NMR Methodology for Measuring Dissolved O2 and Transport in Lithium-Air Batteries.

Similar to fuel cells, poor mass transport of redox active species, such as dissolved oxygen gas, is one of the challenges faced by lithium-air batteries (LABs). Capitalizing on the paramagnetic properties of O2, we used nuclear magnetic resonance (NMR) spectroscopy to measure oxygen concentration and transport in LAB electrolytes. Lithium bis(trifluoromethane) sulfonylimide (LiTFSI) in glymes or dimethyl sulfoxide (DMSO) solvents were investigated with 1H, 13C, 7Li, and 19F NMR spectroscopy, with the results showing that both the 1H, 13C, 7Li, and 19F bulk magnetic susceptibility shifts and the change in 19F relaxation times were accurate measures of dissolved O2 concentration. O2 saturation concentrations and diffusion coefficients were extracted that are comparable to values measured by electrochemical or pressure methods reported in the literature, highlighting the validity of this new methodology. This method also provides experimental evidence of the local O2 solvation environment, with results again comparable to previous literature and supported by our molecular dynamics simulations. A preliminary in situ application of our NMR methodology is demonstrated by measuring O2 evolution during LAB charging using LiTFSI in the glyme electrolyte. While the in situ LAB cell showed poor coulombic efficiency, since no additives were used, the O2 evolution was successfully quantified. Our work demonstrates the first usage of this NMR methodology to quantify O2 in LAB electrolytes, experimentally demonstrate solvation environments of O2, and detect O2 evolution in situ in a LAB flow cell.

Functionalized Silicon Particles for Enhanced Half- and Full-Cell Cycling of Si-Based Li-Ion Batteries.

Vinylene carbonate (VC) and polyethylene oxide (PEO) have been investigated as functional agents that mimic the solid electrolyte interphase (SEI) chemistry of silicon (Si). VC and PEO are known to contribute to the stability of Si-based lithium-ion batteries as an electrolyte additive and as a SEI component, respectively. In this work, covalent surface functionalization was achieved via a facile route, which involves ball-milling the Si particles with sacrificial VC and PEO. Thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy indicate that the additives are strongly bound to Si. In particular, MAS NMR shows Si-R or Si-O-R groups, which confirm functionalization of the Si after milling in VC or PEO. Particle size analysis by dynamic light scattering reveals that the additives facilitate particle size reduction and that the functionalized particles result in more stable dispersions based on zeta potential measurements. Raman mapping of the electrodes fabricated from the VC and PEO-coated active material with a polyacrylic acid (PAA) binder reveals a more homogenous distribution of Si and the carbon conductive additive compared to the electrodes prepared from the neat Si. Furthermore, the VC-milled Si strikingly exhibited the highest capacity in both half- and full-cell configurations, with more than 200 mAh g-1 measured capacity compared to the neat Si in the half-cell format. This is linked to an improved electrode processing based on the Raman and zeta potential measurements as well as a thinner SEI (with more organic components for the functionalized Si relative to the neat Si) based on XPS analysis of the cycled electrodes. The effect of binder was also investigated by comparing PAA with P84 (polyimide type), where an increased capacity is observed in the latter case.

Effects of Atmospheric Gases on Li Metal Cyclability and Solid-Electrolyte Interphase Formation.

For Li-air batteries, dissolved gas can cross over from the air electrode to the Li metal anode and affect the solid-electrolyte interphase (SEI) formation, a phenomenon that has not been fully characterized. In this work, the impact of atmospheric gases on the SEI properties is studied using electrochemical methods and ex situ characterization techniques, including X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The presence of O2 significantly improved the lithium cyclability; less lithium is consumed to form the SEI or is lost because of electrical disconnects. However, the SEI resistivity and plating overpotentials increased. Lithium cycled in an "air-like" mixed O2/N2 environment also demonstrated improved cycling efficiency, suggesting that dissolved O2 participates in electrolyte reduction, forming a homogeneous SEI, even at low concentrations. The impact of gas environments on Li metal plating and SEI formation represents an additional parameter in designing future Li-metal batteries.

Functionally Graded, Bone- and Tendon-Like Polyurethane for Rotator Cuff Repair.

Critical considerations in engineering biomaterials for rotator cuff repair include bone-tendon-like mechanical properties to support physiological loading and biophysicochemical attributes that stabilize the repair site over the long-term. In this study, UV-crosslinkable polyurethane based on quadrol (Q), hexamethylene diisocyante (H), and methacrylic anhydride (M; QHM polymers), which are free of solvent, catalyst, and photoinitiator, is developed. Mechanical characterization studies demonstrate that QHM polymers possesses phototunable bone- and tendon-like tensile and compressive properties (12-74 MPa tensile strength, 0.6-2.7 GPa tensile modulus, 58-121 MPa compressive strength, and 1.5-3.0 GPa compressive modulus), including the capability to withstand 10 000 cycles of physiological tensile loading and reduce stress concentrations via stiffness gradients. Biophysicochemical studies demonstrate that QHM polymers have clinically favorable attributes vital to rotator cuff repair stability, including slow degradation profiles (5-30% mass loss after 8 weeks) with little-to-no cytotoxicity in vitro, exceptional suture retention ex vivo (2.79-3.56-fold less suture migration relative to a clinically available graft), and competent tensile properties (similar ultimate load but higher normalized tensile stiffness relative to a clinically available graft) as well as good biocompatibility for augmenting rat supraspinatus tendon repair in vivo. This work demonstrates functionally graded, bone-tendon-like biomaterials for interfacial tissue engineering.

Development of mRuby2-Transfected C3H10T1/2 Fibroblasts for Musculoskeletal Tissue Engineering.

Mouse C3H10T1/2 fibroblasts are multipotent, mesenchymal stem cell (MSC)-like progenitor cells that are widely used in musculoskeletal research. In this study, we have established a clonal population of C3H10T1/2 cells stably-transfected with mRuby2, an orange-red fluorescence reporter gene. Flow cytometry analysis and fluorescence imaging confirmed successful transfection of these cells. Cell counting studies showed that untransfected C3H10T1/2 cells and mRuby2-transfected C3H10T1/2 cells proliferated at similar rates. Adipogenic differentiation experiments demonstrated that untransfected C3H10T1/2 cells and mRuby2-transfected C3H10T1/2 cells stained positive for Oil Red O and showed increased expression of adipogenic genes including adiponectin and lipoprotein lipase. Chondrogenic differentiation experiments demonstrated that untransfected C3H10T1/2 cells and mRuby2-transfected C3H10T1/2 cells stained positive for Alcian Blue and showed increased expression of chondrogenic genes including aggrecan. Osteogenic differentiation experiments demonstrated that untransfected C3H10T1/2 cells and mRuby2-transfected C3H10T1/2 cells stained positive for alkaline phosphatase (ALP) as well as Alizarin Red and showed increased expression of osteogenic genes including alp, ocn and osf-1. When seeded on calcium phosphate-based ceramic scaffolds, mRuby2-transfected C3H10T1/2 cells maintained even fluorescence labeling and osteogenic differentiation. In summary, mRuby2-transfected C3H10T1/2 cells exhibit mRuby2 fluorescence and showed little-to-no difference in terms of cell proliferation and differentiation as untransfected C3H10T1/2 cells. These cells will be available from American Type Culture Collection (ATCC; CRL-3268™) and may be a valuable tool for preclinical studies.