Anodic Passivation Research Articles

Hydrogen production in a combined electrochemical system: Cathode process

Today, hydrogen is recognized as a promising fuel, which is characterized by high heat generation and combustion temperature. It is also characterized by environmental safety due to the fact that no greenhouse gases are formed during the combustion of hydrogen. There are various methods of hydrogen production: traditional methods, which include electrolysis of water and conversion of hydrocarbons, and thermochemical ones. A cheap method of hydrogen obtaining from natural gas and coke is accompanied by the carbon oxides formationю Thermochemical methods are require high temperatures (up to 1000°C). The method for hydrogen production by electrolysis of aqueous solutions of alkali metal hydroxides is the most energy-intensive. However, it is considered one of the most promising in the European Union. To reduce energy consumption for hydrogen production, the authors suggest replacingthe positive electrode, which normally produces oxygen, with a dissolving anode with an equilibrium potential lower than that of oxygen, such as an iron electrode. In this case, with such a combined electrochemical method, the decomposition voltage in the system will be 0.44 V against 1.23 V with traditional water electrolysis. The overvoltage of iron dissolution in a chloride medium is several tens of millivolts. However, the potential difference between the anode and cathode ΔU becomes smaller than the equilibrium potential difference ΔE0 = 0.44 V. This research aims to substantiate the choice of the composition and concentration of electrolytes: catholyte –to ensure conditions for reducing energy consumption for hydrogen release; anolyte – to prevent passivation of the iron anode, which can lead to the oxygen release. This work results in research of the cathodic process of hydrogen release in the following solutions: 1 M (= mol/L) NaCl with the addition of 1 M hydrochloric acid in the amount of 5, 10, 15, 20 mL. Platinum is used as a cathode for the electrolysis process. The anode material is an iron, St3 grade. It has been found that in the range of changes in the composition of the electrolyte from neutral (1 M NaCl) to acidic (1 M HCl), a change in the mechanism of water discharge is observed. In a neutral medium, the discharging occurs according to the Heyrovsky mechanism, and in an acidic medium - according to the Volmer mechanism. The choice of the anolyte composition and concentration is complicated by the need to provide an acidic medium containing chlorine ions to prevent passivation of the anode. The acidity of the solution must be at least 3 for the successful extraction of dissolution products of the iron anode.

Effect of Impurity Ions and Additives in Solution of Copper Electrorefining on the Passivation Behavior of Low-Grade Copper Anode

Cu electrorefining using a low-grade copper anode is desirable from the standpoint of electric power savings. Cu electrolysis was carried out in an unagitated sulfate solution with a low-grade copper anode, and the effect of impurity ions and additives in the solution on the passivation of the anode was investigated. The time when anode passivation firstly occurs shortened significantly in a solution containing 0.596 mol·dm−3 of Ni2+ ions as impurity and shortened somewhat in a solution containing As5+(0.053 mol·dm−3) or Bi3+(0.0005 mol·dm−3) ions. Sn2+(0.0004 mol·dm−3) and As3+(0.053 mol·dm−3) ions slightly decreased the time to passivation, but Sb3+(0.004 mol·dm−3) ions did not. The viscosity coefficient of the solution increased when the 0.596 mol·dm−3 of Ni2+ ions were added to the solution, while the diffusion coefficient of Cu2+ ions decreased. The compound of the As–Sb–O or As–Bi–O system was formed in anode slime when the As5+(0.053 mol·dm−3) or Bi3+(0.0005 mol·dm−3) ions were added to the solution, which seemed to increase the compactness of slime. The time to passivation was slightly longer in thiourea-free solution but shortened when the concentration of thiourea was increased from 0.525 to 2.24 mmol·dm−3. The time to passivation was constant in solutions containing 0 to 1.13 mmol·dm−3 of Cl− ions, but significantly decreased as the concentration of Cl− ions increased above 1.13 mmol·dm−3. Cl− ions formed Cu–Cl at the upper area of anode slime, which increased the compactness of slime and promoted the passivation.

A novel calcium fluorinated alkoxyaluminate salt as a next step towards Ca metal anode rechargeable batteries.

Ca metal anode rechargeable batteries are seen as a sustainable high-energy density and high-voltage alternative to the current Li-ion battery technology due to the low redox potential of Ca metal and abundance of Ca. Electrolytes are key enablers on the path towards next-generation battery systems. Within this work, we synthesize a new calcium tetrakis(hexafluoroisopropyloxy) aluminate salt, Ca[Al(hfip)4]2, and benchmark it versus the state-of-the-art boron analogue Ca[B(hfip)4]2. The newly developed aluminate-based electrolyte exhibits improved performance in terms of conductivity, Ca plating/stripping efficiency, and oxidative stability as well as Ca battery cell performance. A marked improvement of 0.5 V higher oxidative stability can pave the path towards high-voltage Ca batteries. A critical issue of solvent quality during salt synthesis is identified as well as solvent decomposition at the Ca metal/electrolyte interface, which leads to passivation of the Ca metal anode. However, the new aluminate salt with preferable electrochemical properties over the existing boron analogue opens up a new area for future Ca battery research based on aluminium compounds.

Dimethyl sulfoxide as a function additive on halogen-free electrolyte for magnesium battery application.

Practical Mg batteries still face significant challenges in their development, like the lack of simple compatible electrolytes, self-discharge, the rapid passivation of the Mg anode, and the slow conversion reaction pathway. Here, we propose a simple halogen-free electrolyte (HFE) based on magnesium nitrate (Mg(NO3)2), magnesium triflate Mg(CF3SO3)2, and succinonitrile (SN) dissolved in acetonitrile (ACN)/tetraethylene glycol dimethyl ether (G4) cosolvents, with dimethyl sulfoxide as a functional additive. The addition of DMSO to the HFE changes the interfacial structure at the magnesium anode surface and facilitates the transport of magnesium ions. The as-prepared electrolyte shows high conductivity (σ b = 4.48 × 10-5, 6.52 × 10-5 and 9.41 × 10-5 S cm-1 at 303, 323, and 343 K, respectively) and a high ionic transference number (tmg +2 = 0.91/0.94 at room temperature/55 °C) for the matrix containing 0.75 ml of DMSO. Also, the cell with 0.75 ml of DMSO shows high oxidation stability, a very low overpotential, and steady Mg stripping/plating up to 100 h. Postmortem analysis of pristine Mg and Mg anodes extracted from disassembled Mg/HFE/Mg and Mg/HFE_0.75 ml DMSO/Mg cells after stripping/plating reveals the role of DMSO in improving Mg-ion passage through HFE by evolving the anode/electrolyte interface at the Mg surface. Further optimization of this electrolyte is expected to achieve excellent performance and good cycle stability when applied to the magnesium battery in future work.

Cobalt free refractory high entropy alloys for total joint arthroplasty: In-vitro wear, corrosion and cytocompatibility evaluation

CoCrMo alloys are extensively used for bearing surfaces in total joint arthroplasty (TJA); however, Co poisoning remains a concern. Therefore, we propose a Co free refractory metal based high entropy alloys (RHEAs) for use in TJA. In this work, TiMoNbTaW based RHEA was prepared by arc melting. The alloy was further modified by Cr addition for improvement in wear, corrosion and cytocompatibility. X-ray diffraction revealed single bcc crystal structure where lattice constant decreased upon Cr addition. The improved hardness, yield strength and a ten-fold enhancement in wear resistance with Cr addition is ascribed to its severely distorted bcc lattice. In-vitro corrosion in Hank’s salt solution (HBSS) suggests superior thermodynamic stability and passivation of both RHEAs. Enhanced pitting resistance was seen upon Cr addition. Further, electrochemical impedance spectroscopy (EIS) analysis of the surface film showed an increase in film resistance by an order of magnitude attributed to the presence of Cr2O3 on the TiMoNbTaWCr surface as confirmed by X-Ray photoelectron spectroscopy (XPS) analysis after anodic passivation. Meanwhile, the live/dead imaging and MTT assay indicated good cell viability and proliferation of RHEAs. However, an enhanced cell adhesion and growth on TiMoNbTaWCr RHEA proves its potential applicability as a bearing surface in TJA.

Direct Ink Writing of 3D Zn Structures as High‐Capacity Anodes for Rechargeable Alkaline Batteries

The relationship between structure and performance in alkaline Zn batteries is undeniable, where anode utilization, dendrite formation, shape change, and passivation issues are all addressable through anode morphology. While tailoring 3D hosts can improve the electrode performance, these practices are inherently limited by scaffolds that increase the mass or volume. Herein, a direct write strategy for producing template‐free metallic 3D Zn electrode architectures is discussed. Concentrated inks are customized to build designs with low electrical resistivity (5 × 10−4 Ω cm), submillimeter sizes (200 μm filaments), and high mechanical stability (Young's modulus of 0.1–0.5 GPa at relative densities of 0.28–0.46). A printed Zn lattice anode versus NiOOH cathode with an alkaline polymer gel electrolyte is then demonstrated. This Zn||NiOOH cell operates for over 650 cycles at high rates of 25 mA cm−2 with an average areal capacity of 11.89 mAh cm−2, a cumulative capacity of 7.8 Ah cm−2, and a volumetric capacity of 23.78 mAh cm−3. A thicker Zn anode achieves an ultrahigh areal capacity of 85.45 mAh cm−2 and a volumetric capacity of 81.45 mAh cm−3 without significant microstructural changes after 50 cycles.

The passivity breakdown of zinc antimony alloy as an anode in the alkaline batteries

Zn is utilized as an anode in alkaline batteries because of its propensity to produce a passive colloidal layer on its surface. Then the surface should be reactivated in the passive region. Therefore, the passive state on the surface can be significantly hindered by utilizing a tiny percentage of Sb alloyed with Zn. Accordingly, the effect of minor Sb alloying with Zn on the performance of anodic dissolution and passivation in concentrated alkaline media (6 M KOH, which is used in the batteries) was studied using potentiodynamic and potentiostatic techniques. Besides, the passive layers formed at various anodic potentials were characterized utilizing scanning electron microscopy (SEM) and X-ray diffraction (XRD). The data of potentiodynamic measurements exhibited the active–passive transition curve of all studied specimens. All obtained results revealed that passivation is gradually hindered with increasing Sb content in the alloy, and less passivity was obtained at 1% Sb. Along this, a dramatic rise in current density at a particular positive potential (+ 2.0 V vs. SCE) to markedly higher values only of the electrodes containing Sb is observed.

Suppression of Heavy Ion Generation in a Vacuum Diode with a Passive Anode

Suppression of Heavy Ion Generation in a Vacuum Diode with a Passive Anode

Employing cationic kraft lignin as electrolyte additive to enhance the electrochemical performance of rechargeable aqueous zinc-ion battery

Rechargeable Zn//MnO2 batteries, the most widely studied aqueous zinc-ion batteries, suffer from poor electrochemical performance due to a series of issues on the zinc anode including corrosion, dendrites, and passivation. In this study, abundant and low-cost kraft lignin is used as a raw material to synthesize quaternized lignin (QL80), which is upgraded to an electrolyte additive for the Zn//α-MnO2 battery (ReZMB). According to corrosion and chronoamperometry tests, the electrolyte containing 1 wt% of the QL80 (named as 1 % QL80) has the lowest corrosion on the zinc electrode and is best able to promote the homogenous zinc deposition. Consequently, the ReZMB using the 1 % QL80 records the highest open-circuit voltage after storage at full charge state and the optimal rate capability, and meanwhile, the Zn//Zn symmetric battery exhibits an extended lifespan of 200 h at 5 mA·cm−2, 5 mAh·cm−2. In addition, the passivation of the zinc anode is highly prevented because no byproducts appear on the zinc anode of the ReZMB with 3000 cycles at 1.5 A·g−1, according to the results of XRD and SEM characterizations. Ultimately, the ReZMB using the 1 % QL80 presents more outstanding cyclability (more stable operation and ∼74.5 % higher discharge capacity after 3000 cycles at 1.5 A·g−1) than that of the battery using the reference electrolyte (2 M ZnSO4 + 0.2 M MnSO4). This study paves the new way for designing green lignin-derived electrolyte additives for advanced rechargeable zinc-ion batteries.

A novel electrocoagulation process with centrifugal electrodes for wastewater treatment: Electrochemical behavior of anode and kinetics of heavy metal removal

Anodic passivation is a key problem to impair the efficiency of in the electrocoagulation (EC) process. Process intensification of EC has attracted increasingly greater attention. In this work, a novel centrifugal electrode reactor was designed and applied in EC process to enhance the treatment of simulated heavy metal wastewater using aluminum anode. Results showed that the removal efficiency of heavy metals was significantly improved by the centrifugal electrodes, compared with the stationary electrodes. Electrochemical behavior of centrifugal electrodes was analyzed by an improved rotating disk electrode system. Anodic polarization behavior of aluminium showed a typical characteristic of dissolution in centrifugal electrodes, rather than passivation in static condition. Anode dissolution was controlled by the diffusion of Cl− ion that was enhanced by centrifugal electrodes. Thus, anode passivation was reduced. In addition, the kinetics analysis indicated that the removal of heavy metals in EC by centrifugal electrodes conformed to Variable-Order-Kinetic (VOK) model based on the Langmuir adsorption.

Advanced Investigation of the Electrolyte-Mg Anode Interphase for the Development of Mg-Ion Batteries

Magnesium-ion batteries (MIBs) represent a promising chemistry to potentially substitute lithium-ion technologies in the e-mobility and stationary energy storage applications. This is due to the favourable properties of metallic Mg, such as: abundancy, non-toxic nature, high recycling rate1, low redox potential (-2.37 vs SHE), safety (smooth Mg2+ electrodeposition), as well as divalent character of Mg2+ cations which leads to higher theoretical volumetric capacity (3833 mAh/cm3) than Li (2046 mAh/cm3) and commercial graphite (760 mAh/cm3).2 However, the major obstacle in the further development of MIBs is the incompatibility of Mg metal anode with conventional electrolyte solutions, which are formed by mixing simple Mg-based salts (e.g Mg(TFSI)2, Mg(ClO4)2, etc.) and polar aprotic solvents (e.g. acetonitrile, carbonates, etc.). These solutions decompose at the surface of metallic Mg forming an electronic and ionic insulating layer, leading to the passivation of the Mg anode and poor performance of the overall cell. Conversely, organoborate (Mg-tetrakis(hexafluorosisopropyloxy)borate in monoglyme, MgBOR)3 or organoaluminate (1:2 AlCl3:PhMgCl in THF, APC)4 ethereal solutions are known to prevent the passivation of the Mg metal anode, allowing the reversible electrochemical Mg2+ electrodeposition onto its surface.Despite a great effort has been done in the development of MIB,5 very little is known about the formation, evolution and degradation of the solid electrolyte interphase (SEI) formed at the interface between metallic Mg and electrolyte. This work, therefore, aims to investigate the interactions between Mg metal and passivating (Mg(TFSI)2 in monoglyme:diglyme) and non-passivating (MgBOR and APC) electrolytes combining ex-situ and in-situ spectroscopic and microscopic techniques with electrochemical testing. The properties of the SEIs will be evaluated at different states of charge (ex-situ) and during cell cycling (in-situ).Raman, Fourier transformed infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies are used to identify the composition of the electrolyte interphases, as well as monitor their changes upon cell discharge-charge cycles. Scanning electron microscopy (SEM) is performed to analyse the interphase morphologies, whereas scanning microwave microscopy (SMM)6,7 locally probes the impedance of the SEI layer. Atomic force microscopy (AFM) is also employed to evaluate the roughness of the Mg metal electrodes. Cyclic voltammetry (CV) and galvanostatic cycling with potential limitation (GCPL) are carried out in order to determine the electrochemical performance of bare Mg metal or covered with SEI layers. Furthermore, electrochemical impedance spectroscopy (EIS) is employed to probe the Mg2+ diffusion coefficients through the SEI layers at different state of charge (e.g. open circuit voltage, etc.) and determine charge transfer evolution with cycling time of the Mg metal anode.As the first step, a successful polishing method was developed to remove the native oxide layer form the surface of Mg discs allowing to expose a bare Mg metal to the electrolyte solutions and to evaluate their interactions. The polishing method also enabled to perform SMM imaging of the Mg metal since a roughness between 1-2.5 µm was achieved. The Mg discs were then immersed in the electrolyte solutions and an initial deposition of interfacial species (few nanometre thickness) was observed by SEM when Mg(TFSI)2 in monoglyme:diglyme was used, whereas a smooth surface was detected with MgBOR and APC electrolytes. This resulted in different electrochemical behaviours. In fact, symmetric cells (Mg||Mg) with MgBOR electrolyte showed a significantly higher cycling stability (> 250 h) than those with Mg(TFSI)2 in monoglyme:diglyme solution. In addition, when the latter electrolyte was used, fluorinated by-products were identified by XPS. In order to study the SEI formation and growth further, in-situ spectroscopic techniques (e.g. Raman and SMM) were employed to establish a correlation between the chemical composition of the electrolyte, the voltage range of the electrochemical tests and cycling time. In particular, the SMM method was applied to MIB technologies for the first time in this work. References I. R. P. United Nations Environment Programme, (available at https://wedocs.unep.org/20.500.11822/8702);J. Niu, Z. Zhang, D. Aurbach, Adv. Energy Mater., 2020, 10, 2000697;Z. Zhao-Karger, M. E. Gil Bardaji, O. Fuhr, M. Fichtner, J. Mater. Chem. A, 2017, 5, 10815–10820;D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich, E. Levi, Nature, 2000, 407, 724;R. Dominko, J. Bitenc, R. Berthelot, M. Gauthier, G. Pagot, V. Di Noto, J. Power Sources, 2020, 478, 229027;A. Buchter, J. Hoffmann, A. Delvallée, E. Brinciotti, D. Hapiuk, C. Licitra, K. Louarn, A. Arnoult, G. Almuneau, F. Piquemal, M. Zeier, F. Kienberger, Rev. Sci. Instrum., 2018, 89, 23704;J. Hoffmann, M. Wollensack, M. Zeier, J. Niegemann, H. Huber, F. Kienberger, in 2012 12th IEEE International Conference on Nanotechnology (IEEE-NANO), pp. 1–4.

In-situ electrochemical study of chalcopyrite pressure oxidation leaching from 110 °C to 150 °C under saturated vapor pressure

Pressure oxidation leaching behavior of chalcopyrite in sulfuric acid solution from 110 °C to 150 °C were investigated by in-situ electrochemical methods. Leaching experiments under saturated vapor pressure conditions were used to simulate the anoxic environment that may be encountered in industrial applications. Scanning electron microscope and X-ray photoelectron spectroscopy were used to characterize the morphology and the chemical status of chalcopyrite surface. Results show that the copper extraction was increased with the increase of leaching temperature. Under the optimal leaching conditions under saturated vapor pressure, the copper and iron extraction are 8.3% and 29.8%, respectively. When the temperature increased from 110 °C to 150 °C, the self-corrosion potential and electrochemical reaction resistance firstly increased and then decreased. In contrast, the resistance of the passive film was always increased with the increase of temperature. The electrochemical study results indicated that the increase in temperature affected the oxidation of chalcopyrite by altering the kinetics of the cathodic reaction and the anodic passivation. Both the self-corrosion current density ( i corr ) and rate constant were affected by the reduction of Fe(III). The XPS results show that elemental sulfur and H 3 O(Fe 3 (SO 4 ) 2 (OH) 6 ) were the main leaching solid products. The formation of H 3 O(Fe 3 (SO 4 ) 2 (OH) 6 ) not only caused a decrease in cathodic reaction kinetics, but also increased the resistance of mass transfer process. Due to the faster release of iron, copper-rich sulphides were formed, which mixed with the elemental sulfur and/or H 3 O(Fe 3 (SO 4 ) 2 (OH) 6 ) led to coverage of the chalcopyrite surface.

TFSI Anion Grafted Polymer as an Ion-Conducting Protective Layer on Magnesium Metal for Rechargeable Magnesium Batteries

Rechargeable Mg batteries are one of the most promising candidates for next-generation batteries because of their safety, low cost, and high energy density. However, passivation of the Mg anode by the formation of an ion-blocking interphase layer in common organic electrolytes requires an electrolyte compatible with Mg. Herein, we propose a facile and processable method to fabricate Mg 2+ ion-permeable protective polymer layers for Mg metal anodes. The trifluoromethanesulfonimide (TFSI) anion can be grafted onto a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer backbone, significantly amorphizing the structure and boosting Mg 2+ ion conductivity through the polymer layer. TFSI anion grafting is validated through spectroscopic analyses, and the mechanism of grafting is primarily ascribed to the polarity of the PVDF-HFP molecule. This anion-grafted polymer can form a film-like, high-surface-coverage coating layer on the Mg surface, preventing Mg from directly contacting the electrolyte. The Mg anode with this Mg 2+ ion-permeable protection layer presents markedly improved performance in both Mg symmetric cells and Mg/V 2 O 5 full cells using a common electrolyte of Mg(TFSI) 2 in propylene carbonate. We expect that this study will stimulate Mg battery research through the use of various common organic electrolytes.

Quantifying and rationalizing polarization curves of Zn-air fuel-cells: A simple enabling contribution to device-scale analysis and monitoring

Zinc-air fuel cells (ZAFCs) with flowing particulate Zn anode are gaining momentum with respect to cognate and competing flow-battery technologies, such as zinc-air batteries with immobilized zinc anode zinc-bromine, zinc-cerium and zinc-vanadium flow-batteries, owing to better energy storage flexibility and control of recharge, as well as environmental compatibility. Notwithstanding its appeal, the ZAFC concept still exhibits several operational aspects that warrant dedicated studies, mainly regarding the impact of operating conditions on anode passivation and air cathode degradation. To this aim, systematic experimentation with real devices and simple, but robust electroanalytical approaches, that would enable quantitative handling of large corpora of experimental data, are highly desirable. The literature available to date, is mainly concerned with specific issues regarding device engineering or cathode materials, while systematic and quantitative work on the electrochemical response of the device is missing. This work contributes to bridging this gap, proposing a simple and physically transparent method to follow the variations of cell response to changes in operating conditions, through the measurement of polarization curves and their fitting with a very simple, but original and robust macro-electrokinetic equation, enabling a clear correlation between overvoltage components and cell state. In addition to original measurements with a self-built laboratory-scale device, we fitted and analysed all ZAFC polarization curves reported in the literature. Parametric analysis of the model is complemented by materials-science data, targeting selected observables, relevant to polarization curve analysis.

Anode passivation mitigation by homogenizing current density distribution in electrocoagulation

Electrode passivation is the most challenging technical problem in electrocoagulation (EC) water treatment process, but research on understanding and mitigating passivation evolution are still lacking. Herein, homogenization of current density (CD) distribution was found to be a critical factor in alleviating the anode passivation during EC process. Decreasing electrode area decelerated the growth of passivation layer on anode through homogenizing CD distribution, which was quantified by the ratios of CD distributed at the electrode edges and centers. When aluminum anode area decreased from 8 cm2 to 2 cm2 with a constant CD, the homogenization degree increased by 24.0%, and passivation was reduced by 24.3%. The depth profiles of passivated anodes confirmed the inhomogeneity of the anode passivation. Thicker passivation layers were observed at edges due to high CD distributions, which originated from the “edge effect” of electric field distribution between parallel plate electrodes. A facile strategy to homogenize CD distribution by splitting electrodes into smaller electrodes is then proposed for passivation mitigation, which can save energy consumption by 21.8% with unchanged removal efficiency. This study provides a unique insight into anode passivation mitigation and a feasible electrode design in EC.

Production and Characterization of Bacterial Cellulose Separators for Nickel-Zinc Batteries

The need for energy-storing technologies with lower environmental impact than Li-ion batteries but similar power metrics has revived research in Zn-based battery chemistries. The application of bio-based materials as a replacement for current components can additionally contribute to an improved sustainability of Zn battery systems. For that reason, bacterial cellulose (BC) was investigated as separator material in Ni-Zn batteries. Following the biotechnological production of BC, the biopolymer was purified, and differently shaped separators were generated while surveying the alterations of its crystalline structure via X-ray diffraction measurements during the whole manufacturing process. A decrease in crystallinity and a partial change of the BC crystal allomorph type Iα to II was determined upon soaking in electrolyte. Electrolyte uptake was found to be accompanied by dimensional shrinkage and swelling, which was associated with partial decrystallization and hydration of the amorphous content. The separator selectivity for hydroxide and zincate ions was higher for BC-based separators compared to commercial glass-fiber (GF) or polyolefin separators as estimated from the obtained diffusion coefficients. Electrochemical cycling showed good C-rate capability of cells based on BC and GF separators, whereas cell aging was pronounced in both cases due to Zn migration and anode passivation. Lower electrolyte retention was concluded as major reason for faster capacity fading due to zincate supersaturation within the BC separator. However, combining a dense BC separator with low zincate permeability with a porous one as electrolyte reservoir reduced ZnO accumulation within the separator and improved cycling stability, hence showing potentials for separator adjustment.

Dual Passivation of Cathode and Anode through Electrode–Electrolyte Interface Engineering Enables Long-Lifespan Li Metal–SPAN Batteries

Dual Passivation of Cathode and Anode through Electrode–Electrolyte Interface Engineering Enables Long-Lifespan Li Metal–SPAN Batteries

(Invited) A Micelle Electrolyte Enabled By Fluorinated Ether Additives for Polysulfide Suppression, High Voltage Cathode, and Li Metal Anode Stabilization

The Li-S battery is a promising next-generation technology due to its high theoretical energy density (2600 Wh/kg) and low active material cost. However, poor cycling stability and coulombic efficiency caused by polysulfide dissolution have proven to be major obstacles for a practical Li-S battery implementation. In this work, we develop a novel strategy to suppress polysulfide dissolution using hydrofluoroethers (HFEs) with bi-functional, amphiphlic surfactant-like design: a polar lithiophilic “head” attached to a fluorinated lithiophobic “tail.” A unique solvation mechanism is proposed for these solvents whereby dissociated lithium ions are readily coordinated with lithiophilic “head” to induce self-assembly into micelle-like complex structures. Complex formation is verified experimentally by changing the additive structure and concentration using small angle X-ray and neutron scattering. These HFE-based electrolytes are found to prevent polysulfide dissolution and to have excellent chemical compatibility with lithium metal: Li||Cu stripping/plating tests reveal high coulombic efficiency (>99.5%), modest polarization, and smooth surface morphology of the uniformly deposited lithium. Li-S cells are demonstrated with 1395 mAh/g initial capacity and 71.9% retention over 100 cycles at >99.5% efficiency—evidence that the micelle structure of the amphiphilic additives in HFEs can prohibit polysulfide dissolution while enabling facile Li+ transport and anode passivation. In addition, this type of electrolytes is also stable toward high voltage cathode to enable a lithium metal anode and high voltage cathode high-energy density rechargeable lithium battery.

(Invited) Deeply Rechargeable Zinc Anodes for High-Energy Rechargeable Aqueous Batteries

Zinc-based aqueous batteries are promising alternative to many mainstream battery technologies today, due to the superior safety. However, existing zinc anodes suffer from either poor cycle life or low utilization in both neutral and alkaline aqueous electrolytes. Passivation, dissolution, and hydrogen evolution are three main reasons for irreversibility of zinc anodes in alkaline electrolytes, which limits the rechargeability and usable energy density. In this talk, I will present our recent works on using nanoscale material design to overcome passivation, dissolution, and hydrogen evolution issues of zinc anode, towards a deeply rechargeable zinc-based battery. I will also introduce the battery-gas chromatography quantitative analysis, as well as in situ microscopy methodologies we have developed, to quantify gas evolution side reaction, as well as visualize the reaction on electrodes during operation.

Organic additives in alkaline electrolyte to improve cycling life of aqueous Zn–Ni batteries

Aqueous secondary Zn–Ni batteries have attracted extensive attention as a potential candidate to meet the increasing demand for energy storage device since they are environmental friendly and can provide inherent safety, high energy density and power density. However, the uneven deposition, passivation and corrosion of ZnO anode severely reduce the cycling life of the battery. Herein, tetraethylammonium bromide (TEAB) and polyethylene oxide (PEO) are introduced into the battery as electrolyte additives. The Zn–Ni battery achieves an excellent cycling life of 450 h since the additives provide more reduction sites and hinder the formation of dead zinc. In addition, the electrolyte additives can also reduce the corrosion current density of the anode and maintain the stable cycle of the battery under floating charge mode for more than 40 days. These results confirm the great practical application potential of aqueous Zn–Ni battery.