Direct Observation of Alternating Octahedral and Prismatic Sodium Layers in O3‐Type Transition Metal Oxides

The oxygen stacking of O3‐type layered sodium transition metal oxides (O3‐NaTMO₂) changes dynamically upon topotactic Na extraction and reinsertion. While the phase transition from octahedral to prismatic Na coordination that occurs at intermediate desodiation by transition metal slab gliding is well understood, the structural evolution at high desodiation, crucial to achieve high reversible capacity, remains mostly uncharted. In this work, the phase transitions of O3‐type layered NaTMO₂ at high voltage are investigated by combining experimental and computational approaches. An OP2‐type phase that consists of alternating octahedral and prismatic Na layers is directly observed by in situ X‐ray diffraction and high‐resolution scanning transmission electron microscopy. The origin of this peculiar phase is explained by atomic interactions involving Jahn–Teller active Fe⁴⁺ and distortion tolerant Ti⁴⁺ that stabilize the local Na environment. The path‐dependent desodiation and resodiation pathways are also rationalized in this material through the different kinetics of the prismatic and octahedral layers, presenting a comprehensive picture about the structural stability of the layered materials upon Na intercalation.     

Ethylene Carbonate‐Free Electrolytes for High‐Nickel Layered Oxide Cathodes in Lithium‐Ion Batteries

Layered lithium nickel oxide (LiNiO₂) can provide very high energy density among intercalation cathode materials for lithium‐ion batteries, but suffers from poor cycle life and thermal‐abuse tolerance with large lithium utilization. In addition to stabilization of the active cathode material, a concurrent development of electrolyte systems of better compatibility is critical to overcome these limitations for practical applications. Here, with nonaqueous electrolytes based on exclusively aprotic acyclic carbonates free of ethylene carbonate (EC), superior electrochemical and thermal characteristics are obtained with an ultrahigh‐nickel cathode (LiNi_0.94Co_0.06O₂), capable of reaching a 235 mA h g^?1 specific capacity. Pouch‐type graphite|LiNi_0.94Co_0.06O₂ cells in EC‐free electrolytes withstand several hundred charge–discharge cycles with minor degradation at both ambient and elevated temperatures. In thermal‐abuse tests, the cathode at full charge, while reacting aggressively with EC‐based electrolytes below 200 °C, shows suppressed self‐heating without EC. Through 3D chemical and structural analyses, the intriguing impact of EC is visualized in aggravating unwanted surface parasitic reactions and irreversible bulk structural degradation of the cathode at high voltages. These results provide important insights in designing high‐energy electrodes for long‐lasting and reliable lithium‐ion batteries.     

Controlled Oxygen Redox for Excellent Power Capability in Layered Sodium‐Based Compounds

A high‐rate of oxygen redox assisted by cobalt in layered sodium‐based compounds is achieved. The rationally designed Na_0.6[Mg_0.2Mn_0.6Co_0.2]O₂ exhibits outstanding electrode performance, delivering a discharge capacity of 214 mAh g^?1 (26 mA g^?1) with capacity retention of 87% after 100 cycles. High rate performance is also achieved at 7C (1.82 A g^?1) with a capacity of 107 mAh g^?1. Surprisingly, the Na_0.6[Mg_0.2Mn_0.6Co_0.2]O₂ compound is able to deliver capacity for 1000 cycles at 5C (at 1.3 A g^?1), retaining 72% of its initial capacity of 108 mAh g^?1. X‐ray absorption spectroscopy analysis of the O K‐edge indicates the oxygen‐redox species (O^2?/1?) is active during cycling. First‐principles calculations show that the addition of Co reduces the bandgap energy from ≈2.65 to ≈0.61 eV and that overlapping of the Co 3d and O 2p orbitals facilitates facile electron transfer, enabling the long‐term reversibility of the oxygen redox, even at high rates. To the best of the authors' knowledge, this is the first report on high‐rate oxygen redox in sodium‐based cathode materials, and it is believed that the findings will open a new pathway for the use of oxygen‐redox‐based materials for sodium‐ion batteries.     

A Stable Layered Oxide Cathode Material for High‐Performance Sodium‐Ion Battery

As one of the most promising cathode candidates for room‐temperature sodium‐ion batteries (SIBs), P2‐type layered oxides face the challenge of simultaneously realizing high‐rate performance while achieving long cycle life. Here, a stable Na_2/3Ni_1/6Mn_2/3Cu_1/9Mg_1/18O₂ cathode material is proposed that consists of multiple‐layer oriented stacking nanoflakes, in which the nickel sites are partially substituted by copper and magnesium, a characteristic of the material that is confirmed by multiscale scanning transmission electron microscopy and electron energy loss spectroscopy techniques. Owing to the optimal morphology structure modulation and chemical element substitution strategy, the electrode displays remarkable rate performance (73% capacity retention at 30C compared to 0.5C) and outstanding cycling stability in Na half‐cell system couple with unprecedented full battery performance. The underlying thermal stability, phase stability, and Na⁺ storage mechanisms are clearly elucidated through the systematical characterizations of electrochemical behaviors, in situ X‐ray diffraction at different temperatures, and operando X‐ray diffraction upon Na⁺ deintercalation/intercalation. Surprisingly, a quasi‐solid‐solution reaction is switched to an absolute solid‐solution reaction and a capacitive Na⁺ storage mechanism is demonstrated via quantitative electrochemical kinetics calculation during charge/discharge process. Such a simple and effective strategy might reveal a new avenue into the rational design of excellent rate capability and long cycle stability cathode materials for practical SIBs.     

Microstructure‐Controlled Ni‐Rich Cathode Material by Microscale Compositional Partition for Next‐Generation Electric Vehicles

A multicompositional particulate Li[Ni_0.9Co_0.05Mn_0.05]O₂ cathode in which Li[Ni_0.94Co_0.038Mn_0.022]O₂ at the particle center is encapsulated by a 1.5 µm thick concentration gradient (CG) shell with the outermost surface composition Li[Ni_0.841Co_0.077Mn_0.082]O₂ is synthesized using a differential coprecipitation process. The microscale compositional partitioning at the particle level combined with the radial texturing of the refined primary particles in the CG shell layer protracts the detrimental H2 → H3 phase transition, causing sharp changes in the unit cell dimensions. This protraction, confirmed by in situ X‐ray diffraction and transmission electron microscopy, allows effective dissipation of the internal strain generated upon the H2 → H3 phase transition, markedly improving cycling performance and thermochemical stability as compared to those of the conventional single‐composition Li[Ni_0.9Co_0.05Mn_0.05]O₂ cathodes. The compositionally partitioned cathode delivers a discharge capacity of 229 mAh g^?1 and exhibits capacity retention of 88% after 1000 cycles in a pouch‐type full cell (compared to 68% for the conventional cathode). Thus, the proposed cathode material provides an opportunity for the rational design and development of a wide range of multifunctional cathodes, especially for Ni‐rich Li[Ni_xCo_yMn_1‐x‐y]O₂ cathodes, by compositionally partitioning the cathode particles and thus optimizing the microstructural response to the internal strain produced in the deeply charged state.     

Some ‘ant’swers: Application of a layered barcode approach to problems in ant taxonomy

DNA barcoding has emerged as a routine tool in modern taxonomy. Although straightforward, this approach faces new challenges, when applied to difficult situation such as defining cryptic biodiversity. Ants are prime examples for high degrees of cryptic biodiversity due to complex population differentiation, hybridization and speciation processes. Here, we test the DNA barcoding region, cytochrome c oxidase 1 and two supplementary markers, 28S ribosomal DNA and long‐wavelength rhodopsin, commonly used in ant taxonomy, for their potential in a layered, character‐based barcoding approach across different taxonomic levels. Furthermore, we assess performance of the character‐based barcoding approach to determine cryptic species diversity in ants. We found (i) that the barcode potential of a specific genetic marker varied widely among taxonomic levels in ants; (ii) that application of a layered, character‐based barcode for identification of specimens can be a solution to taxonomical challenging groups; (iii) that the character‐based barcoding approach allows us to differentiate specimens even within locations based on pure characters. In summary, (layered) character‐based barcoding offers a reliable alternative for problematic species identification in ants and can be used as a fast and cost‐efficient approach to estimate presence, absence or frequency of cryptic species.     

Layered Double Hydroxide Nanostructured Photocatalysts for Renewable Energy Production

An enormous research effort is currently being directed towards the development of efficient visible‐light‐driven photocatalysts for renewable energy applications including water splitting, CO₂ reduction and alcohol photoreforming. Layered double hydroxide (LDH)‐based photocatalysts have emerged as one of the most promising candidates to replace TiO₂‐based photocatalysts for these reactions_, owing to their unique layered structure, compositional flexibility, controllable particle size, low manufacturing cost and ease of synthesis. By introducing defects into LDH materials through the control of their size to the nanoscale, the atomic structure, surface defect concentration, and electronic and optical characteristics of LDH materials can be strategically engineered for particular applications. Furthermore, through the use of advanced characterization techniques such as X‐ray absorption fine structure, positron annihilation spectrometry, X‐ray photoelectron spectroscopy, electron spin resonance, density‐functional theory calculations, and photocatalytic tests, structure‐activity relationships can be established and used in the rational design of high‐performance LDH‐based photocatalysts for efficient solar energy capture. LDHs thus represent a versatile platform for semiconductor photocatalyst development with application potential across the energy sector.