Potassium Prussian Blue Nanoparticles: A Low‐Cost Cathode Material for Potassium‐Ion Batteries

Potassium‐ion batteries (KIBs) in organic electrolytes hold great promise as an electrochemical energy storage technology owing to the abundance of potassium, close redox potential to lithium, and similar electrochemistry with lithium system. Although carbon materials have been studied as KIB anodes, investigations on KIB cathodes have been scarcely reported. A comprehensive study on potassium Prussian blue K_0.220Fe[Fe(CN)₆]_0.805?4.01H₂O nanoparticles as a potential cathode material is for the first time reported. The cathode exhibits a high discharge voltage of 3.1–3.4 V, a high reversible capacity of 73.2 mAh g^?1, and great cyclability at both low and high rates with a very small capacity decay rate of ≈0.09% per cycle. Electrochemical reaction mechanism analysis identifies the carbon‐coordinated Fe^III/Fe^II couple as redox‐active site and proves structural stability of the cathode during charge/discharge. Furthermore, for the first time, a KIB full‐cell is presented by coupling the nanoparticles with commercial carbon materials. The full‐cell delivers a capacity of 68.5 mAh g^?1 at 100 mA g^?1 and retains 93.4% of the capacity after 50 cycles. Considering the low cost and material sustainability as well as the great electrochemical performances, this work may pave the way toward more studies on KIB cathodes and trigger future attention on rechargeable KIBs.     

Mixed-Valence Copper Selenide as an Anode for Ultralong Lifespan Rocking-Chair Zn-Ion Batteries: An Insight into its Intercalation/Extraction Kinetics and Charge Storage Mechanism

Environment-friendly and low-cost aqueous zinc-ion batteries (ZIBs) have received considerable attention for large-scale energy storage. However, the low coulombic efficiency and potential safety hazards of Zn-metal anodes severely hinder their practical implementations. Herein, for the first time, mixed-valence Cu_2−xSe is proposed as a new intercalation anode to construct Zn-metal-free rocking-chair ZIBs with a long lifespan. It is found that the introduction of low-valence Cu not only modify active sites for Zn²⁺ ion storage, but also optimizes the electronic interaction between the active sites and the intercalated Zn²⁺ ion, leading to a favorable intercalation formation energy (−0.68 eV) and reduced diffusion barrier, as demonstrated by first-principles calculation. Ex situ X-ray diffraction, ex situ transmission electron microscopy and galvanostatic intermittent titration technique measurements reveal the reversible insertion/extraction of Zn²⁺ in Cu_2−xSe via an intercalation reaction mechanism. Owing to the rigid host structure and facile Zn²⁺ diffusion kinetics, the Cu_2−xSe nanorod anode shows an enhanced coulombic efficiency (above 99.5%), outstanding rate capability and excellent cycling stability. The as-fabricated Zn_xMnO₂||Cu_2−xSe Zn-ion full battery exhibits an impressive electrochemical performance, particularly an ultralong cycle life of over 20 000 cycles at 2 A g⁻¹. This study is expected to provide new opportunities for developing high-performance rechargeable aqueous ZIBs.     

Ultrathin Layered Hydroxide Cobalt Acetate Nanoplates Face‐to‐Face Anchored to Graphene Nanosheets for High‐Efficiency Lithium Storage

The dramatically increasing demand of high‐energy lithium‐ion batteries (LIBs) urgently requires advanced substitution for graphite‐based anodes. Herein, inspired from the extra capacity of lithium storage in solid‐electrolyte interface (SEI) films, layered hydroxide cobalt acetates (LHCA, Co(Ac)_0.48(OH)_1.52·0.55H₂O) are introduced as novel and high‐efficiency anode materials. Furthermore, ultrathin LHCA nanoplates are face‐to‐face anchored on the surface of graphene nanosheets (GNS) through a facile solvothermal method to improve the electronic transport and avoid agglomeration during repeated cycles. Profiting from the parallel structure, LHCA//GNS nanosheets exhibit extraordinary long‐term and high‐rate performance. At the current densities of 1000 and 4000 mA g^?1, the reversible capacities maintain ≈1050 mAh g^?1 after 200 cycles and ≈780 mAh g^?1 after 300 cycles, respectively, much higher than the theoretical value of LHCA according to the conversion mechanism. Fourier transform infrared spectroscopy confirms the conversion from acetate to acetaldehyde after lithiation. A reasonable mechanism is proposed to elucidate the lithium storage behaviors referring to the electrocatalytic conversion of OH groups with Co nanocatalysts. This work can help further understand the contribution of SEI components (especially LiOH and LiAc) to lithium storage. It is envisaged that layered transition metal hydroxides can be used as advanced materials for energy storage devices.     

Facile Synthesis of Blocky SiOx/C with Graphite‐Like Structure for High‐Performance Lithium‐Ion Battery Anodes

SiO_x‐containing graphite composites have aroused great interests as the most promising alternatives for practical application in high‐performance lithium‐ion batteries. However, limited loading amount of SiO_x on the surface of graphite and some inherent disadvantages of SiO_x such as huge volume variation and poor electronic conductivity result in unsatisfactory electrochemical performance. Herein, a novel and facile fabrication approach is developed to synthesize high‐performance SiO_x/C composites with graphite‐like structure in which SiO_x particles are dispersed and anchored in the carbon materials by restoring original structure of artificial graphite. The multicomponent carbon materials are favorable for addressing the disadvantages of SiO_x‐based anodes, especially for the formation of stable solid electrolyte interphase, maintaining structural integrity of electrode materials and improving electrical conductivity of electrode. The resultant SiO_x/C anodes demonstrate high reversible capacities (645 mA h g^?1), excellent cycling stability (≈90% capacity retention for 500 cycles), and superior rate capabilities. Even at high pressing density (1.3 g cm^?3), SiO_x/C anodes still present superior cycling performance due to the high tap density and structural integrity of electrode materials. The proposed synthetic method can also be developed to address other anode materials with inferior electronic conductivity and huge volume variation.     

A General Route for Encapsulating Monodispersed Transition Metal Phosphides into Carbon Multi-Chambers toward High-Efficient Lithium-Ion Storage with Underlying Mechanism Exploration

Transition metal phosphides (MP_x) with high theoretical capacities and low cost are regarded as the most promising anodes for lithium-ion batteries (LIBs), but the large volume variations and sluggish kinetics largely restrict their development. To solve the above challenges, herein a generic but effective method is proposed to encapsulate various monodispersed MP_x into flexible carbon multi-chambers (MP_x@NC, MNi, Fe, Co, and Cu, etc.) with pre-reserved voids, working as anodes for LIBs and markedly boosting the Li⁺ storage performance. Ni₂P@NC, one representative example of MP_x@NC anode, shows high reversible capacity (613 mAh g⁻¹, 200 cycles at 0.2 A g⁻¹), and superior cycle stability (475 mAh g⁻¹, 800 cycles at 2 A g⁻¹). Full cell coupled with LiFePO₄ displays a high reversible capacity (150.1 mAh g⁻¹ at 0.1 A g⁻¹) with stable cycling performance. In situ X-ray diffraction and transmission electron microscope techniques confirm the reversible conversion reaction mechanism and robust structural integrity, accounting for enhanced rate and cycling performance. Theoretical calculations reveal the synergistic effect between MP_x and carbon shells, which can significantly promote electron transfer and reduce diffusion energy barriers, paving ways to design high-energy-density materials for energy storage systems.     

Porosity‐ and Graphitization‐Controlled Fabrication of Nanoporous Silicon@Carbon for Lithium Storage and Its Conjugation with MXene for Lithium‐Metal Anode

Silicon (Si) and lithium metal are the most favorable anodes for high‐energy‐density lithium‐based batteries. However, large volume expansion and low electrical conductivity restrict commercialization of Si anodes, while dendrite formation prohibits the applications of lithium‐metal anodes. Here, uniform nanoporous Si@carbon (NPSi@C) from commercial alloy and CO₂ is fabricated and tested as a stable anode for lithium‐ion batteries (LIBs). The porosity of Si as well as graphitization degree and thickness of the carbon layer can be controlled by adjusting reaction conditions. The rationally designed porosity and carbon layer of NPSi@C can improve electronic conductivity and buffer volume change of Si without destroying the carbon layer or disrupting the solid electrolyte interface layer. The optimized NPSi@C anode shows a stable cyclability with 0.00685% capacity decay per cycle at 5 A g^?1 over 2000 cycles for LIBs. The energy storage mechanism is explored by quantitative kinetics analysis and proven to be a capacitance‐battery dual model. Moreover, a novel 2D/3D structure is designed by combining MXene and NPSi@C. As lithiophilic nucleation seeds, NPSi@C can induce uniform Li deposition with buffered volume expansion, which is proven by exploring Li‐metal deposition morphology on Cu foil and MXene@NPSi@C. The practical potential application of NPSi@C and MXene@NPSi@C is evaluated by full cell tests with a Li(Ni_0.8Co_0.1Mn_0.1)O₂ cathode.     

A Stable Conversion and Alloying Anode for Potassium‐Ion Batteries: A Combined Strategy of Encapsulation and Confinement

Potassium‐ion batteries based on conversion/alloying reactions have high potential applications in new‐generation large‐scale energy storage. However, their applications are hindered by inherent large‐volume variations and sluggish kinetics of the conversion/alloying‐type electrode materials during the repeated insertion and extraction of bulky K⁺ ions. Although some efforts have been focused on this issue, the reported potassium‐ion batteries still suffer from poor cycling lifespans. Here, a superior stable antimony selenide (Sb₂Se₃) anode is reported for high‐performance potassium‐ion batteries through a combined strategy of conductive encapsulation and 2D confinement. The Sb₂Se₃ nanorods are uniformly coated with a conductive N‐doped carbon layer and then confined between graphene nanosheets. The synergistic effects between conductive coating and confinement effectively buffer the large volumetric variation of the conversion/alloying anodes, which can maintain structural stability for superior cyclability. The as‐prepared anodes exhibit a high reversible specific capacity of ≈590 mA h g^?1 and outstanding cycling stability over 350 cycles. In situ and ex situ characterizations reveal a high structural integration of the large‐volume‐change Sb₂Se₃ anodes during a reversible K storage mechanism of two‐step conversion and multistep alloying processes. This work can open up a new possibility for the design of stable conversion/alloying‐based anodes for high‐performance potassium‐ion batteries.     

Understanding of the Ultrastable K‐Ion Storage of Carbonaceous Anode

Carbon‐based materials are considered to be one of the most promising materials for negative electrodes of the future, because of their good chemical stability, high electrical conductivity, and environmental benignity. However, to date, the underlying principles of K‐ion storage in carbonaceous anodes remain elusive, which greatly hinders the development of such a category of anodes. Herein, the ultrastable K‐ion storage of carbonaceous anode through systematic analyses, including comprehensive electrochemical characterizations, kinetics calculations, and structural/compositional evolution mechanism studies, is theoretically elucidated and experimentally verified. Specifically, it is found that the uniquely envelope‐like nitrogen‐doped carbon nanosheets with high pseudocapacitive could bring ultrastable storage of potassium ions, delivering a high initial reversible capacity of 367 mAh g^?1 at a current density of 50 mA g^?1 and retain 70.5 and 75.6% at current densities of 500 and 1000 mA g^?1 after 1000th cycle, respectively. This study could enlighten researchers on further progress in the field of carbonaceous K‐ion battery negative electrode with a long cycle life.     

Multiple Active Sites Carbonaceous Anodes for Na+ Storage: Synthesis,Electrochemical Properties and Reaction Mechanism Analysis

Owing to the earth-abundant resources, cost effective materials and stable electrochemical properties, sodium-ions batteries (SIBs) show long-term potential in responding to the rapid consumption of lithium resources and the ever-increasing development of new energy storage devices. Nevertheless, the intrinsic properties of the large ion radius (Na⁺ 1.02 Å vs Li⁺ 0.76 Å) and positive reduction potential (Na/Na⁺ −2.71 V vs Li/Li⁺ −3.04 V) may impede ion diffusion, thus causing serious volume expansion, resulting in poor cycling stability. To address these issues, the incorporation of active sites into carbonaceous anode is considered as an efficient strategy to enhance interfacial compatibility, enlarge interlayer distance, and supply reversible Faradic pseudo-capacitance. Herein, the multiple active sites carbonaceous anodes for SIBs anode are comprehensively reviewed. Typically, carbonaceous materials are categorized into diffusion and surface controlled based on Na storage mechanism, and the concepts of intrinsic/extrinsic active sites are proposed according to the types of active sites. Furthermore, to reveal the reaction kinetics and guide the rational design of high performance anodes, the (spectro) electrochemical analysis methods and corresponding key parameters are introduced. Additionally, primary superiorities, essential issues, and supposed solutions of multiple active sites carbonaceous Na anodes are discussed and the future development directions are also proposed. This review may provide new design thoughts for high performance carbonaceous Na storage anodes.     

Achieving High Volumetric Lithium Storage Capacity in Compact Carbon Materials with Controllable Nitrogen Doping

Although nanostructured/nanoporous carbon and silicon‐based materials are a potential replacement for graphite as cost‐effective anodes for lithium ion batteries (LIBs), their extremely low packing density leads to considerably reduced volumetric capacities. Herein, a highly compact carbon anode material constructed from sub‐2 nm nanosized graphitic domains is reported that exhibits excellent capacity density. By introducing a coordination agent in the synthesis precursors, an unusually high concentration of N‐doping (≈26.56 wt%) is achieved, which is mainly confined at the graphitic edges with the pyrrolic‐N and pyridinic‐N configurations. As further supported experimentally and theoretically, the edge‐N dopants, particularly the pyrrolic‐N, favor both ion diffusion kinetics and lithium storage via adsorption. Based on the lithiation‐state electrode volume, the compact anode shows a capacity density of 951 mAh cm_total^?3 that is comparable with Si anodes and surpasses all reported carbon‐based anodes, revealing its potential in promoting the performance of future LIBs.     

Electrochemical Mg2+ Displacement Driven Reversible Copper Extrusion/Intrusion Reactions for High-Rate Rechargeable Magnesium Batteries

Rechargeable magnesium batteries (RMBs) based on metal Mg anodes have shown great potential owing to the abundant natural resources, high volumetric capacity, and low safety hazard. Nevertheless, the development of RMBs is hampered by the sluggish kinetics of Mg²⁺ diffusion and the limited cyclability of cathode materials. Herein, nonstoichiometric copper selenide (Cu_2–xSe) are synthesized via a solution-based method and exploited as a durable cathode material based on ionic displacement mechanism for RMBs. The copper ions in the Se²⁻ based sub-lattices are reversibly exchanged by Mg²⁺ ions without causing lattice collapse. Owing to the same face-centered cubic Se²⁻ sub-lattices and similar unit cell size of Cu_2–xSe and MgSe, the energy barrier for lattice reconstruction during cycling processes is very low, significantly improving the rate performance, structural stability, and cycle life of the Cu_2–xSe cathode. Moreover, metal Cu is in situ generated during discharging, thus greatly facilitating electron transport. Comprehensive characterizations confirm that the Cu_2–xSe cathode undergoes reversible copper ion extrusion/reinjection during the discharge−charge steps. This work suggests the great potential for exploring high-performance electrode materials based on ionic displacement mechanism for advanced multivalent-ion secondary batteries.     

3D Porous Honeycomb-Like CoN-Ni3N/N-C Nanosheets Integrated Electrode for High-Energy-Density Flexible Supercapacitor

Transition metal nitrides (TMNs) are considered as potential electrode materials for high-performance energy storage devices. However, the structural instability during the electrochemical reaction process severely hinders their wide application. A general strategy to overcome this obstacle is to fabricate nanocomposite TMNs on the conducting substrate. Herein, the honeycomb-like CoN-Ni₃N/N-C nanosheets are in situ grown on a flexible carbon cloth (CC) via a mild solvothermal method with post-nitrogenizing treatment. As an integrated electrode for the supercapacitor, the optimized CoN-Ni₃N/N-C/CC achieves remarkable electrochemical performance due to the enhanced intrinsic conductivity and increased concentration of the active sites. In particular, the flexible quasi-solid-state asymmetric supercapacitor assembled with CoN-Ni₃N/N-C/CC cathode and VN/CC anode delivers an excellent energy density of 106 μWh cm⁻², maximum power density of 40 mW cm⁻², along with an outstanding cycle stability. This study provides a neoteric perspective on construction of high-performance flexible energy storage devices with novel metallic nitrides.     

Neuromorphic Carbon for Fast and Durable Potassium Storage

Graphitic carbon materials (GCs) are attractive as anodes for the industrialization of potassium ion batteries (PIBs). However, the poor cycle and rate performance of GC-based anodes hinder the development of PIBs. In this study, inspired by the nervous system, neuromorphic GCs (NGCs) are designed to use as potassium anodes with high cycling stability and excellent rate performance. The inherent neuromorphic nature of NGCs enables fast signal transmission via multiwalled carbon nanotubes (MWCNTs), which serve as efficient pathways for electronic transmission. Meanwhile, the low-stress properties of hollow carbon spheres effectively support the cycling stability of PIBs. As a result, NGC-based potassium anodes achieved an unprecedented cycle life over 18 months (2400 cycles) with a reversible capacity of up to 225 mAh g⁻¹ at a current density of 100 mA g⁻¹. Moreover, the novel anode exhibits exceptional rate performance (73.6 mAh g⁻¹ at 1 A g⁻¹). The research presented here offers a practical and straightforward method for potassium's long-term and high-rate storage and beyond.     

Empowering Metal Phosphides Anode with Catalytic Attribute toward Superior Cyclability for Lithium‐Ion Storage

Due to high capacity, moderate redox voltage, and relatively low polarization, metal phosphides (MPs) attract much attention as viable anode materials for lithium‐ion storage. However, severe capacity decay induced by the poor reversibility of discharge product (Li₃P) in these anodes suppresses their practical applications. Herein, it is first revealed that N‐doped carbon can effectively catalyze the oxidation of Li₃P by density functional theory calculations and activation experiments. By anchoring Ni₂P nanoparticles on N‐doped carbon sheets (Ni₂P@N‐C) via a facile method, an MP‐based anode rendered with a catalytic attribute is successfully fabricated for improving the reversibility of Li₃P during lithium‐ion storage. Benefiting from this design, not only can high capacity and rate performance be reached, but also an extraordinary cyclability and capacity retention be realized, which is the best among all other phosphides reported so far. By employing such a Ni₂P@N‐C composite and a commercialized active carbon as the anode and cathode, respectively, hybrid lithium‐ion capacitors can be fabricated with an ultrahigh energy density of 80 Wh kg^?1 at a power density of 12.5 kW kg^?1. This strategy of designing electrodes may be generalized to other energy storage systems whose cycling performance needs to be improved.     

A New Strategy to Effectively Suppress the Initial Capacity Fading of Iron Oxides by Reacting with LiBH4

In this work, a new facile and scalable strategy to effectively suppress the initial capacity fading of iron oxides is demonstrated by reacting with lithium borohydride (LiBH₄) to form a B‐containing nanocomposite. Multielement, multiphase B‐containing iron oxide nanocomposites are successfully prepared by ball‐milling Fe₂O₃ with LiBH₄, followed by a thermochemical reaction at 25–350 °C. The resulting products exhibit a remarkably superior electrochemical performance as anode materials for Li‐ion batteries (LIBs), including a high reversible capacity, good rate capability, and long cycling durability. When cycling is conducted at 100 mA g^?1, the sample prepared from Fe₂O₃–0.2LiBH₄ delivers an initial discharge capacity of 1387 mAh g^?1. After 200 cycles, the reversible capacity remains at 1148 mAh g^?1, which is significantly higher than that of pristine Fe₂O₃ (525 mAh g^?1) and Fe₃O₄ (552 mAh g^?1). At 2000 mA g^?1, a reversible capacity as high as 660 mAh g^?1 is obtained for the B‐containing nanocomposite. The remarkably improved electrochemical lithium storage performance can mainly be attributed to the enhanced surface reactivity, increased Li⁺ ion diffusivity, stabilized solid‐electrolyte interphase (SEI) film, and depressed particle pulverization and fracture, as measured by a series of compositional, structural, and electrochemical techniques.     

Strengthening the Interface between Flower‐Like VS4 and Porous Carbon for Improving Its Lithium Storage Performance

Carbon materials are frequently used to improve the cycle and rate performance of VS₄ as anode material for lithium ion batteries. However, the interfacial interaction between VS₄ and carbon has not been elucidated clearly. Various VS₄@C composites are prepared and the interface between VS₄ and porous carbon is investigated by X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and first‐principles calculations. The interfacial structure between VS₄ and carbon and the mechanism of flower‐like VS₄ growth on carbon substrate are revealed clearly. The results indicate that C?V bonds and C?O?V bonds are formed when oxygen functional groups are introduced into the porous carbon, and the C?V bonds and C?O?V bonds accelerate the electron transport and enhance structural stability of the VS₄@C composite. Deriving from the unique structure and robust interfacial interaction, the electrochemical performances of VS₄@C composite are much better than that of pure VS₄. Moreover, through the study of lithium storage mechanism of VS₄ anode, it is found that there is an irreversible amorphization change of the original VS₄ in the first cycle, and that during the following electrochemical process, the main storage behavior of lithium ions derives from the insertion?extraction reactions in the amorphous VS₄ with the reaction between V⁴⁺ and V³⁺.     

High-Power and Ultrastable Aqueous Calcium-Ion Batteries Enabled by Small Organic Molecular Crystal Anodes

Calcium ion batteries (CIBs) are pursued as potentially low-cost and safe alternatives to current Li-ion batteries due to the high abundance of calcium element. However, the large and divalent nature of Ca²⁺ leads to strong interaction with intercalation hosts, sluggish ion diffusion kinetics and low power output. Herein, a small molecular organic anode is reported, tetracarboxylic diimide (PTCDI), involving carbonyl enolization (CO↔C O⁻) in aqueous electrolytes, which bypasses the diffusion difficulties in intercalation-type electrodes and avoid capacity sacrifice for polymer organic electrodes, thus manifesting rapid and high Ca storage capacities. In an aqueous Ca-ion cell, the PTCDI presents a reversible capacity of 112 mAh g⁻¹, a high-capacity retention of 80% after 1000 cycles and a high-power capability at 5 A g⁻¹, which rival the state-of-the-art anode materials in CIBs. Experiments and simulations reveal that Ca ions are diffusing along the a axis tunnel to enolize carbonyl groups without being entrapped in the aromatic carbon layers. The feasibility of PTCDI anodes in practical CIBs is demonstrated by coupling with cost-effective Prussian blue analogous cathodes and CaCl₂ aqueous electrolyte. The appreciable Ca storage performance of small molecular crystals will spur the development of green organic CIBs.     

Low-Cost Zinc Substitution of Iron-Based Prussian Blue Analogs as Long Lifespan Cathode Materials for Fast Charging Sodium-Ion Batteries

Iron-based Prussian blue analogs (Fe-PBAs) are extensively studied as promising cathode materials for rechargeable sodium-ion batteries owing to their high theoretical capacity, low-cost and facile synthesis method. However, Fe-PBAs suffer poor cycle stability and low specific capacity due to the low crystallinity and irreversible phase transition during excess sodium-ion storage. Herein, a modified co-precipitation method to prepare highly crystallized PBAs is reported. By introducing an electrochemical inert element (Zn) to substitute the high-spin Fe in the Fe-PBAs (ZnFeHCF-2), the depth of charge/discharge is rationally controlled to form a highly reversible phase transition process for sustainable sodium-ion storage. Minor lattice distortion and highly reversible phase transition process of ZnFeHCF-2 during the sodium-ions insertion and extraction are proved by in-situ tests, which have significantly impacted the cycling stability. The ZnFeHCF-2 shows a remarkably enhanced cycling performance with capacity retention of 58.5% over 2000 cycles at 150 mA g⁻¹ as well as superior rate performance up to 6000 mA g⁻¹ (fast kinetics). Furthermore, the successful fabrication of the full cell on the as-prepared cathode and commercial hard carbon anode demonstrates their potential as high-performance electrode materials for large-scale energy storage systems.     

Unraveling the Voltage Failure Mechanism in Metal Sulfide Anodes for Sodium Storage and Improving Their Long Cycle Life by Sulfur-Doped Carbon Protection

Metal sulfides are emerging as a promising anode material for sodium-ion batteries with high reversible capacities and fast reaction kinetics, but achieving long-cycling-life remains a great challenge. Here, taking cobalt sulfide as an example, its electrochemical sodium-ion storage failure phenomenon is first reported, which indicates that the battery cannot reach the cut-off voltage during charging. Detailed analyses demonstrate that such failure may originate from the dissolution and escape of polysulfide intermediates, further reacting with the released copper-ions from the current collector and inducing the occurrence of the shuttle effect. Based on the explored failure mechanism, a sulfur-doped carbon matrix with polar carbon sulfur bonds, which can firmly immobilize the dissolved polysulfides, is deliberately introduced into the Co_1−xS active particles (Co_1−xS/s-C) to improve their cycle stability. Consequently, the cycle life of the Co_1−xS/s-C anode for sodium-ion storage is extended from the original 125 to present 2000 cycles, even at high-rate current densities. Moreover, utilizing the carbon current collector instead of traditional copper can effectively delay the occurrence of the failure phenomenon. The present work promotes better fundamental understanding of the structural evolution of metal sulfide anodes during cycles, and the solution strategy can be extended to apply in other metal sulfides (ZnS, NiS).     

Hard–Soft Carbon Composite Anodes with Synergistic Sodium Storage Performance

A series of hard–soft carbon composite materials is produced from biomass and oil waste and applied as low‐cost anodes for sodium‐ion batteries to study the fundamentals behind the dependence of Na storage on their structural features. A good reversible capacity of 282 mAh g^?1 is obtained at a current density of 30 mA g^?1 with a high initial Coulombic efficiency of 80% at a carbonization temperature of only 1000 °C by adjusting the ratio of hard to soft carbon. The performance is superior to the pure hard or soft carbon anodes produced at the same temperatures. This synergy between hard and soft carbon resulting in an excellent performance is due to the blockage of some open pores in hard carbon by the soft carbon, which suppresses the solid electrolyte interface formation and increases the reversible sodium storage capacity.