Na‐Ion Intercalation and Charge Storage Mechanism in 2D Vanadium Carbide

2D vanadium carbide MXene containing surface functional groups (denoted as V₂CT_x , where T_x are surface functional groups) is synthesized and studied as anode material for Na‐ion batteries. V₂CT_x anode exhibits reversible charge storage with good cycling stability and high rate capability through electrochemical test. The charge storage mechanism of V₂CT_x material during Na⁺ intercalation/deintercalation and the redox reaction of vanadium are studied using a combination of synchrotron based X‐ray diffraction, hard X‐ray absorption near edge spectroscopy (XANES), and soft X‐ray absorption spectroscopy (sXAS). Experimental evidence of a major contribution of redox reaction of vanadium to the charge storage and the reversible capacity of V₂CT_x during sodiation/desodiation process are provided through V K ‐edge XANES and V L _2,3‐edge sXAS results. A correlation between the CO₃^2? content and the Na⁺ intercalation/deintercalation states in the V₂CT_x electrode observed from C and O K ‐edge in sXAS results implies that some additional charge storage reactions may take place between the Na⁺‐intercalated V₂CT_x and the carbonate‐based nonaqueous electrolyte. The results of this study provide valuable information for the further studies on V₂CT_x as anode material for Na‐ion batteries and capacitors.     

In Situ Electrochemical Synthesis of MXenes without Acid/Alkali Usage in/for an Aqueous Zinc Ion Battery

The traditional method to fabricate a MXene based energy storage device starts from etching MAX phase particles with dangerous acid/alkali etchants to MXenes, followed by device assembly. This is a multistep protocol and is not environmentally friendly. Herein, an all‐in‐one protocol is proposed to integrate synthesis and battery fabrication of MXene. By choosing a special F‐rich electrolyte, MAX V₂AlC is directly exfoliated inside a battery and the obtained V₂CT_X MXene is in situ used to achieve an excellent battery performance. This is a one‐step process with all reactions inside the cell, avoiding any contamination to external environments. Through the lifetime, the device experiences three stages of exfoliation, electrode oxidation, and redox of V₂O₅. While the electrode is changing, the device can always be used as a battery and the performance is continuously enhanced. The resulting aqueous zinc ion battery achieves outstanding cycling stability (4000 cycles) and rate performance (97.5 mAh g^?1 at 64 A g^?1), distinct from all reported aqueous MXene‐based counterparts with pseudo‐capacitive properties, and outperforming most vanadium‐based zinc ion batteries with high capacity. This work sheds light on the green synthesis of MXenes, provides an all‐in‐one protocol for MXene devices, and extends MXenes’ application in the aqueous energy storage field.     

Dial the Mechanism Switch of VN from Conversion to Intercalation toward Long Cycling Sodium‐Ion Battery

Transition metal nitrides are promising energy storage materials in regard to good metallic conductivity and high theoretical specific capacity, but their cycling stability is impeded by the huge volume change caused by the conversion reaction mechanism. Here, a simple strategy to produce an intercalation pseudocapacitive‐type vanadium nitride (VN) by one‐step ammonification of V₂C MXene for sodium‐ion batteries is reported. Profiting from a distinctive layered structure pillared by Al atoms in the layer spacing, it delivers a high capacity of 372 mA h g^?1 at 50 mA g^?1 and a desirable rate performance. More importantly, it shows remarkably long cycling stability over 7500 cycles without capacity attenuation at 500 mA g^?1. As expected, it is found that the intercalation pseudocapacitance plays an important role in the excellent performance, by using in situ X‐ray diffraction and ex situ X‐ray absorption structure characterization. Even more remarkable, are the high energy and power density of the sodium‐ion capacitor after coupling with a carbon‐based cathode. The hybrid device possesses an energy density of 78.43 Wh kg^?1 at power density of 260 W kg^?1. The results clearly show that such a unique‐layered VN with outstanding Na storage capability is an excellent new material for energy storage systems.     

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.     

Black Phosphorus Quantum Dot/Ti3C2 MXene Nanosheet Composites for Efficient Electrochemical Lithium/Sodium‐Ion Storage

The exploration of new and efficient energy storage mechanisms through nanostructured electrode design is crucial for the development of high‐performance rechargeable batteries. Herein, black phosphorus quantum dots (BPQDs) and Ti₃C₂ nanosheets (TNSs) are employed as battery and pseudocapacitive components, respectively, to construct BPQD/TNS composite anodes with a novel battery‐capacitive dual‐model energy storage (DMES) mechanism for lithium‐ion and sodium‐ion batteries. Specifically, as a battery‐type component, BPQDs anchored on the TNSs are endowed with improved conductivity and relieved stress upon cycling, enabling a high‐capacity and stable energy storage. Meanwhile, the pseudocapacitive TNS component with further atomic charge polarization induced by P? O? Ti interfacial bonds between the two components allows enhanced charge adsorption and efficient interfacial electron transfer, contributing a higher pseudocapacitive value and fast energy storage. The DMES mechanism is evidenced by substantial characterizations of X‐ray photoelectron spectroscopy and X‐ray absorption fine structure spectroscopy, density functional theory calculations, and kinetics analyses. Consequently, the composite electrode exhibits superior battery performance, especially for lithium storage, such as high capacity (910 mAh g^?1 at 100 mA g^?1), long cycling stability (2400 cycles with a capacity retention over 100%), and high rate capability, representing the best comprehensive battery performance in BP‐based anodes to date.     

Low‐Temperature Reduction Strategy Synthesized Si/Ti3C2 MXene Composite Anodes for High‐Performance Li‐Ion Batteries

Silicon is attracting enormous attention due to its theoretical capacity of 4200 mAh g^?1 as an anode for Li‐ion batteries (LIBs). It is of fundamental importance and challenge to develop low‐temperature reaction route to controllably synthesize Si/Ti₃C₂ MXene LIBs anodes. Herein, a novel and efficient strategy integrating in situ orthosilicate hydrolysis and a low‐temperature reduction process to synthesize Si/Ti₃C₂ MXene composites is reported. The hydrolysis of tetraethyl orthosilicate leads to homogenous nucleation and growth of SiO₂ nanoparticles on the surface of Ti₃C₂ MXene. Subsequently, SiO₂ nanoparticles are reduced to Si via a low‐temperature (200 °C) reduction route. Importantly, Ti₃C₂ MXene not only provides fast transfer channels for Li⁺ and electrons, but also relieves volume expansion of Si during cycling. Moreover, the characteristics of excellent pseudocapacitive performance and high conductivity of Ti₃C₂ MXene can synergistically contribute to the enhancement of energy storage performance. As expected, Ti₃C₂/Si anode exhibits an outstanding specific capacity of 1849 mAh g^?1 at 100 mA g^?1, even retaining 956 mAh g^?1 at 1 A g^?1. The low‐temperature synthetic route to Si/Ti₃C₂ MXene electrodes and involved battery‐capacitive dual‐model energy storage mechanism has potential in the design of novel high‐performance electrodes for energy storage devices.     

Realizing Reversible Conversion‐Alloying of Sb(V) in Polyantimonic Acid for Fast and Durable Lithium‐ and Potassium‐Ion Storage

Finding suitable electrode materials for alkali‐metal‐ion storage is vital to the next‐generation energy‐storage technologies. Polyantimonic acid (PAA, H₂Sb₂O₆ · nH₂O), having pentavalent antimony species and an interconnected tunnel‐like pyrochlore crystal framework, is a promising high‐capacity energy‐storage material. Fabricating electrochemically reversible PAA electrode materials for alkali‐metal‐ion storage is a challenge and has never been reported due to the extremely poor intrinsic electronic conductivity of PAA associated with the highest oxidation state Sb(V). Combining nanostructure engineering with a conductive‐network construction strategy, here is reported a facile one‐pot synthesis protocol for crafting uniform internal‐void‐containing PAA nano‐octahedra in a composite with nitrogen‐doped reduced graphene oxide nanosheets (PAA?N‐RGO), and for the first time, realizing the reversible storage of both Li⁺ and K⁺ ions in PAA?N‐RGO. Such an architecture, as validated by theoretical calculations and ex/in situ experiments, not only fully takes advantage of the large‐sized tunnel transport pathways (0.37 nm²) of PAA for fast solid‐phase ionic diffusion but also leads to exponentially increased electrical conductivity (3.3 S cm^?1 in PAA?N‐RGO vs 4.8 × 10^?10 S cm^?1 in bare‐PAA) and yields an inside‐out buffer function for accommodating volume expansion. Compared to electrochemically irreversible bare‐PAA, PAA?N‐RGO manifests reversible conversion‐alloying of Sb(V) toward fast and durable Li⁺‐ and K⁺‐ion storage.     

Tailored Plum Pudding‐Like Co2P/Sn Encapsulated with Carbon Nanobox Shell as Superior Anode Materials for High‐Performance Sodium‐Ion Capacitors

Sodium‐ion capacitors (SICs) are emerging energy storage devices with high energy, high power, and durable life. Sn is a promising anode material for lithium storage, but the poor conductivity of the a‐NaSn phase upon sodaition hinders its implementation in SICs. Herein, a superior Sn‐based anode material consisting of plum pudding‐like Co₂P/Sn yolk encapsulated with nitrogen‐doped carbon nanobox (Co₂P/Sn@NC) for high‐performance SICs is reported. The 8–10 nm metallic nanoparticles produced in situ are uniformly dispersed in the amorphous Sn matrix serving as conductive fillers to facilitate electron transfer in spite of the formation of electrically resistive a‐NaSn phase during cycling. Meanwhile, the carbon shell buffers the large expansion of active Sn and provides a stable electrode–electrolyte interface. Owing to these merits, the yolk–shell Co₂P/Sn@NC demonstrates a large capacity of 394 mA h g^?1 at 100 mA g^?1, high rate capability of 168 mA h g^?1 at 5000 mA g^?1, and excellent cyclability with 87% capacity retention after 10 000 cycles. By integrating the Co₂P/Sn@NC anode with a peanut shell‐derived carbon cathode in the SIC, high energy densities of 112.3 and 43.7 Wh kg^?1 at power densities of 100 and 10 000 W kg^?1 are achieved.     

SnO2 as Advanced Anode of Alkali‐Ion Batteries: Inhibiting Sn Coarsening by Crafting Robust Physical Barriers,Void Boundaries,and Heterophase Interfaces for Superior Electrochemical Reaction Reversibility

Superior reaction reversibility of electrode materials is urgently pursued for improving the energy density and lifespan of batteries. Tin dioxide (SnO₂) is a promising anode material for alkali‐ion batteries, having a high theoretical lithium storage capacity of 1494 mAh g^? based on the reactions of SnO₂ + 4Li⁺ + 4e^? ? Sn + 2Li₂O and Sn + 4.4Li⁺ + 4.4e^? ? Li_4.4Sn. The coarsening of Sn nanoparticles into large particles induced reaction reversibility degradation has been demonstrated as the essential failure mechanism of SnO₂ electrodes. Here, three key strategies for inhibiting Sn coarsening to enhance the reaction reversibility of SnO₂ are presented. First, encapsulating SnO₂ nanoparticles in physical barriers of carbonaceous materials, conductive polymers or inorganic materials can robustly prevent Sn coarsening among the wrapped SnO₂ nanoparticles. Second, constructing hierarchical, porous or hollow structured SnO₂ particles with stable void boundaries can hinder Sn coarsening between the void‐divided SnO₂ subunits. Third, fabricating SnO₂‐based heterogeneous composites consisting of metals, metal oxides or metal sulfides can introduce abundant heterophase interfaces in cycled electrodes that impede Sn coarsening among the isolated SnO₂ crystalline domains. Finally, a perspective on the future prospect of the structural/compositional designs of SnO₂ as anode of alkali‐ion batteries is highlighted.     

Additional Sodium Insertion into Polyanionic Cathodes for Higher‐Energy Na‐Ion Batteries

Na‐ion technology is increasingly studied as a low‐cost solution for grid storage applications. Many positive electrode materials have been reported, mainly among layered oxides and polyanionic compounds. The vanadium oxy/flurophosphate solid solution Na₃V₂(PO₄)₂F_3‐y O_2y (0 ≤ y ≤ 1), in particular, has proven the ability to deliver ≈500 Wh kg^‐1, operating on the V³⁺/V⁴⁺ (y = 0) or V⁴⁺/V⁵⁺ redox couples (y = 1). This paper reports here on a significant increase in specific energy by enabling sodium insertion into Na₃V₂(PO₄)₂FO₂ to reach Na₄V₂(PO₄)₂FO₂ upon discharge. This occurs at ≈1.6 V and increases the theoretical specific energy to 600 Wh kg^?1, rivaling that of several Li‐ion battery cathodes. This improvement is achieved by the judicious modification of the composition either as O for F substitution, or Al for V substitution, both of which disrupt Na‐ion ordering and thereby enable insertion of the 4th Na. This paper furthermore shows from operando X‐Ray Diffraction (XRD) that this energy is obtained in the cycling range Na₄V₂(PO₄)₂FO₂–NaV₂(PO₄)₂FO₂ with a very small overall volume change of 1.7%, which is one of the smallest volume changes for Na‐ion cathodes and which is a crucial requisite for stable long‐term cycling.     

Mechanism of Na+ Insertion in Alkali Vanadates and Its Influence on Battery Performance

Sodium‐ion batteries may become an alternative to the widespread lithium‐ion technology due to cost and kinetic advantages provided that cyclability is improved. For this purpose, the interplay between electrochemical and structural processes is key and is demonstrated in this work for Na_2.46V₆O₁₆ (NVO) and Li_2.55V₆O₁₆ employing operando synchrotron X‐ray diffraction. When NVO is cycled between 4.0 and 1.6 V, Na‐ions reversibly occupy two crystallographic sites, which results in remarkable cyclability. Upon discharge to 1.0 V, however, Na‐ions occupy also interstitial sites, inducing irreversible structural change with some loss of crystallinity concomitant with a decrease in capacity. Capacity fading increases with the ionic radius of the alkali ions (K⁺ > Na⁺ > Li⁺), suggesting that smaller ions stabilize the structure. This correlation of structural variation and electrochemical performance suggests a route toward improving cycling stability of a sodium‐ion battery. Its essence is a minor Li⁺‐retention in the A_2+xV₆O₁₆ structure. Even though the majority of Li‐ions are replaced by the abundant Na⁺, the residual Li‐ions (≈10%) are sufficient to stabilize the layered structure, diminishing the irreversible structural damage. These results pave the way for further exploitation of the role of small ions in lattice stabilization that increases cycling performance.     

A Hollow‐Shell Structured V2O5 Electrode‐Based Symmetric Full Li‐Ion Battery with Highest Capacity

The symmetric batteries with an electrode material possessing dual cathodic and anodic properties are regarded as an ideal battery configuration because of their distinctive advantages over the asymmetric batteries in terms of fabrication process, cost, and safety concerns. However, the development of high‐performance symmetric batteries is highly challenging due to the limited availability of suitable symmetric electrode materials with such properties of highly reversible capacity. Herein, a triple‐hollow‐shell structured V₂O₅ (THS‐V₂O₅) symmetric electrode material with a reversible capacity of >400 mAh g^?1 between 1.5 and 4.0 V and >600 mAh g^?1 between 0.1 and 3.0 V, respectively, when used as the cathode and anode, is reported. The THS‐V₂O₅ electrodes assembled symmetric full lithium‐ion battery (LIB) exhibits a reversible capacity of ≈290 mAh g^?1 between 2 and 4.0 V, the best performed symmetric energy storage systems reported to date. The unique triple‐shell structured electrode makes the symmetric LIB possessing very high initial coulombic efficiency (94.2%), outstanding cycling stability (with 94% capacity retained after 1000 cycles), and excellent rate performance (over 140 mAh g^?1 at 1000 mA g^?1). The demonstrated approach in this work leaps forward the symmetric LIB performance and paves a way to develop high‐performance symmetric battery electrode materials.     

Formation of Solid–Electrolyte Interfaces in Aqueous Electrolytes by Altering Cation‐Solvation Shell Structure

Aqueous lithium/sodium‐ion batteries (AIBs) have received increasing attention because of their intrinsic safety. However, the narrow electrochemical stability window (1.23 V) of the aqueous electrolyte significantly hinders the development of AIBs, especially the choice of electrode materials. Here, an aqueous electrolyte composed of LiClO₄, urea, and H₂O, which allows the electrochemical stability window to be expanded to 3.0 V, is developed. Novel [Li (H₂O)_x(organic)_y]⁺ primary solvation sheath structures are developed in this aqueous electrolyte, which contribute to the formation of solid–electrolyte interface layers on the surfaces of both the cathode and anode. The expanded electrochemical stability window enables the construction of full aqueous Li‐ion batteries with LiMn₂O₄ cathodes and Mo₆S₈ anodes, demonstrating an operating voltage of 2.1 V and stability over 2000 cycles. Furthermore, a symmetric aqueous Na‐ion battery using Na₃V₂(PO₄)₃ as both the cathode and anode exhibits operating voltage of 1.7 V and stability over 1000 cycles at a rate of 5 C.     

A Pair of NiCo2O4 and V2O5 Nanowires Directly Grown on Carbon Fabric for Highly Bendable Lithium‐Ion Batteries

Mechanically bendable and flexible functionalities are urgently required for next‐generation battery systems that will be included in soft and wearable electronics, active sportswear, and origami‐based deployable space structures. However, it is very difficult to synthesize anode and cathode electrodes that have high energy density and structural reliability under large bending deformation. Here, vanadium oxide (V₂O₅) and nickel cobalt oxide (NiCo₂O₄) nanowire‐carbon fabric electrodes for highly flexible and bendable lithium ion batteries are reported. The vanadium oxide and nickel cobalt oxide nanowires were directly grown on plasma‐treated carbon fabric and were used as cathode and anode electrodes in a full cell lithium ion battery. Most importantly, a pre‐lithiation process was added to the nickel cobalt oxide nanowire anode to facilitate the construction of a full cell using symmetrically‐architectured nanowire‐carbon fabric electrodes. The highly bendable full cell based on poly(ethylene oxide) polymer electrolyte and room temperature ionic liquid shows high energy density of 364.2 Wh kg^?1 at power density of 240 W kg^?1, without significant performance degradation even under large bending deformations. These results show that vanadium oxide and lithiated nickel cobalt oxide nanowire‐carbon fabrics are a good combination for binder‐free electrodes in highly flexible lithium‐ion batteries.     

Nanoparticles Encapsulated in Porous Carbon Matrix Coated on Carbon Fibers: An Ultrastable Cathode for Li‐Ion Batteries

Nanostructured V₂O₅ is emerging as a new cathode material for lithium ion batteries for its distinctly high theoretic capacity over the current commercial cathodes. The main challenges associated with nanostructured V₂O₅ cathodes are structural degradation, instability of the solid‐electrolyte interface layer, and poor electron conductance, which lead to low capacity and rapid decay of cyclic stability. Here, a novel composite structure of V₂O₅ nanoparticles encapsulated in 3D networked porous carbon matrix coated on carbon fibers (V₂O₅/3DC‐CFs) is reported that effectively addresses the mentioned problems. Remarkably, the V₂O₅/3DC‐CF electrode exhibits excellent overall lithium‐storage performance, including high Coulombic efficiency, excellent specific capacity, outstanding cycling stability and rate property. A reversible capacity of ≈183 mA h g^?1 is obtained at a high current density of 10 C, and the battery retains 185 mA h g^?1 after 5000 cycles, which shows the best cycling stability reported to date among all reported cathodes of lithium ion batteries as per the knowledge. The outstanding overall properties of the V₂O₅/3DC‐CF composite make it a promising cathode material of lithium ion batteries for the power‐intensive energy storage applications.     

A Stable Layered Oxide Cathode Material for High‐Performance Sodium‐Ion Battery

As one of the most promising cathode candidates for room‐temperature sodium‐ion batteries (SIBs), P2‐type layered oxides face the challenge of simultaneously realizing high‐rate performance while achieving long cycle life. Here, a stable Na_2/3Ni_1/6Mn_2/3Cu_1/9Mg_1/18O₂ cathode material is proposed that consists of multiple‐layer oriented stacking nanoflakes, in which the nickel sites are partially substituted by copper and magnesium, a characteristic of the material that is confirmed by multiscale scanning transmission electron microscopy and electron energy loss spectroscopy techniques. Owing to the optimal morphology structure modulation and chemical element substitution strategy, the electrode displays remarkable rate performance (73% capacity retention at 30C compared to 0.5C) and outstanding cycling stability in Na half‐cell system couple with unprecedented full battery performance. The underlying thermal stability, phase stability, and Na⁺ storage mechanisms are clearly elucidated through the systematical characterizations of electrochemical behaviors, in situ X‐ray diffraction at different temperatures, and operando X‐ray diffraction upon Na⁺ deintercalation/intercalation. Surprisingly, a quasi‐solid‐solution reaction is switched to an absolute solid‐solution reaction and a capacitive Na⁺ storage mechanism is demonstrated via quantitative electrochemical kinetics calculation during charge/discharge process. Such a simple and effective strategy might reveal a new avenue into the rational design of excellent rate capability and long cycle stability cathode materials for practical SIBs.     

All Pseudocapacitive MXene‐RuO2 Asymmetric Supercapacitors

2D transition metal carbides and nitrides, known as MXenes, are an emerging class of 2D materials with a wide spectrum of potential applications, in particular in electrochemical energy storage. The hydrophilicity of MXenes combined with their metallic conductivity and surface redox reactions is the key for high‐rate pseudocapacitive energy storage in MXene electrodes. However, symmetric MXene supercapacitors have a limited voltage window of around 0.6 V due to possible oxidation at high anodic potentials. In this study, the fact that titanium carbide MXene (Ti₃C₂T_x) can operate at negative potentials in acidic electrolyte is exploited, to design an all‐pseudocapacitive asymmetric device by combining it with a ruthenium oxide (RuO₂) positive electrode. This asymmetric device operates at a voltage window of 1.5 V, which is about two times wider than the operating voltage window of symmetric MXene supercapacitors, and is the widest voltage window reported to date for MXene‐based supercapacitors. The complementary working potential windows of MXene and RuO₂, along with proton‐induced pseudocapacitance, significantly enhance the device performance. As a result, the asymmetric devices can deliver an energy density of 37 µW h cm^?2 at a power density of 40 mW cm^?2, with 86% capacitance retention after 20 000 charge–discharge cycles. These results show that pseudocapacitive negative MXene electrodes can potentially replace carbon‐based materials in asymmetric electrochemical capacitors, leading to an increased energy density.     

Amorphous Tin‐Based Composite Oxide: A High‐Rate and Ultralong‐Life Sodium‐Ion‐Storage Material

Energy‐storage technology is moving beyond lithium batteries to sodium as a result of its high abundance and low cost. However, this sensible transition requires the discovery of high‐rate and long‐lifespan anode materials, which remains a significant challenge. Here, the facile synthesis of an amorphous Sn₂P₂O₇/reduced graphene oxide nanocomposite and its sodium storage performance between 0.01 and 3.0 V are reported for the first time. This hybrid electrode delivers a high specific capacity of 480 mA h g^?1 at a current density of 50 mA g^?1 and superior rate performance of 250 and 165 mA h g^?1 at 2 and 10 A g^?1, respectively. Strikingly, this anode can sustain 15 000 cycles while retaining over 70% of the initial capacity. Quantitative kinetic analysis reveals that the sodium storage is governed by pseudocapacitance, particularly at high current rates. A full cell with sodium super ionic conductor (NASICON)‐structured Na₃V₂(PO₄)₂F₃ and Na₃V₂(PO₄)₃ as cathodes exhibits a high energy density of over 140 W h kg^?1 and a power density of nearly 9000 W kg^?1 as well as stability over 1000 cycles. This exceptional performance suggests that the present system is a promising power source for promoting the substantial use of low‐cost energy storage systems.     

Stabilizing Reversible Oxygen Redox Chemistry in Layered Oxides for Sodium‐Ion Batteries

Triggering oxygen‐related activity is demonstrated as a promising strategy to effectively boost energy density of layered cathodes for sodium‐ion batteries. However, irreversible lattice oxygen loss will induce detrimental structure distortion, resulting in voltage decay and cycle degradation. Herein, a layered structure P2‐type Na_0.66Li_0.22Ru_0.78O₂ cathode is designed, delivering reversible oxygen‐related and Ru‐based redox chemistry simultaneously. Benefiting from the combination of strong Ru 4d‐O 2p covalency and stable Li location within the transition metal layer, reversible anionic/cationic redox chemistry is achieved successfully, which is proved by systematic bulk/surface analysis by in/ex situ spectroscopy (operando Raman and hard X‐ray absorption spectroscopy, etc.). Moreover, the robust structure and reversible phase transition evolution revealed by operando X‐ray diffraction further establish a high degree reversible (de)intercalation processes (≈150 mAh g^?1, reversible capacity) and long‐term cycling (average capacity drop of 0.018%, 500 cycles).     

High‐Performance Aqueous Rechargeable Li‐Ni Battery Based on Ni(OH)2/NiOOH Redox Couple with High Voltage

New energy storage and conversion systems require large‐scale, cost‐effective, good safety, high reliability, and high energy density. This study demonstrates a low‐cost and safe aqueous rechargeable lithium‐nickel (Li‐Ni) battery with solid state Ni(OH)₂/NiOOH redox couple as cathode and hybrid electrolytes separated by a Li‐ion‐conductive solid electrolyte layer. The proposed aqueous rechargeable Li‐Ni battery exhibits an approximately open‐circuit potential of 3.5 V, outperforming the theoretic stable window of water 1.23 V, and its energy density can be 912.6 W h kg^‐1, which is much higher than that of state‐of‐the‐art lithium ion batteries. The use of a solid‐state redox couple as cathode with a metallic lithium anode provides another postlithium chemistry for practical energy storage and conversion.