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. [2]
The crystal structure of NASICON compounds was characterized in 1968. It is a covalent network consisting of ZrO6 octahedra and PO4/SiO4 tetrahedra that share common corners. Sodium ions are located at two types of interstitial positions. They move among those sites through bottlenecks, whose size, and thus the NASICON electrical conductivity, depends on the NASICON composition, on the site occupancy, [3] and on the oxygen content in the surrounding atmosphere. The conductivity decreases for x < 2 or when all Si is substituted for P in the crystal lattice (and vice versa); it can be increased by adding a rare-earth compound to NASICON, such as yttria. [1]
NASICON materials can be prepared as single crystals, polycrystalline ceramic compacts, thin films or as a bulk glass called NASIGLAS. Most of them, except NASIGLAS and phosphorus-free Na4Zr2Si3O12, react with molten sodium at 300 °C, and therefore are unsuitable for electric batteries that use sodium as an electrode. [2] However, a NASICON membrane is being considered for a sodium-sulfur battery where the sodium stays solid.
The main application envisaged for NASICON materials is as the solid electrolyte in a sodium-ion battery. Some NASICONs exhibit a low thermal expansion coefficient (< 10−6 K−1), which is useful for precision instruments and household ovenware. NASICONs can be doped with rare-earth elements, such as Eu, and used as phosphors. Their electrical conductivity is sensitive to molecules in the ambient atmosphere, a phenomenon that can be used to detect CO2, SO2, NO, NO2, NH3 and H2S gases. Other NASICON applications include catalysis, immobilization of radioactive waste, and sodium removal from water. [2]
The development of sodium-ion batteries is important since it makes use of an earth-abundant material and can serve as an alternative to lithium-ion batteries which are experiencing ever-increasing demand despite the limited availability of lithium. Developing high-performance sodium-ion batteries is a challenge because it is necessary to develop electrodes that meet the requirements of high-energy density and high cycling stability while also being cost-efficient. NaSICON-based electrode materials are known for their wide range of electrochemical potentials, high ionic conductivity, and most importantly their structural and thermal stabilities. [4] NaSICON-type cathode materials for sodium-ion batteries have a mechanically robust three-dimensional (3D) framework with open channels that endow it with the capability for fast ionic diffusion. [5] A strong and lasting structural framework allows for repeated Na+
ion de-/insertions with relatively high operating potentials. Its high safety, high potential, and low volume change make NaSICON a promising candidate for sodium-ion battery cathodes. [6]
NaSICON cathodes typically suffer from poor electrical conductivity and low specific capacity which severely limits their practical applications. Efforts to enhance the movement of electrons, or electrical conductivity, include particle downsizing [7] and carbon-coating [8] which have both been reported to improve the electrochemical performance.
It is important to consider the relationship between lattice parameters and activation energy as the change in lattice size has a direct influence on the size of the pathway for Na+
conduction as well as the hopping distance of the Na+
ions to the next vacancy. A large hopping distance requires a high activation energy. [9]
NaSICON-phosphate Na
3V
2(PO
4)
3 compounds are considered promising cathodes with a theoretical specific energy of 400 W h kg−1. Vanadium-based compounds exhibit satisfactory high energy densities that are comparable to those of lithium-ion batteries as they operate through multi-electron redox reactions (V3+/V4+ and V4+/V5+) and a high operating voltage. [10] The use of vanadium is toxic and expensive which introduces a critical issue in real applications. This concern holds true for other electrodes based on costly 3d transition metal elements such as Ni- or Co-based electrodes. The most abundant and non-toxic 3d element, iron, is the favored choice as the redox center in the polyanionic or mixed-polyanion system. [11]
Some lithium phosphates also possess the NASICON structure and can be considered as the direct analogues of the sodium-based NASICONs. [12] The general formula of such compounds is LiM
2(PO
4)
3, where M identifies an element like titanium, germanium, zirconium, hafnium, or tin. [2] [13] Similarly to sodium-based NASICONs, lithium-based NASICONs consist of a network of MO6 octahedra connected by PO4 tetrahedra, with lithium ions occupying the interstitial sites among them. [14] Ionic conduction is ensured by lithium hopping among adjacent interstitial sites. [14]
Lithium NASICONs are promising materials to be used as solid electrolytes in all-solid-state lithium-ion batteries. [15]
The most investigated lithium-based NASICON materials are LiZr
2(PO
4)
3, LiTi
2(PO
4)
3, [2] and LiGe
2(PO
4)
3. [16]
Lithium zirconium phosphate, identified by the formula LiZr
2(PO
4)
3 (LZP), has been extensively studied because of its polymorphism and interesting conduction properties. [2] [17] At room temperature, LZP has a triclinic crystal structure (C1) and undergoes a phase transition to rhombohedral crystal structure (R3c) between 25 and 60 °C. [17] The rhombohedral phase is characterized by higher values of ionic conductivity (8×10−6 S/cm at 150 °C) compared to the triclinic phase (≈ 8×10−9 S/cm at room temperature): [17] such difference may be ascribed to the peculiar distorted tetrahedral coordination of lithium ions in the rhombohedral phase, along with the large number of available empty sites. [2]
The ionic conductivity of LZP can be enhanced by elemental doping, for example replacing some of the zirconium cations with lanthanum, [17] titanium, [2] or aluminium [18] [19] atoms. In case of lanthanum doping, the room-temperature ionic conductivity of the material approaches 7.2×10−5 S/cm. [17]
Lithium titanium phosphate, with general formula LiTi
2(PO
4)
3 (LTP or LTPO), is another lithium-containing NASICON material in which TiO6 octahedra and PO4 tetrahedra are arranged in a rhombohedral unit cell. [16] The LTP crystal structure is stable down to 100 K and is characterized by a small coefficient of thermal expansion. [16] LTP shows low ionic conductivity at room temperature, around 10−6 S/cm; [12] however, it can be effectively increased by elemental substitution with isovalent or aliovalent elements (Al, Cr, Ga, Fe, Sc, In, Lu, Y, La). [12] [16] [20] The most common derivative of LTP is lithium aluminium titanium phosphate (LATP), whose general formula is Li
1+xAl
xTi
2-x(PO
4)
3. [16] Ionic conductivity values as high as 1.9×10−3 S/cm can be achieved when the microstructure and the aluminium content (x = 0.3 - 0.5) are optimized. [12] [16] The increase of conductivity is attributed to the larger number of mobile lithium ions necessary to balance the extra electrical charge after Ti4+ replacement by Al3+, together with a contraction of the c axis of the LATP unit cell. [16] [20]
In spite of attractive conduction properties, LATP is highly unstable in contact with lithium metal, [16] with formation of a lithium-rich phase at the interface and with reduction of Ti4+ to Ti3+. [15] Reduction of tetravalent titanium ions proceeds along a single-electron transfer reaction: [21]
Both phenomena are responsible for a significant increase of the electronic conductivity of the LATP material (from 3×10−9 S/cm to 2.9×10−6 S/cm), leading to the degradation of the material and to the ultimate cell failure if LATP is used as a solid electrolyte in a lithium-ion battery with metallic lithium as the anode. [15]
Lithium germanium phosphate, LiGe
2(PO
4)
3 (LGP), is closely similar to LTP, except for the presence of GeO6 octahedra instead of TiO6 octahedra in the rhombohedral unit cell. [16] Similarly to LTP, the ionic conductivity of pure LGP is low and can be improved by doping the material with aliovalent elements like aluminium, resulting in lithium aluminium germanium phosphate (LAGP), Li
1+xAl
xGe
2-x(PO
4)
3. [16] Contrary to LGP, the room-temperature ionic conductivity of LAGP spans from 10−5 S/cm up to 10−3 S/cm, [20] depending on the microstructure and on the aluminium content, with an optimal composition for x ≈ 0.5. [13] In both LATP and LAGP, non-conductive secondary phases are expected for larger aluminium content (x > 0.5 - 0.6). [16]
LAGP is more stable than LATP against lithium metal anode, since the reduction reaction of Ge4+ cations is a 4-electron reaction and has a high kinetic barrier: [21]
However, the stability of the lithium anode-LAGP interface is still not fully clarified and the formation of detrimental interlayers with subsequent battery failure has been reported. [23]
Phosphate-based materials with a NASICON crystal structure, especially LATP and LAGP, are good candidates as solid-state electrolytes in lithium-ion batteries, [16] even if their average ionic conductivity (≈10−5 - 10−4 S/cm) is lower compared to other classes of solid electrolytes like garnets and sulfides. [15] However, the use of LATP and LAGP provides some advantages:
A high-capacity lithium metal anode could not be coupled with a LATP solid electrolyte, because of Ti4+ reduction and fast electrolyte decomposition; [15] on the other hand, the reactivity of LAGP in contact with lithium at very negative potentials is still debated, [21] but protective interlayers could be added to improve the interfacial stability. [23]
Considering LZP, it is predicted to be electrochemically stable in contact with metallic lithium; the main limitation arises from the low ionic conductivity of the room-temperature triclinic phase. [18] Proper elemental doping is an effective route to both stabilize the rhombohedral phase below 50 °C and improve the ionic conductivity. [18]
A lithium-ion or Li-ion battery is a type of rechargeable battery that uses the reversible intercalation of Li+ ions into electronically conducting solids to store energy. In comparison with other commercial rechargeable batteries, Li-ion batteries are characterized by higher specific energy, higher energy density, higher energy efficiency, a longer cycle life, and a longer calendar life. Also noteworthy is a dramatic improvement in lithium-ion battery properties after their market introduction in 1991: within the next 30 years, their volumetric energy density increased threefold while their cost dropped tenfold.
A lithium polymer battery, or more correctly lithium-ion polymer battery, is a rechargeable battery of lithium-ion technology using a polymer electrolyte instead of a liquid electrolyte. Highly conductive semisolid (gel) polymers form this electrolyte. These batteries provide higher specific energy than other lithium battery types and are used in applications where weight is a critical feature, such as mobile devices, radio-controlled aircraft and some electric vehicles.
Molten-salt batteries are a class of battery that uses molten salts as an electrolyte and offers both a high energy density and a high power density. Traditional non-rechargeable thermal batteries can be stored in their solid state at room temperature for long periods of time before being activated by heating. Rechargeable liquid-metal batteries are used for industrial power backup, special electric vehicles and for grid energy storage, to balance out intermittent renewable power sources such as solar panels and wind turbines.
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.
Nanobatteries are fabricated batteries employing technology at the nanoscale, particles that measure less than 100 nanometers or 10−7 meters. These batteries may be nano in size or may use nanotechnology in a macro scale battery. Nanoscale batteries can be combined to function as a macrobattery such as within a nanopore battery.
Lithium iron phosphate or lithium ferro-phosphate (LFP) is an inorganic compound with the formula LiFePO
4. It is a gray, red-grey, brown or black solid that is insoluble in water. The material has attracted attention as a component of lithium iron phosphate batteries, a type of Li-ion battery. This battery chemistry is targeted for use in power tools, electric vehicles, solar energy installations and more recently large grid-scale energy storage.
A lithium-ion capacitor is a hybrid type of capacitor classified as a type of supercapacitor. It is called a hybrid because the anode is the same as those used in lithium-ion batteries and the cathode is the same as those used in supercapacitors. Activated carbon is typically used as the cathode. The anode of the LIC consists of carbon material which is often pre-doped with lithium ions. This pre-doping process lowers the potential of the anode and allows a relatively high output voltage compared to other supercapacitors.
Rechargeable lithium metal batteries are secondary lithium metal batteries. They have metallic lithium as a negative electrode, sometimes referred to as the battery anode. The high specific capacity of lithium metal, very low redox potential and low density make it the ideal anode material for high energy density battery technologies. Rechargeable lithium metal batteries can have a long run time due to the high charge density of lithium. Several companies and many academic research groups are currently researching and developing rechargeable lithium metal batteries as they are considered a leading pathway for development beyond lithium-ion batteries. Some rechargeable lithium metal batteries employ a liquid electrolyte and some employ a solid-state electrolyte.
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 to conduct ion movements between the electrodes, instead of the liquid or polymer gel electrolytes found in conventional batteries. Solid-state batteries theoretically offer much higher energy density than the typical lithium-ion or lithium polymer batteries.
The lithium–air battery (Li–air) is a metal–air electrochemical cell or battery chemistry that uses oxidation of lithium at the anode and reduction of oxygen at the cathode to induce a current flow.
A potassium-ion battery or K-ion battery is a type of battery and analogue to lithium-ion batteries, using potassium ions for charge transfer instead of lithium ions. It was invented by the Iranian/American chemist Ali Eftekhari in 2004.
Sodium-ion batteries (NIBs, SIBs, or Na-ion batteries) are several types of rechargeable batteries, which use sodium ions (Na+) as its charge carriers. In some cases, its working principle and cell construction are similar to those of lithium-ion battery (LIB) types, but it replaces lithium with sodium as the intercalating ion. Sodium belongs to the same group in the periodic table as lithium and thus has similar chemical properties. Although, in some cases (such as aqueous Na-ion batteries) they are quite different from Li-ion batteries.
Research in lithium-ion batteries has produced many proposed refinements of lithium-ion batteries. Areas of research interest have focused on improving energy density, safety, rate capability, cycle durability, flexibility, and cost.
Lithium hybrid organic batteries are an energy storage device that combines lithium with an organic polymer. For example, polyaniline vanadium (V) oxide (PAni/V2O5) can be incorporated into the nitroxide-polymer lithium iron phosphate battery, PTMA/LiFePO4. Together, they improve the lithium ion intercalation capacity, cycle life, electrochemical performances, and conductivity of batteries.
Mixed conductors, also known as mixed ion-electron conductors(MIEC), are a single-phase material that has significant conduction ionically and electronically. Due to the mixed conduction, a formally neutral species can transport in a solid and therefore mass storage and redistribution are enabled. Mixed conductors are well known in conjugation with high-temperature superconductivity and are able to capacitate rapid solid-state reactions.
The glass battery is a type of solid-state battery. It uses a glass electrolyte and lithium or sodium metal electrodes.
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.
This is a history of the lithium-ion battery.
