FeSe2 clusters with excellent cyclability and rate capability for sodium-ion batteries

Sodium-ion batteries (SIBs) have great promise for sustainable and economical energy-storage applications. Nevertheless, it is a major challenge to develop anode materials with high capacity, high rate capability, and excellent cycling stability for them. In this study, FeSe₂ clusters consisting of nanorods were synthesized by a facile hydrothermal method, and their sodium-storage properties were investigated with different electrolytes. The FeSe₂ clusters delivered high electrochemical performance with an ether-based electrolyte in a voltage range of 0.5–2.9 V. A high discharge capacity of 515 mAh·g^–1 was obtained after 400 cycles at 1 A·g^–1, with a high initial columbic efficiency of 97.4%. Even at an ultrahigh rate of 35 A·g^–1, a specific capacity of 128 mAh·g^–1 was achieved. Using calculations, we revealed that the pseudocapacitance significantly contributed to the sodium-ion storage, especially at high current rates, leading to a high rate capability. The high comprehensive performance of the FeSe₂ clusters makes them a promising anode material for SIBs.

     

High power and stable P-doped yolk-shell structured Si@C anode simultaneously enhancing conductivity and Li+ diffusion kinetics

Silicon is a low price and high capacity ancxje material for lithium-ion batteries.The yolk-shell structure can effectively accommodate Si expansion to improve stability.However,the limited rate performance of Si anodes can't meet people's growing demand for high power density.Herein,the phosphorus-doped yolk-shell Si@C materials(P-doped Si@C)were prepared through carbon coating on P-doped Si/SiO_xmatrix to obtain high power and stable devices.Therefore,the as-prepared P-doped Si@C electrodes delivered a rapid increase in Coulombic efficiency from 74.4%to 99.6%after only 6 cycles,high capacity retention of-95%over 800 cycles at 4 A·g^-1,and great rate capability(510 mAh·g^-1at 35 A·g^-1).As a result,P-doped Si@C anodes paired with commercial activated carbon and LiFePO₄cathode to assemble lithium-ion capacitor(high power density of?61,080 W·kg^-1at 20 A·g^-1)and lithium-ion full cell(good rate performance with 68.3 mAh·g^-1at 5 C),respectively.This work can provide an effective way tofurther improve power density and stability for energy storage devices.     

Fast and stable K-ion storage enabled by synergistic interlayer and pore-structure engineering

Carbon-based material has been regarded as one of the most promising electrode materials for potassium-ion batteries (PIBs). However, the battery performance based on reported porous carbon electrodes is still unsatisfactory, while the in-depth K-ion storage mechanism remains relatively ambiguous. Herein, we propose a facile “in situ self-template bubbling” method for synthesizing interlayer-tuned hierarchically porous carbon with different metallic ions, which delivers superior K-ion storage performance, especially the high reversible capacity (360.6 mAh·g⁻¹@0.05 A·g⁻¹), excellent rate capability (158.6 mAh·g⁻¹@10.0 A·g⁻¹) and ultralong high-rate cycling stability (82.8% capacity retention after 2,000 cycles at 5.0 A·g⁻¹). Theoretical simulation reveals the correlations between interlayer distance and K-ion diffusion kinetics. Experimentally, deliberately designed consecutive cyclic voltammetry (CV) measurements, ex situ Raman tests, galvanostatic intermittent titration technique (GITT) method decipher the origin of the excellent rate performance by disentangling the synergistic effect of interlayer and pore-structure engineering. Considering the facile preparation strategy, superior electrochemical performance and insightful mechanism investigations, this work may deepen the fundamental understandings of carbon-based PIBs and related energy storage devices like sodium-ion batteries, aluminum-ion batteries, electrochemical capacitors, and dual-ion batteries.

     

2D interspace confined growth of ultrathin MoS2-intercalated graphite hetero-layers for high-rate Li/K storage

Herein,a two-dimensional(2D)interspace-confined synthetic strategy is developed for producing MoS₂intercalated graphite(G-MoS₂)hetero-layers composite through sulfuring the pre-synthesized stage-1 MoCI5-graphite intercalation compound(M0 CI5-GIC).The in situ grown MoS₂nanosheets(3-7 layers)are evenly encapsulated in graphite layers with intimate interface thus forming layer-by-layer MoS₂-intercalated graphite composite.In this structure,the unique merits of MoS₂and graphite components are integrated,such as high capacity contribution of MoS₂and the flexibility of graphite layers.Besides,the tight interfacial interaction between hetero-layers optimizes the potential of conductive graphite layers as matrix for MoS₂.As a result,the G-MoS₂exhibits a high reversible Li+storage of 344 mAh·g^-1even at 10 A·g^-1and a capacity of 539.9 mAh·g^-1after 1,500 cycles at 5 A·g^-1.As for potassium ion battery,G-MoS₂delivers a reversible capacity of 377.0 mAh·g^-1at 0.1 A·g^-1and 141.2 mAh·g^-1even at 2 A·g^-1.Detailed experiments and density functional theory calculation demonstrate the existence of hetero-layers enhances the diffusion rates of Li⁺and K⁺.This graphite interspace-confined synthetic methodology would provide new ideas for preparing function-integrated materials in energy storage and conversion,catalysis or other fields.     

Graphene oxide-decorated Fe<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> microflowers as a promising anode for lithium and sodium storage

Mixed transition metal oxides (MTMOs) have received intensive attention as promising anode materials for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). In this work, we demonstrate a facile one-step water-bath method for the preparation of graphene oxide (GO) decorated Fe₂(MoO₄)₃ (FMO) microflower composite (FMO/GO), in which the FMO is constructed by numerous nanosheets. The resulting FMO/GO exhibits excellent electrochemical performances in both LIBs and SIBs. As the anode material for LIBs, the FMO/GO delivers a high capacity of 1,220 mAh·g^–1 at 200 mA·g^–1 after 50 cycles and a capacity of 685 mAh·g^–1 at a high current density of 10 A·g^–1. As the anode material for SIBs, the FMO/GO shows an initial discharge capacity of 571 mAh·g^–1 at 100 mA·g^–1, maintaining a discharge capacity of 307 mAh·g^–1 after 100 cycles. The promising performance is attributed to the good electrical transport from the intimate contact between FMO and graphene oxide. This work indicates that the FMO/GO composite is a promising anode for high-performance lithium and sodium storage.

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Improved Na storage and Coulombic efficiency in TiP2O7@C microflowers for sodium ion batteries

Ti-based anode materials in sodium ion batteries have attracted extensive interests due to its abundant resources,low toxicity,easy synthesis and long cycle life.However,low Coulombic efficiency and limited specific capacity affect their applications.Here,cubic-phase TiP₂O₇is examined as anode materials,using in-situ/ex-situ characterization techniques.It is concluded that the redox reactions of Ti4⁺/Ti³⁺and Ti³⁺/Ti⁰consecutively occur during the discharge/charge processes,both of which are highly reversible.These reactions make the specific capacity of TiP₂O₇even higher than the case of TiO2 that only contains a simple anion,0^2-.Interestingly,Ti species participate only one of the redox reactions,due to the remarkable difference in local structures related to the sodiation process.The stable discharge/charge products in TiP₂O₇reduce the side reactions and improve the Coulombic efficiency as compared to T i02.These features make it a promising Ti-based anode for sodium ion batteries.Therefore,TiP₂O₇@C microflowers exhibit excellent electrochemical performances,?109 mAh·g^-1after 10,000 cycles at 2 A·g^-1,or 95.2 mAh·g^-1at 10 A·g^-1.The results demonstrate new opportunities for advanced Ti-based anodes in sodium ion batteries.     

Facile fabrication of integrated three-dimensional C-MoSe<Subscript>2</Subscript>/reduced graphene oxide composite with enhanced performance for sodium storage

Scrupulous design and fabrication of advanced electrode materials are vital for developing high-performance sodium ion batteries. Herein, we report a facile one-step hydrothermal strategy for construction of a C-MoSe₂/rGO composite with both high porosity and large surface area. Double modification of MoSe₂ nanosheets is realized in this composite by introducing a reduced graphene oxide (rGO) skeleton and outer carbon protective layer. The MoSe₂ nanosheets are well wrapped by a carbon layer and also strongly anchored on the interconnected rGO network. As an anode in sodium ion batteries, the designed C-MoSe₂/rGO composite delivers noticeably enhanced sodium ion storage, with a high specific capacity of 445 mAh·g^-1 at 200 mA·g^-1 after 350 cycles, and 228 mAh·g^-1 even at 4 A·g^-1; these values are much better than those of C-MoSe₂ nanosheets (258 mAh·g^-1 at 200 mA·g^-1 and 75 mAh·g^-1 at 4 A·g^-1). Additionally, the sodium ion storage mechanism is investigated well using ex situ X-ray diffraction and transmission electron microscopy methods. Our proposed electrode design protocol and sodium storage mechanism may pave the way for the fabrication of other high-performance metal diselenide anodes for electrochemical energy storage.

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Nanostructured Bi<Subscript>2</Subscript>S<Subscript>3</Subscript> encapsulated within three-dimensional N-doped graphene as active and flexible anodes for sodium-ion batteries

Sodium-ion batteries (SIBs) have been increasingly attracting attention as a sustainable alternative to lithium-ion batteries for scalable energy storage. The key to advanced SIBs relies heavily upon the development of reliable anodes. In this respect, Bi₂S₃ has been extensively investigated because of its high capacity, tailorable morphology, and low cost. However, the common practices of incorporating carbon species to enhance the electrical conductivity and accommodate the volume change of Bi₂S₃ anodes so as to boost their durability for Na storage have met with limited success. Herein, we report a simple method to realize the encapsulation of Bi₂S₃ nanorods within three-dimensional, nitrogen-doped graphene (3DNG) frameworks, targeting flexible and active composite anodes for SIBs. The Bi₂S₃/3DNG composites displayed outstanding Na storage behavior with a high reversible capacity (649 mAh·g^–1 at 62.5 mA·g^–1) and favorable durability (307 and 200 mAh·g^–1 after 100 cycles at 125 and 312.5 mA·g^–1, respectively). In-depth characterization by in situ X-ray diffraction revealed that the intriguing Na storage process of Bi₂S₃ was based upon a reversible reaction. Furthermore, a full, flexible SIB cell with Na_0.4MnO₂ cathode and as-prepared composite anode was successfully assembled, and holds a great promise for next-generation, wearable energy storage applications.

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Unveiling nanoplates-assembled Bi2MoO6 microsphere as a novel anode material for high performance potassium-ion batteries

Bismuth (Bi)-based electrode has aroused tremendous interest in potassium-ion batteries (PIBs) on account of its low cost, high electronic conductivity, low charge voltage and high theoretical capacity. However, the rapid capacity fading and poor lifespan induced by the normalized volume expansion (up to ~ 406%) and serious aggregation of Bi during cycling process hinder its application. Herein, bismuth molybdate (Bi₂MoO₆) microsphere assembled by 2D nanoplate units is successfully prepared by a facile solvothermal method and demonstrated as a promising anode for PIBs. The unique microsphere structure and the self-generated potassium molybdate (K-Mo-O species) during the electrochemical reactions can effectively suppress mechanical fracture of Bi-based anode originated from the volume variation during charge/discharge of the battery. As a result, the Bi₂MoO₆ microsphere without hybridizing with any other conductive carbon matrix shows superior electrochemical performance, which delivers a high reversible capacity of 121.7 mAh·g⁻¹ at 100 mA·g⁻¹ over 600 cycles. In addition, the assembled perylenetetracarboxylic dianhydride (PTCDA)//Bi₂MoO₆ full-cell coupled with PTCDA cathode demonstrates the potential application of Bi₂MoO₆ microsphere. Most importantly, the phase evolution of Bi₂MoO₆ microsphere during potassiation/depotassiation process is successfully deciphered by ex situ X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), and transmission electron microscopy (TEM) technologies, which reveals a combination mechanism of conversion reaction and alloying/dealloying reaction for Bi₂MoO₆ anode. Our findings not only open a new way to enhance the performance of Bi-based anode in PIBs, but also provide useful implications to other alloy-type anodes for secondary alkali-metal ion batteries.

     

High N-doped hierarchical porous carbon networks with expanded interlayers for efficient sodium storage

Sodium-ion batteries (SIBs) have been attracting considerable attention as a promising candidate for large-scale energy storage because of the abundance and low-cost of sodium resources. However, lack of appropriate anode materials impedes further applications. Herein, a novel self-template strategy is designed to synthesize uniform flowerlike N-doped hierarchical porous carbon networks (NHPCN) with high content of N (15.31 at.%) assembled by ultrathin nanosheets via a self-synthesized single precursor and subsequent thermal annealing. Relying on the synergetic coordination of benzimidazole and 2-methylimidazole with metal ions to produce a flowerlike network, a self-formed single precursor can be harvested. Due to the structural and compositional advantages, including the high N doping, the expanded interlayer spacing, the ultrathin two-dimensional nano-sized subunits, and the three-dimensional porous network structure, these unique NHPCN flowers deliver ultrahigh reversible capacities of 453.7 mAh·g⁻¹ at 0.1 A·g⁻¹ and 242.5 mAh·g⁻¹ at 1 A·g⁻¹ for 2,500 cycles with exceptional rate capability of 5 A·g⁻¹ with reversible capacities of 201.2 mAh·g⁻¹. The greatly improved sodium storage performance of NHPCN confirms the importance of reasonable engineering and synthesis of hierarchical carbon with unique structures.

     

Rational design of novel ultra-small amorphous Fe2O3 nanodots/graphene heterostructures for all-solid-state asymmetric supercapacitors

Constructing graphene-based heterostructures with large interfacial area is an efficient approach to enhance the electrochemical performance of supercapacitors but remains great challenges in their synthesis.Herein,a novel ultra-small amorphous Fe₂O₃nanodots/graphene heterostructure(a-Fe₂O₃NDs/RGO)aerogel was facilely synthesized via excessive metal-ion-induced self-assembly and subsequent calcination route using Prussian blue/graphene oxide(PB/GO)composite aerogel as precursors.The deliberately designed a-Fe₂O₃NDs/RGO heterostructure offers a highly interconnected porous conductive network,large heterostructure interfacial area,and plenty of accessible active sites,greatly facilitating the electron transfer,electrolyte diffusion,and pseudocapacitive reactions.The obtained a-Fe₂O₃NDs/RGO aerogel could be used as flexible free-standing electrodes after mechanical compression,which exhibited a significantly enhanced specific capacitance of 347.4 F·g^-1at 1 A·g^-1,extraordinary rate capability of 184 F·g^-1at 10 A·g^-1,and decent cycling stability.With the as-prepared a-Fe₂O₃NDs/RGO as negative electrodes and the Co₃O₄NDs/RGO as positive electrodes,an all-solid-state asymmetric supercapacitor(a-Fe₂O₃NDs/RGO//Co₃O₄NDs/RGO asymmetric supercapacitor(ASC))was assembled,which delivered a high specific capacitance of 69.1 F·g^-1at 1 A·g^-1and an impressive energy density of 21.6 W·h·k·g^-1at 750 W·k·g^-1,as well as good cycling stability with a capacity retention of 94.3%after 5,000 cycles.This work provides a promising avenue to design high-performance graphene-based composite electrodes and profound inspiration for developing advanced flexible energy-storage devices.     

Flower-like NiCo2S4 nanosheets with high electrochemical performance for sodium-ion batteries

A three-dimensional flower-like NiCo₂S₄ formed by two-dimensional nanosheets is synthesized by a facile hydrothermal method and utilized as the anode for sodium-ion batteries. Studies have shown that materials can achieve the best performance under the ether-based electrolyte system with voltage ranging from 0.3 to 3 V, which could effectively avoid the dissolution of polysulfides and over-discharge of the material. Here, sodium storage mechanism and charge compensation behaviors of this ternary metal sulfide are comprehensively investigated by ex situ X-ray diffraction. Moreover, ex situ Raman spectra, ex situ X-ray photoelectron spectroscopy and transmission electron microscopy measurements are used to related tests for the first time. Additionally, quantitative kinetic analysis unravels that sodium storage partially depends on the pseudocapacitance mechanism, resulting in good specific capacity and excellent rate performance. The initial discharge capacity is as high as 748 mAh·g⁻¹ at a current density of 0.1 A·g⁻¹ with the initial coulomb efficiency of 94%, and the capacity can still maintain at 580 mAh·g⁻¹ with the Coulomb efficiency close to 100% after following 50 cycles. Moreover, by the long cycle test at a high current density of 2 A·g⁻¹, the capacity can still reach at 376 mAh·g⁻¹ after over 500 cycles.

     

Recent advances in anode materials for potassium-ion batteries: A review

Potassium-ion batteries (PIBs) are appealing alternatives to conventional lithium-ion batteries (LIBs) because of their wide potential window, fast ionic conductivity in the electrolyte, and reduced cost. However, PIBs suffer from sluggish K⁺ reaction kinetics in electrode materials, large volume expansion of electroactive materials, and the unstable solid electrolyte interphase. Various strategies, especially in terms of electrode design, have been proposed to address these issues. In this review, the recent progress on advanced anode materials of PIBs is systematically discussed, ranging from the design principles, and nanoscale fabrication and engineering to the structure-performance relationship. Finally, the remaining limitations, potential solutions, and possible research directions for the development of PIBs towards practical applications are presented. This review will provide new insights into the lab development and real-world applications of PIBs.

     

Yolk–shell-structured (Fe0.5Ni0.5)9S8 solid-solution powders: Synthesis and application as anode materials for Na-ion batteries

Multicomponent metal sulfide materials with a yolk–shell structure and a single phase were studied for the first time as anode materials for sodium-ion batteries. Yolk–shell-structured Fe–Ni–O powders with a molar ratio of iron and nickel components of 1/1 were prepared via one-pot spray pyrolysis. The prepared Fe–Ni–O powders were transformed into yolk–shell-structured (Fe_0.5Ni_0.5)₉S₈ solid-solution powders via a sulfidation process. The initial discharge and charge capacities of the (Fe_0.5Ni_0.5)₉S₈ powders at a current density of 1 A·g⁻¹ were 601 and 504 mA·h·g⁻¹, respectively. The discharge capacities of the (Fe_0.5Ni_0.5)₉S₈ powders for the 2^nd and 100^th cycle were 530 and 527 mA·h·g⁻¹, respectively, and their corresponding capacity retention measured from the 2^nd cycle was 99%. The (Fe_0.5Ni_0.5)₉S₈ powders had high initial discharge and charge capacities at a low current density of 0.1 A·g⁻¹, and the reversible discharge capacity decreased slightly from 568 to 465 mA·h·g⁻¹ as the current density increased from 0.1 to 5.0 A·g⁻¹. The synergetic effect of the novel yolk–shell structure and the multicomponent sulfide composition of the (Fe_0.5Ni_0.5)₉S₈ powders resulted in excellent sodium-ion storage performance.

     

Heterogeneous lamellar-edged Fe-Ni(OH)2/Ni3S2 nanoarray for efficient and stable seawater oxidation

Development of efficient non-precious catalysts for seawater electrolysis is of great significance but challenging due to the sluggish kinetics of oxygen evolution reaction(OER)and the impairment of chlorine electrochemistry at anode.Herein,we report a heterostructure of Ni₃S₂nanoarray with secondary Fe-Ni(OH)₂lamellar edges that exposes abundant active sites towards seawater oxidation.The resultant Fe-Ni(OH)₂/Ni₃S₂nanoarray works directly as a free-standing anodic electrode in alkaline artificial seawater.It only requires an overpotential of 269 mV to afford a current density of 10 mA·cm^-2and the Tafel slope is as low as 46 m V·dec^-1.The 27-hour chronopotentiometry operated at high current density of 100 mA·cm^-2shows negligible deterioration,suggesting good stability of the Fe-Ni(OH)₂/Ni₃S₂@NF electrode.Faraday efficiency for oxygen evolution is up to?95%,revealing decent selectivity of the catalyst in saline water.Such desirable catalytic performance could be benefitted from the introduction of Fe activator and the heterostructure that offers massive active and selective sites.The density functional theory(DFT)calculations indicate that the OER has lower theoretical overpotential than Cl₂ evolution reaction in Fe sites,which is contrary to that of Ni sites.The experimental and theoretical study provides a strong support for the rational design of high-performance Fe-based electrodes for industrial seawater electrolysis.     

Walnut-inspired microsized porous silicon/graphene core–shell composites for high-performance lithium-ion battery anodes

Silicon is considered an exceptionally promising alternative to the most commonly used material, graphite, as an anode for next-generation lithium-ion batteries, as it has high energy density owing to its high theoretical capacity and abundant storage. Here, microsized walnut-like porous silicon/reduced graphene oxide (P-Si/rGO) core–shell composites are successfully prepared via in situ reduction followed by a dealloying process. The composites show specific capacities of more than 2,100 mAh·g^?1 at a current density of 1,000 mA·g^?1, 1,600 mAh·g^?1 at 2,000 mA·g^?1, 1,500 mAh·g^?1 at 3,000 mA·g^?1, 1,200 mAh·g^?1 at 4,000 mA·g^?1, and 950 mAh·g^?1 at 5,000 mA·g^?1, and maintain a value of 1,258 mAh·g^?1 after 300 cycles at a current density of 1,000 mA·g^?1. Their excellent rate performance and cycling stability can be attributed to the unique structural design: 1) The graphene shell dramatically improves the conductivity and stabilizes the solid–electrolyte interface layers; 2) the inner porous structure supplies sufficient space for silicon expansion; 3) the nanostructure of silicon can prevent the pulverization resulting from volume expansion stress. Notably, this in situ reduction method can be applied as a universal formula to coat graphene on almost all types of metals and alloys of various sizes, shapes, and compositions without adding any reagents to afford energy storage materials, graphene-based catalytic materials, graphene-enhanced composites, etc.

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Supersaturated bridge-sulfur and vanadium co-doped M0S2 nanosheet arrays with enhanced sodium storage capability

The low specific capacity and sluggish electrochemical reaction kinetics greatly block the development of sodium-ion batteries (SIBs). New high-performance electrode materials will enhance development and are urgently required for SIBs. Herein, we report the preparation of supersaturated bridge-sulfur and vanadium co-doped MoS₂ nanosheet arrays on carbon cloth (denoted as V-MoS_2+x/CC). The bridge-sulfur in MoS₂ has been created as a new active site for greater Na⁺ storage. The vanadium doping increases the density of carriers and facilitates accelerated electron transfer. The synergistic dual-doping effects endow the V-MoS_2+x/CC anodes with high sodium storage performance. The optimized V-MoS_2.49/CC gives superhigh capacities of 370 and 214 mAh·g⁻¹ at 0.1 and 10 A·g⁻¹ within 0.4−3.0 V, respectively. After cycling 3,000 times at 2 A·g⁻¹, almost 83% of the reversible capacity is maintained. The findings indicate that the electrochemical performances of metal sulfides can be further improved by edge-engineering and lattice-doping co-modification concept.

     

Infiltrating lithium into carbon cloth decorated with zinc oxide arrays for dendrite-free lithium metal anode

Lithium metal anode for batteries has attracted extensive attentions, but its application is restricted by the hazardous dendritic Li growth and dead Li formation. To address these issues, a novel Li anode is developed by infiltrating molten Li metal into conductive carbon cloth decorated with zinc oxide arrays. In carbonate-based electrolyte, the symmetric cell shows no short circuit over 1,500 h at 1 mA·cm⁻², and stable voltage profiles at 3 mA·cm⁻² for ∼ 300 h cycling. A low overpotential of ∼ 243 mV over 350 cycles at a high current density of 10 mA·cm⁻² is achieved, compared to the seriously fluctuated voltage and fast short circuit in the cell using bare Li metal. Meanwhile, the asymmetric cell withstands 1,000 cycles at 10 C (1 C = 167 mAh·g⁻¹) compared to the 210 cycles for the cell using bare Li anode. The excellent performance is attributed to the well-regulated Li plating/stripping driven from the formation of LiZn alloy on the wavy carbon fibers, resulting in the suppression of dendrite growth and pulverization of the Li electrode during cycling.

     

Facile synthesis of porous germanium-iron bimetal oxide nanowires as anode materials for lithium-ion batteries

Germanium-based oxide has been found to be a promising high-capacity anode material for lithium-ion batteries (LIBs). However, it exhibits poor electrochemical performance because of the drastic volume change during cycling. Herein, we designed porous Ge-Fe bimetal oxide nanowires (Ge-Fe-O_x-700 NWs) by a large-scale and facile solvothermal reaction. When used as the anode material for LIBs, these Ge-Fe-O_x-700 NWs exhibited superior electrochemical performance (～ 1,120 mAh·g^?1 at a current density of 100 mA·g^?1) and good cycling performance (～ 750 mAh·g^?1 after 50 cycles at a current density of 100 mA·g^?1). The improved performance is due to the small NW diameter, which allows for better accommodation of the drastic volume changes and zero-dimensional nanoparticles, which shorten the diffusion length of ions and electrons.

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Exploiting oleic acid to prepare two-dimensional assembly of Si@graphitic carbon yolk-shell nanoparticles for lithium-ion battery anodes

Carbon coating has been a routine strategy for improving the performance of Si-based anode materials for lithium-ion batteries. The ability to tailor the thickness, homogeneity and graphitization degree of carbon-coating layers is essential for addressing issues that hamper the real applications of Si anodes. Herein, we report the construction of two-dimensional (2D) assemblies of interconnected Si@graphitic carbon yolk-shell nanoparticles (2D-Si@gC) from commercial Si powders by exploiting oleic acid (OA). The OA molecules act as both the surface-coating ligands for facilitating 2D nanoparticle assembly and the precursor for forming uniform and conformal graphitic shells as thin as 4 nm. The as-prepared 2D-Si@gC with rationally designed void space exhibits excellent rate capability and cycling stability when used as anode materials for lithium-ion batteries, delivering a capacity of 1,150 mAh·g⁻¹ at an ultrahigh current density of 10 A·g⁻¹ and maintaining a stabilized capacity of 1,275 mAh·g⁻¹ after 200 cycles at 4 A·g⁻¹. The formation of yolk-shell nanoparticles confines the deposition of solid electrolyte interphase (SEI) onto the outer carbon shell, while simultaneously providing sufficient space for volumetric expansion of Si nanoparticles. These attributes effectively mitigate the thickness variations of the entire electrode during repeated lithiation and delithiation, which combined with the unique 2D architecture and interconnected graphitic carbon shells of 2D-Si@gC contributes to its superior rate capability and cycling performance.