Thermal Management of Lithium-Ion Battery Packs in Electric Vehicles

Abstract

The performance, safety, and service life of electric-vehicle (EV) battery packs are governed by their operating temperature. Lithium-ion cells deliver optimal efficiency within a narrow window of roughly 15 to 35 degrees Celsius and demand a cell-to-cell temperature spread below about 5 degrees Celsius to avoid accelerated and uneven ageing; excursions beyond 50 degrees Celsius can trigger thermal runaway. This paper presents a comparative thermal analysis of four battery thermal management system (BTMS) architectures forced air, liquid cold-plate, phase-change-material (PCM), and a PCM–liquid hybrid for a representative pouch-cell module subjected to discharge rates from 0.5C to 5C. A coupled electrothermal model, validated against published cell calorimetry, was used to predict peak temperature, cell-to-cell uniformity, and parasitic energy consumption. At a 3C discharge the hybrid system limited the maximum cell temperature to 33.4 degrees Celsius and the cell-to-cell spread to 1.9 degrees Celsius, against 44.8 degrees Celsius and 8.6 degrees Celsius for forced air, while consuming 38 percent less pump power than standalone liquid cooling. The study quantifies the trade-offs among cooling capacity, temperature uniformity, parasitic load, and system complexity, providing design guidance for next-generation high-power EV battery packs.