Browsing by Author "Xu, Jianan"

Now showing 1 - 3 of 3
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    Cobalt-free cathode materials for Li-ion batteries: synthesis, processing, characterization and evaluation of the electrochemical performances
    (2023-04-20) Xu, Jianan; Ajayan, Pulickel
    Li-ion batteries cathode materials play an important role in limiting the overall capacity and energy density of the cell, due to their relatively lower specific capacity (~200 mAh/g) compared to that of the anode counterparts (Graphite 372 mAh/g, Si 4212 mAh/g). The chronological development of the classical cathode materials is reviewed. Li1.2Mn0.4Ti0.4O2 (LMTO) belonging to the emerged cation-disordered rock-salt cathodes family, is then selected due to its high specific capacity larger than 250 mAh/g and the Co-free inexpensive feature. While the typical cathode material loading is only 70.0 wt.% with additional components, a chemical vapor deposition method is applied to increase the electrical conductivity by coating a carbon layer on the LMTO particle surface. On the other hand, carbon nanotube is selected to be the ball milling additive and a 78.7 wt.% cathode loading is reached, which increases the cathode gravimetric capacity from 44 mAh/g to 121 mAh/g after fifty cycles. Li1.079Ni0.400Ti0.476O2 is then selected and ball-milled, and the PITT measurement is applied to extract the Li+ diffusivity value. The obtained DLi+ on the order of 10-15 cm2/s successfully explains the kinetic requirement for the particle size less than 200 nm, giving a 10 mA/g current density. Furthermore, the effects of ball milling on the electrochemical capacity and interfacial stability of Li2MnO3 cathode material is studied, which reveals the inducing of Li2CO3 contaminant species even though the capacity is largely enhanced, its further decomposition into CO2 during first charge and the reduction of CO2 to carbonate species during the following discharge. Next, an all-fluorinated electrolyte is coupled with the LMTO material which increases the coulombic efficiency to 90.0 % and 99.0 % for the first cycle and subsequent cycles, respectively, with a F-rich cathode-electrolyte-interphase characterized by XPS. Finally, several types of hydrothermal methods and a flash joule heating method are adopted to directly synthesize the LMTO material with nano-sized primary particles. As a result, spinel structure LiMnTiO4 is found to be the stable phase and LMTO can only be synthesized via traditional solid-state method.
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    Hard carbon anode for lithium-, sodium-, and potassium-ion batteries: Advancement and future perspective
    (Elsevier, 2024) Saju, Sreehari K.; Chattopadhyay, Shreyasi; Xu, Jianan; Alhashim, Salma; Pramanik, Atin; Ajayan, Pulickel M.
    Due to its overall performance, hard carbon (HC) is a promising anode for rechargeable lithium-, sodium-, and potassium-ion batteries (LIBs, NIBs, KIBs). The microcrystalline structure morphology of HCs facilitates the alkali metal -ion uptake and fast ion intercalation and deintercalation throughout the pores with low-potential intercalation properties. However, the large-scale industrial application of HCs is still lagging because of the first-cycle reversible capacity, which results in low initial Coulombic efficiency (ICE) and voltage hysteresis. This review focuses on the fundamental mechanism of HCs as alkali metal-ion batteries, with the current issues being discussed. This includes the formation of solid electrolyte interphase during the first cycle with low ICE, safety concerns, and improved performances, which are vital for practical applicability. The current state-of-the-art of HC anodes is discussed here with recent literature. Furthermore, the challenges and the corresponding effective strategies to overcome the difficulties related to the commercialization of HCs as rechargeable battery anodes are discussed.
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    Metal Oxide Catalysts for the Synthesis of Covalent Organic Frameworks and One-Step Preparation of Covalent Organic Framework-Based Composites
    (American Chemical Society, 2021) Zhu, Yifan; Zhu, Dongyang; Yan, Qianqian; Gao, Guanhui; Xu, Jianan; Liu, Yifeng; Alahakoon, Sampath B.; Rahman, Muhammad M.; Ajayan, Pulickel M.; Egap, Eilaf; Verduzco, Rafael; Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment
    The integration of covalent organic frameworks (COFs) with inorganic materials provides opportunities to develop a new class of composite materials with high surface areas and novel functionalities relevant to photocatalysis, chemical adsorption, and magnetic resonance imaging. However, current methods for the preparation of COF-based composites require challenging, multistep synthetic protocols. Herein, we report a one-pot synthesis approach using a wide range of metal oxides to catalyze the synthesis of highly crystalline and porous COFs. We found that a large variety of metal oxides served as effective catalysts for the synthesis of imine COFs, including niobium(V) oxide (Nb2O5), nickel(II) oxide (NiO), manganese(IV) dioxide (MnO2), ruthenium(IV) oxide (RuO2), zinc(II) oxide (ZnO), lead(II) oxide (PbO), tellurium(IV) dioxide (TeO2), tin(IV) oxide (SnO2), manganese(III) oxide (Mn2O3), zirconium(IV) dioxide (ZrO2), and aluminum(III) oxide (Al2O3). Nb2O5 was effective for the synthesis of a wide range of COFs with different functional groups and pore sizes, and these reactions produced a metal oxide/COF composite. By using Fe3O4 nanoparticles (NPs) as the catalyst, we produced COF-based nanocomposites with Fe3O4 NPs distributed throughout the final COF product. The Fe3O4/COF nanocomposite had a high surface area of 2196 m2 g–1. This work demonstrates a class of novel, low-cost catalysts for synthesizing COFs and a new approach to produce metal oxide/COF composite materials.