Published on April 17th, 2013 | by Yellow Magpie4
Lithium Batteries: The Ideal Choice For Electric Bicycles
Lithium Batteries: Photo By Claus Ableiter
Lithium batteries are proving to be the ideal choice for electric bicycles. With batteries that have a longer cycle-life, greater performance and high safety features it has never been a better time to be an owner of an electric bicycle. Here we shall take a look at the main types of lithium chemistry and explore the different aspects or characteristics of lithium batteries.
Batteries are thought to be have been invented as far back as 1,800 years ago in ancient Iraq but it is only in the last couple of decades that significant advancements have made electric vehicles a practical, everyday reality.
Lithium batteries come in five main chemistries that each have their advantages and disadvantages. Characteristics that makes them ideal for some applications but a poor choice for others.
Lithium Iron Phosphate (LiFePO4)
Lithium iron phosphate was pioneered by A123 Systems (which has since been re-branded to B456). Lithium iron phosphate or LiFePO4 is a very safe chemistry with a very long cycle life lasting between one and two thousand full cycles. It can also be completely discharged very quickly in less than two minutes while taking as little as 12 minutes to charge.
Lithium iron phosphate is one of the safest chemistries and will resist fire even when punctured. For this reason it is one of the most popular types of chemistry available.
Lithium Cobalt Oxide (LiCoO2)
The most common lithium variant is lithium cobalt oxide which is a chemistry found in laptops and mobile phones.
The advantages of this battery is that it has a very high C-rate and is one of the densest lithium batteries currently on offer in terms of volumetric, gravimetric and specific energy criteria. Due to its popularity lithium cobalt oxide is relatively inexpensive.
The types of lithium cobalt oxide batteries found in electric bicycles are usually taken from the electric model aeroplane and toy helicopter industry. This means that there are severe disadvantages to using this chemistry for electric bicycles. Lithium batteries produced specifically for model aeroplanes do not have the same type of quality control that is associated with this chemistry in other consumer products.
The first drawback is that type of battery is complicated to use and must be carefully balance-charged every certain number of cycles to ensure that all the individual cells that comprise the battery are at the correct voltage.
Potential Fire Hazard
The second and most concerning issue arising from this chemistry is its propensity to become a fire hazard due to over-charging/discharging or defects in the manufacturing process. Though the lithium in lithium batteries are far less reactive than pure metallic lithium they do contain oxidant. This makes it very difficult to put out and together with hazardous gas mean that this chemistry can be a potently dangerous.
If you do happen to have a lithium fire, be it from a laptop or other consumer device there are really only two methods of subduing the blaze if you do not happen to have the correct type of fire-extinguisher – salt and sand.
For this reason lithium cobalt oxide batteries are not sold to members of the public as part of either e-bike kits or turnkey electric bicycles. People who use this chemistry have to assemble the battery themselves as well as purchase the correct charging equipment. Those who do use this chemistry are likely to be fully aware of the risks and take the necessary precautions while dealing with a potential hazard.
Lithium cobalt oxide has a cycle life of between 300 and 500 full discharges.
Lithium Manganese DiOxide (LiMnO2)
Lithium Manganese DiOxide or LiMnO2 is also a popular chemistry for electric bicycles. Two characteristics that make it ideal are its relative safety and its specific energy density making it very lightweight. Lithium manganese dioxide is generally rated for 500 full cycles but it does not have the same performance as lithium cobalt oxide when it comes to specific energy density.
Lithium Nickel Manganese Oxide (NMC)
Lithium nickel manganese oxide or NMC is one of the newest stable of the rechargeable range of lithium batteries. It is even safer than lithium iron phosphate and may have a longer cycle life. Though not quite as specific energy dense as lithium cobalt oxide, NMC is quite close in this respect.
As this chemistry is just a recent development it is still more expensive to purchase for electric bicycle purposes compared to other lithium batteries. NMC is believed to last for between two and three thousand cycles.
Lithium Titanate (LiTiO2)
Finally, lithium Titanate is the one of the newest developments in lithium battery technology. This battery can give 20,000 full cycles, can be recharged in ten minutes and has an estimated lifespan of 20 years or more.
The drawbacks for lithium titanate are two-fold. As it is a niche product it is produced in far fewer quantities than other mass-market lithium battery chemistries. This makes lithium titanate easily the most expensive of all the the chemistries mentioned above.
Its second disadvantage is that it has a very low specific energy density. This puts it almost on a par with lead-acid. For these reasons it is not the most suitable chemistry for electric bicycles although it may make an ideal short-range lithium battery that is sure to last many years.
The Best Lithium Batteries
The best lithium batteries are those that meet your particular criteria. Price, size, weight, range and performance all come into play. Currently, you have to compromise on some areas in order to secure as today’s batteries cannot do everything well at once. Heavier lithium batteries will invariably be relatively inexpensive compared to lighter variants.
Therefore, you should spend some time researching the correct lithium battery to meet your needs. Best of luck.
Visit Endless Sphere for more information on electric bikes and suitable chemistries for lithium batteries from one of the best internet forums on the subject.