The lithium intercalation into graphite from electrolyte and from solid lithium

The values of diffusion coefficient (D) of lithium in thermoexpanded graphite during cathodic intercalation from aprotic electrolyte, and upon direct contact with lithium metal, are measured. In the first case galvanostatic switch-on curves were registered, in the second case the method of x-ray diffraction was used. In the both cases D was close to 10^-10 cm²/s.Presented at the 3rd International Meeting "Advanced Batteries and Accumulators," June 16th–20th 2002, Brno, Czech Republic     

Decreasing Irreversible Capacity of Graphite Electrodes in Lithium-Ion Batteries by Direct Contact of Graphite with Metallic Lithium

The feasibility of reducing the irreversible capacity of negative graphite electrodes in lithium-ion batteries by a direct contact of such electrodes with lithium in the electrolyte is studied. It is shown that the dynamics of the formation of the passive film on graphite and the degree of the decrease in the irreversible capacity depend on the ratio between weights of graphite and lithium in contact. This method of reducing the irreversible capacity does not diminish the reversible capacity of graphite during the cycling. The irreversible capacity of the initial graphite cycled in 1 M LiPF₆ in a mixture of propylene carbonate and diethyl carbonate at a current density of 20 mA g^–1 is 550–1150 mA h g^–1. The reversible capacity of electrodes cycled in the same conditions reaches 290 mA h g^–1.     

Lithium intercalation into amorphous-silicon thin films: An electrochemical-impedance study

Lithium intercalation into 0.25-μm-thick films of amorphous silicon is studied using the electrochemical-impedance technique. An equivalent circuit, proposed for such electrodes, comprises the electrolyte resistance and three units connected in series, each unit being a parallel combination of a resistance and a constant-phase element. The units relate to the charge transfer processes at the silicon/electrolyte interface, charge transfer though the passive film on the silicon, and the lithium diffusion into the silicon bulk. During potential cycling, changes occur largely in the unit related to the passive film. The lithium diffusion coefficient in the amorphous silicon is estimated as ～ 10^?13 cm² s^?1.     

Study of the “Diamond—Pyrolytic Carbon” nanocomposites using lithium intercalation

Electrochemical behavior of the diamond-based composites: a nanodiamond—pyrocarbon composite and Carbal, as well as vacuum-high-temperature-annealed polycrystalline diamond is studied by the cathodic lithium incorporation from LiPF ₆ solution in a (1 : 4) propylene carbonate—diethyl carbonate mixture. The amount of incorporated lithium steadily increases with the nondiamond (graphite-like) carbon content in the composite. The intercalation capacity of Carbal equals ~33 mA-h per g of the graphite-like carbon. It is concluded that the graphite-like carbon distributed in the nano-(or micro-)diamond carcass is the electrochemically active phase in the composites.Translated from Elektrokhimiya, Vol. 40, No. 12, 2004, pp. 1508–1513.Original Russian Text Copyright © 2004 by Pleskov, Kulova, Skundin, Krotova, Ralchenko, Korchagina, Gordeev.     

Electrochemical insertion of sodium into nanostructured materials based on germanium

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The possibility of electrochemical lithium intercalation into a nanodiamond

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The Effect of Particle Size on the Processes of Charging and Discharging of the LiFe<Subscript>0.97</Subscript>Ni<Subscript>0.03</Subscript>PO<Subscript>4</Subscript>/C/Ag Cathode Material

Olivine-structured LiFe_0.97Ni_0.03PO₄/C/Ag nanomaterials of varying dispersibility are prepared by using sol–gel synthesis with subsequent milling. The materials are certified using X-ray diffraction analysis, scanning electron microscopy, low-temperature nitrogen adsorption, and electrochemical testing under the lithium-ion battery operating conditions. The LiFe_0.97Ni_0.03PO₄/C/Ag cathode material primary particles’ size was shown to decrease, under the intensifying of ball-milling, from 42 to 31 nm, while the material’s specific surface area increased from 48 to 65 m²/g. The discharge capacity, under slow charging–discharging (C/8), approached a theoretical one for all materials under study. It was found that under fast charging–discharging (6 C and 30 C) the discharge capacity is inversely proportional to the particles’ mean size. The discharge capacity under the 6 С current came to 75, 94, 97, and 106 mA h/g for the initial material and that milled at a rotation velocity of 300, 500, and 700 rpm, respectively. An increase in the lithium diffusion coefficient upon the samples’ intense milling is noted.     

Lithium Intercalation into Nanostructured Films Based on Oxides of Tin and Titanium

The lithium intercalation into nanostructured films of mixed tin and titanium oxides is studied. X-ray diffraction and Moessbauer spectroscopy analyses reveal that films consist of a rutile solid solution (Sn, Ti)O₂ and an amorphous tin oxide enriched with Sn²⁺ ions. The films specific capacity during the first cathodic polarization in a 1 M lithium imide solution in dioxolane is 200–700 mA h/g, of which nearly one half is the irreversible capacity. During the second cycle, the latter is 15% of that in the first cycle. As the films are thin (<1 m), their capacity does not depend on the current density at 1–80 mA/g. During the electrode cycling, the capacity decreases by 2 mA h/g each cycle. The effective lithium diffusion coefficient, determined by a pulsed galvanostatic method, is 10^–11 cm²/s; it slightly increases with the film lithiation. During the first cycle, the amorphous phase of oxides is reduced to tin metal, the solid solution (Sn, Ti)O₂ decomposes, SnO₂ disperses to become an x-ray amorphous phase, and TiO₂ precipitates as a rutile phase. Lithium reversibly incorporates into the tin metal, yielding Li _y Sn, and into a disperse SnO₂ phase, yielding Li _x SnO₂.     

Irreversible processes during the lithium intercalation into graphite: the passive film formation

Comparative studies of three type of carbonaceous materials—the modified oxidized graphite, thermoexpanded graphite, and carbon paper—prior to and after galvanostatic cycling in 1 M LiClO₄ solution in propylene carbonate-dimethoxyethane mixture are carried out using standard porosimetry. It was shown that the mean (effective) thickness of the passive film [solid electrolyte interface (SEI)] at the electrodes of the modified oxidized graphite and thermoexpanded graphite equals a few nanometers. The comparison of porosimetric and electrochemical data shows that the passive film comprises both lithium carbonate and alkylcarbonates. Additionally, this comparison allows corroborating the concept on the formation of polymer (or oligomer) component of the passive film at least at the thermoexpanded graphite electrodes.     

Active Layer Thickness Effect on the Behavior of Electrodes Based on Lithium Iron Phosphate

Russian Journal of Electrochemistry - The effect of the active layer thickness (the amount of active material per unit area of the electrode) on the behavior of electrodes based on lithium iron...