Published on December 5th, 2018 | by Dr. Maximilian Holland0
2019 Nissan LEAF — Still No Liquid-Cooled Battery?
December 5th, 2018 by Dr. Maximilian Holland
A report on the upcoming 60 kWh Nissan LEAF from respected German news site Electrive.net suggests that it will still lack liquid cooling of the battery. This is despite increased charging rates of 100 kW and increase power output of 149 kW. Notably, with higher power comes higher heat generation. Are we going to see #Rapidgate all over again?
Anyone following EVs for a while is aware of the thermal management issues that have beset the 40 kWh Nissan LEAF as well as previous generations of the car, and that have disappointed a great many owners of the vehicle as a result. I covered the overheating problems in depth earlier this year, and even suggested some strategies that drivers could take to try to best manage the problem on long journeys. The advertising standards agency in the UK even ruled against Nissan’s original marketing of the LEAF, due to Nissan not clearly disclosing the thermal management issues and related charging performance throttling.
Electrive recently spoke with Nissan dealer circles in Germany and uncovered some new (and as yet unconfirmed) information about the eagerly anticipated 60 kWh LEAF. We have known for a while that the battery output power would increase to 149 kW (200 hp), up from the current 110 kW (147 hp). We’ve seen photo evidence that the DC charging power has been increased to 102 kW (at least on the prototypes). This charge rate may be trimmed slightly, to just under 100 kW, on the release model. The charging standard will still be CHAdeMO, even in Europe, which may be a strategic mistake by Nissan. We also know that the battery cell supply will change from Nissan’s partially owned subsidiary AESC to newer-chemistry LG Chem cells.
Most of us were hoping that — given the battery heat problems with the current-generation LEAF — Nissan would get with the program and equip the 60 kWh LEAF with decent battery thermal management, using active liquid cooling.
Despite these hopes, according to the news, the 60 kWh LEAF will stick with air cooling, albeit this time with some active fans (not present in the current LEAF) and, I would speculate, a cold-air-redirect from the passenger compartment’s air conditioning cooler. This is the type of battery cooling system employed in the current 40 kWh Nissan e-NV200 light commercial van. Even with this, some charge power throttling does still occur to avoid excessive battery pack heating.
The current LEAF and e-NV200 both have the 40 kWh pack, typically charging at between 35 and 45 kW. The 60 kWh pack on the new LEAF is 50% larger and will charge at 2× the kW power. Here’s a reminder of the massive amounts of heat added during a single DC fast charge of the current 40 kWh LEAF (consider that this is only at 46 kW peak charging power):
Given that a 70% top-up on the current LEAF, even limited to 46 kW, adds 20° Celsius worth of heat to the pack, it seems unavoidable that a 50% greater amount of energy added via 92 kW charging will — other things being equal — add at least twice the heat (yes, that’s 40° Celsius of added heat from a single DC charge). This is the challenge that a battery cooling system must overcome. With all current battery cell chemistries, it is simply not possible to charge a battery pack at around 100 kW for 20–30 minutes (adding 33 to 50 kWh of energy) without generating a huge and potentially damaging amount of heat in the cells. The only solution is for this heat to be rapidly transferred away from the cells — typically by actively circulating cooling liquid through the battery pack and out through a radiator, as almost all recent EVs are designed to do. The only conceivable ways around having a well designed active liquid cooling system are either:
- To continue the infamous charge throttling #Rapidgate saga (say it ain’t so!), or
- For LG Chem to provide a cell chemistry with magically low internal resistance (unlikely), or
- For the pack voltage to move from the current 360 volts up to 600 or 800 volts (very unlikely), or
- For Nissan to fit the LEAF with an industrial-strength air cooling system (hopefully)
The report author, Peter Schwierz, suggests that the 60 kWh LEAF, which Nissan originally planned to be unveiled at the recent LA Auto Show, will now be unveiled at the Consumer Electronics Show in early January 2019, just over a month from now. The 60 kWh LEAF is said to have the same body design as the current 40 kWh LEAF, and perhaps largely the same passenger compartment design, just with an upgraded battery and powertrain. The 60 kWh LEAF will be available on sale in Europe from May 2019.
It’s my sad prediction that a charge throttling “solution” looks set to still be an unwelcome but reliable “feature” of the 60 kWh LEAF, especially on long high-speed highway drives requiring several DC charges in warm and hot climates. What do you think? Is Nissan really going to go without active liquid cooling yet again, even after all of the problems it has caused LEAF customers in the past? Do they have a clever work-around which will be a better solution than the tried, tested, and proven liquid-cooling designs now standard in successful EVs? Or are we going to see #Rapidgate all over again? Please let us know what you think in the comments.