Hollow structured cathode materials for rechargeable batteries

High-Voltage Spinel Cathode Materials: Navigating the Structural Evolution for Lithium-Ion Batteries

High-voltage LiNi0.5Mn1.5O4 (LNMO) spinel oxides are highly promising cobalt-free cathode materials to cater to the surging demand for lithium-ion batteries (LIBs). However, commercial application of LNMOs is still challenging despite decades of research. To address the challenge, the understanding of their crystallography and structural evolutions during synthesis and electrochemical operation is critical. This review aims to illustrate and to update the fundamentals of crystallography, phase transition mechanisms, and electrochemical behaviors of LNMOs. First, the research history of LNMO and its development into a LIB cathode material is outlined. Then the structural basics of LNMOs including the classic and updated views of the crystal polymorphism, interconversion between the polymorphs, and structure-composition relationship is reviewed. Afterward, the phase transition mechanisms of LNMOs that connect structural and electrochemical properties are comprehensively discussed from fundamental thermodynamics to operando dynamics at intra- and inter-particle levels. In addition, phase evolutions during overlithiation as well as thermal-/electrochemical-driven phase transformations of LNMOs are also discussed. Finally, recommendations are offered for the further development of LNMOs as well as other complex materials to unlock their full potential for future sustainable and powerful batteries.

ZnO-CeO2 Hollow Nanospheres for Selective Determination of Dopamine and Uric Acid

ZnO-CeO2 hollow nanospheres have been successfully synthesized via the hard templating method, in which CeO2 is used as the support skeleton to avoid ZnO agglomeration. The synthesized ZnO-CeO2 hollow nanospheres possess a large electrochemically active area and high electron transfer owing to the high specific surface area and synergistic effect of ZnO and CeO2. Due to the above advantages, the resulting ZnO-CeO2 hollow spheres display high sensitivities of 1122.86 μA mM-1 cm-2 and 908.53 μA mM-1 cm-2 under a neutral environment for the selective detection of dopamine and uric acid. The constructed electrochemical sensor shows excellent selectivity, stability and recovery for the selective analysis of dopamine and uric acid in actual samples. This study provides a valuable strategy for the synthesis of ZnO-CeO2 hollow nanospheres via the hard templating method as electrocatalysts for the selective detection of dopamine and uric acid.

Terephthalic Acid Intercalated CoNi-LDH Materials for Improved Li-O2 Battery

CoNi-LDH (layered CoNi double hydroxides) hollow nanocages with specific morphology are obtained by Ni ion etching of ZIF-67 (Zeolitic imidazolate framework-67). The structure of the layered materials is further modified by molecular intercalation. The original interlayer anions are replaced by the ion exchange effect of terephthalic acid, which helps to increase the interlayer distance of the material. The intercalated cage-like structures not only benefit for the storage of oxygen, and the discharge product reaction, but also have more support between the material layers. The experimental results show that the excessive use of intercalation agent will affect structural stability of the intercalated CoNi-LDH. By adjusting the amount of terephthalic acid, the intercalated CoNi-LDH-2 (with 0.02 mmol terephthalic acid intercalated) is not easy to collapse after 209 cycles and shows the best electrochemical performance in Li-O2 battery.

Pathways to Next-Generation Fire-Safe Alkali-Ion Batteries

High energy and power density alkali-ion (i.e., Li+ , Na+ , and K+ ) batteries (AIBs), especially lithium-ion batteries (LIBs), are being ubiquitously used for both large- and small-scale energy storage, and powering electric vehicles and electronics. However, the increasing LIB-triggered fires due to thermal runaways have continued to cause significant injuries and casualties as well as enormous economic losses. For this reason, to date, great efforts have been made to create reliable fire-safe AIBs through advanced materials design, thermal management, and fire safety characterization. In this review, the recent progress is highlighted in the battery design for better thermal stability and electrochemical performance, and state-of-the-art fire safety evaluation methods. The key challenges are also presented associated with the existing materials design, thermal management, and fire safety evaluation of AIBs. Future research opportunities are also proposed for the creation of next-generation fire-safe batteries to ensure their reliability in practical applications.

Multishell SnO2 Hollow Microspheres Loaded with Bimetal PdPt Nanoparticles for Ultrasensitive and Rapid Formaldehyde MEMS Sensors

Low-cost and real-time formaldehyde (HCHO) monitoring is of great importance due to its volatility, extreme toxicity, and ready accessibility. In this work, a low-cost and integrated microelectromechanical system (MEMS) HCHO sensor is developed based on SnO₂ multishell hollow microspheres loaded with a bimetallic PdPt (PdPt/SnO₂-M) sensitizer. The MEMS sensor exhibits a high sensitivity to HCHO ((R_a/R_g - 1) % = 83.7 @ 1 ppm), ultralow detection limit of 50 ppb, and ultrashort response/recovery time (5.0/7.0 s @ 1 ppm). These excellent HCHO sensing properties are attributed to its unique multishell hollow structure with a large and accessible surface, abundant interfaces, suitable mesoporous structure, and synergistic catalytic effects of bimetal PdPt. The well-defined multishell hollow structure also shows fascinating capacities as good hosts for noble metal loading. Therefore, PdPt bimetallic nanoparticles can be employed to construct a synergistic sensitizer with a high content and good dispersity on this multishell hollow structure, further exhibiting a reduced working temperature and ultrasensitive detection of HCHO. This PdPt/SnO₂-M-based MEMS sensor presents a unique and highly sensitive means to detect HCHO, establishing its great promise for potential application in environmental monitoring.

Hollow Hemispherical Lithium Iron Silicate Synthesized by an Ascorbic Acid-Assisted Hydrothermal Method as a Cathode Material for Li Ion Batteries

High-capacity and high-voltage cathode materials are required to meet the increasing demand for energy density in Li ion batteries. Lithium iron silicate (Li2FeSiO4) is a cathode material with a high theoretical capacity of 331 mAh·g-1. However, its poor conductivity and low Li ion diffusion coefficient result in poor capability, hindering practical applications. Morphology has an important influence on the properties of materials, and nanomaterials with hollow structures are widely used in electrochemical devices. Herein, we report a novel hollow hemispherical Li2FeSiO4 synthesized by a template-free hydrothermal method with the addition of ascorbic acid. The hollow hemispherical Li2FeSiO4 consisted of finer particles with a shell thickness of about 80 nm. After carbon coating, the composite was applied as the cathode in Li ion batteries. As a result, the hollow hemispherical Li2FeSiO4/C exhibited a discharge capacity as high as 192 mAh·g-1 at 0.2 C, and the average capacities were 134.5, 115.5 and 93.4 mAh·g-1 at 0.5, 1 and 2 C, respectively. In addition, the capacity increased in the first few cycles and then decayed with further cycling, showing a warm-up like behavior, and after 160 cycles the capacities maintained 114.2, 101.6 and 79.3 mAh·g-1 at 0.5, 1 and 2 C, respectively. Such a method of adding ascorbic acid in the hydrothermal reaction can effectively synthesize hollow hemispherical Li2FeSiO4 with the enhanced electrochemical performance.

Double shelled hollow CoS2@MoS2@NiS2 polyhedron as advanced trifunctional electrocatalyst for zinc-air battery and self-powered overall water splitting

Electrocatalysts play important role in various energy conversion and storage devices. The catalytic performance of electrocatalysts can be enhanced through the increasement of intrinsic catalytic activity by optimizing electronic structure and the improvement of exposed active sites by designing proper nanostructures. In this work, CoS₂@MoS₂@NiS₂ nano polyhedron with double-shelled structure was prepared using metal organic framework as a precursor. Due to the rational integration of multifunctional active center, the strong electronic interaction of the various component, the high electrochemical surface area and shortened mass transport induced by the special structure, CoS₂@MoS₂@NiS₂ exhibits high catalytic activity for hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Specifically, low overpotentials of 156 and 200 mV was achieved to deliver a current density of 10 mA cm^-2 for HER and OER, and a high half-wave potential of 0.80 V was observed for ORR. More importantly, the Zn-air battery assembled by CoS₂@MoS₂@NiS₂ exhibits a high-power density of 80.28 mW cm^-2 and could effectively drive overall water splitting. This work provides a new platform for designing multifunctional catalysts with high activity for energy conversion and storage.