Temperature-Dependent Fracture Resistance of Silicon Nanopillars during Electrochemical Lithiation.

During the lithation of silicon anodes, the solid-state diffusion of lithium into LixSi follows the Arrhenius law, the resulting morphology and fracture behavior are determined by the silicon anode operation temperature. Here, we reveal the temperature dependence of the lithiation mechanics of crystalline silicon nanopillars (SiNPs) via microscopic observations of the anisotropic growth and fracture behavior. We fabricated 1D SiNP structures with various orientations (⟨100⟩, ⟨110⟩, and ⟨111⟩) as working electrodes and operated them at temperatures ranging from -20 to 40 °C. The lithiation of crystalline silicon at low temperatures exhibited preferential volume expansion along ⟨110⟩ and decreased fracture resistance. Furthermore, low temperatures caused the catastrophic fracture of amorphous silicon after the second lithiation. Our findings demonstrate the importance of silicon anode temperature control to prevent mechanical fracture during the cycle of lithium-ion batteries in harsh environments (e.g., electric vehicles in winter).

Copper Hexacyanoferrate Thin Film Deposition and Its Application to a New Method for Diffusion Coefficient Measurement.

The use of Prussian blue analogues (PBA) materials in electrochemical energy storage and harvesting has gained much interest, necessitating the further clarification of their electrochemical characteristics. However, there is no well-defined technique for manufacturing PBA-based microelectrochemical devices because the PBA film deposition method has not been well studied. In this study, we developed the following deposition method for growing copper hexacyanoferrate (CuHCFe) thin film: copper thin film is immersed into a potassium hexacyanoferrate solution, following which the redox reaction induces the spontaneous deposition of CuHCFe thin film on the copper thin film. The film grown via this method showed compatibility with conventional photolithography processes, and the micropattern of the CuHCFe thin film was successfully defined by a lift-off process. A microelectrochemical device based on the CuHCFe thin film was fabricated via micropatterning, and the sodium ion diffusivity in CuHCFe was measured. The presented thin film deposition method can deposit PBAs on any surface, including insulating substrates, and it can extend the utilization of PBA thin films to various applications.

Tear-Based Aqueous Batteries for Smart Contact Lenses Enabled by Prussian Blue Analogue Nanocomposites.

Batteries for contact lenses fabricated by conventional methods could cause severe damage to the eyes if broken. Herein, we present flexible aqueous batteries that operate in tears and provide a safe power supply to smart contact lenses. Nanocomposite flexible electrodes of carbon nanotubes and Prussian blue analogue nanoparticles for cathode and anode were embedded in UV-polymerized hydrogel as not only a soft contact lens but also an ion-permeable separator. The battery exhibited a discharging capacity of 155 µAh in an aqueous electrolyte of 0.15 M Na-ions and 0.02 M K-ions, equivalent to the ionic concentration of tears. The power supply was enough to operate a low-power static random-access memory. In addition, we verified the mechanical stability, biocompatibility and compatibility with a contact lens cleaning solution. It could ultimately enable a safe power supply for smart contact lenses without risk of injury due to the leakage or breakage of the battery.

Efficient Low-Grade Heat Harvesting Enabled by Tuning the Hydration Entropy in an Electrochemical System.

Harvesting of low-grade heat (<100 °C) is promising, but its application is hampered by a lack of efficient and low-cost systems. The thermally regenerative electrochemical cycle (TREC) is a potential alternative system with high energy-conversion efficiency. Here, the temperature coefficient (α), which is a key factor in a TREC, is studied by tuning the hydration entropy of the electrochemical reaction. The change of α in copper hexacyanoferrate (CuHCFe) with intercalation of different monovalent cations (Na+ , K+ , Rb+ , and Cs+ ) and a larger α value of -1.004 mV K-1 being found in the Rb+ system are observed. With a view to practical application, a full cell is constructed for low-grade heat harvesting. The resultant ηe is 4.34% when TREC operates between 10 and 50 °C, which further reaches 6.21% when 50% heat recuperation is considered. This efficiency equals to 50% of the Carnot efficiency, which is thought to be the highest ηe reported for low-grade heat harvesting systems. This study provides a fundamental understanding of the mechanisms governing the TREC, and the demonstrated efficient system paves the way for low-grade heat harvesting.

Thermal Conductive 2D Boron Nitride for High-Performance All-Solid-State Lithium-Sulfur Batteries.

Polymer-based solid-state electrolytes are shown to be highly promising for realizing low-cost, high-capacity, and safe Li batteries. One major challenge for polymer solid-state batteries is the relatively high operating temperature (60-80 °C), which means operating such batteries will require significant ramp up time due to heating. On the other hand, as polymer electrolytes are poor thermal conductors, thermal variation across the polymer electrolyte can lead to nonuniformity in ionic conductivity. This can be highly detrimental to lithium deposition and may result in dendrite formation. Here, a polyethylene oxide-based electrolyte with improved thermal responses is developed by incorporating 2D boron nitride (BN) nanoflakes. The results show that the BN additive also enhances ionic and mechanical properties of the electrolyte. More uniform Li stripping/deposition and reversible cathode reactions are achieved, which in turn enable all-solid-state lithium-sulfur cells with superior performances.

Anodic aluminium oxide membranes for immunoisolation with sufficient oxygen supply for pancreatic islets.

Immunoisolation membranes have been developed for various cell encapsulations for therapeutic purposes. However effective encapsulation systems have been hindered by low oxygen (O2) permeability or imperfect immunoisolation caused by either low porosity or non-uniform pore geometry. Here, we report an encapsulation method that uses an anodic aluminum oxide membrane formed by polyethylene oxide self-assembly to obtain nanochannels with both high selectivity in excluding immune molecules and high permeability of nutrients such as glucose, insulin, and O2. The extracorporeal encapsulation system composed of these membranes allows O2 flux to meet the O2 demand of pancreatic islets of Langerhans and provides excellent in vitro viability and functionality of islets.

Robust superhydrophilic/hydrophobic surface based on self-aggregated Al2O3 nanowires by single-step anodization and self-assembly method.

Superhydrophilic and superhydrophobic surfaces were studied with an eye to industrial applications and use as research tools. Conventional methods involve complex and time-consuming processes and cannot feasibly produce large-area three-dimensional surfaces. Here, we report robust and large-area alumina nanowire structures with superhydrophobic or superhydrophilic properties, generated by an inexpensive single-step anodization process that can routinely create arbitrary three-dimensional shapes. This process is expected to open up diverse applications.

A polyethylene oxide-functionalized self-organized alumina nanochannel array for an immunoprotection biofilter.

Nanochannel membranes have been fabricated for many biological and engineering applications. However, due to low-throughput process, high cost, unsuitable pore geometries, and low chemical/mechanical stability, we could not have obtained optimized nanochannel membranes for biomedical treatments as well as a novel building block for artificial cell membranes. Here, we report a PEO-functionalized straight nanochannel array based on a self-organized porous alumina for a novel biofilter with antifouling, superior immunoprotection and high permeability of nutrients, which have excellent in vivo mechanical stability. Thus, our strategy may provide great advantages in novel membrane biotechnologies such as biofiltration, artificial cells, and drug delivery.