Vanchiappan Aravindan

Insertion-Type Electrodes for Nonaqueous Li-Ion Capacitors

Vanchiappan Aravindan,*,† Joe Gnanaraj,*,‡ Yun-Sung Lee,* and Srinivasan Madhavi*,†,∥ †Energy Research Institute @ NTU (ERI@N), Nanyang Technological University, Research Techno Plaza, 50 Nanyang Drive, Singapore 637553, Singapore ‡Yardney Technical Products, Inc., 2000 South County Trail, East Greenwich, Rhode Island 02818, United States Faculty of Applied Chemical Engineering, Chonnam National University, Gwang-ju 500-757, Korea School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore

LiMnPO4 – A next generation cathode material for lithium-ion batteries

Development of an eco-friendly, low cost and high energy density (∼700 W h kg−1) LiMnPO4 cathode material became attractive due to its high operating voltage ∼4.1 V vs. Li falling within the electrochemical stability window of conventional electrolyte solutions and offers more safety features due to the presence of a strong P–O covalent bond. The vacancy formation energy for LiMnPO4 was 0.19 eV higher than that for LiFePO4, resulting in a 10−3 times-diluted complex concentration, which represents the main difference between the kinetics in the initial stage of charging of two olivine materials. This review highlights the overview of current research activities on LiMnPO4 cathodes in both native and substituted forms along with carbon coating synthesized by various synthetic techniques. Further, carbon coated LiMnPO4 was also prepared by a solid-state approach and the obtained results are compared with previous literature values. The challenges and the need for further research to realize the full performance of LiMnPO4 cathodes are described in detail.

Lithium-ion conducting electrolyte salts for lithium batteries

This paper presents an overview of the various types of lithium salts used to conduct Li(+) ions in electrolyte solutions for lithium rechargeable batteries. More emphasis is paid towards lithium salts and their ionic conductivity in conventional solutions, solid-electrolyte interface (SEI) formation towards carbonaceous anodes and the effect of anions on the aluminium current collector. The physicochemical and functional parameters relevant to electrochemical properties, that is, electrochemical stabilities, are also presented. The new types of lithium salts, such as the bis(oxalato)borate (LiBOB), oxalyldifluoroborate (LiODFB) and fluoroalkylphosphate (LiFAP), are described in detail with their appropriate synthesis procedures, possible decomposition mechanism for SEI formation and prospect of using them in future generation lithium-ion batteries. Finally, the state-of-the-art of the system is given and some interesting strategies for the future developments are illustrated.

3D micro-porous conducting carbon beehive by single step polymer carbonization for high performance supercapacitors: the magic of in situ porogen formation

We report non-templated synthesis of interconnected microporous carbon (IMPC) sheets having beehive morphology by direct pyrolysis of poly(acrylamide-co-acrylic acid) potassium salt in inert atmosphere without any activation. The presence of the alkali metal in the selected polymer precursor results in a high specific surface area of 1327 m2 g−1. Importantly, 80% of the pore volume is contributed by micropores with pore size ranging from 1–2 nm which is ideal for use as an electrode for supercapacitors. Whereas the rest of the surface area was contributed by a small fraction of mesopores and macropores due to the interconnected structure. The presence of three different types of pores make the material ideal for supercapacitor electrodes. IMPC was tested as an electrode in both aqueous and non-aqueous supercapacitors. All the aqueous measurements were done in 1 M H2SO4 solution with a potential window 1 V. A specific capacitance of 258 F g−1 was realized at a constant charge–discharge current of 0.5 A g−1 and it maintained at a value of 150 F g−1 at 30 A g−1. A long cycle stability of 90% capacitance retention was observed after 5000 charge–discharge cycles at a current density of 2 A g−1. At the highest power density 13 600 W kg−1 the energy density was found to be 3.1 W h kg−1. Non aqueous performance was tested in the presence of 1 M LiPF6 in ethylene carbonate–di-methyl carbonate with 5 mg active material loading. A specific capacitance of 138 F g−1 was obtained at a current density of 0.25 A g−1 and it retained at a value of 100 F g−1 at 10 A g−1. The material can deliver an energy density of 31 W h kg−1 at its highest power density of 11 000 W kg−1 in a two electrode system based on active material loading.

Activated carbons derived from coconut shells as high energy density cathode material for Li-ion capacitors

In this manuscript, a dramatic increase in the energy density of ~ 69 Wh kg−1 and an extraordinary cycleability ~ 2000 cycles of the Li-ion hybrid electrochemical capacitors (Li-HEC) is achieved by employing tailored activated carbon (AC) of ~ 60% mesoporosity derived from coconut shells (CS). The AC is obtained by both physical and chemical hydrothermal carbonization activation process, and compared to the commercial AC powders (CAC) in terms of the supercapacitance performance in single electrode configuration vs. Li. The Li-HEC is fabricated with commercially available Li4Ti5O12 anode and the coconut shell derived AC as cathode in non-aqueous medium. The present research provides a new routine for the development of high energy density Li-HEC that employs a mesoporous carbonaceous electrode derived from bio-mass precursors.

Influence of carbon towards improved lithium storage properties of Li2MnSiO4 cathodes

Superior lithium storage in Li2MnSiO4 cathodes was observed by altering carbon content during the formulation of electrodes. Initially, Li2MnSiO4 was prepared by a conventional solid-state reaction at 900 °C under Ar flow with a fixed amount of adipic acid, which acts as a gelating agent during synthesis. The phase formation was confirmed through powder X-ray diffraction measurements. Scanning electron microscope pictures indicate the particulate morphology of synthesized Li2MnSiO4 particles. Various compositions of electrodes were formulated using the conducting carbon (ketjen black) from 3 to 11 mg along with active material. All the fabricated electrodes were cycled in a Li/Li2MnSiO4 cell configuration to evaluate its lithium storage performance at 0.05 C rate. Among the electrodes, 42% carbon in the composite electrode exhibited a very stable discharge behaviour ∼140 mA h g−1 for 40 cycles at room temperature. Such storage performance was ascribed to the improved electronic conductivity of Li2MnSiO4 electrodes by incorporating carbon. This improvement was supported by electrochemical impedance spectroscopy measurements. Rate performance studies were also conducted and presented in the manuscript.

Carbon supported, Al doped-Li3V2(PO4)3 as a high rate cathode material for lithium-ion batteries

A high rate and high performance Li3V2(PO4)3 cathode was prepared by applying a carbon coating and Al substitution using the conventional solid-state approach. X-Ray diffraction was used to observe the structural properties of the synthesized powders. The presence of the carbon coating was confirmed by HR-TEM and reflected well with the Raman analysis. The Li/C-Li3V1.98Al0.02(PO4)3 cell displayed a discharge capacity of 182 mA h g−1 between 3 and 4.8 V vs. Li at a current density of 0.1 mA cm−1, which is ∼20 mA h g−1 higher than that of the native compound. The capacity retention was found to be 84 and 74% after 40 and 100 cycles, respectively. The C-Li3V1.98Al0.02(PO4)3 powders demonstrated excellent rate performance at 20 C with a discharge capacity of ∼120 mA h g−1 over 100 cycles. The elevated temperature performance was also evaluated and found to be similar to that under room temperature conditions.

Adipic acid assisted sol–gel synthesis of Li2MnSiO4 nanoparticles with improved lithium storage properties

An adipic acid assisted sol–gel route was employed to prepare phase pure Li2MnSiO4 under the optimized conditions. Powder X-ray diffraction measurements confirm the formation of orthorhombic Li2MnSiO4 with Pmn21 space group. The oxidation state of Mn(II) was confirmed by electron paramagnetic resonance (EPR) studies. FTIR study was conducted to ensure the formation of a tetrahedral SiO4 group. Morphological features confirmed the appearance of evenly dispersed Li2MnSiO4 spherical nanoparticles with size of ∼30 nm. The Li/Li2MnSiO4 cell was constructed to study the electrochemical performance of Li2MnSiO4 nanoparticles and the cell delivers a stable discharge capacity profile (∼125 mAh g−1) for observed 50 cycles.

Constructing high energy density non-aqueous Li-ion capacitors using monoclinic TiO2-B nanorods as insertion host

We report the construction and electrochemical performance of a high power Li-ion hybrid electrochemical capacitor (Li-HEC) using monoclinic TiO2-B nanorods as anodes with activated carbon cathodes. First, TiO2-B nanorods are synthesized by a conventional hydrothermal approach and a subsequent ion-exchange reaction with protons. Phase formation and morphological features are investigated through X-ray diffraction and scanning and transmission electron microscopy, respectively. Li-insertion properties are evaluated in half-cell configurations and reversible insertion of 0.52 moles of Li at a current density of 100 mA g−1 were found. The Li-HEC is constructed with optimized mass loading of the electrodes along with Whatman and electrospun PVdF–HFP membranes. Among them, electrospun PVdF–HFP comprising Li-HEC is found to be superior in terms of cyclability, higher energy and power densities. The electrospun PVdF–HFP comprising Li-HEC delivered the maximum energy and power densities of 23 W h kg−1 and 2.8 kW kg−1, respectively, with a capacitance retention of ∼73% after 1200 cycles at a current density of 1.5 A g−1.

Exceptional Performance of TiNb2O7 Anode in All One-Dimensional Architecture by Electrospinning

We report the extraordinary performance of an Li-ion battery (full-cell) constructed from one-dimensional nanostructured materials, i.e. nanofibers as cathode, anode, and separator-cum-electrolyte, by scalable electrospinning. Before constructing such a one-dimensional Li-ion battery, electrospun materials are individually characterized to ensure its performance and balancing the mass loading as well. The insertion type anode TiNb2O7 exhibits the reversible capacity of ∼271 mAh g(-1) at current density of 150 mA g(-1) with capacity retention of ∼82% after 100 cycles. Under the same current density, electrospun LiMn2O4 cathode delivered the discharge capacity of ∼118 mAh g(-1). Gelled electrospun polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP) nanofibers membrane is used as the separator-cum-electrolyte in both half-cell and full-cell assembly which exhibit the liquid like conductivity of ∼2.9 mS cm(-1) at ambient conditions. Full-cell, LiMn2O4|gelled PVdF-HFP|TiNb2O7 is constructed by optimized mass loading of cathode with respect to anode and tested between 1.95 and 2.75 V at room temperature. The full-cell delivered the reversible capacity of ∼116 mAh g(-1) at current density of 150 mA g(-1) with operating potential and energy density of ∼2.4 V and ∼278 Wh kg(-1), respectively. Further, excellent cyclability is noted for such configuration irrespective of the applied current densities.