Dendrites
Burning electric cars and smouldering smartphones are often caused by microscopic crystal structures known as dendrites. They occur in batteries, where they have dangerous consequences. How can dendrites in batteries be detected and prevented?
Table of contents
What are dendrites?
In metallography and crystallography, dendrites or skeleton crystals are a specific type of crystal structure. As their name suggests, their appearance is reminiscent of a tree: dendrite is derived from the ancient Greek word for tree, déndron.
Dendrites occur as branch-like structures during the crystallization of materials, for example in metallic alloys or on lithium-metal anodes in lithium-ion batteries. In the latter case, the dendrites can spread so far that they penetrate the separator membrane - a fine layer that separates the electrodes from each other. The result: a short circuit or destruction of the battery.
Quality Analysis examines
your batteries for dendrites
At Quality Analysis, we offer both non-destructive and destructive examinations of the battery assembly and its structures. The technology of FIB-SEM microscopy and scanning electron microscopy enables us to visualize areas deep below the surface in high resolution - ideal for identifying dendrites.
- Examination of internal defects and anomalies by means of industrial computer tomography – without opening and disassembly - and optical examination of the outer wall
- Macroscopic and stereomicroscopic examination of the complete electrode stack and the separator foil using cell dissection of the battery in an air atmosphere
- Scanning electron microscopic examination of conspicuous areas on the anode, the cathode and the composite foil in top view and examination of the cross-sections
- Cross-sectioning through conspicuous areas on the electrode to assess the respective coating and the arrester foil
- Analysis and evaluation of the energy storage materials (coatings) and the arrester foils
- FIB-SEM analysis (depth analysis) on defective areas of the separator, the anode and the cathode.
How do dendrites form in batteries?
Dendrites form in batteries and accumulators in which lithium metals are used. The reason for this can be disturbed charging and discharging conditions.
While the battery is being charged, lithium ions migrate from the positive side, the cathode, to the negative side, the anode. At the anode, it can happen that the lithium metal is not evenly distributed over the surface and more lithium collects in some places than in others. This can be due to ionic contamination, for example.
This leads to a problem: dendrites form in the areas with too much lithium. As already mentioned, these are tiny, needle-shaped structures that extend from the anode like small needles. If these dendrites become too large, they can break through the protective layer between the anode and cathode, the so-called separator membrane, and a short circuit occurs in the battery.
Consequences of dendrites in batteries
Dendrites in batteries can have serious consequences for the performance and safety of these energy storage devices, for example short circuits. These can lead to overheating and fires – and, in the worst case, cause the battery to fail completely.
Dendrites can also lead to accelerated self-discharge, which impairs the overall performance of the battery. To avoid these problems, researchers are working hard to develop methods that minimize or prevent the formation of dendrites. This is particularly important in applications such as electric vehicles and other technologies that rely on powerful and safe batteries.
How can dendrites be avoided in lithium-ion batteries?
The control and prevention of dendrites is crucial for various technological applications, as it is the only way to ensure the safety, performance and reliability of electronic systems. This is mainly relevant for electric vehicles and other technologies that rely on high-performance batteries - to develop long-lasting and safe batteries.
There are different approaches to overcome the challenges associated with dendrites on lithium metal anodes. For example, lithium ions are embedded in graphite, which increases the volume and weight of the batteries - but reduces the range accordingly.
The application of surface coatings to prevent dendrite growth is also being practiced. Controlling the temperature during charging and discharging or limiting the current during charging can also prevent growth.
Briefly summarized: Dendrites
Dendrites are microscopic crystal structures that can cause short circuits in batteries and have serious consequences. FIB-SEM microscopy and scanning electron microscopy are used to identify these structures, while researchers are intensively searching for methods to minimize their formation and improve the performance of batteries.
