Carbon- and Binder-Free NiCo2O4 Nanoneedle Array Electrode for Sodium-Ion Batteries: Electrochemical Performance and Insight into Sodium Storage Reaction

Sodium (Na)-ion batteries (NIBs) have attracted significant interest as an alternative chemistry to lithium (Li)-ion batteries for large-scale stationary energy storage systems. Discovering high-performance anode materials is a great challenge for the commercial success of NIB technology. Transition metal oxides with tailored nanoarchitectures have been considered as promising anodes for NIBs due to their high capacity. Here, we demonstrate the fabrication of a nanostructured oxide-only electrode, i.e., carbon- and binder-free NiCo2O4 nanoneedle array (NCO-NNA), and its feasibility as an anode for NIBs. Furthermore, we provide an in-depth experimental study of the Na storage reaction (sodiation and desodiation) in NCO-NNA. The NCO-NNA electrode is fabricated on a conducting substrate by a hydrothermal method with subsequent heat treatment. When tested in an electrochemical Na half-cell, the NCO-NNA electrode exhibits excellent Na storage capability: a charge capacity as high as 400 mAh g(-1) is achieved at a current density of 50 mA g(-1). It also shows a greatly improved cycle life (~215 mAh g(-1) after 50 cycles) in comparison to a conventional powder-type electrode (~30 mAh g(-1)). However, the Na storage performance is still inferior to that of Li, which is mainly due to sluggish kinetics of sodiation-desodiation accompanied by severe volume change.

Mechanoporation of living cells for delivery of macromolecules using nanoneedle array

Efficient and rapid delivery of macromolecule probes, such as quenchbodies and other large biomarkers that cannot readily pass through the plasma membrane, is necessary for live-cell imaging and other intracellular analyses. We present here an alternative, simple method for delivery of macromolecules into live cells. In this method, which we term here mechanoporation, a nanoneedle array is used for making transient pores in the plasma membrane to allow access of desired macromolecules into thousands of live cells, simultaneously. This rapid, 3-step method facilitates an efficient delivery by adding macromolecules into the medium, inserting nanoneedles into the cells and oscillating the nanoneedle array, a process that takes no more than 5 min in total. In addition, we demonstrate here how this method can repeatedly and reproducibly deliver molecules into specifically-selected locations on a given cell culture dish. The results presented here show how this unique mechanoporation method enables rapid and high-throughput bio-macromolecule delivery and live-cell imaging.