Jahn-Teller Research Articles

Synthesis Strategies for Highly Stable Sodium and Potassium Manganese Hexacyanoferrates

Sodium- and potassium-ion batteries (NIBs and KIBs) have been recognized as a promising alternative to lithium-ion batteries (LIBs), especially for stationary grid-scale applications that favor inexpensive storage over high energy density.1 NASICON-structured phosphates and alluaudite sulfates offer cheap synthesis routes but demonstrate low energy density2,3. Layered oxides can provide a higher energy density but require complex synthesis routes and degrade quickly4. Prussian Blue Analogues (PBAs) benefit from facile precipitation synthesis, flat voltage plateaus, and specific capacities greater than 150 mAh g-1.5 However, capacity fading due to Jahn-Teller distortion, manganese dissolution, and residual interstitial water limit their cycle life6,7. In this study, synthesis parameters and post-synthesis treatment of Na2Mn[Fe(CN)6] and K2Mn[Fe(CN)6] are discussed. Furthermore, the addition of solubilized conductive carbon additives to synthesis solutions, both to enhance electronic conductivity and provide a flexible framework to reduce strain during cycling, is explored. Na2Mn[Fe(CN)6] electrodes demonstrate a specific capacity of 149.6 mAh g-1 and surpass 250 cycles at 1C before dipping below 80% capacity retention. K2Mn[Fe(CN)6] electrodes demonstrate a specific capacity of 155.1 mAh g-1 with negligible capacity fading over the first 50 cycles at 0.1C. Our results indicate that lowering the temperature during synthesis improves morphology and cycling performance even when a chelating agent is used to control the reaction speed. References (1) Liu, J. Addressing the Grand Challenges in Energy Storage. Advanced Functional Materials. February 25, 2013, pp 924–928. https://doi.org/10.1002/adfm.201203058.(2) Zhang, X.; Rui, X.; Chen, D.; Tan, H.; Yang, D.; Huang, S.; Yu, Y. Na 3 V 2 (PO 4 ) 3 : An Advanced Cathode for Sodium-Ion Batteries. Nanoscale. Royal Society of Chemistry February 14, 2019, pp 2556–2576. https://doi.org/10.1039/c8nr09391a.(3) Niu, Y.; Zhao, Y.; Xu, M. Manganese‐based Polyanionic Cathodes for Sodium‐ion Batteries. Carbon Neutralization 2023, 2 (2), 150–168. https://doi.org/10.1002/cnl2.48.(4) Xiao, J.; Li, X.; Tang, K.; Wang, D.; Long, M.; Gao, H.; Chen, W.; Liu, C.; Liu, H.; Wang, G. Recent Progress of Emerging Cathode Materials for Sodium Ion Batteries. Materials Chemistry Frontiers. Royal Society of Chemistry May 21, 2021, pp 3735–3764. https://doi.org/10.1039/d1qm00179e.(5) Wang, Q.; Li, J.; Jin, H.; Xin, S.; Gao, H. Prussian-Blue Materials: Revealing New Opportunities for Rechargeable Batteries. InfoMat. John Wiley and Sons Inc June 1, 2022. https://doi.org/10.1002/inf2.12311.(6) Shang, Y.; Li, X.; Song, J.; Huang, S.; Yang, Z.; Xu, Z. J.; Yang, H. Y. Unconventional Mn Vacancies in Mn–Fe Prussian Blue Analogs: Suppressing Jahn-Teller Distortion for Ultrastable Sodium Storage. Chem 2020, 6 (7), 1804–1818. https://doi.org/10.1016/j.chempr.2020.05.004.(7) Ge, J.; Fan, L.; Rao, A. M.; Zhou, J.; Lu, B. Surface-Substituted Prussian Blue Analogue Cathode for Sustainable Potassium-Ion Batteries. Nat Sustain 2022, 5 (3), 225–234. https://doi.org/10.1038/s41893-021-00810-7.

Operando Tracking the Dissolution and Deposition Dynamics in Aqueous Zn-MnO2 Batteries

Aqueous Zn–MnO2 batteries have received extensive attention for next-generation large-scale energy storage because of their low cost and outstanding safety. Despite efforts to achieve better performances, the charge-storage chemistry of MnO2 cathodes remains controversial. Zn-ion insertion, Zn-ion/proton co-insertion, proton insertion, and electro-dissolution have been proposed as the mechanism of the MnO2 cathodes. More specifically, the pathway of Mn dissolution is debatable: while intercalation chemistry leads to dissolution caused by the Jahn–Teller effect of Mn(III), electro-dissolution relies on a conversion from Mn(IV) to Mn(II). Furthermore, it is recently considered that Mn dissolution/redeposition efficiency is crucial to the reversibility of MnO2 cathodes, depending on pre-added Mn in the electrolyte. The role of trace Mn additive is also confusing. Last but not least, Mn dissolution and deposition is conjectured to be linked to the dissolution/redeposition of Zn‐based species-that is, Zn4SO4·(OH)6·xH2O (ZSH). To understand these key scientific questions that enlighten the further design of materials and electrolytes, it is imperative to develop operando measurements of the MnO2 cathodes. In our study, we utilized synchrotron X-ray fluorescence microscopy with high spatial resolution to probe the evolution of Zn and Mn species during electrochemical cycling. We can quantify the relationship between Zn and Mn concentrations from the electrode level to the single-particle level. We conclude that during the first discharge, MnO2 delivers the capacity by electro-dissolution, accompanied by the rapid precipitation of ZSH due to change of pH. ZSH surrounds the MnO2, which has high reversibility with the pre-added Mn additive in electrolytes. Our work provides in-depth insights into the complex Zn/Mn deposition and deposition near the electrode surface which will guide the further development of aqueous Zn-MnO2 batteries.

High-Entropy Strategy to Suppress Volumetric Strain and Enhance Diffusion Rate of Na3V2(PO4)2F3 Cathode for Durable and High-Areal-Capacity Zinc-Ion Battery Pouch Cells

The burgeoning global environmental awareness and the escalating demand for renewable energy storage have intensified the critical need for next-generation battery technologies.1,2 In recent decades, there has been a sustained pursuit of grid-scale energy storage systems that balance practicality and efficiency. In this context, aqueous zinc-ion batteries (AZIBs) have emerged as a promising contender, driven by the distinct advantages of the 2.8-fold higher volumetric capacity (5849 mAh cm-3) of zinc metal over lithium metal (2062 mAh cm-3), and the use of non-toxic, cost-effective aqueous electrolyte. To date, substantial efforts have been dedicated to investigating suitable AZIB cathode materials, including Prussian blue analogs (PBAs), transition-metal (TM) oxides (e.g., MnO2 and V2O5), organic compounds, and polyanion-type compounds.Recently, there has been a notable surge of interest in polyanion-type compounds. Na3V2(PO4)2F3 (NVPF), demonstrates an operating potential of exceeding 1.60 V and an enhanced energy density of 97.5 Wh kg-1. Regrettably, these advantages are often counterbalanced by undesirable side reactions and sluggish ion kinetics, culminating in incompetent rate capabilities and suboptimal cycling stability.3 High-entropy (HE) materials have emerged as promising candidates for facilitating ion transport and fortifying cathode stability across various energy storage systems due to their exceptional design flexibility and compositional tunability.4,5 Inspired by conventional HE stabilization strategies, this work introduces a carbon-coated Na3V1.9(AlZnMnCrNb)0.1(PO4)2F3 cathode, denoted as HE-NVPF@C. Employing this cathode, coupled with a carbon-film-functionalized Zn anode, referred to as Zn@CF, and acetonitrile(AN)-water hybrid electrolyte, we configured an AZIB with substantial enhancements in long-term cycling stability and high areal capacity. AZIBs based on HE-NVPF@C cathodes presented a high reversible capacity of 77.45 mAh g−1 at 2C and remarkable cycling stability with a capacity loss of a mere 0.0031% per cycle over 6,000 cycles at 20C. In particular, the areal capacity of the HE-NVPF@C cathode reached up to 2.17 mAh cm-2, and HE-NVPF@C also attained a high capacity density of 78.2 mAh g-1 and 61.6 mAh g-1 when working under 50 and -20°C, making it more competitive among the reported cathodes in AZIBs. In addition, the pouch cell provides a long cycling lifespan with 90.8% capacity retention at 5C after 200 cycles. More importantly, the Zn2+ storage mechanism of the high-entropy NASICON-type cathode was systematically studied for the first time. In-situ X-ray diffraction (XRD) and density functional theory (DFT) calculations revealed that NVPF@C with high-entropy doping improved cycling stability due to the mitigated Jahn-Teller distortion, enhanced Zn2+ diffusion rate, and reduced lattice volumetric strain upon Zn2+ extraction and insertion. This work not only lays the door for developing stable AZIBs but also enriches the mechanistic discussion about the improved cycling or structural stability of high-entropy NASICON structures.Keywords: Zinc-ion battery; High-entropy material; NASICON; Na3V2(PO4)2F3; Pouch cellReference1 Cao, Y. et al. Bridging the academic and industrial metrics for next-generation practical batteries. Nat. nanotechnol. 14, 200-207, (2019).2 Xue, M. et al. Carbon-assisted anodes and cathodes for zinc ion batteries: From basic science to specific applications, opportunities and challenges. Energy Storage Mater. 62, 102940, (2023).3 Zhu, L. et al. A comprehensive review on the fabrication, modification and applications of Na3V2(PO4)2F3 cathodes. J. Mater. Chem. A 8, 21387-21407, (2020).4 Zeng, Y. et al. High-entropy mechanism to boost ionic conductivity. Science 378, 1320-1324, (2022).5 Yang, C. et al. All-temperature zinc batteries with high-entropy aqueous electrolyte. Nat. Sustain. 6, 325-335, (2023).

Regulations of Bulk and Interfacial Chemistry of Mn-Based Cathode Materials for Sodium Ion Batteries

Sodium ion batteries (SIBs) show the great potential to achieve large-scale energy storage due to their low cost and good safety as well as abundant resources of sodium. Among the cathode materials for SIBs, manganese-based layered oxides with adjustable structure have been attached great interest for the high energy density and low-cost SIBs. . Particularly, P2-type Mn-based materials exhibit anionic redox during charge and discharge processes, which can not only elevate the battery potential but also provide extra capacity, drastically boosting the energy density of the batteries. However, the irreversible phase transition, Jahn-Teller effect of manganese and interphase degradation at high charge cutoff voltage during anionic redox largely affect the cyclic stability of the cathodes. Therefore, it is essential to develop effective strategies to regulate the structural and interfacial chemistry for suppressing the phase transition and voltage hysteresis as well as increasing the cycle life of cathode materials. In this work, various electrochemical inert/active elements have been introduced into Mn-based P2 type cathode materials for regulating the electronic structure of the cathodes to promote more anionic redox and improve the structural stability. In addition, a new type of ionic liquid is introduced to build a stable interphase and improve the high voltage stability of the cathode material. Multi-model synchrotron-based X-ray characterization techniques combined with first-principles calculation are used to reveal the effectiveness of different strategies on the electrochemical properties of SIBs. The results provide valuable information for the development of high-performance cathode materials. Acknowledgement This work at Shanghai Jiao Tong University was financially supported by the National Natural Science Foundation of China (No. 22209106).

An orbital strategy for regulating the Jahn-Teller effect.

The Jahn-Teller effect (JTE) arising from lattice-electron coupling is a fascinating phenomenon that profoundly affects important physical properties in a number of transition-metal compounds. Controlling JT distortions and their corresponding electronic structures is highly desirable to tailor the functionalities of materials. Here, we propose a local coordinate strategy to regulate the JTE through quantifying occupancy in the [Formula: see text] and [Formula: see text] orbitals of Mn and scrutinizing the symmetries of the ligand oxygen atoms in MnO6 octahedra in LiMn2O4 and Li0.5Mn2O4. The effectiveness of such a strategy has been demonstrated by constructing P2-type NaLi x Mn1 - x O2 oxides with different Li/Mn ordering schemes. In addition, this strategy is also tenable for most 3d transition-metal compounds in spinel and perovskite frameworks, indicating the universality of local coordinate strategy and the tunability of the lattice-orbital coupling in transition-metal oxides. This work demonstrates a useful strategy to regulate JT distortion and provides useful guidelines for future design of functional materials with specific physical properties.

Origin of Magnetism in a Supposedly Nonmagnetic Osmium Oxide.

A supposedly nonmagnetic 5d^{1} double perovskite oxide is investigated by a combination of spectroscopic and theoretical methods, namely, resonant inelastic x-ray scattering, x-ray absorption spectroscopy, magnetic circular dichroism, and multiplet ligand-field calculations. We found that the large spin-orbit coupling admixes the 5d t_{2g} and e_{g} orbitals, covalency raises the 5d population well above the nominal value, and the local symmetry is lower than O_{h}. The obtained electronic interactions account for the finite magnetic moment of Os in this compound and, in general, of 5d^{1} ions. Our results provide direct evidence of elusive Jahn-Teller distortions, hinting at a strong electron-lattice coupling.

Tailoring Co‐Free LiNi0.5Mn1.5O4 Material for High‐Voltage Lithium‐Ion Batteries: Particle Design & Grain Boundary Engineering

AbstractCobalt‐free LiNi0.5Mn1.5O4 (LNMO) is a promising cathode material for high‐energy and power‐density lithium‐ion batteries (LIBs). However, its commercial adoption is hindered by rapid capacity degradation due to the unstable LNMO/electrolyte interface caused by LNMO's high operating voltage. Structural degradation from Jahn–Teller distortion and metal‐ion dissolution also contributes to poor cycling stability. Additionally, producing industrial‐grade LNMO with high tap density, low surface area and reduced metal‐ion dissolution is challenging. This study addresses these challenges through a rational material design approach, synthesizing LNMO with large spherical secondary particles (>14.0 µm) and high tap density (>2.0 g cm−3). The primary particles (1.5–6.0 µm) exhibit a truncated‐octahedral shaped morphology that predominantly exposes (111) surface facets, with fewer (100) surfaces, stabilizing the LNMO/electrolyte interface, reducing metal dissolution, and enhancing lithium‐ion kinetics. Silicon infusion into grain boundaries further improves structural integrity by forming a silicon‐rich phase. The tailored LNMO demonstrates exceptional rate capability, cycling stability, and improved interfacial kinetics, significantly advancing the potential for cobalt‐free LNMO in high‐voltage LIBs. This work highlights the importance of tailored cathode material design for achieving the performance and stability required for emerging high‐voltage LIBs applications.

Unveiling enhanced electrochemical performance of LiMn1-xCoxPO4/C cathode materials through co-doping strategy

LiMnPO4(LMP), an olivine-type material, is considered as a cathode for lithium-ion battery material, but faces challenges such as the Jahn-Teller effect, poor conductivity, and low ionic conductivity. To overcome these limitations, we explored Co doping as a potential solution. By utilizing a solvothermal method, we successfully synthesized LiMn1-xCoxPO4/C (x is the mass fraction of Co doping in LiMnPO4 sample) materials with a high (200) exposed surface. Our first-principles calculations indicated that Co doping significantly impacts the material's structure and electrochemical performance. Notably, the LiMn0.95Co0.05PO4/C sample demonstrated the highest performance, delivering capacities of 164.7 mAh g−1 at 0.1 C and 97.5 mAh g−1 at 1 C, while maintaining a remarkable 95.4 % capacity retention after 100 cycles at 0.5 C. Furthermore, the preferential growth on the b-c plane results in an enhanced (200) orientation, which exposes more reactive sites and facilitates Li+ migration. This study not only offers a straightforward approach for obtaining high-performance electrode materials but also bridges the gap between theory and experiment, providing a new avenue for understanding cation doping in polyanionic cathode materials.

Gradient doping–induced triphasic intergrowth hexacyanoferrate cathode for high-performance sodium-ion batteries

As a high-capacity, high-voltage, and low-cost cathode material for sodium-ion batteries (SIBs), Na/Mn-based hexacyanoferrates (NaxMn[Fe(CN)6]1−y·□y·nH2O) typically exhibit poor structural reversibility and interfacial stability during cycling. In this study, we report the in-situ construction of a triphasic intergrowth Na/Mn/Zn-based hexacyanoferrate (mcr-Zn0.2Mn0.8) with concentration-gradient Zn distribution by an anion-controlled fractional precipitation route. Density functional theory calculations verify that the unique heterostructure arises from the different binding energies between cations and anions. A small amount of Zn2+ doping in the inner cubic/monoclinic phases enhances their structural reversibility during cycling by impeding lattice deformation induced by the Jahn–Teller effect of Mn3+. Meanwhile, the rhombohedral Zn-based hexacyanoferrate epitaxially grown on the surface diminishes the particle size of mcr-Zn0.2Mn0.8 resulting in short Na+ diffusion distance, and provides interface protection that suppresses detrimental electrolyte decomposition. Consequently, mcr-Zn0.2Mn0.8 exhibits a high discharge capacity of 121.1 mAh/g at 15 mA g−1, improved cycling stability at 750 mA g−1 with a capacity retention of 65.0 % after 2000 cycles, and enhanced rate capability with a discharge capacity of 71.4 mAh/g at 6000 mA g−1. The successful implementation of simultaneous surface and bulk modifications through a one-step reaction opens new possibilities for developing high-performance hexacyanoferrate cathode materials for SIBs.

Theoretical study of Jahn Teller effect on ion diffusion in trigonal prismatic 1H-MnO2

The trigonal prismatic MnO6 is a basic structural unit of Mn-based compound which has been seldom explored in theoretical and experimental studies. In this paper, the diffusion potential energy surfaces of Li+, Na+, K+, Mg2+, Al3+, and NH4+ ion in trigonal prismatic 1H-MnO2 are presented, which give an intuitionistic picture of the Jahn-Teller effect on the diffusion process. Based on the nudged elastic band method, it is found that the diffusion of ions in trigonal prismatic MnO2 is accompanied by consecutive structural distortion. The low diffusion barriers indicate trigonal prismatic MnO2 is a fast ion conductor. Band structure calculations show the semimetal characteristic of the intercalated compound, which is fit for high electrochemical performance. The details of the diffusion process are also highlighted. Our theoretical study provides an in-depth understanding and research on the fundamentals of the diffusion process in the special configuration in MnO2 and helps to develop novel high-performance electrodes.

Unlocking the potential of cation vacancy-enriched ZnMn1.75O4 cathode for advanced aqueous aluminum-ion batteries

Manganese oxides are widely utilized in aqueous aluminum-ion batteries (AIBs) due to their high voltage and diverse crystal structures. However, the Jahn-Teller effect induced by Mn-O6 units results in irreversible structural damage. Here, we synthesized ZnMn1.75O4 (ZMO) cathodes loaded onto a carbon framework with manganese vacancies (VMn) for AIBs through ion substitution, manganese extraction, and carbonization on Mn-MIL. VMn stabilizes the ZMO structure by damping Mn-O bond vibrations and fosters Mn-O-C bonds between oxide particles and the carbon framework, effectively suppressing irreversible Mn2+ dissolution. Vacancy-modified cathodes provide more ion insertion sites, promoting ion diffusion. Ex-situ characterization revealed dominant H+ and Al3+ insertion behavior during different voltage regimes. Upon initial discharge, ion insertion into vacant lattice sites causes lattice distortions in adjacent unit cells, prompting ZMO to undergo a crystal structure transition and partial zinc deintercalation, resulting in a more stable cathode structure. Therefore, Al/ZMO batteries exhibit enhanced electrochemical performance.

Suppressed O3–P3 phase transition of Cu/Fe/Mn-based layered oxides as cathode materials for high performance sodium-ion batteries

O3-type Cu/Fe/Mn-based layered oxides are regarded as promising cathode materials for sodium-ion batteries due to the abundance of elements in the Earth's crust and the imperative for large-scale energy storage. However, these materials still encounter some challenges, including low capacity and insufficient rate performance. In this study, Al-doped, cobalt-free, and nickel-free Na0.9Cu0.18Fe0.3Mn0.52-xAlxO2 (x = 0, 0.03, 0.05, 0.08) are successfully synthesized by using the solid-state method to introduce non-electrochemically active elements to stabilize the crystal structure and enhance the electrochemical performance. The impact of Al-doping is comprehensively analyzed by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), galvanostatic intermittent titration technique (GITT), and electrochemical impedance spectroscopy (EIS). Al-doping effectively enhances the diffusion coefficient of Na+, reduces the Jahn-Teller effect caused by Mn3+ and mitigates the transition from O3 to P3 phase. Finally, it stops the partial phase transitions from O3 to P3, which can be found in pristine oxide without Al-doping during charge-discharge cycling. Notably, the Na0.9Cu0.18Fe0.3Mn0.47Al0.05O2 electrode exhibits a reversible capacity of 123.89 mAh g−1 at 0.1 C, a capacity retention rate of 91.1 % after 200 cycles at 1 C, and a discharge capacity of 66.36 mAh g−1 at a high rate of 5 C.

Cesium-doped manganese-based Prussian blue analogue as a high-efficiency cathode material for potassium-ion batteries

Prussian blue analogues (PBAs) are regarded as promising cathode materials for potassium-ion batteries (PIBs) owing to their low cost and high reversible capacity. Compared to other PBAs, potassium manganese hexacyanoferrate (KMnHCF) stands out for its superior capacity and operating voltage. However, Jahn-Teller effect of Mn3+ and the structural collapse caused by potassium ion insertion/extraction still affect the structural stability and electrochemical performance of this material. Herein, a green and efficient synthesis method is adopted to substitute potassium ions in KMnHCF with an appropriate amount of cesium ions to form a column effect. Cesium-doped KMnHCF (Cs-KMnHCF) mitigates the irreversible structural damage caused by potassiation/depotassiation and the Jahn-Teller effect, thereby improving the cycling stability. In addition, it widens the lattice channels, reduces the diffusion barrier of potassium ions, and optimizes the diffusion kinetics. By rationally controlling the doping amount of Cs+, the obtained K1.71Cs0.05Mn[Fe(CN)6]0.95·0.05·0.88H2O exhibits remarkable electrochemical performance, with an initial discharge capacity of 137.6 mA h g−1 at a current density of 20 mA g−1 and a capacity retention of 89.6% after 600 cycles at 200 mA g−1. More importantly, when assembled with a pitch-derived soft carbon anode, the full cell manifests excellent cycle stability and rate performance. This work is expected to provide a highly efficient cathode material for the practical application of PIBs.

Improving LiFe0.4Mn0.6PO4 Nanoplate Performance by a Dual Modification Strategy toward the Practical Application of Li-Ion Batteries

A novel composite consisting of fluorine-doped carbon and graphene double-coated LiMn0.6Fe0.4PO4 (LMFP) nanorods was synthesized via a facile low-temperature solvothermal method that employs a hybrid glucose and polyvinylidene fluoride as carbon and fluorine sources. As revealed by physicochemical characterization, F-doped carbon coating and graphene form a ‘point-to-surface’ conductive network, facilitating rapid electron transport and mitigating electrochemical polarization. Furthermore, the uniform thickness of the F-doped carbon coating alters the growth of nanoparticles and prevents direct contact between the material and the electrolyte, thereby enhancing structural stability. The strongly electronegative F− can inhibit the structural changes in LMFP during charge/discharge, thus reducing the Jahn–Teller effect of Mn3+. The distinctive architecture of the LMFP/C-F/G cathode material exhibits excellent electrochemical properties, exhibiting an initial discharge capacity of 163.1 mAh g−1 at 0.1 C and a constant Coulombic efficiency of 99.7% over 100 cycles. Notably, the LMFP/C-F/G cathode material achieves an impressive energy density of 607.6 Wh kg−1, surpassing that of commercial counterparts. Moreover, it delivers a reversible capacity of 90.3 mAh g−1 at a high current rate of 5 C. The high-capacity capability and energy density of the prepared materials give them great potential for use in next-generation lithium-ion batteries.

Engineering interleaved large and small Na4MnV(PO4)3@NC microspheres cathode towards high performance sodium ion batteries

The booming consumption of energy storage devices spontaneously accelerates the urgent development of robust cathode materials for sodium-ion batteries (SIBs). In view of this, the sodium superionic conductor Na4MnV(PO4)3 (NMVP), with considerable energy density of 425 Wh kg−1, has become the focus in SIB research. Despite this, the performance of NMVP is substantially compromised by Jahn-Teller distortion of Mn3+ ions in conjunction with inherently limited electronic conductivity. In order to address this limitation, this study introduces a series of N-doped carbon (NC) coated NMVP materials with interleaved large and small microsphere morphology. Of particular note, the optimized NMVP-NC2 shows the most excellent performance, maintaining a capacity of 65.7 mAh g−1 at 5C over 500 cycles. A full cell configuration employing an NMVP-NC2 cathode and a commercial hard carbon (HC) anode manifests commendable circular stability with a capacity of 80.7 mAh g−1 underneath 100 cycles at 1C, with an impressive 95.3 % capacity preservation. This distinctive architecture imparts the materials with a high tap density and a relatively low surface area, which is beneficial to the industrial employment. In addition, density functional theory (DFT) calculations indicate that the NC regulation significantly narrows the NMVP's bandgap and facilitates electron transfer, thereby accelerating electron/ion transport kinetics. The NC coating approach combined with large-scale spray drying tactic in this work offers a clear strategy to industrialize NMVP cathode towards high-performance SIBs.

Investigation of cation doping on the structure and electrochemical properties of K0.5MnO2 cathode materials based on first-principles calculation

In an effort to find high-energy-density and high-mobility cathode material for K-Ion batteries, this paper presents a systematic study of multiple doping concentrations of P3-type K0.5Mn1-xMxO2 (M = Fe, Ti, and Cu) materials using first-principles approach. The most thermodynamically stable phase of each material is predicted by the formation of mixing enthalpy, and the optimal doping concentration of each doping element is screened. It is found that the redox activity of K0.5Mn1-xMxO2 is derived from the anion redox of O2−/O1− during depotassium. At the same time, doped Mn-based cathode materials have the characteristics of large capacity, stable structure, good thermal stability and small diffusion energy barrier. Among them, Fe doping will promote the charge compensation of O 2p-electrons in the intercalation process and reduce the Jahn-Teller distortion caused by Mn3+ (ratio < 46.67 %). Ti doping can improve the lattice stability of O, inhibit the precipitation reaction of oxygen, make TiO more covalent, and reduce the structural change during depotassium. Therefore, the overall thermal stability of the material is improved. Cu doping reduces the diffusion barrier of the material (0.54 eV). Through the basic understanding of the redox reaction mechanism in K0.5Mn1-xMxO2, the work of this paper lays a foundation for the rational design of high-performance K-ion batteries.

Octahedral Hexanuclear Rhenium Cluster Dimers Bridged by Pyrazine or 4,4'-Bipyridine with 23- and 24-Electron Configurations.

New pyrazine (pz)- and 4,4'-bipyridine (4,4'-bpy)-bridged octahedral hexanuclear rhenium(III) cluster dimers, [{Re6(μ3-S)8Cl5}2(μ-L)]6- (L = pz, [1]6-; L = 4,4'-bpy, [2]6-), with 2 × 24 d-electrons {Re6(24e)}2 were obtained in a single-step reaction via photoirradiation of [Re6(μ3-S)8Cl6]4- with L in a 2:1 ratio at room temperature. The {Re6(23e)}2 dimers, [{Re6(μ3-S)8Cl5}2(μ-L)]4- (L = pz, [1']4-; L = 4,4'-bpy, [2']4-), were synthesized through two-electron oxidation of [1]6- and [2]6-, respectively. The single-crystal X-ray structures of [1]6- and [1']4- were determined, revealing structural distortion of the Re6 core of [1']4- due to the Jahn-Teller effect. The cyclic voltammograms of [1]6- and [2]6- showed two steps of one-electron redox processes attributable to Re6(23e)Re6(24e)/{Re6(24e)}2 and {Re6(23e)}2/Re6(23e)Re6(24e), respectively. The separation between the two redox potentials is small (0.056 V for [1]6- and 0.039 V for [2]6-). The magnetic susceptibilities of [1']4- and [2']4- were almost temperature-independent, with values of 2.98 and 2.85 μB, respectively, indicating paramagnetism. These results suggest weak electronic interaction between two cluster units bridged by pz or 4,4'-bpy in the intercluster mixed valence state. The compounds [1]6- and [2]6- show photoluminescence in the near-infrared region at 296 K in the solid state.

Protective layer constructed by liquid phase quenching for long lifespan potassium ion batteries

Manganese-based transition metal layered oxides have garnered considerable attention for potassium-ion batteries (KIBs) due to their high energy density, high conversion efficiency, long lifespan and simple manufacturing processes. However, the slow K+ diffusion rate and poor stability fail to meet the increasing requirements of the energy storage system. The quenching technology was employed herein to in-situ form a thin protective layer of KMn4(PO4)3 with a high K+ diffusion rate on the surface of K0.5Mn0.85Co0.1Fe0.05O2. The introduction of the protective layer enhances electrochemical kinetics to promote high-rate electrochemical performance and reinforcing the ion diffusion dynamics, thus alleviating stress caused by uneven K+ distribution. Meanwhile, the reduction in Mn3+ content plays a crucial role in suppressing the Jahn-Teller distortion effect, contributing to enhanced cyclic stability. It exhibits an excellent electrochemical performance with a reversible specific capacity of 100.5 mAh g−1 at 0.2C, maintaining 72.97 % capacity after 500 cycles at 2C (1C=100 mA g−1). Coupled with graphite as the anode, the full cell shows a capacity retention of 73.53 % after 650 cycles at 2C, highlighting the potential for future practical applications.

Na+ orientates Jahn-Teller effect to tune Li+ diffusion pathway and kinetics for Single-Crystal Ni-rich LiNixCoyMn1-x-yO2 cathode materials

Single-crystallization is an effective strategy for enhancing both capacity and stability of Ni-rich LiNi1-x-yCoxMnyO2 (NCM) cathode materials, especially at high cut-off voltages. However, the kinetics limitation of solid-phase Li+ diffusion is a major concern because of the long diffusion path in large single-crystal particles. To address this issue, we synthesize a Na-doped single-crystal LiNi0.82Co0.125Mn0.055O2 (NCM-Na) cathode material by a facile mixed-molten-salt sintering process. Na+ is revealed to be uniformly doped at the Li+ lattice sites within the entire single-crystal particles. This Na+ doping effectively enhances the dynamics of Li+ transport in the layered oxide phases. The NCM-Na material with 2 at.% Na doping shows a Li+ diffusion coefficient up to more than 8 times higher than pristine NCM. In-situ X-ray diffraction and finite element analysis demonstrate significantly facilitated H1-H2-H3 phase transition in NCM-Na materials, compared with the severe phase separation phenomenon in NCM counterpart, hoisting their rate capacity and structure stability. Thus, the NCM-Na material achieves a superior reversible capacity of 177.7 mAh/g at 5C, and a capacity retention of 94.4 % after 100 cycles at 0.5C at a high cut-off voltage of 4.5 V. By density function theory calculations, we reveal that Na+ doping can selectively stabilize the surrounding Li+ at the second farthest hexagonal vertexes by tuning the orientation of the Jahn-Teller effect of Ni3+. These Li+ ions frame a high-speed pathway for preferential Li+ diffusion, which promotes the Li+ diffusion kinetics even in highly delithiated states. Our findings provide insights into the Na+ doping mechanism and present a low-cost, highly efficient, and scalable method to enhance the performance of single-crystal Ni-rich NCM materials.

Effect of Mo6+ induced valence changes of transition metal ions in Mn-rich layered cathode materials on electrochemical performance

Layered cathode materials for lithium-ion batteries have been extensively investigated; however, comparatively scant attention has been paid to Mn-rich layered cathode materials. Herein, LiNi0.5Mn0.5O2 cathode materials are doped to investigate the effect of doping elements on the electrochemical properties of Mn-rich layered cathodes. XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy), and SQUID (superconducting quantum interference device) results reveal that Mo doping affects the electrochemical properties of the cathode materials by changing the valence state of transition metal ions. Due to the Mo6+ ions doping, a large proportion of Mn3+ ions present in LiNi0.5Mn0.5O2 were converted to Mn4+ ions, which alleviated the Jahn-Teller effect and reduced the elongated Mn-O octahedra, thus increasing the Li layer spacing and facilitating Li+ diffusion. Therefore, 1 % Mo-doped cathode exhibits a significantly improved Li-ion diffusion coefficient and superior rate performance with a specific discharge capacity of 103 mAh·g−1 at 5C. Meanwhile, the cathode materials significantly improve cycling performance due to the reduction in the amount of Mn3+. The current study provides guidelines for the modification of Mn-rich layered cathodes in the future.