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Creators/Authors contains: "Deivanayagam, Ramasubramonian"

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  1. Abstract

    Solid‐state lithium batteries are widely believed to be the most feasible next‐generation battery technology. New material candidates for solid electrolytes are typically screened using meticulous characterization methods and ranked using metrics such as ionic conductivity, transference number, decomposition voltage, and deposition/stripping overpotential. The determination of these metrics requires the use of a variety of electrochemical experiments, the details of which are scattered across existing literature and could be time‐consuming for a beginner to locate. Here, we present a comprehensive overview of the electrochemical concepts, methods, and protocols adopted to characterize the polymer and ceramic electrolyte candidates for rechargeable batteries. This work facilitates the understanding of the key parameters involved in solid‐state electrolyte characterization and in interpreting their data.

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  2. Abstract

    Proper distribution of thermally conductive nanomaterials in polymer batteries offers new opportunities to mitigate performance degradations associated with local hot spots and safety concerns in batteries. Herein, a direct ink writing (DIW) method is utilized to fabricate polyethylene oxide (PEO) composite polymers electrolytes (CPE) embedded with silane‐treated hexagonal boron nitride (S‐hBN) platelets and free of any volatile organic solvents. It is observed that the S‐hBN platelets are well aligned in the printed CPE during the DIW process. The in‐plane thermal conductivity of the printed CPE with the aligned S‐hBN platelets is 1.031 W−1K−1, which is about 1.7 times that of the pristine CPE with the randomly dispersed S‐hBN platelets (0.612 W−1K−1). Thermal imaging shows that the peak temperature (°C) of the printed electrolytes is 24.2% lower than that of the CPE without S‐hBN, and 10.6% lower than that of the CPE with the randomly dispersed S‐hBN, indicating a superior thermal transport property. Lithium‐ion half‐cells made with the printed CPE and LiFePO4cathode displayed high specific discharge capacity of 146.0 mAh g−1and stable Coulombic efficiency of 91% for 100 cycles at room temperature. This work facilitates the development of printable thermally‐conductive polymers for safer battery operations.

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  3. Abstract

    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−2at 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. 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.

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  4. Abstract

    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.

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  5. Abstract

    LiCoO2is a prime 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. Here, it is shown that an atomically thin layer of reduced graphene oxide can suppress oxygen release from LixCoO2particles 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 LixCoO2. 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. Finally, density functional theory and ab initio molecular dynamics calculations show that the rGO layers could suppress O2formation more effectively due to the strong COcathodebond 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.

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