While LiFePO4 cells have lower voltage and energy density than LiCoO2 Li-ion cells, this disadvantage is offset over time by the slower rate of capacity loss (aka greater calendar-life) of LiFePO4 when compared with other lithium-ion battery chemistries (such as LiCoO2 cobalt or LiMn2O4 manganese spinel based lithium-ion polymer batteries or lithium-ion batteries).For example:
After one year on the shelf, a LiFePO4 cell typically has approximately the same energy density as a LiCoO2 Li-ion cell.Beyond one year on the shelf, a LiFePO4 cell is likely to have higher energy density than a LiCoO2 Li-ion cell due to the differences in their respective calendar-lives.
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[11] (>320 J/g)
100% DOD cycle life (number of cycles to 80% of original capacity) = 2,000–7,000 [12]
Cathode composition (weight)
90% C-LiFePO4, grade Phos-Dev-12
5% Carbon EBN-10-10 (superior graphite)
5% PVDF
Cell Configuration
Carbon-coated aluminum current collector 15
1.54 cm2 cathode
Electrolyte: EC-DMC 1-1 LiClO4 1M
Anode: Metallic lithium
Experimental conditions: ** Note the following is for Cobalt Cathode LiIon cells - should be changed for LiFePO
Room temperature
Voltage limits: 2.5 – 4.2 V
Charge: C/4 up to 4.2 V, then potentiostatic at 4.2 V until I < C/24
Safety
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. Only under extreme heating (generally over 800 °C) does breakdown occur and this bond stability greatly reduces the risk of thermal runaway when compared with LiCoO2.
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.
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.
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