Posted on May 08, 2018 by Charles Morris
When it comes to electric vehicles, it’s all about the batteries. The appearance of powerful, low-cost batteries was the technological advance that made modern EVs possible. Tesla’s battery technology is one of the major reasons it has been able to leapfrog the legacy automakers. And it’s batteries that hold the key to the future of electrification: the quest to deliver an EV that can truly replace the fossil-fuel vehicle centers on improving battery technology.
Above: Tesla's Model S (Instagram: carspottershk)
So, anyone who would understand EVs, and Tesla in particular, needs to have at least a basic understanding of batteries. A series of three videos from EV-Tech Explained offers a step-by-step exploration of Tesla’s battery system. This mini-course in battery tech seems to be aimed at aspiring battery technicians, as it includes a wealth of technical detail. However, it’s also suitable as an overview for the layperson (who will probably choose to fast-forward through some of the math).
An automotive battery pack consists of individual cells, which are organized into modules, which fit together to form a complete pack. The three videos correspond to these three hierarchical levels.
The first video is about battery cells, which generally come in three varieties: cylindrical, prismatic and pouch. When Tesla designed the Roadster, it chose to use cylindrical cells. These tend to be the cheapest of the three options, and to have the best energy density, meaning that they pack more energy into a given space, but the main reason Tesla chose them was that they were (and are) widely available from various vendors, as they are used in vast quantities for consumer electronics such as laptops. As a young company, Tesla didn’t have the capital to develop its own battery cells, but it could easily buy cylindrical cells on the open market.
Above: A look into Tesla's battery cell technology (Youtube: EV-Tech Explained)
In the next video, we learn why cells are grouped into modules. The most obvious reason is scalability - you can make battery packs of different sizes by including different numbers of modules. However, the modular approach has many other advantages: it makes a battery pack easier and safer to manufacture, it makes it easier to service, and it makes it safer in the event of a cell failure or a crash, because damage can be contained in a single module.
A battery module is more than just a mechanical frame that holds the cells - it also includes bus bars to connect the cells electrically, a cooling interface and a sensing harness, which sends information about the state of each cell to the battery management system.
Above: A look into Tesla's battery module (Youtube: EV-Tech Explained)
In the third installment of this battery briefing, we learn how the modules fit into a complete Tesla battery pack. The components of the pack mirror those of each individual module: it has a frame to hold the modules together, and networks of electrical, cooling and sensing connections. The pack also includes a battery management system (BMS), which controls the individual cells and monitors their state of charge, temperature and other parameters in real time.
Because this additional hardware has weight and takes up space, energy density is necessarily lower at the pack level than at the cell level. Tesla’s battery technology is admired for the efficiency of its design - 63% of the weight of the pack consists of energy-storing cells. However, the battery pack in a Tesla isn’t just a container for batteries. It’s also a structural part of the vehicle that contributes to handling and crash resistance. In this video, we examine the sturdy frame that gives the pack maximum rigidity without adding too much weight or bulk, and keeps the modules separate to reduce the spread of fire in a battery malfunction or crash.
Above: A look into Tesla's battery pack (Youtube: EV-Tech Explained)
Tesla’s battery pack is full of nifty little features that keep the cells humming along efficiently and safely, as the driver sits atop it, oblivious to the high-tech housekeeping taking place each millisecond. “Tesla’s battery technology will go down in history as a key technological advancement which has disrupted the automotive industry,” says EV-Tech Explained. Will the company maintain its lead, or will the big boys finally decide to bring their massive expertise and capital to bear on battery tech, and catch up to the Silicon Valley upstarts? We’ll see.