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Creators/Authors contains: "Mukherjee, Partha P."

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  1. Abstract

    As solid‐state batteries (SSBs) with lithium (Li) metal anodes gain increasing traction as promising next‐generation energy storage systems, a fundamental understanding of coupled electro‐chemo‐mechanical interactions is essential to design stable solid‐solid interfaces. Notably, uneven electrodeposition at the Li metal/solid electrolyte (SE) interface arising from intrinsic electrochemical and mechanical heterogeneities remains a significant challenge. In this work, the thermodynamic origins of mechanics‐coupled reaction kinetics at the Li/SE interface are investigated and its implications on electrodeposition stability are unveiled. It is established that the mechanics‐driven energetic contribution to the free energy landscape of the Li deposition/dissolution redox reaction has a critical influence on the interface stability. The study presents the competing effects of mechanical and electrical overpotential on the reaction distribution, and demarcates the regimes under which stress interactions can be tailored to enable stable electrodeposition. It is revealed that different degrees of mechanics contribution to the forward (dissolution) and backward (deposition) reaction rates result in widely varying stability regimes, and the mechanics‐coupled kinetics scenario exhibited by the Li/SE interface is shown to depend strongly on the thermodynamic and mechanical properties of the SE. This work highlights the importance of discerning the underpinning nature of electro‐chemo‐mechanical coupling toward achieving stable solid/solid interfaces in SSBs.

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  2. The utilization of alkali metal anodes is hindered by an inherent instability in organic electrolytes. Sodium is of growing interest due to its high natural abundance, but the carbonate electrolytes popular in lithium systems cannot form a stable solid electrolyte interphase (SEI) with a sodium electrode. Using half-cell and symmetric-cell analysis, we identify specific glyme (chain ether) electrolytes that produce thin, predominantly inorganic SEI at the sodium metal interface, and we study the effect of ethylene carbonate and fluoroethylene carbonate (FEC) additives on the SEI formed in these systems via X-ray photoelectron spectroscopy. Through in situ optical microscopy, we observe the onset and growth of sodium dendrites in these electrolytes. We determine that the SEI formed by glyme alone may not support extensive or extreme cycling conditions, but the addition of FEC provides a more robust SEI to facilitate numerous consistent sodium plating and stripping cycles. 
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  3. Abstract The development of next-generation batteries, utilizing electrodes with high capacities and power densities requires a comprehensive understanding and precise control of material interfaces and architectures. Electro-chemo-mechanics plays an integral role in the morphological evolution and stability of such complex interfaces. Volume changes in electrode materials and the chemical interactions of electrode/electrolyte interfaces result in nonuniform stress fields and structurally different interphases, fundamentally affecting the underlying transport and reaction kinetics. The origin of this mechanistic coupling and its implications on degradation is uniquely dependent on the interface characteristics. In this review, the distinct nature of chemo–mechanical coupling and failure mechanisms at solid–liquid interfaces and solid–solid interfaces is analyzed. For lithium metal electrodes, the critical role of surface/microstructural heterogeneities on the solid electrolyte interphase (SEI) stability and dendrite growth in liquid electrolytes, and on the onset of contact loss and filament penetration with solid electrolytes is summarized. With respect to composite electrodes, key differences in the microstructure-coupled electro-chemo-mechanical attributes of intercalation- and conversion-based chemistries are delineated. Moving from liquid to solid electrolytes in such cathodes, we highlight the significant impact of solid–solid point contacts on transport/mechanical response, electrochemical performance, and failure modes such as particle cracking and delamination. Finally, we present our perspective on future research directions and opportunities to address the underlying electro-chemo-mechanical challenges for enabling next-generation lithium metal batteries. 
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  4. Polymer Electrolyte Fuel Cells (PEFCs) exhibit considerable performance decay with cycling owing to the degradation of platinum (Pt) catalysts, resulting in the loss of the valuable electrochemically active surface area. Catalyst inventory retention is thus a necessity for a sustained cathodic oxygen reduction reaction (ORR) and to ameliorate the life expectancy of PEFCs. We demonstrate a thermo-kinetic model cognizant of processes like platinum particle dissolution–reprecipitation and oxide formation coupled with an electrochemical reactive transport model to derive mechanistic insights into the deleterious phenomena at the interfacial scale. The heterogeneous nature of particle aging in a catalyst layer environment is delineated through coarsening–shrinking zones and further comprehension of instability signatures is developed from the dissolution affinity of diameter bins through a metric, onset time. The severe degradation at high temperature and under fully humidified conditions is intertwined with the local transport resistance and the critical transient, where the catalyst nanoparticles reach a limiting diameter stage. We further reveal the degradation-performance characteristics through variation in the ionomer volume fraction and the mean size of the particle distribution in the electrode. It has been found that the kinetic and transport characteristics are crucially dependent on the interplay of two modes – one leading to the depletion of the catalyst nanoparticles and the other that emanates from catalyst coarsening. 
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  5. Solid-state batteries (SSBs) hold the potential to enhance the energy density, power density, and safety of conventional lithium-ion batteries. The theoretical promise of SSBs is predicated on the mechanistic design and comprehensive analysis of various solid–solid interfaces and microstructural features within the system. The spatial arrangement and composition of constituent phases (e.g., active material, solid electrolyte, binder) in the solid-state cathode dictate critical characteristics such as solid–solid point contacts or singularities within the microstructure and percolation pathways for ionic/electronic transport. In this work, we present a comprehensive mesoscale discourse to interrogate the underlying microstructure-coupled kinetic-transport interplay and concomitant modes of resistances that evolve during electrochemical operation of SSBs. Based on a hierarchical physics-based analysis, the mechanistic implications of solid–solid point contact distribution and intrinsic transport pathways on the kinetic heterogeneity is established. Toward designing high-energy-density SSB systems, the fundamental correlation between active material loading, electrode thickness and electrochemical response has been delineated. We examine the paradigm of carbon-binder free cathodes and identify design criteria that can facilitate enhanced performance with such electrode configurations. A mechanistic design map highlighting the dichotomy in kinetic and ionic/electronic transport limitations that manifest at various SSB cathode microstructural regimes is established. 
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