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Stringent Corporate Average Fuel Economy (CAFE) standards in North America require 54.5 miles per gallon (~4.5 L/100 km) fuel economy for passenger vehicles by 2025. Industry has responded to this [...]

Spinel lithium titanate (Li4Ti5O12) is the most promising negative electrode material for energy storage which can be applied in lithium‐ion batteries lithium‐sulphur batteries, and supercapacitors. However, the high cost of Li4Ti5O12 powder and its high molecular weight limit its application due to the complicated synthesis process. In this work, a facile solid‐state reaction in a fluidized bed reactor was used for the first time to synthesize spinel Li4Ti5O12 using lithium carbonate and titanium oxide as solid reactants. We investigated the fluidization behaviour of starting materials and studied different synthesis temperature in fluidized and fixed beds. X‐ray diffraction and scanning electron microscopy were employed to characterize the samples. The results demonstrate that the mixture of Li2CO3 and TiO2 had a complete fluidization velocity of 0.88 cm/s and showed good fluidization behaviour. Pure spinel Li4Ti5O12 was obtained via solid‐state reaction in a fluidized bed reactor at 800°C for 30 minutes, which is much lower than a conventional solid‐state reaction in a fixed bed or muffle furnace. By this novel method, the micro‐sized Li4Ti5O12 particles (6‐8 μm) have hollow porous structure composed of nano‐sized particles (<100 nm) synthesized. According to the experimental results, we proposed a different reaction mechanism for the synthesis of Li4Ti5O12 in fluidized beds which explains how the Li2CO3 and TiO2 react to form hollow lithium titanate nano‐structured micro‐particles in fluidized beds. The bulk density, surface area, and bulk conductivity of the synthesized Li4Ti5O12 are 3240 kg/m3, 4.6 m2/g, and 3.90 × 10−6 S/cm, respectively. [ABSTRACT FROM AUTHOR]

LiFePO4 (LFP) is a safe and low cost cathode material for Li‐ion batteries. Its solid‐state synthesis requires micron‐sized reactants yielding high production costs. Here, we melt‐synthesized up to 5 kg batches of LFP from low‐cost coarse Fe2O3 (509 µm) in an induction furnace. Graphite from the crucible was an effective reducing agent. Adding metallic Fe or CO increased the Fe2+ content and reaction kinetics. Metallic Fe improves the lifetime of the graphite crucible but requires a premixing step for it to be effective, otherwise the Fe powder agglomerates due to the presence of a eutectic in the LiPO3‐Fe‐Fe2O3 system. In a pushout furnace configuration, for an hour‐long holding period, injecting CO into the melt increased the Fe2+ content from 0.301 to 0.315 g/g, which we attributed to melt protection. Likewise, graphite powder floating on top of the melt further improved the Fe2+ content to 0.331 g/g. The Fe2+ content reached 0.325 g/g when using fine Fe3+ (142 µm) and CO as reducing agent at half the holding period at 1150 °C. We attribute the higher reaction rate to the improved contact between the suspended Fe3+ and the CO reducing gas. When the graphite crucible is the unique reducing agent, the reaction rate was proportional to the crucible base surface area. A zero‐order kinetic model characterized the solids disappearance with time. A thermal model developed to compare lab‐scale data against small pilot‐scale demonstrated that the charge lagged the furnace temperature by as much as 22 min at 1000 °C. [ABSTRACT FROM AUTHOR]

Lithium iron phosphate (LiFePO4 or LFP) is a promising cathode material for large‐scale rechargeable lithium ion batteries. It suffers, however, from low ionic and low electronic conductivities. Size reduction to nanoparticles and uniform coating of conductive carbon overcome the conductivity issues. The conventional solid or liquid carbon coating processes drawbacks include the following: carbon excess; non‐uniform carbon layer; and undesired carbon type. Furthermore, economical liquid‐ and solid‐based carbon sources, being wastes derived from other industries, may also introduce impurities detrimental to the battery performance. This article presents a new fluidized bed chemical vapour deposition process (FB‐CVD) to coat carbon on LFP nanoparticles, with a secondary size representing particles of the Geldart's group B powders, through the pyrolysis of propylene. This gas‐phase process is used to overcome challenges in conventional carbon coating processes. Operating conditions including reaction time, gas residence time, reaction temperature, inlet concentration of propylene, and catalytic effect of LiFePO4 powders were investigated to produce C‐LiFePO4 (or C‐LFP) powders with desired mass and uniformity of coated carbon while avoiding sintering of the material. In addition, a mechanism for gas‐phase C‐LFP production from LFP is proposed. [ABSTRACT FROM AUTHOR]

Since Goodenough's team laid the foundation to apply LiFePO4 as an alternative to lithium cobalt oxide for Li‐ion positive electrodes,[1,2] Web of Science (WoS)[3] has indexed over 6000 articles related to lithium iron phosphate—LFP. Manufacturers synthesize LFP with both solid state and solvent assisted hydrothermal technology. Both have their advantages and disadvantages but society requires inexpensive batteries for automobile applications and fixed electrical storage. Here we scale up each step of the nascent melt synthesis process, which has the potential to displace the current commercial technology because of its superior economics related to raw materials. The research challenges include raw material selection, melt synthesis conditions, thermodynamics, micronization to form nano‐powders, followed by spray drying, and carbon coating. [ABSTRACT FROM AUTHOR]

Compared with large‐scale processes, the LiFePO4 (LFP) melt‐synthesis is a low‐cost method with short dwell times and rapid reaction rates. However, secondary phases and impurities remaining in the olivine structure lower the cathode's electrochemical properties. Starting from a low‐cost Fe3+ precursor, we evaluated tin and silver charged metallic baths to purify the melt‐synthesis of LiFePO4 at laboratory scale. In the tin bath exploration, an x‐ray diffraction (XRD) confirmed the olivine structure and a temperature‐dependent generation of Li3PO4 and Li4P2O7. An SEM image analysis identified tin‐rich phases (SnxPyOz) segregated from the LFP structure and FexP phases on the internal walls of the crucible. A multi‐element analysis (ICP‐AES) detected more than 0.03 g of Sn/g of LFP. The tin bath prepared samples delivered up to156 mAh/g of LFP in a carbon‐free basis, 3 % lower than the capacity of the high purity Fe2O3‐based material at 0.1 C. The silver bath‐based LFP samples produced cleaner XRD patterns (less than 160 ppm of Ag in the LFP ingots), closer to the estimated molar ratios and neither silver compounds nor silver oxides. In this case, the sample delivered 161 mAh/g of LFP, the same capacity as the cathode prepared without a metallic bath. Starting from a commodity Fe3+ source, future work should explore the silver bath roles as a reactive media, a heating source, a crucible insulator, and a potential contaminant trap for the melt‐synthesis of LiFePO4. [ABSTRACT FROM AUTHOR]

Removing solvents from nanoparticle solid suspensions requires the same diligence as drying pharmaceutical ingredients. LiFePO4 nanoparticles suspension in water oxidize, sinter, and Li3PO4 segregates on the surface when they dry in a furnace. Spray drying preserves the material properties because contact times are on the orders of seconds; furthermore, the atomized droplets ensure particles are small (5 μm to 20 μm) and dispersed. A Yamato GA‐32 (120 mm inner diameter) spray dried in co‐current flow a nanoparticle suspension of LiFePO4 in water, with a solid content up to 60 %. Atomization gas velocities of 140 m s−1 to 350 m s−1 agglomerated the nanomaterial into spherical particles that ranged from 3 μm to 10 μm. The particle diameters ranged from 10 μm to 20 μm at atomization velocities of 50 m s−1 to 140 m s−1. At this condition, yield was lower because the semi‐dried particles adhere on the wall. At 150 ∘C to 200 ∘C the surface area reached 26 m2g−1 while from 50 ∘C to 100 ∘C it varied from 14 m2 g−1 to 20 m2 g−1. The trend for mesoporosity versus spray drying temperature is the same as for surface area: pore volumes are higher (0.18 cm3g−1) above 200∘C and 20 % lower below 200∘C. Drying temperature modifies drying speed; low temperatures compact the powders more than high temperature which results in lower surface area and porosity. [ABSTRACT FROM AUTHOR]

The water crossover flux in polymer electrolyte membrane (PEM) fuel cells was measured using a novel in situ measurement device designed to achieve an accuracy of better than 0.01 in water crossover factor by Sauriol et al. [J. Fuel Cell Sci. Technol. 6, 041014 (2009)]. The average anode-to-cathode water crossover flux was linear with respect to current density, suggesting a constant distribution of generated water through anode and cathode channels under the conditions studied. Varying the inlet relative humidity difference between anode and cathode for a given temperature and pressure shifted the water crossover flux- current density line vertically, whereas an increase in cathode pressure changed its slope. The experimental results were used to estimate parameters in the model by Berg et al. [J. Electrochem. Soc. 151, A341 (2004)]. If the current density was used as the only fitting criteria, only poor agreement was observed between the measured and calculated water crossover flux. When both current density and water crossover flux were used in the fitting process, the trends in the fitted kinetic and transport model parameters were more consistent, and a good compromise in fitting both polarization and water crossover flux data was obtained. The results highlight the importance of using additional validation data to increase confidence in fitting parameters used for performance prediction of PEM fuel cells. [ABSTRACT FROM AUTHOR]