Session: 09-03-01: Advanced Electrochemical Energy Materials: Characterization, Modeling, and Theoretical Analysis

Paper Number: 173440

Mechanics of Pure Metal Anodes of Rechargeable Batteries Across Length and Time Scales 

Despite their prevalence, rechargeable batteries currently utilize materials with relatively low energy densities that add substantial weight and volume to vehicles and portable electronics. Recently, several high-capacity electrode materials have been identified, but these materials often suffer from severe issues of cyclability and safety that have precluded their practical use. While the electrochemistry of these systems has received extensive examination, at the heart of many issues lies a mechanics of materials problem: as atoms rearrange under electrochemical driving forces, materials deform, thereby generating stresses under constraint. These stresses can result in fracture, detachment, and/or unstable deformation of the electrodes, diminishing their capacity. With these ideas in mind, this talk will discuss our recent experimental and modeling studies that provide basic understanding of mechanical behavior in several high-capacity pure metal anodes, including lithium, sodium, potassium, calcium, and zinc. The talk will particularly stress the variation in mechanical properties in these systems across various length and time scales and the corresponding implications for practical deployment of these materials in rechargeable battery systems. As one set of examples, alkali metal electrodes paired with solid electrolytes show promise in improving the energy density and safety of rechargeable batteries. However, electrolyte cracking and loss of interfacial contact between the anode and solid electrolyte represent fundamental mechanical obstacles. This talk will present systematic experimental studies that characterize the mechanical behavior of lithium, sodium, and potassium across temperatures from 0 to 45 C, strain rates from 10^-2 to 10^-4 s^-1, and length scales from the nano to the bulk. Temperature-dependent and size-dependent deformation mechanism maps emerge from the measurements. The talk will discuss how length scales associated with plasticity may affect the stresses generated in metal electrodeposits of alkali metals for solid-state batteries. As another example, zinc is a multivalent metal that holds significant promise as an anode material in rechargeable batteries owing to its high capacity. Likewise, zinc-based batteries’ compatibility with aqueous electrolytes enhances their safety by minimizing the risk of thermal runaway, a common concern in alkali-metal-based batteries. Bulk-scale mechanical properties of Zn have been well-studied. However, electrodeposits that form during electrochemical cycling often initiate at the nano-scale and grow to bulk-scales; as such, this talk will detail experimental studies of the mechanical properties of Zn metal across length-scales, from nano to bulk, utilizing various mechanical testing techniques. Our findings revealed that Zn exhibits a comparably moderate ‘size effect’ of hardness between the nano and bulk scales but that its mechanical properties are significantly sensitive to strain rate. The talk will conclude by discussing the implications of these findings in the context of secondary battery applications.

Presenting Author: Matt Pharr Texas A&M University

Presenting Author Biography: Matt Pharr is an Associate Professor and J. Mike Walker ’66 Faculty Fellow in Mechanical Engineering at Texas A&M University with a courtesy appointment in Materials Science & Engineering. He received his Ph.D. from Harvard University and performed postdoctoral research at the University of Illinois at Urbana-Champaign. His research focuses on mechanics of materials in areas including energy storage and conversion, soft materials, irradiated materials, stretchable electronics, and materials for neuromorphic computing. He has received an NSF CAREER Award, a Kaneka Junior Faculty Award, a Texas A&M Young Faculty Fellow Award, a TMS Young Leaders Award, the Peggy L. & Charles Brittan ’65 Outstanding Undergraduate Teaching Award, a Montague-Center for Teaching Excellence Scholar Award, and an Association of Former Students Distinguished Achievement in Teaching Award.

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