Size‐, Water‐, and Defect‐Regulated Potassium Manganese Hexacyanoferrate with Superior Cycling Stability and Rate Capability for Low‐Cost Sodium‐Ion Batteries

Potassium manganese hexacyanoferrate (KMHCF) is a low‐cost Prussian blue analogue (PBA) having a rigid and open framework that can accommodate large alkali ions. Herein, the synthesis of KMHCF and its application as a high‐performance cathode in sodium‐ion batteries (NIBs) is reported. High‐quality KMHCF with low amounts of crystal water and defects and with homogeneous microstructure is obtained by controlling the nucleation and grain growth by using a high‐concentration citrate solution as a precipitation medium. The obtained KMHCF exhibits superior cycling and rate performance as a NIB cathode, showing 80% capacity retention after 1000 cycles at 1 C and a high capacity of 95 mA h g^?1 at 20 C. Unlike conventional single‐cation batteries, the hybrid NIB with KMHCF as cathode and Na as anode in Na‐ion electrolyte displays three reversible plateaus that involve stepwise insertion/extraction of both K⁺ and Na⁺ in the PBA framework. In later cycling, the K⁺–Na⁺ cointercalated phase is partially converted into a cubic sodium manganese hexacyanoferrate (NaMHCF) phase due to the increasing replacement of Na⁺ for K⁺.     

High Rate,Long Lifespan LiV3O8 Nanorods as a Cathode Material for Lithium‐Ion Batteries

LiV₃O₈ nanorods with controlled size are successfully synthesized using a nonionic triblock surfactant Pluronic‐F127 as the structure directing agent. X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques are used to characterize the samples. It is observed that the nanorods with a length of 4–8 µm and diameter of 0.5–1.0 µm distribute uniformly. The resultant LiV₃O₈ nanorods show much better performance as cathode materials in lithium‐ion batteries than normal LiV₃O₈ nanoparticles, which is associated with the their unique micro–nano‐like structure that can not only facilitate fast lithium ion transport, but also withstand erosion from electrolytes. The high discharge capacity (292.0 mAh g^?1 at 100 mA g^?1), high rate capability (138.4 mAh g^?1 at 6.4 A g^?1), and long lifespan (capacity retention of 80.5% after 500 cycles) suggest the potential use of LiV₃O₈ nanorods as alternative cathode materials for high‐power and long‐life lithium ion batteries. In particular, the synthetic strategy may open new routes toward the facile fabrication of nanostructured vanadium‐based compounds for energy storage applications.     

Metal–Semiconductor Phase Twinned Hierarchical MoS2 Nanowires with Expanded Interlayers for Sodium‐Ion Batteries with Ultralong Cycle Life

Sodium‐ion batteries (SIBs) are considered a prospective candidate for large‐scale energy storage due to the merits of abundant sodium resources and low cost. However, a lack of suitable advanced anode materials has hindered further applications. Herein, metal–semiconductor mixed phase twinned hierarchical (MPTH) MoS₂ nanowires with an expanded interlayer (9.63 Å) are engineered and prepared using MoO₃ nanobelts as a self‐sacrificed template in the presence of a trace amount of (NH₄)₆Mo₇O₂₄·4H₂O as initiator. The greatly expanded interlayer spacing accelerates Na⁺ insertion/extraction kinetics, and the metal–semiconductor mixed phase enhances electron transfer ability and stabilizes electrode structure during cycling. Benefiting from the structural merits, the MPTH MoS₂ electrode delivers high reversible capacities of 200 mAh g^?1 at 0.1 A g^?1 for 200 cycles and 154 mAh g^?1 at 1 A g^?1 for 2450 cycles in the voltage range of 0.4–3.0 V. Strikingly, the electrode maintains 6500 cycles at a current density of 2 A g^?1, corresponding to a capacity retention of 82.8% of the 2nd cycle, overwhelming the all reported MoS₂ cycling results. This study provides an alternative strategy to boost SIB cycling performance in terms of reversible capacity by virtue of interlayer expansion and structure stability.     

Bismuth Nanoparticle@Carbon Composite Anodes for Ultralong Cycle Life and High‐Rate Sodium‐Ion Batteries

Bismuth has emerged as a promising anode material for sodium‐ion batteries (SIBs), owing to its high capacity and suitable operating potential. However, large volume changes during alloying/dealloying processes lead to poor cycling performance. Herein, bismuth nanoparticle@carbon (Bi@C) composite is prepared via a facile annealing method using a commercial coordination compound precursor of bismuth citrate. The composite has a uniform structure with Bi nanoparticles embedded within a carbon framework. The nanosized structure ensures a fast kinetics and efficient alleviation of stress/strain caused by the volume change, and the resilient and conductive carbon matrix provides an interconnected electron transportation pathway. The Bi@C composite delivers outstanding sodium‐storage performance with an ultralong cycle life of 30 000 cycles at a high current density of 8 A g^?1 and an excellent rate capability of 71% capacity retention at an ultrahigh current rate of 60 A g^?1. Even at a high mass loading of 11.5 mg cm^?2, a stable reversible capacity of 280 mA h g^?1 can be obtained after 200 cycles. More importantly, full SIBs by pairing with a Na₃V₂(PO₄)₃ cathode demonstrates superior performance. Combining the facile synthesis and the commercial precursor, the exceptional performance makes the Bi@C composite very promising for practical large‐scale applications.     

Unique Cobalt Sulfide/Reduced Graphene Oxide Composite as an Anode for Sodium‐Ion Batteries with Superior Rate Capability and Long Cycling Stability

Exploitation of high‐performance anode materials is essential but challenging to the development of sodium‐ion batteries (SIBs). Among all proposed anode materials for SIBs, sulfides have been proved promising candidates due to their unique chemical and physical properties. In this work, a facile solvothermal method to in situ decorate cobalt sulfide (CoS) nanoplates on reduced graphene oxide (rGO) to build CoS@rGO composite is described. When evaluated as anode for SIBs, an impressive high specific capacity (540 mAh g^?1 at 1 A g^?1), excellent rate capability (636 mAh g^?1 at 0.1 A g^?1 and 306 mAh g^?1 at 10 A g^?1), and extraordinarily cycle stability (420 mAh g^?1 at 1 A g^?1 after 1000 cycles) have been demonstrated by CoS@rGO composite for sodium storage. The synergetic effect between the CoS nanoplates and rGO matrix contributes to the enhanced electrochemical performance of the hybrid composite. The results provide a facile approach to fabricate promising anode materials for high‐performance SIBs.     

Monolithic Graphene Trees as Anode Material for Lithium Ion Batteries with High C‐Rates

Monolithically structured reduced graphene oxide (rGO), prepared from a highly concentrated and conductive rGO paste, is introduced as an anode material for lithium ion batteries with high rate capacities. This is achieved by a mixture of rGO paste and the water‐soluble polymer sodium carboxymethylcellulose (SCMC) with freeze drying. Unlike previous 3D graphene porous structures, the monolithic graphene resembles densely branched pine trees and has high mechanical stability with strong adhesion to the metal electrodes. The structures contain numerous large surface area open pores that facilitate lithium ion diffusion, while the strong hydrogen bonding between the graphene layers and SCMC provides high conductivity and reduces the volume changes that occur during cycling. Ultrafast charge/discharge rates are obtained with outstanding cycling stability and the capacities are higher than those reported for other anode materials. The fabrication process is simple and straightforward to adjust and is therefore suitable for mass production of anode electrodes for commercial applications.     

Conversion Synthesis of Self‐Standing Potassium Zinc Hexacyanoferrate Arrays as Cathodes for High‐Voltage Flexible Aqueous Rechargeable Sodium‐Ion Batteries

Prussian blue analogs exhibit great promise for applications in aqueous rechargeable sodium‐ion batteries (ARSIBs) due to their unique open framework and well‐defined discharge voltage plateau. However, traditional coprecipitation methods cannot prepare self‐standing electrodes to meet the needs of wearable energy storage devices. In this work, a water bath method is reported to grow microcube‐like K₂Zn₃(Fe(CN)₆)₂·9H₂O on carbon cloth (CC) using Zn nanosheet arrays as the zinc source and reducing agent, directly serving as a self‐standing cathode. Benefiting from fast ion diffusion and high conductivity, the cathode delivers a high areal capacity of 0.76 mAh cm^?2 at 0.5 mA cm^?2 and excellent capacity retention of 57.9% as the current density increases to 20 mA cm^?2. By coupling with NaTi₂(PO₄)₃ grown on CC as an anode, a quasi‐solid‐state flexible ARSIB with a high output voltage plateau of 1.6 V is successfully assembled, exhibiting a superior areal capacity of 0.56 mAh cm^?2 and energy density of 0.92 mWh cm^?2. In particular, the device shows admirable mechanical flexibility, maintaining 90.3% of initial capacity after 3000 bending cycles. This work is anticipated to open a new avenue for the rational design of self‐standing electrodes used in high‐voltage flexible ARSIBs.     

Glucose‐Induced Synthesis of 1T‐MoS2/C Hybrid for High‐Rate Lithium‐Ion Batteries

1T phase MoS₂ possesses higher conductivity than the 2H phase, which is a key parameter of electrochemical performance for lithium ion batteries (LIBs). Herein, a 1T‐MoS₂/C hybrid is successfully synthesized through facile hydrothermal method with a proper glucose additive. The synthesized hybrid material is composed of smaller and fewer‐layer 1T‐MoS₂ nanosheets covered by thin carbon layers with an enlarged interlayer spacing of 0.94 nm. When it is used as an anode material for LIBs, the enlarged interlayer spacing facilitates rapid intercalating and deintercalating of lithium ions and accommodates volume change during cycling. The high intrinsic conductivity of 1T‐MoS₂ also contributes to a faster transfer of lithium ions and electrons. Moreover, much smaller and fewer‐layer nanosheets can shorten the diffusion path of lithium ions and accelerate reaction kinetics, leading to an improved electrochemical performance. It delivers a high initial capacity of 920.6 mAh g^?1 at 1 A g^?1 and the capacity can maintain 870 mAh g^?1 even after 300 cycles, showing a superior cycling stability. The electrode presents a high rate performance as well with a reversible capacity of 600 mAh g^?1 at 10 A g^?1. These results show that the 1T‐MoS₂/C hybrid shows potential for use in high‐performance lithium‐ion batteries.     

A Heterostructure Coupling of Bioinspired,Adhesive Polydopamine,and Porous Prussian Blue Nanocubics as Cathode for High‐Performance Sodium‐Ion Battery

Prussian blue (PB) and its analogues are recognized as promising cathodes for rechargeable batteries intended for application in low‐cost and large‐scale electric energy storage. With respect to PB cathodes, however, their intrinsic crystal regularity, vacancies, and coordinated water will lead to low specific capacity and poor rate performance, impeding their application. Herein, nanocubic porous Na_xFeFe(CN)₆ coated with polydopamine (PDA) as a coupling layer to improve its electrochemical performance is reported, inspired by the excellent adhesive property of PDA. As a cathode for sodium‐ion batteries, the Na_xFeFe(CN)₆ electrode coupled with PDA delivers a reversible capacity of 93.8 mA h g^?1 after 500 cycles at 0.2 A g^?1, and a discharge capacity of 72.6 mA h g^?1 at 5.0 A g^?1. The sodium storage mechanism of this Na_xFeFe(CN)₆ coupled with PDA is revealed via in situ Raman spectroscopy. The first‐principles computational results indicate that Fe^II sites in PB prefer to couple with the robust PDA layer to stabilize the PB structure. Moreover, the sodium‐ion migration in the PB structure is enhanced after coating with PDA, thus improving the sodium storage properties. Both experiments and computational simulations present guidelines for the rational design of nanomaterials as electrodes for energy storage devices.     

Polypyrrole‐Coated Zinc Ferrite Hollow Spheres with Improved Cycling Stability for Lithium‐Ion Batteries

Here, ZnFe₂O₄ double‐shell hollow microspheres are designed to accommodate the large volume expansion during lithiation. A facile and efficient vapor‐phase polymerization method has been developed to coat the ZnFe₂O₄ hollow spheres with polypyrrole (PPY). The thin PPY coating improves not only the electronic conductivity but also the structural integrity, and thus the cycling stability of the ZnFe₂O₄ hollow spheres. Our work sheds light on how to enhance the electrochemical performance of transition metal oxide‐based anode materials by designing delicate nanostructures.     

O3‐Type Layered Ni‐Rich Oxide: A High‐Capacity and Superior‐Rate Cathode for Sodium‐Ion Batteries

Inspired by its high‐active and open layered framework for fast Li⁺ extraction/insertion reactions, layered Ni‐rich oxide is proposed as an outstanding Na‐intercalated cathode for high‐performance sodium‐ion batteries. An O3‐type Na_0.75Ni_0.82Co_0.12Mn_0.06O₂ is achieved through a facile electrochemical ion‐exchange strategy in which Li⁺ ions are first extracted from the LiNi_0.82Co_0.12Mn_0.06O₂ cathode and Na⁺ ions are then inserted into a layered oxide framework. Furthermore, the reaction mechanism of layered Ni‐rich oxide during Na⁺ extraction/insertion is investigated in detail by combining ex situ X‐ray diffraction, X‐ray photoelectron spectroscopy, and electron energy loss spectroscopy. As an excellent cathode for Na‐ion batteries, O3‐type Na_0.75Ni_0.82Co_0.12Mn_0.06O₂ delivers a high reversible capacity of 171 mAh g^?1 and a remarkably stable discharge voltage of 2.8 V during long‐term cycling. In addition, the fast Na⁺ transport in the cathode enables high rate capability with 89 mAh g^?1 at 9 C. The as‐prepared Ni‐rich oxide cathode is expected to significantly break through the limited performance of current sodium‐ion batteries.     

A High‐Temperature Na‐Ion Battery: Boosting the Rate Capability and Cycle Life by Structure Engineering

High‐temperature sodium ion batteries (SIBs) have drawn significant heed recently for large‐scale energy storage. Yet, conventional SIBs are in the depths of inferior charge/discharge efficiency and cyclability at elevated temperatures. Rational structure design is highly desirable. Hence, a 3D hierarchical flower architecture self‐assembled by carbon‐coated Na₃V₂(PO₄)₃ (NVP) nanosheets (NVP@C‐NS‐FL) is fabricated via a microwave‐assisted glycerol‐mediated hydrothermal reaction combined with a post heat‐treatment. The growth mechanism of NVP@C‐NS‐FL is systematically investigated, by forming a microspherical glycerol/polyglycerol‐NVP complex initially and then converting into flower‐like architecture during the subsequent annealing at a low temperature ramping rate. Benefiting from the integrated structure, fast Na⁺ transportation, and highly effective heat transfer, the as‐obtained NVP@C‐NS‐FL exhibits an excellent high‐temperature SIB performance, e.g., 65 mAh g^?1 (100 C) after 1000 cycles under 60 °C. When coupled with NaTi₂(PO₄)₃ anode, the full cell can still display superior power capability of 1.4 kW kg^?1 and long‐term cyclability (2000 cycles) under 60 °C.