Jahn-Teller Research Articles

Lithium extraction via capacitive deionization: AlF3 coated LiMn2O4 spheres for enhanced performance

The escalating demand within the lithium battery sector has intensified the pursuit of efficient methods for lithium's selective extraction from brines. Particularly, LiMn2O4 (LMO) emerges as a prime candidate, celebrated for its robust redox properties and considerable theoretical adsorption capacity. Nonetheless, its application is hampered by structural instability due to Jahn-Teller distortion, which triggers a phase shift from cubic to tetragonal and Mn dissolution, undermining the material's lithium extraction efficiency. In response, this study introduces an innovative, multifunctional amorphous AlF3 coating on LMO spheres, employing a novel synthesis approach combining co-precipitation, solid-phase transformation, and a final AlF3 deposition. This method not only mitigates Mn leaching but also curtails the adverse effects of Jahn-Teller distortion by integrating trace amounts of Al3+ into the LMO lattice, thus fortifying both the surface and bulk structure of the material. Significantly, the AlF3-coated LMO demonstrates an enhanced lithium extraction capacity of 31.5 mg g−1 at 1.2 V with feedwater concentration of 150 mg L−1. Additionally, the optimally coated sample exhibits superior cycling stability, maintaining high-capacity retention and minimal manganese dissolution across multiple absorption-desorption cycles. Furthermore, the optimized electrode exhibits exceptional selectivity for lithium over magnesium in solutions with high Mg2+/Li+ ratios, achieving a notable separation factor of 7.66. Additionally, this electrode demonstrates efficient separation capabilities in synthetic brine, effectively distinguishing Li+ from competing ions such as Na+, K+, Ca2+, and Mg2+, which underscores its substantial potential for effective lithium recovery from complex brines.

A Strategy to Mitigate Jahn Teller Effect of Mn-Rich NASICON Framework for Sodium-Ion Batteries.

Mn-based sodium superionic conductors have driven attention to the low-cost advanced cathode materials for sodium-ion batteries (SIBs). However, low-rate capability and unsatisfactory cyclic performance due to the Jahn teller effect of Mn3+ redox couple which occurs from the change in Mn-O bond length at the octahedral site of crystal structure during charge-discharge, eventually limiting their application. Herein, a disordered and sodium deficient NASICON Na4-xMn(FeVCrTi)0.25(PO4)3 (termed as Na4-xMn(HE)) is synthesized to mitigate this Jahn teller effect to achieve high rate and ultrastable cathode material. Interestingly, the as-prepared Na3.5Mn(HE) shows five reversible electron reactions (i.e., Ti3+/Ti4+, Fe2+/Fe3+, V3+/V4+, Mn2+/Mn3+, and Mn3+/Mn4+) and demonstrates 141mA h g-1 at 0.2 C with 80% capacity retention at 1 C after 500 cycles which is far superior to its counterparts binary Mn-based materials. The excellent cyclic performance is due to the remediation of the Jahn teller effect in sodium-deficient entropy-stabilized material. The structural reversibility, enhanced kinetics, and electronic properties are further studied in detail by in situ X-ray diffraction (XRD), ex situ X-ray photoelectron spectroscopy (XPS), and first principal calculations. Na3.5Mn(HE)//HC full cell delivered 89.7 mAh g-1 capacity at 0.2 C. This work sheds light on designing Mn-based cathodes with superior electrochemical performance for wide energy storage applications.

Copper substituted manganese Prussian blue analogue composite nanostructures for efficient aqueous zinc-ion batteries

Aqueous zinc (Zn)-ion batteries (AZIBs) are considered a promising green energy storage alternative due to their large capacity, low cost, and exceptional safety. Prussian blue analogues (PBAs) with a robust three-dimensional structure and extensive ion channels are highly favorable for Zn2+ insertion/extraction, surpassing manganese (Mn) and vanadium oxides. Herein, copper (Cu) substituted Mn PBA (CuMn PBA) composite nanostructures are synthesized via a simple water-based co-precipitation technique using different concentrations of Cu and Mn sources. The partial substitution of Cu and the formation of Mn vacancies prevent Jahn-Teller distortions of MnN6 octahedra, extending the lifespan. The CuMn PBA-2 electrode exhibits a high discharge capacity of 175.14 mA h g−1 at 0.5 A g−1, superior rate capability of 89.08 mA h g−1 at 2.4 A g−1, and robust cycling stability, maintaining 73.15 mA h g−1 over 2000 cycles at 3 A g−1. Furthermore, the distinct structure provides numerous active sites and reduces volume volatility during cycling. The presence of Cu enhances electrode conductivity, thereby promoting a higher rate of Zn-ion diffusion between electrodes. The reversible intercalation and deintercalation of Zn2+ ions in the CuMn PBA-2 cathode are substantiated by ex-situ analysis methods. This work presents a novel approach for producing high-performance and stable PBA cathode materials for AZIBs.

Enhanced high-rate and long-cycle performance of Mg2+-Al3+ co-doped spinel LiMn2O4 cathode materials for Li-ion batteries

Spinel LiMn2O4 has the potential to be used as a cathode material in lithium-ion batteries because of its affordability, low toxicity, and excellent charge/discharge capability. However, severe capacity attenuation results from the degradation of its long-cycle and high-rate performance caused by the Jahn-Teller distortion and Mn dissolution. Herein, a simple solid-state combustion process is used to successfully prepare the Mg2+-Al3+ co-doped LiMn2O4 with truncated octahedral morphology. The Jahn-Teller distortion is inhibited by the stable Mn-O framework and the decreased lattice constant, which in turn lowers the dissolution of Mn. Moreover, Mg2+-Al3+ co-doped LiMn2O4 have lower activation energy and greater Li+ diffusion coefficient. As a result, the optimized LiMg0.03Al0.10Mn1.87O4 delivers satisfied initial capacity of 102.1 mAh‧g−1 with a capacity retention of 76.2 % after 1000 cycles at 10 C. Even at the ultra-high rate of 15 C and 20 C, Mg2+-Al3+ co-doped sample also remain desired structure stability and cycling performance, which remains 73.8 % of its original capacity after 1000 cycles at 20 C. This work provides a reference for developing high-performance and stability cathode materials for lithium-ion battery.

Electrodeposition of Ni/Cu Bimetallic Conductive Metal-Organic Frameworks Electrocatalysts with Boosted Oxygen Reduction Activity for Zinc-Air Batteries.

Zinc-air batteries employing non-Pt cathodes hold significant promise for advancing cathodic oxygen reduction reaction (ORR). However, poor intrinsic electrical conductivity and aggregation tendency hinder the application of metal-organic frameworks (MOFs) as active ORR cathodes. Conductive MOFs possess various atomically dispersed metal centers and well-aligned inherent topologies, eliminating the additional carbonization processes for achieving high conductivity. Here, a novel room-temperature electrochemical cathodic electrodeposition method is introduced for fabricating uniform and continuous layered 2D bimetallic conductive MOF films cathodes without polymeric binders, employing the organic ligand 2,3,6,7,10,11-hexaiminotriphenylene (HITP) and varying the Ni/Cu ratio. The influence of metal centers on modulating the ORR performance is investigated by density functional theory (DFT), demonstrating the performance of bimetallic conductive MOFs can be effectively tuned by the unpaired 3d electrons and the Jahn-Teller effect in the doped Cu. The resulting bimetallic Ni2.1Cu0.9(HITP)2 exhibits superior ORR performance, boasting a high onset potential of 0.93V. Moreover, the assembled aqueous zinc-air battery demonstrates high specific capacity of 706.2mA h g-1, and exceptional long-term charge/discharge stability exceeding 1250 cycles.

Multimode Luminesce Tailoring PMA4Na(In,Sb)Cl8 Organic-inorganic Hybrid Metal Halidevia Rigid Benzene Ring Induced Local Lattice Distortion.

Low dimensional organic-inorganic hybrid metal halide materials have attracted extensive attention due to their superior optoelectronic properties. However, low photoluminescence quantum yields (PLQYs) caused by parity-forbidden transition hinder their further application in optoelectronic devices. Herein, a novel yellow-emitting PMA4Na(In,Sb)Cl8 (C7H10N+, PMA+) low-dimensional OIMHs single crystal with a PLQY as high as 88% was successfully designed and synthesized, originating from the fact that the doping of Sb3+ effectively relaxes the parity-forbidden transition by strong spin-orbit (SO) coupling and Jahn-Teller (JT) interaction. The as-prepared crystal shows an efficient dual emission peaking 495 and 560 nm at low temperature, which are ascribed to different levels of 3P1 → 1S0 transitions of Sb3+ in [SbCl6]3- octahedral caused by JT deformation. Moreover, wide-range luminescence tailoring from cyan to orange can be achieved through adjusting excitation energy and temperature because of flexible [SbCl6]3- octahedral in the PNIC lattice. Based on a relative stiff lattice environment, the 560 nm yellow emission under 350 nm light excitation exhibits abnormal anti-thermal quenching from 8 to 400 K owing to the suppression of non-radiative transition. The multimode luminescence regulation enriches PMA4Na(In,Sb)Cl8 great potential in the field of optoelectronics such as temperature sensing, low temperature anti-counterfeiting and WLED applications.

Strain-induced antiferromagnetic domain switching via the spin Jahn-Teller effect

Strain-induced antiferromagnetic domain switching via the spin Jahn-Teller effect

Lithium substitution modulation of P2-type manganese-rich oxide toward high-stable and high-voltage cathode for sodium-ion batteries

P2-type manganese-rich layered oxide have attracted much attention as cathodes of sodium-ion batteries owing to the low cost, high capacity and fast sodium ion diffusion kinetics. However, the Jahn-Teller effect of Mn3+, P2-O2 phase transition and anionic redox on charging to the high-voltage, resulted in a severe capacity delay. Herein, an effective Li substitution strategy is proposed to suppress the Jahn-Teller effect of Mn3+, the harmful phase transition of P2-O2 and the anionic redox. As a result, the as-prepared sample Na0.67(Ni0.25Mn0.75)0.9Li0.1O2 (67L10) displays a discharge specific capacity of 168.6 mA h g−1 at 0.1 C, enhanced average working voltage, and improved cycling stability at 1 C after 200 cycles within 1.5–4.5 V voltage window (capacity retention of 83.3 %, specific capacity of 106.8 mA h g−1) compared with that of pristine Na0.67Ni0.25Mn0.75O2(capacity retention of 34.2 %, specific capacity of 51.3 mA h g−1). This work demonstrates the favorable effect of Li doping in P2-type layered materials to suppress the phase transition and inhibit the redox activity of Mn and O ions, and it provides an effective approach for the development of cathodes for sodium-ion batteries with high specific energy and long life.

Designing delafossite CuAl1-xTMxO2 solid solutions: the role of 3d transition metal spin states in photo(electro)catalytic performance

This study delves into the effects of 3d transition metal (TM) spin states on the structural and electronic properties of CuAl1-xTMxO2 solid solutions, focusing on their implications for photo(electro)catalytic performance. The research reveals that the Jahn–Teller distortion, associated with TM3+, is a critical factor in determining the lattice parameters and photo(electro)catalytic performances. Solid solutions without Jahn–Teller distortion adhere to Vegard's law, whereas those with strong distortion exhibit deviations, indicating the influence of TMO6 octahedral distortion on solubility and lattice parameters. The electronic structure of solid solutions with weak Jahn–Teller distortion is governed by the O–Cu–O and TMO6 crystal fields, which leads to a narrowed bandgap and reduced conduction band minimum (CBM), impacting the hydrogen evolution potential. In particular, the CuAl0.5Cr0.5O2 shows a significant enhancement in photocurrent density and hydrogen production rate due to its balanced light absorption and effective charge carrier separation. In contrast, the weak Jahn–Teller distortion in CuAl1-xFexO2 results in localized electronic states at CBM, leading to diminished carrier mobility. Solid solutions with strong Jahn–Teller distortion, such as CuAl1-xTMxO2 (TM = Mn and Ni), display a range of electronic properties from semiconductor to semimetallic, with the semimetallic CuAl0.9Mn0.1O2 capable of infrared light absorption and efficient photocatalytic hydrogen and oxygen production.

Hexagonal Boron Nitride Quantum Simulator: Prelude to Spin and Photonic Qubits.

The quest for qubit operation at room temperature is accelerating the field of quantum information science and technology. Solid state quantum defects with spin-optical properties are promising spin- and photonic qubit candidates for room temperature operations. In this regard, a single boron vacancy within hexagonal boron nitride (h-BN) lattice such as VB- defect has coherent quantum interfaces for spin and photonic qubits owing to the large band gap of h-BN (6 eV) that can shield a computational subspace from environmental noise. However, for a VB- defect in h-BN to be a potential quantum simulator, the design and characterization of the Hamiltonian involving mutual interactions of the defect and other degrees of freedom are needed to fully understand the effect of defects on the computational subspace. Here, we studied the key coupling tensors such as zero-field splitting, Zeeman effect, and hyperfine splitting in order to build the Hamiltonian of the VB- defect. These eigenstates are spin triplet states that form a computational subspace. To study the phonon-assisted single photon emission in the VB- defect, the Hamiltonian is characterized by electron-phonon interaction with Jahn-Teller distortions. A theoretical demonstration of how the VB- Hamiltonian is utilized to relate these quantum properties to spin- and photonic-quantum information processing. For selecting promising host 2D materials for spin and photonic qubits, we present a data-mining perspective based on the proposed Hamiltonian engineering of the VB- defect in which h-BN is one of four materials chosen to be room temperature qubit candidates.

Spiro‐buckybowls: Synthesis and Selective Transformations toward Chiral and Nonlinear Optical Polycycles

Integration of spirocycles with buckybowls is a promising strategy to construct three‐dimensional (3D) curved π‐systems and to endow distinctive physicochemical features arising from buckybowls. Herein, a series of carbon‐bridged spiro‐type heterosumanenes (spiro‐HSEs) were synthesized by combining 9,9′‐spirobifluorene and dichalcogenasumanenes (DCSs). It is found that spiro‐conjugation plays an important role in the geometric and electronic structures of spiro‐HSEs. The bowl depth of DCSs moiety becomes larger in the spiro‐HSEs. Owing to the Jahn‐Teller (J‐T) effect, two DCSs segments of spiro‐HSEs have different bowl depths accompanied with the unequal distribution of charge in radical cation state. Taking advantage of the typical reactions of DCSs, selective transformations of spiro‐HSEs have been adopted in accordance to the nature of chalcogen atoms (S, Se, Te) to bestow the value‐added functionalities. The emissive property is enhanced by converting the thiophene rings of S‐doped spiro‐HSE into thiophene S,S‐dioxides. A chiroptical polycycle could be produced by ring‐opening of the edge benzene of Se‐doped spiro‐HSE. The covalent adduct of Te‐doped spiro‐HSE with Br2 forms non‐centrosymmetric halogen‐bonded networks, resulting in the high performance second‐order nonlinear optics (NLO).

Facile and efficient fabrication of Cu1.04Mn0.96O2 nanosheet anodes with superior electrochemical lithium storage capability

In this work, Cu1.04Mn0.96O2 nanosheets were synthesized via a simple hydrothermal method, and their electrochemical lithium storage properties and reaction mechanisms were investigated. The nanosheet structure effectively promotes electron transfer and shortens the transport path. Additionally, the partial substitution of Cu for Mn decreases the Jahn-Teller distortion of the MnO6 octahedron. Employing as an anode for Li-ion batteries, the specific capacity reached 610.91 mAh g−1 after 100 cycles at a current density of 100 mA g−1.

Zr-doped O3-type NaNi1/3Fe1/3Mn1/3O2 cathodes with enhanced structure stability for sodium-ion batteries

O3-type NaTMO2 (TM = transition metal) is highly anticipated as a cathode for sodium-ion batteries due to its high theoretical specific capacity and low cost. However, the irreversible phase transition during sodiation/desodiation and the Jahn-Teller effect induced by Mn3+ have hindered its steps towards industrialization. Herein, we propose a doping strategy to enhance the structural stability of O3-type NaNi1/3Fe1/3Mn1/3O2 through Zr doping. On the one hand, the Na+ transport channels are broadened due to the enlarged layer spacing, which accelerates the kinetic processes. On the other hand, Zr doping maintains structural integrity, inhibiting the decay of the layered structure. As a result, the uniquely designed material NNFMZO-6000 exhibited a discharge specific capacity of 113.8 mAh g−1 at 1 C and a capacity retention of 67.54 % after 200 cycles. This work presents an effective modification method to optimize the properties of O3-type NaTMO2 materials.

Structure, Thermodynamics, Chemomechanics, and Kinetics: The Hidden Complexities of LiNiO2

After being abandoned due to mechanical and thermodynamic instabilities, layered transition metal oxides with ultra-high Ni content currently see a revival as promising cathode active material in the effort of further pushing the energy density of lithium ion batteries. Because such materials are in many aspects closely related to the pure LiNiO2, understanding the properties and mechanisms of this model system on an atomic level is vital for the development of more complex materials. Therefore, we have analyzed the structure, thermodynamics, chemomechanics and kinetics of LiNiO2 and its delithiated states including the presence of native defects by making use of atomistic simulations to grasp the peculiarities of this material.What makes the structure and related properties of LiNiO2 especially interesting and challenging is the presence of dynamic Jahn-Teller distortions of the NiO6 octahedra. This leads to local monoclinic distortions and our simulations revealed why the material still appears to be of rhombohedral symmetry on a global scale.[1]Upon delithiation and the concurrent oxidation to Ni4+, the Jahn-Teller distortions start to vanish and particularly stable Li orderings may be observed. In this context, we used a cluster expansion approach and were able to reproduce the experimental phase diagram. Moreover, we included native defects in the analysis because LiNiO2 can hardly be prepared stoichiometric. Instead, many synthesis approaches lead to additional Ni ions occupying the Li layers (NiLi). The introduction of such defects as well as other substitutionals in a surrogate model shows that single phase regions tend to be suppressed and solid-solution behavior is favored. This smooths the voltage curves and gives good agreement with experiments.[2]We then focused on more extended defects in layered transition metal oxides: Stacking faults (observed at low Li content and responsible for stacking changes from O3 to O1-type layering) and dislocations (needed to drive stacking changes through the material). We found that the energetics and gliding barriers of stacking faults in stoichiometric LiNiO2 are similar to LiCoO2 for all degrees of lithiation. However, by acknowledging the presence of NiLi we quantified for the first time how this defect hinders layer gliding: In the fully delithiated material, 2% of NiLi in the Li layer has a similar effect as 11%-15% Li, effectively increasing the gliding barriers. In terms of dislocations, their excess energies in LiNiO2 are much lower than in LiCoO2, which we mostly attribute to the Jahn-Teller distortions that are able to collinearly orient in the vicinity of a dislocation in LiNiO2, effectively taking a part of the strain. Moreover, dislocations are able to attract both Li and O vacancies, potentially affecting the kinetics of the material as well as acting as a precursor for further degradation mechanisms.[3]Lastly, we mention our recent analysis again focusing on NiLi defects. Our simulations show that such Ni ions remain in a +2 oxidation state independent on the degree of lithiation. This contradicts the broad opinion of an oxidation state change to +3 at low Li content, which is believed to lead to a local constriction of the layer that can hardly be relithiated again. Nevertheless, we show that NiLi indeed leads to an attraction of Li vacancies within two lattice sites and the potential to split fast divacancies into two considerably slower single vacancies. These observations together with the fact that any NiLi depicts an obstacle for diffusing Li ions or Li vacancies shed light on the kinetics of non-stoichiometric LiNiO2 and support the development of further optimization schemes.[4][1] Chem. Mater. 2020, 32, 23, 10096–10103[2] J. Mater. Chem. A , 2021,9, 14928-14940[3] Chem. Mater. 2023, 35, 2, 584–594[4] https://doi.org/10.26434/chemrxiv-2023-hkmsn-v3

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.