Unleashed Remarkable Energy Storage Performance in Bi0.5K0.5TiO3-based Relaxor Ferroelectrics by Local Structural Fluctuation.

Dielectric capacitors harvest energy through an electrostatic process, which enables an ultrafast charging-discharging rate and ultrahigh power density. However, achieving high energy density (Wrec) and efficiency (η) simultaneously, especially when preserving them across a wide frequency/temperature range or cycling numbers, remains challenging. In this work, by especially introducing NaTaO3 into the representative ferroelectric relaxor of Bi0.5K0.5TiO3-Bi0.5Na0.5TiO3 and leveraging the mismatch between B-site atoms, we proposed a method of enhancing local structural fluctuation to refine the polar configuration and to effectively improve its overall energy-storage performances. As a consequence, the ceramic exhibits an ultrahigh Wrec of 15.0 J/cm3 and high η up to 80%, along with a very wide frequency stability of 10 - 200 Hz and extensive cycling number up to 108. In-depth local structure and chemical environment investigations, consisting of atom-scale electron microscopy, neutron total scattering, and solid-state nuclear magnetic resonance, reveal that the randomly distributed A/B-site atom pairs emerge in the system, leading to the evident local structural fluctuations and concomitant polymorphic polar nanodomains. These key ingredients contribute to the large polarization, minimal hysteresis, and high breakdown strength, thereby promoting energy-storage performances. This work opens a new path for designing high-performance dielectric capacitors via manipulating local structural fluctuations.

Defect Structure, Oxygen Ion Conduction, and Conducting Mechanism in Ruddlesden-Popper Sr3Zr2-xMxO7-0.5x (M = Ga, Y, In).

Ruddlesden-Popper (RP)-structured materials based on transition metals with a variable valence, such as Fe, Mn, Ni, and so on, have been well documented for their potential of being used as electrodes in solid-oxide fuel cells. However, RP materials with pure or dominant ionic conduction are rare. Here, a series of Zr-based RP materials Sr3Zr2-xMxO7-0.5x (M = Ga, Y, In) with electrical conductivity as high as 3.25 × 10-3 S cm-1 at 900 °C in air was reported, which represents the highest conductivity for the Zr-based RP materials and is comparable to that of the recently reported In-based RP oxide-ion conductors, such as NdBaInO4-based and La2BaIn2O7-based materials. Under low oxygen partial pressure (pO2), the doped samples show pure ionic conducting behaviors without n-type electronic conductivity. The defect formation energies, local structure around the oxygen vacancies, and oxide-ion-conducting mechanism of the acceptor-doped Sr3Zr2O7-based materials were studied for the first time. The results revealed a two-dimensional oxide ion migration characteristic within the perovskite slabs. This work therefore provides a good reference for developing new oxide-ion conductors in the Zr-based RP-structured materials.

In situ p-block protective layer plating in carbonate-based electrolytes enables stable cell cycling in anode-free lithium batteries.

'Anode-free' Li metal batteries offer the highest possible energy density but face low Li coulombic efficiency when operated in carbonate electrolytes. Here we report a performance improvement of anode-free Li metal batteries using p-block tin octoate additive in the carbonate electrolyte. We show that the preferential adsorption of the octoate moiety on the Cu substrate induces the construction of a carbonate-less protective layer, which inhibits the side reactions and contributes to the uniform Li plating. In the mean time, the reduction of Sn2+ at the initial charging process builds a stable lithophilic layer of Cu6Sn5 alloy and Sn, improving the affinity between the Li and the Cu substrate. Notably, anode-free Li metal pouch cells with tin octoate additive demonstrate good cycling stability with a high coulombic efficiency of ~99.1%. Furthermore, this in situ p-block layer plating strategy is also demonstrated with other types of p-block metal octoate, as well as a Na metal battery system, demonstrating the high level of universality.

Correlating local structure and migration dynamics in Na/Li dual ion conductor Na5YSi4O12.

Na5YSi4O12 (NYSO) is demonstrated as a promising electrolyte with high ionic conductivity and low activation energy for practical use in solid Na-ion batteries. Solid-state NMR was employed to identify the six types of coordination of Na+ ions and migration pathway, which is vital to master working mechanism and enhance performance. The assignment of each sodium site is clearly determined from high-quality 23Na NMR spectra by the aid of Density Functional Theory calculation. Well-resolved 23Na exchangespectroscopy and electrochemical tracer exchange spectra provide the first experimental evidence to show the existence of ionic exchange between sodium at Na5 and Na6 sites, revealing that Na transport route is possibly along three-dimensional chain of open channel-Na4-open channel. Variable-temperature NMR relaxometry is developed to evaluate Na jump rates and self-diffusion coefficient to probe the sodium-ion dynamics in NYSO. Furthermore, NYSO works well as a dual ion conductor in Na and Li metal batteries with Na3V2(PO4)3 and LiFePO4 as cathodes, respectively.

Enhancing Reversibility and Kinetics of Anionic Redox in O3-NaLi1/3Mn2/3O2 through Controlled P2 Intergrowth.

Anionic redox chemistry can surpass theoretical limits of conventional layered oxide cathodes in energy density. A recent model system of sodium-ion batteries, O3-NaLi1/3Mn2/3O2, demonstrated full anionic redox capacity but is limited in reversibility and kinetics due to irreversible structural rearrangement and oxygen loss. Solutions to these issues are missing due to the challenging synthesis. Here, we harness the unique structural richness of sodium layered oxides and realize a controlled ratio of P2 structural intergrowth in this model compound with the overall composition maintained. The resulted O3 with 27 % P2 intergrowth structure delivers an excellent initial Coulombic efficiency of 87 %, comparable to the state-of-the-art Li-rich NMCs. This improvement is attributed to the effective suppression of irreversible oxygen release and structural changes, evidenced by operando Differential Electrochemical Mass Spectroscopy and X-ray Diffraction. The as-prepared intergrowth material, based on the environmentally benign Mn, exhibits a reversible capacity of 226 mAh g-1 at C/20 rate with excellent cycling stability stemming from the redox reactions of oxygen and manganese. Our work isolates the role of P2 structural intergrowth and thereby introduces a novel strategy to enhance the reversibility and kinetics of anionic redox reactions in sodium layered cathodes without compromising capacity.

Superfine Nanodomain Engineering Unleashing Ferroelectricity in Incipient Ferroelectrics.

Incipient ferroelectrics have emerged as an attractive class of functional materials owing to their potential to be engineered for exotic ferroelectric behavior, holding great promise for expanding the ferroelectric family. However, thus far, their artificially engineered ferroelectricity has fallen far short of rivaling classic ferroelectrics. In this study, we address this challenge by developing a superfine nanodomain engineering strategy. By applying this approach to representative incipient ferroelectric of SrTiO3-based films, we achieve unprecedentedly strong ferroelectricity, not only surpassing previous records for incipient ferroelectrics but also being comparable to classic ferroelectrics. The remanent polarization of the thin film reaches up to 17.0 µC cm-2 with an ultrahigh Curie temperature of 973 K. Atomic-scale investigations elucidate the origin of this robust ferroelectricity in the emergent high-density superfine nanodomains spanning merely 3-10 unit cells. Combining experimental results with theoretical assessments, we unveil the underlying mechanism, where the intentionally introduced diluted foreign Fe element creates a deeper Landau energy well and promotes a short-range ordering of polarization. Our developed strategy significantly streamlines the design of unconventional ferroelectrics, providing a versatile pathway for exploring new and superior ferroelectric materials.

Hexagonal Halide Perovskite Cs2LiInCl6: Cation Ordering, Face-Shared Octahedral Trimers and Mn2+ Luminescence.

The In-based double perovskite halides have been widely studied for promising optical-electric applications. The halide hexagonal perovskite Cs2LiInCl6 was isolated using solid-state reactions and investigated using X-ray diffraction and solid-state NMR spectra. The material adopts a 12-layered hexagonal structure (12R) consisting of layered cationic orders driven by the cationic charge difference and has Li+ cations in the terminal site and In3+ in the central site of face-shared octahedron trimers. Such a cationic ordering pattern is stabilized by electrostatic repulsions between the next-nearest neighboring cations in the trimers. The LiCl6 octahedron displays large distortion and is confirmed by 7Li SS NMR in the Cs2LiInCl6. The Cs2LiInCl6 material has a direct bandgap of ~4.98 eV. The Cs2LiInCl6: Mn2+ displays redshift luminescence (centered at ~610-622 nm) from the substituted Mn2+ emission in octahedron with larger PLQY (17.8 %-48 %) compared with that of Cs2NaInCl6: Mn2+. The Mn-doped materials show luminescent concentration quenching and thermal quenching. The composition Cs2Li0.99In0.99Mn0.02Cl6 exhibits the highest PL intensity, a maximum PLQY of 48 %, and high luminescent retention rate of ~86 % below 400 K and is suitable for application for pc-LED. These findings contribute to our understanding of the chloride perovskites and hold potential for widespread optical applications.

The glass phase in the grain boundary of Na3Zr2Si2PO12, created by gallium modulation.

Na3Zr2Si2PO12 has been proven to be a promising electrolyte for solid-state sodium batteries. However, its poor conductivity prevents application, caused by the large ionic resistance created by the grain boundary. Herein, we propose an additional glass phase (Na-Ga-Si-P-O phase) to connect the grain boundary via Ga ion introduction, resulting in enhanced sodium-ion conduction and electrochemical performance. The optimized Na3Zr2Si2PO12-0.15Ga electrolyte exhibits Na+ conductivity of 1.65 mS cm-1 at room temperature and a low activation energy of 0.16 eV, with 20% newly formed glass phase enclosing the grain boundary. Temperature-dependent NMR line shapes and spin-lattice relaxation were used to estimate the Na self-diffusion and Na ion hopping. The dense glass-ceramic electrolyte design strategy and the structure-dynamics-property correlation from NMR, can be extended to the optimization of other materials.

Ferroelectric BaTiO3 Regulating the Local Electric Field for Interfacial Stability in Solid-State Lithium Metal Batteries.

Solid-state Li metal batteries (SSLMBs) are widely investigated since they possess promising energy density and high safety. However, the poor interfacial compatibility between the electrolyte and electrodes limits their promising development. Herein, a robust composite electrolyte (poly(vinyl ethylene carbonate) electrolyte with 3 wt % of BaTiO3, PVEC-3BTO) with excellent interfacial performance is rationally designed by incorporating ferroelectric BaTiO3 (BTO) nanoparticles into the poly(vinyl ethylene carbonate) (PVEC) electrolyte matrix. Benefiting from the high dielectric constant and ferroelectric properties of BTO, the interfacial compatibility between electrolytes and electrodes was significantly improved. The enhanced Li+ transference number (0.64) of solid electrolyte and in situ generated BaF2 inorganic interphase contribute to the enhanced cycling stability of PVEC-3BTO based Li//Li symmetrical batteries. Furthermore, the antioxidation ability of PVEC-3BTO has also been enhanced by modulating the local electric field for good pairing with high-voltage LiCoO2 material. Therefore, in this work, the mechanism of BTO for improving interfacial compatibility is revealed, and also useful methods for addressing the interface issues of SSLMBs have been provided.

Insights into the Phase Purity and Storage Mechanism of Nonstoichiometric Na3.4 Fe2.4 (PO4 )1.4 P2 O7 Cathode for High-Mass-Loading and High-Power-Density Sodium-Ion Batteries.

Mixed-anion-group Fe-based phosphate materials, such as Na4 Fe3 (PO4 )2 P2 O7 , have emerged as promising cathode materials for sodium-ion batteries (SIBs). However, the synthesis of pure-phase material has remained a challenge, and the phase evolution during sodium (de)intercalation is debating as well. Herein, a solid-solution strategy is proposed to partition Na4 Fe3 (PO4 )2 P2 O7 into 2NaFePO4 ⋅ Na2 FeP2 O7 from the angle of molecular composition. Via regulating the starting ratio of NaFePO4 and Na2 FeP2 O7 during the synthesis process, the nonstoichiometric pure-phase material could be successfully synthesized within a narrow NaFePO4 content between 1.6 and 1.2. Furthermore, the proposed synthesis strategy demonstrates strong applicability that helps to address the impurity issue of Na4 Co3 (PO4 )2 P2 O7 and nonstoichiometric Na3.4 Co2.4 (PO4 )1.4 P2 O7 are evidenced to be the pure phase. The model Na3.4 Fe2.4 (PO4 )1.4 P2 O7 cathode (the content of NaFePO4 equals 1.4) demonstrates exceptional sodium storage performances, including ultrahigh rate capability under 100 C and ultralong cycle life over 14000 cycles. Furthermore, combined measurements of ex situ nuclear magnetic resonance, in situ synchrotron radiation diffraction and X-ray absorption spectroscopy clearly reveal a two-phase transition during Na+ extraction/insertion, which provides a new insight into the ionic storage process for such kind of mixed-anion-group Fe-based phosphate materials and pave the way for the development of high-power sodium-ion batteries.

Outstanding Energy-Storage Density Together with Efficiency of above 90% via Local Structure Design.

Dielectric ceramic capacitors with high recoverable energy density (Wrec) and efficiency (η) are of great significance in advanced electronic devices. However, it remains a challenge to achieve high Wrec and η parameters simultaneously. Herein, based on density functional theory calculations and local structure analysis, the feasibility of developing the aforementioned capacitors is demonstrated by considering Bi0.25Na0.25Ba0.5TiO3 (BNT-50BT) as a matrix material with large local polarization and structural distortion. Remarkable Wrec and η of 16.21 J/cm3 and 90.5% have been achieved in Bi0.25Na0.25Ba0.5Ti0.92Hf0.08O3 via simple chemical modification, which is the highest Wrec value among reported bulk ceramics with η greater than 90%. The examination results of local structures at lattice and atomic scales indicate that the disorderly polarization distribution and small nanoregion (∼3 nm) lead to low hysteresis and high efficiency. In turn, the drastic increase in local polarization activated via the ultrahigh electric field (80 kV/mm) leads to large polarization and superior energy storage density. Therefore, this study emphasizes that chemical design should be established on a clear understanding of the performance-related local structure to enable a targeted regulation of high-performance systems.

Electrochemically induced crystalline-to-amorphization transformation in sodium samarium silicate solid electrolyte for long-lasting sodium metal batteries.

Exploiting solid electrolyte (SE) materials with high ionic conductivity, good interfacial compatibility, and conformal contact with electrodes is essential for solid-state sodium metal batteries (SSBs). Here we report a crystalline Na5SmSi4O12 SE which features high room-temperature ionic conductivity of 2.9 × 10-3 S cm-1 and a low activation energy of 0.15 eV. All-solid-state symmetric cell with Na5SmSi4O12 delivers excellent cycling life over 800 h at 0.15 mA h cm-2 and a high critical current density of 1.4 mA cm-2. Such excellent electrochemical performance is attributed to an electrochemically induced in-situ crystalline-to-amorphous (CTA) transformation propagating from the interface to the bulk during repeated deposition and stripping of sodium, which leads to faster ionic transport and superior interfacial properties. Impressively, the Na|Na5SmSi4O12|Na3V2(PO4)3 sodium metal batteries achieve a remarkable cycling performance over 4000 cycles (6 months) with no capacity loss. These results not only identify Na5SmSi4O12 as a promising SE but also emphasize the potential of the CTA transition as a promising mechanism towards long-lasting SSBs.

Insights into Reversible Sodium Intercalation in a Novel Sodium-Deficient NASICON-Type Structure:Na3.40 □0.60 Co0.5 Fe0.5 V(PO4 )3.

The rational design of novel high-performance cathode materials for sodium-ion batteries is a challenge for the development of the renewable energy sector. Here, a new sodium-deficient NASICON phosphate, namely Na3.40 □0.60 Co0.5 Fe0.5 V(PO4 )3 , demonstrating the excellent electrochemical performance is reported. The presence of Co allows a third Na+ to participate in the reaction thus exhibiting a high reversible capacity of ≈155 mAh g-1 in the voltage range of 2.0-4.0 V versus Na+ /Na with a reversible single-phase mechanism and a small volume shrinkage of ≈5.97% at 4.0 V. 23 Na solid-state nuclear magnetic resonance (NMR) combined with ex situ X-ray diffraction (XRD) refinements provide evidence for a preferential Na+ insertion within the Na2 site. Furthermore, the enhanced sodium kinetics ascribed to Co-substitution is also confirmed in combination with electrochemical impedance spectroscopy (EIS), galvanostatic intermittent titration technique (GITT), and theoretical calculation.

Pressure-Stabilized High-Entropy (FeCoNiCuRu)S2 Sulfide Anode toward Simultaneously Fast and Durable Lithium/Sodium Ion Storage.

Pressure-stabilized high-entropy sulfide (FeCoNiCuRu)S2 (HES) is proposed as an anode material for fast and long-term stable lithium/sodium storage performance (over 85% retention after 15 000 cycles @10 A g-1 ). Its superior electrochemical performance is strongly related to the increased electrical conductivity and slow diffusion characteristics of entropy-stabilized HES. The reversible conversion reaction mechanism, investigated by ex-situ XRD, XPS, TEM, and NMR, further confirms the stability of the host matrix of HES after the completion of the whole conversion process. A practical demonstration of assembled lithium/sodium capacitors also confirms the high energy/power density and long-term stability (retention of 92% over 15 000 cycles @5 A g-1 ) of this material. The findings point to a feasible high-pressure route to realize new high-entropy materials for optimized energy storage performance.

Ordered Van der Waals Hetero-nanoribbon from Pressure-Induced Topochemical Polymerization of Azobenzene.

Pressure-induced topochemical polymerization of molecular crystals with various stackings is a promising way to synthesize materials with different co-existing sub-structures. Here, by compressing the azobenzene crystal containing two kinds of intermolecular stacking, we synthesized an ordered van der Waals carbon nanoribbon (CNR) heterostructure in one step. Azobenzene polymerizes via a [4 + 2] hetero-Diels-Alder (HDA) reaction of phenylazo-phenyl in layer A and a para-polymerization reaction of phenyl in layer B at 18 GPa, as evidenced by in situ Raman and IR spectroscopies, X-ray diffraction, as well as gas chromatography-mass spectrometry and the solid-state nuclear magnetic resonance of the recovered products. The theoretical calculation shows that the obtained CNR heterostructure has a type II (staggered) band gap alignment. Our work highlights a high-pressure strategy to synthesize bulk CNR heterostructures.

Achieving giant electrostrain of above 1% in (Bi,Na)TiO3-based lead-free piezoelectrics via introducing oxygen-defect composition.

Piezoelectric ceramics have been extensively used in actuators, where the magnitude of electrostrain is key indicator for large-stroke actuation applications. Here, we propose an innovative strategy based on defect chemistry to form a defect-engineered morphotropic phase boundary and achieve a giant strain of 1.12% in lead-free Bi0.5Na0.5TiO3 (BNT)-based ceramics. The incorporation of the hypothetical perovskite BaAlO2.5 with nominal oxygen defect into BNT will form strongly polarized directional defect dipoles, leading to a strong pinning effect after aging. The large asymmetrical strain is mainly attributed to two factors: The defect dipoles along crystallographic [001] direction destroy the long-range ordering of the ferroelectric and activate a reversible phase transition while promoting polarization rotation when the dipoles are aligned along the applied electric field. Our results not only demonstrate the potential application of BNT-based materials in low-frequency, large-stroke actuators but also provide a general methodology to achieve large strain.

Molecular Self-Assembled Ether-Based Polyrotaxane Solid Electrolyte for Lithium Metal Batteries.

Poly(ethylene oxide) has been widely investigated as a potential separator for solid-state lithium metal batteries. However, its applications were significantly restricted by low ionic conductivity and a narrow electrochemical stability window (<4.0 V vs Li/Li+) at room temperature. Herein, a novel molecular self-assembled ether-based polyrotaxane electrolyte was designed using different functional units and prepared by threading cyclic 18-crown ether-6 (18C6) to linear poly(ethylene glycol) (PEG) via intermolecular hydrogen bond and terminating with hexamethylene diisocyanate trimer (HDIt), which was strongly confirmed by local structure-sensitive solid/liquid-state nuclear magnetic resonance (NMR) techniques. The designed electrolyte has shown an obviously increased room-temperature ionic conductivity of 3.48 × 10-4 S cm-1 compared to 1.12 × 10-5 S cm-1 without assembling polyrotaxane functional units, contributing to the enhanced cycling stability of batteries with both LiFePO4 and LiNi0.8Co0.15Al0.05O2 cathode materials. This advanced molecular self-assembled strategy provides a new paradigm in designing solid polymer electrolytes with demanded performance for lithium metal batteries.

From Biomass to Functional Crystalline Diamond Nanothread: Pressure-Induced Polymerization of 2,5-Furandicarboxylic Acid.

2,5-Furandicarboxylic acid (FDCA) is one of the top-12 value-added chemicals from sugar. Besides the wide application in chemical industry, here we found that solid FDCA polymerized to form an atomic-scale ordered sp3-carbon nanothread (CNTh) upon compression. With the help of perfectly aligned π-π stacked molecules and strong intermolecular hydrogen bonds, crystalline poly-FDCA CNTh with uniform syn-configuration was obtained above 11 GPa, with the crystal structure determined by Rietveld refinement of the X-ray diffraction (XRD). The in situ XRD and theoretical simulation results show that the FDCA experienced continuous [4 + 2] Diels-Alder reactions along the stacking direction at the threshold C···C distance of ∼2.8 Å. Benefiting from the abundant carbonyl groups, the poly-FDCA shows a high specific capacity of 375 mAh g-1 as an anode material of a lithium battery with excellent Coulombic efficiency and rate performance. This is the first time a three-dimensional crystalline CNTh is obtained, and we demonstrated it is the hydrogen bonds that lead to the formation of the crystalline material with a unique configuration. It also provides a new method to move biomass compounds toward advanced functional carbon materials.

A Methyl-Modified Silica Layer Supported on Porous Ceramic Membranes for the Enhanced Separation of Methyl Tert-Butyl Ether from Aqueous Solution.

As a kind of volatile organic compound (VOC), methyl tert-butyl ether (MTBE) is hazardous to human health and destructive to the environment if not handled properly. MTBE should be removed before the release of wastewater. The present work supported the methyl-modified silica layer (MSL) on porous α-Al2O3 ceramic membranes with methyltrimethoxysilane (MTMS) as a precursor and pre-synthesized mesoporous silica microspheres as dopants by the sol-gel reaction and dip-coating method. MTMS is an environmentally friendly agent compared to fluorinated alkylsilane. The MSL-supported Al2O3 ceramic membranes were used for MTBE/water separation by pervaporation. The NMR spectra revealed that MTMS evolves gradually from an oligomer to a highly cross-linked methyl-modified silica species. Methyl-modified silica species and pre-synthesized mesoporous silica microspheres combine into hydrophobic mesoporous MSL. MSL makes the α-Al2O3 ceramic membranes transfer from amphiphilic to hydrophobic and oleophilic. The MSL-supported α-Al2O3 ceramic membranes (MSL-10) exhibit an MTBE/water separation factor of 27.1 and a total flux of 0.448 kg m-2 h-1, which are considerably higher than those of previously reported membranes that are modified by other alkylsilanes via the post-grafting method. The mesopores within the MSL provide a pathway for the transport of MTBE molecules across the membranes. The presence of methyl groups on the external and inner surface is responsible for the favorable separation performance and the outstanding long-term stability of the MSL-supported porous α-Al2O3 ceramic membranes.

Tailoring the Luminescent Properties of SrS:Ce3+ by Sr-Deficiency and Na+ Doping.

Ce3+-doped SrS phosphors with a charge-compensating Na+ addition were successfully synthesized via a solid-state reaction method, and the related X-ray diffraction patterns can be indexed to the rock-salt-like crystal structure of the Fm3̅m space group. SrS:(Ce3+)x (0.005 ≤ x ≤ 0.05) and SrS:(Ce3+)0.01,(Na+)y (0.005 ≤ y ≤ 0.030) phosphors were excited by 430 nm UV-Vis light, targeted to the 5d1 → 4f1 transition of Ce3+. The composition-optimized SrS:(Ce3+)0.01, (Na+)0.015 phosphors showed an intense broad emission band at λ = 430-700 nm. The doping of Na+ was probed by solid-state nuclear magnetic resonance. The 430 nm pumped white light-emitting diode structure fabricated with a combination of SrS:(Ce3+)0.01,(Na+)0.015 and Sr2Si5N8:Eu2+ phosphors shows a color-rendering index (Ra) of 89.7. The proposed strategy provides new avenues for the design and realization of novel high color quality solid-state LEDs.