Polyanionic Structure Research Articles

Synergistically Boosting Li Storage Performance of MnWO4 Nanorods Anode via Carbon Coating and Additives

Polyanionic structures, (MO4)n−, can be beneficial to the transport of lithium ions by virtue of the open three-dimensional frame structure. However, an unstable interface suppresses the life of the (MO4)n−-based anode. In this study, MnWO4@C nanorods with dense nanocavities have been synthesized through a hydrothermal route, followed by a chemical deposition method. As a result, the MnWO4@C anode exhibits better cycle and rate performance than MnWO4 as a Li-ion battery; the capacity is maintained at 718 mAh g−1 at 1000 mA g−1 after 400 cycles because the transport of lithium ions and the contribution of pseudo-capacitance are increased. Generally, benefiting from the carbon shell and electrolyte additive (e.g., FEC), the cycle performance of the MnWO4@C electrode is also effectively improved for lithium storage.

Effect of the Polyanion Structure on the Mechanism of Alcohol Oxidation with H2O2 Catalyzed by Zr-Substituted Polyoxotungstates.

Zr-monosubstituted polyoxometalates (Zr-POMs) of the Lindqvist (Bu4N)6[{W5O18Zr(μ-OH)}2] (1), Keggin (Bu4N)8[{PW11O39Zr(μ-OH)}2] (2), and Wells-Dawson (Bu4N)11.3K2.5H0.2[{P2W17O61Zr}2(μ-OH)2] (3) structures catalyze oxidation of alcohols using aqueous hydrogen peroxide as an oxidant. With 1 equiv of H2O2 and 1 mol % of Zr-POM, selectivity toward aldehydes and ketones varied from good to excellent, depending on the alcohol nature. Catalytic activity and attainable substrate conversions strongly depended on the Zr-POM structure and most often decreased in the order 1 > 2 ≫ 3. The reaction mechanism was probed using a test substrate, cyclobutanol, radical and 1O2 scavengers, and kinetic and spectroscopic (attenuated total reflectance-Fourier transform infrared (ATR-FT-IR), 31P NMR and electrospray ionization-mass spectrometry (ESI-MS)) tools. The results point to heterolytic alcohol oxidation in the presence of 1 and 2 and homolytic alcohol oxidation in the presence of 3. Kinetic and spectroscopic studies implicated an oxidation mechanism that involves both alcohol and peroxide binding to 2 followed by an inner-sphere heterolytic H-abstraction from the α-C-H bond by the Zr-hydroperoxo group, leading to a carbonyl compound. The unique capability of 1 to generate 1O2 upon interaction with H2O2 complicates the reaction kinetics and improves the product yield. Spectroscopic studies coupled with stoichiometric experiments unveiled that dimeric monoperoxo {Zr2(μ-η2:η2-O2)} and monomeric hydroperoxo {Zr(η2-OOH)} species accomplish the transformation of alcohols to carbonyl compounds.

Deciphering the Degradation Mechanisms and Realize High-Voltage Stability of A3V2(PO4)3 (A=Li+, Na+) in Aqueous Dual-Ion Batteries.

Polyanionic A3V2(PO4)3 (A=Li+, Na+) with open channels have been extensively utilized as cathode materials for aqueous zinc-metal batteries (AZMBs), whereas suffering from severe capacity fading and rapid operation voltage decay during cycling. when used as In this work, it is disclosed that the rapid degradation is induced by an irreversible phase change from electrochemical active Li3V2(PO4)3 to nonactive monoclinic LiZnPO4, as well as active Na3V2(PO4)3 to nonactive rhombic Zn3(PO4)2(H2O)4. Subsequently, a rational dual-cation (Al-Fe) doping strategy is proposed to suppress these detrimental transformations. Such dual-cation doping entails stronger P-O and V-O bonds, thus stabilizing the initial polyanionic structures. Consequently, the optimized member of Li3V1.775Al0.075Fe0.225(PO4)3 (LVAFP) exhibits desirable cycling stability (1000 cycles, 68.5% capacity retention) and notable rate capability (92.1% of the initial capacity at 10 C). Moreover, the dual-cation doping methodology is successfully extended to improve the stability of Na3V2(PO4)3 cathode in aqueous dual-ion batteries, signifying the versatility and feasibility of this strategy. The comprehensive identification of local structural evolution in these polyanions will broaden the scope of designing high-performance alkali-vanadyl-phosphates for multivalent aqueous batteries.

Sodium Polysulfides As Catholytes for Redox Flow Batteries

Redox flow batteries based on sodium polysulfide (Na2Sx) show promise due to sodium's high solubility in organic solvents (e.g., diglyme. However, when x is lower than 5, sodium polysulfide exhibits low solubility (less than 0.1 molal), limiting the nominal capacity of this redox-active material. Sodium phosphorothioate complexes, Na2P2Sx, have been reported as an alternative to Na2Sx. Incorporating phosphorus into the polysulfide structure improves their solubility in organic solvents, specifically in diglyme.This presentation will describe the synthesis and characterization of sodium phosphorothioate complexes (Na2P2Sx, where x = 6, 7, 8, and 9) for nonaqueous redox flow batteries. The structure of these materials is explored using 31P NMR and 23Na NMR spectroscopy, Raman spectroscopy, and X-ray diffraction analysis. Overall, 31P NMR results indicate that P5+ is tetrahedrally coordinated in all structures and that Na-P-S compounds have a common PS3- moiety. Ongoing efforts are aimed at providing more precise assignments to the 31P bands and correlating these findings with complementary structural information obtained from 23Na NMR and Raman spectroscopy.Electrochemical properties of sodium polysulfide and sodium thiophosphate catholytes, specifically Na2S8 and Na2P2S8, were also compared using CV. The voltammogram of Na2S8 revealed two clear redox reactions in the 1.5-3 V range vs. Na/Na+ due to a multi-step electron transfer process involving the S2-/S0 redox center. In contrast, Na2P2S8 exhibited a larger peak separation (~2 V) and lower peak currents at a given scan rate, potentially indicating a significant activation barrier associated with the rearrangement of the thiophosphate’s polyanionic structure during reduction/oxidation. Despite the substantial voltage hysteresis, Na2P2S8 displayed stable cycling performance, with a slight increase in peak current after 100 cycles. This behavior is consistent with measurements on RFBs containing a Na2P2Sx catholyte, where an electrode activation process increased the cell’s reversible capacity, likely due to subtle changes in the electrode’s surface chemistry during repeated oxidation/reduction. Finally, preliminary flow cell measurements on Na2P2S7 catholyte show reversible voltage profiles after the formation step with deep discharge. Overall, this presentation demonstrates that Na-P-S catholytes represent a promising material for high energy, low-cost redox flow batteries.AcknowledgementsThis research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) and is sponsored by the U.S. Department of Energy through the Energy Storage Program in the Office of Electricity.

Novel NASICON-type Mn0.5Ti2(PO4)3@F-doped carbon composite with high electrochemical performance as anode materials for potassium-ion batteries

Mn0.5Ti2(PO4)3 with a NASICON structural is used as an anode material in potassium-ion batteries due to its abundance of vacancies that can hold potassium ions. This characteristic not only contributes to its excellent stability but also results in a high specific capacity. However, the poor electrical conductivity of the polyanionic type structure limits the material's ability to fully utilize its capacity. In this paper, the conductivity and electrochemical stability of the Mn0.5Ti2(PO4)3 anode material are enhanced through composite formation with an F-doped carbon layer. The introduction of F into the carbon matrix creates a large number of vacancy defects and F active sites. The vacancies enhance the transport of potassium ions on the Mn0.5Ti2(PO4)3 material's surface, while the active sites exhibit strong electronegativity, improving the absorption of potassium ions. Therefore, the diffusion impedance of potassium ions is significantly reduced, leading to an increased diffusion rate of potassium ions. Attributing to the improved reaction kinetics, the Mn0.5Ti2(PO4)3@F-doped carbon composite demonstrates a high specific capacity of 86 mA h g−1 at 10,000 mA g−1 when used as the anode for potassium-ion batteries. Even more, the specific capacity remains a capacity of 136 mA g−1 after 3000 cycles at 1000 mA h g−1. This study enhances our comprehension of material design by investigating the alteration of carbon matrix to promote the electrochemical characteristics of materials.

Construction of a novel heteropoly molybdophosphate/graphitized carbon nitride s-scheme heterostructure with enhanced photocatalytic H2O2 evolution activity

The preparation of hydrogen peroxide using a photochemical energy conversion process is a promising green pathway. Herein, a series of graphite-phase carbon nitride/Polyoxometalate (CN-HMoP) composite photocatalysts were prepared by interlayer coordination and segregation strategies. During the synthesis process, the presence of –NH2 or H ions at the CN terminus makes it display a positive charge, which is capable of attracting HMoP with a polyanionic structure. Subsequently, the N atoms on the triazine ring preferentially coordinate with the Mo ions in HMoP to form Mo-N bonds, and the HMoP nanoparticles are able to be inserted layer by layer into the CN nanosheets by interlayer coordination to make the sheet exfoliation, which contributes to the enhancement of the transmission of photogenerated carriers. Notably, the establishment of the S-Scheme heterostructure facilitates the spatial separation of electron-hole pairs and maintains the strongest redox potential. More importantly, under solar/visible light irradiation, the H2O2 generation rate of CN-HMoP reached 137.1 μmol L-1h−1 and 113.1 μmol L-1h−1, which was 17.7 and 16.8 times higher than pristine CN. Therefore, this work can provide guidance for the synthesis of semiconductor photocatalysts for more efficient and green generation of H2O2.

K3V3(PO4)4/C: A new carbon-coated layered structure cathode material for potassium-ion batteries

The emergence of layered structure materials has positioned itself as a focal point in the progress of potassium-ion battery (KIBs) cathode materials, as it faces challenges concerning cycling-induced structural stability. In this particular investigation, the successful synthesis of a carbon-coated polyanionic layered composite denoted as K3V3(PO4)4/C has been achieved. K3V3(PO4)4/C was subsequently employed as a novel positive electrode material for KIBs. Upon subjecting it to 100 cycles at a current density of 200 mA g−1, the discharge specific capacity exhibited a remarkable value of 37 mAh g−1, thus showcasing a capacity retention of 88%. Impressively, even after undergoing 300 cycles at a high current density of 400 mA g−1, the capacity retention remained constant at 85%. The superior long-term cycling performance and high capacity retention observed in K3V3(PO4)4/C can be attributed to the inherent stability of the polyanionic layered structure and the dual contributions derived from the carbon coating. Furthermore, the application of characterization techniques such as synchrotron X-ray absorption near-edge structure spectroscopy (XANES) revealed a V valence state of + 3 within the synthesized sample. By establishing a structural model for K3V3(PO4)4/C and conducting first-principles calculations on its band structure and density of states, it was confirmed that the material facilitates electron transfer. An investigation into potassium ion migration and diffusion elucidated the involvement of tetrahedral site hopping (TSH). The successful synthesis of K3V3(PO4)4/C material not only provides valuable insights but also serves as a reference for the development of KIBs cathode materials.

K7In4As6 and K3InAs2 ‐ Two more Zintl phases showing the rich variety of In‐As polyanion structures

AbstractBinary phases of triel (Tr) and pentel (Pn) elements (III‐V semiconductors) represent a unique compound class due to their tunable intrinsic band gap in dependency of the element combination. We report here on two new compounds in the ternary system K−In−As. In K3InAs2 the edge‐sharing tetrahedral InAs4 units are connected via opposed edges of the tetrahedra forming linear [InAs2]3− chains and are thus iso(valence)‐ electronic with SiS2. In K7In4As6, the InAs4 tetrahedra are connected via neighboring edges of the tetrahedra forming zig‐zag chains. These chains are linked in two directions through dimeric [As3In−InAs3] units. Both reported Zintl phases extend the number of structures that possess the same In−As ratio. In K3InAs2 a one‐dimensional polyanion in contrast to known Na3InAs2 comprising a three‐dimensional polyanion structure is found. K7In4As6 forms together with the known phases K2In2As3 and K3In2As3 a series of Zintl phases with the ratio In : As=2 : 3. Even though the three phases differ only slightly in their valence electron concentration (VEC) of the polyanion, the VECs have a strong influence on the structures. Syntheses, crystal structures and the electronic band structures are reported. The compounds are discussed in the context of the Zintl concept.

Ultrafast synthesis and pressureless densification of multicomponent nitride and carbonitride ceramics

High-entropy nitride and carbonitride ceramics have received wide attention for their excellent properties such as high hardness, high melting point, and high wear resistance, but the susceptibility of nitrides to decomposition at high sintering temperatures has rendered their densification challenging. In this work, four multicomponent nitrides and five multicomponent carbonitrides (containing five to seven cations) were prepared through ultrafast high-temperature sintering. While only (Cr1/7Zr1/7Nb1/7Hf1/7Ta1/7Ti1/7V1/7)N formed a single phase among the nitrides, all carbonitride systems formed a single-phase high-entropy solid solution with a relative density exceeding 92%. The polyanionic structure of carbonitrides is responsible for their high configurational entropy, which in turn results in their high solid solubility. Although carbonitrides showed higher hardness and modulus than nitrides with the same cations, their fracture toughness was lower. Among carbonitrides with different C/N ratios, the system with a C/N ratio of 5:5 showed the highest solid solubility and best overall mechanical properties.

Electrochemical lithium storage mechanism exploration of a 4.1 V cathode material with high energy/power density and low cost

In this work, cost effective and high energy/power density Na2.4Fe1.8(SO4)3 (NFS) is adopted as cathode material in Lithium ion Batteries (LIBs) for the first time. The carbon coated NFS is synthesized via a simple solid state method under 400 °C. The highly effective multidimensional electron transport path and stable polyanion structure enables extremely high electrochemical lithium storage performance of NFS. The optimized NFS composite displays high specific capacity and discharge voltage (101.2 mAh/g, 3.82 V at 1C), superb rate performance (88.1 mAh/g at 20C with average discharge voltage plateau of 3.46 V vs. Li+/Li) and excellent cycle stability (92.6% of the initial capacity after 1000 cycles at 10C). Electrochemical and non-electrochemical behaviors of NFS cathode in lithium ions contained electrolyte have been thoroughly studied to better understanding the Lithium storage mechanism. This work proves that the low cost Fe-based sulfate NFS is a very competitive candidate as cathode material for LIBs.

Ab initio study of the lattice distortion and the vacancy defects in multi-anion oxycarbonitride ceramics TiCNO and TiZrCNO

Multicomponent ceramics have received much attention due to the tunning physicochemical properties and the huge compositional space, while multicomponent ceramics with the mixing of multi-anion are rarely studied. In this work, the local lattice distortion and vacancy formation energy in TiCNO and TiZrCNO are systematically investigated by density functional theory calculations combining with the special quasi-random structure model. The present results show that multi-anionic mixed oxycarbonitride ceramics exhibit obvious local lattice distortion. The quantified displacive distortions of C, N, and O in TiCNO are relatively large, being in order of C < N < O, although metallic elements Ti has larger distortion than nonmetals. Within incorporative mixing of Zr in cation sublattice, the distortions of Ti, C, N, and O increase evidently, the distortion degree for nonmetal elements is still in order of C < N < O. The distortion of Ti is still the largest, whereas Zr possesses almost the smallest distortion. The electronic structure shows a close association with the degree of distortion, the larger DOS at the Fermi level corresponds to the larger distortion. The vacancy defects are further studied. Our consequences show that the vacancy formation energies of non-metal elements with large local distortions are relatively low, suggesting that the local chemical environment profoundly affects the vacancy formation energy and defect-related properties. The present study reveals the important correlation of lattice distortion with electronic structure and vacancy generation, so it is valuable to deepen the understanding of the excellent properties of multicomponent ceramics with multi-anion mixing, and develop novel multicomponent ceramics with polyanionic structures.

Titanium doping induced the suppression of irreversible phase transformation at high voltage for V-based Phosphate Cathodes of Na-ion Batteries.

Polyanionic material, specifically the NASICON-type material, is considered a promising cathode material for Na-ion batteries (SIBs) because of its stable structure and high operating voltage. Further, it improves the energy density correlated with the well utilization of all Na in the compound. For Na3V2(PO4)2F3(NVPF), the extraction of the third Na, reported as the electrochemical inactivated, can be realized at a high voltage region while forming an irreversible tetragonal phase. In this study, we introduce Ti doping to the Na2VTi(PO4)2F3(NVTPF) material; we reveal that the Ti-doped NVTPF could effectively suppress the irreversible phase transformation, thus successfully harnessing Na in a wide voltage range. Experimental study discloses that the Ti-substituted Na2VTi(PO4)2F3 could take up the Na+ from Amam phase to Cmc21 phase between 1.0 V and 4.8 V reversibly accounting for the 2 Na+ transportation that shows favorable Na+ kinetics and structural stability. Our research provides the strategy to stabilize the polyanion structure upon charging at a high voltage range and inspires the utilization of full sodium in the polyanionic materials, which could be considered as a material design for future conventional applications.

A Novel Polyurethane-Based Polyion Complex Material with Tunable Selectivity against Interferents for Selective Dopamine Determination

Polyion complex (PIC) materials have been widely used in biosensors due to their molecular selectivity. However, achieving both widely controllable molecular selectivity and long-term solution stability with traditional PIC materials has been challenging due to the different molecular structures of polycations (poly-C) and polyanions (poly-A). To address this issue, we propose a novel polyurethane (PU)-based PIC material in which the main chains of both poly-A and poly-C are composed of PU structures. In this study, we electrochemically detect dopamine (DA) as the analyte and L-ascorbic acid (AA) and uric acid (UA) as the interferents to evaluate the selective property of our material. The results show that AA and UA are significantly eliminated, while DA can be detected with a high sensitivity and selectivity. Moreover, we successfully tune the sensitivity and selectivity by changing the poly-A and poly-C ratios and adding nonionic polyurethane. These excellent results were employed in the development of a highly selective DA biosensor with a detection range from 500 nM to 100 μM and a 3.4 μM detection limit. Overall, our novel PIC-modified electrode has the potential to advance biosensing technologies for molecular detection.

Synthesis of Thermoresponsive PNIPAM-Grafted Cellulose Sulfates for Bioactive Multilayers via Layer-by-Layer Technique.

The robust thermoresponsive and bioactive surfaces for tissue engineering by combining poly-N-isopropylacrylamide (PNIPAM) and cellulose sulfate (CS) remain highly in demand but not yet realized. Herein, PNIPAM-grafted cellulose sulfates (PCSs) with diverse degrees of substitution ascribed to sulfate groups (DSS) are synthesized for the first time. Higher sulfated PCS2 generally forms larger aggregates than lower sulfated PCS1 at their cloud point temperatures (TCP) of around 33 °C, whereas PCS1 leads to larger aggregates at body temperature (37 °C). Via the layer-by-layer (LbL) technique, biocompatible polyelectrolyte multilayers (PEMs) composed of PCSs as polyanions in combination with poly-l-lysine (PLL) or quaternized chitosan (QCHI) as polycations were fabricated. The resulting surfaces contained a more intermingled structure of polyanions with both polycations, while higher sulfated cellulose derivatives (CS2 and PCS2) displayed greater stability. Studies on toxicity and biocompatibility of PEM using 3T3 mouse fibroblasts showed a lower cytotoxicity of PEM with PCS2 and CS2 than PCS1 and CS1. Furthermore, the PEM using PCS2 particularly in combination with QCHI demonstrated excellent biocompatibility that is promising for new bioactive, thermoresponsive coatings on biomaterials and substrata for culturing adhesion-dependent cells.

Study of interactions between CFH gene polymorphism and retinal pigment epithelium phenotype in age-related macular degeneration

Annotation. AMD (age-related macular degeneration) is one of the leading causes of blindness in the world, associated with the formation of extracellular deposits called drusen in the macula, i.e. in the central part of the retina. These drusen contain cellular debris and proteins, including components of the complement system, such as the regulator CFH (complement factor H). Complement dysregulation is believed to play a major role in the development of AMD. CFH acts through its ability to recognize polyanionic structures (eg, sulfated GAGs (glycosaminoglycans)) found in host tissues, and thus CFH inactivates any complement system (C3b) that is deposited. Importantly, the common CFH (Y402H) polymorphism was strongly associated with an increased risk of AMD. Recent studies have shown that the disease-associated allotype 402H interacts more poorly (compared to 402Y) with binding sites in the macula (eg, Bruch's membrane), where GAGs (glycosaminoglycans), heparan sulfate, and dermatan sulfate play a major role in mediating the interaction with CFH. Decreased binding of the 402H allotype may lead to complement dysregulation, leading to chronic local inflammation that may contribute to drusen accumulation and thus the initiation, development, and progression of AMD. That is why the goal of our study was to highlight the effect of the rs1061170 polymorphism of the CFH gene on the occurrence and development of age-related macular degeneration and to clarify the intensity of this pathological effect. The study group consisted of 291 people suffering from AMD (89 – with the “dry” form, 97 – with the “wet” form), the comparison group – 105 people without a history of ophthalmic pathology of the corresponding age. Optical coherence tomography (SOCT Copernicus “Optopol”) of the macular area of the retina was used in the study. We used the parameter ILM-RPE (internal limiting membrane-retinal pigmented epithelium). DNA was isolated from the biological material obtained by the buccal scraping method using the Bio-Rad Chelex ® 100 kit. Polymerase chain reaction was used to detect the rs1061170 polymorphism of the CFH gene. Statistical processing of the obtained results was carried out using Statistica 10 (StatSoft, Inc., USA) and SPSS 23.0 programs. The following were used: Hardy-Weinberg equilibrium (Hardy–Weinberg); Kruskal-Wallis test ANOVA by Ranks and Friedman ANOVA and Kendall Coeff. of Concordance; H-criterion; indicators of the odds ratio (OR; Odds Ratio – OR) and 95% probable interval (±95% CI; Confidence limit for means Interval – CI); used the method of analysis of operating characteristic curves (ROC – Receiver Operating Characteristic curve analysis); used special formulas using 2x2 tables. Our results confirm the high prognostic significance of the rs1061170 polymorphism of the CFH gene on the development and progression of AMD in the Ukrainian population. Indicators of specificity and sensitivity of SNP genotypes are ambiguous.

Hydrothermal synthesis of Cs0.3WO3 with uniform morphology and size via a dynamic balance of pH

Nanoscale tungsten bronze, MxWO3 (M: alkali elements or NH4+, 0 < x < 1), is a kind of functional material with a property of near-infrared absorption that is closely related to its morphology and size. A change of pH corresponds to a shift in composition and structure of tungstate polyanion, along with the resultant mutations in the morphology and size related with the properties of nano-MxWO3. Consequently, a reversible imine reaction was conducted to create a dynamic balance of pH system, in where uniform CsxWO3 was expected to synthesize in this study. The results show that an initial nucleation stage, morphology directing of CH3CH2COO−, and Oswald ripening work synergistically to evolve both morphology and size of Cs0.3WO3. Under a moderate pH level, chemical reaction inhibits growth of Cs0.3WO3 nuclei and gains uniform particles. Under a higher pH, Oswald ripening following the nucleating period ultimately dominates uniform Cs0.3WO3.

Effect of thermal treatment on K3PW12O40 for cyclohexene oxidation reaction to adipic acid

The use of heteropolysalts in the cyclohexene oxidation reaction has shown good results, but there is still a significant solubility of this catalyst in the aqueous phase of the reaction medium which is not discussed in most articles dealing with this subject. A thermal treatment, such as calcination step, can significantly affect the properties of a catalyst, including its solubility, sedimentation and acidity. These effects are very important in batch reaction processes and frequently neglected. Thus, the main objective of this work was to study the effect of different calcination temperatures (200 and 600 °C) on the solubility and the acidity of Keggin-type catalysts (K3PW12O40). In addition, the effect of reaction temperature (65, 75 and 85 °C) on the conversion and distribution of products in the oxidation of cyclohexene with these two catalysts was analyzed. The heteropolysalts were characterized using XRD, Raman spectroscopy, N2 physisorption, SEM-EDS, acid-base titration and NH3-TPD. XRD and Raman results showed that the catalysts synthesis was carried out successfully and the thermal treatments did not affect the polyanion structures, even at the highest temperature (600 °C). When compared to the catalyst treated at 600 °C, the KPW-200 catalyst showed greater solubility in the reaction medium. However, it achieved 100% conversion and the highest yield of adipic acid (89%) at 75 °C, in addition to the highest density of acid sites. Tests were performed using the aqueous phase of the post-reaction solution to evaluate the occurrence of homogeneous catalysis under the same conditions. The results showed that, despite the solubilization of the catalyst, there was no adipic acid formation, only of intermediate compounds. Thus, the contribution of homogeneous catalysis in the synthesis of adipic acid is discarded, and the acidity of the catalyst seems to be the determining parameter in the formation of this product. Acidity can influence both the oxidation and hydrolysis steps present in the reaction mechanism and can justify these results.

Optimization of VOSO4@C cathode materials with CNT and GO for lithium-ion batteries

VOSO 4 is a promising cathode material for lithium-ion batteries owing to its polyanionic structure and the polyvalency of vanadium. In this study, carbon nanotubes (CNTs) and graphene oxide (GO) were adopted for modifying the microstructure and improving the overall performance of VOSO 4 . Before the chemical synthesis of VOSO 4 , the CNTs were firstly combined with precursor and CNT-VOSO 4 @C was formed via a one-step chemical synthesis. The results showed that CNTs could improve the charge–discharge performance of the VOSO 4 @C. The initial discharge specific capacity of CNT-VOSO 4 @C was up to 151.6 mAh·g −1 at 0.05 C, and even at 1 C the capacity could reach 66.06 mAh·g −1 . The discharge–capacity retention rate is 100% after a long circulation. Secondly, CNTs and GO were composited with the synthesized VOSO 4 @C and the obtained composites VOSO 4 @C-CNT and VOSO 4 @C-GO exhibited good electrochemical properties with initial discharge specific capacities of 135.7 and 141.8 mAh·g −1 at 0.05 C, respectively. This may be attributed to the high specific surface areas and conductivities of CNTs and GO. When grinding the composites, CNTs and GO are uniformly distributed among the particles, forming bridges between the particles, that can increase the electrical conductivity between the particles and reduce the volume expansion of electrode materials. CNT-VOSO 4 @C exhibits the best modification effect. This study proposes a feasible approach for applying VOSO 4 in lithium-ion batteries, particularly under weak currents. • CNT and GO act as bridges between the VOSO 4 @C particles. • CNT-VOSO 4 @C has the best initial discharge capacity and capacity retention rate. • This work provides a feasible approach for applying VOSO 4 in lithium-ion battery, especially at weak currents.

Kasha's Rule and Koopmans' Correlations for Electron Tunnelling through Repulsive Coulomb Barriers in a Polyanion.

The long-range electronic structure of polyanions is defined by the repulsive Coulomb barrier (RCB). Excited states can decay by resonant electron tunnelling through RCBs, but such decay has not been observed for electronically excited states other than the first excited state, suggesting a Kasha-type rule for resonant electron tunnelling. Using action spectroscopy, photoelectron imaging, and computational chemistry, we show that the fluorescein dianion, Fl2–, partially decays through electron tunnelling from the S2 excited state, thus demonstrating anti-Kasha behavior, and that resonant electron tunnelling adheres to Koopmans’ correlations, thus disentangling different channels.

Stabilization of Multicationic Redox Chemistry in Polyanionic Cathode by Increasing Entropy.

Polyanionic compounds have large compositional flexibility, which creates a growing interest in exploring the property limits of electrode materials of rechargeable batteries. The realization of multisodium storage in the polyanionic electrodes can significantly improve capacity of the materials, but it often causes irreversible capacity loss and crystal phase evolution, especially under high‐voltage operation, which remain important challenges for their application. Herein, it is shown that the multisodium storage in the polyanionic cathode can be enhanced and stabilized by increasing the entropy of the polyanionic host structure. The obtained polyanionic Na3.4Fe0.4Mn0.4V0.4Cr0.4Ti0.4(PO4)3 cathode exhibits multicationic redox property to achieve high capacity with good reversibility under the high voltage of 4.5 V (vs Na/Na+). Exploring the underlying mechanism through operando characterizations, a stable trigonal phase with reduced volume change during the multisodium storage process is disclosed. Besides, the enhanced performance of the HE material also derives from the synergistic effect of the diverse TM species with suitable molarity. These results reveal the effectiveness of high‐entropy concept in expediting high‐performance polyanionic cathodes discovery.