solubility experiment ks2

Enjoy our range of fun science experiments for kids that feature awesome hands-on projects and activities that help bring the exciting world of science to life.

Dissolving Sugar at Different Heats

Learn about solutions as you add more and more sugar cubes to different temperature water. This easy experiment shows that you can only dissolve a certain amount and that this changes as the water gets hotter.

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Year 5: Properties of materials

Properties and Changes of Materials has been split into two lists , which look at properties and changes of materials and changes of state.This list consists of lesson plans and activities to support the teaching of properties and changes of materials in Year Five. It contains tips on using the resources, suggestions for further use and background subject knowledge. Possible misconceptions are highlighted so that teachers may plan lessons to facilitate correct conceptual understanding. Designed to support the new curriculum programme of study it aims to cover many of the requirements for knowledge and understanding and working scientifically. The statutory requirements are that children are taught to:

· compare and group together everyday materials based on evidence from comparative and  fair tests, including their hardness, solubility, transparency, conductivity (electrical and thermal), and response to magnets

· understand that some materials will dissolve in liquid to form a solution, and describe how to recover a substance from a solution

· use knowledge of solids, liquids and gases to decide how mixtures might be separated, including through filtering, sieving and evaporating

·  give reasons, based on evidence from comparative and fair tests, for the particular uses of everyday materials, including metals, wood and plastic

· demonstrate that dissolving, mixing and changes of state are reversible changes

Visit the primary science  webpage to access all lists.

Properties and Changes of Materials *suitable for home teaching*

Quality Assured Category: Science Publisher: Sigma Science

Activity ideas and worksheets which support the teaching of materials and their properties, good for homework sheets.

The Chemedian: Starting Secondary School

Quality Assured Category: Science Publisher: University of the West of England (Bristol)

Introduce dissolving with this colourful comic, which children will love. Carrying out an investigation which looks at the effect of temperature on dissolving will highlight the importance of fair testing. Further investigations look at different factors, such as the speed of stirring and the weight of salt added.

Children often confuse dissolving and melting so it is worth discussing the difference and providing examples of each.

Melting requires heat and dissolving requires a solvent to take place. Further information and activity ideas may be found here .

Growing Crystals

Quality Assured Category: Science Publisher: Centre for Science Education

Children will often describe a solid as 'disappearing' when it dissolves in a solvent such as water, because this is what they observe. This activity is a great way of showing them that salt is still present in the resulting solution and how to recover. Children could use a microscope to observe and draw the shapes of some of the resulting crystals as the water evaporates from the solution and the salt appears.

Although salt or sugar is generally used for this activity, alum (aluminium potassium sulfate) will grow the best crystals and is available from any chemical supplier.

How can we clean our dirty water?

Quality Assured Category: Careers Publisher: Royal Society

This resource provides a set of videos and a practical investigation aimed at supporting experimental science in the classroom and relating it to real world experiences.   In the first video Professor Brian Cox joins a teacher to find out how to set up and run an investigation to find out how to turn dirty water into clean water. Provided with a water mixture including stones, sand and salt children are asked to separate it to get pure water using sieves, filters and evaporation. In the next video he then joins the class carrying out their investigation. Further videos show Brian Cox visiting a sewage treatment plant to see how sewage is cleaned by various processes so it can be returned to rivers. He also meets a scientist using chromatography as a separation technique. 

Kitchen Concoctions

Quality Assured Category: Science Publisher: Centre for Industry Education Collaboration (CIEC)

Children can explore a range of mixtures, through fun kitchen science practicals and scenarios. 

Pinch of Salt

Children can explore solutions, evaporation and filtering through the real world applications of salt.

Plastics Playtime

Children can explore the properties of materials, including thermal insulation, through a range of activities linked to plastics.

Runny Liquids

A range of activities linked to Y5 materials, investigating properties of liquids.

Polymers: Physical Testing

Quality Assured Category: Physics Publisher: Centre for Industry Education Collaboration (CIEC)

Activities linked to year 5 materials.

Product Design: Polymers in Sleeping Bags

Quality Assured Category: Design and technology Publisher: Centre for Industry Education Collaboration (CIEC)

Product Design: Sports Shoes

Product design: pop bottles, let sleeping bags lie.

Lots of activities to test different properties of materials.

Science Specials Needs Supplement

Lots of real life problems for children to solve involving materials and their properties.

Science of Healthy Skin

Relates to Y5 materials.

Pulp to paper (in forces and recycling)

Children explore materials through making their own recycled paper.

Amazing Solubility: Exploring How Things Dissolve

Key Concept 1: What is Solubility?

Solubility is a magical property that describes how well a substance can dissolve in another substance, usually water. When a substance is soluble, it means it can mix well with the other substance and form a solution. Imagine a substance disappearing into another, like sugar vanishing into a cup of water!

Key Concept 2: Soluble and Insoluble Substances

Substances can be categorized as soluble or insoluble based on their ability to dissolve in water. Soluble substances can dissolve in water, while insoluble substances do not dissolve and remain as separate particles.

To understand this concept, let's conduct a simple experiment! Take a cup of water and add some sugar. Stir the water until the sugar disappears. The sugar has dissolved in water, making it a soluble substance. Now, try adding sand to the water and stir. You'll notice that the sand does not dissolve and remains as separate particles, making it an insoluble substance.

Key Concept 3: Solubility Rules (advanced)

To better understand solubility, scientists have developed solubility rules that can help predict whether a substance will dissolve in water. These rules are based on the chemical properties of different substances, such as the charges of their ions and their molecular structures. Some common solubility rules include:

• Most salts containing alkali metal ions (like sodium, potassium) and ammonium ions are soluble.
• Most salts containing nitrate, acetate, or perchlorate ions are soluble.
• Most chloride, bromide, and iodide salts are soluble, except those containing silver, lead, or mercury.
• Most sulfate salts are soluble, except those containing barium, calcium, strontium, lead, or mercury.

While these rules can help predict solubility, it is essential to remember that there are exceptions and that solubility can still be influenced by factors like temperature and concentration.

Key Concept 4: Factors Affecting Solubility

Solubility can be influenced by several factors:

Temperature : Temperature plays a crucial role in solubility. In general, most substances dissolve better in warmer water. For example, try dissolving salt in cold water and hot water separately. You'll observe that salt dissolves more quickly and to a greater extent in hot water than in cold water.

Stirring : Stirring or agitating a mixture can speed up the dissolution process. By stirring, you help distribute the particles and increase their contact with the solvent, allowing for faster and more complete dissolution.

Surface Area : The size of particles also affects solubility. Smaller particles have a larger surface area, which means more contact with the solvent. As a result, substances with smaller particles dissolve more quickly than those with larger particles. Compare the solubility of sugar cubes and powdered sugar. You'll find that powdered sugar dissolves much faster because its particles are smaller.

Nature of the Substances : Different substances have different solubilities due to their chemical properties. Some substances have a high solubility in water, like sugar and salt, while others, such as oil and wax, have low solubility or are insoluble.

Experiment: Investigating Solubility

• Several small cups
• Coffee or cocoa powder
• Sand or pebbles
• Stirring rods or spoons
• Label the cups as "Sugar," "Salt," "Coffee/Cocoa," and "Sand/Pebbles."
• Fill each cup with the same amount of water, approximately half full.
• Add a spoonful of sugar to the "Sugar" cup and stir until it dissolves completely.
• Repeat the process with salt, coffee or cocoa powder, and sand or pebbles, stirring each until no further dissolution occurs.
• Observe and record the results. Which substances dissolved completely? Which ones remained visible?

Discussion:

• Reflect on the experiment and discuss the findings with the children. Emphasize the differences between soluble and insoluble substances based on their observations.
• Explain that substances like sugar and salt are soluble because their particles are attracted to water molecules, allowing them to dissolve and form a solution. On the other hand, substances like sand and pebbles do not dissolve because their particles are not attracted to water molecules.
• Ask the children to think about other examples of soluble and insoluble substances they might have encountered in everyday life. Engage them in a discussion about the practical applications of solubility in various fields, such as cooking, cleaning, and manufacturing.

Activity: Solubility Scavenger Hunt

Organize a solubility scavenger hunt to help children further explore the concept of solubility. Provide a list of household items or substances that are either soluble or insoluble in water. Ask the children to find and collect these items or substances and then, under supervision, test their solubility in water. Encourage them to observe and record their findings.

Congratulations! You've successfully completed our amazing solubility science lesson. We hope you enjoyed learning about the fascinating world of solubility, conducting experiments, and observing the power of this incredible property. Remember, understanding solubility can help you in various aspects of your daily life, from cooking to cleaning and beyond. Keep exploring and experimenting with solubility, and you'll continue to uncover the incredible secrets it holds!

back to KidZone Science

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Subject: Chemistry

Age range: 11-14

Resource type: Lesson (complete)

Last updated

25 May 2024

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This fully resourced lesson on solubility is designed to help Year 7 students develop their understanding of the meaning of solubility and some factors that affect it through engaging activities, clear explanations, and differentiated materials .

This lesson is the 3rd in a series of lessons and covers the content from the AQA KS3 3.5.2 Separating mixtures topic and the Activate 1 (OUP) 5a: The particle model, 5.2.3 Solubility lesson.

The lesson includes all necessary resources, making it easy to implement in your classroom and the lesson’s text is adaptable, allowing you to adjust the duration and depth of the activities based on your students’ progress and time constraints.

Presentation contains (36 slides) : ● Lesson Prep and Technician Notes : Guidance notes for teachers to prepare the lesson and technician instructions. ● Bell Work / Do Now Activity : Engaging task to activate student prior knowledge and set the stage for the lesson. ● Clear Lesson Aim, Objectives & Success Criteria : Explicitly defined learning targets to guide students and measure their understanding. ● Discussion Slides : Thought-provoking prompts and questions to introduce the topic. ● Information Slides with Levelled Content : Varied levels of information catering to diverse learning styles and abilities. ● Differentiated Activities (Group Work) : Collaborative tasks in small groups to encourage active participation and enhance learning. ● Practical Activity : Hands-on experience to apply concepts and gain practical skills. ● Differentiated Questions with Answers : Comprehensive questions with accompanying solutions for self-assessment and note-taking. ● Student Worksheets/Handouts : Printable materials for students to complete and gather notes.

Aimed at a mixed ability Year 7 class, with three levels of demand to accommodate different learning styles and levels : ● K- Know (low demand) ● A- Apply (standard demand) ● E- Extend (high demand)

This lesson is also available as a digital worksheet, which is ideal for absent students to catch-up missed work, distance learning, home schooling, or independent study. Solubility Distance learning

If you require more assistance, please contact me at- [email protected]

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Get this resource as part of a bundle and save up to 41%

A bundle is a package of resources grouped together to teach a particular topic, or a series of lessons, in one place.

Activate 1 Particle model and separating mixtures

**Particle model and Separating mixtures bundle contains 14 fully resourced lessons designed to help Year 7 students develop their understanding of the particle model of matter, states of matter, changes of state, and different techniques for separating mixtures through engaging activities, clear explanations, and differentiated materials**. These lessons cover the content from the AQA KS3 3.5.1 The particle model and 3.5.2 Separating mixtures topics and the Activate 7 (OUP) 5a: Matter chapter. The lessons include all necessary resources, making them easy to implement in your classroom. Additionally, the editable text allows you to adjust the duration and depth of the activities based on your students' progress and time constraints. **Each editable presentation contains**: ● **Lesson Prep and Technician Notes**: Guidance notes for teachers to prepare the lesson and technician instructions. ● **Bell Work / Do Now Activity**: Engaging task to activate student prior knowledge and set the stage for the lesson. ● **Clear Lesson Aim, Objectives & Success Criteria**: Explicitly defined learning targets to guide students and measure their understanding. ● **Discussion Slides**: Thought-provoking prompts and questions to introduce the topic. ● **Information Slides with Levelled Content**: Varied levels of information catering to diverse learning styles and abilities. ● **Differentiated Activities (Group Work)**: Collaborative tasks in small groups to encourage active participation and enhance learning. ● **Practical Activity (if appropriate)**: Hands-on experience to apply concepts and gain practical skills. ● **Differentiated Questions with Answers**: Comprehensive questions with accompanying solutions for self-assessment and note-taking. ● **Student Worksheets/Handouts (if appropriate)**: Printable materials for students to complete and gather notes. ● **Homework Activities (if appropriate)**: Varied homework tasks to cater to individual needs and promote independent learning. **Aimed at a mixed ability Year 7, with three levels of demand to accommodate different learning styles and levels**: ● K- Know (low demand) ● A- Apply (standard demand) ● E- Extend (high demand) Each lesson is also available as a digital worksheet, which are ideal for absent students to catch-up missed work, distance learning, home schooling, or independent study. [Particle model and Separating mixtures Distance learning bundle](https://www.tes.com/teaching-resource/resource-12459592) If you require more assistance, please contact me at- [email protected]

Solubility Lesson bundle

**This lesson bundle provides the solubility lesson in both classroom and distance learning formats: PowerPoint for classroom instruction and digital worksheets for distance learning. Solubility is an engaging and differentiated lesson designed to help Year 7 students develop their understanding of the meaning of solubility and some factors that affect it**. This lesson is the 3rd in a series of lessons and covers the content from the AQA KS3 3.5.2 Separating mixtures topic and the Activate 1 (OUP) 5a: The particle model, 5.2.3 Solubility lesson. The bundle includes all necessary resources, making it easy to implement and is fully editable, allowing you to adjust the duration and depth of the activities based on your students' progress and time constraints. Aimed at a mixed ability Year 7 class. **Bundle contents**: **1. Classroom-based presentation and resources**: ● Lesson Prep and Technician Notes ● Bell Work / Do Now Activity ● Clear Lesson Aim, Objectives & Success Criteria ● Discussion Slides ● Information Slides with Levelled Content ● Differentiated Activities (Group Work) ● Practical Activity ● Differentiated Questions with Answers ● Student Worksheets/Handouts **2. Digital worksheet**: ● Teacher guidance and answers ● Engage ● Explore ● Explain ● Apply ● Extend ● **Please note**: To fully utilise this resource, students need a computer with internet access. This resource is recommended for use in Google Doc™ format. While it can be converted to Word/Excel, some tasks may not function properly in these formats. If you require more assistance, please contact me at- [email protected]

Activate 1 part 2 of 5

**This bundle contains presentations covering the content for lessons 21-40 from the AQA KS3 Activate 1 (Year 7) scheme**. **Bundle contains presentations for the following chapters**: * 4a Waves x 9 * 5a Matter x 11 (part of chapter the rest are in part 3) **Each presentation contains**- * Bell work activity * Lesson objective and success criteria * Information slides * Challenge activities (group work) * Practical activity (where appropriate) * Demonstrate understanding tasks (with answers) * Lesson resources (additional to scheme) **Please note: (Kerboodle) worksheets from scheme are not included due to license**. If you require more assistance, please contact me at- [email protected]

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• Published: 05 September 2024

Designing electrolytes with high solubility of sulfides/disulfides for high-energy-density and low-cost K-Na/S batteries

• Liying Tian 1 , 2   na1 ,
• Zhenghao Yang 1   na1 ,
• Shiyi Yuan 1 ,
• Tye Milazzo 3 ,
• Qian Cheng   ORCID: orcid.org/0000-0001-5510-2977 1 ,
• Syed Rasool   ORCID: orcid.org/0009-0009-3604-165X 1 ,
• Wenrui Lei   ORCID: orcid.org/0009-0009-7637-6534 4 ,
• Wenbo Li 1 ,
• Yucheng Yang 1 ,
• Tianwei Jin 1 ,
• Shengyu Cong 1 ,
• Joseph Francis Wild 1 ,
• Yonghua Du   ORCID: orcid.org/0000-0003-2655-045X 5 ,
• Tengfei Luo   ORCID: orcid.org/0000-0003-3940-8786 4 ,
• Donghui Long   ORCID: orcid.org/0000-0002-3179-4822 2 &
• Yuan Yang   ORCID: orcid.org/0000-0003-0264-2640 1  

Nature Communications volume  15 , Article number:  7771 ( 2024 ) Cite this article

Metrics details

Alkaline metal sulfur (AMS) batteries offer a promising solution for grid-level energy storage due to their low cost and long cycle life. However, the formation of solid compounds such as M 2 S 2 and M 2 S (M = Na, K) during cycling limits their performance. Here we unveil intermediate-temperature K-Na/S batteries utilizing advanced electrolytes that dissolve all polysulfides and sulfides (K 2 S x , x = 1–8), significantly enhancing reaction kinetics, specific capacity, and energy density. These batteries achieve near-theoretical capacity (1655 mAh g −1 sulfur) at 75 °C with a 1 M sulfur concentration. At a 4 M sulfur concentration, they deliver 830 mAh g −1 at 2 mA cm −2 , retaining 71% capacity after 1000 cycles. This new K-Na/S battery with specific energy of 150-250 Wh kg −1  only employs earth-abundant elements, making it attractive for long-duration energy storage.

Introduction

Grid-level energy storage is important for addressing climate change and realizing a sustainable future 1 , 2 since it can stabilize intermittent power generation from renewable solar and wind energy 3 . Long-duration energy storage (LDES) with an operational period over one day is of particular importance as it enables stable power output under extreme conditions and leverages seasonal variations 4 , 5 , 6 . However, LDES is highly challenging due to the demanding requirement on low cost 7 , since it is operated for a limited number of cycles 8 , such as ~1500 times for weekly operation and ~ 400 times for monthly operation in 30 years, which is much less than short-term energy storage with everyday cycling and thus ~ 10,000 cycles in 30 years 9 , 10 .

Na/S and K/S batteries are promising for LDES since all elements involved are earth-abundant and inexpensive 11 , 12 , 13 , 14 . High-temperature (HT) Na/S batteries operated at 300–350  o C have been commercialized, which use β″-alumina solid electrolytes (BASE) to separate the sulfur cathode and the Na anode 15 , 16 . The full cell reaction is 2 Na + x S → Na 2 S x (x = 3–5) with an average voltage of 2.0 V 17 , 18 . Although the HT Na/S battery offers a high theoretical energy density and a long cycle life 19 , its high operating temperature causes substantial challenges such as corrosion and thermal management 20 . On the other end, room-temperature (RT) Na/S and K/S batteries use liquid organic electrolytes to mitigate these issues 21 , 22 , 23 , but encounter new challenges such as strong polysulfide shuttling, metal dendrites, and poor sulfur utilization 24 , 25 , 26 , 27 , 28 . The cell voltage also decreases to 1.2–1.5 V 29 .

Intermediate-temperature (IT) Na/S and K/S batteries, which function at 100–150  o C, are receiving increasing attention because they take advantage of their HT and RT counterparts 30 , 31 . IT Na/S and K/S batteries use BASE to fully prevent polysulfide shuttling and greatly suppress metal dendrites, and organic liquid electrolytes (e.g., tetraglyme/TEGDME) at the cathode side to enhance kinetics 17 , 32 .

A common challenge for all HT/IT/RT Na/S and K/S batteries is the formation of solid M 2 S 2 and M 2 S (M = Na, K) with ultralow ionic diffusivity in discharge 33 , which limits the specific capacity of the cathode to only ~ 500 mAh g −1 for Na/S and ~ 400 mAh g −1 for K/S, which corresponds to only M 2 S 4 /M 2 S 3 31 , 34 , 35 . Limited outliers report initial capacities at 600-800 mAh/g, but they either use excessive matrix such as polyacrylonitrile (PAN) 36 or show fast capacity decay 37 (Supplementary Note  1 ). To address this issue and substantially enhance discharge capacity, here we propose a new family of amide electrolytes that show reasonable solubility of M 2 S 2 /M 2 S (e.g., 1-2 M), which drastically enhances ionic diffusivity and reaction kinetics on the cathode side. We apply this new design principle to IT K-Na alloy/S batteries (K-Na/S for short) in this work because 1) BASE in IT can eliminate the shuttle effect caused by such a high solubility, and 2) IT K-Na/S batteries have a higher average voltage of ~ 2.1 V than 1.2–1.5 V in RT Na/S and K/S batteries. 3) The high solubility can also substantially lower the operation temperature from 150 °C in reported IT Na/S and K/S batteries to 50–100 °C.

Specifically, an acetamide/ɛ-caprolactam (CPL) eutectic solvent is used, which can dissolve K 2 S up to 1.43 M at 75 °C and has a lower melting point (− 8 °C) than acetamide (82 °C) and CPL (71 °C) 38 . With such a new electrolyte, a K-Na alloy/ K + -conducting BASE (K-BASE)/1 M [S] battery can reach a nearly theoretical discharge capacity of 1655 mAh g −1 sulfur at 75  o C. When [S] reaches 4 M, the specific capacity still remains at 830 mAh g −1 sulfur at 2 mA cm −2 with a capacity retention of 71 % after 1000 cycles. A discharge capacity of 703 mAh g −1 sulfur is also achieved at [S] of 8 M. Note that [S] counts sulfur from all polysulfides and sulfides inside the solution. These values correspond to specific energies of 150–250 Wh kg −1 at the cell level with BASE and packaging considered. Given the earth abundance of all elements involved, this system has the potential to achieve attractive cost and performance for LDES.

Design principle of K-Na/S batteries with soluble sulfides and disulfides

The cathode is polysulfide dissolved in a mixture of CPL and acetamide (with 1:1 molar ratio, Fig.  1a , since it has the lowest melting point). Therefore, the cathode reaction in the range of S 3 2− /S 2− is 2S 3 2− (l) + 2e − → 3S 2 2− (l) and S 2 2− (l) + 2e − → 2S 2− (l) instead of 2S 3 2− (l) + 2e −  + 6 K + → 3K 2 S 2 (s) and K 2 S 2 (s) + 2e −  + 2 K + → 2K 2 S (s) in conventional ether electrolytes. Such soluble redox significantly boosts reaction kinetics as the sluggish diffusion in solids is avoided. This catholyte is separated from a K-Na liquid alloy anode (1:1) by a commercial K-BASE, which does not conduct Na + [, 31 . The liquid alloy anode is used to reduce the anode/K-BASE interfacial impedance 39 , 40 , 41 . Therefore, the full cell reaction is S + 2 K → K 2 S.

a A schematic of the proposed K-Na/S battery. The liquid K-Na alloy anode wets K-BASE well, leading to low anode/solid electrolyte interfacial impedance. K-BASE only conducts K + but not Na + , so the mechanism is of K/S batteries. The acetamide/CPL solvent dissolves K 2 S x (x = 1–8), which promotes ionic transport in K 2 S 2 and K 2 S, and thus reaction kinetics and specific capacity. The synergy of these two strategies leads to K/S batteries with high energy density even at 75  o C. b The concentration dependence of theoretical (dash line) and practical energy densities of the proposed K-Na/S battery. Blue and red lines are for discharge times of 1 week and 1 day, respectively.

The energy density of such a system depends on the concentration of sulfur. Based on the theoretical specific capacity of sulfur (1675 mAh g −1 ) and K (687 mAh g −1 ), the theoretical specific energy reaches 95.8, 295, and 452 Wh kg −1 at 1 M, 4 M and 8 M sulfur, respectively, with the mass of sulfur, liquid electrolyte and anode considered (Fig.  1b ). When masses of BASE and packaging are included, the cell-level specific energy is expected to reach 136 and 186 Wh kg −1 at 4 M and 8 M sulfur, respectively (24 h discharge), and 179 and 276 Wh kg −1 at 4 M and 8 M sulfur (one week discharge), respectively. It should be noted that the calculation is only for materials themselves and the N/P ratio of 1, while the dependence of energy density on the N/P ratio is shown in Supplementary Fig.  1 . Details can be found in Supplementary Note  2 .

Dissolution behavior in the CPL/acetamide mixture

To validate our new design, we first test the solubility of K 2 S x in CPL/acetamide. This mixed solvent readily dissolves K 2 S 8 , K 2 S 4 , K 2 S 2, and K 2 S with 1.2 M [S] at 25 °C (Fig.  2a ), meanwhile being transparent and allowing light to pass straightly (Fig.  2b ). In contrast, the solubility of K 2 S in a conventional TEGDME electrolyte is less than 0.1 M at 25 °C, as reflected by the milky appearance of its suspension (Fig.  2b ). Further temperature-dependent solubility tests show that the solubilities of K 2 S 2 /K 2 S are 1.44 M/1.40 M at 60 °C, 1.50 M/1.43 M at 75 °C, 1.64 M/1.47 M at 100 °C and 1.72 M/1.50 M at 120 °C, respectively (Fig.  2c ). As the length of polysulfide increase, the solubility even goes higher (Fig.  2d ). The solubility for CPL/acetamide with other mixing ratios are also tested and shown in Supplementary Fig.  2 . Such high solubilities suggest that the electrochemical reaction in discharge involves soluble sulfide (S 2 2− ) and polysulfide ions (S x 2− ) instead of solid K 2 S and K 2 S x , which is expected to significantly enhance ionic diffusion and reaction kinetics 42 .

a The dissolution behavior of K 2 S x (x = 1, 2, 4, 8) in CPL/acetamide at 25  o C. The concentrations of sulfur in all samples are 1.2 M. b Tyndall effect tests for 1.2 M K 2 S in CPL/acetamide eutectic solvent (ES) and 0.1 M K 2 S in TEGDME, excluding the possibility of forming colloids in ES. c Solubilities of K 2 S and K 2 S 2 in ES and TEGDME from 60  o C to 120  o C. d Solubilities of K 2 S, K 2 S 2, and K 2 S 3 in ES and TEGDME in 75  o C. e Calculated radial distribution function of molecular dynamics (MD) simulations of K 2 S and K 2 S 2 in ES and TEGDME. The larger peak height in ES indicates stronger bonding between K + and ES. f Fourier Transform Infrared Spectroscopy (FTIR) spectra of pure ES and 0.2 M/0.4 M K 2 S in ES. A peak representing K + – solvent interaction shows up at 1550 cm −1 with an increasing concentration of K 2 S.

Molecular dynamics (MD) simulations were conducted to better understand the different dissolution behaviors of K 2 S in CPL/acetamide and TEGDME (Supplementary Fig.  3 and Supplementary Note  3 ). MD results show that the free energy of K + and S 2- when dissolved in CPL/acetamide is – 5.2 kJ mol −1 compared to the state where these ions are in a vacuum, while in TEGDME, this value is 199.6 kJ mol −1 . This clearly indicates that K 2 S is significantly more soluble in CPL/acetamide than TEGDME. To explore the molecular level origin of this trend, we compared radial distribution functions (RDF) of the dissolved ions around the polar groups in CPL/acetamide and TEGDME. The K-O peak in CPL/acetamide exhibited a much higher first peak compared to that in TEGDME, and the position of the first peak in CPL/acetamide is at a shorter distance (~ 0.27 Å) than in TEGDME (~ 0.36 Å). This indicates that the C = O group in CPL/acetamide has a stronger interaction towards K + and can attract more K + ions closer to the O atom in CPL/acetamide than in TEGDME (Fig.  2e ), which contributes to the dissolution of K 2 S.

Such simulation results are also consistent with FTIR results (Fig.  2f ). As the concentration of K 2 S increases, a characteristic peak appeared at 1550 cm −1 , next to the C = O bond at 1650 cm −1 . This peak arises from the interaction between K + and the C = O bond 43 . Furthermore, MD RDF for other ion/polar group pairs also shows stronger interaction in CPL/acetamide than TEGDME (Supplementary Fig.  4 ).

K-Na/S Batteries with 1 M [S] in CPL/acetamide

To demonstrate that high solubilities of K 2 S 2 /K 2 S in CPL/acetamide can enhance the discharge capacity, we assembled K-Na alloy/K-BASE/polysulfide catholyte coin cells with carbon fiber papers as the cathode current collector. The CPL/acetamide solvent is stable between 1.3 and 3.0 V vs. K + /K-Na (1:1) (Supplementary Fig.  5 ). The amount of catholyte corresponds to 1.41 mAh cm −2 at 1 M [S], 5.64 mAh cm −2 at 4 M [S] and 11.3 mAh cm −2 at 8 M [S] with the theoretical capacity of sulfur assumed.

On the anode side, 1.25 wt% carbon black (CB) was added to the K-Na alloy (1:1), which reduces the interfacial impedance of K-Na alloy/BASE from ~ 21 ohm without CB to ~ 7 Ω with CB (Supplementary Figs.  6 and 7a ). In K-Na/BASE/K-Na symmetric cells, the overpotential reduces from ~ 40 mV without CB to ~ 20 mV with CB at 2.6 mA cm −2 (Fig.  3a ), and the critical current density increases from 40 mA cm −2 without CB to 70 mA cm −2 with CB (Supplementary Fig.  7b and Supplementary Note  4 ).

a Cycling of K-Na/BASE/K-Na symmetric cells with carbon black (blue) and without carbon black (orange) at different current densities. b Charge/discharge voltage profiles of 1 M [S] cells in CPL/acetamide eutectic solvent (ES) and TEGDME electrolyte, respectively. The initial composition is Na 2 S 8 , with K + ions passing BASE. c Cycling performance of cells with ES and TEGDME electrolytes at 0.5 mA cm −2 . Electrochemical impedance spectroscopy of cells at ( d ) the fully charged state, and ( e ) discharged to 598 mAh g −1 sulfur, corresponding to M 2 S 2.8 . The range of frequency is 1 MHz – 1 mHz. All tests are done at 75  o C in an oven.

We first test cells with 1 M [S] catholyte where K 2 S 2 /K 2 S are fully soluble. At 0.5 mA cm −2 (0.35 C, 1 C = 1675 mA g −1 ), the first discharge plateaus (2.1 – 2.7 V) in both CPL/acetamide and TEGDME electrolyte overlap well, reflecting good kinetics of S/S 4 2− in both electrolytes (Fig.  3b ). However, a sudden drop was observed in TEGDME at ~ 600 mAh g −1 sulfur, due to formation of solid K 2 S 2 /K 2 S with low diffusivity and poor kinetics. The capacity reaches 630 mAh g −1 in cycle 33, and 567 mAh g −1 in cycle 100, which corresponds to a capacity retention of 90% or 99.84 %/cycle from cycle 33 to 100.

On the other hand, the cell with CPL/acetamide shows high discharge specific capacities of 1591 mAh g −1 sulfur in cycle 2 and 1655 mAh g −1 in cycle 7, which are almost the same as the theoretical value of 1675 mAh g −1 (Fig.  3c ). The capacity remains at 1263 mAh g −1 after 300 cycles, corresponding to a capacity retention of 76.3%, or 99.91%/cycle (Fig.  3c ). These results obviously reflect that the soluble nature of K 2 S 2 /K 2 S in CPL/acetamide dramatically improves reaction kinetics and thus enhances the discharge capacity.

We further performed electrochemical impedance spectroscopy (EIS) to understand how solubility affects electrochemical performance. At full charge (Fig.  3d ), impedances of cells with TEGDME and CPL/acetamide are both low, since the redox of high-order polysulfides is kinetically fast. Moreover, the diffusion tails are both negligible, indicating fast diffusion in the liquid phase. On the other side, at 598 mAh g −1 , which corresponds to M 2 S 2.8 and 99.1 % of the full discharge capacity in TEGDME, the cell with TEGDME shows a long diffusion tail with a diffusivity of ~ 8 × 10 −16  cm 2  s −1 , validating poor ionic transport in solid K 2 S 2 /K 2 S. However, the diffusion tail in CPL/acetamide is still negligible (Fig.  3e ). Further ionic conductivity measurements indicate that the diffusivity is ~ 3 × 10 −7  cm 2  s −1 in the liquid phase (Supplementary Note  5 ).

To verify the absence of solid precipitation in CPL/acetamide, several characterization methods were applied to elucidate the precipitation dynamics. First, ex-situ scanning electron microscope (SEM) images of the cathode at 1.5 V revealed a smooth carbon surface without noticeable solid precipitates in CPL/acetamide (Fig.  4a ). Moreover, S and K signals are very weak in Energy Dispersive Spectroscopy (EDS) spectrum, and their ratio corresponds to K 2 S 1.0 , proving the full transformation from sulfur to K 2 S. In contrast, in TEGDME cells, there are plenty of micron-sized particles, and EDS indicates that their compositions are K 2 S 2.8 (Fig.  4b and Supplementary Fig.  8 ), corresponding to the discharge ending capacity of 562 mAh g −1 (K 2 S 3.0 ). The same results are also observed by ex-situ Synchrotron-based X-ray Absorption. Near Edge Structure (XANES) mapping of sulfur shows that the intensities of sulfur signals in CPL/acetamide after 1 and 10 cycles are less than 1/10 of those in TEGDME, indicating no or very little solid precipitation (Fig.  4c ).

a , b Scanning Electron Microscope (SEM) imaging and Energy Dispersive Spectroscopy (EDS) spectrum results of carbon paper from cells after the first cycle with 1 M [S] CPL/acetamide eutectic solvent (ES) ( a ) and TEGDME ( b ). c , d X-ray Absorption Near Edge Structure (XANES) mapping of sulfur element for carbon paper from cells after 1 or 10 cycles with ES ( c ) and TEGDME ( d ). e , f Operando optical microscope imaging of catholyte at room temperature in ( e ), ES where no precipitation is observed even at the end of discharge and ( f ), TEGDME where precipitation starts to appear in the middle of discharge. Precipitates are marked by red dashed circles. [S] in the catholyte and temperature are 1 M and 75  o C, respectively, for ( a–d ), and 0.5 M and 25  o C, respectively, in ( e ) and ( f ).

Operando optical imaging further supports that there is indeed no solid precipitation with the CPL/acetamide catholyte even at the end of discharge at 25 °C (1500 mAh g −1 , Fig.  4e and Supplementary Video  1 and 3 ). In contrast, in TEGDME, precipitation begin to appear as early as 513 mAh g −1 (K 2 S 3.3 , Fig.  4f and Supplementary Video  2 ), and granular solid precipitates exist everywhere over carbon fibers at the end of discharge (609 mAh g −1 , K 2 S 2.8 , Fig.  4f and Supplementary Video  4 ). These imaging results clearly show that high solubility of K 2 S 2 and K 2 S can avoid solid precipitation and greatly extend the discharge range of sulfur cathode in K-Na/S batteries.

K-Na/S Batteries with 4 M and 8 M [S] in CPL/acetamide

We further test samples with 4 M and 8 M [S] to enhance the energy density of K-Na/S batteries. As [S] is higher than the solubility of K 2 S 2 and K 2 S, the cathode reaction involves solid formation such as 2S 3 2− (l) + 2e −  + 6K + → 3K 2 S 2 (s) and K 2 S 2 (l) + 2e −  + 2 K + → 2K 2 S (s), which further contributes to cell capacity in parallel with liquid/liquid transformation among S 3 2− /S 2 2− /S 2− .

At 0.5 mA cm −2 (0.09 C), the 4 M [S] cell in CPL/acetamide shows an initial discharge capacity of 913 mAh g −1 , which increases gradually to 1106 mAh g −1 at cycle 46 and remains at 1086 mAh g −1 (98.2%) after 100 cycles. Such capacity corresponds to ~ 3.9 mAh cm −2 (Fig.  5 a, b ). The average coulombic efficiency (CE) is 100.2% from cycle 1 to 100, indicating no shuttle effect or noticeable side reactions. The gradual capacity increase in CPL/acetamide upon cycling probably comes from better wetting between the catholyte and the carbon substrate, which is supported by decreasing charge transfer resistance upon cycling (Supplementary Fig.  9 ). In contrast, 4 M [S] in TEGDME only gives an initial discharge capacity of 467 mAh g −1 , which remains at 439 mAh g −1 after 100 cycles (94.0 %). The corresponding average CE is 100.1%.

a Charge/discharge voltage profiles of cells with 4 M sulfur in CPL/acetamide eutectic solvent (ES) and TEGDME catholyte. The current densities are 0.5 mA cm − 2 (0.09 C). b Cycling performance of cells with sulfur concentrations of 4 M and 8 M [S] in the cathode. The current densities are 0.5 mA cm −2 . c Rate performance of cells with 4 M sulfur in ES electrolyte and TEGDME electrolyte. d Cycling performance of cells with 4 M sulfur in the cathode at 2 mA cm −2 . The first 5 cycles are at 0.5 mA cm −2 . e Charge/discharge voltage profiles of cells with various C-rates. f Electrochemical impedance spectroscopy of cells with 4 M sulfur in the cathode at the fully charged state (C) and at a discharge capacity of 460 mAh g −1 sulfur (DC). The electrolytes are ES and TEGDME, respectively. g The discharge time dependence of material cost for K-Na/S battery with 1 M [S] /4 M [S] /8 M [S] at 2 mA cm −2 . h Eutectic solvent with a separator (ES, left) and conventional Li-ion battery electrolyte with a separator (LP40, right) on fire. Samples with polysulfides inside can be found in Supplementary Video  5 . All electrochemical tests for a–f are done in a 75 °C oven.

When [S] further increases to 8 M, the cell in CPL/acetamide shows an initial discharge capacity of 411 mAh g −1 , which gradually increases to 672 mAh g −1 after 100 cycles (Fig.  5b ). The average CE is 100.5 % from cycle 1 to 100. The increasing capacity is likely a result of improved wetting during cycling since 8 M [S] in ES is viscous. The increasing capacity is probably the reason for CE exceeding 100%, as more and more capacity can be utilized during cycling. On the other hand, 8 M [S] in TEGDME only gives an initial discharge capacity of 432 mAh g −1 , which remains at 424 mAh g −1 after 100 cycles.

Such results also echo with impedance data. Again, no significant diffusion tail is observed at full charge due to fast kinetics (Fig.  5f ). However, a long diffusion tail is observed at the end of discharge in TEGDME with an estimated diffusivity of 9 × 10 −14  cm 2  s −1 . This higher diffusivity than that number in Fig.  3f may arise from a lower discharge capacity with 4 M sulfur, which corresponds to a higher order of polysulfides. On the other hand, the diffusion tail remains negligible in CPL/acetamide, indicating that even if solid K 2 S 2 /K 2 S is formed in CPL/acetamide, the presence of soluble K 2 S 2 /K 2 S still helps enhance ionic diffusion and discharge capacity significantly.

We further demonstrate long-term cycling at 2 mA cm −2 (0.38 C) in 4 M [S] cells, which corresponds to a discharge time of 1.3 h. The initial discharge capacity is 830 mAh g −1 , which remains at 712 mAh g −1 (86%) after 500 cycles, 593 mAh g −1 (71%) after 1000 cycles, and 505 mAh g −1 (61%) after 1500 cycles. The variation in CE comes from environment disturbance, which happens averagely once every ~ 50 cycles (10 days, Supplementary Fig.  10 ). In contrast, the TEGDME cell only has an initial specific capacity of 378 mAh g −1 at 2 mA cm −2 , which remains at 343 mAh g −1 after 1000 cycles. The reason for better retention of TEGDME cells is discussed in Supplementary Note  6 . Such superior capacity further confirms that the high solubility of K 2 S 2 /K 2 S in CPL/acetamide helps enhance kinetics and increase energy density even at a concentration of sulfur beyond solubility. The cycling performance of cells with CPL/acetamide is also promising for practical LDES.

The K-Na/S cell with 4 M [S] in CPL/acetamide also shows reasonable power capability. At 0.5 mA cm −2 (0.09 C), the discharge capacity is 1025 mAh g −1 , and it remains at 895 and 765 mAh g −1 at 1.5 mA cm −2 (0.26 C) and 2.5 mA cm −2 (0.51 C), respectively (Fig.  5c and e ). For comparison, the specific capacities of TEGDME catholyte counterparts are around 430 mAh g −1 between 0.5–2.5 mA cm −2 . Impedance data show that the contribution from BASE, K-Na/BASE interface, and cathode are 15 Ω, 19 Ω, and 122 Ω at the end of discharge, respectively (Fig.  5f ). This suggests that cathode impedance is the main limiting factor for power capability, which can be further reduced by increasing the surface area of current collector, or surface modifications to enhance wetting between K 2 S 2 /K 2 S and the carbon substrate.

Besides electrochemical performance, we also further perform preliminary experiments to understand the thermal stability of CPL/acetamide electrolytes. Acetamide and CPL have melting points of 80 and 69 °C, respectively, indicating that they both have low vapor pressure compared to common carbonate and ether electrolytes and reasonable thermal stability at 60–120 °C. We also put CPL/acetamide on fire from ignited paper with and without polysulfides inside (Fig.  5h and Supplementary Video  5 and 6 ), and these liquids did not catch fire in both cases. These results indicate that such electrolytes have reasonable thermal stability and are promising for grid-scale energy storage.

We further estimate the cost at the cell level, including all components (electrolytes, BASE, electrode materials, and packaging), and the details can be found in Supplementary Note  7 44 . Based on 2 mA cm −2 and a discharge time of 24 h, the materials costs are $54 and $41 kWh −1 for 4 and 8 M sulfur, respectively. When the discharge time increases to one week, the cell-level materials costs are further reduced to $39 and $26 kWh −1 for 4 and 8 M sulfur, respectively (Fig.  5g ). With a higher current density of 5 mA cm −2 , the material cost can be further reduced by 3–8% (Supplementary Fig.  11 ). Such low costs are attributed to inexpensive active materials 45 .

In addition, manufacturing costs should also be considered. Although this is difficult to evaluate, it is likely to be on pair with or less than Li-ion batteries 46 . This is because no slurry coating or drying is needed for alkaline metal sulfur batteries, which count for the majority part of manufacturing cost in Li-ion batteries 47 . On the other hand, Na and K need to be handled in an air-free environment.

Beside K-Na/S batteries, the same design principle can also be applied to Na/S batteries as Na 2 S and Na 2 S 2 also have solubilities of 1.85 M and 2.80 M in CPL/acetamide at 75 °C, respectively. We also see a high discharge capacity of 940 mAh/g in the first cycle (Supplementary Fig.  12 ). The cycling performance needs to be improved due to poor interfaces between Na metal and BASE at 75 °C. We will report this in the future.

In summary, we developed a new acetamide/CPL-based eutectic solvent electrolyte with high solubilities over 1 M for all polysulfides and sulfide (K 2 S x , x = 1–8) between 60 and 120 °C. Such high solubilities remarkably enhance ionic diffusion and reaction kinetics of K 2 S 2 and K 2 S, leading to AMS batteries with high energy density and low cost. Experimentally, a nearly theoretical discharge capacity of 1655 mAh g −1 is achieved with 1 M sulfur in the catholyte at 75  o C, 2.6 times that with conventional TEGDME electrolytes. When the sulfur concentration further increases to 4 M, a high capacity of 830 mAh g −1 is still delivered with 71 % capacity retention after 1000 cycles at 2 mA cm −2 and 75  o C. Further energy density and economic analysis show that this new design has the potential to achieve a specific energy of 150–250 Wh kg −1 at the cell level, and materials cost as low as ~$30 kWh −1 under weekly operation. Such performances are promising for long-duration energy storage.

Materials preparation

All chemicals were of analytical grade purity. For the CPL/acetamide mixture, one mole each of ε-caprolactam (CPL, 99% purity, Sigma Aldrich) and acetamide (99% purity, Sigma Aldrich) were dried at 50 °C within an argon-filled glovebox overnight prior to use. Subsequently, the two compounds were mixed and stirred at 50 °C for 30 min. Then, it was rested in a vacuum oven at 60 °C overnight to eliminate any trapped gas.

To form a catholyte, 0.125 M/0.5 M/1 M of anhydrous Na 2 S (98%, Sigma Aldrich), 0.5 M potassium bis(trifluoromethanesulfonyl)imide (KTFSI, 97%, Sigma Aldrich), and 1.25 wt% (of solvent) Super C65 carbon black were mixed with CPL/acetamide and stirred at 80 °C until a homogeneous mixture was formed. Then a suitable amount of sulfur was added and stirred at 80 °C to form CPL/acetamide-based catholyte with different concentrations of [S]. TEGDME catholytes were prepared by the same procedure except that TEGDME was used instead of CPL/acetamide.

For the K-Na alloy anode, 0.01 mol potassium (98%, Sigma Aldrich) was mixed with 0.01 mol sodium (99.8%, Sigma Aldrich) in an aluminum container in an argon-filled glovebox. The liquid alloy was then combined with 1.25 wt% C65 carbon black, followed by stirring for 20 min.

Solubility test

The solubility of K 2 S x in electrolytes was evaluated using the following procedure: First, K 2 S (Thermal Fisher Scientific) was mixed with sulfur with a 1:x molar ratio in a glass vial containing 500 µL of solvent. The mixture was then stirred on a hot plate set to a specific temperature. If the solution became clear, then additional K 2 S and sulfur would be added in the 1:x molar ratio. Otherwise, an additional amount of solvent was added. This process was repeated until the following conditions were met: first, a certain concentration, C 0 , of K 2 S x was found to be soluble, as defined by the absence of solid in the vial after at least 2 h of sedimentation; second, C 0  + 0.05 M was not soluble, as indicated by the presence of solid precipitates after 2 hours. Once these conditions were satisfied, the solubility of K 2 S 2 at the given temperature was considered to be C 0 .

Cell assembly

CR2032 coin cells were used for cell assembly. Potassium-β″-alumina (K-BASE) with 1 mm thickness was purchased from Ionotec Inc. and cut into disks with 15 mm diameter. For Na-K symmetric cells, stainless steel foil was cut into round disks to fit the size of O rings. Then a thin layer of K-Na alloy with carbon black was coated on it. The components were then stacked in the following order: Anode case, 0.2 mm SAE-316L stainless steel spacer, wave disk spring, stainless steel foil, PTFE O-ring, K-BASE disk, PTFE O-ring, stainless steel foil, wave disk spring, 0.2 mm stainless steel spacer and cathode case. Finally, the assembled cell was compressed at 800 psi using a hydraulic press.

For K-Na/BASE/S full cells, carbon paper (Fuel Cell Earth) was cut into round disks to fit the size of the O-rings. During the assembly process, 26.7 μL cm −2 of catholyte was dispensed onto two layers of carbon paper. The components were then stacked in the same order as the K-Na symmetric cell, except that one K-Na electrode was replaced by catholyte-soaked carbon paper. The corresponding configuration is shown in Supplementary Fig.  13 .

Electrochemical measurement

Galvanostatic cycling electrochemistry measurement was performed on Landt battery tester CT3002A. Electrochemical impedance spectroscopy test (EIS) was performed on Bio-logic VMP3, with frequency ranged from 0.01 Hz to 1 MHz and voltage amplitude of 10 mV. All cells were kept at 75  o C in convection drying ovens (MTI Corp.).

Molecular dynamics simulation

To assist in validating the experimental data we utilized Molecular Dynamics (MD) simulation to calculate relative free energy of different solutes (e.g., K 2 S & K 2 S 2 ) in the key solvents (e.g., CPL/acetamide solvent & TEGDME) and to examine the radial distribution function (RDF) for key atoms. Using the Maginn Force Field Archive (MAFFA) 48 we assigned the Generalized Amber Force Field (GAFF) parameters for each molecule and generated atomic charges using the Restrained Electrostatic Potential (RESP) method 48 . We then created an equidistant box with significantly more solvent molecules than the analyte. We then began an MD simulation using the Groningen Machine for Chemical Simulations (GROMACS) package 49 .

In GROMACS, we set up a series of simulations that slowly add interaction between the solute and solvent using a coupling factor, λ. We started with a separated system with no interaction ( λ  = 0) and eventually reached a fully interacting environment ( λ  = 1). Once this simulation series was complete, we would have the available data to calculate the relative free energy difference and RDF for key atoms in the solution. Using a type of program called alchemical analysis we calculated Thermodynamic Integration (TI) and Multistate Bennett Acceptance Ratio (MBAR) values 50 , 51 . Similarly, we ran a GROMACS code to produce RDF values. More details can be found in Supplementary Note  3 .

Scanning electron,microscope (SEM) imaging and energy dispersive spectroscopy (EDS) element mapping

K-Na/S coin cells containing 0.125 M K 2 S 8 (1 M sulfur) in either CPL/acetamide or TEGDME solvent were assembled and cycled in a 75 °C oven. K 2 S 8 catholyte was formed by mixing K 2 S (Thermal Fisher Scientific) and S (Sigma Aldrich) with the stoichiometric ratio in either CPL/acetamide or TEGDME and stirred at a 75 °C heat plate overnight. KTFSI and carbon black were not added to the catholyte. After the cycling process, the cell was dissembled to retrieve carbon paper in the cathode side for characterization. For TEGDME cells, the carbon paper was washed in the sequence of TEGDME and acetone and then dried inside the glovebox. For CPL/acetamide cells, Kimwipe paper was used to absorb the remaining liquid. The sample was sealed in an aluminum pouch during transportation to the facility. The SEM imaging with EDS mapping was done by Zeiss Sigma VP SEM with a voltage of 15 eV.

X-ray Absorption near edge structure (XANES) element mapping

K-Na/S coin cells containing 0.125 M K 2 S 8 (1 M sulfur) in either CPL/acetamide or TEGDME solvent were assembled and cycled in a 75  ° C oven. KTFSI and carbon black was not added to the catholyte. After cycling process, the cell was dissembled to retrieve carbon paper in the cathode side for characterization. The sample was sealed in aluminum pouch during transportation to the facility.

The XANES mapping was done in Brookhaven National Lab (BNL) with the 8-BM technique. 200 pixels * 200 pixels 2D scanning was done and the data was then analyzed and turned into 2D image by PyXRF software.

Operando optical microscopy and Fourier transform infrared (FTIR) spectroscopy

K-Na/S coin cells containing 0.0625 M K 2 S 8 (0.5 M sulfur) in either CPL/acetamide or TEGDME solvent were assembled. O-shaped cathode cases (MTI Corp.) were employed to allow light transmission. For the cathode side, Kapton tape O-rings (Digikey) were used to replace PTFE O-rings. The cell images and videos were captured using NMM800TR metallurgical microscope in dark field and reflective modes. The discharge process for the cells was conducted by Bio-logic SP-5.

A Nicolet iS 5 FTIR Spectrometer was used to conduct FTIR experiments. The scanning range was from 400 to 4000 cm −1 , and the spectrum resolution was 4 cm −1 .

Data availability

The authors declare that the data supporting this study's findings are available within the paper and its supplementary information files.  Source data are provided in this paper.

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Acknowledgements

Y.Y. acknowledges support from Columbia University, the Air Force Office of Scientific Research (FA9550-22-1-0226), and the program of Electrochemical Systems at the National Science Foundation (Award No. 2341994). Support from SEAS Interdisciplinary Research Seed (SIRS) and Climate School Seed Funding at Columbia University. T.M. thank Dr. Eliseo Marin Rimoldi for the discussion on MD simulations. This research uses 8-BM of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704.

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These authors contributed equally: Liying Tian, Zhenghao Yang.

Authors and Affiliations

Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, US

Liying Tian, Zhenghao Yang, Shiyi Yuan, Qian Cheng, Syed Rasool, Wenbo Li, Yucheng Yang, Tianwei Jin, Shengyu Cong, Joseph Francis Wild & Yuan Yang

Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai, China

Liying Tian & Donghui Long

Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN, US

Tye Milazzo

Department of chemistry, Columbia University, New York, NY, US

Wenrui Lei & Tengfei Luo

National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY, US

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Contributions

Y.Y., D.L., and T.L. conceptualized the project, supervised the experiments, and contributed to the writing and revision of the manuscript, with Y.Y. serving as the principal supervisor. L.T. and Z.Y. designed and conducted the experiments, collected and analyzed data, performed characterization tests, and wrote the manuscript. S.Y., T. M., Q.C., S. R., W. Li., W. Lei., Y. C. Y., T. J., S. C., and J. W. assisted in the analysis and characterization of experimental data. Y. D. provided additional support and collaboration throughout the project.

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Correspondence to Tengfei Luo , Donghui Long or Yuan Yang .

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Tian, L., Yang, Z., Yuan, S. et al. Designing electrolytes with high solubility of sulfides/disulfides for high-energy-density and low-cost K-Na/S batteries. Nat Commun 15 , 7771 (2024). https://doi.org/10.1038/s41467-024-51905-6

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Received : 20 June 2023

Accepted : 19 August 2024

Published : 05 September 2024

DOI : https://doi.org/10.1038/s41467-024-51905-6

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