We are breaking fresh ground as we introduce a new topic to our world of batteries. We’ll take this one slowly, as we explore it, and explain it to you. Your takeaway is space charge layers in solid state lithium-based batteries obstruct the flow of ions, during charging and discharging.
Opening a Window Into Space Charge Layers
The Max Planck Institute in Germany has teamed with several universities in Japan, to unravel this new enigma. The scientists have approached it on the basis that a battery is a ‘kind of a pump’:
- The charged atoms we call ions move inside a battery between the electrodes.
- Electrons must flow outside the battery between the contacts to balance this flow.
However, and here’s the catch in the case of lithium-based solid state batteries, ‘space layers’ can form at the internal interfaces as the ions flow. These layers act as barriers preventing other ions completing their journey.
In other words, these space charge layers in solid state batteries increase internal resistance at electrode-electrolyte interfaces. The Max Planck Institute has established that this barrier occurs mainly at the positive electrode.
What We Know About This Solid State Resistance
The charge layer in solid state, lithium-based batteries, is a 50 nanometer thick ‘wall’ as thin as the thinnest part of a soap bubble. However, this obstruction is more than solid enough to impede the flow of ions.
A few nanometers can have a significant effect on the world of atoms in batteries. The space charge layer in these solid state batteries was responsible for 7% of internal resistance in the laboratory. Although this factor could be greater with other electrolytes.
The team involved in this ground-breaking study plans to modify their electrode material, to see if they can decrease the resistance at the interface. This could in turn improve the performance of solid state batteries, and take us closer to using them in the real world.
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