Solid-state electrolyte batteries could store more energy while reducing certain fire risks. However, their development remains limited by internal short circuits.
A team from MIT and the Technical University of Munich has identified the mechanism that explains this problem, and has found a solution to resolve it.
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In these batteries, the liquid electrolyte of conventional models is replaced by a solid material. This material conducts lithium ions between the electrodes. It must also prevent the direct passage of electrons, in order to avoid an uncontrolled reaction.
The solid electrolyte is not, however, made up of a perfectly uniform block. It gathers many microscopic crystals, called grains. The areas where these crystals meet form particular boundaries, whose properties differ from those of the grains.
The researchers studied these boundaries in a common electrolyte, composed of lithium, lanthanum, zirconium, and oxygen. Their analyses revealed local electrical imbalances. These charges create fields that slow down lithium ions and promote electron accumulation.
Under these conditions, some lithium ions can transform into metallic lithium. Small deposits then appear along the boundaries between crystals. They can gradually form branched structures, known as dendrites.
These dendrites disrupt the battery's operation and can eventually cross the electrolyte. They then establish a direct connection between the electrodes. This short circuit reduces the cell's lifespan and can compromise its safety.
The scientists then modified the manufacturing conditions of the electrolyte. This intervention reduced the negative charges present at the boundaries. The ions thus circulated more easily, while electron leaks decreased.
The modified electrolyte supported a critical current density more than 300% higher than that of a reference sample. This result could enable faster charging and delay short circuits.