25 Feb 2016


Addressing Li-ion energy loss in cold temperatures, researchers at Penn State, with colleagues at EC Power, a Penn State University spin-off, have developed a lithium-ion battery structure - the ‘all-climate battery’ (ACB) cell - that heats itself up from below zero degrees Celsius without requiring external heating devices or electrolyte additives. The self-heating mechanism creates an electrochemical interface that is favorable for high discharge/charge power. Because only a fraction of the battery energy is used for self-heating, the ACB could address winter range anxiety issues for EV drivers, as well as proving useful for applications in robotics and space exploration, the team said in a paper published in the journal Nature.

The ACB warms itself up to 0 degrees Celsius within 20  seconds starting at -20 ˚C and within 30 seconds at -30 ˚C, consuming 3.8% and 5.5% of cell capacity, respectively. (EC Power projects that it will be able further to reduce the self-heating time from -20˚C to 0 ˚C to 5 seconds by 2017, and reduce energy consumption to 1%.) The self-heated all-climate battery cell yields a discharge/regeneration power of 1,061/1,425 watts per kilogram at a 50% state of charge and at -30 ˚C, delivering 6.4 to 12.3 times the power of state-of-the-art lithium-ion cells.

The researchers calculated that the all-climate battery could enable engine stop–start technology capable of saving 5–10% of the fuel for 80 million new vehicles manufactured every year.

Lithium-ion batteries suffer severe power loss at temperatures below zero degrees Celsius, limiting their use in applications such as electric cars in cold climates and high-altitude drones. The practical consequences of such power loss are the need for larger, more expensive battery packs to perform engine cold cranking, slow charging in cold weather, restricted regenerative braking, and reduction of vehicle cruise range by as much as 40%. Previous attempts to improve the low-temperature performance of lithium-ion batteries4 have focused on developing additives to improve the low-temperature behaviour of electrolytes, and on externally heating and insulating the cells.

The all-climate battery uses a nickel foil of 50-micrometer thickness with one end attached to the negative terminal and the other extending outside the cell to create a third terminal. A temperature sensor attached to a switch causes electrons to flow through the nickel foil to complete the circuit. This rapidly heats up the nickel foil through resistance heating and warms the inside of the battery. Once the battery is at 32 degrees Fahrenheit, the switch turns off and the electric current flows in the normal manner. While other materials could also serve as a resistance-heating element, nickel is low cost and works well.

The researchers, relying on previous patents by EC Power, developed the all-climate battery to weigh only 1.5% more and cost only 0.04% of the base battery.


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