Solutions for brazing challenges in battery coolers – Part 1 – Aluminium Brazing

Leszek Orman, Sebastian Gutmann, Solvay Fluor GmbH, Germany

Abstract

Thermal management of electric vehicles is faced with challenges, as batteries need to be kept at a defined temperature range between 15°C and 35°C in order to function at peak performance throughout the life of a vehicle. The manufacture of such battery cooling systems involves controlled atmosphere brazing technology using noncorrosive flux. OEMs develop different battery cooler designs that require adapted fluxing methods. In this paper, selected cases of fluxing and brazing challenges in the manufacturing of battery cooling systems will be presented. Brazing experts will provide guidelines for fluxing and brazing of battery coolers.

1. Introduction

Batteries currently used in electrical vehicles [EV] can operate within temperature between –30°C and 50°C; however at temperature extremes, their performance is reduced and also battery life time suffers quite significantly. At high temperatures above 70°C, a chain reaction can occur causing destruction of the battery pack. Also during fast charging, batteries must be cooled down. High current going into the battery produces heat that must be removed. EV batteries perform the best at temperature between 20°C and 25°C ^[1].

EV batteries can be cooled using air cooling or liquid cooling. Liquid cooling is the method of choice to meet modern cooling requirements.
Air cooling systems use air to cool the battery and exists in the passive and active forms. Passive air cooling uses air from the outdoor or from the cabin to cool the battery. It is usually limited to a few hundred watts of heat dissipation. Active air cooling gets its air intake from an air conditioner, which includes an evaporator and a heater to control the air’s temperature. It is usually limited to 1kW of cooling and can be used to cool or heat the cabin.

Liquid cooling is the most popular cooling technology. It usually uses a liquid coolant such as water mixed with ethylene glycol and a corrosion inhibitor. Components carrying the liquid prevent direct electrical contact between the cells and the liquid coolant.
Like in air cooling, passive and active systems exist. Active liquid cooling is more complex and expensive but provides better performances for propulsion and charging power and the cooling results are much more reliable, thus nowadays, most batteries for EV are liquid cooled using active cooling, despite the fact that the active cooling is more expensive since it includes more components, such as a heat pump, a heat exchanger, a circulating pump, valves, and multiple temperature sensors ^[2].

Types of EV battery water coolers

An aluminium component is surrounding the battery cells. The component is filled with liquid coolant, which carries the heat to another location, such as a radiator. There is no direct electrical contact between the cells and the liquid coolant. The cooling component is usually located at the bottom of the car cabin.