Electrostatic Spray Deposition Method Research Articles

Investigation of Dry-Made NMC 811 Electrodes with Varying Binder and the Conductive Agent Contents

Lithium-ion battery electrode materials consist of active materials (AM), conductive agents, and binders. Although conductive agents and polymeric binders occupy a small portion of the electrode, they play an indispensable role. Conductive agents are needed to improve the electronic conductivity of the electrode, while binders ensure mechanical integrity by providing particle/particle cohesion and electrode-film/substrate adhesion. Optimizing the interactions of active materials, conductive agents, and binders is crucial for achieving the desired electrode performance and durability. Although multiple studies have explored the impact of electrode composition for slurry-based electrodes, it is still unclear how composition affects the electrodes made by dry processes. In this study, we performed a detailed investigation of the effects of the different electrode compositions by changing the ratio of polyvinylidene difluoride (PVDF) binder and carbon black (CB) for dry-made LiNi0.8Mn0.1Co0.1O2 (NMC 811) electrodes. The electrostatic spray deposition method was used as a dry electrode fabrication process due to its many advantages, such as reduced energy consumption and inexpensive processing requirements. We investigated electrodes of four different compositions, 96:3:1, 96:2:2, 90:7.5:2.5, and 90:5:5 (AM:PVDF: CB), corresponding to PVDF/CB mass ratios of 1:1 and 3:1.We found that electrodes with a high PVDF/CB ratio of 3:1 have larger impedance than electrodes with a low PVDF/CB ratio of 1:1 due to the insulating aggregates of PVDF alone, causing deteriorated electrochemical performance. At the PVDF/CB ratio of 1:1, an even distribution of PVDF/CB on the AM particle surfaces and in the pores between the AM particles was observed. For both PVDF/CB ratios of 1:1 and 3:1, increasing the total amount of PVDF and CB (e.g., decreasing the AM amount) in the composite electrode enhanced both the C-rate and cycling performance. However, electrodes with the PVDF/CB ratio of 1:1 at high AM content (96%) still showed a comparable C-rate performance to that with lower AM content (90%). Thus, dry-made electrodes with high AM content can achieve a good high C-rate performance, especially for high-energy-density applications.This study provides a better understanding of the effects of CB/PVDF, which is key to finding an optimal structure and composition of the dry-made electrodes.

A Large-Area Patterned Hydrogen-Bonded Organic Framework Electrochromic Film and Device.

Fabrication of a patterned hydrogen-bonded organic framework (HOF) films on a large scale is an extreme challenge. In this work, a large area HOF film (30 × 30 cm2 ) is prepared via an efficient and low-cost electrostatic spray deposition (ESD) approach on the un-modified conductive substrates directly. Combining the ESD with a template method, variously patterned HOF films can be easily produced, including deer- and horse-shaped films. The obtained films exhibit excellent electrochromic performance with multicolor change from yellow to green and violet, and two-band regulation at 550 and 830nm. Benefiting from the inherently present channels of HOF materials and the additional film porosity created by ESD, the PFC-1 film could quickly change color (within 10 s). Furthermore, the large-area patterned EC device is constructed based on the above film to prove practical potential application. The presented ESD method can be extended to other HOF materials; thus, this work paves a feasible path for constructing large-area patterned HOF films for practical optoelectronic applications.

Crystallinity Tuning of Na3 V2 (PO4 )3 : Unlocking Sodium Storage Capacity and Inducing Pseudocapacitance Behavior.

As a promising cathode material of sodium-ion batteries, Na3 V2 (PO4 )3 (NVP) has attracted extensive attention in recent years due to its high stability and fast Na+ ion diffusion. However, the reversible capacity based on the two-electron reaction mechanism is not satisfactory limited by the inactive M1 lattice sites during the insertion/extraction process. Herein, self-supporting 3D porous NVP materials with different crystallinity are fabricated on carbon foam substrates by a facile electrostatic spray deposition method. The V5+ /V4+ redox couple is effectively activated and the three-electron reactions are realized in NVP for sodium storage by a proper crystallinity tuning. In a disordered NVP sample, an ultra-high specific capacity of 179.6 mAh g-1 at 0.2 C is achieved due to the coexistence of redox reactions of the V4+ /V3+ and V5+ /V4+ couples. Moreover, a pseudocapacitive charge storage mechanism induced by the disordered structure is first observed in the NVP electrode. An innovative model is given to understand the disorder-induced-pseudocapacitance phenomenon in this polyanion cathode material.

Electrostatic spray deposition of boronate affinity imprinted membrane to be used as adsorption separation material

In recent years, membrane separation technology has become more and more practical in the field of separation and purification due to its simple operation, low energy consumption, high efficiency and no phase change. In this work, shikimic acid molecularly imprinted polymers (SA-MIPs) were uniformly sprayed on the cellulose acetate membrane (CAM) substrate by electrostatic spray deposition (ESD) method for the first time to prepare the boronate affinity membrane (MIPs-PVA/CAM), which could specifically separate shikimic acid (SA). Thanks to the ESD process, the active binding sites were exposed on the surface, avoiding the encapsulation of MIPs in the membrane compared with traditional blending method, meanwhile, averting the contact with excessive polar solvents used in imprinted process to ensure the membrane integrity. In the adsorption test, the maximum adsorption of SA reached 51.57 mg g−1 in 70 min under pH 7.5, indicating the acceptable binding capacity and fast binding rate. Additionally, MIPs-PVA/CAM possesses remarkable binding selectivity towards SA due to boronate affinity and favorable reusability of 7.68% loss after five continuous cycles. According to the results, ESD holds great promise to prepare molecularly imprinted membrane platform with inherent tailored sites for separation of cis-diols compounds.

Flash Light Sintered SOFC Cathode Functional Layer through Electrostatic Spray Deposition

Solid oxide fuel cells(SOFCs), which are attracting attention as an eco-friendly power generation system, are being actively studied due to their fuel flexibility and high efficiency. Since the charge carriers are oxygen ions and have to pass through the solid oxide electrolyte, they require a higher operating temperature (~900 oC) than other fuel cells. To overcome the disadvantages of high-temperature operation, research is being conducted to lower the operating temperature of the SOFCs. In particular, in order to minimize performance degradation even at low operating temperatures, research is being conducted to fabricate cell components as thin films or to apply electrodes with high catalytic activity and large reaction areas.Among the methods of manufacturing thin films, the deposition method using chemical solution deposition(CSD) has the advantage of being cost effective and easily controllable compared to the vacuum deposition method. Electrostatic spray deposition(ESD), one of the CSD deposition methods, is simple to set-up and a variety of compounds can easily be made by controlling the proportions of the precursors. However, a characteristic of the CSD method is that a post heat treatment process is required to obtain desired properties, which consumes a lot of time and cost during the entire process. To solve this problem, processes such as rapid thermal annealing, microwave, and excimer laser ablation are being studied, but these processes have limitations in that they damage the substrate, have a long cooling time, and have a small sintering area. [1, 2] On the other hand, the flash light sintering method using a xenon lamp can perform a post-heat treatment process quickly at room temperature and atmospheric pressure using intense pulsed light, and has the advantage of minimizing damage to the substrate and being applicable to a large area. [3, 4]In this study, the cathode functional layer, which is closely related to the performance of SOFC, was fabricated using the ESD method, and the flash light sintering method was applied for the post-heat treatment process. By applying the flash light sintering method, the heat treatment process, which used to take tens of hours, was shortened to just a few seconds. The sintering behavior of the film produced by flash light sintering was confirmed by comparing the microstructure and crystallinity. In addition, it was confirmed that the film manufactured by flash light sintering worked successfully by comparing the performance with the cell manufactured by the conventional thermal sintering method. Reference [1] R. Bayati et al., "Modification of Properties of Yttria Stabilized Zirconia Epitaxial Thin Films by Excimer Laser Annealing," (in English), Acs Applied Materials & Interfaces, vol. 6, no. 24, pp. 22316-22325, Dec 24 2014.[2] H. S. Hao, L. H. Xu, Y. Huang, X. M. Zhang, and Z. P. Xie, "Kinetics mechanism of microwave sintering in ceramic materials," (in English), Science in China Series E-Technological Sciences, vol. 52, no. 9, pp. 2727-2731, Sep 2009.[3] J. S. Park, D. J. Kim, W. H. Chung, Y. Lim, H. S. Kim, and Y. B. Kim, "Rapid, cool sintering of wet processed yttria-stabilized zirconia ceramic electrolyte thin films," (in English), Scientific Reports, vol. 7, Sep 29 2017.[4] J. S. Park, H. Lee, S. Heo, and Y. B. Kim, "Heater-assisted intense pulsed light irradiation for lanthanum strontium cobaltite thin film electrode fabrication," (in English), Thin Solid Films, vol. 697, Mar 1 2020.

Preparation and characterization of zinc sulfide thin film by electrostatic spray deposition of nano-colloid

In this investigation, condensed and adhesive zinc sulfide (ZnS) layers were productively sprayed onto Fluorine doped Tin Oxide glass substrate at room temperatures using a facile, non-vacuum and economical electrostatic spray deposition (ESD) method. Used ZnS colloidal in the ESD process prepared by a one-pot thermolysis synthesis method. The effects of applied voltage, liquid flow rate, and distance of the nozzle to substrate on the morphology of ZnS thin films, were investigated. It revealed optimized conditions at the voltage of 24 kV, the flow rate of 1 μl/min, and nozzle to substrate distance of 8 cm. The ultraviolet-visible absorption spectroscopy revealed direct optical band gap of the deposited layer is around 3.44 eV. At a wavelength larger than 350 nm, the visible region (transparency area) of ZnS film was observed. Energy dispersion X-ray analysis and scanning electron microscope showed the ZnS film has a thickness of more than 300 nm with Zn1-xS (x ≈ 0.3–0.4) chemical composition.

Preparation of porous polyamide films with enhanced electrochromic performance by electrostatic spray deposition

Porous polyamide films were prepared by a simple electrostatic spray deposition method for the first time. The polymer solution quickly was dispersed into micron-sized droplets and deposited on the substrate under the electrostatic field forces. With the continue depositing of the droplets and evaporating of the solvent, many voids formed between the droplets to form a porous structure. Thanks to existence of these porous channels, the ion transmission could be effectively increased. Therefore, compared with the film prepared by traditional blade coating, the porous film exhibited a smaller redox potential interval and shorter response time. Introducing of silver nanowires (AgNWs) into the polymer solution wouldn't impede the formation of porous structure, and electrochromic response time for the obtained polyamide/AgNWs film can be effectively improved. The bleaching/coloring time could reach 0.8 s/1.2 s, which is the best record for the polyamide based electrochromic film. These results showed that, electrostatic spraying technology is a promising and efficiently method to prepare polymer film with good electrochromic property. • The organic electrochromic polymer films with rough surface and stacked structure were prepared by electrostatic spraying. • Porous structure films were prepared by electrostatic spraying after introducing AgNWs into the solution. • Films exhibited small redox potential interval, short response time and high coloration efficiency.

Binder-assisted electrostatic spray deposition of LiCoO2 and graphite films on coplanar interdigitated electrodes for flexible/wearable lithium-ion batteries

Flexible battery technologies have lately attracted much attention in the field of wearable electronics. A coplanar interdigitated electrode design encompasses the merits of bending tolerance and increased kinetics owing to shortened diffusion length for applications in these batteries. However, the fabrication of a coplanar patterned electrode remains a challenge because the conventional slurry casting method is unsuitable. In this study, we present a new process to prepare an interdigitated coplanar electrode using binder-assisted electrostatic spray deposition (ESD) without vacuum or high-cost techniques. Using the binder-assisted ESD method, it is possible to deposit powder of any type or size. Moreover, this approach is versatile and universal for application to the design of any coplanar cell configuration and is achieved using a binder-assisted dispersion method based on a commercially available active material. A full-cell flexible battery is fabricated with a coplanar interdigitated electrode using a LiCoO2 cathode and graphite anode. The low cost, simplicity, efficacy, and flexibility of this method are very promising attributes in the design and fabrication of flexible/wearable batteries.

Small molecule/polymer blends prepared by environmentally-friendly process for mechanically-stable flexible organic field-effect transistors

Abstract We fabricated flexible organic field-effect transistors (OFETs) based on a blend film composed of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) as a π-conjugated small-molecule semiconductor and poly(methylmethacrylate) (PMMA) as a polymer insulator deposited on polyethylene naphthalate (PEN) films with Al bottom-gate electrodes. The blend films were prepared by using an electrostatic spray deposition (ESD) method with environmentally-friendly (i.e., non-aromatic and halogen-free) solvents of n-butyl acetate, acetone, and hexane. The TIPS pentacene and PMMA layers were stratified separately just after the film deposition (TIPS pentacene (top) and PMMA (bottom)). The phase-separated interface with molecular-level flatness was formed with the PMMA buffer layer inserted between the blend film and Al bottom-gate electrode, which leads to superior charge transport properties. Furthermore, the flexible OFETs with a sharp phase-separated interface demonstrated superior operational stability under applied mechanical strain.

Three-dimensional porous Zn2VO4/ZnO/C thin film anode materials for high-performance Li-ion batteries

A new type of Zn2VO4/ZnO/carbon composite (three-dimensional porous architecture) was firstly fabricated on a Ni-metal foam substrate thorough a facile electrostatic spray deposition (ESD) method followed by a calcination process. As a binder-free electrode in high performance lithium-ion batteries (LIBs), the composite electrode displays an outstanding long cycling performance, and it exhibits a high specific capacity of 930.8 mAh g−1 at 2 A g−1 even after 800 cycles without any capacity fading. And, the composite also shows a good rate performance with specific charge capacities of 742.1, 658.7, 804.9, 567.3 and 519.3 mAh g−1 at 0.1, 2, 5, 10 and 12 A g−1, respectively.

Toward High Power-High Energy Sodium Cathodes: A Case Study of Bicontinuous Ordered Network of 3D Porous Na3 (VO)2 (PO4 )2 F/rGO with Pseudocapacitance Effect.

Developing high power-high energy electrochemical energy storage systems is an ultimate goal in the energy storage field, which is even more difficult but significant for low-cost sodium ion batteries. Here, fluoride is successfully prepared by the electrostatic spray deposition (ESD) technique, which greatly expands the application scope of ESD. A two-step strategy (solvothermal plus ESD method) is proposed to construct a bicontinuous ordered network of 3D porous Na3 (VO)2 (PO4 )2 F/reduced graphene oxide (NVOPF/rGO). This two-step strategy makes sure that NVOPF can be prepared by ESD, since it avoids the loss of F element during synthesis. The obtained NVOPF particles are as small as 15 nm, and the carbon content is only 3.5% in the final nanocomposite. Such a bicontinuous ordered network and small size of electroactive particles lead to the significant contribution of the pseudocapacitance effect to sodium storage, resulting in real high power-high energy sodium cathodes. The cathode exhibits excellent rate capability and cycling stability, whose rate performance is one of the best ever reported in both half cells and full cells. Moreover, this work provides a general and promising strategy for developing high power-high energy electrode materials for various electrochemical energy storage systems.

Reduced graphene oxide thin film prepared by electrostatic spray deposition technique

Abstract Reduced graphene oxide (rGO) thin films were prepared by one-step electrostatic spray deposition (ESD) technique with a precursor solution of graphene oxide in mixed alcohol solvent. The deposited rGO films showed decreasing thicknesses ranging from approximately 340 nm–120 nm as substrate temperature increased from 150 °C to 275 °C. Raman spectroscopy indicated lowest intensity ratio of D to G band (ID/IG) of the rGO films at substrate temperature of 275 °C. Highest carbon per oxygen (C/O) ratio was also obtained at substrate temperature of 275 °C. The ESD technique was used for film deposition on an area of 5 × 5 cm2, while an acetone gas sensor based on single layer rGO film was fabricated by one-step ESD technique. Results indicated the possibility of controlling thickness components in the rGO film, and the capability of large-area production by this scalable ESD method.

Synthesis of CoMn2O4 thin films on Ni foams by electrostatic spray deposition as anodes for sodium–ion batteries

CoMn2O4 films on nickel foam were successfully synthesized by electrostatic spray deposition method followed by annealing in Ar atmosphere for sodium–ion battery anodes. The CoMn2O4 film exhibits porous architecture with a pore size of around 3–4 µm. The CoMn2O4 electrode as a binder-free anode exhibits superior reversible cycling performance and rate capability. It remains reversible specific capacity of 185 mAh g−1 at 100 mA g−1 after 50th cycle. The stable electrochemical performance could be attributed to the unique CoMn2O4 architecture on Ni foam, which could provide high contact area with electrolyte, pronounced tolerance to volume variation, and enhance the electrical conductivity.

Protective properties of Al2O3 + TiO2 coating produced by the electrostatic spray deposition method

Abstract Mechanical resistance of Al 2 O 3 + TiO 2 nanocomposite ceramic coating deposited by electrostatic spray deposition method onto X10CrAlSi18 steel to thermal and slurry tests was investigated. The coating was produced from colloidal suspension of TiO 2 nanoparticles dispersed in 3 wt% solution of Al 2 (NO 3 ) 3 , as Al 2 O 3 precursor, in ethanol. TiO 2 nanoparticles of two sizes, 15 nm and 32 nm, were used in the experiments. After deposition, coatings were annealed at various temperatures, 300, 1000 and 1200 °C, and next exposed to cyclic thermal and slurry tests. Regardless of annealing temperature and the size of TiO 2 nanoparticles, the outer layer of all coatings was porous. The first five thermal cycles caused a rapid increase of aluminum content of the surface layer to 30–37 wt%, but further increase in the number of thermal cycles did not affect the aluminum content. The oxidation rate of coating-substrate system was lower during the thermal tests than during annealing. The oxidation rate was also lower for smaller TiO 2 particles (15 nm) forming the coating than for the larger ones (32 nm). The protective properties of Al 2 O 3 + TiO 2 coating against intense oxidation of substrate were lost at 1200 °C. Slurry tests showed that coatings annealed at 1000 °C had the best slurry resistance, but thermal tests had weakened this slurry resistance, mainly due to decreasing adhesion of the coating.

Synthesis of MnO@multi-walled CNTs composite film electrodes for lithium-ion batteries by an improved electrostatic spray deposition method

MnO@multi-walled CNTs (MnO@MWCNTs) composite film electrodes with porous structure are synthesized by the improved electrostatic spray deposition (ESD) setup. The content of 5.47 wt% MWCNTs is found to be optimal, which can improve the conductivities of MnO film electrodes without destroying their porous structure and obtain good cycling performance (588 mAh g−1 after 100 cycles at 1 C) and high rate capabilities (424 mAh g−1 at 5 C). The effects of MWCNTs on the morphology of the electrodes and the electrochemical performances have been studied. It is found that the electrostatic repulsion between the charged spray droplets can be remarkably reduced by excessive adding MWCNTs, which leads to the breakdown of the 3D porous morphology of the MnO film electrodes and the electrochemical performance becomes worse.

Lithium-Ion Capacitor Based on LiFePO4 and Nanostructured Carbon By Electrostatic Spray Deposition

Many efforts have demonstrated the practicability of power units based on electrical double-layer capacitors (EDLCs) to replace or complement batteries, generally because of their ability to deliver higher power density, faster charge and discharge rate as wells as longer operational life cycle. However, EDLCs exhibit relatively poor energy density. This limitation is revealed in portable electronic systems whose functions demand high energy and power density at the same time. In order to overcome the low energy density limitation of EDLCs, lithium-ion capacitors have gained much interest. Lithium-ion capacitors are hybrid electrochemical charge storage devices that combine the high energy density capability of lithium-ion batteries and the high power density in EDLCs. This is typically achieved by using electrodes based on battery-type lithium intercalating material as the high energy density source, and a capacitor-type material as the high power density source, in a lithium-containing electrolyte. In this work, we evaluated the electrochemical performance of lithium-ion capacitor comprising lithium iron phosphate (LiFePO4) battery-type cathode and reduced graphene oxide-carbon nanotube (RGO-CNT) composite as capacitor-type anode for half and full cells. The electrodes were prepared via electrostatic spray deposition (ESD) method, a thin-film deposition method capable of operating in ambient conditions. The choice of LiFePO4 is mainly because it is relatively inexpensive and exhibit attractive electrochemical properties such as good cycling stability, high intercalating potential of ~3.5 V versus Li+/Li as well as flat voltage plateaus. On the other hand, among a variety of nanostructured carbon materials, RGO-CNT composite has been shown as a good double-layer electrode material in EDLCs with high power density capability. Material characterization of the electrodes was carried out using scanning electron microscopy (SEM) and X-Ray diffractometry (XRD) respectively. Detailed results will be presented at the meeting.

Thermoelectric properties of bismuth-substituted calcium manganite Ca<sub>1−</sub><i><sub>x</sub></i>Bi<i><sub>x</sub></i>MnO<sub>3−δ</sub> prepared via the electrostatic spray deposition method

Thermoelectric properties of bismuth-substituted calcium manganite Ca<sub>1−</sub><i><sub>x</sub></i>Bi<i><sub>x</sub></i>MnO<sub>3−δ</sub> prepared via the electrostatic spray deposition method

Fabrication of three-dimensional porous ZnMn2O4 thin films on Ni foams through electrostatic spray deposition for high-performance lithium-ion battery anodes

Three-dimensional (3D) porous ZnMn2O4 thin films on nickel foam substrates have been successfully synthesized through electrostatic spray deposition (ESD) method followed by an annealing process for lithium-ion battery anodes. These films exhibit excellent cycling performance with a reversible capacity of around 982 mAh g−1 after 100 cycles at 400 mA g−1. The ZnMn2O4 films also display good rate capability with 455 mAh g−1 at 5 A g−1. The superior battery performances of ZnMn2O4 films are ascribed to 3D porous ZnMn2O4 film directly deposited on Ni foam, which can offer effective empty space to accommodate the large volume variation during cycling, increase reaction sites, and improve the electron transport. The ESD strategy is facile, cost-effective, which can be potentially utilized to construct other 3D porous mixed transition-metal oxides materials as well.

1-D Microstructure Evolution of Electrostatic Sprayed Thermosetting Phenol-formaldehyde Resin Coating

Microstructure evolutions of thermosetting resin coating layers fabricated by electrostatic spray deposition (ESD) at various processing conditions were investigated. Two different typical polymer systems, a thermosetting phenol-formaldehyde resin and a thermoplastic polyvinylpyrrolidone (PVP), were employed for a comparative study. Precursor solutions of the phenol-formaldehyde resin and of the PVP were electro-sprayed on heated silicon substrates. Fundamental differences in the thermomechanical properties of the polymers resulted in distinct ways of microstructure evolution of the electro-sprayed polymer films. For the thermosetting polymer, phenol-formaldehyde resin, vertically aligned micro-rod structures developed when it was deposited by ESD under controlled processing conditions. Through extensive microstructure and thermal analyses, it was found that the vertically aligned micro-rod structures of phenol-formaldehyde resin were formed as a result of the rheological behavior of the thermosetting phenol-formaldehyde resin and the preferential landing phenomenon of the ESD method.

Thermal resistance of Al2O3 coating produced by electrostatic spray deposition method

Results of experimental investigation of effect of Al2O3 nanoparticle sizes on morphology and thermal resistance of Al2O3-based coating deposited by means of electrostatic spray deposition technique on X10CrAlSi18 steel substrate are presented in this paper. Microscopic observations showed that all coatings were porous and built from agglomerates, whose size was depended on the size of primary Al2O3 nanoparticles. It was noticed that surface roughness was lower for primary Al2O3 nanoparticles of larger size. Thermal cycles caused many cracks in the coating, which were located around the agglomerates. Larger number of cracks was formed in the coating produced from smaller Al2O3 particles, and it was observed that the number of cracks decreased with an increase of Al2O3 particle size, but at the same time, the depth of these cracks increased. With an increase of the number of thermal cycles, the surface roughness and the number of cracks slightly decreased. No delamination of the coating was noted at any specimen after all thermal cycles.