To be Updated with new approved abstracts

Metal fluorides (MFx) are known as promising cathode materials for secondary Li batteries that exhibit high theoretical operating voltages as well as large specific capacities. The high ionicity of M-F bonds results in higher reaction potentials that other metal compounds, and multiple Li ions per unit formula participated in the charge/discharge process based on conversion reactions. However, a limited number of synthetic methods for preparing MFx electrodes currently exist, which has made it difficult to control the morphology of particles and fabricate designed nanostructures to alleviate the intrinsic chemical and electrochemical drawbacks of MFx.
In this study, we developed a new synthetic route to anhydrous MFx(CuF2, FeF3, and CoF2) nanocomposites using ammonium fluoride(NH4F). We discovered that various metal precursors can be directly converted to anhydrous MFx through heat treatment with NH4F under an inert atmosphere. This simple, less-hazardous, and versatile method enabled synthesis of MFx nanoparticles confined in nanoporous carbon efficiently. Moreover, using XRD analysis, we also proposed the reaction mechanism of this synthetic method. As the cathodes of secondary Li batteries, all MFx nanocomposites (MFx/nanoporous carbon) showed noticeable improvements in electrochemical performance through conversion reactions. Especially, in the case of FeF3 nanocomposites, it maintained a capacity of 650 mAh/g,FeF3 over 50 cycles (~90% of its initial capacity); to the best of our knowledge, no such a superior cyclability of FeF3 with a high capacity has been reported previously. CuF2 and CoF2 nanocomposites also maintained discharge capacities of ~200 mAh/g,CuF2 (20th cycle) and ~400 mAh/g,CoF2 (30th cycle), respectively. It is expected that this study will motivate further research into various MFx for high capacity cathodes of secondary batteries.

Conventional, state-of-the-art, wet slurry mixing and coating processes of making battery electrodes are over 100 years old and have been recognized as slow, high-cost, low-quality steps in battery manufacturing. The mixing process is used to produce a slurry that consists of active material, polymer binder, conductive filler, and organic solvent. When an appropriate viscosity is obtained, the slurry is coated onto a conductive metal foil. Because of the large amount of organic solvent used, the coating must be dried in an oven for several hours before it is calendered to form the desired thickness and porosity. Evaporation of the organic solvent consumes energy, requires the use of a large amount of material that is not part of the final product, and has a negative environmental impact.
We recently developed an electrostatic spray process for making the positive and negative electrodes in lithium-ion batteries. This process does not use organic solvents that are used in conventional wet slurry manufacturing processes, thus eliminating volatile organic compound emission and reducing the time and energy associated with thermal drying. The performance and durability of electrodes made by the dry and wet processes are comparable, suggesting that solvent-free dry coating processes, such as electrostatic spraying, may replace the conventional wet slurry method of making battery electrodes.

Processing and characterization of nanostructured materials play an important role in developing the next-generation anode materials for Li-ion batteries of high energy density and capacity in order to reduce the dependence on the use of fossil fuels and thus decrease the emission of greenhouse gases. The use of nanostructured materials, in particular, TiO2-based nanocomposites has become a promising strategy for improving the electrochemical performance and safety of Li-ion batteries. To increase the electrical conductivity of TiO2 (~10-13 S�cm-1), Au@TiO2 nanotube arrays are prepared via magnetron sputtering and heat treatment. The heat treatment not only leads to the transformation of TiO2 nanotube arrays from amorphous phase to anatase phase but also results in the diffusion of Au nanoparticles. X-ray diffraction, Field Emission Scanning Electron microscope, and Transmission Electron Microscope are used to characterize the microstructural evolution of the Au@TiO2 nanotube arrays. The prepared Au@TiO2 nanotube arrays are used as anode materials in lithium ion batteries, which deliver a higher capacity than pure TiO2 nanotube arrays.

Lithium-sulfur (Li-S) batteries are among the most promising candidates for the next generation rechargeable batteries due to their high energy density, low raw material cost and environmental friendliness. Although Li-S batteries possess a high theoretical cathode specific capacity of 1,672 mAh g-1, the energy density of practical Li-S batteries is much smaller and depends on electrolyte/sulfur (E/S in mL g-1) ratio. From previous works, successful operation of Li-S batteries under lean electrolyte conditions can be challenging, especially in the case when the solubility of lithium polysulfide (LiPS) sets an upper bound for polysulfide dissolution. Very recently, we have demonstrated that the E/S ratio of Li-S cells has a significant effect on both performance and theoretical energy density of Li-S batteries. Since the lower-bound for E/S ratio is restricted by the solubility of LiPS in the organic electrolyte, the theoretical energy density of Li-S batteries is significantly reduced. Experimentally, it was approved that when the LiPS concentration reached to the solubility limitation in the electrolyte, the reaction rate of reducing sulfur to LiPS in the cathode will reduce significantly. In this talk, we will discuss the relationship between theoretical specific energy and the solubility of LiPS in the electrolyte. The experiments were also proved that the solubility of LiPS could be the ultimate limitation to the energy density of Li-S batteries.

Lithium ion secondary batteries (LIBs) have been extensively studied because of their potential use as power sources in mobile electronics, hybrid-electric vehicles and next-generation electric mobilities. Recently, we are especially focusing on all-crystal (solid)-state LIBs. They have attracted significant attention due to their high energy densities, that is, originating from the device miniaturization, and high safety caused by their non-flammability. However, there is extremely large innovation gap between general LIBs and all-solid-state LIBs because of difficulties in smooth lithium ion transfer, i.e., diffusion of lithium ions and electrons are interfered at interfaces of different solid materials. Therefore, we have tried to control and design their interfaces between active materials and solid electrolytes and fabricate materials for all-solid-state LIBs on the basis of crystal science and engineering. Water-splitting by photocatalysts have been investigated because of expectation to supply clean and recyclable hydrogen energy. In general, photocatalysts, as represented by TiO2, are activated by only ultraviolet light illumination due to their wide band gap. Although these UV-light-driven photocatalysts can split water in a proper condition, the solar energy conversion efficiency is rather low because UV light energy is just several percent in total energy of sun light on the earth, and visible light accounts for almost half of the solar energy. From the viewpoint of increase the efficiency and industrial application of solar hydrogen production, visible-light-driven photocatalysts have intensively attracted research interests. In particular, oxynitride and nitride semiconductor photocatalysts are one of promising materials for construction of photocatalytic water splitting system.
Our group has researched a classic flux method for preparing active materials and solid electrolytes for all-solid-state LIBs, and visible-light-driven photocatalysts for solar hydrogen production, and developed flux coating method for fabricating highly crystalline layers on metal collectors. The flux method is a nature-mimetic liquid phase crystal growth technique, and has several advantages over other methods like solid state reaction. It is a relatively low-temperature process that requires very simple equipment, and high-quality crystals with well-developed facets can be grown. The details of materials preparation and interfaces design by use of our flux crystal growth concepts will be presented in the SIPS2017 conference.

Development of high-power density battery is one of important issues for managing high-performance energetic applications including electric vehicles, rescue robots, elevating machines, and so on. Lithium cobalt oxide, LiCoO2, is one of the most popular active materials in lithium ion secondary batteries because of exhibiting good conductivities with reasonable capacity. Toward the application of LiCoO2 as high-output uses, there are still some issues to be solved. Usually, LiCoO2 was prepared by solid-state reaction, which provided a few micron-size polycrystals with inhomogeneous distribution in shapes. Under high loading rate, it is presumed that the usual LiCoO2 particles undergo local overcurrent and volume changes during lithiation / delithiation caused by aggregation and inhomogeneous natures of them. Since these electrochemical overloads would lead serious degradation in the cycle abilities, improvements of LiCoO2 are inevitable.
There are two kinds of approaches for the improvement. The first one is modification of chemical compositions, including doping with other elements, coating with inactive materials, and the second one is control of crystallographic characteristics, such as crystal habits, particle dispersibility, and sizes. Combining them, synergetic improvement of LiCoO2 toward high-output battery would be possible. Recently, we have grown LiCoO2 single crystals by using flux method, which is one of liquid-phase crystal growth techniques. Exhibiting submicron-size, dispersed, low-aspect ratio with rich a, b faces, and high crystalline natures, which commonly provide efficient electron and Li+ transportations, it is expected that the flux grown LiCoO2 crystals inhibit the unfavorable electrochemical degradations at high electrochemical load.
In this report, we applied the flux grown LiCoO2 crystals to the active materials for high-output batteries. The effects of crystallographic characteristics of the LiCoO2 to the battery performances were examined at 10C rate, coupled with their degradation manners in terms of morphologies and chemical phases.

In this study, a new hybrid 3D structure electrode is, for the first time, proposed that can achieve high battery performance, such as high areal energy and power density. The proposed structure utilizes the advantages of digital structure to break through the limitation posed by the conventional laminated structure, which can be applied to large scale battery formats. An extrusion-based additive manufacturing method is used to fabricate this hybrid 3D structure by using the conventional solution, which resolves the typical challenges in preparing solutions for the extrusion process. The results indicate that significantly enhanced areal energy and power densities can be achieved with the hybrid 3D structure. The hybrid 3D structure LiMn2O4 battery shows superior performances, in terms of specific capacity and areal capacity. More importantly, compared to the conventional structure, the hybrid 3D structure was more efficient and had much higher lithium ions utilization, which presents a new possibility for preparing an electrode with excellent electrochemical performance. This work resolved fabrication, solution preparation, and assembly issues for a scaled up 3D battery via the extrusion-based additive manufacturing method. It demonstrated that the proposed 3D structures provide a high specific surface area and quick responses, which are the key challenges in the area of materials science involving two interfaces and their kinetic reactions.

Si is the most promising anode for Li-ion batteries, as it allows for a capacity that is 10 times greater than that of commercially used graphite. The limiting factor in commercializing it, however, is the severe fracture it experiences from the first electrochemical cycle, which reduces the capacity over 50% after the first few cycles. A new type of microstructure is presented here that can inhibit fracture in Si anodes by patterning the Si surface with microcones which have a nano-porous surface. Such microstructures did not exhibit the typical dry-bed fracture that Si films exhibit from the first electrochemical cycle, and retained their structural stability for twenty cycles. Furthermore, a very thin solid electrolyte interface layer was observed. To understand this unique behavior a multi physics model is developed that can capture the behavior of continuous and patterned Si films, by considering stress-assisted diffusion.

Polymer electrolytes have potential for use in next generation lithium and sodium batteries. Replacing the liquid electrolyte currently used has several advantages: it allows use of high energy density solid lithium as the anode, removes toxic solvents, improves safety, and eliminates the need for heavy casings. Despite their advantages, the conductivity of solid polymer electrolytes is not sufficient for use in batteries. As a result, considerable effort towards improving conductivity and understanding mechanisms of lithium transport has taken place over the last 30 years. This talk considers the use of mixed anions in polymer electrolytes. In simulations on Na conducting polymer membranes, we observe that ions aggregate in linear chains when the anion contains a ring structure. When the charge localization is varied, the length of the ion chains changes. Through this type of “experiment”, we find that ion-assisted, superionic, conduction occurs when ions move quickly along the outside of the ion chain, or in hop on/hop off collective events. Both are sensitive to the ion chain length. In this artificial tuning, the ion chain length is not predictable. Further, the corresponding experimental control is lacking. Here, we present a method to control the length of ion chains using mixed anions. A strongly binding anion forms the core of the ion chain, while weakly binding anions leave cations that lead to superionic conduction. The ratio of “core” anions to “mobile” anions controls the length of ion chains, and is easily duplicated in experiments.

Generalized moving least squares (GMLS) is a discretization that generates numerical solution of partial differential equations using only particle degrees of freedom and requires no underlying mesh. This makes the method ideal for problems involving complex multiphysics whose boundaries evolve over time. In particular, we are interested in developing techniques allowing the coupling of surface physics on an evolving manifold together with transport phenomena in a bulk domain. Such processes are representative of a range of mesoscale devices, and we consider a toy problem representing the mechanical degradation of a lithium ion battery which requires concurrent coupling of many physics – a deposition process where mass transport of lithium ions leads to an evolving interface between active lithium particles and a surrounding carbon matrix. In turn, this swelling of the interface imparts compressive stresses on the surrounding matrix and eventually leads to fracture. We use this simplified model as a driver for the development of a new method that is able to concurrently couple bulk-manifold diffusion, manifold evolution, and linear elasticity solvers while maintaining high-order accuracy.

One of the key obstacles in the realization of high energy density lithium batteries exceeding 500 Wh/kg is the development of scalable manufacturing methods to produce stable and high mass and areal loading sulfur cathodes. In this talk, I will discuss our recent efforts that have addressed the manufacturing challenges posed by thermal melt diffusion infiltration of sulfur, which remains the most widely used technique to produce carbon-sulfur composites, through the development of a scalable capillary force driven manufacturing technique. This technique enables thick carbon host materials to be site-selectively infiltrated with sulfur (over 70 wt.%) in a matter of minutes with low-temperature thermal processing below 170 oC. This is compared to melt infiltration methods that usually require over 12 hours of processing at similar temperatures, yield no control of sulfur morphology or location, and hence exhibit poor sample-to-sample reproducibility. By leveraging this technique, our team has been able to iterate across numerous studies that I will discuss evaluating and demonstrating critical performance criteria that can enable lithium-sulfur batteries with energy density in packaged battery systems exceeding 500 Wh/kg. This includes (1) stability enabled by nanoscale V2O5 binding materials that mitigate polysulfide dissolution that lowers Coulombic efficiency and leads to anode fouling, (2) high areal capacities exceeding 19 mAh/cm2 with sulfur mass loading exceeding 75 wt.%, and (3) high sulfur utilization and retention that is strongly associated with combined sulfur morphology and polar binding properties in a sulfur-carbon composite material. Our work gives promise to a route that bypasses the high cathode material and processing cost in Li-ion batteries, sustains the scalability, throughput, and reliability needed for battery manufacturing, and overcomes performance limitations of prior approaches described in the literature that rely heavily on melt diffusion processing of sulfur-carbon composite cathodes.

Lithium-sulfur rechargeable battery using metallic lithium as anode has a theoretical energy density of 2600 Wh Kg¨C1. This means that lithium-sulfur battery will be one of the promising next generation batteries for mobile devices like cell phones and electrical vehicles. However, the highly reactive metallic lithium in lithium-sulfur batteries can easily induce a series of problems, such as unstable lithium/electrolyte interface, uneven deposition/dissolution of lithium, and massive surface defects. As a result, lithium-sulfur batteries can be thoroughly destroyed after some charge-discharge cycles due to powderization of metallic lithium anode. Here we introduce our works on protection of metallic lithium anode, including the application of the protective layer, optimization of battery fabrication, alloying of anode, and the introduction of electrolyte additives. These efforts can effectively restrain the reactive activity of lithium anode, and improve stabilization of lithium anode in the cycling of lithium sulfur rechargeable batteries. It is very significant for developing long cycling lithium sulfur rechargeable batteries.

In this paper, we study the effects of stress-diffusion interactions on the fracture behaviour and the crack growth of Lithium ion battery electrodes. A coupled mechanical equilibrium and Lithium diffusion accounting for the effect of stress on diffusion and the effect of advancement of the front to the crack growth is considered. The discontinuous fields are represented independent of the mesh within the framework of the XFEM and linear elastic fracture mechanics. The advancing front is represented by the level sets and the stress distribution and the fracture parameters are estimated to understand the stress development during lithiation. The fracturing is simulated based on the maximum principal stress criterion. The numerical results are compared with available experimental results. The proposed framework will provide insights into understanding the failure and degradation of the electrodes under potentiostatic and galvanostatic conditions. The influence of the particle size and shape on the fracture parameters and the stress distribution is also investigated.