Graphene Oxide Involved Air-Controlled Electrospray for Uniform, Fast, Instantly Dry, and Binder-Free Electrode Fabrication

Reprecipitation: A Rapid Synthesis of Micro-Sized Silicon-Graphene Composites for Long-lasting Lithium-Ion Batteries

Silicon microparticles (SiMPs) have gained significant attention as a lithium-ion battery anode material due to their 10 times higher theoretical capacity compared to conventional graphite anodes as well as their much lower production cost than silicon nanoparticles (SiNPs). However, SiMPs have suffered from poorer cycle life relative to SiNPs because their larger size makes them more susceptible to volume changes during charging and discharging. Creating a wrapping structure in which SiMPs are enveloped by carbon layers has proven to be an effective strategy to significantly improve the cycling performance of SiMPs. However, the synthesis processes are complex and time-/energy-consuming and therefore not scalable. In this study, a wrapping structure is created by using a simple, rapid, and scalable "modified reprecipitation method". Graphene oxide (GO) and SiMP dispersion in tetrahydrofuran is injected into n-hexane, in which GO and SiMP by themselves cannot disperse. GO and SiMP therefore aggregate and precipitate immediately after injection to form a wrapping structure. The resulting SiMP/GO film is laser scribed to reduce GO to a laser-scribed graphene (LSG). Simultaneously, SiOx and SiC protection layers form on the SiMPs through the laser process, which alleviates severe volume change. Owing to these desirable characteristics, the modified reprecipitation method successfully doubles the cycle life of SiMP/graphene composites compared to the simple physically mixing method (50.2% vs. 24.0% retention at the 100th cycle). The modified reprecipitation method opens a new synthetic strategy for SiMP/carbon composites.

Designing interphases for practical aqueous zinc flow batteries with high power density and high areal capacity

Aqueous zinc flow batteries (AZFBs) with high power density and high areal capacity are attractive, both in terms of cost and safety. A number of fundamental challenges associated with out-of-plane growth and undesirable side reactions on the anode side, as well as sluggish reaction kinetics and active material loss on the cathode side, limit practical deployment of these batteries. We investigated artificial interphases created using a simple electrospray methodology as a strategy for addressing each of these challenges. The effectiveness of the electrospray interphases in full cell zinc-iodine flow batteries was evaluated and reported; it is possible to simultaneously achieve high power density [115 milliwatts per square centimeter (mW/cm²)] and high areal capacity [25 milliampere hour per square centimeter (mA·hour/cm²)]. Last, we extended it to aqueous zinc-bromine and zinc-vanadium flow batteries of contemporary interest. It is again found that high power density (255 and 260 mW/cm², respectively) and high areal capacity (20 mA·hour/cm²) can be simultaneously achieved in AZFBs.

Prelithiation Reagents and Strategies on High Energy Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have been widely employed in energy-storage applications owing to the relatively higher energy density and longer cycling life. However, they still need further improvement especially on the energy density to satisfy the increasing demands on the market. In this respect, the irreversible capacity loss (ICL) in the initial cycle is a critical challenge due to the lithium loss during the formation of solid electrolyte interphase (SEI) layer on the anode surface. The strategy of prelithiation was then proposed to compensate for the ICL in the anode and recover the energy density. Here, various methods of the prelithiation are summarized and classified according to the basic working mechanism. Further, considering the critical importance and promising progress of prelithiation in both fundamental research and real applications, this Review article is intended to discuss the considerations involved in the selection of prelithiation reagents/strategies and the electrochemical performance in full-cells. Moreover, insights are provided regarding the practical application prospects and the challenges that still need to be addressed.

Achieving Superhydrophobic Surfaces via Air-Assisted Electrospray

Superhydrophobic surface is an enabling technology in numerous emerging and practical applications such as self-cleaning, anticorrosion, antifouling, anti-icing coatings, and oil-water separation. Here, we report a facile air-assisted electrospray approach to achieve a superhydrophobic surface by systematically studying spray conditions and the chemistry of a coating precursor solution consisting of silicon dioxide nanoparticles, polyacrylonitrile, and N,N-dimethylformamide. The wettability behavior of the surface was analyzed with contact angle measurement and correlated with surface structures. The superhydrophobic coating exhibits remarkable water and oil repellent characteristics, as well as good robustness against abrasion and harsh chemical conditions. This air-assisted electrospray technique has shown great control over the coating process and properties and thus can be potentially used for various advanced industrial applications for self-cleaning and anticorrosion surfaces.

High-performance bag filter with a super-hydrophobic microporous polytetrafluoroethylene layer fabricated by air-assisted electrospraying

Reducing PM emissions from industrial sites has become increasingly important as the adverse health effects of particulate matter have been demonstrated by multiple epidemiological and toxicological studies. High-performance bag filters are often used for this purpose. We fabricated polytetrafluoroethylene (PTFE) nanoparticle (NP)-coated high-efficiency bag filters using air-assisted electrospraying (AAES) technology. AAES functionalized with a combination of airflow drag force and an applied electric field facilitates high-throughput without requiring additional purification or preparation process of a PTFE emulsion. PTFE NPs form a unique three-dimensional microporous structure on a foam-filter medium, enhancing mechanical filtration performance (diffusion and interception). Moreover, the surface hydrophobicity was significantly improved as the PTFE NPs covered the bag filter surface. These factors highlight the feasibility of large-scale implementation of PTFE NP-coated bag filters for reducing PM emissions from industrial sources.

A prospect of cost-effective handling and transportation of graphene oxides: folding and redispersion of graphene oxide microsheets

Controlling the assembly of 2D materials such as graphene oxides (GO) has a significant impact on their properties and performance. One of the critical issues on the processing and handling of GO is that they need to be in dilution solution (0.5 to 2.5 wt%) to maintain their high degree of exfoliation and dispersion. As a result, the shipment of GO in large quantity involves a huge volume of solvent (water) and thus the transportation costs for large sales volume would become extremely high. Through cross-sectional scanning electron microscopy and polarized optical microscopy together with x-ray diffraction and small-angle x-ray scattering studies, we demonstrated that the assembly and structure of GO microsheets can be preserved without restacking, when assembled GO via water-based wet spinning are re-dispersed into solution. A couple of alkyl ammonium bromides, CTAB and TBAB, as well as NaOH, were examined as coagulants and the resulting fibers were redispersed in an aqueous solution. The redispersed solution of fibers that were wet-spun into the commonly used CTAB and TBAB coagulation baths, maintained their physico-chemical properties (similar to the original GO dispersion) however, did not reveal preservation of liquid crystallinity. Meanwhile, the redispersed fibers that were initially spun into NaOH coagulation bath were able to maintain their liquid crystallinity if the lateral size of the GO sheets was large. Based on these findings, a cost-effective solid handling approach is devised which involves (i) processing GO microsheets in solution into folded layers in solid-state, (ii) transporting assembled GO to the customers, and (iii) redispersion of folded GO into a solution for their use. The proposed solid handling of GO followed by redispersion into solution can greatly reduce the transportation costs of graphene oxide materials by reducing the transportation volume by more than 90%.

Yolk-void-shell Si-C nano-particles with tunable void size for high-performance anode of lithium ion batteries

Silicon is a promising anode for new-generation lithium ion batteries due to high theoretical lithium storage capacity (4200 mAh g^-1). However, the low conductivity and large volumetric expansion hamper the commercialization of the silicon anode. In this case, we present a yolk-void-shell Si-C anode (denoted as Si@Void@C), which is synthesized through nano-Si oxidation, surface carbonization and etching of SiO _x . The void can be fabricated only by the self-generation and etching of SiO _x layer on the Si surface, without the help of template materials. Moreover, the void size can be adjusted only by means of the annealing temperature, which can be easily and precisely operated. The Si@Void@C/rGO with void size of 5 nm offers a discharge capacity of 1294 mAh g^-1 after 100 cycles at a current density of 500 mA g^-1. These enhanced performances can be ascribed to an appropriate size (5 nm) of void space which sufficiently accommodates the silicon volume expansion and stabilizes the carbon shell. At the same time, the voids effectively inhibit the growth of the solid electrolyte interface layer by depressing the decomposition of the electrolyte on the surface of Si in Si@Void@C/rGO. Furthermore, interfaces between Si@Void@C particles and rGO sheets construct bridges for electrons' conduction. In general, the present work provides a viable strategy for synthesizing silicon-carbon anode materials with long life.

Facile Production of Graphenic Microsheets and Their Assembly via Water-Based, Surfactant-Aided Mechanical Deformations

Expandable graphite (EG) and few-layer graphene (FLG) have proven to be instrumental materials for various applications. The production of EG and FLG has been limited to batch processes using numerous intercalating agents, especially organic acids. In this study, a Taylor-Couette reactor (TCR) setup is used to expand and exfoliate natural graphite and produce a mixture of EG and FLG in aqueous solutions using an amphiphilic dispersant and a semiflexible stabilizer. Laminar Couette flow structure and high shear rates are achieved via the rotation of the outer cylinder while the inner cylinder is still, which circumvents vortex formation because of the suppression of centrifugal forces. Our results reveal that the level of expansion and exfoliation using an aqueous solution and a TCR is comparable to that using commercial EG (CEG) synthesized by intercalating sulfuric acid. More importantly, the resultant EG and FLG flakes are more structurally homogeneous than CEG, the ratio of FLG to EG increases with increasing shearing time, and the produced FLG sheets exhibit large lateral dimensions (>10 μm). The aqueous solutions of EG and FLG are wet-spun to produce ultralight fibers with a bulk density of 0.35 g/cm³. These graphene fibers exhibit a mechanical strength of 0.5 GPa without any modification or thermal treatment, which offers great potential in light-weight composite applications.

Fabrication of Polymeric Microparticles by Electrospray: The Impact of Experimental Parameters

Microparticles (MPs) with controlled morphologies and sizes have been investigated by several researchers due to their importance in pharmaceutical, ceramic, cosmetic, and food industries to just name a few. In particular, the electrospray (ES) technique has been shown to be a viable alternative for the development of single particles with different dimensions, multiple layers, and varied morphologies. In order to adjust these properties, it is necessary to optimize different experimental parameters, such as polymer solvent, voltage, flow rate (FR), type of collectors, and distance between the collector and needle tip, which will all be highlighted in this review. Moreover, the influence and contributions of each of these parameters on the design and fabrication of polymeric MPs are described. In addition, the most common configurations of ES systems for this purpose are discussed, for instance, the main configuration of an ES system with monoaxial, coaxial, triaxial, and multi-capillary delivery. Finally, the main types of collectors employed, types of synthesized MPs and their applications specifically in the pharmaceutical and biomedical fields will be emphasized. To date, ES is a promising and versatile technology with numerous excellent applications in the pharmaceutical and biomaterials field and such MPs generated should be employed for the improved treatment of cancer, healing of bone, and other persistent medical problems.

Effective Suppression of the Polysulfide Shuttle Effect in Lithium-Sulfur Batteries by Implementing rGO-PEDOT:PSS-Coated Separators via Air-Controlled Electrospray

Lithium-sulfur (Li-S) batteries have been earning significant attention because of their high energy density and cost efficiency. Albeit these outstanding qualities, the polysulfide shuttling effect and low electrical conductivity of the sulfur active material in this battery chemistry results in poor cycling performance. In an attempt to overcome these problems, a hybrid structure of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) and reduced graphene oxide was developed and coated on the surface of a conventional separator using air-controlled electrospray. Implementing these coated separators in Li-S batteries led to lower polarization and stymied the polysulfide shuttling effect through the combining effects of electrostatic, physical, and chemical interactions. Our results reveal that the capacity and rate capacity are drastically improved via coating the separator, leading to more than twice the capacity of over 800 mA h g^-1 after 100 cycles at 0.5 C rate, when it is compared to those with the pristine separator. Overall, this hybrid coating material shows great promise in enhancing the current Li-S battery technology.