5 research outputs found
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Electrotunable liquid sulfur microdroplets.
Manipulating liquids with tunable shape and optical functionalities in real time is important for electroactive flow devices and optoelectronic devices, but remains a great challenge. Here, we demonstrate electrotunable liquid sulfur microdroplets in an electrochemical cell. We observe electrowetting and merging of sulfur droplets under different potentiostatic conditions, and successfully control these processes via selective design of sulfiphilic/sulfiphobic substrates. Moreover, we employ the electrowetting phenomena to create a microlens based on the liquid sulfur microdroplets and tune its characteristics in real time through changing the shape of the liquid microdroplets in a fast, repeatable, and controlled manner. These studies demonstrate a powerful in situ optical battery platform for unraveling the complex reaction mechanism of sulfur chemistries and for exploring the rich material properties of the liquid sulfur, which shed light on the applications of liquid sulfur droplets in devices such as microlenses, and potentially other electrotunable and optoelectronic devices
Simultaneous Purification and Perforation of Low-Grade Si Sources for Lithium-Ion Battery Anode
Silicon is regarded as one of the
most promising candidates for lithium-ion battery anodes because of
its abundance and high theoretical capacity. Various silicon nanostructures
have been heavily investigated to improve electrochemical performance
by addressing issues related to structure fracture and unstable solid–electrolyte
interphase (SEI). However, to further enable widespread applications,
scalable and cost-effective processes need to be developed to produce
these nanostructures at large quantity with finely controlled structures
and morphologies. In this study, we develop a scalable and low cost
process to produce porous silicon directly from low grade silicon
through ball-milling and modified metal-assisted chemical etching.
The morphology of porous silicon can be drastically changed from porous-network
to nanowire-array by adjusting the component in reaction solutions.
Meanwhile, this perforation process can also effectively remove the
impurities and, therefore, increase Si purity (up to 99.4%) significantly
from low-grade and low-cost ferrosilicon (purity of 83.4%) sources.
The electrochemical examinations indicate that these porous silicon
structures with carbon treatment can deliver a stable capacity of
1287 mAh g<sup>–1</sup> over 100 cycles at a current density
of 2 A g<sup>–1</sup>. This type of purified porous silicon
with finely controlled morphology, produced by a scalable and cost-effective
fabrication process, can also serve as promising candidates for many
other energy applications, such as thermoelectrics and solar energy
conversion devices
Precise Perforation and Scalable Production of Si Particles from Low-Grade Sources for High-Performance Lithium Ion Battery Anodes
Alloy anodes, particularly
silicon, have been intensively pursued as one of the most promising
anode materials for the next generation lithium-ion battery primarily
because of high specific capacity (>4000 mAh/g) and elemental abundance.
In the past decade, various nanostructures with porosity or void space
designs have been demonstrated to be effective to accommodate large
volume expansion (∼300%) and to provide stable solid electrolyte
interphase (SEI) during electrochemical cycling. However, how to produce
these building blocks with precise morphology control at large scale
and low cost remains a challenge. In addition, most of nanostructured
silicon suffers from poor Coulombic efficiency due to a large surface
area and Li ion trapping at the surface coating. Here we demonstrate
a unique nanoperforation process, combining modified ball milling,
annealing, and acid treating, to produce porous Si with precise and
continuous porosity control (from 17% to 70%), directly from low cost
metallurgical silicon source (99% purity, ∼ $1/kg). The produced
porous Si coated with graphene by simple ball milling can deliver
a reversible specific capacity of 1250 mAh/g over 1000 cycles at the
rate of 1C, with Coulombic efficiency of first cycle over 89.5%. The
porous networks also provide efficient ion and electron pathways and
therefore enable excellent rate performance of 880 mAh/g at the rate
of 5C. Being able to produce particles with precise porosity control
through scalable processes from low-grade materials, it is expected
that this nanoperforation may play a role in the next generation lithium
ion battery anodes, as well as many other potential applications such
as optoelectronics and thermoelectrics
Scalable Production of Si Nanoparticles Directly from Low Grade Sources for Lithium-Ion Battery Anode
Silicon, one of the most promising
candidates as lithium-ion battery anode, has attracted much attention
due to its high theoretical capacity, abundant existence, and mature
infrastructure. Recently, Si nanostructures-based lithium-ion battery
anode, with sophisticated structure designs and process development,
has made significant progress. However, low cost and scalable processes
to produce these Si nanostructures remained as a challenge, which
limits the widespread applications. Herein, we demonstrate that Si
nanoparticles with controlled size can be massively produced directly
from low grade Si sources through a scalable high energy mechanical
milling process. In addition, we systematically studied Si nanoparticles
produced from two major low grade Si sources, metallurgical silicon
(∼99 wt % Si, 0.6/kg). It is found that nanoparticles produced from ferrosilicon
sources contain FeSi<sub>2</sub>, which can serve as a buffer layer
to alleviate the mechanical fractures of volume expansion, whereas
nanoparticles from metallurgical Si sources have higher capacity and
better kinetic properties because of higher purity and better electronic
transport properties. Ferrosilicon nanoparticles and metallurgical
Si nanoparticles demonstrate over 100 stable deep cycling after carbon
coating with the reversible capacities of 1360 mAh g<sup>–1</sup> and 1205 mAh g<sup>–1</sup>, respectively. Therefore, our
approach provides a new strategy for cost-effective, energy-efficient,
large scale synthesis of functional Si electrode materials