ORGANIC/INORGANIC HYBRID STRUCTURES BY MOLECULAR ASSEMBLY

Ph.DDOCTOR OF PHILOSOPH

High energy Li-ion capacitor and battery using graphitic carbon spheres as an insertion host from cooking oil

We report a facile low-temperature synthesis of graphitic carbons with a spherically shaped morphology (CO-CS) and high purity by the modified catalytic chemical vapour deposition using vegetable cooking oil as a carbon source. The excellent Li-insertion properties are noted with high reversibility (∼369 mA h g−1) in the half-cell assembly, which is very close to the theoretical capacity of graphite. Further explored the suitability to be used as an anode in the practical configurations, the intercalation type LiFePO4 and double layer forming activated carbon (AC) have been used as the cathodes toward the fabrication of Li-ion battery (LIB) and Li-ion capacitor (LIC), respectively. Prior to the LIC assembly, CO-CS has been pre-lithiated electrochemically. Both LiFePO4/CO-CS and AC/CO-CS assemblies display a maximum energy density of ∼337 and ∼108 W h kg−1 (based on an active material loading), respectively. The obtained values are better than those of the state-of-the-art LIB and LIC based on a graphitic anode. A decent cycle-ability is also registered for both cases.NRF (Natl Research Foundation, S’pore

Electrochemical route to alleviate irreversible capacity loss from conversion type α-Fe₂O₃ anodes by LiVPO₄F prelithiation

We report a new electrochemical procedure to suppress the irreversible capacity loss (ICL) from high capacity anodes, specifically for high capacity anodes that undergo either alloying or conversion reaction with Li. In the present work, tavorite type LiVPO₄F is used as Li-reservoir and conversion type α-Fe₂O₃ nanofibers as an anode. Unfortunately, LiVPO₄F cannot be used as the promising anode (∼1.7 V vs Li) because of its poor cycling stability, but it can be used to accommodate the desired amount of Li for ICL compensation. Accordingly, LiVPO₄F is electrochemically prelithiated (Li₁.₂₆VPO₄F) and paired with α-Fe₂O₃ nanofibers with optimized loadings. The full cell is displaying a maximum capacity of ∼755 mAh g⁻¹ (calculated on the basis of anode mass) with notable cycling profile. Before the fabrication of the full cell, half-cell studies are performed to assess the Li-storage capability at the same current rate for mass balance.Ministry of Education (MOE)National Research Foundation (NRF)This work was financially supported by Ministry of Education (MOE TIER 2 Funding (MOE2015-T2-1-046), Singapore and NTU-HUJ Create Phase II which is a joint research programme between the Hebrew University of Jerusalem (HUJ, Israel) and Nanyang Technological University (NTU, Singapore) with CREATE (Campus for Research Excellence and Technological Enterprise) funding from National Research Foundation of Singapore (NRF, SIngapore). V.A. acknowledges financial support from the Science & Engineering Research Board (SERB), a statutory body of the Department of Science & Technology, Government of India, through the Ramanujan Fellowship (SB/S2/RJN-088/2016)

From electrodes to electrodes : building high‐performance Li‐ion capacitors and batteries from spent lithium‐ion battery carbonaceous materials

We report the possibility of recycling carbonaceous materials (GC) from used/spent Li‐ion batteries (LIBs) and re‐using the material again as a negative electrode. In addition to LIB, the possibility of using them in Li‐ion capacitor (LIC) configuration with activated carbon is also explored. First, the carbonaceous materials are recovered from the mechanical treatment and subsequent leaching process. After the successful recovery, the Li‐insertion properties are studied in half‐cell assembly and it exhibits very decent electrochemical activity. While re‐using GC as an anode, large irreversibility is noted compared to fresh usage. Therefore, the elimination of such irreversible capacity is desperately required prior to the fabrication of either LIBs or LICs. Full‐cell LIB is assembled with olivine phase LiFePO4 cathode and the configuration delivers a maximum energy density of ∼313 Wh kg−1. Similarly, the GC is used as an anode in LIC assembly with commercial activated carbon. The LIC displays an energy density of ∼112 Wh kg−1 with decent cycling profiles.National Environmental Agency (NEA)Submitted/Accepted versionVA thank the financial support from Science & Engineering Research Board (SERB), a statutory body of the Department of Science & Technology, Govt. of India through Ramanujan Fellowship (SB/S2/RJN-088/2016). SM would like to thank the grant award from NEA (National Environmental agency) on Singapore – CEA Alliance for Research in Circular Economy (SCARCE), award number USS-IF-2018-4

Elongated graphitic hollow nanofibers from vegetable oil as prospective insertion host for constructing advanced high energy Li-Ion capacitor and battery

We report the facile and low temperature synthesis of one dimensional graphitic fibers with hollow structured morphology (VO-CF) by modified chemical vapor deposition using vegetable oil as a carbon source. Graphitization of the prepared phase is validated with various analytical tools. Prior to the fabrication of charge storage devices like Li-ion battery (LIB) and Li-ion capacitor (LIC), Li-insertion properties of VO-CF is studied in half-cell assembly. Mass adjustment between the electrodes are very crucial and adjusted for aforesaid energy storage devices. Pre-treatment or pre-lithiation is carried out using an electrochemical approach in Swagelok fittings with Li. LIB assembly with LiFePO4 delivered a maximum energy density of ∼233 Wh kg−1 whereas the LIC displayed the energy density of ∼112 Wh kg−1 when paired with activated carbon electrode. Both LIB and LIC assemblies rendered very decent cycling profiles for extended 500 and 10000 cycles, respectively.NRF (Natl Research Foundation, S’pore

Perspective of electrospun nanofibers in energy and environment

This review summarizes the recent developments of electrospun semiconducting metal oxide/polymer composite nanostructures in energy and environment related applications. Electrospinning technique has the advantage of synthesizing nanostructures with larger surface to volume ratio, higher crystallinity with phase purity and tunable morphologies like nanofibers, nanowires, nanoflowers and nanorods. The electrospun nanostructures have exhibited unique electrical, optical and catalytic properties than the bulk counter parts as well as nanomaterials synthesized through other approaches. These nanostructures have improved diffusion and interaction of molecules, transfer of electrons along the matrix and catalytic properties with further surface modification and functionalization with combination of metals and metal oxides

Biomass derived palygorskite-carbon nanocomposites:Synthesis, characterisation and affinity to dye compounds

Clay minerals can act as a uniform dispersion medium for nano-sized carbon particles. However, literature on the preparation and characteristics of palygorskite-carbon nanocomposites is scant. Using a hydrothermal carbonisation technique this study developed two nanocomposites on fibrous palygorskite from starch: the first without a post-synthesis treatment (Composite 1); and the second with an activation at 550°C for 3h (ramp at 10°Cmin-1) under CO2 environment (200mLmin-1) (Composite 2). A uniform dispersion of nano-scale carbon spheres was formed on partially destroyed palygorskite structures. Composite 2, which indicated the formation of graphitised carbon nanoparticles, generated a 17-fold greater specific surface area than Composite 1 and also created micro- and mesopores in its structure. The nanocomposites, especially in Composite 1, contained organic surface functional groups (CH, CC, CO) and indicated variable affinity to cationic and anionic dye compounds. While Composite 2 adsorbed a larger amount of anionic orange II dye (23mgg-1), Composite 1 adsorbed more cationic methylene blue (46.3mgg-1). Isothermal and kinetic modelling of the adsorption data indicated that in addition to electrostatic attraction for methylene blue adsorption on both nanocomposites, a pore diffusion mechanism was involved and the boundary resistance was greater for orange II than methylene blue adsorption. Being a material developed from green biomass (starch) and an abundant natural resource (palygorskite), these nanocomposites have immense potential for application in environmental remediation including in situ immobilisation of contaminants in soil

Unveiling the Fabrication of “Rocking-Chair” Type 3.2 and 1.2 V Class Cells Using Spinel LiNi_0.5Mn_1.5O₄ as Cathode with Li₄Ti₅O₁₂

We first report the possibility of using spinel LiNi_0.5Mn_1.5O₄ (LNM) nanofibers as cathode for constructing high (∼3.2 V) and low (∼1.2 V) voltage “rocking-chair” type Li-ion cells with spinel Li₄Ti₅O₁₂ (LTO) by utilizing Li-insertion into tetrahedral (Ni^2+/4+) and octahedral (Mn^4+/3+) sites of LNM. We also explored the possibility of constructing symmetric cells (LNM/LNM) with a working potential of ∼1.8 V. Among the three configurations investigated, LNM/LTO (electrochemically prelithiated) is found superior in terms of high rate capability, cyclability, and good capacity retention characteristics. High performance spinel LNM nanofibers are prepared via a scalable electrospinning technique and their Li-insertion properties are evaluated in half-cell assembly. The half-cell studies are used for adjusting the mass balance while fabricating “rocking-chair” Li-ion cells

Gold nanoparticle immobilization on ZnO nanorods via bi-functional monolayers: A facile method to tune interface properties

10.1016/j.susc.2015.05.005Surface Science64123-2