Electrochemical Behavior of Li5FeO4 (LFO) in Energy Storage Applications

The push for high capacity cathodes capable of Li storage greater than Li/TM (TM=transition metal) ratio of one in Li-ion batteries (LIB) is extremely challenging, but necessary to increase energy densities. The rock-salt layered lithium oxide material, Li 2 MnO 3 , is particularly well studied and can release essentially all of its Li during electrochemical charge on the first cycle yielding over 400 mAh/g (cycled >4.6 V vs. Li metal), but this process is irreversible, and capacity rapidly fades. Recently we have been studying the electrochemical behavior of higher lithium-content containing phase, Li 5 FeO 4 (LFO) (a defect anti-fluorite structure, with large lithium content, Li/Fe = 5), in the following three roles: (1) as a reversible 2.8 to 3.0 V cathode, (2) as a Li-source additive to enable Si anode for LIBs, and (3) as a hybrid Li-ion•Li-O 2 cathode material. 1 As reported by our group, this LFO can provide over 700 mAh/g specific capacity below 4.4 V vs. Li metal 2 which now identifies it as an ideal candidate for a myriad of energy storage applications. This poster highlights the LFO material and addresses the following aspects: (1) synthesis of LFO, (2) electrode fabrication, blends and implementation in LIB full cells. The LFO is particularly effective at full cell cycle improvement due to both elimination of high first cycle irreversible capacity losses (ICL), and cycle-to-cycle inefficiencies. Lastly we will back-up our findings through a number of characterization methods in addition to first principles modeling. For example we make use of novel fast operando Mössbauer spectroscopy in order to decipher the charge compensation and the stability of tetravalent iron (Fe 4+ ) during real-time cycling of Li/LFO pouch cells. All these results taken together have given us ample understanding of the material, its versatility and extreme effectiveness in energy storage. [1] L. Trahey, et al., Electrochem. and Solid State Lett. , 14 , A64 (2011) [2] C. S. Johnson, et al., Chemistry of Materials , 22 , 1263-1270 (2010) This work was supported as part of the Center for Electrochemical Energy Science (CEES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. Use of the Center for Nanoscale Materials, (Raman) The Advanced Photon Source (operando XRD), and the Electron Microscopy Center (SEM) is supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.