Li-Po vs ENEPAQ li-ion battery modules: a comparison report

Is lower internal resistance more critical than higher energy density? In the Li-Po vs. ENEPAQ Li-Ion Battery Modules Comparison Report, we explore the differences between power-oriented and energy-oriented cells to help you understand which better suit your needs.

Developers of high-performance applications, including e-formula teams, face various challenges when choosing battery technology. Some teams prefer Li-Po over Li-Ion cells, and others go with more energy-dense Li-Ion options. Interestingly, ENEPAQ recently received a battery log from one e-formula student team, which was taken during endurance race on a racing track. This gave us an opportunity to investigate actual racing conditions and analyze these two options.

The team have indicated that they did their research on comparing multiple cell options. Among the top candidates, there was ENEPAQ Li1x5pVTC6 module, containing five 18650 Sony VTC6 cells, and an unnamed/redacted LiPo pouch cell of similar capacity. Main difference between these two is that pouch cell has lower internal resistance, while ENEPAQ’s module offers higher capacity per weight. According to the data report, due to higher overall internal resistance and resulting voltage drop, Li-Po may look like a better candidate. However, after analyzing battery discharge current provided by the team, as depicted on graph 1, several things were noted.

Graph 1 showing current change over time for student formula run on track, extracted from the provided logs

Graph 2 showing how many seconds the current was in one of the five current ranges.

Very quickly it was discovered that the e-formula runs at maximum power for a relatively short period of time, while overall average power is much lower. A histogram on Graph 2 shows the current intervals and how long the battery is discharged in that interval. Most of the time, the battery is discharged at a current of 0-18A. Based on this, we were able to calculate a total energy, lost to heat due to voltage drop.

From the available data, we have compared two hypothetical e-formula battery packs around 6.5kWh in size, made from both Li-PO and Enepaq modules (table 1).

Table 1. Comparison of cells characteristics

From this, straight away we can see that ENEPAQ modules provide higher energy density: 194Wh/kg vs. 177Wh/kg, which is roughly 10% higher, and leads to lower weight. But the most interesting data point is Energy wasted to heat, due to internal resistance and voltage drop. While resistance and simulated wasted heat energy of ENEPAQ modules is roughly 4 times greater, this still only totals at 140Wh (if whole pack was drained) and equals to only 2% of total capacity of the pack.

From this we can see that, if we build two packs of identical weight, the one made with ENEPAQ’s modules will end up having +8% of useful energy. Another worthy note is that Li-Po pouch cells require compression and overly more complex/heavy assembly, which makes the difference even more significant.

The main advantages of Enepaq Battery Modules after the comparison:

• Roughly 10% lower battery weight at the same energy capacity.
• Longer cycle life compared to Li-po batteries.
• Higher reliability and calendar life due to use of world leading cells.
• Significantly easier and cheaper battery assembly.
• A more rugged body, compared to pouch cell.
• Built in cell fuses and unique multi-point temperature sensor.

All ENEPAQ modules come in a perfect balance within few mV.