Battery Taxonomy: The Differences between Hybrid as well as EV Batteries

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Battery Taxonomy: The Differences between Hybrid as well as EV Batteries

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2017 Chevrolet Bolt EV battery system

2017 Chevrolet Bolt EV battery system

via the November 2016 issue

The battery pack of an electrified vehicle isn’t just a fuel tank for its motors. the item’s also a metaphorical fuel pump dictating the peak power of which can be delivered to a motor. While electric vehicles require both range as well as power via 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 as well as lands somewhere within 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.

“the item’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 actually one of the first fundamentals of which you do in an engine design.”

Battery engineers establish the power-to-energy ratio early within the design process by defining the thicknesses of both the current collectors as well as their chemical coatings. A hybrid’s brief spurts of peak power mean higher electrical current, as well as higher current requires larger wires. The current collectors—aluminum or copper plates through which electrons exit as well as enter the battery—are a battery’s internal analog to wires. Hybrids use thicker collectors than EVs to carry more current.

The opposite is actually true of the chemical coatings applied to the collectors. Thin coatings allow the electrons to flow through the battery quicker for higher power delivery in hybrids. EVs, with more individual cells, can discharge each cell more slowly through thicker coatings of which help increase their energy capacity. These coatings are the secret sauces (such as lithium-manganese-oxide) of which define the electricity-generating chemical reactions, although the chemistry is actually not critical to determining if the cell is actually more power- or energy-dense.

When batteries are connected in series, the voltage of each cell is actually cumulatively added; cells wired in parallel increase the capacity of a pack, adding the ampere-hours of each cell together. The pack is actually wired to achieve the necessary operating voltage as well as capacity, with more cells in parallel for plug-in vehicles. within the Chevrolet Bolt EV’s pack, GM welds the tabs of three cells in parallel, then wires 96 of those triplets in series. A Volt plug-in hybrid uses pairs of cells wired in parallel, while all 80 cells within the Malibu hybrid’s pack are wired in series.

Malibu
Hybrid

Volt

Bolt EV
Energy capacity1.5 kWh18.4 kWh60.0 kWh
Discharge power52 kW0 kW140 kW
Power-to-energy Ratio34.7 W/Wh6.5 W/Wh2.3 W/Wh
Pack weight95 lb403 lb948 lb
Pack volume1.4 cu ft5.4 cu ft10.1 cu ft
Cell count80192288
CoolingAirLiquidLiquid
Cell supplierHitachiLG ChemLG Chem

Battery Taxonomy: The Differences between Hybrid as well as EV Batteries

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