Ju-Myung Kim

Conducting Polymer-Skinned Electroactive Materials of Lithium-Ion Batteries: Ready for Monocomponent Electrodes without Additional Binders and Conductive Agents

Rapid growth of mobile and even wearable electronics is in pursuit of high-energy-density lithium-ion batteries. One simple and facile way to achieve this goal is the elimination of nonelectroactive components of electrodes such as binders and conductive agents. Here, we present a new concept of monocomponent electrodes comprising solely electroactive materials that are wrapped with an insignificant amount (less than 0.4 wt %) of conducting polymer (PEDOT:PSS or poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate)). The PEDOT:PSS as an ultraskinny surface layer on electroactive materials (LiCoO2 (LCO) powders are chosen as a model system to explore feasibility of this new concept) successfully acts as a kind of binder as well as mixed (both electrically and ionically) conductive film, playing a key role in enabling the monocomponent electrode. The electric conductivity of the monocomponent LCO cathode is controlled by simply varying the PSS content and also the structural conformation (benzoid-favoring coil structure and quinoid-favoring linear or extended coil structure) of PEDOT in the PEDOT:PSS skin. Notably, a substantial increase in the mass-loading density of the LCO cathode is realized with the PEDOT:PSS skin without sacrificing electronic/ionic transport pathways. We envisage that the PEDOT:PSS-skinned electrode strategy opens a scalable and versatile route for making practically meaningful binder-/conductive agent-free (monocomponent) electrodes.

Multifunctional semi-interpenetrating polymer network-nanoencapsulated cathode materials for high-performance lithium-ion batteries

As a promising power source to boost up advent of next-generation ubiquitous era, high-energy density lithium-ion batteries with reliable electrochemical properties are urgently requested. Development of the advanced lithium ion-batteries, however, is staggering with thorny problems of performance deterioration and safety failures. This formidable challenge is highly concerned with electrochemical/thermal instability at electrode material-liquid electrolyte interface, in addition to structural/chemical deficiency of major cell components. Herein, as a new concept of surface engineering to address the abovementioned interfacial issue, multifunctional conformal nanoencapsulating layer based on semi-interpenetrating polymer network (semi-IPN) is presented. This unusual semi-IPN nanoencapsulating layer is composed of thermally-cured polyimide (PI) and polyvinyl pyrrolidone (PVP) bearing Lewis basic site. Owing to the combined effects of morphological uniqueness and chemical functionality (scavenging hydrofluoric acid that poses as a critical threat to trigger unwanted side reactions), the PI/PVP semi-IPN nanoencapsulated-cathode materials enable significant improvement in electrochemical performance and thermal stability of lithium-ion batteries.

Agarose-biofunctionalized, dual-electrospun heteronanofiber mats: toward metal-ion chelating battery separator membranes

A facile and efficient way to impart compelling chemical functionality is the utilization of bio-related materials that are easily accessible from natural products. Here, inspired by anomalous physicochemical features and natural abundance of agarose, we demonstrate a new class of agarose-biofunctionalized, dual-electrospun heteronanofiber mats as a chemically active separator membrane for high-performance lithium-ion batteries. The agarose-enabled metal ion chelation effect of the separator membrane, in combination with its highly porous structure and superior electrolyte wettability, provides unprecedented improvement in cell performance far beyond those accessible with conventional battery separator membranes.

Multifunctional natural agarose as an alternative material for high-performance rechargeable lithium-ion batteries

Agarose, which is one of the natural polysaccharides that is generally extracted from seaweed, has recently attracted great attention as an environmentally-benign building element for a wide variety of applications. Notably, its disaccharide repeating units bearing ether/hydroxyl groups carry unprecedented performance benefits far beyond those accessible with traditional synthetic polymers. Herein, intrigued by these unusual chemical features of agarose, we explore its potential applicability as an alternative electrode binder and also as a carbon source for high-performance rechargeable lithium-ion batteries. The agarose binder enables silicon (Si) active materials to be tightly adhered to copper foil current collectors, thereby providing significant improvement in the electrochemical performance of the resulting Si anode (specific capacity = 2000 mA h g−1 and capacity retention after 200 cycles = 71%). In addition, agarose can be exploited as a cathode binder. An LiMn2O4 cathode containing agarose binder shows an excellent cell performance (initial coulombic efficiency of ∼96.2% and capacity retention after 400 cycles of ∼100%). Through the selective carbonization of Si-dispersed agarose, Si/C (hard carbon) composite active materials are successfully synthesized. Eventually, the Si/C composite anode and the LiMn2O4 cathode mentioned above are assembled to produce a full cell featuring the use of agarose as an alternative green material. Benefiting from the exceptional multifunctionality of agarose, the full cell presents a stable cycling performance (capacity retention after 50 cycles of >87%).

Beyond Slurry-Cast Supercapacitor Electrodes: PAN/MWNT Heteromat-Mediated Ultrahigh Capacitance Electrode Sheets

Supercapacitors (SCs) have garnered considerable attention as an appealing power source for forthcoming smart energy era. An ultimate challenge facing the SCs is the acquisition of higher energy density without impairing their other electrochemical properties. Herein, we demonstrate a new class of polyacrylonitrile (PAN)/multi-walled carbon tube (MWNT) heteromat-mediated ultrahigh capacitance electrode sheets as an unusual electrode architecture strategy to address the aforementioned issue. Vanadium pentoxide (V2O5) is chosen as a model electrode material to explore the feasibility of the suggested concept. The heteromat V2O5 electrode sheets are produced through one-pot fabrication based on concurrent electrospraying (for V2O5 precursor/MWNT) and electrospinning (for PAN nanofiber) followed by calcination, leading to compact packing of V2O5 materials in intimate contact with MWNTs and PAN nanofibers. As a consequence, the heteromat V2O5 electrode sheets offer three-dimensionally bicontinuous electron (arising from MWNT networks)/ion (from spatially reticulated interstitial voids to be filled with liquid electrolytes) conduction pathways, thereby facilitating redox reaction kinetics of V2O5 materials. In addition, elimination of heavy metallic foil current collectors, in combination with the dense packing of V2O5 materials, significantly increases (electrode sheet-based) specific capacitances far beyond those accessible with conventional slurry-cast electrodes.

Postactivation treatment with nocodazole maintains normal nuclear ploidy of cloned pig embryos by increasing nuclear retention and formation of single pronucleus

The objective of this study was to investigate the effects of postactivation treatment with nocodazole on morphologic changes of donor nuclei and in vitro and in vivo development of somatic cell nucleus transfer (SCNT) embryos in pigs (Sus scrofa). Somatic cell nucleus transfer oocytes were either untreated (control) or treated with nocodazole or demecolcine after electric activation, then cultured in vitro or transferred to surrogate pigs. Treatment with nocodazole (30%) and demecolcine (29%) after electric activation improved embryo development to the blastocyst stage compared with the control (16%). The rate of oocytes that formed single clusters of chromosomes or a pronucleus 4h after activation was higher after treatment with nocodazole (82%) and demecolcine (86%) than under the control conditions (66%), and this tendency was not altered even 12h after activation. Pseudo-polar body extrusion was inhibited by nocodazole and demecolcine, and the rate of embryos with diploid chromosomes was higher after treatment with nocodazole (86%) and demecolcine (77%) than under control conditions (58%). Nocodazole treatment resulted in a farrowing rate of 50% with a 1.7% efficiency of piglet production, whereas controls showed a farrowing rate of 60% and a production efficiency of 3.8%. Our results demonstrate that postactivation treatment with nocodazole maintains normal nuclear ploidy of cloned embryos likely by increasing nuclear retention and formation of single pronuclei. In vivo development could be achieved from the transfer of nocodazole-treated embryos but showed some defects compared with control.

Facile surface modification of high-voltage lithium-ion battery cathode materials with electroconductive zinc antimonate colloidal nanoparticles

The high-voltage cell approach has garnered a great deal of attention as a simple and effective way to increase the energy density of lithium-ion batteries. Here, we demonstrate a new class of surface modification based on electroconducitve zinc antimonate (AZO, ZnSb2O6) colloidal nanoparticles as a facile and scalable interface engineering strategy for high-voltage cathode materials. The electroconductive AZO colloidal nanoparticles are directly introduced on the surface of cathode materials via simple one-pot solution coating followed by post heat-treatment, in contrast to traditional surface modification using metal oxide precursors that often requires complex sol–gel reaction and high-temperature calcination. LiCoO2 (LCO) powder is chosen as a model cathode material to explore the feasibility of AZO nanoparticle coatings. A salient feature of the AZO nanoparticle layers, as compared to conventional metal oxides-based coating layers that are electrically inert, is the provision of electronic conduction, which thus boosts the electronic conductivity of LCO powders. This beneficial effect of the AZO nanoparticle layers, in collaboration with their contribution to suppressing unwanted interfacial side reactions between delithiated LCO and liquid electrolytes, enables significant improvement in high-voltage (here, 4.4 V) cell performance (AZO nanoparticle-deposited LCO (AZO–LCO) vs. pristine LCO: capacity retention after 50th cycle = 84% vs. 28%, discharge rate capability (2.0 C/0.2 C) = 78% vs. 55%). The potential application of AZO–LCO in high-voltage cells is also discussed with an in-depth consideration of the variation in AC impedance and electrode polarization of cells during cycling.

Molecularly designed, dual-doped mesoporous carbon/SWCNT nanoshields for lithium battery electrode materials

Formidable challenges facing lithium-ion rechargeable batteries, which involve performance degradations and safety failures during charge/discharge cycling, mostly arise from electrode–electrolyte interface instability. Here, as a polymeric ionic liquid (PIL)-mediated interfacial control strategy to address this long-standing issue, we demonstrate a new class of molecularly designed, ion/electron-conductive nanoshields based on single-walled carbon nanotube (SWCNT)-embedded, dual-doped mesoporous carbon (referred to as “SMC”) shells for electrode materials. The SMC shell is formed on cathode materials through solution deposition of the SWCNT/PIL mixture and subsequent carbonization. The PIL (denoted as “PVIm[DS]”) synthesized in this study consists of poly(1-vinyl-3-ethylimidazolium) cations and dodecyl sulfate counter anions, whose molecular structures are rationally designed to achieve the following multiple functions: (i) precursor for the conformal/continuous nanothickness carbon shell, (ii) dual (N and S)-doping source, (iii) porogen for the mesoporous structure, and (iv) SWCNT dispersant. Driven by such chemical/structural uniqueness, the SMC shell prevents direct exposure of cathode materials to bulk liquid electrolytes while facilitating redox reaction kinetics. As a consequence, the SMC-coated cathode materials enable significant improvements in cell performance and also thermal stability. We envision that the SMC shell can be suggested as a new concept of effective and versatile surface modification strategy for next-generation high-performance electrode materials.

One-pot surface engineering of battery electrode materials with metallic SWCNT-enriched, ivy-like conductive nanonets

A longstanding challenge facing energy conversion/storage materials is their low electrical conductivity, which often results in unwanted sluggish electrochemical reactions. Here, we demonstrate a new class of one-pot surface engineering strategy based on metallic single-walled carbon nanotube (mSWCNT)-enriched, ivy-like conductive nanonets (mSC nanonets). The mSC nanonets are formed on the surface of electrode materials through a poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO)-assisted sonication/filtration process. PFO is known as a dispersant for SWCNTs that shows a higher affinity for semiconducting SWCNTs (sSWCNTs) than for mSWCNTs. Driven by this preferential affinity of PFO, sSWCNTs are separated from mSWCNTs in the form of sSWCNT/PFO hybrids, and the resulting enriched mSWCNTs are uniformly deposited on electrode materials in the form of ivy-like nanonets. Various electrode materials, including lithium-ion battery cathodes/anodes and perovskite catalysts, are chosen to explore the feasibility of the proposed concept. Due to their ivy-like conductive network, the mSC nanonets increase the electronic conductivity of the electrode materials without hindering their ionic transport, eventually enabling significant improvements in their redox reaction rates, charge/discharge cyclability, and bifunctional electrocatalytic activities. These exceptional physicochemical advantages of the mSC nanonets, in conjunction with the simplicity/versatility of the one-pot surface engineering process, offer a new and facile route to develop advanced electrode materials with faster electrochemical reaction kinetics.

In vitro-growth and Gene Expression of Porcine Preantral Follicles Retrieved by Different Protocols

This study was conducted to determine how the isolation method of the porcine preantral follicles influenced the following follicular growth in vitro. Mechanical and enzymatical isolations were used for retrieving the follicles from prepubertal porcine ovaries, and in vitro-growth of the follicles and the expression of folliculogenesis-related genes were subsequently monitored. The enzymatic retrieval with collagenase treatment returned more follicles than the mechanical retrieval, while the percentage of morphologically normal follicles was higher with mechanical retrieval than with enzymatic retrieval. After 4 days of culture, mechanically retrieved, preantral follicles yielded more follicles with normal morphology than enzymatically retrieved follicles, which resulted in improved follicular growth. The mRNA expression of FSHR, LHR Cx43, DNMT1 and FGFR2 genes was significantly higher after culture of the follicles retrieved mechanically. These results suggest that mechanical isolation is a better method of isolating porcine preantral follicles that will develop into competent oocytes in in vitro culture.