Lithium iron phosphate

Lithium iron phosphate (LiFePO₄) is a compound salt with an olivine (LiMPO₄) structure that has a particular application in battery cathodes. The substance was first reported in the chemical literature by Ralph P. Santoro and Robert E. Newnham at MIT (Cambridge, MA) in a 1966 US Air Force Materials Laboratory survey of magnetoelectric materials. The following year, the same authors described the magnetic structure of LiFePO₄, which showed that it is antiferromagnetic.

In a 2009 article, Dragana Jugović* and Dragan Uskoković at the Institute of Technical Sciences of the Serbian Academy of Sciences and Arts (Belgrade) reviewed procedures for preparing LiFePO₄ powders for use in batteries. The compound occurs in nature as the mineral triphylite¹, but that source lacks the purity required for battery applications.

Hundreds of technical articles have explored the use of LiFePO₄ in cathodes. In an example this month, Yitao He*, Xiaoxiang Shen, and Yaohui Zhang* at Anhui University of Technology (Ma’anshan) and Harbin Institute of Technology (both in China) reviewed the use of nanosized LiFePO₄ and other cathode salts in layered 2-D batteries. The authors explained how the nanomaterials enhance battery performance.

The recycling and reuse of battery materials is highly desirable. Also this month, Lei Song, Hairong Yue, and co-workers at Sichuan University (Chengdu, China) proposed a two-step process for recycling LiFePO₄ in spent cathodes:

1. In an acid-free system, lithium is leached from the cathode using potassium persulfate² (K₂S₂O₈) as the leaching agent. K₂S₂O₈ also oxidizes the iron to iron(III) phosphate³ (FePO₄).
2. The residual carbon⁴ in the leaching residue is used to reduce FePO₄ to iron(II) pyrophosphate⁵ (Fe₂P₂O₇), which is a component of some battery anodes.

LiFePO₄ is used in ≈30% of lithium-ion batteries in electric vehicles, increasing the demand for the compound. In September 2023, LG Chem (Seoul, South Korea) and Huayou Group (Tongxian, China) announced a plan to build a LiFePO₄ cathode materials plant in Morocco. The plant is expected to produce enough material for 500,000 EV batteries annually when it starts up in 2026.

This Earth Week, join your fellow chemists to celebrate batteries!

1. CAS Reg. No. 13816-45-0.
2. CAS Reg. No. 7727-21-1.
3. CAS Reg. No. 10045-86-0.
4. The carbon sources are the poly(vinylidene fluoride) binder and the conductive carbon in the cathode.
5. CAS Reg. No. 15600-46-1.