Back in November 2013, when the Volkswagen e-Golf made its US debut at the 2013 Los Angeles Auto Show, Volkswagen put out a press released containing this statement:
"The liquid-cooled lithium-ion battery accounts for 701 pounds of the e-Golf model's 3090-pound curb weight. It is composed of a total of 264 individual prismatic cells, which are integrated into 27 modules (each with six or twelve cells). Collectively, the cells have a nominal rating of 323 volts, with an overall capacity of 24.2 kWh. A battery management controller (BMC) performs diagnosis and monitoring functions and also regulates the temperature balance in the battery junction controller (the interface to the motor's energy supply). When the car is not in use or in the event of a collision, power from the battery is automatically cut off."
After extensive testing, Volkswagen engineers say that "e-Golf has passed various long-term engineering evaluation milestones in desert temperatures and cold weather climates, without the necessity of a cooling system."
News of this switch to air cooling comes via Darryll Harrison, VW US's manager of brand public relations, who emailed AutoblogGreen.
In the email, Harrison writes:
"Generally speaking, regarding the system, it's important to note that the e-Golf was designed with efficiency in mind. The battery pack utilizes ultra-efficient lithium-ion cells that deliver 25Ah per cell with an energy density of 59Wh per lb. The pack is comprised of 264 cells, packaged into 27 modules (of either 6 or 12 cells) delivering 323 volts and weighing in at 700 lbs. As it relates to battery temperature, VW has developed a Battery Management Unit with an intelligent thermal control that allows the pack to remain within an optimal temperature window, helping to maintain performance and range in a variety of temperatures. This system allows the e-Golf to operate, even in more extreme temperatures, without the need of a cooling system and without dramatic impacts in performance based on testing."
"In terms of the battery pack, the engineering goal was to develop a highly efficient system as opposed to one that focused on charge-time or capacity (like some of our competitors). In partnership with Panasonic, VW utilizes a lithium-ion cells designed for gentle charge and de-charge during use which helps to reduce heat and energy consumption often associated with cells designed for rapid charging and de-charging. Our engineers refer to them as "marathon cells." Additionally, without a cooling system weight savings are achieved which aides in overall efficiency of the vehicle. Due to the efficiencies achieved, minimal waste heat is created during operation (i.e. during fast charging) and is quickly directed by the battery metal structure into the chassis, away from the battery, helping to prevent extreme temperature conditions inside the pack."
If liquid cooling isn't needed, then VW made the right choice in eliminating the complexity of that system. Air cooling, if adequate for the given type of battery chemistry, is far simpler and less costly than liquid (active) cooling.
We believe VW made the right choice here, but do you?