Developments and Perspectives on Robust Nano- and Microstructured Binder-Free Electrodes for Bifunctional Water Electrolysis and Beyond

The development of robust nano- and microstructured catalysts on highly conductive substrates is an effective approach to produce highly active binder-free electrodes for energy conversion and storage applications. As a result, nanostructured electrodes with binder-free designs have abundant advantages that provide superior electrocatalytic performance; these include more exposed active sites, large surface area, strong adhesion to substrates, facile charge transfer, high conductivity, high intrinsic catalytic activity, and fine-tuning of its electronic nature through nanostructure modification. Notably, the interface chemistry of an electrocatalyst plays a significant role in their optimized electrocatalytic activity and stability. This review provides an overview of recent progress in nano- and microstructured catalysts, such as one, two, and 3D catalysts as binder-free electrodes for electrocatalytic water splitting via the hydrogen evolution reaction and oxygen evolution reaction, and beyond. Furthermore, this review focuses on the current challenges and synthesis strategies of binder-free electrodes, with a focus on the impact of nanostructure on their functional property relationships and enhanced bifunctional electrocatalytic performance. Finally, an outlook for their future advances in energy conversion and storage is provided.</p

Effect of aging on the ionic conductivity of polyvinylidenefluoride–hexafluoropropylene (PVdF–HFP) membrane impregnated with different lithium salts

The aging towards the ionic conductivity have been studied using of different lithium salts namely, lithium bis(oxalate)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium fluoroalkylphosphate (LiFAP) and LiPF6 in polyvinylidenefluoride–hexafluoropropylene (PVdF–HFP) matrix. The crystallization behavior of LiBOB and LiDFOB has been noticed for the first time during storage of such membranes within the texture of PVdF–HFP matrix. At the same time, such behavior has not been observed in the case of LiFAP and LiPF6 based membranes. The growth of such crystallites would certainly hinder the mobility mechanism of Li+ ions and it has been confirmed by ionic conductivity measurements. The formation of such crystals has been validated through scanning electron microscopic studies

Synthesis and characterization of novel LiFeBO3/C cathodes for lithium batteries

Carbon-coated LiFeBO3 has been successfully synthesized by solid state reaction method at 750 °C under Ar atmosphere. Adipic acid was chosen for the source material for carbon during synthesis process. X-ray diffraction pattern confirms the formation of phase with monoclinic structure. Scanning electron microscopic study vindicates the particulate nature of the synthesized LiFeBO3 with weak agglomeration. Electrochemical impedance spectroscopy parallels the enhanced conducting properties of carbon-coated LiFeBO3 rather pristine LiFeBO3. The Li/carbon-coated LiFeBO3 and LiFeBO3 cells presented the initial discharge capacities 93 and 47 mAh/g, respectively. After few cycles, the carbon-coated LiFeBO3 exhibited stable discharge behavior (~53 mAh/g), whereas bare LiFeBO3 is concerned because poor electrochemical performance has resulted.Accepted versio

Novel polymer electrolyte based on cob-web electrospun multi component polymer blend of polyacrylonitrile/poly(methyl methacrylate)/polystyrene for lithium ion batteries : preparation and electrochemical characterization

The aim of the present work is to prepare a novel polymer electrolyte (PE) based on multi component polymer blend of polyacrylonitrile (PAN), poly(methyl methacrylate) (PMMA) and polystyrene (PS) with varying compositions by electrospinning. Structural characterization is carried out using X-ray diffraction (XRD). The thermal and crystalline properties of the blend are studied by thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively. Morphology of the membrane is examined by field emission scanning electron microscope (FE-SEM). The voids and cavities generated by the interlaying of the fibers are effectively utilized for the preparation of PE by loading with lithium hexafluorophosphate (LiPF6) dissolved in ethylene carbonate (EC)/diethyl carbonate (DEC). The ionic conductivity of the polymer blend electrolyte is studied by varying the PMMA and PS content in the PAN matrix. The blend polymer electrolyte shows ionic conductivity of about 3.9 × 10(−3) S cm(−1). The performance evaluation in coin cells show good charge–discharge properties and stable cycle performance under the test conditions. The result shows that the prepared polymer blend electrolytes are promising materials for lithium ion batteries.Accepted versio

Electrochemical performance of NASICON type carbon coated LiTi2(PO4)3 with a spinel LiMn2O4 cathode

NASICON type LiTi2(PO4)3 particles are synthesized by a modified pechini type polymerizable complex method at 1000 °C in an air atmosphere. The synthesized LiTi2(PO4)3 particles are ball milled and subsequently carbon coated from the carbonization of glucose (C–LiTi2(PO4)3). Li-insertion properties are evaluated in half-cell configurations (Li/C–LiTi2(PO4)3) and delivered an initial discharge capacity of 117 mAh g−1 at a current density of 15 mA g−1. Carbon coating alleviates the severe capacity fading of LiTi2(PO4)3 during cycling. A full-cell with an operating potential of 1.5 V is constructed employing C–LiTi2(PO4)3 as the anode with a spinel cathode, LiMn2O4, which delivered the first discharge capacity of 103 mAh g−1 at current density of 150 mA g−1. The LiMn2O4/C–LiTi2(PO4)3 cell retains 72% of initial discharge capacity after 200 cycles and the results suggest that, the full-cell can be used for miniature applications by replacing other rechargeable systems like lead–acid, Ni–Cd and Ni–MH

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

High power lithium-ion hybrid electrochemical capacitors using spinel LiCrTiO4 as insertion electrode

We report the synthesis and electrochemical performance of sub-micron size LiCrTiO4 particles prepared by a solid-state approach. X-ray diffraction and transmission electron microscopic studies are used to analyze the structural and morphological properties, respectively, of the synthesized powders. Electrochemical Li-insertion properties are evaluated in half-cell configurations (Li/LiCrTiO4) by means of both galvanostatic and potentiostatic modes between 1 and 2.5 V vs. Li. Reversible insertion of almost one mole of lithium (155 mA h g−1) is noted at a low current rate of 15 mA g−1 and rendered an excellent cycling profile as well. A non-aqueous Li-ion electrochemical hybrid capacitor (Li-HEC) is fabricated with an optimized mass loading of activated carbon (AC) cathode and synthesized LiCrTiO4 as anode in 1 M LiPF6 in ethylene carbonate–diethyl carbonate solution and cycled between 1 and 3 V under ambient conditions. The Li-HEC delivered maximum specific energy and power densities of 23 W h kg−1 and 4 kW kg−1, respectively

Electrochemical lithium insertion behavior of combustion synthesized V2O5 cathodes for lithium-ion batteries

Sub-micron size vanadium pentoxide (V2O5) particles are synthesized by novel urea assisted combustion method. Comprehensive characterization and electrochemical studies related to sintering temperature and duration are presented. X-ray diffraction (XRD) patterns showed the formation of pure-phase V2O5 and the surface morphologies are studied by field emission scanning electron microscopy (FE-SEM). Electrochemical properties of the sintered V2O5 as a cathode in lithium-ion batteries are explored with respect to synthesis parameters using cyclic voltammetry and galvanostatic charge-discharge studies. The V2O5 particles obtained from 600°C sintering temperature for 1 h exhibits a higher initial discharge capacity ∼320 mAh g−1 (∼2.2 Li per V2O5) between 1.75–4.0 V vs. Li/Li+ at 0.1 C rate and shows good capacity retention of >70% after 50 cycles. Electrochemical impedance spectroscopy (EIS) studies show that the urea combustion method enables increased Li+ ion diffusion pathways and electro-active surface area in V2O5 particles. Ball milling procedure with or without carbon is also adopted to further reduce the particle size of V2O5 and related electrochemical properties are evaluated and described.Published versio

Chemical lithiation studies on combustion synthesized V2O5 cathodes with full cell application for lithium ion batteries

Fundamental studies on Li-intercalation into layered vanadium pentoxide (V2O5), synthesized by urea combustion method, have been successfully carried out by chemical lithiation using butyl lithium at various concentrations. Morphological and structural changes during chemical lithiation are analyzed by field-emission scanning electron microscopy and X-ray diffraction measurements, respectively. Furthermore, chemical states and elemental concentration of these lithiated V2O5 phases were elucidated by X-ray photoelectron spectroscopy and inductively coupled plasma. Electrochemical studies via potentiostatic and galvanostatic modes show that the chemically-lithiated V2O5 phases undergo similar redox behavior as bare V2O5 at respective discharge-states. The electrochemical studies confirmed the occurrence of various phase transformations at various levels of discharge relating to both reduction of vanadium (V5+) and intercalation of lithium ions in V2O5. Finally, the full-cell comprising of lithiated V2O5 cathode and spinel Li4Ti5O12 anode is demonstrated to study their compatibility toward insertion type anodes, delivering the reversible capacity of 80 mAh g−1.Published versio

Towards Commercialization of Graphite as an Anode for Na-ion Batteries: Evolution, Virtues, and Snags of Solvent Cointercalation

Sodium-ion storage in graphite through a solvent cointercalation mechanism is extremely robust regarding cycling stability, rate performance, and Coulombic efficiency. The graphite half cell has a low working voltage and high power density. The respectable capacity, even at high current rates, makes graphite in a glyme-based system a versatile energy storage device. This perspective comprehensively looks at graphite-based sodium-ion full cells and how they perform. Electrolyte composition, cathode working voltage, irreversibility, precycling, and high current performance are the key points to consider during full-cell fabrication. Some general factors to consider during the full-cell assembly are put forward in this perspective