The lithium iron phosphate battery (LiFePO4 battery) or LFP battery (lithium ferrophosphate) is a type of lithium-ion battery using lithium iron phosphate (LiFePO4) as the cathode material, and a graphitic carbon electrode with a metallic backing as the anode. The energy density of an LFP battery is lower than that of other common lithium ion battery types such as Nickel Manganese Cobalt (NMC) and Nickel Cobalt Aluminum (NCA), and also has a lower operating voltage. Because of its lower cost, low toxicity, long cycle life and other factors, LFP batteries are finding a number of roles in vehicle use, utility scale stationary applications, and backup power. LFP batteries are cobalt-free.

Lithium iron phosphate battery

History

LiFePO4 is a natural mineral of the olivine family (triphylite). Arumugam Manthiram and John B. Goodenough first identified the polyanion class of cathode materials for lithium ion batteries. LiFePO4 was then identified as a cathode material belonging to the polyanion class for use in batteries in 1996 by Padhi et al. Reversible extraction of lithium from LiFePO4 and insertion of lithium into FePO4 was demonstrated. Because of its low cost, non-toxicity, the natural abundance of iron, its excellent thermal stability, safety characteristics, electrochemical performance, and specific capacity (170 mA·h/g, or 610 C/g) it has gained considerable market acceptance.

The chief barrier to commercialization was its intrinsically low electrical conductivity. This problem was overcome by reducing the particle size, coating the LiFePO4 particles with conductive materials such as carbon nanotubes, or both. This approach was developed by Michel Armand and his coworkers. Another approach by Yet Ming Chiang's group consisted of doping LFP with cations of materials such as aluminium, niobium, and zirconium.

Negative electrodes (anode, on discharge) made of petroleum coke were used in early lithium-ion batteries; later types used natural or synthetic graphite.

Multiple Lithium Iron Phosphate modules are wired in series and parallel to create a 2800Ah 52V battery module. Total battery capacity is 145.6 kWh. Note the large, solid tinned copper busbar connecting the modules together. This busbar is rated for 700 amps DC to accommodate the high currents generated in a 48 volt DC system.

Lithium Iron Phosphate modules, each 700 Ah amp-hours 3.25 volts. Two modules are wired in parallel to create a single 3.25 V 1400 Ah battery pack with a capacity of 4.55 kWh.

Specifications

Cell voltage
Minimum discharge voltage = 2.5 V
Working voltage = 3.0 ~ 3.2 V
Maximum charge voltage = 3.65 V
Volumetric energy density = 220 Wh/L (790 kJ/L)
Gravimetric energy density > 90 Wh/kg (> 320 J/g). Up to 160 Wh/kg (580 J/g).
Cycle life from 2,700 to more than 10,000 cycles depending on conditions.

Advantages and disadvantages

The LFP battery uses a lithium-ion-derived chemistry and shares many advantages and disadvantages with other lithium-ion battery chemistries. However, there are significant differences.

More abundant constituents with lower human and environmental impact

LFP contain neither nickel nor cobalt, both of which are supply-constrained and expensive. As with lithium, human rights and environmental concerns have been raised concerning the use of cobalt. Environmental concerns have also been raised regarding the extraction of nickel.

Price

In 2020, the lowest reported LFP cell prices were $80/kWh (12.5Wh/$) .

A 2020 report published by the Department of Energy compared the costs of large scale energy storage systems built with LFP vs NMC. It found that the cost per kwh of LFP batteries was about 6% less than NMC, and it projected that the LFP cells would last about 67% longer (more cycles). Because of differences between the cell's characteristics, the cost of some other components of the storage system would be somewhat higher for LFP, but in balance it still remains less costly per kwh than NMC.

Better ageing and cycle-life characteristics

LFP chemistry offers a considerably longer cycle life than other lithium-ion chemistries. Under most conditions it supports more than 3,000 cycles, and under optimal conditions it supports more than 10,000 cycles. NMC batteries support about 1,000 to 2,300 cycles, depending on conditions. 

LFP cells experience a slower rate of capacity loss (aka greater calendar-life) than lithium-ion battery chemistries such as cobalt (LiCoO2) or manganese spinel (LiMn
2O4) lithium-ion polymer batteries (LiPo battery) or lithium-ion batteries.

Viable alternative to lead-acid batteries

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. Along with the good safety characteristics of LFP batteries, this makes LFP a good potential replacement for lead-acid batteries in 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, equalisation 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, due to irreversible deintercalation of LiFePO4 into FePO4.

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 dioxide spinels through omission of the cobalt, with its negative temperature coefficient of resistance that can encourage thermal runaway. The P–O bond in the (PO4)3− ion is stronger than the Co–O bond in the (CoO2)− ion, so that when abused (short-circuited, overheated, etc.), the oxygen atoms are released more slowly. This stabilization of the redox energies also promotes faster 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 LFP cell. (In a LiCoO2 cell, approximately 50% remains.) LiFePO4 is highly resilient during oxygen loss, which typically results in an exothermic reaction in other lithium cells.As a result, LiFePO4 cells are harder to ignite in the event of mishandling (especially during charge). The LiFePO4 battery does not decompose at high temperatures.

Lower energy density

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.

Uses

Home energy storage

Enphase pioneered LFP home storage batteries for reasons of cost and fire safety, although the market remains split among competing chemistries. The lower energy density compared to other lithium chemistries adds mass and volume, both may be more tolerable in a static application. In 2021, there were several suppliers to the home end user market, including SonnenBatterie and Enphase. Tesla Motors continues to use NMC batteries in its home energy storage products, but in 2021 switched to LFP for its utility-scale battery product. The most quoted home energy storage battery in the U.S. is the Enphase, which in 2021 surpassed Tesla Motors and LG.

Transportation

Higher discharge rates needed for acceleration, lower weight and longer life makes this battery type ideal for forklifts, bicycles and electric cars. 12V LiFePO4 batteries are also gaining popularity as a second (house) battery for a caravan, motor-home or boat.

Tesla Motors currently uses LFP batteries in certain vehicles, including its Chinese-made Standard Range Models 3 and Y, and some Model 3 units in the United States beginning around August 2021. In October 2021, Tesla announced that all standard-range Models 3 and Y will begin using LFP battery chemistry.

In late 2021, Our Next Energy demonstrated a long range test of a Model S retrofitted with an LFP battery traveling for 752 miles on a single charge.

Solar-powered lighting systems

Single "14500" (AA battery–sized) LFP cells are now used in some solar-powered landscape lighting instead of 1.2 V NiCd/NiMH.

LFP's higher (3.2 V) working voltage lets a single cell drive an LED without circuitry to step up the voltage. Its increased tolerance to modest overcharging (compared to other Li cell types) means that LiFePO4 can be connected to photovoltaic cells without circuitry to halt the recharge cycle. The ability to drive an LED from a single LFP cell also obviates battery holders, and thus the corrosion, condensation and dirt issues associated with products using multiple removable rechargeable batteries.

By 2013, better solar-charged passive infrared security lamps emerged. As AA-sized LFP cells have a capacity of only 600 mAh (while the lamp's bright LED may draw 60 mA), the units shine for at most 10 hours. However, if triggering is only occasional, such units may be satisfactory even charging in low sunlight, as lamp electronics ensure after-dark "idle" currents of under 1 mA.

Other uses

Some electronic cigarettes use these types of batteries. Other applications include flashlights, radio-controlled models, portable motor-driven equipment, amateur radio equipment, industrial sensor systems and emergency lighting.