This is the first report of impedance technique run on single particle LiCoO 2 electrodes with the aim of clarifying its electronic and ionic transport properties. Measurements were successfully conducted on a LiCoO 2 particle of 15 m diam resulting in impedance magnitude on the order of M⍀. The impedance spectra exhibited ͑i͒ one semicircle in the high frequency region, ͑ii͒ Warburg impedance in low frequencies, and finally, ͑iii͒ a limiting capacitance in the very low frequencies. The spectra were analyzed using a modified Randles-Ershler circuit, so that the reaction kinetics could be precisely evaluated. The charge transfer resistance decreased as the potential increased, whereas the double layer capacitance was almost invariant with the potential. Thus, the apparent chemical diffusion coefficient (D app ) of lithium ions was determined to be 10 Ϫ11 to 10 Ϫ7 cm 2 /s as function of electrode potential. These results are in agreement with those obtained by potential step chronoamperometry technique.
Novel binderless carbon nanotube aerogel (CNAG) electrodes are developed. The materials exhibit a remarkable specific surface area of 1059 m2 g–1 with a special textural porosity with almost equal amounts of mesopores and micropores. These nanostructured CNAG electrodes (see figure) have a wide range of potential applications in electrochemical power sources. The CNAGs great potential as electrodes for supercapacitor applications is demonstrated by a specific capacitance as high as 524 F g–1.
The kinetics of Li-ion extraction and insertion at LiMn 2 O 4 single particles ͑8-21 m diam͒ were investigated by cyclic voltammetry, potential step chronoamperometry ͑PSCA͒, and electrochemical impedance spectroscopy ͑EIS͒ methods using a microelectrode technique. The EIS measurements in a frequency range from 110 kHz to 11 mHz were conducted successfully on a LiMn 2 O 4 single particle resulting in the magnitude of M⍀ orders. The impedance spectra exhibited ͑i͒ a single semicircle in the high frequency region, ͑ii͒ a Warburg impedance in the low frequency region, and ͑iii͒ a limiting capacitance in the very low frequency region. The EIS spectra were fitted to a modified Randles-Ershler circuit, so that the reaction kinetics could be evaluated precisely. The dependences of the charge transfer resistance (R ct ) and the apparent diffusion coefficient of Li within the particle on the electrode potential were evaluated. Obtained values for D app were in the range of 10 Ϫ10 to 10 Ϫ6 cm 2 /s from EIS measurements, in fair agreement with those from PSCA results. Finally, the apparent chemical diffusion coefficients of Li-ion in the single crystal, thin-film, and single particle of LiMn 2 O 4 are compared.
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