Sung-Wook Kim

Ternary metal fluorides as high-energy cathodes with low cycling hysteresis

Transition metal fluorides are an appealing alternative to conventional intercalation compounds for use as cathodes in next-generation lithium batteries due to their extremely high capacity (3–4 times greater than the current state-of-the-art). However, issues related to reversibility, energy efficiency and kinetics prevent their practical application. Here we report on the synthesis, structural and electrochemical properties of ternary metal fluorides (M1yM21-yFx: M1, M2=Fe, Cu), which may overcome these issues. By substituting Cu into the Fe lattice, forming the solid–solution CuyFe1-yF2, reversible Cu and Fe redox reactions are achieved with surprisingly small hysteresis (<150u2009mV). This finding indicates that cation substitution may provide a new avenue for tailoring key electrochemical properties of conversion electrodes. Although the reversible capacity of Cu conversion fades rapidly, likely due to Cu+ dissolution, the low hysteresis and high energy suggest that a Cu-based fluoride cathode remains an intriguing candidate for rechargeable lithium batteries.

Bio-Inspired Synthesis of Electrode Materials for Lithium Rechargeable Batteries

Human history has been made through endless challenges, searching for universal truths of nature. Sometimes, nature becomes a crucial barrier that human beings should overcome, however, repeatedly, it inspires us to make progress in science and results in a better life. Nature always provides pointers in developing technologies; emulating nature serves as a very helpful methodology for such development (Bensaude-Vincent et al., 2002). Figure 1 shows some examples of creations that were invented through the emulation of nature. Especially, living organisms are excellent teachers whose metabolism, vital activity, and growth present novel synthetic routes for the formation of organic (or inorganic) biomaterials (Sanchez et al., 2005). The study of on the biomaterials, highly ordered forms of molecules in a biological system with complex nanostructures, has opened up a new era for fabricating nanomaterials through the emulation of biological processes (Dickerson et al., 2008). This chapter briefly introduces the bio-inspired synthetic routes of nanostructured electrode materials for lithium (Li) rechargeable batteries using biomaterials as structural templates. Various biomaterials have been synthesized both naturally, i.e., inside living bodies (in vivo), and intentionally in the laboratory (in vitro), (Sanchez et al., 2005; Dickerson et al., 2008). One can synthesize biomaterials that possess unique nanostructures without much difficulty. By controlling the synthesis conditions, the nanostructure of biomaterials can be varied from a simple 0-D structure to complex 3-D structures (Lv et al., 2008). The unique nanostructures of the biomaterials can be applied to various research fields, including not only bio-applications but also non-bio-applications such as semiconductors, display devices, catalysts, and energy conversion/storage devices, by hybridizing them with various functional materials at the nanoscale (Katz et al., 2004; Su et al., 2008; Li et al., 2009). As the minimizing of a material’s dimension in a certain shape often provides distinctive material properties due to a large surface-to-volume ratio, geometry, and/or quantum effects, This could lead to breakthroughs in overcoming the limitations of conventional bulk materials (Moriarty, 2001). Thus, the hybridization of nanostructured biomaterials with functional materials frequently offers improved material properties under simple nanofabrication principles.