Differential Capacitance Curves Research Articles

The effects of Fe/Al co-modified Ni-rich Li[Ni1-x-yCoxMny]O2 for enhancing electrochemical performance

Various impurities such as Cu, Al, and Fe can be incorporated in the leachate of spent lithium-ion batteries (LIB) after a conventional acidic leaching process. Here, we synthesize Fe/Al co-modified Ni-rich Li[Ni1-x-yCoxMny]O2 (NCM) cathode materials via a coprecipitation reaction for Fe doping and the subsequent calcination process for additional Al doping. The purpose of this work is to seek a potential of utilizing the positive effects of impurity elements for improving the LIB performance of Ni-rich NCM. The physicochemical properties of cathode materials are compared by scanning electron microscopy, energy dispersive spectroscopy, inductively coupled plasma optical emission spectroscopy and X-ray diffraction analysis. Electrochemical analyses including galvanostatic intermittent titration technique, differential capacity curves from cycling data are systematically performed to assess the effects of the sequential doping processes. It is found that an Al doping content of 1% in Fe-doped NCM is optimal in terms of rate and cycle performances. This study proposes a rational design for upgrading the resynthesized Ni-rich NCM cathode materials from the leachate of spent LIBs.

Lithium-ion batteries health prognosis via differential thermal capacity with simulated annealing and support vector regression

Accurate state of health (SOH) estimation is a key issue for lithium-ion batteries management and control. In this paper, a novel SOH estimation method is proposed based on the fusion of the simulated annealing algorithm and support vector regression (SVR). Firstly, considering the electrochemical and thermodynamic characteristics of the battery aging process, we extract the health factors by analyzing and sampling the differential thermal capacity (DTC) curves which are based on temperature, voltage, and current. Then, an SVR model is constructed to estimate the SOH. The mean-variance obtained from cross-validation is used as the evaluation function, and hyperparameters of the SVR are optimized using the simulated annealing algorithm. Finally, we conduct two sets of experiments on the Oxford dataset for verification. Experimental results not only show the outperformance of the DTC curves for describing the battery aging but also illustrate that our proposed prediction model exhibits higher accuracy and less error of SOH estimation under the premise of ensuring real-time performance than the other two comparative models.

Molecular Dynamics Simulations of Metal Electrode/Molten LiCl-KCl-UCl3 Mixtures Interface

The structural and dynamical properties of the interface between metal electrode/molten LiCl-KCl-UCl3 mixtures were studied through constant charge molecular dynamics simulation. We observed a layered structure of the metal electrode/molten LiCl-KCl-UCl3 mixtures interface composed by multiple layers of anions and cations. The distribution of U3+ at the interface was ordered, and the increase of electrode charges promoted this ordered interfacial distribution. The differential capacitance curve was a flattened and bell-like shape with the maximum at a negative surface charge due to the characteristic adsorption of cations. Moreover, the interfacial dynamical properties were described qualitatively, and an additional barrier to the diffusion along z-direction caused by layered distribution was found to explain the limitation of diffusion in z-direction at the interface.

Fe3+-assistantly carbon-impregnated porous SiO2 mesoscale tubes as Li-ion battery anode materials with highly enhanced performances

Porous SiO 2 mesoscale tubes (SiO 2 -pMT) impregnated with carbon in the pores within their tube walls were successfully prepared for the first time by making use of the Fe 3+ assisted anchoring of dopamine (DA) on the surface of SiO 2 as carbon source, and thereby endowed with highly enhanced anode performances for Li-ion batteries. Typically, a reversible specific capacity of 512.8 mAh g −1 was achieved after 500 cycles at 1 A g −1 when the SiO 2 -pMT impregnated with carbon by Fe 3+ assistance was used as anode material, which is about 10 times that of SiO 2 -pMT with no carbon impregnation and 25% higher than that of the SiO 2 -pMT with carbon impregnated at double the concentration of dopamine but in the absence of Fe 3+ cations. It has been found that the carbon impregnation of the SiO 2 -pMT may be achieved more easily and homogeneously with the assistance of Fe 3+ cations and, as a result, 3-dimensional porous carbon-networks with higher connectivity can be built up, which greatly facilitate the transport of electrons to more potential reaction sites where Li-ions are available and provide fast channel for Li-ions diffusion, leading to enhanced electrochemical kinetics, as unveiled by the differential capacity curves and electrochemical impedance spectra acquired at different intervals during the initial cycle. Furthermore, as shown by XPS data, such benefitial assistance of Fe 3+ cations is believed to arise from their coupling effects between the phenolic hydroxyl groups of dopamine molecules and the surface of SiO 2 through the chemical bondings of C-O-Fe and Fe-O-Si. Fe 3+ -assisted carbon impregnation of porous SiO 2 mesoscale tubes (SiO 2 -pMT) with dopamine as carbon source (via path 1) leading to remarkable enhancement in carbon content, structural homogeneity, and anode performance in Li-ion battery in contrast to that achieved with no Fe 3+ -assistance (via path 2). • Fe 3+ was firstly introduced into dopamine for the fabrication of SiO 2 -pMT@iC. • The carbon impregnation was achieved more homogeneously with the assistance of Fe 3+ . • The coupling effect of Fe 3+ exists through the chemical bonds of C-O-Fe and Fe-O-Si. • High connected porous carbon network enable SiO 2 -pMT@iC with enhanced performance.

Remaining Useful Life Early Prediction of Batteries Based on the Differential Voltage and Differential Capacity Curves

Accurate prediction of the remaining useful life (RUL) of batteries is of great importance for the health management of different equipment and machines, such as electric vehicles and smartphones. It gives operators information about when the battery should be replaced. Predicting the batteries’ RUL using the data only from early cycles can also be beneficial for manufacturers. For example, it can reduce the batteries’ testing costs during the research and development phase. This article focuses on batteries’ RUL early prediction using data-driven methods. The differential capacity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$dQ/dV)$ </tex-math></inline-formula> and differential voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$dV/dQ)$ </tex-math></inline-formula> curves can reveal the potential capacity and voltage of a battery, respectively, and they are known to be indicators of the batteries’ degradation. We will present a practical method for batteries’ RUL early prediction using features extracted from those two curves. Accordingly, 19 features generated from the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$dQ/dV$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$dV/dQ$ </tex-math></inline-formula> curves are analyzed and extracted. The Sparse Bayesian Learning (SBL) method is a popular machine learning method in the field of RUL prediction, and it is used to achieve an RUL early prediction for batteries. In the end, the training and test errors are investigated to evaluate the presented method’s efficiency. Moreover, we compared our results with two other methods (lasso and elastic net), which have been recognized as best performing methods in this field so far, and the comparisons showed our proposed method outperforms those two methods in the term of accuracy. The presented method is generic and can be used for RUL early prediction of different batteries.

Identifying the Potential of Zero Charge and Faradaic Reactions By Step Potential Electrochemical Spectroscopy

The study of electrode processes at carbon electrodes has great relevance to a variety of electrochemical applications. The wide range of carbon materials, their possible combination, the variability of electrode design and fabrication techniques, the specific application purposes, all these elements show the richness and complexity of this research area in electrochemistry. In particular, Activated Carbon (AC) electrodes are widely used for charge storage in supercapacitors and capacitive deionization cells. For their porous structure and surface characteristics, this class of electrodes may pose serious challenges to the capacity of routine electrochemical methods to achieve an in-depth analysis and the deconvolution of different electrode processes. A relatively new and interesting method, the Step Potential Electrochemical Spectroscopy (SPECS), has been shown to be an effective way to separate the contributions of faradaic and non-faradaic processes to the total current at AC electrodes1. The technique consists in applying to the working electrode (WE) a series of small potential steps and recording the current decay during a time interval long enough to allow for equilibration. Relatively simple models are fitted to the transients, to derive parameters of capacitive charging and faradaic processes. In the present work, we explore further the capability of SPECS to characterize electrode processes at AC electrodes, having in mind two objectives in particular: the determination of the Potential of Zero Charge (EPZC ) and the separation and possible identification of faradaic processes, through a closer examination of experimental data.AC (YEC-8A) paste electrodes (80% AC, 10% carbon black and 10% PTFE) on graphite current collector (130 μm thick foil) were used as WE in 0.1 M NaClaq electrolyte. The EPZC was determined as the minimum of differential capacitance vs. potential plot (single-frequency EIS measurement at 5 mHz). SPECS was performed over the potential window from –0.25 to 0.75 VSCE both in the anodic and cathodic direction, using a step of 25 mV and equilibration time of 300 s (sampling time 0.1 s). SPECS current transients are simulated by a two-exponential decay function with a residual current.Normalized differential capacitance curves from EIS and SPECS are shown in Figure 1a. The value of EPZC is found at about 0.175 and 0.190 VSCE by EIS and SPECS, respectively. Additionally, a good agreement is found between the absolute capacitance minimum determined by either technique at electrolyte concentration from 0.01 to 1.0 M, see inset of Figure 1a. The plot of residual currents vs. potential from the analysis of SPECS data is shown in Figure 1b. The trend of the currents, in both scan directions, highlights two “inversion” potentials: at about 0 VSCE, during forward polarization, and at about 0.57 VSCE, during backward polarization; in other words, the residual current is positive on the anodic side and negative on the cathodic side vs. the inversion potential, thus recreating the typical shape of a polarization curve. With this premise, though speculative, we identify tentatively two different reactions in the anodic and in the cathodic scan of the SPECS measurements, corresponding to carbon oxidation and oxygen reduction, respectively. Notably, the equilibrium potential of these reactions2 is reasonably close to the inversion potential observed in Figure 1b.1. Dupont, M. F. & Donne, S. W. Separating Faradaic and Non-Faradaic Charge Storage Contributions in Activated Carbon Electrochemical Capacitors Using Electrochemical Methods I . Step Potential Electrochemical Spectroscopy. 162, 1246–1254 (2015).2. Zhang, C., He, D., Ma, J., Tang, W. & Waite, T. D. Faradaic reactions in capacitive deionization (CDI) - problems and possibilities: A review. Water Research 128, 314–330 (2018). Figure 1

Suppressing Cu-based cathode dissolution in rechargeable aqueous zinc batteries with equilibrium principles

Cathode materials with conversion reaction would offer higher theoretical capacities than intercalation-type materials. Copper-based materials can undergo two electron transfers from the redox couples of Cu2+/Cu+ and Cu+/Cu, which at the same time provides desirable redox potentials as cathode materials for aqueous zinc batteries. However, most Cu2+ components are soluble in water, leading to the continuous loss of active material and capacity decay upon cycling. Herein, we prevent Cu2+ dissolution with fundamental equilibrium principles. The CuO cathode experiences rapid capacity decay within few cycles in conventional zinc electrolytes upon the formation of soluble charged products. The dissolution equilibrium is effectively shifted to the left by increasing the concentration of the associated anion TFSI- in the electrolyte of 21 m LiTFSI + 1 m Zn(TFSI)2, and Cu2+ is confined in the cathode in the forms of Cu(TFSI)2 and CuO. A stable capacity retention of 91.2% realized after 300 cycles, and the stable evolution of differential capacity curves furthermore demonstrates the well-preserved energy storage process. A good capacity of 180 mAh g−1 is achieved at 100 mA g−1. This work provides a feasible strategy to suppress active material dissolution and highlights the potential utilization of copper-based conversion cathode materials for aqueous zinc batteries.

Electrochemical characteristics of molten iron electrodes in slag and electrochemical properties of their interface

Kinetic characteristics of molten iron/slag reactions and interfacial properties between molten iron/slag are of profound importance in steelmaking but quantitative electrochemical descriptions are lacking. Therefore, a detailed electrochemical investigation of pure (carbon-free) molten iron in slag was performed in the present work, using mostly impedance spectroscopy. Measurements were made between 1600–1700 °C at the rest potential and also at direct current biases to elucidate changes in interfacial properties when metal/slag reactions take place. Various fundamental physiochemical properties were measured for the first time including exchange currents, standard heterogeneous rate constants, Nernst diffusion layer thicknesses in slag, differential capacitance curves, potentials of zero charge, excess charge density curves, and electrocapillary curves. Results and discussion inform about the electric double layer formed between molten iron and slag.

Effects of Silicon Content in Silicon-Graphite Composite Anode on Capacity Degradation

Silicon, with its theoretical capacity of 4200 mAh g-1,[1] has been exploited as a capacity-booster for mature graphite anodes. However, silicon is prone to fast degradation due to significant volume expansion, which may undermine the intrinsic stability of the graphite, resulting in shorter cycle life. The trade-off between higher capacity and shorter cycle life is therefore worth optimizing. This study investigates the effects of silicon content on the cycling performance of silicon-graphite composite anodes. The composite electrodes were synthesized by mixing both materials at various weight ratios, along with carbon black and polyacrylic acid solution, and coated on a copper foil. A mixture of 1 M of LiPF6 in EC: DMC, 1:1, v/v, and Fluoroethylene carbonate (FEC) was used as the electrolyte. The samples consist of electrodes with silicon content from 8% to 40%. Galvanostatic test was done at various C-rates to determine the specific capacity at each cycle, and the correlation between the voltage and the capacity during the test was used to create differential capacitance curves. Electron microscopy and energy-dispersive X-ray spectroscopy were used to study morphology and to detect agglomeration of silicon particles. The results show that the initial capacity and the capacity retention of each sample indeed depend on the silicon content. As expected, higher silicon contents yield higher initial specific capacities but cause faster degradation. However, the trends do not continue beyond 32% of Si content. This suggests that there is a limit for silicon to enhance the initial specific capacity at a fixed C-rate. Differential capacitance curves show the gradual disappearance of silicon peaks, e.g., a peak at 0.45 V, which indicates that the primary cause of the capacity loss is the degradation of silicon material. Elemental analysis shows the high content of silicon content can promote particle agglomeration. Future tasks will include establishing the relationship between the silicon content and quantifying the amount of silicon agglomeration using X-ray spectroscopy. The results from this study can be used to assess an appropriate amount of silicon in anode material.

Capacity fade characteristics of nickel-based lithium-ion secondary battery after calendar deterioration at 80 °C

In this study, we evaluated the calendar deterioration behavior of nickel-based lithium-ion secondary batteries by storing them at 80 °C for different durations. The results indicate that the battery capacity decreased with the increasing number of storage days in a high-temperature environment. From the differential capacity curves, we found that the change in the overvoltage, which was caused by the electrode reaction, that appeared at approximately 4.2 V was most significant. To analyze this phenomenon, electrochemical impedance spectroscopy of the deteriorated battery was measured at 4.2 V, and it was confirmed that the cathode-based resistance of the battery increased significantly at this potential. Furthermore, post-mortem analysis revealed that the cathode active material of the tested batteries clearly deteriorated; however, no significant change in the active material in the anode was observed. Therefore, it is considered that the cathode materials of nickel-based lithium-ion secondary batteries deteriorate by storing at 80 °C, thereby resulting in reduced battery capacity and increased cathode component resistance after storing at high temperatures.

Origin of anomalous high-rate Na-ion electrochemistry in layered bismuth telluride anodes

Summary van der Waals layered metal chalcogenide Bi2Te3 has shown exceptional capacity and rate capability in alkali-ion batteries but the underlying reaction mechanism with Li+, Na+, and K+ remains undiscovered. It is unexpected that Na+ electrochemistry outperforms Li+ and K+ at high current densities. Here, in situ transmission electron microscopy is used to uncover nanoscale transformations during lithiation, sodiation, and potassiation, which follows two-step conversion and alloying reactions with Li+ and Na+, and three-step intercalation-conversion-alloying reactions with K+. Counterintuitively, sodiation exhibits the highest reaction kinetics, and its origin can be elucidated by first-principles and finite-element simulations in two aspects. The lower interfacial strain accommodation energy between Bi2Te3 and its Na-conversion products allows more facile sodiation phase transformation than Li- and K-ion reactions. The higher electrochemo-mechanical stress concentration at the concave-shaped sodiation reaction front facilitates continued Na-ion diffusion and reaction propagation. These fundamental insights are essential for fast-charging alkali-ion batteries.

4,4'-Bipyridine Adsorption on Sb(111) from Ionic Liquid- in Situ STM and EIS Study

Room-temperature ionic liquids (RTIL) draw a lot of attention in modern electrochemical research due to their high stability under applied electrode potential, the wide electrochemical window and dual usability as a solvent and an electrolyte RTILs have become very attractive. Molecular self-assembly at solid surfaces, resulting in the formation of nanostructures with well-controlled properties and functionality presents multiple prospective applications in science and technology [2], e.g., the smart tailoring of the structural properties of the functionalized electrodes attracts a lot of attention due to an ability to trigger the specific electrochemical processes.In this study, the in situ scanning tunnelling microscopy (STM) and impedance spectroscopy methods have been applied to study the structure and adsorption properties of the electrochemically polished Sb(111) single crystal electrode | EMImBF4, and EMImBF4 + X% 4,4'-bipyridine (x= 1; 2; 5), interface.During the measurements, atomically flat areas have been observed on the in situ STM images of Sb(111) single crystal electrode surface in EMImBF4 and atomic resolution was obtained. The in situ STM data show that there is no quick surface reconstruction process. The surface structure is stable within the potential region investigated (-0.8 — -0.1 vs. Ag/AgCl|EMImBF4) as it has been shown for inactive electrolyte solutions [3].Additionally, the influence of electrode potential on the adsorption kinetics of 4,4'-bipyridine on Sb(111) has been demonstrated. Within the region of maximal adsorption, the capacitance pits in the differential capacitance vs. electrode potential curves have been observed, depending on the 4,4'-bipyridine concentration [4]. The influence of electrode potential (E) on the adsorption kinetics of 4,4'-BiPy on Sb(111) has been demonstrated. From the in situ STM data it has been found that 4,4’-BP adsorbs in a form of a stripe pattern on antimony single crystal electrodes.AcknowledgementsThis work was supported by Estonian Research Council grants PUT PSG249 and RSG676, and by the EU through the European Regional Development Fund under project TK141 (2014-2020.4.01.15-0011).

Tin-based anode material with good reversibility of conversion reaction for lithium ion battery

Nanometerization of tin-based materials is beneficial to alleviate the volume effect, and thus improving the cycle stability of tin-based materials. Meanwhile, the smaller size can enhance the reversibility of the conversion reaction, which is crucial for increasing the capacity of tin-based materials. Therefore, reducing the size of tin-based materials may bring the advantages of cycle stability and specific capacity. In this work, we tried to disperse tin ions with organic skeleton to maximize the dispersion of active materials. Tin-based anode material based on polyethyleneimine‑sodium xanthogenate is synthesized by in-situ method at room temperature, and the thiocarboxyl group of polyethyleneimine‑sodium xanthogenate greatly increases the dispersion of metal ions. Carbon nanotubes (CNTs) are further introduced to improve the conductibility of tin-based materials owing to the existence of non-conductive organic groups. The anode material exhibits a long cycle life which delivers a specific capacity of 560 mAh g−1 after 1000 cycles. By analyzing the differential charge capacity (dQ/dV) curves, we find that the conversion reaction of tin-based materials is highly reversible.

Crack-free single-crystal LiNi0.83Co0.10Mn0.07O2 as cycling/thermal stable cathode materials for high-voltage lithium-ion batteries

The needs for lightweight portable electronic devices and long-duration electric vehicles impel the development of high-energy lithium-ion batteries (LIBs). As a promising cathode material, the high nickel content (x) and cutoff voltage facilitate to increase energy density of LiNixCoyMnzO2 (x+y+z=1) whereas they impair cycling and thermal stability. Herein, we first synthesize crack-free single crystal LiNi0.83Co0.10Mn0.07O2 (SC-NCM) materials, which possess superior cycling and thermal stability at high voltages by decreasing the inter-granular fracture induced by anisotropic volume changes to retain the interior particle morphology integrity during long charge–discharge processes. Specifically, SC-NCM in full cells between 3.00 V and 4.35 V delivers reversible capacity of 167.0 mAh g−1 and capacity retention of 84.8% after 400 cycles at 0.5 C/25 °C, which are far larger than 107.7 mAh g−1 and 54.1% of conventional polycrystalline LiNi0.83Co0.10Mn0.07O2 (PC-NCM). The enhanced high-voltage cyclability of SC-NCM is attributed to lower transition metal dissolution, higher anti-crack performances, better phase transition reversibility and smaller volume change, revealed by in-situ X-ray diffraction and differential capacity curves between 3.0 and 4.9 V. The SC-NCM has better floating charge durability than PC-NCM at high temperature by depressing side reactions between cathode and electrolyte, and formation of nickel dendrite-induced internal short dots.

Structural and thermodynamic properties of the electrical double layer in slit nanopores: A Monte Carlo study.

Grand canonical Monte Carlo (GCMC) simulation techniques at a constant electrode-electrolyte potential drop are employed to study the differential capacitance of a planar electric double layer in slit nanopores. According to the technique, a single randomly selected ion is exchanged between a simulation box and a reservoir. The probability of this step is given by the GCMC algorithm. To preserve the electroneutrality of the system after the ion exchange, the electrode charge is adequately modified, which produces electrode charge fluctuations. The charge fluctuations are used to calculate the differential capacitance of the double layer. Results for the ion distributions, electrode surface charge density, and differential capacitance in slit nanopores are reported for a symmetric system of +1:-1 ionic valences with a common ionic diameter of 0.4 nm at electrolyte concentrations of 0.2M, 1.0M, and 2.5M, pore widths of 0.6 nm, 0.8 nm, and 1.2 nm, a potential drop of 0.05 V, a relative permittivity of 78.5, and a temperature of 298.15 K. These results are compared with the corresponding data for a +1:-2 valence asymmetric system and a size asymmetric system with ionic diameters of 0.4 nm and 0.3 nm. The results show that with increasing electrolyte concentration, the range of confinement effects decreases. For divalent anions, the width dependence of electrode charge and differential capacitance reveals a maximum. The differential capacitance curves show a camel shape to bell shape transition as the electrolyte concentration increases. Asymmetry in both ionic valences and diameters leads to asymmetric capacitance curves.

Tin-based organic sulfides with highly reversibility of conversion reaction synthesized at room temperature as anode for lithium storage

Increasing the degree of dispersion is of great significance for improving the electrochemical performance of tin-based materials. The smaller size is conducive to alleviating the volume effect and improving the reversibility of the conversion reaction, thus improving the cyclic stability and reversible capacity of tin-based anode materials. In this work, tin-based organic sulfide is synthesized by potassium ethyl xanthate, and graphene is added to enhance the conductivity of the electrode material. The anode material exhibits excellent performance with the residual capacity of 657 mAh g−1 after 400 cycles at the current density of 200 mA g−1. The differential charge capacity (dQ/dV) curves show that the conversion reaction of electrode materials has good reversibility and is maintained until the end of the cycle. We also investigated the effect of calcination temperature on the conversion reaction, and verified that it is important to maintain the tin-organic structure for the reversibility of the conversion reaction.

Enforced Freedom: Electric‐Field‐Induced Declustering of Ionic‐Liquid Ions in the Electrical Double Layer

Ions in the bulk of solvent‐free ionic liquids bind into ion pairs and clusters. The competition between the propensity of ions to stay in a bound state, and the reduction of the energy when unbinding in electric field, determines the portion of free ions in the electrical double layer. We present the simplest possible mean‐field theory to study this effect. “Cracking” of ion pairs into free ions in electric field is accompanied by the change of the dielectric response of the ionic liquid. The predictions from the theory are verified and further explored by molecular dynamics simulations. A particular finding of the theory is that the differential capacitance vs potential curve displays a bell shape, despite the low concentration of free charge carriers, because the dielectric response reduces the threshold concentration for the bell‐ to camel‐shape transition. The presented theory does not take into account overscreening and oscillating charge distributions in the electrical double layer. But in spite of the simplicity of the model, its findings demonstrate a clear physical effect: a preference to be a charged monopole rather than a dipole (or higher order multipole) in strong electric field.

Delayed Phase Transition and Improved Cycling/Thermal Stability by Spinel LiNi0.5Mn1.5O4 Modification for LiCoO2 Cathode at High Voltages.

Increasing the upper cutoff voltage is capable of achieving higher charge capacity, whereas this strategy always causes a dramatic degradation of cycling and thermal stability. In this study, we first report spinel LiNi0.5Mn1.5O4-modified LiCoO2 (LiCoO2@LiNi0.5Mn1.5O4) as an outstanding cathode material. LiCoO2@LiNi0.5Mn1.5O4 retains capacity retention of 81.4% in a full cell between 4.45 and 3.00 V after 400 cycles at 0.5 C and is superior to 55.3% of pure LiCoO2. In situ X-ray diffraction at an upper cutoff voltage of 4.75 V in combination with differential capacity curve reveals that the promoted cycling performance is ascribed to a delay of O3 → H1-3 → O1 phase transitions and a suppression of cobalt dissolution-induced side reactions. Moreover, LiNi0.5Mn1.5O4 modification improves the thermal stability of LiCoO2 by depressing the release of oxygen and the formation of cobalt dendrites.

Nicotinamide as a Catalyst for Zn2+ Electroreduction in Acetate Buffer

The paper presents the catalytic influence of nicotinamide on Zn2+ electroreduction. Changes in differential capacitance curves of the double layer Hg/acetate buffer pH = 6.0 as well as changes in zero charge potential values indicate nicotinamide adsorption with the aromatic ring on the electrode surface. This adsorption is responsible for its catalytic influence on the kinetics of Zn2+ ion electroreduction from the acetate buffer solution. The effect is stronger with increasing nicotinamide concentration. It is confirmed by the following factors: the increase in standard electrode rate constants, the reduction in the distance between anode and cathodic peaks on CV voltamperograms, and the decrease in activation resistance associated with the electrode reaction for nicotinamide solutions relative to those obtained in the case of reference solution. A very high catalytic capacity of vitamin B3 on Zn2+ ion electroreduction kinetics from pH = 6.0 acetate buffer can be explained by the formation of an active complex on the surface of the mercury electrode: Zn2+ nicotinamide, which can be described as a bridge facilitating electron exchange.Graphical An active complex NAM-Zn2+ is formed on the surface of the mercury electrode and it is a “bridge” that facilitates charge exchange during the electrode process.

Interfacial structure and differential capacitance of ionic liquid/graphite interface: A perturbed-chain SAFT density functional theory study

The perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EoS) was combined with the electrostatic free energy from the mean spherical approximation (MSA) theory, and applied to represent densities of pure imidazolium ionic liquids (ILs) with anion [BF4]−. The PC-SAFT parameters of cations were linearized with their molar mass and obtained by simultaneously fitting the model predictions to experimental densities of some ILs. The PC-SAFT-MSA model provides accurate correlations and predictions of densities comparing with experimental data. Then a classical density functional theory (DFT) was developed based on PC-SAFT-MSA. The DFT model was applied to explore the structure and differential capacitance of the electrical double layer (EDL) in ILs on graphite. The model predicts similar density profiles for both cation and anion on a neutral surface, and layered structure with alternating layers of cations and anions on a charged surface. The charge inversion phenomena were also studied based on ion distributions. We further studied the effects of the alkyl chain length, temperature and non-electrostatic solid-fluid interactions on the differential capacitance of the EDL. The model provides bell-shaped differential capacitance curves. The peak positions of differential capacitance curves shift toward positive potentials as ions size asymmetry increases in agreement with previous experiments and simulations studies. The maximum capacitance decreases with increasing alkyl chain length as well as increasing temperature.