Wong Chui Ling

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.

Unveiling TiNb2O7 as an Insertion Anode for Lithium Ion Capacitors with High Energy and Power Density

This is the first report of the utilization of TiNb2 O7 as an insertion-type anode in a lithium-ion hybrid electrochemical capacitor (Li-HEC) along with an activated carbon (AC) counter electrode derived from a coconut shell. A simple and scalable electrospinning technique is adopted to prepare one-dimensional TiNb2 O7 nanofibers that can be characterized by XRD with Rietveld refinement, SEM, and TEM. The lithium insertion properties of such electrospun TiNb2 O7 are evaluated in the half-cell configuration (Li/TiNb2 O7 ) and it is found that the reversible intercalation of lithium (≈3.45 mol) is feasible with good capacity retention characteristics. The Li-HEC is constructed with an optimized mass loading based on the electrochemical performance of both the TiNb2 O7 anode and AC counter electrode in nonaqueous media. The Li-HEC delivers very high energy and power densities of approximately 43 Wh kg(-1) and 3 kW kg(-1) , respectively. Furthermore, the AC/TiNb2 O7 Li-HEC delivers a good cyclability of 3000 cycles with about 84% of the initial value.

Synthesis of porous LiMn2O4 hollow nanofibers by electrospinning with extraordinary lithium storage properties

We report the extraordinary lithium storage performance of porous LiMn2O4 hollow nanofibers synthesized by electrospinning technique. The electrospun LiMn2O4 hollow nanofibers retained 87% of initial reversible capacity after 1250 cycles at the 1 C rate. Further, excellent cycling profiles at 55 °C and cubic spinel to tetragonal phase transformation are also noted.

Nonaqueous Lithium‐Ion Capacitors with High Energy Densities using Trigol‐Reduced Graphene Oxide Nanosheets as Cathode‐Active Material

One HEC of a material: The use of trigol-reduced graphene oxide nanosheets as cathode material in hybrid lithium-ion electrochemical capacitors (Li-HECs) results in an energy density of 45 Wh kg(-1) ; much enhanced when compared to similar devices. The mass loading of the active materials is optimized, and the devices show good cycling performance. Li-HECs employing these materials outperform other supercapacitors, making them attractive for use in power sources.

Free-standing electrospun carbon nanofibres—a high performance anode material for lithium-ion batteries

Free-standing carbon nanofibres (CNFs) are prepared by the carbonization of poly-acrylonitrile using a simple electro-spinning technique. The electro-spun fibres are studied as an anode material for lithium-ion batteries in half-cell configurations. The fibres showed an initial discharge capacity of 826 mAh g −1 at a current density of 200 mA g −1 and exhibited an appreciable capacity profile during cycling. The Li-storage mechanism has been explained based on the cyclic voltametric and galvanostatic cycling results. (Some figures may appear in colour only in the online journal)

LiCrTiO4 : a high-performance insertion anode for lithium-ion batteries

Since the commercialization of lithium-ion batteries by Sony in 1991, carbonaceous materials, particularly graphite, has dominated in the battery industry as anode material in practical cells due to its advantages, such as availability, lower operating potential (<0.25 V vs. Li), acceptable theoretical capacity (372 mAh g ), good cycleability and eco-friendliness. However, such anodes endure the problem of lithium platting, durability, and are expensive to process. Furthermore, the lower working potential versus Li leads to electrolyte decomposition, thus resulting in the formation of a solid electrolyte interphase (SEI) which consumes Li during initial cycles. Moreover, the SEI is necessary for graphitic anodes for safe operation of the cell during prolonged cycling. Hence, several alternative insertion hosts such as TiO2, [5] Li4Ti5O12, [6] TiP2O7, [7] LiTi2(PO4)3 [8, 9] and so forth, with different morphologies and shapes have been proposed as an alternative to graphite as anodes to overcome aforementioned setbacks towards employing the net potential of the Li-ion cell. Among the insertion hosts proposed, materials comprising spinel-type AB2O4 structures, for example Li(Li1/3Ti5/3)O4 (can be written as Li4Ti5O12), seems to be more promising for accommodating Li ions, rather than other insertion hosts, due to its lower and thermodynamically flat potential [~1.5 V vs. Li, ~1.8 V vs. Li for anatase TiO2, ~2.6 V vs. Li for both TiP2O7 and LiTi2(PO4)3] with a theoretical capacity of 175 mAh g 1 and almost negligible volume change during Li insertion/extraction (known as a zero-strain insertion host). It is easy to prepare and enables good battery characteristics. However, the main problem with Li4Ti5O12 is low power characteristics that stem from an inherently poor Li diffusion coefficient (<10 6 cm s ) and poor electronic conductivity (<10 13 S cm ). Hence, achieving the theoretical capacity is difficult unless the nanostructures is coated with carbon or made into composites with carbon. Nonetheless, introduction of either a carbon coating or making composites results in a decrease in the volumetric capacity of Li4Ti5O12. [11] Therefore, the search for an alternative insertion host is warranted without sacrificing the volumetric capacity. LiCrTiO4 belongs to the AB2O4 spinel family also and exhibits the favourable characteristics mentioned earlier for its counterpart Li4Ti5O12, such as a flat potential of ~1.5 V versus Li, a small change in volume during the charge–discharge process (+ 0.7 %), a slightly lower theoretical capacity (157 mAh g ) than Li(Li1/3Ti5/3)O4 (175 mAh g ) and ease of production on an industrial scale. However, there are only few reports available on the electrochemical performance of LiCrTiO4 towards Li-ion battery or hybrid electrochemical capacitor applications. 12–14] Hence, taking into account the advantages of LiCrTiO4, an attempt was made to synthesize it by a solid-state route. The electrochemical performance of LiCrTiO4 was carried out in both halfand full-cell configurations and are described in detail. The Rietveld refined powder X-ray diffraction pattern of synthesized LiCrTiO4 is illustrated in Figure 1 a. The observed pattern clearly reveals the formation of single-phase spinel

Carbon‐Coated LiTi2(PO4)3: An Ideal Insertion Host for Lithium‐Ion and Sodium‐Ion Batteries

We report the extraordinary performance of carbon-coated sodium super ion conductor (NASICON)-type LiTi2 (PO4 )3 as an ideal host matrix for reversible insertion of both Li and Na ions. The NASICON-type compound was prepared by means of a Pechini-type polymerizable complex method and was subsequently carbon coated. Several characterization techniques such as XRD, thermogravimetric analysis (TGA), field-emission (FE) SEM, TEM, and Raman analysis were used to study the physicochemical properties. Both guest species underwent a two-phase insertion mechanism during the charge/discharge process that was clearly evidenced from galvanostatic and cyclic voltammetric studies. Unlike that of Li (≈1.5 moles of Li), Na insertion exhibits better reversibility (≈1.59 moles of Na) while experiencing a slightly higher capacity fade (≈8 % higher than Li) and polarization (780 mV) than Li. However, excellent rate capability profiles were noted for Na insertion relative to its counterpart Li. Overall, the Na insertion properties were found to be superior relative to Li insertion, which makes carbon-coated NASICON-type LiTi2 (PO4 )3 hosts attractive for the development of next-generation batteries.

High energy Li-ion capacitors with conversion type Mn3O4 particulates anchored to few layer graphene as the negative electrode

We report the fabrication of high energy Li-ion capacitors (LICs) using conversion type Mn3O4 octahedrons anchored to few layer graphene (Mn3O4-G) as the negative electrode with activated carbon (AC) as the positive one. First, the Mn3O4-G composite is prepared via a hydrothermal approach using commercially available graphene nanosheets. Li-storage studies of both electrodes (AC and Mn3O4-G) are conducted in single electrode/half-cell configuration with metallic Li to assess the mass balance. Prior to the fabrication of LICs, Mn3O4-G is pre-lithiated in Swagelok fittings with Li and subsequently paired with the desired loading of AC. The AC/Mn3O4-G based LIC delivered a maximum energy density of ∼142 W h kg−1 with excellent cyclability of 9000 cycles with ∼80% retention. This result certainly provides new avenues for the development of high energy LICs using conversion type negative electrodes rather than traditional insertion type anodes.