Charge Compensation Mechanism Research Articles

Self‐reduction and enhanced luminescence in transparent Mn2+‐doped mullite glass‐ceramics derived from EMT‐type zeolite

AbstractMn2+ activated glass‐ceramic (GC) has received tremendous attention in the exploration of luminescent materials for solid‐state lighting due to the high stability, broad red emission, and low toxicity. However, the doped Mn2+ ions still suffer from the oxidation and uncontrollable ions migration during the melting process of conventional preparation techniques, which is detrimental to the luminescence performance. Herein, transparent Mn2+‐doped mullite GCs have been prepared at low temperature (∼850°C) via the spark plasma sintering of EMT‐type zeolite. The GC samples show typical red emission peaking at 620 nm that can be assigned to spin‐forbidden 4T1(G)→6A1(S) transition of Mn2+ located in the octahedral coordination site of the host. Owing to the charge compensation mechanism and produced oxygen vacancies, the self‐reduction of Mn3+ to Mn2+ ions is realized and the oxidization is inhibited. The mullite nanocrystals acted as additional scattering centers introduce Rayleigh scattering to enhance the emission intensity. Moreover, benefitted from the established mullite nanocrystals network, the Mn2+‐doped GCs exhibit improved thermal conductivity up to 1.79 W K−1 m−1 and more excellent mechanical properties than conventional GCs, simultaneously.

Efficient removal of uranium (VI) with a phytic acid-doped polypyrrole/ carbon felt electrode using double potential step technique

In order to efficiently extract uranium from uranium-containing wastewater, a novel acid doped polypyrrole/carbon felt (PA-PPy/CF) electrode was prepared via a facile electrodeposition method. For this material, PA and PPy combined to form a stable chemical structure by a charge compensation mechanism. The electrochemical characterization results showed that PA-PPy can significantly accelerate the electrochemical reduction rate of uranium ions. Moreover, a double potential step technique (DPST) was applied to prevent water splitting and maintained the electrocatalytic reduction activity of the surface groups during the electrochemical adsorption process. The removal efficiency obtained by the DPST method was six times higher than that obtained by the conventional chemical adsorption. When the concentrations of uranyl nitrate were 10, 20, 50, and 100 mg/L, the removal efficiencies of uranium were 98.8%, 98.1%, 94.6%, and 93.7%, and the adsorption capacities of uranium were 164.7, 326.9, 788.5, and 1562.0 mg/g, respectively. This material also showed an excellent recycling performance and remarkable selectivity for uranium ions. This work may shed light on the development of removal system for uranium (VI).

Interfacial charge storage mechanisms of composite electrodes based on poly(ortho-phenylenediamine)/carbon nanotubes via advanced electrogravimetry.

To reach a deeper understanding of the charge storage mechanisms of electrode materials is one of the challenges toward improving their energy storage performance. Herein, we investigate the interfacial ion exchange of a composite electrode made of carbon nanotube/poly(ortho-phenylenediamine) (CNT/PoPD) in a 1M NaCl aqueous electrolyte via advanced electrogravimetric analyses based on electrochemical quartz crystal microbalance (EQCM). Classical EQCM at different scan rates of the potential revealed the complex electrogravimetric behavior likely due to multi-species participation at different temporal scales. Thereafter, in order to better understand the behavior of each species (ions, counter ions, and co-ions) in the charge compensation mechanism, the electrogravimetric impedance spectroscopy analysis (also called ac-electrogravimetry) was pursued. Ac-electrogravimetry revealed the role of each species where Na+ cations and Cl- anions as well as protons participate in the charge compensation mechanism of the CNT/PoPD composite with different kinetics and proportions. The water molecules with opposite flux direction with the cations are also detected, suggesting their exclusion during cationic species transfer. Having analyzed ac-electrogravimetry responses in depth, the synergistic interaction between the CNT and PoPD is highlighted, revealing the improved accessibility of species to new sites in the composite.

High dielectric permittivity and dielectric relaxation behavior in a Y2/3Cu3Ti4O12 ceramic prepared by a modified Sol−Gel route

In this work, Y2/3Cu3Ti4O12 ceramics were fabricated via a modified sol−gel route. Structural, dielectric, and electrical parameters were systematically investigated. The XRD results indicate that a CaCu3Ti4O12 phase (JCPDS No. 75–2188) is present in every sintered sample. SEM images of Y2/3Cu3Ti4O12 ceramics disclose a fine-grained ceramic microstructure. Interestingly, high dielectric permittivity, ∼6600–7600, with loss tangents of ∼0.918–1.086 were achieved in the sintered Y2/3Cu3Ti4O12 samples. Density functional theory (DFT) calculations were used to investigate the most stable structure of the Y2/3Cu3Ti4O12 ceramics. Our DFT results reveal that two calcium vacancies (VCa) are isolated from each other. We also determined the lowest energy configuration of an oxygen vacancy (VO) in the Y2/3Cu3Ti4O12 ceramics occurred during the sintering process. We found that the VO is trapped close to the Y atom in this structure. Both computational and experimental studies specify that the oxygen vacancy is located close to the Y atom in the Y2/3Cu3Ti4O12 lattice and it might be a bivalent oxygen vacancy. As a result, due to charge balance, charge compensation of the transition ions, i.e., Cu and Ti ions, might take place. The charge compensation mechanisms in the Y2/3Cu3Ti4O12 lattice were verified using an XPS technique. Impedance spectroscopy confirms the presence of an inhomogeneous microstructure consisting of semiconducting grains and insulating grain boundaries in the sintered Y2/3Cu3Ti4O12 ceramics. This electrical result is consistent with the computational analysis, showing that a charge compensation mechanism might be involved in generation of the grains' semiconductive region due to the presence of a VO. Consequently, high dielectric permittivity in Y2/3Cu3Ti4O12 may have originated from an internal barrier layer capacitor (IBLC) effect.

Elucidation of the redox activity of Ca2MnO3.5 and CaV2O4 in calcium batteries using operando XRD: charge compensation mechanism and reversibility

Ca2MnO3.5 and CaV2O4 were found to be potentially interesting as positive electrode materials for calcium metal-based high-energy density batteries with DFT-predicted average voltages of 3.7 V and 2.5 V and energy barriers for Ca migration of 1.1 eV and 0.6 eV, respectively. Both compounds were prepared by solid state reaction under reducing atmospheres. Optimum conditions to achieve Ca2MnO3.5 comprised the reduction of Ca2MnO4 under NH3 gas at 420⁰C with a flow rate of 1200 ml/min while CaV2O4 was achieved by reduction of CaV2O6 at 700 ⁰C under H2 flow. Electrochemical oxidation of Ca2MnO3.5 in lithium or calcium cells resulted in the formation of an orthorhombic phase with cell parameter (a= 5.2891(1), b= 10.551(2), c= 12.1422(1)). Operando synchrotron radiation diffraction experiments indicate that the charge compensation mechanism is not related to Ca2+ extraction but to intercalation of F− (originated from electrolyte salt decomposition) into the anion vacancy position, as confirmed by EELS and EDS. This process was found to be irreversible. In the case of CaV2O4, oxidation induces the electrochemical extraction of calcium with the formation of an orthorhombic phase (space group Pbnm) with cell parameters a = 10.72008(9) Å, b = 9.20213(2) Å and c = 2.89418(3) Å. The process was also investigated via operando synchrotron radiation diffraction, with the oxidized phase being found to reintercalate Ca2+ ions upon reduction, with the formation of a solid solution. Preliminary cycling tests reveals a decrease in the polarization after the first cycle and call for further investigation of this system.

Cationic Vacancies in Anatase (TiO2): Synthesis, Defect Characterization, and Ion-Intercalation Properties.

As one of the most studied materials, research on titanium dioxide (TiO2) has flourished over the years owing to technological interest ranging from energy conversion and storage to medical implants and sensors, to name a few. Within this scope, the development of synthesis routes enabling the stabilization of reactive surface structure has been frequently investigated. Among these routes, solution-based synthesis has been utilized to tailor the material's properties spanning its atomic structural arrangement, or morphological aspects. One of the most investigated methods of stabilizing crystals with tailored facets relies on the use of fluoride-based precursors. Fluoride ions not only provide a driving force for the stabilization of metastable/reactive surface structures but also alter the reactivity of titanium molecular precursors and in turn the structural features of the stabilized crystals. Here, we review recent progress in the solution-based synthesis of anatase (one of the polymorphs of TiO2) employing a fluoride precursor, with an emphasis on how cationic vacancies are stabilized by a charge-compensating mechanism and the resulting structural features associated with these defects. Finally, we will discuss the ion-intercalation properties of these sites with respect to lithium and polyvalent ions such as Mg2+ and Al3+. We will discuss in more detail the relevant parameters of the synthesis that allow controlling the phase composition with the coexistence of oxide, fluoride, and hydroxide ions within the anatase framework. The mechanism of formation of defective anatase nanocrystals has highlighted a solid-state transformation mostly implying an oxolation reaction (the condensation of hydroxide ions) that results in a decrease in the vacancy content, which can be synthetically controlled. The investigation of local fluorine environments probed by solid-state 19F NMR revealed up to three coordination modes with different numbers of coordinated Ti4+ and vacancies. It further revealed the occurrence of single and adjacent pairs of vacancies. These different host sites including native interstitial (and single/paired vacancies) display different ion-intercalation properties. We notably discussed the influence of the local anionic environments of vacancies on the thermodynamics of intercalation properties. The selective intercalation of polyvalent cations such as Mg2+ and Al3+ further supports the beneficial uses of defect chemistry for developing post-lithium-ion batteries. It is expected that the ability to characterize the local structure of defects is key to the design of unique, tailored-made materials.

Charge compensation mechanisms of BaTiO3 ceramics co-doped with La2O3 and Bi2O3

Doping modification is commonly used to improve the electrical properties of BaTiO 3 (BT). In this study, the ((1- x )BT- x (Bi 2 O 3 –La 2 O 3 )) ceramics were synthesised to investigate the charge balance compensation mechanisms of BT ceramics co-doped with La 2 O 3 and Bi 2 O 3 as donors at A-site. The XRD results showed that a pseudo-cubic phase was formed by intruding dopants. The Raman spectroscopy revealed that the samples, which x = 0.10 and 0.16, had relatively more oxygen and titanium vacancies. After heat-treatment the samples in oxygen atmosphere, the dielectric constant of the sample with x = 0.10 was higher than that of the untreated, but for x = 0.16, it was almost no changed. These results indicated that the different charge balance compensation mechanism was exist in the samples with x = 0.10 and 0.16. Impedance measurements showed that the resistance tendency exhibited initial decrease and subsequent increase, leading to the electronic and ionic compensation mechanisms with x = 0.10 and 0.16, respectively. Ferroelectric properties also implied charge balance compensation mechanism transition, due to P s and P r were higher for x = 0.10 than for x = 0.16, respectively. This work provides a new strategy for modulating the electric properties of BT-based ceramics.

Anionic Redox Activities Boosted by Aluminum Doping in Layered Sodium-Ion Battery Electrode.

Sodium-ion batteries (SIBs) have attracted widespread attention for large-scale energy storage, but one major drawback, i.e., the limited capacity of cathode materials, impedes their practical applications. Oxygen redox reactions in layered oxide cathodes are proven to contribute additionally high specific capacity, while such cathodes often suffer from irreversible structural transitions, causing serious capacity fading and voltage decay upon cycling, and the formation process of the oxidized oxygen species remains elusive. Herein, a series of Al-doped P2-type Na0.6 Ni0.3 Mn0.7 O2 cathode materials for SIBs are reported and the corresponding charge compensation mechanisms are investigated qualitatively and quantitatively. The combined analyses reveal that Al doping boosts the reversible oxygen redox reactions through the reductive coupling reactions between orphaned O 2p states in NaOAl local configurations and Ni4+ ions, as directly evidenced by X-ray absorption fine structure results. Additionally, Al doping also induces an increased interlayer spacing and inhibits the unfavorable P2 to O2 phase transition upon desodiation/sodiation, which is common in P2-type Mn-based cathode materials, leading to the great improvement in capacity retention and rate capability. This work provides deeper insights into the development of structurally stable and high-capacity layered cathode materials for SIBs with anion-cation synergetic contributions.

Reactive flash sintering and electrical transport properties of high‐entropy (MgCoNiCuZn)1‐xLixO oxides

AbstractIn this paper, high‐entropy (MgCoNiCuZn)1‐xLixO oxides (x = 0, 0.1, 0.15, 0.2, and 0.3) were synthesized via reactive flash sintering (RFS), and the effect of RFS process on the microstructure and electrical property of the materials were studied. The Li‐doped materials exhibited a mixed ionic–electronic transport behavior. The oxidation of Co2+ into Co3+ upon Li incorporation into the materials synthesized via the conventional solid‐state reaction route was not evidenced in the flash sintered materials. Instead, the charge unbalance in the Li‐doped materials synthesized via RFS was compensated by oxygen vacancies and holes in the valence band of the oxides, which were accounted for the ionic conduction and electronic conduction, respectively. The ionic conductivity increased upon increasing the Li concentration as more oxygen vacancies were formed. The attraction between defects with different charges (LiM/ and VO••), which formed defect complexes, led to a decrease in the mobility of the defects, thus resulting in a less pronounced increase in the ionic conductivity at high Li concentrations. The change in the charge compensation mechanism of the materials indicates that the microstructure of such kind of oxides could be altered through RFS, and thus the property may be manipulated.

Unraveling the State of Charge-Dependent Electronic and Ionic Structure–Property Relationships in NCM622 Cells by Multiscale Characterization

LiNi0.6Co0.2Mn0.2O2 (NCM622) undergoes crystallographic and electronic changes when charging and discharging, which drive the cathode material close to or even beyond its stability window. To unravel the charge compensation mechanism of NCM622, spatially resolved atomic force microscopy (AFM) measurements in electrochemical strain microscopy (ESM) and conductive AFM (C-AFM) modes are obtained, and the spectroscopic information and crystallographic information are compared. All experiments are performed with two sets of samples: state-of-the-art samples that are composed of a binder, a conductive additive, and an active material and polished samples for single-particle analysis. Near-edge X-ray absorption fine structure spectroscopy shows that ionic Ni2+ reacts to give Ni3+ when charging and forms covalent bonds with its oxygen neighbors. A Ni2+/Ni3+ gradient across the particles balances out with the increasing state of charge, as verified by ESM. Therefore, the results also provide an important view that improves the mechanistic understanding of ESM in electrode materials. Finally, the interplay between the electronic and ionic conductivities and the crystallinities of NCM622 cathodes is elaborated and discussed.

Influence of Ti Substitution on Electrochemical Performance and Evolution of LiMn1.5−x Ni0.5TixO4 (x = 0.05, 0.1, 0.3) as a High Voltage Cathode Material with a Very Long Cycle Life

The high voltage spinel material LiMn1.5Ni0.5O4 (LMNO) has the potential to increase the energy density of lithium batteries. However, its battery performance suffers from poor long-term cycling and high-temperature stability. In order to overcome these limitations, we have studied the effect of partial substitution of Mn with Ti and LiMn1.5−x Ni0.5TixO4 (x = 0.05, 0.1, 0.3), LMNTO, materials have been synthesized in a newly modified sol-gel method and then characterized by TEM, SEM (EDX), AC Electrochemical Impedance Spectroscopy and Soft X-ray Spectromicroscopy. We have demonstrated that the long-term cycling limitation with these types of materials can be resolved and herein 2000 cycles at a high C-rate have been demonstrated in half cells. We have attributed this behavior to a possible charge compensation mechanism as evidenced by a Soft X-ray Spectromicroscopy study of delithiated LMNTO materials. This work takes high energy density batteries based on high voltage spinel material one step further towards commercialization, and it is believed that further improvement can be achieved using new electrolyte formulations.

Structural change and charge compensation mechanism for Li1+x(Fe0.1Ni0.1Mn0.8)1-xO2 (0 < x

Samples containing 10% Fe- and Ni-substituted Li2MnO3 calcined in air and N2 were prepared and characterized. The sample calcined in N2 atmosphere exhibited higher initial capacities than the sample calcined in air. X-ray and electron diffraction data showed that calcining in N2 suppressed the formation of cubic spinel at the end of charging. The 57Fe Mössbauer spectra showed that the sample calcined in N2 effectively utilizes Fe3+ ions as a redox center. The Mn L-edge and Mn K-edge XANES spectra of the same sample showed that it underwent partial reduction to the trivalent state during discharging. The Ni K-edge XANES spectra indicated that oxidation or reduction did not occur. The O K-edge XANES spectra revealed the irreversible reaction of the oxide ion as a redox center. The development of a more practical synthetic process resulted in both samples showing promise as high-capacity materials for the positive electrode.

Multi-dimensional correlation of layered Li-rich Mn-based cathode materials

Lithium-rich manganese-based cathode materials are expected to promote the commercialization of lithium-ion batteries to a new stage by virtue of their ultrahigh specific capacity and energy density advantages. However, they are still restricted by complex phase transitions and electrochemical performance degradation caused by labile anion charge compensation. A deep understanding of the electrochemical properties contained in their intrinsic structures and the key driving factors of structural deterioration during cycling are crucial to guide the preparation and optimization of lithium-rich materials. Considering recent progress, this review introduces the intrinsic properties of Li-rich manganese-based cathode materials from interatomic interactions to particle morphology at multiple scales in the spatial dimension. The charge compensation mechanism and energy band reorganization of the initial charge and discharge, the structural evolution during cycling and the electrochemical reaction kinetics of the materials are analyzed in the temporal dimension. Based on the relationship between structure and electrochemical performance, preparation methods and modification methods are introduced to guide and design cathode materials. Effective characterization methods for studying anion charge compensation behavior are also demonstrated. This review provides important guidance and suggestions for making full use of the high specific capacity in these materials derived from anion redox and the maintaining of its stability.

Revealing the different effects of VIB transition metals X (X = Cr, Mo, W) on the electrochemical performance of Li-rich cathode Li2MnO3 by first-principles calculations.

Transition metal (TM) doping is widely applied to optimize the electrochemical performance of Li2MnO3, a promising cathode material of next-generation Li-ion batteries. The effect of doping on the performance of Li2MnO3 can vary with the elemental period of the doped TM. However, the rules of the different effects have not been well summarized, especially for TM elements within the same group. In this work, the effects of TM element (Cr, Mo, and W in group VIB) dilute doping on the electrochemical performance of Li2MnO3 are investigated through first-principles calculations. The results show that Mo and W can induce more obvious local lattice distortion. Although Cr, Mo and W doping can improve the electrochemical activity of Li2MnO3, they modify the charge compensation mechanism in different ways. At the initial stage of delithiation, both Cr and O undergo significant oxidation, and Mo can act as the main oxidation center, while W can trigger the electrochemical activity of Mn around it. The O ions around Mo and W are more stable during the delithiation due to the mild oxidation and the strong bonding of Mo-O and W-O. Furthermore, Cr, Mo and W dilute doping can promote the interlayer diffusion of Li at the initial charging state, which is gradually enhanced with the increase of the period of the doped elements, but Mo and W doping would hinder the intralayer diffusion of Li near the doping sites during further delithiation process. Our results highlight the difference in the effects of TM (in the same group) doping on the performance of Li2MnO3 and would facilitate fast and good design of Li-rich cathodes.

Reaction Mechanism of Li2MnO3 Electrodes in an All-Solid-State Thin-Film Battery Analyzed by Operando Hard X-ray Photoelectron Spectroscopy.

Li2MnO3 is a promising cathode candidate for Li-ion batteries because of its high discharge capacity; however, its reaction mechanism during cycling has not been sufficiently explicated. Observations of Mn and O binding energy shifts in operando hard X-ray photoelectron spectroscopy measurements enabled us to determine the charge-compensation mechanism of Li2MnO3. The O 1s peak splits at an early stage during the first charge, and the concentration of lower-valence O changes reversibly with cycling, indicating the formation of a low-valence O species that intrinsically participates in the redox reaction. The O 1s peak-splitting behavior, which indicates the number of valences of O in Li2MnO3, is supported by the computational results for an O3 to O1 structural transition. This is in agreement with the results of our previous study, wherein we confirmed this O3 to O1 transition based on in situ surface X-ray diffraction analysis, X-ray photoelectron spectroscopy, and first-principles formation energy calculations.

Structure design enables stable anionic and cationic redox chemistry in a T2-type Li-excess layered oxide cathode

Coupled with anionic and cationic redox chemistry, Li-rich/excess cathode materials are prospective high-energy-density candidates for the next-generation Li-ion batteries. However, irreversible lattice oxygen loss would exacerbate irreversible transition metal migration, resulting in a drastic voltage decay and capacity degeneration. Herein, a metastable layered Li-excess cathode material, T2-type Li0.72[Li0.12Ni0.36Mn0.52]O2, was developed, in which both oxygen stacking arrangement and Li coordination environment fundamentally differ from that in conventional O3-type layered structures. By means of the reversible Li migration processes and structural evolutions, not only can voltage decay be effectively restrained, but also excellent capacity retention can be achieved upon long-term cycling. Moreover, irreversible/reversible anionic/cationic redox activities have been well assigned and quantified by various in/ex-situ spectroscopic techniques, further clarifying the charge compensation mechanism associated with (de)lithiation. These findings of the novel T2 structure with the enhanced anionic redox stability will provide a new scope for the development of high-energy-density Li-rich cathode materials.

Design a rare-earth free broadband NIR phosphor and improve the photoluminescence intensity by alkali charge compensation

Near-infrared (NIR) phosphors, promising non-destructive measurement materials for food, have attracted extensive attention worldwide. Herein, we designed a low-cost rare-earth free Mg2B2O5:Cr3+ phosphor. Under the excitation of 450 nm, the Mg2B2O5:Cr3+ phosphors show a broadband near-infrared emission at 800 nm, for 4T2 (4F) → 4A2 transition. The optimal concentration of Cr3+ was about 0.003 and a higher concentration will lead to concentration quenching owing to dipole-dipole interaction. Moreover, considering the unequal substitution of Mg2+ by Cr3+, charge compensation had been applied to improve the photoluminescence. The mechanism of alkali charge compensation and its effect on polyhedron distortion had been illustrated. The relationship between decay lifetime and charge compensation had been discussed. Finally, the activation energy for thermal quenching of as-prepared samples was calculated. The increasing polyhedron distortion result in worse thermal stability, which was explained by the configurational coordinate model. The above results are helpful in the development of low-cost near-infrared phosphors and the enhancement of photoluminescence intensity.

Enhancement of photoluminescence of Cd0.95Eu0.05SiO3 phosphor using Na+ and K+ as charge compensators

Despite its high photoluminescence (PL) performance, cadmium silicate (CdSiO 3 ) as a luminescence host has not been comprehensively studied. In this article, we present a simple solution combustion method for the synthesis of Na + and K + co-doped Cd 0.95 Eu 0.05 SiO 3 phosphor. The influence of charge compensators such as Na + and K + on the luminescence performance of Cd 0.95 Eu 0.05 SiO 3 was systematically investigated. X-ray diffraction results confirms that Cd 0.95 Eu 0.05 SiO 3 :Na + and Cd 0.95 Eu 0.05 SiO 3 : K + phosphors are in monoclinic phase and found to increase in the crystallinity as concentration of Na + and K + increases. Scanning electron microscope images exhibit agglomerated particles having nanoscale dimension. PL excitation spectra of Cd 0.95 Eu 0.05 SiO 3 , Cd 0.95 Eu 0.05 SiO 3 :Na + and Cd 0.95 Eu 0.05 SiO 3 :K + phosphors exhibit excitation peaks in the ultra-violet (UV), near-UV and far-UV regions. Very interestingly, the intensity of PL emission was found to increase with increase in the Na + and K + concentrations. The optimum co-dopant concentrations were found to be 7 mol% for both phosphors. The emission intensity of 613 nm peak was enhanced by a factor of 1.78 and 1.66 with Na + and K + co-doping respectively. The enhancement in PL emission has been explained by the mechanism of charge compensation and phosphor crystallinity. The PL results confirms that these phosphors could be potential materials for optoelectronic applications.

Dynamic structural evolution and controllable redox potential for abnormal high-voltage sodium layered oxide cathodes

Developing high-voltage cathode materials for sodium-ion batteries (SIBs) is both challenging and extremely urgent. Here, we report an abnormal high-voltage Na 2/3 Ni 1/3 Sn 2/3 O 2 cathode material with a P2-structure stoichiometric composition and an O3-type layered phase. Using a classic P2-type layered oxide cathode Na 2/3 Ni 1/3 Mn 2/3 O 2 as a model system, we demonstrate the accurate manipulation of orbital hybridization between transition metal and oxygen atoms to regulate the redox potential through engineering the chemical composition and corresponding electronic structure. Meanwhile, an in-depth systematic investigation of dynamic structural evolution during the formation process and highly reversible O3–P3 phase transition as well as charge compensation mechanism throughout Na + intercalation/deintercalation process is clearly demonstrated through various in situ techniques. Overall, this study not only reveals intrinsic chemical and structural properties, adjustable electrochemical behavior, and dynamic evolution process, but also explores an orbital-level understanding of controllable redox potential for high-voltage SIBs. • Abnormal cathode has P2 stoichiometric composition with O3 layered phase • Dynamic structural evolution and controllable redox potential • Accurate manipulation of orbital hybridization is demonstrated • Orbital-level understanding for high-voltage sodium oxide cathode Zhu et al. construct a high-voltage O3-type Na 2/3 Ni 1/3 Sn 2/3 O 2 cathode through accurate regulation of orbital hybridization between transition metal and oxygen atoms based on the P2-type Na 2/3 Ni 1/3 Mn 2/3 O 2 as a proof-of-concept material. A systematic investigation of the dynamic phase transitions and orbital-level understanding for high-voltage SIBs is presented.

Realizing continuous cation order-to-disorder tuning in a class of high-energy spinel-type Li-ion cathodes

<h2>Summary</h2> Conventional Li-ion cathode materials are dominated by well-ordered structures, in which Li and transition metals occupy distinct crystallographic sites. We show in this paper that profoundly new degrees of freedom for the optimization of electrochemical properties may be accessed if controllable cation disorder is introduced. In a class of high-capacity spinel-type cathode materials, we identify cation to anion ratio in synthesis as a key parameter for tuning the structure continuously from a well-ordered spinel, through a partially ordered spinel, to rocksalt. We find that the varying degree of cation disorder modifies the voltage profile, rate capability, and charge-compensation mechanism in a rational and predictable way. Our results indicate that spinel-type order is most beneficial for achieving high-rate performance as long as the cooperative 8a to 16c phase transition is suppressed, while more rocksalt-like disorder facilitates O redox, which can increase capacity. Our findings reveal an important tuning handle for achieving high energy and power in the vast space of partially ordered cathode materials.