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The effects of multiwalled carbon nanotubes (MWNTs) and carbon black (CB) as conducting additives on the rate capability of natural graphite negative electrodes in lithium-ion (Li-ion) batteries is investigated within concentration ranges where no degradation of anode capacity is observed. MWNT or CB solutions prepared with Nafion in an 80:20 volume mixture of water:1-propanol are incorporated into graphite precursor suspensions consisting of graphite particulates, carboxymethyl cellulose, and styrene butadiene rubber prepared in an aqueous medium. While negative electrodes with MWNTs demonstrate much better rate behaviour than those without MWNTs at a high C-rate, the rate capability of negative electrodes with MWNTs is not much different from that with CB. The reason for this similar behaviour is investigated with respect to the structural changes and aspect ratio of MWNTs, as well as the density difference between MWNTs and carbon black. Scanning electron microscopy images and Raman spectra for the dispersed MWNTs indicate that MWNTs are significantly damaged and shortened during dispersion, which reduces their electrical conductivity and increases their percolation threshold. This damage negatively affects the rate capability of graphite-nanotube composite electrodes.
Influence of mixing carbonate-modified siloxane into 1 M (M: mol L−1) LiPF6-ethylene carbonate (EC)/ethylmethyl carbonate (EMC) (mixing volume ratio = 3:7) mixed solvent electrolytes on charge–discharge cycling properties of lithium is examined. As siloxane, 4-(2-bis(trimethylsilyloxy)methylsilylethyl)-1,3-dioxolan-2-one is investigated. Charge–discharge cycling efficiencies of lithium metal anodes are improved and impedance of anode/electrolyte interface decreases by mixing siloxane, compared with those in 1 M LiPF6-EC/EMC alone. Mechanism of enhancement of lithium cycling efficiency is considered to be due to the suppression of excess reduction of LiPF6-EC/EMC by lithium and growth of surface film (SEI, solid electrolyte interphase) on lithium. Infrared study indicates that SEI formed in LiPF6-EC/EMC with siloxane contains more inorganic compounds than that in LiPF6-EC/EMC alone. Better cycling behavior of α-Fe2O3 and Si–SiO2–carbon composite anodes is obtained by mixing siloxane. Thermal behavior of electrolyte solutions toward graphite-lithium anodes is evaluated with a differential scanning calorimeter. Heat-output of graphite–lithium anodes with 1 M LiPF6-EC/EMC electrolyte solutions tends to decrease by mixing siloxane.
Dyes such as indigo and anthraquinone derivatives that find extensive use in industrial colorant applications contain electron density donor (–NH– or –OH) and acceptor (>CO) groups linked by conjugated bonds in their molecular structure, which are responsible for their deep shades. Departing from this stabilized redox state (“push–pull”) requires substantial energy and we found that with a proper choice of aqueous electrolyte these dyes are able to both reversibly oxidize and reduce, developing two-sets of fast two proton–electron transfers separated by ∼1 V. These large flat molecules are poorly soluble due to extensive “π” stacking, and the classical strategy of appending a sulphonate (–SO3Na) group appeared insufficient to reach ≈1 M. Herein, we have further boosted the solubility of these dyes in water up to 1.6 M by replacing Na+ with an organic cation such as tetrakis(hydroxyethyl)-ammonium [N(CH2CH2OH)4]+ or tetrakis(hydroxymethyl)-phosphonium [P(CH2OH)4]+ that are non-chelatable and very hygroscopic while maintaining a reversible charge transfer and a large electrochemical potential window in dilute protic acids (0.1 M HClO4), or in neutral pH buffered aqueous solutions (Britton–Robinson buffer). The corresponding pure salts melt even near ambient temperature. Our findings imply that the same electroactive material could be used as a catholyte and an anolyte in a 1 V symmetrical redox flow cell at neutral or close to neutral pH, with all its advantages in terms of cell corrosion and membrane requirements.
Tin nitride is a relatively unknown compound. In this study, the tin nitride thin film is examined as a negative electrode for a thin-film microbattery. Reactive rf magnetron sputtering is used for deposition of films with varying deposition temperature. The charge–discharge properties of thin films deposited at room temperature, 100 and 200°C are found to be satisfactory. As the irreversible capacity fraction increases, rechargeability is improved. Finally, it is suggested that the electrochemical characteristics of tin nitride are similar to those of the tin oxide system. The charge–discharge characteristics are investigated in several ways.
Applying surface coatings to alloying anodes for Li-ion batteries can improve rate capability and cycle life, but it is unclear how this second phase affects mechanical deformation during electrochemical reaction. Here, in-situ transmission electron microscopy is employed to investigate the electrochemical lithiation and delithiation of silicon nanowires (NWs) with copper coatings. When copper is coated on only one sidewall, the NW bilayer structure bends during delithiation due to length changes in the silicon. Tensile hoop stress causes conformal copper coatings to fracture during lithiation without undergoing bending deformation. In addition, in-situ and ex-situ observations indicate that a copper coating plays a role in suppressing volume expansion during lithiation. Finally, the deformation characteristics and dimensional changes of amorphous, polycrystalline, and single-crystalline silicon are compared and related to observed electrochemical behavior. This study reveals important aspects of the deformation process of silicon anodes, and the results suggest that metallic coatings can be used to improve rate behavior and to manage or direct volume expansion in optimized silicon anode frameworks.
A sandwich-structured NiMn2O4@reduced graphene oxide (NiMn2O4@rGO) nanocomposite consisting of ultrathin NiMn2O4 sheets uniformly anchored on both sides of a three-dimensional (3D) porous rGO is presented. The NiMn2O4@rGO nanocomposites prepared through a dipping process combining with a hydrothermal method show a good electrochemical performance including a high reversible capability of 1384 mAh g−1 at 1000 mA g−1 over 1620 cycles, and an superior rate performance. Thus, a full cell consisting of a commercial LiCoO2 cathode and the NiMn2O4@rGO anode delivers a stable capacity of about 1046 mAh g−1 (anode basis) after cycling at 50 mA g−1 for 60 times. It is demonstrated that the 3D porous composite structure accommodates the volume change during the Li+ insertion/extraction process and facilitates the rapid transport of ions and electrons. The high performance would enable the presented NiMn2O4@rGO nanocomposite a promising anode candidate for practical applications in Li-ion batteries.
Physically-based analytical models that provide insights into the diffusion and/or interface charge transfer effects in bulk (lithiating/delithiating) electrodes are needed to truly assess the performance/limitations of electrode materials for Li-ion batteries. In this context, an analytical modeling framework is constructed here to predict the electrochemical charge–discharge characteristics during lithiation and delithiation of solid amorphous Si (a-Si) thin film electrodes. The framework includes analytical expressions that satisfy Fick's second law for Li transport and the requisite flux boundary conditions of lithiation and delithiation steps. The expressions are derived here by the method of separation of variables. They enable the determination of transient Li concentration profiles in the thin film electrode as a function of state of charge/discharge. The time-dependent electrode surface concentrations (at the electrode–electrolyte interface) obtained from these profiles were used to determine the activation overpotentials and thus, the non-equilibrium cell potentials, as a function of state of charge/discharge using Butler–Volmer kinetics. The simulated charge/discharge characteristics agreed well with the experimental data of a-Si thin film electrodes obtained at different C-rates. The model offers insights into how the charge-discharge behavior is controlled by diffusion limitation within electrode and/or the activation overpotentials at the interface. The analytical framework is also shown to predict successfully the hysteretic behavior of lithiation/delithiation voltage curves.
Mixtures of IrO2+MnO2 (30:70 mol%) have been electrochemically studied by cyclic voltammetry (CV) in acid solution. The crystalline structure, morphology and the electrochemical properties of the electrodes have been studied as a function of the annealing temperature. X-ray diffraction analysis (XRD), show absence of Mn2O3 phase formation and suggest the possible of formation of a solid solution of IrO2 and MnO2 mainly between 400 and 450°C. The voltammetric behavior depends on the potential cycle number and annealing temperature employed in the preparation of the oxide layer. A good potential window in aqueous H2SO4 and high electroactive area are obtained due to the contribution of Ir redox transitions. Energy-dispersive X-ray (EDX) and scanning electron microscopy (SEM) analysis suggest an enrichment of the Ir content on the surface at the cost of the dissolution of the manganese present in the film when the electrode is submitted to the continuous potential scan. The electrodes have been found to perform well in electrochemical capacitor applications with a specific capacitance close to 550 F g−1. The large capacitance exhibited by this system arises from a combination of the double-layer capacitance and pseudocapacitance associated with surface redox-type reactions.
In this work, the electrochemical activation of graphite felt electrode for vanadium redox flow battery (VRB) was studied. Graphite felt (GF) electrode was oxidized at a range of electrochemical oxidation degrees in H2SO4 solution. The electrochemical performance of the treaded GF was discussed, and the law of the surface properties of GF which changed along with the electrochemical oxidation degree was proposed. The structure, composition, surface tension and electrochemical properties of the oxidized GF (OGF) were characterized using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), contact angle measurements, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The GF oxidized at 560–840mAhg−1 exhibited the best activity toward VO2+/VO2 + redox reaction, according with the highest COH and COOH content (ca. 34%) on its surface. The mechanisms of VO2+/VO2 + redox reaction on OGF were also discussed. VRB single cell with pristine GF and OGF as the electrode were test at various charge–discharge current densities, respectively. The columbic efficiency (CE), voltage efficiency (VE) and energy efficiency (EE) of the cell using OGF electrode are much higher than the cell using pristine GF, suggested that the electro-oxidation method is a promising technology for the activation of GF electrode.
It is well known that many electrochemical devices such as fuel cells, electrolyzers, batteries, etc. degrade under various operating conditions. Many devices are based on solid electrolytes. In many cases, degradation manifests as electrode delamination and/or cracking of the electrolyte. An apparently obvious conclusion often reached is that this must be due to weak interfaces and some approach to mechanical strengthening or toughening should alleviate the problem. It is the intent of this manuscript to show that such electrochemical degradation often occurs due to electrochemical-mechanical coupling effects which result in extremely large internal pressures. So large can be the pressures that no amount conventional strengthening or toughening can prevent degradation. In fact, even a perfect lattice can be disrupted by electrochemically induced pressure leading to failures. In order to prevent failures, it is necessary to fully understand the role of coupling and develop strategies of mitigating high pressure formation by optimizing ion and electron transporting properties of the membrane. This manuscript discusses a fundamental mechanism of electrochemical failure of solid oxide fuel cells, solid oxide electrolyzer cells, and oxygen separators based on oxygen ion conducting solid electrolytes. Experimental results on two types solid electrolyte cells are presented in support of the mechanism.
Lithium (Li) metal with an ultrahigh specific theoretical capacity and the lowest reduction potential is strongly considered as a promising anode for high-energy-density batteries. However, uncontrolled lithium dendrites and infinite volume change during repeated plating/stripping cycles hinder its practical applications immensely. Herein, a house-like Li anode (housed Li) was designed to circumvent the above issues. The house matrix was composed of carbon fiber matrix and affords a stable structure to relieve the volume change. An artificial solid electrolyte layer was formed on composite Li metal, just like the roof of a house, which facilitates uniform Li ions diffusion and serves as a physical barrier against electrolyte corrosion. With the combination of solid electrolyte layer and matrix in the composite Li metal anode, both dendrite growth and volume expansion are remarkably inhibited. The housed Li | LiFePO4 batteries exhibited over 95% capacity retention after 500 cycles at 1.0 C in coin cell and 85% capacity retention after 80 cycles at 0.5 C in pouch cell. The rationally combination of solid electrolyte layer protection and housed framework in one Li metal anode sheds fresh insights on the design principle of a safe and long-lifespan Li metal anode for Li metal batteries.
The protection layer was introduced to the surface of the Li anode to enhance the charge/discharge performance of lithium/sulfur batteries. The protection layer was formed by a cross-linking reaction of the curable monomer in the presence of liquid electrolyte and a photoinitiator. When the Li anode is coated with the protection layer, the unit cells with a liquid electrolyte showed an enhanced charge/discharge performance as compared to cells based on a polymer electrolyte, resulting in an average discharge capacity of 270mAh/g-cathode during 100 cycles. All the charge/discharge tests were performed at room temperatures.
Presented are the results of a comparative analysis to identify abundant, non-toxic binary materials with potential applicability for photovoltaics. Materials other than the conventional Si, CdTe, and Cu(In,Ga)Se2 (CIGS) are examined. The screening is based on the materials’ bulk properties and a set of environmental, physical, and chemical criteria. The screening process is detailed and the properties and applicability of the screened materials are discussed.
When the rechargeable Lithium coin battery is employed as the storage component for indoor energy harvesting, the leakage current of the battery cannot be ignored, especially in ultra-low-power applications. The leakage current of the Lithium coin battery is commonly believed in the low μA range. However the exact value is unknown. An experimental method to measure leakage current by applying a known charge current in μAs to a stabilized post-charge battery to observe the sign of the battery terminal voltage change is proposed. When the applied charge current is larger than the leakage current, a positive sign (terminal voltage increase) can be observed. Otherwise a negative sign appears. By gradually changing the charge current using the successive approximation search algorithm, the leakage current will finally converge to the applied charge current. The convergence happens after the sign changes in two successive search procedures, demonstrating that charge currents are approaching the leakage current from both directions. The accuracy of the approximation can be improved by adjusting the number of sign changes in the successive approximation search algorithm. The proposed method permits the full capacity of a rechargeable Lithium coin battery to be utilised in ultra-low-power applications.
The popularity of small-scale residential energy production using photovoltaic power generation is predicted to increase. Self-production of electricity for self-consumption has become profitable mainly because of high-distribution costs and taxes imposed by the service providers on commercially produced electricity or because of the subsidies which reduce installation costs. Electrical energy storage can be used to increase the self-consumption potential of photovoltaic power. Additionally, electrical energy storage can lead to other benefits such as demand response or avoiding high load peaks. In this study, the profitability and sizing of a photovoltaic system with an associated electrical energy storage are analyzed from an economic perspective. The novel theory of sizing for profitability is presented and demonstrated using case studies of an apartment building and detached houses in Finland. To maximize the benefits, several alternative models for electricity metering and pricing are used and compared. The results demonstrated that the optimal size of the photovoltaic system could be increased by using electrical energy storage and suitable electricity pricing. This could lead to an increasing amount of photovoltaic production in the residential sector. Additionally, it is possible that when all the incentives are taken into account, electrical energy storage in combination with photovoltaic power generation would be more profitable than photovoltaic power generation alone. Photovoltaic power generation also increased the profitability of electrical energy storage, which could mean that the implementation of electrical energy storage in the residential sector could likewise increase.
This study reports on a novel approach to fabrication of carbon-sulfur composite material and demonstrates its application as cathode for Li–S batteries. Firstly, highly porous carbon material has been prepared by exploiting PMMA colloidal crystal arrays as sacrificial template and subsequently mixing with elemental sulfur at 155 °C. The resulting carbon-sulfur composite cathode material possess very high intrinsic surface area, conductivity and has been found to demonstrate as high as 1600 mAh g− 1 capacity in 1st discharge cycle and about 300–400 mAh g− 1 in 50th discharge cycle.
PVdF-HFP (polyvinylidenefluoride-hexafluoropropylene) polymer electrolytes comprising cross-linkable PEGDMA (polyethylene glycol dimethacrylate) oligomers with thermal shutdown characteristic have been developed. In contrast to the melting mechanism of polyolefin, this new polymer electrolyte possesses a thermal shutdown characteristic by a rapid cross-linking reaction of PEGDMA. The cross-linked PEGDMA network inside the PVdF-HFP matrix can provide the mechanical strength for the electrolytes, while the un-cross-linked PEGDMA oligomers serve as plasticizers for PVdF-HFP to improve the mobility of lithium ions at normal operation temperatures. In addition, the un-cross-linked PEGDMA oligomers can initiate cross-linking upon a sudden rise of temperature and thus provide thermal shutdown protection at elevated temperatures.
Redox behavior of electronically conducting polymers (ECPs) and inorganic active metal oxides intercalation electrodes (IEs) were analyzed by using Frumkin-type intercalation isotherms. Using such isotherms appears to be very useful in fast screening and classification of various electroactive materials. It provides a clear tool for linking the equilibrium properties of these materials to their dynamic (transport) characteristics. In this article, we review and discuss the common features of these materials with distinctions between micro- and macrostructures, including host expansion, distortion and structural transitions; ions and solvent permeation (partioning) into the hosts; conformational flexibility and morphological changes; ordering and energetic dispersion of sites; electronic and ionic conductivity, etc.; and the ways in which these structural aspects may affect their redox behavior.
Mesoporous Au@MnO2 was fabricated via a facile self-decomposition process and is used as the electrode material for supercapacitors. Au@MnO2 electrode gave a high capacitance of 906.4 F g−1 with outstanding rate capability and excellent stability (97.2% of the original capacitance was retained after 5000 cycles). A two-electrode cell assembled by Au@MnO2 network and activated graphene oxide/Au mixture delivers an energy density of 62.8 Wh kg−1 at the power density of 1000 W kg−1.
As a recent addition to the family of van der Waals layered crystals, indium selenide (InSe) possesses unique optoelectronic and photonic properties, enabling high-performance electronic devices for broad applications. Nevertheless, the lithium storage behavior of InSe flakes is thus largely unexplored due to its low electronic conductivity and challenges associated with its exfoliation. Here, we prepare few-layered InSe flakes through liquid-phase exfoliation of wet-chemistry-synthesized layered InSe single crystals, and percolate the flakes with carbon nanotube (CNT) networks in order to form flexible anodes to store lithium (Li). We demonstrate, with the support of CNTs, that exfoliated InSe flakes possess superior Li storage capacity to bulk InSe; the capacity increases over prolonged cycling up to 1224 mA h g−1 from 520 mA h g−1, coupled with excellent rate handling properties and long-term cycling stability. The operando X-ray diffraction results suggest that the alloying of indium with Li dominates the Li storage reactions. By combining with density-functional theory calculations and post-mortem analysis, we believe that the in situ formed indium gradually reduces the domain size, forming nanoclusters which allow the accommodation of 4 Li+ per atomic indium, and leading to extra capacity beyond the traditional theoretical value. This new “nanoscluster alloying” Li storage mechanism may inspire new architectures or methods to synthesize few-layered InSe, thereby presenting broad opportunities for high-performance Li-ion battery anode technologies.
The performance of a lithium-ion battery is closely related to its manufacturing and can be impacted by variability in the electrodes. Typically, manufacturers must set aside cells which are deemed to be of insufficient quality, thus contributing to the cost of manufacturing high quality cells. The performance of a lithium-ion battery module, that is, a string of cells configured in series, depends on the performance of the weakest cell. In this work, the single particle model was adapted to simulate the coupled behaviour of an arbitrary number of cells configured in series. The impact of slight variations in the manufacturing of electrodes was then investigated with a goal of linking electrode properties such as variations in thickness, electrode density and active material weight fraction with the performance of battery modules made from these cells. Results indicate that the initial capacity, the rate of capacity fade and other important aspects such as the distribution of state-of-charge from one cell to another depends on the extent of variability in the manufacturing of the electrodes. In this work, the variation in the performance of the module has been quantified as a function of manufacturing variation at the electrode level.