Sookyung Jeong

Spindle-like Mesoporous α-Fe2O3 Anode Material Prepared from MOF Template for High-Rate Lithium Batteries

Spindle-like porous α-Fe(2)O(3) was prepared from an iron-based metal organic framework (MOF) template. When tested as anode material for lithium batteries (LBs), this spindle-like porous α-Fe(2)O(3) shows greatly enhanced performance of Li storage. The particle with a length and width of ∼0.8 and ∼0.4 μm, respectively, was composed of clustered Fe(2)O(3) nanoparticles with sizes of <20 nm. The capacity of the porous α-Fe(2)O(3) retained 911 mAh g(-1) after 50 cycles at a rate of 0.2 C. Even when cycled at 10 C, comparable capacity of 424 mAh g(-1) could be achieved.

Roles of Surface Chemistry on Safety and Electrochemistry in Lithium Ion Batteries

Motivated by new applications including electric vehicles and the smart grid, interest in advanced lithium ion batteries has increased significantly over the past decade. Therefore, research in this field has intensified to produce safer devices with better electrochemical performance. Most research has focused on the development of new electrode materials through the optimization of bulk properties such as crystal structure, ionic diffusivity, and electric conductivity. More recently, researchers have also considered the surface properties of electrodes as critical factors for optimizing performance. In particular, the electrolyte decomposition at the electrode surface relates to both a lithium ion batterys electrochemical performance and safety. In this Account, we give an overview of the major developments in the area of surface chemistry for lithium ion batteries. These ideas will provide the basis for the design of advanced electrode materials. Initially, we present a brief background to lithium ion batteries such as major chemical components and reactions that occur in lithium ion batteries. Then, we highlight the role of surface chemistry in the safety of lithium ion batteries. We examine the thermal stability of cathode materials: For example, we discuss the oxygen generation from cathode materials and describe how cells can swell and heat up in response to specific conditions. We also demonstrate how coating the surfaces of electrodes can improve safety. The surface chemistry can also affect the electrochemistry of lithium ion batteries. The surface coating strategy improved the energy density and cycle performance for layered LiCoO2, xLi2MnO3·(1 - x)LiMO2 (M = Mn, Ni, Co, and their combinations), and LiMn2O4 spinel materials, and we describe a working mechanism for these enhancements. Although coating the surfaces of cathodes with inorganic materials such as metal oxides and phosphates improves the electrochemical performance and safety properties of batteries, the microstructure of the coating layers and the mechanism of action are not fully understood. Therefore, researchers will need to further investigate the surface coating strategy during the development of new lithium ion batteries.

Elastic a-silicon nanoparticle backboned graphene hybrid as a self-compacting anode for high-rate lithium ion batteries.

Although various Si-based graphene nanocomposites provide enhanced electrochemical performance, these candidates still yield low initial coloumbic efficiency, electrical disconnection, and fracture due to huge volume changes after extended cycles lead to severe capacity fading and increase in internal impedance. Therefore, an innovative structure to solve these problems is needed. In this study, an amorphous (a) silicon nanoparticle backboned graphene nanocomposite (a-SBG) for high-power lithium ion battery anodes was prepared. The a-SBG provides ideal electrode structures-a uniform distribution of amorphous silicon nanoparticle islands (particle size <10 nm) on both sides of graphene sheets-which address the improved kinetics and cycling stability issues of the silicon anodes. a-Si in the composite shows elastic behavior during lithium alloying and dealloying: the pristine particle size is restored after cycling, and the electrode thickness decreases during the cycles as a result of self-compacting. This noble architecture facilitates superior electrochemical performance in Li ion cells, with a specific energy of 468 W h kg(-1) and 288 W h kg(-1) under a specific power of 7 kW kg(-1) and 11 kW kg(-1), respectively.

Etched Graphite with Internally Grown Si Nanowires from Pores as an Anode for High Density Li-Ion Batteries

A novel architecture consisting of Si nanowires internally grown from porous graphite is synthesized by etching of graphite with a lamellar structure via a VLS (vapor-liquid-solid) process. This strategy gives the high electrode density of 1.5 g/cm(3), which is comparable with practical anode of the Li-ion battery. Our product demonstrates a high volumetric capacity density of 1363 mAh/cm(3) with 91% Coulombic efficiency and high rate capability of 568 mAh/cm(3) even at a 5C rate. This good electrochemical performance allows porous graphite to offer free space to accommodate the volume change of Si nanowires during cycling and the electron transport to efficiently be improved between active materials.

3D Amorphous Silicon on Nanopillar Copper Electrodes as Anodes for High-Rate Lithium-Ion Batteries

We present an amorphous Si anode deposited on a Cu nanopillar current collector, fabricated using a thermal roll-to-roll process followed by electroformation and LPCVD, for application in high-rate Li-ion batteries. Cu nanopillar current collectors with diameters of 250 and 500 nm were patterned periodically with 1 μm pitch and 2 μm height to optimize the diameters of the pillars for better electrochemical performance. Void spaces between Cu nanopillars allowed not only greater effective control of the strain caused by the Si expansion during lithiation than that allowed by a nonpatterned electrode but also significantly improved cycle performance even at 20 C measured after the same rate test: After 100 cycles at 0.5 C, the patterned electrodes with 250 and 500 nm diameter nanopillars showed high capacity retentions of 86% and 84%, respectively. These electrodes retained discharge capacities of 1057 and 780 mAh/g even at 20 C, respectively.

Lithium reaction mechanism and high rate capability of VS4–graphene nanocomposite as an anode material for lithium batteries

A graphene-attached VS4 composite prepared by a simple hydrothermal method is studied in terms of its lithium reaction mechanism and high rate capability. The nanocomposite exhibits a good cycling stability and an impressive high-rate capability for lithium storage, delivering a comparable capacity of 630 and 314 mA h g−1, even at high rates of 10 and 20 C (=10 and 20 A g−1, or 10 and 20 mA cm−2), respectively. In addition, full-cell (LiMn2O4/VS4–graphene) test results also exhibited a good capacity retention. The mechanism of Li storage is systematically studied and a conversion reaction with an irreversible phase change during the initial discharge–charge process is proposed.

Spinel LiCo0.7Mn1.3O4 Nanowire Clusters as Electrode Materials

the presence of high-spin Mn 3 + :t2g 3 eg 1 ions—resulting in a huge change of volume and severe fading of the capacity. [7] The power density (rate capability) of these cathode materials with bulk sizes in the micrometer-regime is generally low due to the high level of polarization at high charge–discharge rates (above 2 C). This high polarization is believed to result from slow lithium diffusion or low electrical conductivity in the active material. Therefore, “nanostructuring” was introduced to overcome these shortcomings, through shortening the diffusion paths for mass transport and increasing the surface area for charge transfer. [8–10] In addition, electrode density is considered to be one of the factors that affects the energy density: a higher electrode density leads to a higher energy density. [11] A