How does a lithium iron battery compare to a lithium ion battery? Is the only difference the letter "R" in "iron" versus "ion"?
The newest rechargeable lithium batteries are made of lithium iron phosphate, or LiFePO4. The older lithium ion, or "Li-ion", battery is made of lithium cobalt dioxide or LiCoO2.
Important Characteristics of Rechargeable Lithium Batteries
High-performance rechargeable lithium batteries are used in cameras, laptops, and electric vehicles ranging from bicycles through scooters to automobiles. Some important characteristics in any of these applications are discussed below.
A Rechargeable Lithium Iron Battery is Safer In Use
The battery should not overheat, melt, or burn regardless if it is being overcharged or else being discharged too quickly. The safety of laptop batteries became a very public issue when many were recalled by the manufacturer.
The lithium iron battery wins on safety considerations. Under stress, a lithium ion battery can heat up very rapidly and cause a fire. Under the same circumstances, a lithium iron battery can keep its cool. If well-designed, it should only vent gas at a reasonably low temperature.
Material Safety
The materials should be non-toxic, non-irritating, and safe to manage at the end of the battery's life. Material safety is a concern for both manufacturers and waste disposal sites. Toxic or hazardous chemicals are difficult to work with, and should not be dumped to pollute the environment.
Lithium iron phosphate is a safer material than the lithium cobalt used in Li-ion batteries. The material handling sheet information indicates that lithium cobalt is a hazard which may irritate or harm the eyes, respiratory tract and skin; may be harmful if swallowed. By contrast, the material handling sheet data for LiFePO4 treats it as a fairly safe powder, unless it happens to be burning. Neither should be ingested or rubbed in one's eyes; but the same would be said for baby powder.
Performance of Rechargeable Lithium Batteries
The battery should deliver enough power without being bulky or heavy. Size and weight are especially problematic for electric cars. The rechargeable lithium iron battery pack is heavy and even more bulky than a gasoline tank. In any application, once the size of a battery is limited, the performance characteristics put a limit on the power draw and the total time the device can run.
The Li-ion battery still holds an edge in performance, especially when new. This advantage slips with age and over more recharge cycles from deeper discharge levels. So depending on usage, the rechargeable lithium iron battery may hold a slim advantage.
Recharge Cycles
Good batteries should survive well over 1,500 charge/discharge cycles. Replacing any lithium battery pack is expensive, so the battery must survive many recharge cycles. Many consumers frequently drain their rechargeable batteries completely. This high "depth of discharge" severely reduces the number of recharge cycles for some types of batteries.
Some tests show lithium iron phosphate batteries survive about 2,000 recharge cycles, compared to about 1,500 for Li-ion.
Shelf Life of Rechargeable Lithium Batteries
A battery should survive for at least a year and continue to perform "like new". Aging batteries can store less power long before completely failing. The shelf life of lithium batteries is quite limited. Consumers find it extremely aggravating to replace a battery pack that has died without being used.
Shelf life for some LiFePO4 batteries was found to be at least 50 days longer than the 300 or so for lithium ion batteries.
Convenience of Rechargeable Lithium Batteries
The quicker the battery charger does its job, the sooner the battery can get back to work. For laptops and cameras, it is more convenient to carry extra batteries than to wait hours to recharge. Spare batteries are impractical for electric vehicles, although "swap-out" stations are being considered.
For the convenience of a quicker recharge, it is not clear that either battery has an advantage.
Economics of Rechargeable Lithium Batteries
Lower costs for materials, machinery and labour to manufacture the rechargeable batteries lead to better affordability. Consumers should remember, however, that "total cost of ownership" is most important. For batteries, this means considering the cost for the initial purchase plus the replacement costs over the life of the product. For example, paying 10% more for a product that lasts 20% longer than its competitor, saves 5% by the time the competitor has been replaced six times.
Economics favours LiFePO4. Iron is less expensive than cobalt. Safer materials make it less expensive to manufacture and to recycle. A price advantage to the consumer should become apparent when the new products are produced in sufficient quantities.
Lithium Iron Might Just be the Start [Updated Aug. 12, 2011]
An August 2011 study found that LiFePO4 is a "single phase", rather than "double phase" cathode. The lithium iron battery's high discharge rate had been a mystery because it is a "double phase" material after it has charged. This would slow the process; but it actually charges in a single phase but separates into two at equilibrium.
This finding does not change the lithium iron battery's properties or how it is used. However, scientists now have reason to review yet more materials previously thought to be "double phase". This study could lead to significant new formulations in the future.
The Lithium Iron Battery and the Consumer
The lithium iron phosphate battery has many advantages over lithium ion. Consumer availability may be the next stumbling block. It is well worth checking the type of battery when purchasing one's next camera, laptop or electric vehicle.
Disclaimer: The information contained in this article is for educational purposes only and should not be used to guide purchases without the opinion of a technical professional.
References:
Allan Chen, Berkeley Lab, " Batteries of the Future II ", published Feb. 2007, referenced Oct. 16, 2010.
Rho, Nazar, Perry and Ryan, Journal of The Electrochemical Society, "Surface Chemistry of LiFePO4 Studied by Mössbauer and X-Ray Photoelectron Spectroscopy and Its Effect on Electrochemical Properties", published Feb. 9 2007, referenced Oct. 16, 2010.
Michel Gautier, Université de Montréal, "Phostech’s advanced C-LiFePO4 cathode for EV-PHEV-HEV", published Sept. 2009, referenced Oct. 16, 2010.
Guerfi, Charest, Dontigny, Peticlerc and Zaghib, Hydro-Québec, "Olivines for HEV and PHEV Applications", published Nov. 200, referenced Oct. 16, 2010.
Sigma-Aldrich, "Material Data Handling Sheet (Lithium cobalt(III) oxide)", revised Feb. 28, 2010, referenced Oct. 16, 2010.
MTI Corp., "Material Data Handling Sheet (LiFePO4 Powder for Li-ion battery Cathode)", revised June, 2010, referenced Oct. 16, 2010.
MetaEfficient.com for two images, referenced Oct. 15, 2010.
(Aug. 2011) David L. Chandler, Phys Org, "A systematic way to find battery materials", Aug. 12, 2011, referenced Aug. 12, 2011.
Mike DeHaan - Copyright (c) Mike DeHaan, B. Math., of DeHaan Services. Well written and well researched freelance articles; ghost writing for clients.
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