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Electrochemical Li+ extraction technology applied to salt lake brine has received considerable attention in recent years for its low energy consumption and low emissions. However, the current electrochemical Li+ extraction method often requires the use of anion trapping electrodes or anion exchange membranes, which reduce their working lives and adaptabilities. To solve these problems, this study proposes a high Mg2+/Li+ ratio brine electrochemical Li+ extraction method based on the LiFePO4-Zn battery system. By discharging in the brine and charging in a ZnCl2 solution, the Li+ in the brine was successfully transferred to the ZnCl2 solution.

Widening the operational voltage window (OVW) of electrolytes has long been attracting researchers’ attention as an effective solution for improving the energy density of supercapacitors (SCs). However, the application of commercial cellulose separators in SCs under high voltage is impeded because of the hygroscopic property of hydroxyl functional groups and high self-discharges. Herein, the dielectric materials poly(vinylidene fluoride-co-hexafluoropropylene) PVDF-HFP and TiO2 are employed to modify the surfaces of cellulose separators, which has improved the rate (100% capacitance retention at 20 A g−1) and cyclic (over 83% capacitance retention after 10000 cycles) performance of SCs significantly. In addition, the OVW of the organic electrolyte is widened from 2.7 V to 3.8 V. The possible mechanism underlying the function of dielectric materials in SCs is discussed by establishing a model and performing inferential calculation.

The intrinsic ring-opening polymerization of five-membered cyclic ether induced by Lewis acid hinder its practical application as electrolyte solvents in sodium-ion batteries. In this work, we find that introducing tris (2,2,2-trifluoroethyl) borate (TTFEB), an anion acceptor additive, into cyclic ether-based electrolyte solution effectively inhibits its polymerization by tethering the PF6 − anion. In addition, a stable inorganics-rich SEI layer is formed in TTFEB-containing electrolyte solution, which ensures fast Na+ transport kinetics upon extensive cycles. As a result, the cycle stability and rate capability of HC anodes in 1,3-dioxolane-based electrolyte solutions are evidently improved by TTFEB additive. Our study paves the way for the application of cyclic ethers in sodium-ion batteries.

A flexible and knittable symmetric all-solid-state fiber supercapacitor (ASSFS) was fabricated by using two polypyrrole (PPy) microcone arrays coated stainless steel yarns (SSY) as fiber electrodes and current collectors. The microcone arrays and interconnected network structure of PPy could increase transport path for ions/electrons and enlarge the real contact area between PPy and electrolyte, leading to superior specific capacitance. In addition, the fiber electrode has a high tensile strength of ~1200 MPa and elongation at break is 12.5%. The outstanding mechanical performance of the fiber electrode is attributed to the high mechanical properties of the SSY and the protection of PPy coating. The resultant ASSFS exhibits maximum specific capacitance of 42.7 F/cm3, energy density of 3.8 mWh/cm3 and power density of 388 mW/cm3 (normalized to the whole device). The specific capacitance maintains 100% at different bending angles and 93.5% of its initial value after 1000 bending cycles. As a demonstration, a fabric and a bracelet knitted with five ASSFSs connected in series can light a LED.

Zn–Ni battery is an attractive aqueous alkaline secondary battery due to its low cost, safety, and environmental friendliness. However, the problems of hydrogen evolution reaction, zinc dendrites growth and deformation of zinc anodes hampering the commercial application of Zn–Ni battery. In this work, the dynamic imbalance behavior of capacity of the Zn–Ni battery which caused by low coulombic efficiency of the anode is studied. Results reveal that due to the hydrogen evolution effect of the anode, the sintered Ni(OH)2 cathode which commonly used in the research of anode of Zn–Ni batteries cannot be fully discharged. Residual capacity will increase the potential of the cathode continuously, shorten the constant current charging time, and cause the battery cycle capacity decay rapidly. This phenomenon is confirmed by adding nano Bi powders to suppresse the hydrogen evolution of the zinc anode. This work reveals that the decline in the cycle life of Zn–Ni batteries is not only due to irreversible changes in the electrode structure but also due to the coulombic efficiency mismatch of the cathode and anode.

A one-dimensional model is developed and validated to study platinum degradation and the subsequent electrochemical surface area (ECA) loss in the cathode catalyst layer (CL) of polymer electrolyte fuel cells (PEFCs). The model includes two mechanisms of Pt degradation: Ostwald ripening on carbon support and Pt dissolution-re-precipitation through the ionomer phase. Impact of H2 | N2 or H2 | Air operation, operating temperature, and relative humidity (RH) on Pt degradation during voltage cycling is explored. It is shown that ECA loss is non-uniform across the cathode CL with a zone of exacerbated Pt degradation and hence much lower ECA found near the membrane. This non-uniform Pt degradation is caused by consumption of Pt ions by crossover H2 in both H2 | N2 and H2 | Air systems. An important consequence is that thinning the cathode electrode in a fuel cell would lead to more ECA loss as a higher fraction of the thin CL would fall in this exacerbated degradation zone. We have quantified the effect of thin cathode CLs on Pt degradation for the first time. © 2015 The Electrochemical Society. [DOI: 10.1149/2.0101508jes] All rights reserved.

Safety has become an increasingly pressing issue in large-format, energy-dense Li-ion batteries for automotive applications. Among various abusive scenarios for Li-ion batteries, internal short-circuit is most dangerous and has been the root cause for several highly publicized catastrophic accidents in recent years. Nail penetration and crush tests are commonly used as experimental proxy for internal shorting, but fail to truly emulate the internal short-circuits seen in field accidents. Also, experimental methods only give a simple pass/fail result, providing little insight into fundamental mechanisms governing the battery thermal and electrochemical response during internal shorting. In this study, a 3D electrochemical-thermal coupled model is used to scrutinize the internal shortcircuit process in a large-format Li-ion cell with a stacked-electrode design. The model reveals the 3D electrochemical and thermal processes inside the battery cell during internal shorting. A parametric study is carried out, showing that the short-circuit resistance and the number of shorted electrode layers have the most significant influence on cell electrochemical and thermal behavior. Novel experimental methods, designed to precisely control these key parameters, must be developed in order to advance the understanding and improvement of Li-ion battery safety.

With the increasing interest in large-format Li-ion batteries for automotive applications, safety has become a primary concern due to the high energy density of Li-ion batteries and wide-ranging working conditionsforelectricvehiclescomparedwithelectronicapplications. Safety must be maintained for electric vehicles. Even a single accident due to battery failure could turn public opinion against electric

Temperature is critical to the performance, durability and safety of Li-ion batteries. This paper reports in situ measurement of the radial temperature distribution inside a cylindrical Li-ion battery cell. 18650-size cylindrical cells with multiple micro thermocouples embedded are designed and manufactured. The radial temperature distribution is obtained under various operating conditions. The effects of critical parameters, such as discharge C rate, ambient temperature, and cooling condition, are investigated. It is found that higher discharge C rate and lower ambient temperature lead to higher temperature rise and larger temperature gradient within the battery cell. Stronger cooling results in smaller temperature rise but larger temperature gradient. Correlation between relative temperature gradient and cooling coefficient suggests that the assumption of uniform temperature distribution is applicable under natural-convection conditions but not applicable under strong forced convection conditions. The present results provide valuable experimental data that can be readily used to validate electrochemical-thermal coupled (ECT) battery models.

This paper reports in-situ measurements of current distribution in a Li-ion battery using a newly developed pouch cell with a segmented electrode. It is shown that current distribution is non-uniform from the beginning of discharge and evolves dramatically as discharge proceeds. Initially, segments closer to the negative tab generate higher local currents, which is attributed to the ohmic potential drop along the negative current collector. However, toward the end of discharge the current distribution reverses in pattern due to local SOC non-uniformity developed by uneven current production in early stages. Current distribution is more uniform at lower C rates and lower temperatures. In cells operated close to the equilibrium (e.g. at low C-rates or higher temperatures), current distributiontendstobewavyasitisdominatedbytheSOCnon-uniformityeffectandreflectiveofmultipleplateausintheopen-circuit voltage vs. SOC curve. In contrast, current distribution exhibits a monotonic variation in cells operated at highly non-equilibrium as the ohmic potential drop along the current collector becomes more controlling. Local SOC distribution is calculated based on measured local currents. The SOC distribution is found not uniform, even at cutoff during high C rate discharge, suggesting strongly under-utilization of active materials.

Solid phase diffusivity Ds is a key parameter in Lithium-Ion cell models because solid phase diffusion typically dominates the voltage transients. The Galvanostatic Intermittent Titration Technique (GITT) is easy to implement and universally accepted as the standard for diffusivity measurement, but the accuracy of GITT diffusivity measurement is unknown. This paper develops a Least Squares GITT (LS-GITT) that uses all of the voltage data from a GITT test to optimally tune the diffusivity in a reduced order solid phase diffusion model. The accuracies of the GITT and LS-GITT diffusivity measurements are evaluated using the RMS error between the model predicted and experimentally measured voltages. Based on experimental results from a NCM half cell, LS-GITT is more accurate than GITT, often by an order of magnitude. The GITT test overestimates Ds because the underlying model neglects the effects of bulk capacity on the voltage transients. LS-GITT gives results accurate to 1 mV RMS from 15%–100% SOC where GITT provides the same level of accuracy over less than half that SOC range. Neither technique provides accurate Ds measurements below 10% SOC.

To quantify the impact of non-uniform current distribution in a large-format Li-ion cell on its overall energy density, five cell configurationswithdifferentpositivetabnumbersandlocations weredeveloped.Thiswas enabledbyaspecially designedsegmented cell with reconfigurable positive tabs on the outside. Current distribution and overall discharge performance were measured and correlated with each other for all five cell configurations. It is shown that tab number and location have significant effects on the performance and current distribution of a Li-ion battery cell. Fewer tabs typically cause lower performance but excessive tabs do not help. The 1-tab-co-located configuration causes both very non-uniform current distribution and very low overall discharge performance,andshouldbeavoidedintabdesignforcellsbiggerthan ∼2.4Ah.Theeffectsoftabconfigurationonoverallperformance can be attributed to and explained by current distribution. Discharge energy of the experimental cell decreases almost linearly with a current density non-uniformity factor. Non-uniform current distribution results in non-uniform utilization of active materials, reducing energy density, and likely also accelerating degradation of the Li-ion cell. Future research on diagnosing and improving current density uniformity in large format Li-ion batteries that enable vehicle- and grid-energy storage is highly warranted.

This paper seeks to gain a better understanding of the thermal behavior of Li-ion cells using a previously developed two-dimensional, first principles-based thermal-electrochemical modeling approach. The model incorporates the reversible, irreversible, and ohmic heats in the matrix and solution phases, and the temperature dependence of the various transport, kinetic, and mass-transfer parameters based on Arrhenius expressions. Experimental data on the entropic contribution for the manganese oxide spinal and carbon electrodes, recently published in the literature, are also incorporated into the model in order to gauge the importance of this term in the overall heat generation. Simulations were used to estimate the thermal and electrical energy and the active material utilization at various rates in order to understand the effect of temperature on the electrochemistry and vice versa. In addition, the methodology of using experimental data, instead of an electrochemical model, to determine the heat-generation rate is examined by considering the differences between the local and lumped thermal models, and the assumption of using heat generation rate determined at a particular thermal environment under other conditions. Model simulations are used to gain insight into the appropriateness of various approximations in developing comprehensive thermal models for Li-ion cells. © 2002 The Electrochemical Society. All rights reserved.

A dual‐reaction model has been proposed to explain the mechanism of direct copper plating on a nonconductor with the assistance of PdS. The reaction in which charge passes through the sulfur ligand is responsible for the lateral growth of copper on the surface. The other reaction is the conventional cupric/copper deposition, which is responsible for the vertical growth of copper deposit. The exchange current density and rest potential of these two reactions have been evaluated via the potentiostatic method. When the is above 0.3 M, the exchange current densities of these two reactions were found comparable. However, for a low , the of lateral reaction is significantly higher than that of vertical reaction. Furthermore, the slope is about 0.58 for the vertical reaction, which is similar to that for the common copper deposition reaction, but is only about one‐third of that for the lateral reaction, which implies the occurrence of a different reaction. Regarding the effect of copper concentration on the equilibrium potential, is about 28 mV/dec, which is reasonable based on the Nernst equation. However, in the case of lateral reaction induced by sulfet ligand, the slope is only 18 mV/dec, indicating again the existence of a different reaction. © 1999 The Electrochemical Society. All rights reserved.

A micro-macroscopic coupled model, aimed at incorporating solid-state physics of electrode materials and interface morphology and chemistry, has been developed for advanced batteries and fuel cells. Electrochemical cells considered consist of three phases: a solid matrix (electrode material or separator), an electrolyte (liquid or solid), and a gas phase. Macroscopic conservation equations are derived separately for each phase using the volume averaging technique and are shown to contain interfacial terms which allow for the incorporation of microscopic physical phenomena such as solid-state diffusion and ohmic drop, as well as interfacial phenomena such as phase transformation, precipitation, and passivation. Constitutive relations for these interfacial terms are developed and linked to the macroscopic conservation equations for species and charge transfer. A number of nonequilibrium effects encountered in high-energy-density and high-power-density power sources are assessed. Finally, conditions for interfacial chemical and electrical equilibrium are explored and their practical implications are discussed. Simplifications of the present model to previous macrohomogeneous models are examined. In a companion paper, illustrative calculations for nickel-cadmium and nickel-metal hydride batteries are carried out. The micro-macroscopic model can be used to explore material and interfacial properties for desired cell performance.

A numerical model is developed to predict transient behaviors of electric vehicle lead-acid batteries during discharge and charge processes. The model not only accounts for coupled processes of electrochemical kinetics and mass transport occurring in a battery cell, but also considers free convection resulting from density variations due to acid stratification. A single set of conservation equations valid for both porous electrodes and the free electrolyte region is derived and numerically solved using a computational fluid dynamics technique. This numerical methodology is capable of simulating a two-dimensional cell with the fluid flow taken into consideration and requires only tens of minutes of central processing unit time on engineering workstations. Four sample calculations are presented in this work to provide rigorous validation of the developed simulator. The simulator is capable of predicting the transient behavior of the acid concentration, the porosity of the electrodes, and the state of charge of the battery during discharge, rest, and charge cycles. The model can also be used to investigate the effects of various system parameters, such as electrode dimensions, separator design, temperature, and electrolyte composition on the battery performance (voltage, power, cold cranking amperage, etc.).

The mechanism of copper deposition by direct plating on a nonconductive substrate has been investigated. Studies using electron spectroscopic chemical analysis show that the immersion of a sodium sulfide solution does lead to the formation of palladium sul ide. Sulfide acts as a bridging ligand ; it can increase the speed of direct plating dramatically. Compounds with similar bridging property were later found to show the same promotion effect in the direct plating process. These compounds include thiourea, sodium thiocyanate, potassium iodide, and sodium cyanide. It was also found that the addition of these compounds could cause a shift of the rest potential. In addition, copper was found to partially dissolve if the current was interrupted. These phenomena can all be explained by the proposed mechanism.