다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Each cell of a battery stores electrical energy as chemical energy in two electrodes, a reductant (anode) and an oxidant (cathode), separated by an electrolyte that transfers the ionic component of the chemical reaction inside the cell and forces the electronic component outside the battery. The output on discharge is an external electronic current I at a voltage V for a time Δt. The chemical reaction of a rechargeable battery must be reversible on the application of a charging I and V. Critical parameters of a rechargeable battery are safety, density of energy that can be stored at a specific power input and retrieved at a specific power output, cycle and shelf life, storage efficiency, and cost of fabrication. Conventional ambient-temperature rechargeable batteries have solid electrodes and a liquid electrolyte. The positive electrode (cathode) consists of a host framework into which the mobile (working) cation is inserted reversibly over a finite solid–solution range. The solid–solution range, which is...

The Li-ion rechargeable battery: a perspective.

Li-ion battery technology has become very important in recent years as these batteries show great promise as power sources that can lead us to the electric vehicle (EV) revolution. The development of new materials for Li-ion batteries is the focus of research in prominent groups in the field of materials science throughout the world. Li-ion batteries can be considered to be the most impressive success story of modern electrochemistry in the last two decades. They power most of today's portable devices, and seem to overcome the psychological barriers against the use of such high energy density devices on a larger scale for more demanding applications, such as EV. Since this field is advancing rapidly and attracting an increasing number of researchers, it is important to provide current and timely updates of this constantly changing technology. In this review, we describe the key aspects of Li-ion batteries: the basic science behind their operation, the most relevant components, anodes, cathodes, electrolyte solutions, as well as important future directions for R&D of advanced Li-ion batteries for demanding use, such as EV and load-leveling applications.

Challenges in the development of advanced Li-ion batteries: a review

Li-ion battery materials: present and future

In the system Li-Mn-O, spinels Li1+xMn2-xO4 exist as a continuous series of solid solution in the range 0.00≤x≤0.33 [1]. It is generally accepted that Li-rich spinels behave with improved electrochemical performance but physical properties of such materials are rather sparse. In this work, we report on the local structure of Li1+xMn2-xO4 compounds using magnetic measurements. Magnetic measurements were made on SQUID magnetometer using a liquid helium cooled amplifier to measure the magnetic moment in the range from 10 to 300 emu. Two kinds of measurements were carried out in the temperature range 4–300K: M(H) in the field range 0-30 kOe and temperature dependence of magnetic susceptibility recorded during heating the samples in the zero–field cooled (ZFC) and field– cooled (FC) mode at magnetic field 10 kOe. The χ(T) curves and isothermal M(H) plots were correlated to achieve a complete analysis of magnetic properties of the Li1+xMn2-xO4 materials. The temperature dependence of the magnetization of LiMn2O4 samples measured under an applied field of 10 kOe is reported in Fig. 1. The main difference is observed in the temperature range 40–50 K for the samples sintered at 800 °C. The magnetization curves for these samples show that the anomaly corresponds to the onset of an extrinsic magnetic component which saturates very fast with the magnetic field, superposed to the paramagnetic intrinsic component. This is the fingerprint of the ferrimagnetic Mn3O4 impurity phase identified by its spin ordering temperature at 42 K [2]. The comparison at T=4 K between the low field magnetization in our sample and the magnetization of Mn3O4 [3] allows us to deduce the amount of this impurity phase in the sample, namely 0.5%. It could not be detected by the X-ray diffractometry. The sample LiMn2O4 sintered at 750 °C shows anomaly at low temperature where the ZFC magnetic susceptibility goes through a maximum. It could be the onset of some antiferromagnetic domains of finite size. This behavior is consistent with the magnetic diffused peak in the range 10–65 K observed in the neutron spectra of some Mn3O4 samples [4]. The Curie-Weiss law is approximately satisfied for all samples in the temperature range 200-300 K, from which we can find the Curie (C) and Weiss (Θ) constant and calculate effective magnetic moment (μeff). The Θ constant decreases almost linearly with x from -267 K for the LiMn2O4 sample heated at 800 °C to -13 K for x=0.25 and then vanishes at x=0.3. The effective magnetic moment decreases with x from 5.93 μB for stoichiometric sample heated at 800 °C with mixed valence state (Mn) to 4.38 μB for Li1.33Mn1.67O4 heated at 750 °C in which the Mn ions are only in the Mn valence state (Fig. 2). Calculated value of effective magnetic moment for Mn (3.39 μB) differs from theoretical one (3.87 μB), but is in good agreement with experimental data.

http://ma.ecsdl.org/content/MA2006-02/4/209.full.pdf

A New Approach Toward Local Structure of Spinel Compounds Using Magnetic Properties

We report the electrochemical behavior of various layered oxides in Li cells. A series of LiNiyMnyCozO2 materials (with z=1-2y) was synthesized by “chimie douce” and investigated as positive electrodes in rechargeable lithium batteries. Electrochemical performances of LiNiyMnyCozO2 oxides are tested cell using non-aqueous 1M LiPF6 dissolved in EC-DEC. Charge discharge profiles are investigated as a function of the rate capability, the voltage window and the synthesis parameters of the cathode. A relation is found between the gravimetric capacity and the cation disorder of materials as indicated by magnetometry analysis.

Electrochemical Features of Li-Ni-Mn-Co Oxides

We examine the reactivity of the non-aqueous electrolyte at the surface of 5-volts positive electrode materials for Li-ion batteries. LiPF6-based electrolytes include various solutes as ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and 1,2-dimethoxyethane (DME), which react with the surface of LiNi0.5Mn1.5O4 in the voltage range 3.0-4.9 V vs. Li0/Li+. Effects with mixed salts and electrolyte additive are also examined.

Reactivity of Electrolyte with the Surface of 5-Volts Positive Electrode Materials for Li-Ion Batteries

Introduction Because the low cost and abundance of sodium, there is a renewed interest in the development of Na-based electrodes, especially those that can be synthesized by hydrothermal method. Known for their excellent redox abilities and thermal stability, transition-metal polyphosphates have been studied in great detail [1]. Recently, Recham et al. [2] have shown the Na-cells with NaxFePO4F positive electrode display chargedischarge profiles in the 3-volt region.

http://ma.ecsdl.org/content/MA2010-03/1/469.full.pdf

Characterization of Na-Based Electrodes for Electrochemical Cells

In situ X-ray diffraction has been carried out to study the structural changes of the bare and Cr-doped LiMn1.5Ni0.5O4 crystallized samples in the disordered phase (Fd3m space group) during the galvanostatic charge/discharge process at C/24 rate. The de-intercalation of lithium proceeds through a series of first-order phase transitions with two regions of two-phase coexistence. The phase diagram is analyzed and discussed, together with the differences among different results reported in the literature.

Christian M. Julien

Papers

A New Approach Toward Local Structure of Spinel Compounds Using Magnetic Properties

Electrochemical Features of Li-Ni-Mn-Co Oxides

Reactivity of Electrolyte with the Surface of 5-Volts Positive Electrode Materials for Li-Ion Batteries

Characterization of Na-Based Electrodes for Electrochemical Cells

In situ XRD Study of the Phase Evolution in LixMn1.5Ni0.5O4 as 4.7-Volt Positive Electrode Materials for Li-ion Batteries