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.     

Formation of Hierarchical Cu‐Doped CoSe2 Microboxes via Sequential Ion Exchange for High‐Performance Sodium‐Ion Batteries

Electrode materials based on electrochemical conversion reactions have received considerable interest for high capacity anodes of sodium‐ion batteries. However, their practical application is greatly hindered by the poor rate capability and rapid capacity fading. Tuning the structure at nanoscale and increasing the conductivity of these anode materials are two effective strategies to address these issues. Herein, a two‐step ion‐exchange method is developed to synthesize hierarchical Cu‐doped CoSe₂ microboxes assembled by ultrathin nanosheets using Co–Co Prussian blue analogue microcubes as the starting material. Benefitting from the structural and compositional advantages, these Cu‐doped CoSe₂ microboxes with improved conductivity exhibit enhanced sodium storage properties in terms of good rate capability and excellent cycling performance.     

Golden Bristlegrass‐Like Hierarchical Graphene Nanofibers Entangled with N‐Doped CNTs Containing CoSe2 Nanocrystals at Each Node as Anodes for High‐Rate Sodium‐Ion Batteries

Golden bristlegrass‐like unique nanostructures comprising reduced graphene oxide (rGO) matrixed nanofibers entangled with bamboo‐like N‐doped carbon nanotubes (CNTs) containing CoSe₂ nanocrystals at each node (denoted as N‐CNT/rGO/CoSe₂ NF) are designed as anodes for high‐rate sodium‐ion batteries (SIBs). Bamboo‐like N‐doped CNTs (N‐CNTs) are successfully generated on the rGO matrixed nanofiber surface, between rGO sheets and mesopores, and interconnected chemically with homogeneously distributed rGO sheets. The defects in the N‐CNTs formed by a simple etching process allow the complete phase conversion of Co into CoSe₂ through the efficient penetration of H₂Se gas inside the CNT walls. The N‐CNTs bridge the vertical defects for electron transfer in the rGO sheet layers and increase the distance between the rGO sheets during cycles. The discharge capacity of N‐CNT/rGO/CoSe₂ NF after the 10 000th cycle at an extremely high current density of 10 A g^?1 is 264 mA h g^?1, and the capacity retention measured at the 100th cycle is 89%. N‐CNT/rGO/CoSe₂ NF has final discharge capacities of 395, 363, 328, 304, 283, 263, 246, 223, 197, 171, and 151 mA h g^?1 at current densities of 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 A g^?1, respectively.     

High‐Energy/Power and Low‐Temperature Cathode for Sodium‐Ion Batteries: In Situ XRD Study and Superior Full‐Cell Performance

Sodium‐ion batteries (SIBs) are still confronted with several major challenges, including low energy and power densities, short‐term cycle life, and poor low‐temperature performance, which severely hinder their practical applications. Here, a high‐voltage cathode composed of Na₃V₂(PO₄)₂O₂F nano‐tetraprisms (NVPF‐NTP) is proposed to enhance the energy density of SIBs. The prepared NVPF‐NTP exhibits two high working plateaux at about 4.01 and 3.60 V versus the Na⁺/Na with a specific capacity of 127.8 mA h g^?1. The energy density of NVPF‐NTP reaches up to 486 W h kg^?1, which is higher than the majority of other cathode materials previously reported for SIBs. Moreover, due to the low strain (≈2.56% volumetric variation) and superior Na transport kinetics in Na intercalation/extraction processes, as demonstrated by in situ X‐ray diffraction, galvanostatic intermittent titration technique, and cyclic voltammetry at varied scan rates, the NVPF‐NTP shows long‐term cycle life, superior low‐temperature performance, and outstanding high‐rate capabilities. The comparison of Ragone plots further discloses that NVPF‐NTP presents the best power performance among the state‐of‐the‐art cathode materials for SIBs. More importantly, when coupled with an Sb‐based anode, the fabricated sodium‐ion full‐cells also exhibit excellent rate and cycling performances, thus providing a preview of their practical application.     

High‐Performance Flexible Freestanding Anode with Hierarchical 3D Carbon‐Networks/Fe7S8/Graphene for Applicable Sodium‐Ion Batteries

Sodium‐ion batteries (SIBs) have gained tremendous interest for grid scale energy storage system and power energy batteries. However, the current researches of anode for SIBs still face the critical issues of low areal capacity, limited cycle life, and low initial coulombic efficiency for practical application perspective. To solve this issue, a kind of hierarchical 3D carbon‐networks/Fe₇S₈/graphene (CFG) is designed and synthesized as freestanding anode, which is constructed with Fe₇S₈ microparticles well‐welded on 3D‐crosslinked carbon‐networks and embedded in highly conductive graphene film, via a facile and scalable synthetic method. The as‐prepared freestanding electrode CFG represents high areal capacity (2.12 mAh cm^?2 at 0.25 mA cm^?2) and excellent cycle stability of 5000 cycles (0.0095% capacity decay per cycle). The assembled all‐flexible sodium‐ion battery delivers remarkable performance (high areal capacity of 1.42 mAh cm^?2 at 0.3 mA cm^?2 and superior energy density of 144 Wh kg^?1), which are very close to the requirement of practical application. This work not only enlightens the material design and electrode engineering, but also provides a new kind of freestanding high energy density anode with great potential application prospective for SIBs.     

High‐Safety Nonaqueous Electrolytes and Interphases for Sodium‐Ion Batteries

Rapidly developed Na‐ion batteries are highly attractive for grid energy storage. Nevertheless, the safety issues of Na‐ion batteries are still a bottleneck for large‐scale applications. Similar to Li‐ion batteries (LIBs), the safety of Na‐ion batteries is considered to be tightly associated with the electrolyte and electrode/electrolyte interphase. Although the knowledge obtained from LIBs is helpful, designing safe electrolytes and obtaining stable interphases in Na‐ion batteries is still a huge challenge. Therefore, it is of significance to investigate the key factors and develop new strategies for the development of high‐safety Na‐ion batteries. This comprehensive review introduces the recent efforts from nonaqueous electrolytes and interphase aspects of Na‐ion batteries, proposes their design strategies and requirements for improving safety characteristics, and discusses the potential issues for practical applications. The insight to formulate safe electrolytes and design the stable interphase for Na‐ion batteries with high safety is intended to be provided herein.     

Mesoporous Hollow Sb/ZnS@C Core–Shell Heterostructures as Anodes for High‐Performance Sodium‐Ion Batteries

Combining the advantage of metal, metal sulfide, and carbon, mesoporous hollow core–shell Sb/ZnS@C hybrid heterostructures composed of Sb/ZnS inner core and carbon outer shell are rationally designed based on a robust template of ZnS nanosphere, as anodes for high‐performance sodium‐ion batteries (SIBs). A partial cation exchange reaction based on the solubility difference between Sb₂S₃ and ZnS can transform mesoporous ZnS to Sb₂S₃/ZnS heterostructure. To get a stable structure, a thin contiguous resorcinol‐formaldehyde (RF) layer is introduced on the surface of Sb₂S₃/ZnS heterostructure. The effectively protective carbon layer from RF can be designed as the reducing agent to convert Sb₂S₃ to metallic Sb to obtain core–shell Sb/ZnS@C hybrid heterostructures. Simultaneously, the carbon outer shell is beneficial to the charge transfer kinetics, and can maintain the structure stability during the repeated sodiation/desodiation process. Owing to its unique stable architecture and synergistic effects between the components, the core–shell porous Sb/ZnS@C hybrid heterostructure SIB anode shows a high reversible capacity, good rate capability, and excellent cycling stability by turning the optimized voltage range. This novel strategy to prepare carbon‐layer‐protected metal/metal sulfide core–shell heterostructure can be further extended to design other novel nanostructured systems for high‐performance energy storage devices.     

Recent Progress in Rechargeable Sodium‐Ion Batteries: toward High‐Power Applications

The increasing demands for renewable energy to substitute traditional fossil fuels and related large‐scale energy storage systems (EES) drive developments in battery technology and applications today. The lithium‐ion battery (LIB), the trendsetter of rechargeable batteries, has dominated the market for portable electronics and electric vehicles and is seeking a participant opportunity in the grid‐scale battery market. However, there has been a growing concern regarding the cost and resource availability of lithium. The sodium‐ion battery (SIB) is regarded as an ideal battery choice for grid‐scale EES owing to its similar electrochemistry to the LIB and the crust abundance of Na resources. Because of the participation in frequency regulation, high pulse‐power capability is essential for the implanted SIBs in EES. Herein, a comprehensive overview of the recent advances in the exploration of high‐power cathode and anode materials for SIB is presented, and deep understanding of the inherent host structure, sodium storage mechanism, Na⁺ diffusion kinetics, together with promising strategies to promote the rate performance is provided. This work may shed light on the classification and screening of alternative high rate electrode materials and provide guidance for the design and application of high power SIBs in the future.     

Surface‐Engineered Black Niobium Oxide@Graphene Nanosheets for High‐Performance Sodium‐/Potassium‐Ion Full Batteries

Nanoscale surface‐engineering plays an important role in improving the performance of battery electrodes. Nb₂O₅ is one typical model anode material with promising high‐rate lithium storage. However, its modest reaction kinetics and low electrical conductivity obstruct the efficient storage of larger ions of sodium or potassium. In this work, partially surface‐amorphized and defect‐rich black niobium oxide@graphene (black Nb₂O_5?x@rGO) nanosheets are designed to overcome the above Na/K storage problems. The black Nb₂O_5?x@rGO nanosheets electrodes deliver a high‐rate Na and K storage capacity (123 and 73 mAh g^?1, respectively at 3 A g^?1) with long‐term cycling stability. Besides, both Na‐ion and K‐ion full batteries based on black Nb₂O_5?x@rGO nanosheets anodes and vanadate‐based cathodes (Na_0.33V₂O₅ and K_0.5V₂O₅ for Na‐ion and K‐ion full batteries, respectively) demonstrate promising rate and cycling performance. Notably, the K‐ion full battery delivers higher energy and power densities (172 Wh Kg^?1 and 430 W Kg^?1), comparable to those reported in state‐of‐the‐art K‐ion full batteries, accompanying with a capacity retention of ≈81.3% over 270 cycles. This result on Na‐/K‐ion batteries may pave the way to next‐generation post‐lithium batteries.     

An Advanced MoS2/Carbon Anode for High‐Performance Sodium‐Ion Batteries

Molybdenum disulfide (MoS₂) is a promising anode for high performance sodium‐ion batteries due to high specific capacity, abundance, and low cost. However, poor cycling stability, low rate capability and unclear electrochemical reaction mechanism are the main challenges for MoS₂ anode in Na‐ion batteries. In this study, molybdenum disulfide/carbon (MoS₂/C) nanospheres are fabricated and used for Na‐ion battery anodes. MoS₂/C nanospheres deliver a reversible capacity of 520 mAh g^?1 at 0.1 C and maintain at 400 mAh g^?1 for 300 cycles at a high current density of 1 C, demonstrating the best cycling performance of MoS₂ for Na‐ion batteries to date. The high capacity is attributed to the short ion and electron diffusion pathway, which enables fast charge transfer and low concentration polarization. The stable cycling performance and high coulombic efficiency (～100%) of MoS₂/C nanospheres are ascribed to (1) highly reversible conversion reaction of MoS₂ during sodiation/desodiation as evidenced by ex‐situ X‐ray diffraction (XRD) and (2) the formation of a stable solid electrolyte interface (SEI) layer in fluoroethylene carbonate (FEC) based electrolyte as demonstrated by fourier transform infrared spectroscopy (FTIR) measurements.     

Carbon‐Supported Nickel Selenide Hollow Nanowires as Advanced Anode Materials for Sodium‐Ion Batteries

Carbon‐supported nickel selenide (Ni_0.85Se/C) hollow nanowires are prepared from carbon‐coated selenium nanowires via a self‐templating hydrothermal method, by first dissolving selenium in the Se/C nanowires in hydrazine, allowing it to diffuse out of the carbon layer, and then reacting with nickel ions into Ni_0.85Se nanoplates on the outer surface of the carbon. Ni_0.85Se/C hollow nanowires are employed as anode materials for sodium‐ion batteries, and their electrochemical performance is evaluated via the cyclic voltammetry and electrochemical impedance spectroscopy combined with ex situ X‐ray photoelectron spectroscopy and X‐ray diffraction measurements. It is found that Ni_0.85Se/C hollow nanowires exhibit greatly enhanced cycle stability and rate capability as compared to Ni_0.85Se nanoparticles, with a reversible capacity around 390 mA h g^?1 (the theoretical capacity is 416 mA h g^?1) at the rate of 0.2 C and 97% capacity retention after 100 cycles. When the current rate is raised to 5 C, they still deliver capacity of 219 mA h g^?1. The synthetic methodology introduced here is general and can easily be applied to building similar structures for other metal selenides in the future.