History Solid state ionics

1 history

1.1 foundations
1.2 first theories , applications
1.3 ionic conductivity in silver halides
1.4 point defects in ionic crystals
1.5 other types of disorder

1.5.1 ionic glasses
1.5.2 polymer electrolytes
1.5.3 nanostructures

history
foundations

michael faraday in 1842

in 1830s, michael faraday laid foundations of electrochemistry , solid-state ionics discovering motion of ions in liquid , solid electrolytes. earlier, around 1800, alessandro volta used liquid electrolyte in voltaic pile, first electrochemical battery, failed realize ions involved in process. meanwhile, in work on decomposition of solutions electric current, faraday used not ideas of ion, cation, anion, electrode, anode, cathode, electrolyte , electrolysis, present-day terms them. faraday associated electric current in electrolyte motion of ions, , discovered ions can exchange charges electrode while transformed elements electrolysis. quantified processes 2 laws of electrolysis. first law (1832) stated mass of product @ electrode, Δm, increases linearly amount of charge passed through electrolyte, Δq. second law (1833) established proportionality between Δm , “electrochemical equivalent” , defined faraday constant f f = (Δq/Δm)(m/z), m molar mass , z charge of ion.

in 1834, faraday discovered ionic conductivity in heated solid electrolytes ag2s , pbf2. in pbf2, conductivity increase upon heating not sudden, spread on hundred degrees celsius. such behavior, called faraday transition, observed in cation conductors na2s , li4sio4 , anion conductors pbf2, caf2, srf2, srcl2 , laf3.

later in 1891, johann wilhelm hittorf reported on ion transport numbers in electrochemical cells, , in 20th century numbers determined solid electrolytes.

first theories , applications

the voltaic pile stimulated series of improved batteries, such daniell cell, fuel cell , lead acid battery. operation largely understood in late 1800s theories wilhelm ostwald , walther nernst. in 1894 ostwald explained energy conversion in fuel cell , stressed efficiency not limited thermodynamics. ostwald, jacobus henricus van t hoff, , svante arrhenius, founding father of electrochemistry , chemical ionic theory, , received nobel prize in chemistry in 1909.

his work continued walther nernst, derived nernst equation , described ionic conduction in heterovalently doped zirconia, used in nernst lamp. nernst inspired dissociation theory of arrhenius published in 1887, relied on ions in solution. in 1889 realized similarity between electrochemical , chemical equilibria, , formulated famous equation correctly predicted output voltage of various electrochemical cells based on liquid electrolytes thermodynamic properties of components.

besides theoretical work, in 1897 nernst patented first lamp used solid electrolyte. contrary existing carbon-filament lamps, nernst lamp operate in air , twice more efficient emission spectrum closer of daylight. aeg, lighting company in berlin, bought nernst’s patent 1 million german gold marks, fortune @ time, , used 800 of nernst lamps illuminate both @ world’s fair exposition universelle (1900).

ionic conductivity in silver halides

temperature-dependent ionic conductivity of silver halides, original graph tubandt , lorenz.

among several solid electrolytes described in 19th , 20th century, α-agi, high-temperature crystalline form of silver iodide, regarded important one. electrical conduction characterized carl tubandt , e. lorenz in 1914. comparative study of agi, agcl , agbr demonstrated α-agi, thermally stable , highly conductive between 147 , 555 °c; conductivity weakly increased temperature in range , dropped upon melting. behavior reversible , excluded non-equilibrium effects. tubandt , lorenz described other materials similar behavior, such α-cui, α-cubr, β-cubr, , high-temperature phases of ag2s, ag2se , ag2te. associated conductivity cations in silver , cuprous halides , ions , electrons in silver chalcogenides.

point defects in ionic crystals

frenkel defect in agcl

in 1926, yakov frenkel suggested in ionic crystal agi, in thermodynamic equilibrium, small fraction of cations, α, displaced regular lattice sites interstitial positions. related α gibbs energy formation of 1 mol of frenkel pairs, Δg, α = exp(-Δg/2rt), t temperature , r gas constant; typical value of Δg = 100 kj/mol, α ~ 1×10 @ 100 °c , ~6×10 @ 400 °c. idea naturally explained presence of appreciable fraction of mobile ions in otherwise defect-free ionic crystals, , ionic conductivity in them.

frenkel’s idea expanded carl wagner , walter schottky in 1929 theory, described equilibrium thermodynamics of point defects in ionic crystals. in particular, wagner , schottky related deviations stoichiometry in crystals chemical potentials of crystal components, , explained phenomenon of mixed electronic , ionic conduction.

wagner , schottky considered 4 extreme cases of point-defect disorder in stoichiometric binary ionic crystal of type ab:

type-3 disorder not occur in practice, , type 2 observed in rare cases when anions smaller cations, while both types 1 , 4 common , show same exp(-Δg/2rt) temperature dependence.

later in 1933, wagner suggested in metal oxides excess of metal result in electrons, while deficit of metal produce electron holes, i.e., atomic non-stoichiometry result in mixed ionic-electronic conduction.

other types of disorder
ionic glasses

the studies of crystalline ionic conductors excess ions provided point defect continued though 1950s, , specific mechanism of conduction established each compound depending on ionic structure. emergence of glassy , polymeric electrolytes in late 1970s provided new ionic conduction mechanisms. relatively wide range of conductivites attained in glasses, wherein mobile ions dynamically decoupled matrix. found conductivity increased doping glass salts, or using glass mixture. conductivity values high 0.03 s/cm @ room temperature, activation energies low 20 kj/mol. compared crystals, glasses have isotropic properties, continuously tunable composition , workability; lack detrimental grain boundaries , can molded shape, understanding ionic transport complicated lack of long-range order.

historically, evidence ionic conductivity provided in 1880s, when german scientists noticed well-calibrated thermometer made of thuringian glass show −0.5 °c instead of 0 °c when placed in ice shortly after immersion in boiling water, , recover after several months. in 1883, reduced effect 10 times replacing mixture of sodium , potassium in glass either sodium or potassium. finding helped otto schott develop first accurate lithium-based thermometer. more systematic studies on ionic conductivity in glass appeared in 1884, received broad attention century later. several universal laws have been empirically formulated ionic glasses , extended other ionic conductors, such frequency dependence of electrical conductivity σ(ν) – σ(0) ~ ν, exponent p depends on material, not on temperature, @ least below ~100 k. behavior fingerprint of activated hopping conduction among nearby sites.

polymer electrolytes

in 1975, peter v. wright, polymer chemist sheffield (uk), produced first polymer electrolyte, contained sodium , potassium salts in polyethylene oxide (peo) matrix. later type of polymer electrolytes, polyelectrolyte, put forward, ions moved through electrically charged, rather neutral, polymer matrix. polymer electrolytes showed lower conductivities glasses, cheaper, more flexible , easier machined , shaped various forms. while ionic glasses typically operated below, polymer conductors typically heated above glass transition temperatures. consequently, both electric field , mechanical deformation decay on similar time scale in polymers, not in glasses. between 1983 , 2001 believed amorphous fraction responsible ionic conductivity, i.e., (nearly) complete structural disorder essential fast ionic transport in polymers. however, number of crystalline polymers have been described in 2001 , later ionic conductivity high 0.01 s/cm 30 °c , activation energy of 0.24 ev.

nanostructures

in 1970s–80s, realized nanosized systems may affect ionic conductivity, opening new field of nanoionics. in 1973, reported ionic conductivity of lithium iodide (lii) crystals increased 50 times adding fine powder of ‘’insulating’’ material (alumina). effect reproduced in 1980s in ag- , tl-halides doped alumina nanoparticles. similarly, addition of insulating nanoparticles helped increase conductivity of ionic polymers. these unexpected results explained charge separation @ matrix-nanoparticle interface provided additional conductive channels matrix, , small size of filler particles required increase area of interface. similar charge-separation effects observed grain boundaries in crystalline ionic conductors.