O2 Material Research Articles

Effect of increasing alkali layer spacing on the performance of O3-NaNi1/3Fe1/3Mn1/3O2 cathode materials

O3-Na1-xCax/2Ni1/3Fe1/3Mn1/3O2 (NaCNFMx, x=0, 0.05, 0.1, 0.15) was prepared by doping calcium ions and replacing the sodium sites in the NaNi1/3Fe1/3Mn1/3O2 (NaNFM) material using ball milling spray. XRD, SEM and XPS results demonstrated that the calcium element was successfully embedded in the lattice. The electrochemical performance of NaCNFM0.1 is the best when the doping amount of calcium ion is 0.1. The sodium diffusion coefficient of NaCNFM0.1 cathode material after 3 cycles is 1.67×10-14 cm2/s. The first specific discharge capacity at 1C is 121.1mAh/g. Even at the high current density of 5C, the 200cycles capacity of 103.6mAh/g is much higher than NaNFM's 95.2mAh/g, and the capacity retention rate is as high as 91.5%. Ex-situ XRD and SEM analyses manifested that the moderate amount of calcium doping improved the stability of the layered structure. These results show that the cathode material has great application potential.

The Effect of Nickel Addition on α-Fe2O3 Synthesis Using NaOH and Application as Lithium-Ion Battery Anode Material

Research has been conducted in the pursuit of developing the performance of batteries. The increasing demand for electronic devices and electric vehicles has driven the development of high-performance lithium-ion batteries (LIBs). Among the various anode materials, α-Fe2O3 has attracted significant attention due to its high theoretical specific capacity of 1007 mAh/g. However, its low conductivity and poor rate capability limit its practical application. To address these issues, this study investigates the addition of nickel (Ni) into α-Fe2O3 through a co-precipitation method. The synthesized materials were characterized using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and Scanning Electron Microscopy with Energy-Dispersive X-ray spectroscopy (SEM-EDX). The electrochemical performance was evaluated using an LCR meter and charge-discharge cycling. The results showed the addition of Ni improved the conductivity of the α-Fe2O3 material. The optimal Ni content was found as much as 18×10-4 mol which exhibits the highest conductivity and specific capacity. The synthesized α-Fe1.965Ni0.035O3 material demonstrated a specific charging capacity of 1.8433 mAh/g and a specific discharging capacity of 1.8388 mAh/g. These findings suggest that Ni-doped α-Fe2O3 has the potential to be a promising anode material for high-performance lithium-ion batteries (LIBs).

Mitigating Mechanical Stress by the Hierarchical Crystalline Domain for High-Energy P2/O3 Biphasic Cathode Materials.

Sodium-ion batteries (SIBs) have captured widespread attention for grid-scale energy storage owing to the wide distribution and low cost of sodium resources. Delivery of high energy density with stable retention remains a challenge in developing cathode candidates for rechargeable SIBs. Inspired by the concept of "cationic potential", here, we present a hierarchical crystalline domain in hexagonal particles with target chemical composition (Na0.8Li0.03Mg0.05Ni0.28Fe0.05Mn0.54Ti0.05O2) from the inner bulk O3 phase (71.1 wt %) to the outer P2-type shell (28.9 wt %) of the structure. Benefiting from the mitigated mechanical stress of the predominant bulk O3 phase under the protection of the surficial P2 crystalline domain at the microscale during Na+ (de)intercalation, the brittle fracture, plastic yielding, and structural damage of the bulk O3 phase are effectively prohibited during battery cycling, thereby achieving good structural integrity. As a consequence, the biphasic P2/O3-Na0.8Li0.03Mg0.05Ni0.28Fe0.05Mn0.54Ti0.05O2 material exhibits satisfactory electrochemical properties, with a high energy density of 506 Wh kg-1 and good capacity retention of 85.5% over 200 cycles. This work highlights the importance of tailoring the crystalline domain to mitigate the reaction-induced stress and particle fracture of layered biphasic cathode materials for high-energy SIBs.

Enhancing electrochemical performance of high-entropy Co/Ni-free P2/O3 hybrid-phase layered metal oxide cathode for sodium-ion batteries

Sodium-ion batteries (SIBs) have currently garnered increasing attention due to their promising applications and potential advantages. Despite the cost and performance advantages, the Co/Ni-free Fe-Mn-based cathode materials tends to undergo a large phase transition in the sodium (de)intercalation layer, which will result in the material structure damage. In this work, high entropy P2/O3-Na0.75Cu0.1Fe0.2Mg0.2Mn0.4Ti0.1O2 (NCFMMT) materials were successfully prepared by employing NaTi2(PO4)3 (NTP) as the modification layer. It can be distinctly seen that the cyclic stability of NCFMMT@NTP has been significantly improved, and the first capacity at 0.2C reaches 165.32 mAh/g and the capacity can maintain 86.73 % after 100 cycles. Moreover, the voltage hysteresis after triggering anionic redox can be clearly ameliorated. Apparently, the high-entropy strategy not only can satisfactorily optimize the lattice structure and stability of the cathode material during sodium intercalation/de-intercalation process, but also can increase the ion mobilization rate and promote further electrochemical properties. Therefore, this study provides valuable exploration for the design and preparation of cobalt/nickel-free cathodes with excellent electrochemical performance.

Enhanced Performance of Sodium-Ion Battery Cathodes with Ti and V Co-Doped P2-Type Na0.67Fe0.5Mn0.5O2 Materials

Enhanced Performance of Sodium-Ion Battery Cathodes with Ti and V Co-Doped P2-Type Na0.67Fe0.5Mn0.5O2 Materials

New Insights into Anionic Redox in P2-Type Oxide Cathodes for Sodium-Ion Batteries.

Manganese/nickel-based layered transition metal oxides have caught the attention of studies as promising cathodes for sodium-ion batteries (SIBs). It is reported that utilizing both cationic and anionic redox reactions is a promising method for higher energy density cathodes. However, the anionic redox reaction comes at the expense of irreversible oxygen release. Hence, a Li-Mg cosubstituted P2-Na0.67Li0.07Mg0.07Ni0.28Mn0.58O2 material with a honeycomb-ordered superstructure was designed. The Ni3+/Ni4+ redox couple and the anionic redox reaction are proven to have a competitive relationship. Density functional theory calculations reveal the effect of O 2p nonbonding states from Li and prove that Mg-O bonds can stabilize the Ni-O eg states. In situ electrochemical impedance spectroscopy measurements and galvanostatic charging/discharging derived dV/dQ, representing resistance changes with time, are obtained to reveal the mechanism of the anionic redox reaction. This study presents the effect and mechanism of the O 2p nonbonding state and Mg-O bonds of manganese/nickel-based layered oxides.

Enhanced cyclability and energy density of mid-nickel layered oxide cathode material LiNi0.55Mn0.25Co0.20O2 by niobium doping via solvothermal method

Ni-based layered oxide materials are among the most promising cathode materials for the next generation of lithium-ion batteries due to their higher energy capacity. However, capacity decay occurs due to degradation mechanisms that reduce the electrochemical performance of this type of material. This work aims to synthesize Nb-doped LiNi0.55Mn0.25Co0.20O2 (Nb-NCM) materials via the solvothermal method to enhance the cyclability and energy density of the layered oxide cathode. The effects of Nb doping on the microstructure and the electrochemical performance of the cathodes are investigated. The introduction of the contents of Nb expands the structural lattice parameters and decreases the Li+/Ni2+ cation mixing degree of the NCM cathode. Furthermore, the Nb doping enhances the electrochemical activity of LiNi0.55Mn0.25Co0.20O2, increasing its initial discharge capacity to 169.61 mAhg−1 when 1% of Nb was used as a dopant (1%Nb-NCM) in contrast to the capacity of 149.45 mAhg−1 presented by the pristine material. The modified 1.0%Nb-NCM material also exhibits remarkable cycling performance with a capacity retention of 92.7% after 100 cycles at the rate of 1 C (2.8–4.3 V). This work suggests a rational strategy for high-performance cathode for lithium-ion batteries, proposing the extension of Nb doping to enhance Ni-mid material's cyclability.

Stabilizing the Layer-Structured Oxide Cathode by Modulating the Oxygen Redox Activity for Sodium Ion Batteries.

The layer-structured oxide cathode for sodium-ion batteries has attracted a widespread attention due to the unique redox properties and the anionic redox activity providing additional capacity. Nevertheless, such excessive oxygen redox reactions will lead to irreversible oxygen release, resulting in a rapid deterioration of the cycling stability. Herein, sulfur ion is successfully introduced to the O3-NaNi0.3Mn0.5Cu0.1Ti0.05W0.05O2 material through high-temperature quenching, thereby developing a novel Na2S-modified O3/P2-NaNi0.3Mn0.5Cu0.1Ti0.05W0.05O2 composite with extended cycling life. The S2- is analyzed for the ability to enhance the reversibility of oxidation-reduction reactions under high voltage and suppress the loss of lattice oxygen during cycling. The stable S─O covalent bonds are found to inhibit the oxygen generation and release within the structure. Benefiting from these improvements, the Na₂S-modified O3/P2-NaNi0.3Mn0.5Cu0.1Ti0.05W0.05O2 exhibited a high reversible capacity of 173.1mA h g-1 over a wide voltage range of 1.5-4.3V under test conditions at 0.1 C and 81.5% capacity retention after 120 cycles at 1 C. The Na₂S-modified O3/P2-NaNi0.3Mn0.5Cu0.1Ti0.05W0.05O2 demonstrates the excellent rate capability with the reversible capacities of 173.1,137.0,114.7,96.7, and 80.1mA h g-1 at 0.1, 0.2, 0.5, 1, and 2 C.

Exploring the structural, morphology, optical and magnetic properties of ZnCoxMn(2-x)O4 prepared using hydrothermal method

Here we report the structural and physical property of ZnCoxMn(2-x)O4 (x = 0, 0.1 and 0.2) materials. The hierarchical ZnCoxMn2-xO4 (x = 0, 0.1 and 0.2) have been successfully synthesized by hydrothermal method. The surface of the ZnCoxMn(2-x)O4 varies according to its composition which is investigated. The absorption and band gap of the material were measured by UV-Vis diffuse reflectance spectroscopy (DRS) in the range of 200 – 800 nm. It was observed that the band gap gets decreased from the parent compound. The room temperature photoluminescence emission spectra of ZnCoxMn(2-x)O4 (x = 0,0.1 and 0.2) has been investigated. The magnetic property of material shows an antiferromagnetic nature. Further, X-ray photoelectron spectroscopy analysis confirms the substitution of Co on Mn site.

Improved ferroelectricity and endurance in Ca doped Hf0.5Zr0.5O2 films

Doped Hf0.5Zr0.5O2 materials have drawn increasing attention due to the excellent ferroelectric properties, but the relevant research is just in the preliminary stage and the reported doped systems are rare. In this work, Ca doped Hf0.5Zr0.5O2 (Ca:HZO) ferroelectric films were successfully fabricated via chemical solution deposition and investigated for the first time. It is observed that Ca doping induces a phase transformation from monoclinic to orthorhombic/tetragonal and then to monoclinic/tetragonal. The highest orthorhombic phase fraction is achieved in 2.5 mol% Ca doped HZO film, contributing to the optimum ferroelectric property with the largest remnant polarization of 14.00 μC/cm2 after 105 cycles. Additionally, the leakage current density is observed to decrease with increasing Ca content, which is mainly associated with the changes of grain size and surface roughness. As a result, the endurance is significantly improved in the Ca doped films, and an excellent endurance of 1010 cycles is achieved in the 2.5 mol% Ca doped film. These results suggest that Ca doping can enhance the ferroelectric and endurance properties of HZO films by optimizing the phase and morphological structure.

LaCo0.95Mo0.05O3/CeO2 composite can promote the effective activation of peroxymonosulfate via Co3+/Co2+ cycle and realize the efficient degradation of hydroxychloroquine sulfate

Hydroxychloroquine sulfate (HCQ) is extensively utilized due to its numerous therapeutic effects. Because of its properties of high solubility, persistence, bioaccumulation, and biotoxicity, HCQ can potentially affect water bodies and human health. In this study, the LaCo0.95Mo0.05O3-CeO2 material was successfully prepared by the sol–gel process, and it was applied to the experiment of degrading HCQ by activating peroxymonosulfate (PMS). The results of characterization analysis showed that LaCo0.95Mo0.05O3-CeO2 material had good stability, and the problem of particle agglomeration had been solved to some extent. Compared with LaCo0.95Mo0.05O3 material, it had a larger specific surface area and more oxygen vacancies, which was helpful to improve the catalytic activity for PMS. Under optimal conditions, the LaCo0.95Mo0.05O3-CeO2/PMS system degraded 95.5 % of HCQ in 10 min. The singlet oxygen, superoxide radicals, and sulfate radicals were the main radicals for HCQ degradation. The addition of Mo6+/Mo4+ and Ce4+/Ce3+ promoted the redox cycle of Co3+/Co2+ and enhanced the degradation rate of HCQ. Based on density functional theory and experimental analysis, three HCQ degradation pathways were proposed. The analysis of T.E.S.T software showed that the toxicity of HCQ was obviously reduced after degradation. The LaCo0.95Mo0.05O3-CeO2/PMS system displayed excellent reusability and the ability to remove pollutants in a wide range of real-world aqueous environments, with the ability to treat a wide range of pharmaceutical wastewater. In summary, this study provides some ideas for developing heterogeneous catalysts for advanced oxidation systems and provide an efficient, simple, and low-cost method for treating pharmaceutical wastewater that has good practical application potential.

Balancing intrinsic properties of cathode materials allows high performance for protonic ceramic fuel cells

AbstractThe cathode performance significantly impacts the overall performance of protonic ceramic fuel cells (PCFCs). Many properties of the material, such as oxygen vacancies, protonation, charge carrier transport abilities, and surface oxygen reduction reaction activity, can affect cathode performance. However, which parameter has more weight is still being debated. In this work, we use Ba0.5Sr0.5Zr0.25Fe0.65X0.1O3 as a case study (X = Zn, Cu, Mn, Ni, and Co). First‐principle calculations and experimental research are used to study and compare the critical parameters that determine cathode performance. It is discovered that no dopant can improve all the properties of the material. Balancing distinct intrinsic properties is a viable and rational approach. The more balanced, the better performance. When compared to other dopants, nickel dopant is shown to be the most effective in the Ba0.5Sr0.5Zr0.25Fe0.65X0.1O3 material system, allowing a high fuel cell performances of 1862, 1450, and 1085 mW cm−2 at 700°C, 650°C, and 600°C, with a low polarization resistance of 0.041 Ω cm2 at 700°C, which is higher than the majority of cobalt‐free cathodes for PCFCs. The current study not only presents a promising cathode candidate, but more importantly, also an effective and fundamental methodology to design cathodes for PCFCs.

Optical, magnetic and electrical properties of new binary MnTiO3-modified Ba(Zr,Ti)O3 materials as solid solution

The complex binary MnTiO3-modified lead-free ferroelectric Ba(Zr0.2Ti0.8)O3 materials were successfully fabricated using a simple wet chemical method. X-ray diffraction and Raman scattering spectral studies revealed that Mn cations were randomly distributed within the host lattice, reducing the optical band gap energy from 3.16 eV (pure Ba(Zr0.2Ti0.8)O3) to 2.43 eV (9 mol.% MnTiO3). The magnetic properties of Ba(Zr0.2Ti0.8)O3 compounds varied with MnTiO3 addition, transitioning from weak-ferromagnetism to typical ferromagnetism and further exhibiting antiferromagnetic-like and/or paramagnetic-like behavior. The maximum magnetic moment was obtained at around 19.4 memu/g, along with a coercive field and remanent magnetization of 92 Oe and 0.6 memu/g, respectively. Additionally, nonlinear polarization with a maximum electrical polarization of 3.11 μC/cm2 remained at 9 mol.% MnTiO3-modified Ba(Zr0.2Ti0.8)O3 compounds. We expected that the observed both ferromagnetism and nonlinear polarization in MnTiO3-modified Ba(Zr0.2Ti0.8)O3 compounds at room temperature would facilitate their use in smart electronic devices.

Ti-Substituted O3-NaNi0.5Mn0.3Ti0.2O2 Material with a Disordered Transition Metal Layer and a Stable Structure.

O3-type NaNi0.5Mn0.5O2 (NNM) is very competitive for sodium-ion batteries (SIBs) due to its high capacity and easy production. Nevertheless, the intricate phase transitions during the charging-discharging significantly impede its practical application. This paper proposes a strategy for successfully synthesizing NaNi0.5Mn0.3Ti0.2O2 (NNMT) by combining coprecipitation and a high-temperature solid-state method. This method introduces Ti elements while retaining the electrochemically active Ni2+ content, thus, the NNMT has a high initial specific capacity of 151.4 mAh g-1 at 1 C. It is demonstrated that introducing Ti4+ leads to the transition metal layers becoming disordered by ex situ XRD, thus mitigating the irreversible phase transition of the material. In addition, Ti4+ does not have an outer electron, which can reduce electron delocalization in the transition metal layer and improve the material's cyclic stability. The NNMT possesses a capacity retention rate of 60.66% after 150 cycles, much higher than the initial NNM's 18.96%. It also exhibits an excellent discharge capacity of 86.8 mAh g-1 at 5 C. In conclusion, the cycling and rate performance of the Ti-substituted NNMT are greatly improved without capacity loss, which offers innovative concepts for the modification means of the SIBs layered oxide cathode materials.

Achieving ultra-low voltage fading in Co-free Li-rich layered oxides via effortless surface defect engineering

Cobalt (Co)-free lithium (Li)-rich layered oxides (LLOs) have emerged as promising cathode materials for the next generation of Li-ion batteries, attributed to their competitive market positioning and high energy density. Nevertheless, challenges arise from surface oxygen loss due to irreversible anionic redox reactions, leading to severe voltage and capacity decay that hinder the large-scale adoption of LLOs. Herein, we present an innovative, facile, and environmentally friendly hydrothermal approach to induce surface reconstruction of Li1.2Mn0.6Ni0.2O2 material. A multifaceted combination involving the spinel phase, oxygen vacancies, and reduced manganese is orchestrated to alleviate the irreversible oxygen redox and impressively enhance Li-ion diffusion. The modified sample, owing to this surface transition, demonstrates low-strain and low-distortion properties along with a substantial improvement in structural stability, supported by both experimental validations and theoretical studies. As a result, the engineered sample exhibits exceptional capacity retention of 97.12% after 150 cycles at 1C, with an ultra-low voltage decay (0.91 mV cycle−1). Additionally, noteworthy enhancements in initial coulombic efficiency and rate performance are also observed. This straightforward surface defect engineering method offers a pathway to developing “low-strain” LLOs with superior electrochemical performance, thereby laying a solid foundation for future commercial applications.

Understanding Surface Degradation Mechanisms in Ni-Rich Cathodes for Li-Ion Batteries

High Ni-rich layered cathodes, such as; LiNi0.8Co0.15Al0.05O2 (NCA) and LiNi0.8Mn0.1Co0.1O2 (NMC811) materials, offer very high capacity and excellent rate capability fulfilling the pressing priorities. However, the cyclic performance is poor compared to other cathodes with lower Ni content. Due to high surface reactivity, first-cycle irreversibility is quite high in all these Ni-rich cathodes. Such surface reactions lead to different electrochemically inactive phases and reduce cyclic performance. Herein, we report a comprehensive analysis of plane selective cathode and electrolyte interface reactions and link the relationship between the formation of different cathode-electrolyte interphase (CEI) by-products with surface reconstruction mechanisms. Moreover, we established a guiding principle of coating strategy to enhance plane selective surface properties. Both bulk and thin-film Ni-rich NMC811 electrodes were used to investigate the surface properties. We fabricated epitaxial thin films of Ni-rich NMC811 cathodes of different orientations, such as; (104), (018), and (003). Al2O3 was chosen as a model coating material to understand how it modulates surface properties. The surface by-products depend highly on the surface charge and subsequently change with Al2O3 coating. Likewise, the surface reconstruction depends on these crystallographic planes and the coating layer exposed to the electrolyte. Keywords: NMC811; Thin film; Epitaxial; CEI; Surface reconstruction

Unexpected Elevated Working Voltage by Na+/Vacancy Ordering and Stabilized Sodium-Ion Storage by Transition-Metal Honeycomb Ordering.

Na+/vacancy ordering in sodium-ion layered oxide cathodes is widely believed to deteriorate the structural stability and retard the Na+ diffusion kinetics, but its unexplored potential advantages remain elusive. Herein, we prepared a P2-Na0.8Cu0.22Li0.08Mn0.67O2 (NCLMO-12 h) material featuring moderate Na+/vacancy and transition-metal (TM) honeycomb orderings. The appropriate Na+/vacancy ordering significantly enhances the operating voltage and the TM honeycomb ordering effectively strengthens the layered framework. Compared with the disordered material, the well-balanced dual-ordering NCLMO-12 h cathode affords a boosted working voltage from 2.85 to 3.51 V, a remarkable ~20 % enhancement in energy density, and a superior cycling stability (capacity retention of 86.5 % after 500 cycles). The solid-solution reaction with a nearly "zero-strain" character, the charge compensation mechanisms, and the reversible inter-layer Li migration upon sodiation/desodiation are unraveled by systematic in situ/ex situ characterizations. This study breaks the stereotype surrounding Na+/vacancy ordering and provides a new avenue for developing high-energy and long-durability sodium layered oxide cathodes.

Unexpected Elevated Working Voltage by Na+/Vacancy Ordering and Stabilized Sodium‐Ion Storage by Transition‐Metal Honeycomb Ordering

AbstractNa+/vacancy ordering in sodium‐ion layered oxide cathodes is widely believed to deteriorate the structural stability and retard the Na+ diffusion kinetics, but its unexplored potential advantages remain elusive. Herein, we prepared a P2‐Na0.8Cu0.22Li0.08Mn0.67O2 (NCLMO‐12 h) material featuring moderate Na+/vacancy and transition‐metal (TM) honeycomb orderings. The appropriate Na+/vacancy ordering significantly enhances the operating voltage and the TM honeycomb ordering effectively strengthens the layered framework. Compared with the disordered material, the well‐balanced dual‐ordering NCLMO‐12 h cathode affords a boosted working voltage from 2.85 to 3.51 V, a remarkable ~20 % enhancement in energy density, and a superior cycling stability (capacity retention of 86.5 % after 500 cycles). The solid‐solution reaction with a nearly “zero‐strain” character, the charge compensation mechanisms, and the reversible inter‐layer Li migration upon sodiation/desodiation are unraveled by systematic in situ/ex situ characterizations. This study breaks the stereotype surrounding Na+/vacancy ordering and provides a new avenue for developing high‐energy and long‐durability sodium layered oxide cathodes.

New 1D Nickel-Rich Ncm Cathode Materials for the Lithium-Ion Battery: Synthesis and Cyclic Stability Improvement

Lithium-ion batteries (LIBs) are considered the most promising energy system due to their low cost, high energy density, excellent performance, and long service life, implemented in several consumer devices such as cell phones, laptops, cameras, and electric vehicles [1]. In general, the chemical properties of LIA are constantly evolving, and from the point of view of cathode materials, layered LiMO2 oxides, in which M is a combination of Ni, Mn, and Co – the so-called NCM are attracting more and more attention and is considered a potential next-generation cathode material for LIA, due to their increased specific capacity (more than 150 mAh g-1) and thermal stability [2]. In addition, NCM-based cathodes can outperform the popular lithium-iron-phosphate LiFePO4 (LFP) cathodes in many areas, especially in terms of operating voltage, in which LFP-based LIBs can produce voltages below 3.4 V and suffer from high self-discharge rates. The composition of Ni, Mn, and Co can be significantly changed to optimize the capacity, performance, structural stability, and cost of lithium-ion batteries [3]. The data indicate that the B-doped NCM811 cathodes offer notable benefits, including higher capacity retention, improved rate capability, and lower mechanical strain in their charged state [4].In this study, we focus on synthesizing 1D LiNi0.8Co0.1Mn0.1O2 (NCM811) material by electrospinning method and its enhancement upon doping with Boron and morphological modifications. The electrospinning technique has already been used to obtain NCM material [5]. B-doped and undoped NCM811 nanofibers with the 1D structure were obtained by electrospinning method and characterized. The morphology and nanofiber structure of the resulting NCM811 samples (doped, un-doped) were studied using scanning electron microscope (SEM) and transmission electron microscope (TEM). X-ray phase analysis (XRD) studied the samples, and a series of peaks that entirely corresponded to the diffraction pattern of NCM811 were recorded. It is highly expected that the results may introduce some new ideas in the field of morphology modification and doping, which will be helpful for the rational design and manufacture of highly efficient cathode materials. Acknowledgments This research was funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP19679855).

Unraveling the Role of Li and Mg Substitution in Layered Sodium Oxide Cathodes for Sodium-Ion Batteries.

Substituting electrochemically active elements such as Li and Mg in P2-type layered sodium oxide is an effective strategy for developing competitive cathode materials for sodium-ion batteries. However, the lack of atomic-level understanding regarding the distribution of substitution positions complicates the comprehension of the roles of substituting atoms and the mechanism of sodium-ion intercalation. In this study, we identified the stable configurations of Na in Na0.75Ni0.3Mn0.7O2 and Na0.75Li0.15Mg0.05Ni0.1Mn0.7O2 materials using the site exclusion method. Through simulating the complete charging process for both materials, the structure evolution of the cathodes during the cycling and the impact of the partial substitution of Ni elements by Li and Mg atoms were comprehensively elucidated. Our findings revealed that Mg atoms effectively regulate the distribution of forces within the materials, essentially serving as supportive pillars within the cathode. Meanwhile, Li atoms efficiently mitigated electron localization, consequently diminishing volume fluctuations during the charging process. More importantly, the substitution with Li and Mg atoms could synergistically reduce the interaction between transition metals and sodium ions, thereby reducing the diffusion energy barrier of Na ions. This study not only enhances the comprehension of substituted metal atoms in P2 layered oxides but also offers new insights for the development of sodium-ion cathode materials.