High-density positive electrodes containing carbon nanotubes for use in Li-ion cells

摘要

Multi-walled carbon nanotubes (MWNT) are evaluated as a conducting agent in a high-density cathode for a Li-ion cell. Cathodes of LiCoO_2 with a density of up to 4.0 g cm~(3) are fabricated using alternate conducting agents of MWNT and conventional carbon black (Super P). An electrode containing MWNT (MWNT-cathode) is superior to one containing Super P (Super P-cathode) in terms of both high-rate (1 C) performance and cycle-life. Results from ac impedance and scanning electron microscopy (SEM) studies indicate that the improved performance of the former electrode is due largely to the resilience of the MWNT aggregates that form conductive bridges between particles of the active material. These resilient bridges maintain intimate contacts between the particles even when the composite expands on cycling. By contrast, similar but rigid bridges of carbon black in the Super P-cathode are broken on cycling. Overall, it is found that MWNT is a good candidate conducting agent to replace Super P and other carbon blacks and hence develop a high-energy Li-ion cell.