This thesis describes research to understand the relationships between materials, microstructure, transport processes, and battery performance for primary alkaline battery cathodes. Specifically, the effect of various carbon additives, with different physical properties, on electronic transport or conductivity within battery cathodes was investigated. Generally, the electronic conductivity increases with carbon additives that have higher aspect ratios, smaller particle diameters, higher surface areas, and lower bulk densities. Other favorable carbon aspects include more aggregated and elongated carbon domains which permit good particleto-particle contacts. Of the various carbon additives investigated, graphene nanopowder was the best performer. This graphene nanopowder had the smallest particle diameter, highest surface area, and one of the lowest Scott densities of the carbon additives investigated as well as well-connected, interspersed carbon pathways. Notably, a typical effective ionic conductivity is more than 50 times less than the electronic conductivity (5.7 S/m to 300 S/m, respectively) for a high-performance cathode. Thus, alkaline battery cathodes could be redesigned to improve ionic conductivity for optimal performance. This work expanded on previously published work by relating additional carbon-additive material properties--specifically, particle morphology, surface area and Scott density--and their corresponding cathode microstructure to the fundamental transport processes in alkaline battery cathodes.

<p dir="ltr">Lithium-ion batteries (LIBs) are at the forefront of the energy storage technology for portable electronic devices and are playing a pivotal role in vehicle electrification. As the conventional LIBs consisting of a graphite anode and a transition metal oxide cathode approach their theoretical energy density limits, significant research efforts are being made towards developing next-generation batteries that can meet the ever-increasing energy density demands. In this regard, solid-state batteries (SSBs), employing lithium metal anode and a composite cathode, have garnered significant attention as a promising alternative to conventional LIBs, offering enhanced energy density and safety. However, the development of stable, high-performance SSBs is hindered by several interfacial and chemo-mechanical challenges due to solid-solid nature of interfaces. Limited solid-solid contact between the interacting species leads to severe transport and reaction limitations, which exacerbate during cycling due to progressive delamination at the interfaces. Such a phenomenon also results in current constriction at the remaining point contacts, which ultimately leads in the formation of electrochemical and mechanical hotspots within the SSB, impacting both the rate capability and cycling performance.</p><p dir="ltr">In this thesis, a comprehensive mesoscale investigation of solid-state battery (SSB) cathode architectures will be presented, elucidating the complex interplay between microstructure, kinetic-transport interactions and chemo-mechanical coupling. By examining the key limiting mechanisms that manifest at various SSB cathode microstructural regimes, a mechanistic design map highlighting the dichotomy in reaction and ionic/electronic transport limitations will be established. The impact of cathode microstructural heterogeneity on spatio-temporal dynamics, thermo-electrochemical behavior, and lithium metal anode stability will be revealed. In addition, the impact of stack pressure on solid-state cathode performance will be studied and how stack pressure influences the microstructure-dependent reaction and transport interactions will be delineated. Lastly, this thesis will investigate crystallographically oriented dense cathode architectures for high energy density SSBs, providing critical insights into their performance limitations and potential pathways for optimization. Overall, the dissertation will focus on the fundamental insights into the mesoscale behavior of the solid-state cathodes and establish the mechanistic pain points and design guidelines for consideration in the future development of improved SSB cathode architectures.</p>