CNT-Intertwined Polymer Electrode toward the Practical Application of Wearable Devices

SCOBY-based bacterial cellulose as free standing electrodes for safer, greener and cleaner energy storage technology

Bacterial Cellulose (BC) derived from local market or symbiotic culture of bacteria and yeast (SCOBY) was employed as the polymer matrix for hydroxyl multi-walled carbon nanotube (MWCNT-OH)-based electrochemical double-layer capacitor (EDLC). Chitosan (CS)-sodium iodide (NaI)-glycerol (Gly) electrolyte systems were used as the polymer electrolyte. CS-NaI-Gly electrolyte possesses conductivity, potential stability and ionic transference number of (1.20 ± 0.26) × 10^-3 S cm^-2, 2.5 V and 0.99, respectively. For the electrodes, MWCNT-OH was observed to be well dispersed in the matrix of BC which was obtained via FESEM analysis. The inclusion of MWCNT-OH reduced the crystallinity of the BC polymeric structure. From EIS measurement, it was verified that the presence of MWCNT-OH decreased the electron transfer resistance of BC-based electrodes. Cyclic voltammetry (CV) showed that the shape of the CV plots changed to a rectangular-like shape plot as more MWCNT were added, thus verifying the capacitive behavior. Various amount of MWCNT-OH was used in the fabrication of the EDLC where it was discovered that more MWCNT-OH leads to a better EDLC performance. The EDLC was tested for 5000 complete charge-discharge cycles. The optimum performance of this low voltage EDLC was obtained with 0.1 g MWCNT where the average specific capacitance was 8.80 F g^-1. The maximum power and energy density of the fabricated EDLC were 300 W kg^-1 and 1.6 W h kg^-1, respectively.

Stretchable and Self-Adhesive PEDOT:PSS Blend with High Sweat Tolerance as Conformal Biopotential Dry Electrodes

Dry epidermal electrodes that can always form conformal contact with skin can be used for continuous long-term biopotential monitoring, which can provide vital information for disease diagnosis and rehabilitation. But, this application has been limited by the poor contact of dry electrodes on wet skin. Herein, we report a biocompatible fully organic dry electrode that can form conformal contact with both dry and wet skin even during physical movement. The dry electrodes are prepared by drop casting an aqueous solution consisting of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), poly(vinyl alcohol) (PVA), tannic acid (TA), and ethylene glycol (EG). The electrodes can exhibit a conductivity of 122 S cm^-1 and a mechanical stretchability of 54%. Moreover, they are self-adhesive to not only dry skin but also wet skin. As a result, they can exhibit a lower contact impedance to skin than commercial Ag/AgCl gel electrodes on both dry and sweat skins. They can be used as dry epidermal electrodes to accurately detect biopotential signals including electrocardiogram (ECG) and electromyogram (EMG) on both dry and wet skins for the users at rest or during physical movement. This is the first time to demonstrate dry epidermal electrodes self-adhesive to wet skin for accurate biopotential detection.

Are Redox-Active Organic Small Molecules Applicable for High-Voltage (>4 V) Lithium-Ion Battery Cathodes?

While organic batteries have attracted great attention due to their high theoretical capacities, high-voltage organic active materials (> 4 V vs Li/Li+ ) remain unexplored. Here, density functional theory calculations are combined with cyclic voltammetry measurements to investigate the electrochemistry of croconic acid (CA) for use as a lithium-ion battery cathode material in both dimethyl sulfoxide and γ-butyrolactone (GBL) electrolytes. DFT calculations demonstrate that CA dilitium salt (CA-Li2 ) has two enolate groups that undergo redox reactions above 4.0 V and a material-level theoretical energy density of 1949 Wh kg-1 for storing four lithium ions in GBL-exceeding the value of both conventional inorganic and known organic cathode materials. Cyclic-voltammetry measurements reveal a highly reversible redox reaction by the enolate group at ≈4 V in both electrolytes. Battery-performance tests of CA as lithium-ion battery cathode in GBL show two discharge voltage plateaus at 3.9 and 3.1 V, and a discharge capacity of 102.2 mAh g-1 with no capacity loss after five cycles. With the higher discharge voltages compared to the known, state-of-the-art organic small molecules, CA promises to be a prime cathode-material candidate for future high-energy-density lithium-ion organic batteries.

Cross-Linked PVA/HNT Composite Separator Enables Stable Lithium-Organic Batteries under Elevated Temperature

Li-organic batteries (LOBs) are promising advanced battery systems because of their unique advantages in capacity, cost, and sustainability. However, the shuttling effect of soluble organic redox intermediates and the intrinsic dissolution of small-molecular electrodes have hindered the practical application of these cells, especially under high operating temperatures. Herein, a cross-linked membrane with abundant negative charge for high-temperature LOBs is prepared via electrospinning of poly(vinyl alcohol) containing halloysite nanotubes (HNTs). The translocation of negatively charged organic intermediates can be suppressed by the electronic repulsion and the cross-linked network while the positively charged Li⁺ are maintained, which is attributed to the intrinsic electronegativity of HNTs and their well-organized and homogeneous distribution in the PVA matrix. A battery using a PVA/HNT composite separator (EPH-10) and an anthraquinone (AQ) cathode exhibits a high initial discharge capacity of 231.6 mAh g^-1 and an excellent cycling performance (91.4% capacity retention, 300 cycles) at 25 °C. Even at high temperatures (60 and 80 °C), its capacity retention is more than 89.2 and 80.4% after 100 cycles, respectively. Our approach demonstrates the potential of the EPH-10 composite membrane as a separator for high-temperature LOB applications.

Photo-Patternable, High-Speed Electrospun Ultrafine Fibers Fabricated by Intrinsically Negative Photosensitive Polyimide

This work describes polyimide (PI) ultrafine fibrous membranes (UFMs) with aligned fibrous structures, fabricated via the high-speed electrospinning procedure. Organo-soluble intrinsically photosensitive PI is utilized as the fiber-forming agent. The effects of different rotating speeds on the fiber morphology and properties are studied. The aligned UFMs possess hydrophobicity, favorable optical properties, and improved deformation durability. The extension strength of the UFMs reinforces obviously with the increased rotating speed and reaches the maximum of 9.18 MPa at 2500 rpm. In addition, due to the photo-cross-link nature of the PI resin, the UFMs present lithography capability, which can obtain micro-sized patterns on aluminum substrates, and even part of the fibrous structure was retained after development. This work shows promise in manufacturing fiber-based photolithographic hierarchical structures on flexible substrates, which exhibit potential in achieving multiple functions on fiber-based electronic devices.