Energy-Storage Performance of High-Entropy (NaBiBa)0.205 (SrCa)0.1925TiO3-La(Mg0.5Zr0.5)O3 Ceramic Under Moderate Electric Fields

Preparation and dielectric properties of lead-free perovskite-structured high-entropy ceramics of (La0.25Sr0.25Ba0.25Na0.25)(Ti0.5Me0.5)O3-δ (Me=Sn, Zr, Hf) via doping at both A and B sites

Novel Na0.5Bi0.5TiO3 based, lead-free energy storage ceramics with high power and energy density and excellent high-temperature stability

Energy storage material that provide both high power and high energy density are needed to meet current needs. Pseudocapacitive materials have become a focus of research in the field of electrochemical energy storage because of their high specific capacitance and good rate performance. To increase the energy and power density, the key lies in selecting suitable electrode material types or optimizing the electrode layer structure to increase the potential window. This review, starting from the pseudocapacitive materials, introduces the energy storage mechanism of pseudocapacitance, describes the general development of pseudocapacitive materials including oxide materials and their derivative, development of Hägg-phase compounds extended by the MXenes in the past decade, and focuses on the development of several Hägg-phase compounds and the advantages of high-entropy ceramics as future pseudocapacitive materials. Due to the “high-entropy effect,” high-entropy ceramics have better physical and chemical properties to become the most candidate pseudocapacitive material. Focusing on the application potential of the high-entropy ceramics in pseudocapacitive research, they will provide a new pseudocapacitive material system.

In order to obtain large room-temperature electrocaloric effect (ECE) and wide operation temperature range simultaneously in lead-free ceramics, we proposed designing a relaxor ferroelectric with a Tm (the temperature at which the maximum dielectric permittivity is achieved) near-room temperature and glass addition. Based on this strategy, we designed and fabricated lead-free 0.76NaNbO3-0.24BaTiO3 (NN-24BT) ceramics with 1wt.% BaO-B2O3-SiO2 glass addition, which showed distinct relaxor ferroelectric characteristics with strongly diffused phase transition and a Tm near-room temperature. Based on a direct measurement method, a large ΔT (adiabatic temperature change) of 1.3 K was obtained at room temperature under a high field of 11.0 kV mm-1. Additionally, large ECE can be maintained (>0.6 K@6.1 kV mm-1) over a broad temperature range from 23 °C to 69 °C. Moreover, the ECE displayed excellent cyclic stability with a variation in ΔT below ±7% within 100 test cycles. The comprehensive ECE performance is significantly better than other lead-free ceramics. Our work provides a general and effective approach to designing lead-free, high-performance ECE ceramics, and the approach possesses the potential to be utilized to improve the ECE performance of other lead-free ferroelectric ceramic systems.

Synergistic effect of multi-phase and multi-domain structures induced high energy storage performances under low electric fields in Na0.5Bi0.5TiO3-based lead-free ceramics

Considering the large demand for electricity in the era of artificial intelligence and big data, there is an urgent need to explore novel energy storage media with higher energy density and intelligent temperature self-check functions. High-entropy (HE) ceramic capacitors are of great significance because of their excellent energy storage efficiency and high power density (PD). However, the contradiction between configurational entropy and polarization in traditional HE systems greatly restrains the increase in energy storage density. Herein, the contradiction is effectively solved by regulating the octahedral tilt and cationic displacement in ABO3-type perovskite HE ceramics, i.e., (1-x)[0.6(Bi0.47Na0.47Yb0.03Tm0.01)TiO3-0.4(Ba0.5Sr0.5)TiO3]-xSr(Zr0.5Hf0.5)O3 (BNYTT-BST-xSZH). Combining the tape-casting process and cold isostatic pressing, the optimal BNYTT-BST-0.06SZH ceramic displays a large recoverable energy storage density (10.46 J cm-3) at 685kV cm-1 and a high PD (332.88 MW cm-3). More importantly, due to Tm/Yb codoping, abnormal fluorescent negative thermal expansion and excellent real-time temperature sensing are developed, thus the application of fault detection and warning in high-voltage transmission line systems is conceptualized. This study provides an effective strategy for enhancing the polarization of energy-storing HE ceramics and offers a promising material for overcoming the problems of insufficient capacitor density and thermal runaway in terminal communication.

Achieving high energy storage properties in perovskite oxide via high-entropy design

Simultaneously enhanced energy storage density and efficiency in novel BiFeO3-based lead-free ceramic capacitors

Grain size engineered lead-free ceramics with both large energy storage density and ultrahigh mechanical properties

Dielectric ceramics with high energy storage performance are crucial for the development of advanced high-power capacitors. However, achieving ultrahigh recoverable energy storage density and efficiency remains challenging, limiting the progress of leading-edge energy storage applications. In this study, (Bi1/2Na1/2)TiO3 (BNT) is selected as the matrix, and the effects of different A-site elements on domain morphology, lattice polarization, and dielectric and ferroelectric properties are systematically investigated. Mg, La, Ca, and Sr are shown to enhance relaxation behavior by different magnitudes; hence, a high-entropy strategy for designing local polymorphic distortions is proposed. Based on atomic-scale investigations, a series of BNT-based high-entropy compositions are designed by introducing trace amounts of Mg and La to improve the electric breakdown strength and further disrupt the polar nanoscale regions (PNRs). A disordered polarization distribution and ultrasmall PNRs with a minimum size of ≈1 nm are detected in the high-entropy ceramics. Ultimately, a high recoverable energy density of 10.1 Jcm-3 and an efficiency of 90% are achieved for (Ca0.2Sr0.2Ba0.2Mg0.05La0.05Bi0.15Na0.15)TiO3. Furthermore, it displays a high-power density of 584 MWcm-3 and an ultrashort discharge time of 27 ns. This work presents an effective approach for designing dielectric energy storage materials with superior comprehensive performance via a high-entropy strategy.

The growth of piezo science is phenomenal since the discovery of piezoelectricity in 1880. Among various piezoelectric materials, lead zirconate titanate (PZT) is a very popular and exhaustively studied piezo system which allows synthesis of large number of materials with wide range of properties due to formation of solid solutions over large range of Zr:Ti ratio. Also, this system accommodates wide range of dopants for modification of crystal structure. Due to this versatile nature, PZT has emerged as very popular among users and researchers worldwide. However, considering the toxicity of lead oxide, development of lead free piezo ceramics is encouraged in recent years. Some lead free piezo material systems such as BNT, BKT, KNN, BZT-BCT have been explored. However, development of lead free piezo devices and their performance in comparison with PZT devices are yet to be established. At this juncture, it was felt that an article reviewing the current status of development of piezo materials highlighting the change from PZT to various lead free systems would be of very much interest to the researchers. Therefore, efforts are made to bring out the recent developments on R&D of piezo materials in this review article.

Enhancing energy storage efficiency in lead-free dielectric ceramics through relaxor and lattice strain engineering

Synchronously enhancing energy storage density, efficiency and power density under low electric field in lead-free ferroelectric (1-x)(Bi0.5Na0.5)0.7Sr0.3TiO3-xSr1/2La1/3(Ti0.7Zr0.3)O3 ceramics

Energy storage is crucial in numerous applications. Various technologies, such as super capacitors, batteries and fuel cells are being developed to satisfy the demands in terms of cost, life cycle, safety, power and energy density, etc. Generally speaking a tradeoff has to be made depending on technology; fuel cells, for example, show satisfying energy density but suffer from low power density. Batteries, on the other hand, are more cost effective and offer higher power densities, but cannot achieve as high energy densities. Research groups in different fields try to overcome the drawbacks through the incorporation of novel materials, compositions, designs, etc.While lithium based batteries and proton exchange fuel cells are chosen by a vast number of research groups as the basic technology in each field, we have chosen a quite uncommon approach by using a nickel metal-hydride (NiMH) battery as a basis for meeting the demands in power and energy density. By modifying both its structure and materials, we work to achieve a hybrid Fuel Cell/Battery (FCB) system satisfying our goals.Metal hydride, used as the anode in NiMH batteries, is well known to absorb hydrogen efficiently, wherefore we regard it as the material of choice in the FCB system. As the electrolyte, we also use what is commonly chosen in NiMH batteries, i.e. a potassium hydroxide (KOH) solution. On the cathode side, however, bigger changes have to be made, as nickel hydroxide cannot be oxidized with oxygen once discharged. Thus, another material had to be found.Manganese Dioxide (MnO2), used for example in primary alkaline batteries, is a very interesting material due to its low-cost, environmental friendliness and catalytic capabilities. In alkaline batteries, discharging MnO2 leads to Mn2O3, which is electrochemically stable. To avoid this state and instead obtain rechargeable MnOOH, it was found in previous research that limiting the discharge potential to -0.5 V vs. Ag/AgCl inhibits the creation of Mn2O3. Thus, if oxidization of MnOOH with oxygen can be obtained, a FCB which runs according to following reaction is achieved.AnodeElectrochemical charge/discharge: M + H2O + e- ↔ MH + OH- (1) Charge with H2: M + 1/2 H2 → MH (2)CathodeElectrochemical charge/discharge: MnOOH + OH- ↔ MnO2 + H2O + e- (3)Charge with O2: MnOOH + 1/4 O2 → MnO2 + 1/2 H2O (4)According to equation (1) and (3), the FCB can work as a rechargeable alkaline battery, thus providing high power density. Additionally, by charging the FCB with hydrogen and oxygen according to equations (2) and (3), it can run as a fuel cell, leading to high energy densities.In this work, we have focused on the cathode side – both improving electrochemical rechargeability and oxidization under O2 exposure. In order to achieve satisfying results, we first had to analyze different crystalloid and particle structures of MnO2. The crystalloid structure of MnO2 consists of MnO6 building blocks which are arranged to create different tunnel structures. In our work, we investigated the capabilities of α-, β-, γ- and δ-MnO2 structure on their performance as cathode for both secondary battery (i.e. rechargeability) and alkaline fuel cell (i.e. oxidization with O2). Furthermore, we studied the effects of the particle size by synthesizing all four MnO2 structures through a sol-gel method and via hydrothermal treatment. While former method leads to particles with comparatively large diameters, latter synthesis leads to nano-sized rods with diameters of few dozen nanometers and thus high surface areas for improved FCB capabilities.

7 - Electrocaloric effect in lead-free ferroelectric perovskites