Graphite has been the conventional lithium-ion anode for the negative electrode for the past three decades. One of the major challenges for graphite anodes is the exfoliation of graphite framework on deep cycling at a fast current rate, leading to a gradual capacity fade. In this regard, poly(vinylidene fluoride) (PVDF) has been the conventional binder widely used for stabilizing the graphite framework. Unfortunately, its nonconducting nature, slow dissolution in the electrolyte, and poor adherence to the current collector limit its utility as a robust binder for lithium-ion batteries with a long cycle life. Here, we report an n-type conjugated copolymer bis-imino-acenaphthenequinone-paraphenylene (BP) as an alternate binder material for the graphite anode. The BP binder-based anodic half-cells outperformed the PVDF-based counterpart, showing an excellent performance with a reversible capacity of 260 mA h g–1, cyclability up to 1735 long cycles at 1 C rate, and 95% capacity retention. The superior performance of the BP binder was attributed to its ability to provide mechanical robustness to the electrode laminate, maintain electronic conductivity within the electrode, and undergo n-doping in the anodic environment, influencing the formation of a thin solid electrolyte interface with low interfacial impedance.
Natural abundance and high theoretical capacity make silicon a promising anode material in Li-ion batteries (LIBs). However, repeated cycling causes the pulverization of Si particles due to the large volume expansion that results in their rapid breakdown, delamination from the current collector, loss of electrical contact, and thick solid–electrolyte interphase (SEI) formation. This results in their poor performance. To overcome these drawbacks, the application of functional polymers as binders to silicon anodes has emerged as a competitive strategy. In this regard, here, the design, synthesis, and application of a highly robust n-type self-healing polymer composite poly(bisiminoacenaphthenequinone)/poly(acrylic acid) (P-BIAN/PAA) as a binder for Si anodes is reported. On its application, P-BIAN/PAA was evaluated to (i) provide mechanical robustness to the large volume expansion of Si particles, (ii) maintain electrical conductivity within the electrode laminate, and (iii) facilitate the formation of a thin SEI by restricting the extent of electrolyte decomposition on the surface of anode because of its low-lying lowest unoccupied molecular orbital (LUMO) that empowers its n-doping in the reducing environment. As a result, Si anodes could be stabilized for over 600 cycles of charge–discharge with a high reversible capacity of about 2100 mAh g–1 Si, ∼95% capacity retention, and >99% Coulombic efficiency. The extent of suppression of electrolyte decomposition that led to a facile and thin interphase-SEI and the corresponding interfacial components with respective impedance values were not only theoretically evaluated but also supported by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and dynamic-EIS. Further, the postmortem characterization of the anode by X-ray photoelectron spectroscopy (XPS) justified the thin SEI formation on Si anode with P-BIAN/PAA composite binder.
Given widespread fluoride in the ground water, there is a need for effective defluoridation in several geographical areas. In this regard, we explored heavily doped cationic nano-composites of hydroxyapatite (HA) given its surface chemistry for adsorption of the specific anion. We synthesized and extensively characterized HA nano-rods (HA-NR), Al/Mg-HA nanocomposites and amorphous aluminum hydroxide, and optimized their efficient defluoridation. The kinetics and thermodynamics of adsorption were further evaluated to establish the mechanistic rationale and its spontaneity. We report the optimized ideal adsorbents for the near-total removal of fluoride that demonstrated 99.99% and 99.98% efficiency with adsorption capacities of 83.3 and 81.3mg/g respectively. The adsorbent composites were (Mg-HA)-Al(OH)3 and (HA-NR)-Al(OH)3 in 1:1 ratio. The optimal conditions for defluoridation were 25mg of adsorbent in 25ml (10mg/L) fluoride solution at room temperature agitated for 10h in the pH range of 4.88–7.20.
The uncontrolled oxidative decomposition of electrolyte while operating at high potential (> 4.2 V vs Li/Li+) severely affects the performance of high-energy density transition metal oxide-based materials as cathodes in Li-ion batteries. To restrict this degradative response of electrolyte species, the need for functional molecules as electrolyte additives that can restrict the electrolytic decomposition is imminent. In this regard, bio-derived molecules are cost-effective, environment friendly, and non-toxic alternatives to their synthetic counter parts. Here, we report the application of microbially synthesized 2,5-dimethyl-3,6-bis(4-aminobenzyl)pyrazine (DMBAP) as an electrolyte additive that stabilizes high-voltage (4.5 V vs Li/Li+) LiNi1/3Mn1/3Co1/3O2 cathodes. The high-lying highest occupied molecular orbital of bio-additive (DMBAP) inspires its sacrificial in situ oxidative decomposition to form an organic passivation layer on the cathode surface. This restricts the excessive electrolyte decomposition to form a tailored cathode electrolyte interface to administer cyclic stability and enhance the capacity retention of the cathode.
Water electrolysis (WE) using proton exchange membrane water electrolyser (PEMWE) stands as one of the cleanest methods to produce hydrogen from water which is the greener alternative that can replace fossil fuels. Oxygen evolution reaction (OER) that happens at its anode is both thermodynamically and kinetically demanding. IrO2 is the only known catalyst that can be used in acidic conditions but its high overpotential ~330 mV and cost preclude its future use. In the past, several attempts have been made to tune the catalytic activity, durability and overpotential by changing the morphology and electronic structure. The high surface area nanostructures could achieve decent activity but the overpotential and durability are still at stake. The high surface area nanostructures could achieve decent activity but the overpotential and durability are still at stake. Norskov1 et al., showed a linear relation between metal oxide d band centre and binding energies to O (intermediates) to the surface (ΔEO) which play a key role in determining the overpotential of the system. Hence, tuning of electronic structure by doping with other metals like Ru, Ni, Co, Pb, Y, Se, Sn, Sr2 etc or with fluorine3 was found to be trending in recent years. But, the leaching of alloying metals (durability) and precise tuning of electronic structure are not achieved. Recently our group has come up with a novel strategy of tuning the electronic structure of IrO2 nanoparticles (nps) by (a) using electrochemically stable carbon and doped carbon substrates4,5 (b) very strong metal substrate interaction and (c) changing the electronic structure of IrO2. By using 10 at% nitrogen doped graphene, overpotential was reduced to 260-270 mV with very high durability. There is always a limit for heteroatom doping using conventional ways. Further very less works on precise tuning of electronic structure and anchoring of IrO2 nanoparticles to substrate gives a scope of research. In this regard conducting polymers as substrates with coordination sites for anchoring the nanoparticles and tuning the electronic structure was explored in this study. An electropolymerizable monomer bearing α-diimine and thienyle groups was prepared by condensation between acenaphthequinone and 2 equivalents of aminothiophene. Electropolymerization technique was utilized to prepare polythiophene (PTh) on TiO2 nanotube (PTh-TNT) array as substrate. Further, the α-diimine moiety was utilized to prepare polythiophene-Ir metal complex. Ir metal complex centers could act as the nucleation sites for the growth of IrO2 nanoparticles due to which the electronic interaction with IrO2 and the diimine ligand will be still active. This interaction may lead to alter the electronic states of IrO2 like that of Ir in the complex at the same time will anchor the IrO2 nanoparticles strongly that results in high activity and durability during OER. For comparison TNT-PTh-IrO2 material without prior complexation was also prepared. Shift in the electron structure was characterized by X-ray photoelectron spectroscopy. The shift of binding energy (BE) of Ir 4f peak of TNT-PTh-IrO2 (with complex) to a lower BE compared to TNT-PTh-IrO2 (without complex) was a clear indication for increased electron cloud on IrO2. This shift of electron cloud will modulate the bond length of intermediate ions and help in their easy mass transfer leading to higher activity. Electrocatalytic OER activity was studied by linear-sweep voltammetry (LSV) technique in 3 electrode system in 1 M H2SO4. The effect of anchoring through coordination showed twice the activity compared to IrO2 on polythiophene without anchoring (Figure 1). Further a clear reduction in overpotential was also observed. When compared with TNT-IrO2, TNT-PTh-IrO2 with complexation showed at least 10 times higher current density. Further, preliminary chronopotentiometry showed no change in the over potential at 10 mAcm2 for 5 h. Thus, utilization of strong coordination of α-diimine in the polythiophene structure was key in modifying the electronic structure and anchoring resulting very high OER activity in acidic environment. Acknowledgement: We thank financial support by JSPS, KAKENHI, grant number 19K15674. References: Norskov J.K., et al., Catal. 2000, 45, 71. Kumta N.P., et al., Phys. Chem. C, 2013, 117, 20542. Thomas F. J., et al., Science, 2016, 353, 1011. Badam R., et al., J. Hydrog. Energy, 2018, 43, 18095. Badam R., et al., ECS Trans., 2018, 85, 27 Figure 1
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