Spinel‐Layered Core‐Shell Cathode Materials for Li‐Ion Batteries

In an attempt to overcome the problems associated with LiNiO₂, the solid solution series of lithium nickel‐metal oxides, Li[Ni_1–xM_x]O₂ (with M = Co, Mn, Al, Ti, Mg, etc.), have been investigated as favorable cathode materials for high‐energy and high‐power lithium‐ion batteries. However, along with the improvement in the electrochemical properties in Ni‐based cathode materials, the thermal stability has been a great concern, and thus violent reaction of the cathode with the electrolyte needs to be avoided. Here, we report a heterostructured Li[Ni_0.54Co_0.12Mn_0.34]O₂ cathode material which possesses both high energy and safety. The core of the particle is Li[Ni_0.54Co_0.12Mn_0.34]O₂ with a layered phase (R3‐m) and the shell, with a thickness of < 0.5 μm, is a highly stable Li_1+x[CoNi_xMn_2–x]₂O₄ spinel phase (Fd‐3m). The material demonstrates reversible capacity of 200 mAhg‐1 and retains 95% capacity retention under the most severe test condition of 60 °C. In addition, the amount of oxygen evolution from the lattice in the cathode with two heterostructures is reduced by 70%, compared to the reference sample. All these results suggest that the bulk Li[Ni_0.54Co_0.12Mn_0.34]O₂ consisting of two heterostructures satisfy the requirements for hybrid electric vehicles, power tools, and mobile electronics.     

Synthesis and Characterization of High‐Energy,High‐Power Spinel‐Layered Composite Cathode Materials for Lithium‐Ion Batteries

Spinel‐layered composites, where a high‐voltage spinel is incorporated in a layered lithium‐rich (Li‐rich) cathode material with a nominal composition x{0.6Li₂MnO₃ · 0.4[LiCo_0.333Mn_0.333Ni_0.333]O₂} · (1 – x) Li[Ni_0.5Mn_1.5]O₄ (x = 0, 0.3, 0.5, 0.7, 1) are synthesized via a hydroxide assisted coprecipitation route to generate high‐energy, high‐power cathode materials for Li‐ion batteries. X‐ray diffraction patterns and the cyclic voltammetry investigations confirm the presence of both the parent components in the composites. The electrochemical investigations performed within a wide potential window show an increased structural stability of the spinel component when incorporated into the composite environment. All the composite materials exhibit initial discharge capacities >200 mAh g^–1. The compositions with x = 0.5 and 0.7 show excellent cycling stability among the investigated materials. Moreover, the first cycle Coulombic efficiency achieve a dramatic improvement with the incorporation of the spinel component. More notably, the composite materials with increased spinel component exhibit superior rate capability compared with the parent Li‐rich material especially together with the highest capacity retention for x = 0.5 composition, making this as the optimal high‐energy high‐power material. The mechanisms involved in the symbiotic relationship of the spinel and layered Li‐rich components in the above composites are discussed.     

Engineering Temperature‐Dependent Carrier Concentration in Bulk Composite Materials via Temperature‐Dependent Fermi Level Offset

Precise control of carrier concentration in both bulk and thin‐film materials is crucial for many solid‐state devices, including photovoltaic cells, superconductors, and high mobility transistors. For applications that span a wide temperature range (thermoelectric power generation being a prime example) the optimal carrier concentration varies as a function of temperature. This work presents a modified modulation doping method to engineer the temperature dependence of the carrier concentration by incorporating a nanosize secondary phase that controls the temperature‐dependent doping in the bulk matrix. This study demonstrates this technique by de‐doping the heavily defect‐doped degenerate semiconductor GeTe, thereby enhancing its average power factor by 100% at low temperatures, with no deterioration at high temperatures. This can be a general method to improve the average thermoelectric performance of many other materials.     

Studies on Thermoelectric Properties of n‐type Polycrystalline SnSe1‐xSx by Iodine Doping

Iodine‐doped n‐type SnSe polycrystalline by melting and hot pressing is prepared. The prepared material is anisotropic with a peak ZT of ≈0.8 at about 773 K measured along the hot pressing direction. This is the first report on thermoelectric properties of n‐type Sn chalcogenide alloys. With increasing content of iodine, the carrier concentration changed from 2.3 × 10¹⁷ cm^?3 (p‐type) to 5.0 × 10¹⁵ cm^?3 (n‐type) then to 2.0 × 10¹⁷ cm^?3 (n‐type). The decent ZT is mainly attributed to the intrinsically low thermal conductivity due to the high anharmonicity of the chemical bonds like those in p‐type SnSe. By alloying with 10 at% SnS, even lower thermal conductivity and an enhanced Seebeck coefficient were achieved, leading to an increased ZT of ≈1.0 at about 773 K measured also along the hot pressing direction.     

All‐Organic Battery Composed of Thianthrene‐ and TCAQ‐Based Polymers

An all‐organic battery consisting of two redox‐polymers, namely poly(2‐vinylthianthrene) and poly(2‐methacrylamide‐TCAQ) is assembled. This all‐organic battery shows excellent performance characteristics, namely flat discharge plateaus, an output voltage exceeding 1.3 V, and theoretical capacities of both electrodes higher than 100 mA h g^?1. Both organic electrode materials are synthesized in two respective three synthetic steps using the free‐radical polymerization technique. Li‐organic batteries manufactured from these polymers prove their suitability as organic electrode materials. The cathode material poly(2‐vinylthianthrene) (3) displays a discharging plateau at 3.95 V versus Li⁺/Li and a discharge capacity of 105 mA h g^?1, corresponding to a specific energy of about 415 mW h g^?1. The anode material poly(2‐methacrylamide‐TCAQ) (7) exhibits an initial discharge capacity of 130 mA h g^?1, corresponding to 94% material activity. The combination of both materials results in an all‐organic battery with a discharge voltage of 1.35 V and an initial discharge capacity of 105 mA h g^?1 (95% material activity).     

A High‐Energy NASICON‐Type Cathode Material for Na‐Ion Batteries

Over the last decade, Na‐ion batteries have been extensively studied as low‐cost alternatives to Li‐ion batteries for large‐scale grid storage applications; however, the development of high‐energy positive electrodes remains a major challenge. Materials with a polyanionic framework, such as Na superionic conductor (NASICON)‐structured cathodes with formula Na_xM₂(PO₄)₃, have attracted considerable attention because of their stable 3D crystal structure and high operating potential. Herein, a novel NASICON‐type compound, Na₄MnCr(PO₄)₃, is reported as a promising cathode material for Na‐ion batteries that deliver a high specific capacity of 130 mAh g^?1 during discharge utilizing high‐voltage Mn^2+/3+ (3.5 V), Mn^3+/4+ (4.0 V), and Cr^3+/4+ (4.35 V) transition metal redox. In addition, Na₄MnCr(PO₄)₃ exhibits a high rate capability (97 mAh g^?1 at 5 C) and excellent all‐temperature performance. In situ X‐ray diffraction and synchrotron X‐ray diffraction analyses reveal reversible structural evolution for both charge and discharge.     

Single‐Crystalline Nanomesh Tantalum Nitride Photocatalyst with Improved Hydrogen‐Evolving Performance

Tantalum nitride (Ta₃N₅) with a suitable bandgap (≈2 eV) is regarded as one of the most promising photocatalysts for efficient solar energy harvesting and conversion. However, Ta₃N₅ suffers from low hydrogen production activity due to the low carrier mobility and fast carrier recombination. Thus, the design of Ta₃N₅ nanostructures to facilitate charge carrier transport and improve photocatalytic performance remains a challenge. This study reports a new type of ultrathin (≈2 nm) Ta₃N₅ nanomesh with high specific surface area (284.6 m² g^?1) and excellent crystallinity by an innovative bottom‐up graphene oxide templated strategy. The resulting Ta₃N₅ nanomeshes demonstrate drastically improved electron transport ability and prolonged lifetime of charge carriers, due to the nature of high surface area and excellent crystallinity. As a result, when used as photocatalysts, the Ta₃N₅ nanomeshes exhibit a greater than tenfold improvement in solar hydrogen production compared to bulk counterparts. This work provides an effective and generic strategy for designing 2D ultrathin nanomesh structures for nonlayered materials with improved catalytic activity.     

Mn‐Rich P′2‐Na0.67[Ni0.1Fe0.1Mn0.8]O2 as High‐Energy‐Density and Long‐Life Cathode Material for Sodium‐Ion Batteries

Herein, P′2‐type Na_0.67[Ni_0.1Fe_0.1Mn_0.8]O₂ is introduced as a promising new cathode material for sodium‐ion batteries (SIBs) that exhibits remarkable structural stability during repetitive Na⁺ de/intercalation. The O? Ni? O? Mn? O? Fe? O bond in the octahedra of transition‐metal layers is used to suppress the elongation of the Mn? O bond and to improve the electrochemical activity, leading to the highly reversible Na storage mechanism. A high discharge capacity of ≈220 mAh g^?1 (≈605 Wh kg^?1) is delivered at 0.05 C (13 mAg^?1) with a high reversible capacity of ≈140 mAh g^?1 at 3 C and excellent capacity retention of 80% over 200 cycles. This performance is associated with the reversible P′2–OP4 phase transition and small volume change upon charge and discharge (≈3%). The nature of the sodium storage mechanism in a full cell paired with a hard carbon anode reveals an unexpectedly high energy density of ≈542 Wh kg^?1 at 0.2 C and good capacity retention of ≈81% for 500 cycles at 1 C (260 mAg^?1).     

A New Spinel‐Layered Li‐Rich Microsphere as a High‐Rate Cathode Material for Li‐Ion Batteries

Li‐rich layered materials are considered to be the promising low‐cost cathodes for lithium‐ion batteries but they suffer from poor rate capability despite of efforts toward surface coating or foreign dopings. Here, spinel‐layered Li‐rich Li‐Mn‐Co‐O microspheres are reported as a new high‐rate cathode material for Li‐ion batteries. The synthetic procedure is relatively simple, involving the formation of uniform carbonate precursor under solvothermal conditions and its subsequent transformation to an assembled microsphere that integrates a spinel‐like component with a layered component by a heat treatment. When calcined at 700 °C, the amount of transition metal Mn and Co in the Li‐Mn‐Co‐O microspheres maintained is similar to at 800 °C, while the structures of constituent particles partially transform from 2D to 3D channels. As a consequence, when tested as a cathode for lithium‐ion batteries, the spinel‐layered Li‐rich Li‐Mn‐Co‐O microspheres obtained at 700 °C show a maximum discharge capacity of 185.1 mA h g^?1 at a very high current density of 1200 mA g^?1 between 2.0 and 4.6 V. Such a capacity is among the highest reported to date at high charge‐discharge rates. Therefore, the present spinel‐layered Li‐rich Li‐Mn‐Co‐O microspheres represent an attractive alternative to high‐rate electrode materials for lithium‐ion batteries.     

Molecular Engineered Hole‐Extraction Materials to Enable Dopant‐Free,Efficient p‐i‐n Perovskite Solar Cells

Two hole‐extraction materials (HEMs), TPP‐OMeTAD and TPP‐SMeTAD, have been developed to facilitate the fabrication of efficient p‐i‐n perovskite solar cells (PVSCs). By replacing the oxygen atom on HEM with sulfur (from TPP‐OMeTAD to TPP‐SMeTAD), it effectively lowers the highest occupied molecular orbital of the molecule and provides stronger Pb? S interaction with perovskites, leading to efficient charge extraction and surface traps passivation. The TPP‐SMeTAD‐based PVSCs exhibit both improved photovoltaic performance and reduced hysteresis in p‐i‐n PVSCs over those based on TPP‐OMeTAD. This work not only provides new insights on creating perovskite‐HEM heterojunction but also helps in designing new HEM to enable efficient organic–inorganic hybrid PVSCs.