Safe,Low‐Cost,Fast‐Kinetics and Low‐Strain Inorganic‐Open‐Framework Anode for Potassium‐Ion Batteries

A key challenge for potassium‐ion batteries is to explore low‐cost electrode materials that allow fast and reversible insertion of large‐ionic‐size K⁺. Here, we report an inorganic‐open‐framework anode (KTiOPO₄), which achieves a reversible capacity of up to 102 mAh g^?1 (307 mAh cm^?3), flat voltage plateaus at a safe average potential of 0.82 V (vs. K/K⁺), a long lifespan of over 200 cycles, and K⁺‐transport kinetics ≈10 times faster than those of Na‐superionic conductors. Combined experimental analysis and first‐principles calculations reveal a charge storage mechanism involving biphasic and solid solution reactions and a cell volume change (9.5 %) even smaller than that for Li⁺‐insertion into graphite (≈10 %). KTiOPO₄ exhibits quasi‐3D lattice expansion on K⁺ intercalation, enabling the disintegration of small lattice strain and thus high structural stability. The inorganic open‐frameworks may open a new avenue for exploring low‐cost, stable and fast‐kinetic battery chemistry.     

Realizing Complete Solid‐Solution Reaction in High Sodium Content P2‐Type Cathode for High‐Performance Sodium‐Ion Batteries

P2‐type layered oxides suffer from an ordered Na⁺/vacancy arrangement and P2→O2/OP4 phase transitions, leading them to exhibit multiple voltage plateaus upon Na⁺ extraction/insertion. The deficient sodium in the P2‐type cathode easily induces the bad structural stability at deep desodiation states and limited reversible capacity during Na⁺ de/insertion. These drawbacks cause poor rate capability and fast capacity decay in most P2‐type layered oxides. To address these challenges, a novel high sodium content (0.85) and plateau‐free P2‐type cathode‐Na_0.85Li_0.12Ni_0.22Mn_0.66O₂ (P2‐NLNMO) was developed. The complete solid‐solution reaction over a wide voltage range ensures both fast Na⁺ mobility (10^?11 to 10^?10 cm² s^?1) and small volume variation (1.7 %). The high sodium content P2‐NLNMO exhibits a higher reversible capacity of 123.4 mA h g^?1, superior rate capability of 79.3 mA h g^?1 at 20 C, and 85.4 % capacity retention after 500 cycles at 5 C. The sufficient Na and complete solid‐solution reaction are critical to realizing high‐performance P2‐type cathodes for sodium‐ion batteries.     

A Porous Network of Bismuth Used as the Anode Material for High‐Energy‐Density Potassium‐Ion Batteries

Potassium‐ion batteries (KIBs) are plagued by a lack of materials for reversible accommodation of the large‐sized K⁺ ion. Herein we present, the Bi anode in combination with the dimethoxyethane‐(DME) based electrolyte to deliver a remarkable capacity of ca. 400 mAh g^?1 and long cycle stability with three distinct two‐phase reactions of Bi? KBi₂?K₃Bi₂?K₃Bi. These are ascribed to the gradually developed three‐dimensional (3D) porous networks of Bi, which realizes fast kinetics and tolerance of its volume change during potassiation and depotassiation. The porosity is linked to the unprecedented movement of the surface Bi atoms interacting with DME molecules, as suggested by DFT calculations. A full KIB of Bi//DME‐based electrolyte//Prussian blue of K_0.72Fe[Fe(CN)₆] is demonstrated to present large energy density of 108.1 Wh kg^?1 with average discharge voltage of 2.8 V and capacity retention of 86.5 % after 350 cycles.     

An Aqueous Dual‐Ion Battery Cathode of Mn3O4 via Reversible Insertion of Nitrate

We report reversible electrochemical insertion of NO₃^? into manganese(II, III) oxide (Mn₃O₄) as a cathode for aqueous dual‐ion batteries. Characterization by TGA, FTIR, EDX, XANES, EXAFS, and EQCM collectively provides unequivocal evidence that reversible oxidative NO₃^? insertion takes place inside Mn₃O₄. Ex situ HRTEM and corresponding EDX mapping results suggest that NO₃^? insertion de‐crystallizes the structure of Mn₃O₄. Kinetic studies reveal fast migration of NO₃^? in the Mn₃O₄ structure. This finding may open a new direction for novel low‐cost aqueous dual‐ion batteries.     

A Low‐Cost and Environmentally Friendly Mixed Polyanionic Cathode for Sodium‐Ion Storage

Sodium‐ion batteries (NIBs) are the most promising alternatives to lithium‐ion batteries in the development of renewable energy sources. The advancement of NIBs depends on the exploration of new electrode materials and fundamental understanding of working mechanisms. Herein, via experimental and simulation methods, we develop a mixed polyanionic compound, Na₂Fe(C₂O₄)SO₄?H₂O, as a cathode for NIBs. Thanks to its rigid three dimensional framework and the combined inductive effects from oxalate and sulfate, it delivered reversible Na insertion/desertion at average discharging voltages of 3.5 and 3.1 V for 500 cycles with Coulombic efficiencies of ca. 99 %. In situ synchrotron X‐ray measurements and DFT calculations demonstrate the Fe²⁺/Fe³⁺ redox reactions contribute to electron compensation during Na⁺ desertion/insertion. The study suggests mixed polyanionic frameworks may provide promising materials for Na ion storage with the merits of low cost and environmental friendliness.     

An Adjustable‐Porosity Plastic Crystal Electrolyte Enables High‐Performance All‐Solid‐State Lithium‐Oxygen Batteries

The limited triple‐phase boundaries (TPBs) in solid‐state cathodes (SSCs) and high resistance imposed by solid electrolytes (SEs) make the achievement of high‐performance all‐solid‐state lithium‐oxygen (ASS Li‐O₂) batteries a challenge. Herein, an adjustable‐porosity plastic crystal electrolyte (PCE) has been fabricated by employing a thermally induced phase separation (TIPS) technique to overcome the above tricky issues. The SSC produced through the in‐situ introduction of the porous PCE on the surface of the active material, facilitates the simultaneous transfer of Li⁺/e^?, as well as ensures fast flow of O₂, forming continuous and abundant TPBs. The high Li⁺ conductivity, softness, and adhesion of the dense PCE significantly reduce the battery resistance to 115 Ω. As a result, the ASS Li‐O₂ battery based on this adjustable‐porosity PCE exhibits superior performances with high specific capacity (5963 mAh g^?1), good rate capability, and stable cycling life up to 130 cycles at 32 °C. This novel design and exciting results could open a new avenue for ASS Li‐O₂ batteries.     

A Black Phosphorus–Graphite Composite Anode for Li‐/Na‐/K‐Ion Batteries

Black phosphorus (BP) is a desirable anode material for alkali metal ion storage owing to its high electronic/ionic conductivity and theoretical capacity. In‐depth understanding of the redox reactions between BP and the alkali metal ions is key to reveal the potential and limitations of BP, and thus to guide the design of BP‐based composites for high‐performance alkali metal ion batteries. Comparative studies of the electrochemical reactions of Li⁺, Na⁺, and K⁺ with BP were performed. Ex situ X‐ray absorption near‐edge spectroscopy combined with theoretical calculation reveal the lowest utilization of BP for K⁺ storage than for Na⁺ and Li⁺, which is ascribed to the highest formation energy and the lowest ion diffusion coefficient of the final potassiation product K₃P, compared with Li₃P and Na₃P. As a result, restricting the formation of K₃P by limiting the discharge voltage achieves a gravimetric capacity of 1300 mAh g^?1 which retains at 600 mAh g^?1 after 50 cycles at 0.25 A g^?1.     

Low‐Temperature Synthesis of Honeycomb CuP2@C in Molten ZnCl2 Salt for High‐Performance Lithium Ion Batteries

Phosphorus‐rich metal phosphides have very high lithium storage capacities, but they are difficult to prepare. A low‐temperature phosphorization method based on Mg reducing PCl₃ in ZnCl₂ molten salt at 300 °C is developed to synthesize phosphorus‐rich CuP₂@C from a Cu‐MOF derived Cu@C composite. Abnormal oxidation of Cu by Zn²⁺ in the molten salt is observed, which leads to the porous honeycomb nanostructure and homogeneously distributed ultrafine CuP₂ nanocrystals. The honeycomb CuP₂@C exhibits excellent lithium storage performance with high reversible capacity (1146 mAh g^?1 at 0.2 A g^?1) and superior cycling stability (720 mAh g^?1 after 600 cycles at 1.0 A g^?1), showing the promising application of P‐rich metal phosphides in lithium ion batteries.     

Multi‐Electron Reactions Enabled by Anion‐Based Redox Chemistry for High‐Energy Multivalent Rechargeable Batteries

The development of multivalent metal (such as Mg and Ca) based battery systems is hindered by lack of suitable cathode chemistry that shows reversible multi‐electron redox reactions. Cationic redox centres in the classical cathodes can only afford stepwise single‐electron transfer, which are not ideal for multivalent‐ion storage. The charge imbalance during multivalent ion insertion might lead to an additional kinetic barrier for ion mobility. Therefore, multivalent battery cathodes only exhibit slope‐like voltage profiles with insertion/extraction redox of less than one electron. Taking VS₄ as a model material, reversible two‐electron redox with cationic–anionic contributions is verified in both rechargeable Mg batteries (RMBs) and rechargeable Ca batteries (RCBs). The corresponding cells exhibit high capacities of >300 mAh g^?1 at a current density of 100 mA g^?1 in both RMBs and RCBs, resulting in a high energy density of >300 Wh kg^?1 for RMBs and >500 Wh kg^?1 for RCBs. Mechanistic studies reveal a unique redox activity mainly at anionic sulfides moieties and fast Mg²⁺ ion diffusion kinetics enabled by the soft structure and flexible electron configuration of VS₄.     

A Peapod‐like CoP@C Nanostructure from Phosphorization in a Low‐Temperature Molten Salt for High‐Performance Lithium‐Ion Batteries

A mild phosphorization process in low‐temperature molten salt (NaCl‐KCl‐AlCl₃) has been developed to synthesize peapod‐like CoP@C nanostructures by using low‐toxicity industrial PCl₃ as the phosphorus source and Mg as the reductant at 250 °C. Importantly, high efficiency of the phosphorous source is achieved since only stoichiometric PCl₃ is required to complete the reaction. The molten NaCl‐KCl‐AlCl₃ not only provides a liquid environment but also participates in the electron transport by the reversible conversion of the Al³⁺/Al redox couple. The obtained 0D‐in‐1D peapod CoP@C structure exhibits excellent lithium storage performance, delivering a superiorly stable capacity of 500 mAh g^?1 after 800 cycles at a high current of 1.0 A g^?1.     

A Self‐Standing and Flexible Electrode of Yolk–Shell CoS2 Spheres Encapsulated with Nitrogen‐Doped Graphene for High‐Performance Lithium‐Ion Batteries

Flexible lithium‐ion batteries (LIBs) have recently attracted increasing attention with the fast development of bendable electronic systems. Herein, a facile and template‐free solvothermal method is presented for the fabrication of hybrid yolk–shell CoS₂ and nitrogen‐doped graphene (NG) sheets. The yolk–shell architecture of CoS₂ encapsulated with NG coating is designed for the dual protection of CoS₂ to address the structural and interfacial stability concerns facing the CoS₂ anode. The as‐prepared composite can be assembled into a film, which can be used as a binder‐free and flexible electrode for LIBs that does not require any carbon black conducting additives or current collectors. When evaluating lithium‐storage properties, such a flexible electrode exhibits a high specific capacity of 992 mAh g^?1 in the first reversible discharge capacity at a current rate of 100 mA g^?1 and high reversible capacity of 882 mAh g^?1 after 150 cycles with excellent capacity retention of 89.91 %. Furthermore, a reversible capacity as high as 655 mAh g^?1 is still achieved after 50 cycles even at a high rate of 5 C due to the yolk–shell structure and NG coating, which not only provide short Li‐ion and electron pathways, but also accommodate large volume variation.     

Rechargeable Room‐Temperature Na–CO2 Batteries

Developing rechargeable Na–CO₂ batteries is significant for energy conversion and utilization of CO₂. However, the reported batteries in pure CO₂ atmosphere are non‐rechargeable with limited discharge capacity of 200 mAh g^?1. Herein, we realized the rechargeability of a Na–CO₂ battery, with the proposed and demonstrated reversible reaction of 3 CO₂+4 Na?2 Na₂CO₃+C. The battery consists of a Na anode, an ether‐based electrolyte, and a designed cathode with electrolyte‐treated multi‐wall carbon nanotubes, and shows reversible capacity of 60000 mAh g^?1 at 1 A g^?1 (≈1000 Wh kg^?1) and runs for 200 cycles with controlled capacity of 2000 mAh g^?1 at charge voltage <3.7 V. The porous structure, high electro‐conductivity, and good wettability of electrolyte to cathode lead to reduced electrochemical polarization of the battery and further result in high performance. Our work provides an alternative approach towards clean recycling and utilization of CO₂.     

Phosphorus‐Modulation‐Triggered Surface Disorder in Titanium Dioxide Nanocrystals Enables Exceptional Sodium‐Storage Performance

Structural modulation and surface engineering have remarkable advantages for fast and efficient charge storage. Herein, we present a phosphorus modulation strategy which simultaneously realizes surface structural disorder with interior atomic‐level P‐doping to boost the Na⁺ storage kinetics of TiO₂. It is found that the P‐modulated TiO₂ nanocrystals exhibit a favourable electronic structure, and enhanced structural stability, Na⁺ transfer kinetics, as well as surface electrochemical reactivity, resulting in a genuine zero‐strain characteristic with only approximately 0.1 % volume variation during Na⁺ insertion/extraction, and exceptional Na⁺ storage performance including an ultrahigh rate capability of 210 mAh g^?1 at 50 C and a strong long‐term cycling stability without significant capacity decay up to 5000 cycles at 30 C.     

Long‐Life Room‐Temperature Sodium–Sulfur Batteries by Virtue of Transition‐Metal‐Nanocluster–Sulfur Interactions

Room‐temperature sodium–sulfur (RT‐Na/S) batteries hold significant promise for large‐scale application because of low cost of both sodium and sulfur. However, the dissolution of polysulfides into the electrolyte limits practical application. Now, the design and testing of a new class of sulfur hosts as transition‐metal (Fe, Cu, and Ni) nanoclusters (ca. 1.2 nm) wreathed on hollow carbon nanospheres (S@M‐HC) for RT‐Na/S batteries is reported. A chemical couple between the metal nanoclusters and sulfur is hypothesized to assist in immobilization of sulfur and to enhance conductivity and activity. S@Fe‐HC exhibited an unprecedented reversible capacity of 394 mAh g^?1 despite 1000 cycles at 100 mA g^?1, together with a rate capability of 220 mAh g^?1 at a high current density of 5 A g^?1. DFT calculations underscore that these metal nanoclusters serve as electrocatalysts to rapidly reduce Na₂S₄ into short‐chain sulfides and thereby obviate the shuttle effect.     

A Promising Carbon/g‐C3N4 Composite Negative Electrode for a Long‐Life Sodium‐Ion Battery

2D graphitic carbon nitride (g‐C₃N₄) nanosheets are a promising negative electrode candidate for sodium‐ion batteries (NIBs) owing to its easy scalability, low cost, chemical stability, and potentially high rate capability. However, intrinsic g‐C₃N₄ exhibits poor electronic conductivity, low reversible Na‐storage capacity, and insufficient cyclability. DFT calculations suggest that this could be due to a large Na⁺ ion diffusion barrier in the innate g‐C₃N₄ nanosheet. A facile one‐pot heating of a mixture of low‐cost urea and asphalt is strategically applied to yield stacked multilayer C/g‐C₃N₄ composites with improved Na‐storage capacity (about 2 times higher than that of g‐C₃N₄, up to 254 mAh g^?1), rate capability, and cyclability. A C/g‐C₃N₄ sodium‐ion full cell (in which sodium rhodizonate dibasic is used as the positive electrode) demonstrates high Coulombic efficiency (ca. 99.8 %) and a negligible capacity fading over 14 000 cycles at 1 A g^?1.     

MoS2 Nanoflowers with Expanded Interlayers as High‐Performance Anodes for Sodium‐Ion Batteries

MoS₂ nanoflowers with expanded interlayer spacing of the (002) plane were synthesized and used as high‐performance anode in Na‐ion batteries. By controlling the cut‐off voltage to the range of 0.4–3 V, an intercalation mechanism rather than a conversion reaction is taking place. The MoS₂ nanoflower electrode shows high discharge capacities of 350 mAh g^?1 at 0.05 A g^?1, 300 mAh g^?1 at 1 A g^?1, and 195 mAh g^?1 at 10 A g^?1. An initial capacity increase with cycling is caused by peeling off MoS₂ layers, which produces more active sites for Na⁺ storage. The stripping of MoS₂ layers occurring in charge/discharge cycling contributes to the enhanced kinetics and low energy barrier for the intercalation of Na⁺ ions. The electrochemical reaction is mainly controlled by the capacitive process, which facilitates the high‐rate capability. Therefore, MoS₂ nanoflowers with expanded interlayers hold promise for rechargeable Na‐ion batteries.     

Generalized Low‐Temperature Fabrication of Scalable Multi‐Type Two‐Dimensional Nanosheets with a Green Soft Template

Two‐dimensional nanosheets with high specific surface areas and fascinating physical and chemical properties have attracted tremendous interests because of their promising potentials in both fundamental research and practical applications. However, the problem of developing a universal strategy with a facile and cost‐effective synthesis process for multi‐type ultrathin 2 D nanostructures remains unresolved. Herein, we report a generalized low‐temperature fabrication of scalable multi‐type 2 D nanosheets including metal hydroxides (such as Ni(OH)₂, Co(OH)₂, Cd(OH)₂, and Mg(OH)₂), metal oxides (such as ZnO and Mn₃O₄), and layered mixed transition‐metal hydroxides (Ni‐Co LDH, Ni‐Fe LDH, Co‐Fe LDH, and Ni‐Co‐Fe layered ternary hydroxides) through the rational employment of a green soft‐template. The synthesized crystalline inorganic nanosheets possess confined thickness, resulting in ultrahigh surface atom ratios and chemically reactive facets. Upon evaluation as electrode materials for pseudocapacitors, the Ni‐Co LDH nanosheets exhibit a high specific capacitance of 1087 F g^?1 at a current density of 1 A g^?1, and excellent stability, with 103 % retention after 500 cycles. This strategy is facile and scalable for the production of high‐quality ultrathin crystalline inorganic nanosheets, with the possibility of extension to the preparation of other complex nanosheets.     

Boosting Low‐Valent Aluminum(I) Reactivity with a Potassium Reagent

The reagent RK [R=CH(SiMe₃)₂ or N(SiMe₃)₂] was expected to react with the low‐valent (^DIPPBDI)Al (^DIPPBDI=HC[C(Me)N(DIPP)]₂, DIPP=2,6‐iPr‐phenyl) to give [(^DIPPBDI)AlR]^?K⁺. However, deprotonation of the Me group in the ligand backbone was observed and [H₂C=C(N‐DIPP)?C(H)=C(Me)?N?DIPP]Al^?K⁺ ( 1 ) crystallized as a bright‐yellow product (73 %). Like most anionic Al^I complexes, 1 forms a dimer in which formally negatively charged Al centers are bridged by K⁺ ions, showing strong K⁺???DIPP interactions. The rather short Al–K bonds [3.499(1)–3.588(1) Å] indicate tight bonding of the dimer. According to DOSY NMR analysis, 1 is dimeric in C₆H₆ and monomeric in THF, but slowly reacts with both solvents. In reaction with C₆H₆, two C?H bond activations are observed and a product with a para‐phenylene moiety was exclusively isolated. DFT calculations confirm that the Al center in 1 is more reactive than that in (^DIPPBDI)Al. Calculations show that both Al^I and K⁺ work in concert and determines the reactivity of 1 .     

Ruthenium‐Oxide‐Coated Sodium Vanadium Fluorophosphate Nanowires as High‐Power Cathode Materials for Sodium‐Ion Batteries

Sodium‐ion batteries are a very promising alternative to lithium‐ion batteries because of their reliance on an abundant supply of sodium salts, environmental benignity, and low cost. However, the low rate capability and poor long‐term stability still hinder their practical application. A cathode material, formed of RuO₂‐coated Na₃V₂O₂(PO₄)₂F nanowires, has a 50 nm diameter with the space group of I4/mmm. When used as a cathode material for Na‐ion batteries, a reversible capacity of 120 mAh g^?1 at 1 C and 95 mAh g^?1 at 20 C can be achieved after 1000 charge–discharge cycles. The ultrahigh rate capability and enhanced cycling stability are comparable with high performance lithium cathodes. Combining first principles computational investigation with experimental observations, the excellent performance can be attributed to the uniform and highly conductive RuO₂ coating and the preferred growth of the (002) plane in the Na₃V₂O₂(PO₄)₂F nanowires.     

Multiple Active Sites: Lithium Storage Mechanism of Cu‐TCNQ as an Anode Material for Lithium‐Ion Batteries

Recently, carboxylate metal‐organic framework (MOF) materials were reported to perform well as anode materials for lithium‐ion batteries (LIBs); however, the presumed lithium storage mechanism of MOFs is controversial. To gain insight into the mechanism of MOFs as anode materials for LIBs, a self‐supported Cu‐TCNQ (TCNQ: 7,7,8,8‐tetracyanoquinodimethane) film was fabricated via an in situ redox routine, and directly used as electrode for LIBs. The first discharge and charge specific capacities of the self‐supported Cu‐TCNQ electrode are 373.4 and 219.4 mAh g^?1, respectively. After 500 cycles, the reversible specific capacity of Cu‐TCNQ reaches 280.9 mAh g^?1 at a current density of 100 mA g^?1. Mutually validated data reveal that the high capacity is ascribed to the multiple‐electron redox conversion of both metal ions and ligands, as well as the reversible insertion and desertion of Li⁺ ions into the benzene rings of ligands. This work raises the expectation for MOFs as electrode materials of LIBs by utilizing multiple active sites and provides new clues for designing improved electrode materials for LIBs.