A Family of High‐Performance Cathode Materials for Na‐ion Batteries,Na3(VO1−xPO4)2 F1+2x (0 ≤ x ≤ 1): Combined First‐Principles and Experimental Study

Room‐temperature Na‐ion batteries (NIBs) have recently attracted attention as potential alternatives to current Li‐ion batteries (LIBs). The natural abundance of sodium and the similarity between the electrochemical properties of NIBs and LIBs make NIBs well suited for applications requiring low cost and long‐term reliability. Here, the first successful synthesis of a series of Na₃(VO_1?x PO₄)₂F_1+2x (0 ≤ x ≤ 1) compounds as a new family of high‐performance cathode materials for NIBs is reported. The Na₃(VO_1?x PO₄)₂F_1+2x series can function as high‐performance cathodes for NIBs with high energy density and good cycle life, although the redox mechanism varies depending on the composition. The combined first‐principles calculations and experimental analysis reveal the detailed structural and electrochemical mechanisms of the various compositions in solid solutions of Na₃(VOPO₄)₂F and Na₃V₂(PO₄)₂F₃. The comparative data for the Na _y (VO_1?x PO₄)₂F_1+2x electrodes show a clear relationship among V³⁺/V⁴⁺/V⁵⁺ redox reactions, Na⁺?Na⁺ interactions, and Na⁺ intercalation mechanisms in NIBs. The new family of high‐energy cathode materials reported here is expected to spur the development of low‐cost, high‐performance NIBs.     

Polyanion Sodium Vanadium Phosphate for Next Generation of Sodium‐Ion Batteries—A Review

Polyanion‐type sodium (Na) vanadium phosphate in the form of Na₃V₂(PO₄)₃ has demonstrated reasonably high capacity, good rate capability, and excellent cyclability. Two of three Na ions per formula can be deintercalated at a potential 3.4 V versus Na⁺/Na with oxidation of V^3+/4+. In the reversible process, two Na ions intercalate back resulting in a discharge capacity of 117.6 mAh g^?1. Further intercalation is possible but at a low potential of 1.4 V versus Na⁺/Na accompanied by vanadium reduction V^3+/2+, leading to a capacity of 60 mAh g^?1. Due to its marvelous electrochemical performance, it has attracted a lot of attention since its discovery in the 1990s. To develop truly useable polyanion‐type vanadium phosphate, better understanding of its crystal configuration, sodium ions' transportation, and electronic structure is essential. Therefore, this review only focuses on the inside of crystal configuration and electronic structure of polyanion‐type vanadium phosphate, Na₃V₂(PO₄)₃, since there are a few good reviews on various processing technologies.     

A Na3V2(PO4)2O1.6F1.4 Cathode of Zn‐Ion Battery Enabled by a Water‐in‐Bisalt Electrolyte

Aqueous zinc‐ion batteries are receiving increasing attention; however, the development of high‐voltage cathodes is limited by the narrow voltage window of conventional aqueous electrolytes. Herein, it is reported that Na₃V₂(PO₄)₂O_1.6F_1.4 exhibits the excellent performance, optimal to date, among polyanion cathode materials in a novel neutral water‐in‐bisalts electrolyte of 25 m ZnCl₂ + 5 m NH₄Cl. It delivers a reversible capacity of 155 mAh g^?1 at 50 mA g^?1, a high average operating potential of ≈1.46 V, and stable cyclability of 7000 cycles at 2 A g^?1.     

Urchin‐Like CoSe2 as a High‐Performance Anode Material for Sodium‐Ion Batteries

Urchin‐like CoSe₂ assembled by nanorods has been synthesized via simple solvothermal route and has been first applied as an anode material for sodium‐ion batteries (SIBs) with ether‐based electrolytes. The CoSe₂ delivers excellent sodiation and desodiation properties when using 1 m NaCF₃SO₃ in diethyleneglycol dimethylether as an electrolyte and cycling between 0.5 and 3.0 V. A high discharge capacity of 0.410 Ah g^?1 is obtained at 1 A g^?1 after 1800 cycles, corresponding to a capacity retention of 98.6% calculated from the 30th cycle. Even at an ultrahigh rate of 50 A g^?1, the capacity still maintains 0.097 Ah g^?1. The reaction mechanism of the as‐prepared CoSe₂ is also investigated. The results demonstrate that at discharged 1.56 V, insertion reaction occurs, while two conversion reactions take place at the second and third plateaus around 0.98 and 0.65 V. During the charge process, Co first reacts with Na₂Se to form Na_xCoSe₂ and then turns back to CoSe₂. In addition to Na/CoSe₂ half cells, Na₃V₂(PO₄)₃/CoSe₂ full cell with excessive amount of Na₃V₂(PO₄)₃ has been studied. The full cell exhibits a reversible capacity of 0.380 Ah g^?1. This work definitely enriches the possibilities for anode materials for SIBs with high performance.     

Dual‐Doped Hematite Nanorod Arrays on Carbon Cloth as a Robust and Flexible Sodium Anode

Rechargeable batteries with flexibility can find tremendous applications in wearable and bendable electronics. One central mission for the advancement of such high‐performance batteries is the exploration of flexible anodes with electrochemical and mechanical robustness. Herein reported is a robust and flexible sodium‐ion anode based on self‐supported hematite nanoarray grown on carbon cloth. The ammonia treatment that results in dual doping of both nitrogen and low‐valent iron renders surface reactivity and electric conductivity to the material. The dual‐doped hematite arrays afford a robust activity for sodium storage, exhibiting reversible capacities of 895 and 382 mAh g^?1 at current rates of 0.1 and 5 A g^?1, respectively, or 615 and 356 mAh g^?1 by removing the contribution of the substrate. They also sustain 85% of the initial capacity upon 200 cycles at 0.2 A g^?1. To demonstrate the flexibility, full cells composed of a hematite array anode and Na₃V₂(PO₄)₃/C cathode are assembled. The cell is capable of affording an energy density of 201 Wh kg^?1 and sustaining repeated bending without performance decay, demonstrating a significant potential in practical application.     

FeP Quantum Dots Confined in Carbon‐Nanotube‐Grafted P‐Doped Carbon Octahedra for High‐Rate Sodium Storage and Full‐Cell Applications

Transition metal phosphides (TMPs) possess high theoretical sodium storage capacities, but suffer from poor rate performance, due to their intrinsic low conductivity and large volume expansion upon sodiation/desodiation. Compositing TMPs with carbon materials or downsizing their feature size are recognized as efficient approaches to address the above issues. Nevertheless the surface‐controlled capacitive behavior is generally dominated, which inevitably compromises the charge/discharge platform, and decreases the operational potential window in full‐cell constructions. In this work, a novel architecture (FeP@OCF) with FeP quantum dots confined in P‐doped 3D octahedral carbon framework/carbon nanotube is rationally designed. Such structure enables a simultaneous enhancement on the diffusion‐controlled capacity in the platform region (2.3 folds), and the surface‐controlled capacity in the slope region (2.9 folds) as compared to that of pure FeP. As a result, an excellent reversible capacity (674 mAh g^?1@ 0.1 A g^?1) and a record high‐rate performance (262 mAh g^?1 @ 20 A g^?1) are achieved. A full‐cell FeP@OCF// Na₃V₂(PO₄)₃ is also constructed showing an outstandingly high energy density of 185 Wh kg^?1 (based on the total mass of active materials in both electrodes), which outperforms the state‐of‐the art TMP‐based sodium‐ion battery full cells.     

Overcoming the Unfavorable Kinetics of Na3V2(PO4)2F3//SnPx Full‐Cell Sodium‐Ion Batteries for High Specific Energy and Energy Efficiency

In this work, a full‐cell sodium‐ion battery (SIB) with a high specific energy approaching 300 Wh kg^?1 is realized using a sodium vanadium fluorophosphate (Na₃V₂(PO₄)₂F₃, NVPF) cathode and a tin phosphide (SnP_x) anode, despite both electrode materials having greatly unbalanced specific capacities. The use of a cathode employing an areal loading more than eight times larger than that of the anode can be achieved by designing a nanostructured nanosized NVPF (n‐NVPF) cathode with well‐defined particle size, porosity, and conductivity. Furthermore, the high rate capability and high potential window of the full‐cell can be obtained by tuning the Sn/P ratio (4/3, 1/1, and 1/2) and the nanostructure of an SnP_x/carbon composite anode. As a result, the full‐cell SIBs employing the nanostructured n‐NVPF cathode and the SnP_x/carbon composite anode (Sn/P = 1/1) exhibit outstanding specific energy (≈280 Wh kg^?1_{(cathode+anode)}) and energy efficiency (≈78%); furthermore, the results are comparable to those of state‐of‐the‐art lithium‐ion batteries.     

Studies of Functional Defects for Fast Na‐Ion Conduction in Na3−yPS4−xClx with a Combined Experimental and Computational Approach

All‐solid‐state rechargeable sodium (Na)‐ion batteries are promising for inexpensive and high‐energy‐density large‐scale energy storage. In this contribution, new Na solid electrolytes, Na_3?yPS_4?xCl_x, are synthesized with a strategic approach, which allows maximum substitution of Cl for S (x = 0.2) without significant compromise of structural integrity or Na deficiency. A maximum conductivity of 1.96 mS cm^?1 at 25 °C is achieved for Na_3.0PS_3.8Cl_0.2, which is two orders of magnitude higher compared with that of tetragonal Na₃PS₄ (t‐Na₃PS₄). The activation energy (E_a) is determined to be 0.19 eV. Ab initio molecular dynamics simulations shed light on the merit of maximizing Cl‐doping while maintaining low Na deficiency in enhanced Na‐ion conduction. Solid‐state nuclear magnetic resonance (NMR) characterizations confirm the successful substitution of Cl for S and the resulting change of P oxidation state from 5+ to 4+, which is also verified by spin moment analysis. Ion transport pathways are determined with a tracer‐exchange NMR method. The functional detects that promote Na ‐ion transport are maximized for further improvement in ionic conductivity. Full‐cell performance is demonstrated using Na/Na_3.0PS_3.8Cl_0.2/Na₃V₂(PO₄)₃ with a reversible capacity of ≈100 mAh g^‐1 at room temperature.     

MoSe2‐Covered N,P‐Doped Carbon Nanosheets as a Long‐Life and High‐Rate Anode Material for Sodium‐Ion Batteries

MoSe₂ grown on N,P‐co‐doped carbon nanosheets is synthesized by a solvothermal reaction followed with a high‐temperature calcination. This composite has an interlayer spacing of MoSe₂ expanded to facilitate sodium‐ion diffusion, MoSe₂ immobilized on carbon nanosheets to improve charge‐transfer kinetics, and N and P incorporated into carbon to enhance its interaction with active species upon cycling. These features greatly improve the electrochemical performance of this composite, as compared to all the controls. It presents a specific capacity of 378 mAh g^?1 after 1000 cycles at 0.5 A g^?1, corresponding to 87% of the capacity at the second cycle. Ex situ Raman spectra and high‐resolution transmission electron microscopy images confirm that it is element Se, rather than MoSe₂, formed after the charging process. The interaction of the active species with modified carbon is simulated using density functional theory to explain this excellent stability. The superior rate capability, where the capacity at 15 A g^?1 equals ≈55% of that at 0.5 A g^?1, could be associated with the significant contribution of pseudocapacitance. By pairing with homemade Na₃V₂(PO₄)₃/C, this composite also exhibits excellent performances in full cells.     

A New Strategy to Build a High‐Performance P′2‐Type Cathode Material through Titanium Doping for Sodium‐Ion Batteries

Herein, Ti⁴⁺ in P′2‐Na_0.67[(Mn_0.78Fe_0.22)_0.9Ti_0.1]O₂ is proposed as a new strategy for optimization of Mn‐based cathode materials for sodium‐ion batteries, which enables a single phase reaction during de‐/sodiation. The approach is to utilize the stronger Ti–O bond in the transition metal layers that can suppress the movements of Mn–O and Fe–O by sharing the oxygen with Ti by the sequence of Mn–O–Ti–O–Fe. It delivers a discharge capacity of ≈180 mAh g^?1 over 200 cycles (86% retention), with S‐shaped smooth charge–discharge curves associated with a small volume change during cycling. The single phase reaction with a small volume change is further confirmed by operando synchrotron X‐ray diffraction. The low activation barrier energy of ≈541 meV for Na⁺ diffusion is predicted using first‐principles calculations. As a result, Na_0.67[(Mn_0.78Fe_0.22)_0.9Ti_0.1]O₂ can deliver a high reversible capacity of ≈153 mAh g^?1 even at 5C (1.3 A g^?1), which corresponds to ≈85% of the capacity at 0.1C (26 mA g^?1). The nature of the sodium storage mechanism governing the ultrahigh electrode performance in a full cell with a hard carbon anode is elucidated, revealing the excellent cyclability and good retention (≈80%) for 500 cycles (111 mAh g^?1) at 5C (1.3 A g^?1).     

High‐Performance Manganese Hexacyanoferrate with Cubic Structure as Superior Cathode Material for Sodium‐Ion Batteries

Sodium manganese hexacyanoferrate (Na_xMnFe(CN)₆) is one of the most promising cathode materials for sodium‐ion batteries (SIBs) due to the high voltage and low cost. However, its cycling performance is limited by the multiple phase transitions during Na⁺ insertion/extraction. In this work, a facile strategy is developed to synthesize cubic and monoclinic structured Na_xMnFe(CN)₆, and their structure evolutions are investigated through in situ X‐ray diffraction (XRD), ex situ Raman, and X‐ray photoelectron spectroscopy (XPS) characterizations. It is revealed that the monoclinic phase undergoes undesirable multiple two‐phase reactions (monoclinic ? cubic ? tetragonal) due to the large lattice distortions caused by the Jahn–Teller effects of Mn³⁺, resulting in poor cycling performances with 38% capacity retention. The cubic Na_xMnFe(CN)₆ with high structural symmetry maintains the structural stability during the repeated Na⁺ insertion/extraction process, demonstrating impressive electrochemical performances with specific capacity of ≈120 mAh g^?1 at 3.5 V (vs Na/Na⁺), capacity retention of ≈70% over 500 cycles at 200 mA g^?1. In addition, the TiO₂//C‐MnHCF full battery is fabricated with an energy density of 111 Wh kg^?1, suggesting the great potential of cubic Na_xMnFe(CN)₆ for practical energy storage applications.     

Copper Thiophosphate (Cu3PS4) as Electrode for Sodium‐Ion Batteries with Ether Electrolyte

Lithium and sodium thiophosphates (and related compounds) have recently attracted attention because of their potential use as solid electrolytes in solid‐state batteries. These compounds, however, exhibit only limited stability in practice as they react with the electrodes. The decomposition products partially remain redox active hence leading to excess capacity. The redox activity of thiophosphates is explicitly used to act as electrode for sodium‐ion batteries. Copper thiophosphate (Cu₃PS₄) is used as a model system. The storage behavior between 0.01 and 2.5 V versus Na⁺/Na is studied in half cells using different electrolytes with 1 m NaPF₆ in diglyme showing the best result. Cu₃PS₄ shows highly reversible charge storage with capacities of about 580 mAh g^?1 for more than 200 cycles @120 mA g^?1 and about 450 mAh g^?1 for 1400 cycles @1 A g^?1. The redox behavior is studied by operando X‐ray diffraction and X‐ray photoelectron spectroscopy. During initial sodiation, Cu₃PS₄ undergoes a conversion reaction including the formation of Cu and Na₂S. During cycling, the redox activity seems dominated by sulfur. Interestingly, the capacity of Cu₃PS₄ for lithium storage is smaller, leading to about 170 mAh g^?1 after 200 cycles. The results demonstrate that thiophosphates can lead to reversible charge storage over several hundred cycles without any notable capacity decay.     

Atomic Structure and Kinetics of NASICON NaxV2(PO4)3 Cathode for Sodium‐Ion Batteries

Na₃V₂(PO₄)₃ is one of the most important cathode materials for sodium‐ion batteries, delivering about two Na extraction/insertion from/into the unit structure. To understand the mechanism of sodium storage, a detailed structure of rhombohedral Na₃V₂(PO₄)₃ and its sodium extracted phase of NaV₂(PO₄)₃ are investigated at the atomic scale using a variety of advanced techniques. It is found that two different Na sites (6b, M1 and 18e, M2) with different coordination environments co‐exist in Na₃V₂(PO₄)₃, whereas only one Na site (6b, M1) exists in NaV₂(PO₄)₃. When Na is extracted from Na₃V₂(PO₄)₃ to form NaV₂(PO₄)₃, Na⁺ occupying the M2 site (CN = 8) is extracted and the rest of the Na remains at M1 site (CN = 6). In addition, the Na atoms are not randomly distributed, possibly with an ordered arrangement in M2 sites locally for Na₃V₂(PO₄)₃. Na⁺ ions at the M1 sites in Na₃V₂(PO₄)₃ tend to remain immobilized, suggesting a direct M2‐to‐M2 conduction pathway. Only Na occupying the M2 sites can be extracted, suggesting about two Na atoms able to be extracted from the Na₃V₂(PO₄)₃ structure.     

Novel Insoluble Organic Cathodes for Advanced Organic K‐Ion Batteries

Organic redox‐active molecules are inborn electrodes to store large‐radius potassium (K) ion. High‐performance organic cathodes are important for practical usage of organic potassium‐ion batteries (OPIBs). However, small‐molecule organic cathodes face serious dissolution problems against liquid electrolytes. A novel insoluble small‐molecule organic cathode [N,N′‐bis(2‐anthraquinone)]‐perylene‐3,4,9,10‐tetracarboxydiimide (PTCDI‐DAQ, 200 mAh g^?1) is initially designed for OPIBs. In half cells (1–3.8 V vs K⁺/K) using 1 m KPF₆ in dimethoxyethane (DME), PTCDI‐DAQ delivers a highly stable specific capacity of 216 mAh g^?1 and still holds the value of 133 mAh g^?1 at an ultrahigh current density of 20 A g^?1 (100 C). Using reduced potassium terephthalate (K₄TP) as the organic anode, the resulting K₄TP||PTCDI‐DAQ OPIBs with the electrolyte 1 m KPF₆ in DME realize a high energy density of maximum 295 Wh kg^?1_cathode (213 mAh g^?1_cathode × 1.38 V) and power density of 13 800 W Kg^?1_cathode (94 mAh g^?1 × 1.38 V @ 10 A g^?1) during the working voltage of 0.2–3.2 V. Meanwhile, K₄TP||PTCDI‐DAQ OPIBs fulfill the superlong lifespan with a stable discharge capacity of 62 mAh g^?1_cathode after 10 000 cycles and 40 mAh g^?1_cathode after 30 000 cycles (3 A g^?1). The integrated performance of PTCDI‐DAQ can currently defeat any cathode reported in K‐ion half/full cells.     

A High‐Power Symmetric Na‐Ion Pseudocapacitor

Batteries and supercapacitors are critical devices for electrical energy storage with wide applications from portable electronics to transportation and grid. However, rechargeable batteries are typically limited in power density, while supercapacitors suffer low energy density. Here, a novel symmetric Na‐ion pseudocapacitor with a power density exceeding 5.4 kW kg^?1 at 11.7 A g^?1, a cycling life retention of 64.5% after 10 000 cycles at 1.17 A g^?1, and an energy density of 26 Wh kg^?1 at 0.585 A g^?1 is reported. Such a device operates on redox reactions occurring on both electrodes with an identical active material, viz., Na₃V₂(PO₄)₃ encapsulated inside nanoporous carbon. This device, in a full‐cell scale utilizing highly reversible and high‐rate Na‐ion intercalational pseudocapacitance, can bridge the performance gap between batteries and supercapacitors. The characteristics of the device and the potentially low‐cost production make it attractive for hybrid electric vehicles and low‐maintenance energy storage systems.     

Fast Potassium Storage in Hierarchical Ca0.5Ti2(PO4)3@C Microspheres Enabling High‐Performance Potassium‐Ion Capacitors

Hybrid potassium‐ion capacitors (KICs) show great promise for large‐scale storage on the power grid because of cost advantages, the weaker Lewis acidity of K⁺ and low redox potential of K⁺/K. However, a huge challenge remains for designing high‐performance K⁺ storage materials since K⁺ ions are heavier and larger than Li⁺ and Na⁺. Herein, the synthesis of hierarchical Ca_0.5Ti₂(PO₄)₃@C microspheres by use of the electrospraying method is reported. Benefiting from the rich vacancies in the crystal structure and rational nanostructural design, the hybrid Ca_0.5Ti₂(PO₄)₃@C electrode delivers a high reversible capacity (239 mA h g^?1) and superior rate performance (63 mA h g^?1 at 5 A g^?1). Moreover, the KIC employing a Ca_0.5Ti₂(PO₄)₃@C anode and activated carbon cathode, affords a high energy/power density (80 W h kg^?1 and 5144 W kg^?1) in a potential window of 1.0–4.0 V, as well as a long lifespan of over 4000 cycles. In addition, in situ X‐ray diffraction is used to unravel the structural transition in Ca_0.5Ti₂(PO₄)₃, suggesting a two‐phase transition above 0.5 V during the initial discharge and solid solution processes during the subsequent K⁺ insertion/extraction. The present study demonstrates a low‐cost potassium‐based energy storage device with high energy/power densities and a long lifespan.     

B‐doped Carbon Coating Improves the Electrochemical Performance of Electrode Materials for Li‐ion Batteries

An evolutionary modification approach, boron doped carbon coating, is initially used to improve the electrochemical properties of electrode materials of lithium‐ion batteries, such as Li₃V₂(PO₄)₃, and demonstrates apparent and significant modification effects. Based on the precise analysis of X‐ray photoemission spectroscopy results, Raman spectra, and electrochemical impedance spectroscopy results for various B‐doped carbon coated Li₃V₂(PO₄)₃ samples, it is found that, among various B‐doping types (B₄C, BC₃, BC₂O and BCO₂), the graphite‐like BC₃ dopant species plays a huge role on improving the electronic conductivity and electrochemical activity of the carbon coated layer on Li₃V₂(PO₄)₃ surface. As a result, when compared with the bare carbon coated Li₃V₂(PO₄)₃, the electrochemical performances of the B‐doped carbon coated Li₃V₂(PO₄)₃ electrode with a moderate doping amount are greatly improved. For example, when cycled under 1 C and 20 C in the potential range of 3.0–4.3 V, this sample shows an initial capacity of 122.5 and 118.4 mAh g^?1, respectively; after 200 cycles, nearly 100% of the initial capacity is retained. Moreover, the modification effects of B‐doped carbon coating approach are further validated on Li₄Ti₅O₁₂ anode material.     

Atomic Sulfur Covalently Engineered Interlayers of Ti3C2 MXene for Ultra‐Fast Sodium‐Ion Storage by Enhanced Pseudocapacitance

2D MXenes have been widely applied in the field of electrochemical energy storage owning to their high electrical conductivity and large redox‐active surface area. However, electrodes made from multilayered MXene with small interlayer spacing exhibit sluggish kinetics with low capacity for sodium‐ion storage. Herein, Ti₃C₂ MXene with expanded and engineered interlayer spacing for excellent storage capability is demonstrated. After cetyltrimethylammonium bromide pretreatment, S atoms are successfully intercalated into the interlayer of Ti₃C₂ to form a desirable interlayer‐expanded structure via Ti? S bonding, while pristine Ti₃C₂ is hardly to be intercalated. When the annealing temperature is 450 °C, the S atoms intercalated Ti₃C₂ (CT‐S@Ti₃C₂‐450) electrode delivers the improved Na‐ion capacity of 550 mAh g^?1 at 0.1 A g^?1 (≈120 mAh g^?1 at 15 A g^?1, the best MXene‐based Na⁺‐storage rate performance reported so far), and excellent cycling stability over 5000 cycles at 10 A g^?1 by enhanced pseudocapacitance. The enhanced sodium‐ion storage capability has also been verified by theoretical calculations and kinetic analysis. Coupling the CT‐S@Ti₃C₂‐450 anode with commercial AC cathode, the assembled Na⁺ capacitor delivers high energy density (263.2 Wh kg^?1) under high power density (8240 W kg^?1), and outstanding cycling performance.     

Electronic Structure Regulation of Layered Vanadium Oxide via Interlayer Doping Strategy toward Superior High‐Rate and Low‐Temperature Zinc‐Ion Batteries

Currently, development of suitable cathode materials for zinc‐ion batteries (ZIBs) is plagued by the sluggish kinetics of Zn²⁺ with multivalent charge in the host structure. Herein, it is demonstrated that interlayer Mn²⁺‐doped layered vanadium oxide (Mn_0.15V₂O₅·nH₂O) composites with narrowed direct bandgap manifest greatly boosted electrochemical performance as zinc‐ion battery cathodes. Specifically, the Mn_0.15V₂O₅·nH₂O electrode shows a high specific capacity of 367 mAh g^?1 at a current density of 0.1 A g^?1 as well as excellent retentive capacities of 153 and 122 mAh g^?1 after 8000 cycles at high current densities up to 10 and 20 A g^?1, respectively. Even at a low temperature of ?20 °C, a reversible specific capacity of 100 mAh g^?1 can be achieved at a current density of 2.0 A g^?1 after 3000 cycles. The superior electrochemical performance originates from the synergistic effects between the layered nanostructures and interlayer doping of Mn²⁺ ions and water molecules, which can enhance the electrons/ions transport kinetics and structural stability during cycling. With the aid of various ex situ characterization technologies and density functional theory calculations, the zinc‐ion storage mechanism can be revealed, which provides fundamental guidelines for developing high‐performance cathodes for ZIBs.     

A High‐Energy Aqueous Aluminum‐Manganese Battery

Rechargeable aluminum‐ion batteries have drawn considerable attention as a new energy storage system, but their applications are still significantly impeded by critical issues such as low energy density and the lack of excellent electrolytes. Herein, a high‐energy aluminum‐manganese battery is fabricated by using a Birnessite MnO₂ cathode, which can be greatly optimized by a divalence manganese ions (Mn²⁺) electrolyte pre‐addition strategy. The battery exhibits a remarkable energy density of 620 Wh kg^?1 (based on the Birnessite MnO₂ material) and a capacity retention above 320 mAh g^?1 for over 65 cycles, much superior to that with no Mn²⁺ pre‐addition. The electrochemical reactions of the battery are scrutinized by a series of analysis techniques, indicating that the Birnessite MnO₂ pristine cathode is first reduced as Mn²⁺ to dissolve in the electrolyte upon discharge, and Al_xMn_(1?x)O₂ is then generated upon charge, serving as a reversible cathode active material in following cycles. This work provides new opportunities for the development of high‐performance and low‐cost aqueous aluminum‐ion batteries for prospective applications.