|Image Source : http://www.nissanusa.com/electric-cars/leaf/colors-photos/#_exterior|
The all electric Nissan Leaf was the first affordable, mass produced, lithium battery electric vehicle. Key to the Leaf's success was a battery design that balances safety, performance, cycle life, calendar life, energy density, power density, charge rate, discharge rate, weight, structural integrity, and thermal management.
The custom made (by Nissan) cells, modules and packs give the Nissan Leaf specific advantages that translated into superior overall cost efficiency and performance. The Leaf's battery pack for example only costs Nissan about $9,000 to build, or about $375 per kWh. This is significantly less expensive than the energy storage solutions employed by other battery electric vehicle manufacturers.
The Leaf BatteryThe Nissan Leaf's battery is made of 48 modules. Each module is made with 4 large surface area laminate Lithium Manganese/ Lithium Nickel batteries. The module battery configuration is 2p 2s, meaning that two of the cells are wired in parallel and then this pair of cells is wired to the other pair in series. The results in a 7.4v nominal voltage battery module with approximately 33ah. The modules are encased in an aluminum enclosure. Together these 48 modules form a string that produces between about 290v empty and 400v full. The total energy storage capacity of this battery system is approximately 24kWh, enough to propel the Nissan Leaf about 120 miles at low speed or about 72 miles at faster freeway speeds. See the first image above, where the individual battery cell is in the upper left, the 2p 2s four cell module in its aluminum case it in the upper right, and the entire battery assembly is in the bottom part of the image.
Nissan choose to develop a custom laminated large surface area battery for greatly improved passive thermal management and cost reduction. The large surface area of the Nissan Leaf battery cells and the battery modules give them excellent thermal properties (ie they do not heat up significantly when charged or discharged).
If you think about the mechanical design of a heat sink (large surface area to radiate heat away from the heat source), it should become obvious why a large thin flat battery has better intrinsic cooling than a tightly wound up cylinder battery. By utilizing a custom size, custom format, custom chemistry, and custom mechanical and thermal solution, Nissan was able to keep the costs down, while also optimizing the performance of the battery system in harmony with the overall design of the vehicle. By doing all of the design, optimization and cell fabrication in house, Nissan was also able to vertically integrate the production of the Leaf battery in a way that significantly reduced productions costs of the battery.
Innovative Cost Reduction
The Nissan Leaf battery cells are manufactures by roll lamination. Large rolls of anode, cathode, separator films and pack encasing material are cut into segments and them assembled into layers by robots. The cells are then injected with the electrolyte, aged properly to format the cells, charged and cycled, then tested and matched. Welded into pairs again by machines, the pairs and welded into a series of two pairs and put into a case. 48 cases are assembled into each battery assembly, which acts as a structural member of the Leaf's frame. The heavy under slung battery of the Leaf also improves its handling performance and the overall vehicle dynamics. Take a look at the following info-graphic that that outlines the innovative cost production process used to produce each Leaf battery.
18650 Heat Problems in Other Vehicles
If you have read about the battery in the Tesla Roadster, or Telsa Model S or the Chevy Volt, you will notice that liquid cooling was used because these vehicles use commodity 18650 cells. The 18650 is the strong metal cylinder battery found in most laptop computers. The use of the 18650 in these designs came down to supply issues, as the 18650 and many chemical variants of it have been mass produced for more than 10 years. Heat ruins 18650 cells if they are not actively cooled. Each 18650 is built like a tiny thermos bottle, and unfortunately they cannot passively dissipate heat effectively and must be actively cooled by complex, heavy and costly liquid cooling solutions.
Torque is King
The Leaf's electromotive power-train produce the acceleration of a V6, with an instant torque output that is unique to electric vehicles. For commuting in traffic the Leaf's power delivery is buttery smooth, strong and highly refined. Electric motors only have 1 moving part and as such are very mechanically robust, and in the case of the Leaf's motor, very electrically efficient.
Nissan has a long history of electromotive experience with lithium electric vehicles. Back in 1998 the Nissan Altra gave Nissan real world experience and reference data for the onging refinement, optimization and improvements that went into the Leaf. The Altra used lithium batteries and the Altra's motor was very similar to the version used in the Leaf.
My Next Car
I plan on buying a used Nissan Leaf in the future. The research that went into this posting was related to my ongoing efforts to understand the Nissan Leaf and the technology in the Leaf. I am confident after reviewing information about the Leaf that the battery will hold up well over time in Leafs that were operated in cool climates, by people who rarely charged them to full, and who rarely discharged them to very low states of charge. I will probably review hundreds of used Nissan Leaf's before selecting one to purchase based on a review of the on-board diagnostic output that gives the battery use and charging history information. I am only going to buy a Leaf if the battery in that Leaf was not abused. It might be challenging to find one like this, but give than many of the people that buy Leaf's are EV enthusiasts, I am sure it will not be a huge challenge.
In past postings I have noted what Lithium Ion batteries dislike, abuse. They do not like being heated (abuse), being overcharged (abuse) or being discharged to low states of charge (abuse). If a lithium Ion battery is shallow cycled between 30% State of Charge and 80% State of Charge it will last dramatically longer than a Lithium Ion battery that is charged to full and discharged to nearly empty on every cycle. Abused lithium ion batteries tend to begin failing after 200 to 300 cycle. Carefully treated lithium ion cells tend to hold up for thousands of cycles. As noted early heat is extremely hard on lithium ion batteries. Electric vehicles operated in "hot climates" will correspondingly experience more rapid deterioration of their batteries than electric vehicles operated in cooler and temperate climates. I live in a cooler climate, and will look for a local Leaf when I am in the market for one.
You can find easy to read reference materials that were used to produce this posting on the following web site.
You may also find information about the Nissan Leaf's Battery in PDF available from the following page:
Comments and Extension
If you have ever read www.greencarcongrees.com you probably noticed the amazing quantity of battery innovations in the postings. There seems to be dozens of research innovations aimed at improving the lithium battery every week. Thousands of teams of people in colleges and in corporations are all working at building better lithium ion batteries. A durable rechargeable Lithium Air battery is widely regarded as the innovation needed to usher in the electromotive era to a broad global marketplace.
Most of the research and development on Lithium Ion batteries revolves around improving the cathode and anode designs and materials. Other areas of innovation are aimed refining the electrolyte by producing solid electrolytes that hold up well over time. Cost reduction, cycle life, and calendar life improvements are the main objectives of the ongoing widespread lithium ion battery research and development. The CEO of Tesla Motors Elon Musk predicts that the Price of Lithium Ion EV batteries will decrease from $750 per kWh of today to around $100 per kWh in 10 years.
Cost reduction is the most critical aspect of EV battery development. To this end mass produce Lithium Iron Phosphate batteries may prove critical in coming years. While not as dense as Lithium Cobalt Oxide or Lithium Manganese or Lithium NMC, the LFP battery is robust, long lasting, and can be manufactured at a very reasonable price is production is scaled sufficiently to much larger volumes. I have a Lithium Iron Phosphate powered electric bicycle, and the retail price of a replacement 430watt hour 36v 12ah battery is about $450. This puts the battery cost of Eberts battery at well north of $1000 per kWh. I can only fathom what kind of awesome electric motorcycles will be possible with cheaper LFP cells. I am very much looking forward to the future innovations in battery energy storage systems.
Today, smart phone users are plagued by poor battery life, and I have written about this before. The phone makers put undersized batteries into the phones, usually around 1,300mAh when 3,000mAh would be required to give decent battery life. If any market is to see the early innovations in Lithium Ion, it will be the consumer electronics sector. A $40 cell phone battery has a cost of thousands of dollars per kWh of storage. Here expensive ultra-high tech battery technology can be deployed in a feasible way. Apple for example builds custom lithium batteries for its Macbook line, iPads and iPhones. Other CE companies like Samsung tend to stick to cheaper battery cell construction methods and materials. One of the really cool innovations missing in consumer electronics batteries is safe ultra high speed charging. Technology already exists to produce phone batteries that can be charged from empty to 80% full in under 10 minutes. Think of how nice it would be to be able to fill your phone battery in just a few minutes....
Laptop computers need heat resistant lithium batteries. The heat generated by a laptop causes premature deterioration of the Lithium Ion batteries. The heat sensitive batteries in a laptop get worked really hard by the electrical and thermal loads produced by the laptops operation. In these applications a battery with excellent heat resistance would be a great improvement over what is available today.
Nissans "passive cooling" design is the real key for electric vehicle applications. We need batteries that are designed to stay cool if they are heat sensitive. Liquid cooling is cumbersome and costly and complicated, the evidence is in the lack of widespread liquid cooling solutions in desktop performance computers. Why use a water, and tubes and pumps if a simple fan and some air ducts will do the trick. Fans and air ducts are far less heavy and far less complicated to utilize. This is why Toyota used forced air heat management in the Prius battery. Nissans heat dissipating by design approach makes the Nissan Leaf battery intrinsically more stable than liquid cooled 18650 designs used by other automakers. That being said, with enough money, it is possible to build really cool electric vehicles with 18650 battery cells, and the coolest albeit somewhat expensive Tesla Model S proves this over and over again :)