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20 October 2014
What Causes Lithium-Ion to Age Part 1
When charging lithium tends to gravitate to the negative electrode, or the graphite anode. When this happens the voltage potential changes. A full reset does not occur when the lithium is removed. Solid electrolyte interface (SEI), a film that consists of lithium atoms appears on top of the anode. SEI is composed of lithium carbonate and Lithium oxide. As the battery goes through these cycles the film thickens and forms an obstruction.
The positive electrode (cathode) forms a similar layer of film that is known as electrolyte oxidation. Dr. Dahn’s research has make it clear that any voltage that is more than 4.10V/cell causes this to occur. This process gets worse the longer the battery stays in these conditions. While experts have known that this happens for some time, Dr. Dahn’s system of measuring CE is more scientific and give us a better understanding of the process.
The energy density has always been the standard specification for which a battery is measured. After the recall in 2008 of Li-ion batteries, safety became more of a concern and batteries became safer for consumers. After the invention of electric vehicles, longer lasting batteries have been the main focus of experts. Since then experts have been working tirelessly to figure out what causes batteries to fail.
The average battery life of a laptop or mobile phone battery is two or three years, or approximately 500 cycles. The eight year warranty that is standard or electric vehicles seems to come up short, considering the cost of replacing the battery in an electric vehicle is just short of the price of a compact car. If experts can come up with a way to extend the life of a battery up to 20 years, it would make driving an electric vehicle much more economical.
Nissan is currently being sued by those who purchased the Nissan Leaf in California and Arizona. The owners are doing so because of the premature capacity loss of the battery. The hot climate in these states is taking the blame for the sudden loss of power and heat. The battery that came standard in these vehicles was not equipped with a system to keep the battery cells cool in warmer temperatures.
A manganese-based Li-ion battery cam standard in the Nissan Leaf. It was chosen by Nissan because of it’s superior performance; however it is still not strong enough to provide power for the life of the vehicle. Testing showed that it was capable of a rapid charge , and a 20 minute discharge. Even under perfect conditions the battery is likely to loose about 10% after 500 cycles or one to two years of driving.
In most cases with a new product, we don’t notice the defects until after a few years. Professor Jeff Dahn of Dalhousie University is working together with his team of colleagues to develop coulombic efficiency also known as CE. This method helps to make the process more efficient. Using his method electrons are transferred in an electro chemical system.
