Hyundai’s new 2019 Kona Electric, with its 64 kWh battery and an EPA-rated 258 miles of range, has gotten many positive initial reviews but until now we haven’t known much about some important aspects of its internal powertrain design.
We knew the basic size, shape, and layout of the pack. We were pretty sure the battery cells inside the Kona pack were liquid-cooled unlike all previous plug-in cars from Hyundai and its sister company Kia. Those earlier designs used a fan to actively blow cabin air through the inside of their packs.
However, many questions remained unanswered.
The electric motor and related power electronics usually need liquid cooling but would they now be on their own separate cooling loop or would there be some way to exchange heat between them and the battery’s new coolant loop?
And just how does heating the battery work in colder weather? And what do the battery cells even look like? For the Kona Electric we had some tentative hints in our “first drive” review but it was still a bit of a mystery.
We already know the basic answers to these questions for the Chevrolet Bolt EV, the Jaguar I-PACE, and even the soon arriving Audi e-tron. Now, Hyundai has revealed these details to Electric Revs for their new generation of all-electric cars.
See also: Jaguar and Chevy have LG in common
Let’s dig in.
First off, what does the battery pack look like with the lid popped off? Hyundai showed a cutaway version of a Kona Electric prototype at the car’s official introduction at the Geneva Auto Show earlier this year in March.
These two images above show a topless battery pack with the left (driver’s) side of the seat and floor also removed along with part of the rear seat. Each of the dark gray strips seen under the floor is an individual lithium ion pouch cell mounted in a carrier frame (as illustrated below) and collectively packaged into a battery module.
The cells in the Kona Electric are made by LG and use a cathode chemistry known as NMC 622 which stands for a ratio of 60 percent nickel, 20 percent manganese, and 20 percent cobalt. The cells in the Kia Niro EV are similar but are made by SK Innovation.
According to Jerome Gregeois, a senior manager at the Hyundai Kia America Technical Center, the full 64 kWh pack consists of five modules. Three are under the main cabin floor and two stacked modules are under the rear seats. Each module consists of cell groups as seen in the illustration below (the second stacked module below the rear seats is not shown).
The 294 cells in the pack are wired together three at a time into 98 cell groups which are shown as alternating blue and brown bands in the image. Each of the three floor modules has 20 cell groups. The two stacked modules each contain 19 cell groups.
Here’s an “exploded” illustration of the pack.
The battery modules sit above cooling plates that channel the same type of water and glycol mix that is used for cooling conventional gasoline engines except the heat emitted from batteries is not normally as intense.
Inside the 64 kWh pack there are three coolant sub-loops running through the five modules. One sub-loop runs through the driver-side floor module and one of the stacked modules. A second sub-loop runs though the passenger-side floor module and the other stacked module. The third sub-loop cools only the middle floor module.
What about when the pack needs to be warmed in winter conditions?
When Hyundai initially briefed the media on the US version of the Kona Electric there was some ambiguity about whether the car would have a dedicated battery heater. The company engineers have designed the Kona as a global vehicle with a menu of engineering choices that can be tailored to each marketing region to optimize for price and performance in different climate conditions.
At least for the 2019 model year, all Kona Electric’s sold in the US will come without a dedicated battery heater while all Canadian versions will include one. Similarly, all US deliveries will come with 5.5 kW PTC direct resistive cabin air heating alone while all Canadian deliveries will include a heat pump (reversible A/C system) to more efficiently assist cabin heating.
These choices implicitly assume that most, or at least a very large fraction, of the US deliveries will go to areas of California that rarely experience severe cold weather. Skipping the heat pump and dedicated battery heater saves money and helps lower the consumer price of the vehicle.
Despite the lack of a dedicated battery heater, the US version of the Kona does have the ability to scavenge heat from the electric motor and power electronics in addition to the heat dissipated by the battery itself to help keep the battery warm when operating in colder conditions.
There is one overall thermal management loop with computer-controlled valves that allow a battery pack sub-loop to either run separately or join together with the coolant that runs through the motor, motor inverter and other power electronics, and the on-board (AC) battery charger.
When a dedicated 2 kW battery heater is available (as in the Canadian version), it is used primarily at sub-zero temperatures (0C or 32F) or when the driver enables an optional “Winter Mode”. The battery heater, if present, is located outside the battery pack and warms the liquid “coolant” just before it enters into the pack.
The winter mode uses extra energy to warm the battery pack to allow for full regenerative braking and quicker fast DC charging. Colder pack temperatures force the battery management system to restrict the amount of power that can recharge the battery in order to avoid damaging the carbon graphite anode. This is an issue common to most lithium ion batteries. Cold temperatures are not much of an issue for power coming out of the battery except under rare and extreme conditions like down near -40 degrees.
The chart below, supplied by Hyundai, shows the different operating modes of the dynamically configurable thermal management loops.
Three coolant loop modes
The three modes (Heating, LTR or Low Temperature Radiator, and Chiller) correspond to the three different computer-controlled valve settings and coolant flow diagrams.
During much of the year in mild climate conditions the thermal system typically starts up in LTR mode (labeled “Cool Condition” above) which circulates coolant through a single interconnected loop to warm the battery up to its optimal operating temperature when cold and to maintain that temperature with the help of a radiator and fan.
The three-way valves switch to Chiller Mode (labeled “Hot Condition” above) when the battery starts to get too warm. Hyundai hasn’t said what the exact parameters are. The coolant flows through a “chiller” which exchanges heat with the vehicle’s air conditioning refrigerant loop.
In the Chevrolet Bolt EV, the A/C system begins helping to chill the battery coolant when it reaches much above 32C (90F). But the Bolt has a dedicated coolant loop just for the battery and no valves to allow the exchanging of heat with the motor and power electronics loop.
When temperatures are really cold, the dedicated battery heater kicks in (if present) even if “Winter Mode” isn’t enabled. Like a hot battery in Chiller Mode, the battery coolant sub-loop circulates independently because the battery heater is only needed to warm the battery and not the rest of the components.
This thermal management strategy is somewhat similar to that used by Tesla, and the startup automaker Rivian among others.
The recently introduced Tesla Model 3 can flexibly connect its coolant loops and does not have a dedicated battery heater but it does reportedly have the ability to generate excess heat from its motor and power inverter by deliberately operating inefficiently which is then used in place of a dedicated heater.
Rivian also has a similar flexibly configurable thermal loop that includes a dedicated battery heater.
Owner experiences will demonstrate over the next year how well Hyundai’s design and configuration choices perform in the real world.
Hyundai and Kia are using this new overall battery pack and thermal management design in the 2019 Kia Niro EV and the 2020 Kia Soul EV as well as in the 2019 Hyundai Kona Electric.
The companies also market a smaller 39.2 kWh version of the battery pack outside of the US and Canada. That smaller pack reportedly skips the two modules under the rear seat and reorganizes the three modules under the floor into 90 cell groups using pairs of the same cells used in the 64 kWh version of the pack. This smaller pack continues to use the same liquid-cooled thermal management design as the larger 64 kWh pack.
According to Kia, the North American version of the 2019 Niro EV will come standard with a heat pump to more efficiently assist with cabin heating and the dedicated battery heater will be an optional feature. In the 2020 Soul EV, both the heat pump and battery heater are listed as optional features.