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Nanoionics [1] is the study and application of phenomena, properties, effects, methods and mechanisms of processes connected with fast ion transport (FIT) in all-solid-state nanoscale systems. The topics of interest include fundamental properties of oxide ceramics at nanometer length scales, and fast ion conductor (advanced superionic conductor)/electronic conductor heterostructures. [2] Potential applications are in electrochemical devices (electrical double layer devices) for conversion and storage of energy, charge and information. The term and conception of nanoionics (as a new branch of science) were first introduced by A.L. Despotuli and V.I. Nikolaichik (Institute of Microelectronics Technology and High Purity Materials, Russian Academy of Sciences, Chernogolovka) in January 1992. [1]
A multidisciplinary scientific and industrial field of solid state ionics, dealing with ionic transport phenomena in solids, considers Nanoionics as its new division. [3] Nanoionics tries to describe, for example, diffusion&reactions, in terms that make sense only at a nanoscale, e.g., in terms of non-uniform (at a nanoscale) potential landscape.
There are two classes of solid-state ionic nanosystems and two fundamentally different nanoionics: (I) nanosystems based on solids with low ionic conductivity, and (II) nanosystems based on advanced superionic conductors (e.g. alpha–AgI, rubidium silver iodide–family). [4] Nanoionics-I and nanoionics-II differ from each other in the design of interfaces. The role of boundaries in nanoionics-I is the creation of conditions for high concentrations of charged defects (vacancies and interstitials) in a disordered space-charge layer. But in nanoionics-II, it is necessary to conserve the original highly ionic conductive crystal structures of advanced superionic conductors at ordered (lattice-matched) heteroboundaries. Nanoionic-I can significantly enhance (up to ~108 times) the 2D-like ion conductivity in nanostructured materials with structural coherence, [5] but it is remaining ~103 times smaller relatively to 3D ionic conductivity of advanced superionic conductors.
The classical theory of diffusion and migration in solids is based on the notion of a diffusion coefficient, activation energy [6] and electrochemical potential. [7] This means that accepted is the picture of a hopping ion transport in the potential landscape where all barriers are of the same height (uniform potential relief). Despite the obvious difference of objects of solid state ionics and nanoionics-I, -II, the true new problem of fast ion transport and charge/energy storage (or transformation) for these objects (fast ion conductors) has a special common basis: non-uniform potential landscape on nanoscale [8] (for example) which determines the character of the mobile ion subsystem response to an impulse or harmonic external influence, e.g. a weak influence in Dielectric spectroscopy (impedance spectroscopy). [9]
Being a branch of nanoscience and nanotechnology, nanoionics is unambiguously defined by its own objects (nanostructures with FIT), subject matter (properties, phenomena, effects, mechanisms of processes, and applications connected with FIT at nano-scale), method (interface design in nanosystems of superionic conductors), and the criterion (R/L ~1, where R is the length scale of device structures, and L is the characteristic length on which the properties, characteristics, and other parameters connected with FIT change drastically).
The International Technology Roadmap for Semiconductors (ITRS) relates nanoionics-based resistive switching memories to the category of "emerging research devices" ("ionic memory"). The area of close intersection of nanoelectronics and nanoionics had been called nanoelionics (1996). Now, the vision of future nanoelectronics constrained solely by fundamental ultimate limits is being formed in advanced research. [10] [11] [12] [13] The ultimate physical limits to computation [14] are very far beyond the currently attained (1010 cm−2, 1010 Hz) region. What kind of logic switches might be used at the near nm- and sub-nm peta-scale integration? The question was the subject matter already in, [15] where the term "nanoelectronics" [16] was not used yet. Quantum mechanics constrains electronic distinguishable configurations by the tunneling effect at tera-scale. To overcome 1012 cm−2 bit density limit, atomic and ion configurations with a characteristic dimension of L <2 nm should be used in the information domain and materials with an effective mass of information carriers m* considerably larger than electronic ones are required: m* =13 me at L =1 nm, m* =53 me (L =0,5 nm) and m* =336 me (L =0,2 nm). [13] Future short-sized devices may be nanoionic, i.e. based on the fast ion transport at the nanoscale, as it was first stated in. [1]
The examples of nanoionic devices are all-solid-state supercapacitors with fast ion transport at the functional heterojunctions (nanoionic supercapacitors), [4] [17] lithium batteries and fuel cells with nanostructured electrodes, [18] nano-switches with quantized conductivity on the basis of fast ion conductors [19] [20] (see also memristors and programmable metallization cell). These are well compatible with sub-voltage and deep-sub-voltage nanoelectronics [21] and could find wide applications, for example in autonomous micro power sources, RFID, MEMS, smartdust, nanomorphic cell, other micro- and nanosystems, or reconfigurable memory cell arrays.
An important case of fast ionic conduction in solid states is in the surface space-charge layer of ionic crystals. Such conduction was first predicted by Kurt Lehovec. [22] A significant role of boundary conditions with respect to ionic conductivity was first experimentally discovered by C.C. Liang [23] who found an anomalously high conduction in the LiI-Al2O3 two-phase system. Because a space-charge layer with specific properties has nanometer thickness, the effect is directly related to nanoionics (nanoionics-I). The Lehovec effect has become the basis for the creation of a multitude of nanostructured fast ion conductors which are used in modern portable lithium batteries and fuel cells. In 2012, a 1D structure-dynamic approach was developed in nanoionics [24] [25] [26] for a detailed description of the space charge formation and relaxation processes in irregular potential relief (direct problem) and interpretation of characteristics of nanosystems with fast ion transport (inverse problem), as an example, for the description of a collective phenomenon: coupled ion transport and dielectric-polarization processes which lead to A. K. Jonscher's "universal" dynamic response.
Nanotechnology is the manipulation of matter with at least one dimension sized from 1 to 100 nanometers (nm). At this scale, commonly known as the nanoscale, surface area and quantum mechanical effects become important in describing properties of matter. This definition of nanotechnology includes all types of research and technologies that deal with these special properties. It is common to see the plural form "nanotechnologies" as well as "nanoscale technologies" to refer to research and applications whose common trait is scale. An earlier understanding of nanotechnology referred to the particular technological goal of precisely manipulating atoms and molecules for fabricating macroscale products, now referred to as molecular nanotechnology.
A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre. More generally, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less and an unconstrained length. At these scales, quantum mechanical effects are important—which coined the term "quantum wires".
A proton conductor is an electrolyte, typically a solid electrolyte, in which H+ are the primary charge carriers.
Kurt Lehovec was one of the pioneers of the integrated circuit. While also pioneering the photo-voltaic effect, light-emitting diodes and lithium batteries, he innovated the concept of p-n junction isolation used in every circuit element with a guard ring: a reverse-biased p-n junction surrounding the planar periphery of that element. This patent was assigned to Sprague Electric.
Beta-alumina solid electrolyte (BASE) is a fast ion conductor material used as a membrane in several types of molten salt electrochemical cell. Currently there is no known substitute available. β-Alumina exhibits an unusual layered crystal structure which enables very fast ion transport. β-Alumina is not an isomorphic form of aluminium oxide (Al2O3), but a sodium polyaluminate. It is a hard polycrystalline ceramic, which, when prepared as an electrolyte, is complexed with a mobile ion, such as Na+, K+, Li+, Ag+, H+, Pb2+, Sr2+ or Ba2+ depending on the application. β-Alumina is a good conductor of its mobile ion yet allows no non-ionic (i.e., electronic) conductivity. The crystal structure of the β-alumina provides an essential rigid framework with channels along which the ionic species of the solid can migrate. Ion transport involves hopping from site to site along these channels. Since the 1970's this technology has been thoroughly developed, resulting in interesting applications. Its special characteristics on ion and electrical conductivity make this material extremely interesting in the field of energy storage.
In materials science, fast ion conductors are solid conductors with highly mobile ions. These materials are important in the area of solid state ionics, and are also known as solid electrolytes and superionic conductors. These materials are useful in batteries and various sensors. Fast ion conductors are used primarily in solid oxide fuel cells. As solid electrolytes they allow the movement of ions without the need for a liquid or soft membrane separating the electrodes. The phenomenon relies on the hopping of ions through an otherwise rigid crystal structure.
Nanoelectronics refers to the use of nanotechnology in electronic components. The term covers a diverse set of devices and materials, with the common characteristic that they are so small that inter-atomic interactions and quantum mechanical properties need to be studied extensively. Some of these candidates include: hybrid molecular/semiconductor electronics, one-dimensional nanotubes/nanowires or advanced molecular electronics.
Nanofluidics is the study of the behavior, manipulation, and control of fluids that are confined to structures of nanometer characteristic dimensions. Fluids confined in these structures exhibit physical behaviors not observed in larger structures, such as those of micrometer dimensions and above, because the characteristic physical scaling lengths of the fluid, very closely coincide with the dimensions of the nanostructure itself.
Ionic conductivity is a measure of a substance's tendency towards ionic conduction. Ionic conduction is the movement of ions. The phenomenon is observed in solids and solutions. Ionic conduction is one mechanism of current.
An advanced superionic conductor (AdSIC) in materials science, is fast ion conductor that has a crystal structure close to optimal for fast ion transport (FIT).
Rubidium silver iodide is a ternary inorganic compound with the formula RbAg4I5. Its conductivity involves the movement of silver ions within the crystal lattice. It was discovered while searching for chemicals which had the ionic conductivity properties of alpha-phase silver iodide at temperatures below 146 °C for AgI.
Solid-state ionics is the study of ionic-electronic mixed conductor and fully ionic conductors and their uses. Some materials that fall into this category include inorganic crystalline and polycrystalline solids, ceramics, glasses, polymers, and composites. Solid-state ionic devices, such as solid oxide fuel cells, can be much more reliable and long-lasting, especially under harsh conditions, than comparable devices with fluid electrolytes.
A solid-state battery is an electrical battery that uses a solid electrolyte for ionic conductions between the electrodes, instead of the liquid or gel polymer electrolytes found in conventional batteries. Solid-state batteries theoretically offer much higher energy density than the typical lithium-ion or lithium polymer batteries.
The transport of heat in solids involves both electrons and vibrations of the atoms (phonons). When the solid is perfectly ordered over hundreds of thousands of atoms, this transport obeys established physics. However, when the size of the ordered regions decreases new physics can arise, thermal transport in nanostructures. In some cases heat transport is more effective, in others it is not.
NASICON is an acronym for sodium (Na) super ionic conductor, which usually refers to a family of solids with the chemical formula Na1+xZr2SixP3−xO12, 0 < x < 3. In a broader sense, it is also used for similar compounds where Na, Zr and/or Si are replaced by isovalent elements. NASICON compounds have high ionic conductivities, on the order of 10−3 S/cm, which rival those of liquid electrolytes. They are caused by hopping of Na ions among interstitial sites of the NASICON crystal lattice.
Caesium bisulfate or cesium hydrogen sulfate is an inorganic compound with the formula CsHSO4. The caesium salt of bisulfate, it is a colorless solid obtained by combining Cs2SO4 and H2SO4.
Silicon nanowires, also referred to as SiNWs, are a type of semiconductor nanowire most often formed from a silicon precursor by etching of a solid or through catalyzed growth from a vapor or liquid phase. Such nanowires have promising applications in lithium ion batteries, thermoelectrics and sensors. Initial synthesis of SiNWs is often accompanied by thermal oxidation steps to yield structures of accurately tailored size and morphology.
Multi-tip scanning tunneling microscopy extends scanning tunneling microscopy (STM) from imaging to dedicated electrical measurements at the nanoscale like a ″multimeter at the nanoscale″. In materials science, nanoscience, and nanotechnology, it is desirable to measure electrical properties at a particular position of the sample. For this purpose, multi-tip STMs in which several tips are operated independently have been developed. Apart from imaging the sample, the tips of a multi-tip STM are used to form contacts to the sample at desired locations and to perform local electrical measurements.
A solid-state electrolyte (SSE) is a solid ionic conductor and electron-insulating material and it is the characteristic component of the solid-state battery. It is useful for applications in electrical energy storage (EES) in substitution of the liquid electrolytes found in particular in lithium-ion battery. The main advantages are the absolute safety, no issues of leakages of toxic organic solvents, low flammability, non-volatility, mechanical and thermal stability, easy processability, low self-discharge, higher achievable power density and cyclability. This makes possible, for example, the use of a lithium metal anode in a practical device, without the intrinsic limitations of a liquid electrolyte thanks to the property of lithium dendrite suppression in the presence of a solid-state electrolyte membrane. The use of a high capacity anode and low reduction potential, like lithium with a specific capacity of 3860 mAh g−1 and a reduction potential of -3.04 V vs SHE, in substitution of the traditional low capacity graphite, which exhibits a theoretical capacity of 372 mAh g−1 in its fully lithiated state of LiC6, is the first step in the realization of a lighter, thinner and cheaper rechargeable battery. Moreover, this allows the reach of gravimetric and volumetric energy densities, high enough to achieve 500 miles per single charge in an electric vehicle. Despite the promising advantages, there are still many limitations that are hindering the transition of SSEs from academia research to large-scale production, depending mainly on the poor ionic conductivity compared to that of liquid counterparts. However, many car OEMs (Toyota, BMW, Honda, Hyundai) expect to integrate these systems into viable devices and to commercialize solid-state battery-based electric vehicles by 2025.
Lithium aluminium germanium phosphate, typically known with the acronyms LAGP or LAGPO, is an inorganic ceramic solid material whose general formula is Li
1+xAl
xGe
2-x(PO
4)
3. LAGP belongs to the NASICON family of solid conductors and has been applied as a solid electrolyte in all-solid-state lithium-ion batteries. Typical values of ionic conductivity in LAGP at room temperature are in the range of 10–5 - 10–4 S/cm, even if the actual value of conductivity is strongly affected by stoichiometry, microstructure, and synthesis conditions. Compared to lithium aluminium titanium phosphate (LATP), which is another phosphate-based lithium solid conductor, the absence of titanium in LAGP improves its stability towards lithium metal. In addition, phosphate-based solid electrolytes have superior stability against moisture and oxygen compared to sulfide-based electrolytes like Li
10GeP
2S
12 (LGPS) and can be handled safely in air, thus simplifying the manufacture process. Since the best performances are encountered when the stoichiometric value of x is 0.5, the acronym LAGP usually indicates the particular composition of Li
1.5Al
0.5Ge
1.5(PO
4)
3, which is also the typically used material in battery applications.