Lithium iron phosphate battery (LiFePO4)

 

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The lithium iron phosphate (LiFePO₄) battery, also called LFP battery, is a type of rechargeable battery, specifically a lithium-ion battery, which uses LiFePO₄ as a cathode material.

 

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

 

History

LiFePO₄ was discovered by John Goodenough's research group at the University of Texas in 1996,^[1][2] 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.^[3][4]

Its key barrier to commercialization was intrinsically low electrical conductivity. This problem, however, was then overcome by reducing the particle size, coating the LiFePO₄ particles with conductive materials such as carbon, and doping^[3] 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. It was later shown that most of the conductivity improvement was due to the presence of nanoscopic carbon originating from organic precursors.^[5] 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.^{[citation needed]}

Most lithium-ion batteries (Li-ion) used in consumer electronics products use lithium cobalt oxide cathodes (LiCoO₂). Other varieties of lithium-ion batteries include lithium manganese oxide (LiMn₂O₄) and lithium nickel oxide (LiNiO₂). The batteries are named after the material used for their cathodes; the anodes are generally made of carbon and a variety of electrolytes are used.^{[citation needed]}

Advantages and disadvantages

The LiFePO₄ 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.^[6]

The use of phosphates avoids cobalt's cost and environmental concerns, particularly concerns about cobalt entering the environment through improper disposal.^[6]

LiFePO₄ has higher current or peak-power ratings than LiCoO₂.^[7]

The energy density (energy/volume) of a new LFP battery is some 14% lower than that of a new LiCoO₂ battery.^[8] 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). However, A123Systems claims 100C pulse discharge rate.^[9]

LiFePO₄ 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.^[10][11] After one year on the shelf, a LiFePO₄ cell typically has approximately the same energy density as a LiCoO₂ Li-ion cell, because of LFP's slower decline of energy density. Thereafter, LiFePO₄ likely has a higher density.

Safety

One important advantage over other lithium-ion chemistries is thermal and chemical stability, which improves battery safety.^[6] LiFePO₄ 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.^{[citation needed]}

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 LiFePO₄ are structurally similar which means that LiFePO₄ cells are more structurally stable than LiCoO₂ cells.^{[citation needed]}

No lithium remains in the cathode of a fully charged LiFePO₄ cell—in a LiCoO₂ cell, approximately 50% remains in the cathode. LiFePO₄ is highly resilient during oxygen loss, which typically results in an exothermic reaction in other lithium cells.^[4]

As a result, lithium iron phosphate cells are much harder to ignite in the event of mishandling especially during charge, however any battery (LiFePO4 included) after exhausting chemical ability to absorb any more energy can only dissipate overcharge energy as heat. Therefore, unlike commonly cited impression of bullet proof safety, with high enough rate of prolonged [over]charging, at some point it will ignite itself and its surroundings potentially causing catastrophic outcome. It is commonly accepted that LiFePO4 battery does not decompose at high temperatures.^[6] The difference between LFP and the LiPo battery cells commonly used in the aeromodeling hobby is particularly notable.^{[citation needed]}

Specifications

• Cell voltage = min. discharge voltage = 2.8 V. Working voltage = 3.0 V – 3.3 V. Max. charge voltage = 3.6 V.
• Volumetric energy density = 220 Wh/dm³ (790 kJ/dm³)
• Gravimetric energy density = >90 Wh/kg^[12] (>320 J/g)
• 100% DOD cycle life (number of cycles to 80% of original capacity) = 2,000–7,000^[13]
• Cathode composition (weight)
  • 90% C-LiFePO4, grade Phos-Dev-12
  • 5% Carbon EBN^{[disambiguation needed ]}-10-10 (superior graphite)
  • 5% PVDF
• Cell Configuration
  • Carbon-coated aluminium current collector 15
  • 1.54 cm² cathode
  • Electrolyte: EC-DMC 1-1 LiClO₄ 1M
  • Anode: Graphite or Hard Carbon with intercalated Metallic lithium
• 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

Usage

One Laptop per Child

This type of battery technology is used on the One Laptop per Child (OLPC) project.^[14] The batteries are manufactured by BYD Company of Shenzhen, China, the world's largest producer of Li-ion batteries.

OLPC uses LFP batteries in its XO laptops because they contain no toxic heavy metals in compliance with the European Union's Restriction of Hazardous Substances Directive.^[15]

Vehicles

LFP batteries were featured on the November 5, 2008 episode of Prototype This!. They were used as the power source for a hexapod (walking) vehicle.^{[citation needed]}

This battery is used in the electric cars made by Aptera^[16] and QUICC.^[17]

Killacycle, the worlds fastest electric motorcycle, uses lithium iron phosphate batteries.^[18]

Roehr Motorcycle Company, uses a 5.8 kW·h capacity LFP battery pack to power its supersport electric motorcycle.^{[citation needed]}

LFP batteries are used by electric vehicles manufacturer Smith Electric Vehicles to power its products.^{[citation needed]}

Minneapolis Electric Bike and Chicago Electric Bicycles use LFP batteries.^{[citation needed]}

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.^[19]

In May 2007 Lithium Technology Corp. announced a Lithium Iron Phosphate battery with cells large enough for use in hybrid cars, claiming they are "the largest cells of their kind in the world.".^[20]

Some electronic cigarettes use these types of batteries.^{[citation needed]}

Shorai Inc. makes lithium-iron batteries for a variety of powersport vehicles (motorcycles, ATVs, etc...)