AB2O4 Spinel Research Articles

Enhanced electrochemical performance of MgFeO4 spinel as anode materials for Lithium-ion batteries through manganese doping

Existing graphite anode materials are reaching their limits, and iron-based AB2O4 spinel materials are considered as potential anodes for Li-ion batteries owing to their significant theoretical capacities. In this work, novel nanocrystalline MgFe2-xMnxO4 (x = 0, 0.1, 0.2, and 0.3) spinel ferrites were evaluated as anode materials for high-capacity Li-ion batteries. The Mn-doped MgFe2-xMnxO4 (x = 0, 0.1, 0.2, and 0.3) spinel ferrites were synthesized through a facile sol-gel synthesis method coupled with an annealing process. Their crystal structure, morphology, and purity were examined via X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). The X-ray diffraction analyses with Rietveld refinement of the synthesized ferrites reveal pure cubic structure with a characteristic Fd3̅m space group for all prepared samples. This was confirmed by Raman spectroscopy by revealing five spinel Raman active modes. The SEM images showed interconnected nanosized particles for all compositions, which led to a porous morphology. Their electrochemical proprieties as anode materials for Li-ion batteries were examined by cyclic voltammetry and galvanostatic charge-discharge tests. For all compositions, the cyclic voltammetry plots demonstrate the conversion type for the Li-ion storage mechanism. At an applied current density of 150 mA g−1, the compositions x = 0, 0.1, 0.2, and 0.3 show initial discharge/charge capacities of 1235/712, 1187/680, 1542/938, and 1239/768 mAh g−1, respectively. After 100 operational cycles, their galvanostatic charge/discharge capacities remain 529/534, 612/606, 642/663, and 700/700 mAh g−1. However, the compositions x = 0.2 and 0.3 exhibit excellent cycling stability during 100 cycles, even at higher rates. As a result, the Mn doping led to enhanced specific capacity and cycling stability of the MgFe2O4 spinel. The optimized compositions with x = 0.2 and 0.3 are, thus, proposed as promising anodes materials compositions for Li-ion batteries.

Ammonia-regulated CuCo2O4 spinel oxide embedded in Y zeolite for methanol oxidation

Morphology-controlled synthesis with a tailor-made structure is a promising approach to enhance the catalytic properties of inexpensive spinel oxides as a viable alternative to noble metals. AB2O4 spinel oxides, particularly, have garnered significant attention in mitigating volatile organic compounds (VOCs) emissions. The catalytic performance of these oxides can be improved through the modification of tetrahedrally coordinated A sites. In this study, we present a novel strategy for the preparation of CuCo2O4 spinel oxide nanoparticles embedded on Y zeolite. This involves the co-loading of Cu and Co oxides on Y zeolite, followed by successive treatment with NH3-reduction and re-oxidation. The resulting morphology-confined CuCo2O4 spinel oxides exhibit significantly higher catalytic activities and stabilities for the oxidation of CH3OH compared to their unrestrained counterparts. Our exploration into the in-situ formation of spinel oxides on Y zeolite, along with an investigation into their catalytic oxidation mechanism, lays the foundation for the rational design of non-noble metal oxide VOC catalysts.

High‐Temperature Oxidation Behavior of Medium‐Manganese Austenitic Steel

The high‐temperature oxidation behavior of medium‐manganese austenitic steel is investigated. The double‐layered oxide scale is formed in the investigated samples. The outer oxide layer consists of (Fe,Mn)‐rich oxides, while the inner oxide layer is mainly composed of AB2O4 spinel oxides. When the oxidation temperature is 800 °C, a region composed of oxide and ferrite is formed in the substrate surface layer. When the oxidation temperature is 900 and 1000 °C, there is no such region observed in the substrate surface layer. Although the content of Al in the Fe–Mn–Al sample and the content of Si in the Fe–Mn–Si sample are relatively lower than the content of Cr in the Fe–Mn–Cr sample, the oxidation resistance of the Fe–Mn–Al and Fe–Mn–Si samples is still better than that of the Fe–Mn–Cr sample. The oxidation resistance of the Fe–Mn–Cr–Al and Fe–Mn–Cr–Si samples is also better than that of the Fe–Mn–Cr sample. The addition of Al and Si can improve the oxidation resistance of the Fe–Mn–Cr sample. Besides, the oxidation resistance improvement effect of adding Si to the Fe–Mn–Cr sample is better than that of adding Al to the Fe–Mn–Cr sample.

Design and Performance of a New Zn0.5Mg0.5FeMnO4 Porous Spinel as Anode Material for Li-Ion Batteries.

Due to the low capacity, low working potential, and lithium coating at fast charging rates of graphite material as an anode for Li-ion batteries (LIBs), it is necessary to develop novel anode materials for LIBs with higher capacity, excellent electrochemical stability, and good safety. Among different transition-metal oxides, AB2O4 spinel oxides are promising anode materials for LIBs due to their high theoretical capacities, environmental friendliness, high abundance, and low cost. In this work, a novel, porous Zn0.5Mg0.5FeMnO4 spinel oxide was successfully prepared via the sol-gel method and then studied as an anode material for Li-ion batteries (LIBs). Its crystal structure, morphology, and electrochemical properties were, respectively, analyzed through X-ray diffraction, high-resolution scanning electron microscopy, and cyclic voltammetry/galvanostatic discharge/charge measurements. From the X-ray diffraction, Zn0.5Mg0.5FeMnO4 spinel oxide was found to crystallize in the cubic structure with Fd3¯m symmetry. However, the Zn0.5Mg0.5FeMnO4 spinel oxide exhibited a porous morphology formed by interconnected 3D nanoparticles. The porous Zn0.5Mg0.5FeMnO4 anode showed good cycling stability in its capacity during the initial 40 cycles with a retention capacity of 484.1 mAh g-1 after 40 cycles at a current density of 150 mA g-1, followed by a gradual decrease in the range of 40-80 cycles, which led to reaching a specific capacity close to 300.0 mAh g-1 after 80 cycles. The electrochemical reactions of the lithiation/delithiation processes and the lithium-ion storage mechanism are discussed and extracted from the cyclic voltammetry curves.

A new type of Sr(Zr0.2Hf0.2Ce0.2Yb0.2Me0.2)O3−x (Me = Y, Gd) high‐entropy ceramics used in thermal barrier coatings

AbstractSeeking for new ceramics with excellent thermophysical properties as thermal barrier coatings candidate materials has become a hot research field. In this study, Sr(Zr0.2Hf0.2Ce0.2Yb0.2Me0.2)O3−x high‐entropy ceramic powders were successfully synthesized by the method of solid‐state reaction, and the ceramics with single phase were prepared by pressureless sintering at 1600°C. The phase composition, microstructure, element distribution, high‐temperature thermal stability, and thermophysical properties of the ceramics were studied. The results showed that Sr(Zr0.2Hf0.2Ce0.2Yb0.2Me0.2)O3−x ceramics were composed of SrZrO3 phase and the second phase of AB2O4 spinel (i.e., SrY2O4 and SrGd2O4). The content of the second phase was gradually increased after heat treatment at 1400°C, which significantly improved the thermophysical and mechanical properties of the ceramics. The microhardness and fracture toughness of the ceramics were improved compared with that of SrZrO3. The thermal conductivities of Sr(Zr0.2Hf0.2Ce0.2Yb0.2Me0.2)O3−x (Me = Y, Gd) ceramics were 1.30 and 1.28 W m−1 K−1 at 1000°C, which were about 35% and 40% lower than that of SrZrO3 (1.96 W m−1 K−1) and yttria‐stabilized zirconia (2.12 W m−1 K−1), respectively. The thermal expansion coefficients of Sr(Zr0.2Hf0.2Ce0.2Yb0.2Me0.2)O3−x (Me = Y, Gd) ceramics were 12.8 × 10−6 and 14.1 × 10−6 K−1 at 1300°C, respectively, which was more closer to the superalloys compared with SrZrO3 ceramic (11.0 × 10−6 K−1).

The effect of Ce addition on purification and inclusion modification of CoCrFeNiMn high entropy alloy

This study focuses on purification and inclusion modification mechanism of equiatomic CoCrFeNiMn high entropy alloys with addition of various cerium (within the range of 0–0.0445 %) smelted by Vacuum Arc Melting (VAM), It was found that there are three types of inclusions in CoCrFeNiMn alloys: Mn(S, Se), AB2O4 spinel type, mixed type (Mn(S, Se) wraps AB2O4), and the average size of the three types of inclusions are 1.1 µm, 5.6 µm, and 4.8 µm, respectively. The addition of cerium can significantly reduce the oxygen content, as well as the sulfur content and selenium content are declined, the inclusions are refined and spheroidized simultaneously. The oxygen content, sulfur content and selenium content were reduced from 150 ppm, 46 ppm, and 105 ppm to 5–7 ppm, 22 ppm, and 80 ppm, respectively. When the cerium content is 0.0012 %, some of the inclusions are modified into three types of inclusions: Mn(S, Se) + Ce2O3, Mn(S, Se) + CeCrO3 and Mn(S, Se) + Ce2O3 + CeCrO3, while the average size of some unmodified AB2O4 spinel inclusions was reduced to 3.1 µm, and the average size of mixed inclusions was dropped to 2.6 µm. When the cerium content is 0.019 %, the inclusions in the alloy are completely modified into Ce2O2(S, Se) + Ce2(S, Se)3. Furthermore, the number density and area fraction of the inclusions are descended from 216.92 mm−2 and 0.1150 % of no cerium alloys to 121.64 mm−2 and 0.0602 %, the inclusions are well spheroidized, and the average size of cerium inclusions is 2.2 µm. Finally, the mechanism on the modification by cerium was discussed based on the composition evolution of inclusion during solidification with Factsage calculation and experimental results. The compositions of inclusions were also analyzed based on the inclusion evolution model.

Electronic Structure Study of Various Transition Metal Oxide Spinels Reveals a Possible Design Strategy for Charge Transport Pathways

The charge transport properties in solids play an important role in the selection of materials for electrochemical devices. Spinels are a special class of solids that are very versatile and possess different properties based on changes in stoichiometry and cation distribution. In that way, their properties can be tailored to fit certain uses. Here we report a density functional theory study of the electronic structures of nine normal and inverse ternary AB2O4 (A, B = Fe, Co, Ni, Mn) and A3O4 spinels. We found that changing the cation distribution of CoMn2O4 into (Mn)[CoMn]O4 lowers the bandgap by about three times. Additionally, charge transport occurs mostly through octahedral sites while in (Co)[CoNi]O4 it occurs through tetrahedral sites. Bulk-based band alignment results are also reported for the spinels in this work in order to design materials with preferred charge transport pathways.

Preparation and characterisation of green nano-sized ceramic pigments with the spinel structure AB2O4 (A = Co, Ni and B = Cr, Al)

Inorganic pigments based on AB2O4 (A = Co, Ni; B = Cr, Al) spinel structures with green colour were successfully synthesised by the polymeric route. The effect of the substitution of trivalent and divalent cations on the structural, optical and morphological properties of the pigments was investigated. The synthesised nanopowders were examined using thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller analysis (BET), UV–vis diffuse reflectance measurements, and CIEL*a*b* colorimetric analyses. The results show that the CoCr2O4 spinel and the spinels substituted by nickel and aluminium cations were obtained with a single phase after heat treatment at 900 °C. The produced powders present shades of the green colour with improvement in morphology for the substituted samples. The Ni0·5Co0·5CrAlO4 nanoparticles consisted of grains of quasi-spherical shape with sizes between 50 and 75 nm. This powder was used in small quantities with glazes for colouring tests on the surfaces of ceramic substrates.

Ab initio comparative study of the magnetic, electronic and optical properties of AB2O4 (A, B= Mn, Fe) spinels

The comparison of the magnetic, electronic, and optical properties of the spinel transition-metal oxides AB2O4 (A, B = Fe, Mn) and their relationship with the structure and composition were studied within DFT-GGA + U approximation. The spinels were considered both in the normal and inverse structure. We have found that regardless of composition and structure, the studied spinels are ferrimagnetic with antiparallel magnetic moments on A- and B-site cations. Electronic and structural properties of spinels depend on the composition: FeMn2O4 has a tetragonal structure and half-metallic properties; however, in the inverse FeMn2O4, the bandgap opens for the spin-up channel. MnFe2O4 is a cubic insulator with a bandgap of about 1.5 eV, which decreases in the inverse structure. The superexchange constants estimate within the simple indirect coupling model and have values close to the experimental ones. The total magnetization of FeMn2O4 is drop-down to zero under hydrostatic pressure above 60 GPa due to the strong dependence of the magnetic moment of octahedral manganese ion on the pressure. The microscopic mechanisms of the relationship between the structure, composition and properties are studied.

Interrelation between cationic distribution and electromagnetic properties of vanadium-substituted Mn–Zn ferrites

This study manifests the outcomes of varying vanadium (V) concentration in Mn–Zn ferrites with the general composition Mn0.6Zn0.4VxFe2−xO4 (x = 0.00—0.10, in steps of 0.02) synthesized by the solid-state reaction method. X-ray diffraction (XRD) analysis of all the samples confirmed the formation of the spinel structure. The cell parameter slightly decreases with the increase in V content. The substitution of V noticeably enhanced densification in samples sintered at 1250 °C. The grain size of the starting compositions varied from 13.0 to 27.9 µm. The Fourier Transform Infrared (FTIR) spectra indicate the preference of vanadium ions at octahedral sites. The saturation magnetization (Ms) and the experimental magnetic moments nB (µB) are observed to increase for x = 0.02 with = $${M}_{\mathrm{S}}$$ 61.73 emu/g. This happens for the reduction of the A–B interaction in the AB2O4 spinel type ferrites. After that, Ms and nB (µB) values decreased for higher V contents. The magnetization obtained is explained by redistribution of cations in the tetrahedral and octahedral sites and spin canting due to weakening of exchange interaction. The magnetic permeability and dielectric constant show a decreasing trend with increasing V concentration. The Cole–Cole plots demonstrate the grain and grain boundary effects. The manifestation of single semicircle after x = 0.06 indicates the precedence of grains in the overall resistance. The complex modulus graphs were also studied to understand the mechanism of the electrical processes.

Three-Dimensional-Order Macroporous AB2O4 Spinels (A, B =Co and Mn) as Electrodes in Zn-Air Batteries.

In this work, atomically substituted three-dimensionally ordered macroporous (3DOM) spinels based on Co and Mn (MnCo2O4 and CoMn2O4) were synthetized and used as cathodic electrocatalysts in a primary Zn-air battery. Scanning/transmission electron microscopy images show a 3DOM structure for both materials. Skeleton sizes of 114.4 and 140.8 nm and surface areas of 65.3 and 74.6 m2 g-1 were found for MnCo2O4 and CoMn2O4, respectively. The increase in surface area and higher presence of Mn3+ and Mn4+ species in the CoMn2O4 3DOM material improved battery performance with a maximum power density of 101.6 mW cm-2 and a specific capacity of 1440 mA h g-1, which shows the highest battery performance reported to date using similar spinel materials. The stability performance of the electrocatalyst was evaluated in half-cell and battery cell systems, showing the higher durability of CoMn2O4, which was related to its better capability to perform the electrocatalytic process as adsorption, electron transfer, and desorption. It was found through density functional theory calculations that the CoMn2O4 spinel has a higher density of states in the Fermi level vicinity and better conductivity. Finally, the unique shape of 3DOM spinels promoted a high interaction between electroactive species and catalytic sites, making them suitable for oxygen reduction reaction applications.

Structural, electronic, magnetic and optical properties of AB2O4 (A = Ge, Co and B = Ga, Co) spinel oxides

Structural, magnetic, optical and electronic properties of GeGa2O4, CoGa2O4, GeCo2O4 and CoCo2O4 spinel oxides have been studied. Spinel oxides are studied by performing theoretical calculations based on density functional theory. In non-magnetic host GeGa2O4 spinel oxide, significant effects of Co occupancy (at A, B and/or both sites) on the electronic, magnetic and optical behavior have been observed. Among the spinel oxides, the CoGa2O4, GeCo2O4 and CoCo2O4 spinel oxides show 100% spin-polarization and exhibit stable cubic structure in ferromagnetic phase. The calculated structural and magnetic parameters predict the cation distribution at A and B sites as follows: (Ge2+)[Ga23+]O4−2, (Co2+)[Ga23+]O4−2, (Ge4+)[Co22+]O4−2 and (Co+2)[Co23+]O4−2 for GeGa2O4, CoGa2O4, GeCo2O4 and CoCo2O4 spinel oxides, respectively. The electronic band gap is found to be decreased from 1.605 eV to 0.762 eV for spin↑ state while it is decreased from 1.578 eV to 0.000 eV for spin↓ state with Co occupancy in host GeGa2O4 lattice. Lattice constant decreases (8.7877 Å to 8.1390 Å) as Co occupies B site and/or both (A and B) sites. For GeCo2O4 spinel oxide, the calculated value of total magnetic moment (mtot = 6.12 μB/f.u) and saturation magnetization (MS = 134.22 emu/g) is found to maximum. Optical properties reveal that the CoGa2O4, GeCo2O4 and CoCo2O4 spinel oxides have less threshold electronic transition energy relative to host GeGa2O4 spinel oxide. Electronic, magnetic and optical characteristics show potential integration of these spinel oxides in magnetic-semiconducting devices.

A study on the vibrational frequencies, elastic properties and sound velocities of vanadium spinel oxides AV2O4 (A = Mn, Fe and Zn) short-range non-Coulomb potential theoretical model

Owing to the fact of the AB2O4 spinel oxide’s chemical and thermal stability, and other intriguing properties make them suitable candidate materials for many applications, including chemical looping and catalytic reactions. To do our investigations, a short-range non-Coulomb potential theoretical model is used to calculate the zone-centre, elastic constants, infrared phonon mode frequencies, Raman phonon mode frequencies, velocities of the sound wave along the highly symmetric three crystallographic-axes and Debye temperature of the vanadium spinel oxides AV2O4 (A = Mn, Fe and Zn). The preliminary results of our calculations show that the interaction in the second neighbour (V–O) is much stronger than the interaction of the first neighbour (A–O). Moreover, from the analysis of the obtained results of elastic constants, the nature of the studied vanadium spinels are found to be ductile.

Novel franklinite-like synthetic zinc-ferrite redox nanomaterial: synthesis, and evaluation for degradation of diclofenac in water

The current study investigates a novel redox technology based on synthetic franklinite-like zinc-ferrite nanomaterial with magnetic properties and redox nature for potential use in water treatment. Physicochemical characterization revealed the nanoscale size and AB2O4 spinel configuration of the zinc-ferrite nanomaterial. The redox activity of nanoparticles was tested for degradation of diclofenac (DCF) pharmaceutical in water, without any added external oxidants and under dark experimental conditions. Results revealed ∼90% degradation in DCF (10 μM) within 2 min of reaction using 0.17 g/L Zn1.0Fe2.0O4. Degradation of DCF was due to chemical reduction by surface electrons on zinc-ferrite and oxidation by oxygen-based radicals. Three byproducts from reduction route and eight from oxidation pathways were identified in the reaction system. Reaction pathways were suggested based on the identified byproducts. Results demonstrated the magnetic zinc-ferrite is a standalone technology that has a great promise for rapid degradation of organic contaminants, such as DCF in water.

Spin reorientation by Ni doping in Cu1−xNixCr2O4 spinels with x = 0 and 0.1, and evidence for canted magnetic Cr order above the onset of a ferromagnetic Cu

In ferrimagnetic spinels AB2O4 the magnetic structure is strongly influenced by lattice distortions, geometric frustration and the electronic properties of the cations at the A and B sites. Here, we report a comprehensive study on the temperature dependence of the magnetic structure of CuCr2O4 and Cu0.9Ni0.1Cr2O4 using neutron diffraction. CuCr2O4 undergoes a first continuous magnetic transition around 155 K into a canted long-range spin order on the Cr sublattice established by an antiferromagnetic and a ferromagnetic mode. Below 130 K a second transition occurs into a ferromagnetic order on the Cu sublattice resulting in a ferrimagnetic spin arrangement. Correlations between the appearance of magnetic modes and changes in the lattice geometry at different temperatures are discussed giving insight to magnetoelastic coupling. The occurrence of a ferromagnetic Cr mode above 130 K questions the common interpretation that a strong antiferromagnetic coupling between A and B spins in ferrimagnetic AB2O4 spinels is responsible for spin canting. From our neutron diffraction measurements of Cu1−xNixCr2O4 we identify a spin reorientation for the ferromagnetic modes with a nickel content between x = 0 and 0.1.

Robust and facile strategy for tailoring CoMn2O4 and MnCo2O4 structures as high capacity anodes for Li-ions batteries

Two AB2O4 spinel structures have been synthesized by alternating the A- and B-site atoms in the forms (MnCo2O4 and CoMn2O4) through implementing the low-cost co-precipitation technique. Structural investigation results indicated the pronounced phase transformation from cubic of MnCo2O4 to the tetragonal spinel of CoMn2O4, while no change in the crystallite size was detected in both compounds. The observed microstructure via FE-SEM revealed MnCo2O4 nanoparticles with cup-like crystal shape and the CoMn2O4 nanoparticles with bubble-like morphology were manifested. FT-IR results showed a significant shift towards larger wavelengths in the vibrational bands of metal-oxygen bonds of CoMn2O4. The CoMn2O4 electrode exhibited initial discharge capacity (~1710 mAhg−1) higher than that of (~1443 mAhg−1) for MnCo2O4 electrode when cycled at 100 mAg−1 versus Li/Li+. The assembled MnCo2O4 cell delivered 58 mAhg−1, while CoMn2O4 cell gained 92.3 mAhg−1 of specific discharge capacity over 50 cycles of different current densities.

Synthesis, characterization and properties of Ni2+-doped ZnAl2O4-based spinel-type solid acid catalysts: SO42−/Zn1-xNixAl2O4

A novel series of SO42−/Zn1-xNixAl2O4 spinel-type solid acid catalysts were prepared simply by doping Ni2+ ions in the lattice of spinel ZnAl2O4 and applied in the synthesis of n-butyl acetate. The crystal structures, surface molecular structures, morphologies and acidic properties were characterized by the methods of XRD, Raman, FE-SEM, EDS and FT-IR (direct and NH3 adsorbed). The experimental results revealed that both Ni2+ content and the doping ion had a significant influences on the stability of spinel structure and the acidic properties of the catalysts. Doping Ni2+ played a significant role in stabling the spinel structure and consequently increasing the number of active acid centers. Compared with undoped SO42−/ZnAl2O4 and Cu2+-doped SO42−/Zn0.9Cu0.1Al2O4, Ni2+-doped SO42−/Zn0.9Ni0.1Al2O4 presented the higher catalytic activity with 92.0% conversion of acetic acid in the esterification of acetic acid with n-butanol. Moreover, Ni2+-doped SO42−/Zn0.9Ni0.1Al2O4 exhibited the better excellent reusability, which remained above 60% conversion of acetic acid even after being used six times in the esterification of acetic acid with n-butanol. Raman and FT-IR results proved that M-O bonds in tetrahedral (Td) and octahedral (Oh) sites were covalently linked with sulfate species to generate surface acid sites, which provided the main basis for the establishment of acid center formation model on AB2O4 spinel oxides. In addition, a possible Eley-Rideal model mechanism for the esterification of carboxylic acid with alcohol was proposed on this basis of both the characterization results and the results of the catalytic activities.

Stabilized Lithium, Manganese AB2O4 Spinel for Rechargeable Lithium Electrochemical Systems through A and B Site Doping

Lithium manganese oxide doped with potassium and cobalt produces a promising cathode material for rechargeable lithium-ion cells. Modifying the A site and B site of the spinel structure works to limit cathodic capacity fading by enhancing the robustness of the material. LixKyMn2-zCozO4 was synthesized as the active ingredient for the cathode with x=1, y=0.1, and both z=0.1 and 0.2, and was tested against metallic lithium to evaluate performance. Through high-rate discharge, pulse cycling, and deep discharge tests, the electrochemistry of the cathode exhibited excellent reversibility and overall performance stability. LiK0.1Mn2-zCozO4 proved to be a capable abuse tolerant option for use in rechargeable battery applications.

From cation flexibility to multifaceted industrial adoptability: a voyage to the resourceful spinel

ABSTRACTSignature of cation flexibility associated with the order–disorder structure of three spinel families, namely aluminates (MgAl2O4/ZnAl2O4), ferrites (NiFe2O4/ZnxNi1−xFe2O4), and titanate (Li4Ti5O12) was probed using the X-ray diffraction and Raman spectroscopy. Cation flexibility (also known as antisite defects or (dis)order structural transitions) is a unique feature of many oxide AB2O4 spinel systems in which the cations exchange their sites under external influence. This feature generates functionality in many different ways. In some cases, such as ferrites, the flexibility of zinc to occupy tetrahedral sites enhances the magnetic properties, whereas the flexibility of lithium in lithium titanate brings exotic electrochemical feature with zero strain. Similarly, cation flexibility of magnesium and aluminium makes the structure tolerant towards nuclear irradiation. Some such salient features of spinel systems are described highlighting the underlying crystal structures.Enriched with enormous chemical versatility, order–disorder structure, vacancy, interstitials and mixed-cation occupancy, ‘Spinel is a world in itself’. This is why, exploring its huge accomplishments never gets enough. Ever wonder, where from this versatility stems in! This review endeavours to seek the answer by combining the flexible order–disorder structure, supporting diagnosis tools and tuneable properties of this versatile class: The Spinels.

Stabilized Lithium, Manganese AB2O4 Spinel for Rechargeable Lithium Electrochemical Systems through A and B Site Doping

Lithium manganese spinel (LixMn2O4) has been extensively investigated as a safe and affordable lithium ion cathode material that can provide a great lattice for lithium intercalation. However, a major obstacle when utilizing LixMn2O4 cathodes is the loss of cycle capacity that occurs during cell charge and discharge. Lithium manganese oxide doped with potassium and cobalt produces a promising cathode material for rechargeable lithium-ion cells. Modifying the A site and B site of the spinel structure works to limit cathodic capacity fading by enhancing the robustness of the material. Successfully preventing degradation of the spinel matrix is key to maintaining the electrochemistry’s reversibility over prolonged cycling and abusive conditions. LixKyMn2-zCozO4 was prepared by modifying a stabilized lithium manganese-based AB2O4 spinel material with potassium A site and cobalt B site dopants. This was done using a two-step method where a manganese mixed metal oxide precursor was synthesized and subsequently used in a solid state reaction. LixKyMn2-zCozO4 was synthesized as the active ingredient for the cathode with x=1, y=0.1, and both z=0.1 and 0.2, and was tested against metallic lithium to evaluate performance. In order to assess the robustness of the LixKyMn2-zCozO4 cathode material at both z=0.1 and z=0.2, a number of cycling tests were run and analyzed in comparison to each cell’s baseline performance. A 2 mA cycling test between 3.0 or 2.5 V and 4.5 V was run initially on all cells to establish baseline performance, and was run between high rate discharge tests, pulse cycling tests, and deep discharge tests in order to compare to the cell’s baseline. Different groups of cells were discharged at 2, 4, 8, 12, 16, and 20 mA, pulse charged and discharged for 1 second with a 1 second rest, and deep discharged down to 2.5 V in order to assess the reversibility of the LixKyMn2-zCozO4 cathode chemistry when compared back to baseline performance. Through high-rate discharge, pulse cycling, and deep discharge tests, the electrochemistry of the cathode exhibited excellent reversibility and overall performance stability. For example, Figure 1 shows a Li \\ LiK0.1Mn1.8Co0.2O4 cell that retains its full capacity when tested at the 2 mA cycling baseline after high discharge rates of 4, 12, 16, and 20 mA for 10 cycles at a time. Figure2 illustrates the maintenance of the base thermodynamics of the same cell after these high-rate discharges, exhibiting the stability of the LiK0.1Mn1.8Co0.2O4 chemistry. An Li \\ LiK0.1Mn1.8Co0.2O4 cell was additionally shown to withstand a deep discharge test down to 2.5 V in Figure 3, and a pulse cycling test in Figure 4. Following each abusive test, the cell’s capacity returned to its previous value when cycled at baseline conditions, showing the stabilizing effect of the spinel’s modifications on capacity retention. Doping the LiMn2O4 spinel with potassium in the A site and cobalt in the B site proved to be a promising chemistry to prevent cathodic capacity fading in a lithium-ion cell, as well as a capable abuse tolerant option for use in rechargeable battery applications. Figure 1