High‐Performance Reversible Aqueous Zn‐Ion Battery Based on Porous MnOx Nanorods Coated by MOF‐Derived N‐Doped Carbon

Rechargeable aqueous zinc‐ion batteries (ZIBs) have been emerging as potential large‐scale energy storage devices due to their high energy density, low cost, high safety, and environmental friendliness. However, the commonly used cathode materials in ZIBs exhibit poor electrochemical performance, such as significant capacity fading during long‐term cycling and poor performance at high current rates, which significantly hinder the further development of ZIBs. Herein, a new and highly reversible Mn‐based cathode material with porous framework and N‐doping (MnO_x@N‐C) is prepared through a metal–organic framework template strategy. Benefiting from the unique porous structure, conductive carbon network, and the synergetic effect of Zn²⁺ and Mn²⁺ in electrolyte, the MnO_x@N‐C shows excellent cycling stability, good rate performance, and high reversibility for aqueous ZIBs. Specifically, it exhibits high capacity of 305 mAh g^?1 after 600 cycles at 500 mA g^?1 and maintains achievable capacity of 100 mAh g^?1 at a quite high rate of 2000 mA g^?1 with long‐term cycling of up to 1600 cycles, which are superior to most reported ZIB cathode materials. Furthermore, insight into the Zn‐storage mechanism in MnO_x@N‐C is systematically studied and discussed via multiple analytical methods. This study opens new opportunities for designing low‐cost and high‐performance rechargeable aqueous ZIBs.     

Iron‐Oxide‐Based Advanced Anode Materials for Lithium‐Ion Batteries

Iron oxides, such as Fe₂O₃ and Fe₃O₄, have recently received increased attention as very promising anode materials for rechargeable lithium‐ion batteries (LIBs) because of their high theoretical capacity, non‐toxicity, low cost, and improved safety. Nanostructure engineering has been demonstrated as an effective approach to improve the electrochemical performance of electrode materials. Here, recent research progress in the rational design and synthesis of diverse iron oxide‐based nanomaterials and their lithium storage performance for LIBs, including 1D nanowires/rods, 2D nanosheets/flakes, 3D porous/hierarchical architectures, various hollow structures, and hybrid nanostructures of iron oxides and carbon (including amorphous carbon, carbon nanotubes, and graphene). By focusing on synthesis strategies for various iron‐oxide‐based nanostructures and the impacts of nanostructuring on their electrochemical performance, novel approaches to the construction of iron‐oxide‐based nanostructures are highlighted and the importance of proper structural and compositional engineering that leads to improved physical/chemical properties of iron oxides for efficient electrochemical energy storage is stressed. Iron‐oxide‐based nanomaterials stand a good chance as negative electrodes for next generation LIBs.     

High‐Abundance and Low‐Cost Metal‐Based Cathode Materials for Sodium‐Ion Batteries: Problems,Progress, and Key Technologies

Recently, room‐temperature stationary sodium‐ion batteries (SIBs) have received extensive investigations for large‐scale energy storage systems (EESs) and smart grids due to the huge natural abundance and low cost of sodium. The SIBs share a similar “rocking‐chair” sodium storage mechanism with lithium‐ion batteries; thus, selecting appropriate electrodes with a low cost, satisfactory electrochemical performance, and high reliability is the key point for the development for SIBs. On the other hand, the carefully chosen elements in the electrodes also largely determine the cost of SIBs. Therefore, earth‐abundant‐metal‐based compounds are ideal candidates for reducing the cost of electrodes. Among all the high‐abundance and low‐cost metal elements, cathodes containing iron and/or manganese are the most representative ones that have attracted numerous studies up till now. Herein, recent advances on both iron‐ and manganese‐based cathodes of various types, such as polyanionic, layered oxide, MXene, and spinel, are highlighted. The structure–function property for the iron‐ and manganese‐based compounds is summarized and analyzed in detail. With the participation of iron and manganese in sodium‐based cathode materials, real applications of room‐temperature SIBs in large‐scale EESs will be greatly promoted and accelerated in the near future.     

On the Functionality of Coatings for Cathode Active Materials in Thiophosphate‐Based All‐Solid‐State Batteries

The last decade has seen considerable advancements in the development of solid electrolytes for solid‐state battery applications, with particular attention being paid to sulfide superionic conductors. Importantly, the intrinsic electrochemical instability of these high‐performance separators highlights the notion that further progress in the field of solid‐state batteries is contingent on the optimization of component material interfaces in order to secure high energy and power densities, while maintaining device safety and a practical cycle life. On the cathode side, the need for a protective coating to inhibit solid electrolyte degradation is clear; however, a mechanistic understanding of the coating functionality remains unresolved, and there is still much room for improvement regarding the methodology and associated material properties. Herein, the essential requirements for a suitable coating are specified and fundamental considerations are discussed in detail. Additionally, this article will provide an overview of the various material classes, assessment protocols and practical coating methods, as well as an outlook on the development of coatings for cathode active materials in thiophosphate‐based solid‐state batteries.     

Thermodynamic Aspects of Cathode Coatings for Lithium‐Ion Batteries

Metal oxide cathode coatings are capable of scavenging the hydrofluoric acid (HF) (present in LiPF₆‐based electrolytes) and improving the electrochemical performance of Li‐ion batteries. Here, a first‐principles thermodynamic framework is introduced for designing cathode coatings that consists of four elements: i) HF‐scavenging enthalpies, ii) volumetric and iii) gravimetric HF‐scavenging capacities of the oxides, and iv) cyclable Li loss into coating components. 81 HF‐scavenging reactions involving binary s‐, p‐ and d‐block metal oxides and fluorides are enumerated and these materials are screened to find promising coatings based on attributes (i‐iv). The screen successfully produces known effective coating materials (e.g., Al₂O₃ and MgO), providing a validation of our framework. Using this design strategy, promising coating materials, such as trivalent oxides of d‐block transition metals Sc, Ti, V, Cr, Mn and Y, are predicted. Finally, a new protection mechanism that successful coating materials could provide by scavenging the wide bandgap and low Li ion conductivity LiF precipitates from the cathode surfaces is suggested.     

Pseudo‐Zn–Air and Zn‐Ion Intercalation Dual Mechanisms to Realize High‐Areal Capacitance and Long‐Life Energy Storage in Aqueous Zn Battery

Aqueous zinc batteries are considered as promising alternatives to lithium ion batteries owing to their low cost and high safety. However, the developments of state‐of‐the‐art zinc‐ion batteries (ZIB) and zinc–air batteries (ZAB) are limited by the unsatisfied capacities and poor cycling stabilities, respectively. It is of significance in utilizing the long‐cycle life of ZIB and high capacity of ZAB to exploit advanced energy storage systems. Herein, a bulk composite of graphene oxide and vanadium oxide (V₅O₁₂·6H₂O) as cathode material for aqueous Zn batteries in a mild electrolyte is employed. The battery performance is demonstrated to arise from a combination of the reversible cations insertion/extraction in vanadium oxide and especially the electrochemical redox reactions on the surface functional groups of graphene oxide (named as pseudo‐Zn–air mechanism). Along with adjusting the hydroxyl content on the surface of graphene oxide, the specific capacity is significantly increased from 342 mAh g^?1 to a maximum of 496 mAh g^?1 at 100 mA g^?1. The surface‐controlled kinetics occurring in the bulk composite ensure a high areal capacity of 10.6 mAh cm^?2 at a mass loading of 26.5 mg cm^?2, and a capacity retention of 84.7% over 10 000 cycles at a high current density of 10 A g^?1.     

Recent Advances in Vanadium‐Based Aqueous Rechargeable Zinc‐Ion Batteries

Aqueous zinc‐ion batteries (AZIBs) have attracted considerable attention as promising next‐generation power sources because of the abundance, low cost, eco‐friendliness, and high security of Zn resources. Recently, vanadium‐based materials as cathodes in AZIBs have gained interest owing to their rich electrochemical interaction with Zn²⁺ and high theoretical capacity. However, existing AZIBs are still far from meeting commercial requirements. This article summarizes recent advances in the rational design of vanadium‐based materials toward AZIBs. In particular, it highlights various tactics that have been reported to increase the intercalation space, structural stability, and the diffusion ability of the guest Zn²⁺, as well as explores the structure‐dependent electrochemical performance and the corresponding energy storage mechanism. Furthermore, this article summarizes recent achievements in the optimization of aqueous electrolytes and Zn anodes to resolve the issues that remain with Zn anodes, including dendrite formation, passivation, corrosion, and the low coulombic efficiency of plating/stripping. The rationalization of these research findings can guide further investigations in the design of cathode/anode materials and electrolytes for next‐generation AZIBs.     

Lattice‐Cell Orientation Disorder in Complex Spinel Oxides

Transition metal (TM) substitution has been widely applied to change complex oxides crystal structures to create high energy density electrodes materials in high performance rechargeable lithium‐ion batteries. The complex local structure in the oxides imparted by the TM arrangement often impacts their electrochemical behaviors by influencing the diffusion and intercalation of lithium. Here, a major discrepancy is demonstrated between the global and local structures of the promising high energy density and high voltage LiNi_0.5Mn_1.5O₄ spinel cathode material that contradicts the existing structural models. A new single‐phase lattice‐cell orientation disorder model is proposed as the mechanism for the local ordering that explains how the inhomogeneous local distortions and the coherent connection give rise to the global structure in the complex oxide. Further, the single‐phase model is consistent with the electrochemical behavior observation of the materials.     

The Sodium Storage Mechanism in Tunnel‐Type Na0.44MnO2 Cathodes and the Way to Ensure Their Durable Operation

Tunnel‐type sodium manganese oxide is a promising cathode material for aqueous/nonaqueous sodium‐ion batteries, however its storage mechanism is not fully understood, in part due to the complicated sodium intercalation process. In addition, low cyclability due to manganese dissolution has limited its practical application in rechargeable batteries. Here, the intricate sodium intercalation mechanism of Na_0.44MnO₂ is revealed by combination of electrochemical characterization, structure determination from powder X‐ray diffraction data, 3D bond valence difference maps, and barrier‐energy calculations of the sodium diffusion. NaI is proposed as an important electrolyte solution additive. It is shown to form a thin, beneficial, and durable cathode surface film that prevents manganese dissolution. The addition of 0.01 m NaI to electrolyte solutions based on alkyl carbonate solvents and NaClO₄ greatly improves the cycling efficiency, raising the capacity retention from 86% to 96% after 600 cycles. This study determines the core aspects of the sodium intercalation mechanism in tunnel‐type sodium manganese oxide and shows how it can serve as a durable cathode material for rechargeable Na batteries.     

Ultrahigh‐Capacity and Fire‐Resistant LiFePO4‐Based Composite Cathodes for Advanced Lithium‐Ion Batteries

The growing demand for advanced energy storage devices with high energy density and high safety has continuously driven the technical upgrades of cell architectures as well as electroactive materials. Designing thick electrodes with more electroactive materials is a promising strategy to improve the energy density of lithium‐ion batteries (LIBs) without alternating the underlying chemistry. However, the progress toward thick, high areal capacity electrodes is severely limited by the sluggish electronic/ionic transport and easy deformability of conventional electrodes. A self‐supported ultrahigh‐capacity and fire‐resistant LiFePO₄ (UCFR‐LFP)‐based nanocomposite cathode is demonstrated here. Benefiting from the structural and chemical uniqueness, the UCFR‐LFP electrodes demonstrate exceptional improvements in electrochemical performance and mass loading of active materials, and thermal stability. Notably, an ultrathick UCFR‐LFP electrode (1.35 mm) with remarkably high mass loading of active materials (108 mg cm^?2) and areal capacity (16.4 mAh cm^?2) is successfully achieved. Moreover, the 1D inorganic binder‐like ultralong hydroxyapatite nanowires (HAP NWs) enable the UCFR‐LFP electrode with excellent thermal stability (structural integrity up to 1000 °C and electrochemical activity up to 750 °C), fire‐resistance, and wide‐temperature operability. Such a unique UCFR‐LFP electrode offers a promising solution for next‐generation LIBs with high energy density, high safety, and wide operating‐temperature window.     

Transition Metal Oxide Anodes for Electrochemical Energy Storage in Lithium‐ and Sodium‐Ion Batteries

Lithium‐ion batteries (LIBs) with outstanding energy and power density have been extensively investigated in recent years, rendering them the most suitable energy storage technology for application in emerging markets such as electric vehicles and stationary storage. More recently, sodium, one of the most abundant elements on earth, exhibiting similar physicochemical properties as lithium, has been gaining increasing attention for the development of sodium‐ion batteries (SIBs) in order to address the concern about Li availability and cost—especially with regard to stationary applications for which size and volume of the battery are of less importance. Compared with traditional intercalation reactions, conversion reaction‐based transition metal oxides (TMOs) are prospective anode materials for rechargeable batteries thanks to their low cost and high gravimetric specific capacities. In this review, the recent progress and remaining challenges of conversion reactions for LIBs and SIBs are discussed, covering an overview about the different synthesis methods, morphological characteristics, as well as their electrochemical performance. Potential future research directions and a perspective toward the practical application of TMOs for electrochemical energy storage are also provided.     

High‐Voltage‐Driven Surface Structuring and Electrochemical Stabilization of Ni‐Rich Layered Cathode Materials for Li Rechargeable Batteries

Layered lithium–nickel–cobalt–manganese oxide (NCM) materials have emerged as promising alternative cathode materials owing to their high energy density and electrochemical stability. Although high reversible capacity has been achieved for Ni‐rich NCM materials when charged beyond 4.2 V versus Li⁺/Li, full lithium utilization is hindered by the pronounced structural degradation and electrolyte decomposition. Herein, the unexpected realization of sustained working voltage as well as improved electrochemical performance upon electrochemical cycling at a high operating voltage of 4.9 V in the Ni‐rich NCM LiNi_0.895Co_0.085Mn_0.02O₂ is presented. The improved electrochemical performance at a high working voltage at 4.9 V is attributed to the removal of the resistive Ni²⁺O rock‐salt surface layer, which stabilizes the voltage profile and improves retention of the energy density during electrochemical cycling. The manifestation of the layered Ni²⁺O rock‐salt phase along with the structural evolution related to the metal dissolution are probed using in situ X‐ray diffraction, neutron diffraction, transmission electron microscopy, and X‐ray absorption spectroscopy. The findings help unravel the structural complexities associated with high working voltages and offer insight for the design of advanced battery materials, enabling the realization of fully reversible lithium extraction in Ni‐rich NCM materials.     

Challenges in Developing Electrodes,Electrolytes, and Diagnostics Tools to Understand and Advance Sodium‐Ion Batteries

Considering the natural abundance and low cost of sodium resources, sodium‐ion batteries (SIBs) have received much attention for large‐scale electrochemical energy storage. However, smart structure design strategies and good mechanistic understanding are required to enable advanced SIBs with high energy density. In recent years, the exploration of advanced cathode, anode, and electrolyte materials, as well as advanced diagnostics have been extensively carried out. This review mainly focuses on the challenging problems for the attractive battery materials (i.e., cathode, anode, and electrolytes) and summarizes the latest strategies to improve their electrochemical performance as well as presenting recent progress in operando diagnostics to disclose the physics behind the electrochemical performance and to provide guidance and approaches to design and synthesize advanced battery materials. Outlook and perspectives on the future research to build better SIBs are also provided.     

Progress in High‐Voltage Cathode Materials for Rechargeable Sodium‐Ion Batteries

Room‐temperature rechargeable sodium‐ion batteries are considered as a promising alternative technology for grid and other storage applications due to their competitive cost benefit and sustainable resource supply, triumphing other battery systems on the market. To facilitate the practical realization of the sodium‐ion technology, the energy density of sodium‐ion batteries needs to be boosted to the level of current commercial Li‐ion batteries. An effective approach would be to elevate the operating voltage of the battery, which requires the use of electrochemically stable cathode materials with high voltage versus Na⁺/Na. This review summarizes the recent progress with the emerging high‐voltage cathode materials for room‐temperature sodium‐ion batteries, which include layered transitional‐metal oxides, Na‐rich materials, and polyanion compounds. The key challenges and corresponding strategies for these materials are also discussed, with an emphasis placed on the intrinsic structural properties, Na storage electrochemistry, and the voltage variation tendency with respect to the redox reactions. The insights presented in this article can serve as a guide for improving the energy densities of room‐temperature Na‐ion batteries.     

Recent Advances in Rechargeable Magnesium‐Based Batteries for High‐Efficiency Energy Storage

Benefiting from higher volumetric capacity, environmental friendliness and metallic dendrite‐free magnesium (Mg) anodes, rechargeable magnesium batteries (RMBs) are of great importance to the development of energy storage technology beyond lithium‐ion batteries (LIBs). However, their practical applications are still limited by the absence of suitable electrode materials, the sluggish kinetics of Mg²⁺ insertion/extraction and incompatibilities between electrodes and electrolytes. Herein, a systematic and insightful review of recent advances in RMBs, including intercalation‐based cathode materials and conversion reaction‐based compounds is presented. The relationship between microstructures with their electrochemical performances is comprehensively elucidated. In particular, anode materials are discussed beyond metallic Mg for RMBs. Furthermore, other Mg‐based battery systems are also summarized, including Mg–air batteries, Mg–sulfur batteries, and Mg–iodine batteries. This review provides a comprehensive understanding of Mg‐based energy storage technology and could offer new strategies for designing high‐performance rechargeable magnesium batteries.     

Recent Advances in Perovskite Oxides as Electrode Materials for Nonaqueous Lithium–Oxygen Batteries

Lithium–oxygen batteries are considered the next‐generation power sources for many applications. The commercialization of this technology, however, is hindered by a variety of technical hurdles, including low obtainable capacity, poor energy efficiency, and limited cycle life of the electrodes, especially the cathode (or oxygen) electrode. During the last decade, tremendous efforts have been devoted to the development of new cathode materials. Among them, perovskite oxides have attracted much attention due to the extraordinary tunability of their compositions, structures, and functionalities (e.g., high electrical conductivities and catalytic activities), demonstrating the potential to achieve superior battery performance. This article focuses on the recent advances of perovskite oxides as the electrode materials in nonaqueous lithium–oxygen batteries. The electrochemical mechanisms of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on the surface of perovskite oxides are first summarized. Then, the effect of nanostructure and morphology on ORR and OER activities is reviewed, from nanoparticles to hierarchical porous structures. Moreover, perovskite‐oxide‐based composite electrodes are discussed, highlighting the enhancement in electrical conductivities, catalytic activities, and durability under realistic operating conditions. Finally, the remaining challenges and new directions for achieving rational design of perovskite oxides for nonaqueous lithium–oxygen batteries are outlined and discussed.     

Rational Design of Metal Oxide–Based Cathodes for Efficient Dye‐Sensitized Solar Cells

Recently, there is an urgent need for alternative energy resources due to the nonrenewable nature of fossil fuels and increasing CO₂ greenhouse gas emissions. The photovoltaic technologies which directly utilize the abundant and sustainable solar energy are critical. Among various photovoltaic devices (solar cells), dye‐sensitized solar cells (DSSCs) have gained increasing attention due to their high efficiency and easy fabrication process in the past decade. The cathode is a critical part in DSSCs while the benchmark Pt cathode suffers from high cost and scarcity. Thus, the development of alternative Pt‐free cathodes has attracted significant attention with the aim to heighten the cost competitiveness of DSSCs. Among various cathodes, metal oxides are of growing interest due to their superior activity, robust stability, and low cost. Simple oxides such as WO₃ and SnO₂ are used as cathodes for DSSCs. Considering the fixed atomic environment in simple oxides, complex oxides are more attractive as cathodes because of their more flexible physical and chemical properties. This review attempts to present the rational design of simple/complex metal oxide–based cathodes in DSSCs and then to provide useful guidance for the future design of Pt‐free cathodes. The demonstrated design strategies can be extended to other electrocatalysis‐based applications.     

Mixed Metal Difluorides as High Capacity Conversion‐Type Cathodes: Impact of Composition on Stability and Performance

With the most recent development of ultrahigh capacity anodes, such as Li‐ or Si‐based anodes, metal fluorides hold promise as complementary high‐capacity conversion cathode materials for next‐generation energy storage devices. Despite their higher theoretical energy density compared to cells with sulfur cathodes, these materials have received dramatically less attention and little is understood about the origins of their electrochemical behavior. Here, the successful methodology to produce highly uniform size‐controlled mixed metal difluoride nanocomposites is reported. It is discovered that such materials undergo reduction in a single step with a reduction potential intermediate to those for the corresponding single‐metal difluorides and that a solid solution is reformed upon charging, which is advantageous for practical applications. For the first time the progressive formation of metal trifluorides upon repeated cycling of difluorides is reported. Systematic electrochemical measurements in combination with postmortem analyses lead to the conclusion that the cathode stability strongly depends on the ability to prevent formation and growth of a resistive cathode solid electrolyte interphase, which, in turn, strongly depends on the metal composition. This methodology and new findings will help to elucidate a path to developing metal fluoride–based commercial Li‐ion batteries and provide guidelines for material selection.     

Ethylene Carbonate‐Free Electrolytes for High‐Nickel Layered Oxide Cathodes in Lithium‐Ion Batteries

Layered lithium nickel oxide (LiNiO₂) can provide very high energy density among intercalation cathode materials for lithium‐ion batteries, but suffers from poor cycle life and thermal‐abuse tolerance with large lithium utilization. In addition to stabilization of the active cathode material, a concurrent development of electrolyte systems of better compatibility is critical to overcome these limitations for practical applications. Here, with nonaqueous electrolytes based on exclusively aprotic acyclic carbonates free of ethylene carbonate (EC), superior electrochemical and thermal characteristics are obtained with an ultrahigh‐nickel cathode (LiNi_0.94Co_0.06O₂), capable of reaching a 235 mA h g^?1 specific capacity. Pouch‐type graphite|LiNi_0.94Co_0.06O₂ cells in EC‐free electrolytes withstand several hundred charge–discharge cycles with minor degradation at both ambient and elevated temperatures. In thermal‐abuse tests, the cathode at full charge, while reacting aggressively with EC‐based electrolytes below 200 °C, shows suppressed self‐heating without EC. Through 3D chemical and structural analyses, the intriguing impact of EC is visualized in aggravating unwanted surface parasitic reactions and irreversible bulk structural degradation of the cathode at high voltages. These results provide important insights in designing high‐energy electrodes for long‐lasting and reliable lithium‐ion batteries.     

High‐Quality Graphene Microflower Design for High‐Performance Li–S and Al‐Ion Batteries

Poor quality and insufficient productivity are two main obstacles for the practical application of graphene in electrochemical energy storage. Here, high‐quality crumpled graphene microflower (GmF) for high‐performance electrodes is designed. The GmF possesses four advantages simultaneously: highly crystallized defect‐free graphene layers, low stacking degree, sub‐millimeter continuous surface, and large productivity with low cost. When utilized as carbon host for sulfur cathode, the GmF‐sulfur hybrid delivers decent areal capacities of 5.2 mAh cm^?2 at 0.1 C and 3.8 mAh cm^?2 at 0.5 C. When utilized as cathode of Al‐ion battery, the GmF affords a high capacity of 100 mAh g^?1 with 100% capacity retention after 5000 cycles and excellent rate capability from 0.1 to 20 A g^?1. This facile and large‐scale producible GmF represents a meaningful high‐quality graphene powder for practical energy storage technology. Meanwhile, this unique high‐quality graphene design provides an effective route to improve electrochemical properties of graphene‐based electrodes.