The researchers of Indian Institute of Sciences (IISc) have discovered a key reason solid-state lithium batteries fail. Taking advantage of this knowledge, they have devised a method that allows them to develop a strategy to create longer life, faster charging and more reliable than current. To reach these conclusions, the team studied the formation of dendrites in solid-state batteries, which are one of the most viable alternatives to replace current lithium batteries with liquid electrolyte.
The researchers found that the appearance of microscopic voids on one of the electrodes of the device it is a key reason for the formation of dendrites, thin filaments that cross the separating barrier between the cathode and the anode. dendrites can cause shorts and thus complete battery failures, which is why scientists have been working for years to get to the root of the problem.
Dendrites in solid electrolyte batteries?
In batteries with solid electrolyte, the medium through which lithium ions travel from an electrode, a liquid, becomes a solid material, usually ceramic. In addition, the graphite that is usually used in the anode to create its microstructure is replaced by metallic lithium.
At higher temperatures, ceramic electrolytes tend to perform better than those based on other materials (which is especially useful in the country where the research was conducted). The anode lithium is also lighter and stores more charge than graphite, which can significantly reduce the cost of battery production.
However, as with wet electrolyte batteries, solid-state batteries also suffer from the dendrite growth problem under certain conditions, which can also cause a short circuit between the anode and the cathode, explains Naga Phani Aetukuri, assistant professor at the Solid State and Structural Chemistry Unit (SSCU) of the Indian Institute of Sciences and director of the project.
To investigate why this is happening, doctoral student Vikalp Raj of Aetukuri’s team artificially induced the formation of dendrites in the battery by repeatedly charging hundreds of cells, carving thin sections of the lithium-electrolyte interface, and examining them under a scanning electron microscope.
In this way, the team discovered that microscopic voids with currents at their edges some 10,000 times larger than the average currents were forming in the lithium anode during discharge, causing the stress of the solid electrolyte and accelerated the growth of dendrites.
The solution: add metals to the electrolyte
As Aetukuri explained, “This means that now our task to make very good batteries is very simple: all we need is to make sure that no voids form.”
However, he also acknowledges that this is easier said than done. The IISc team used their discovery to develop a technique they said can significantly delay the formation of these dendrites: the addition of a thin layer of metals to the surface of the electrolyteeither. This solution also served to extend battery life and enable faster charging.
To solve the problem, the researchers placed an ultrathin layer of a refractory metal between the lithium anode and the solid electrolyte as a shield to protect the solid electrolyte from stress and redistribute current. A refractory metal is one that is resistant to heat and wear.
To carry out this part of the project, the Indian team collaborated with researchers from Carnegie Mellon University, who performed the computational analysis. This study demonstrated to the research team that the refractory metal layer effectively retarded the growth of microscopic lithium voids.