storage for the future.
Source: Max Planck Society.
