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Microsized‐silicon (µ‐Si, >1 µm) is one of the ideal anodes for lithium‐ion batteries due to its low‐cost, high tap density, and high specific capacity. However, during repeated lithiation/delithiation processes, µ‐Si undergoes huge volume changes. This leads to continued capacity loss during cycling due to severe particle pulverization, separation from the conductive network and uncontrolled growth of an unstable solid‐electrolyte interphase (SEI). Herein, an electrode construction strategy is proposed by carbonization of the slurry‐casting µ‐Si electrode. The organic binder serves as both carbon resource and physical framework, which is carbonized to form a carbon binder that is chemically bonded with the µ‐Si particles and within the electrode. The electrode with carbon binder ensures stable electric channel and promotes formation of a stable and passivating SEI at the interface with a high µ‐Si content up to 82 wt%. The carbon binder offers physical buffer that shield against localized strain and modifies the surface reactivity, which enables a high initial Coulombic efficiency (91.85%) and stable cycle performance at commercial‐level areal capacities (2 mAh cm−2). This work offers an easily scalable yet practical approach for the current battery industry without any electrolyte modification or complicated manufacturing methods. [ABSTRACT FROM AUTHOR]

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 Co1−xS active particles (Co1−xS/s‐C) to improve their cycle stability. Consequently, the cycle life of the Co1−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). [ABSTRACT FROM AUTHOR]

Transition‐metal sulfides (TMSs) are extensively investigated as anodes of low‐cost sodium‐ion batteries (SIBs) and potassium‐ion batteries (KIBs) due to their abundant resources and high theoretical capacity. However, their poor cyclability and low initial coulombic efficiency (ICE) in ester‐based electrolytes severely impede their application in SIBs and KIBs. To overcome these drawbacks, ether‐based electrolytes are considered as alternatives, but its fundamental principle remains rarely reported and poorly understood. Herein, the electrochemical performance of MoS2@C electrodes is explored using both carbonate and ether‐based solvents. The MoS2@C exhibits a higher ICE and Na/K‐ion storage capacity (a reversible specific capacity of 625 mAh g−1 with ICE of 80% for SIBs, and a capacity of 241 mAh g−1 with ICE of 81% for KIBs, respectively) in dimethyl ether (DME) electrolytes than in ethylene carbonate and diethylene carbonate (EC/DEC) electrolytes. Experimental measurements and theoretical calculation show that the DME electrolytes help to optimize the solid‐electrolyte interphase (SEI) composition, facilitate charge transport, reduce the energy barrier for Na/K‐ions migration and reinforcing geometry architecture, thus endowing excellent electrochemical performance. Importantly, this electrolyte optimization solution can be extended to other TMSs, such as Fe7S8@C anodes, demonstrating an exact match between the TMSs and DME electrolytes. [ABSTRACT FROM AUTHOR]

Although hard carbon has been considered as one of the most promising anodes for sodium-ion batteries, however, the poor performance and ambiguous sodium storage mechanism limit the further development. Herein, a novel epoxy phenol novolac resin is used as precursor for the first time to construct excellent electrochemical performance anode by pyrolyze it at different temperature. The results demonstrate that the plateau region in discharge curve of hard carbon is ascribed to Na insertion into the long-range ordered carbon structure. Improving ordering degree with suitable interlayer distance can both enhance the plateau capacity and total capacity. With the increasing of pyrolysis temperature, the graphitization degree of hard carbon is gradually enhanced. The cured epoxy phenol novolac resin pyrolyzed at 1800 °C delivers the reversible capacity of 480.3 mAh g−1 at 50 mA g−1, high initial coulombic efficiency of 84.6%, and capacity retention of 92% after 1000 cycles at 500 mA g−1. The "adsorption-intercalation mechanism" for Na storage in EPNHC-1800 is verified by in-situ Raman spectroscopy analysis. We believe that the sodium storage mechanism of hard carbon is "adsorption-intercalation-filling", namely, the adsorption of Na-ions on the surface of carbon layers providing the slope capacity, the intercalation of Na-ions between carbon layers and filling in the nanopores providing the plateau capacity. This study offers a novel precursor to synthesize low cost and high-performance hard carbon anode material for sodium-ion batteries, delivering great opportunity for the commercialization of anode. [Display omitted] • Hard carbon is constructed by using novel epoxy phenol novolac resin as precursor. • The structural evolution of hard carbon from precursor is studied systematically. • The anode delivers the high reversible capacity of 480.3 mAh g−1 at 50 mA g−1. • The anode material shows remarkable capacity retention of 92% after 1000 cycles. • "Adsorption-intercalation-filling" is dominated in the sodium storage mechanism. [ABSTRACT FROM AUTHOR]

The slow kinetics and lithium deposition of graphite anode are considered the key limitations of fast-charging lithium-ion batteries. Expanded graphite has shown tremendous potential for the improvement of rate performance due to its massive active sites released and lifted lithium storage platform. However, the risk of structural collapse caused by fast charging will reduce the cycling life of the expanded graphite anode. Herein, this study designed a stable structure of expanded graphite by filling its layer pores with pitch-derived soft carbon (EGC). The honeycomb-like EGC is a great fast-charging candidate material with rich active sites, enlarged ion transport channels, and efficient ion transport interfaces. As the experimental and simulation results, the EGC electrode demonstrated significantly fast lithium-ions storage kinetics and durable long cycle life, compared to commercial fast-charging graphite anode. Notably, the EGC//LiNi 0.8 Co 0.1 Mn 0.1 O 2 full cell delivered a superior fast-charging and stability performance (near 20 min charging for 80 % State of Charge). The simple multifunctional modification strategy for graphite anode in this work provides a new approach for superior fast-charging lithium-ion batteries. A stable EGC structure prepared by pitch-derived soft carbon filling in the layer pores of expanded graphite, showing great fast-charging potential and durable long cycle life, with rich active sites, enlarged ion transport channels, and efficient ion transport interfaces. Notably, the EGC//LiNi 0.8 Co 0.1 Mn 0.1 O 2 full cell delivered a superior fast-charging and stability performance (near 20 min charging for 80 % State of Charge). [Display omitted] • A robust structure (EGC) of expanded graphite frame regulated with soft carbon, boosts lithium-ion diffusion kinetics. • EGC electrode demonstrated significantly fast lithium-ions storage and durable long cycle life. • EGC//NCM811 full cell shows a firm capacity retention rate and durable cycling behavior. [ABSTRACT FROM AUTHOR]

It is a significant way to improve the sodium storage performance of mesocarbon microbeads (MCMBs) by adjusting the size and microcrystalline structure of it. A petroleum-based MCMBs with an ultra-large size and loose microcrystalline structure was synthesized by introducing functionalized graphene (FNG). The results indicate that the FNG can hinder the ordered stacking of planar aromatic macromolecules, prevent the coalescence and prolong the growth time of mesophase spheres. Mesophase spheres are easier to grow to an ultra-large size with looser microcrystalline structure. The MCMBs with a size of 250 µm and a larger microcrystalline spacing can be achieved by adding 1.0 wt% FNG during the polycondensation process. Such MCMBs deliver a competitive specific capacity of 123.4 mAh g−1 at a current density of 1.0 A g−1 with a high initial coulombic efficiency of 81.79% and an excellent stability of cycle performance when applied as anode of SIBs. This work provides a valuable and efficient method to enhance the SIB performance by designing the size and microcrystalline structure of MCMBs. [Display omitted] • Providing a new method to synthesize ultra-large sized mesocarbon microbeads. • The microcrystalline spacing of mesocarbon microbeads were expanded effectively. • The sodium storage performance was improved by the application of ultra-large sized MCMBs. [ABSTRACT FROM AUTHOR]

This work demonstrated the mechanism that sulfur replaces part of nitrogen and binds covalently to carbon to form C S bonds, where S-rich hollow carbon nanofibers (NHCFs-S) are synthesized. The new NHCFs-S anode shows excellent K-ion storage properties due to enhanced electronic conductivity, Faraday reaction activity and pseudocapacitive adsorption behavior. [Display omitted] • The tendency of sulfur to replace pyrrolic nitrogen is demonstrated. • The sulfur replaces part of nitrogen atoms and form C S bonds with binds covalently to carbon skeleton. • The introduction of high S-doping results to the improvement of electrochemical reaction dynamics. • For potassium-ion batteries, the NHCFs-S electrode delivers a desirable rate capability of 261 mAh g−1 at 5.0 A g−1. Sulfur doping can bridge durable active sites to induce C S electron coupling to produce unparalleled Faraday conversion, breaking the limitations of ion storage capacitance, and therefore it is an effective way to design carbon materials with improved electrochemical performance. However, sulfur doping methods, especially how to design S-rich by atomic transition among carbon membered-ring structure of anodes remains a confusing topic. Herein, the linear relationship between sulfur and nitrogen content is found, and the tendency of sulfur to replace pyrrolic nitrogen is demonstrated. The sulfur replaces part of nitrogen atoms and form C S bonds with binds covalently to carbon skeleton, where S-rich hollow carbon nanofibers (NHCFs-S) are synthesized. The introduction of high sulfur doping in carbon results to the improvement of conductivity, Faraday reaction activity and pseudocapacitive adsorption behavior. For potassium-ion batteries, the fabricated NHCFs-S material delivers a 369 mAh/g high capacity at 1.0 A/g after 100 cycles with 80 % initial coulombic efficiency and a desirable rate capability of 261 mAh/g even at 5.0 A/g. This work provides a selection for high-performance anodes design and a reference for the future research of high sulfur doped in carbon materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • N-doped CNTs with unique 1D nanotubular structure are prepared by a novel strategy. • The high N-doping and tunable interlayer spacing are exhibited for N-CNTs. • N-CNTs display excellent high-rate capability and long-term cycling performance. • Kinetic analysis and ex-situ Raman reveal the sodium storage mechanism. • DFT demonstrates the strong adsorption ability for Na-DME on pyrrolic N site. The graphitic carbon nitride (g-C 3 N 4) as a promising high-nitrogen carbon material has attracted abundant attentions in energy storage field. In this work, the N-doped carbon nanotubes (N-CNTs) are synthesized through a facile one-step pyrolysis of g-C 3 N 4 precursor assisting by Ni catalyst. The obtained N-CNTs possess unique one-dimensional (1D) nanotubular structure, high conductivity, suitable N-doping around 8.73 ∼ 14.72 at.% and tunable interlayer distance up to 0.462 nm which can accommodate sufficiently Na+. Serving as anodes for sodium-ion batteries (SIBs), the resultant N-CNTs exhibit a promising specific capacity of 290.3 mAh⋅g−1 at 0.05 A⋅g−1 and superior rate capability of 164.5 mAh⋅g−1 at 10 A⋅g−1, as well as excellent long-term cycling performance at 0.5 A⋅g−1 for 1000 cycles. Further kinetic analysis and ex-situ Raman reveal the sodium storage mechanism of N-CNTs, which simultaneously combines the diffusion and the dominated capacitive mechanisms together. According to the first principles, density functional theory (DFT) calculations from the perspective of atomic structure further demonstrate that the superior electrochemical performance of N-CNTs is attributed to the strong adsorption interaction between Na+ in ether-based electrolyte and pyrrolic N site. This work provides a facile method to synthesize N-doped carbon nanotube with remarkable electrochemical performance, which is a promising nanotube-structured anode material for the practical application of SIBs. [ABSTRACT FROM AUTHOR]

• The facile and cost-effective preparation process of yolk-shell Si/C composites and modification methods with high scalability. • The designed pore channel structures endowing the optimal lithium storage capacity and volume change tolerance. • The high crystallinity ensures the outstanding electronic conductivity and robust carbon shell. • The optimal Si/C composite with a well matching microstructure of carbon shell exhibits excellent cycling performance and rate capacity (55% retention at 300th cycle, 743 mAh g−1 at 2 A g−1). • Correlation between microstructural feature (crystallinity and pores) of the carbon shell and the electrochemical behaviors of the Si/C electrodes is established. Silicon-carbon composites have proved to be effective in addressing the issues of silicon anodes, however, few works focus on understanding the effect of the microstructure of the carbon component on their electrochemical performance. Herein, we prepare a series of yolk-shell structured silicon-carbon nanocomposites with adequate voids through a facile and scalable process. By deliberately selecting the pitch species and delicately adjusting the heat treatment temperature, the microcrystal texture and pore structure of the soft carbon can be easily tuned. Finally, a well matching of the crystalline and pore structure ensure the rapid charge transport and the good structural robustness, further endowing the optimal lithium storage, cycle performance and rate capability of the electrodes. The Si/C composite with an optimized carbon shell delivers a reliable cycle stability with a capacity retention ratio of 55% after 300 cycles at 0.2 A g−1 and a remained capacity of 743 mAh g−1 at a high current density of 2.0 A g−1. Importantly, the correlation between the lithium storage of the Si/C composites and the microstructure features (crystallinity and pores) of the carbon shell has been established, which may provide an effective guidance for optimizing the microstructure design of the promising Si/C anode materials. We established the relationship between designed microstructural feature (crystallinity and pores) of the carbon shell and corresponding electrochemical performance of the Si/C anodes. Image, graphical abstract [ABSTRACT FROM AUTHOR]