A Transmission Electron Microscopy Study of Degradation Mechanisms in a Tin-Carbon Fibre Composite Anode for Rechargeable Lithium-Ion Batteries

Abstract

Electrochemical degradation mechanisms of an Sn-carbon fibre composite anode, fabricated by electrodepositing an ultrafine grain (350 nm) Sn coating on a carbon fibre paper (CFP) and tested in a Li-ion cell, were studied. Using a current density of 1.50 mA cm-2, a reversible planar capacity of 2.96 mAh cm-2 and a capacity retention of 50% after twenty cycles were measured. TEM studies showed that lithiation/ delithiation was not uniform along the diameter of the carbon fibres. Additionally, the lithiation/ delithiation of the Sn coating gradually transformed the initial Sn grains with a (200) orientation to 4 nm-size Sn nanoclusters with a (220) orientation. This created a mixture of nanoparticles with different sizes (4-100 nm) and orientations embedded in an amorphous matrix that filled the micro-pores between the carbon fibres. Thus, the short-range electronic connection in the composite anode was undermined, and a reduction in the cell's capacity occurred.