Li+ Battery Characteristics and Technology

Since the 2016 Prius models debut production level of Li+ battery, replacing the old NiMH battery technologies, here's a good reading for Lithium ion technologies.

Safety of Lithium-ion Batteries – Battery University

Here's an except:

Lithium ion batteries come in many variations and Tesla chose the high-energy nickel cobalt aluminum chemistry (NCA) for the S-Model. Made by Panasonic, the cell is rated at 3,100mAh, a specific energy that is slightly higher than most contenders. Other advantages of the NCA are high specific power for exuberant acceleration and long life. The negatives are high cost and a lower safety margin than other Li-ion systems. Figure 2 outlines six of the most important characteristics of a battery in a spider web.



Batteries for the electric powertrain need high loading and a long life, and the NMC is another popular Li-ion system. NMC stands for nickel-manganese-cobalt and is also used in e-bikes, power tools and military and medical devices. The cathode may consist of one-third nickel, one-third manganese and one-third cobalt, but other combinations are also used to satisfy special requirements. These blends lower the raw material cost due to reduced cobalt content. Figure 3 demonstrates the characteristics of the NMC.



Another popular Li-ion system for electric powertrains is the Lithium Iron Phosphate (LiFePO4). Its strength lays in long life and superior safety, but it has a lower capacity than cobalt-based Li-ion systems. A further tradeoff is the lower nominal voltage of 3.3V/cell rather than the customary 3.6V/cell of other Li-ion systems. Figure 4 summarizes the attributes of Li-phosphate.



Lithium-ion has much improved. In 1994, the capacity of an 18650 cell was 1,100mAh at a manufacturing cost of over $US10 per cell. In 2001, the price dropped to $2 and the capacity rose to 1,900mAh. Today, high energy-dense 18650 cells deliver over 3,000mAh and the costs have gone down further. This, however, does not come without compromise. Newer cells are more delicate than older ones and this can affect the cycle count.