Even after over 8,000 full load cycles for the 46Ah and 3,000 full load cycles for the 53Ah, the modules were able to retain around 80 percent of their original capacity. They were even able to continue to run on a residual capacity of 30 percent, thereby enabling a total of 15,000 cycles to be completed. The uniform deterioration of the individual cells is another satisfying result, as this significantly reduces the loss of capacity in the assembly. This means that the end of the battery’s service life is delayed until much later on.

—Dr. Björn Eberleh, Head of Project Management, Testing and Service at AKASOL

The AKAMODULE 46Ah still has 80% of its original capacity after more than 8,000 full loadcycles. (Credit: AKASOL) Click to enlarge.

In a test environment set up in-house, the AKASOL engineers subjected their 46Ah and 53Ah battery modules to extreme conditions. At temperatures of 50 to 55 degrees Celsius, the battery components worked for 1.5 years in full cycles at a constant load of 100A. The measured values in terms of capacities, differences in cell voltage and internal resistances confirmed the prognoses of the battery experts. In some areas, their expectations were even exceeded.

The AKAMODULE 46Ah and 53Ah models go far beyond the service life specified by the manufacturer of the battery cells, exceeding them by up to 50 percent. This is due to the liquid-cooled module developed in-house and the homogeneous integration of the cells. In a typical application, such as a fully electric city bus, the battery would still be in service after it reaches the million-kilometer mark.

—Dr. Eberleh

As disparities in the production of the cells and various operating conditions lead, in practice, to the cell charges within a particular energy storage unit becoming uneven, the battery management system must be able to bring the individual cells to the same charge level. In a multicell battery, this act of balancing enables the capacity of the entire system to be utilized on a long-term basis.

Our 46Ah battery module only had to be rebalanced once during the entire test period, which consisted of 8,000 full load cycles. Usually, battery management systems have to perform the same balance control over ten times more often to ensure that the cells deteriorate evenly and guarantee that full capacity continues to be available.

—Dr. Eberleh

Despite the extremely high functional integration on a modular level, the AKAMODULE achieves energy density of more than 140 Wh/kg. This enables long vehicle range with simultaneously exceptional durability.

Every AKAMODULE is cooled with a water-glycol fluid mix. The production of modules with integrated liquid cooling was previously considered to be very complex. AKASOL has discovered a manufacturing method to simplify this. The result is a significant reduction in volume.