By InfiniEnergy | 27 May 2017 | 1 Comentários
What is LiFePO4 Battery?
The lithium iron phosphate (LiFePO4) battery, also called LFP battery (with "LFP" standing for "lithium phosphate"), is a type of rechargeable battery, specifically a lithium-ion battery, which uses LiFePO4 as a cathode material. LiFePO4 batteries have somewhat lower energy density than the more common lithium cobalt oxide (LiCoO2) design found in consumer electronics, but offer longer lifetimes, better power density (the rate that energy can be drawn from them) and are inherently safer. LiFePO4 is finding a number of roles in vehicle use and backup power.
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.
Like nickel-based rechargeable batteries (and unlike other lithium ion batteries),LiFePO4 batteries have a very constant discharge voltage. Voltage stays close to 3.2 V during discharge until the cell is exhausted. This allows the cell to deliver virtually full power until it is discharged. And it can greatly simplify or even eliminate the need for voltage regulation circuitry.
Because of the nominal 3.2 V output, four cells can be placed in series for a nominal voltage of 12.8 V. This comes close to the nominal voltage of six-cell lead-acid batteries. And, along with the good safety characteristics of LFP batteries, this makes LFP a good potential replacement for lead-acid batteries in many applications such as automotive and solar applications, provided the charging systems are adapted not to damage the LFP cells through excessive charging voltages (beyond 3.6 volts DC per cell while under charge), temperature-based voltage compensation, equalization attempts or continuous trickle charging. The LFP cells must be at least balanced initially before the pack is assembled and a protection system also needs to be implemented to ensure no cell can be discharged below a voltage of 2.5 V or severe damage will occur in most instances.
The use of phosphates avoids cobalt's cost and environmental concerns, particularly concerns about cobalt entering the environment through improper disposal, as well as the potential for the thermal runaway characteristic of cobalt-content rechargeable lithium cells manifesting itself.LiFePO4 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, as well as cells within a given brand of LFP batteries, 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 ampere hours) if low-current batteries must be used. Better yet, a high current LFP cell (which will have a higher discharge rate than a lead acid or LiCoO2 battery of the same capacity) can be used.
LiFePO4 cells experience a slower rate of capacity loss (aka greater calendar-life) than lithium-ion battery chemistries such as LiCoO2
cobalt or LiMnO24 manganese spinal lithium-ion polymer batteries (Li-Po battery) or lithium-ion batteries. 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.
Safety
One important advantage over other lithium-ion chemistries is thermal and chemical stability, which improves battery safety. LiFePO4 is an intrinsically safer cathode material than LiCoO2 and manganese spinal. 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 radix energy 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 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.
As a result, lithium iron phosphate cells are much harder to ignite in the event of mishandling (especially during charge) although any fully charged battery 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 Li-Po battery cells commonly used in the aeromodelling hobby is particularly notable.
| Lithium iron phosphate battery | |
| Specific energy | 90–110 Wh/kg (320–400 J/g or kJ/kg) |
| Energy density | 220 Wh/L (790 kJ/L) |
| Specific power | around 200 W/kg |
| Energy/consumer-price | 3.0–24 Wh/US$ |
| Time durability | > 10 years |
| Cycle durability | 2,000 cycles |
| Nominal cell voltage | 3.2 V |
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.
Like nickel-based rechargeable batteries (and unlike other lithium ion batteries),LiFePO4 batteries have a very constant discharge voltage. Voltage stays close to 3.2 V during discharge until the cell is exhausted. This allows the cell to deliver virtually full power until it is discharged. And it can greatly simplify or even eliminate the need for voltage regulation circuitry.
Because of the nominal 3.2 V output, four cells can be placed in series for a nominal voltage of 12.8 V. This comes close to the nominal voltage of six-cell lead-acid batteries. And, along with the good safety characteristics of LFP batteries, this makes LFP a good potential replacement for lead-acid batteries in many applications such as automotive and solar applications, provided the charging systems are adapted not to damage the LFP cells through excessive charging voltages (beyond 3.6 volts DC per cell while under charge), temperature-based voltage compensation, equalization attempts or continuous trickle charging. The LFP cells must be at least balanced initially before the pack is assembled and a protection system also needs to be implemented to ensure no cell can be discharged below a voltage of 2.5 V or severe damage will occur in most instances.
The use of phosphates avoids cobalt's cost and environmental concerns, particularly concerns about cobalt entering the environment through improper disposal, as well as the potential for the thermal runaway characteristic of cobalt-content rechargeable lithium cells manifesting itself.LiFePO4 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, as well as cells within a given brand of LFP batteries, 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 ampere hours) if low-current batteries must be used. Better yet, a high current LFP cell (which will have a higher discharge rate than a lead acid or LiCoO2 battery of the same capacity) can be used.
LiFePO4 cells experience a slower rate of capacity loss (aka greater calendar-life) than lithium-ion battery chemistries such as LiCoO2
cobalt or LiMnO24 manganese spinal lithium-ion polymer batteries (Li-Po battery) or lithium-ion batteries. 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.
Safety
One important advantage over other lithium-ion chemistries is thermal and chemical stability, which improves battery safety. LiFePO4 is an intrinsically safer cathode material than LiCoO2 and manganese spinal. 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 radix energy 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 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.
As a result, lithium iron phosphate cells are much harder to ignite in the event of mishandling (especially during charge) although any fully charged battery 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 Li-Po battery cells commonly used in the aeromodelling hobby is particularly notable.
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