Because of their nanometer-scale diameter, large aspect ratio, good electrical conductivity, and superior elasticity, multi-walled carbon nonotubes (MWCNTs) can be ideal reinforcement and conductive additive of the anode materials of lithium-ion batteries.
In this dissertation, we studied the electrochemical lithium storage performance of MWCNTs. As a result, MWCNTs showed a high first discharge capacity of 523.5mAh/g, and a low charge capacity of 248.3mAh/g. The first coulomb efficiency was as low as 47.4%. There is no plateau observed in the potential-time curve. The graphitized MWCNTs showed a plateaus and an improved cycling ability, while their first capacity and coulomb efficiency were not improved. Therefore, MWCNTs, graphitized or not, are not suitable to be used as the anode material of lithium-ion batteries.
MWCNTs/SnO2 composite anode material was prepared, and the effect of heat treatment temperature on their electrochemical properties was studied. The results showed that the materials heat treated at 450℃ displayed optimized performance: a capacity higher than graphite anode, and a cyclic performance superior to tin.
A new approach was proposed for the dispersion of MWCNTs. By using a wet ball-milling method, a conductive additive composed of well-dispersed cut MWCNTs and carbon black particles was prepared in sphere natural graphite. It was shown that when 5% conductive additive was added into natural graphite, their first discharge capacity and coulomb efficiency were improved, as well as the performance. After 20 cycles, 81.8% of the capacity was remained, compared to 58.3% of those using carbon black as additive. Through analyzing the electrical conducting distance and the geometry shapes of MWCNT, carbon black and sphere graphite, a model was proposed to explain the function of the composite conductive additives.
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