Delicate Control of Multishelled Zn-Mn-O Hollow Microspheres as a High-Performance Anode for Lithium-Ion Batteries

From amorphous to crystalline: a universal strategy for structure regulation of high-entropy transition metal oxides

High-entropy materials (HEMs) exhibit extensive application potential owing to their unique structural characteristics. Structure regulation is an effective strategy for enhancing material performance. However, the fabrication of HEMs by integrating five metal elements into a single crystalline phase remains a grand challenge, not to mention their structure regulation. Herein, an amorphous-to-crystalline transformation route is proposed to simultaneously achieve the synthesis and structure regulation of high-entropy metal oxides (HEMOs). Through a facile hydrothermal technique, five metal sources are uniformly integrated into amorphous carbon spheres, which are transformed to crystalline HEMOs after calcination. Importantly, by controlling ion diffusion and oxidation rates, HEMOs with different structures can be controllably achieved. As an example, HEMO of the five first-row transition metals CrMnFeCoNiO is synthesized through the amorphous-to-crystalline transformation route, and structure regulation from solid spheres to core-shell spheres, and then to hollow spheres, is successfully realized. Among the structures, the core-shell CrMnFeCoNiO exhibits enhanced lithium storage performance due to the component and structural advantages. Our work expands the synthesis methods for HEMs and provides a rational route for structure regulation, which brings them great potential as high-performance materials in energy storage and conversion.

Facile Construction of Porous ZnMn2O4 Hollow Micro-Rods as Advanced Anode Material for Lithium Ion Batteries

Spinel ZnMn₂O₄ is considered a promising anode material for high-capacity Li-ion batteries due to their higher theoretical capacity than commercial graphite anode. However, the insufficient cycling and rate properties seriously limit its practical application. In this work, porous ZnMn₂O₄ hollow micro-rods (ZMO HMRs) are synthesized by a facile co-precipitation method coupled with annealing treatment. On the basis of electrochemical analyses, the as-obtained samples are first characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and scanning electron microscopy techniques. The influences of different polyethylene glycol 400 (PEG 400) additions on the formation of the hollow rod structure are also discussed. The abundant multi-level pore structure and hollow feature of ZMO HMRs effectively alleviate the volume expansion issue, rendering abundant electroactive sites and thereby guaranteeing convenient Li⁺ diffusion. Thanks to these striking merits, the ZMO HMRs anode exhibits excellent electrochemical lithium storage performance with a reversible specific capacity of 761 mAh g^-1 at a current density of 0.1 A g^-1, and a long-cycle specific capacity of 529 mAh g^-1 after 1000 cycles at 2.0 A g^-1 and keep a remarkable rate capability. In addition, the assembled ZMO HMRs-based full cells deliver an excellent rate capacity, and when the current density returns to 0.05 A g^-1, the specific capacity can still reach 105 mAh g^-1 and remains at 101 mAh g^-1 after 70 cycles, maintaining a material-level energy density of approximately 273 Wh kg^-1. More significantly, such striking electrochemical performance highlights that porous ZMO HMRs could be a promising anode candidate material for LIBs.

Template-free formation of one-dimensional mesoporous ZnMn2O4 tube-in-tube nanofibers towards lithium-ion batteries as anode materials

Mesoporous ZnMn2O4 tube-in-tube nanofibers are firstly synthesized via a template-free strategy as an anode material towards lithium-ion batteries, along with a tentative formation mechanism.

Sequential Templating Approach: A Groundbreaking Strategy to Create Hollow Multishelled Structures

Thanks to their distinguished properties such as optimized specific surface area, low density, high loading capacity, and sequential matter transfer and storage, hollow multishelled structures (HoMSs) have attracted great interest from scientists in broad fields, including catalysis, drug delivery, solar cells, supercapacitors, lithium-ion batteries, electromagnetic wave absorption, and sensors. However, traditional synthesis methods such as soft-templating and hierarchical self-assembly methods can hardly realize the controllable synthesis of HoMSs, thus limiting their development and application. Here, the development process of HoMSs is first succinctly reviewed and the shortcomings of the traditional synthesis method are concluded. Subsequently, the sequential templating approach, which shows great generality for the synthesis of HoMSs with controllable composition and geometry configuration and exhibits remarkable effect on the scientific research field, is introduced. The basic material science and chemical reaction mechanism involved in the synthesis and manipulation of HoMSs using the sequential templating approach are then explained in detail. In addition, the effect of the geometric characteristics of HoMSs on their application properties is highlighted. Finally, the current challenges and future research directions of HoMSs are also suggested.

Formaldehyde Controlling the Synthesis of Multishelled SiO2/Fe xO y Hollow Porous Spheres

A concise and facile sol-gel method to prepare multiple magnetic SiO₂/Fe _xO _y hollow porous spheres was developed. A series of SiO₂/Fe _xO _y hollow porous spheres consisting of single shell, yolk-shell, double shells, and triple shells could be obtained by simply adjusting the formaldehyde amount, as Fe(acac)₃ was used as the shell-forming promoter. As the formaldehyde amount increases, the morphology of the as-prepared hollow spheres changed from single-shelled, yolk-shelled, double-shelled, to triple-shelled and then turned back. The spheres possess a large specific surface area (∼966 m²/g), uniform mesopores (∼4.5 nm), and large pore volume (1.37 cm³/g). Moreover, the yolk-shelled spheres have been successfully used in in situ adsorbing and reducing heavy metal ions in aqueous solution; the results suggested that it was an efficient adsorbent and convenient to concentrate from water.

Formation of Mn–Cr mixed oxide nanosheets with enhanced lithium storage properties

Novel carbon-free Mn₂O₃/MnCr₂O₄ hybrid nanosheets are synthesized. As an anode for lithium-ion batteries, they deliver a wonderful electrochemical performance.