Vertically Aligned n-Type Silicon Nanowire Array as a Free-Standing Anode for Lithium-Ion Batteries.

Due to its high theoretical specific capacity, a silicon anode is one of the candidates for realizing high energy density lithium-ion batteries (LIBs). However, problems related to bulk silicon (e.g., low intrinsic conductivity and massive volume expansion) limit the performance of silicon anodes. In this work, to improve the performance of silicon anodes, a vertically aligned n-type silicon nanowire array (n-SiNW) was fabricated using a well-controlled, top-down nano-machining technique by combining photolithography and inductively coupled plasma reactive ion etching (ICP-RIE) at a cryogenic temperature. The array of nanowires ~1 µm in diameter and with the aspect ratio of ~10 was successfully prepared from commercial n-type silicon wafer. The half-cell LIB with free-standing n-SiNW electrode exhibited an initial Coulombic efficiency of 91.1%, which was higher than the battery with a blank n-silicon wafer electrode (i.e., 67.5%). Upon 100 cycles of stability testing at 0.06 mA cm-2, the battery with the n-SiNW electrode retained 85.9% of its 0.50 mAh cm-2 capacity after the pre-lithiation step, whereas its counterpart, the blank n-silicon wafer electrode, only maintained 61.4% of 0.21 mAh cm-2 capacity. Furthermore, 76.7% capacity retention can be obtained at a current density of 0.2 mA cm-2, showing the potential of n-SiNW anodes for high current density applications. This work presents an alternative method for facile, high precision, and high throughput patterning on a wafer-scale to obtain a high aspect ratio n-SiNW, and its application in LIBs.

Red Bean Pod Derived Heterostructure Carbon Decorated with Hollow Mixed Transition Metals as a Bifunctional Catalyst in Zn-Air Batteries.

Design and synthesis of low-cost and efficient bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in Zn-air batteries are essential and challenging. We report a facile method to synthesize heterostructure carbon consisting of graphitic and amorphous carbon derived from the agricultural waste of red bean pods. The heterostructure carbon possesses a large surface area of 625.5 m2 g-1 , showing ORR onset potential of 0.89 V vs. RHE and OER overpotential of 470 mV at 5 mA cm-2 . Introducing hollow FeCo nanoparticles and nitrogen dopant improves the bifunctional catalytic activity of the carbon, delivering ORR onset potential of 0.93 V vs. RHE and OER overpotential of 360 mV. Electron energy-loss spectroscopy (EELS) O K-edge map suggests the presence of localized oxygen on the FeCo nanoparticles, suggesting the oxidation of the nanoparticles. Zn-air battery with these carbon-based catalysts exhibits a peak power density as high as 116.2 mW cm-2 and stable cycling performance over 210 discharge/charge cycles. This work contributes to the advancement of bifunctional oxygen electrocatalysts while converting agricultural waste into value-added material.

Facile synthesis of battery waste-derived graphene for transparent and conductive film application by an electrochemical exfoliation method.

One of the emerging challenges in tackling environmental issues is to treat electronic waste, with fast-growing battery waste as a notable threat to the environment. Proper recycling processes, particularly the conversion of waste to useful & value-added materials, are of great importance but not readily available. In this work, we report a facile and fast production of graphene from graphite extracted from spent Zn-C batteries. The graphene flakes are produced by electrochemically exfoliating graphite under varying DC voltages in poly(sodium 4-styrenesulfonate) (PSS) solution of different concentrations. The exfoliation takes place via the insertion of PSS into the interlayers of graphite to form C-S bonds as confirmed by FTIR and XPS studies. Under an applied voltage of 5 V and in 0.5 M PSS, high quality graphene flakes are obtained in a good yield, giving an I D/I G ratio of about 0.86 in Raman spectroscopy. The transparent conductive film prepared from the dispersion of high quality graphene flakes shows great promise due to its low sheet resistance (R s) of 1.1 kΩ sq-1 and high transmittance of 89%. This work illustrates an effective and low-cost method to realize large scale production of graphene from electronic waste.