Past and Present of LiFePO4: From Fundamental Research to Industrial Applications

In this overview, we go over the past and present of lithium iron phosphate (LFP) as a successful case of technology transfer from the research bench to commercialization. The evolution of LFP technologies provides valuable guidelines for further improvement of LFP batteries and the rational design of next-generation batteries. In this overview, we go over the past and present of lithium iron phosphate (LFP) as a successful case of technology transfer from the research bench to commercialization. The evolution of LFP technologies provides valuable guidelines for further improvement of LFP batteries and the rational design of next-generation batteries. As an emerging industry, lithium iron phosphate (LiFePO4, LFP) has been widely used in commercial electric vehicles (EVs) and energy storage systems for the smart grid, especially in China. Recently, advancements in the key technologies for the manufacture and application of LFP power batteries achieved by Shanghai Jiao Tong University (SJTU) and BYD won the State Scientific and Technological Progress Award of China. This indicates that China has become the global leader in the manufacture and application of LFP power batteries. The arguments on the choice of cathode materials involving layered Li transition-metal oxides (lithium nickel manganese cobalt oxide [NMC] or lithium nickel cobalt aluminum oxide [NCA]), spinel Mn oxides, or olivine-type LFPs, as well as the intellectual-property disputes in LFP technologies, have never ended throughout the past decades. The reduction or even cancellation of government subsidies for EVs has recently called for the optimization of battery technologies in terms of energy density, cycle life, safety, and cost. The cost advantage of LFP over NCM and NCA lies in the earth-abundant elements (Fe and P) present in the former, in contrast to the more expensive Ni and Co in the latter two. In addition to the distinct advantages of cost, safety, and durability, LFP has reached an energy density of >175 and 125 Wh/kg in battery cells and packs, respectively. Thus, the application of LFP power batteries in energy storage systems and EVs (e.g., buses, low-speed EVs, and other specialized vehicles) will continue to flourish. Further advancements in LFP technologies will ensure its indispensable market and prolonged prosperity among various batteries, as in the case of the lead-acid battery. Herein, we go over the past and present of LFP, including the crystal structure characterization, the electrochemical process of the extraction and insertion of Li+, and the large-scale application in high-power Li-ion batteries (Figure 1). Extensive efforts from physicists, chemists, materials scientists, and engineers have been devoted to the research and development of LFP. As a successful case of technology transfer from the research bench to commercialization, this overview on the evolution of LFP technologies provides valuable insights for other research and should help guide us in the quest for next-generation batteries. LiFePO4 was first discovered in 1950 by Destenay1Geller S. Durand J.L. Refinement of the structure of LiMnPO4.Acta Crystallogr. 1960; 13: 325-331Crossref Google Scholar in the minerals triphylite and lithiophilite, where the Li orthophosphates of divalent Fe and Mn formed a solid solution series isomorphous with olivine. In 1957, John M. Mays2Mays J.M. Second-nearest-neighbor nuclear magnetic resonance shifts in iron group phosphates.Phys. Rev. 1957; 108: 1090-1091Crossref Scopus (8) Google Scholar from Bell Telephone Laboratories first reported the behavior of the second-nearest-neighbor NMR shifts in a number of iron-group phosphates as a function of temperature on the basis of the original measurements on mineral specimens of lithiophilite, and he proposed that the LiMPO4 (M = Mn, Fe, Co) compounds undergo antiferromagnetic or ferromagnetic transitions above He temperatures. As confirmed by three-dimensional X-ray diffraction, the crystal structure of LiMPO4 (M = Mn, Fe, Co) belongs to the space group D-Pnma (Z = 4), where the transition-metal ions occupy the mirror symmetry sites. In the 1960s, the research focused on the anisotropy in magnetic properties and electronic structures of single-crystal LiFePO4. Mercier et al. from Université de Grenoble reported the growth of single crystals of LiMPO4 (M = Mn, Co, Ni, Fe) via a flux method3Mercier M. Gareyte J. Un nouveau corps magneto-electrique: LiMnPO4.Solid State Commun. 1967; 5: 139-142Crossref Scopus (16) Google Scholar and identified the isostructural transition-metal Li orthophosphates (LiMPO4) as magnetoelectric systems. Then, Santoro et al.4Santoro R.P. Newnham R.E. Antiferromagnetism in LiFePO4.Acta Crystallogr. 1967; 22: 344-347Crossref Google Scholar from the Massachusetts Institute of Technology (MIT) studied the magnetic structure and magnetic susceptibility of LFP. The synthetic LFP was first prepared from the solid-state reaction:4Santoro R.P. Newnham R.E. Antiferromagnetism in LiFePO4.Acta Crystallogr. 1967; 22: 344-347Crossref Google Scholar2Fe3(PO4)2⋅8H2O + 2(NH4)2HPO4 + 3Li2CO3 → 6LiFePO4 + 19H2O↑ + 3CO2↑ + 4NH3↑ The petroleum crisis in the early 1970s triggered extensive research in energy storage technologies, and the Li-ion battery (LIB) is the hottest and most widely used one. Whittingham introduced the first LIB (Li-Al/TiS2 cell)5Winter M. Barnett B. Xu K. Before Li ion batteries.Chem. Rev. 2018; https://doi.org/10.1021/acs.chemrev.8b00422Crossref PubMed Scopus (1087) Google Scholar with the reversible accommodation of Li+ in transition-metal dichalcogenides (TiS2). The successful commercialization of the LIB was realized by the discovery of transition-metal oxides as new cathode materials. Goodenough and co-workers6Mizushima K. Jones P.C. Wiseman P.J. Goodenough J.B. LixCoO2 (04.0 V versus Li/Li+). In 1996, Goodenough and co-workers revealed the electrochemical extraction and insertion of Li from LiFePO4.7Padhi A.K. Nanjundaswamy K.S. Goodenough J.B. Phospho-olivines as positive-electrode materials for rechargeable lithium batteries.J. Electrochem. Soc. 1997; 144: 1188-1194Crossref Scopus (6900) Google Scholar Because of the low cost and high safety of LFP, extensive efforts have been devoted to enhancing their intrinsic low conductivity since then, and there have been numerous attempts to develop new approaches for the large-scale production of LFP. Particularly, various strategies for the synthesis of nanometric LFP with enhanced conductivity and/or specific capacity were reported in the past decades.8Chung S.Y. Bloking J.T. Chiang Y.M. Electronically conductive phospho-olivines as lithium storage electrodes.Nat. Mater. 2002; 1: 123-128Crossref PubMed Scopus (2780) Google Scholar Carbon coating was demonstrated to be the most efficient way to improve the conductivity and rate performance of LFP. In the meanwhile, a variety of LFP battery manufacturers (such as BYD and A123 Systems) emerged and promoted the engineering application of LFP. The advantages in effectiveness, practicality, and economics of new technologies are indispensable for their widespread applications. Similarly, designing a cost-effective production process with controlled quality is critical for the commercialization of LFP batteries. Instead of the widely used P ((NH4)2HPO4 or Fe3(PO4)2) and Fe (Fe(CH3CO2)2) sources, we proposed a novel synthetic route using ferric FePO4: Fe + 2FePO4 + Li3PO4⋅0.5H2O → 3LiFePO4 + 0.5H2O.9Liao X.Z. Ma Z.F. Wang L. Zhang X.M. Jiang Y. He Y.S. A novel synthesis route for LiFePO4/C cathode materials for lithium-ion batteries.Electrochem. Solid-State Lett. 2004; 7: 522-525Crossref Scopus (81) Google Scholar This new process is greener than other reported synthetic routes of LFP (Table 1)10Chang H.H. Chang C.C. Wu H.C. Guo Z.Z. Yang M.H. Chiang Y.P. Sheu H.S. Wu N.L. Kinetic study on low-temperature synthesis of LiFePO4 via solid state reaction.J. Power Sources. 2006; 158: 550-556Crossref Scopus (38) Google Scholar in terms of atom economy. Moreover, it eliminates the release of hazardous gas, including NH3, CO, or NOx, which in turn reduces the investments in gas purification systems.Table 1Synthesis Processes for LiFePO4Starting MaterialsCalcination ConditionsContributorLi SourceP SourceFe SourceLi2CO3(NH4)2HPO4Fe3(PO4)2·8H2O800°C for 48 hr in N2MIT (1967)Li2CO3(NH4)2HPO4Fe(CH3CO2)2800°C for 24 hr in ArGoodenough (1997)Li2CO3(NH4)2HPO4FeC2O4·2H2O800°C for 36 hr in N2Sweden (2000)Li3PO4Fe3(PO4)2·5H2O_hydrothermal and 550°C for 15 min in N2France (2002)Li3PO4Fe3(PO4)2·8H2O–700°C for 7 hr in ArSweden (2003)LiNO3(NH4)2HPO4Fe3(NO3)3·9H2O750°C for 12 hr in ArKomaba (2004)LiClH3PO4FeCl2·4H2O700°C for 12 hr in N2Nazar (2001)Li2CO3NH4H2PO4Fe(CH3CO2)2550°C for 24 hr in N2Sony (2001)Li2CO3Fe[(C6H5PO3)(H2O)]–>600°C for >16 hr in N2Italy (2004)Li2CO3NH4H2PO4FeC2O4·2H2O600°C and –800°C in ArMIT and A123 Systems (2002)Li(Ac)H3PO4Fe3(NO3)3·9H2Osol-gel 500°C for 10 hr in N2 and 600°C for 10 hr in N2Lawrence Berkeley National Laboratory (2004)LiH2PO4–Fe2O3750°C for 8 hr in ArValance (2003)Li3PO4·H2OFePO4FePO4, Fe600°C for 30 min in ArSJTU and Ma (2004) Open table in a new tab As one of the leading manufacturers of LFP batteries, BYD has devoted extensive efforts to the design and manufacture of LFP batteries since 2003 and achieved a single-cell capacity of more than 200 Ah to date. The global sales volume of EVs and hybrid EVs with LFP batteries as power sources is over 1,000,000 now. In 2009, BYD and SJTU started a joint project on LFP-battery-based energy storage systems. A highly efficient battery management system was developed on the basis of the precise prediction model of the state of charge and state of health of the LIB. From the discovery of LFP to the widespread application of the LFP battery, we noticed that this new technology was not born at a single “eureka” moment but developed gradually through the constant exploration and practice of numerous researchers. Thus, this short overview of the past and present of LFP provides valuable guidelines for further improvement of LFP batteries and the rational design of next-generation batteries.