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Since the discovery of Zintl phases in the 1891s, they have attracted considerable interests because of their novel structures, fascinated bonding and special physical properties. However, the research about Zintl phases is not complete, limiting the development of this discipline. Hence, in this work we systematically introduce the preparation approaches of Zintl phases and Zintl anions to understand the originations of their attractive structures. More importantly, the recent developments about their applications (such as thermoelectricity, catalysis, superconductor and magnetism) are thoroughly concluded. Especially, their devotions utilized as precursors for preparing functional materials are summarized. Additionally, the remaining challenges and perspectives of Zintl phases are further discussed. This review is aimed to provide a comprehensive understanding of the Zintl phases, offering a directional guideline towards broad applications.

There is an urgent need for dielectric capacitors with high energy density and efficiency with the rapid progress of power electronic devices. Inorganic/organic composites were once considered as a potential candidate for dielectrics. However, the inevitable defects induced by the inorganic fillers always lead to the decreased breakdown strength and limited energy density and efficiency. In this work, carbon quantum dots (CQDs) with abundant functional groups were synthetized and introduced into linear dielectric polyethyleneimine (PEI) matrix. Due to the unique Coulomb-blockade effect of quantum dots, the movement of carriers can be hindered under the applied electric field, leading to the improvement of breakdown strength. Compared with most of the reported nanocomposites with high loading of fillers, the nanocomposites in this work with extremely low loading of CQDs exhibit obviously enhanced performance. The nanocomposite with 0.5 wt% CQDs exhibits a high discharge energy density of 10.66 J/cm3 and efficiency of 88.3% at 600 kV/mm, corresponding to a 62.3% improvement over that of PEI (6.57 J/cm3 at 490 kV/mm). This work provides an effective strategy to break down the long-standing contradiction between the enhancement of dielectric constant and the reduced in breakdown strength. The film dielectrics with extremely low loading of fillers contributing to enhanced energy density and high energy efficiency is very important for practical applications.

Further commercial development of polycrystalline Ni-rich layered cathode is severely hindered by the deep-rooted particle microcracking, mainly initiated among the randomly orientated grain boundaries of the primary particles. Herein, robust single-crystalline Ni-rich LiNi0.83Co0.11Mn0.06O2 (SC83) prepared by molten salt-assisted method shows the enhanced structure stability and cycling durability. It’s found that the particle microcracking is effectively removed for SC83 cathode during prolonged cycling helped with its eliminated grain boundaries and slight crystal shrinkage, leading to superior capacity retention of 92.8% after 100 cycles. Notably, the discharge capacity and energy density are effectively boosted with increasing Ni fraction majorly based on the more available Ni2+/Ni3+ redox, giving rise to high capacities of 211.2 and 219.4 mAh g−1 for LiNi0.88Co0.06Mn0.06O2 (SC88) and LiNi0.95Co0.03Mn0.02O2 (SC95) cathodes, respectively. However, the particle microcracking is progressively exacerbated owing to the aggravated Li/Ni mixing and H2 ↔ H3 phase transition with Ni proportion higher than or equal to 88% in SC cathodes, resulting in severe structure collapse and capacity fading during high-rate cycling, in which a poor capacity retention of 51.8% after 250 cycles at 5C is observed for single-crystalline SC95cathode. This work sheds light on the rational design of single-crystalline Ni-rich cathodes, and highlighted the trade-off between the energy density and cycling durability, facilitating the extensive applications of single-crystalline Ni-rich cathodes in high-performance electric vehicles (EVs).

Layered O3-type NaMn0.5Ni0.5O2 has been widely investigated as cathode material for sodium-ion batteries (SIBs). However, it usually suffers from detrimental phase transformation upon high voltage (>4.1 V) and sluggish Na+ migration kinetics, leading to rapid capacity decay and limited rate capability. Herein, guided by the first principles calculations, a structure modulation strategy to construct mechanically robust transition metal oxides (TMO2) layers for O3-NaMn0.5Ni0.5O2 is realized through Mg/Ti co-substitution. After Mg/Ti co-substitution, the capability of the TMO2 layers framework of O3 phase has been significantly improved to go against and tolerant strains and distortions, and thus remarkably enhanced the electrochemical performance of O3 phase upon high voltage. The as-prepared O3-type NaMn0.45Ni0.45Mg0.05Ti0.05O2 exhibits an initial discharge capacity of 177.7 mAh g−1 at a current density of 0.1 C in a voltage range of 2.0–4.2 V, and the detrimental P3-O1 phase transition upon 4.0 V can be effectively suppressed as well as the Na+ diffusion kinetics is enhanced under high voltage, subsequently leading to improved high voltage cycling-stability and rate-capability.

Formation of an inferior solid-electrolyte interface (SEI) over the electrode severely diminishes the specific capacity and cyclic stability of Li-ion batteries (LIB). Although this issue is tackled to some extent by the in-situ generation of SEI coatings via the use of electrolyte additives, the control over the optimum thickness and composition of SEI is still challenging. To address this issue, porous and flexible SEI coating is electrochemically deposited over the active electrode material from an aqueous deep-eutectic solvent. The uniform SEI film of 20 to 35 nm with the composition of C, N, F, O, and Li elements is preformed on the surface of a self-assembled composite of 1T-MoS2 and the positively charged reduced graphene oxide. With the aid of preformed SEI, the composite electrode significantly increases its specific capacity from 907 to 1350 mAh g−1 and rate capability from 28 to 75%. Even at a higher current density of 1 A g−1, specific capacity gradually rises from 960 to 1647 mAh g−1 after 2000 charge/ discharge cycles. Furthermore, the device shows indistinct electrolyte decomposition and negligible increase of charge transfer resistance during cycling. Our novel approach is extrapolated as a general protocol to improve the performance of LIBs.

High-performance sodium-ion capacitors (SICs) are regarded as new-generation electrochemical energy-storage systems that are critically restricted due to the kinetic and capacity mismatch between the capacitor-type cathode and battery-type anode derived from the low capacity of carbon cathodes and the weak charge transfer kinetics of the anodes. In this study, for the first time, we investigate the pseudocapacitive storage mechanism of both ClO4− and Na ions in carbon cathode/anode with a novel NH3 plasma strategy at room temperature. Interestingly, the implementation of pseudocapacitance greatly enhances the capacity in cathodes and the kinetics in anodes, effectively reducing the mismatch between two electrodes. With the ingenious NH3 plasma strategy, which breaks the barriers of conventional methods of synthesizing N-functional carbon materials, various types and substances of N/O pseudocapacitive sites can be controlled directionally and accurately. The time-sensitive NH3 plasma treatment utilized in this work has been demonstrated to be a state-of-art method for producing high content of pyridinic-N/C O bond and introducing ultrafast pseudocapacitance on the surface of the samples. Impressively, in-situ/ex-situ characterizations demonstrate the highly reversible evolution of Pyridinic-N and C O during the charging/discharging processes in cathodes/anodes, which is well consistent with electrochemical results and DFT calculations, presenting the “adsorption-pseudocapacitive reactions” and “adsorption-pseudocapacitive reactions-intercalation” mechanisms for cathodes and anodes respectively. Furthermore, the SICs deliver an energy density of 107 W h kg−1 at a power density of 200 W kg−1. The current results are expected to be a powerful tool and an exciting opportunity to accelerate the practical application of SICs and achieve high-performance cathodes and anode materials.

Electrochemical exfoliation of layered van der Waals solids is becoming a promising method for the fabrication of two-dimensional (2D) materials beyond graphene. Nevertheless, most of bulk layered starting solids are semiconductive or even nonconductive, which will reduce the exfoliation efficiency. In addition, the strong bonding interaction between the layers of van der Waals crystal will lead to the incomplete exfoliation. These deficiencies will hinder the application of this method in the synthesis of two-dimensional semiconductive and insulating materials. Herein, one-pot electrochemical potential-cycles exfoliation has been introduced to fabricate nonconductive 2D layered birnessite-type manganese oxide utilizing non-layered metal as starting precursor, demonstrating that monolayer and few layer birnessite sheets can be obtained through tuning the potential sweep rate. More importantly, this strategy promotes a high exfoliation yield up to 96%, which is much higher than that of electrochemical exfoliation of layered precursors. Additionally, this method can overwhelm the drawbacks such as hindrance of intrinsic/contact high resistance and incomplete exfoliation of the layered starting material presented by electrochemical exfoliation of bulk layered van der Waals solids. When utilized as cathode material for Zn-ion batteries, the exfoliated birnessite can deliver a capacity of 325 mAh g−1 at a current density of 200 mA g−1 and achieved capacity retention of 84% over 1000 cycles at 1000 mA g−1. As exfoliation parameters can be manipulated, this effective method is applicable to producing various 2D layered transition metal oxides and layered double hydroxides regardless of electric conductivity, which will contribute to plentiful applications.

Adding Cu2+ has substantially boosted the practical potentiality of Fe/Mn-based layered cathodes for sodium ion batteries (SIBs) owing to the enhanced stabilities, which were previously ascribed to the raised valence of Mn. Herein, the roles of Cu2+ are verified by investigating Cu2+-substituted materials with the stoichiometry of Na0.5+xCuxFe0.5-xMn(IV)0.5O2. Surprisingly, it is found that Mn valence can hardly reach the expected value (IV) even by adjusting Cu2+ content. For the first time, the separation of CuO, which has been previously detected but rarely explained, is ascribed to the restrained chemical states of Mn. Detailed analyses show that, Mn(II) is generated while Mn(III) is decreased in pace of Cu2+ substitution, actually lowering down the oxidation states of Mn. Moreover, Mn4+/3+ redox can be efficiently restricted by importing Cu2+. Albeit the loss of capacity, the cycling stability is greatly enhanced, achieving a high capacity retention of 92.3% after 200 cycles within 4.2–2.5 V. Therefore, the suppression of Jahn-Teller Mn(III) should be intrinsically responsible for the superior cycling stability after Cu2+ substitution. These findings may present a new sight to probe the roles of Cu in layered NaxMO2 system for the design of advanced cathodes for SIBs.

Vanadium oxides are considered as promising cathode materials for aqueous zinc ions batteries (AZIBs). However, the long diffusion distance, low diffusion coefficient, and strong electrostatic interactions with divalent Zn2+ in bulk vanadium oxide restrict their practical application. In this work, vanadium oxide nanofibers with physical and chemical defects were facilely fabricated by electrospinning for the application in AZIBs. The hierarchical framework exhibits structure stability during insertion/ extraction processes of zinc ions, and the extracted zinc ions are easily confined in the caverns of porous fibers to shorten the diffusion paths. Furthermore, the electrochemical reaction mechanism was verified by using in situ Raman and ex situ XPS and HRTEM, demonstrating a co-insertion mechanism of zinc ions and H+. The cathode shows a fast activation process, exhibiting a high capacity of 256 mAh g−1 at 1 A g−1, and the capacity fading of only 17% is observed after 1000 cycles at 5 A g−1. The outstanding electrochemical performances and efficient Zn2+ transportation can be attributed to the synergism of physical and chemical defects. This strategy of dual defects may provide new insights into the improvements of AZIBs performance.

Aqueous Zn-ion batteries (ZIBs) attract ever-growing attention due to low cost, high safety, and environmental friendliness. Among the limited cathode candidates, manganese-based oxides stand out owing to large ion channels and multiple valence of Mn. Notably, MnO, thought to be inactive before, actually exhibits high energy densities in AZIBs, thus arousing wide interests. Herein, the electrochemical behavior of MnO electrode is extensively investigated in ZnSO4 electrolytes with different concentration of MnSO4. It is confirmed that the inactive MnO is electrochemically activated during the initial charge process. Greatly, the initial capacity and the following cycling stability of MnO electrode strongly depends on the concentration of MnSO4, indicating that the activation of MnO could be attributed to Mn dissolution, leading to the higher valence of Mn as evidenced by ex-situ XPS analysis. Greatly, a H+/Zn2+ co-insertion mechanism is suggested for the as-activated Mn1-xO electrode according to the ex-situ XRD results. In addition, by constructing a core-sheath MnO@N-doped graphene scrolls (MnO@NGS) configuration through a modified hydrothermal process, the reversible capacity of MnO has been successfully improved to 288 mAh g−1 (0.1 A g−1), leading to high energy density of 367 mWh g−1. More importantly, benefiting from the graphene wrapping and sufficient internal voids, 98% of the initial capacity can be retained after 300 cycles (0.5 A g−1), much better than the unmodified MnO and MnO2 electrodes. This work is expected to deepen the understanding of the charge-storage mechanism of MnO and help to design durable manganese-based cathodes for ZIBs.

Antimony-based materials with high theoretical capacity have been considered as a promising anode materials for potassium-ion batteries (PIBs). Unfortunately, the large volume expansion leads to rapid capacity fading and poor rate capability. In this work, Sb2S3 (Sb2Se3) nanodots/carbon composites are constructed through pyrolysis and co-sulfurization (selenylation) process of sodium stibogluconate for the first time. In the composite, Sb2S3 (Sb2Se3) nanodots with diameters of 15–25 nm are uniformly inlaid into S(Se)-doped carbon skeleton. Notably the ultrafine nanodots can remarkedly shorten the ions diffusion distance with enhanced kinetic process. Also the S(Se)-doped carbon would provide the stable structure support and conductive path. When applied as the anode for PIBs, they all show satisfactory potassium-storage properties in terms of high reversible capacity and superior rate capability, especially the excellent electrochemical performances of Sb2Se3 nanodots/carbon with a reversible capacity of 312.03 mAh g−1 at 1000 mA g−1 after 200 cycles, which can be attributed to the synergistic effect of nanodots and doped carbon, minimizing potassiation-induced deformations and facilitating the reversible adsorption of K ions. More importantly, the volume changes during the K+ intercalation/deintercalation process have been analyzed in details, which is well consistent with the result of electrochemical performance, as expected.

Poor cycle performance and low coulombic efficiency are bottleneck problems that hinder the further development of lithium–sulfur (Li–S) batteries. In this study, vapor silica-supported S is prepared by using a facile impregnation method and applied as cathode for Li–S batteries. Results indicate that approximately 43.7% of S is loaded into polyporous vapor silica. The prepared material also displays excellent electrochemical performance. After 200 cycles at a current density of 1000 mA·g−1, a capacity of 710 mAh·g−1 with a reversible capacity retention rate of 85% with coulombic efficiency of 100% is obtained. At a large current density of 2000 mA·g−1, the capacity of 605 mAh·g−1 is maintained after 300 cycles. This material contributes impressive surface-controlled pseudocapacity and high Li ion diffusion coefficient, which helps obtain high capacity and good rate performance during cycles. These results suggest that the prepared vapor silica-supported S can meet the needs of next-generation long-life Li–S batteries.

Present work demonstrated the facile preparation of silica microspheres with various structures (solid, hollow, hollow with a hole and filbert-like solid). These were prepared by first forming monodisperse silica sol droplets in a simple microfluidic device, followed by extracting the solvent from the droplets in an extractant or at the interface between the extractant and liquid paraffin at different conditions. The effect of different extractants and extracting temperature was investigated. The products were characterized by optical microscope and scanning electron microscope. Extraction in fatty acid methyl ester (FAME) at room temperature led to formation of solid silica microspheres, while extraction at the interface between FAME and liquid paraffin at 60 °C resulted in formation of hollow silica microspheres. Use of mixture of castor oil (CO) and dimethyl carbonate (DMC) as extractant resulted in formation of hollow silica microspheres with a hole on the surface, whereas increase in the DMC content in extracting medium led to formation of filbert-like silica solid microspheres. Change in size of cavity and hole was studied by changing the extracting temperature. The formation process and mechanism of these silica microspheres are proposed based on the diffusion rate. The relationship between the size of the microspheres and the state of the droplet at the interface is correlated.