Effect of Mechanical Grinding on the Lithium Intercalation Process in Graphites and Soft Carbons

Abstract

The effects of mechanical grinding on morphology and electrochemical performance of graphite and soft carbon powders with respect to lithium insertion were studied. The morphology of the milled graphitic powders was found to depend strongly upon the nature of the interactions (e.g., impact or shear) generated by the two kinds of mixer mills used. For the same milling time, crystallite size was smallest and the density of defects highest for graphitic powders that were ballmilled using impact interactions. The specific surface area of the milled samples does not increase indefinitely with increased milling time, but there is a critical milling time (me) beyond which the specific surface area goes through a maximum (graphite) or levels off for cokes. By controlling milling conditions, graphite and soft carbon powders with welldefined morphology, d-spacings, surface area, and crystallite size can be made. The reversible (reversible amount of inserted Li) vs. irreversible capacity (irreversible lithium loss between the first discharge and charge) was measured for various C/Li cells using various tailor-made graphite and soft carbon powders. A direct correlation between the irreversible capacity of the milled samples and their specific surface area was observed, consistent with catalytically induced reduction of the electrolyte. For milling times greater than m,, the irreversible capacity remains constant or even decreases while the reversible capacity still increases. With mechanical grinding, both graphite and coke samples having irreversible capacity of 328 mAh/g for a reversible capacity of 708 mAh/g (-Li 2 C 6 ) were obtained.

Characterization of Nanocrystalline Si-MCMB Composite Anode Materials

“…The irreversible capacity in the first cycle is considered coming from the formation of a passivating film, which consumes lithium at the electrode materials/electrolyte interface. [21][22][23] From SEM observation, we found that the spherical MCMB particles were severely damaged after 20 h ballmilling. Therefore, the sample F ͑ballmilled for 20 h͒ anode exhibited a very high irreversible capacity.…”

Hallmarks of mechanochemistry: from nanoparticles to technology

“…In order to achieve lithium intercalation, a milling process has been performed in graphite and soft carbons. 211,212 The effects of milling on the morphology and electrochemical performance of graphite and soft carbon powders with respect to lithium insertion were studied. The morphology of the milled graphite powders was found to depend strongly upon the nature of the interactions (i.e.…”

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.…”

“…[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.…”