Experimental Investigation of a Hybrid Thermal Management System for LFP Battery Packs Using Ag 2 O Nano Fluid–Cooled Serpentine Copper Tubes Embedded in Graphite‐Enhanced PCM

Effective thermal management is critical to ensure the safety, reliability, and performance of lithium‐ion battery modules under high thermal loads. While hybrid phase change material (PCM)–liquid cooling systems have been widely explored, the present study introduces a novel material‐level enhancement through the use of an Ag 2 O–ethylene glycol Nano fluid, whose application in battery thermal management remains largely unexplored. A compact 4S5P battery module comprising 21 700‐type lithium iron phosphate (LFP) cells (14 V, 22.5 Ah) is experimentally investigated under 1C, 1.5C, and 2C discharge rates, along with 1C charging conditions. The proposed hybrid BTMS integrates PCM with active liquid cooling using Ag 2 O Nano fluid at varying concentrations (1–5 wt.%), enabling a systematic evaluation of its thermo‐physical impact. The results demonstrate that, in the absence of thermal management, the module temperature rapidly increases to approximately 60°C at 2C, indicating severe thermal stress. In contrast, the proposed system significantly enhances heat dissipation, maintaining the maximum cell temperature within 30°C–32°C, thereby achieving a reduction of 5%. Furthermore, increasing nanoparticle concentration improves convective heat transfer, with optimal performance observed at 5 wt.%, reaching temperature to 29°C resulting in improved temperature uniformity across the module. Results demonstrate the effectiveness of Ag 2 O nanofluid relative to base fluid under the investigated operating conditions. This study not only demonstrates the feasibility of Ag 2 O‐based Nano fluids in BTMS but also provides a scalable and high‐performance thermal management solution for high‐power cylindrical battery modules in electric vehicles and energy storage systems.