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Why Did Nissan Develop an EV Battery?

It’s one year since the release of Nissan Leaf, the first affordable mass production electric vehicle. Recently Nissan announced the car’s battery can also be used to supply households with power. This is the inside story of the extraordinary Nissan EV Lithium-ion battery.

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2012/02/07

Why did Nissan develop a battery? Nissan’s EV Energy Development Department project leader Takeshi Miyamoto has the answer: “Even if we bought batteries from suppliers, there just weren’t batteries on the market that we were satisfied with.” And the biggest reason? Ambition: “A battery needs total balance. If we don’t make it ourselves to our precise level, then we won’t be able to make a reality the new mobility we are aiming for.” Developing a battery appropriate to the unique characteristics of the car enhances the energy efficiency of the EV. Likewise, this logic also applies to the motor and inverter: For an EV, parts must be developed that are organic to the overall EV concept.

There’s another reason why Nissan developed its own battery – cost. Nissan Leaf is intended as a production vehicle for the general consumer, so it needs to be sold at a price affordable for most drivers. Cutting the cost of the battery is key to reducing the overall costs of the car.

Miyamoto joined Nissan in 1981. Following involvement with development of batteries for one of Nissan’s earlier EV efforts, the Nissan Altra, Miyamoto then became the engineer responsible for creating Nissan Leaf’s battery.

(EV) Experience makes a difference

Nissan already has an established history with electric vehicles. The experiences, findings and know-how accumulated from the Altra EV that went into production in 1998, and the Hypermini from 1999, were all vital to the development of the new Leaf. For example, data on how an EV is actually used by drivers or a battery’s thermal performance all contributed immensely to Leaf’s R&D.

And before Leaf went on sale, experiments were conducted for over a year with a prototype vehicle in Arizona, California, New York, Detroit, and other places, in order to test if the data acquired from the previous EVs actually worked as expected in reality.

A battery without a cooling system?

When Leaf was released, possibly one aspect of its technology surprised other carmakers’ engineers the most: Nissan Leaf’s battery has no cooling system. To achieve this, the temperature is controlled by adjustment of the battery’s internal resistance, keeping the increase in battery temperature down. Based on findings from past EV technology, engineers performed simulations examining temperature increase alongside the Leaf concept, the amount of electricity used, and the frequency of charging.

When a battery has a cooling system, then more space and cost are also needed to install the system, and that can also mean a vehicle that costs more and a battery that deteriorates faster. In a nutshell, a battery without a cooling system has more merits for the customer.

A battery that can control its heating temperature without a cooling mechanism is also longer lasting, since the biggest cause of a battery’s lifespan being shortened is overheating. In other words, having a cooling system to lower the temperature of a battery in case of overheating has adverse effects on the battery’s durability – it’s better to engineer a battery system that works to avoid overheating to begin with.

A laminated structure for layout flexibility

Nissan Leaf’s battery uses a special laminated battery cell. Each battery module features a set of four laminated battery cells, for a total of 192 cells and 48 modules in the battery pack mounted below the floor of the vehicle.
battery
Upper left: A laminated battery cell. Upper right: A battery module set of four laminated battery cells. Bottom: A battery pack made up of 48 modules.
The thin laminated cells are unusual in that they can be installed both vertically and horizontally, and their layout flexibility is indispensable in maximizing passenger and cargo space in the vehicle. The thin shape of the cells helps keep them stacked closely underneath the floor of the cabin.

The structure is thin but with a wide surface area, making for superior heat release qualities, and a major reason why the Leaf battery system does not need a special cooling mechanism.

The biggest challenge for the battery development was whether such a slim laminated battery cell design could actually work as part of an automobile in reality. Developed in partnership with a laminated film manufacturer, the lamination material was selected after looking at different varieties of plastic and thickness, and eventually a special lamination was developed just for Nissan Leaf. In the years leading up to Leaf going on sale, the reliability of the lamination was checked on test cars, before the right material was found for the final model.

A battery working with the whole car body

It’s not only the battery design that determines the performance of the battery. For Nissan Leaf, the design areas outside the battery cell also contribute to the battery’s capabilities.

Take the safety performance in case of collision. Of course, this means possessing sufficient durability if the battery itself suffers an impact. In addition, body structure also plays an important role. By carefully designing the vehicle and battery structures, it becomes possible to provide a larger battery mounting space and maintain safety performance.
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The lightweight and low-drag nature of the vehicle also has a hand in extending the EV’s electricity consumption, or in other words, its cruising distance range. Achieving both safety for collisions and simultaneously a lighter car body and reduction in air drag is no easy matter. Precisely because of its specialized EV chassis and car body engineering, the Nissan Leaf battery delivers on performance: Nissan total car body design technology is boosting its range capabilities.

An EV battery that only a carmaker could create

“It can be a tradeoff between the battery’s capacity, output, resistance, safety, and reliability. Balancing all of them is the most important,” says Miyamoto.

To give an extreme example, if we take out the back seats of the car and load more batteries it is, of course, possible to further extend the cruising distance range of the vehicle. However, Nissan Leaf is a five-seater, and is setting the standard for the post-gasoline car era’s EV vehicles for the general consumer. Due to the spread of EVs, now you can sometimes hear people talk about how, if you just have a motor and battery then anyone can build a car these days – not just carmakers. “Well, yes, you can ‘build’ a car,” explains Miyamoto. “But I always want to say to them that they should try making one to the level of Leaf! With an EV, you also need to ensure the safety of your passengers.”

A safe and secure EV could only be created since its makers thought holistically, creating a car design that considers the entire vehicle: Not the battery technology by itself, but also a car body, motor and controls that work in tandem with the battery. That is why Nissan is pouring its energies into developing fully intuitive and integrated EV batteries.