LongâLife PolysulfideâPolyhalide Batteries with a Mediator-ion Solid

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Long–Life Polysulfide–Polyhalide Batteries with a Mediator-ion Solid Electrolyte Martha M Gross, and Arumugam Manthiram ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.9b00253 • Publication Date (Web): 19 Apr 2019 Downloaded from http://pubs.acs.org on April 19, 2019

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ACS Applied Energy Materials

Long–Life Polysulfide–Polyhalide Batteries with a Mediator-ion Solid Electrolyte Martha M. Gross and Arumugam Manthiram* Materials Science and Engineering Program and Texas Materials Institute The University at Texas at Austin, Austin, TX 78712, United States KEYWORDS: redox flow batteries, aqueous batteries, polysulfides, polyhalides, solid electrolyte

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Abstract Polysulfide-polybromide and polysulfide-polyiodide batteries are promising redox-flow systems due to their use of low-cost and abundant active materials. However, these systems have traditionally suffered from substantial crossover of redox active materials, causing loss of active material and the necessity of reconditioning their electrolytes, which has the overall effect of lowering battery lifetimes and adding system level costs. This work demonstrates how using a solid electrolyte instead of the traditional Nafion separator completely prevents crossover of redox active species, enabling long cycle life batteries. To achieve this, a “mediator-ion” strategy is employed, in which Li+ or Na+ ions transfer ionic charge through the solid electrolyte to achieve charge balance without active participation in the anode and cathode reactions. This is demonstrated both with polysulfide-polybromide (PSB) and polysulfide-polyiodide (PSI) batteries. The effect of the solid electrolyte on battery rate performance, as well as the long-term stability of the ceramic electrolyte in the corrosive polybromide and polyiodide catholytes, is examined.


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Introduction The world is seeing a steady increase in the use and deployment of renewable energy sources. Recent years have seen the cost of renewable energy drop considerably, and as a result, it is becoming an attractive option for electricity generation.1-2 However, intermittent renewable sources such as solar and wind often do not produce energy as it is demanded.3-4 The future deployment of solar and wind generation is increasingly limited by their intermittency as their costs continue to drop. As such, an effective utilization of renewable energy relies heavily on cost-effective, long-life energy storage systems. Despite the great demand, large-scale energy storage lags behind renewable energy in terms of both development and deployment and is rapidly becoming the bottleneck towards substantial renewable energy generation.5 Batteries are widely considered excellent candidates for grid-scale energy storage, but the unique demands of the grid mean that currently no one battery chemistry is dominant. Grid-scale energy storage requires batteries to have 20 year lifetimes, long storage duration (> 10 h), and very inexpensive levelized cost of storage.6 Lithium-ion batteries, though seeing some development for use in the grid, are not projected to meet these metrics in large part due to the cost of their active materials.6-8 As such, research needs to focus on development of battery materials that are abundant, geographically widespread, and economically feasible to extract on a terawatt scale.8-10 Redox flow batteries that make use of such chemistries are particularly attractive, as their ability to decouple their energy and power parameters means they can be deployed for multiple applications ranging from load-leveling operations to bulk power management.11-12 There are, however, a number of unresolved issues with regard to developing redox flow batteries with inexpensive materials. One pressing issue is the separator used in flow batteries.133 ACS Paragon Plus Environment


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Unlike in traditional rechargeable batteries, which use solid anode and cathode materials,

redox flow batteries use redox active liquids as anolytes and catholytes. They, therefore, require a separator to allow ionic contact between the anolyte and catholyte while keeping the redox active species in solution physically separate. The membrane, therefore, has three key requirements: (i) high ionic conductivity, (ii) high chemical stability in the electrolytes, and (iii) high ion selectivity to prevent crossover of redox active species.15-16 Chemical stability and ion selectivity are particularly important for long-lifetime batteries. However current separators that have desirable chemical stability, such as Nafion membranes, typically have poor ion selectivity and a high cost. Furthermore, many membranes allow hydroxide and proton transfer, creating osmotic pressure effects and limiting the use of anolytes and catholytes with different pHs.14, 17-18 Batteries with these membranes require periodic rebalancing of their electrolytes for long-term cycling, which adds system-level expenses over the battery lifetime. These issues with the membrane have led to a resurging interest in novel membranes with improved performances.13, 15-16 One emerging idea is the use of solid electrolytes. Use of a solid electrolyte as a separator completely prevents cross-contamination and osmotic pressure effects, as their crystal structure allows perfect selectivity towards the desired ionic species. Improvements in the manufacturing of solid electrolytes can decrease their cost, so they will not be prohibitively expensive. The U.S. Department of Energy now forecasts solid electrolyte costs to drop as low as $10 m-2.19 There is a drive to develop many novel high ionic conductivity solid electrolytes, but current commercially available solid electrolytes are limited to Li+ and Na+ conductors. To overcome this limitation, several systems have recently demonstrated the use of a “mediator-ion” strategy in which the Li+ or Na+ cation does not actively participate in the anode and cathode reactions, but instead acts as a passive ionic mediator of charge transfer through the


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solid electrolyte. This strategy has allowed the development of many novel battery couples, including zinc-air, zinc-ferricyanide, iron-air, and polysulfide-air.20-24 In this work, we apply the use of a mediator-ion solid electrolyte to polysulfidepolyhalide battery systems to eliminate chemical crossover and enhance battery cycle life. We demonstrate polysulfide-polybromide batteries with Na+ and Li+ mediator ions, and polysulfidepolyiodide batteries with a Na+ mediator ion. We further discuss the effect of the solid electrolyte on power performance and its stability in the chemically aggressive catholytes. Experimental Details Synthesis of Polysulfide Anolyte Polysulfide anolytes were prepared under flowing N2 atmosphere in a Schlenk line. Deionized water was purged with N2 prior to the synthesis of polysulfide solutions. Sodium polysulfide anolyte was prepared by dissolving anhydrous sodium sulfide (Na2S) and sulfur in a 1 : 1: ratio in 0.1 M sodium hydroxide (NaOH) solution to form a nominal solution of 1 M Na2S2 + 0.1 M NaOH. Lithium polysulfide anolyte was prepared in the same manner, substituting anhydrous Li2S for Na2S and LiOH for NaOH. Synthesis of Polyhalide Catholytes Polybromide catholyte was prepared by first forming a solution of sodium bromide (NaBr) in deionized water, and then mixing in bromine (Br2) to the desired concentrations. Polybromide catholyte with 100 % state of charge (SOC) was used for galvanostatic cycling, and soaking tests consisted of 1 M Br2 + 2 M NaBr. 50 % SOC polybromide catholyte for rate testing consisted of 0.5 M Br2 + 3 M NaBr. Catholyte for Li+ mediator-ion batteries was synthesized in the same manner, substituting LiBr for NaBr. Polyiodide catholyte was prepared by first forming a 5 ACS Paragon Plus Environment


solution of sodium iodide (NaI) of the desired concentration in 0.5 M sodium sulfate (Na2SO4) solution, and then adding iodine (I2) as needed. Batteries for galvanostatic cycling tests were assembled with 0 % SOC polyiodide catholyte containing 1.5 M NaI + 0.5 M Na2SO4. 50 % SOC polyiodide catholyte for rate testing contained 0.25 M I2 + 1 M NaI + 0.5 M Na2SO4. Concentrated catholyte for soaking tests contained 0.5 M I2 + 2 M NaI + 0.5 M Na2SO4. Synthesis of Polysulfide Catalytic Electrode Copper sulfide (CuS) microtubes were synthesized following the method previously described by Yao et al.,25 in which equimolar amounts of cupric chloride (CuCl2) and thioacetamide were mixed in deionized water and rested without stirring in a 60 °C oil bath for 24 h. The CuS was recovered by vacuum filtration, rinsed with a deionized water/ethanol mixture, and transferred to a 50 °C vacuum oven to dry overnight. Then, 50 mg of CuS was sonicated in deionized water with 20 % w/w lithiated Nafion binder (LithION, Ion Power Inc.) to form an ink, which was then deposited on a Teflon-coated carbon substrate (Sigracet GDL 10 BA) to give a mass loading of 2.5 mg cm-2 of CuS. Assembly of Polysulfide-Polyhalide Batteries Anodes were assembled using custom housing, as we have previously described for zincpolysulfide batteries.26 Anodes consisted of a stainless steel mesh current collector, CuS electrode, 80 µL of polysulfide anolyte, and a solid electrolyte. Solid electrolytes used were Na+ion conductor NASICON (Na3Zr2Si2PO12), hand polished to 0.5 mm, or Li+-ion conductor LATP (Li1+x+yAlxTi2-xP3-ySiyO12), used as-received (thickness = 150 µm). A corresponding custom cathode chamber was used, made of Teflon. Battery cells were made by first assembling the anode chamber in an N2-purged glovebag with attached solid electrolyte. Next, a carbon


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electrode and Ti mesh current collector were inserted into the cathode chamber. Carbon electrodes consisted of buckypaper unless otherwise noted. The chamber was filled with 60 µL of polyhalide catholyte and sealed to the solid electrolyte by compression with a Viton O-ring. Materials and Electrochemical Characterization Morphology and elemental composition of the solid electrolyte and electrodes was performed with a FEI Quanta 650 field emission scanning electron microscope (SEM) and Bruker energydispersive x-ray spectrometer (EDS). Phase identification was performed with a Rigaku MiniFlex x-ray diffractometer (XRD). Ceramic electrolytes were soaked in polybromide and polyiodide catholytes for a minimum of 500 h. Carbon electrodes were cleaned by repeated soaking in deionized water to remove absorbed catholyte before analysis. Cyclic voltammetry (CV) was performed with a CH Instruments 1040A potentiostat, saturated calomel reference electrode, carbon foam counter electrode, and glassy carbon working electrode at a scan rate of 5 mV s-1. CV electrolytes consisted of 5 mM NaBr or NaI + 0.5 M NaCl. Galvanostatic cycling and rate performance testing was performed with an Arbin BT 2000 battery cycler. Polysulfide-polybromide batteries were assembled with 100 % SOC catholyte for galvanostatic cycling. First discharge of these cells was performed at 0.5 mA cm-2 for 30 minutes, then 1 mA cm-2 for 10 minutes, and then 1.5 mA cm-2 for the remainder of the cycle. All subsequent charge and discharge cycles occurred at 1.5 mA cm-2 current density. Polysulfide-polyiodide batteries were assembled with 0 % SOC catholyte for galvanostatic cycling tests and cycled at 0.5 mA cm-2 current density. Polysulfide-polybromide and polysulfide-polyiodide batteries were assembled with their respective 50 % SOC catholytes for rate performance testing. Polarization curves were obtained by charging and discharging each cell for 20 minutes for 5 cycles at the specified current density. Polysulfide-polybromide 7 ACS Paragon Plus Environment


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batteries with a Li+ mediator ion were cycled for rate performance testing before undergoing galvanostatic cycling without disassembly. Results & Discussion Polysulfide-Polybromide System Polysulfide-polybromide (PSB) batteries use as their active material sulfur, a cheap byproduct of oil and gas refining, and bromine, an inexpensive primary product used in a variety of commercial industries.27 Both sulfur and bromine exhibit high solubility in aqueous systems in the presence of, respectively, sulfide and bromide salts where they complex to form polysulfide and polybromide.28-29 They, therefore, promise a high system energy density of 117 W h L-1, including the anolyte and catholyte, at low cost. The polysulfide-polybromide couple consists of the following reactions: 2𝑆22− → 𝑆42− + 2𝑒 −

E0 ≈ − 0.5 V vs SHE

(1)

𝐵𝑟3− + 2𝑒 − → 3𝐵𝑟 −

E0 = 1.05 V vs SHE

(2)

to give a theoretical cell voltage of approximately 1.55 V. The exact potential depends on the concentration and composition of the polysulfide.30 The polysulfide anolyte is kept at an alkaline pH (9 – 14), which is necessary to suppress H2S formation and S precipitation, as well as to increase the chemical stability of the polysulfide species, which otherwise thermodynamically favor degradation to thiosulfate.31-32 In contrast, the polybromide catholyte is mildly acidic (pH ~ 3), which necessitates good ionic selectivity against hydroxide and proton migration through the separator.33 Traditional ion-exchange membranes (IEMs) and porous membranes fail to prevent crossover of water and redox active species, which results in changing electrolyte pH, sulfate formation, sulfur precipitation and clogging of electrodes, and loss of active material. As the 8 ACS Paragon Plus Environment

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following section will demonstrate, the use of a mediator-ion solid electrolyte eliminates these issues.

Figure 1. Schematic of a polysulfide-polybromide battery with polysulfide anolyte, Na+ ion solid-state electrolyte (SSE), and polybromide catholyte. Polysulfide-Polybromide Battery Performance PSB batteries were assembled with a Na+ mediator ion in the charge state, as shown in Figure 1. Catholyte consisted of 1 M Br2 + 2 M NaBr. Excess NaBr was used to ensure solubility of Br2 in the Br3- complex. A NASICON ceramic was used as the solid electrolyte. The first discharge of the cell was performed at 0.5 mA cm-2 for 30 minutes before stepping the current to 1.0 and then 1.5 mA cm-2, at which all the remaining cycling was performed. Cells were charged to 50% state of charge (SOC) and discharged to 0.6 V. PSB batteries exhibited two plateaus in the first cycle as shown in Figure 2a. This is reflected in an increase in the efficiencies in the first few cycles (Figure 2b). This may be due to activation of the carbon electrode, or local trapping of the Br2 active material. This was seen in PSB batteries assembled with Toray paper carbon electrodes, like that shown in Figure 2, and PSB batteries assembled with buckypaper carbon electrodes, like that shown in Figure S1 in the supporting information. PSB batteries showed good stability,



maintaining a high coulombic efficiency of 98.6 % over 50 cycles. The batteries were disassembled after 50 cycles. Disassembly showed that while the Viton O-ring seal used to assemble our cells was an effective seal for the liquid polybromide catholyte, it failed to contain fumed Br2 gas, which proceeded to react with the cell parts outside of the seal, as shown in Figure S2a. This was emphasized in the cells in which excess fuming during assembly and cycling led to a low initial capacity, such as the cell shown in Figure S1. These cells saw an increase in overpotential during cycling, which is likely due to the increasing mass transport resistances as Br3- concentration dropped. Despite these challenges, the high coulombic efficiency of the cell indicates substantial progress over previous PSB cells, which Zhou et al. reported to have achieved 97 % coulombic efficiency or lower, by eliminating the electrolyte crossover typical of a polymeric ion-exchange membrane.34-35 Unlike in the PSB batteries that use a Nafion membrane, no sulfur precipitation was observed on the catholyte’s carbon electrode, confirming no crossover occurred in the cell, as shown in Figure S3.


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Figure 2. Electrochemical performance of a PSB battery at 1.5 mA cm-2 and 50% state of charge (SOC) cycling. (a) Galvanostatic cycling and (b) cycling efficiency, including coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE). Bromine is a highly corrosive material, and often requires specialized materials and engineering controls to avoid corrosion and to prevent escape of dangerous Br2 gas and loss of active material. The NASICON ceramic was examined by SEM to determine its stability after exposure to the concentrated polybromide catholyte. The NASICON was studied after cycling in a PSB battery and after long-term soaking in fresh 100% SOC polybromide catholyte, as shown in Figure 3 a − f. After 50 cycles in a PSB battery, or ~ 600 h of cycling, the NASICON shows some corrosion of the surface shown in Figure 3 c − d, compared to fresh NASICON (Figure 3 a − b). Corrosion of the ceramic is most prevalent around the pores in the ceramic. The ceramic soaked in the fresh catholyte, however, showed signs of severe corrosion, as shown in Figure 11 ACS Paragon Plus Environment


3e−f. XRD and EDS of the soaked NASICON reveal a loss of the ZrO2 impurity phase and changing relative ratios of oxygen and sodium, as shown in Figures S4 and S5. Based on these results, it can be concluded that the complexed Br3- ions or non-complexed Br2 are the most likely corrosive agents, as the cycled ceramic is exposed to substantially less charge product (Br3- or Br2) over the same period of time compared to the soaked ceramic. This implies that while the NASICON appears to be unstable in the polybromide catholyte, its life can be extended by careful design of cycling parameters, and storage of the battery in the discharge state where only NaBr is present when the battery is not being cycled. Improvements in the microstructure by minimizing the impurities and the number and size of the pores may also help to extend the battery lifetime. Furthermore, a Li+-ion conductor, LATP, was also tested for its stability against polybromide catholyte. The LATP, as shown in Figure 3 g − h, exhibits substantially higher stability than the NASICON. After soaking in the polybromide catholyte, a slight lengthening of nanometer-sized cracks in the LATP is observed. Otherwise no corrosion is apparent. This represents a substantial improvement over the NASICON and indicates that careful selection of the solid electrolyte material can also improve battery lifetime.


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Figure 3. SEM of polished NASICON: (a – b) uncycled, (c – d) cycled in a PSB battery, and (e – f) soaked in 1 M Br2 + 2 M NaBr catholyte. SEM of LATP: (g) as-received and (h) soaked in 1 M Br2 + 2 M LiBr catholyte. The rate performance of PSB batteries assembled with a Na+ mediator ion and a Li+ mediator ion was tested. As Figure 4 shows, PSB batteries assembled with a Li+ mediator ion



achieve a substantially lower peak power density (1.6 mW cm-2) compared to PSB batteries assembled with a Na+ mediator ion (3.9 mW cm-2). This may be due to a variety of reasons. The LATP has a lower ionic conductivity (~ 1.0 x 10-4 S cm-1) than the NASICON (~ 1.0 x 10-3 S cm1

). Based on the thickness and active area of the ceramic, the LATP still exhibits a lower

extrinsic conductance of ~ 1.2 mS, compared to the extrinsic conductance of NASICON (~ 3.6 mS) in this demonstration system. Furthermore, as we have shown in our previous work, both the LiBr and the Li2Sx redox couples show more sluggish redox kinetics compared to their Na+ ion counterparts.21, 26 This is largely attributed to the lower dissociation behavior of the Br– and Sx2– anions in the presence of Li+ compared to Na+ cations. This lower rate performance is reflected in the higher cycling overpotential and lower voltage and energy efficiencies observed in PSB batteries assembled with a Li+ mediator ion, as shown in Figure S6. Future work will have to study the optimization of solid electrolyte stability in the presence of Br3- to balance cycle life and safety with battery performance. Our cells, being assembled in a static mode and with unoptimized cell components including planar 2D electrodes and a very thick ceramic in the case of Na+ mediator ion cells, demonstrate a lower power performance compared to PSB batteries that use other separators like Nafion, which has a conductivity an order of magnitude higher than that of our NASICON ceramic (~2 mS cm-1).39 However, the power and energy densities achieved in this study are substantially higher than the only other PSB system demonstrated with a solid electrolyte by Wang et al. This can largely be attributed to the use of a fully aqueous system and a catalyst for the polysulfide redox reactions, compared to Wang et al.’s use of THF for the polysulfide solvent. The use of high concentration anolyte and catholyte also boosts the power performance by lessening mass transport limitations.36 A summary of prior art on single-cell PSB batteries can be found in Table S1.


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Further study of the power performance will require not only optimization of the conductivity and thickness of the ceramic and electrolyte composition, but also optimization of the flow fields and stack design of the batteries in flow mode, which is an area of future study beyond the scope of this work.

Figure 4. Discharge polarization curves of PSB batteries assembled with (a) Na+ and (b) Li+ mediator ions. Polysulfide-Polyiodide System The corrosive and toxic nature of bromine presents a number of issues, introducing restraints on the types of materials used and vapor management systems to improve system safety, such as the one developed by Regenesys for their PSB battery system as described by the Tennessee Valley 15 ACS Paragon Plus Environment


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Authority.37 As our own work in the previous section demonstrates, these limitations can be difficult to overcome. These constraints can introduce higher system-level costs than the lowcost active materials would imply. As a result, iodine has been explored recently as an alternative material.38-39 It is less corrosive than bromine, and polyiodide is both less toxic and has a lower vapor pressure.39 This, however, comes at the cost of a lower cell potential. The reactions in a polysulfide-polyiodide (PSI) battery are as follows: 𝑆22− + 2𝑒 − → 2𝑆 2−

E0 ≈ − 0.51 V vs SHE

(3)

3𝐼 − → 𝐼3− + 2𝑒 −

E0 = 0.54 V vs SHE

(4)

Giving a total theoretical voltage of approximately 1.05 V. Unlike in the polysulfidepolybromide battery, the lower-order polysulfides are cycled in the PSI battery. This is done to boost the voltage of the cell, as the polyiodide half-cell voltage is so much lower than half-cell voltage of polybromide. Despite the lower voltage, the PSI battery system has a theoretical system energy density of 92 W h L-1, including the anolyte and catholyte, due to the higher solubility of NaI compared to NaBr. A schematic of the PSI battery is shown in Figure 5.


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Figure 5. Schematic of a polysulfide-polyiodide battery with polysulfide anolyte, Na+ solid-state electrolyte (SSE), and polyiodide catholyte. The PSI battery behaves similarly to the PSB battery, requiring the use of iodide salts to achieve a high solubility of I2 in an aqueous solvent. Like sulfur and bromine, iodine has a high crustal abundance and low cost, being both a byproduct of oil and gas refining and present in nitrate mines, as well as being extractable from seaweed and kelp.8, 27 Polysulfide-Polyiodide Battery Performance Polysulfide-polyiodide batteries were assembled with a Na+ mediator ion in the discharge state with an initial catholyte concentration of 1.5 M NaI + 0.5 M Na2SO4. Excess NaI was used to prevent precipitation of insoluble I2 in the catholyte. Cells were cycled with a 50% SOC upper capacity limit and discharged to 0.3 V at a current density of 0.5 mA cm-2. Cell cycling performance is shown in Figure 6. Initial cycles show increasing cell efficiency reflective of electrode activation, though unlike in the polybromide cell, only a single plateau is observed from the first cycle. The PSI battery shows remarkably stable performance, with an average coulombic efficiency of 98.7 % over 100 cycles. In later cycles a small second plateau begins to form at the end of charge. This may be related to loss of active material over time. The PSI cells suffer from the same fuming seen in the PSB cells, as shown in Figure S1b. However, as the vapor pressure of I2 is lower compared to that of Br2, it is to be expected that the material loss is at a lower rate compared to the PSB cells. Therefore, despite the known leaks in the cathode, the PSI cells as assembled are capable of achieving 100 cycles over 1600+ h. The rate performance of the PSI battery was tested as well. Li et al. argued that the sluggish kinetics of the polybromide couple would hinder its power performance compared to



the polyiodide couple.38 Cyclic voltammetry confirmed that the polybromide couple does show more sluggish redox kinetics, as shown in Figure S7. However, at the low current densities required by this demonstration system, the lower voltage of the polyiodide couple had a much more profound impact on its power performance. As shown in Figure 6c, the peak power density of the PSI battery with a Na+ mediator ion is 2.8 mW cm-2, compared to the 3.9 mW cm-2 of the PSB battery, though it is higher than the PSB battery with a Li+ mediator ion (1.6 mW cm-2). Furthermore, the overpotential of the PSB battery during rate testing is almost identical to the overpotential of the PSI battery, as shown in Figure S8, and only begins to substantially deviate at higher current densities. This indicates that the conductivity of solid electrolyte is more limiting on the power density than the redox kinetics of the polyhalide couple at low current densities.

Figure 6. Electrochemical performance of PSI battery at 0.5 mA cm-2 and 50% state of charge (SOC) cycling. (a) Galvanostatic cycling, with the inset showing the second plateau on 100th charge, (b) cycling efficiency including coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE), and (c) discharge polarization curves. The NASICON ceramic was analyzed by SEM to further determine its stability in I2 catholyte. Images of the surface of the NASICON after cycling for more than 1600 h in a PSI battery show only a slight texturing of the ceramic surface, when compared to polished, uncycled 18 ACS Paragon Plus Environment

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NASICON as shown in Figure 7 a – d. Please note that differences in pore sizes between images are due to natural variation between samples of NASICON. Soaking the NASICON in 0.5 M I2 + 2 M NaI catholyte for over 500 h did reveal some corrosion of the ceramic. This corrosion, however, is substantially less than the corrosion observed in polybromide-soaked NASICON. Additional analysis of LATP, shown in Figure S9, reveals that as with the polybromide catholyte, LATP shows very good stability with the polyiodide catholyte.

Figure 7. SEM of polished NASICON: (a – b) uncycled, (c – d) cycled in a PSI battery, and (e – f) soaked in 0.5 M Ir2 + 2 M NaI catholyte.



Conclusion This work demonstrates two polysulfide-polyhalide battery systems: polysulfide-polybromide (PSB) and polysulfide-polyiodide (PSI), with a mediator-ion solid electrolyte to eliminate crossover of redox active species and enable long battery lifetimes. PSB and PSI batteries were demonstrated for, respectively, 50 cycles with an average coulombic efficiency of 98.6 % and 100 cycles with an average coulombic efficiency of 98.7 %. Na+ ion-conducting NASICON ceramics show corrosion when soaked in concentrated polybromide and polyiodide catholytes but ceramics from cycled batteries show very little comparative corrosion. Furthermore, Li+ ionconducting LATP ceramics show excellent stability against the polybromide and polyiodide catholytes, though its use comes at a cost of lower power density. These results indicate that careful selection of ceramic materials for their stability with polybromide and polyiodide catholytes can enable long-life polysulfide-polyhalide batteries. ASSOCIATED CONTENT Supporting Information. Cycling performance of PSB battery, characterization of cell components, cyclic voltammetry of NaBr and NaI. AUTHOR INFORMATION Corresponding Author *Email: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.


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Acknowledgment This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering under Award No. DE-SC0005397.



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LongâLife PolysulfideâPolyhalide Batteries with a Mediator-ion Solid

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