Qingfang Shi

In Situ Raman Spectroscopy of Single Microparticle Li+−Intercalation Electrodes

Modifications in the vibrational properties of a single microparticle of LiMn2O4 induced by extraction and subsequent injection of Li+ into the lattice have been monitored in situ via simultaneous acquisition of Raman scattering spectra and cyclic voltammetry data in 1 M LiClO4 solutions in ethylene carbonate (EC):diethyl carbonate (DEC) mixtures (1:1 by volume). Statistical analyses of the spectra in the range 15 < SOD < 45%, where SOD represents the state of discharge (in percent) of the nominally fully charged material, i.e., λ-MnO2, were found to be consistent with the coexistence of two distinct phases of lithiated metal oxide in agreement with information derived from in situ X-ray diffraction (XRD) measurements involving more conventional battery-type electrodes (J. Electrochem. Soc. 2002, 149, A1164).

In situ Raman spectroscopy of single particle microelectrodes zinc passivation in alkaline electrolytes

An electrochemically sharpened W tip was used as a spear to capture and manipulate single, quasi-spherical particles of metallic Zn a few tens of micrometers in diameter, harvested from the anode of a commercial Zn/MnO 2 battery. This tactic made it possible to acquire in situ Raman spectra of Zn passive films formed by potential step techniques on individual Zn microparticles in 1 M KOH aqueous solutions using a shallow electrochemical cell placed directly beneath the objective of the Raman microscope. The results obtained were in good agreement with those reported earlier for Zn disk electrodes, a few millimeters in diameter, in alkaline electrolytes using the same Raman instrument without a microscope. More specifically, films formed by stepping the potential from -1.55 V to either -0.7 or -0.8 V vs. SCE, displayed a largely enhanced feature at ca. 565 cm - 1 ascribed to the E 1 longitudinal optical (LO) phonon modes of ZnO, an effect associated with the presence of interstitial Zn and oxygen deficiencies in the lattice. In addition, significant amounts of crystalline ZnO could be detected only for passive films formed at the same two potentials after the electrodes had been microroughened by a single passivation-reduction step.

Single Particle Electrode Microbatteries

Methods are herein described for the assembly and electrochemical characterization of a Li + battery consisting of a single microparticle (ca. 50 μm diam) of LiMn 2 O 4 as the cathode, and a single spherical mesocarbon microbead (MCMB) as the anode, using either 1 M LiClO 4 in ethylene carbonate EC/diethyl carbonate DEC mixture (1:1 by volume) or 1 M LiPF 6 in EC/dimethyl carbonate (1:1 by volume) as the electrolyte. Self-discharge curves were recorded by monitoring the potential of the battery as a function of time after charging independently each of the microparticle electrodes to full capacity. The results obtained showed that charge retention is vastly superior for the LiPF 6 , compared to LiClO 4 -containing electrolyte, in agreement with results published elsewhere using more conventional devices. This behavior has been attributed to the chemical instability of perchlorate ion toward the charged cathode.

Topographical and Electrochemical Characterization of Optically Smooth Zn Films Prepared by Physical Vapor Deposition

Optically smooth Zn films supported on Cu-coated glass and quartz substrates have been obtained by physical vapor deposition of Zn in metallic form. The method employed involves resistive heating of a Mo boat filled with high purity Zn shot in an Ar atmosphere at pressures of about 3-5 m Torr. Atomic force mieroscopy images revealed that the resulting Zn deposits consist of smooth features (rms roughness ca. 0.3 nm) with dimensions on the order of 200 nm. Preliminary results indicate that the electrochemical behavior of these films in strongly alkaline solutions is somewhat different than that observed for Zn in hulk commercial form.