Lithium iron phosphate
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iron(2+) lithium phosphate (1:1:1)
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Lithium iron phosphate (LiFePO
4), also known as LFP, is a compound used in lithium iron phosphate batteries (related to Li-Ion batteries). It is targeted for use in power tools, electric vehicles and solar energy installations. It is also used in OLPC XO education laptops.
Most lithium batteries (Li-ion) used in 3C (computer, communication, consumer electronics) products use cathodes of other lithium molecules, such as lithium cobalt oxide (LiCoO2) lithium manganese oxide (LiMn2O4) and lithium nickel oxide (LiNiO2). The anodes are generally made of carbon.
The annual production of lithium carbonate available to the automotive industry is estimated at only 30,000 tonnes in 2015. While a natural lithium iron phosphate mineral exists (triphylite) issues with purity and structure make it unsuitable for use in batteries.
4 is a member of the olivine group, which has a general chemical formula of LiMPO4, where M refers to any metal, including Fe, Co, Mn and Ti. The first commercial LiMPO4 was C/LiFePO
4 and therefore, people refer to the whole group of LiMPO4 as lithium iron phosphate, LiFePO
4. However, more than one olivine compound may be used as a battery's cathode material. Olivine compounds such as AyMPO4, Li1-xMFePO4, and LiFePO
4-zM have the same crystal structures as LiMPO4 and may replace in a cathode. All may be referred to as “LFP”.
4 became a candidate for use in batteries in 1996 when Akshaya Padhi demonstrated the reversible extraction of lithium from LiFePO
4 and insertion of lithium into FePO4.
Physical and chemical properties
It is gray, red-grey, brown or black.
4 lithium has +1 valence, iron has +2 valence and phosphate has -3 valence.
The iron atom and 6 oxygen atoms form a corner-shared octahedron - FeO6 - with the iron atom in the center. The phosphorus atom with the four oxygen atoms forms an edge-shared tetrahedron - PO4 - with phosphorus in the center. A zigzag three-dimensional framework is formed by FeO6 octahedra sharing common-O corners with PO4 tetrahedra. Lithium ions reside within the octahedral channels in a zigzag structure. In the lattice, FeO6 octahedra are connected by sharing the corners of the bc face.[clarification needed][clarification needed] LiO6 groups form a linear chain of edge-shared octahedra parallel to the b axis. A FeO6 octahedron shares edges with two LiO6 octahedra and one PO4 tetrahedron. In crystallography, this structure is thought to be the Pmnb space group of the orthorhombic crystal system. The lattice constants are: a=6.008A, b=10.334A, and c=4.693A. The volume of the unit lattice is 291.4 A3. The phosphates of the crystal stabilize the framework and give LFP thermal stability and cycling performance.
Different from the two traditional cathode materials - LiMnO4 and LiCoO2, lithium ions of LiMPO4 move in the lattice's one-dimensional free volume. During charge/discharge, the lithium ions are extracted from/inserted into LiMPO4 while the central iron ions are oxidized/reduced. This extraction/insertion process is reversible.
The insertion/extraction reaction of the lithium ions is
LiFe(II)PO4 <-> Fe(III)PO4 + Li + e- (1)
Extracting lithium from LiFePO
4 produces FePO4 with a similar structure. FePO4 has a Pmnb space group.[clarification needed] Its lattice constants are a=5.792A, b=9.821A and c=4.788A. The volume of the unit lattice is 272.4 A3. Extraction of lithium ions reduces the lattice volume, as is the case with lithium oxides. LiMPO4's corner-shared FeO6 octahedra are separated by the oxygen atoms of the PO43- tetrahedra and cannot form a continuous FeO6 network, reducing conductivity.
A nearly close-packed hexagonal oxygen atom array provides a relatively small free volume for lithium ion motion and therefore lithium ions in the lattice have small migration speeds at ambient temperate. During charge, lithium ions and corresponding electrons are extracted from the structure and a new phase of FePO4 and a new phase interface forms. During discharge, lithium ions and the corresponding electrons are reinserted into the structure and LiMPO4 forms. Hence, the lithium ions of spherical cathode particles go through an inward or an outward structural phase transition. A critical step of charge and discharge is the formation of the phase interface between LixFePO4 and Li1-xFePO4. As the insertion/extraction of lithium ions proceeds, the surface area of the interface shrinks. When a critical surface area is reached, the electrons and ions of the resulting FePO4 have low conductivity and two-phase structures are formed. Thus, LiMPO4 at the center of the particle is not fully consumed, especially under the condition of large discharge current.
The lithium ions have high diffusion constants. The olivine structures experiencing charge and discharge remain stable and the iron atom continues to reside in the center of the octahedron giving LiMPO4 good cycling performance. During a charge, the iron atom in the center of the octahedron has a high spin state.[clarification needed]
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LFP's major commercial advantages are that it does not have safety concerns such as overheating and explosion, has 4 to 5 times longer cycle lifetimes, 8 to 10 times higher power density and has a wider operating temperature range.
Power plants use LFP.
LFP has strong oxygen covalent bonds and does not explode following a short-circuit, a key advantage for transportation applications.
According to US Advanced Automotive Battery (AAB) statistics, one of 70,000 hybrid vehicles (PHEV, HEV, BEV) using batteries containing cobalt or manganese will experience battery explosions if they have the same incidence rate as the lithium batteries of notebooks and cell phones.
BAE has announced that their HybriDrive Orion 7 hybrid bus uses about 180KW LFP battery cells. US company AES has developed multi-trillion watt battery systems that are capable of subsidiary services of the power network, including spare capacity and frequency adjustment.
In recent years he discovered that when adding the expensive conductive polymers in the lithium iron phosphate (LFP), the grams capacity 166Ah/g of LFP can be made in the laboratory, and then microwaved it to speed up the ceramic powder process.
In China, battery manufacturers BAK and Tianjin Lishen announced their plans for LFP factories to have annual outputs of 20,000,000 batteries, to be completed in 2008-2009 with an investment of 600 million dollars.
Although LFP has 25% less capacity than other lithium batteries due to its material structure, it has 70% more than nickel-hydrogen batteries.
The major differences between LFP batteries and ordinary lithium batteries are that LFP batteries do not have safety concerns such as overheating and explosion, that they have 4 to 5 times longer cycle lifetimes than the lithium batteries 8 to 10 times higher discharge power and 30 to 50% less weight.
LFP batteries have drawbacks including higher costs given less time on the learning curve. The energy density is significantly lower than LiCoO2 (although higher than the nickel-metal hydride battery).
Lithium cobalt oxide has multiple disadvantages. It is one of the more expensive components of traditional li-ion batteries. The cobalt in LiCoO2 is listed as a possible human carcinogen by IARC. LiCoO2 can experience problems with runaway overheating and outgassing, particularly in lithium polymer battery packs.
LFP batteries do not need the sophisticated charge monitoring in traditional li-ion, but still benefit from balance charging on a regular basis, especially in repeated high-current discharge rate uses like electric-powered flying model aircraft.
The root patents of LFP compounds are held by three companies: Li1-xMFePO4 by A123, LiMPO4 by Phostech and LiFePO
4 • zM by Aleees. These patents underly mature mass production technologies. The largest production capacity is up to 250 tons per month. The key feature of Li1-xMFePO4 from A123 is the nano-LFP, which modifies its physical properties and adds noble metals in the anode, as well as the use of special graphite as the cathode.
The main feature of LiMPO4 from Phostech is increased capacitance and conductivity by an appropriate carbon coating. The special feature of LiFePO
4 • zM from Aleees a high capacitance and low impedance obtained by the stable control of the ferrites and crystal growth. This improved control is realized by applying strong mechanical stirring forces to the precursors in high oversaturation states, which induces crystallization of the metal oxides and LFP.
In patent lawsuits in the US in 2005 and 2006, the University of Texas-Austin and Hydro-Québec claimed that LiFePO
4 as the cathode infringed their patents, US 5910382 and US 6514640 . The patent claims involved a unique crystal structure and a chemical formula of the battery cathode material.
On April 7, 2006, A123 filed an action seeking a declaration of non-infringement and invalidity UT's patents. A123 separately filed two ex parte Reexamination Proceedings before the United States Patent and Trademark Office (USPTO), in which they sought to invalidate the patents based upon prior art.
In a parallel court proceeding, UT sued Valence Technology, Inc. ("Valence") - a company that commercializes LFP products that alleged infringement.
The USPTO issued a Reexamination Certificate for the '382 patent on April 15, 2008 and for the '640 patent on May 12, 2009, by which the claims of these patents were amended. This allowed the current patent infringement suits filed by Hydro-Quebec against Valence and A123 to proceed. After a markman hearing, on April 27, 2011 the Western District Court of Texas held that the claims of the reexamined patents had a narrower scope than as originally granted.
On Dec 9th, 2008, the European Patent Office revoked Dr. Goodenough’s patent numbered 0904607. This decision basically reduced the patent risk of using LFP in European automobile applications. The decision is believed to be based on the lack of novelty.
The first major large settlement was the lawsuit between NTT and the University of Texas-Austin (UT). In October 2008, NTT announced that they would settle the case in the Japan Supreme Civil Court for $30 million. As part of the agreement UT agreed that NTT did not steal the information and that NTT would share its LFP patents with UT. NTT’s patent is also for an olivine LFP, with the general chemical formula of AyMPO4 (A is for alkali metal and M for the combination of Co and Fe), now used by BYD Company. Although chemically the materials are nearly the same, from the viewpoint of patents, AyMPO4 of NTT is different from the materials covered by UT. AyMPO4 has higher capacity than LiMPO4. At the heart of the case was that NTT engineer Okada Shigeto, who had worked in the UT labs developing the material, was accused of stealing UT’s intellectual property.
LFP has two shortcomings: low conductivity and low lithium diffusion constant, both of which limit the charge/discharge rate. Adding conducting particles in delithiated FePO4 raises its electron conductivity. For example, adding conducting particles with good diffusion capability like graphite and carbon  to LiMPO4 powders significantly improves conductivity between particles, increases the efficiency of LiMPO4 and raises its reversible capacity up to 95% of the theoretical values. LiMPO4 shows good cycling performance even under charge/discharge current as large as 5C.
Coating LFP with inorganic oxides can make LFP’s structure more stable and increase conductivity. Traditional LiCoO2 with oxide coating shows improved cycling performance. This coating also inhibits dissolution of Co and slows the decay of LiCoO2 capacity. Similarly, LiMPO4 with an inorganic coating such as ZnO and ZrO2, has a better cycling lifetime, larger capacity and better characteristics under rapid discharge. The addition of a conductive carbon increases efficiency. Mitsui Zosen and Aleees reported that addition of conducting metal particles such as copper and silver increased efficiency. LiMPO4 with 1 wt% of metal additives has a reversible capacity up to 140mAh/g and better efficiency under high discharge current.
Substituting other metals for the iron or lithium in LiMPO4 can also raise efficiency. Substituting zinc for iron increases crystallinity of LiMPO4 because zinc and iron have similar ion radii. Cyclic voltammetry confirms that LiFe1-xMxPO4, after metal substitution, has higher reversibility of lithium ion insertion and extraction. During lithium extraction, Fe (II) is oxidized to Fe (III) and the lattice volume shrinks. The shrinking volume changes lithium’s returning paths.
Mass production with stable and high quality still faces many challenges.
Similar to lithium oxides, LiMPO4 may be synthesized by the a variety of methods, including: solid-phase synthesis, emulsion drying, sol-gel process, solution coprecipitation, vapor phase deposition, electrochemical synthesis, electron beam irradiation, microwave process, hydrothermal synthesis, ultrasonic pyrolysis and spray pyrolysis. example, in the emulsion drying process, the emulsifier is first mixed with kerosene.
Next, the solutions of lithium salts and iron salts are added to this mixture. This process produces nanocarbon particles. Hydrothermal synthesis produces LiMPO4 with good crystallinity. Conductive carbon is obtained by adding polyethylene glycol to the solution followed by thermal processing. Vapor phase deposition produces a thin film LiMPO4. In flame spray pyrolysis FePO4 is mixed with Lithium carbonate and glucose and charged with electrolytes. The mixture is then injected inside a flame and filtered to collect the synthesized LiFePO4.
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