Advancing safer lithium energy storage

by Erica Marchand

Paris, France (SPX) Feb 04, 2025

Charging our phones has become so routine that we rarely reflect on the breakthrough that made it possible. Rechargeable lithium-ion batteries, introduced commercially in the 1990s, propelled a technological revolution that earned their creators the 2019 Nobel Prize in Chemistry. This key innovation underpins the functionality of today’s smartphones, wireless headphones, and electric vehicles, making them both financially and environmentally practical.

As our devices grow more advanced, the demand for batteries that pack more power while remaining safe continues to rise. Yet engineering such power sources is far from simple. One promising design is the lithium metal battery, which could deliver more stored energy than standard battery types. Unfortunately, its potential is curtailed by a persistent issue: the emergence of tiny threads, or dendrites, that accumulate with each charge. When dendrites build up, they can form metallic connections that degrade battery functionality and pose a serious fire hazard. Until recently, researchers had limited approaches to probe and understand dendrite formation. In a new study led by Dr. Ayan Maity in the lab of Prof. Michal Leskes at the Weizmann Institute of Science’s Molecular Chemistry and Materials Science Department, scientists developed a novel method to identify the factors that spark dendrite growth, as well as to rapidly evaluate various battery components for improved safety and performance.

Rechargeable batteries function by allowing positively charged ions to migrate between the anode (negative electrode) and the cathode (positive electrode) through an electrolyte. Charging forces the ions back into the anode, counter to the usual flow in a typical chemical reaction, thus preparing the battery for another cycle of use. Lithium metal batteries take a different approach by employing a pure lithium metal anode, enabling higher energy storage. However, lithium metal is chemically reactive and quickly forms dendrites when it interacts with the electrolyte. Over time, enough dendrites can short-circuit the battery and raise the likelihood of combustion.

One way to avoid fire risks is to replace the volatile liquid electrolyte with a solid, nonflammable one, often comprising a polymer-ceramic composite. While altering the ratio of polymer to ceramic can influence dendrite growth, finding the ideal formulation remains a challenge for extending battery life.

To investigate, the team employed nuclear magnetic resonance (NMR) spectroscopy, a standard tool for pinpointing chemical structures, and tracked both dendrite formation and the chemical interplay within the electrolyte. “When we examined the dendrites in batteries with differing ratios of polymer and ceramic, we found a kind of ‘golden ratio’: Electrolytes that are composed of 40 percent ceramic had the longest lives,” Leskes explains. “When we went above 40 percent ceramic, we encountered structural and functional problems that impeded battery performance, while less than 40 percent led to reduced battery life.” Intriguingly, batteries with that optimal ratio displayed more dendrites overall, but those dendrites were effectively confined in a way that prevented destructive bridging.

These insights prompted a larger question: what halts the extension of the dendrites? The team hypothesized that a thin covering on the surface of dendrites, called the solid electrolyte interphase (SEI), might be crucial. This layer, formed when dendrites interact with the electrolyte, can affect how lithium ions travel through the battery, and it can also either prevent or accelerate the movement of harmful substances between electrodes. Both of these factors, in turn, can stifle or foster further dendrite development.

Probing the chemical composition of such thin SEI films is inherently difficult, since they measure only a few dozen nanometers thick. The researchers tackled this problem by enhancing the signals in their NMR data using dynamic nuclear polarization. This specialized technique leverages the strong spin of polarized lithium electrons, bolstering signals from the atomic nuclei in the SEI and exposing its chemical makeup. Through this refined lens, the researchers discovered precisely how lithium metal interacts with polymer or ceramic materials, revealing that certain SEI layers can simultaneously improve ion transport and block hazardous substances.

Their findings pave the way to design sturdier, safer, and more powerful batteries that will store greater energy for a longer duration with reduced environmental and economic costs. Such next-generation batteries could power larger devices without having to increase the physical size of the battery itself, while also extending the battery’s life cycle.

“One of the things I love most about this study is that, without a profound scientific understanding of fundamental physics, we would not have been able to understand what happens inside a battery. Our process was very typical of the work here at the Weizmann Institute. We started with a purely scientific question that had nothing to do with dendrites, and this led us to a study with practical applications that could improve everybody’s life,” Leskes says.

Research Report:Tracking dendrites and solid electrolyte interphase formation with dynamic nuclear polarization-NMR spectroscopy

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Weizmann Institute of Science

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Enhancing Durability and Efficiency in Tin-based Perovskite Solar Cells

by Riko Seibo

Tokyo, Japan (SPX) Jan 30, 2025

Tin-based perovskite solar cells are being hailed as a promising alternative for next-generation solar energy solutions due to their high efficiency, flexibility, and the potential for low-cost printing. However, replacing lead with tin to avoid environmental issues linked to lead toxicity presents its own challenges. Tin’s propensity to oxidize quickly results in reduced performance and durability compared to lead-based counterparts.

Researchers have developed a method to enhance the stability of tin-based perovskite by incorporating large organic cations into the perovskite structure. This results in a unique two-dimensional layered configuration known as Ruddlesden-Popper (RP) tin-based perovskites. Despite its potential, the precise internal structure and the mechanism through which this configuration improves performance have remained unclear.

In this study, researchers employed electron spin resonance (ESR) to analyze the internal behavior of the RP perovskite solar cell during operation at a microscopic level. Their findings revealed two key insights about the interaction of the materials under different conditions.

First, when the RP perovskite solar cell was not exposed to light, the holes in the hole transport layer diffused into the RP perovskite. This movement created an energy barrier at the interface between the hole transport layer and the RP tin perovskite, preventing electron backflow and leading to better performance.

Second, when exposed to sunlight, the high-energy electrons produced by short-wavelength light (such as ultraviolet rays) moved from the RP tin perovskite to the hole transport layer. This transfer further elevated the energy barrier, thereby enhancing the device’s efficiency.

Understanding the mechanisms behind these performance improvements is crucial for developing tin-based perovskite solar cells with greater efficiency and longer lifespans. These findings could provide important insights for future advancements in the field of solar energy.

Research Report:Operando spin observation elucidating performance-improvement mechanisms during operation of Ruddlesden-Popper Sn-based perovskite solar cells

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University of Tsukuba

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A look into the dark

by Robert Schreiber

Berlin, Germany (SPX) Jan 31, 2025

An international team of researchers, led by the University of Gottingen, has introduced a new technique to observe the formation of dark excitons – elusive energy carriers with potential applications in solar cells, LEDs, and detectors. Their findings, published in *Nature Photonics*, offer new insights into these energy states, which had previously been challenging to track in real-time.

Dark excitons are particle pairs formed when an excited electron leaves behind a positively charged vacancy, or “hole,” to which it remains bound by Coulomb interaction. Unlike typical excitons, dark excitons do not emit light, making them difficult to detect. These states are particularly significant in ultra-thin, two-dimensional semiconductor materials, where they can influence the efficiency of future optoelectronic devices.

Professor Stefan Mathias and his team at Gottingen University have previously described how dark excitons form and behave using quantum mechanical theory. In their latest study, they have advanced the field further by developing “Ultrafast Dark-field Momentum Microscopy” to directly observe these excitons in real-time. This new approach allowed them to track the formation of dark excitons in tungsten diselenide (WSe2) and molybdenum disulphide (MoS2) with an unprecedented temporal resolution of just 55 femtoseconds (0.000000000000055 seconds) and a spatial resolution of 480 nanometers (0.00000048 meters).

“This method enabled us to measure the dynamics of charge carriers very precisely,” stated Dr. David Schmitt, the study’s first author from the Faculty of Physics at Gottingen University. “Our results provide fundamental insights into how material properties influence charge carrier movement, which can be leveraged to enhance the efficiency of solar cells.”

Dr. Marcel Reutzel, Junior Research Group Leader in Mathias’ team, emphasized the broader implications of the technique: “This approach is not limited to the specific systems we studied. It can also be applied to new materials, helping to push the boundaries of material science and nanotechnology.”

The findings open the door to optimizing optoelectronic devices by better understanding the behavior of dark excitons. With improved efficiency in solar cells and other applications, this breakthrough offers exciting possibilities for future advancements in renewable energy and semiconductor technology.

Research Report:Ultrafast nano-imaging of dark excitons

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University of Gottingen

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