Lithium Intercalation into Mechanically Milled Natural Graphite: Electrochemical and Kinetic Characterization

Abstract

The electrochemical lithium intercalation into natural graphite milled in various atmospheres was investigated. The atmosphere in which the natural graphite was milled has a strong influence on its final morphology and microstructure. These physical properties in turn have a pronounced effect on the electrochemical lithium intercalation process. The lithium storage capacity increases with the amount of disorder present, but it is also associated with a more pronounced discharge and charge potential hysteresis. Although a milled sample with a larger specific surface area is more susceptible to first cycle irreversible reactions, it has a smaller charge-transfer resistance. The chemical diffusion coefficient of intercalated lithium decreases when a large amount of disorder has been introduced into the sample by the mechanical milling process.Carbons are widely used as anode materials in lithium-ion batteries. This is due to their ability to intercalate and deintercalate lithium reversibly at potentials close to that of metallic lithium. However, carbon electrodes suffer complex irreversible reactions 1-3 when they electrochemically intercalate lithium for the first time. These irreversible reactions, involving the electrolyte, solvent, and the carbon electrode, cease when an electronic insulating solid electrolyte interface ͑SEI͒ 4 forms between the carbon electrode and the liquid electrolyte. This phenomenon diminishes the overall specific capacity and energy density of lithium-ion batteries because additional cathode material is required to balance the irreversible reactions. A number of large capacity disordered carbons have been developed in the hope of improving the overall performance of lithium-ion batteries. These large capacity disordered carbons are usually prepared via the pyrolysis of polymeric and organic precursors 5-7 although mechanically milled graphite and soft carbons 8-11 have also been reported to offer large lithium intercalation capacities. However, a better understanding of the lithium intercalation process in these large capacity disordered carbons is needed to optimize their performance.Recently, we have reported that the morphology and microstructure of natural graphite milled in the absence of oxygen evolve very differently from that milled in the presence of oxygen. 12 In this study, the electrochemical lithium intercalation into natural graphite milled in oxygen and nitrogen was investigated. Of particular interest is the effect of the microstructure and morphology of the milled samples resulting from the different milling atmospheres, on the electrochemical lithium intercalation process. ExperimentalThe graphite used was natural graphite ͑230U͒ from Asbury Carbons, Inc., with an average particle size of 15 m. With a ball-topowder weight ratio of 20, 3.52 g of the graphite powder and 20 hardened steel balls ͑9.8 mm in diam͒ were loaded into a hardened steel vial. They were then placed inside a glove bag and purged with nitrogen ͑Ͼ99.9%͒ or oxygen ͑Ͼ99%͒ for 20 min before being sealed. ...

Electrochemical Properties of Carbon Composites Prepared by Using Graphite Ball-milled in Argon and Air Atmosphere

“…These characteristics related to ball-milled graphites have been previously reported. [7][8][9][10][11][12] A noticeable feature noted from the XRD patterns in Figure 3(b) and (c) is that in the case of argon milled sample the (002) diffraction peak of graphite recovers after annealing at temperatures above 1000 o C, while for air milled graphite, the XRD profile near the (002) peak position of graphite appears to be similar before and after annealing. This means that the disordered structure of ballmilled graphite is more stabilized by milling under air atmosphere than under argon.…”

“…The low capacity and coulombic efficiency of the composite with argon-milled graphite are probably associated with the crystallization of ball-milled graphite during heat treatment for pyrolysis reaction of PVC. Considering that the large reversible capacities of highly ballmilled graphites (disordered carbons) are due to lithium being stored in microvoids, microcavities and active surface sites introduced by ball milling, [7][8][9] it is assumed that such defects would be reduced as a result of crystallization of ballmilled graphites, which leads to a reduced reversible capacity for the composite with argon-milled graphite as Table 1 shown in Figure 5. Moreover, the graphitization increases the active edge planes, susceptible to the irreversible reactions.…”

“…[7][8][9][10][11][12] However, ballmilled graphites exhibit a large irreversible capacity loss during the first charge (intercalation) due to their large specific surface areas. [7][8][9] To solve the problem, encapsulating the ball-milled graphite particles with a soft carbon is an effective method, making them less susceptible to irreversible reactions. On the other hand, the structure and properties of ball-milled graphite is significantly influenced by the atmosphere during ball-milling.…”

Synthesis, Structure And Properties of Electrochemically Active Nanocomposites

“…x>1 in Li x C 6 . Research on disordered carbon includes the modification of graphitic surface using mild oxidation [73,74], the use of carbon with a smaller particle size [75,76], creating extensive disorder by mechanical milling [77], etc. However, there are still problems to be solved despite their high capacities such as high irreversible loss and poor cycling performance.…”

Short-Time Transient Analysis of Intercalation of an Ion into a Sphere

“…The parameter values and their confidence intervals indicate that the short-time analysis presented here is a reliable method for estimating parameters. Estimation of kinetic and transport parameters of an intercalation particle has been obtained by many researchers using different methods such as electrochemical impedance spectroscopy ͑EIS͒, [15][16][17][18][19][20][21][22][23] potential intermittent titration technique ͑PITT͒, galvanostatic intermittent titration technique ͑GITT͒, [24][25][26][27] and relaxation techniques. 28,29 The techniques used so far have made use of the long-time solutions, which is in contrast to the use of short-time solutions in this paper.…”