As the demand for high-energy-density lithium-ion batteries grows, research increasingly focuses on high-capacity anode materials to substitute low-capacity graphite. Silicon is a promising, high-theoretical-capacity (4200 mAh g-1) anode material. However, suffering from severe volumetric expansion (approximate to 400%) and poor conductivity (approximate to 10-5 S cm-1), the silicon anode shows unsatisfactory cycling stability and rate performance. Here, a 3D interconnected conductive and porous carbon network is constructed by self-assembling carbon nanotubes onto silicon nanoparticles encapsulated in vertically aligned graphene through the spray drying method. The carbon network provides efficient space, accommodating volumetric expansion of Si. Vertical graphene provides directional ion transportation and carbon nanotubes accelerate the electron transfer due to their high conductivity. The collaboration constructs a 3D robust conductive network to boost charge transport throughout the electrode. With these structural advantages, the electrodes deliver high capacities of 904 mAhg-1 at 5 Ag-1 with high capacity retention of 78.0% after 1000 cycles and 418 mAhg-1 at 20 Ag-1, while exhibiting only a 2.6% thickness change in the cross-sectional direction after 100 cycles at 0.5 Ag-1. Furthermore, the lithium storage mechanism of the silicon-carbon anode is elucidated through cyclic voltammetry and ex situ X-ray diffraction.

All-vanadium redox flow batteries (VRFBs) have emerged as a research hotspot and future direction of massive energy storage systems due to their advantages of intrinsic safety, long-duration energy storage, long...

Polymer-based composite solid electrolytes (PCSEs) are increasingly studied in all-solid-state lithium-metal batteries (ASSLMBs) due to the combined advantages of better flexibility of polymer and higher ion conductivity of ceramic electrolytes. However, most reported PCSEs are overly thick, increasing internal resistances. Besides, the poor stability at the Li metal-electrolyte interfaces often leads to severe lithium dendrite formation and reduced cycling stability. Here, we fabricate an ultrathin PCSE with a thickness of 12.4 mu m, incorporating polyacrylonitrile (PAN) nanofibers as the structural matrix, and a filler with polyethylene oxide and Li6.5La3Zr1.5Ta0.5O12 (LLZTO). Due to the formation of the LiCN layer on the surface of the lithium metal and the Li-ion transport pathways induced by the dehydrocyanation reaction at the LLZTO/PAN interfaces, the PCSE exhibits a high critical current density of 1.8 mA cm-2 and a low energy barrier of 0.278 eV for Li-ion transfer, accommodating the fast Li-ion migration to avoid Li-dendrite growth. In addition, the stable nitrile groups and the dehydrocyanation reaction ensure the electrochemical stability of the PCSE with a high oxidation voltage of 5.5 V and an exceptional cycling stability (2100 h) in Li||PCSE||Li symmetric cells. Additionally, the Li||PCSE||LiFePO4 full cells demonstrate a high volumetric energy density of 338.3 Wh L-1 at 0.1 C and a robust stability over 100 cycles at 0.5 C. The study offers a new approach for fabricating ultrathin PCSEs and provides insights into the mechanisms of dendrite-free formation, guiding the development of high-performance PCSEs for ASSLMBs.

Conversion-type transition-metal sulfides (CT-TMSs) have been extensively studied as the anode of Li/Na/K-ion batteries due to their high theoretical capacity. An issue with the use of the material in the battery is that a large capacity difference is commonly observed. However, the underlying mechanism leading to the problem is still unknown. Here, the large capacity difference mechanisms of CT-TMSs anodes in the Li/Na/K-ion storage are elucidated, which arises from the difference in conversion degree and size of conversion products. Specifically, the increase in ionic radius will cause the increase in insertion-reaction ion diffuse energy barrier and conversion-reaction Gibbs free energies of phase transformation to decrease reaction kinetics, which causes a decrease in conversion degree and an increase in size of conversion products, thus leading to reduction in capacity. The increase in size and the decrease in the amount of conversion products inevitably reduce the amount of spin-polarized electrons injection into Fe and corresponding ions storage amount into sulfides during the ion-electron decoupling storage, thus reducing the capacity. The research clarifies the capacity difference mechanisms of CT-TMSs anodes in Li/Na/K storage, providing valuable insights for designing Li/Na/K storage high-capacity anodes.

Anatase TiO2 as sodium-ion-battery anode has attracted increased attention because of its low volume change and good safety. However, low capacity and poor rate performance caused by low electrical conductivity and slow ion diffusion greatly impede its practical applications. Here, a bi-solvent enhanced pressure strategy that induces defects (oxygen vacancies) into TiO2 via N doping and reduces its size by using mutual-solvent ethanol and dopant dimethylformamide as pressure-increased reagent of tetrabutyl orthotitanate tetramer is proposed to fabricate N-doped TiO2/C nanocomposites. The induced defects can increase ion storage sites, improve electrical conductivity, and decrease bandgap and ion diffuse energy barrier of TiO2. The size reduction increases contact interfaces between TiO2 and C and shortens ion diffuse distance, thus increasing extra ion storage sites and boosting ion diffusion rate of TiO2. The N-doped TiO2 possesses highly stable crystal structure with a slightly increase of 0.86% in crystal lattice spacing and 3.2% in particle size after fully sodiation. Consequently, as a sodium-ion battery anode, the nanocomposite delivers high capacity and superior rate capability along with ultralong cycling life. This work proposes a novel pressure-induced synthesis strategy that provides unique guidance for designing TiO2-based anode materials with high capacity and excellent fast-charging capability.

Fe7S8 as a conversion-type anode shows high capacity in lithium-ion batteries (LIBs). Nevertheless, the sluggish ion transport rate, low electron conduction behavior, and large volume change upon cycling limit its applications in fast-charging wide-temperature-range LIBs. Here, a simple hydrothermal and subsequent solid-phase high-pressure sulfidation route is proposed to synthesize a hollow Fe7S8/N-doped C microsphere structure. The hollow space is enveloped by the spheres' shell consisting of ultrafine Fe7S8 nanocrystals (approximate to 8 nm) embedded into N-doped C matrix, which enhances ion transport and electrical conduction, and accommodates the volume expansion of Fe7S8. Remarkably, in situ magnetometry reveals that spin-polarized surface capacitance occurs during the stage of conversion reaction, in which the formed Fe and Li2S act as electrons and ions acceptor, respectively, to construct space charge zone at their interfaces, thus enhancing lithium transport and storage. Accordingly, the hollow microspheres show high gravimetric energy density and outstanding fast-charging capability along with excellent cycling stability in Ah-level pouch cells operating from -40 to 60 degrees C. For the first time, this work confirms the effectiveness of spin-polarized surface capacitance effect on enhancing ion storage and transport in fast-charging wide-temperature-range LIBs.

Iron sulfide (FeS) has been extensively studied as sodium-ion battery anodes due to its high theoretical capacity (609 mAh g-1), but its large volume expansion and low electrical conductivity result in unsatisfactory cycling life and poor rate performance. Moreover, the sodium ion storage mechanism of FeS at a voltage range of 0.01-1 V involving conversion reactions and subsequent ion storage process is unclear yet. Here, the study proposes a vapor-pressure induced synthesis route to fabricate FeS/C yolk-shell structure that ultrathin carbon layers coat on the surface of FeS nanosheets, which can accommodate volume expansion of FeS during sodiation observed via in situ transmission electron microscope and improve its electrical conductivity. Remarkably, an in situ magnetometry reveals that vast spin-polarized electrons can be injected into superparamagnetic Fe nanoparticles (approximate to 3 nm) formed during conversion reaction to induce evolution of electrode magnetization between 0.01 and 1 V, during which spin-polarized surface capacitance effect occurs at Fe/Na2S interfaces to increase extra ion storage and boost ion transport stably. Consequently, the FeS/C yolk-shell nanosheets deliver a high reversible capacity of 664.9 mAh g-1 at 0.1 A g-1, and 300.4 mAh g-1 after 10 000 cycles at 10 A g-1 with a capacity retention of 81.1%. Here, a FeS/C yolk-shell structure is fabricated to alleviate volume expansion during sodiation and improve electrical conductivity of FeS, thus enhancing cycling and rate performances. Remarkably, in situ magnetometry confirms that superparamagnetic Fe conversion induces evolution of electrode magnetization between 0.01 and 1 V, during which spin-polarized surface capacitance effect occurs to increase extra ion storage and boost ion transport stably. image

Fe1-xS, known for its high theoretical capacity, abundant resources, and intrinsic safety, has become a focal point as a universal anode for Li+/Na+/K+ batteries. However, its fast-charging capability is unsatisfactory due to sluggish ion transport rate and low electrical conductivity. Furthermore, its Li+/Na+/K+ storage mechanisms are still unclear. Here, we fabricate a single-crystal Fe1-xS/N-doped carbon composite nanosheet interwoven structure, in which N-doped carbon layers onto surface of Fe1-xS nanosheets ameliorate the electrical conduction and the interwoven nanosheets form open pore channels that favor permeation of electrolytes to boost ion transport. In-situ magnetometry reveals that ion-electron decoupling storage and transport occur in two-phase composites of Fe/Li2S, Fe/Na2S, and Fe/K2S, in which Fe phase stores and transports electrons and sulfide phase stores and transports ions in a space-charge form, resulting in extra ion storage and fast ion transport. Consequently, the nanosheet interwoven structure delivers high capacities (1320.1/652.2/350.6 mAh g-1), outstanding fast-charging performances (679.6/295.4/106.4 mAh g-1 at 20Ag-1), and long cycling life over 5000 cycles as Li+/Na+/K+ battery anodes, respectively

Improving the long-term cycling stability and energy density of all-solid-state lithium (Li)-metal batteries (ASSLMBs) at room temperature is a severe challenge because of the notorious solid–solid interfacial contact loss and sluggish ion transport. Solid electrolytes are generally studied as two-dimensional (2D) structures with planar interfaces, showing limited interfacial contact and further resulting in unstable Li/electrolyte and cathode/electrolyte interfaces. Herein, three-dimensional (3D) architecturally designed composite solid electrolytes are developed with independently controlled structural factors using 3D printing processing and post-curing treatment. Multiple-type electrolyte films with vertical-aligned micro-pillar (p-3DSE) and spiral (s-3DSE) structures are rationally designed and developed, which can be employed for both Li metal anode and cathode in terms of accelerating the Li+ transport within electrodes and reinforcing the interfacial adhesion. The printed p-3DSE delivers robust long-term cycle life of up to 2600 cycles and a high critical current density of 1.92 mA cm−2. The optimized electrolyte structure could lead to ASSLMBs with a superior full-cell areal capacity of 2.75 mAh cm−2 (LFP) and 3.92 mAh cm−2 (NCM811). This unique design provides enhancements for both anode and cathode electrodes, thereby alleviating interfacial degradation induced by dendrite growth and contact loss. The approach in this study opens a new design strategy for advanced composite solid polymer electrolytes in ASSLMBs operating under high rates/capacities and room temperature.

All-vanadium redox flow batteries (VRFBs) have experienced rapid development and entered the commercialization stage in recent years due to the characteristics of intrinsically safe, ultralong cycling life, and long-duration energy storage. However, VRFBs still face cost challenges, making it necessary to comprehensively optimize the performance and reduce the manufacturing costs of each component. The review first introduces the development history of VRFBs and emphasizes their huge market demand. Second, the bottlenecks existing in key components (electrodes, bipolar plates, membranes, and electrolytes) and battery management systems of VRFBs are summarized, and the corresponding latest improvement examples are proposed. Last, the review points out the future development direction of key components and systems of VRFBs. The review discusses the latest technology routes for reducing the cost and optimizing the performance of VRFBs, which are needed for accelerating applications and penetrations in large-scale and long-duration energy storage.

The germanium (Ge) anode attains wide attention in lithium-ion batteries because of its high theoretical volumetric capacity (8646 mAh cm-3). However, the huge volume expansion (approximate to 230%) results in its poor electrochemical performances. The strategies reported in the literature to solve the issue often cause a low packing density, lowering the volumetric capacity. Here, a pressure-induced route is proposed to fabricate a Ge architecture, in which nano-sized Ge (approximate to 15 nm) is encapsulated by robust TiO2 and highly conductive carbon, which offer the advantages of a low stress-strain characteristic, low volume expansion in thickness change, high electrical conductivity (463.2 S m-1), high Li-ion diffusion coefficient (9.55 x 10-9-8.51 x 10-12 cm2 s-1), and high tapping density (1.79 g cm-3). As a result, the dense architecture obtains outstanding volumetric capacities of 3559.8 mAh cm-3 at 0.1 A g-1 and 2628.2 mAh cm-3 at 20 A g-1, along with excellent cycling life over 5000 cycles at 10 A g-1. Remarkably, the full cell achieves a high volumetric energy density of 1760.1 Wh L-1, along with impressive fast-charging performances and long cycling life. This work provides a new synthesis strategy and deep insight into the design of high-volumetric capacity alloy-based lithium-ion-battery anodes. High-volumetric-capacity Ge-based anodes while maintaining excellent fast-charging capability and long cycling life are highly desired for LIBs but limited by large volume expansion and low packing density. This work proposes a pressure-induced route to fabricate a dense Ge architecture with low stress-strain characteristics, high tapping density, and fast charge transport capability, showing unprecedented volumetric lithium storage under industrial electrode conditions. image