Carbon scrolls stabilize silicon nanoparticles in lithium-ion batteries
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a
A
336
μm 3 < D
Robust electrical content Lithiated Si
Stable electrical After cycling contact
CNT/Cel-carbon cage Highly dispersed Si NPs
Stable SEI and morphology
Strong and flexible microscrolls L > 100 μm, Si content enable to 92% for anode by mass
Lithiated state
c
b
Voids Si
Si NPs CNT/C CNT/Carbon Cage 20 nm
200 nm
Restraint layer
d Coulombic Efficiency (%)
joint research team led by Huiqiao Li of Huazhong University of Science and Technology, Yi Cui of Stanford University, and Qingfeng Sun of Zhejiang A&F University, has developed a carbonscroll strategy that effectively helps stabilize silicon nanoparticles in Li-ion batteries. Si is a high-capacity, but highly unstable, anode material for Li-ion batteries. With a high Si content of 84.5 wt%, electrodes compromising Si nanoparticles mixed with carbon nanotubes (CNTs) and wrapped in carbon sheets exhibited consistently high capacity above 2000 mAh/g over 300 consecutive charge-discharge cycles. This performance was in sharp contrast to a bare Si nanoparticle electrode that displayed rapid capacity loss. This work was published in Energy & Environmental Science (doi:10.1039/ c9ee02615k). The topological warping of cellulose nanosheets enabled the scrolling strategy. The researchers mixed cellulose nanosheets, commercial Si nanoparticles, and CNTs (electrically conductive scaffolds) in water. The aqueous mixture was then freeze-dried into an aerogel. During freeze-drying, the cellulose nanosheets rolled up and wrapped CNTs and Si nanoparticles inside. The researchers believed that the freeze-drying process dehydrated and rolled up the cellulose nanosheets due to formation of hydrogen bonds, a process similar to wet paper rolling up when dried. Additionally, mechanical simulations revealed that the Si nanoparticles exerted stress that directed the cellulose nanosheets to wrap around them. The as-formed aerogels were subsequently pyrolyzed at 800°C to convert the electrically insulating cellulose into conductive carbon. According to Li, this work was born from an unexpected observation. “Our original plan was combining cellulose nanosheets with silicon to prepare silicon-carbon aerogels. In this process, we were surprised to find a unique scroll structure assembled by silicon and cellulose nanosheets, regardless of the addition of CNTs,” Li says.
Cel-carbon Spiral CNTs framework Void space
Specific Capacity ( mAh g –1electrode )
Carbon scrolls stabilize silicon nanoparticles in lithium-ion batteries
372 mAh g–1
Cycle Number
(a) Scheme showing the stabilization of Si nanoparticles by carbon nanotube/cellulose-derived carbon (CNT/C) wrapping. (b) Scanning electron micrograph and (c) transmission electron micrograph images of CNT/C-wrapped Si nanoparticles. (d) Cycling stability of CNT/C-wrapped Si nanoparticles with 74 wt% (Si-74), 85 wt% (Si-85), and 92 wt% Si (Si-92), in comparison with bare Si nanoparticles (Si NPs). Credit: Energy & Environmental Science.
The researchers discovered that the carbon-scrolled Si nanoparticles served as hi
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