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Formulation strongly influences the structure, properties, and electrochemical performance of composite electrodes. The role of polymeric binders is especially critical for electrodes containing high volume change active materials, such as silicon. In this study, we investigated the impact of polyimide binder in silicon microparticle electrodes. The impact of binder content on electrode adhesion to the current collector, cohesion, porosity, electrical resistivity, local electrical connectivity, and silicon utilization was characterized in pristine and cycled electrodes to elucidate the mechanisms driving the electrochemical performance during rate and cycle life tests of Si-NMC622 full cells. We observed that capacity retention improved with increasing binder content, but rate performance suffered with excess binder content, indicating that there is an optimal binder weight fraction to balance the trade-off between these two metrics. Our research reveals important design principles for the optimization of binder content in silicon electrode formulations and can be applied to the development of electrodes containing other active materials and conductive additives.

Hybrid organic–inorganic halometallates, with different organic and inorganic components, can provide a wide array of tunable physical properties. While many optoelectronic phenomena are being explored, research on the mechanical properties of this class of materials, especially fracture toughness, is lacking, resulting in conclusions on material flexibility being drawn from their elastic modulus and hardness alone with an implicit assumption that these properties correlate with material flexibility. In this Letter, we report nanoindentation results on the elastic modulus, hardness, and fracture toughness of single crystal samples of hybrid organic–inorganic histammonium chlorozincate, HistZnCl4 along the [001] axis. We find that the elastic modulus is 12.078 ± 1.034 GPa, and the hardness is 0.611 ± 0.089 GPa. Moreover, the fracture toughness of this sample is measured to be 0.098 MPa m12. Although these materials have a hardness to modulus ratio similar to that of metals, they fracture like brittle materials, demonstrating the importance of conducting studies on a material fracture toughness before determining their applicability in flexible device applications.

A lateral force microscopy (LFM) calibration technique utilizing a random low-profile surface is proposed that is successfully employed in the low-load non-linear frictional regime using a single layer of graphene on a supporting oxide substrate. This calibration at low loads and on low friction surfaces like graphene has the benefit of helping to limit the wear of the LFM tip during the calibration procedure. Moreover, the low-profiles of the calibration surface characteristic of these layered 2D materials, on standard polished oxide substrates, result in a nearly constant frictional, adhesive, and elastic response as the tip slides over the surface, making the determination of the calibration coefficient robust. Through a detailed calibration analysis that takes into account non-linear frictional response, it is found that the adhesion is best described by a nearly constant vertical orientation, rather than the more commonly encountered normally directed adhesion, as the single asperity passes over the low-profile graphene-coated oxide surface.

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