Dana A. Totir

Electrochemical characterization of lithiated transition metal oxide cathode particles in the absence of carbon, binders and other additives

Abstract A novel method is herein described for the electrochemical characterization of lithiated transition metal oxides in powder form as cathode materials for lithium ion batteries. The procedure involves application of sufficiently high pressures to a layer of oxide powder evenly dispersed on the surface of a Au foil so as to embed the particles into the soft metal substrate, thereby avoiding the use of carbon, binders and other additives. Implementation of this methodology for battery-grade LiMn2O4, LiCoO2 and LiCo0.15Ni0.85O2 particles supplied by various commercial sources yielded electrodes of excellent mechanical integrity displaying close to ideal cyclic voltammetric behavior in electrolytes of relevance to battery applications. The charge capacity of each of these compounds could be estimated quantitatively by dissolving the array of oxide particles in acid, once the electrochemical experiments were completed and then determining the amount of metal in the solutions by ICP-MS analysis. An analysis of voltammetric measurements as a function of scan rate yielded values of mean diffusion coefficients for Li in LiMn2O4 on the order of 5×10−10 cm2 s−1.

In situ sulfur K-edge X-ray absorption near edge structure of an embedded pyrite particle electrode in a non-aqueous Li+-based electrolyte solution

Abstract Changes in the composition of embedded pyrite (FeS 2 ) particle electrodes in 1 M LiClO 4 propylene carbonate solutions as a function of the applied potential have been examined in situ by S K-edge fluorescence X-ray absorption near edge structure (XANES), using a specially designed cell that minimizes attenuation of low energy X-rays. Pyrite electrodes that had been scanned from 3.0 V versus Li/Li + , i.e. close to the open circuit voltage, down to 1.0 V (fully discharged state, i.e. 4e − -reduction) and then half recharged (2e − -reoxidation) by scanning the potential in the positive direction up to 2.2 V versus Li/Li + , revealed features consistent with the presence of Li 2 FeS 2 , in agreement with in situ Fe K-edge results reported earlier by this research group. Moreover, only subtle changes were discerned between the in situ S K-edge XANES of the half-, and fully-recharged electrodes. This close resemblance may reflect similarities between the spectral signatures of Li 2 FeS 2 and Fe 1− x S (pyrrhotite), which is the main product of the discharge reaction. Evidence for the formation of elemental sulfur and Li 2 S, which are believed to be minor products of the reaction, was obtained from analysis of the first differential S XANES and selected difference spectra. The compositional variations of the embedded pyrite particles throughout the course of the electrochemical processes occur in the presence of a persistent sulfate coating.

Structural, Spectroscopic, and Electrochemical Characterization of Boron‐Doped Diamond Films from Different Provenances

Morphological, spectroscopic, and electrochemical aspects of boron-doped diamond (BDD) films grown on silicon surfaces originating from three different laboratories have been examined by atomic force microscopy (AF), Raman scattering, Auger electron spectroscopy, and cyclic voltammetry in polyethylene oxide LiClO{sub 4} electrolytes in ultrahigh vacuum. All specimens displayed AFM images characteristic of diamond and Raman spectra consistent with a wide range of boron concentrations (10{sup 19} to 10{sup 21} B atom/cm{sup 3}), with no evidence for the presence of gross graphitic impurities. The cyclic voltammetry of two of the specimens (denoted as GV2 and CWRU), however, showed features at potentials positive to lithium bulk deposition attributed to lithium-ion intercalation/deintercalation phenomena in non-diamond carbon present as a surface impurity, perhaps at the grain boundaries. This finding is consistent with earlier results for a specimen of type GV2 in aqueous electrolytes for which rates of heterogeneous electron transfer for certain redox couples were found higher than those for nominally clean BDD surfaces.