# Lithium iron phosphate battery

The lithium iron phosphate battery (LiFePO $_4$ battery) or LFP battery (lithium ferrophosphate) is a type of lithium-ion battery using lithium iron phosphate (LiFePO $_4$) as the cathode material, and a graphitic carbon electrode with a metallic backing as the anode. Because of their low cost, high safety, 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. As of September 2022, LFP type battery market share for EVs reached 31%, and of that, 68% were from EV makers Tesla and BYD alone. Chinese manufacturers currently hold a near monopoly of LFP battery type production. With patents having started to expire in 2022 and the increased demand for cheaper EV batteries, LFP type production is expected to rise further and surpass lithium nickel manganese cobalt oxides (NMC) type batteries in 2028.
The specific energy of LFP batteries is lower than that of other common lithium-ion battery types such as nickel manganese cobalt (NMC) and nickel cobalt aluminum (NCA). As of 2024, the specific energy of CATL's LFP battery is claimed to be 205 watt-hours per kilogram (Wh/kg) on the cell level. BYD's LFP battery specific energy is 150 Wh/kg. The best NMC batteries exhibit specific energy values of over 300 Wh/kg. Notably, the specific energy of Panasonic’s “2170” NCA batteries used in Tesla’s 2020 Model 3 mid-size sedan is around 260 Wh/kg, which is 70% of its "pure chemicals" value. LFP batteries also exhibit a lower operating voltage than other lithium-ion battery types.

## History

LiFePO $_4$ is a natural mineral known as triphylite. Arumugam Manthiram and John B. Goodenough first identified the polyanion class of cathode materials for lithium ion batteries. LiFePO $_4$ 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 LiFePO $_4$ and insertion of lithium into FePO $_4$ 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 LiFePO $_4$ particles with conductive materials such as carbon nanotubes, or both. This approach was developed by Michel Armand and his coworkers at Hydro-Québec and the Université de Montréal in 2015. Another approach by Yet Ming Chiang's group at MIT 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.

## Specifications

* Cell voltage
** Minimum discharge voltage = 2.0-2.8 V
** Working voltage = 3.0 ~ 3.3 V
** Max Viable voltage = 2.5 ~ 3.47 V
** Maximum charge voltage = 3.60-3.65 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). Latest version announced in end of 2023, early 2024 made significant improvements in energy density from 180 up to 205 Wh/kg without increasing production costs.
* Cycle life from 2,500 to more than 9,000 cycles depending on conditions. Next gen high energy density versions have increased charging lifecycles probably around 15000 max cycles.

## Comparison with other battery types

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.

### Resource availability

Iron and phosphates are very common in the Earth's crust. LFP contains 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.

### Cost

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.
In 2020, the lowest reported LFP cell prices were $80/kWh (12.5 Wh/$) with an average price of $137/kWh, while in 2023 the average price had dropped to $100/kWh. By early 2024, VDA-sized LFP cells were available for less than RMB 0.5/Wh ($70/kWh), while Chinese automaker Leapmotor stated it buys LFP cells at RMB 0.4/Wh ($56/kWh) and believe they could drop to RMB 0.32/Wh ($44/kWh). By mid 2024, assembled LFP batteries were available to consumers in the US for around $115/kWh.

### Better aging 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 (a.k.a. greater calendar-life) than lithium-ion battery chemistries such as cobalt (LiCoO $_2$) or manganese spinel (LiMn $_2$O $_4$) 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 LiFePO$_4$ into FePO$_4$.

### Safety

One important advantage over other lithium-ion chemistries is thermal and chemical stability, which improves battery safety. LiFePO $_4$ is an intrinsically safer cathode material than LiCoO $_2$ and manganese dioxide spinels through omission of the cobalt, whose negative temperature coefficient of resistance can encourage thermal runaway. The P–O bond in the (PO $_4$)$^{3−}$ ion is stronger than the Co–O bond in the (CoO $_2$)$^−$ 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 LiCoO $_2$ cell, the CoO $_2$ undergoes non-linear expansion that affects the structural integrity of the cell. The fully lithiated and unlithiated states of LiFePO $_4$ are structurally similar which means that LiFePO $_4$ cells are more structurally stable than LiCoO $_2$ cells.
No lithium remains in the cathode of a fully charged LFP cell. In a LiCoO $_2$ cell, approximately 50% remains. LiFePO $_4$ is highly resilient during oxygen loss, which typically results in an exothermic reaction in other lithium cells. As a result, LiFePO $_4$ cells are harder to ignite in the event of mishandling (especially during charge). The LiFePO $_4$ battery does not decompose at high temperatures.

### Lower energy density

The energy density (energy/volume) of a new LFP battery as of 2008 was some 14% lower than that of a new LiCoO $_2$ battery. 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.

## Uses
### Home energy storage

Enphase pioneered LFP along with SunFusion Energy Systems LiFePO$_4$ Ultra-Safe ECHO 2.0 and Guardian E2.0 home or business energy storage batteries for reasons of cost and fire safety, although the market remains split among competing chemistries. Though 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 continued to use NMC batteries in its home energy storage products until the release of the Power Wall 3 in 2023. Tesla utility-scale batteries switched to using LFP in 2021. According to EnergySage the most frequently quoted home energy storage battery brand in the U.S. is Enphase, which in 2021 surpassed Tesla Motors and LG.

### Vehicles

Higher discharge rates needed for acceleration, lower weight and longer life makes this battery type ideal for forklifts, bicycles and electric cars. Twelve-volt LiFePO$_4$ batteries are also gaining popularity as a second (house) battery for a caravan, motor-home or boat.
Tesla Motors uses LFP batteries in all standard-range Models 3 and Y made after October 2021 except for standard-range vehicles made with 4680 cells starting in 2022, which use an NMC chemistry.
As of September 2022, LFP batteries had increased its market share of the entire EV battery market to 31%. Of those, 68% were deployed by two companies, Tesla and BYD.
Lithium iron phosphate batteries officially surpassed ternary batteries in 2021 with 52% of installed capacity. Analysts estimate that its market share will exceed 60% in 2024.
In February 2023, Ford announced that it will be investing $3.5 billion to build a factory in Michigan that will produce low-cost batteries for some of its electric vehicles. The project will be fully owned by a Ford subsidiary, but will use technology licensed from Chinese battery company Contemporary Amperex Technology Co., Limited (CATL).

### 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 (compared to NiMH/NiCd) 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 LiFePO $_4$ can be connected to photovoltaic cells without circuitry to halt the recharge cycle.
By 2013, better solar-charged passive infrared motion detector 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.

### Recreational Vehicles (RV) & Marine

Traditionally, batteries used in RVs and marine applications are sealed lead acid, such as flooded cells, AGM and GEL. With the advancement of LiFePO4 and with higher consumer awareness, LiFePO4 batteries are becoming the norm. RV manufacturers, boat manufacturers along with consumers are using lithium batteries to for both deep cycle and starting applications, such as for lighting, fridges and charging their electronics. One of the major advantages of LiFePO4 over lead batteries is of course their cycle life, but also their useable capacity. Lead batteries have a useable capacity of about 50% while lithium can be fully utilized, saving a lot real-estate in the RV. Gone are the days where you need 10 heavy batteries to run your RV full-time!

### Other uses

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

## Recent developments

* LFP batteries can be improved by using a more stable material as the separator. Disassembly of overheated LFP cells found a brick-red compound. This suggested that the separator suffered molecular breakdown, in which side-reactions consumed lithium ions so they could not be shuttled.
* Three-electrode batteries have emerged that let external devices detect that internal shorts have formed.