Flame-assisted Spray Pyrolysis Research Articles

Multi-component precursor droplet evaporation in spray synthesis of cathode materials

Spray synthesis methods are highly attractive for manufacturing materials for energy storage and conversion owing to their scalability and controllability. The key to achieving high controllability in spray synthesis is understanding the complex relationship between the precursor spray droplet evaporation process and the final product structure. Although several studies on precursor droplet evaporation have been reported, very few consider multi-component droplets, which are relevant in practical applications. In this study, we analysed the evaporation of multi-component single precursor droplets used in flame-assisted spray pyrolysis (FASP) of Li(Ni0.8Co0.1Mn0.1)O2 (NCM811) cathode materials. The product particles of FASP were characterized using SEM, EDS and EELS to determine the structure and morphology of particles obtained from precursors with and without urea additives. The qualitative and quantitative changes during evaporation were analysed using high-speed visualization of suspended single droplets on cross-wires. An in-house developed numerical model was used to track the trajectory of the solutes within the evaporating droplet and elucidate the connection between the evaporation process and the final product structure. It was found that evaporating droplets with multiple precursor solutes (Li, Ni, Co, and Mn) formed product particles with gradient element distribution in the radial direction. However, the addition of a small amount of urea (2.5 wt%) caused significant disturbances in the droplet evaporation process triggered by the urea decomposition reaction leading to uniformly distributed elements in the final product particle. The study contributes towards enhancing fundamental knowledge on multi-component droplet evaporation leading to improved design of spray drying and synthesis processes.

Effects of the preheating temperature on flame-assisted spray pyrolysis of nickel-rich cathode materials

Reducing the cost and improving the performance of lithium-ion batteries (LIBs) are crucial for their applications in transportation electrification and grid energy storage. Much research effort has been devoted to develop novel synthesis methods for LIB cathodes, since traditional methods such as coprecipitation suffer long synthesis time and complex steps. In contrast, flame-based spray methods have great potential in manufacturing LIB cathode materials due to their features such as continuous, fast, and scalable operation. Nevertheless, flame-based spray methods also need improvement in controlling the morphology and improving the electrochemical performance of LIBs. The current work demonstrated a modified flame-assisted spray pyrolysis (FASP) method that used a preheating section for morphology control and electrochemical performance enhancement. The goal is to investigate the effect of preheating temperature on the particle morphology and electrochemical performance of Li(Ni0.8Co0.1Mn0.1)O2 (NCM811) cathode materials. Results showed that the preheating temperature could significantly alter the particle morphology by affecting the drying process. X-ray diffraction measurements demonstrated that the cation mixing level of NCM811 samples was sensitive to the preheating temperature, where introducing the preheating section was effective in inhibiting cation mixing and improving cation ordering at certain temperatures. However, a preheating temperature higher than 325 °C would notably encourage cation mixing. Moreover, the electrochemical tests showed that increasing the preheating temperature could improve the discharge capacity and stabilize the long-time cycling performance. Overall, carefully choosing the preheating temperature of FASP not only improved the particle uniformity by inhibiting the formation of hard-to-break agglomerations in calcinated powders, but also enhanced the electrochemical performance by hindering cation mixing.

Accelerated synthesis of Li(Ni0.8Co0.1Mn0.1)O2 cathode materials using flame-assisted spray pyrolysis and additives

Nickel-rich cathode materials are promising in lithium-ion battery applications because of their high energy density and low material cost. Unfortunately, reducing the synthesis cost of nickel-rich cathode materials is challenging because of the time-consuming and energy-intensive calcination. Therefore, the current work aims to explore strategies for significantly reducing the calcination time of nickel-rich cathode material Li(Ni0.8Co0.1Mn0.1)O2 (NCM811). We used a flame-assisted spray pyrolysis method to synthesize samples with and without using low-cost urea as an additive. Both in situ thermal X-ray diffraction (XRD) and ex situ XRD revealed that urea addition weakened the sensitivity of crystallization and cation mixing to calcination conditions. As a result, with only 20 min of calcination at 875 °C and without any preheating and ramping steps, the NCM811 sample showed an ordered layered structure and comparable electrochemical performance to those with long-time calcination. Moreover, the current work demonstrated that the shortened post calcination was benefited from lithium-embedded particles that likely improved the uniformity of lithium distribution in as-synthesized powder. Therefore, carefully designing initial lithium distribution in particles prior to calcination could also be a useful strategy for other synthesis methods to shorten high-temperature calcination steps, leading to significant reductions in energy consumption and fabrication cost.

In-situ flame deposition of Pt catalysts on Nb-doped SnO2 nanoparticles

Metal oxide supports have attracted much attention for improving the performance and durability of polymer electrolyte fuel cells. In this study, niobium-doped tin oxide (NTO) nanoparticles with a network structure were synthesized and Pt catalysts deposited on them using a flame aerosol technology. Because the flame method involves a variety of particle formation processes, which depend on the type of raw material and combustion method used, the effect of these processes on the particle structure of the flame-made Pt/NTO was evaluated. When Pt/NTO nanoparticles were prepared by flame-assisted spray pyrolysis (FASP) using an inorganic raw material (metal chloride) with lower combustion enthalpy, the precursor liquid burned incompletely and Pt aggregation was observed. However, when flame spray pyrolysis (FSP) using a combustible precursor solution was used, the precursor rapidly evaporated in spray flames, and NTO with uniformly dispersed Pt was synthesized through gas-to-particle conversion. The electrochemical surface area and mass activity values of 5.44 wt% Pt-loaded NTO particles prepared by FSP were 48.2 m2 g−1 Pt and 338 mA mg−1 Pt, respectively. Flame aerosol synthesis of supported metal catalysts can be widely used as a dry one-step process that does not involve any complicated post-treatment. The two types of noble metal loading processes revealed in this study provide important insights for determining particle design guidelines for in-situ production of supported metal catalysts in flames.

Structural Characterization of Ceria-Supported Pt Nanoparticles by Flame-Assisted Spray Pyrolysis Using a Burner Diffusion Flame

Structural Characterization of Ceria-Supported Pt Nanoparticles by Flame-Assisted Spray Pyrolysis Using a Burner Diffusion Flame

Spherical submicron YAG:Ce particles with controllable particle outer diameters and crystallite sizes and their photoluminescence properties.

The purpose of this study was to demonstrate the preparation of spherical submicron YAG:Ce particles with controllable particle outer diameters and crystallite sizes and their photoluminescence (PL) properties, which were produced using a flame-assisted spray-pyrolysis method followed by the annealing process. The correlation of particle outer diameter, crystallite size, and PL performance of the prepared particles was also investigated. Experimental results showed that the increases in the particle outer diameters have an impact on the obtainment of higher PL performance. Large particle outer diameters permitted the crystallites to grow more, whereas this is in contrast to the condition for small particle outer diameter having limitations in crystallite growth. This study also found that too large outer diameter (>557 nm) was not effective since crystallites cannot grow anymore and it permits possible scattering problems. This study provides significant information for optimizing synthesis parameters for controlling particle outer diameters and crystallite sizes, which could be relevant to other functional properties, especially for lens, solar cell, and LED applications.

Techno-economic analysis of cathode material production using flame-assisted spray pyrolysis

The cost of cathode materials contributes approximately 32.7% of the total cell construction cost of lithium-ion batteries, significantly affecting the price of battery packs. To reduce the cathode material manufacturing cost, a flame-assisted spray pyrolysis (FSP) method has been developed to utilize a sustainable solvent of glycerol to manufacture the LiNi1/3Mn1/3Co1/3O2 (NMC333) cathode materials. The objective of this study is to evaluate the minimum cathode material selling price (MCSP) of the FSP processes compared with a traditional carbonate co-precipitation pathway. Results show that the MCSP of the FSP is $19.1/kg that is 17% lower than the traditional carbonate co-precipitation pathway as a result of lower fixed operating cost and variable overhead. Sensitivity analysis shows that when the new process is integrated with in-situ sintering and processing, the MCSP can be as low as $15.6/kg. When all the material prices are decreased by 20%, the FSP process can synthesize NMC333 at a price of $2.3/kg lower. According to the simulation result, LiNi0·8Mn0·1Co0·1O2 (NMC811) has the best potential to meet the U.S. Department of Energy battery price target of $125/kWh, demonstrating that the FSP process is an attractive manufacturing technology for NMC cathode powder material production.

A scalable approach of using biomass derived glycerol to synthesize cathode materials for lithium-ion batteries

Glycerol, a main byproduct of biodiesel, was used as the fuel agent in a scalable flame-assisted spray pyrolysis approach to synthesize micron-size cathode materials. Single droplet combustion, particle morphology, and electrochemical performance were examined considering the effects of salt concentration, water addition, and post-annealing time on synthesizing Li(Ni1/3Co1/3Mn1/3)O2 (NCM111) cathode materials. Single droplet tests showed that a sufficient amount of water in the glycerol-based precursor could delay droplet inflation and ignition. Moreover, using a two-fluid atomization nozzle, spray tests demonstrated that adding water would result in less wrinkled and more uniform particles. Nevertheless, increasing water proportion in the precursor could reduce the reaction heat, resulting in that samples prepared with water addition needed longer post-annealing time to improve their electrochemical performance. Using the precursor without water, the best performed NCM111 cathode material was synthesized with only 2 h of post-annealing. It has a discharge capacity of 163.3 mAh/g at 0.1C and 85.5% capacity retention at 1C after 100 cycles. The current work confirmed the capability of using glycerol as a sustainable fuel agent to synthesize NCM111 cathode materials, and also provided basic conditions for the development of large-scale production in the future.

Fast Production of High Performance LiNi0.815Co0.15Al0.035O2 Cathode Material via Urea-Assisted Flame Spray Pyrolysis

The high throughput and rapid flame-assisted spray pyrolysis method has been adapted to synthesize cathode materials LiNi0.apCo0.15Al0.035O2 (NCA). This method is considered low cost and simple. By varying the precursor solution concentration and sintering temperature, the optimal condition was established at temperature sintering of 800 °C and precursor solution concentration of 1 M. X-ray diffraction patterns showed the as-prepared NCA particles exhibit a pure well-ordered hexagonal layer structure with high crystallinity. Polyhedral shaped micro-sized particles are confirmed by SEM images. Galvanostic charge–discharge tests were conducted using cylindrical full-cell utilizing artificial graphite as the anode. The highest specific initial discharge capacity measured between 2.7 and 4.3 V is 155 mAh g−1 with capacity retention of 92% after cycled at 0.2 C for 50 cycles. Thus, this method is considered as a satisfying approach for NCA mass production.

Synthesis of LiNi0.8Co0.15Al0.05O2 cathode material via flame-assisted spray pyrolysis method

Long reaction and long heat treatments have become major obstacles in producing cathode materials NCA (LiNi0.8Co0.15Al0.05O2) for Li-ion batteries. Flame assisted spray pyrolysis (FASP) method followed by sintering process requires shorter reaction and sintering time and considered suitable economical alternative in NCA production. The obtained ternary oxides particles from FASP have high crystalline and homogenous properties. Furthermore, XRD pattern of NCA products obtained by lithiation of ternary oxides exhibit well-ordered layered hexagonal structure. Electrochemical performance of NCA was tested in an NCA/graphite system at 2.7–4.3 V and current density of 20 mA/g. At the optimum sintering condition (under O2 rich atmosphere for 9 h), NCA particles show the initial specific discharge capacity of 143 mAh/g, and the capacity retention of 92% after 20 cycles. This results is higher from commercial available NCA particles (specific discharge capacity of 138 mAh/g) which indicates the promise of this approach for NCA production.

High retention rate NCA cathode powders from spray drying and flame assisted spray pyrolysis using glycerol as the solvent

This paper reports the synthesis of LiNi0.8Co0.15Al0.05O2 (NCA) cathode powders using a simple flame assisted spray pyrolysis (FSP) and a spray drying (SD) processes, in which metal salt precursors dissolved in glycerol were used for spraying. X-ray diffraction confirms that the NCA powders have a layered structure, with a low order of cationic mixing. Electron microscopy shows that the particles produced by FSP have a relatively smaller size and a smoother surface than that produced by SD. The NCA powder from the FSP process has an initial discharge capacity of 200.2 mAh/g in voltage range of 3.0–4.3 V at 0.1C. It shows very good capacity retention of 91.5% at 1C and 89.4% at 5C after 200 cycles. These results demonstrate that glycerol can replace water and be used as a solvent in spray processes to make cathode powders, promising a new environmentally-friendly synthesis route for battery powder materials production.

Flame‐assisted spray pyrolysis of lithium and manganese precursors to polycrystalline LiMn2O4

AbstractLithium manganese oxide cathodes have a smaller environmental footprint compared to cathodes with cobalt and nickel. Flame assisted spray pyrolysis (FASP) is an emerging technique that may improve the economics of the process at the commercial scale while controlling purity. reacts with to form . Carbon from the flame coats the particles and, together with the Mn oxides, they reduce electrical capacity. The reaction temperature and droplet residence time are the main parameters that determine manganese oxide content and therefore the product purity. LECO carbon analysis confirms that the fuel and precursor type affect carbon content. It increases from % with nitrate precursors to 2 % with carbonate and acetate precursors. The temperature profile as well as the solute type and concentration change the product morphology. The particle surface is wrinkled at a mild temperature and blowholes form at a high temperature. Primary nano‐crystals (5–8 nm) agglomerate to form 1 polycrystalline particles from a 0.5 nitrate precursors solution, while a 5 solution produces 10 powders. We modelled the reaction kinetics based on thermogravimetric analyses to identify the principle reaction steps. Oxide formation increases below 400C and above 800C, while fast heating rates and short residence time reduce purity.

Synthesis of highly crystalline hexagonal cesium tungsten bronze nanoparticles by flame-assisted spray pyrolysis

Highly crystalline and hexagonal single-phase cesium tungsten bronze (Cs0.32WO3) nanoparticles were successfully synthesized by a flame-assisted spray pyrolysis followed by annealing under a reducing gas atmosphere. The resulting Cs0.32WO3 nanoparticles featured a pure hexagonal Cs0.32WO3 phase with a high crystallinity and homogeneous chemical composition. Unlike conventional methods, the proposed process in this paper has several advantages, including a short reaction time and the ability to yield products with high purity and good energy efficiency. Furthermore, the Cs0.32WO3 nanoparticles produced in this research showed a remarkable near-infrared shielding ability with a 97.7% cut-off at 1500 nm.

Synthesis of nanocrystalline alumina (Al2O3) particles from an aqueous precursor by flame-assisted spray pyrolysis

Nanocrystalline alumina particles were successfully synthesized in an indigenously built flame-assisted spray pyrolysis (FASP) setup. Aluminium nitrate nonahydrate was dissolved in deionized water in the desired amount to get a precursor solute concentration of 0.01 mol L-1. The solution was then atomized by using a jet nebulizer. The droplets were then pyrolyzed in an oxy-LPG (liquifiedpetroleum gas) flame producing nanocrystalline alumina particles which were confirmed by x-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. Particle morphology was studied using scanning electron microscopy (SEM). The synthesized powders were predominantly metastable transition aluminas exhibiting spherical morphology and were unagglomerated. The synthesized powders were then calcined at 1473 K for 2 hour to transform into the stable α-Al2O3 (corundum) phase.

Flame-assisted spray pyrolysis to size-controlled LiyAlxMn2−xO4: a supervised machine learning approach

Flame assisted spray pyrolysis synthesizes Al-doped LiMn2O4 where Al promotes carbon formation and increases the specific surface area by 90%.

Synthesis of Potassium Silicate Nanoparticles from Rice Straw Ash Using a Flame-assisted Spray-pyrolysis Method

The purpose of this study was to synthesize potassium silicate nanoparticles from rice straw ash using a flame-assisted spray-pyrolysis method. Rice straw, as one of the agricultural wastes, was used as a source of silica. In the experimental procedure, rice straw was burned at 700°C for 3 hours to produce rice straw ash. Then, the rice straw ash was extracted using an alkaline method. We used potassium hydroxide (KOH) as an alkaline chemical agent as well as a source of potassium. The solution was then put into the flame-assisted spray-pyrolysis apparatus to produce potassium silicate nanoparticles. The results showed that the spray method can assist the production of spherical potassium silicate nanoparticles with sizes of about 50 nm.

Sintering inhibition of flame-made Pd/CeO2 nanocatalyst for low-temperature methane combustion

Dispersed palladium on the high-surface-area ceria support is synthesized via one-step flame-assisted spray pyrolysis method, which applies a highly-quenched stagnation-point flame controlling catalyst sizes and structures. The X-ray photoelectron spectroscopy (XPS) spectra of Pd show a significantly high binding energy for flame-made Pd/CeO2 catalysts, possessing a value of 1.7eV larger than the reference value in literature. It suggests that the partial electron transfer occurs from metal Pd to their supports during the synthesis process, which creates Pd electron-deficient (cationic Pdδ+) and Ce electron-rich (anion Ceδ−), respectively. The catalytic activities of CH4 oxidation are performed over the temperatures ranging from 200°C to 600°C. In comparison with inert support materials, the synergistic effect is found between palladium and support ceria that leads to the enhanced catalytic activity. During the heating and cooling cycles of CH4 oxidation, Pd/CeO2 catalysts exhibit an exceptional inhibition effect against the sintering of Pd cluster and its dispersion decrement, which is related to strong electronic interaction of metal-support interfaces induced by the aforementioned partial electron transfer.

Flame synthesis of novel ternary nanocatalysts Pd/CeO2[sbnd]TiO2 with promotional low-temperature catalytic oxidation properties

One-step flame-assisted spray pyrolysis with highly-quenched premixed stagnation flame is developed to synthesize the supported palladium catalysts on the mixed ceria-titania oxides. Promotional oxygen reducibility and inherent high activity of the catalysts are discovered in contrast to the same loading palladium catalyts on either single support, and the complete methane oxidation is achieved at as low as 450 °C. Palladium valence electronic structure analysis from X-ray photoemission spectroscopy (XPS) indicates that the metal palladium is highly positively charged and electrons transfer from palladium clusters to support oxides during the flame synthesis process. Similar electron transfer can even occur during the cyclic catalytic process for the initially non-charged clusters. From the cyclic experiments, theelectrostatic interaction built up at the metal–support interface plays a major role in the superior sintering resistance for palladium-based catalysts during the combustion process. Moreover, the introduction of water vapor to the feedstock induces a negative effect on the methane oxidation at low temperatures. XPS spectra reveals that the palladium 3d binding energy varies and the interfacial electron transfer flow changes over heating–cooling cycles when exposed to water vapor. More importantly, the excellent thermal stability performances remain even under the water vapor environment.

Dissolution and storage stability of nanostructured calcium carbonates and phosphates for nutrition

Rapid calcium (Ca) dissolution from nanostructured Ca phosphate and carbonate (CaCO3) powders may allow them to be absorbed in much higher fraction in humans. Nanosized Ca phosphate and CaCO3 made by flame-assisted spray pyrolysis were characterized by nitrogen adsorption, X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy. As-prepared nanopowders contained both CaCO3 and CaO, but storing them under ambient conditions over 130 days resulted in a complete transformation into CaCO3, with an increase in both crystal and particle sizes. The small particle size could be stabilized against such aging by cation (Mg, Zn, Sr) and anion (P) doping, with P and Mg being most effective. Calcium phosphate nanopowders made at Ca:P ≤ 1.5 were XRD amorphous and contained γ-Ca2P2O7 with increasing hydroxyapatite content at higher Ca:P. Aging of powders with Ca:P = 1.0 and 1.5 for over 500 days gradually increased particle size (but less than for CaCO3) without a change in phase composition or crystallinity. In 0.01 M H3PO4 calcium phosphate nanopowders dissolved ≈4 times more Ca than micronsized compounds and about twice more Ca than CaCO3 nanopowders, confirming that nanosizing and/or amorphous structuring sharply increases Ca powder dissolution. Because higher Ca solubility in vitro generally leads to greater absorption in vivo, these novel FASP-made Ca nanostructured compounds may prove useful for nutrition applications, including supplementation and/or food fortification.

Laser-based investigation of the transition from droplets to nanoparticles in flame-assisted spray synthesis of functional nanoparticles

Mechanisms involved in flame-assisted-spray-pyrolysis (FASP) synthesis of TiO2-based functional nanoparticles are investigated using in situ phase-selective laser-induced breakdown spectroscopy. Specifically, the transition from droplets to nanoparticles is examined, as well as the particle growth process in the post flame region. In contrast to vapor-fed flame synthesis, the existence of the precursor breakdown in sprayed droplets is observed by both Ti atomic signal and Bremsstrahlung emissions. The emission signal intensity variation reveals the transition from droplets to nanoparticles, indicating that the competition between precursor vaporization and nascent particle formation is the rate determining factor. For the ensuing particle growth regime, the prediction of the particle size evolution by a polydispersed population balance model is in good agreement with TEM and laser-diagnostics results, demonstrating that the particle growth is governed by the collision-coagulation mechanism. Besides, the transition from droplets to nanoparticles can be accelerated with sufficient OH radicles provided by combustible solvents. Furthermore, doping of TiO2 with V and Zr will lead to changes in band gap of the nanoparticle observed, i.e., a distinct strengthening by 23% with V doping and a weakening by 22% with Zr doping in the intensity of Ti signal, respectively.