General Motors and its storied Chevrolet brand have been in the news quite often of late, but largely for the wrong reasons. Yet even as GM teeters on the brink of bankruptcy, engineers at Chevrolet are working on one of the boldest innovations in GM's history: the Chevy Volt.

Unveiled at the Detroit Automotive Show in 2007, the Volt project has become GM's most ambitious effort: a range-extended electric vehicle powered by a revolutionary battery platform called the Voltec. The pet project of vice president of global development Bob Lutz, the Volt is GM's "Hail Mary"--the one innovation deemed capable of pulling the company back from the precipice. Lutz has known from the start, however, that if the car is to succeed at its planned launch in November 2010, its battery technology--the heart of the Volt--needs to be the car's greatest innovation, and it had best not skip a beat. If the production battery proves less than perfect, the Volt will be dead on arrival--and GM's fate, analysts have predicted, could likewise be sealed.

Battery rollout at North American International Auto Show Source: GM.com

The challenge

Developing a reliable, cost-effective battery would thus be one of the largest technical hurdles facing the Volt project team. GM believed that to achieve an end product that would meet its standards for the Volt's battery, an open competition would be required. The challenge presented to the interested parties was straightforward: Develop a lithium-ion battery that could be recharged for 4,000 cycles and would last a minimum of 10 years. Sounds simple enough, until you consider that there was next to nothing on the Li-ion market that could come close to meeting those criteria.

From the initial field of 27 entrants, the competition was narrowed to two prospective partners in June 2007. The two finalists were A123Systems, a Michigan-based company with expertise in Li-ion technology, and a coalition team of LG Chem and Compact Power Inc. Both teams were awarded contracts to develop prototypes in parallel. Considering the critical nature of the battery, GM believed it was necessary to have two organizations engaged in developing the technology at the same time. The reasoning was that with two teams openly competing for the final production contract, the very best battery would be developed--one that would not only meet the car maker's criteria but exceed them. Prototypes were to be developed by January 2008 for GM to test in "mules," or mock-ups of the Volt made with Malibu body cases, with a final decision to follow.

In January 2009, GM selected the design from the team of LG Chem and Compact Power as the one that would best fit the Voltec platform from a structural standpoint. The cells in the LG Chem battery were deemed the most appropriate in structural integrity testing, and the cell size was the best fit with the cooling system that GM had designed for the Volt. The LG Chem battery provided the best results in rear-impact and side-impact crash tests. Most important to GM, which would be footing most of the manufacturing cost, was its confidence in the battery's ease of manufacturability and LG Chem's established track record in Li-ion manufacturing (A123 Systems was essentially a startup). The battery would be manufactured in Michigan in a facility that would be the first lithium-ion battery plant in the United States to be operated by a major automaker.

Battery testing at LG Chem Source: GM-Volt.com

The uniqueness of the Volt battery can be seen right away in the T-shaped design of the battery pack. The pack contains a number of modules connected in series, as well as components used for the control and monitoring of discharge or charge energy from each module. Also included within the T-shaped battery back are temperature sensors to control cooling, flexible interconnects between each battery module, and manifolds and coolant lines that allow for heat exchange with the cell surfaces in each module.

The power comes from the individual battery modules within the battery pack. Each module consists of numerous lithium ion cells, with each cell delivering its electric current as the result of an electrochemical reaction. As the lithium ions move from the positive electrode (cathode) to the negative electrode (anode) during charging and vice versa during discharging, the electrical current is generated.

The Volt's battery consists of more than 200 cells (288, according to some estimates) with each cell weighing less than a pound and measuring 5 by 7 inches and less than a quarter-inch thick. Each cell contains a carbon anode, a manganese-based cathode (with additives to improve its life span under high-temperature conditions) and a reinforced separator that is the medium for the transfer of charge ions between the anode and the cathode.

Inside the Chevrolet Volt battery Source: GM-Volt.com

LG Chem's proprietary Safety Reinforced Separator (SRS), coated with ceramics, serves as the semi-permeable insulating membrane between the electrodes in the cells. LG Chem says the ceramic coatings differentiate its separator from competitors, as the SRS enhances the abuse tolerance already provided by the manganese base used in cells. The design is said to offer superior mechanical and thermal protection from abuse conditions such as internal shorts and extreme overcharge.

The end result is a battery with an energy capacity of 16 kilowatt-hours, or an effective capacity of 8.8 kWh when you take into account a maximum charge of 85 percent and the fuel-based engine's kicking in at 30 percent. The battery at this capacity meets GM's requirement of operating up to 40 miles on pure electrical power from the battery. After 40 miles, the battery reaches a 30 percent discharge mode (a number chosen to maintain optimal performance of the Li-ion battery for at least 10 years of use) and the fuel-based engine begins to operate, driving a generator to allow the battery to maintain a 30 percent state of charge until the driver can get to an electrical outlet and fully recharge. The approximate charging time for the battery is six to seven hours.

With the battery design complete, the largest obstacle for the Volt's development has been cleared. "It's almost scary that we aren't seeing any problems with them," Lutz said of the batteries.

Before he stepped down as CEO, Rick Wagoner made the Volt a focal point in the revitalization of GM and, in his testimony to Congress, a key argument for a government bailout of the beleaguered automaker.

Only time and further rigorous testing will determine whether the battery will deliver on LG Chem's promised electrical output and durability over a 10-year span. For now, however, the Chevrolet Volt continues to roll toward its November 2010 launch date.

Allan Yogasingam is a technology analyst for TechOnline.