Regulating the Electron Distribution of Metal-Oxygen for Enhanced Oxygen Stability in Li-rich Layered Cathodes.

Li-rich Mn-based layered oxides (LLO) hold great promise as cathode materials for lithium-ion batteries (LIBs) due to their unique oxygen redox (OR) chemistry, which enables additional capacity. However, the LLOs face challenges related to the instability of their OR process due to the weak transition metal (TM)-oxygen bond, leading to oxygen loss and irreversible phase transition that results in severe capacity and voltage decay. Herein, a synergistic electronic regulation strategy of surface and interior structures to enhance oxygen stability is proposed. In the interior of the materials, the local electrons around TM and O atoms may be delocalized by surrounding Mo atoms, facilitating the formation of stronger TM─O bonds at high voltages. Besides, on the surface, the highly reactive O atoms with lone pairs of electrons are passivated by additional TM atoms, which provides a more stable TM─O framework. Hence, this strategy stabilizes the oxygen and hinders TM migration, which enhances the reversibility in structural evolution, leading to increased capacity and voltage retention. This work presents an efficient approach to enhance the performance of LLOs through surface-to-interior electronic structure modulation, while also contributing to a deeper understanding of their redox reaction.

Na2.5 Cr0.5 Zr0.5 Cl6 : A New Halide-Based Fast Sodium-Ion Conductor.

All-solid-state batteries employing solid electrolytes (SEs) have received widespread attention due to their high safety. Recently, lithium halides are intensively investigated as promising SEs while their sodium counterparts are less studied. Herein, a new sodium-ion conductor with a chemical formula of Na2.5 Cr0.5 Zr0.5 Cl6 is reported, which exhibits high room temperature ionic conductivity of 0.1 mS cm-1 with low migration energy barrier of ≈0.41 eV. Na2.5 Cr0.5 Zr0.5 Cl6 has a Fm-3m structure with 41.67 mol.% of cationic vacancies owing to the occupation of Cr (8.33 mol.%) and Zr (8.33 mol.%) ions at Na sites. Supercell calculations show that the lowest columbic energy configuration has Cr/Zr/V (where V is the vacancy) clusters in the structure. Nonetheless, the clusters have mixed effects on the sodium ion conduction pathway, based on the Bond Valence Energy Landscape calculation. A global 3D Na-ion transport percolation network can be revealed in the lowest energy supercell. Effective pathways are connected through the NaCl6 and VCl6 nodes. Besides, Raman spectroscopy and 23 Na solid-state nuclear magnetic resonance spectroscopy further prove the tunable structure of the SEs with different Cr to Zr ratios. The optimization between the concentration of Na+ and vacancies is crucial to create an improved network of Na+ diffusion channels.

Taming heat with tiny pressure.

Heat is almost everywhere. Unlike electricity, which can be easily manipulated, the current ability to control heat is still highly limited owing to spontaneous thermal dissipation imposed by the second law of thermodynamics. Optical illumination and pressure have been used to switch endothermic/exothermic responses of materials via phase transitions; however, these strategies are less cost-effective and unscalable. Here, we spectroscopically demonstrate the glassy crystal state of 2-amino-2-methyl-1,3-propanediol (AMP) to realize an affordable, easily manageable approach for thermal energy recycling. The supercooled state of AMP is so sensitive to pressure that even several megapascals can induce crystallization to the ordered crystal, resulting in a substantial temperature increase of 48 K within 20 s. Furthermore, we demonstrate a proof-of-concept device capable of programable heating with an extremely high work-to-heat conversion efficiency of ∼383. Such delicate and efficient tuning of heat may remarkably facilitate rational utilization of waste heat.

Promoting high-voltage stability through local lattice distortion of halide solid electrolytes.

Stable solid electrolytes are essential to high-safety and high-energy-density lithium batteries, especially for applications with high-voltage cathodes. In such conditions, solid electrolytes may experience severe oxidation, decomposition, and deactivation during charging at high voltages, leading to inadequate cycling performance and even cell failure. Here, we address the high-voltage limitation of halide solid electrolytes by introducing local lattice distortion to confine the distribution of Cl-, which effectively curbs kinetics of their oxidation. The confinement is realized by substituting In with multiple elements in Li3InCl6 to give a high-entropy Li2.75Y0.16Er0.16Yb0.16In0.25Zr0.25Cl6. Meanwhile, the lattice distortion promotes longer Li-Cl bonds, facilitating favorable activation of Li+. Our results show that this high-entropy halide electrolyte boosts the cycle stability of all-solid-state battery by 250% improvement over 500 cycles. In particular, the cell provides a higher discharge capacity of 185 mAh g-1 by increasing the charge cut-off voltage to 4.6 V at a small current rate of 0.2 C, which is more challenging to electrolytes|cathode stability. These findings deepen our understanding of high-entropy materials, advancing their use in energy-related applications.

Long-range ordered porous carbons produced from C60.

Carbon structures with covalent bonds connecting C60 molecules have been reported1-3, but their production methods typically result in very small amounts of sample, which restrict the detailed characterization and exploration necessary for potential applications. We report the gram-scale preparation of a new type of carbon, long-range ordered porous carbon (LOPC), from C60 powder catalysed by α-Li3N at ambient pressure. LOPC consists of connected broken C60 cages that maintain long-range periodicity, and has been characterized by X-ray diffraction, Raman spectroscopy, magic-angle spinning solid-state nuclear magnetic resonance spectroscopy, aberration-corrected transmission electron microscopy and neutron scattering. Numerical simulations based on a neural network show that LOPC is a metastable structure produced during the transformation from fullerene-type to graphene-type carbons. At a lower temperature, shorter annealing time or by using less α-Li3N, a well-known polymerized C60 crystal forms owing to the electron transfer from α-Li3N to C60. The carbon K-edge near-edge X-ray absorption fine structure shows a higher degree of delocalization of electrons in LOPC than in C60(s). The electrical conductivity is 1.17 × 10-2 S cm-1 at room temperature, and conduction at T < 30 K appears to result from a combination of metallic-like transport over short distances punctuated by carrier hopping. The preparation of LOPC enables the discovery of other crystalline carbons starting from C60(s).

Synergistic activation of anionic redox via cosubstitution to construct high-capacity layered oxide cathode materials for sodium-ion batteries.

As a potential substitute for lithium-ion battery, sodium-ion batteries (SIBs) have attracted a tremendous amount of attention due to their advantages in terms of cost, safety and sustainability. Nevertheless, further improvement of the energy density of cathode materials in SIBs remains challenging and requires the activation of anion redox reaction (ARR) activity to provide additional capacity. Herein, we report a high-performance Mn-based sodium oxide cathode material, Na0.67Mg0.1Zn0.1Mn0.8O2 (NMZMO), with synergistic activation of ARR by cosubstitution. This material can deliver an ultra-high capacity of âˆ¼233 mAh/g at 0.1 C, which is significantly higher than their single-cation-substituted counterparts and among the best in as-reported MgMn or ZnMn-based cathodes. Various spectroscopic techniques were comprehensively employed and it was demonstrated that the higher capacity of NMZMO originated from the enhanced ARR activity. Neutron pair distribution function and resonant inelastic X-ray scattering experiments revealed that out-of-plane migration of Mg/Zn occurred upon charging and oxygen anions in the form of molecular O2 were trapped in vacancy clusters in the fully-charged-state. In NMZMO, Mg and Zn mutually interacted with each other to migrate toward tetrahedral sites, which provided a prerequisite for further ARR activity enhancement to form more trapped molecular O2. These findings provide unique insight into the ARR mechanism and can guide the development of high-performance cathode materials through ARR enhancement strategies.

Slight compositional variation-induced structural disorder-to-order transition enables fast Na+ storage in layered transition metal oxides.

The omnipresent Na+/vacancy orderings change substantially with the composition that inevitably actuate the ionic diffusion in rechargeable batteries. Therefore, it may hold the key to the electrode design with high rate capability. Herein, the influence of Na+/vacancy ordering on Na+ mobility is demonstrated firstly through a comparative investigation in P2-Na2/3Ni1/3Mn2/3O2 and P2-Na2/3Ni0.3Mn0.7O2. The large zigzag Na+/vacancy intralayer ordering is found to accelerate Na+ migration in P2-type Na2/3Ni1/3Mn2/3O2. By theoretical simulations, it is revealed that the Na+ ordering enables the P2-type Na2/3Ni1/3Mn2/3O2 with higher diffusivities and lower activation energies of 200 meV with respect to the P3 one. The quantifying diffusional analysis further prove that the higher probability of the concerted Na+ ionic diffusion occurs in P2-type Na2/3Ni1/3Mn2/3O2 due to the appropriate ratio of high energy ordered Na ions (Naf) occupation. As a result, the interplay between the Na+/vacancy ordering and Na+ kinetic is well understood in P2-type layered cathodes.

Lithiated Prussian blue analogues as positive electrode active materials for stable non-aqueous lithium-ion batteries.

Prussian blue analogues (PBAs) are appealing active materials for post-lithium electrochemical energy storage. However, PBAs are not generally suitable for non-aqueous Li-ion storage due to their instability upon prolonged cycling. Herein, we assess the feasibility of PBAs with various lithium content for non-aqueous Li-ion storage. We determine the crystal structure of the lithiated PBAs via neutron powder diffraction measurements and investigate the influence of water on structural stability and Li-ion migration through operando X-ray diffraction measurements and bond valence simulations. Furthermore, we demonstrate that a positive electrode containing Li2-xFeFe(CN)6⋅nH2O (0 ≤ x ≤ 2) active material coupled with a Li metal electrode and a LiPF6-containing organic-based electrolyte in coin cell configuration delivers an initial discharge capacity of 142 mAh g-1 at 19 mA g-1 and a discharge capacity retention of 80.7% after 1000 cycles at 1.9 A g-1. By replacing the lithium metal with a graphite-based negative electrode, we also report a coin cell capable of cycling for more than 370 cycles at 190 mA g-1 with a stable discharge capacity of about 105 mAh g-1 and a discharge capacity retention of 98% at 25 °C.

Neutron Total Scattering Investigation of the Dissolution Mechanism of Trehalose in Alkali/Urea Aqueous Solution.

The atomic picture of cellulose dissolution in alkali/urea aqueous solution is still not clear. To reveal it, we use trehalose as the model molecule and total scattering as the main tool. Three kinds of alkali solution, i.e., LiOH, NaOH and KOH are compared. The most probable all-atom structures of the solution are thus obtained. The hydration shell of trehalose has a layered structure. The smaller alkali ions can penetrate into the glucose rings around oxygen atoms to form the first hydration layer. The larger urea molecules interact with hydroxide groups to form complexations. Then, the electronegative complexation can form the second hydration layer around alkali ions via electrostatic interaction. Therefore, the solubility of alkali aqueous solution for cellulose decreases with the alkali cation radius, i.e., LiOH > NaOH > KOH. Our findings are helpful for designing better green solvents for cellulose.

Octahedral rotations trigger electronic and magnetic transitions in strontium manganate under volume expansion.

The perovskite structure of manganate yields a series of intriguing physical properties. Based on the results of first-principles calculations, strontium manganate appears to undergo a magnetic phase transition and a metal-insulator transition-from antiferromagnetic insulator to ferromagnetic metal and then to ferromagnetic insulator-under isotropic volume expansion combined with oxygen octahedral distortions. Interestingly, the results show that increasing the Mn-O bond length and adding rotation of the oxygen octahedra can soften the breathing distortion and account for the insulator phase. We further build a simple model to explain such transitions. Due to electron transfer and the favoring of a hole state of ligandporbitals, the electron state transfer from2(t2g3)to2(eg1+t2g2)and then tot2g3eg1+(t2g3L̲1). Such rearrangement of charges is responsible for the transitions of its magnetic order and electronic structure. Furthermore, we calculate spin susceptibility under the bare conditions and random phase approximation. The magnetic order of the intermediate metal state of itinerant electrons behaves as a ferromagnetic.

The Kinetic Behaviors of H Impurities in the Li/Ta Bilayer: Application for the Accelerator-Based BNCT.

Hydrogen bubble phenomenon is one of the key issues to be solved in the development of a long-life target system for boron neutron capture therapy (BNCT). In this study, we assessed the kinetic behaviors of H impurities in the nano-composite target from the atomic level. Firstly, two kinds of Li/Ta nanolayer models were constructed, based on the calculated lattice parameters and surface energies. The H solution energy, diffusion mechanism, and hydrogen bubbles formation in the Li/Ta nanostructured bilayer were studied, through theoretical modeling and simulation. Our results show that the Li/Ta interfaces are effective sinks of H atoms because the H solution energies in the interface are lower. Meanwhile, due to the relatively low diffusion barriers, the large-scale H transport through the interface is possible. In addition, although it is more likely to form hydrogen bubbles in the Ta layer, compared with the Li layer, the anti-blistering ability of Ta is more impressive compared with most of other candidate materials. Therefore, the Ta layer is able to act as the hydrogen absorber in the Li/Ta bilayer, and relieve the hydrogen damage of the Li layer in the large-scale proton radiations.

Uniform Doping of Titanium in Hematite Nanorods for Efficient Photoelectrochemical Water Splitting.

Doping elements in hematite nanostructures is a promising approach to improve the photoelectrochemical (PEC) water-splitting performance of hematite photoanodes. However, uniform doping with precise control on doping amount and morphology is the major challenge for quantitatively investigating the PEC water-splitting enhancement. Here, we report on the design and synthesis of uniform titanium (Ti)-doped hematite nanorods with precise control of the Ti amount and morphology for highly effective PEC water splitting using an atomic layer deposition assisted solid-state diffusion method. We found that Ti doping promoted band bending and increased the carrier density as well as the surface state. Remarkably, these uniformly doped hematite nanorods exhibited high PEC performance with a pronounced photocurrent density of 2.28 mA/cm(2) at 1.23 V vs reversible hydrogen electrode (RHE) and 4.18 mA/cm(2) at 1.70 V vs RHE, respectively. Furthermore, as-prepared Ti-doping hematite nanorods performed excellent repeatability and durability; over 80% of the as-fabricated photoanodes reproduced the steady photocurrent density of 1.9-2.2 mA/cm(2) at 1.23 V vs RHE at least 3 h in a strong alkaline electrolyte solution.