Factors affecting the energy harvesting efficiency of graphite thermoelectric materials

Thermoelectric materials have attracted significant attention for their ability to utilize waste heat for power generation whereas natural flake graphite holds great potential as a thermoelectric material. In this work, a pressure-assisted molding process was employed to fabricate graphite bulks using natural flake graphite with different purities and particle sizes. The effect of structure on the properties of the samples was analyzed. It was found that increasing the purity of graphite is beneficial for its electrical and thermal conductivity. Notably, the thermoelectric performance of graphite initially improves and then decreases with increasing purity. The decrease of flake graphite particle size is advantageous for enhancing the Seebeck coefficient of the samples but detrimental to their electrical and thermal conductivity. It is verified that changing the forming pressure can alter the arrangement orientation of flake graphite in the sample. However, the ordered arrangement of flake graphite is not conducive to the thermoelectric properties of the sample. Ultimately, an optimized process for preparing thermoelectric materials containing graphite was obtained, namely minimizing the orientation of flake graphite in the sample, and selecting graphite with a purity of about 99 % and a particle size of nearly 50 mu m.