Sang-Ok Kim

A facile, low-cost synthesis of high-performance silicon-based composite anodes with high tap density for lithium-ion batteries

Micro-sized carbon-coated Si-based composites have been developed by a simple mechanochemical reaction between SiO, Ni, and Al, followed by an additional milling process with graphite. The resultant carbon-coated Si-based composite exhibits a reversible capacity of over 580 mA h g−1 after 200 cycles with a considerably higher tap density of ∼1.34 g cm−3 compared to nanosized Si (∼0.16 g cm−3). The improvement in the electrochemical performance is achieved due to both highly conductive NiSi2 nanoinclusions and amorphous Al2O3 buffer matrix in the composite. Upon cycling, the multifunctional NiSi2 phase not only provides enhanced electronic conductivity but also suppresses the formation of crystalline Li15Si4 that causes an inhomogeneous volume change. Simultaneously, amorphous Al2O3 plays a crucial role in maintaining particle connectivity by impeding the agglomeration of active Si nanocrystallites. The combination of these advantages with a low-cost, scalable, and environmentally benign synthetic process make the Si-based composite a promising alternative anode for high performance Li-ion batteries.

Particulate inverse opal carbon electrodes for lithium-ion batteries.

Inverse opal carbon materials were used as anodes for lithium ion batteries. We applied particulate inverse opal structures and their dispersion in the formation of anode electrodes via solution casting. We prepared aminophenyl-grafted inverse opal carbons (a-IOC), inverse opal carbons with mesopores (mIOC), and bare inverse opal carbons (IOC) and investigated the electrochemical behavior of these samples as anode materials. Surface modification by aminophenyl groups was confirmed by XPS measurements. TEM images showed mesopores, and the specific area of mIOC was compared with that of IOC using BET analysis. A half-cell test was performed to compare a-IOC with IOC and mIOC with IOC. In the case of the a-IOC structure, the cell test revealed no improvement in the reversible specific capacity or the cycle performance. The mIOC cell showed a reversible specific capacity of 432 mAh/g, and the capacity was maintained at 88%-approximately 380 mAh/g-over 20 cycles.

Three-dimensional hierarchical self-supported multi-walled carbon nanotubes/tin(iv) disulfide nanosheets heterostructure electrodes for high power Li ion batteries

It is of great significance to improve the power density of Li ion batteries (LIBs) in pursuit of high-end products and technologies. Herein, we investigated the three-dimensional (3D) hierarchical self-supported multi-walled carbon nanotubes (MWCNTs)/tin(IV) disulfide nanosheets (SnS2 NS) heterostructured electrodes, demonstrating superior rate capabilities of 480 and 420 mAh g−1 even at the very high c-rates of 5C and 10C (charging in 6 min), respectively. The origins of the enhancement of the rate capabilities were discussed in detail by focusing on the roles of MWCNTs, which were directly grown on the metallic current collector. Furthermore, we have delicately dealt with the in-plane and plane-normal growth mechanisms of hexagonal SnS2 NS from the crystallographic point of view.

Silicon/copper dome-patterned electrodes for high-performance hybrid supercapacitors

This study proposes a method for manufacturing high-performance electrode materials in which controlling the shape of the current collector and electrode material for a Li-ion capacitor (LIC). In particular, the proposed LIC manufacturing method maintains the high voltage of a cell by using a microdome-patterned electrode material, allowing for reversible reactions between the Li-ion and the active material for an extended period of time. As a result, the LICs exhibit initial capacities of approximately 42 F g−1, even at 60 A g−1. The LICs also exhibit good cycle performance up to approximately 15,000 cycles. In addition, these advancements allow for a considerably higher energy density than other existing capacitor systems. The energy density of the proposed LICs is approximately nine, two, and 1.5 times higher than those of the electrochemical double layer capacitor (EDLC), AC/LiMn2O4 hybrid capacitor, and intrinsic Si/AC LIC, respectively.

Phosphorus-Rich CuP2 Embedded in Carbon Matrix as a High-Performance Anode for Lithium-Ion Batteries

Phosphorus-rich CuP2 and its carbon composites have been investigated as an anode material for lithium-ion batteries. Through a facile, low-cost mechanochemical reaction, microsized composites composed of active CuP2 particles uniformly embedded in the carbon matrix have been successfully synthesized. Combined structural and electrochemical characterizations show that phosphorus-rich CuP2 undergoes irreversible reaction with lithium, giving metal-rich Cu3P and amorphous phosphorus at the end of the first cycle. Both Cu3P and phosphorus are reversibly formed in subsequent cycles, contributing to a high reversible capacity of >1000 mA h g-1. By controlling the carbon content, the electrochemical reversibility and stability of CuP2 are greatly improved. The carbon composite demonstrates a remarkable lithium-storage capability in terms of a stable capacity of >720 mA h g-1 over 100 cycles at 200 mA g-1, a high initial Coulombic efficiency of ∼83%, and a good rate capability with a capacity of >637 mA h g-1 at 1.6 A g-1. The performance improvement is mainly associated with the formation of the conductive carbon network that offers high conductivity and fast reaction kinetics, as well as enhanced structural stability of CuP2 anode.

High-Performance Zn–TiC–C Nanocomposite Alloy Anode with Exceptional Cycle Life for Lithium-Ion Batteries

A Zn-based nanocomposite has been prepared through a facile, low-cost high-energy mechanochemical process and employed as an anode material for lithium-ion batteries. Structural characterization reveals that the micrometer-sized Zn-TiC-C nanocomposite is composed of Zn nanocrystals uniformly dispersed in a multifunctional TiC and conductive carbon matrix with a tap density of 1.3 g cm(-3). The Zn-TiC-C nanocomposite exhibits high reversible volumetric capacity (468 mA h cm(-3)), excellent cyclability over 800 cycles (79.2% retention), and good rate performance up to 12.5C (75% of its capacity at 0.25C rate). The enhanced electrochemical performance is mainly due to the presence of the well-mixed TiC+C matrix that plays an important role in providing high conductivity as well as mechanical buffer that mitigates the huge volume expansion and contraction during prolonged cycling. In addition, it prevents the particle growth by uniformly dispersing nanosized Zn within itself during cycling, maintaining high utilization (∼100%) and fast reaction kinetics of Zn anode.

HYDROGENATED AMORPHOUS/NANOCRYSTALLINE SILICON THIN FILMS ON POROUS ANODIC ALUMINA SUBSTRATE

Hydrogenated amorphous and nanocrystalline silicon thin films were grown on porous anodic alumina substrates using electron cyclotron resonance-chemical vapor deposition technique from argon, hydrogen and silane gas composition. The structural characterization of the deposited hydrogenated silicon films were performed by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction studies. The results revealed that mixed amorphous/nanocrystalline silicon phases with specific novel morphology were obtained on textured surfaces. The evolution of the film on ripple-like surface exhibited amorphous dominant structure, however, the film deposited on tipped/ribbed surface consisted of amorphous and nanocrystalline phases composite. The growth process strongly depends on the textured substrate pattern, which influences on the nanostructure shapes and crystallinity.

Lithium diffusivity in antimony-based intermetallic and FeSb–TiC composite anodes as measured by GITT

The diffusion coefficient of lithium is an important parameter in determining the rate capability of an electrode and its ability to deliver high power output. Galvanostatic intermittent titration technique (GITT) is a quick electrochemical method to determine diffusion coefficients in electrode materials and is applied here to antimony-based anodes for lithium-ion batteries. Like other alloy anodes, antimony suffers from large volume change and a short cycle life, so GITT is also applied to determine the effects on lithium diffusivity of antimony intermetallics and composite electrodes designed to mitigate these issues. Pure antimony is measured to have a diffusion coefficient of 4.0 × 10(-9) cm(2) s(-1), in agreement with previously measured values. The intermetallics NiSb, FeSb, and FeSb2 all demonstrate diffusivity values within an order of magnitude of antimony, while Cu2Sb shows roughly an order of magnitude improvement due to the persistence of the Cu2Sb phase during cycling. The composite electrode FeSb-TiC is shown to offer significant enhancement of the diffusion coefficient positively correlated with higher concentrations of TiC in the composite up to a maximum value of 1.9 × 10(-7) cm(2) s(-1) at 60 wt% TiC, nearly two full orders of magnitude greater than that of pure antimony.

Thermal stability of Sn anode material with non-aqueous electrolytes in sodium-ion batteries

The thermal behavior of fully lithiated and sodiated Sn electrodes cycled in a MePF6 (Me = Li or Na)-based electrolyte was studied using differential scanning calorimetry (DSC). The sodiated Sn electrode cycled in the NaPF6-based electrolyte showed a thermal reaction with much greater heat generation (1719.4 J g−1) during the first exothermic reaction corresponding to the thermal decomposition reaction of the solid electrolyte interface (SEI) layer, compared to that of the lithiated Sn electrode (647.7 J g−1) in the LiPF6-based electrolyte because of the formation of a thicker surface film on the Sn electrode. The NaPF6-based electrolyte yielded a slightly less conductive and/or a thicker SEI layer than the NaClO4-based electrolyte, resulting in the intense thermal decomposition of the SEI layer. The DSC results for the fully sodiated Sn electrode cycled in FEC-containing electrolytes clearly demonstrate that an exothermic reaction corresponding to the SEI decomposition mostly disappears because of the formation of a thermally stable and thin SEI layer on active materials via the electrochemical decomposition of FEC. X-ray photoelectron spectroscopy reveals the formation of SEI with a relatively high proportion of NaF, which is known to be a thermally stable inorganic solid at high temperatures.

Conducting Polymer Coating on a High-Voltage Cathode Based on Soft Chemistry Approach toward Improving Battery Performance

The surface of a 5 V class LiNi0.5Mn1.5O4 particle is modified with poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer by utilizing the hydrophobic characteristics of the 3,4-ethylenedioxythiophene (EDOT) monomer and the tail group of cetyl trimethyl ammonium bromide (CTAB) surfactants, in addition to the electrostatic attraction between cationic CTAB surfactant and cathode materials with a negative ζ potential in aqueous solution. With this novel concept, we design and prepare a uniform EDOT monomer layer on the cathode materials, and chemical polymerization of the EDOT coating layer is then carried out to achieve PEDOT-coated cathode materials via a simple one-pot preparation process. This uniform conducting polymer layer provides notable improvement in the power characteristics of electrodes, and stable electrochemical performance can be obtained especially at severe operating conditions such as the fully charged state and elevated temperatures owing to the successful suppression of the side reaction between the oxide particle and the electrolyte as well as the suppression of Mn dissolution from the oxide material.