Session: 

Paper Number: 150575

150575 - Characterization and Thermomechanical Modeling of Polymeric Binder Materials for Lithium-Ion Batteries 

Lithium-ion batteries (LIBs) are pivotal to the electrification of transportation, driven by their high energy density. The continuous advancement of positive active materials, alongside negative electrodes combining graphite with Si, underscores the importance of innovative composite electrode designs. These emerging active materials exhibit distinct electrochemical and mechanical properties compared to conventional materials, necessitating a reevaluation of binder materials to maintain electrode integrity and performance.

To enhance energy density, it is required to increase the active material content and reduce inactive components, including binders and conductive additives. As a result, a trade-off emerges with mechanical properties, rate capability, cycle life, and heat generation. Binders are crucial in this context, as they secure active materials, prevent delamination, and improve electrical conductivity by integrating with conductive materials. However, the binders themselves undergo mechanical degradation due to the repetitive expansion and contraction of active materials, challenging the longevity of LIBs.

Despite their critical role, the mechanical behavior of binders within composite electrodes is often oversimplified as purely elastic in the literature. This approach is inadequate for accurately predicting the mechanical behaviors of composite electrodes. Furthermore, inconsistencies in experimentally measured mechanical properties of binders across studies complicate their direct application in electrode design and battery modeling. The real-world mechanical properties of binders are also affected by swelling due to electrolyte impregnation, significantly reducing fracture stress, as evidenced by a 90% decrease in PVdF films post-electrolyte impregnation.

This study addresses the need for standardized mechanical property measurements of binders through systematic analysis. The mechanical properties of the four most commonly used binders—polyvinylidene fluoride (PVdF), poly(acrylic acid) (PAA), polyethylene oxide (PEO), and a carboxymethyl cellulose/styrene-butadiene rubber (CMC/SBR) blend—are comprehensively evaluated. Uniaxial tensile tests, fatigue tests, stress relaxation and creep tests, and peel tests are conducted at various constant temperature conditions to characterize and compare the mechanical properties of each binder. Additionally, their conductivities are measured and analyzed.

This work also presents a coupled thermomechanical viscoelastic-viscoplastic model developed within a continuum framework for accurately predicting the temperature and rate-dependent mechanical response of polymeric binders. The ultimate goal is to integrate this framework into multiphysics electrode and battery models for accurate prediction of binder response.

The results provide a thorough understanding of the mechanical and conductive properties of these binders, offering crucial insights for the optimization of binder materials in LIB applications. This study underscores the importance of advanced characterization and modeling techniques in enhancing the mechanical stability and performance of next-generation lithium-ion batteries.

Presenting Author: Royal Ihuaenyi Northeastern University

Presenting Author Biography: Royal Chibuzor Ihuaenyi is a Postdoctoral Research Associate jointly affiliated with Northeastern University's Department of Mechanical and Industrial Engineering and the MIT-NEU Center for Battery Sustainability. He obtained his Ph.D. in Mechanical Engineering from Michigan State University, where he focused on the characterization and thermomechanical modeling of highly anisotropic thin-film polymeric separators. He also holds a master’s degree in mechanical engineering from Moscow State Automobile and Road Technical University, graduating with honors, and a bachelor’s degree in mechanical engineering from Kazan National Research Technical University.

Royal's research interests lie at the intersection of applied mechanics, materials science, and energy storage systems. He is deeply engaged in the intelligent information integration in the mechanics of complex engineered systems and investigating the role of mechanics in extending the lifetime of energy storage systems. His doctoral and postdoctoral research endeavors have established the framework of his research. During his doctoral training, he worked on two projects sponsored by Ford and General Motors, which demonstrate his expertise in material characterization and constitutive modeling: (1) the characterization and thermomechanical modeling of polymeric battery separators for the detection of internal short circuits, and (2) the probabilistic finite element modeling of composite materials with randomly distributed properties (Finite Elements in Analysis and Design, 2023). His Ph.D. thesis, entitled "Thermomechanical Modeling of Polymeric Battery Separators," provides a comprehensive mechanical characterization and thermomechanical modeling of polymeric battery separators, covering more constitutive behaviors of separators compared to other published studies in this field. His Ph.D. research has been implemented into computational codes for industrial applications.

Throughout his academic journey, Royal has received multiple academic and research awards, including the Outstanding Graduate Student in Mechanical Engineering for 2022-2023. In his current postdoctoral position, his research has extended into information-driven mechanics with applications to inverse learning and the design of test specimens. He is also investigating the role of mechanics in extending the lifetime and sustainability of energy storage materials and systems.

Looking ahead, Royal plans to continue his endeavors as a tenure-track faculty member at an esteemed university, where he aims to further his contributions to the fields of applied mechanics, materials science, and energy storage systems.

Authors:

Royal Ihuaenyi Northeastern University
Jihun Song Northeastern University
Yichen Wan Northeastern University
Ruobing Bai Northeastern University
Juner Zhu Northeastern University