2017 Chevrolet Bolt EV battery system
From the November 2016 issue
The battery pack of an electrified vehicle isn?t just a fuel tank for its motors. It?s also a metaphorical fuel pump dictating the peak power that can be delivered to a motor. While electric vehicles require both range and power from the battery pack, hybrids require similar power with far less energy. Accordingly, the individual cells are optimized to deliver brief bursts of power in hybrids or long-lasting energy to maximize range for EVs. A plug-in hybrid?s battery pack straddles both priorities and lands somewhere in the middle. A battery?s output-to-storage-capacity ratio (what the industry calls its power-to-energy ratio, or watts per watt-hour) characterizes these differences. ?It?s kind of like designing an engine,? said Pablo Valencia, senior manager in global battery engineering at GM. ?Am I trying to get high-speed power or am I trying to get fuel economy" Your piston-diameter-­to-stroke ratio is one of the first fundamentals that you do in an engine design.?
Battery engineers establish the power-to-energy ratio early in the design process by defining the thicknesses of both the current collectors and their chemical coatings. A hybrid?s brief spurts of peak power mean higher electrical current, and higher current requires larger wires. The current collectors?aluminum or copper plates through which electrons exit and enter the battery?are a battery?s internal analog to wires. Hybrids use thic...