A Nearly Packaging-Free Design Paradigm for Light, Powerful, and Energy-Dense Primary Microbatteries.

Billions of internet connected devices used for medicine, wearables, and robotics require microbattery power sources, but the conflicting scaling laws between electronics and energy storage have led to inadequate power sources that severely limit the performance of these physically small devices. Reported here is a new design paradigm for primary microbatteries that drastically improves energy and power density by eliminating the vast majority of the packaging and through the use of high-energy-density anode and cathode materials. These light (50-80 mg) and small (20-40 µL) microbatteries are enabled though the electroplating of 130 µm-thick 94% dense additive-free and crystallographically oriented LiCoO2 onto thin metal foils, which also act as the encapsulation layer. These devices have 430 Wh kg-1 and 1050 Wh L-1 energy densities, 4 times the energy density of previous similarly sized microbatteries, opening up the potential to power otherwise unpowerable microdevices.

3D Printing of Supramolecular Polymer Hydrogels with Hierarchical Structure.

Liquid crystalline hydrogels are an attractive class of soft materials to direct charge transport, mechanical actuation, and cell migration. When such systems contain supramolecular polymers, it is possible in principle to easily shear align nanoscale structures and create bulk anisotropic properties. However, reproducibly fabricating and patterning aligned supramolecular domains in 3D hydrogels remains a challenge using conventional fabrication techniques. Here, a method is reported for 3D printing of ionically crosslinked liquid crystalline hydrogels from aqueous supramolecular polymer inks. Using a combination of experimental techniques and molecular dynamics simulations, it is found that pH and salt concentration govern intermolecular interactions among the self-assembled structures where lower charge densities on the supramolecular polymers and higher charge screening from the electrolyte result in higher viscosity inks. Enhanced hierarchical interactions among assemblies in high viscosity inks increase the printability and ultimately lead to greater nanoscale alignment in extruded macroscopic filaments when using small nozzle diameters and fast print speeds. The use of this approach is demonstrated to create materials with anisotropic ionic and electronic charge transport as well as scaffolds that trigger the macroscopic alignment of cells due to the synergy of supramolecular self-assembly and additive manufacturing.

Creasable Batteries: Understanding Failure Modes through Dynamic Electrochemical Mechanical Testing.

Thin-film batteries that can be folded, bent, and even repeatedly creased with minimal or no loss in electrochemical performance have been demonstrated and systematically evaluated using two dynamic mechanical testing approaches for either controlled bending or creasing of flexible devices. The results show that mechanically robust and flexible Li-ion batteries (Li4Ti5O12//LiFePO4) based on the use of a nonwoven multiwalled carbon nanotube (MWNT) mat as a current collector (CC) exhibited a 14-fold decrease in voltage fluctuation at a bending strain of 4.2%, as compared to cells using traditional metal foil CCs. More importantly, MWNT-based full-cells exhibited excellent mechanical integrity through 288 crease cycles, whereas the foil full-cell exhibited continuously degraded performance with each fold and catastrophic fracture after only 94 folds. The enhancements due to MWNT CCs can be attributed to excellent interfacial properties as well as high mechanical strength coupled with compliancy, which allow the batteries to easily conform during mechanical abuse. These results quantitatively demonstrate the substantial enhancement offered in both mechanical and electrochemical stability which can be realized with traditional processing approaches when an appropriate choice of a flexible and robust CC is utilized.

Understanding charge transfer in carbon nanotube-fullerene bulk heterojunctions.

Semiconducting single-walled carbon nanotube/fullerene bulk heterojunctions exhibit unique optoelectronic properties highly suitable for flexible, efficient, and robust photovoltaics and photodetectors. We investigate charge-transfer dynamics in inverted devices featuring a polyethylenimine-coated ZnO nanowire array infiltrated with these blends and find that trap-assisted recombination dominates transport within the blend and at the active layer/nanowire interface. We find that electrode modifiers suppress this recombination, leading to high performance.

Shape-reprogrammable polymers: encoding, erasing, and re-encoding.

Shape-reprogramming in a polymer is demonstrated, where prescribed 3D geometric information can be encoded, decoded, erased, and re-encoded. In essence, the shape-reprogrammable polymer (SRP) acts as computer hardware that can be reformatted and reprogrammed repeatedly. Such SRPs have the potential to be repurposed directly without going through material disposal and recycling.

Remote, local, and chemical programming of healable multishape memory polymer nanocomposites.

We show that the combination of remote, local, and chemical programming of the multishape memory effects offers unparalleled shape and function control in carbon nanotube-Nafion composites. This strategy not only allows the high-fidelity encoding and extraction of designed material shapes at different length scales (macro, micro, and nano) but also enables the reversible tunability of material functions, such as shape memorizability, mechanical properties, surface hydrophobicity, and material resealability, in a single nanocomposite.

Efficient transport of gold atoms with a scanning tunneling microscopy tip and a linker molecule.

A thiophene-containing molecule attached to a scanning tunneling microscopy (STM) tip is used to transport gold atoms on a Au(111) surface. The molecule contains eight thiophene rings and therefore has sulfur atoms that are known to bind to gold atoms. Using a gold-coated tip, the molecules previously deposited on the surface bind to the lower-coordination gold atoms of the tip. When that tip is used to scan the surface, the still free thiophene rings (not all of the sulfur atoms bind to the tip) can attach to gold atoms from the surface and drag them along the scanning direction, depositing them either at the position where the tip changes its scanning direction or where the tip encounters an "up step", whichever event occurs first.