Abstract: With the development of the coal chemical industry, the production of coal-based solid waste including coal gasification slag is increasing annually, and it is increasingly urgent for its high-value resource utilization. Functional materials prepared from coal gasification slag include zeolite, activated carbon, carbon-silicon composite materials, etc. These materials are mainly applied in fields including adsorbents, construction materials and catalysts. However, the application of coal gasification slags was relatively limited compared to other coal based solid wastes. Therefore, it is necessary to expand new application. Coal gasification slag, which is rich in elements including iron, silicon, aluminum, and calcium, serves as an excellent raw material for sustainably and economically preparing nanofluids, which are promising in heat transfer enhancement applications. Nanofluids can obviously enhance both one-phase and two-phase heat transfer with negligible extra energy consumption, which enable nanofluids as promising materials for battery thermal management. Water-based Fe₂O₃ nanofluid was prepared from coal gasification coarse slag and experimental research on battery thermal management based on nanofluid was conducted. Nanofluid with a mass fraction of 0.1% to 0.3% and an average particle diameter of 85 nm was prepared through chemical activation, element separation, pH adjustment, calcination and supersonic dispersion. The effects of nanofluid mass fraction, flow rate, and discharge rate on heat transfer performance were investigated. The nanofluids can decrease the maximum temperature rise of the battery surface by 22% and the maximum temperature difference by 34% without obvious extra pressure drop. Besides, the overall performance evaluation criterion was enhanced significantly with the application of nanofluids. Enhanced thermal conductivity and the disturbance effect of nanoparticles are related to the heat transfer enhancement. This research provides a new method for high value utilization of coal gasification slag and battery thermal management.