The renewability and inherent hierarchical structure of biomass make it a promising precursor for hard carbon anodes in sodium-ion batteries. In this study, three locally abundant agroforestry byproducts were used to synthesize hard carbons: lightweight walnut wood with extensive vascular bundles, dense but vascular-retaining jujube wood, and compact, non-vascular walnut shells. Structural characterization revealed that all three hard carbons exhibit similar microstructural features, including comparable graphitization degree, an interlayer spacing > 0.38 nm, a closed-pore diameter > 2 nm, and residual surface oxygen-containing groups. Electrochemical evaluations demonstrated that all samples deliver reversible specific capacities of at least 300 mAh g−1, in which the plateau capacity accounts for ∼70% of the total capacity. Notably, the initial Coulombic efficiencies are no less than 89%. The key difference lies in their rate capability. Walnut wood-derived hard carbon retains 69.15% of its capacity at high current density, while walnut shell-derived hard carbon retains only 55.82%. Mechanistic analysis indicates that the intrinsic three-dimensional vascular bundle structure of woody precursors is partially preserved during carbonization. This architecture enables efficient electrolyte infiltration through interconnected macropores and allows mesopores in the bundle walls to act as fast ion transport channels, mitigating diffusion limitations at high current densities. These findings clarify the structure-dependent electrochemical behavior of biomass-derived hard carbons, highlighting the critical role of natural vascular architectures in enhancing sodium storage performance. These findings also provide experimental validation and design principles for optimizing hard carbon anodes through structural engineering, such as the artificial construction of hierarchical ion transport pathways.

A schematic of NaHMDS as a sacrificial sodium source for highly reversible anode-free sodium batteries with stable SEI/CEI interphases and dendrite-free deposition.

Heteroatom doping effectively modulates hard carbon anodes, yet research remains focused on conventional elements (N, P, S), leaving silicon largely unexplored. This work innovatively employs a hydrosilylation reaction to construct uniformly distributed Si-C/Si-O-C bonds. During carbonization, silicon species synergistically expand the interlayer spacing and refine the graphitic domain size, enhancing disorder and defect density. This creates more active sites and shortens Na+ diffusion paths, boosting plateau capacity and kinetics. Theoretical calculations further demonstrate that after silicon doping, the system exhibits significantly enhanced adsorption energy toward sodium ions along with a notably reduced diffusion barrier, thereby revealing the atomic-scale mechanism underlying the performance improvement. Consequently, the optimized Si-doped hard carbon achieves a high first-cycle Coulombic efficiency of 89.4 % and a dramatically improved reversible capacity of 200.9 mAh g- 1 at 3.2 A g- 1, versus 15.8 mAh g- 1 for the undoped sample. This study validates silicon's synergistic role and offers new insights for designing high-performance sodium-ion battery anodes.

NASICON-type Na3.5V1.5Mn0.5(PO4)3 (NVMP) is a cost-effective cathode candidate for sodium-ion batteries (SIBs). Nevertheless, its practical deployment is hindered by sluggish reaction kinetics and severe structural degradation. Herein, by incorporating synergistic dopants (Al, Ni, Zr) into transition metal sites, a Na3.5V1.35Mn0.5Al0.05Ni0.05Zr0.05(PO4)3/C (NVMANZP) is constructed. This multi-cation substitution increases configurational entropy, fundamentally altering the inherent biphasic reaction (in pristine NVMP) to a predominantly solid-solution-like mechanism in NVMANZP, which reduces the Na+ migration barrier and accelerates reaction kinetics. Moreover, this entropy-stabilized mechanism minimizes Jahn-Teller lattice strain, enhancing cycling stability. Consequently, NVMANZP delivers 118.3 mAh g-1 at 0.2C (1C = 110 mA g-1), retains 77.3 mAh g-1 at 100C (vs. 52.4 mAh g-1 for pristine), and maintains 80.76% capacity retention after 4,000 cycles at 10C. The full cell achieves 378 Wh kg-1 at 0.2C (based on mass of cathode). This work establishes NVMANZP as a high-rate, long-life SIB cathode and reveals how entropy-driven mechanisms tailor NASICON reaction kinetics.

Reconciling fast-charging kinetics with high initial Coulombic efficiency (ICE) in biomass-derived hard carbon (HC) anodes for sodium-ion batteries (SIBs) remains a formidable challenge due to the intrinsic trade-off between accessible porosity and severe interfacial side reactions. Herein, a topological distortion strategy via molecular regulation is proposed to comprehensively engineer hard carbon materials. This tailored pyrolytic pathway yields a unique carbon architecture with an abundant and highly distorted closed-pore network. Internally, the highly curved carbon layers and closed pores establish unhindered bicontinuous highways for ultrafast Na+ diffusion and electron transport, deeply unlocking kinetic limitations in the plateau region. Externally, the specifically distorted surface creates localized microenvironments that promote the specific adsorption of PF6- anions, catalyzing the in-situ formation of an ultrathin and NaF-rich anion-guided interphase. This advanced interphase facilitates rapid Na+ desolvation while thoroughly suppressing continuous irreversible electrolyte consumption. Consequently, the optimized anode achieves an exceptional ICE of 92.6% with a large reversible capacity of 321 mAh g-1 in an ether-based electrolyte. Impressively, it unlocks ultrafast sodium storage, retaining 200 mAh g-1 even at a stringent current density of 5000 mA g-1, and demonstrating outstanding full-cell viability. This work elucidates the critical interplay among precursor chemistry, topological defects, and SEI engineering, offering a molecular blueprint for next-generation power-type SIBs.

Lithium manganese iron phosphate (LMFP) is a promising cathode material for lithium-ion batteries (LIBs) due to its cost-effectiveness, high safety, and high-energy density. However, its practical deployment is critically hindered by sluggish Li+ diffusion kinetics. Herein, we propose to utilize Zr4+ as a lattice bond-stiffness topological optimizer to reconstruct the atomic interaction landscape of LiMn0.7Fe0.3PO4. Through precise charge compensation and local strain engineering, the Zr4+ dopant induces a unique stiff-skeleton/flexible-ion topological configuration. Specifically, it shortens the Mn/Fe & horbar;O bonds to rigidify the polyanionic framework against distortion, while simultaneously elongating the Li & horbar;O bonds to weaken the electrostatic confinement of Li+. Consequently, this bond-stiffness modulation effectively decouples the tradeoff between structural stability and ionic mobility. The optimized LMZ0.015FP cathode delivers superior reversible capacities of 166.99, 136.13, and 119.01 mAh g-1 at 0.1, 20, and 50 C, respectively, along with outstanding cycling stability (99.6% retention after 300 cycles at 1 C). Even in a graphite||LMZ0.015FP full cell, a high capacity retention of 97.3% is maintained after 150 cycles. This work demonstrates that lattice bond-stiffness topological engineering not only accelerates Li+ diffusion kinetics and promotes a solid-solution reaction pathway but also establishes a rational paradigm for designing next-generation fast-charging polyanionic cathodes.

The practical application of composite solid-state sodium metal batteries is critically limited by poor organic-inorganic compatibility, causing particle agglomeration, high interfacial resistance, and dendrite growth. Here, a covalent surface grafting strategy constructs a multifunctional interlayer covalently anchored on Na3Zr2Si2PO12, featuring a cross‑linked siloxane network and terminal ─NH2 groups. Covalent anchorage transforms inert particle surfaces into dispersible units, while ─NH2 groups anchor TFSI- and confine residual solvent via hydrogen bonding and Lewis acid‑base interactions. This dual regulation decouples ion transport from side reactions, yielding a high Na+ transference number (0.58) and a stable, NaF‑rich, thin solid‑electrolyte interphase (SEI). The optimized electrolyte enables symmetric cells with exceptional cycling stability and high critical current density (CCD). Full cells achieve fast‑charging (92 mAh g-1 at 15 C) and ultralong cycle life (76.4% retention after 7000 cycles at 10 C). A flexible pouch cell retains 97% capacity after 150 cycles. This work establishes that precise molecular‑level interfacial design, rather than simple physical blending, is key to high‑performance, dendrite‑resistant solid‑state sodium batteries.

Sodium-metal batteries (SMBs) are seen as a promising energy storage option due to their high energy density, abundant sodium resources, and cost-effectiveness. However, traditional organic liquid electrolytes (LEs) suffer from inherent safety risks, including leakage and flammability. Solid polymer electrolytes (SPEs) are regarded as a viable alternative to LEs for safer SMBs. However, the poor interfacial contact and insufficient ion transport associated with conventional ex situ prepared SPEs make it difficult for them to outperform LEs. The in situ polymerization technique, characterized by its process scalability and ability to form conformal interfaces, has proven effective in overcoming the obstacles associated with SPEs. In this review, we summarize recent research on in situ polymerization techniques for SMBs, including free-radical polymerization, ionic polymerization, electropolymerization, and related approaches. The importance of in situ polymerization in streamlining the preparation process, enhancing the compatibility of the electrode-electrolyte interface, bolstering battery safety, and optimizing electrochemical performance is highlighted. Furthermore, we systematically discuss the multiscale design principles of this technology, emphasizing precursor formulation, reaction kinetics, and targeted bulk-matrix properties. The advanced functional applications of in situ polymerization in SMBs, particularly in suppressing crosstalk effects, regulating solvation structures, and designing artificial interfacial layers and materials, are discussed. Finally, critical challenges, future prospects and pathways toward the practical, large-scale application of in situ polymerization are evaluated. This review aims to provide systematic insights to facilitate the rapid progress and implementation of in situ-polymerized electrolytes in SMBs.

Hetero-Li + regulates Na + solvation through competitive coordination in a same-anion electrolyte, enabling the formation of a hierarchical Na-rich/LiF-rich interphase and highly reversible Na plating/stripping in anode-free sodium batteries.

Harnessing anionic oxygen redox is pivotal for boosting the capacity of O3-type layered transition metal oxides for sodium ion batteries (SIBs), yet it often triggers severe lattice distortion and irreversible oxygen release. Herein, we propose an in situ electrochemical surface reconstruction strategy to stabilize the O3-type NaNi1/3Fe1/3Mn1/3O2 (NFM) cathode. By strictly controlling the initial anionic redox reactions at an ultra-high potential of 4.6 V, a robust heterostructure comprising an ordered layered core and a disordered rocksalt shell is constructed. This unique surface architecture serves as an isotropic strain buffer that effectively mitigates particle cracking and provides dense surface passivation to suppress interfacial side reactions. Furthermore, the induced rocksalt phase stabilizes the surface TM-O coordination, thereby preventing lattice oxygen loss during subsequent cycling. Consequently, when cycled within 2.0-4.0 V, the electrochemically pretreated cathode (DRS(4.6)@NFM) exhibits significantly reduced lattice distortion and superior electrochemical durability (capacity retention ratio of 90.77% after 300 cycles) with negligible voltage decay (retaining 98.56% of the initial voltage). Even when cycled up to 4.2 V, a capacity retention ratio of 87.4% after 300 cycles is still maintained. This work elucidates the interplay between electrochemical pretreatment and structural evolution, providing a decisive foundation for designing high-voltage and durable sodium-ion cathodes.

Polyanion-type phosphate cathodes with three-dimensional (3D) frameworks and open ion channels show promise for sodium-ion batteries (SIBs). Na2VTi(PO4)3 (NVTP) exhibits excellent structural stability and high theoretical capacity. However, its sluggish electron transfer kinetics causes severe polarization, limiting its practical energy density. Density functional theory (DFT) calculations reveal that electron transfer in NVTP predominantly occurs on transition metals (TM) and ligand oxygens, with negligible contribution from the phosphate framework. Guided by this fundamental mechanistic insight, we rationally designed an anion-doped Na2.08VTi(PO4)2.92(SiO4)0.08 (NVTP-Si). Lower-electronegativity Si dopants displace adjacent oxygen atoms toward TM centers, promoting ligand oxygen electron delocalization and accelerating the kinetics of both Ti3+/Ti4+ and V2+/V3+/V4+ redox couples. NVTP-Si delivers extended voltage plateaus, excellent rate capability, and a high energy density of 440.1 Wh kg−1 (active material basis). Reinforced TM–O bonds mitigate lattice strain during Na+ (de)intercalation, enabling 94.6% capacity retention after 2000 cycles at 500 mA g−1. This work clarifies the electron transfer mechanism and volume strain origin in NVTP, providing an effective anion doping strategy to boost NASICON cathode performance for SIBs.

As a key component enabling the commercialization of SIBs, hard carbon anodes have attracted extensive interest. The promise of SIBs is anchored in their cost advantage, which necessitates the development of electrode materials through cost-effective routes. Biomass is abundant and low-cost, serve as ideal precursors for hard carbon anodes. In this work, commercial walnut shell biochar was used as the starting material to synthesize hard carbon through simple acid washing and thermal treatment. Structural analysis shows that the obtained hard carbon possesses a relatively large interlayer spacing and well-developed closed pore structure with a diameter of 2.22 nm. The material HHC1300 exhibits a reversible sodium storage capacity of 287.41 mAh g- 1 and an ICE of 89.38%. Notably, the low-voltage plateau region contributes about 70% of the total capacity. These performance metrics exceed those of commercial hard carbon and most laboratory-reported hard carbons derived from lignocellulosic biomass. Furthermore, due to the intrinsically low ash content of the precursor, samples carbonized directly without acid washing can still achieve an ICE of 88.91%. This study demonstrates that incorporating mature industrial carbonization processes into hard carbon fabrication is an effective strategy, paving a practical route toward low-cost, high-performance electrode materials for scalable SIB production.

The development of solid-state batteries is often hindered by interfacial instability, particularly between the electrolyte and the lithium metal anode. To address this challenge, we fabricate a bilayer solid-state electrolyte composed of Li3InCl6 and Li6PS5Cl, which demonstrates excellent mutual compatibility and high ionic conductivity. Furthermore, a robust, LiF-rich solid electrolyte interphase (SEI) was pre-formed on the lithium metal anode via a pre-treatment strategy in a fluoroethylene carbonate-containing electrolyte. This dual design not only ensures stable interfacial contact but also effectively suppresses interfacial side reactions. When integrated into an all-solid-state lithium metal battery with a LiCoO2 cathode, the assembled cell delivers exceptional cycling stability, retaining over 85% of its initial capacity after 100 cycles at a rate of 0.2C. This work highlights the synergistic role of a compatible bilayer electrolyte and an artificial LiF-rich SEI in enabling high-performance and long-lasting solid-state lithium metal batteries.

O3-NaNi1/3Fe1/3Mn1/3O2 (NFM) layered oxides have shown promise as cost-effective cathode materials for sodium-ion batteries (SIBs). However, under harsh operational conditions such as high-voltage cycling (>4.2 V), elevated temperature, and humid environments, the practical application of NFM cathode is hindered by significant performance degradation caused by irreversible oxygen oxidation, detrimental phase transitions, and moisture-induced surface degradation. To address these issues, we propose a one-step Gd-doping strategy to address these challenges synergistically. The unique electronic configuration of Gd3+ can effectively regulate charge distribution, enhance oxygen redox reversibility and suppress irreversible oxygen release. Simultaneously, its appropriate ionic radius helps to reduce interlayer spacing and mitigate phase transition strain to stabilize the layered structure. The optimized Gd-doped NFM cathode delivers a high capacity of 180.47 mAh/g at 0.1 C (1 C = 150 mA/g), outstanding rate capability (130.10 mAh/g at 5 C), and exceptional cycling stability (87.5% retention after 200 cycles at 5 C). More importantly, it demonstrates remarkable resilience under high-temperature and humid conditions, offering a practical design strategy for high-performance SIBs operable under realistic harsh environments.

Metallic tin (Sn) is a promising anode material for sodium-ion batteries (SIBs) due to the high theoretical capacity and suitable operating voltage. Nevertheless, its widespread application is hindered by significant volume fluctuations during sodiation/desodiation, leading to mechanical degradation, unstable solid-electrolyte interphase (SEI), and rapid capacity fading. Herein, a rational composite design is developed by confining nano-Sn within a bamboo-derived porous carbon matrix through a facile melt-impregnation strategy, followed by coating with a pitch-derived carbon layer. This hierarchical architecture not only accommodates the large volume variation of Sn but also mitigates unnecessary side reactions by limiting direct electrolyte contact. Moreover, the multimodal pore system provides spatially separated domains: open meso/macropores for Sn encapsulation and closed micropores for efficient Na+ storage, enabling both mechanisms to operate synergistically without interference. As a result, the optimized Sn@PC/C electrode delivers a high reversible capacity of 447.5 mAh g- 1 at 0.03 A g-1 with a remarkable initial Coulombic efficiency of 90.4%, and demonstrates outstanding long-term cyclability, retaining 77.5% of its capacity after 1000 cycles at 0.9 A g-1. When paired with a NFPP cathode, the full cell maintains over 80% capacity after 500 cycles at 0.3 A g-1, substantially outperforming the control cell. The scalable synthesis combined with the multimodal-pore domain concept offers a compelling pathway toward high-performance alloy-based anodes for next-generation SIBs.

Unlocking the full potential of sodium-ion batteries (SIBs) heavily relies on pushing the energy-density limits of hard carbon (HC) anodes. However, the rational engineering of closed-pore architecture largely relies on trial-and-error, while the intrinsic thermodynamic/kinetic roles of carbon-framework electronic restructuring in driving pore closure have rarely been clarified. Herein, defect/pore inheritance coupled with local electronic-state reconstruction is proposed to successfully tailor closed-pore evolution. During pyrolysis, the evaporation of volatile zinc species generates abundant intrinsic defects and vacancies, whose retention triggers spontaneous electronic redistribution within the carbon skeleton. This reduces the work function and promotes spatial electron delocalization, thereby substantially lowering the energy barrier for carbon-atom migration and facilitating open-pore-wall fusion into abundant closed pores at high temperatures. Benefiting from this electronic-driven pore regulation, the optimized RFZ-HC delivers a superior reversible capacity of 417.1 mAh g−1, with the remarkably enhanced plateau capacity of 302.4 mAh g−1 originating from optimal closed-pore confinement. Mechanistic analyses collectively confirm a sequential sodium storage behavior. Furthermore, full cells pairing the RFZ-HC anode with an NFPP cathode deliver outstanding long-term cycling stability (85% capacity retention after 1000 cycles at 2C). This work establishes a novel defect-electron-pore engineering paradigm for designing next-generation high-energy-density SIBs.

Sodium storage capacity of hard carbon (HC) is governed by both interlayer spacing and the abundance of closed pores. However, achieving their balance remains challenging, due to the limited understanding of precursor-derived structure-activity relationships and the scarcity of precise molecular-level regulation strategies. Herein, we introduce a spatial reconfiguration strategy that directs the growth of resorcinol formaldehyde resin into a unique architecture: a rigid 3D interior skeleton decorated with external long linear chains. This distinct configuration, diverging from conventional linear or 3D network growth, favors the formation of carbon microcrystals with large lateral size (L-a) and expanded interlayer spacing, while the rigid skeleton constrains stacking along the c-axis (L-c), yielding thin-walled nanopores that efficiently host sodium clusters. The optimized HC delivers a remarkable reversible capacity of 394.7 mAh g(-1) with an impressive low-voltage (<0.1 V) capacity of 283 mAh g(-1). In full-cell paired with a high loading Na4Fe3(PO4)(2)P2O7 cathode (similar to 12.4 mg cm(-2)), the anode enables stable cycling over 1000 times at 2C with a minimal decay rate of 0.0178% per cycle. Beyond performance, this study deciphers the precursor-to-HC structure correlation and demonstrates a targeted molecular-design pathway for advanced carbon anodes.

O3-type sodium nickel-iron-manganese oxide (NaNi1/3Fe1/3Mn1/3O2) is recognized as a promising cathode material for sodium ion batteries (SIBs) due to its high capacity, low cost, and ease of synthesis. However, it suffers from structural instability, short cycling life, and environmental sensitivity caused by structural distortion and interfacial deterioration during cycling. Herein, a multifunctional composite coating and Zr doping are developed using an in situ one-step method. The multifunctional coating (MFC) layer can optimize the composition of grain boundaries to facilitate the rapid transfer of sodium ions and inhibit the interfacial erosion of the electrolyte and high-temperature side effects. In addition, the strong Zr-O bond stabilizes the internal crystal structure, suppressing undesirable phase transformations. Experimental tests demonstrate that the Zr-doped NFM material with the MFC layer demonstrates enhanced structural stability with a capacity retention of 80.02% after 300 cycles compared to 62.02% retention of the bare sample at 1C. Remarkably, at a high rate of 10C, it retains a specific discharge capacity of 102.1 mA h g-1. When integrated into a full battery with a commercial hard carbon anode, it delivers an energy density of 346.38 W h kg-1 (calculated based on cathode material mass), highlighting its substantial potential for practical deployment in SIBs.

In order to improve the electrochemical performance of PVDF-HFP solid-state electrolytes, we introduced hexagonal-BN into the PVDF-HFP polymer matrix. The strong interaction of hexagonal-BN on TFSI- promotes the dissociation of sodium salts and restricts the movement of TFSI-, which improves the Na+ transference number and the interfacial stability of solid-state electrolytes.