Novel Nanocrystalline Silver Alloy Coatings to Boost Performance of EV High Voltage Interconnects and Charging Interfaces 2022-01-0723

Electric vehicle performance needs challenge connector designers and powertrain engineers with new paradigms for performance under more rigorous operational conditions. Traditional connector design protocols direct the engineer to silver plating for the contact interface, but these coatings have a maximum interface temperature of 170 C (ambient temperature plus T-rise). To avoid thermal runaway, engineers have to derate the ampacity of powertrain connections, which reduces available energy delivery as the temperature increases. This is especially true during transient power events like regenerative braking and acceleration. The soft nature of silver coatings makes them well suited for power delivery and low contact resistance, but requires an engineering trade-off for wear durability. This is especially problematic for charging connectors which require tens of thousands of mating cycles before failure.

In this work, we demonstrate the performance enhancements that can be achieved using a novel nanocrystalline silver-tungsten alloy. The alloy was designed from fundamental thermodynamic principles to ensure stability at elevated temperatures, enhanced corrosion resistance and strength. Silver-tungsten resists softening up to 250 C, allowing significantly higher maximum operating temperatures compared to silver. Indentation studies at temperature reveal that Ag-W is twice the hardness of silver at room temperature and at temperatures up to 210 C. Long term aging tests, 4000 hours at 210 C, show that the contact resistance is low and stable while silver plating shows rapid increases. The stable nanocrystalline alloy has improved contact a-spot stability leading to a 5% improved transient and steady state ampacity at temperature. Lastly, while silver plating often fails through galling wear, the nanocrystalline silver alloy was designed to resist galling wear; this enables charger connector cycle life of tens of thousands of cycles or more.