Kisuk Kang

Fabrication of FeF3 Nanoflowers on CNT branches and their application to high power lithium rechargeable batteries.

Growing interest in electric vehicles, storage of energy from renewable sources, and load-leveling has positioned Li rechargeable batteries at the center of great attention, as they provide outstanding performance in terms of energy storage. [ 1 , 2–6 ] In the past decade, Li rechargeable battery technology has monopolized portable electric device markets such as mobile phones and laptop computers. However, further research on battery performance is still necessary for new applications such as electric vehicles and large scale power storage systems. [ 2–5 ] In essence, new technologies require electrodes with higher energy and power density to store and deliver more energy faster . Therefore, the development of new electrode materials that meet the requirements mentioned above is of utmost importance. Since the pioneering work of Tarascon and coworkers revealed a new strategy for high capacity electrodes by demonstrating that metal oxides can store more than one Li ion per transition metal atom through conversion reaction, [ 7 ] many researchers have investigated various conversion reaction compounds, such as metal nitrides, [ 8,9 ] sulfi des, [ 10,11 ] fl uorides, [ 12–16 ]

Structural evolution of layered Li1.2Ni0.2Mn0.6O2 upon electrochemical cycling in a Li rechargeable battery

Recently Li1.2Ni0.2Mn0.6O2, one of the most promising cathode candidates for next generation Li rechargeable batteries, has been consistently investigated especially because of its high lithium storage capacity, which exceeds beyond the theoretical capacity based on conventional chemical concepts. Yet the mechanism and the origin of the overcapacity have not been clearly understood. Previous reports on simultaneous oxygen evolution during the first delithiation may only explain the high capacity of the first charge process, and not of the subsequent cycles. In this work, we report a clarified interpretation of the structural evolution of Li1.2Ni0.2Mn0.6O2 upon the electrochemical cycling, which is the key element in understanding its anomalously high capacity, through careful study of electrochemical profiles, exsitu X-ray diffraction, HR-TEM, Raman spectroscopy, and first principles calculation. Moreover, we successfully resolved the intermediate states of structural evolution upon electrochemical cycles by intentionally synthesizing sample with large particle size. All observations made through various tools lead to the result that spinel-like cation arrangement and lithium environment are gradually created and locally embedded in layered framework during repeated electrochemical cycling. Moreover, through analyzing the intermediate states of the structural transformation, this gradual structural evolution could explain the mechanism of the continuous development of the electrochemical activity below 3.5 V and over 4.25 V.

Influence of carbon towards improved lithium storage properties of Li2MnSiO4 cathodes

Superior lithium storage in Li2MnSiO4 cathodes was observed by altering carbon content during the formulation of electrodes. Initially, Li2MnSiO4 was prepared by a conventional solid-state reaction at 900 °C under Ar flow with a fixed amount of adipic acid, which acts as a gelating agent during synthesis. The phase formation was confirmed through powder X-ray diffraction measurements. Scanning electron microscope pictures indicate the particulate morphology of synthesized Li2MnSiO4 particles. Various compositions of electrodes were formulated using the conducting carbon (ketjen black) from 3 to 11 mg along with active material. All the fabricated electrodes were cycled in a Li/Li2MnSiO4 cell configuration to evaluate its lithium storage performance at 0.05 C rate. Among the electrodes, 42% carbon in the composite electrode exhibited a very stable discharge behaviour ∼140 mA h g−1 for 40 cycles at room temperature. Such storage performance was ascribed to the improved electronic conductivity of Li2MnSiO4 electrodes by incorporating carbon. This improvement was supported by electrochemical impedance spectroscopy measurements. Rate performance studies were also conducted and presented in the manuscript.

Mineralization of Self‐assembled Peptide Nanofibers for Rechargeable Lithium Ion Batteries

S.-W.K and J. R. contributed equally to this work. This study was supported by grants from the National Research Foundation (NRF) National Research Laboratory (R0A-2008-000-20041-0; C. B. P.), Engineering Research Center (2008-0062205; C. B. P.), Converging Research Center (2009-0082276; C. B. P.), and WCU (31-2008-000-10055-0; K. K.) nprograms. This research was supported by Energy Resource Technology RD K. K.) funded by the Ministry of Knowledge Economy, Republic of Korea. This work was also supported nby the National Research Foundation (NRF) Grant funded by the Korean Government (MEST) (NRF-2009-0094219; K. K.).

Phase Stability Study of Li1-xMnPO4 (0 ≤ x ≤ 1) Cathode for Li Rechargeable Battery

The phase stability of Li 1-x MnPO 4 (0≤x≤ 1) is investigated in this study for different Li compositions and temperatures by high temperature X-ray diffraction and electron microscopy. The map of stable phases is determined at temperature ranges between room temperature and 410°C. While pure LiMnPO 4 phase is stable at high temperature, partial phase transformation of MnPO 4 into Mn 2 P 2 O 7 is observed in delithiated phases above 210°C. Electron microscopy study also indicates the instability of the delithiated phase. The morphology of LiMnPO 4 is severely damaged upon delithiation. The instability of the delithiated phase and the phase transformation into Mn 2 P 2 O 7 may imply that safety concerns can be raised regarding the LiMnPO 4 cathode, unlike its Fe counterpart.

Simple Preparation of High-Quality Graphene Flakes without Oxidation Using Potassium Salts

Graphene is a 2D sheet of sp 2 -hybridized carbon with interesting properties, including exceptionally high thermal/electrical conductivity, surface area, and mechanical strength. [ 1–5 ] Many fabrication methods have been proposed to obtain graphene so as to utilize these interesting properties. The approaches to fabricate graphene can be roughly categorized into two classes: i) top-down exfoliation of multilayer graphene or graphite by breaking pi-bonding between carbon atoms, [ 6–10 ] and ii) bottom-up formation of sp 2 -bonding between carbon atoms in a monolayer. [ 11–16 ] Mechanical and chemical exfoliation methods fall into the fi rst category, while chemical vapor deposition (CVD) and epitaxial growth from silicon carbide (SiC) belong to the second. Flake-types of graphene promise potential applications in the fi elds of transparent electrodes, energy storage, electromagnetic (EM) shields, etc. [ 17–19 ] Dispersed graphene fl akes are mostly produced by a chemical exfoliation method, through chemical oxidation and reduction, known as Hummers’ method. [ 20 ] Hummers’ method is a lowcost process applicable to mass production. However, the quality of the achieved graphene is often below desired levels, mainly due to the presence of residual oxygen, even after a suffi cient reduction process. [ 21 ] Here, we fi rstly introduce a new method to acquire high-quality graphene fl akes by simply using metal salts without oxidation. Graphite intercalation compounds (GICs) are typically formed by the insertion of atomic or molecular species, called intercalants, between layers in a graphite host. The formation of GICs has been an active fi eld of research especially in relation to lithium ion batteries because graphite can store a large amount

Mg and Fe Co-doped Mn Based Olivine Cathode Material for High Power Capability

Here we demonstrate that the electrochemical properties of Mn based olivine cathode materials can be significantly improved by small amount of co-dopants, Fe and Mg. While nucleation and growth are important in determining the kinetics of a two-phase reaction based olivine electrode, the presence of Fe and Mg in LiMnPO 4 framework notably enhances the power capability of a LiMnP0 4 electrode providing multiple nucleation sites. The electrochemical activity of an Fe―Mg co-doped Mn olivine cathode material measured by galvanostatic charge/discharge indicates that a discharge capacity of about 140 mAh g ―1 can be obtained at a C/5 rate and this high capacity is retained at even higher current rates (110 mAh g ―1 at 3C), which has yet to be achieved in LiMnPO 4 without nucleation enhancers.

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.