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We present a semimathematical model for the simulation of the impedance spectra of a rechargeable lithium batteries consisting of porous electrodes with spherical Li + intercalation particles. The particles are considered to have two distinct homogeneous phases as a result of the intercalation and deintercalation of Li + during charge and discharge. The diffusion of Li + ions in the two phases and the charge transfer at the solid electrolyte interface ͑SEI͒ are described with a mathematical model. The SEI and the electrolyte are modeled using passive electronic elements. First, this model is derived for a single intercalation particle consisting of two different solid phases. This model is then transformed to a continuous model and applied to a single porous electrode, where the sizes of the particles are assumed to have on average two grain sizes where the radii are Gaussian distributions. Finally, this model is further developed to simulate the impedance of a rechargeable lithium-ion battery. In general, aging of dynamic systems is a major concern and finding relevant aging mechanisms is then of vital importance. For batteries, many efforts have been undertaken in order to estimate the calendar life of these systems. In the case of the more recent Li-ion batteries, a lot of work was already performed within the Department of Energy's Advanced Technology Program ͑DoE-ATP͒. Electrochemical studies including impedance spectroscopy are widely used for that purpose. Unfortunately, these methods can only provide indirect proof of certain aging mechanisms. Therefore, additional research, such as postmortem analysis, is a prerequisite to determine the most relevant mechanisms that contribute to aging. Subsequently, these aging parameters then should be translated into electrochemical behavior that is monitored with electrochemical equipment. During the last decade, many aging mechanisms have been identified for Li-ion batteries. A wide overview that comprises cathode, anode, electrolyte, and current collectors is given in Ref.1. The present model uses a transformation of a complex model in the time domain into the frequency domain, which is typically the outcome of impedance spectroscopy. The aging then is introduced via typical aging parameters identified in Ref. 1. For the current calculations, the focus is on the positive electrode, as it has been reported recently that this electrode is the major source for aging. [2][3][4] The idea is to show the influence of potential sources of degradation on impedance with focus on aging, which may result in reduction of the particle size and changes in the particle size distribution, due for instance, to dissolution of material, and on changes in the solid electrolyte interface that may occur during the lifetime of a battery. Besides, when the system is subject to even small crystallographic changes, the diffusion coefficient may be altered as well.LiNiO 2 and LiCoO 2 are well-known compounds for use as positive electrodes in lithium secondary batteries because of their high ...

Aqueous Zn-ion batteries (ZIBs) have acquired great attention because of their high safety and environmentally friendly properties. However, the uncontrollable Zn dendrites and the irreversibility of electrodes seriously affect their practical application. Herein, hexagonal WO3/three-dimensional porous graphene (h-WO3/3DG) is investigated as an intercalation anode for ZIBs. As a result, the h-WO3/3DG//Zn half-battery shows excellent electrochemical performance with a high capacity of 115.6 mAh g–1 at 0.1 A g–1 and 89% capacity retention at 2.0 A g–1 after 10 000 cycles. The reason could be that the crystalline structure of WO3, which has hexagonal channels, with a diameter of 5.36 Å, much higher than the diameter of Zn2+ (0.73 Å), accelerating the insertion/extraction of Zn ions. A zinc metal-free full battery using h-WO3/3DG as the anode and ZnMn2O4/carbon black (ZnMn2O4/CB) as the cathode is constructed, exhibiting an initial capacity of 66.8 mAh g–1 at 0.1 A g–1 corresponding to an energy density of 73.5 W h kg–1 (based on the total mass of anode and cathode-active materials) and a capacity retention of 76.6% after 1000 cycles at 0.5 A g–1. This work demonstrates the high potential of hexagonal WO3 as an advanced intercalation anode material for Zn metal-free batteries and may inspire new ideas for the development of other intercalation anode hosts for ZIBs.

Because of their good mechanical flexibility and large exposed surfaces, two-dimensional (2D) nanostructures have attracted tremendous attention in the fields of renewable energy storage and conversion devices. However, fabricating 2D nanostructures with a facile and low-cost route remains a big challenge. In this work, a very facile thermal-decomposition strategy is proposed for preparing 2D NiO porous nanosheets by using nickel chloride and glucose as raw materials. In contrast to the microsized NiO polyhedrons, the 2D NiO porous nanosheets show significantly improved lithium storage capability. Benefiting from the robust 2D framework and porous nanostructure, the 2D NiO porous nanosheets exhibit high reversible capacity (926.5 mA h g–1 after 500 cycles at 1 A g–1), long cycling stability (557.7 mA h g–1 after 1100 cycles at 3 A g–1), and high-rate capability (350.7 mA h g–1 at 10 A g–1). The lithium storage mechanism of the 2D NiO porous nanosheets is explored based on ex situ X-ray diffraction, fourier transformation infrared spectrometry, transmission electron microscopy, and X-ray photoelectron spectroscopy measurements, combined with cyclic voltammetry and electrochemical impedance spectroscopy measurements. It reveals that the capacitive-controlled lithium storage originating from the reversible formation/dissolution of polymer/gel-like layer gives a remarkable contribution to the overall capacity of the 2D NiO porous nanosheets, which leads to the outstanding lithium storage performance. The 2D NiO porous nanosheets also show a good cycling performance when used as an anode material for full-cell lithium-ion battery (NiO//LiCoO2). The reported facile and low-cost method provides an avenue for the design and massive production of 2D nanostructured electrode materials for high performance lithium-ion batteries.