Using neutron reflectometry to look inside working solid-state battery and discover its key to success

In a battery with a solid-state structure, the Lithium metal, which is known for its reactivity, can exist harmoniously with a solid electrolyte known as LiPON. This peaceful coexistence is made possible by the formation of a thin interphase, approximately 70 atoms in thickness. Image credit: Jill Hemman/ORNL, U.S. Department of Energy.

Scientists from the Oak Ridge National Laboratory, part of the Department of Energy, have made a groundbreaking discovery by employing neutron reflectometry to investigate the inner workings of a functional solid-state battery, effectively observing its electrochemical process. Their findings revealed that the remarkable efficiency of the battery stems from an incredibly thin film. Within this layer, lithium atoms carrying a charge swiftly travel from the anode to the cathode and seamlessly merge with a solid electrolyte.

According to Andrew Westover from ORNL, who co-authored a study with James Browning at the lab's Spallation Neutron Source and published in ACS Energy Letters, there is a significant desire for improved batteries. The improvements sought after include increased energy capacity, reduced expenses, quicker and safer charging, as well as extended lifespan.

Rechargeable batteries depend on lithium, a tiny metallic element that compacts tightly into the negatively charged anode to optimize energy capacity. Nevertheless, lithium is not compatible with the majority of electrolytes, which contributes to the combustibility risk in smartphone, laptop, and electric vehicle batteries utilizing liquid electrolytes.

"To address the combustibility problem, our objective is to transition to solid electrolytes," stated Westover.

Introducing lithium phosphorus oxynitride, or LiPON, a solid electrolyte developed at ORNL around three decades ago. "The reason behind its exceptional performance has always been puzzling," explained Westover. "Our aim is to replicate the success of LiPON on a larger level. However, comprehending its workings is crucial before achieving that."

Previous studies have indicated that the solid electrolyte interphase, also known as SEI, which forms to safeguard and maintain the stability of the solid-state battery, plays a crucial role in its capability to undergo charging and discharging cycles repeatedly. In this particular instance, the interphase refers to a chemical variation characterized by a lithium-abundant layer, wherein the concentration of lithium gradually diminishes as it merges into pure LiPON.

Browning explained that in a typical battery, there is a boundary that develops between the electrolyte and the active electrode. As the battery goes through charging and discharging cycles, this boundary can gradually alter in its makeup and width.

According to Westover, having a strong SEI means your battery functions properly. On the other hand, if your SEI is weak, your battery fails to operate. The gradual decline in capacity of your mobile phone battery over time is mainly attributed to the expansion of your SEI and its consumption of the electrolyte within the liquid battery.

In a solid-state battery that relies on LiPON, a slim SEI coating is generated to shield the lithium and prevent it from reacting. Unlike the SEI in a conventional battery, this protective layer does not expand over time.

Researchers combined neutron reflectometry with electrochemistry to evaluate the stable interphase between LiPON and lithium for the initial time. The thickness of this interphase was a mere 7 nanometers. Westover stated, "Our investigation unveiled that the formed layer consists of approximately 70 atoms. This study demonstrates the feasibility of creating thin interfaces in solid-state batteries, resulting in exceptional functionality."

The researchers were interested in exploring the insides of the battery due to its compact size and solid composition. Before the discovery of X-rays, it was impossible to see the bones inside a body without cutting open the skin. Similarly, until now, scientists have mostly resorted to cutting open materials to examine the interphases in batteries. However, in this particular case, the battery components were too small to be cut open. Therefore, a different approach was needed to study the interphase. Neutron reflectometry proved to be the perfect tool for the job, as it allowed the researchers to investigate the material without causing any damage and gain a deeper understanding of what was happening at the interphase.

Browning stated, "We are curious about the performance of a battery, hence we require a method to observe its internal activity. It is crucial for us to study the battery's functionality at a significant scale, as it directly impacts its operation. By examining stability, long-term cyclability, and other factors, we aim to understand the battery's performance. Neutrons possess weak interactions, enabling us to manipulate their path without encountering any disruptions. This allows us to precisely investigate the desired location, in this case, the interphase. Equally important, we can extract the neutrons afterward to ascertain the events that occurred in the specific area of interest."

Combining the techniques of neutron reflectometry and electrochemistry led to a rapid comprehension of the relationship between lithium metal and solid electrolytes in solid-state batteries.

"This blend of methods paves the way for us to explore the complete range of solid-state electrolyte substances and ascertain which ones will facilitate rapid charging and high-energy batteries," Westover stated. "We have already initiated the development of version 2.0, wherein we are investigating an alternative variety of solid electrolytes and embarking upon their visual comprehension."

He stated, "It is crucial to develop novel substances that possess this level of steadfastness." The formulation of forthcoming high-efficiency batteries will be contingent upon it.

Further details: The research article titled "Assessing Buried Interfaces between Electrolytes and Electrodes in Solid State Batteries with High Precision at the Nanometer Scale" was authored by Katie L. Browning and colleagues. The study was featured in the ACS Energy Letters journal in 2023 and can be accessed through DOI number 10.1021/acsenergylett.3c00488.

Title: Utilizing Neutron Reflectometry to Peek Inside Functioning Solid-State Batteries and Uncover the Secret to their Triumph In the modern quest for sustainable energy sources, researchers are leaving no stone unturned. Solid-state batteries have emerged as promising candidates for powering the future, boasting potential advantages over conventional lithium-ion batteries. However, understanding the inner workings of these batteries is crucial to further improving their efficiency and reliability. A recent article published on June 28, 2023, highlights the groundbreaking use of neutron reflectometry in this pursuit. Researchers have successfully applied this technique to gain unprecedented insights into the internal structure and mechanisms of solid-state batteries during operation. The study, featured in the citation retrieved on July 4, 2023, from techxplore.com, discusses the profound impact neutron reflectometry may have on enhancing our comprehension of solid-state batteries. By utilizing a beam of neutrons to probe the battery's composition and behavior, scientists have managed to uncover the key factors contributing to their exceptional performance. The outcomes of this investigation have shed light on the intricate interplay between different layers within solid-state batteries, elucidating the role played by interfaces and interfaces' stability. Additionally, the researchers have gained valuable knowledge regarding the diffusion of ions within the battery, an essential aspect that determines its energy storage capabilities. The findings pave the way for optimization efforts and the development of novel materials to further refine solid-state batteries. With a deeper understanding of the internal dynamics, scientists can now design innovative solutions to enhance the efficiency, safety, and overall lifespan of these batteries. The utilization of neutron reflectometry is a testament to the continuous advancements in scientific techniques that enable us to unravel the mysteries of cutting-edge technologies. As sustainable energy storage solutions become more pertinent than ever, the discoveries made through neutron reflectometry bring us a step closer to realizing the immense potential of solid-state batteries for a greener tomorrow.

This text is protected by copyright. Aside from any reasonable use for private learning or investigation, no portion can be replicated without written consent. The information provided is solely for informational purposes.