A study of cokes used as anodic materials in lithium ion rechargeable batteries

A variety of cokes pretreated at different temperatures are used as anodic materials and their electrochemical characteristics are examined by cyclic voltammetry. It is found that for some cokes such as petroleum coke (preheated at 1300 degrees C), pitch coke (1300 degrees C), needle coke (1900 degrees C), metallurgical coke (1900 degrees C), high capacity and cyclic efficiency are achieved. Needle coke (1900 degrees C) and metallurgical coke (1900 degrees C) in particular give a capacity of over 200 mAh/g and a cyclic efficiency of nearly 100%, whereas poor performance is exhibited by those pretreated at higher or lower temperatures, e.g., petroleum cokes (500 degrees C, 2800 degrees C), pitch coke (500 degrees C) and needle coke (2800 degrees C). The cyclic voltammograms show two electrochemical processes, one at about 0.1 V vs. Li+/Li which is electrochemically reversible, and may be attributed to the intercalation/deintercalation of lithium ions while the other, at about 0.6 V vs. Li+/Li, is electrochemically irreversible and may be assigned to the decomposition of the electrolyte solvent, which leads to formation of the passive film on the anode surface. The experimental results strongly suggest that the pretreatment temperature of cokes and of the solvent are determining factors for the growth, structure and properties of the passive film.

Synthèse de titanates de lithium nanostructurés par plasma inductif pour les batteries lithium-ion

Le marché des accumulateurs lithium-ion est en expansion. Cette croissance repose partiellement sur la multiplication des niches d’utilisation et l’amélioration constante de leurs performances. En raison de leur durabilité exceptionnelle, de leur faible coût, de leur haute densité de puissance et de leur fiabilité, les anodes basées sur les titanates de lithium, et plus particulièrement le spinelle Li4Ti5O12, présentent une alternative d’intérêt aux matériaux classiques d’anodes en carbone pour de multiples applications. Leur utilisation sous forme de nanomatériaux permet d’augmenter significativement la puissance disponible par unité de poids. Ces nanomatériaux ne sont typiquement pas contraints dans une direction particulière (nanofils, nanoplaquettes), car ces formes impliquent une tension de surface plus importante et requièrent donc généralement un mécanisme de synthèse dédié. Or, ces nanostructures permettent des réductions supplémentaires dans les dimensions caractéristiques de diffusion et de conduction, maximisant ainsi la puissance disponible, tout en affectant les propriétés habituellement intrinsèques des matériaux. Par ailleurs, les réacteurs continus reposant sur la technologie du plasma thermique inductif constituent une voie de synthèse démontrée afin de générer des volumes importants de matériaux nanostructurés. Il s’avère donc pertinent d’évaluer leur potentiel dans la production de titanates de lithium nanostructurés. La pureté des titanates de lithium est difficile à jauger. Les techniques de quantification habituelles reposent sur la fluorescence ou la diffraction en rayons X, auxquelles le lithium élémentaire se prête peu ou pas. Afin de quantifier les nombreuses phases (Li4Ti5O12, Li2Ti3O7, Li2TiO3, TiO2, Li2CO3) identifiées dans les échantillons produits par plasma, un raffinement de Rietveld fut développé et validé. La présence de γ-Li2TiO3 fut identifiée, et la calorimétrie en balayage différentiel fut explorée comme outil permettant d’identifier et de quantifier la présence de β-Li2TiO3. Différentes proportions entre les phases produites et différents types de morphologies furent observés en fonction des conditions d’opération du plasma. Ainsi, des conditions de trempe réductrice et d’ensemencement en Li4Ti5O12 nanométrique semblent favoriser l’émergence de nanomorphologies en nanofils (associés à Li4Ti5O12) et en nanoplaquette (associées à Li2TiO3). De plus, l’ensemencement et les recuits augmentèrent significativement le rendement en la phase spinelle Li4Ti5O12 recherchée. Les recuits sur les poudres synthétisées par plasma indiquèrent que la décomposition du Li2Ti3O7 produit du Li4Ti5O12, du Li2TiO3 et du TiO2 (rutile). Afin d’approfondir l’investigation de ces réactions de décomposition, les paramètres cristallins du Li2Ti3O7 et du γ-Li2TiO3 furent définis à haute température. Des mesures continues en diffraction en rayon X à haute température furent réalisées lors de recuits de poudres synthétisées par plasma, ainsi que sur des mélanges de TiO2 anatase et de Li2CO3. Celles-ci indiquent la production d’un intermédiaire Li2Ti3O7 à partir de l’anatase et du carbonate, sa décomposition en Li4Ti5O12 et TiO2 (rutile) sur toute la plage de température étudiée, et en Li2TiO3 et TiO2 (rutile) à des températures inférieures à 700°C.

Effects of synthetic conditions on the structural, stability and ion conducting properties of Li0.30(La0.50Ln0.50)0.567TiO3 (Ln= La, Pr, Nd) solid electrolytes for rechargeable lithium batteries

The structure, thermal stability, morphology and ion conductivity of titanium perovskites with the general formula Li3xLn2/3−xTiO3 (Ln = rare earth element; 3x= 0.30) are studied in the context of their possible use as solid electrolyte materials for lithium ion batteries. Materials are prepared by a glycine-nitrate method using different sintering treatments, with a cation-disorder-induced structural transition from tetragonal to cubic symmetry, detected as quenching temperature increases. SEM images show that the average grain size increases with increasing sintering temperature and time. Slightly higher bulk conductivity values have been observed for quenched samples sintered at high temperature. Bulk conductivity decreases with the lanthanide ion size. A slight conductivity enhancement, always limited by grain boundaries, is observed for longer sintering times. TDX measurements of the electrolyte/cathode mixtures also show a good stability of the electrolytes in the temperature range of 30-1100ºC.

New lithium-ion conductors based on the NASICON structure

Lithium-ion conduction in mixed-metal phosphates, (LiMMIII)-M-V(PO,), [M-V = Nb, Ta; M-III = Al, Cr, Fe], possessing the rhombohedral (R (3) over bar c) NASICON structure has been investigated. Among the phosphates investigated, LiTaAl(PO4)(3) exhibits the highest conductivity, sigma approximate to 1.0 x 10(-2) S cm(-1) at 350 degrees C (E-a = 0.47 eV), comparable to the conductivity of LiTi2(PO4)(3). Unlike LiTi2(PO4)(3) which contains lithium-reducible Ti-IV, LiTaAl(PO4)(3) contains stable Ta-V and Al-III oxidation states and hence deserves further attention towards tailoring new lithium-ion conductors for application as electrolytes in solid state lithium batteries.

Synthesis and Electrochemical Characterization of LiNi0.8Co0.2O2 as Cathode Material for Aqueous Rechargeable Lithium Batteries

LiNi0.8Co0.2O2 cathode material for lithium ion batteries is synthesized by reaction under autogenic pressure at elevated temperature (RAPET) method. The simple synthesis procedure is time and energy saving, and thus is promising for commercial application. The structure and stability of the material have been characterized by means of XRD and TG-DTA. The electrochemical properties of the LiNi0.8Co0.2O2 cathode are investigated in 2 M Li2SO4 aqueous electrolyte and they are compared to that in an organic electrolyte. A battery cell consisting of LiNi0.8Co0.2O2 as cathode in 2 M Li2SO4 solution is constructed in combination with LiTi2 (PO4)(3) as anode. The cell retained almost constant discharge capacity over hundred cycles. The electrochemical impedance spectral ( EIS) studies in aqueous and nonaqueous electrolytes revealed that the mechanism of lithium ion intercalation and deintercalation processes in LiNi0.8Co0.2O2 electrode follow almost similar mechanism in both aqueous and nonaqueous electrolytes. The chemical diffusion coefficient was calculated from slow scan rate cyclic voltammetry and EIS. (C) 2012 The Electrochemical Society. DOI: 10.1149/2.075205jes] All rights reserved.

Binder free three-dimensional sulphur/few-layer graphene foam cathode with enhanced high-rate capability for rechargeable lithium sulphur batteries.

A novel ultra-lightweight three-dimensional (3-D) cathode system for lithium sulphur (Li-S) batteries has been synthesised by loading sulphur on to an interconnected 3-D network of few-layered graphene (FLG) via a sulphur solution infiltration method. A free-standing FLG monolithic network foam was formed as a negative of a Ni metallic foam template by CVD followed by etching away of Ni. The FLG foam offers excellent electrical conductivity, an appropriate hierarchical pore structure for containing the electro-active sulphur and facilitates rapid electron/ion transport. This cathode system does not require any additional binding agents, conductive additives or a separate metallic current collector thus decreasing the weight of the cathode by typically ∼20-30 wt%. A Li-S battery with the sulphur-FLG foam cathode shows good electrochemical stability and high rate discharge capacity retention for up to 400 discharge/charge cycles at a high current density of 3200 mA g(-1). Even after 400 cycles the capacity decay is only ∼0.064% per cycle relative to the early (e.g. the 5th cycle) discharge capacity, while yielding an average columbic efficiency of ∼96.2%. Our results indicate the potential suitability of graphene foam for efficient, ultra-light and high-performance batteries.

The role of structure in the electrochemical performance of nanostructured metal oxides for lithium ion battery anodes

The Li-ion battery has for a number of years been a key factor that has enabled an ever increasing number of modern consumer devices, while in recent years has also been sought to power a range of emerging electric and hybrid electric vehicles. Due to their importance and popularity, a number of characteristics of Li-ion batteries have been subjected to intense work aimed at radical improvement. Although electrode material selection intrinsically defines characteristics like maximum capacity or voltage, engineering of the electrode structure may yield significant improvements to the lifetime performance of the battery, which would not be available if the material was used in its bulk form. The body of work presented in this thesis describes the relationship between the structure of electrochemically active materials and the course of the electrochemical processes occurring within the electrode. Chapter one describes the motivation behind the research presented herein. Chapter two serves to highlight a number of key advancements which have been made and detailed in the literature over recent years, pertaining to the use of nanostructured materials in Li-ion technology. Chapter three details methods and techniques applied in developing the body of work presented in this thesis. Chapter four details structural, molecular and electrochemical characteristics of tin oxide nanoparticle based electrodes, with particular emphasis on the relationship between the size distribution and the electrode performance. Chapter five presents findings of structural, electrochemical and optical study of indium oxide nanoparticles grown on silicon by molecular beam epitaxy. In chapter 6, tin oxide inverted opal electrodes are investigated for the conduct of the electrochemical performance of the electrodes under varying rate of change of potential. Chapter 7 presents the overall conclusions drawn from the results presented in this thesis, coupled with an indication of potential future work which may be explored further.

Characterizing capacity loss of lithium oxygen batteries by impedance spectroscopy

Polymer based carbon aerogels were prepared by synthesis of a resorcinol formaldehyde gel followed by pyrolysis at 1073K under Ar and activation of the resultant carbon under CO2 at different temperatures. The prepared carbon aerogels were used as active materials in the preparation of cathode electrodes for lithium oxygen cells and the electrochemical performance of the cells was evaluated by galvanostatic charge/discharge cycling and electrochemical impedance measurements. It was shown that the storage capacity and discharge voltage of a Li/O2 cell strongly depend on the porous structure of the carbon used in cathode. EIS results also showed that the shape and value of the resistance in the impedance spectrum of a Li/O2 cell are strongly affected by the porosity of carbon used in the cathode. Porosity changes due to the build up of discharge products hinder the oxygen and lithium ion transfer into the electrode, resulting in a gradual increase in the cell impedance with cycling. The discharge capacity and cycle life of the battery decrease significantly as its internal resistance increases with charge/discharge cycling.

Structural, electrical and electrochemical characterization of high frequency magnetron sputtered spinel oxide cathode films for lithium ion battery applications

The main challenges in the deposition of cathode materials in thin film form are the reproduction of stoichiometry close to the bulk material and attaining higher rates of deposition and excellent crystallinity at comparatively lower annealing temperatures. There are several methods available to develop stoichiometric thin film cathode materials including pulsed laser deposition; plasma enhanced chemical vapor deposition, electron beam evaporation, electrostatic spray deposition and RF magnetron sputtering. Among them the most versatile method is the sputtering technique, owing to its suitability for micro-fabricating the thin film batteries directly on chips in any shape or size, and on flexible substrates, with good capacity and cycle life. The main drawback of the conventional sputtering technique using RF frequency of 13.56MHz is its lower rate of deposition, compared to other deposition techniques A typical cathode layer for a thin film battery requires a thickness around one micron. To deposit such thick layers using convention RF sputtering, longer time of deposition is required, since the deposition rate is very low, which is typically 10-20 Å/min. This makes the conventional RF sputtering technique a less viable option for mass production in an economical way. There exists a host of theoretical and experimental evidences and results that higher excitation frequency can be efficiently used to deposit good quality films at higher deposition rates with glow discharge plasma. The effect of frequencies higher than the conventional one (13.56MHz) on the RF magnetron sputtering process has not been subjected to detailed investigations. Attempts have been made in the present work, to sputter deposit spinel oxide cathode films, using high frequency RF excitation source. Most importantly, the major challenge faced by the thin film battery based on the LiMn2O4 cathode material is the poor capacity retention during charge discharge cycling. The major causes for the capacity fading reported in LiMn2O4cathode materials are due to, Jahn-Teller distortion, Mn2+ dissolution into the electrolyte and oxygen loss in cathode material during cycling. The work discussed in this thesis is an attempt on overcoming the above said challenges and developing a high capacity thin film cathode material.

Lithium Ion Electro-Insertion and Spectroelectrochemical Properties of Films from Hexaniobate

Layer-by-layer (LbL) films from K(2)Nb(6)O(17)(2-) and polyallylamine (PAH) and dip-coating films of H(2)K(2)Nb(6)O(17) were prepared on a fluorine-doped tin-oxide (FTO)-coated glass. The atomic force microscopy (AFM) images were carried out for morphological characterization of both materials. The real surface area and the roughness factor were determined on the basis of pseudocapacitive processes involved in the electroreduction/electrooxidation of gold layers deposited on these films. Next, lithium ion insertion into these materials was examined by means of electrochemical and spectroelectrochemical measurements. More specifically, cyclic voltammetry and current pulses under visible light beams were used to investigate mass transport and chromogenic properties. The lithium ion diffusion coefficient (D(Li)) within the LbL matrix is significantly higher than that within the dip-coating film, ensuring high storage capacity of lithium ions in the self-assembled electrode. Contrary to the LbL film, the potentiodynamic profile of absorbance change (Delta A) as a function of time is not similar to that obtained in the case of current density for the dip-coating film. Aiming at analyzing the rate of the coloration front associated with lithium ion diffusion, a spectroelectrochemical method based on the galvanostatic intermittent titration technique (GITT) was employed so as to determine the ""optical"" diffusion coefficient (D(op)). In the dip-coating film, the method employed here revealed that the lithium ion rate is higher in diffusion pathways formed from K(2)Nb(6)O(17)(2-) sites that contribute more significantly to Delta A. Meanwhile, the presence of PAH contributed to the increased ionic mobility in diffusion pathways in the LbL film, with low contribution to the electrochromic efficiency. These results aided a better understanding of the potentiodynamic profile of the temporal change of absorbance and current density during the insertion/deinsertion of lithium ions into the electrochromic materials.

Effect of the Electrolyte Formulation on the Performances of Edlc and Li-Ion Batteries

One of the most important components in electrochemical storage devices (batteries and supercapacitors) is undoubtedly the electrolyte. The basic function of any electrolyte in these systems is the transport of ions between the positive and negative electrodes. In addition, electrochemical reactions occurring at each electrode/electrolyte interface are the origin of the current generated by storage devices. In other words, performances (capacity, power, efficiency and energy) of electrochemical storage devices are strongly related to the electrolyte properties, as well as, to the affinity for the electrolyte to selected electrode materials. Indeed, the formulation of electrolyte presenting good properties, such as high ionic conductivity and low viscosity, is then required to enhance the charge transfer reaction at electrode/electrolyte interface (e.g. charge accumulation in the case of Electrochemical Double Layer Capacitor, EDLC). For practical and safety considerations, the formulation of novel electrolytes presenting a low vapor pressure, a large liquid range temperature, a good thermal and chemical stabilities is also required.

This lecture will be focused on the effect of the electrolyte formulation on the performances of electrochemical storage devices (Li-ion batteries and supercapacitors). During which, a summary of the physical, thermal and electrochemical data obtained by our group, recently, on the formulation of novel electrolyte-based on the mixture of an ionic liquid (such as EmimNTf2 and Pyr14NTf2) and carbonate or dinitrile solvents will be presented and commented. The impact of the electrolyte formulation on the storage performances of EDLC and Li-ion batteries will be also discussed to further understand the relationship between electrolyte formulation and electrochemical performances. This talk will also be an opportunity to further discuss around the effects of additives (SEI builder: fluoroethylene carbonate and vinylene carbonate), ionic liquids, structure and nature of lithium salt (LiTFSI vs LiPF6) on the cyclability of negative electrode to then enhance the electrolyte formulation. For that, our recent results on TiSnSb and graphite negative electrodes will be presented and discussed, for example 1,2.

1-C. Marino, A. Darwiche1, N. Dupré, H.A. Wilhelm, B. Lestriez, H. Martinez, R. Dedryvère, W. Zhang, F. Ghamouss, D. Lemordant, L. Monconduit “ Study of the Electrode/Electrolyte Interface on Cycling of a Conversion Type Electrode Material in Li Batteries” J. Phys.chem. C, 2013, 117, 19302-19313

2- Mouad Dahbi, Fouad Ghamouss, Mérièm Anouti, Daniel Lemordant, François Tran-Van “Electrochemical lithiation and compatibility of graphite anode using glutaronitrile/dimethyl carbonate mixtures containing LiTFSI as electrolyte” 2013, 43, 4, 375-385.

Microwave-assisted synthesis and local analyses of positive insertion electrodes for Li-ion batteries

Efficient energy storage holds the key to reducing waste energy and enabling the use of advanced handheld electronic devices, hydrid electric vehicles and residential energy storage. Recently, Li-ion batteries have been identified and employed as energy storage devices due to their high gravimetric and volumetric energy densities, in comparison to previous technologies. However, more research is required to enhance the efficiency of Li-ion batteries by discovering electrodes with larger electrochemical discharge capacities, while maintaining electrochemical stability. The aims of this study are to develop new microwave-assisted synthesis routes to nanostructured insertion cathodes, which harbor a greater affinity for lithium extraction and insertion than bulk materials. Subsequent to this, state-of-the-art synchrotron based techniques have been employed to understand structural and dynamic behaviour of nanostructured cathode materials during battery cell operation. In this study, microwave-assisted routes to a-LiFePO4, VO2(B), V3O7, H2V3O8 and V4O6(OH)4 have all been developed. Muon spin relaxation has shown that the presence of b-LiFePO4 has a detrimental effect on the lithium diffusion properties of a-LiFePO4, in agreement with first principles calculations. For the first time, a-LiFePO4 nanostructures have been obtained by employing a deep eutectic solvent reaction media showing near theoretical capacity (162 mAh g–1). Studies on VO2(B) have shown that the discharge capacity obtained is linked to the synthesis method. Electrochemical studies of H2V3O8 nanowires have shown outstanding discharge capacities (323 mAh g–1 at 100 mA g–1) and rate capability (180 mAh g–1 at 1 A g–1). The electrochemcial properties of V4O6(OH)4 have been investigated for the first time and show a promising discharge capacity of (180 mAh g–1). Lastly, in situ X-ray absorption spectroscopy has been utilised to track the evolution of the oxidation states in a-LiFePO4, VO2(B) and H2V3O8, and has shown these can all be observed dynamically.

Fabrication of Nb2O5 nanosheets for high-rate lithium ion storage applications

Nb2O5 nanosheets are successfully synthesized through a facile hydrothermal reaction and followed heating treatment in air. The structural characterization reveals that the thickness of these sheets is around 50 nm and the length of sheets is 500~800 nm. Such a unique two dimensional structure enables the nanosheet electrode with superior performance during the charge-discharge process, such as high specific capacity (~184 mAh.g-1) and rate capability. Even at a current density of 1 A.g-1, the nanosheet electrode still exhibits a specific capacity of ~90 mAh.g-1. These results suggest the Nb2O5 nanosheet is a promising candidate for high-rate lithium ion storage applications.

Microporous bamboo biochar for lithium-sulfur batteries

Being simple, inexpensive, scalable and environmentally friendly, microporous biomass biochars have been attracting enthusiastic attention for application in lithium-sulfur (Li-S) batteries. Herein, porous bamboo biochar is activated via a KOH/annealing process that creates a microporous structure, boosts surface area and enhances electronic conductivity. The treated sample is used to encapsulate sulfur to prepare a microporous bamboo carbon-sulfur (BC-S) nanocomposite for use as the cathode for Li-S batteries for the first time. The BC-S nanocomposite with 50 wt.% sulfur content delivers a high initial capacity of 1,295 mA·h/g at a low discharge rate of 160 mA/g and high capacity retention of 550 mA·h/g after 150 cycles at a high discharge rate of 800 mA/g with excellent coulombic efficiency (⩾95%). This suggests that the BC-S nanocomposite could be a promising cathode material for Li-S batteries.

SnO2 decorated graphene nanocomposite anode materials prepared via an up-scalable wet-mechanochemical process for sodium ion batteries

A facile and up-scalable wet-mechanochemical process is designed for fabricating ultra-fine SnO2 nanoparticles anchored on graphene networks for use as anode materials for sodium ion batteries. A hierarchical structure of the SnO2@graphene composite is obtained from the process. The resultant rechargeable SIBs achieved high rate capability and good cycling stability.