Binder-free freestanding flexible Si nanoparticle-multi-walled carbon nanotube composite paper anodes for high energy Li
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m P. Zheng Materials Science & Engineering, Florida State University, Tallahassee, Florida 32310, USA; Aero-propulsion, Mechatronics and Energy Center (AME), Florida State University, Tallahassee, Florida 32310, USA; Center for Advanced Power Systems (CAPS), Florida State University, Tallahassee, Florida 32310, USA; and Department of Electrical & Computer Engineering, Florida A&M University-Florida State University College of Engineering, Tallahassee, Florida 32310, USA
Zhiyong Liang Materials Science & Engineering, Florida State University, Tallahassee, Florida 32310, USA; High-Performance Materials Institute (HPMI), Florida State University, Tallahassee, Florida 32310, USA; and Department of Industrial and Manufacturing Engineering, Florida A&M University-Florida State University College of Engineering, Tallahassee, Florida 32310, USA (Received 10 October 2017; accepted 8 December 2017)
Si nanoparticles and multi-walled carbon nanotubes (MWNTs) were combined using the simple, inexpensive, and scalable approach involving ultrasonication and positive-pressure filtration to generate binder-free freestanding flexible Si–MWNT (Si–MW) composite paper anodes for Li-ion batteries. Through controlling the Si/carbon nanotube (CNT) weight ratio, the composite with 3:2 Si/CNT ratio exhibited the optimal balance between the high capacity of SiNPs and high conductivity and structural stabilization quality of MWNTs, leading to high rate capability as well as specific capacity and cyclability surpassing the conventional slurry-cast SiNP electrode using binder and current collector and other complicated freestanding Si/carbon composite designs. After 100 cycles, our electrode retained a capacity of 1170 mA h/g at 100 mA/g and 750 mA h/g at 500 mA/g. Moreover, a different electrolyte composition enabled a reversible capacity of 1300 mA h/g at 100 mA/g after 100 cycles. The freestanding feature of our electrodes is promising for enhanced energy density of Li-ion cells.
I. INTRODUCTION
Li-ion batteries (LIBs) have become the dominant power source for portable electronics and are also used in electric vehicles (EVs), which are gaining traction due to the environmental concerns caused by conventional fuel-powered vehicles. To facilitate the wide application of EVs, their range anxiety issues must be addressed, which necessitate the search for novel electrode materials that are able to endow LIBs with higher capacity and energy density. Extensive R&D efforts have been devoted to developing new high-capacity anode materials, like tin (993 mA h/g, Li4.4Sn), germanium (1620 mA h/g, Li4.4Ge), and silicon (4200 mA h/g, Li4.4Si), as alternatives to the current graphite anode (372 mA h/g, LiC6). Among them, Si is undoubtedly a promising candidate
Contributing Editor: Sung-Yoon Chung a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.475
due to its high capacity and abundance. However, Si suffers from large intrinsic volumetric expansion (;400%) upon Li insertion and contraction upon Li extraction, whi
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