Structure and Morphology of Photoreactive Monomer–Nanoparticle Mixtures Under Patterned Irradiation

Establishing processing–structure relationships is central to materials science. In this work, we seek answers to whether morphology can be controlled during Light–Induced Self–Writing (LISW) in polymer composite materials, and if yes, how? LISW is based on the ability of light to undergo divergence–free propagation in photoreactive media due to photopolymerization–induced rise in refractive index of the medium. Notably, LISW in polymeric materials has found use predominantly for the fabrication of optical waveguides but has not been explored in polymer–inorganic mixtures. Using through–mask projection which creates a spatially periodic array of optical beams, this work extends LISW to nanoparticle–monomer mixtures to develop functional polymer composite materials. In a model photoreactive system containing Si nanoparticles dispersed in triacrylate monomer mixture undergoing LISW, it is found that the extent of nanoparticle dynamics can be controlled by controlling the incident light intensity used for photopolymerization. LISW at high incident light intensity revealed arrested nanoparticle dynamics, whereas this effect was not observed at low incident light intensity. By controlling the exposure time and exposure intensity, Si–decorated carbon pillars were fabricated and their application as Li–ion battery anodes was evaluated. Extension to TiO2 nanoparticle–containing mixtures resulted in a conformal nanoparticle top coating on underlying bump–like polymer structures. Correlation between nanoparticle weight fraction and exposure time with water contact angles revealed an optimum beyond which superhydrophobicity decreased. Exemplary processability and anti–wetting behavior of these materials was demonstrated. Additionally, Fe3O4–containing polymer pillars were fabricated for stimuli–responsive materials. Although polymer core–nanoparticle shell morphologies were observed at the μm–scale, stimuli response was not detected most likely owing to the rigidity of the polymer. Lastly, superhydrophobic powders were synthesized via rapid maskless photopolymerization of chemically dissimilar mixtures that form droplets. Final morphology was found to be marginally correlated to initial composition but not to the initial state of the mixtures

Si–containing Carbon Composite Pillars Developed via Light–Induced Self–Writing

We report here the fabrication of Si-containing carbon pillars for Li-ion battery anodes using a processing technique known as Light-Induced Self-Writing (LISW). An array of optical beams generated using a photomask elicits the growth of vertically-aligned polymer pillars in nanoparticle-containing monomer mixtures. Simultaneously, we direct the Si nanoparticles to the outer walls of the polymer pillars based on established principles of nanoparticle phase-behavior during the LISW process. This concurrent structure growth and controlled nanoparticle distribution yields Si-decorated polymer pillars, which, upon pyrolysis, demonstrate promise as Li-ion battery anodes. Specifically, the composite pillar anodes demonstrate improved cycling stability over a standard planar electrode. This materials fabrication technique can be extended to other nanoparticle-monomer mixtures for other important applications such as chemical and gas sensing, cell-growth, and droplet manipulation

Vinylimidazole–based Polymer Electrolytes with Superior Conductivity and Promising Electrochemical Performance for Calcium Batteries

Calcium batteries are next–generation energy storage technologies with promising techno-economic benefits. However, performance bottlenecks associated to conventional electrolytes with oxygen–based coordination chemistries must be overcome to enable faster cation transport. Here, we report an imidazole–based polymer electrolyte with the highest reported conductivity and promising electrochemical properties. The polymerization of vinylimidazole in the presence of calcium bis(trifluoromethanesulfonyl)imide (Ca(TFSI)2) salt creates a gel electrolyte comprising a polyvinyl imidazole (PVIm) host infused with vinylimidazole liquid. Calcium ions effectively coordinate with imidazole groups, and the electrolytes present room temperature conductivities >1 mS/cm. Reversible redox activity in symmetric Ca cells is demonstrated at 2 V overpotentials, stably cycling at 0.1 mA/cm2 and areal capacities of 0.1 mAh/cm2. Softer coordination, polarizability, and closer coordinating site distances of the imidazole groups can explain the enhanced properties. Hence, imidazole is a suitable benchmark chemistry for future design and advancement of polymer electrolytes for calcium batteries

Why Is Tetrahydrofuran a Good Solvent for Calcium Batteries? Insights From Ab Initio Molecular Dynamics Simulations

Calcium batteries are rapidly emerging as a potential, future energy storage technology; however, their advancement relies heavily on understanding of the liquid electrolyte component in terms of stability and interactions with a calcium metal anode. Tetrahydrofuran, a cyclic ether, is an experimentally common and promising solvent for the preparation of stable and efficient calcium electrolytes. However, insights into the reasons why are lacking, which could unveil key principles to electrolyte design. In this report, we provide a theoretical study employing ab initio molecular dynamics (AIMD) simulations of the interactions of Ca metal with the cyclic ether tetrahydrofuran (THF). The results show that the electrochemical breakdown and decomposition of THF at the Ca surface is highly orientation- and surface-site dependent, thereby significantly reducing the likelihood of its instability in a randomly organized bulk solvent. Likewise, in bulk electrolytes, its likelihood for breakdown is further diminished, in preference for coordination Ca2+ to form solvated structure. Hence, the finding that molecules require such strict conditions for their decomposition is an important selection and design principle for any solvent to prepare suitable calcium electrolytes. These findings are critical to the advancement of the calcium batteries

A Computational Study on the Ca2+ Solvation, Coordination Environment, and Mobility in Electrolytes for Calcium Ion Batteries

Calcium (ion) batteries are promising next-generation energy storage systems, owing to their numerous benefits in terms of performance metrics, low-cost, mineral abundance, and economic sustainability. A central and critical area to the advancement of the technology is the development of suitable eletrolytes that allow for good salt solubility, ion mobility, electrochemical stability, and reversible redox activity. At this time, the study of different solvent-salt combinations is very limited. Here, we present a computational study on the coordination environment, solvation energetics, and diffusivity of calcium ions over a range of pertinent ionic liquids, cyclic and acylic alkyl carbonates, and specific alkyl nitriles and alkyl formamides, using the salts calcium bis(trifluoromethylsulfonyl)imide (Ca(TFSI)2) and calcium perchlorate (Ca(ClO4)2). Key findings are that several solvents from different solvent classes present comparable solvation environments and mobilities. Ca(TFSI)2 is prefered over Ca(ClO4)2 owing to the former’s mix coordination of Ca2+ to O and N atoms. Ionic liquids with alkyl sulfonate anions provide better coordation over TFSI, which leads to greater diffusivity. Binary organic mixtures (carbonates) provide the best solvation of Ca2+, however, single organic solvents also provide good solvation, such as EC, THF and DMF, as well as some acyclic carbonates. Ion pairing with the salt anion is always present, but can be mitigated through solvent selection, which also correlates to greater mobility; however, there are examples in which strong ion pairing is not significantly adverse to diffusivity. The solvent incorporate into the solvation structure with binary organic mixtures correlates well with the solvation capabilities of the individual solvents. Finally, we show that ionic liquids (specifically alkyl imidazole (cation) alkyl sulfonate (anion) ionic liquids) do not decompose when coordinating at a Ca metal interface, which indicates its promising stability. Overall, this study contributes further generalized understanding of the correlation between solvent and salt and the resultant Ca2+ complexes and Ca2+ mobility in a range of electrolytes, and reveals a range of possible solvents suitable for exploration in calcium (ion) batteries

Hard Carbon Derived from Avocado Peels as a High-Capacity, High-Performance Anode Material for Sodium-Ion Batteries

Deriving battery grade materials from natural sources is a key element to establishing sustainable energy storage technologies. In this work, we present the use of avocado peels as a sustainable source for conversion into hard carbon based anodes for sodium ion batteries. The avocado peels are simply washed and dried then proceeded to a high temperature conversion step. Materials characterization reveals conversion of the avocado peels in high purity, highly porous hard carbon powders. When prepared as anode materials they show to the capability to reversibly store and release sodium ions. The hard carbon-based electrodes exhibit excellent cycling performance, namely, a reversible capacity of 352.55 mAh/g at 0.05 A/g, rate capability up to 86 mAh/g at 3500 mA/g, capacity retention of >90%, and 99.9% coulombic efficiencies after 500 cycles. This study demonstrates avocado derived hard carbon as a sustainable source that can provide excellent electrochemical and battery performance as anodes in sodium ion batteries

Synthesis of Micropillar Arrays via Photopolymerization: An in Situ Study of Light-Induced Formation, Growth Kinetics, and the Influence of Oxygen Inhibition

We report a study on the growth kinetics and resultant structures of arrays of pillars in photo-cross-linkable films during irradiation with a periodic array of microscale optical beams under ambient conditions. The optical beams experience a self-focusing nonlinearity owing to the photopolymerization-induced changes in refractive index, thereby concentrating light and driving the concurrent, parallel growth of microscale pillars along their path length. We demonstrate control over the pillar spacing and pillar height with the irradiation intensity, film thickness, and the size and spacing of the optical beams. The growth of individual pillars in a periodic array arises from the combination of intense irradiation in the beam regions and oxygen inhibition afforded by the open, ambient conditions under which growth is carried out. We propose a kinetic model for pillar growth that includes free-radical generation and oxygen inhibition in thick films of photoinitiated media in order to interpret the experimental results. The model effectively correlates micropillar array structure to the oxygen inhibition effects. This approach of growing micropillar arrays through photopolymerization is straightforward and scalable and opens opportunities for the design of textured surfaces for applications