Jaekook Kim

A manganese oxyiodide cathode for rechargeable lithium batteries

The increasing demand for portable electronic devices is driving the development of compact lightweight batteries of high energy density. Lithium-ion batteries tend to be the systems of choice, as they offer higher energy densities and longer operational lifetimes than other rechargeable battery systems,. But commercially available lithium-ion batteries make use of layered LiCoO2 cathodes,, and the high cost and toxicity of cobalt therefore motivate the development of cheaper and environmentally benign cathode materials. In this regard, manganese oxides are attractive alternatives, and the spinel LiMn2O4 has been investigated intensively as a cathode,; however, the fading on cycling of its energy-storage capacity poses problems. More recently, attention has been focused on the synthesis of layered LiMnO2 as a cathode material, but its cycling characteristics remain to be established. Here we report the synthesis and electrochemical performance of a new manganese oxide cathode, the oxyiodide Li1.5Na0.5MnO2.85I0.12. Our material exhibits a high reversible capacity of 260 mA h g−1 in the range 1.5–4.3 V with excellent cycling characteristics. Furthermore, the amorphous nature of the material (as determined by X-ray diffraction) and smooth discharge behaviour may help to overcome the problems associated with lattice distortions that have plagued manganese oxides with more crystalline structures

Co3V2O8 Sponge Network Morphology Derived from Metal–Organic Framework as an Excellent Lithium Storage Anode Material

Metal-organic framework (MOF)-based synthesis of battery electrodes has presntly become a topic of significant research interest. Considering the complications to prepare Co3V2O8 due to the criticality of its stoichiometric composition, we report on a simple MOF-based solvothermal synthesis of Co3V2O8 for use as potential anodes for lithium battery applications. Characterizations by X-ray diffraction, X-ray photoelectron spectroscopy, high resolution electron microscopy, and porous studies revealed that the phase pure Co3V2O8 nanoparticles are interconnected to form a sponge-like morphology with porous properties. Electrochemical measurements exposed the excellent lithium storage (∼1000 mAh g(-1) at 200 mA g(-1)) and retention properties (501 mAh g(-1) at 1000 mA g(-1) after 700 cycles) of the prepared Co3V2O8 electrode. A notable rate performance of 430 mAh g(-1) at 3200 mA g(-1) was also observed, and ex situ investigations confirmed the morphological and structural stability of this material. These results validate that the unique nanostructured morphology arising from the use of the ordered array of MOF networks is favorable for improving the cyclability and rate capability in battery electrodes. The synthetic strategy presented herein may provide solutions to develop phase pure mixed metal oxides for high-performance electrodes for useful energy storage applications.

Low temperature synthesis and electrode properties of Li4Mn5O12

Stoichiometric L 4 Mn 6 O 12 spinel oxide has been synthesized by an oxidation of Mn 2+ by lithium peroxide in the presence of excess lithium hydroxide followed by firing at T ≤ 500°C. The sample has been characterized by X-ray diffraction, elemental and oxidation state analyses, and thermogravimetric analysis. X-ray results indicate that Li 4 Mn 5 O 12 begins to disproportionate at T > 500°C to give Li 1+x Mn 2-x O 4 (x < 0.33) and Li 2 MnO 3 . The samples fired at 400 and 500°C show in the voltage range 3.3-2.3 V, an initial capacity of 160 and 153 mAh/g, respectively, which is close to the theoretical value. The sample fired at 500°C shows excellent cyclability with <2% capacity decline over 40 cycles.

Synthesis and Lithium Intercalation Properties of Nanocrystalline Lithium Iron Oxides

Lithium iron oxides Li{sub x}Fe{sub y}O{sub z} were synthesized by oxidizing Fe{sup 2+} with lithium peroxide in the presence of lithium hydroxide in aqueous solutions followed by firing the precursors at 200 {le} T {le} 800 C. The samples were characterized by X-ray powder diffraction, transmission electron microscopy, wet-chemical analyses, and surface-area measurements. The Li/Fe ratio in the samples depends on the concentrations and volumes of the reactants used in the synthesis. Samples fired at a lower temperature of 200 C with a nanocrystalline microstructure and optimum Li/Fe ratio exhibit a capacity of about 140 mAh/g in the range 1.5--4.3 V with excellent cyclability. On the other hand, samples fired at higher temperatures T {ge} 400 C with well-defined crystalline phases exhibit much lower capacity (< 50 mAh/g).

Pyro-synthesis of a high rate nano-Li3V2(PO4)3/C cathode with mixed morphology for advanced Li-ion batteries.

A monoclinic Li3V2(PO4)3/C (LVP/C) cathode for lithium battery applications was synthesized by a polyol-assisted pyro-synthesis. The polyol in the present synthesis acts not only as a solvent, reducing agent and a carbon source but also as a low-cost fuel that facilitates a combustion process combined with the release of ultrahigh exothermic energy useful for nucleation process. Subsequent annealing of the amorphous particles at 800°C for 5 h is sufficient to produce highly crystalline LVP/C nanoparticles. A combined analysis of X-ray diffraction (XRD) and neutron powder diffraction (NPD) patterns was used to determine the unit cell parameters of the prepared LVP/C. Electron microscopic studies revealed rod-type particles of length ranging from nanometer to micrometers dispersed among spherical particles with average particle-sizes in the range of 20–30 nm. When tested for Li-insertion properties in the potential windows of 3–4.3 and 3–4.8 V, the LVP/C cathode demonstrated initial discharge capacities of 131 and 196 mAh/g (~100% theoretical capacities) at 0.15 and 0.1 C current densities respectively with impressive capacity retentions for 50 cycles. Interestingly, the LVP/C cathode delivered average specific capacities of 125 and 90 mAh/g at current densities of 9.6 C and 15 C respectively within the lower potential window.

Cation and oxygen disorder in the structures TlSr2CuO5 and (Pb0.63Cu0.37)Sr2CoO5

TlSr2CuO5: Mr = 523.15, tetragonal, P4/mmm, a = 3.7344(5) A, c = 9.007(1) A, V = 125.61(5) A3, Z = 1, Dx = 6.92 g cm−3, λ = 0.71069 A, μ = 569 cm−1, F(000) = 226, room temperature, R = 0.033 for 143 unique reflections greater than 5σ(F). (Pb0.63Cu0.37)Sr2CoO5: Mr = 468.21, tetragonal, P4/mmm, a = 3.7591(4) A, c = 8.962(5) A, V = 126.6(1) A3, Z = 1, Dx = 6.14 g cm−3, λ = 0.71069 A, μ = 460.6 cm−1, F(000) = 205.4, room temperature, R = 0.064 for 130 unique reflections greater than 5σ(F). The compounds are isostructural. The oxygen ion at the idealized position built12built12 0 is displaced along [110] by about 0.5 A. The thallium and lead ions at the origin have r.m.s. vibrational amplitudes in the basal plane that are twice as large as those perpendicular to the plane. Static displacements of the cation and oxygen in the basal plane can result in an octahedral environment with reasonable metal-oxygen bond lengths, i.e. 2.3 A or less. The copper and cobalt ions are in a distorted octahedral coordination. The two apical distances for CuO are 2.489(16) A and for CoO = 2.38(4) A. The four equatorial bond lengths are CuO = 1.8672(2) A and CoO = 1.880(2) A. The strontium ion is in nine-fold coordination to the oxygens that are at the corners of a monocapped square antiprism; the capping ion is the disordered oxygen. In the thallium compound four SrO = 2.718(4) A, four SrO = 2.626(1) A and the capping SrO = 2.687(3) A. In the lead phase four SrO = 2.716(8) A four SrO = 2.616(2) A and the capping SrO = 2.700(8) A. The partial replacement lead by copper does not occur at the same site but is displaced along [100] by 0.6 A. The copper exists in a tetrahedral environment.

Structural investigations of Li{sub 1.5+x}Na{sub 0.5}MnO{sub 2.85}I{sub 0.12} electrodes by Mn X-ray absorption near edge spectroscopy

Mn K-edge X-ray absorption near edge spectroscopy (XANES) has been performed on an amorphous, Mn-based oxide, Li{sub 1.5}Na{sub 0.5}MnO{sub 2.85}I{sub 0.12}, and on electrodes containing this material to determine the changes that occur in the local atomic and electronic structure with state of charge and with cycling. Comparison of the XANES data with those from {lambda}-MnO{sub 2}, LiMn{sub 2}O{sub 4}, and Li{sub 2}Mn{sub 2}O{sub 4} reveals that the Mn are octahedrally coordinated and reduced from Mn{sup 4+} to Mn{sup 3+} during discharge to 2 V. Additionally, it was found that the amorphous nature of Li{sub 1.5}Na{sub 0.5}MnO{sub 2.85}I{sub 0.12} results in less dramatic changes upon inserting Li{sup +}, leading to increased cycling stability and the potential for better rate capabilities within the 4-2 V range in comparison to LiMn{sub 2}O{sub 4}.

A new phase in the SrPbCu oxide system: The crystal structure of Sr5−xPb3+xCuyO12−δ

Abstract A single crystal with compositions Sr 4.79 Pb 3.21 Cu 0.66 O 11.12 was grown from a reaction mixture of nominal composition 2 Pb:1 Sr:1 Cu that was fired at 860°C in air. M r = 1304.6,hexagonal, P ¯62 m , a = 10.072(3)A, c = 3.542(3)A, V = 311.2(4)A 3 , Z = 1, Dx = 6.96 g cm −3 , λ = 0.71069A˚, μ = 645 cm −1 , F (000) = 553.34,room temperature, R = 0.040for 323 unique reflections5σ( F o ).The Pb atoms are in octahedral coordination; the octahedra form a chain parallel to c by edge-sharing. Sr is coordinated by nine oxygen atoms that form a capped trigonal prism. The trigonal prisms form a chain parallel to c by face-sharing. TheSr/Pbsite is surrounded by seven oxygen ions. The polyhedron can be described as a tricapped trigonal prism with one edge of the prism missing. The octahedra and trigonal prisms articulate by corner sharing into a three-dimensional framework. Two crystallographically independent Cu atoms are disordered and occupy tetrahedral interstices. One oxygen site is partially occupied. The presence of Pb 2+ on the Pb site distorts the octahedron by lengthening two bonds to 2.44(3)A˚; the average of the other four bond lengths is 2.137(19)A˚. The Sr O bond lengths to the six apices of the prism are 2.632(14) and 2.935(3)A˚to the three capping atoms. The disorderedSr/Pb atom site has four oxygen neighbors at 2.544(17)A˚, two at 2.621(5)A˚, and one at 2.42(2)A˚. The compound is an electrical insulator.

Phase relations in the composition(Pb1−yCuy)Sr2(Ln1−xCax)Cu2O7 and the crystal structure of La8−xSrxCu8−yO20

Abstract The compound (Pb 0.71 Cu 0.29 )Sr 2 (Ln 1−x Ca x )Cu 2 O 7 (1212) has been synthesized as single phase material for La, Pr, Nd, Gd, Er, and Y from the proper starting compositions fired above 950°C. Calcium can be substituted up to x = 0.5 . When this limit is exceeded the 1212 phase, SrCuO 2 , and a hexagonal phase are formed. When x = 1 only SrCuO 2 and the hexagonal phase are formed. The hexagonal phase has the general composition Sr 5− x Pb 3+ x Cu y O 11+ z . When a mixture corresponding to PbSr 2 Co 0.5 Cu 0.5 O z is fired above 960°C a tetragonal phase isostructural with TlSr 2 CuO 5 (121) forms, but below 960°C the hexagonal phase is formed. A nominal mixture of PbSr 2 CaCu 2 (1212) fired at 930°C and quenched forms primarily the SrCuO 2 phase and some of the hexagonal compound, but slow cooling in the furnace produces a nearly single phase hexagonal product. The crystal structure of a crystal found in a reaction product from a nominal mixture PbSr 2 LaCu 2 (1212) fired at 1050°C was determined from three-dimensional X-ray diffraction data. Its composition is (La 6.16 Sr 1.84 )Cu 7.66 O 20 , M r = 1823.6 , tetragonal, P4/mbm, a = 10.7468(8) A, c = 3.8633(3) A, V = 446.2(1) A 3 , Z = 1, D x = 6.79g cm −3 , λ = 0.71069A, μ = 288.0 cm −1 , R = 0.032, wR = 0.034 for 385 observed reflections. The structure is formed by the articulation of Cu octahedra, square pyramids, and square coplanar nets into a three-dimensional framework. LaSr are in 10-fold coordination to oxygen atoms that are in a perovskite-like arrangement. The octahedral Cul site contains 17% vacancies on the basis of the least-squares refinement of the site occupancy. The two apical Cul O bond lengths are 1.9317(1)A, and the four equatorial lengths are 1.978(7)A. The square Cu2 O bond lengths are 1.9317(1) and 1.869(6)A, respectively. The square pyramidal Cu3 O bond lengths are 2.364(6)Ato the apex and 1.9322(2) and 1.878(7)A, respectively, to pairs of the four equatorial oxygen ions. Valence bond calculation and the abence of Jahn-Teller distortion around the octahedrally coordinated Cu1 indicate that it is trivalent.

Fluorine substitution in YBa2Cu3O7−x

Abstract Superconducting YBa2Cu3O6.94 is sealed with ZnF2 in 2:1 and 1:1 mole ratios in evacuated Vycor tubes, care being taken to keep the powdered materials physically separate. The ampules are heated at 280–290°C for several days. The ZnF2 is converted to ZnO and F- is introduced to produce YBa2Cu3OxFy. The composition of one preparation appears to be YBa2Cu3O6.6F0.4. The fluorinated phases are semiconductors. When they are heated to 600 °C BaF2 and CuO is produced as the lattice F- reacts. At 900 °C Y2BaCuO5 is also observed in an x-ray diffraction diagram in addition to a remaining superconducting oxide component that had Tc ≈ 85K.