One of the most notable applications of prismatic lithium-ion batteries is in General Motors’ Voltec propulsion system. In the Chevrolet Volt, this system takes the form of a 437 lb. battery pack made up entirely of lithium-ion batteries (1). There are electric cars that do not use Li-ion batteries, but GM gave the following reasoning for using Li-ion batteries in the Volt:
…it [the lithium-ion battery pack] packs two to three times the power of a nickel metal hydride battery in a much smaller package. It is also more efficient, offers more configurability, suffers little loss of charge when not in use and is less prone to ‘lazy battery’ syndrome, when batteries gradually lose their maximum energy capacity from repeated recharging after being partially discharged (1).
Each cell in the Volt’s battery pack contains a carbonaceous anode and a manganese cathode. Groups of 288 cells form the “building blocks” of the battery back, and nine of these building blocks linked together form the overall battery pack. The pack is positioned in the center of the vehicle in a t-shape, as seen above (1).
The vehicle is a plug-in, in that the battery is charged by connecting the battery pack to an outlet through a power cord (1).
A common characteristic of batteries is for their cycle life to be lowered whenever it is fully charged or fully depleted. To prevent this from happening, the Volt contains mechanisms that ensure that the battery is never fully charged or depleted—the battery operates within a 65% charge window. This window is raised on the lower end (the minimum charge of the battery is raised) in demanding conditions to ensure that the battery will always have enough power if its reserves need to be dipped into. This energy management system helps give the Volt a relatively long battery life (1).
At the time of its release in December 2010, the Volt contained the first mass-produced battery whose temperature could be precisely regulated. The battery modules are pervaded and cooled by circulating liquid. The temperature of the batteries is constantly monitored and the liquid’s temperature controlled by internal heat exchangers. The cooling of batteries is crucial because lithium-ion batteries can become unstable at high temperatures. To ensure functionality in lower temperatures, the battery pack can be preheated during charging. The battery is designed for optimal operation from -25°C to +50°C (1).
The battery pack has been improved several times since 2010. Tweaks in the chemistry of the cells has resulted in increased vehicle range and cell durability (2).
The 2017 Chevrolet Bolt has a slightly different battery pack. Battery modules are still made up of 288 cells, but there are 10 modules instead of 9, resulting in a total weight of 960 lbs. for the battery pack. The cells are still prismatic but contain more nickel than those in the Volt. The added nickel allows the battery to operate in a wider range of temperatures, allowing Chevrolet to make the cooling system smaller (3).