Effect of low concentration electrolytes on the formation and corrosion resistance of PEO coatings on AM50 magnesium alloy

In this paper,the formation process,morphology,and electrochemical performance of PEO coatings on AM50 magnesium alloy prepared in low concentration phosphate,aluminate,and phosphate-aluminate electrolytes were systematically studied.The results show that the coatings prepared from the phosphate electrolytes have a higher thickness and better corrosion resistance properties compared to the other electrolytes.The coatings prepared from low concentration phosphate-aluminate mixed electrolytes have slightly thinner thickness,a similar coating structure and an order of magnitude lower value of electrochemical impedance compared with phosphate electrolyte coatings.The Coatings prepared from low concentration aluminate electrolytes have the lowest thickness and the worst corrosion resistance properties which gets close to corrosion behavior of the bare AM50 under the same test conditions.Considering application,coatings prepared from single low concentration phosphate electrolytes and low concentration phosphate-aluminate electrolytes have greater potential than single low concentration aluminate coatings.However,reducing the electrolyte concentrations of coating forming ions too much has negative influence on the coating growth rate.

Diluted low concentration electrolyte for interphase stabilization of high-voltage LiNi_(0.5)Mn_(1.5)O_(4) cathode

The Co-free Li Ni_(0.5)Mn_(1.5)O_(4)(LNMO)is a promising cathode for lithium-ion batteries owing to its high operating voltage and low costs.However,the synthesis of LNMO is generally time and energy consuming,and its practical application is hindered by the lack of a compatible electrolyte.Herein,a spray pyrolysis-based energy-saving synthesis method as well as a diluted low concentration electrolyte(0.5 M LiPF_(6) in a mixture of fluoroethylene carbonate/dimethyl carbonate/1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether(FEC:DMC:TTE,1:4:5 by volume))are proposed to address these challenges.Owing to the unique features of the precursor prepared by spray pyrolysis,well-crystallized LNMO single-crystal can be obtained within 1 h calcination at 900℃.Besides,the fluorinated interphases derived from the diluted low concentration electrolyte not only mitigate the Mn dissolution and Al corrosion at the cathode side,but also suppresses dendritic Li deposition at the anode side,thus enabling stable cycling of both LNMO and Li metal anode.Thus,30μm Li|LNMO(1.75 m A h cm^(-2))cells achieve a high capacity retention(90.9%)after 168 cycles in the diluted low concentration electrolyte.

Moderately concentrated electrolyte enabling high-performance lithium metal batteries with a wide working temperature range

The electrolyte integrated with lithium metal anodes is subjected to the issues of interfacial compatibility and stability,which strongly influence the performances of high-energy lithium metal batteries.Here,we report a new electrolyte recipe viz.a moderately concentrated electrolyte comprising of 2.4 M lithium bis(fluorosulfonyl)imide(LiFSI)in a cosolvent mixture of fluorinated ethylene carbonate(FEC)and dimethyl carbonate(DMC)with relatively high ion conductivity.Owing to the preferential decomposition of LiFSI and FEC,an inorganic-rich interphase with abundant Li_(2)O and LiF nanocrystals is formed on lithium metal with improved robustness and ion transfer kinetics,enabling lithium plating/stripping with an extremely low overpotential of~8 mV and the average CE of 97%.When tested in Li||LiFePO_(4) cell,this electrolyte provides long-term cycling with a capacity retention of 98.3%after 1000 cycles at 1 C and an excellent rate performance of 20 C,as well as an areal capacity of 1.35 mA h cm^(-2)at the cathode areal loading of 9 mg cm^(-2).Moreover,the Li||LiFePO_(4) cell exhibits excellent wide-temperature performances(-40~60℃),including long-term cycling stability over 2600 cycles without visible capacity fading at 0℃,as well as extremely high average CEs of 99.6%and 99.8% over 400 cycles under-20℃ and 45℃.

Concentrated ternary ether electrolyte allows for stable cycling of a lithium metal battery with commercial mass loading high-nickel NMC and thin anodes

A new concentrated ternary salt ether-based electrolyte enables stable cycling of lithium metal battery(LMB)cells with high-mass-loading(13.8 mg cm^(−2),2.5 mAh cm^(−2))NMC622(LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2))cathodes and 50μm Li anodes.Termed“CETHER-3,”this electrolyte is based on LiTFSI,LiDFOB,and LiBF4 with 5 vol%fluorinated ethylene carbonate in 1,2-dimethoxyethane.Commer-cial carbonate and state-of-the-art binary salt ether electrolytes were also tested as baselines.With CETHER-3,the electrochemical performance of the full-cell battery is among the most favorably reported in terms of high-voltage cycling stability.For example,LiNi_(x)Mn_(y)Co_(1-x-y)O_(2)(NMC)-Li metal cells retain 80%capacity at 430 cycles with a 4.4 V cut-off and 83%capacity at 100 cycles with a 4.5 V cut-off(charge at C/5,discharge at C/2).According to simulation by density functional theory and molecular dynamics,this favorable performance is an outcome of enhanced coordination between Li^(+)and the solvent/salt molecules.Combining advanced microscopy(high-resolution transmission electron microscopy,scanning electron microscopy)and surface science(X-ray photoelectron spectroscopy,time-of-fight secondary ion mass spectroscopy,Fourier-transform infrared spectroscopy,Raman spectroscopy),it is demonstrated that a thinner and more stable cathode electrolyte interphase(CEI)and solid electrolyte interphase(SEI)are formed.The CEI is rich in lithium sulfide(Li_(2)SO_(3)),while the SEI is rich in Li_(3)N and LiF.During cycling,the CEI/SEI suppresses both the deleterious transformation of the cathode R-3m layered near-surface structure into disordered rock salt and the growth of lithium metal dendrites.

Electrolyte Concentration Regulation Boosting Zinc Storage Stability of High-Capacity K0.486V2O5 Cathode for Bendable Quasi-Solid-State Zinc Ion Batteries

Vanadium-based cathodes have attracted great interest in aqueous zinc ion batteries(AZIBs)due to their large capacities,good rate performance and facile synthesis in large scale.However,their practical application is greatly hampered by vanadium dissolution issue in conventional dilute electrolytes.Herein,taking a new potassium vanadate K0.486V2O5(KVO)cathode with large interlayer spacing(~0.95 nm)and high capacity as an example,we propose that the cycle life of vanadates can be greatly upgraded in AZIBs by regulating the concentration of ZnCl2 electrolyte,but with no need to approach“water-in-salt”threshold.With the optimized moderate concentration of 15 m ZnCl2 electrolyte,the KVO exhibits the best cycling stability with ~95.02% capacity retention after 1400 cycles.We further design a novel sodium carboxymethyl cellulose(CMC)-moderate concentration ZnCl2 gel electrolyte with high ionic conductivity of 10.08 mS cm^-1 for the first time and assemble a quasi-solid-state AZIB.This device is bendable with remarkable energy density(268.2 Wh kg^−1),excellent stability(97.35% after 2800 cycles),low self-discharge rate,and good environmental(temperature,pressure)suitability,and is capable of powering small electronics.The device also exhibits good electrochemical performance with high KVO mass loading(5 and 10 mg cm^-2).Our work sheds light on the feasibility of using moderately concentrated electrolyte to address the stability issue of aqueous soluble electrode materials.

Coupled heat/mass-balance model for analyzing correlation between excess AlF_3 concentration and aluminum electrolyte temperature

The influence of aluminum electrolyte component on its temperature is an important issue within the field of aluminum reduction with pre-baked cells. The characteristic correlation between excess AlF3 concentration and aluminum electrolyte temperature was explored through the modeling of heat and mass transfer processes in industrial pre-baked aluminum reduction cells. A coupled heat/mass-balance model was derived theoretically from the mass and energy balance of an electrolysis cell, and then was simplified properly into a practical expression. The model demonstrates that if environmental temperature and Al2O3 concentration keep constant, the excess AlF3 concentration decreases with the aluminum electrolyte temperature linearly and its decrease rate is dependent on the heat transfer property of aluminum electrolyte, side wall and cell shell. Secondly, experiments were conducted on site with two industrial cells in an aluminum electrolysis plant. Excess AlF3 concentration and aluminum electrolyte temperature were obtained simultaneously together with other parameters such as Al2O3, CaF2, MgF2 and LiF concentrations. Results show that the maximum absolute error between the tested value and the calculated value of excess AlF3 concentration using the proposed model is less than 2%. This reveals that the coupled heat/mass-balance model can appropriately characterize the correlation between excess AlF3 concentration and aluminum electrolyte temperature with good accuracy and practicability.

Tuning hybrid liquid/solid electrolytes by lowering Li salt concentration for lithium batteries

Hybrid liquid/solid electrolytes（HLSEs） consisting of conventional organic liquid electrolyte（LE）, polyacrylonitrile（PAN）, and ceramic lithium ion conductor Li（1.5）Al（0.5）Ge（1.5）（PO4）3（LAGP） are proposed and investigated. The HLSE has a high ionic conductivity of over 2.25 × 10^（-3） S/cm at 25？C, and an extended electrochemical window of up to 4.8 V versus Li/Li＋. The Li｜HLSE｜Li symmetric cells and Li｜HLSE｜Li FePO4 cells exhibit small interfacial area specific resistances（ASRs） comparable to that of LE while much smaller than that of ceramic LAGP electrolyte, and excellent performance at room temperature. Bis（trifluoromethane sulfonimide） salt in HLSE significantly affects the properties and electrochemical behaviors. Side reactions can be effectively suppressed by lowering the concentration of Li salt. It is a feasible strategy for pursuing the high energy density batteries with higher safety.

Flame-retardant concentrated electrolyte enabling a Li F-rich solid electrolyte interface to improve cycle performance of wide-temperature lithium–sulfur batteries

Lithium–sulfur batteries have been regarded as the most promising high-energy electrochemical energy storage device owing to the high energy density, low cost and environmental friendliness. However, traditional lithium–sulfur batteries using ether-based electrolytes often suffer from severe safety risks(i.e. combustion). Herein, we demonstrated a novel kind of flame-retardant concentrated electrolyte(6.5 M lithium bis(trifluoromethylsulphonyl)imide/fluoroethylene carbonate) for highly-safe and widetemperature lithium–sulfur batteries. It was found that such concentrated electrolyte showed superior flame retardancy, high lithium-ion transference number(0.69) and steady lithium plating/stripping behavior(2.5 m Ah cm^(-2) over 3000 h). Moreover, lithium–sulfur batteries using this flame-retardant concentrated electrolyte delivered outstanding cycle performance in a wide range of temperatures(-10 °C, 25 °C and 90 °C). This superior battery performance is mainly attributed to the LiF-rich solid electrolyte interphase formed on lithium metal anode, which can effectively suppress the continuous growth of lithium dendrites. Above-mentioned fascinating characteristics would endow this flame-retardant concentrated electrolyte a very promising candidate for highly-safe and wide-temperature lithium–sulfur batteries.

Stable interfaces constructed by concentrated ether electrolytes to render robust lithium metal batteries

Lithium metal batteries(LMBs)are highly considered as promising candidates for next-generation energy storage systems.However,routine electrolytes cannot tolerate the high potential at cathodes and low potential at anodes simultaneously,leading to severe interfacial reactions.Herein,a highly concentrated electrolyte(HCE)region trapped in porous carbon coating layer is adopted to form a stable and highly conductive solid electrolyte interphase(SEI)on Li metal surface.The protected Li metal anode can potentially match the high-voltage cathode in ester electrolytes.Synergistically,this ingenious design promises high-voltage-resistant interfaces at cathodes and stable SEI with abundance of inorganic components at anodes simultaneously in high-voltage LMBs.The feasibility of this interface-regulation strategy is demonstrated in Li|LiFePO_(4) batteries,realizing a lifespan twice as long as the routine cells,with a huge capacity retention enhancement from 46.4%to 88.7%after 100 cycles.This contribution proof-ofconcepts the emerging principles on the formation and regulation of stable electrode/electrolyte interfaces in the cathode and anode simultaneously towards the next-generation high-energy-density batteries.

Designing Advanced Liquid Electrolytes for Alkali Metal Batteries:Principles,Progress,and Perspectives

The ever-growing pursuit of high energy density batteries has triggered extensive efforts toward developing alkali metal(Li,Na,and K)battery(AMB)technologies owing to high theoretical capacities and low redox potentials of metallic anodes.Typically,for new battery systems,the electrolyte design is critical for realizing the battery electrochemistry of AMBs.Conventional electrolytes in alkali ion batteries are generally unsuitable for sustaining the stability owing to the hyper-reactivity and dendritic growth of alkali metals.In this review,we begin with the fundamentals of AMB electrolytes.Recent advancements in concentrated and fluorinated electrolytes,as well as functional electrolyte additives for boosting the stability of Li metal batteries,are summarized and discussed with a special focus on structure-composition-performance relationships.We then delve into the electrolyte formulations for Na-and K metal batteries,including those in which Na/K do not adhere to the Li-inherited paradigms.Finally,the challenges and the future research needs in advanced electrolytes for AMB are highlighted.This comprehensive review sheds light on the principles for the rational design of promising electrolytes and offers new inspirations for developing stable AMBs with high performance.

LiTFSI salt concentration effect to digest lithium polysulfides for high-loading sulfur electrodes

Sulfur utilization improvement and control of dissolved lithium polysulfide(LiPS;Li_(2)S x,2<x≤8)are cru-cial aspects of the development of lithium-sulfur(Li-S)batteries,especially in high-loading sulfur elec-trodes and low electrolyte/sulfur(E/S)ratios.The sluggish reaction in the low E/S ratio induces poor LiPS solubility and unstable Li_(2)S electrodeposition,resulting in limited sulfur utilization,especially under high-loading sulfur electrode.In this study,we report on salt concentration effects that improve sulfur utilization with a high-loading cathode(6 mgs ulfurcm^(-2)),a high sulfur content(80 wt%)and a low E/S ratio(5 m L gs ulfur^(-1)).On the basis of the rapid LiPS dissolving in a low concentration electrolyte,we estab-lished that the quantity of Li_(2)S electrodeposition from a high Li+diffusion coefficient,referring to the reduction of LiPS precipitation,was significantly enhanced by a faster kinetic.These results demonstrate the importance of kinetic factors for the rate capability and cycle life stability of Li-S battery electrolytes through high Li_(2)S deposition under high-loading sulfur electrode.

Concentrated dual-salt electrolytes for improving the cycling stability of lithium metal anodes

Lithium（Li） metal is an ideal anode material for rechargeable Li batteries, due to its high theoretical specific capacity（3860 mAh/g）, low density（0.534 g/cm3）, and low negative electrochemical potential（-3.040 V vs. standard hydrogen electrode）. In this work, the concentrated electrolytes with dual salts, composed of Li[N（SO2F）2]（Li FSI） and Li[N（SO2CF3）2]（Li TFSI） were studied. In this dual-salt system, the capacity retention can even be maintained at 95.7%after 100 cycles in Li｜Li FePO4 cells. A Li｜Li cell can be cycled at 0.5 mA/cm2 for more than 600 h, and a Li｜Cu cell can be cycled at 0.5 m A/cm2 for more than 200 cycles with a high average Coulombi efficiency of 99%. These results show that the concentrated dual-salt electrolytes exhibit superior electrochemical performance and would be a promising candidate for application in rechargeable Li batteries.

Calculating models of mass action concentrations for NaBr(aq), LiNO_3(aq), HNO_3(aq), and KF(aq) binary solutions

The calculating models of mass action concentrations for electrolyte aqueous solutions NaBr-H2O, LiNO3-H2O, HNO3-H2O, and KF-H2O have been developed at 298.15 K and their molalities ranging from 0.1 mol/kg to saturation according to the ion and molecule coexistence theory as well as mass action law. The calculated mass action concentration is based on pure species as the standard state and the mole fraction as the concentration unit, and the reported activities are usually based on infinite dilution as the standard state and molality as the concentration unit. Hence, the calculated mass action concentration must be transformed to the same standard state and concentration unit. The transformation coefficients between calculated mass action concentrations and reported activities of the same component fluctuate in a very narrow range. Thus, the transformed mass action concentrations not only agree well with reported activities, but also strictly obey mass action law. The calculated results show that the new developed models can embody the intrinsic structure of investigated four electrolyte aqueous solutions. The results also indicate that mass action law has its widespread applicability to electrolyte binary aqueous solutions.

Mathematical analysis of SOFC based on co-ionic conducting electrolyte

In co-ionic conducting solid oxide fuel cell （SOFC）, both oxygen ion （O2） and proton （H＋） can transport through the electrolyte, generating steam in both the an-ode and cathode. Thus the mass transport phenomenon in the electrodes is quite different from that in conventional SOFC with oxygen ion conducting electrolyte （O-SOFC） or with proton conducting electrolyte （H-SOFC）. The generation of steam in both electrodes also affects the concentration over-potential loss and further the SOFC performance. However, no detailed modeling study on SOFCs with co-ionic electrolyte has been reported yet. In this paper, a new mathematical model for SOFC based on co-ionic electrolyte was developed to predict its actual performance considering three major kinds of overpotentials. Ohm＇s law and the Butler-Volmer formula were used to model the ion conduction and electrochemical reactions, respectively. The dusty gas model （DGM） was employed to simulate the mass transport processes in the porous electrodes. Parametric simulations were performed to investigate the effects of proton transfer number （tH） and current density （jtotal） on the cell performance. It is interesting to find that the co-ionic conducting SOFC could perform better than O-SOFC and H-SOFC by choosing an appropriate proton transfer number. In addition, the co-ionic SOFC shows smaller difference between the anode and cathode concentration overpotentials than O-SOFC and H-SOFC at certain t H values. The results could help material selection for enhancing SOFC performance.

Recent advances in “water in salt” electrolytes for aqueous rechargeable monovalent-ion(Li^(+), Na^(+), K^(+)) batteries

Aqueous rechargeable batteries have attracted enormous attention owning to their intrinsic characteristics of non-flammability, low cost, and the superior ionic conductivity of the aqueous electrolyte.However, the narrow electrochemical stability window(1.23 V), imposed by hydrogen and oxygen evolution, constrains the overall energy density of batteries. The revolutionary "water-in-salt” electrolytes considerably expand the electrochemical stability window to 3 or even 4 volts, giving rise to a new series of high-voltage aqueous metal-ion chemistries. Herein, the recent advances in "water-in-salt” electrolytes for aqueous monovalent-ion(Li^(+), Na^(+), K^(+)) rechargeable batteries have been systematically reviewed. Meanwhile, the corresponding reaction mechanisms, electrochemical performances and the existing challenges and opportunities are also highlighted.

An Efficient Numerical Method and Parametric Study for Electrolyte Transport in the Renal Medulla

Mathematical models of the mamalian urine concentrating mechanism consist of a large system of coupled, nonlinear and stiff equations. An efficient numerical orthogonal collocation method was employed to solve the steady-state formulation of urine concentrating mechanism. This method was used to solve the stiff and high order equations of electrolyte transport in a central core, single nephron model of the renal outer medulla. The presented results were in good agreement with implicit finite difference method’s results, but this new method was faster and more stable. Due to the greater stability and larger convergence domain of collocation method over Newton’s method, a parametric study on concentrated urine was investigated. The results showed that this model was sensitive to non-ideal countercurrent exchange between medulla interstitium and vasa recta. Although distal tubule lies in the cortex interstitium, it affects on the inflow to the collecting duct. This study showed that the effect of changing membrane transport properties of distal tubule wall on properties of outflow from the outer medulla collecting duct was considerable.

Two-Dimensional Lithium-Ion Battery Modeling with Electrolyte and Cathode Extensions

A two-dimensional model for transport and the coupled electric field is applied to simulate a charging lithium-ion cell and investigate the effects of lithium concentration gradients within electrodes on cell performance. The lithium concentration gradients within electrodes are affected by the cell geometry. Two different geometries are investigated: extending the length of the electrolyte past the edges of the electrodes and extending the length of the cathode past the edge of the anode. It is found that the electrolyte extension has little impact on the behavior of the electrodes, although it does increase the effective conductivity of the electrolyte in the edge region. However, the extension of the cathode past the edge of the anode, and the possibility for electrochemical reactions on the flooded electrode edges, are both found to impact the concentration gradients of lithium in electrodes and the current distribution within the electrolyte during charging. It is found that concentration gradients of lithium within electrodes may have stronger impacts on electrolytic current distributions, depending on the level of completeness of cell charge. This is because very different gradients of electric potential are expected from similar electrode gradients of lithium concentrations at different levels of cell charge, especially for the LixC6 cathode investigated in this study. This leads to the prediction of significant electric potential gradients along the electrolyte length during early cell charging, and a reduced risk of lithium deposition on the cathode edge during later cell charging, as seen experimentally by others.

Relationships between Pitzer's ion interaction coefficients and ionic parameters of electrolyte solutions

Pattern recognition methods were used to treat the experimentally measured data of Pitzer’s coefficients of 107 electrolytes, to find the relationships between the ionic structural parameters of these electrolytes and Pitzer’s coefficients. It is found that these relationships can be approximately expressed as linear equations of four dimensionless numbers, (R_+/R_-), (R_++R_-)/Z_+Z_-, (Z_+/Z_-) and (R_t/R_l), where R_+ and R_- are the cationic and anionic radii respectively; Z_+ and Z_- are the cationic and anionic charge numbers respectively, and (R_t/R_l) denotes the nonsphericity of some non-spherical ions. Besides, it is found that the difference of the nuclear magnetic resonance measured rotational relaxation time of water molecules around cations and anions, |Δτ|, has good correlation with Pitzer’s coefficients. The relationships can be interpreted by the theory of corresponding states of ionic solutions. Based on the relationships, an example of application to some hydrometallurgical process was discussed.

An ultra-low concentration electrolyte with fluorine-free bulky anions for stable potassium metal batteries

Potassium metal battery is a promising alternative to Li-ion battery for large-scale energy storage due to the abundant potassium resources and high energy density.However,it suffers from rapid capacity fading and safety issues due to the uncontrolled dendrite growth.Herein,we design a fluorine-free ultra-low concentration electrolyte(ULCE)with the super bulky[BPh_(4)]^(−) anions for stable potassium metal battery.In this special electrolyte,the migration rate of K+in the electrolyte is about six times faster than that of the[BPh_(4)]^(−) anions because of the super bulky structure of the[BPh_(4)]^(−) anions,thus resulting in a high K^(+)transference number of 0.76.This high transference number can effectively make up for the deficiency of K^(+)in ULCE for ensuring the normal operation of the potassium metal battery.In addition,the improved transference number can also promote the uniform distribution of K^(+)flux on the surface of the K metal anode,resulting in uniform K deposition.As a result,this electrolyte achieves a high K plating/stripping Coulombic efficiency of 92.6%over 200 cycles and a stable discharging/charging for 100 cycles under the full battery configuration(K used as the anode and perylene-3,4,9,10-tetracarboxylic dianhydride used as the cathode).

磷酸酯基阻燃电解液用于高安全锂硫电池

Li–S电池被认为是最有希望的下一代高能量密度二次电池之一,开发高效阻燃电解液对于提升电池安全性极为重要.本文对高浓度磷酸三乙酯(TEP)和磷酸三(2,2,2-三氟乙基)酯(TFP)电解液在锂–硫化聚丙烯腈(Li–PAN/S)电池中的应用展开了深入研究,以同样的锂盐摩尔比和氟代醚稀释梯度,研究了TEP和TFP基局部高浓度电解液对锂金属负极和硫正极稳定性的影响,详细解析了两种溶剂分子在电池循环过程中的界面反应.研究表明,磷酸酯基高浓度电解液在Li–PAN/S电池中展示了较优异的循环稳定性,通过优化TTE的稀释比例,提升了电池的倍率特性.对比基于TEP和TFP的电解液,发现TEP基电解液具有更好的锂沉积/剥离性能,而TFP基电解液在界面生成更多的有机组分,导致不稳定的界面膜.以TEP212为电解液的锂硫电池能够在1C的倍率下稳定循环200圈以上,放电比容量保持在1080.8 mA·h·g-1.