chemistry

LISICON

LISICON is a chemistry 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 LISICON rather than just read about it. In short: LISICON is an acronym for lithium super ionic conductor, which refers to a family of solids with the chemical formula Li2+2xZn1−xGeO4. The first example of this structure was discovered in 1977, providing a chemical formula of Li14Zn(GeO4)4.

Key takeaways

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

Reference excerpt

LISICON is an acronym for lithium super ionic conductor, which refers to a family of solids with the chemical formula Li2+2xZn1−xGeO4. The first example of this structure was discovered in 1977, providing a chemical formula of Li14Zn(GeO4)4. The crystal structure of LISICON consists of a network of [Li11Zn(GeO4)4]3- as well as 3 loosely bonded Li+. The weaker bonds allow for the lithium ions to easily move from site to site, not needing to break strong bonds to do so. Also, this structure forms large “bottlenecks” between the interstitial positions which these ions occupy, additionally lowering the energy required to move from site to site. These two factors allow for the lithium ions to diffuse quickly and easily through the structure. However, because of the shape of the channels through which these lithium ions can diffuse, they are limited to 2 dimensional diffusion. LISICON compounds have relatively high ionic conductivity, on the order of 10−6 S/cm at 25 °C. LISICONs readily react with lithium metal and atmospheric gases such as CO2; as a result, their conductivity decreases with time.

LISICON-like materials There are other LISICON type solid electrolytes which make use of other elements to achieve higher ionic conductivities. One such material has the chemical formula of Li(3+x)GexV(1-x)O4, where the value of x is between 0 and 1. There are two compositions, Li3.5Ge0.5V0.5O4 and Li3.6Ge0.6V0.4O4, which had ionic conductivities of 4*10−5 S/cm and 10−5 S/cm, an order of magnitude of improvement upon the base LISICON structure. These materials show good thermal stability and are stable in contact with CO2 and ambient atmosphere, dealing with some problems extant with the original structure. There are materials with the chemical structure of Li(4-x)Si(1-x)PxO4. This is a solid solution between Li4SiO4 and Li3PO4. This solid solution can be formed over the whole composition range at room temperature. The highest ionic conductivity is achieved at compositions of Li3.5Si0.5P0.5O4 and Li3.4Si0.4P0.6, with conductivity on the order of 10−6 S/cm. This results from the substitution of some Si4+ for P5+ in the lattice, resulting in the addition of interstitial Li-ions which diffuse much more easily. The ionic conductivity is further improved with the doping of Cl− to replace O2- in the lattice. The compositions Li10.42Si1.5P1.5Cl11.92 and Li10.42Ge1.5P1.5Cl11.92 achieved ionic conductivities of 1.03 * 10−5 S/cm and 3.7*10−5 S/cm respectively. This is theorized to be the due to the widening of the “bottlenecks” between interstitial points due to the Cl− ions smaller size, and the weakening of the ionic bonding Li+ ions experienced due to chlorine's lower electronegativity. The conductivities are almost 100 times higher in thio-LISICONs, where oxygen is replaced by sulfur, i.e. the corresponding thiosilicates. The bonding between S2- and Li+ is weaker than that between O2- and Li+, allowing for the Li+ in the sulfide structure to be far more normal than its oxide counterparts. Ceramic thio-LISCON materials based on the chemical formula Li(4-x)Ge(1-x)PxS4 are promising electrolyte materials, with ionic conductivities on the order of 10−3 S/m or 10−2 S/m.

Applications LISICONs can be used as the solid electrolyte in lithium-based solid-state batteries, such as solid state nickel–lithium battery. For this application, solid lithium electrolytes require ionic conductivities greater than 10−4 S/cm, negligible electronic conductivity, and a wide range of electrochemical stability.

References

Worked examples

Example 1 — a first encounter with LISICON

Start with the simplest possible case. Write down what LISICON claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, 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 LISICON 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 LISICON 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 LISICON

In research: LISICON appears in chemistry 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 LISICON 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: LISICON is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electrochemistry, so understanding it makes those chapters shorter.
In everyday life: Look for LISICON 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 LISICON in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what LISICON 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 LISICON out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is LISICON in simple terms?

Why does LISICON matter?

Because it connects several chemistry 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 LISICON?

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 LISICON.