Electrochemical Li-Insertion Processes into Carbons Produced by Milling Graphitic Powders: The Impact of the Carbons’ Surface Chemistry

Abstract

Carbon powders were prepared by milling graphite particles in different atmospheres including air, highly pure argon, nitrogen, and CO 2 . Part of the samples was further exposed to air after milling. The carbonaceous materials thus obtained were tested as Li-insertion anodes in nonaqueous Li salt solutions. It was found that the atmosphere in which the active mass was prepared had a pronounced impact on the specific surface area of the particles obtained, probably due to the effect of surface groups on the carbons developed in the milling process. It was also found that the atmosphere to which the powders were exposed had a remarkable impact on the electrochemical behavior of the carbon electrodes in Li-insertion processes. The milling of the graphite produces highly reactive carbon surface sites, which react readily with active gases such as oxygen and CO 2 . The surface groups thus formed influence the surface chemistry developed on these electrodes in solutions. Since the electrochemical behavior of Li-C insertion electrodes depends strongly on the nature of the passivation films developed on these electrodes at low potentials, the milling atmosphere strongly influences their electrochemical behavior. The electrochemical processes were studied by chronopotentiometry, cyclic voltammetry, and impedance spectroscopy, the electrodes' structure and morphology were explored by X-ray diffraction and scanning electron microscopy, and the carbons' surface chemistry was studied by Fourier transform infrared and X-ray photoelectron spectroscopy.

Novel Impact of Short Term Aging on the Electrochemistry of CO[sub 2] Treated Synthetic Graphite

“…The change in irreversible capacity was strongly dependent upon the age of the treated samples, where samples freshly treated in CO 2 showed a decrease in irreversible capacity with treatment time, and treated samples aged for at least fourteen days ͑in a dry environment͒ showed an increase in irreversible capacity with treatment time. Based on the BET surface area, particle size, particle smoothness, and surface chemistry of the graphite, electrolyte decomposition mechanisms consistent with previous reports [32][33][34]38,54 are proposed here to account for these observations. To our knowledge, this is the first description of a significant change in graphite electrochemistry due simply to short term aging in a dry environment.…”

“…54 In their study of graphite powders milled in different environments, Aurbach and coworkers proposed that graphite samples with higher surface areas, smaller particle sizes, and exposure to active species such as CO 2 would generate more SEI interfering species, resulting in higher irreversible capacities. As described above, we observed a decrease in surface area ͑Fig.…”

The Impact of the Surface Morphology on Energy Characteristics of Nanoporous Carbon Material

“…Whereas there are no visible peaks on the volt-ampere characteristics obtained, as is the case of galvanic cells (batteries supply), it can be argued that the electrolyte has a chemical and electrochemical stability in the attached potential field [1].…”

Two-and three-electrode impedance spectroscopic studies of graphite electrode in the first lithiation

“…obtained in a threeelectrode button cell, indicating that without using an additional lithium foil as reference electrode in the button cell does not affect significantly the EIS features. With the decrease of the electrode polarization potential, the diameter of the HF arc increases by above 1.5 V, and remains invariant between 1.5 and 1.1 V. According to Aurbach and co-workers [6,[10][11][12] , the HF arc is related to SEI film (the resistance of SEI film coupled with SEI film capacitance). If we presume that the HF arc in the Nyquist plots recorded with the two-electrode button cell in this study is mainly related to the SEI film, at least two important aspects can not be interpreted properly: (1) As illustrated by the SEM results, no SEI film is formed on the surface of graphite electrode before electrochemical scan cycles, thus there should be no HF arc in the Nyquist plots at open circuit potential.…”