High-power cables (in the case of cars, currently usually up to 350 kW) are today liquid-cooled (conventionally, with a pump and radiator in the charger), which allows them to remain relatively thin and light.
Without liquid cooling, it would be difficult to increase the power output beyond the basic 50-100 kW,that we saw in the early years, because the cable and plug would be too hot (both for the user and isolation). Its size and weight would have to be enormous.
Michael Degner, senior technical leader, Ford Research and Advanced Engineering said:
“Today, chargers are limited in how quickly they can charge an EV’s battery due to the danger of overheating. Charging faster requires more current to travel through the charging cable. The higher the current, the greater the amount of heat that has to be removed to keep the cable operational.”
However, in the future there might be also different approaches, like the recently announced, patent-pending charging station cable with PCM.
According to the press release, the idea is to use an active cooling agent that changes phase from liquid to vapor when getting hot.
"Purdue researchers are focusing on an alternative cooling method by designing a charging cable that can deliver an increased current. The cable uses liquid as an active cooling agent, which can help extract more heat from the cable by changing phase from liquid to vapor – the key difference between this and current liquid-cooled technology on the market"
"The idea for this technology originated based on the Ford team’s understanding of the challenges faced going to faster charging rates, as well as Purdue researchers’ area of expertise. The teams collaborate regularly to review the latest results and give feedback on areas of focus as the technology is developed."
The transition from one phase to another basically absorbs energy that would normally turn into excessive heat. Once the charging ends, and the temperature would start to decrease below the phase-change point, the PCM would change from vapor to liquid again. This cycle would repeat with every high-power charging.
Of course, the PCM acting as a temporary energy storage would have to have the necessary capacity to handle at least one regular charging session every few minutes, because otherwise charging output would be limited by the cable temperature.
It's an advanced solution with some advantages, but it's difficult to say whether it will be viable. Testing of a prototype charging cable is expected to begin in the next two years.
Purdue University researchers released a chart, which indicates that they can achieve in a laboratory about 5-times higher current (2,500 A), compared to about 500 A in the state-of-the-art commercial solutions today.
As we understand, the maximum value is available only until the PCM capacity is depleted (when the entire active cooling agent turns into vapor). Then everything will depend on the general cooling characteristic of the cable.
If only EVs would be able to accept such currents (2,500 A at 800 V would be 2 MW), they would charge as quickly as a conventional gas station fill-ups.
For us, phase-change materials are not a novelty as we know them as one of the alternatives considered for battery pack cooling. In the U.S., one of the pioneers of the passive thermal management technology with a phase change composite was AllCell Technologies, but so far no electric cars utilized this solution.