Scott Wilmer Spangler

Impact of precursor size on the chain structure and mechanical properties of solvent-swollen epoxy gels

The thermal and mechanical properties of solvent-swollen epoxy gels were investigated as a function of pre-cursor size in a model end-linked network. The epoxy networks were formed by cross-linking diepoxide and diamine precursors in the presence of a low volatility solvent, dibutylphthalate (DBP). Both precursors were end functionalized and contained a poly(propylene glycol) (PPG) spacer between the epoxy and amine functionality, respectively. The lengths of both precursors were controlled by varying the molecular weight of the PPG spacer between functional groups. The glass transition temperature for the gels as a function of solvent loading was well predicted by the Fox equation. The scaling factors of shear storage modulus versus solvent loading increased with increasing diamine precursor molecular weight to values much larger (3.91) than the theoretical value of 2.3, for entanglement dominated network formation in a theta solvent. In contrast, the scaling factor increased with decreasing epoxy precursor molecular weight to values near 4.5. The large, molecular weight dependent scaling factors are attributed to loop defect formation as the result of the amine cross-linker architecture, which consists of two difunctional reactive end groups separated by a spacer. Rather than equal spacing of all four reactive sites, the amine end groups contain two reactive hydrogens that increase the local concentration of reactive species, and facilitates loop formation. We anticipate that this work will aid in the development of non-aqueous gels and provide enhanced tailoring of the gel properties over a broad range of stiffness.

Propagation testing multi-cell batteries.

Propagation of single point or single cell failures in multi-cell batteries is a significant concern as batteries increase in scale for a variety of civilian and military applications. This report describes the procedure for testing failure propagation along with some representative test results to highlight the potential outcomes for different battery types and designs.

Quantification of Lithium-ion Cell Thermal Runaway Energetics

Much of what is known about lithium-ion cell thermal runaway energetics has been measured and extrapolated from data acquired on relatively small cells (< 3 Ah). This work is aimed at understanding the effects of cell size on thermal runaway energetics on cells from 3 to 50 Ah of both LiFePO4 (LFP) and LiNi0.80Co0.15Al0.05O2 (NCA) chemistries. Results show that for both LFP and NCA cells, the normalized heating rate (W/Ah) increases roughly linearly for cells from 3-38 Ah while the normalized total heat released (kJ/Ah) is relatively constant over that cell size range. The magnitude of the normalized heating rate is on the order of 2x greater for NCA relative to LFP chemistries for 2-3 Ah cells, while that difference is on the order of 10x for 30-40 Ah cells. The total normalized heat release is ~ 15-20% greater for NCA relative to LFP cells across the entire size range studied 3-38 Ah.

Multilayer co-extrusion technique for developing high energy density organic devices.

The purpose of this project is to develop multi-layered co-extrusion (MLCE) capabilities at Sandia National Laboratories to produce multifunctional polymeric structures. Multi-layered structures containing layers of alternating electrical, mechanical, optical, or structural properties can be applied to a variety of potential applications including energy storage, optics, sensors, mechanical, and barrier applications relevant to the internal and external community. To obtain the desired properties, fillers must be added to the polymer materials that are much smaller than the end layer thickness. We developed two filled polymer systems, one for conductive layers and one for dielectric layers and demonstrated the potential for using MLCE to manufacture capacitors. We also developed numerical models to help determine the material and processing parameters that impact processing and layer stability.

Packaging Strategies for Printed Circuit Board Components Volume I: Materials & Thermal Stresses

Decisions on material selections for electronics packaging can be quite complicated by the need to balance the criteria to withstand severe impacts yet survive deep thermal cycles intact. Many times, material choices are based on historical precedence perhaps ignorant of whether those initial choices were carefully investigated or whether the requirements on the new component match those of previous units. The goal of this program focuses on developing both increased intuition for generic packaging guidelines and computational methodologies for optimizing packaging in specific components. Initial efforts centered on characterization of classes of materials common to packaging strategies and computational analyses of stresses generated during thermal cycling to identify strengths and weaknesses of various material choices. Future studies will analyze the same example problems incorporating the effects of curing stresses as needed and analyzing dynamic loadings to compare trends with the quasi-static conclusions.