A Yolk–Shell-Structured FePO4 Cathode for High-Rate and Long-Cycling Sodium-Ion Batteries

Amorphous iron phosphate (FePO₄) has attracted enormous attention as a promising cathode material for sodium-ion batteries (SIBs) because of its high theoretical specific capacity and superior electrochemical reversibility. Nevertheless, the low rate performance and rapid capacity decline seriously hamper its implementation in SIBs. Herein, we demonstrate a sagacious multi-step templating approach to skillfully craft amorphous FePO₄ yolk–shell nanospheres with mesoporous nanoyolks supported inside the robust porous outer nanoshells. Their unique architecture and large surface area enable these amorphous FePO₄ yolk–shell nanospheres to manifest remarkable sodium storage properties with high reversible capacity, outstanding rate performance, and ultralong cycle life.     

A Yolk–Shell‐Structured FePO4 Cathode for High‐Rate and Long‐Cycling Sodium‐Ion Batteries

Amorphous iron phosphate (FePO₄) has attracted enormous attention as a promising cathode material for sodium‐ion batteries (SIBs) because of its high theoretical specific capacity and superior electrochemical reversibility. Nevertheless, the low rate performance and rapid capacity decline seriously hamper its implementation in SIBs. Herein, we demonstrate a sagacious multi‐step templating approach to skillfully craft amorphous FePO₄ yolk–shell nanospheres with mesoporous nanoyolks supported inside the robust porous outer nanoshells. Their unique architecture and large surface area enable these amorphous FePO₄ yolk–shell nanospheres to manifest remarkable sodium storage properties with high reversible capacity, outstanding rate performance, and ultralong cycle life.     

Facile Synthesis of Ultra-Small Few-Layer Nanostructured MoSe2 Embedded on N,P Co-Doped Bio-Carbon for High-Performance Half/Full Sodium-Ion and Potassium-Ion Batteries

Sodium/potassium-ion batteries (SIBs/PIBs) arouse intensive interest on account of the natural abundance of sodium/potassium resources, the competitive cost and appropriate redox potential. Nevertheless, the huge challenge for SIBs/PIBs lies in the scarcity of an anode material with high capacity and stable structure, which are capable of accommodating large-size ions during cycling. Furthermore, using sustainable natural biomass to fabricate electrodes for energy storage applications is a hot topic. Herein, an ultra-small few-layer nanostructured MoSe₂ embedded on N, P co-doped bio-carbon is reported, which is synthesized by using chlorella as the adsorbent and precursor. As a consequence, the MoSe₂/NP-C-2 composite represents exceedingly impressive electrochemical performance for both sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). It displays a promising reversible capacity (523 mAh g⁻¹ at 100 mA g⁻¹ after 100 cycles) and impressive long-term cycling performance (192 mAh g⁻¹ at 5 A g⁻¹ even after 1000 cycles) in SIBs, which are some of the best properties of MoSe₂-based anode materials for SIBs to date. To further probe the great potential applications, full SIBs pairing the MoSe₂/NP-C-2 composite anode with a Na₃V₂(PO₄)₃ cathode also exhibits a satisfactory capacity of 215 mAh g⁻¹ at 500 mA g⁻¹ after 100 cycles. Moreover, it also delivers a decent reversible capacity of 131 mAh g⁻¹ at 1 A g⁻¹ even after 250 cycles for PIBs.     

Suppressing the P2–O2 Phase Transition of Na0.67Mn0.67Ni0.33O2 by Magnesium Substitution for Improved Sodium‐Ion Batteries

Room‐temperature sodium‐ion batteries (SIBs) have shown great promise in grid‐scale energy storage, portable electronics, and electric vehicles because of the abundance of low‐cost sodium. Sodium‐based layered oxides with a P2‐type layered framework have been considered as one of the most promising cathode materials for SIBs. However, they suffer from the undesired P2–O2 phase transition, which leads to rapid capacity decay and limited reversible capacities. Herein, we show that this problem can be significantly mitigated by substituting some of the nickel ions with magnesium to obtain Na_0.67Mn_0.67Ni_0.33?xMg_xO₂ (0≤x≤0.33). Both the reversible capacity and the capacity retention of the P2‐type cathode material were remarkably improved as the P2–O2 phase transition was thus suppressed during cycling. This strategy might also be applicable to the modulation of the physical and chemical properties of layered oxides and provides new insight into the rational design of high‐capacity and highly stable cathode materials for SIBs.     

A High-Energy Aqueous All-Sulfur Battery

Rechargeable aqueous batteries are promising energy storage devices because of their high safety and low cost. However, their energy densities are generally unsatisfactory due to the limited capacities of ion-inserted electrode materials, prohibiting their widespread applications. Herein, a high-energy aqueous all-sulfur battery was constructed via matching S/Cu₂S and S/CaS_x redox couples. In such batteries, both cathodes and anodes undergo the conversion reaction between sulfur/metal sulfides redox couples, which display high specific capacities and rational electrode potential difference. Furthermore, during the charge/discharge process, the simultaneous redox of Cu²⁺ ion charge-carriers also takes place and contributes to a more two-electron transfer, which doubles the capacity of cathodes. As a result, the assembled aqueous all-sulfur batteries deliver a high discharge capacity of 447 mAh g⁻¹ based on total mass of sulfur in cathode and anode at 0.1 A g⁻¹, contributing to an enhanced energy density of 393 Wh kg⁻¹. This work will widen the scope for the design of high-energy aqueous batteries.     

NiSe2 nanoparticles encapsulated in CNTs covered and N-doped TiN/carbon nanofibers as a binder-free anode for advanced sodium-ion batteries

Metal selenides are promising anodes for sodium-ion batteries (SIBs) due to the high theoretical capacity through conversion reaction mechanism. However, developing metal selenides with superior electrochemical sodium-ion storage performance is still a great challenge. In this work, a novel composite material of free-standing NiSe₂ nanoparticles encapsulated in N-doped TiN/carbon composite nanofibers with carbon nanotubes (CNTs) in-situ grown on the surface (NiSe₂@N-TCF/CNTs) is prepared by electrospinning and pyrolysis technique. In this composite materials, NiSe₂ nanoparticles on the surface of carbon nanofibers were encapsulated into CNTs, thus avoiding aggregation. The in-situ grown CNTs not only improve the conductivity but also act as a buffer to accommodate the volume expansion. TiN inside the nanofibers further enhances the conductivity and structural stability of carbon-based nanofibers. When directly used as anode for SIBs, the NiSe₂@N-TCF/CNT electrode delivered a reversible capacity of 392.1 mAh/g after 1000 cycles and still maintained 334.4 mAh/g even at a high rate of 2 A/g. The excellent sodium-ion storage performance can be attributed to the fast Na⁺ diffusion and transfer rate and the pseudocapacitance dominated charge storage mechanism, as is evidenced by kinetic analysis. The work provides a novel approach to the fabrication of high-performance anode materials for other batteries.     

Toward Complete Transformation of Sodium Polysulfides by Regulating the Second-Shell Coordinating Environment of Atomically Dispersed Fe

Room temperature sodium-sulfur (RT Na-S) batteries are highly competitive as potential energy storage devices. Nevertheless, their actually achieved reversible capacities are far below the theoretical value due to incomplete transformation of polysulfides. Herein, atomically dispersed Fe-N/S active center by regulating the second-shell coordinating environment of Fe single atom is proposed. The Fe−N₄S₂ coordination structure with enhanced local electronic concentration around the Fermi level is revealed via synchrotron radiation X-ray absorption spectroscopy (XAS) and theoretical calculations, which can not only significantly promote the transformation kinetics of polysulfides, but induce uniform Na deposition for dendrite-free Na anode. As a result, the obtained S cathode delivers a high initial reversible capacity of 1590 mAh g⁻¹, nearly the theoretical value. This work opens up a new avenue to facilitate the complete transformation of polysulfides for RT Na-S batteries.     

Synergetic ternary metal oxide nanodots-graphene cathode for high performance zinc energy storage

Zinc-based electrochemistry energy storage with high safety and high theoretical capacity is considered to be a competitive candidate to replace lithium-ion batteries. In electrochemical energy storage, multi-metal oxide cathode materials can generally provide a wider electrochemical stability window and a higher capacity compared with single metal oxides cathode. Here, a new type of cathode material, MnFe₂Co₃O₈ nanodots/functional graphene sheets, is designed and used for aqueous hybrid Zn-based energy storage. Coupling with a hybrid electrolyte based on zinc sulfate and potassium hydroxide, the as-fabricated battery was able to work with a wide electrochemical window of 0.1∼1.8 V, showed a high specific capacity of 660 mAh/g, delivered an ultrahigh energy density of 1135 Wh/kg and a scalable power density of 5754 W/kg (calculated based on the cathode), and displayed a long cycling life of 1000 cycles. These are mainly attributed to the valence charge density distribution in MnFe₂Co₃O₈ nanodots, the good structural strengthening as well as high conductivity of the cathode, and the right electrolyte. Such cathode material also exhibited high electrocatalytic activity for oxygen evolution reaction and thus could be used for constructing a Zn-air battery with an ultrahigh reversible capacity of 9556 mAh/g.     

Catalytically Active CoSe2 Supported on Nitrogen-Doped Three Dimensional Porous Carbon as a Cathode for Highly Stable Lithium-Sulfur Battery

Lithium-sulfur batteries are promising secondary energy storage devices that are mainly limited by its unsatisfactory cyclability owing to inefficient reversible conversion of sulfur and lithium sulfide on the cathode during the discharge/charging process. In this study, nitrogen-doped three-dimensional porous carbon material loaded with CoSe₂ nanoparticles (CoSe₂-PNC) is developed as a cathode for lithium-sulfur battery. A combination of CoSe₂ and nitrogen-doped porous carbon can efficiently improve the cathode activity and its conductivity, resulting in enhanced redox kinetics of the charge/discharge process. The obtained electrode exhibits a high discharge specific capacity of 1139.6 mAh g⁻¹ at a current density of 0.2 C. After 100 cycles, its capacity remained at 865.7 mAh g⁻¹ thus corresponding to a capacity retention of 75.97 %. In a long-term cycling test, discharge specific capacity of 546.7 mAh g⁻¹ was observed after 300 cycles performed at a current density of 1 C.     

Annealing in Argon Universally Upgrades the Na-Storage Performance of Mn-Based Layered Oxide Cathodes by Creating Bulk Oxygen Vacancies

Manganese-rich layered oxide cathodes of sodium-ion batteries (SIBs) are extremely promising for large-scale energy storage owing to their high capacities and cost effectiveness, while the Jahn–Teller (J–T) distortion and low operating potential of Mn redox largely hinder their practical applications. Herein, we reveal that annealing in argon rather than conventional air is a universal strategy to comprehensively upgrade the Na-storage performance of Mn-based oxide cathodes. Bulk oxygen vacancies are introduced via this method, leading to reduced Mn valence, lowered Mn 3d-orbital energy level, and formation of the new-concept Mn domains. As a result, the energy density of the model P2-Na_0.75Mg_0.25Mn_0.75O₂ cathode increases by ≈50 % benefiting from the improved specific capacity and operating potential of Mn redox. The Mn domains can disrupt the cooperative J–T distortion, greatly promoting the cycling stability. This exciting finding opens a new avenue towards high-performance Mn-based oxide cathodes for SIBs.     

Recent developments on layered 3d-transtition metal oxide cathode materials for sodium-ion batteries

Sodium-ion batteries (SIBs) are now intensively developed as a cost-effective technology alternative to lithium-ion batteries (LIBs) for large-scale energy storage because of their various advantages such as huge abundance of sodium resources, highly safe and significantly low cost. Among many other cathode materials, layered 3d-transition metal oxides (LTMO-Na_xMO₂, x ≤ 1 and M = Co, Ni, Mn, Cr, Cu, Fe and V) have gained an enormous interest and attractive attention among researchers because of their low-cost, high energy density and ease of synthesis. In addition, LTMOs offer higher reversible capacities because of relatively lower molecular weights; however, complex phase transformations limit their cycling life. Based on the previous research, it was examined that the crystalline phase of LTMO highly influences the electrochemical performance of SIBs; therefore, this review mainly focuses on the latest advances of various crystalline phases such as P2-type, P3-type, O3-type and biphase/multiphase materials and its strength as well as future prospects and challenges.     

Highly Reversible Cuprous Mediated Cathode Chemistry for Magnesium Batteries

Sluggish kinetics and poor reversibility of cathode chemistry is the major challenge for magnesium batteries to achieve high volumetric capacity. Introduction of the cuprous ion (Cu⁺) as a charge carrier can decouple the magnesiation related energy storage from the cathode electrochemistry. Cu⁺ is generated from a fast equilibrium between copper selenide electrode and Mg electrolyte during standing time, rather than in the electrochemical process. A reversible chemical magnesiation/de‐magnesiation can be driven by this solid/liquid equilibrium. During a typical discharge process, Cu⁺ is reduced to Cu and drives the equilibrium to promote the magnesiation process. The reversible Cu to Cu⁺ redox promotes the recharge process. This novel Cu⁺ mediated cathode chemistry of Mg battery leads to a high reversible areal capacity of 12.5 mAh cm^?2 with high mass loading (49.1 mg cm^?2) of the electrode. 80 % capacity retention can be achieved for 200 cycles after a conditioning process.     

Three Dimensionally Ordered Mesoporous Carbon as a Stable,High‐Performance Li–O2 Battery Cathode

Enabled by the reversible conversion between Li₂O₂ and O₂, Li–O₂ batteries promise theoretical gravimetric capacities significantly greater than Li‐ion batteries. The poor cycling performance, however, has greatly hindered the development of this technology. At the heart of the problem is the reactivity exhibited by the carbon cathode support under cell operation conditions. One strategy is to conceal the carbon surface from reactive intermediates. Herein, we show that long cyclability can be achieved on three dimensionally ordered mesoporous (3DOm) carbon by growing a thin layer of FeO_x using atomic layer deposition (ALD). 3DOm carbon distinguishes itself from other carbon materials with well‐defined pore structures, providing a unique material to gain insight into processes key to the operations of Li–O₂ batteries. When decorated with Pd nanoparticle catalysts, the new cathode exhibits a capacity greater than 6000 mAh g_carbon⁻¹ and cyclability of more than 68 cycles.     

Ultrahigh rate binder-free Na_3V_2(PO_4)_3/carbon cathode for sodium-ion battery

Sodium ion batteries(SIBs)are very promising for large-scale energy storage in virtue of its high energy density,abundant sodium resources and low environmental impact,etc.However,it is still a big challenge to develop high-performance and durable cathode materials for SIBs.Among different candidate materials,Na_3V_2(PO_4)_3has attracted great attentions due to its high theoretical capacity(117 mAh/g),stable framework structure and excellent ionic conductivity.However,Na_3V_2(PO_4)_3delivers inferior rate capability and cycling stability due to its poor electronic conductivity.In this work,free-standing Na_3V_2(PO_4)_3/carbon nanofiber membranes are synthesized by an electrospinning-sintering route.The sample could deliver excellent cycling capability with specific capacity of 112 mAh/g at 1 C after 250cycles and ultrahigh rate capability with 76.9 mAh/g even at 100 C,which is superior to many state-ofthe-art SIB cathode materials.This can be attributed to the hierarchically distributed Na_3V_2(PO_4)_3crystals in carbon nanofiber network,which possesses outstanding electronic/ionic conductivity and thus leads to an ultrahigh rate capability.     

Three Dimensionally Ordered Mesoporous Carbon as a Stable,High‐Performance Li–O2 Battery Cathode

Enabled by the reversible conversion between Li₂O₂ and O₂, Li–O₂ batteries promise theoretical gravimetric capacities significantly greater than Li‐ion batteries. The poor cycling performance, however, has greatly hindered the development of this technology. At the heart of the problem is the reactivity exhibited by the carbon cathode support under cell operation conditions. One strategy is to conceal the carbon surface from reactive intermediates. Herein, we show that long cyclability can be achieved on three dimensionally ordered mesoporous (3DOm) carbon by growing a thin layer of FeO_x using atomic layer deposition (ALD). 3DOm carbon distinguishes itself from other carbon materials with well‐defined pore structures, providing a unique material to gain insight into processes key to the operations of Li–O₂ batteries. When decorated with Pd nanoparticle catalysts, the new cathode exhibits a capacity greater than 6000 mAh g_carbon^?1 and cyclability of more than 68 cycles.     

SbPS4: A novel anode for high-performance sodium-ion batteries

With the in-depth research of sodium-ion batteries（SIBs）, the development of novel sodium-ion anode material has become a top priority. In this work, tube cluster-shaped SbPS₄ was synthesized by a high-temperature solid phase reaction. Then the typical short tubular ternary thiophosphate SbPS₄ compounded with graphene oxide（SbPS₄/GO） was successfully synthesized after ultrasonication and freeze-drying. SbPS₄ shows a high theoretical specific capacity（1...     

Embedding antimony nanoparticles into metal–organic framework derived TiO2@carbon nanotablets for high-performance sodium storage

Titanium dioxide (TiO₂) has been widely investigated as a candidate for anode materials of sodium-ion batteries (SIBs) due to its low cost and high abundance. However, the intrinsic sluggish ion/electron transfer rate hinders its practical applications for high energy density storage devices. In contrast, antimony (Sb) shows high specific theoretical capacity (660 mAh/g) as well as excellent electron conductivity, but the large volume variation upon cycling usually leads to severe capacity fading. Herein, with the objective of achieving high-performance sodium storage anode materials, TiO₂@C-Sb nanotablets with a small amount of Sb content (6.4 wt%) are developed through calcination Ti-metal–organic framework (MIL-125) derived TiO₂@C/SbCl₃ mixture under reductive atmosphere. Benefitting from the synergetic effect of well-dispersed Sb nanoparticles as well as robust porous TiO₂@C substrate, the TiO₂@C-Sb shows enhanced electron/ion transfer rate and predominantly pseudocapacitive sodium storage behavior, delivering a reversible capacity of 219 mAh/g at 0.5 A/g even after 1000 cycles. More significantly, this method may be commonly used to incorporate other alloy-based high-theoretical materials into MIL-125-derived TiO₂@C, which is promising for developing high-energy-density TiO₂-based energy storage devices.     

碳布负载的缺氧型Na2Ti3O7纳米带阵列作为高性能柔性钠离子电池负极材料

作为锂离子电池的理想替代品,钠离子电池因具有能源储备丰富、成本低廉等优点而受到人们的广泛关注。柔性便携式电子产品的发展亟需柔性储能器件的研制。因此,发展一种廉价、高性能的柔性钠离子电池负极材料成了科研工作者的共同目标。在此项工作中,我们通过简单的水热合成和热还原法发展了一种以柔性碳布为基底,与缺氧型的Na₂Ti₃O₇纳米带(NTO)构成三维阵列结构的新型柔性钠离子电池负极材料。复合材料(R-NTO/CC)的导电性和活性位点得到提高,电化学性能也大幅提升,在200 mA·cm^-2的电流密度下,实现100 mAh·cm^-2的面积比容量,且经过200次循环后仍保留最初电容值的80%。此外,这种电极还具有优良的倍率性能,当电流密度提高到400 mA·cm^-2时,仍保持69.7 mAh·cm^-2的面积比容量,是未引入氧空位材料的三倍之多。这种三维缺氧的电极材料可有效提高载流子浓度,缩短离子传输通道,从而大幅提升电极的电化学性能。此工作为设计合成高储钠性能的新型的负极材料提供了一种实用有效的策略。     

A Biodegradable Polydopamine‐Derived Electrode Material for High‐Capacity and Long‐Life Lithium‐Ion and Sodium‐Ion Batteries

Polydopamine (PDA), which is biodegradable and is derived from naturally occurring products, can be employed as an electrode material, wherein controllable partial oxidization plays a key role in balancing the proportion of redox‐active carbonyl groups and the structural stability and conductivity. Unexpectedly, the optimized PDA derivative endows lithium‐ion batteries (LIBs) or sodium‐ion batteries (SIBs) with superior electrochemical performances, including high capacities (1818 mAh g^?1 for LIBs and 500 mAh g^?1 for SIBs) and good stable cyclabilities (93 % capacity retention after 580 cycles for LIBs; 100 % capacity retention after 1024 cycles for SIBs), which are much better than those of their counterparts with conventional binders.     

A Bipolar and Self‐Polymerized Phthalocyanine Complex for Fast and Tunable Energy Storage in Dual‐Ion Batteries

Bipolar redox organics have attracted interest as electrode materials for energy storage owing to their flexibility, sustainability and environmental friendliness. However, an understanding of their application in all‐organic batteries, let alone dual‐ion batteries (DIBs), is in its infancy. Herein, we propose a strategy to screen a variety of phthalocyanine‐based bipolar organics. The self‐polymerizable bipolar Cu tetraaminephthalocyanine (CuTAPc) shows multifunctional applications in various energy storage systems, including lithium‐based DIBs using CuTAPc as the cathode material, graphite‐based DIBs using CuTAPc as the anode material and symmetric DIBs using CuTAPc as both the cathode and anode materials. Notably, in lithium‐based DIBs, the use of CuTAPc as the cathode material results in a high discharge capacity of 236 mAh g^?1 at 50 mA g^?1 and a high reversible capacity of 74.3 mAh g^?1 after 4000 cycles at 4 A g^?1. Most importantly, a high energy density of 239 Wh kg^?1 and power density of 11.5 kW kg^?1 can be obtained in all‐organic symmetric DIBs.