Lithium Intercalation Capacity Research Articles

ChemInform Abstract: Amorphous Manganese Oxyiodides Exhibiting High Lithium Intercalation Capacity at Higher Current Density.

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Amorphous Manganese Oxyiodides Exhibiting High Lithium Intercalation Capacity at Higher Current Density

Amorphous Manganese Oxyiodides Exhibiting High Lithium Intercalation Capacity at Higher Current Density

Effect of a rhombohedral phase on lithium intercalation capacity in graphite

Five natural graphites with different rhombohedral phase (3R phase) content have been investigated as anode materials for rechargeable lithium-ion batteries. The reversible capacity varies from 250 mA h/g to 350 mA h/g for the same intercalation conditions depending on the content of the 3R-phase. With increasing rhombohedral phase in the graphite, the intercalation capacity will be high. A peak at about 10 mV in the cyclic voltammograms (CV) of a sample with a large 3R-phase content is caused by lithium ions occupying boundaries between the rhombohedral (3R) phase and the hexagonal (2H) phase and is responsible for a capacity exceeding the theoretical value.

Processing and Properties of Amorphous Manganese Dioxide Formed by Sol-Gel Procedures

ABSTRACTSol-gel derived amorphous manganese dioxide (a-MnO2) showed extremely high reversible lithium intercalation capacity. The composition and structure of the material were modified by heating at different temperatures. Cycling performance of the modified samples suggests that lowering the water content in the material is beneficial, while introducing crystallinity is detrimental, to its cyclability. A novel double-solvent-exchange process was tried for the processing of the material. Preliminary results indicated significant improvement in the reversibility of the insertion/release cycles.

Graphite structure and lithium intercalation

The various commercial graphite structures and their lithium intercalation properties were investigated using X-ray diffraction (XRD) and electrochemical voltage spectroscopy (EVS) techniques. It has been found that most commercially available graphites are a mixture of hexagonal (2H) and rhombohedral (3R) phases. For some graphites, the 3R phase content may exceed 30%. The correlation between graphite lithium intercalation capacity, 2H, 3R phase contents and structural disorder in each phase is discussed. A model is proposed to facilitate the understanding of the relationship between the graphite structures and the lithium intercalation properties. It was found that the total reversible lithium capacity is related to both the 2H and the 3R phase contents, and that the lithium intercalation mechanism in the 2H and 3R structures are similar.

Structural aspects of lithiated carbon

In this work, X-ray diffraction (XRD), coulometry titration, X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) were used to study the structure of lithium-intercalated pyrolytic poly (furfural alcohol) (PFA) and mesophase carbons formed at 1000 °C (MCMB1000) and 2800 °C (MCMB2800), respectively. The effect of phosphorus doping on the intercalation capacity was identified through a comparison between PFA and MCMB 1000. It was further verified by a separate experiment, in which MCMB 1000 was treated with phosphoric acid followed by heat treatment at 1000 °C. The maximum lithium intercalation concentration x ( x in Li x C 6) increased sharply with the introduction of phosphorus, whereas it was not reflected in XRD. Although there were two turning points in the open circuit voltage E-x curve of PFA, no staging phenomenon could be observed. A simple model based on mean field theory was used to investigate the effect of the attractive interaction between intercalates on the formation of lithium ordering in the structure of the intercalation compound. It was inferred from the XPS spectra that PFA showed a better ability to accept electrons than MCMB1000, although they have similar crystalline structures. The XPS spectra of Li-PFA also indicated partial covalent property of the Li-PFA interaction, which was further confirmed by ESR data. The influence of crystalline and electronic structures of carbon on lithium intercalation capacity was demonstrated.

Characterization of sprayed and sputtered thin films for lithium ion microbatteries

We have investigated the preparation of thin films of anode and cathode materials for all oxide solid state lithium ion microbatteries. Thin films of LiCoO2 and Li4/3Ti5/3O4 have been deposited by both spray pyrolysis and RF magnetron sputtering. The structural and electrochemical properties of high temperature-LiCoO2 thin films have been determined. Spray pyrolysis prepared higher quality LiCoO2 thin films. Both sprayed and sputtered Li4/3Ti5/3O4 thin films exhibited interesting lithium intercalation capacity. However, it has been demonstrated that RF magnetron sputtering is more efficient than spray pyrolysis for optimizing the interface between Li4/3Ti5/3O4 and the substrate material.

Lithium-ion rechargeable cells with polyacenic semiconductor (PAS) and LiCoO 2 electrodes

Polyacenic semiconductor (PAS), heat-treated at 700°C, has a lithium intercalation capacity as high as 438 mAh g −1 which is higher than the theoretical capacity of 372 mAh g −1 for graphite. The electrochemical behaviour of PAS is examined by studying Li/PAS and Li/graphite cells. In a PAS or graphite anode, three reactions are distinguished: (i) reaction of lithium with the Teflon binder; (ii) decomposition of electrolyte, and (iii) intercalation of Li + ions. Two laboratory cells with liquid organic electrolyte or polymer electrolyte and PAS as the anode demonstrate that PAS is a promising anode material for lithium-ion batteries.

Characteristics of pyrolyzed phenol-formaldehyde resin as an anode for lithium-ion batteries

Polyacenic semiconductor (PAS) is obtained by pyrolyzing phenol-formaldehyde resin (PFR). The properties of PFR heat-treated at different temperatures are investigated. The lithium intercalation capacity of PAS as a function of heat-treatment temperature (HTT) exhibits a maximum at around 700 °C. A knee appears at 700 °C, not only in the plot of atomic ratio [H]/[C] versus HTT, but also in the plot of conductivity versus HTT. For PAS with a HTT of 700 °C, the maximum in the ratio of the relative intensity of Raman spectra at 1360 cm −1 corresponds to nanometer graphite, and that at 1580 cm −1 to graphite. A reasonable explanation of these phenomena is the transformation of nanometer graphite to graphite.

Cokes as negative electrodes in secondary batteries

The lithium intercalated carbons (Li x C 6) have replaced the metallic lithium negative electrodes in secondary lithium batteries. In order to improve high energy density and long cycle life, it is necessary to find those carbonaceous materials that have an excellent lithium intercalation and de-intercalation capacity. In this work, the electrochemical behaviour of various cokes in ethylene carbonate (EC) and dimethyl carbonate (DMC) electrolyte were investigated by charge and discharge cycling processes and cyclic voltammetry technique. The petroleum coke (C342) has the highest capacity during cycling and the lowest irreversible capacity loss during the first cycle. Cyclic voltammetry revealed that the cycle efficiencies of three cokes are very high.

Rechargeable carbon anode

The electrochemical intercalation of lithium into carbon materials is discussed in terms of the effect of different parameters of the crystal structure and surface modifications of carbon to reduce the reaction of carbon with electrolyte solvents. The lithium intercalation capacity in the carbon materials prepared from the same raw materials and by the same preparation methods depends on the heat-treatment temperature. A higher capacity is obtained in the carbons prepared at higher temperatures, which have a graphite structure. The graphite is more reactive in reaction with organic solvents. The reaction of the graphite with solvents is reduced by a pretreatment of the carbon materials with acid and hydrazine.

Charge‐Discharge Characteristics of Mesophase‐Pitch‐Based Carbon Fibers for Lithium Cells

Mesophase‐pitch‐based carbon fibers were heat‐treated at high temperatures (2600 or 2800°C) and examined as anodes for lithium secondary batteries. Four types of carbon fibers were used whose cross‐sectional views are: a radial texture with wedge (type A), a radial texture with fine zigzag layers (type B), a double texture (type C), and a concentric texture (type D). Lithium could not be deintercalated after the first lithium intercalation in the type A carbon fiber. The structure of the type A fiber was destroyed during lithium intercalation. The other three types of carbon fibers showed good rechargeability on the first cycle, but demonstrated different behavior after 30 cycles. The highest lithium intercalation and deintercalation capacity was observed for the radially oriented carbon fiber (type B). The x‐ray results showed a reversible change in the lattice along the c‐axis during the intercalation and deintercalation cycle.