The GM Ultium is a flexible battery pack architecture destined for a number of vehicles. GM is planning on building 1 million EV’s a year by 2025 and hence has invested in a joint venture with LG Chem to produce the Ultium Cell.
Ultium Cell
At the moment the details around the cell are limited and we don’t have a specification sheet, hence these numbers are approximations:
- LG Chem & GM joint venture
- Chemistry is NCMA (nickel cobalt manganese aluminum)
- Double ended pouch cell
- Dimensions ~585 x 100 x 10mm
- Capacity = 103Ah [5]
- Nominal voltage ~3.7V
- Weight ~1.36kg
- gravimetric energy density ~ 272Wh/kg
- volumetric energy density ~ 632Wh/litre
- gravimetric power density ~952W10s/kg
The 100Ah cell is large enough to reduce manufacturing costs, but it does reduce flexibility in total battery pack capacity. The smallest HV pack would be 96s1p = 35.5kWh. Also, the increments in capacity would also be 35.5kWh unless your architecture is flexible in terms of the system operating voltage window.
Ultium Module
Most vehicle designs have limited height under the front and rear occupants feet. This means it is difficult packaging a 100mm high cell along with the cooling system and structure of the module and pack. Tesla’s answer to this problem is to use a 70mm tall cylindrical cell.
GM’s approach with Ultium is to use different types of module design, creating the option to have the cells stacked vertically or horizontally.
This approach creates complexity in the module design, increasing costs in manufacturing, handling, service and end of life even. This is not a first as the 2010 Nissan Leaf packaged the modules such that some cells were vertical and some horizontal. Also, Nissan managed this with a common module design.
GM are now showing the Ultium module with both pouch and prismatic cells [4].
Ultium Pack
The aims of this pack have been described in a number of GM articles:
- Enable a GM-estimated electric range 300+ miles on a full charge with 0-60 mph in as low as 3 seconds.
- Have energy ranges from 50 to more than 200 kWh
- Support front-wheel drive, rear-wheel drive, or all-wheel drive applications
- Banded together, multiple cells form a battery module, and a cluster of battery modules make up a battery pack.
- The flat shape stacks efficiently, allowing for less wasted space, fewer electrical configurations and a simplified cooling system.
- Ultium is so unique that it can contain either vertically- or horizontally-stacked cells to integrate into vehicle design – vertically for trucks, SUVs and crossovers, or horizontally for cars and performance vehicles.
- It gets even better with Ultium’s innovative feature – digital programming. As new chemistry is developed and becomes available, the battery management system could digitally update the modules.
This is a bold set of claims. For a number of these we need to see more details.
The first application of this battery architecture strategy is in the GM Hummer EV, this is a 212kWh battery pack that weighs ~1326kg giving it a pack gravimetric energy density of 160Wh/kg. Not so great when compared to the Tesla Model 3 that achieves 171Wh/kg at pack level and with a pack that is less than half the capacity of the Hummer and hence has a larger proportional overhead.
The Cell to Pack Mass Ratio is 59%, very similar to the 2015 Nissan Leaf that was just 30kWh.
References
- GM, GM Reveals All-New Flexible Platform and Ultium Batteries
- Charged EVs, GM reveals more technical details of its Ultium battery packs
- GM, Hello Ultium
- A Revolution in Battery Innovation, GMC Hummer
- EPA filing for GMC Hummer battery pack