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Rechargeable Zn‐based batteries provide a compelling supplement to subsistent energy storage devices owing to their high energy density, good safety, and low cost. Nevertheless, inherent imperfections such as dendrite growth, side reactions, and andante reaction kinetics, severely impede their commercialization. As new 0D nanomaterials, carbon dots (CDs) with unique characteristics and excellent electrochemical activity, exhibit promising potential exploitation in electrochemistry and electrocatalysis areas. Herein, the adhibition of CDs in resolving the aforementioned drawbacks of Zn‐based batteries is introduced. To begin with, concepts, physicochemical properties, and synthetic methods of CDs are discussed. Next, recent developments and advances exploiting CDs in respectively ameliorating the performance of the Zn anode, the cathode, and electrolytes of Zn ion batteries and bifunctional electrocatalytic activities including oxygen reduction reaction and oxygen evolution reaction for Zn‐air batteries, are roundly reviewed and minutely generalized. Finally, current challenges and prospects are surveyed as well, aiming to offer a reference for the blossom of advanced Zn‐based batteries. [ABSTRACT FROM AUTHOR]

Aqueous rechargeable batteries (ARBs) have attracted wide attention due to their rich resources, environmental friendliness, and safety. The high ionic conductivity, safety and interfacial wettability of the aqueous electrolyte are essential for energy storage devices. However, the narrow electrochemical stability window (ESW) of the aqueous electrolyte and the side reactions of the electrode/electrolyte lead to the low energy density of the ARBs. In the past studies, the above problems were generally solved by improving the ion transport characteristics of the electrolyte and the electrode/electrolyte interface. Herein, we discuss the background, limitations, and key concepts for performance improvement of aqueous electrolytes, aiming to provide a comprehensive perspective and inspiration for further research on aqueous electrolytes and promote their development and application in the field of energy storage. [ABSTRACT FROM AUTHOR]

Hard carbon (HC) is widely regarded as the most promising anode material for sodium‐ion batteries (SIBs). For improving the sodium storage capacity of HC anode, current research primarily focuses on the high‐voltage slope region. Actually, increasing the storage capability in the low‐voltage plateau region is more important for enhancing the energy density of full cells. Therefore, in this study, HC anode with rich closed pore structure is designed and constructed with the help of carbon dots (CDs), and it is demonstrated that the presence of closed pore structure can provide more sodium storage sites in the plateau region, resulting in an obvious increase of sodium storage capacity. Moreover, the pore‐filling and intercalation mechanism for sodium storage in plateau region is revealed by in situ Raman spectroscopy and ex situ transmission electron microscopy (TEM). It is worth noting that the increase in capacity induced by closed pore‐filling is not accompanied by a decrease in initial coulombic efficiency (ICE), due to the fact that the introduction of closed pores does not increase the contact area between electrode and electrolyte. This work presents novel concepts for the structural design of HC and provides valuable insights into the effective utilization of plateau region in SIBs. [ABSTRACT FROM AUTHOR]

Sodium‐ion batteries (SIBs) have rapidly risen to the forefront of energy storage systems as a promising supplementary for Lithium‐ion batteries (LIBs). Na3V2(PO4)2F3 (NVPF) as a common cathode of SIBs, features the merits of high operating voltage, small volume change and favorable specific energy density. However, it suffers from poor cycling stability and rate performance induced by its low intrinsic conductivity. Herein, we propose an ingenious strategy targeting superior SIBs through cross‐linked NVPF with multi‐dimensional nanocarbon frameworks composed of amorphous carbon and carbon nanotubes (NVPF@C@CNTs). This rational design ensures favorable particle size for shortened sodium ion transmission pathway as well as improved electronic transfer network, thus leading to enhanced charge transfer kinetics and superior cycling stability. Benefited from this unique structure, significantly improved electrochemical properties are obtained, including high specific capacity (126.9 mAh g−1 at 1 C, 1 C = 128 mA g−1) and remarkably improved long‐term cycling stability with 93.9% capacity retention after 1000 cycles at 20 C. The energy density of 286.8 Wh kg−1 can be reached for full cells with hard carbon as anode (NVPF@C@CNTs//HC). Additionally, the electrochemical performance of the full cell at high temperature is also investigated (95.3 mAh g−1 after 100 cycles at 1 C at 50 °C). Such nanoscale dual‐carbon networks engineering and thorough discussion of ion diffusion kinetics might make contributions to accelerating the process of phosphate cathodes in SIBs for large‐scale energy storages. [ABSTRACT FROM AUTHOR]

Developing electrode materials with high tap density, low cost, and superior performance poses a formidable challenge in electrochemistry. The impressive performance exhibited by most electrodes comes at the expense of tap density and cost, severely limiting their practical applications. Here, combining computational and experimental results, an approach for the electrode materials with high tap density and rich heterostructure (Cu2S/Na2Sn) from cheap copper smelting slag enabled by an electrochemical process is proposed, reducing the diffusion energy barrier from 0.82 to 0.28 eV for Na+, as well as delivering an impressively high tap density of 3.32 g cm−3. Furthermore, the electrochemical activation process that irreversibly generates more stable Cu2S and Na2Sn after the first charge progress of parent materials is also revealed by in/ex situ analytical techniques. As expected, assembled sodium ion capacitors (SICs) achieve high energy density (74.4 Wh kg−1) at high power density (20 000 W kg−1) with outstanding capacity retention of 81.5% after 10 000 cycles, delivering over 76% of its energy density in 13.4 s, which surpasses the performance achieved by state‐of‐the‐art SICs. This work not only provides novel insights into irreversibly conversion‐type anodes but also introduces a method for efficient value‐added utilization of smelting slag. [ABSTRACT FROM AUTHOR]

Hybrid supercapacitors (HSCs) comprising a battery‐type cathode and capacitive anode have recently become a research hotspot. Nevertheless, the low capacity utilization, poor kinetic behavior, and unstable structure of a single battery‐type oxide cathode restrict the overall performance of the device. Herein, the carbon quantum dots (CQDs) modified NiO/Co3O4 heterostructured flower‐like microspheres are constructed, and enhanced specific capacity, rate capability, and cycling performance are achieved when used as the cathode for HSCs. This is attributed to the fact that the modification of bifunctional CQDs as size regulators and conductive agents and the construction of heterostructure can not only improve the specific surface area and provide more electroactive sites, thereby enhancing the charge storage performance but also regulate the electronic structure and boost the interface charge transfer capability and electronic conductivity, thereby boosting the reaction kinetics and cycle stability. The enhanced electrochemical kinetic behavior is revealed by electrochemical kinetic analyses based on cyclic voltammetry, electrochemical impedance spectroscopy tests and density functional theory calculations. Meanwhile, the electrochemical reaction process and energy storage mechanism are illustrated by ex‐situ X‐ray diffraction and X‐ray photoelectron spectroscopy characterizations. Furthermore, an HSC is further constructed using the CQDs/NiO/Co3O4 heterostructured flower‐like microspheres as the cathode, simultaneously achieving high energy density (40.9 Wh kg−1), high power density (24 kW kg−1), and splendid cyclic stability (94.2% capacity retention after 5000 cycles at 10 A g−1). These synergistic modification strategies of bifunctional CQDs modification and heterostructure design provide a valuable direction for the design and development of HSCs with both high energy density and high power density. [ABSTRACT FROM AUTHOR]

Although lithium-sulfur (Li-S) batteries with high specific energy exhibit great potential for next-generation energy-storage systems, their practical applications are limited by the growth of Li dendrites and lithium polysulfides (LiPSs) shuttling. Herein, a highly porous red phosphorus sponge (HPPS) with well distributed pore structure was efficiently prepared via a facile and large-scale hydrothermal process for polysulfides adsorption and dendrite suppression. As experimental demonstrated, the porous red phosphorus modified separator with increased active site greatly promotes the chemisorption of LiPSs to efficiently immobilize the active sulfur within the cathode section, while Li metal anode activated by Li3P interlayer with abundant ionically conductive channels significantly eliminates the barrier for uniform Li+ permeation across the interlayer, contributing to the enhanced stability for both S cathode and Li anode. Mediated by the HPPS, long-term stability of 1,200 h with minor voltage hysteresis is achieved in symmetric cells with Li3P@Li electrode while Li-S half-cell based on HPPS modified separator delivers an outperformed reversibility of 783.0 mAh·g−1 after 300 cycles as well as high-rate performance of 694.5 mAh·g−1 at 3 C, which further boosts the HPPS tuned full cells in practical S loading (3 mg·cm−2) and thin Li3P@Li electrode (100 µm) with a capacity retention of 71.8% after 200 cycles at 0.5 C. This work provides a cost-effective and metal free mediator for simultaneously alleviating the fundamental issues of both S cathode and Li anode towards high energy density and long cycle life Li-S full batteries. [ABSTRACT FROM AUTHOR]

The ever‐increasing energy density requirements in electric vehicles (EVs) have boosted the development of Ni‐rich layered oxide cathodes for state‐of‐the‐art lithium‐ion batteries. Nevertheless, the commercialization of polycrystalline Ni‐rich cathodes (PCNCs) is hindered by the severe performance degradation and safety concerns that are tightly related to its particle cracking during cycling. Single‐crystalline Ni‐rich cathodes (SCNCs) with eliminated grain boundaries and high mechanical strength have recently attracted extensive attention owing to their superior structural and cycling stability, which present high crack resistance during electrochemical operation. Various articles have focused on the trial‐and‐error synthesis and modifications of SCNCs, as well as the comparison of performances and mechanisms with PCNCs. However, there has been much less effort in systematic analysis and summary to reveal their key challenges, controversies, and the corresponding primary causes. In this review, the advantages and debates in structural and electrochemical properties of SCNCs over PCNCs are summarized to provide fundamental understanding of SCNCs. Then the current practical issues and challenges are comprehensively discussed from the viewpoints of both academia and industry, as well as the proposed modification strategies and underlying mechanisms for SCNCs. The outlook and perspectives are further given to facilitate the commercial applications of SCNCs in high‐performance EVs. [ABSTRACT FROM AUTHOR]

The high‐throughput scalable production of inexpensive and efficient electrode materials at high current densities demanded by industry is a huge challenge for large‐scale implementation of energy storage technologies. Here, inspired by theoretical calculations that a FeS2/TiO2 heterostructure with built‐in electric field (BEF) can reduce the reaction energy barrier and enhance charge transport, the scalable production of cheap FeS2/TiO2 heterostructure is fabricated by utilizing natural ilmenite as precursor, exhibiting excellent electrochemical performances for sodium‐ion capacitors (SICs) anode. Assembling it with activated carbon (AC) cathode for SICs delivers high energy density (73.7 Wh kg−1) and high power density (10 kW kg−1) as well as outstanding cycle lifespan. Impressively, the method breaks through the traditional preparation approach by using natural minerals instead of high‐purity chemical raw materials as precursors for constructing heterojunctions, and price of the mineral is nearly five orders of magnitude lower than that of commercial chemical raw materials with high‐purity, which greatly reduces raw materials cost and is available for mass production. Similarly, the method can be extended to utilize other minerals to construct heterostructures, thus achieving expanded electrochemical performance, which exhibits huge potentials in electrochemical energy storage. [ABSTRACT FROM AUTHOR]

Potassium ion capacitors (PICs) have the potential to combine the advantages of capacitors and batteries, making them promising energy storage substitutes for existing systems. Biomass‐based‐electrodes are very promising materials for potassium storage, however, at present, the acquisition of biomass‐based‐electrodes is mainly dependent on high temperature calcination, which makes the efficient utilization of biomass materials quite challenging. Herein, in accordance with ex‐situ 13C NMR and Raman, a universally directional selection strategy of biomass precursors through an advanced pre‐diagnosis method for calcination intermediates and a sulfur engineering strategy are initially proposed, proving that the carbon materials derived from precursors with fewer aliphatic chains and more aromatic carbons show a higher yield and can be have more K ions inserted. In addition, the evolution mechanism of in‐plane/interlayered CS bonds is thoroughly evaluated. Notably, PICs assembled by such carbon materials as the battery‐type anode, deliver a high energy density of 151 Wh kg‐1 and an ultrahigh power output of 10 kW kg‐1, closing to state‐of‐the‐art values for PICs. This breakthrough opens up a new avenue for targeted design of biomass materials and offers in‐depth insights into the evolution of S‐C bonds, promoting the energy/power density of PICs devices to a higher level. [ABSTRACT FROM AUTHOR]

Sodium‐ion batteries (SIBs) have grasped renewed attentions in recent years owing to the blooming growth of clean energy and corresponding demands of grid‐scale energy storage. Note that, the properties of cathode materials are quite important to the development of SIBs as they largely determine the energy density, cycle life, and cost of a battery. Direct inheriting those Co/Ni based layered cathodes that are successfully utilized in lithium‐ion batteries seems to be impracticable for SIBs in view of the high materials costs. Fortunately, the discovery of the electrochemical activity of Fe3+/Fe4+ redox couple in sodium layered materials has opened a new way to design high capacity/voltage and low‐cost cathodes for SIBs. To date, various Fe‐based layered oxides have been explored, showing encouraging electrochemical performances in SIBs. However, issues and challenges still remain upon the practical utilization of Fe‐based layered cathodes, calling for further targeted and in‐depth investigations. In this review, the developing history, key problems, and current progress of Fe‐based layered cathodes on electrochemical performances and working mechanism are summarized and discussed. In addition, possible research trends and perspectives are proposed. It is believed that Fe‐based layered oxides will be one of the most attractive cathodes for SIBs. [ABSTRACT FROM AUTHOR]

High‐capacity cathodes and anodes in energy storage area are required for delivering high energy density due to the ever‐increasing demands in the applications of electric vehicles and power grids, which suffer from significant safety concerns and poor cycling stability at the current stage. All‐solid‐state lithium batteries (ASSLBs) have been considered to be particularly promising within the new generation of energy storage, owing to the superiority of safety, wide potential window, and long cycling life. As the key component in ASSLBs, individual solid electrolytes that can meet practical application standards are very rare due to poor performance. To the present day, numerous research efforts have been expended to find applicable solid‐state electrolytes and tremendous progress has been achieved, especially for garnet‐type solid electrolytes. Nevertheless, the garnet‐type solid electrolyte is still facing some crucial dilemmas. Hence, the issues of garnet electrolytes' ionic conductivity, the interfaces between electrodes and garnet solid electrolytes, and application of theoretical calculation on garnet electrolytes are focuses in this review. Furthermore, prospective developments and alternative approaches to the issues are presented, with an aim to improve understanding of garnet electrolytes and promote their practical applications in solid‐state batteries. [ABSTRACT FROM AUTHOR]

The practical application of Li‐rich Mn‐based oxide cathode is predominately retarded by the capacity decline and voltage fading, associated with the structure distortion and anionic redox reactions. Here, a linkage‐functionalized modification approach to tackle these challenges via a synchronous lithium oxidation strategy is reported. The doping of Ce in the bulk phase activates the pseudo‐bonding effect, effectively stabilizing the lattice oxygen evolution and suppressing the structure distortion. Interestingly, it also induces the formation of spinel phase Li4Mn5O12 in the subsurface, which in turn constructs the phase boundaries, thereby arousing the interior self‐built‐in electric field to prevent the outward migration of bulk oxygen anions and boost the charge transfer. Moreover, the formed coating layer Li2CeO3 with oxygen vacancies accelerates Li+ diffusion and mitigates electrolyte cauterization. The corresponding cathode exhibits superior long‐cycle stability after 300 cycles with only a 0.013% capacity drop and 1.76 mV voltage decay per cycle. This work sheds new light on the development of Li‐rich Mn‐based oxide cathodes toward high energy density applications. [ABSTRACT FROM AUTHOR]

Sodium‐ion capacitors (SICs) have triggered considerable attention due to potential high energy densities under high power densities. The presodiation process of anodes is very important for the construction of high‐performance SICs; however, in the current presodiation method, metallic sodium is utilized as the presodiation agent through the assembling/disassembling of half‐cells, which is very complicated and dangerous, greatly hindering the development of SICs. Herein, a novel voltage‐induced high‐efficient in situ presodiation approach is successfully realized by introducing organic sodium salts as the sodium sources into the cathode. Moreover, the irreversible electrochemical characteristic of organic sodium salts triggered by high voltage could provide sufficient sodium sources for presodiation without any negative effects for further operation of SICs. Significantly, the diversified anodes like carbon and TiO2 are successfully presodiated and the corresponding SICs manifest excellent electrochemical performances. This rational strategy is anticipated to shed light on a potential avenue for greatly simplifying the assembly process of the SICs, which may largely accelerate the commercialization process of SICs. [ABSTRACT FROM AUTHOR]

Antimony sulfide (Sb 2 S 3 ) has been shown as a promising candidate for sodium ions batteries, in considering the gravimetric energy density and high theoretical capacity. Hollow-sphere Sb 2 S 3 coated with carbon are successfully designed through Oswald ripening process. The Sb 2 S 3 /C utilized as SIBs anode displays excellent electrochemical properties, delivering a high charge capacity of 693.4 mAh g −1 at 0.2 A g −1 between 0.01 and 3.0 V (vs. Na + /Na). Its reversible capacity can keep 545.6 mAh g −1 , with a retention of ∼80% after 100 cycles. Even the current densities return from 6.4 to 0.2 A g −1 , the Sb 2 S 3 /C still maintains 550.8 mAh g −1 after 70 cycles. Combining the large void space with carbon layer, the advantages are noticed when the increased electrolyte penetration area, improved electronic conductivity and shortened Na + diffusion length are attained concurrently, resulting in the excellent specific capacity and cycling stability. The study provides an effect strategy in improving the electrochemical performances of metal sulfides as anode for SIBs. [ABSTRACT FROM AUTHOR]

Co 2 MnO 4 /Co hydroxide chloride (CMO/CHC) nanocomposite is firstly obtained through an electrochemically alternating voltage methodology for supercapacitor applications. The CMO/CHC electrode materials display a high specific capacitance of 779 F g −1 at 1 A g −1 and an excellent rate behavior (77.5% and 63.6% at 20 and 40 A g −1 compared with 1 A g −1 , respectively). An asymmetric supercapacitor based on CMO/CHC as cathode and activated carbon (AC) as anode presents a maximum energy density of 27.8 Wh kg −1 at power density of 570.9 W kg −1 . [ABSTRACT FROM AUTHOR]

Na4Mn1.5Fe1.5(PO4)2P2O7 (NMFPP), with its low cost and high energy density, is essential for accelerating the commercialization of sodium‐ion batteries. However, its practical application is limited by serious voltage hysteresis and detrimental Jahn‐Teller distortions. Herein, a high operating voltage and superior stable Nb‐doped NMFPP with fewer intrinsic anti‐site defects are elaborately designed by the reconstruction of the crystal lattice and electronic distribution. By introducing higher charge density Nb─O bonds, the lengths of Mn‐O bonds are shortened, enhancing lattice stability. As a result, the lattice volume contracted during Na+ extraction/insertion is decreased with niobium‐modified Na4(Mn0.5Fe0.5)2.94Nb0.06(PO4)2P2O7, mitigating lattice distortion from the Jahn‐Teller effect and increasing the capacity retention after 1000 cycles from 57.5% to 82.3%. More importantly, the delayed effect of Mn2+ involvement in redox reactions is significantly reduced, raising the average operating voltage from 3.32 to 3.64 V and increasing the overall energy density by 13%. This study opens new avenues to develop advanced sodium‐ion battery cathode materials with high energy density and long calendar life for energy storage. [ABSTRACT FROM AUTHOR]

Highlights: Pore size and graphitization engineering of carbon cathode were orientated-designed by regulating the molar ratios of Zn/Co ions. Zn90Co10-APC and its assembled PLG//Zn90Co10-APC LIC both deliver the excellent electrochemical performances. The lack of methods to modulate intrinsic textures of carbon cathode has seriously hindered the revelation of in-depth relationship between inherent natures and capacitive behaviors, limiting the advancement of lithium ion capacitors (LICs). Here, an orientated-designed pore size distribution (range from 0.5 to 200 nm) and graphitization engineering strategy of carbon materials through regulating molar ratios of Zn/Co ions has been proposed, which provides an effective platform to deeply evaluate the capacitive behaviors of carbon cathode. Significantly, after the systematical analysis cooperating with experimental result and density functional theory calculation, it is uncovered that the size of solvated PF6− ion is about 1.5 nm. Moreover, the capacitive behaviors of carbon cathode could be enhanced attributed to the controlled pore size of 1.5–3 nm. Triggered with synergistic effect of graphitization and appropriate pore size distribution, optimized carbon cathode (Zn90Co10-APC) displays excellent capacitive performances with a reversible specific capacity of ~ 50 mAh g−1 at a current density of 5 A g−1. Furthermore, the assembly pre-lithiated graphite (PLG)//Zn90Co10-APC LIC could deliver a large energy density of 108 Wh kg−1 and a high power density of 150,000 W kg−1 as well as excellent long-term ability with 10,000 cycles. This elaborate work might shed light on the intensive understanding of the improved capacitive behavior in LiPF6 electrolyte and provide a feasible principle for elaborate fabrication of carbon cathodes for LIC systems. [ABSTRACT FROM AUTHOR]

Titanium dioxide, promising anode materials for sodium ion batteries, nonetheless, suffers from its inferior charge transfer kinetics owing to low diffusion coefficient and poor electronic conductivity, which results in its unsatisfactory high-rate capability. Here, an oxygen vacancy (OV) engineering assisted in high-content anion (S/Se/P) doping strategy to enhance its charge transfer kinetics for ultrafast sodium-storage performance is proposed to address these issues and expectative results have been obtained. [Display omitted] The rate-determining process for sodium storage in TiO 2 is greatly depending on charge transfer happening in the electrode materials owing to its inferior diffusion coefficient and electronic conductivity. Apart from reducing the diffusion distance of ion/electron, the increasement of ionic/electronic mobility in the crystal lattice is also very important for charge transport. Here, an oxygen vacancy (OV) engineering assisted in high-content anion (S/Se/P) doping strategy to enhance charge transfer kinetics for ultrafast sodium-storage performance is proposed. Theoretical calculations indicate that OV-engineering evokes spontaneous S doping into the TiO 2 phase and achieves high dopant concentration to bring about impurity state electron donor and electronic delocalization over S occupied sites, which can largely reduce the migration barrier of Na+. To realize the speculation, high-content anion doped anatase TiO 2 /C composites (9.82 at% for S in A-TiO 2– x -S/C) are elaborately designed. The optimized A-TiO 2– x -S/C anode exhibits extraordinarily high-rate capability with 209.6 mAh g−1 at 5000 mA g−1. The assembled sodium ion capacitors deliver an ultrahigh energy density of 150.1 Wh kg−1 at a power density of 150 W kg−1 when applied as anode materials. This work provides a new strategy to realize high content anion doping concentration, and enhances the charge transfer kinetics for TiO 2 , which delivers an efficient approach for the design of electrode materials with fast kinetic. [ABSTRACT FROM AUTHOR]

[Display omitted] • The voltage failure is reported and suppressed by heterostructure material. • The construction of heterostructure facilitate the migration of sodium ions. • The assembled sodium-ion capacitor delivers high energy and power density. The voltage failure is a widespread problem in electrochemical energy storage. Nevertheless, uncovering the voltage failure mechanism at the molecular level and further solving this problem are still great challenges. Herein, the voltage failure mechanism of SnSe in the ester-based electrolyte is initially revealed and explained by Hard-Soft-Acid-Base (HSAB) theory. Inspired by theoretical calculations that a CoSe 2 /SnSe heterostructure with built-in electric field (BEF) can bring the migration of electrons from the CoSe 2 to SnSe side and result in the conversion of the boundary acid (Sn2+) into a soft acid, an ultra-homogeneous twinned CoSe 2 /SnSe heterostructure is fabricated by employing CoSnO 3 -MOFs as precursor, exhibiting prominent electrochemical performances for sodium-ion capacitors (SICs). Owing to the abundant phase boundaries and BEF, the migration barrier of Na+ decreases from 1.17 eV to 0.39 eV, delivering greatly enhanced charge transport kinetics. Impressively, the SICs assembled by employing this materials as the anode deliver high energy density (146.3 Wh kg−1) and high power density (12 kW kg−1) as well as excellent cycle lifespan, indicating that the voltage failure phenomenon is solved perfectly by the strategy of constructing heterostructures. The work promotes better fundamental understanding of the voltage failure and provides a new strategy to suppress the voltage failure of electrodes, which may also be extended to other electrochemical energy storage system with similar voltage failure phenomenon. [ABSTRACT FROM AUTHOR]

In recent years metal ion capacitors (MICs) and supercapacitors devices have been reported as promising alternatives for energy storage on a large scale. MICs are characterized by superior power density and energy density, combining advantages of metal-ion batteries such as lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, zinc-ion batteries, etc., and those of supercapacitors. Herein we provide a review of recent progress on MICs, focusing on the sodium-ion capacitor (SICs), potassium-ion capacitors (PICs), and zinc-ion capacitors (ZICs); starting from the basic concepts (the perspectives of the design concepts, the configuration of MICs devices, the electrochemical behavior and the energy storage mechanism), the electrode materials and electrolyte systems in details with some examples. The factors impacting the electrochemical performances of the MICs are also provided in this work and end with a conclusion. This review will be helpful for researchers, especially the new researchers in the field of MICs and supercapacitors, to have an overall understanding of MICs and supercapacitors, develop electrochemical storage devices, and respond to the need forenergy storage in electric vehicles and electronic devices. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Functionalized CQDs were synthesized, which showed monodispersity in solvent. • Coulomb-blockade effect of CQDs was utilized to increase the E b of PEI matrix. • The composite with 0.5 wt% CQDs exhibited a high U e of 10.66 J/cm3 at 600 kV/mm. 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. [ABSTRACT FROM AUTHOR]

Robust single-crystalline Ni-rich cathodes with increasing Ni proportion, LiNi 0.83 Co 0.11 Mn 0.06 O 2 (SC83), LiNi 0.88 Co 0.06 Mn 0.06 O 2 (SC88), and LiNi 0.95 Co 0.03 Mn 0.02 O 2 (SC95) were successfully designed with molten salt-assisted method, and the correlation between the Li+ storage properties, particle microcracking, surface phase transitions, and Ni fraction in the single-crystalline Ni-rich cathodes have been profoundly investigated. [Display omitted] • -crystalline Ni-rich cathodes with increasing Ni proportion were designed with molten salt-assisted method. • The single-crystalline LiNi 0.83 Co 0.11 Mn 0.06 O 2 cathode presents superior structural stability and cycling durability. • Performance degradations were attributed to the aggravated Li/Ni mixing and H2 ↔ H3 phase transition. • It provides approach for designing high-energy density and stable single-crystalline Ni-rich cathodes. 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 LiNi 0.83 Co 0.11 Mn 0.06 O 2 (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 LiNi 0.88 Co 0.06 Mn 0.06 O 2 (SC88) and LiNi 0.95 Co 0.03 Mn 0.02 O 2 (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). [ABSTRACT FROM AUTHOR]

P2–Na 2/3 Ni 1/3 Mn 2/3 O 2 as a promising cathode material for sodium ion batteries (SIBs) has attracted much attention owing to high capacity and wide operation voltage. However, it suffers from inferior rate and cycling performances due to P2–O2 phase transition and Na+/vacancy ordering during charge/discharge process. Herein, a Fe/Ti co-substitution strategy is successfully utilized to mitigate these issues. Notably, as probed by In-situ X-ray diffraction, the substitution of Ni with Fe significantly stabilizes the interlayer framework by impeding slab glide during deep Na+ extraction, resulting in reversible P2-OP4 phase transition with smaller volume change of host structure compared to P2–O2 transition. Meanwhile, synchrotron X-ray diffraction shows that, the Na+/vacancy ordering is greatly suppressed by further replacing Mn with Ti, which breaks down the long-range ordering of Ni/Mn distribution, promoting Na ion transport. In addition, the charge compensation mechanism of Fe/Ti co-substituted P2–Na 0.67 Ni 0.23 Fe 0.1 Mn 0.57 Ti 0.1 O 2 (NFMT) revealed by Ex-situ X-ray absorption spectroscopy demonstrates that the incorporation of Fe3+/4+ redox couple largely improve the working voltage. Consequently, the obtained NFMT cathode delivers a high energy density over 420 Wh/kg within 4.3–2.6 V, accompanied with remarkably enhanced kinetics and capacity retention. Such co-substitution strategy provides a promising approach to develop high-voltage and cycle-stable cathode materials for SIBs. [Display omitted] • Fe/Ti co-substitution is proposed to modify the P2–Na 2/3 Ni 1/3 Mn 2/3 O 2 cathode. • Fe substitution can prevent the P2–O2 phase transition. • Ti substitution disrupts cation ordering and Na+/vacancy ordering. • Fe/Ti co-substitution can stabilize the reversible OP4 phase. [ABSTRACT FROM AUTHOR]

The pseudocapacitive storage mechanism of ClO 4 − and Na ions in cathode and anode were explored for the first time with NH 3 plasma strategy. In-situ/ex-situ characterizations and density functional theory (DFT) calculations demonstrate that pyridinic-N and C O could efficiently increase the defects and tune the adsorb properties of ClO 4 −, and build up an expressway for fast Na ions transfer, which further illustrates the "adsorption-pseudocapacitive reactions "processes of cathodes and "adsorption-pseudocapacitive reactions-intercalation" processes of anodes. [Display omitted] • N/O pseudocapacitive sites can be controlled by NH 3 plasma. • Revealing the reversible evolution of Pyridinic-N/C O. • Classifying the different mechanism in SICs. 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 ClO 4 − and Na ions in carbon cathode/anode with a novel NH 3 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 NH 3 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 NH 3 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. [ABSTRACT FROM AUTHOR]

• Mn2+ dissolution enabled MnO to be an active cathode for aqueous Zn-ion battery. • A H+/Zn2+ co-insertion mechanism of the as-activated Mn 1-x O cathode was proposed. • A MnO nanochain@Graphene scroll configuration was obtained by hydrothermal method. • Cycling stability of MnO electrode was greatly enhanced by graphene wrapping. 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 ZnSO 4 electrolytes with different concentration of MnSO 4. 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 MnSO 4 , 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 Mn 1-x O 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 MnO 2 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. [ABSTRACT FROM AUTHOR]