High thermal conductivity negative electrode material for lithium-ion batteries

Experimental thermophysical property data for composites of electrode and electrolyte materials are needed in order to provide better bases to model and/or design high thermal conductivity Li-ion cells. In this study, we have determined thermal conductivity (k) values for negative electrode (NE) materials made of synthetic graphite of various particle sizes, with varying polyvinylidene difluoride (PVDF) binder and carbon-black (C-Black) contents, using various levels of compression pressure. Experiments were conducted at room temperature (RT), 150 and 200 degreesC. Requirements for designing a high thermal conductivity NE-material are suggested. Detailed statistical data analysis shows that the thermal conductivity of the NE-material most strongly depends on compression pressure, followed by graphite particle size, C-Black content and finally PVDF content. The maximum k-value was achieved for the samples made of the largest graphite particles (75 mum), the smallest C-Black content (5 wt.%) and the highest compression pressure (566 kg cm(-2)). Increasing the PVDF content from 10 to 15 wt.% increased the k-values by 11-13% only. The k-values of all samples decreased with increasing temperature; at 200 degreesC, the k-values were close to each other irrespective of preparation procedure and/or raw material contents. This most likely is due to the relaxation of contact pressure among the graphite particles because of PVDF melting at 155-160 degreesC. (C) 2001 Elsevier Science B.V. All rights reserved.