From Wikipedia, the free encyclopedia
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
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.
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
but was unusable due to the low conductivity of LiFePO4
until 2002, when
Yet-Ming Chiang and his coworkers at
doping the cathode with conductive materials — such as
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.
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
LiFePO4 is an intrinsically safer cathode material
than LiCoO2. The Fe-P-O bond is stronger than the
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.
Cheaper, Safer Batteries: New material charges up
lithium-ion battery work" (html).
safer Li ion batteries" (html).
- ^ . "Effect
of conductive additives in LiFePO4 cathode for lithium-ion
Rechargeable batteries |