There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Metal Oxides and Oxysalts as Anode Materials for Li Ion Batteries

Recent developments in cathode materials for lithium ion batteries

Nanostructured materials have shown extraordinary promise for electrochemical energy storage but are usually limited to electrodes with rather low mass loading (~1 milligram per square centimeter) because of the increasing ion diffusion limitations in thicker electrodes. We report the design of a three-dimensional (3D) holey-graphene/niobia (Nb2O5) composite for ultrahigh-rate energy storage at practical levels of mass loading (>10 milligrams per square centimeter). The highly interconnected graphene network in the 3D architecture provides excellent electron transport properties, and its hierarchical porous structure facilitates rapid ion transport. By systematically tailoring the porosity in the holey graphene backbone, charge transport in the composite architecture is optimized to deliver high areal capacity and high-rate capability at high mass loading, which represents a critical step forward toward practical applications.

Three-dimensional holey-graphene/niobia composite architectures for ultrahigh-rate energy storage

Three-Dimensional Holey-Graphene/Niobia Composite Architectures for Ultrahigh-Rate Energy Storage

Memory effects are well known to users of nickel-cadmium and nickel-metal-hydride batteries. If these batteries are recharged repeatedly after being only partially discharged, they gradually lose usable capacity owing to a reduced working voltage. Lithium-ion batteries, in contrast, are considered to have no memory effect. Here we report a memory effect in LiFePO4-one of the materials used for the positive electrode in Li-ion batteries-that appears already after only one cycle of partial charge and discharge. We characterize this memory effect of LiFePO4 and explain its connection to the particle-by-particle charge/discharge model. This effect is important for most battery uses, as the slight voltage change it causes can lead to substantial miscalculations in estimating the state of charge of batteries.

Memory effect in a lithium-ion battery

To understand the relationship between the specific energy and power of lithium (Li)-ion batteries, the dependence of the internal resistance of porous electrodes with high loading weight on thickness was systematically investigated. The ionic resistance in pores (Rion) and charge-transfer resistance for Li intercalation (Rct) normalized per unit electrode geometric area were assessed using a combination of electrochemical impedance spectroscopy with symmetric cells and the transmission line model for cylindrical pores. The changes of Rion and Rct and their magnitude show opposite trends with respect to electrode thickness. For thin electrodes, Rion is lower than Rct. The specific power decreases slightly as the electrodes become thicker because the total internal resistance is predominantly affected by the charge-transfer resistance, and there is no delay of the response in the depth direction. In contrast, for thick electrodes, Rion is higher than or approximately equal to Rct, so there is a delay of th...

Impedance Spectroscopy Characterization of Porous Electrodes under Different Electrode Thickness Using a Symmetric Cell for High-Performance Lithium-Ion Batteries

We used a suite of transmission electron microscopy (TEM) and associated electron spectroscopy methods to examine the local structure and changes in the electronic structure of LiNi 0.8 Co 0.15 Al 0.05 O 2 positive electrode material. We found a scattered rock-salt phase near grain surfaces and grain boundaries, where Ni 3+ turned to Ni 2+ , deduced from relative intensity ratios and fine structures of the L 2,3 white-line peaks of the transition metals. The spatial distribution of the degraded phase throughout the secondary particle was found using a scanning TEM-electron energy loss spectroscopy spectral imaging technique and multivariate analysis. The degradation process and its relationship to the surface reactions with electrolytes is discussed based on the spatial-distribution map of the degraded phases.

Capacity-Fading Mechanisms of LiNiO2-Based Lithium-Ion Batteries II. Diagnostic Analysis by Electron Microscopy and Spectroscopy

I. Analysis by Electrochemical and Spectroscopic Examination Tsuyoshi Sasaki,* Takamasa Nonaka, Hideaki Oka, Chikaaki Okuda, Yuichi Itou, Yasuhito Kondo, Yoji Takeuchi, Yoshio Ukyo,* Kazuyoshi Tatsumi, and Shunsuke Muto* Toyota Central Research and Development Laboratories, Incorporated, Nagoakute 480-1192, Japan Department of Materials, Physics and Energy Engineering, Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan

Tsuyoshi Sasaki

Papers

Memory effect in a lithium-ion battery

Impedance Spectroscopy Characterization of Porous Electrodes under Different Electrode Thickness Using a Symmetric Cell for High-Performance Lithium-Ion Batteries

Capacity-Fading Mechanisms of LiNiO2-Based Lithium-Ion Batteries II. Diagnostic Analysis by Electron Microscopy and Spectroscopy

Capacity-Fading Mechanisms of LiNiO2-Based Lithium-Ion Batteries I. Analysis by Electrochemical and Spectroscopic Examination

Effects of Mg-substitution in Li(Ni,Co,Al)O2 positive electrode materials on the crystal structure and battery performance