science

Superconcentrated electrolytes

Superconcentrated electrolytes is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Superconcentrated electrolytes rather than just read about it. In short: Superconcentrated electrolytes, also known as water-in-salt or solvent-in-salt liquids, usually refer to chemical systems, which are liquid near room temperature and consist of a solvent-to-dissolved salt in a molar ratio near or smaller than ca. 4-8, i.e. where all solvent molecules are coordinated to cations, and no free solvent molecules remain. Since ca. 2010 such liquid electrolytes found several applications…

Key takeaways

Superconcentrated electrolytes belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Superconcentrated electrolytes to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Superconcentrated electrolytes from memory before moving on to harder problems.

Reference excerpt

Superconcentrated electrolytes, also known as water-in-salt or solvent-in-salt liquids, usually refer to chemical systems, which are liquid near room temperature and consist of a solvent-to-dissolved salt in a molar ratio near or smaller than ca. 4-8, i.e. where all solvent molecules are coordinated to cations, and no free solvent molecules remain. Since ca. 2010 such liquid electrolytes found several applications, primarily for batteries. In the case of lithium metal batteries and lithium-ion batteries most commonly used anions for superconcentrated electrolytes are those, that are large, asymmetric and rotationally-vibrationally flexible, such as bis(trifluoromethanesulfonyl)amide and bis(fluorosulfonyl)amide. Noteworthy, lithium chloride and sodium perchlorate also form water-in-salt solutions.

Advantages Superconcentrated electrolytes demonstrate the following advantages: (1) Many show a good oxidative stability. In particular, some can suppress oxidative corrosion of an Al current collector without a source of fluoride ion (such as hexafluorophosphate) and enable the use of 5 V lithium-ion battery cathode materials. (2) Some are resistant to electrochemical reduction. It is believed, that some sulfonimides (e.g., those with S-F and F-(H)C-N fragments, form a solid electrolyte interface similar to that formed by some organic carbonate solvents. Properties #1 and #2 are responsible for very large (4-5 volt) voltage window, which is useful for advanced batteries. (3) Related to #2 is the ability of some superconcentrated electrolytes to allow for reversible intercalation of Li+ ions into graphite in the absence of ethylene carbonate solvent, therefore enabling a new class of safer lithium-ion batteries. (4) Solvent vapor pressure is lower, thermal stability is higher, and flammability is absent, which contributes to a better battery safety. (5) The concentration of charge-carrying ion is larger, which translates into smaller ion travelling distances. (6) In some cases, and contrary to expectations, faster rates of electrode reactions are observed, than in conventional low-salt-concentration electrolytes. (7) Polysulfide dissolution is sometimes suppressed, which enables cycling of such batteries as lithium-sulfur. (8) Some studies report, that Li+ transference number in such liquids is close to one, which means, that Li+ concentration gradient between anode and cathode does not develop during the battery's charge and discharge. (9) Electrodeposition of lithium metal from superconcentrated electrolytes is often nodular (without dendrites) and reversible.

Disadvantages At the same time, highly concentrated electrolytes are not without disadvantages: (1) Their ionic conductivity is generally lower than that of corresponding dilute (~1 M) electrolytes. (2) Their viscosity is higher than that of conventional electrolytes. (3) Their cost is usually higher, because manufacturing of some anions, such as sulfonimides, requires several low-yield synthetic steps.

Origin of the unusual properties The exact mechanism of high-voltage stability of superconcentrated electrolytes have not been established as of 2023. The two main proposed mechanisms are: (1) a decrease of water molecules' thermodynamic activity, when all water molecules are coordinated to cations, such as Li+. (2) decomposition of an anion with the formation of a solid electrolyte interface. Most recent studies suggest, that the anion decomposition mechanism (2) dominates in a majority of cases.

References

Worked examples

Example 1 — a first encounter with Superconcentrated electrolytes

Start with the simplest possible case. Write down what Superconcentrated electrolytes claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Superconcentrated electrolytes before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Superconcentrated electrolytes ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Superconcentrated electrolytes

In research: Superconcentrated electrolytes appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Superconcentrated electrolytes in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Superconcentrated electrolytes is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electric battery, Solutions, so understanding it makes those chapters shorter.
In everyday life: Look for Superconcentrated electrolytes outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Superconcentrated electrolytes in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Superconcentrated electrolytes means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Superconcentrated electrolytes out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Superconcentrated electrolytes in simple terms?

Why does Superconcentrated electrolytes matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Superconcentrated electrolytes?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Superconcentrated electrolytes.