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An Inside Look at Automotive Battery Technology

An Inside Look at Automotive Battery Technology

By Jeff Youngs, February 24, 2012
All cars with a combustion engine are equipped with a rechargeable battery that is tasked with providing power to start the vehicle and provide electricity for vehicle lighting and ignition. About the size of a large shoe box, the familiar battery is usually referred to as an "SLI battery" (meaning starting, lighting and ignition). The typical SLI battery is a lead-acid type. Their construction makes them very heavy, prone to corrosion, and they often have a relatively short service life (not surprising, as they were invented in 1859!). While they do a fair job starting tens of millions of cars each morning, they are simply too heavy and inefficient for a larger role in an automobile.

2009 Toyota Highlander HybridEV Batteries
Electric vehicles (EV) and hybrid-electric vehicles (HEV) are both designed to operate under full or supplemented battery power. The battery packs must be much larger than a standard car battery, as they provide energy in lieu of the power developed by an internal combustion engine. While these batteries operate in much the same manner as the SLI battery, the electrical and service demands on a battery designed for EV and HEV is much more complicated.

Batteries designed for EV and HEV vehicle propulsion are generally described as being in a package, or battery pack. Without overly complicating things, it is easiest to think of a "battery pack" as many small batteries working together to make a large amount of energy-batteries are much more effective when they are arranged in this manner.

Some of these battery packs contain hundreds of smaller batteries, or "cells" (the Toyota Prius uses 168 individual battery cells and the Toyota Highlander Hybrid uses 240 cells, while the Tesla EV uses 6,831 cells!). As a result, they are generally located in the trunk or center of the vehicle where they minimally impede passenger and cargo space.

Today's EV and HEV vehicles primarily use two different types of battery technology: Nickel Metal-Hydride and Lithium Ion.

NiMH and Li-ion
Nickel Metal-Hydride (NiMH)-This type of battery replaced nickel-cadmium (NiCd) technology in laptop computers, as the NiMH holds three times as much energy. The benefits of NiMH include their cadmium-free, environmentally friendly design, high power capacity, and a rapidly dropping price thanks to widespread use. On the downside, they do not hold a charge for very long and they are larger and less efficient than newer, cutting-edge batteries. Some vehicles using nickel metal-hydride battery technology today include the Toyota Prius, Toyota Highlander, Ford Escape, Saturn Vue, and the Honda Insight.

2011 Chevrolet VoltLithium Ion (Li-ion)-This type of battery was also extensively developed for laptop computer use. When compared to the NiMH technology, li-ion batteries have a much higher energy density (they hold more energy by weight-or volume-than other types of rechargeable batteries). They are also lighter and smaller (meaning they are easier to package within an automobile) and they have a very slow discharge rate. Unfortunately, li-ion batteries are temperature sensitive and they must be charged properly or their service life is significantly shortened. Some vehicles using lithium ion battery technology include the Chevrolet Volt, Tesla EV, and the Mercedes-Benz S400 BlueHybrid.

Batteries for automotive EV and HEV fitment are still far from perfect. While they perform an adequate job of storing energy, battery technology remains in its infancy-it continues to fall short in many areas including cost, power output, weight, and service life. Thankfully, consumer demand for efficient and lightweight batteries for all types of products (mobile phones, laptops, automotive, etc.) has engineers working overtime to overcome these hurdles. One thing is for sure-tomorrow's batteries will make today's offerings look as obsolete as the 8-track tape player.


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