Seung-Ho Yu

Galvanic Replacement Reactions in Metal Oxide Nanocrystals

Hollowing Out Metal Oxide Nanoparticles Corrosion is normally a problem, but it can be useful, for example, when you wish to create hollow metal nanoparticles, whereby the reduction of one metal species in solution drives the dissolution of the core of the particle. Oh et al. (p. 964; see the Perspective by Ibáñez and Cabot) adapted this approach to metal oxide nanoparticles by placing Mn3O4 nanocrystals in solution with Fe2+ ions, which replaces the nanocrystal exterior with γ-Fe2O3. At sufficiently high Fe2+ concentrations, hollow γ-Fe2O3 nanocages formed. These hollow structures could be used as anode materials for lithium ion batteries. Hollow mixed-metal oxide nanoparticles can be made by replacing the metal cations through redox reactions in solution. [Also see Perspective by Ibáñez and Cabot] Galvanic replacement reactions provide a simple and versatile route for producing hollow nanostructures with controllable pore structures and compositions. However, these reactions have previously been limited to the chemical transformation of metallic nanostructures. We demonstrated galvanic replacement reactions in metal oxide nanocrystals as well. When manganese oxide (Mn3O4) nanocrystals were reacted with iron(II) perchlorate, hollow box-shaped nanocrystals of Mn3O4/γ-Fe2O3 (“nanoboxes”) were produced. These nanoboxes ultimately transformed into hollow cagelike nanocrystals of γ-Fe2O3 (“nanocages”). Because of their nonequilibrium compositions and hollow structures, these nanoboxes and nanocages exhibited good performance as anode materials for lithium ion batteries. The generality of this approach was demonstrated with other metal pairs, including Co3O4/SnO2 and Mn3O4/SnO2.

Self-assembled Fe3O4 nanoparticle clusters as high-performance anodes for lithium ion batteries via geometric confinement.

Although different kinds of metal oxide nanoparticles continue to be proposed as anode materials for lithium ion batteries (LIBs), their cycle life and power density are still not suitable for commercial applications. Metal oxide nanoparticles have a large storage capacity, but they suffer from the excessive generation of solid-electrolyte interphase (SEI) on the surface, low electrical conductivity, and mechanical degradation and pulverization resulted from severe volume expansion during cycling. Herein we present the preparation of mesoporous iron oxide nanoparticle clusters (MIONCs) by a bottom-up self-assembly approach and demonstrate that they exhibit excellent cyclic stability and rate capability derived from their three-dimensional mesoporous nanostructure. By controlling the geometric configuration, we can achieve stable interfaces between the electrolyte and active materials, resulting in SEI formation confined on the outer surface of the MIONCs.

Conversion Reaction-Based Oxide Nanomaterials for Lithium Ion Battery Anodes.

Developing high-energy-density electrodes for lithium ion batteries (LIBs) is of primary importance to meet the challenges in electronics and automobile industries in the near future. Conversion reaction-based transition metal oxides are attractive candidates for LIB anodes because of their high theoretical capacities. This review summarizes recent advances on the development of nanostructured transition metal oxides for use in lithium ion battery anodes based on conversion reactions. The oxide materials covered in this review include oxides of iron, manganese, cobalt, copper, nickel, molybdenum, zinc, ruthenium, chromium, and tungsten, and mixed metal oxides. Various kinds of nanostructured materials including nanowires, nanosheets, hollow structures, porous structures, and oxide/carbon nanocomposites are discussed in terms of their LIB anode applications.

Facile and economical synthesis of hierarchical carbon-coated magnetite nanocomposite particles and their applications in lithium ion battery anodes

Hierarchical sea urchin-like structured carbon–Fe3O4 nanocomposite particles composed of a nanoporous interior and a carbon-coated surface have been prepared by a simple, economical and scalable synthetic process. When the nanocomposite particles were tested as lithium ion battery anodes, they exhibited high capacity, excellent cycle stability and rate performance due to their unique hierarchical nanoporous structure and carbon shell.

A facile hydrazine-assisted hydrothermal method for the deposition of monodisperse SnO2 nanoparticles onto graphene for lithium ion batteries

In this manuscript, we introduce a facile hydrothermal method for the controlled growth of SnO2 nanoparticles onto graphene oxide. Hydrazine plays a fundamental role in controlling the formation and crystallization of SnO2 nanoparticles, and the reduction of graphene oxide to graphene. The SnO2–graphene composite consists of 3–4 nm monodisperse SnO2 nanocrystals homogeneously dispersed at the surface of graphene. It is demonstrated that the composite can accommodate the large volume change of SnO2 which occurs during lithiation–delithiation cycles. When used as an anode material for lithium ion batteries, it exhibits a first discharge capacity of 1662 mA h g−1, which rapidly stabilizes and still remains at 626 mA h g−1 even after 50 cycles, when cycled at a current density of 100 mA g−1. Even at the very high current density of 3200 mA g−1, the composite displays a stable capacity of 383 mA h g−1 after 50 cycles.

A facile and green strategy for the synthesis of MoS2 nanospheres with excellent Li-ion storage properties

A facile and green process was developed for the synthesis of MoS2 nanospheres by an L-cysteine-assisted hydrothermal method. These MoS2 nanospheres exhibited high specific capacity and good cycle stability because of efficient lithium ion diffusion and the accommodation of mechanical stress owing to their unique structure.

Surfactant-free nonaqueous synthesis of lithium titanium oxide (LTO) nanostructures for lithium ion battery applications

A one-pot template-free solvothermal synthesis of crystalline Li4Ti5O12 nanostructures based on the “benzyl alcohol route” is introduced. The 1–2 µm sized nanostructured spherical particles are constituted of nanocrystallites in the size range of a few nm. This is the first report showing that crystalline Li4Ti5O12 can be directly obtained by soft chemistry solution routes. The as-synthesized crystalline nanostructures show good lithium intercalation/deintercalation performances at high rates (up to 30 C) and good cycling stabilities. Annealing the nanostructures at 750 °C improves the performance, which approaches the theoretical capacity of Li4Ti5O12 with no noticeable (less than 5%) capacity loss after 200 cycles.

Continuous activation of Li2MnO3 component upon cycling in Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 cathode material for lithium ion batteries

Li-rich layered cathode materials are very promising candidates for next generation high energy lithium ion batteries. One of the Li-rich layered cathode materials, Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 is prepared by a co-precipitation method. In this report, we focus on anomalous changes upon cycling in Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 cathode material in a voltage range of 2.0–4.55 V at room temperature. The structural transitions upon cycling are analyzed by ex situ X-ray diffraction. In addition, the changes in local structure during cycling are studied by X-ray absorption near edge structure. With differential capacity plots by controlling the cut-off voltage, the voltage decay during cycling is intensively studied. The continuous activation process of the residual Li2MnO3 component during cycling is correlated with voltage decay during cycling, and increasing capacity during the initial several cycles. Also, the electrochemical performance in Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 cathode material below 4.4 V is discussed. Furthermore, cycle performance is improved by reassembling Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 into another cell after washing.

A one-pot microwave-assisted non-aqueous sol–gel approach to metal oxide/graphene nanocomposites for Li-ion batteries

A one-pot non-aqueous synthesis of crystalline SnO2- and Fe3O4-based graphene heterostructures in just a few minutes is introduced. The combined properties of the microwave heating and the “benzyl alcohol route” allow the selective growth of metal oxide nanoparticles at the surface of graphene oxide, which is reduced during synthesis. The as-fabricated nanostructures show good lithium intercalation–deintercalation performances at high rate and good cycling stability compared to the separated nano-building blocks.

Hybrid Cellular Nanosheets for High-Performance Lithium-Ion Battery Anodes

We report a simple synthetic method of carbon-based hybrid cellular nanosheets that exhibit outstanding electrochemical performance for many key aspects of lithium-ion battery electrodes. The nanosheets consist of close-packed cubic cavity cells partitioned by carbon walls, resembling plant leaf tissue. We loaded carbon cellular nanosheets with SnO2 nanoparticles by vapor deposition method and tested the performance of the resulting SnO2-carbon nanosheets as anode materials. The specific capacity is 914 mAh g(-1) on average with a retention of 97.0% during 300 cycles, and the reversible capacity is decreased by only 20% as the current density is increased from 200 to 3000 mA g(-1). In order to explain the excellent electrochemical performance, the hybrid cellular nanosheets were analyzed with cyclic voltammetry, in situ X-ray absorption spectroscopy, and transmission electron microscopy. We found that the high packing density, large interior surface area, and rigid carbon wall network are responsible for the high specific capacity, lithiation/delithiation reversibility, and cycling stability. Furthermore, the nanosheet structure leads to the high rate capability due to fast Li-ion diffusion in the thickness direction.