Goojin Jeong

Prospective materials and applications for Li secondary batteries

Li-ion batteries have been employed successfully in various small electronic devices for the last two decades, and the types of applications are currently expanding to include electric vehicles (EVs), power tools, and large electric power storage units. In order to be implemented in these emerging markets, novel materials for negative and positive electrodes as well as electrolytes need to be developed to achieve high energy density, high power, and safe lithium rechargeable batteries. Here, the trends of the market and development of materials for each application are introduced, and some of next generation Li-ion batteries are discussed.

Quartz (SiO2): a new energy storage anode material for Li-ion batteries

SiO2 is one of the most abundant materials on Earth. It is cost-effective and also environmentally benign when used as an energy material. Although SiO2 was inactive to Li, it was engineered to react directly by a simple process. It exhibited a strong potential as a promising anode for Li-ion batteries.

Core-shell structured silicon nanoparticles@TiO2-x/carbon mesoporous microfiber composite as a safe and high-performance lithium-ion battery anode.

A core-shell structured Si nanoparticles@TiO2-x/C mesoporous microfiber composite has been synthesized by an electrospinning method. The core-shell composite exhibits high reversible capacity, excellent rate capability, and improved cycle performance as an anode material for Li-ion batteries. Furthermore, it shows remarkable suppression of exothermic behavior, which can prevent possible thermal runaway and safety problems of the cells. The improved electrochemical and thermal properties are ascribed to the mechanically, electrically, and thermally robust shell structure of the TiO2-x/C nanocomposite encapsulating the Si nanoparticles, which is suggested as a promising material architecture for a safe and reliable Si-based Li-ion battery of high energy density.

Characterizations and electrochemical behaviors of disproportionated SiO and its composite for rechargeable Li-ion batteries

Commercially available solid SiO is composed of amorphous Si with silicon suboxides of various valence states. Solid SiO is thermodynamically unstable at all temperatures, which would disproportionate to Si and SiO2. Disproportionation of SiO at several temperatures was characterized with various analytical techniques, such as XRD, XPS, NMR and HRTEM methods, and it was found that the sample heat treated at 1000 °C contained well-developed Si nanocrystals uniformly dispersed within an amorphous SiOx matrix. Using this sample, a nano-Si/SiOx/graphite composite was obtained by a straightforward high-energy mechanical milling technique. The nano-Si/SiOx/graphite composite was tested as an anode material for Li secondary batteries, and showed better electrochemical behaviors than those of pure SiO.

Zr4+ Doping in Li4Ti5O12 Anode for Lithium‐Ion Batteries: Open Li+ Diffusion Paths through Structural Imperfection

One-dimensional nanomaterials have short Li(+) diffusion paths and promising structural stability, which results in a long cycle life during Li(+) insertion and extraction processes in lithium rechargeable batteries. In this study, we fabricated one-dimensional spinel Li4Ti5O12 (LTO) nanofibers using an electrospinning technique and studied the Zr(4+) doping effect on the lattice, electronic structure, and resultant electrochemical properties of Li-ion batteries (LIBs). Accommodating a small fraction of Zr(4+) ions in the Ti(4+) sites of the LTO structure gave rise to enhanced LIB performance, which was due to structural distortion through an increase in the average lattice constant and thereby enlarged Li(+) diffusion paths rather than changes to the electronic structure. Insulating ZrO2 nanoparticles present between the LTO grains due to the low Zr(4+) solubility had a negative effect on the Li(+) extraction capacity, however. These results could provide key design elements for LTO anodes based on atomic level insights that can pave the way to an optimal protocol to achieve particular functionalities.

Multifunctional TiO2 coating for a SiO anode in Li-ion batteries

A titanium dioxide (TiO2) surface coating was applied to improve both the electrochemical and thermal properties of SiO as a high energy density anode for Li-ion batteries. A nano-scale, thin anatase TiO2 coating was achieved using a facile sol–gel process, and coated and non-coated SiO were characterized using various analytical methods. Increased initial Coulombic efficiency and reversible capacity were observed in the TiO2-coated SiO, which resulted in a 30% increase in the volumetric energy density as compared to that of bare SiO. Furthermore, the TiO2 coating remarkably suppressed the high-rate exothermic reactions observed in lithiated bare SiO and carbon-coated SiO, which could retard thermal runaway and the safety problems that it produces. Hence, an interfacial layer of TiO2 could be an alternative or supplementary coating material to carbon for safety-guaranteed and higher energy density Si-based Li-ion batteries.

Controlled Ag-driven superior rate-capability of Li4Ti5O12 anodes for lithium rechargeable batteries

AbstractThe morphology and electronic structure of a Li4Ti5O12 anode are known to determine its electrical and electrochemical properties in lithium rechargeable batteries. Ag-Li4Ti5O12 nanofibers have been rationally designed and synthesized by an electrospinning technique to meet the requirements of one-dimensional (1D) morphology and superior electrical conductivity. Herein, we have found that the 1D Ag-Li4Ti5O12 nanofibers show enhanced specific capacity, rate capability, and cycling stability compared to bare Li4Ti5O12 nanofibers, due to the Ag nanoparticles (<5 nm), which are mainly distributed at interfaces between Li4Ti5O12 primary particles. This structural morphology gives rise to 20% higher rate capability than bare Li4Ti5O12 nanofibers by facilitating the charge transfer kinetics. Our findings provide an effective way to improve the electrochemical performance of Li4Ti5O12 anodes for lithium rechargeable batteries.

Nanosize Si anode embedded in super-elastic nitinol (Ni–Ti) shape memory alloy matrix for Li rechargeable batteries

A nanosize Si embedded in super-elastic Nitinol alloy matrix composite was synthesized in large-scale using arc melting followed by a rapid quenching method. Both X-ray diffraction and high resolution transmission electron microscope with energy dispersive spectroscopy analyses confirmed that approximately 50 nm Si crystallites were surrounded by the Ni–Ti matrix. Ex situsynchrotron XRD was performed to elucidate the phase transition of active materials during lithiation and delithiation. The local structural changes of the Ni–Ti inactive matrix during cycling were investigated by ex situX-ray absorption spectroscopy analyses. This anode material showed an excellent electrochemical stability since the elastic behavior of the inactive Nitinol matrix absorbed the stress generated due to the volume expansion during lithiation of the nanosized Si embedded.

Tin-Based Oxides as Anode Materials for Lithium Secondary Batteries

Nanocrystalline/amorphous Sn 3 O 2 (OH) 2 ; prepared by simple precipitation, was investigated as an alternative anode material for lithium secondary batteries. The material was identified by X-ray diffraction IXRD), and themicrostructure of the precipitates was confirmed by high resolution transmission electron microscopy. Electrochemical tests demonstrated that the first charge and discharge capacities of Sn 3 O 2 (OH) 2 were about 1580 and 1030 mAh/g, respectively. Ex situ XRD showed a drastic structural change of electrode material to an amorphous phase during the first cycle. When the potential window was restricted between 0.0 and 0.8 V, the reversible capacity was 600 mAh/g for the first cycle and could be retained up to about 500 mAh/g even after 100 cycles. The improved cycling performance was attributed to nanocrystalline active material with the restriction of Sn aggregation by voltage cutoff.

Hydrogen Silsequioxane-Derived Si/SiOx Nanospheres for High-Capacity Lithium Storage Materials

Si/SiOx composite materials have been explored for their commercial possibility as high-performance anode materials for lithium ion batteries, but suffer from the complexity of and limited synthetic routes for their preparation. In this study, Si/SiOx nanospheres were developed using a nontoxic and precious-metal-free preparation method based on hydrogen silsesquioxane obtained from sol-gel reaction of triethoxysilane. The resulting Si/SiOx nanospheres with a uniform carbon coating layer show excellent cycle performance and rate capability with high-dimensional stability. This approach based on a scalable sol-gel reaction enables not only the development of Si/SiOx with various nanostructured forms, but also reduced production cost for mass production of nanostructured Si/SiOx.