Battery replacements have a critical impact on the longevity, performance and cost of electrified commercial vehicles. Specialised ultra-high energy battery systems could provide the answer.
Compared to electric cars, electrified commercial vehicles (eCV) demand significantly different priorities from their batteries. For cars, initial purchase cost, energy and power density are primary considerations, but for eCVs, the total cost of ownership is critical and largely dependent on the number of battery replacements during the vehicle’s life. Mechanical robustness, longevity, compact size and battery weight are more important for continuous, long-term usage while keeping vehicle payload capacity as high as possible.
BorgWarner has developed an ultra-high energy (UHE) battery system for energy intensive electric drivetrain applications operating at up to 750V. Battery life is up to 4,000 cycles, and compared to technology currently in use, significantly increases electric vehicle range. Cells can be optimized for power to enable opportunity charging for urban traffic, or optimized for energy density for long distance traffic that charges overnight.
Battery pack specification
BorgWarner’s cylindrical cell (CYC) battery modules serve as the power source in the UHE battery pack. Each CYC module contains 600 Li-ion cells giving an energy density of about 221Wh/kg; nine modules are connected in series to create a 9 AKM battery pack providing 98kWh at up to 750V. Weighing only 560kg and measuring 1,720x700x300mm, this compact, energy-dense solution can equip city buses and intercity coaches with battery system capacities of 400–1,000kWh depending on vehicle size – twice as high as the present generation of batteries.
Battery management and cooling
The battery management system comprises an in-house developed battery management unit and cell supervising circuits plus corresponding software. It provides primary safety functions including over-temperature, over-/under-voltage and over-current protection and also performs detailed diagnosis of all actuators and sensors, as well as innovative high-level functions such as battery state estimation.
The UHE battery pack is equipped with extremely effective liquid cooling at module level to provide even temperature distribution and operation within the preferred temperature range, ensuring high availability of power and energy, and contributing to slow aging of the battery cells.
Safety in operation
Maximum protection against fire propagation resulting from a thermal event is achieved with a combination of active and passive safety devices at both CYC module and battery pack level.
Each cell in the CYC module is separated from the next by a carefully calculated gap and covered by an optimized potting compound. If a thermal event were to occur at cell level, thermal propagation between neighboring cells would be prevented and hot gases safely dissipated in a controlled manner. Triggering of adjacent cells inside the module or in the neighboring module does not occur; they do not even change their state of charge. As an additional safety measure in the event of an internal or external short circuit, the wire bonds connecting the cells to the side PCBs would act as fuses for groups of cells. CYC modules are separated from each other by flame-retardant materials to prevent inter-module fire propagation.
At battery pack level, there are extra safety elements within the hardware and software. The rigid steel construction of the CYC module is supplemented with further bracing between the modules, and a robust stainless steel housing protects the complete battery pack against damage in the event of a vehicle crash. Thermal isolation material surrounds the battery cells to protect against environmental hazards such as a fuel fire. Additional layers of safety are provided by the efficient cooling system and predictive algorithms built into the battery management system software.
Charging and maintenance
Using quick charge facilities, the UHE battery pack can be charged at a rate of up to 1C. Fast charging infrastructure up to 500kW is also compatible. All of the main electronic components apart from the CYC modules are housed in a removable contactor box, allowing the electronics compartment to be exchanged in the field without the need for high-voltage trained technicians or demounting the battery pack from the vehicle.
BorgWarner AKM battery technology earned an Innovation Award from Busworld, the leading trade show of the European bus industry and has already been chosen by the two largest European OEMs for bus and truck applications.