Scientists at the Max Planck Institute for Polymer Research are focusing on solid-state batteries, which are considered the "Holy Grail" of battery research. Unlike current batteries, these batteries do not have a liquid core but are made of a solid material. This brings advantages such as increased safety and the ability to be manufactured on a smaller scale. The scientists aim to enhance the life cycle of these batteries, potentially leading to more durable solid-state batteries in the future.

Figure 1. Solid-state batteries. (Credit: Xue Zhang / MPI-P)

Figure 1 shows Solid-state batteries could offer many advantages in the future, including for the use in electrically powered cars. Rechargeable batteries are widely used in various devices like e-cars, cell phones, and cordless screwdrivers. While they offer convenience, there are some drawbacks to consider. For instance, certain cell phones were prohibited from being taken on airplanes due to safety concerns, and there have been instances of fires in e-cars. One issue with modern commercial lithium-ion batteries is their sensitivity to mechanical stress.

Solid-state batteries, such as those made of ceramics ionic conductors, offer a potential solution to address these issues. Unlike traditional batteries, solid-state batteries do not contain a liquid electrolyte but are composed entirely of solid materials. This unique construction makes them mechanically robust, non-flammable, and resistant to temperature fluctuations. Additionally, solid-state batteries can be easily miniaturized. These properties make solid-state batteries a promising alternative, offering enhanced safety and reliability compared to traditional rechargeable batteries.

Solid-state batteries, while offering advantages such as enhanced safety and resistance to temperature fluctuations, face challenges due to the growth of lithium dendrites during charging cycles. These dendrites gradually connect the positive and negative poles, causing short circuits and battery failure. The exact physical processes behind dendrite formation are not yet well understood. Researchers are actively studying this phenomenon to develop strategies to prevent dendrite growth and improve the longevity and performance of solid-state batteries.

A team led by Rüdiger Berger, under Hans-Jürgen Butt's department, has researched to investigate the growth of lithium dendrites in solid-state batteries. They employed a specialized microscopy method to gain a more detailed understanding of the processes involved. The team focused on determining the starting point of dendrite growth. They aimed to establish whether dendrites grow from the negative pole to the positive pole, from the positive pole to the negative pole, or if they grow equally from both poles. Additionally, they explored the possibility of specific locations within the battery that trigger nucleation and subsequent dendritic growth. By addressing these questions, the researchers aimed to shed light on the fundamental aspects of dendrite formation in solid-state batteries.

Rüdiger Berger's team focused their investigation on the "grain boundaries" present in the ceramic solid electrolyte of solid-state batteries. During the production of the solid layer, these boundaries are formed as a result of small, random fluctuations in crystal growth. While the atoms in the ceramic crystals are typically arranged in a regular pattern, the presence of grain boundaries introduces line-like structures where the arrangement of atoms becomes irregular. These grain boundaries serve as areas of interest for studying dendrite growth in solid-state batteries. By examining the behavior of dendrites in relation to these grain boundaries, the researchers aimed to gain insights into the mechanisms behind dendrite formation and its impact on battery performance.

These grain boundaries are visible with their microscopy method - "Kelvin Probe Force Microscopy" - in which the surface is scanned with a sharp tip. Chao Zhu, a PhD student working with Rüdiger Berger says: “If the solid-state battery is charged, the Kelvin Probe Force Microscopy sees that electrons accumulate along the grain boundaries - especially near the negative pole.” The latter indicates that the grain boundary not only changes the arrangement of the atoms of the ceramics, but also their electronic structure.

Dendrite growth in solid-state batteries occurs due to the accumulation of electrons and the reduction of positively charged lithium ions into metallic lithium within the solid electrolyte. This process leads to the formation of lithium deposits and dendrites. When the battery is repeatedly charged, the dendrites progressively grow until they connect the battery's positive and negative poles, resulting in a short circuit. Notably, the study observed that the initial stages of dendrite growth were solely observed at the negative pole, while no growth was observed at the positive pole.

The scientists hope that with a precise understanding of the growth processes, they will also be able to develop effective ways to prevent or at least limit growth at the negative pole, so that in the future the safer lithium solid-state batteries can also be used in broadband applications.

Source: Max Planck Institute

References:

1. https://www.mpip-mainz.mpg.de/en/press/pr-2023-03
2. https://interestingengineering.com/innovation/solid-state-longer-lasting-batteries

Cite this article:

Hana M (2023), Decoding the Mystery of Dendrite Growth in Solid-State Batteries: Unraveling the Role of Grain Boundaries, AnaTechmaz, pp.431