Jason Fang

Nanoparticle-coated separators for lithium-ion batteries with advanced electrochemical performance

We report a simple, scalable approach to improve the interfacial characteristics and, thereby, the performance of commonly used polyolefin based battery separators. The nanoparticle-coated separators are synthesized by first plasma treating the membrane in oxygen to create surface anchoring groups followed by immersion into a dispersion of positively charged SiO(2) nanoparticles. The process leads to nanoparticles electrostatically adsorbed not only onto the exterior of the surface but also inside the pores of the membrane. The thickness and depth of the coatings can be fine-tuned by controlling the ζ-potential of the nanoparticles. The membranes show improved wetting to common battery electrolytes such as propylene carbonate. Cells based on the nanoparticle-coated membranes are operable even in a simple mixture of EC/PC. In contrast, an identical cell based on the pristine, untreated membrane fails to be charged even after addition of a surfactant to improve electrolyte wetting. When evaluated in a Li-ion cell using an EC/PC/DEC/VC electrolyte mixture, the nanoparticle-coated separator retains 92% of its charge capacity after 100 cycles compared to 80 and 77% for the plasma only treated and pristine membrane, respectively.

A comparative study of ordered mesoporous carbons with different pore structures as anode materials for lithium-ion batteries

In this study, ordered mesoporous carbons (OMCs) with different pore structures, namely 2D hexagonal CMK-3 and 3D cubic CMK-8 prepared by the nanocasting method using mesoporous silicas SBA-15 and KIT-6 as hard templates, respectively, in their pure forms are used as anode materials in lithium ion batteries (LIBs) to evaluate the role of mesoporous structures in their electrochemical performances. The results demonstrate that the CMK-8 electrode exhibits a higher reversible capacity and better cycling stability and rate capability, as compared to the CMK-3 electrode, due to its unique 3D cubic mesostructure. The initial capacities of 1884 and 964 mA h g−1 are obtained for the CMK-8 and CMK-3 electrodes, respectively. The CMK-8 electrode exhibits a higher capacity value (around 37.4% higher) than the CMK-3 electrode at the 100th cycle. The enhanced electrochemical performance of CMK-8 is mainly attributable to its unique 3D channel networks, which are beneficial for efficient Li storage and volume change. Although CMK-3 is the most investigated OMCs used in LIBs, herein we demonstrate that CMK-8 is a better carbon matrix for the fabrication of the electrode materials composed of mesoporous carbons.

Lead-salt quantum-dot ionic liquids.

The electronic energies of lead–salt quantum dots (QDs) are determined primarily by quantum confinement due to their large exciton Bohr radii. The fundamental electronic structure of the QDs (PbS and PbSe) has been worked out by Kang et al., and now research with these materials is turning towards applications. For instance, lead–salt QDs have been used as active materials in photovoltaic devices due to their size-tunable infrared (IR) absorption. They are also efficient IR emitters and could be used in biomedical imaging and in electroluminescent devices. In order for QDs to realize their full potential, their stability (e.g., photostability) and compatibility with other materials must be improved. Accordingly, much effort is devoted to surface passivation and functionalization of QDs, with increasing attention being paid to the use of ionic liquids to passivate the QD surface. Using certain ionic liquid ligands, solid materials can be transferred to a new state that exhibits liquidlike behavior at room temperature. To date, metal nanoparticles and oxide nanoparticles have been functionalized using a polymer ionic liquid. Some semiconductor nanoparticles (e.g., CdSe) functionalized using small-molecule ionic ligands have been reported. In this work, we report the first lead–salt (PbS, PbSe, and PbTe) QD ionic liquid where polymer ionic liquid ligands are used as capping ligands for QDs. The resulting amphiphilic QD ionic liquids exhibit fluidlike behavior at room temperature, even in the absence of solvents. The ionic liquid capping ligands also dramatically improve the photostability of

Superhydrophilic and solvent resistant coatings on polypropylene fabrics by a simple deposition process

A simple, yet general coating method to plasma treated polymeric substrates is presented. The method is based on electrostatic interactions between the surface functionalized nanoparticles and the charged substrate and leads to stable and solvent resistant multilayer coatings. The coatings render polypropylene (PP) hydrophilic and in the case of PP fabric superhydrophilic. The superhydrophilicity is attributed to the topography and increased roughness of the fabric compared to a planar, smooth substrate.

A new highly conductive organic-inorganic solid polymer electrolyte based on a di-ureasil matrix doped with lithium perchlorate

A new hybrid organic-inorganic polymer electrolyte based on poly(propylene glycol) tolylene 2,4-diisocyanate terminated (PPGTDI), poly(propylene glycol)-block–poly(ethylene glycol)-block-poly(propylene glycol) bis(2-aminopropyl ether) (ED2000) and 3-isocyanatepropyltriethoxysilane (ICPTES) has been synthesized and characterized. A maximum ionic conductivity value of 1.0 × 10−4 S cm−1 at 30 °C and 1.1 × 10−3 S cm−1 at 80 °C is achieved for the hybrid electrolyte with a [O]/[Li] ratio of 32. The conductivity mechanism changes from Arrhenius to Vogel-Tamman-Fulcher (VTF) behavior with the increase in temperature from 20 to 80 °C. The present hybrid electrolyte system offers a remarkable improvement in ionic conductivity by at least one order of magnitude higher than the previously reported organic-inorganic electrolytes. The 7Li NMR (nuclear magnetic resonance) results reveal that there exists a strong correlation between the dynamic properties of the charge carriers and the polymer matrix. Two Li+ local environments are identified, for the first time, in such a di-ureasil based polymer electrolyte. The electrochemical stability window is found to be in the range of 4.6–5.0 V, which ensures that the present hybrid electrolyte is a potential polymer electrolyte for solid-state rechargeable lithium ion batteries.

Bifunctional separator as a polysulfide mediator for highly stable Li–S batteries

The shuttling process involving lithium polysulfides is one of the major factors responsible for the degradation in capacity of lithium–sulfur batteries (LSBs). Herein, we demonstrate a novel and simple strategy—using a bifunctional separator, prepared by spraying poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) on a pristine separator—to obtain long-cycle LSBs. The negatively charged SO3− groups present in PSS act as an electrostatic shield for soluble lithium polysulfides through mutual coulombic repulsion, whereas PEDOT provides chemical interactions with insoluble polysulfides (Li2S, Li2S2). The dual shielding effect can provide an efficient protection from the shuttling phenomenon by confining lithium polysulfides to the cathode side of the battery. Moreover, coating with PEDOT:PSS transforms the surface of the separator from hydrophobic to hydrophilic, thereby improving the electrochemical performance. We observed an ultralow decay of 0.0364% per cycle when we ran the battery for 1000 cycles at 0.25C—far superior to that of the pristine separator and one of the lowest recorded values reported at a low current density. We examined the versatility of our separator by preparing a flexible battery that functioned well under various stress conditions; it displayed flawless performance. Accordingly, this economical and simple strategy appears to be an ideal platform for commercialization of LSBs.

Synthesis and characterization of a highly conductive organic–inorganic hybrid polymer electrolyte based on amine terminated triblock polyethers and its application in electrochromic devices

A new highly ion conductive organic–inorganic hybrid electrolyte based on the reaction of triblock co-polymer poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) bis(2-aminopropyl ether) (ED2003) with 3-(glycidyloxypropyl)trimethoxysilane (GLYMO) and followed by co-condensation with 2-methoxy(polyethyleneoxy)propyl trimethoxysilane (MPEOPS) in the presence of LiClO4 was synthesized by a sol–gel process and characterized by a variety of experimental techniques. The maximum ionic conductivities of 1.1 × 10−4 S cm−1 at 30 °C and 6.0 × 10−4 S cm−1 at 80 °C were obtained for the hybrid electrolyte with a [O]/[Li] ratio of 24. The conductivity mechanism changed from Arrhenius at lower temperatures to Vogel–Tamman–Fulcher (VTF) behavior at higher temperatures. The results of solid-state NMR confirmed the structural framework of the hybrids, and provided a microscopic view of the effects of salt concentrations on the dynamic behavior of the polymer chains. The electrochemical stability window was found to be around 3.7–4.5 V, which is sufficient for electrochemical device applications. Preliminary tests performed with prototype electrochromic devices (ECDs) comprising the hybrid electrolyte with various [O]/[Li] ratios and mesoporous WO3 as the cathode layer are extremely encouraging. The best performance device exhibits an optical density change of 0.58, coloration efficiency of 375 cm2 C−1 and a good cycle life with the hybrid electrolyte with a [O]/[Li] ratio of 24. The present hybrid electrolyte offers a remarkable ionic conductivity and coloration efficiency in the solid state than previously reported organic–inorganic hybrid electrolytes.

High-performance graphene/sulphur electrodes for flexible Li-ion batteries using the low-temperature spraying method.

Elementary sulphur (S) has been shown to be an excellent cathode material in energy storage devices such as Li-S batteries owing to its very high capacity. The major challenges associated with the sulphur cathodes are structural degradation, poor cycling performance and instability of the solid-electrolyte interphase caused by the dissolution of polysulfides during cycling. Tremendous efforts made by others have demonstrated that encapsulation of S materials improves their cycling performance. To make this approach practical for large scale applications, the use of low-cost technology and materials has become a crucial and new focus of S-based Li-ion batteries. Herein, we propose to use a low temperature spraying process to fabricate graphene/S electrode material, where the ink is composed of graphene flakes and the micron-sized S particles prepared by grinding of low-cost S powders. The S particles are found to be well hosted by highly conductive graphene flakes and consequently superior cyclability (∼70% capacity retention after 250 cycles), good coulombic efficiency (∼98%) and high capacity (∼1500 mA h g(-1)) are obtained. The proposed approach does not require high temperature annealing or baking; hence, another great advantage is to make flexible Li-ion batteries. We have also demonstrated two types of flexible batteries using sprayed graphene/S electrodes.

A new organic–inorganic hybrid electrolyte based on polyacrylonitrile, polyether diamine and alkoxysilanes for lithium ion batteries: synthesis, structural properties, and electrochemical characterization

A new type of organic–inorganic hybrid polymer electrolyte based on poly(propylene glycol)-block-poly(ethylene glycol)-block-poly-(propylene glycol)bis(2-aminopropyl ether), polyacrylonitrile (PAN), 3-(glycidyloxypropyl)trimethoxysilane (GLYMO) and 3-(aminopropyl)trimethoxysilane (APTMS) complexed with LiClO4 via the co-condensation of organosilicas was synthesized. The structural and electrochemical properties of the materials were systematically investigated by a variety of techniques including differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), multinuclear (13C, 29Si, 7Li) solid-state NMR, AC impedance, linear sweep voltammetry (LSV) and charge–discharge measurement. A maximum ionic conductivity value of 7.4 × 10−5 S cm−1 at 30 °C and 4.6 × 10−4 S cm−1 at 80 °C is achieved for the solid hybrid electrolyte. The 7Li NMR measurements reveal the strong correlation of the lithium cation and the polymer matrix, and the presence of two lithium local environments. After swelling in an electrolyte solvent, the plasticized hybrid membrane exhibited a maximum ionic conductivity of 6.4 × 10−3 S cm−1 at 30 °C. The good value of the electrochemical stability window (∼4.5 V) makes the plasticized hybrid electrolyte membrane promising for electrochemical device applications. The preliminary lithium ion battery testing shows an initial discharge capacity value of 123 mA h g−1 and a good cycling performance with the plasticized hybrid electrolyte.

Modified Separator Performing Dual Physical/Chemical Roles to Inhibit Polysulfide Shuttle Resulting in Ultrastable Li–S Batteries

In this paper we describe a modified (AEG/CH) coated separator for Li-S batteries in which the shuttling phenomenon of the lithium polysulfides is restrained through two types of interactions: activated expanded graphite (AEG) flakes interacted physically with the lithium polysulfides, while chitosan (CH), used to bind the AEG flakes on the separator, interacted chemically through its abundance of amino and hydroxyl functional groups. Moreover, the AEG flakes facilitated ionic and electronic transfer during the redox reaction. Live H-cell discharging experiments revealed that the modified separator was effective at curbing polysulfide shuttling; moreover, X-ray photoelectron spectroscopy analysis of the cycled separator confirmed the presence of lithium polysulfides in the AEG/CH matrix. Using this dual functional interaction approach, the lifetime of the pure sulfur-based cathode was extended to 3000 cycles at 1C-rate (1C = 1670 mA/g), decreasing the decay rate to 0.021% per cycle, a value that is among the best reported to date. A flexible battery based on this modified separator exhibited stable performance and could turn on multiple light-emitting diodes. Such modified membranes with good mechanical strength, high electronic conductivity, and anti-self-discharging shield appear to be a scalable solution for future high-energy battery systems.