Terms Of Cycles Research Articles

Sulfur enriched carbon nanotubols with a Poly(3,4-ethylenedioxypyrrole) coating as cathodes for long-lasting Li-S batteries

Lithium-sulfur (Li-S) batteries are technologically significant for sulfur is cheap, and offers high gravimetric capacity and a large energy density. But achieving long term cyclability with moderate capacity loss, and scalability pose formidable challenges. A solution phase approach for the preparation of a composite of sulfur with hydroxyl groups functionalized multiwalled carbon nanotubes (MWCNTols) and coated with poly(3,4-ethylenedioxypyrrole) (PEDOP) is presented for the first time. Comparison of the Li-S performances at 0.1 C current-rate show that the S based cell with a S-loading of 80% retains a low capacity of 122 mAh gsulfur−1 after 100 cycles, whereas cells with S/MWCNTols and S/MWCNTols/PEDOP composites with sulfur loadings of 73 and 70% respectively, retain capacities of 384 and 624 mAh gsulfur−1 after 200 charge-discharge cycles, with Coulombic efficiencies of 96 and 98.7% respectively. This performance differential illustrates the role of PEDOP in inhibiting sulfur loss and in maximizing cell response. The polymer provides electrical interconnects between the insulating sulfur clusters and facilitates Li+ transfer at the interface. The ease of the synthesis, coupled with the remarkable cycling performance delivered by this composite at a high sulfur-loading, demonstrate the promise that this S/CNT/conducting polymer composite has for practical Li-S batteries.

Development of Large Format NMC-Graphite Lithium Ion Pouch Cell with Aqueous Processed Electrodes

The development of a large format LiNi0.33Mn0.33Co0.33O2 (NMC) - Graphite pouch cell with both electrodes prepared using waterborne PVdF binders is reported. The formulations and design of the positive and negative electrodes have been optimized to meet the MAT4BAT EU project objectives. The negative and positive electrode slurries with elaborated formulations have been scaled up effectively to kilogram scale and ~100 meters length double-side coated electrodes have been manufactured. Finally, an NMC-Graphite pouch cell with nominal capacity 17 Ah demonstrated promising C-rate capability and long term cyclability reaching 80% of initial discharge capacity after 3,200 cycles with 100% depth of discharge.

Development of Large Format NMC-Graphite Lithium Ion Pouch Cell with Aqueous Processed Electrodes

The current lithium ion battery (LIB) technology has reached a very high degree of development and market share [1, 2]. However, several important bottlenecks still impede further spreading of lithium ion batteries into the EV market [2, 3]. Among them, their relatively high price and negative environmental impact have been addressed in this work. In particular, at the electrode manufacturing stage, the replacement of toxic and expensive N-Methyl-2-pyrrolidone (NMP) solvent by water is considered an innovative and promising approach to reduce both the environmental impact and the final price of the batteries [4] without sacrificing electrochemical performance [5]. Here, we report the development of a large format LiNixMnyCozO2 (NMC) - Graphite (C) pouch cell, with both electrodes prepared via aqueous processes using waterborne binders. The NMC-Graphite electrochemical system was chosen because it is considered as one of the most promising combinations for large format batteries for EV applications, in which both active materials are compatible with aqueous binders [6]. The positive electrode was composed of a commercial NMC (111) material. The negative electrode was prepared on the basis of C-NERGY™ ACTILION_1 graphite (IMERYS Graphite & Carbon) specially developed for better processability in aqueous slurries. Waterborne PVdF latexes (SOLVAY SPECIALTY POLYMERS ITALY) have been used as binders for both electrodes. Commercially available sodium carboxymethyl cellulose has been used as a dispersant for negative and positive electrode slurries. The formulation and design of the positive and negative electrodes was tailored to meet the MAT4BAT European project tasks and cell specifications. The negative and positive electrode slurries with elaborated formulations have been successfully scaled up to 3 and 6 kg, respectively. Then, more than 100 metres length double-side coated electrode rolls have been manufactured on a coating pilot line. Finally, several NMC/Graphite pouch cells with a stack design were assembled on automated pilot equipment. As shown in Figure 1, the manufactured NMC/C pouch cell with nominal capacity 17 Ah has demonstrated promising C-rate capability and stable long term cyclability with no negative influence of the aqueous processing. It should be noted that obtained specific energy density of 143 Wh/kg (@ 0.2C discharge) is very close to the commercial benchmark as defined within the MAT4BAT EU project. Thus, presented results allow for the conclusion that aqueous processing is a successful approach for manufacturing large format NMC-Graphite lithium ion cells for EV applications. The study has been performed within the MAT4BAT project funded by the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement #608931. We would like to acknowledge Celaya, Emparanza y Galdós Internacional S.A. for the manufacturing of the NMC/C pouch cells.

Local Transmittance Measurements as Large Area Diagnostic Tool for the Optimization of Porous Si Foils for Li-Ion Battery Anodes

Silicon with its exceptionally high gravimetrical capacity of 4200 mAh/g has a great potential as anode material for Li-ion batteries. However, several critical problems have to be overcome to realize the up-scaling of the anodes from lab scale to mass production, especially with respect to long term cyclability and low cost fabrication techniques. In this paper, large area etched porous silicon foils are optically characterized with respect to local homogeneity in porosity and thickness and further prepared for a novel and promising type of anodes for Li-ion batteries. Since large areas (larger than 250 cm2) have to be analyzed locally with high spatial resolution (smaller than 50 μm), a fast and contactless solar cell local characterization technique (CELLO [J. Carstensen, A. Schütt, G. Popkirov, and H. Föll, Phys. Status Solidi C 8(4), 1342 (2011)]) has been modified to measure the reflectance and transmittance of the porous silicon foils. The successful translation of the map data into local porosity and thickness informations of the porous silicon foils helps to modify the process parameters of the large area etching but more importantly allows a stable and cost effective new anode. This study illustrates the promising new battery concept based on a PorSi foil with adjustable porosities between 40 to 60 %.

Electrochemical synthesis of polyaniline cross-linked NiMoO4 nanofibre dendrites for energy storage devices

An effective cross-linking strategy for grafting polyaniline with a nanomaterial such as nickel molybdate provides long term cyclability for the fabricated energy storage device.

Guar gum: Structural and electrochemical characterization of natural polymer based binder for silicon–carbon composite rechargeable Li-ion battery anodes

Long term cyclability of a composite Li-ion anode electrode comprised of 82 wt.% Si/C lithium ion active material along with 8 wt.% polymeric binder and 10 wt.% Super P conductive carbon black has been studied utilizing polymeric binders exhibiting different elastic/tensile moduli and tensile yield strengths. Accordingly, electrochemically active Si/C composite synthesized by high energy mechanical milling (HEMM), exhibiting reversible specific capacities of ∼780 mAh/g and ∼600 mAh/g at charge/discharge rates of ∼50 mA/g and ∼200 mA/g, respectively were selected as the Li-ion active anode. Polyvinylidene fluoride (PVDF) and purified guar gum (PGG) with reported elastic moduli ∼1000 MPa and ∼3200 MPa, respectively were selected as the binders. Results show that the composite electrode (Si/C + binder + conducting carbon) comprising the higher elastic modulus binder (PGG) exhibits better long term cyclability contrasted with PVDF. 1H-NMR analysis of the polymer before and after cycling shows structural degradation/deformation of the low elastic modulus PVDF, whereas the high elastic modulus PGG binder shows no permanent structural deformation or damage. The results presented herein thus suggest that PGG based polymers exhibiting high elastic modulus are a promising class of binders with the desired mechanical integrity needed for enduring the colossal volume expansion stresses of Si/C based composite anodes.

Developing a light weight lithium ion battery – an effective material and electrode design for high performance conversion anodes

The process of lithium storage by conversion reaction is a subject of intense research in the field of lithium ion batteries as it opens up the possibility of storing more than one mole of lithium per formula unit, leading to very high storage capacities. For instance, lithium storage by conversion reaction in hematite (α-Fe2O3) results in high theoretical capacity of 1005 mAh g−1. Despite numerous attempts, the first cycle reversibility and cyclability achieved in this material have been disappointingly low. To overcome these limitations, we report here an effective “active material-electrode design” incorporating the following features: (i) well-connected active material particles; (ii) adequate active material surface area; (iii) strong particle-current collector adhesion and (iv) superior degree of electrode drying. Incorporating these features in α-Fe2O3 electrodes enhances its overall electrochemical performance. For the first time, a high first cycle reversibility of 90% is reported for lithium storage via conversion reaction in α-Fe2O3. The long term cyclability over 800 cycles demonstrated here is one of highest reported values for this material. Even at high current densities of 5.025 A g−1 (12 mins of charge/discharge), this tailored α-Fe2O3 delivers capacities (446 mAh g−1) in excess of graphite (372 mAh g−1). Most importantly, this anode material shows feasible operation in a full cell containing olivine LiMn0.8Fe0.2PO4 cathode. It is believed that this simple design approach could also be extended to other material systems such as phosphides, sulphides, nitrides and fluorides that store lithium via conversion mechanism.

Manganosite–microwave exfoliated graphene oxide composites for asymmetric supercapacitor device applications

Graphene based materials coupled with transition metal oxides are promising electrode materials in asymmetric supercapacitors owing to their unique properties which include high surface area, good chemical stability, electrical conductivity, abundance, and lower cost profile over time. In this paper a composite material consisting of graphene oxide exfoliated with microwave radiation (mw rGO), and manganosite (MnO) is synthesised in order to explore their potential as an electrode material. The composite material was characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to explore the process occurring at the electrode/electrolyte interface. Long term cyclability and stability were investigated using galvanostatic charge/discharge testing. From the resulting analysis, an asymmetric supercapacitor was constructed with the best composite containing 90% MnO–10% mw rGO (w/w). The device exhibited a capacitance of 0.11F/cm2 (51.5F/g by mass) and excellent capacity retention of 82% after 15,000 cycles at a current density of 0.5A/g.

High surface area nanocrystalline hausmannite synthesized by a solvent-free route

Nanocrystalline high surface area Mn3O4 powder was obtained at low temperature by a solvent-free route. The precursor was a mixture of manganese (II) acetate, 3,6,9-trioxadecanoic acid (TODA) and ammonium acetate that were intimately mixed by grounding in an agate mortar. Nanocrystalline Mn3O4 was obtained by thermal treatment at 120°C. Powder X-ray diffraction, selected area electron diffraction, high resolution transmission electron microscopy, and Fourier transformed infrared characterization confirmed the formation of the hausmannite phase. The as-prepared mesoporous material has high specific surface area (120m2g−1). The performances of tape casted Mn3O4 nanopowder electrodes were investigated as anode material for lithium ion batteries. High capacity values were achieved at diverse C rates. Capacity fading was found to be dependent on the upper cut off voltage, the presence of a plateau at 2.25V vs. Li+/Li being detrimental for long term cyclability.

Alloy Design for Long Term Cyclability of Si Based Anode Materials for Lithium Ion Batteries

Alloy Design for Long Term Cyclability of Si Based Anode Materials for Lithium Ion Batteries

Lithium metal stripping/plating mechanisms studies: A metallurgical approach

In the hope of meeting the requirements of long term cyclability for polymer electrolyte metallic lithium battery (LMP) (>600 cycles) and widening the scope of their commercial application (low temperature operation), numerous studies have been devoted to the understanding of the intrinsic limitations of these systems. Dendritic lithium growth is known to result in short circuits upon cycling. Before considering ways to master lithium deposits morphologies, we have embarked on a study aimed at characterizing by mean of Scanning Electron Microscopy (SEM): (1) the texture of metallic lithium (2) the influence of cycling parameters, such as current densities and liquid electrolyte formulation, on lithium stripping mechanisms and (3) the lithium deposits morphologies on various lithium surface states ( in and ex situ prepared through electrochemical means, physical procedures such as polishing and Pulsed Laser Deposition technique). Different lithium stripping processes have been revealed depending on current densities. They lead to various surface defects from which lithium dendrites will preferentially grow upon following Li plating. Furthermore, cycling experiments have highlighted, for the first time, the internal lithium micro-texture. Pursuing this study, we finally shed light on the crucial role of the electrolytic mix formulation and cell pressure on lithium cycling efficiency.