Lithium iron phosphate battery

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The lithium iron phosphate (LiFePO₄) battery is a type of rechargeable battery based on the original lithium ion chemistry, created by the use of LiFePO₄ as a cathode material. It is not yet widely in use.

LiFePO₄ cells have higher discharge current, do not explode under extreme conditions and weigh less, but have lower voltage and energy density than normal Li-ion cells. Because this type of battery is not widely in production, little performance information is available. Pihsiang Energy Technology Co. LiFePO₄ batteries (distributed by Valence) have already begun shipping in some scooters and electric bicycles.

Contents 1 History 2 Advantages and disadvantages 3 Safety 4 References 5 External links

History

LiFePO₄ was proposed by researchers at the University of Texas in 1997 because of its low cost, non-toxicity, the high abundance of iron, its excellent thermal stability, safety characteristics, good electrochemical per­formance, and high specific capacity (170 mA·h/g)^[1][2] but was unusable due to the low conductivity of LiFePO₄ until 2002, when Yet-Ming Chiang and his coworkers at MIT tried doping the cathode with conductive materials — such as aluminum, niobium, and zirconium.^[1] The increased conductivity allowed development to move forward.

Recent research has included carbon doping — with both carbon black and graphite. In carbon doping, specific capacities of up to 130 mA·h/g were achieved.^[3]

Advantages and disadvantages

Being a lithium-ion-derived chemistry, the LiFePO₄ chemistry shares many of the advantages and disadvantages of lithium ion chemistry. Key differences are safety and current rating. Cost is claimed to be a major difference, but that cannot be verified until the cells are more widely accepted.

Safety

LiFePO₄ is an intrinsically safer cathode material than LiCoO₂. 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. Only under extreme heating (generally over 800 °C) does breakdown occur, which prevents the thermal runaway that LiCoO₂ is prone to.

As lithium migrates out of the cathode in a LiCoO₂ cell, the CoO₂ undergoes non-linear expansion, which 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.

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.^[2]

References

1. ^ ^{a b} "Bigger, Cheaper, Safer Batteries: New material charges up lithium-ion battery work" (html).
2. ^ ^{a b} . "Building safer Li ion batteries" (html).
3. ^ . "Effect of conductive additives in LiFePO4 cathode for lithium-ion batteries" (pdf).

External links

• valence.com
• aleees