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To clarify the role of conducting carbon in porous electrodes for lithium-ion batteries on internal resistance, the dependence of internal resistance on the conductive carbon ratio in positive elec...

The decline of lithium-ion battery (LIB) performance at low temperatures, caused by the nonuniform occurrence of electrochemical reactions during cycling and the resulting irreversible capacity loss, significantly hinders further LIB commercialization. Herein, we report the first solution by analyzing the impedance using symmetric cells in the absence of charge-transfer reactions to obtain a parameter quantitatively describing ion transport in porous electrodes and thus modeling the effects of nonuniform reaction occurrence. The reciprocal of ionic resistance in porous electrodes (Rion-1) is found to be positively correlated with capacity retention during low-temperature cycling and is approximated as the product of maximum capacitance related to electric double-layer formation (Cdl,max) and the associated frequency (f0). Consequently, these ion-transport parameters can be used to predict capacity retention during low-temperature cycling, and the adopted approach therefore can help to mitigate low-temperature LIB performance degradation and thus contribute to the fabrication of next-generation rechargeable batteries.

In this study, we develop methods for extracting reaction parameters (e.g., rate and enthalpy) from the differential scanning calorimetry (DSC) profiles of [battery component + electrolyte] systems to simulate the thermal abuse behavior of NCA-based batteries using a modification of a previously reported 3D thermal model. The obtained parameters and model are validated by comparison of simulated and experimental thermal abuse behaviors, and the validated model is employed to investigate the influence of heat generation due to SEI decomposition and regeneration in the anode. Moreover, the effect of Mg substitution on the thermal runaway temperature of NCA-based batteries is probed by simulating the thermal abuse behaviors of NCA and Mg-NCA batteries, and the relationship between the DSC-determined heat generation behavior of battery components and the simulated thermal abuse behavior of batteries is discussed in detail.

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...

Hard coatings are frequently used to give plastics high scratch resistance. Coating hardness and adhesion to the substrate are considered to be key factors influencing scratch resistance, but it is difficult to produce coatings that have both properties. Hybridization of polymers and inorganic materials is a promising approach for solving this problem. We prepared polymer-silica hybrid coatings by using in situ polymerization to carry out radical polymerization of vinyl monomers in a sol-gel solution of alkoxysilanes, and measured the abrasion resistance of the coatings. However, the expected properties were not obtained because the sol-gel reaction did not perfectly proceed on the surface of the coatings under the N2 conditions. We found that curing the hybrid coatings by UV irradiation in air promoted the sol-gel reaction on the surface, resulting in coatings having excellent abrasion resistance.

The mechanism of the increasing of resistance of lithium-ion batteries using Li(Ni,Co)O2 based material as positive electrode materials was investigated. The increase in resistance of cells with Li(Ni,Co)O2 material and artificial graphite was observed in cycling test at 60 °C. It was found that the increasing of resistance was mainly attributed to that at positive electrode by ‘reconstructed method’. In order to examine the mechanism of the increasing of resistance of positive electrode, the morphological changes of positive particles and local structure of Li(Ni,Co)O2 material were investigated. The clearance and crack were observed at grain boundary inside particle after cycle by FIB (focused ion beam) technique. The change of local structure around Co-atom was observed during charge–discharge process at 60 °C by in situ XAFS (X-ray absorption fine structure spectroscopic) analysis method. It was considered that the morphological and local structural changes of positive material cause the increasing of resistance.

A method of predicting fatigue strengths using fracture mechanics on noched components of ferrous sintered materials is investigated. By applying Lukas's formula for evaluation of AK and a intrinsic crack model for small crack propagation on notched components, a simple formula for predicting fatigue limits was derived. This method requires three material properties: the fatigue limit of smooth specimen, the threshold stress intensity range for long crack, and the threshold value of the effective stress intensity. For experimental verification, a notched specimen for fatigue tests as sintered was designed, and fatigue tests were conducted with notched specimens of ferrous sintered materials with two different pore sizes. The predicted fatigue limits are comparatively in good agreement with the experimental results.

Bending fatigue tests were carried out to clarify the effects of thin hard coatings on the fatigue strength at a number of cycles for steels. Coatings of carbides and nitrides produced by thermoreactive deposition and diffusion, chemical vapour deposition and physical vapour deposition, processes and of electroplated chromium on various steels were tested as well as hardened steels. The results thus obtained revealed that the fatigue strength at a number of cycles highly depended on hardness and residual stress at the substrate surface as in the case of the endurance limit and that the existence of the coatings suppressed the cracking in the substrates to increase the fatigue strength after loading cycles. Effects of coating thickness, surface roughness, notch shape, and post-heat treatment were also examined.

— An hermetic-sealing material for FEDs composed of thermosetting polyimide and glass fiber, has been developed. The main backbone and end-capping material of polyimide were investigated to satisfy both high Tg and high flowability. A thermosetting function, 4-phenylethynylphthalic anhydride (PEPA), was used as the end-capping material. The fracture of a rigid and softening structure was optimized in the main polymer structure. The obtained polyimide demonstrated both a high Tg (265°C) and low viscosity (98 Pa-sec at a sealing temperature of 350°C). In order to improve the gas permeability and the mechanical and thermal characteristics of the sealing material, a mixture of various types of ceramic fillers and polyimide has been investigated, and glass fiber was adopted. When 30 wt.% of glass fiber was combined when the developed polyimide, the Ar permeability and coefficient of thermal expansion of the sealing material decreased to below one-half of the base polyimide. This material enables us to seal at a temperature of about 350°C in nitrogen atmosphere and shows superior performance suitable for glass-to-glass sealing.

A hermetic-sealing material for FED composed of thermosetting polyimide and inorganic filler has been developed. This material enables us to seal at a temperature around 350 °C in nitrogen atmosphere and shows superior performance suitable for glass-to-glass and glass-to-metal sealing.