Lithium iron phosphate battery
|Specific energy||90–110 Wh/kg (320–400 J/g)|
|Energy density||220 Wh/L (790 kJ/L)|
|Specific power||>300 W/kg|
|Energy/consumer-price||0.5-2.5 Wh/US$ (US$0.11–0.56/kJ)|
|Time durability||>10 years|
|Cycle durability||2,000 cycles|
|Nominal cell voltage||3.3 V|
The lithium iron phosphate (LiFePO
4) battery, also called LFP battery (with "LFP" standing for "lithium ferrophosphate"), is a type of rechargeable battery, specifically a lithium-ion battery, which uses LiFePO
4 as a cathode material. LiFePO
4 batteries have somewhat lower energy density than the more common LiCoO
2 design found in consumer electronics, but offers longer lifetimes, better power density (the rate that energy can be drawn from them) and are inherently safer. LiFePO
4 is finding a number of roles in vehicle use and backup power.
4 is a natural mineral of the olivine family. Its use as a battery electrode was first described in published literature by John Goodenough's research group at the University of Texas in 1996, as a cathode material for rechargeable lithium batteries. Because of its low cost, non-toxicity, the high abundance of iron, its excellent thermal stability, safety characteristics, electrochemical performance, and specific capacity (170 mA·h/g, or 610 C/g) it gained some market acceptance.
Its key barrier to commercialization was intrinsically low electrical conductivity. This problem, however, was then overcome by reducing the particle size, coating the LiFePO
4 particles with conductive materials such as carbon, and doping the result with cations of materials such as aluminium, niobium, and zirconium. This approach was developed by Yet-Ming Chiang and his coworkers at MIT. Products are now in mass production and are used in industrial products by major corporations including Black and Decker's DeWalt brand, the Fisker Karma, Daimler, Cessna and BAE Systems.
MIT has introduced a new coating that allows the ions to move more easily within the battery. The "Beltway Battery" utilizes a bypass system that allows the lithium-ions to enter and leave the battery at a speed great enough to fully charge a battery in under a minute. The scientists discovered that by coating particles of lithium iron phosphate in a glassy material called lithium pyrophosphate, ions bypass the channels and move faster than in other batteries. Rechargeable batteries store up and discharge energy as charged atoms, known as ions, from between two electrodes called the anode and the cathode. Their charge and discharge rate are restricted by the speed with which these ions move. Such technology could reduce the weight and size of the batteries. A small prototype battery cell has been developed that can fully charge in 10 to 20 seconds, compared with six minutes for standard battery cells.
Advantages and disadvantages
||This article contains a pro and con list. (November 2012)|
4 battery uses a lithium-ion-derived chemistry and shares many advantages and disadvantages with other Lithium-ion battery chemistries. However, there are significant differences.
LFP chemistry offers a longer cycle life than other lithium-ion approaches.
The use of phosphates avoids cobalt's cost and environmental concerns, particularly concerns about cobalt entering the environment through improper disposal.
4 has higher current or peak-power ratings than LiCoO2.
The energy density (energy/volume) of a new LFP battery is some 14% lower than that of a new LiCoO2 battery. Also, many brands of LFPs have a lower discharge rate than lead-acid or LiCoO2. Since discharge rate is a percentage of battery capacity a higher rate can be achieved by using a larger battery (more ampère-hours).
4 cells experience a slower rate of capacity loss (aka greater calendar-life) than lithium-ion battery chemistries such as LiCoO2 cobalt or LiMn2O4 manganese spinel lithium-ion polymer batteries or lithium-ion batteries. After one year on the shelf, a LiFePO
4 cell typically has approximately the same energy density as a LiCoO2 Li-ion cell, because of LFP's slower decline of energy density. Thereafter, LiFePO
4 likely has a higher density.
One important advantage over other lithium-ion chemistries is thermal and chemical stability, which improves battery safety. LiFePO
4 is an intrinsically safer cathode material than LiCoO2 and manganese spinel. The Fe-P-O bond is stronger than the Co-O bond, so that when abused, (short-circuited, overheated, etc.) the oxygen atoms are much harder to remove. This stabilization of the redox energies also helps fast ion migration.
As lithium migrates out of the cathode in a LiCoO2 cell, the CoO2 undergoes non-linear expansion that affects the structural integrity of the cell. The fully lithiated and unlithiated states of LiFePO
4 are structurally similar which means that LiFePO
4 cells are more structurally stable than LiCoO2 cells.
No lithium remains in the cathode of a fully charged LiFePO
4 cell—in a LiCoO2 cell, approximately 50% remains in the cathode. LiFePO
4 is highly resilient during oxygen loss, which typically results in an exothermic reaction in other lithium cells.
As a result, lithium iron phosphate cells are much harder to ignite in the event of mishandling especially during charge, although any battery, once fully charged, can only dissipate overcharge energy as heat. Therefore failure of the battery through misuse is still possible. It is commonly accepted that LiFePO4 battery does not decompose at high temperatures. The difference between LFP and the LiPo battery cells commonly used in the aeromodeling hobby is particularly notable.
- Cell voltage
- Min. discharge voltage = 2.8 V
- Working voltage = 3.0 ~ 3.3 V
- Max. charge voltage = 3.6 V
- Volumetric energy density = 220 Wh/dm3 (790 kJ/dm3)
- Gravimetric energy density = >90 Wh/kg (>320 J/g)
- 100% DOD cycle life (number of cycles to 80% of original capacity) = 2,000–7,000
- Cathode composition (weight)
- Cell Configuration
- Experimental conditions:
- Room temperature
- Voltage limits: 2.0 – 3.65 V
- Charge: Up to C/1 rate up to 3.6 V, then constant voltage at 3.6 V until I < C/24
LFP cells are now used in some solar powered path lights instead of NiCd. Their higher working voltage allows a single cell to drive an LED without needing a step-up circuit. Some models claim to be 24x brighter than baseline path lights.
One Laptop per Child
This type of battery technology is used on the One Laptop per Child (OLPC) project. The batteries are manufactured by BYD Company of Shenzhen, China, the world's largest producer of Li-ion batteries.
Many home EV conversions use the large format versions as the car's traction pack. With the efficient power to weight ratios, high safety features and the chemistry's refusal to go into thermal runaway, there are few barriers for use by amateur home "makers".
ZBoard electric skateboards use LFP batteries, offering ranges up to 20 miles.
Golfskatecaddy Golf Skate Caddy electric single person golf vehicle use LFP batteries, allowing a full 18 holes of golf.
BYD, also a car manufacturer, plans to use its lithium iron phosphate batteries to power its PHEV, the F3DM and F6DM (Dual Mode), which will be the first commercial dual-mode electric car in the world. It plans to mass-produce the cars in 2009.
Some electronic cigarettes use these types of batteries.
Shorai Inc. makes lithium-iron batteries for a variety of powersport vehicles (motorcycles, ATVs, etc...)
Rimac Automobili have developed an advanced LFP battery system with integrated battery management and liquid cooling systems, primarily for their Concept One electric supercar which will enter production but also for commercial availability of the battery system.
RC model cars may use these batteries, especially as RX and TX packs as a direct replacement of NiMh packs or LiPo packs without need for voltage regulator, as they provide 6.6v nominal voltage over 7.4v of LiPo packs, which is little higher and may require to be regulated down to 6.0v.
- Lithium battery
- Lithium-titanate battery
- Lithium–air battery
- Lithium-ion polymer battery
- Nanowire battery
- Power-to-weight ratio
- Super iron battery
4: A Novel Cathode Material for Rechargeable Batteries", A.K. Padhi, K.S. Nanjundaswamy, J.B. Goodenough, Electrochimical Society Meeting Abstracts, 96-1, May, 1996, pp 73
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- 25 °C...[100% state of charge]...80% after 1 year
- 40 °C...[100% state of charge]...65% after 1 year
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4 used in OLPC nytimes.com
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