Reaction Of Anion Research Articles

DFT Studies of Au(I) Catalysed Reactions: Anion Effects and Reaction Selectivity

AbstractDensity functional theory (DFT) is a powerful tool that can aid in the exploration and development of synthetic chemistry, and its use is often applied in the chemistry of gold(I) catalysis. In this review, we discuss two different facets of these calculations – namely, the exploration and explanation of anion effects, and the regioselectivity and speciation of gold(I)‐catalysed reactions. The research described herein clearly shows the importance of including the anion in DFT studies of Au(I)‐catalysed reactions, especially when using low polarity solvents, or where hydrogen‐bonding is prevalent. Additionally, we show that whilst using DFT to study the selectivity of reactions can be successful, benchmarking the computational results against experimental data is vitally important for ensuring that the model is accurately describing the observed results.

Effect of cooling rate on the structure and electrochemical properties of Mn-based oxyfluorides with cation-disordered rock-salt structure

According to the extensive studies in the field of high-energy cathode materials for lithium-ion batteries (LIBs), Mn-based oxyfluorides Li1.2Mn0.6+0.5yNb0.2–0.5yO2–yFy with Li-excess and cation-disordered rock-salt structure capable of reversible cationic and anionic redox reactions are among the most promising candidates. In this work, a series of Mn-based oxyfluorides with y = 0.05, 0.10, 0.15 were obtained using mechanochemically assisted solid-state synthesis with different cooling rates. Transmission electron microscopy, electron paramagnetic spectroscopy (EPR) and nuclear magnetic resonance spectroscopy (NMR) show that increasing the amount of fluorine promotes local ordering in crystals with the formation of isolated clusters of Mn3+–O2––Mn4+ that interrupt lithium diffusion. The occurrence of local ordering depends on the conditions of synthesis and affects electrochemistry. It was found that more clusters are formed in slowly cooled samples than in quenched ones. The best electrochemical characteristics with reversible capacity of 150 mAh·g–1 at room temperature were demonstrated by the Li1.2Mn0.65Nb0.15O0.90F0.10 sample obtained by quenching.

Anionic Redox Chemistry for Sodium-Ion Batteries: Mechanisms, Advances, and Challenges

The increasing reliance on energy demands has called for continual improvement of sodium-ion batteries (SIBs) due to the abundant Na resources and low cost. Na-based layered transition metal oxides (TMOs) are promising cathode materials due to their unique structural characteristics that provide two-dimensional (2D) ion diffusion channels and maintain structural integrity during the extraction and insertion of Na-ions. However, the energy density of conventional TMO cathodes is mainly limited by cationic redox reactions. Activating anionic redox (O2–/On–) for additional capacity in TMO cathodes is promising to improve the energy density of SIBs, though the chemistry of anionic redox reaction (ARR) is still unclear. This overview focuses on the underlying science, development, and latest advances of ARR in SIBs. The challenges and possible approaches are discussed in light of ARR reversibility and voltage hysteresis. This review will provide insights on improving the energy density of advanced TMOs cathodes with ARR activity.

Intramolecular Tricarbonyl-Ene Reactions and α-Hydroxy-β-Diketone Rearrangements Inspired by the Biosynthesis of Polycyclic Polyprenylated Acylphloroglucinols.

Structurally unique natural products pose biosynthetic puzzles whose solution can inspire new chemical reactions. Herein, we propose a unified biosynthetic pathway towards some complex meroterpenoids—the hyperireflexolides, biyoulactones, hybeanones and hypermonones. This hypothesis led to the discovery of uncatalyzed, intramolecular carbonyl‐ene reactions that are spontaneous at room temperature. We also developed an anionic cascade reaction featuring an α‐hydroxy‐β‐diketone rearrangement and an intramolecular aldol reaction to access four distinct natural product scaffolds from a common intermediate.

Intramolecular Tricarbonyl‐Ene Reactions and α‐Hydroxy‐β‐Diketone Rearrangements Inspired by the Biosynthesis of Polycyclic Polyprenylated Acylphloroglucinols

AbstractStructurally unique natural products pose biosynthetic puzzles whose solution can inspire new chemical reactions. Herein, we propose a unified biosynthetic pathway towards some complex meroterpenoids—the hyperireflexolides, biyoulactones, hybeanones and hypermonones. This hypothesis led to the discovery of uncatalyzed, intramolecular carbonyl‐ene reactions that are spontaneous at room temperature. We also developed an anionic cascade reaction featuring an α‐hydroxy‐β‐diketone rearrangement and an intramolecular aldol reaction to access four distinct natural product scaffolds from a common intermediate.

Gold(III) Complexation in the Presence of the Macropolyhedral Hydridoborate Cluster [B20H18]2−

Gold(III) complexation with the octadecahydrido-eicosaborate anion [B20H18]2− was studied for the first time. It was found that when gold(III) complexes [Au(L)Cl2]BF4 (L = bipy, phen) reacted with [B20H18]2−, complexes [Au(L)Cl2]2[B20H18] were isolated. The compounds consisted of a cationic gold(III) complex [Au(L)Cl2]+ and the hydridoborate cluster as a counterion. X-ray diffraction studies revealed weak B–H...Au interactions for both compounds. Note that more reactive anions [BnHn]2− (n = 10, 12) in similar reactions with gold(III) complexes resulted in gold mirror reactions.

Understanding Hydrogen Bonding Effects on the Reversibility and Redox Potential of Redox Organic Molecules in Deep Eutectic Solvents

Deep eutectic solvent (DES) systems offer unique properties as electrolytes for redox flow batteries. They consist of hydrogen bond donor and acceptor pairs and often offer larger electrochemical windows than traditional aqueous electrolytes with lower vapor pressure than other non-aqueous systems like acetonitrile. They can contain a large concentration of charge carries and have the potential to be high energy density electrolytes1. When paired with redox organic species it is possible to tune both the electrolyte and redox actives to obtain desirable electrochemical properties such as the solubility of active species, kinetic and transport behaviors and even thermodynamic properties such as redox potential2. When attempting to understand these behaviors in DES it becomes important to understand the redox organic molecule’s interaction with the hydrogen bond network. For example, it has been show that altering the ratio of hydrogen bond donor to acceptor sites in a molecule can have dramatic effects on its solubility3. Hydrogen bonding between the DES and the redox organic in its varying charge states can dramatically impact many aspects of the electrochemical behavior.This work focuses on interactions that can have apparent effects on the kinetic and thermodynamic behavior of redox organics. We explore several molecules such as viologen derivatives, PTIO and N-methyl-phthalimide, some of which exhibit reversible behavior in both acetonitrile and a choline chloride and ethylene glycol based DES while other do not. Some see a dramatic shift in redox potential while other do not. We correlate these changes in behavior to influences of hydrogen bonding through the use of IR spectroscopy paired with voltammetry. Red shift in the stretching frequencies of redox active functional groups indicates the presence or lack of hydrogen bonding and this is related to changes in voltammetry as ethylene glycol, a hydrogen bond donor, is added to the redox organic in acetonitrile electrolyte system. It was observed that radical/cation reactions such as PTIO/PTIO+ or viologen were unaffected both kinetically and thermodynamically while reactions involving anionic species such as PTIO-/PTIO or N-methyl-phthalimide would either become irreversible or shift potential. This can be observed for PTIO in the accompanying figure where the cation reaction (more positive couple) does not change while the anion reaction (more negative couple) changes potential dramatically. We propose that some anionic species hydrogen bond more strongly at the redox active sites due to their higher electron density at a hydrogen bond critical point. Electron density has been strongly correlated to hydrogen bond strength4 and molecular modeling is being done to determine the comparative hydrogen bond strength of the anion and cation species as well as reversible and irreversible cationic species. These insights can lead to the intelligent design of highly soluble redox species that remain reversible and make use of the full electrochemical window of a given DES. E. L. Smith, A. P. Abbott and K. S. Ryder, Chem. Rev., 114, 11060–11082 (2014).N. S. Sinclair, D. Poe, R. F. Savinell, E. J. Maginn and J. S. Wainright, J. Electrochem. Soc., 168, 020527 (2021).B. Chen, S. Mitchell, N. Sinclair, J. Wainright, E. Pentzer and B. Gurkan, Mol. Syst. Des. Eng., 5, 1147–1157 (2020).G. Gilli and P. Gilli, J. Mol. Struct., 552, 1–15 (2000). Figure 1

Effect of Heteroatoms Doped Nanoporous Carbon for Aqueous Zinc–Bromine Battery

As interest in renewable energy increases, the importance of batteries that store surplus power is also increasing. However, frequent ignition issues with the lithium-ion secondary battery arose. One of the next-generation batteries, Zinc-Bromine based aqueous flow batteries, are being actively studied based on advantages of high safety and environmental benignity. However, there is an exorbitant price for flow battery due to the use of a membrane, an electrolyte tank, and a pump. In order to eliminate the shortcomings, this research introduced a form of membraneless and flowless systems.In this study, a nanoporous carbon material doped with nitrogen and boron heteroatoms was synthesized and coated on graphite felt. Differences in electrochemical performance were observed when carbon was coated with different slurry compositions (activated carbon: conductive carbon: binder), dopant amount of heteroatoms, and carbon loading mass. Cyclic voltammetry was performed with a three-electrode system to observe the faradaic reaction of active materials according to the potential change. Besides the difference in contact angle for ZnBr2 electrolyte, there are differences in single cell test at 20 mA/cm2 & 2 mAh/cm2 and performance test at 20 mA/cm2 & 24.3 mAh/cm2. These causes can be explained not only by the effect of the different slurry compositions, but also by the interaction of the active material with the coated carbon. Also, the redox reactions of bromine anion during charging process could be a clue for the battery capacity. Cathodic reactions for polybromide [Br2 + Brn – → Brn+2 – , (n=1,3,5...)] can be analyzed by Raman spectroscopy. The peak shift and deconvolution of the Raman data can measure the progress of cathodic reactions. The boron dopants can stabilize the reversibility of faradaic reactions and induce high resistance to strong acid electrolytes (For ZnBr2 electrolyte of 2.0 M or higher, it has a value under the pH 4). Figure 1

(Invited, Digital Presentation) Fundamental Understanding and Challenges in Cathode Materials for Next Generation Li-Ion Batteries

Introducing high-performance Li-ion batteries in current energy storage technologies has great hope in achieving decarbonization goals for sustainable future. The impact of Li-ion batteries in current energy sector is huge, especially portable electronics to electric vehicles. With this energy demand, recently, researchers have been exploring the so-called “Li-rich anion redox” cathode chemistry, in which electrons stored on oxide anions are reversibly utilized during redox reaction along with conventional transition metal redox to obtain high energy storage capability.1-2 Compared to conventional cathodes, the anion redox cathode chemistry is not straightforward as it goes through a complex redox reaction pathway, leading to fundamental issues such as voltage fade, voltage hysteresis and irreversible oxygen release. However, these anionic redox reactions in transition metal oxide-based cathodes attained by extracting excess lithium ions have resulted in stability issues due to weak metal (M) – oxygen(O) ligand covalency.1 In order to increase the tightness between metal–ligand, an alternative strategy was investigated by replacing M–O framework with M–X (X- S, Se) ligands. Based on the experimental studies, it is found that the metal-ligand tunability is the key to achieve highly reversible chalcogen anion redox reactions in various Li based chalcogen cathode materials.3 Further, the lithiation delithiation reactions of cathodes are investigated using in-depth electrochemical analysis and the electronic as well as structural changes during electrochemical reactions are understood using detailed spectroscopy and microscopy characterization. Findings from this research will inspire Ni and Co free chalcogen cathode design and various functional materials in the pursuit of next-generation cathode materials. In parallel, this presentation will also focus on fundamental understanding and importance of fabricating rechargeable high-temperature Li-ion batteries for various demanding applications such as military applications, sensor applications, oil and gas industry drilling applications. In this work, high temperature compatible electrode materials are identified, and their electrode/electrolyte interfacial stability issues at different depth levels are understood using energy tunable X-ray photon electron spectroscopy and further visualized with advanced microscopy imaging. This proof-of-concept study will lead to a new paradigm for transforming ambient temperature Li-ion battery technology to high-temperature applications.

NMR Analysis of Lipid Oxidation in Flaxseed Oil-in-Water Emulsions.

The formation of linolenic (Ln) and linoleic (L) acyl oxidation products during storage of flaxseed oil (FO)-in-water emulsions was monitored using proton nuclear magnetic resonance (1H NMR) spectroscopy, as well as chemical analytical methods and gas chromatography. Emulsions containing 10% FO and 1% Tween 60 were prepared by homogenization and then stored at 37 °C in the dark for 21 days under accelerated oxidation conditions (500 μmol ferrous sulfate). The induction time of the emulsions, after which rapid lipid oxidation was first observed, was 5-7 days, as shown by increases in peroxide values and hydroperoxide concentrations determined by NMR spectroscopy. Analysis of the hexanal and propanal concentrations during storage by HS-SPME-GC indicated that the oxidation of Ln and L acyls in the emulsions occurred simultaneously. The oxidation products originating from the Ln and L acyls were monitored using 1H NMR spectroscopy throughout the oxidation process. These results also showed that the Ln and L acyls oxidized simultaneously, and isomers of hydroperoxy-cyclic hydroperoxides (HCPs), Z,E-conjugated dienic hydroperoxides (ZECDHPs), and E,E-conjugated dienic hydroperoxides (EECDHPs) were the major primary oxidation products. Aldehydes were observed after 7 days, which was taken to be the start of the propagation stage, with the formation of a significant amount of oxygenated α, β-unsaturated aldehydes (OαβUAs). Based on the concentrations of hydroperoxides originating from the Ln and L acyls, our results suggested that the loss rate of L acyls was parallel to that of Ln acyls. This result was consistent with Ln acyls adopting a tighter packing at the oil-water interface in the emulsions than L acyls. This hypothesis was supported by the NMR relaxation time data. A good correlation between the isomer concentrations of ZECDHPs and HCPs in Ln acyls and between ZECDHPs and EECDHPs in L acyls was shown, with the mole ratios between them being 1.2 and 1.1, respectively. Droplet size and microstructure analyses showed that droplet aggregation occurred from 11 days onwards, which was attributed to polar oxidation products located at the oil droplet surfaces promoting coalescence. Zeta-potential measurements indicated that the droplets became more negative during storage, which was attributed to the accumulation of anionic reaction products at the droplet surfaces.

Li‐Rich Mn–Mg Layered Oxide as a Novel Ni‐/Co‐Free Cathode

AbstractAlthough Li2MnO3 exhibits high capacity via anionic oxygen redox, it suffers from rapid capacity decay owing to structural disordering accompanying irreversible Mn migration and O2 release. To promote the reversibility of the anionic redox reaction, Li1.8Mg0.3Mn0.9O3 as a novel cathode material, prepared by partially substituting Li+ and Mn4+ of Li2MnO3 with the redox‐inactive Mg2+ as a structural stabilizer is proposed. Li1.8Mg0.3Mn0.9O3 delivers a high specific capacity and energy density of ≈310 mAh g−1 and ≈915 Wh kg−1, respectively. In particular, the power‐capability and cycle performance of Li1.8Mg0.3Mn0.9O3 greatly surpass those of Li2MnO3. Through first‐principles calculations and various experiments, it is revealed that Mg substitution effectively suppresses the Mn migration by stabilizing Mn cations in the original sites at the charged state. The energetically stabilized layered structure disfavors the distortion of the MnO6 octahedra, which induces the oxygen dimer (OO) formation through the metal–oxygen decoordination, thus mitigating oxygen release.

Capturing dynamic ligand-to-metal charge transfer with a long-lived cationic intermediate for anionic redox.

Reversible anionic redox reactions represent a transformational change for creating advanced high-energy-density positive-electrode materials for lithium-ion batteries. The activation mechanism of these reactions is frequently linked to ligand-to-metal charge transfer (LMCT) processes, which have not been fully validated experimentally due to the lack of suitable model materials. Here we show that the activation of anionic redox in cation-disordered rock-salt Li1.17Ti0.58Ni0.25O2 involves a long-lived intermediate Ni3+/4+ species, which can fully evolve to Ni2+ during relaxation. Combining electrochemical analysis and spectroscopic techniques, we quantitatively identified that the reduction of this Ni3+/4+ species goes through a dynamic LMCT process (Ni3+/4+-O2- → Ni2+-On-). Our findings provide experimental validation of previous theoretical hypotheses and help to rationalize several peculiarities associated with anionic redox, such as cationic-anionic redox inversion and voltage hysteresis. This work also provides additional guidance for designing high-capacity electrodes by screening appropriate cationic species for mediating LMCT.

The hydroperoxyl radical scavenging activity of natural hydroxybenzoic acids in oil and aqueous environments: Insights into the mechanism and kinetics

Foods that contain hydroxybenzoic acid derivatives (HBA) include red fruits, black radish, onion, and potato peel. HBA are widely known for their anti-inflammatory, anti-cancer, and especially antioxidant capabilities; however, a comprehensive study of the mechanism and kinetics of the antiradical action of these compounds has not been performed. Here, we report a study on the mechanisms and kinetics of hydroperoxyl radical scavenging activity of HBA by density functional theory (DFT) calculations. According to the results, HBA exert low HOO• antiradical activity in the nonpolar environment with overall rate constants in the range of koverall = 5.90 × 10−6 − 4.10 × 103 M−1 s−1. However, most HBA exhibit significant HOO• antiradical activity (koverall = 105 − 108 M−1 s−1) by the single electron transfer (SET) reaction of the phenoxide anions in water at physiological pH. The overall rate constant increases with increasing pH values in the majority of the substances studied. At pH ≤ 4, gentisic acid had the best HOO• antiradical activity (log(koverall) = 3.7–4.8), however at pH > 4, the largest HOO• radical scavenging activity (log(koverall) = 4.8–9.8) was almost exclusively found for gallic and syringic acids. Salicylic and 5-sulphosalicylic acids have the lowest antiradical activity across most of the pH range. The activities of the majority of the acids in this study are faster than the reference compound Trolox. Thus, in the aqueous physiological environment, these HBA are good natural antioxidants.

Reversible anionic redox chemistry in layered Li4/7[□1/7Mn6/7]O2 enabled by stable Li–O-vacancy configuration

<h2>Summary</h2> The combination of anionic and cationic activities within Li-rich materials breaks through the traditional capacity limitation and achieves high-energy-density batteries. However, the utilization of anionic oxygen redox reactions always leads to detrimental lattice oxygen release, which accelerates structural distortion and electrochemical performance deterioration. In contrast to the typical Li–O–Li configuration in Li-rich layered oxides, not only can oxygen redox behaviors be triggered within layered Li_4/7[□_1/7Mn_6/7]O₂ (□: Mn vacancy) with Li–O-vacancy configuration, but lattice oxygen loss can be effectively suppressed. Upon Li⁺ (de)intercalations, Mn vacancy within the TM layer also enables reversible structural evolution and Li migration processes, further boosting high output capacity and long-term cycling stability. Besides, not only can the irreversible/reversible anionic/cationic redox reactions be clearly unraveled, but their capacity distributions can be roughly quantified upon cycling. Overall, our findings demonstrate that the introduction of Mn vacancy provides a promising configuration to achieve high-capacity cathode candidates for next-generation Li-ion batteries.

The generation and reactions of sulfenate anions. An update

Sulfenate anions (RSO-) represent the conjugate base of sulfenic acids (RSOH) and are known predominately for their S-nucleophilicity. In the early stages of sulfenate research this often meant the formation of a benzyl or methyl sulfoxide, often to confirm the intermediacy of a sulfenate. Many recent contributions have demonstrated the diversity of functionalization of sulfenates, and those new investigations form the basis of this review. This synopsis begins by describing the predominant methods to generate sulfenates and aspects of their structure. The sections addressing sulfenate reaction chemistry focus on stereoselective S-functionalization chemistry, transition metal catalyzed S–C bond formation (cross-coupling) and bond cleavage, and the discovery of particularly novel reactions and applications. This latter area includes a description of the organocatalytic roles played by sulfenates and some new metal-free sulfenate coupling chemistry. The literature is covered to early 2022.

Capture the missing: formation of (PbBi3)− and {[AuPb5Bi3]2}4− via atom exchange or reorganization of the pseudo‐tetrahedral Zintl anion (Pb2Bi2)2−

Abstract(Pseudo‐)tetrahedral p‐block atom units have been attracting the interest of many scientists, mainly regarding their use as elegant starting materials for compounds with larger molecular or extended architectures. The isoelectronic four‐atomic species that were addressed so far span the range from neutral P4, As4, and AsP3, via the homoatomic Si44− anion and its heavier congeners, to heteroatomic Zintl anions (TrPn3)2− or (Tt2Pn2)2− (Tr = Ga, In, Tl; Tt = Si, Ge, Sn, Pb; Pn = P, As, Sb, Bi). Hence, (Pb2Bi2)2− in the salt [K(crypt‐222)]2(Pb2Bi2)·en (en = ethane‐1,2‐diamine) is isoelectronic and isostructural to white phosphorus, but it exhibits significantly different properties owing to its charge and the different nature of the involved atoms, which affects its stability and reactivity. The recently reported compound [K(crypt‐222)]3[Au{η2‐(Pb2Bi2)}2] (A), isolated from reactions of the binary anion with [AuMePPh3] in en, possesses two intact pseudo‐tetrahedral (Pb2Bi2)2− moieties. In this work, however, the same reaction of [AuMePPh3] with [K(crypt‐222)]2(Pb2Bi2)·en in pyridine instead of en, and subsequent layering with tetrahydrofuran or toluene, yielded two compounds comprising Zintl anions that have not yet been reported to occur in condensed phase. One of them is the (PbBi3)− anion, which crystallizes in the triple salt [K(crypt‐222)]4[(PbBi3)(Pb2Bi2)(AuMe2)]·6py (1). The second is the Pb/Bi moiety in the cluster anion {[AuPb5Bi3]2}4−, which was obtained in the compound [K(crypt‐222)]4{[AuPb5Bi3]2}·2py (2). Density functional theory calculations confirm that the (PbBi3)− monoanion results from an atom exchange reaction whereas {[AuPb5Bi3]2}4− was formed upon more significant reorganization of the reactant (Pb2Bi2)2− in the presence of Au(I) ions. The trimetallic cluster is the yet missing, heaviest homolog of a series of isostructural species. The new compounds were accessed by a careful selection of the solvent mixtures used for crystallization, which demonstrates the importance of a thorough control of the reaction space.Key Points Reactions of (pseudo‐)tetrahedral anions of p‐block (semi‐)metals with transition metal compounds were proven to be a very versatile access of larger multimetallic clusters; we report on the formation and isolation of two predicted, yet so far elusive, species of both types of heterometallic molecules, (PbBi3)− and [(Au2Pb5Bi3)]4−. By means of computational studies applying high‐level density functional theory (DFT) methods, we were able to rationalize the formation of the uncommon anion (PbBi3)−, which is the first monoanionic (pseudo‐)tetrahedral molecule. This study confirms both the need and usefulness of DFT calculations in cluster chemistry. Bi‐ or trimetallic cluster compounds may serve as starting materials for new intermetallic phases or act as reactive species in solution or in the gas phase for bond activation themselves. Hence, the understanding of their formation and access on the one hand, and the expansion of the elemental combinations contribute to reach such goals for materials science.

The gas phase reaction of iridium and iridium carbide anions with 2-hydoxyethylhydrazine (HEH)

Understanding the chemistry of compounds that are similar to hydrazine has two advantages. First, it helps to identify less hazardous propellants to replace hydrazine as the most widely used monopropellant. And second, it helps to gain insight into the reaction mechanism that could be analogous to the decomposition of hydrazine into ammonia and nitrogen. Ionic liquids have already shown to be promising candidates to replace hydrazine. The molecule investigated in this study is 2-hydroxyethlyhydrazine (HOCH2CH2NHNH2; HEH), which is a neutral precursor to the ionic liquid 2-hydroxyethylhydrazinium nitrate (HEHN) and differs from hydrazine by the substitution of a hydrogen with a hydroxyethyl group. Gas phase photoelectron spectroscopy and density functional theory were used to examine the reaction between a HEH molecule and an Ir− anion as well as with IrC−. Suggested by the experimental and theoretical data, Ir− and IrC− react with HEH and can attack the C–N, C–O, N–N, C–H and the C–C bond in HEH.

Entropy and crystal-facet modulation of P2-type layered cathodes for long-lasting sodium-based batteries

P2-type sodium manganese-rich layered oxides are promising cathode candidates for sodium-based batteries because of their appealing cost-effective and capacity features. However, the structural distortion and cationic rearrangement induced by irreversible phase transition and anionic redox reaction at high cell voltage (i.e., >4.0 V) cause sluggish Na-ion kinetics and severe capacity decay. To circumvent these issues, here, we report a strategy to develop P2-type layered cathodes via configurational entropy and ion-diffusion structural tuning. In situ synchrotron X-ray diffraction combined with electrochemical kinetic tests and microstructural characterizations reveal that the entropy-tuned Na0.62Mn0.67Ni0.23Cu0.05Mg0.07Ti0.01O2 (CuMgTi-571) cathode possesses more {010} active facet, improved structural and thermal stability and faster anionic redox kinetics compared to Na0.62Mn0.67Ni0.37O2. When tested in combination with a Na metal anode and a non-aqueous NaClO4-based electrolyte solution in coin cell configuration, the CuMgTi-571-based positive electrode enables an 87% capacity retention after 500 cycles at 120 mA g−1 and about 75% capacity retention after 2000 cycles at 1.2 A g−1.

Effect of lithium doping in P2-Type layered oxide cathodes on the electrochemical performances of Sodium-Ion batteries

Anionic redox reaction offers an effective way to design high-performance cathode materials for sodium-ion batteries. Here to trigger the lattice oxygen redox reaction, the effect of Li doping on the electrochemical performances of P2-type layered oxide cathodes are systematically investigated. Results show that the introduction of Li can not only induce oxygen anions to participate in the charge compensation under high operating voltage, but also suppress the unfavorable P2-O2 transition and facilitate the diffusion of Na+ and electrons during the sodiation/desodiation process. Therefore, Li-doped layered oxide cathodes show improved electrochemical performances with higher reversible capacity, better rate capability, and longer cycling stability. This study may provide a reference point for designing advanced cathode materials through activating the anionic redox reaction.

Tuning anionic redox activity to boost high-performance sodium-storage in low-cost Na0.67Fe0.5Mn0.5O2 cathode

Na-based layered iron-manganese oxide Na0.67Fe0.5Mn0.5O2 containing only low-cost elements is a promising cathode for Na-ion batteries used in large-scale energy storage systems. However, the poor cycle stability restricts its practical application. The capacity decay of Na0.67Fe0.5Mn0.5O2 mainly originates from the irreversible anionic redox reaction charge compensation due to the high-level hybridization between oxygen and iron. Herein, we rationally design a surface Ti doping strategy to tune the anionic redox reaction activity of Na0.67Fe0.5Mn0.5O2 and improve its Na-storage properties. The doped Ti ions not only enlarge the Na migration spacing layer but also improve the structure stability thanks to the strong Ti–O bond. More importantly, the d0-shell electronic structure of Ti4+ can suppress the charge transfer from the oxidized anions to cations, thus reducing the anionic redox reaction activity and enhancing the reversibility of charge compensation. The modified Na0.67Fe0.5Mn0.5O2 cathode shows a reversible capacity of 198 mA h g−1 and an increased capacity retention from 15% to 73% after about 1 month of cycling. Meanwhile, a superior Na-ion diffusion kinetics and rate capability are also observed. This work advances the commercialization process of Na-based layered iron-manganese oxide cathodes; on the other hand, the proposed modification strategy paves the way for the design of high-performance electrode materials relying on anionic redox reactions.