Spinel-structured Materials Research Articles

Data-Driven Design for Electrolyte Additives Supporting High-Performance Lithium-Ion Batteries

We presented here two cases of data-driven electrolyte additive design, using two cathodes as examples. In scenario 1, LiNi0.5Mn1.5O4 (LNMO), a spinel-structured material with an average lithiation/de-lithiation potential at ca. 4.6-4.7 V, was used as an example for the extreme high working potentials and the resultant strains on electrolytes. In this study, we first selected and tested a diverse collection of 28 single and dual additives for the LNMO//Gr system using descriptors representative of chemical functionality.(1) Subsequently, we trained and employed machine learning (ML) models to suggest 6 binary compositions out of 125 based on predicted final area specific impedance (ASI), impedance rise (ΔASI), and final specific capacity(Q). Notably, this approach led to the discovery of a new dual additive which outperforms the initial dataset.In Scenario 2, the AI-guided workflow undergoes further enhancement for accelerated additive optimization employing new data featuring an earth-abundant cathode material of 0.3Li2MnO3·0.7LiMn0.5Ni0.5O2. This phase of the study introduces a more robust machine learning (ML) model for performance prediction, utilizing Figure of Merit Energy (FOME) and Figure of Merit Power (FOMP) as predictive metrics. Following three , Bayesian optimization iterations, 15 out of 78,000 binary and tertiary additive combinations was suggested for experiments, and several novel addtive compositions exhibiting unexpectedly high performance were subsequently identified. The optimal formulation surpasses the current standard by achieving a performance enhancement of 15-19%, as confirmed through experimental testing conducted in coin cells.Overall, our findings not only underscores the efficacy of ML in identifying new additives combinations, but also introduces an accelerated material discovery workflow that directly integrates data-drive methods with battery testing experiments.(1) ACS Omega 2018, 3, 7, 7868–7874

Fabricating highly-active Ni3+ sites of spinel to enhance electrocatalysis oxygen evolution reaction

Oxygen evolution reaction (OER) suffers a complex four-electron process with sluggish kinetics, which severely hinders its practical application. In general, Ni-based spinel-structured materials have emerged as potential electrocatalysts for OER. However, fabricating surface with high efficient Ni3+ active sites for Ni-based spinel is thermodynamically unfavorable, which impedes the future development and application of Ni-based spinel. In this study, we have formulated a octahedral (Oh) sites doping route for the synthesis of a Ni3+-riched Ni(Co1.98Ni0.02)O4. The results demonstrate that the catalyst with high density of surface Ni3+ active sites exhibits an improved OER catalytic activity compared with NiCo2O4 and requires a low overpotential of 349 mV at a current density of 10 mA cm−2.

CO2 conversion improvement of solid-oxide electrolysis cells by inserting buffer layers between MFe2O4 (M = Ni, Cu, Co, Fe) cathode and electrolyte

This study investigated the potential of spinel-structured materials (MFe2O4; M = Ni, Cu, Co, and Fe) as cathodes of solid oxide electrolysis cells (SOECs); at the same time, it revealed that the La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) blocking layers would improve the performance of SOECs by interposing between MFe2O4 and the Sm0.2Ce0.8O2-δ (SDC) electrolytes. The fabricated SOECs were tested under 39% CO2-1% CO-60% He up to 800 °C. Our results showed that the Faradaic efficiency for CO2 reduction was significantly improved and approached the theoretical production rate after the insertion of LSGM blocking layers. In addition, the LSGM barrier layers effectively prevent the short-circuit effect between MFe2O4 and SDC, allowing the open-circuit voltage (OCV) to increase from ∼0.56 V to ∼0.77 V, which dramatically improved the gas generation efficiency of SOECs. According to our optimized SOEC structure, NiFe2O4 and CuFe2O4 exhibited superior electrolytic performance and maintained stable electrolysis after 10 h without degradation. In summary, the inserted LSGM layers would gently modify the interfacial contact and address the mismatch between the spinel-structured materials and SDC to avoid the performance degradation caused by electrode detachment and achieve higher durability than the SOECs without LSGM layers.

Prediction of structure and cation ordering in an ordered normal-inverse double spinel

Spinels represent an important class of technologically relevant materials, used in diverse applications ranging from dielectrics, sensors and energy materials. While solid solutions combining two “single spinels” have been explored in a number of past studies, no ordered “double” spinels have been reported. Based on our first principles computations, here we predict the existence of such a double spinel compound MgAlGaO4, formed by an equimolar mixing of MgAl2O4 normal and MgGa2O4 inverse spinels. After studying the details of its atomic and electronic structure, we use a cluster expansion based effective Hamiltonian approach with Monte Carlo simulations to study the thermodynamic behavior and cation distribution as a function of temperature. Our simulations provide strong evidence for short-ranged cation order in the double spinel structure, even at significantly elevated temperatures. Finally, an attempt was made to synthesize the predicted double spinel compound. Energy Dispersive X-ray Spectrometry and X-ray diffraction Rietveld refinements were performed to characterize the single-phase chemical composition and local configurational environments, which showed a favorable agreement with the theoretical predictions. These findings suggest that a much larger number of compounds can potentially be realized within this chemical space, opening new avenues for the design of spinel-structured materials with tailored functionality.

Investigation of some new hydro(solvo)thermal synthesis routes to nanostructured mixed-metal oxides

We present a study of two new solvothermal synthesis approaches to mixed-metal oxide materials and structural characterisation of the products formed. The solvothermal oxidation of metallic gallium by a diethanolamine solution of iron(II) chloride at 240°C produces a crystalline sample of a spinel-structured material, made up of nano-scale particles typically 20nm in dimension. XANES spectroscopy at the K-edge shows that the material contains predominantly Fe2+ in an octahedral environment, but that a small amount of Fe3+ is also present. Careful analysis using transmission electron microscopy and powder neutron diffraction shows that the sample is actually a mixture of two spinel materials: predominantly (>97%) an Fe2+ phase Ga1.8Fe1.2O3.9, but with a minor impurity phase that is iron-rich. In contrast, the hydrothermal reaction of titanium bis(ammonium lactato)dihydroxide in water with increasing amounts of Sn(IV) acetate allows nanocrystalline samples of the SnO2–TiO2 solid solution to be prepared directly, as proved by powder XRD and Raman spectroscopy.

Spinel-structured Ni-free Zn0.9Cu x Mn2.1-x O4 (0.1 ≤ x ≤ 0.5) thermistors of negative temperature coefficient

Most spinel-structured materials of negative temperature coefficient (NTC) contain Ni, which have high cost. In this work, Ni-free Zn0.9Cu x Mn2.1-x O4 (0.1 ≤ x ≤ 0.5) NTC material system is developed. X-ray diffraction (XRD) spectra show that Zn0.9Cu x Mn2.1-x O\intered at 1100 °C crystallizes in a tetrahedral spinel structure, which is caused by the Jahn-Teller effect of the Mn3+ ions at the B sites. Cu2p3/2 X-ray photoelectron spectra (XPS) demonstrate that most of Cu ions located at B sites are at the valance of 2+. The resistivity of Zn0.9Cu x Mn2.1-x O4 varies from 1,340 Ω cm to 51,489 Ω cm, and B value from 3,357 K to 4,276 K. The resistivity drift after annealing at 150 °C in air for 1,000 h is less than 3 % which is stable enough for practical application.

A series of spinel phase cathode materials prepared by a simple hydrothermal process for rechargeable lithium batteries

A series of spinel-structured materials have been prepared by a simple hydrothermal procedure in an aqueous medium. The new synthetic method is time and energy saving i.e., no further thermal treatment and extended grinding. The main experimental process involved the insertion of lithium into electrolytic manganese dioxide with glucose as a mild reductant in an autoclave. Both the hydrothermal temperature and the presence of glucose play the critical roles in determining the final spinel integrity. Particular electrochemical performance has also been systematically explored, and the results show that Al 3+, F − co-substituted spinels have the best combination of initial capacity and capacity retention among all these samples, exhibited the initial capacity of 115 mAh/g and maintained more than 90% of the initial value at the 50th cycle.

Texture development and deformation mechanisms in ringwoodite

Ringwoodite Mg 2SiO 4 with spinel structure is an important phase in the earth's mantle transition zone. Controlled deformation experiments showed that ringwoodite underwent ductile deformation when compressed axially at 6–10 GPa and at room temperature in a multianvil D-DIA deformation apparatus. Texture evolution during cyclic compression has been recorded in situ using X-ray transparent anvils with monochromatic synchrotron X-ray diffraction and a two-dimensional detector. Quantitative analysis of the images with the Rietveld method revealed a 1 1 0 fiber texture. By comparing this texture pattern with polycrystal plasticity simulations, it is inferred that {1 1 1}〈 1 ¯ 1 0〉 slip is the dominant deformation mechanism in ringwoodite, consistent with high temperature mechanisms observed in other spinel-structured materials. Although strong ringwoodite textures may develop in the transition zone, the contribution to bulk anisotropy is minimal due to the weak single-crystal anisotropy.

A study of the electronic states of Ni xMn 3− xO 4+δ thin films using scanning tunneling microscopy and current imaging tunneling spectroscopy

Ni x Mn 3− x O 4+δ (0.4⩽ x⩽1) are a series of spinel structured materials exhibiting negative temperature coefficient of resistance (NTCR) characteristics. Thin films were produced on <100> silicon substrates using rf magnetron sputtering in an oxygen/argon atmosphere (2.5% oxygen). Following deposition, the films were annealed at 800 °C in air and the crystalline structure studied using X-ray diffraction. Scanning tunneling microscopy (STM) was used to study the topology of the layers in both the as-deposited and annealed states. Annealing resulted in a more uniform and ordered structure. Tunneling conductance (d I/d V vs V) and normalised tunneling conductance {(d I/d V)/(1/ V) vs V} characteristics were measured and used to generate conductance maps {d I/d V ( x, y,eV)} and to study the local density of states (LDOS) of the film surface. The tunneling conductance maps showed islands of bright contrast in an otherwise relatively uniform background of dark contrast. There were substantially fewer bright contrast islands in annealed films and they appear to bear no relation to any topographical features. The distribution of the LDOS in the bright regions was similar to that normally associated with metallic behaviour, while in the regions of dark contrast, the LDOS was more characteristic of semiconductors (LDOS ∼0 at Fermi level). The resistance–temperature characteristics were measured and found to be consistent with conduction models based on electron hopping.

In situ study of the effect of temperature on the electronic structure of NixMn3−xO4+δ thin films using scanning tunneling spectroscopy

Ni x Mn 3−x O 4+δ (0.4⩽x⩽1) are a series of cubic-spinel-structured material exhibiting a negative temperature coefficient of resistance. The resistance as a function of temperature (T) has been measured from 20 to 200 °C and the data have been fitted to a variable range hopping model in which the resistivity is described as ρ=ρ0T exp(T0/T)0.5 where T0 was found to be 2.24×105 K. Scanning tunneling spectroscopy measurements were carried out over the temperature range of 20–300 °C, to study the shape of the local density of states (LDOS). Such measurements have not been carried out on this class of spinel structured materials before. The distribution of the LDOS around the Fermi level was parabolic in agreement with the model of variable range hopping. The evolution of a peak around 1.8 eV was observed with increasing temperature and found to be completely reversible with temperature.

Decomposition of NiMn2O4 spinel: an NTC thermistor material

Abstract Nickel manganate based NTC thermistors are widely used in industrial and domestic applications where cost efficient but reliable temperature sensing, fluid flow rate or pressure sensing devices are required. Single phase, ceramic samples of NiMn2O4 (2:1 Mn:Ni) were synthesised using a conventional mixed oxide route. Thermal analysis confirmed the 2:1 spinel structured material decomposes upon heating above 907°C. After heating at temperatures between 1050 and 1200°C and subsequently quenching to room temperature, regions containing florets of spinel structured material were found using TEM. The surrounding matrix was a NiO rich rock-salt structured material and the florets were manganese rich. A decomposition mechanism based on degree of inversion is proposed to explain the appearance of the florets. Slowly cooling samples from 1250°C led to a microstructure principally composed of cubic spinel but also with regions of much smaller spinel florets in a rock-salt structured phase. The slow-cooled samples showed a larger drift in resistance over time than single phase samples when held at 400°C. XRD measurements carried out before and after electrical characterisation showed a reduction in the amount of rock-salt structured material present in the slow-cooled samples.

Electrode and solid electrolyte thin films for secondary lithium-ion batteries

Electrostatic spray deposition (ESD) was employed to prepare thin layers of Li 1.2Mn 2O 4 (nominal composition) and BPO 4:0.035Li 2O for all-solid-state thin film lithium-ion batteries. The relationships between layer morphologies and deposition conditions such as solvent composition of the precursor solutions and substrate temperature were investigated. It was found that a low substrate temperature and/or high boiling point of the solvent may lead to a relatively dense structure. Reticular porous structures are formed, if films were deposited at 250°C and a mixture of 85 vol.% butyl carbitol and 15 vol.% ethanol was used as the solvent. The Li 1.2Mn 2O 4 layers, formed in the 250–400°C temperature range, were amorphous or micro-crystalline. After annealing beyond 600 °C, they could be crystallized into a spinel-structured material. Glassy BPO 4:0.035Li 2O layers could fill the pores of porous Li 1.2Mn 2O 4 layers to form a dense intermediate electrolyte layer. Thin-film rocking-chair batteries, Li 1.2Mn 2O 4|BPO 4:0.035Li 2O|Li 1.2Mn 2O 4|Al, were prepared and revealed an open-circuit voltage of about 1.2 V after charging.