The effect of compression on natural graphite anode performance and matrix conductivity

Anodes for lithium-ion cells were constructed from three types of natural graphite, two coated spherical and one flaky. Anode samples were compressed from 0 to 300 kg/cm(2) and cycled in half-cells to study the relations between anode density, SEI formation and anode cyclability. The C/25 formation of the SEI layer was found to depend on the nature of the graphite and the anode density. Compression of the uncoated graphite lead to an increased conductivity, but only slight improvements in the efficiency of the formation process. Compression of the anodes made from the amorphous-carbon-coated graphites greatly improved both the reversible capacity and first-cycle efficiency. In addition, the fraction of the irreversible charge associated with the surface of the graphite increased with compression, from both an increase in the electrolyte contact as well as compression of the amorphous layer. The cyclability of all of the anodes tended to improve with compression. This suggests that it is the improvement in the conductivity of the anode plays more of a role in the improvement in the cyclability than the formation process. (C) 2004 Elsevier B.V. All rights reserved.