Engineering topics

Deivanayagam, Ramasubramonian

Publications and source records attributed to Deivanayagam, Ramasubramonian.

7 records

DOE OSTI2020

Highly-Cyclable Room-Temperature Phosphorene Polymer Electrolyte Composites for Li Metal Batteries

Despite significant interest toward solid-state electrolytes owing to their superior safety in comparison to liquid-based electrolytes, sluggish ion diffusion and high interfacial resistance limit their application in durable and high-power density batteries. Here, a novel quasi-solid Li + ion conductive nanocomposite polymer electrolyte containing black phosphorous (BP) nanosheets is reported. The developed electrolyte is successfully cycled against Li metal (over 550 h cycling) at 1 mA cm -2 at room temperature. The cycling overpotential is dropped by 75% in comparison to BP-free polymer composite electrolyte indicating lower interfacial resistance at the electrode/electrolyte interfaces. Molecular dynamics simulations reveal that the coordination number of Li + ions around (trifluoromethanesulfonyl)imide (TFSI - ) pairs and ethylene-oxide chains decreases at the Li metal/electrolyte interface, which facilitates the Li + transport through the polymer host. Here, density functional theory calculations confirm that the adsorption of the LiTFSI molecules at the BP surface leads to the weakening of N and Li atomic bonding and enhances the dissociation of Li + ions. This work offers a new potential mechanism to tune the bulk and interfacial ionic conductivity of solid-state electrolytes that may lead to a new generation of lithium polymer batteries with high ionic conduction kinetics and stable long-life cycling.

2D materials↗

DOE OSTI2020

Solution Blowing Synthesis of Li-Conductive Ceramic Nanofibers

Solid state electrolytes (SSEs) offer great potential to enable high-performance and safe lithium (Li) batteries. However, the scale-up synthesis and processing of SSEs is a major challenge. In this work, three-dimensional networks of lithium lanthanum titanite (LLTO) nanofibers are produced through a scale-up technique based on solution blowing. Compared with the conventional electrospinning method, the solution blowing technique enables high-speed fabrication of SSEs (e.g., 15 times faster) with superior productivity and quality. Additionally, the room-temperature ionic conductivity of composite polymer electrolytes (CPEs) formed from solution-blown LLTO fibers is 70% higher than the ones formed from electrospun fibers (1.9 x 10 -4 vs 1.1 x 10 -4 S cm -1 for 10 wt % LLTO fibers). Furthermore, the cyclability of the CPEs made from solution-blown fibers in the symmetric Li cell is more than 2.5 times that of the CPEs made from electrospun fibers. These comparisons here show that solution-blown ion-conductive fibers hold great promise for applications in Li metal batteries.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Progress in development of electrolytes for magnesium batteries

Over the last few years, there has been an increased interest in developing safe, next-generation battery systems that offer energy densities higher than those of lithium-based batteries. In this context, batteries based on multivalent-ions (Mg 2+ , Zn 2+ , Ca 2+ , and Al 3+ ) have developed their own niche with their capability to achieve at least twice the energy density of monovalent-ion systems such as Li-ion and Na-ion batteries. Among the multivalent-ion battery candidates, magnesium (Mg) batteries appear to be the most viable choice to eventually replace the Li-ion technology because of the high electrode potential, superior safety, and high abundance of Mg-metal. However, the limited development in electrolytes and cathodes has prevented their commercialization to date. There is a lack of suitable electrolytes that can be used at high voltages required for Mg 2+ insertion into cathode hosts. The limited compatibility of organic electrolytes with Mg-metal anode is also a challenge, which requires extensive studies of the metal/electrolyte interactions. Such studies over the last two decades were critical in developing state-of-the-art Mg electrolytes that possess voltage windows of >4.0 V and simultaneously be compatible with Mg-metal anodes. Here, we present a review on the development of Mg battery electrolytes, challenges that impede their performance, and promising strategies that have been adopted to address them. As a result, we believe that this comprehensive review covering all three categories of Mg electrolytes (liquids, polymers, and solids) would enable researchers to get a quick grasp of the prevailing challenges, and consequently motivate them to develop novel electrolyte candidates.

25 ENERGY STORAGE↗

DOE OSTI2019

Anti-Oxygen Leaking LiCoO 2

LiCoO 2 is a great example of widely used cathodes that suffer from the structural/thermal instability issues that lead to the release of their lattice oxygen under nonequilibrium conditions and safety concerns in Li-ion batteries. In this work, it is shown that an atomically thin layer of reduced graphene oxide can suppress oxygen release from LixCoO 2 particles and improve their structural stability. Electrochemical cycling, differential electrochemical mass spectroscopy, differential scanning calorimetry, and in situ heating transmission electron microscopy are performed to characterize the effectiveness of the graphene-coating on the abusive tolerance of LixCoO 2 . Electrochemical cycling mass spectroscopy results suggest that oxygen release is hindered at high cutoff voltage cycling when the cathode is coated with reduced graphene oxide. Thermal analysis, in situ heating transmission electron microscopy, and electron energy loss spectroscopy results show that the reduction of Co species from the graphene-coated samples is delayed when compared with bare cathodes. Lastly, density functional theory and ab initio molecular dynamics calculations reflect that the rGO layers could suppress O 2 formation more effectively due to the strong C—O cathode bond formation at the interface of rGO/LCO where low coordination oxygens exist. This investigation uncovers a reliable approach for hindering the oxygen release reaction and improving the thermal stability of battery cathodes.

25 ENERGY STORAGE↗

DOE OSTI2018

Elevated‐Temperature 3D Printing of Hybrid Solid‐State Electrolyte for Li‐Ion Batteries

Abstract While 3D printing of rechargeable batteries has received immense interest in advancing the next generation of 3D energy storage devices, challenges with the 3D printing of electrolytes still remain. Additional processing steps such as solvent evaporation were required for earlier studies of electrolyte fabrication, which hindered the simultaneous production of electrode and electrolyte in an all‐3D‐printed battery. Here, a novel method is demonstrated to fabricate hybrid solid‐state electrolytes using an elevated‐temperature direct ink writing technique without any additional processing steps. The hybrid solid‐state electrolyte consists of solid poly(vinylidene fluoride‐hexafluoropropylene) matrices and a Li + ‐conducting ionic‐liquid electrolyte. The ink is modified by adding nanosized ceramic fillers to achieve the desired rheological properties. The ionic conductivity of the inks is 0.78 × 10 −3 S cm −1 . Interestingly, a continuous, thin, and dense layer is discovered to form between the porous electrolyte layer and the electrode, which effectively reduces the interfacial resistance of the solid‐state battery. Compared to the traditional methods of solid‐state battery assembly, the directly printed electrolyte helps to achieve higher capacities and a better rate performance. The direct fabrication of electrolyte from printable inks at an elevated temperature will shed new light on the design of all‐3D‐printed batteries for next‐generation electronic devices.

Cheng, Meng↗

DOE OSTI2018

Cations controlled growth of β-MnO 2 crystals with tunable facets for electrochemical energy storage

Engineering crystal facets to enhance their functionalities often require complex processing routes to suppress the growth of surfaces with the lowest thermodynamic energies. Herein, we report a unique method to control the morphologies of β-MnO 2 crystals with different occupancy of {100}/{111} facets through the effect of K + cations. Combining aberration-corrected scanning transmission electron microscopy (STEM), ultramicrotomy, and dynamic functional theory (DFT) simulation, we clarified that the β-MnO 2 crystals were formed through a direct solid-state phase transition process. Increasing the concentration of K + cations in the precursor gradually changed the morphology of β-MnO 2 from bipyramid prism ({100}+{111} facets) to an octahedron structure ({111} facets). The K + cations controlled the morphology of β-MnO 2 by affecting the formation of α-K 0.5 Mn 4 O 8 intermediate phase and the subsequent phase transition. Utilizing the β-MnO 2 crystals as the cathode for Li-ion batteries showed that highly exposed {111} facets offered β-MnO 2 crystal better rate performance, with ~70% capacity retention when the charge-discharge rate increased from 20 mA/g to 200 mA/g. Furthermore, our work revealed a new mechanism to tune the morphology of this earth-abundant metal oxide crystal, which could be used to adjust its electrochemical performance for different applications, such as supercapacitors and catalysts for metal-air batteries and fuel cells.

25 ENERGY STORAGE↗

DOE OSTI2018

Synergistic Effect of Graphene Oxide for Impeding the Dendritic Plating of Li

Dendritic growth of lithium (Li) has severely impeded the practical application of Li-metal batteries. Herein, a 3D conformal graphene oxide nanosheet (GOn) coating, confined into the woven structure of a glass fiber separator, is reported, which permits facile transport of Li-ions thought its structure, meanwhile regulating the Li deposition. Electrochemical measurements illustrate a remarkably enhanced cycle life and stability of the Li-metal anode, which is explained by various microscopy and modeling results. Utilizing scanning electron microscopy, focused ion beam, and optical imaging, the formation of an uniform Li film on the electrode surface in the case of GO-modified samples is revealed. Ab initio molecular dynamics (AIMD) simulations suggest that Li-ions initially get adsorbed to the lithiophilic GOn and then diffuse through defect sites. This delayed Li transfer eliminates the “tip effect” leading to a more homogeneous Li nucleation. Meanwhile, C-C bonds rupture observed in the GO during AIMD simulations creates more pathways for faster Li-ions transport. In addition, phase-field modeling demonstrates that mechanically rigid GOn coating with proper defect size (smaller than 25 nm) can physically block the anisotropic growth of Li. This new understanding is a significant step toward the employment of 2D materials for regulating the Li deposition

25 ENERGY STORAGE↗