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Kim J.-H.,Ulsan National Institute of Science and Technology | Choi E.-S.,LG Corp | Yu H.K.,LG Corp | Kim J.H.,LG Corp | And 4 more authors.
Journal of Power Sources | Year: 2013

Porous structure-tuned cellulose nanofiber paper separators (designated as S-CNP separators) are demonstrated as a promising alternative to commercial polyolefin separators for use in lithium-ion batteries. A new architectural strategy based on colloidal silica (SiO2) nanoparticle-assisted structural control is presented to overcome the difficulty in forming controllable porous structure of pure cellulose nanofiber paper separators (designated as CNP separators) from densely-packed cellulose nanofibers (CNFs). The new S-CNP separators proposed herein incorporate SiO2 nanoparticles as a CNF-disassembling agent (i.e., as non-conductive spacer particles). This structural uniqueness allows loose packing of CNFs, thereby facilitating the evolution of more porous structure. The unusual porous structure of S-CNP separators can be fine-tuned by varying SiO2 contents in the CNF suspension. Notably, the S-CNP separator (fabricated with 5 wt.% SiO2 content) exhibits the highest ionic conduction due to the well-balanced combination of nanoporous structure and separator thickness, thus contributing to excellent cell performance. This study underlines that the colloidal SiO2 nanoparticle-directed structural tuning of CNPs offers a promising route for the fabrication of advanced paper separators with optimized attributes and functionality. © 2013 Elsevier B.V. All rights reserved.

Choi K.-H.,Ulsan National Institute of Science and Technology | Cho S.-J.,Ulsan National Institute of Science and Technology | Chun S.-J.,Korea forest Research Institute | Yoo J.T.,Korea Institute of Industrial Technology | And 7 more authors.
Nano Letters | Year: 2014

The rapidly approaching smart/wearable energy era necessitates advanced rechargeable power sources with reliable electrochemical properties and versatile form factors. Here, as a unique and promising energy storage system to address this issue, we demonstrate a new class of heterolayered, one-dimensional (1D) nanobuilding block mat (h-nanomat) battery based on unitized separator/electrode assembly (SEA) architecture. The unitized SEAs consist of wood cellulose nanofibril (CNF) separator membranes and metallic current collector-/polymeric binder-free electrodes comprising solely single-walled carbon nanotube (SWNT)-netted electrode active materials (LiFePO4 (cathode) and Li4Ti5O12 (anode) powders are chosen as model systems to explore the proof of concept for h-nanomat batteries). The nanoporous CNF separator plays a critical role in securing the tightly interlocked electrode-separator interface. The SWNTs in the SEAs exhibit multifunctional roles as electron conductive additives, binders, current collectors and also non-Faradaic active materials. This structural/physicochemical uniqueness of the SEAs allows significant improvements in the mass loading of electrode active materials, electron transport pathways, electrolyte accessibility and misalignment-proof of separator/electrode interface. As a result, the h-nanomat batteries, which are easily fabricated by stacking anode SEA and cathode SEA, provide unprecedented advances in the electrochemical performance, shape flexibility and safety tolerance far beyond those achievable with conventional battery technologies. We anticipate that the h-nanomat batteries will open 1D nanobuilding block-driven new architectural design/opportunity for development of next-generation energy storage systems. © 2014 American Chemical Society.

Kim J.-M.,Ulsan National Institute of Science and Technology | Park C.-H.,Ulsan National Institute of Science and Technology | Wu Q.,Louisianan State University Agricultural Center | Lee S.-Y.,Ulsan National Institute of Science and Technology
Advanced Energy Materials | Year: 2016

The cathode active particles-embedded polyacrylonitrile nanofibers/multiwalled carbon nanotubes heteronanomat cathode (HM cathode) is demonstrated as an effective and versatile electrode platform to address the long-standing challenges of conventional cathodes. The material/structure uniqueness of the HM cathode enables substantial improvements in rate capability, cycling performance and, most notably, areal capacity far beyond those accessible with conventional cathode technologies. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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