A material that conducts ions while remaining solid but conducts almost no electrons. Examples include sulfide and oxide electrolytes for all-solid-state batteries and stabilized zirconia for fuel cells.
Japanese name: 固体電解質
Solid electrolyte appears in 3 practice questions across 2 topics, including Battery and energy materials, Ceramics and glasses.
Field: Battery and energy materials
A solid electrolyte is a material in which specific ions move through a crystal, glass or polymer to carry current, while electrons are hardly conducted at all. Ions need vacant sites or connected interstitial pathways to move, and the conductivity rises steeply with temperature, as in σT = A exp(−Ea/kT). For a material with an activation energy of 0.3 eV, cooling from 25 °C to −20 °C lowers the conductivity to about 1/7, and for 0.5 eV to about 1/27. A classic example is α-AgI, in which Ag⁺ moves almost like a liquid above 147 °C; such materials are called superionic conductors.
Yttria-stabilized zirconia (YSZ), which conducts oxide ions, is used in oxygen sensors and solid oxide fuel cells and needs about 700 °C or more for sufficient conductivity. β-alumina, which conducts Na⁺, is the electrolyte of sodium–sulfur batteries operating at about 300 °C. For all-solid-state lithium batteries, sulfides such as Li₁₀GeP₂S₁₂ (LGPS), with conductivities on the order of 10⁻² S/cm at room temperature, oxides such as garnet-type Li₇La₃Zr₂O₁₂ (LLZO), which are comparatively stable in air, and soft, easily processed polymers such as polyethylene oxide (PEO) are all being researched, and some have been commercialized.
In a liquid electrolyte both cations and anions move, and in lithium-ion battery electrolytes the fraction of current carried by Li⁺ (the transference number) is generally less than half. In many inorganic solid electrolytes, the framework stays put and only Li⁺ moves, so the transference number is nearly 1 and concentration gradients hardly form near the electrodes. Being non-flammable and leak-free are further advantages. On the other hand, contact between solids tends to be at points or along lines, so interfacial resistance tends to be high, and contact is secured by applying pressure or using soft materials.
The ionic conductivity of solid electrolytes is measured by AC impedance spectroscopy, and the response at different frequencies is used to separate the resistance of the grain interiors from that of the grain boundaries. The electronic conductivity is found by applying a DC voltage with ion-blocking electrodes and measuring the remaining current. Even a small electronic current causes self-discharge and makes lithium more likely to deposit inside the electrolyte. Indeed, lithium dendrites, once expected to be stopped by a solid, have been found to grow through solid electrolytes along grain boundaries and defects, a major challenge for realizing safe all-solid-state batteries.
Answer: A. Some match organic liquid electrolytes in ionic conductivity and densify by pressing alone, but they react with moisture to release hydrogen sulfide
Some sulfide solid electrolytes, such as Li₁₀GeP₂S₁₂ (LGPS), Li₇P₃S₁₁ and argyrodite-type Li₆PS₅Cl, show room-temperature ionic conductivities of 10⁻³–10⁻² S/cm, comparable to organic liquid electrolytes (about 10⁻² S/cm). Sulfides are soft and deform easily, so another advantage is that simply pressing the powder at room temperature gives good contact between particles and with the electrodes. On the other hand, they tend to react with moisture in the air and release toxic hydrogen sulfide, so they must be handled in a dry environment. Requiring high-temperature sintering to densify is characteristic of oxide electrolytes such as garnet-type Li₇La₃Zr₂O₁₂ (LLZO). LLZO is relatively stable in air and reacts little with lithium metal, but being hard, it is difficult to form interfaces with the electrodes.
A liquid electrolyte is a lithium salt dissolved in an organic solvent and can burn or leak. A solid electrolyte conducts ions while remaining solid, is hard to ignite, and in many cases only Li⁺ moves.
Sulfides have high conductivity and are soft, so interfaces can be formed simply by pressing, but they react with moisture to release hydrogen sulfide. Oxides are comparatively stable in air but hard, and high-temperature sintering is needed to make them dense.
It is a material that, while solid, shows a high ionic conductivity close to that of liquid electrolytes. α-AgI and some of the sulfides used in all-solid-state batteries are examples.
Some sulfide solid electrolytes, such as Li₁₀GeP₂S₁₂ (LGPS), Li₇P₃S₁₁ and argyrodite-type Li₆PS₅Cl, show room-temperature ionic conductivities of 10⁻³–10⁻² S/cm, comparable to organic liquid electrolytes (about 10⁻² S/cm).
Which statement about sulfide solid electrolytes used in al…At high temperature O²⁻ moves through these oxygen vacancies, so YSZ is used as a solid electrolyte in oxygen sensors and solid oxide fuel cells (SOFCs).
Why does stabilized zirconia (YSZ), ZrO₂ with Y₂O₃ dissolve…However, its volume swells about three- to fourfold on lithiation, so with repeated cycling the particles crack and become electrically isolated, the electrolyte decomposes on the newly exposed surfaces to re-form the SEI (solid electrolyte interphase), and lithium is gradually lost.
Which statement about silicon (Si) as an anode material is …Sintering Vacancy Theoretical capacity Layered rock salt structure Olivine structure Polymer electrolyte fuel cell Shockley–Queisser limit Spinel structure Thermoelectric figure of merit