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

Synergy

Past and Present of LiFePO4: From Fundamental Research to Industrial Applications Jingkun Li1 and Zi-Feng Ma2,*

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 Destenay1 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. Mays2 from Bell Telephone

1Institut

Charles Gerhardt Montpellier, UMR 5253, Centre National de la Recherche Scientifique, Universite´ Montpellier, E´cole Nationale Supe´rieure de Chimie de Montpellier, Place Euge`ne Bataillon, 34095 Montpellier Cedex 5, France 2Shanghai

Electrochemical Energy Devices Research Center, Department of Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China *Correspondence: [email protected] https://doi.org/10.1016/j.chempr.2018.12.012

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Figure 1. Evolution of LFP Technologies

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 Universite´ de Grenoble reported the growth of single crystals of LiMPO4 (M = Mn, Co, Ni, Fe) via a flux method3 and identified the isostructural transition-metal Li orthophosphates (LiMPO4) as magnetoelectric systems. Then, Santoro et al.4 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:4 2Fe3(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)5 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-workers6 correctly predicted that transition-metal oxides rather than sulfides would not only remain stable at high oxidation states but also provide higher potentials (>4.0 V versus Li/Li+). In 1996, Goodenough and co-workers revealed the electrochemical extraction and insertion of Li from LiFePO4.7 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.8 Carbon coating was demonstrated to be the most efficient way to improve the conductivity and rate performance of LFP. In the meanwhile, a variety

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Table 1. Synthesis Processes for LiFePO4 Starting Materials Li Source

P Source

Fe Source

Li2CO3

(NH4)2HPO4

Fe3(PO4)2$8H2O

Calcination Conditions

Contributor

800 C for 48 hr in N2

MIT (1967)



Li2CO3

(NH4)2HPO4

Fe(CH3CO2)2

800 C for 24 hr in Ar

Goodenough (1997)

Li2CO3

(NH4)2HPO4

FeC2O4$2H2O

800 C for 36 hr in N2

Sweden (2000)

Li3PO4

Fe3(PO4)2$5H2O

_

hydrothermal and 550 C for 15 min in N2

France (2002)

Li3PO4

Fe3(PO4)2$8H2O

–

700 C for 7 hr in Ar

Sweden (2003)



LiNO3

(NH4)2HPO4

Fe3(NO3)3$9H2O

750 C for 12 hr in Ar

Komaba (2004)

LiCl

H3PO4

FeCl2$4H2O

700 C for 12 hr in N2

Nazar (2001)

Li2CO3

NH4H2PO4

Fe(CH3CO2)2

550 C for 24 hr in N2

Sony (2001)

Li2CO3

Fe[(C6H5PO3) (H2O)]

–

>600 C for >16 hr in N2

Italy (2004)

Li2CO3

NH4H2PO4

FeC2O4$2H2O

600 C and –800 C in Ar

MIT and A123 Systems (2002)

Li(Ac)

H3PO4

Fe3(NO3)3$9H2O

sol-gel 500 C for 10 hr in N2 and 600 C for 10 hr in N2

Lawrence Berkeley National Laboratory (2004)

LiH2PO4

–

Fe2O3

750 C for 8 hr in Ar

Valance (2003)

Li3PO4$H2O

FePO4

FePO4, Fe

600 C for 30 min in Ar

SJTU and Ma (2004)

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 costeffective 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.9 This new process is greener than other reported synthetic routes of LFP (Table 1)10 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. 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 nextgeneration batteries.

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1. Geller, S., and Durand, J.L. (1960). Refinement of the structure of LiMnPO4. Acta Crystallogr. 13, 325–331. 2. Mays, J.M. (1957). Second-nearest-neighbor nuclear magnetic resonance shifts in iron group phosphates. Phys. Rev. 108, 1090– 1091. 3. Mercier, M., and Gareyte, J. (1967). Un nouveau corps magneto-electrique: LiMnPO4. Solid State Commun. 5, 139–142. 4. Santoro, R.P., and Newnham, R.E. (1967). Antiferromagnetism in LiFePO4. Acta Crystallogr. 22, 344–347.

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7. Padhi, A.K., Nanjundaswamy, K.S., and Goodenough, J.B. (1997). Phospho-olivines as positive-electrode materials for rechargeable lithium batteries. J. Electrochem. Soc. 144, 1188–1194.

10. Chang, H.H., Chang, C.C., Wu, H.C., Guo, Z.Z., Yang, M.H., Chiang, Y.P., Sheu, H.S., and Wu, N.L. (2006). Kinetic study on low-temperature synthesis of LiFePO4 via solid state reaction. J. Power Sources 158, 550–556.