Study finds 50-nm charge layer that blocks ions in solid-state batteries

Researchers at the Max Planck Institute for Polymer Research (MPI-P) in Germany, collaborating with Japanese universities, have identified and precisely measured a nanoscale space-charge layer inside operating lithium solid-state batteries that impairs their performance. This layer, less than 50 nanometers thick and located primarily at the positive electrode interface, acts as a barrier by accumulating electric charge that repels migrating ions, thereby increasing internal resistance. Despite its minuscule size—comparable to the surface thickness of a soap bubble—this charge layer contributes about 7% of the battery’s total resistance, potentially more depending on the materials used. The team employed novel combinations of Kelvin probe force microscopy (KPFM) and nuclear reaction analysis (NRA) to observe the space-charge region in real time and measure lithium accumulation, overcoming previous challenges where estimates of the layer’s thickness varied widely and were not captured under operating conditions. This breakthrough provides a clearer understanding of the internal limitations of solid-state batteries, which are otherwise promising