Breakthrough in Battery Technology: Understanding the Mechanics of Solid-State Energy

The image provided offers a visual representation of the processing, structure, and mechanical characteristics of glassy ion conductors used in solid-state lithium batteries. Credit: Adam Malin/ORNL, U.S. Dept. of Energy

As electricity flows through a battery, the materials contained within it undergo gradual wear and tear. In this process, the physical forces of stress and strain also play a significant role, but their precise impact on the battery’s performance and lifespan remains somewhat enigmatic.

A team of researchers led by the Department of Energy’s Oak Ridge National Laboratory has undertaken a pioneering endeavor, focusing on the mechanical aspects of designing solid-state batteries, abbreviated as SSBs. Their findings, featured in the journal Science, shed light on how these mechanical factors influence the behavior of SSBs during their operational cycles.

Elevating the Role of Mechanics in Battery Performance

Sergiy Kalnaus, a scientist in ORNL’s Multiphysics Modeling and Flows group, articulated their objective succinctly: “Our aim is to underscore the pivotal role of mechanics in battery performance.” While numerous studies have delved into the chemical and electrical properties of batteries, the mechanical underpinnings have often been overlooked.

This research team comprises experts from various ORNL research domains, encompassing computation, chemistry, and materials science. Their collaborative efforts have crafted a more comprehensive perspective on the factors influencing SSBs, spanning the entire scientific spectrum. Kalnaus elaborated, “We are endeavoring to bridge the disciplinary divides.”

Solid Electrolytes: A Secure and Robust Alternative

In conventional batteries, charged particles traverse materials known as electrolytes, primarily in liquid form, such as those found in lithium-ion batteries used in electric vehicles. However, the emerging development of solid electrolytes, typically fashioned from glass or ceramics, holds promise, offering potential advantages like enhanced safety and durability.

Kalnaus elucidated, “True solid-state batteries eliminate the presence of flammable liquids, rendering them less hazardous compared to prevalent battery technologies.”

Challenges in Pioneering Solid-State Batteries

Nonetheless, the journey towards realizing solid electrolytes remains in its infancy, beset by the intricate challenges associated with these novel materials. Components within SSBs undergo expansions and contractions during charge and mass transport processes, causing alterations within the system. Kalnaus remarked, “Electrodes experience constant deformation during battery operation, leading to delamination and voids at the interfaces with the solid electrolyte. In today’s setups, the primary solution involves applying substantial pressure to maintain structural integrity.”

The dimensional changes pose a significant threat to solid electrolytes, typically composed of brittle materials that are prone to breakage under strain and pressure. Enhancing the ductility of these materials is imperative, enabling them to withstand stress by exhibiting flexibility rather than succumbing to fractures. This objective can be achieved through specific techniques that introduce minute crystal defects into ceramic electrolytes.

Engineering Anodes and Solid Electrolytes

An essential aspect of SSBs involves the anodes through which electrons exit the system. In SSBs, these anodes can be fabricated from pure lithium, renowned for its exceptional energy density. However, this material also generates pressures that can adversely affect the electrolytes.

Erik Herbert, the leader of ORNL’s Mechanical Properties and Mechanics group, elucidated, “During the charging process, non-uniform plating and the absence of stress-relief mechanisms can create stress concentrations. These localized pressures facilitate the flow of lithium metal.” To optimize the performance and durability of SSBs, it becomes imperative to engineer the next generation of anodes and solid electrolytes that can sustain mechanically stable interfaces without causing fractures in the solid electrolyte separator.

This research aligns with ORNL’s longstanding commitment to exploring materials for SSBs. In the early 1990s, the lab introduced a glassy electrolyte known as lithium phosphorous oxynitride (LiPON). LiPON has found extensive use as an electrolyte in thin-film batteries featuring a metallic lithium anode. Notably, LiPON’s ductile properties allow it to endure numerous charge-discharge cycles without failure, responding to mechanical stresses by flowing rather than cracking.

Nancy Dudney, an ORNL scientist who led the team responsible for developing LiPON, affirmed, “In recent years, we have discovered that LiPON possesses robust mechanical properties that complement its chemical and electrochemical durability.”

This collaborative effort illuminates a relatively under-explored facet of SSBs, offering insight into the factors that shape their longevity and effectiveness. As Kalnaus emphasized, “The scientific community required a roadmap,” and their paper provides precisely that by outlining the mechanics of materials relevant to solid-state electrolytes, urging fellow scientists to consider these factors when designing innovative batteries.

Reference: “Solid-state batteries: The critical role of mechanics” by Sergiy Kalnaus, Nancy J. Dudney, Andrew S. Westover, Erik Herbert, and Steve Hackney, 22 September 2023, Science. DOI: 10.1126/science.abg5998

This study received funding from the US Department of Energy.

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• Science: “Solid-state batteries: The critical role of mechanics”
• Oak Ridge National Laboratory (ORNL)
• U.S. Department of Energy
• Lithium Phosphorous Oxynitride (LiPON)
• Advancements in Battery Technology
• Solid-State Batteries
• Materials Science
• Energy Storage Solutions