MnO2 Phase Research Articles

Elucidating the nature of secondary phases in LiNi0.5Mn1.5O4 cathode materials using correlative Raman-SEM microscopy

LiNi0.5Mn1.5O4 (LNMO) is a promising next-generation cathode material for lithium-ion batteries (LIBs) due to its high-energy and high-power density. However, its commercial adoption is hindered by the unstable LNMO/electrolyte interface due to high operating voltages and structural degradation arising from Jahn-Teller distortion and metal-ion dissolution resulting in poor cycling stability. Additionally, the high-temperature calcination beyond 700 °C often results in secondary phases such as rock salt NiO, Li1-xNixO, Ni6MnO8 or Li2MnO3, whose precise chemical compositions and their influence on electrochemical performance remain unclear. Traditional analytical techniques such as X-ray diffraction (XRD) or neutron diffraction face challenges in resolving these secondary phases due to low phase fractions and overlapping reflections with the LNMO phase. Here, we address these challenges using correlative Raman-Scanning electron microscopy (Raman-SEM) to characterize secondary phases in LNMO materials that were synthesized under various synthesis conditions and evaluated their impact on the electrochemical performance. Our results reveal the synthesis-dependent emergence of three distinct secondary phases in LNMO materials synthesized at 1000 °C, a phenomenon that, to our knowledge, has not been previously reported. Specifically, LNMO synthesized at 900 °C shows the coexistence of Ni6MnO8 and Li2MnO3 phases, while synthesized at 1000 °C also exhibits a Mn3O4 phase. Furthermore, an increased amount of these secondary phases in LNMO led to a lower discharge capacity due to their electrochemical inactive nature. However, these phases do not negatively impact the rate capability or the long-term cycling performance of the LNMO materials. These insights are crucial for advancing the development of LNMO cathode materials for next-generation LIBs.

Elucidating the diffusion and interaction mechanisms of Zn2+ and H+ in MnO2 for aqueous zinc-ion batteries: A DFT study

MnO2 is a promising cathode material for aqueous zinc-ion batteries (AZIBs) with potential applications in large-scale energy storage systems. However, its practical use is hindered by poor cyclic stability and slow diffusion kinetics. Despite considerable efforts, success has been limited due to an unclear understanding of the intrinsic properties of Zn2⁺ and proton (H⁺) insertion into MnO2. This study investigates the predominant phases of MnO2—α, β, δ, and γ—and elucidates their reaction mechanisms using first-principles computational methods based on density functional theory (DFT). Our research reveals that H⁺ ions exhibit a higher initial insertion voltage compared to Zn2⁺ ions, but their diffusion in MnO2 is significantly impeded by strong interactions with oxygen. Additionally, H⁺ insertion partially obstructs Zn2⁺ ion migration. Furthermore, the insertion of Zn2⁺/H⁺ and the adsorption of H⁺ on the MnO2 surface are intricately linked to the dissolution process of manganese. This work significantly enhances our fundamental understanding of MnO2 as a cathode material for AZIBs.

Activation of the process of layer combustion of bitter coal with iron nitrate and waste of metal rolling production

The influence of metal-rolling production waste and iron nitrate on the characteristics of the process of layer combustion of coal is investigated. As a solid fuel, coal of the T grade was used. Metal scale and iron nitrate were introduced into the fuel by mechanical mixing. According to XRD data, phases of iron oxides Fe3O4 and manganese Mn3O4 were identified in the metal scale. The characteristics of the combustion process of the studied samples were studied using high-speed video with the use of a combustion chamber at a heating medium temperature of 700°C. Combustion Also, the process of activated layer combustion coal was scaled using a solid fuel boiler unit. It has been experimentally established that the use of metal scale and iron nitrate leads to an increase in the reactivity of the fuel, as evidenced by a decrease in the ignition delay time. Due to the intensification of the combustion process, the fuel underburning and the concentration of CO formed in the composition of gas-phase combustion products were reduced.

Characterization of Mn3O4/(x)Nb2O5 thin films as a promising material for supercapacitors

The thin films of Mn3O4/(x)Nb2O5 oxides (x = 0, 2, 4, and 6 %) were prepared by the electron beam evaporation method and then annealed at 400 °C. The structural analysis showed a tetragonal phase of Mn3O4, according to X-ray diffraction results. The quantitative elemental analysis of films confirms the stoichiometry of the Mn3O4, while the Nb2O5 couldn’t be recognized using energy dispersive X-ray fluorescence. The chemical speciation of the films was investigated using X-ray photoelectron spectroscopy. Three oxidation states of Mn were recognized at average binding energies of 645.70±0.35, 642.99±0.40, and 641.58±0.48 eV that correlated to Mn4+, Mn3+, and Mn2+, respectively. As the Nb2O5 increases, a slight decrease in the binding energy of Mn4+ is recognized, whereas it is nearly constant for the deconvoluted Mn3+ and Mn2+. Two electronic transitions (Eg1 and Eg2) of the optical band gap showed an increase with increasing Nb2O5 dopant from 2 % to 6 %. The optical parameters such as Eosc, the single oscillator energy, Edis, the dispersion energy, both moments (M−1) and (M−3), the ratio of carrier concentration/effective mass (N/m*), and the lattice dielectric constant (εL) were determined. From electrochemical measurements of pure Mn3O4 films, it is found that the voltammetric current density is directly proportional to the scan rates of cyclic voltammetry CV, with good cyclic stability, and by increasing the scan rates, the values of specific capacitance decrease while the values of specific power increase. In doped thin films, no potential drop is observed in the discharging process, which indicates good interfacial contact between the active material and the substrate during the charge/discharge process. These results suggest that the obtained Mn3O4 nanoparticles are a better candidate for supercapacitor applications.

Enhancing stability and catalytic activity of layered MnO2 via interfacing with YMn2O5 towards H2O2 decomposition

The low thermal and chemical stability of manganese dioxide (MnO2) in aqueous solutions poses a significant challenge for practical applications. Herein, we stabilize MnO2 through interfacing with mullite oxide YMn2O5 for the efficient catalytic degradation of H2O2. Compared to the pure-phase MnO2, the composite material (MnO2/YMO) exhibits the enhanced thermal and chemical stability, which completely degrades H2O2 (0.5 M) within one minute at 25 °C, surpassing the reported catalysts. Experimental and theoretical results demonstrated that active surface of MnO2 preferentially exposes on YMn2O5. Such an interfacial bonding is crucial for stabilizing the MnO2 phase, as it suppresses phase transition during thermal treatment or chemical reactions. Theoretical calculations revealed that charge transfer between the interfaces optimize the adsorption energy of reaction intermediates, further improving catalytic activity. This work solves the issue of MnO2 instability through interface engineering while remaining its high catalytic performance, providing insight into the development of the next generation of catalysts.

Nano-MnOx prepared by redox method for toluene oxidation removal from air

Catalytic oxidation is an efficient VOCs removal technology with great potential and development advantages. The key to the oxidative elimination of VOCs lies in the development and application of the catalyst with high efficiency. In this work, the nano-MnOx catalysts were prepared by redox method and the catalytic oxidation performance of toluene was studied. The calcination temperature could effectively change the surface chemical composition and the nano-MnOx catalyst structures, which could effectively regulate the number of active centers on the catalyst surface to improve the adsorption, activation, and oxidation ability of the nano-MnOx catalysts for toluene molecules. The nano-MnOx catalyst dominated by the MnO2 phase, which was prepared at the calcination temperature of 400 °C, had a high specific surface area, developed porosity, abundant reactive oxygen species, and oxygen vacancies. The structural characteristics are conducive to the adsorption, activation, and oxidation of toluene molecules, and thus exhibited excellent toluene catalytic oxidation activity. At the reaction temperature of 140 °C, the toluene oxidation conversion was as high as 99.4 %, and the toluene conversion remained above 96.6 % after experiencing a 690 min stability test.

Optical and magnetic properties of Zn0.9Mn0.05Fe0.05O thin films deposited by RF-magnetron sputtering

Zn0.9Mn0.05Fe0.05O were synthesized by rf-magnetron sputtering in an argon gas environment show a hexagonal wurtzite structure without any secondary phases of dopants MnO or Fe2O3. The crystallite (D) parameters estimated from the XRD pattern disclose a significant decrease with argon partial gas pressure from 3.34 to 11.80 nm. The surface morphology of as-deposited films has a dense columnar microstructure with an average grain size of about 14–18 nm with roughness (RMS) from ∼2.86 to 7.67 nm. The sputtered thin films exhibit high optical transmittance in the visible range with a significant redshift as a function of working pressure. The energy band gap shows a slight increase with gas pressure in the range of about ∼3.05–3.36 eV. The films deposited for argon gas pressures of 12 & 15 mTorr have room-temperature ferromagnetism due to oxygen vacancies/defect concentrations in the host ZnO matrix.

Synthesis of manganese oxide thin films deposited on different substrates via atmospheric pressure-CVD

In this study, we report the synthesis of manganese oxide (MnxOy) thin films on stainless steel, silicon, and borosilicate glass substrates via atmospheric pressure chemical vapor deposition (AP-CVD) using Mn(thd)3 and O3 as precursor and reactive gas, respectively. Deposition was achieved at a low temperature of 300 °C under atmospheric pressure, offering a cost-effective and scalable alternative to traditional high-vacuum CVD methods. The films displayed excellent adhesion and reproducibility, with substrate-dependent variations in film coloration, crystal phases, and morphology. X-ray diffraction (XRD) and Raman spectroscopy confirmed the presence of Mn3O4 and Mn2O3 phases, with Mn3O4 predominating on stainless steel and silicon, while Mn2O3 was more prominent on glass. Scanning electron microscopy (SEM) revealed granular structures with uniform grain sizes, particularly on stainless steel substrates. X-ray photoelectron spectroscopy (XPS) confirmed Mn2+ and Mn3+ oxidation states, consistent with the phase distribution observed by XRD and Raman analysis. This work demonstrates the potential of AP-CVD for scalable manganese oxide thin-film synthesis, particularly for energy storage applications, where Mn3O4 and Mn2O3 can serve as precursors to δ-MnO2 in supercapacitors. The method's simplicity, combined with the high-quality films produced, makes it a promising approach for future research and industrial-scale applications.

Magnetocaloric properties of rare-earth element doped LCMO-Mn3O4 nanocomposites

The study reports the synthesis and magnetocaloric properties of the rare-earth element as Eu3+ doped La1.4Ca1.6Mn2O7-Mn3O4 composites prepared by the one-pot autocombustion technique. Eu3+ co-doping enhanced the Curie temperatures from 181 K for La1.4Ca1.6Mn2O7 (LCMO) to 186 K for La1.3Ca1.6Eu0.1Mn2O7 perovskites, which consequently enhanced the relative cooling power value of the compound. Moreover, these composites were also prepared in the presence of 10 wt% of Mn3O4 nanoparticles. The presence of Mn3O4 at the intervening grain boundaries between La1.4Ca1.6Mn2O7 (A) and La1.3Ca1.6Eu0.1Mn2O7 (B) phases altered the double exchange interaction between Mn3+ and Mn4+ ions. The temperature-dependent field-cooled magnetization curves showed that these nanocomposites’ interfacial magnetic interactions significantly expanded the second-order ferromagnetic-to-paramagnetic phase transition temperature. This further enhanced the magnetic entropy magnitudes |ΔSMax| up to 0.521 J kg−1 k−1 and the associated relative cooling power value to 43.67 J kg−1 under a 5T applied magnetic field. The temperature-averaged entropy change (TEC) values of composites outperformed the individual values of samples A and B between the temperature range of 80–240 K. The fundamental key of this work is to demonstrate the potentiality of enhancing the magnetic phase transition temperature and magnetocaloric effect in the framework of interfacial coupling between LCMO and the Mn3O4 phases of the nanocomposites.

Exploring Gas‐Solid Phase Diagrams: Novel Methods for Oxyfluorination of Mn3O4 and Mn2O3 with Molecular Fluorine

AbstractFluorinated, manganese‐redox cation‐disordered rocksalts are promising candidates for high‐performance cobalt‐free Li‐ion cathode active material. A need for reactive fluorinated precursors was however identified. While manganese oxyfluorides are promising precursor candidates, none stable at room temperature was reported prior to 2023. The key to their recent synthesis by reacting molecular fluorine with MnO was a procedure to continuously scan the temperature axis in search of activation temperatures. In line with this philosophy of continuous exploration of the chemical space, two experimental procedures are reported to scan the stoichiometry axis of a gas‐solid phase diagram in search of transitions and intermediate compounds. Their application to F2 ‐ Mn3O4 and F2 ‐ Mn2O3 phase diagrams resulted in the discovery of two new ranges of stable manganese oxyfluorides of respective compositions MnO1.33‐0.13xFx with x<0.5 and MnO1.5‐0.22xFx with x<1.

Phase–activity relationship of MnO2 nanomaterials in periodate oxidation for organic pollutant degradation

Manganese dioxide (MnO2), renowned for its abundant natural crystal phases, emerges as a leading catalyst candidate for the degradation of pollutants. The relationship between its crystal phase and catalytic activity, particularly for periodate activation, has remained both ambiguous and contentious. This study delineates the influence of various synthetic MnO2 phase structures on their capabilities in catalyzing periodate-assisted pollutant oxidation. Five distinct MnO2 phase structures (α-, β-, γ-, δ-, and ε-MnO₂) were prepared and evaluated to activate periodate and degrade pollutants, following the sequence: α-MnO₂ > γ-MnO₂ > β-MnO₂ > ε-MnO₂ > δ-MnO₂. Through quenching experiments, electron paramagnetic resonance tests, and in situ electrochemical studies, we found an electron transfer-mediated process drive pollutant degradation, facilitated by a highly reactive metastable intermediate complex (MnO₂/PI*). Quantitative structure-activity relationship analysis further indicated that degradation efficiency is strongly associated with both the crystal phase and the Mn (IV) content, highlighting it as a key active site. Moreover, the α-MnO₂ phase demonstrated exceptional recycling stability, enabling an effective pollutant removal in a continuous flow packed-bed reactor for 168 h. Thus, α-MnO₂/PI proved highly effective in mineralizing organic pollutants and reducing their toxicities, highlighting its significant potential for environmental remediation.

Doping Induced Enhancement of Activity and Stability for Oxygen Evolution Reaction with Isomaterially Heterostructured MnO2

A “Non-Native” phase (NNP) differs from the thermodynamically most stable bulk Native in its discrete translational symmetry. The relative difference in surface and bulk energy with respect to the native phase (NP)determines the stability of NNP. The isomaterial hetero-structured NP-NNP composite provides a pathway to assemble structures that have optimal properties of NNP and NP. The surface and sub-surface energies can also be modulated by doping as the dopants may segregate and stabilize grain boundaries. This study demonstrates that the isomaterial heterostructure of the NP, β-N MnO2, and Ramsdellite, r-NN1 MnO2, known as γ-N-NN1-MnO2 intergrowth, enhances the OER activity and stability.The hydrothermal route was used to synthesize isomaterial heterostructured γ/N-NN1-MnO2 with varying concentrations of dopants (10%, 15%, and 20% Ni and Co). X-ray diffraction was used to characterize the material, and after Rietveld refinement, phase quantification revealed that as the dopant concentration increased, the amount of the thermodynamically stable β-N MnO2 phase increased. Planes identified in XRD were also confirmed using high-resolution transmission electron microscopy (HRTEM) and the analysis of selective area electron diffraction (SAED) patterns. It appears that doping was successful based on the shifting of peaks in XRD and differences in unit cell volume and crystallite size calculated using the Debye-Scherrer equation before and after doping. With an increase in dopant concentration and thus improved OER activity, the average oxidation state as determined by X-ray photoelectron spectroscopy followed a downward trend, which is known to improve OER activity. The peaks shifted to lower frequency values as seen by Raman spectroscopy, which implies a weakening of Mn—O bond strength, indicating that dopants Ni and Co may have replaced part of the Mn atoms in the MnO2 intergrowth structure. Scanning electron microscopy (SEM) revealed spherical-shaped nanoparticles with spike-like overgrowths, which were further confirmed by HRTEM. The uniform dispersion of dopants was demonstrated by SEM and energy dispersive spectroscopy (EDS). Elemental quantification of the samples was done using EDS and scanning transmission electron microscopy (STEM). Using HRTEM, the presence of grain boundaries was confirmed.The study of dopants segregating to the grain boundary is conducted through DFT simulations. In many instances, the dopants actively contribute to the OER activity, except for the case of Ni in the NN1 sub-phase of the γ-N-NN1-MnO2 intergrowth, which is apparent by the slightly lower activity of Ni-doped samples compared to Co. This is because Ni remains in the bulk while Co segregates to the surface. A three-electrode setup (Ag/AgCl as the reference electrode, Pt mesh as the counter electrode, and catalyst as the working electrode) was used in 1M KOH to conduct electrochemical experiments. To achieve 10 mA/cm2, the 15% Co-doped electrocatalyst used the least amount of overpotential, 320 mV. According to electrochemical measurements and analysis, the doped samples show low Tafel slope, high specific activity, roughness factor, and charge transfer resistance from electrochemical impedance spectroscopy, all of which suggest improved overall activity for the oxygen evolution process (OER) for the doped over undoped samples. DFT simulations rationalize the enhancement of OER using the Bader charge analysis, the associated Gibbs free energy of the Sabatier principle plotted as the volcano plot.

Biochar assisted synthesis of α-MnO2 nanowires with superior performance for non-radical activation of peroxymonosulfate

Non-radical activation of peroxymonosulfate (PMS) is a promising water treatment technology for removing refractory organics, but its mechanism is still ambiguous and the development of highly efficient catalyst is still a challenge. Herein, α-MnO2 nanowires were synthesized by a hydrothermal method with the assistance of biochar and their performance for PMS activation was studied. The characterization results show that the addition of biochar had little effect on the crystal phase and valence state of MnO2 but significantly reduced the size of nanowires. These nanowires had mesoporous structure, high surface area and oxidation ability, resulting in their superior performance for removing organic pollutants with PMS activation. The degradation of phenol by α-MnO2-PMS followed first order kinetics with an activation energy of 14.82 kJ mol−1. Electron paramagnetic resonance and radical scavenging experiments demonstrated that this activation process followed the non-radical mechanism. The quenching effect of scavengers led to the misleading role of singlet oxygen. In fact, surface activated PMS (MnO2–PMS*) rather than singlet oxygen was the reactive species. Weak acidic condition was conducive for the formation of MnO2–PMS* complexes. This catalyst exhibited good reusability and high activity for removing various organic pollutants, and the common substances in real water had little effect on its performance, suggesting its potential application in wastewater treatment.

Unlocking enhanced new type of safe open system lithium-ion battery performance: Mn3O4 nano-cubes and their sulfur mixers cathode material

In the pursuit of advancing lithium-ion (Li-ion) battery technology towards enhanced safety and performance, we present research study on the synthesis and evaluation of manganese oxide-based cathode materials. Different phases of manganese oxides (Mn3O4 and MnO2), alongside their different ratio of two manganese oxides phases and Mn3O4 with sulfur (S) combination, we employed a simple hydrothermal and solid-state grinding techniques. Characterized by field emission transmission electron microscopy (FE-TEM), our synthesized materials revealed distinct phases of MnO2 and Mn3O4 accompanied by nanorods (NRs) and nanocubes (NCs) morphologies, respectively. We conducted a comprehensive assessment of the Li-ion battery performance of these materials, initially without S, within a new type of safe open system framework. Notably, Mn3O4 NCs (MNCs) developed as important, exhibiting a maximum discharge capacity of 346.03 mAh/g at a constant current discharging rate of 0.5 A/g. We introduced 30 % of S into 70 % of the MNCs matrix to form the MNCSs-73 composite, resulting in rather moderate enhancement in capacity performance. The MNCSs-73 displayed an exposed discharge capacity of approximately 394.8 mAh/g under identical testing conditions. Our findings underscore the exceptional potential of MNCs and MNCSs-73 composites cathode materials for highly suitable for open system novel safe Li-ion battery applications and other energy storage research field.

Chemical synthesis and electrochemical performance of Hausmannite Mn3O4/rGO composites for supercapacitor applications

A simple approach for the preparation of hausmannite Mn3O4/rGO composites for supercapacitor electrodes is reported. The individual Mn3O4 and rGO phases were synthesized by dry ball milling and the modified Hummers method, respectively. Subsequently, composites with different Mn3O4/rGO ratios were prepared by ultrasonic treatment. The physicochemical and electrochemical properties were characterized. In addition, the electrochemical performance of an electrode supercapacitor was tested in two different configurations: a three-electrode cell and a symmetric supercapacitor (SSC). The three-electrode cell showed an excellent specific capacitance of 525 F·g1 at 5 mV·s1. To investigate practical applications, Mn3O4/rGO were used as electrodes to construct symmetric supercapacitors. The composite with a volume ratio of Mn3O4:rGO of 7:3 showed a remarkable stability of 85 % after 5000 charge-discharge cycles. This SSC also delivered an energy density of 6.25 W·h·kg−1 at a power density of 125 W·h·kg−1 with a current density of 0.5 A·g−1, and 5.36 W·h·kg−1 at a power density of 500 W·h·kg−1 and 2 A·g−1.

Crystal phase-driven performance of MnO2 in aqueous phase low-temperature thermal catalysis: Synergistic interactions between Mn3+ and surface lattice oxygen

Catalytic oxidation at mild conditions is crucial for mitigating the high pressure and high temperature challenges associated with current catalytic wet air oxidation (CWAO) technologies in wastewater treatment. Among potential materials for catalytic oxidation reactions, polycrystalline MnO2 existed in natural minerals holds considerable promise. However, the relationships between different crystal phases of MnO2 and their catalytic activity sources in aqueous phase remain uncertain and subject to debate. In this research, we synthesized various MnO2 crystal phases, comprising α-, β-, δ-, γ-, ε-, and λ-MnO2, and assessed their catalytic oxidation efficiency during low-temperature heating for treatment of organic pollutants. Our findings demonstrate that λ-MnO2 exhibits the highest catalytic activity, followed by δ-MnO2, γ-MnO2, α-MnO2, ε-MnO2, and β-MnO2. The variations in catalytic activity among different MnO2 are attributed to variances in their oxygen vacancy abundance and redox activity. Furthermore, we identified the primary active species, which include Mn3+ and superoxide radicals (•O2–) generated by surface lattice oxygen of MnO2. This research highlights the critical role of crystal phases in influencing oxygen vacancy content, redox activity, and overall catalytic performance, providing valuable insights for the rational design of MnO2 catalysts tailored for effective organic pollutant degradation in CWAO applications.

Synergism of carbonaceous additives in engineering of the supercapacitive performance of α-and λ-phases of manganese oxide

Owing to the presence of valence shells for charge transfer, a high theoretical specific capacitance, and variable redox properties, MnO2 appears as a promising agent in the realm of energy storage. Crystallographic structures of manganese oxide (MnO2), a transition metal oxide, play a crucial role in determining its capacitive behavior by controlling the ion intercalation and double-layer formation. In this work, two different phases of MnO2 were synthesized using the facile chemical reduction method and biological method, say α-MnO2 and λ-MnO2. The phases were incorporated with different carbonaceous additives including GO and CNT while maintaining a constant weight ratio of 8:1:1 between active materials (MnO2), additive, and PVDF binder. Among different composites formed, the best electrode performance is demonstrated by λ-MnO2/CNT/PVDF composite with an excellent specific capacitance of 356 F/g at a scan rate of 1 A/g. Moreover, the best-performing electrodes are investigated with a symmetrical two-electrode system yielding a wide potential window of 1.8V with an outstanding power density of 13.5 KW/Kg at 5 A/g and an energy density of 53.78 Wh/Kg at 1A/g having a specific capacitance of 190 F/g.

Green Synthesis of Chlorophyta Seaweed Mediated Mn3O4 Nanoparticles: Electrochemical Applications and Evaluation of Capacitive and Diffusive Contributions

This study focuses on the sustainable synthesis of Mn3O4 nanoparticles using Chlorophyta seaweed extracts for electrochemical capacitor applications. X-ray diffraction (XRD), ultraviolet-visible (UV–Visible) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier-transform infrared (FTIR) spectroscopy were used to evaluate the produced nanoparticles to determine their crystallinity, structure, shape, and elemental composition. The XRD results showed diffraction peaks that correspond to the Hausmannite Mn3O4 phase, with a 24.4 nm-sized average crystallite. The electrochemical properties were examined through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). When compared to a bare Ni electrode, the electrochemical analysis showed a voltammetric response that was 17-fold higher. For the kinetics of the electrochemical reaction, the charge transfer coefficient (αa) and apparent electron transfer rate constant (k s) were determined to be 4.0 s−1 and 0.33, respectively. The diffusion coefficient, as evaluated using the Randles-Sevcik equation, was 1.78 × 10−6 cm2/s. The analysis conducted at various scan rates revealed a diffusive contribution of 90.6% at 5 mV/s and 67.7% at 100 mV/s. In contrast, at a scan rate of 100 mV/s, the capacitive contribution increased from 9.4 to 32.3%. The change in the time for the interaction between ions and electrode material is responsible for the reduction in the diffusive component and the increase in the capacitive component.

Stabilizing high temperature operation and calendar life of LiNi0.5Mn1.5O4

Severe capacity degradation at high operating voltages and poor interphase stability at elevated temperature have thus far precluded the practical application of LiNi0.5Mn1.5O4 (LNMO) as a cathode material for lithium-ion batteries. Addressing these challenges through a combination of experimental and theoretical methods in this work, we demonstrate how a fluorinated carbonate electrolyte enables both high-voltage and high temperature operation by mitigating the traditional interfacial reactions observed in electrolytes with conventional carbonate solvents. Computational studies confirm the exceptional oxidation stability of fluorinated carbonate electrolyte which reduces deprotonation at high voltage. The mitigated deprotonation will then minimize the formation of HF acid which corrodes the LNMO surface and leads to phase transformation and poor interphases. With fluorinated carbonate electrolyte at elevated temperature, it was found on LNMO’s subsurface a reduced amount of Mn3O4 phase which can block Li+ transfer and result in drastic cell failure. Leveraging this approach, LNMO/graphite full cells with a high loading of 3.0 mAh/cm2 achieve excellent cycling stability, retaining ∼84 % of their initial capacity at room temperature (25 °C) after 200 cycles and ∼68 % after 100 cycles at 55 °C. This advanced electrolyte also shows promise for improving calendar life, retaining >30 % more capacity than the carbonate baseline after high temperature storage. These results indicate that electrolytes based on fluorinated carbonates are a promising strategy for overcoming the remaining challenges toward practical commercial application of LNMO.

Phase evolution of nanocrystalline Mn-based oxides screened under different calcination temperatures using different precursors for proficient application in near infrared pigmentation

We examined how different calcination temperatures and precursors affect the formation of Mn-based oxides. The formation of these oxides was influenced by both the temperature (400–––1000 °C) and the type of precursors used (MnCl2·4H2O, MnCO3, MnO2, and KMnO4). When MnCl2·4H2O was calcined at 800 and 1000 °C/3h, we obtained pure tetragonal Mn3O4 phase materials. Calcining MnCO3 at 600 and 1000 °C resulted in cubic Mn2O3 and tetragonal Mn3O4 phase materials, respectively. Heating commercial MnO2 powder at 600 and 800 °C transformed it into cubic Mn2O3 phase materials. At 400 °C, the tetragonal MnO2 phase remained, but at 1000 °C, mixed Mn3O4 and Mn2O3 phases formed. Calcining KMnO4 at 1000 °C/3h led to the formation of δ-MnO2 materials. The morphological features of Mn2O3 and Mn3O4 materials exhibited different sizes and shapes, including nanostone-like, nanorod-like, and nanoflakes morphologies. The thermal analysis revealed significant differences in weight loss and thermal events, including exo and endothermic peaks. The Raman spectra and UV–Vis DRS measurements data support the formation of Mn-based oxides. The highest NIR reflectance for the various synthesized materials of Mn3O4 phase indicates a reflectance of 68 % in the solar region and 91 % in the color pigment region.