Open Access Review Just accepted
The emerging high-entropy strategy: a booster to the development of cathode materials for power batteries
Journal of Advanced Ceramics
Available online: 24 May 2024

The coordinated development of new energy vehicles and the energy storage industry has become inevitable to reduce carbon emissions. The cathode material is the key material that determines the energy density and cost of a power battery, while the currently developed and applied cathode material can not meet the requirements of high specific capacity, low cost, safety and good stability. High-entropy material is a new type of single-phase material composed of multiple principal elements in equimolar or near-equimolar ratios. The interaction between multiple elements can play an important role in improving the comprehensive properties of the material, which is expected to solve the limitations of battery materials in practical applications. Based on this, this review provides a comprehensive overview of the current development status and modification strategies of power batteries (lithium-ion battery and sodium-ion battery), proposes a high-entropy design strategy, and analyzes the structure-activity relationship between the high-entropy effect and battery performance. Finally, future research topics of high-entropy cathode materials are proposed, including computational guide design, specific synthesis methods, high-entropy electrochemistry and high-throughput databases. This review aims to provide practical guidance for the development of high-entropy cathode materials for next-generation power batteries.

Open Access Research Article Issue
Synergistic effects of high-entropy engineering and particulate toughening on the properties of rare-earth aluminate-based ceramic composites
Journal of Advanced Ceramics 2023, 12 (4): 861-872
Published: 14 March 2023

Rare-earth aluminates (REAlO3) are potential thermal barrier coating (TBC) materials, but the relatively high thermal conductivity (k0, ~13.6 W·m−1·K−1) and low fracture toughness (KIC, ~1.9 MPa·m1/2) limit their application. This work proposed a strategy to improve their properties through the synergistic effects of high-entropy engineering and particulate toughening. High-entropy (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)AlO3 (HEAO)-based particulate composites with different contents of high-entropy (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 (HEZO) were designed and successfully prepared by solid-state sintering. The high-entropy feature of both the matrix and secondary phases causes the strong phonon scattering and the incorporation of the HEZO secondary phase, remarkedly inhibiting the grain growth of the HEAO phase. As a result, HEAO–xHEZO (x = 0, 5%, 10%, 25%, and 50% in volume) ceramic composites show low thermal conductivity and high fracture toughness. Compared to the most commonly applied TBC material—yttria stabilized-zirconia (YSZ), the HEAO–25%HEZO particulate composite has a lower thermal conductivity of 0.96–1.17 W·m−1·K−1 (298–1273 K), enhanced fracture toughness of 3.94±0.35 MPa·m1/2, and comparable linear coefficient of thermal expansion (CTE) of 10.5×10−6 K−1. It is believed that the proposed strategy should be revelatory for the design of new coating materials including TBCs and environmental barrier coatings (EBCs).

Open Access Research Article Issue
Fast grain growth phenomenon in high-entropy ceramics: A case study in rare-earth hexaaluminates
Journal of Advanced Ceramics 2023, 12 (1): 111-121
Published: 23 December 2022

It is generally reported that the grain growth in high-entropy ceramics at high temperatures is relatively slower than that in the corresponding single-component ceramics owing to the so-called sluggish diffusion effect. In this study, we report a fast grain growth phenomenon in the high-entropy ceramics (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)MgAl11O19 (HEMA) prepared by a conventional solid-state reaction method. The results demonstrate that the grain sizes of the as-sintered HEMA ceramics are larger than those of the corresponding five single-component ceramics prepared by the same pressureless sintering process, and the grain growth rate of HEMA ceramics is obviously higher than those of the five single-component ceramics during the subsequent heat treatment. Such fast grain growth phenomenon indicates that the sluggish diffusion effect cannot dominate the grain growth behavior of the current high-entropy ceramics. The X-ray photoelectron spectroscopy (XPS) analysis reveals that there are more oxygen vacancies (OV) in the high-entropy ceramics than those in the single-component ceramics owing to the variable valance states of Eu ion. The high-temperature electrical conductivities of the HEMA ceramics support this analysis. It is considered that the high concentration of OV and its high mobility in HEMA ceramics contribute to the accelerated migration and diffusion of cations and consequently increase the grain growth rate. Based on this study, it is believed that multiple intrinsic factors for the high-entropy ceramic system will simultaneously determine the grain growth behavior at high temperatures.

Open Access Research Article Issue
Equiatomic 9-cation high-entropy carbide ceramics of the IVB, VB, and VIB groups and thermodynamic analysis of the sintering process
Journal of Advanced Ceramics 2022, 11 (7): 1082-1092
Published: 02 July 2022

The preparation of high-entropy (HE) ceramics with designed composition is essential for verifying the formability models and evaluating the properties of the ceramics. However, inevitable oxygen contamination in non-oxide ceramics will result in the formation of metal oxide impurity phases remaining in the specimen or even escaping from the specimen during the sintering process, making the elemental compositions of the HE phase deviated from the designed ones. In this work, the preparation and thermodynamic analysis during the processing of equiatomic 9-cation HE carbide (HEC9) ceramics of the IVB, VB, and VIB groups were studied focusing on the removing of the inevitable oxygen impurity existed in the starting carbide powders and the oxygen contamination during the powder mixing processing. The results demonstrate that densification by spark plasma sintering (SPS) by directly using the mixed powders of the corresponding single-component carbides will inhibit the oxygen-removing carbothermal reduction reactions, and most of the oxide impurities will remain in the sample as (Zr,Hf)O2 phase. Pretreatment of the mixed powders at high temperatures in vacuum will remove most part of the oxygen impurity but result in a remarkable escape of gaseous Cr owing to the oxygen-removing reaction between Cr3C2 and various oxide impurities. It is found that graphite addition enhances the oxygen-removing effect and simultaneously prevents the escape of gaseous Cr. On the other hand, although WC, VC, and Mo2C can also act as oxygen-removing agents, there is no metal-containing gaseous substance formation in the temperature range of this study. By using the heat-treated powders with added graphite, equiatomic HEC9 ceramics were successfully prepared by SPS.

Open Access Research Article Issue
Self-ball milling strategy to construct high-entropy oxide coated LiNi0.8Co0.1Mn0.1O2 with enhanced electrochemical performance
Journal of Advanced Ceramics 2022, 11 (6): 882-892
Published: 11 May 2022

High-entropy oxides (HEOs) are a new class of emerging materials with fascinating properties (such as structural stability, tensile strength, and corrosion resistance). High-entropy oxide coated Ni-rich cathode materials have great potential to improve the electrochemical performance. Here, we present a facile self-ball milling method to obtain (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 (HEO) coated LiNi0.8Co0.1Mn0.1O2 (NCM811). The HEO coating endows NCM811 with a stable surface, reduces the contact with the external environment (air and electrolyte), and inhibits side reactions between cathode and electrolyte. These favorable effects, especially when the coating amount is 5 wt%, result in a significant reduction of the battery polarization and an increase in the capacity retention from 57.3% (NCM811) to 74.2% (5HEO-NCM811) after 300 cycles at 1 C (1 C = 200 mA·h·g-1). Moreover, the morphology and spectroscopy analysis after the cycles confirmed the inhibitory effect of the HEO coating on electrolyte decomposition, which is important for the cycle life. Surprisingly, HEO coating reduces the viscosity of slurry by 37%-38% and significantly improves the flowability of the slurry with high solid content. This strategy confirms the feasibility of HEO-modified Ni-rich cathode materials and provides a new idea for the design of high-performance cathode materials for Li-ion batteries.

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