Pore Reconstruction of Fermented Biomass‐Derived Hard Carbon for High‐Plateau‐Capacity Sodium Storage

Ti, F Codoped Sodium Manganate of Layered P2-Na _0.7 MnO _2.05 Cathode for High Capacity and Long-Life Sodium-Ion Battery

The inherent kinetic limitations associated with sodium storage in hard carbon (HC) anodes hinder further improvements in the energy density of sodium-ion batteries (SIBs). In this work, we present a facile and scalable synthesis strategy for a fluorine-doped HC anode. The incorporation of fluorine effectively suppresses graphitization during high-temperature carbonization, resulting in a highly disordered carbon structure with an expanded interlayer spacing and abundant surface defects. These structural features introduce numerous active sites and significantly enhance the surface adsorption capability of sodium ions. The optimized material delivers a high reversible specific capacity of 350.3 mAh g–1 in ester-based electrolytes and exhibits superior cycling stability compared to pristine phenolic resin-derived HC─achieving a capacity retention rate of 84.3% after 100 cycles at 100 mA g–1. This study offers a practical and rational design approach for high-performance HC anodes, paving the way toward their viable application in SIBs.

Constructing a homogenous and inorganic-rich solid electrolyte interface (SEI) can efficiently improve the overall sodium-storage performance of hard carbon (HC) anodes. However, the thick and heterogenous SEI derived from conventional ester electrolytes fails to meet the above requirements. Herein, an innovative interfacial catalysis mechanism is proposed to design a favorable SEI in ester electrolytes by reconstructing the surface functionality of HC, of which abundant CO (carbonyl) bonds are accurately and homogenously implanted. The CO (carbonyl) bonds act as active centers that controllably catalyze the preferential reduction of salts and directionally guide SEI growth to form a homogenous, layered, and inorganic-rich SEI. Therefore, excessive solvent decomposition is suppressed, and the interfacial Na+ transfer and structural stability of SEI on HC anodes are greatly promoted, contributing to a comprehensive enhancement in sodium-storage performance. The optimal anodes exhibit an outstanding reversible capacity (379.6 mAh g-1 ), an ultrahigh initial Coulombic efficiency (93.2%), a largely improved rate capability, and an extremely stable cycling performance with a capacity decay rate of 0.0018% for 10 000 cycles at 5 A g-1 . This work provides novel insights into smart regulation of interface chemistry to realize high-performance HC anodes for sodium storage.

Establishing prediction rules for the low-potential plateau (LPP) of hard carbon (HC) anodes is crucial for constructing high-energy-density sodium-ion batteries (SIBs). While current studies suggest that the closed pores of HC can enhance the LPP performance, the rules for directly predicting the LPP from precursors have yet to be established. Here, prediction rules for the LPP of HC anodes in SIBs-the substitution index (Δ) of precursor are introduced. Three carbon models (disordered carbon, closed-pore-dominated carbon, and turbostratic carbon) are constructed to verify the accuracy of Δ and to explore the closed-pore formation and LPP mechanism. In detail, as the Δ increases from 0.06 to 0.22, the LPP capacity rises from 25 to 278mAhg⁻¹, revealing a strong linear correlation between Δ of precursor and LPP capacity. In situ XRD, Raman, and ex situ SAXS, EPR further confirm that sodium storage in HC can be categorized into adsorption (>0.4V), interlayer storage (0.4 to 0.15V), and pore-filling (below 0.15V). This work not only elucidates the sodium storage mechanisms, but also provides one efficient design guideline for advanced carbon anodes in SIBs.

The practical of hard carbon (HC) anodes in sodium-ion batteries is primarily limited by their unsatisfactory initial coulombic efficiency (ICE), cycling stability and rate performance, which are closely related to their interphase chemistry and microstructure. Herein, a unique manipulating interphase chemistry strategy by endogenous N/S doping is proposed to simultaneously achieve the both issues. Specifically, a series of reducing sugars and amino acid have been proven to trigger the Maillard reaction, thereby enabling endogenous N/S doping and microstructural design for HC anodes. Endogenous doping facilitates the formation of an inorganic-enriched solid-electrolyte interface (SEI) layer on cycled HC, which can effectively accelerate ion transport kinetics and reduce side effects for enhanced rate, ICE, cycling performance and reversible capacity. Meanwhile, the increase in the number of closed pores boosts both the platform capacity and cycling stability of HC. Consequently, the features HC anodes demonstrate a splendid reversible capacity (363 mAh g-1 at 0.05 A g-1), superior cycling performance (over 2500 cycles with 79% retention at 5.0 A g-1) and adequate ICE (89%). The assembled full cell with Na3V2(PO4)3 cathode exhibits splendid cycling stability over 700 cycles with capacity retention of 89.2% at 1 C. Surprisingly, the pouch cell with high cathode mass loading of 20.7mgcm-1 maintains 98.1% capacity retention after 175 cycles at 1 C. This strategy provides new ideas and insights for the design and screening of high-performance HC anodes.

Hard carbon (HC) anodes show conspicuously commercialized potential for sodium-ion batteries (SIBs) due to their cost-effectiveness and satisfactory performance. However, the development of hard carbon anodes in SIBs is still hindered by low initial Coulombic efficiency (ICE) and insufficient cyclic stability, which are induced by inappropriate defects in the structure. Herein, we introduce a simple but effective method to tailor the defects in HC by the chemically preadsorbed K + . The soft X-ray absorption spectroscopy at the C K-edges reveals that K + can anchor on the hard carbon via C-O-K bonds, occupying the irreversible reactive sites of Na + . Therefore, the irreversible capacity caused by some C-O bonds can be reduced. Moreover, the preadsorbed K + can induce the rearrangement of carbon layers and lead to a high graphitization structure with fewer defects and large interlayer spacing, which not only improves the structural stability and electrical conductivity of the HC anode but also facilitates fast Na + diffusion. Therefore, the as-obtained optimized anode demonstrates a higher ICE with better cyclic stability and superior rate capacities compared with the anode without preadsorbed K + . This work indicates that K + preadsorbed into hard carbon is a practicable alternative to enhance the Na storage performances of HC anodes for SIBs.

Biomass‐derived hard carbon, despite being promising for anode material of sodium‐ion batteries, usually suffer from low initial coulombic efficiency (ICE), poor rate capacity, and limited cycling stability caused by complex surface defects and low intrinsic conductivity. Herein, phosphorus‐doped porous hard carbon (HC@PC−P) were synthesized by the thermal polymerization of soy lecithin on the surfaces of hard carbon derived from olive kernels. The incorporation of heteroatom phosphorus in the porous hard carbon framework expands the carbon lattice spacing, optimizes the graphitization degree, and increases electrical conductivity, guaranteeing ensuring rapid electron and ion transfer. These coupling effects enable HC@PC−P anode to achieve a high reversible capacity of 350 mAh g−1 at 0.1 A g−1, an impressive initial coulombic efficiency of 89.6 %, and remarkable long‐term cycling stability at 1 A g−1 over 1000 cycles with negligible capacity fade. The mechanisms behind sodium storage and enhanced electrochemical performance were elucidated by ex‐situ Raman spectroscopy and kinetic analysis. Additionally, the assembled HC@PC−P//Na3V2(PO4)3 full cell demonstrated a high energy density of 257.9 Wh kg−1. This work provides a rational guide for designing advanced hard carbon anode materials for high‐energy sodium‐ion batteries.

Sodium-ion batteries (SIBs) are regarded as cost-effective alternatives or competitors to lithium-ion batteries for large-scale electric energy storage applications. However, their development has been hindered by the high cost of hard carbon (HC) anodes and poor electrochemical performance. To enhance the sodium storage capacity and rate performance of HC, this study accelerated the electrochemical performance of coconut-shell-derived HC anodes for SIBs through N/O codoping using ball milling and pyrolysis. Experimental results demonstrate that the simultaneous introduction of N and O generates a synergistic effect, increasing the surface oxygen-containing functional groups, defects, and interlayer spacing of coconut-shell-derived HC through the codoping of light elements. The excellent strategy has increased the slope capacity and platform capacity of HC, and the synergistic modification of N/O has increased its reversible specific capacity from 272 to 343 mA h g-1 (30 mA g-1), with a retention rate of approximately 92.1% after 100 cycles. In addition, it also exhibits an excellent rate performance, reaching 178 mA h g-1 at 1500 mA g-1. In summary, this study presents an effective strategy for modifying biomass-derived HC.

Amorphous carbon, particularly hard carbon (HC), is widely considered as the most promising anode material for sodium-ion batteries (SIBs) due to its high reversible capacity and cost-effectiveness. However, the complex and poorly defined structural properties of HC present challenges in understanding the underlying sodium storage mechanisms. To facilitate the rational design of high-performance HC anodes, a comprehensive understanding of the correlation between microstructure and sodium storage behavior is critical. This Review critically examines the interplay between the structural features of HC and its sodium storage capabilities, focusing on two key factors: pore structure and surface functional groups. It begins by outlining the fundamental sodium storage mechanisms in HC, followed by an in-depth discussion of how pore structure and surface chemistry influence sodium-ion storage. Finally, strategic insights are provided on how to manipulate these structural factors to optimize sodium storage performance. This Review aims to drive the development of next-generation high-performance HC anodes and support the commercialization of SIBs.

Hard carbon (HC) anode shows great potential due to its high capacity and excellent rate performance. However, state-of-the-art HC anode still suffers insufficient initial Coulomb efficiency (ICE) due to the abundant Li-trapping sites. Herein, we demonstrate a facile annealing engineering for HC anodes to improve the ICE and the mechanism is systematically studied. Accordingly, during the annealing process, metastable O- and N-containing functional groups are pyrolyzed, which cause the microstructure reconstruction of HC. Therefore, irreversible lithium ions adsorption is reduced significantly and the conversion of sp3 to sp2 C contributes to the localized graphitization of HC. Consequently, the optimized HC achieves ultra-high ICE of 90% from initial 61%. It is demonstrated that HC will adsorb H2 O and some organic species from environment gradually, causing conversion of some electrochemical stable functional groups to the irreversible Li-trapping sites. This work provides facile strategy and novel insight for high ICE HC anodes.

Overview of electrochemical competing process of sodium storage and metal plating in hard carbon anode of sodium ion battery

Despitelow cost and abundant sources, hard carbon (HC) anodes for sodium-ion batteries (SIBs) exhibit a low initial Coulombic efficiency (ICE) owing to the unstable solid-electrolyte interphase (SEI). In contrast, soft carbon (SC) anodes, demonstrating inferior sodium storage performance, possess a smoother surface facilitatingthe ordered growth of the SEI. To leverage the complementary advantages ofthem, a hard/soft carbon heterointerface material (x-SMCC) is synthesized via a one-step hydrothermal co-assembly of microcrystalline cellulose and Perylene-3,4,9,10-tetracarboxylic dianhydride, following controlled carbonization. The integration of SC modifies the HC interface, reconstructing its surface structure, which significantly guides the formation of sodium clusters within the low-potential plateau region. Moreover, the ordered SC phase serves as an effective substrate to guide the formation of a smoother SEI, thereby enhancing the overall electrochemical performance. Specifically, the optimized 5-SMCC delivers an outstanding reversible capacity of 353.98 mAh g-1 at a current density of 30mA g-1, along with an enhanced ICE of 84.52%. Moreover, it retains 78% of its initial capacity after 1000 cycles at 1.5 A g-1. This structural engineering strategy not only facilitates the development of cost-effective HC anodes for practical SIBs but also offers a systematic design methodology for defect-engineered carbonaceous anode materials.

Biomass hard carbon (BHC) anodes with high low-voltage plateau capacity (LPC) represent promising anode materials for sodium-ion batteries (SIBs). However, the achievement of a high LPC is generally closely associated with the closed-pore filling mechanism. Effectively regulating the closed-pore structure to enhance the LPC remains a significant challenge. Herein, a strategy for grafting cellulose with chitosan is presented to synthesize BHCs with excellent closed-pore structures after high-temperature treatment. The grafting process enables intercalation of chitosan molecules between the cellulose chains, thereby disrupting the crystalline structure and ultimately facilitating cross-linking and structural rearrangement during pyrolysis and polycondensation. Consequently, the resulting hard carbons exhibit suppressed graphite-like phases and a large population of closed-pore architecture. The GCHC1-2 anode exhibits a closed-pore volume of 0.26 cm3 g-1, a LPC of 247.53 mAh g-1, and an initial Coulombic efficiency (ICE) of 87.37%. Moreover, the GCHC1-2 material also shows remarkable cycling stability, maintaining a specific capacity of 257 mAh g-1 after 300 cycles at a current density of 300 mA g-1, corresponding to a capacity retention of 78.07%. Comprehensive kinetic analyses further confirm that the superior electrochemical performance of GCHC1-2 is primarily attributed to the Na+ storage mechanism facilitated by its closed-pore structure. This study demonstrates that the molecular-scale engineering of biomass precursors enables the rational design of high-performance hard carbon anodes for SIBs.

Hard carbon (HC) remains the most viable choice as a negative electrode for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) owing to its higher energy density (discharge up to zero volts), higher capacity (distinct storage mechanisms), and cycling stability. Herein, a biomass jute fiber precursor HC anode (JPC) with varying porosity is reported for the first time as a low-cost and sustainable high-performance HC anode for SIBs and PIBs. Direct carbonization results in micro-meso porous HC (JPC-D), and micro-wave pretreated jute fiber results in ultramicroporous HC (JPC-M). The mesoporosity generated in JPC-D during synthesis outperforms the ultramicroporous JPC-M with a high reversible capacity of 328 mAh g-1 (iCE = 66%) at a current density of 30 mA g-1 (0.1C) with superior capacity retention of 84% after 100 cycles in SIBs. The Na+ ion and K+ ion storage in HCs, especially at lower voltages, shows distinct storage mechanisms that depend on the morphology and porosity of the material. JPC-D contributed 39% of its total capacity through the plateau region capacity (PRC), suggesting more pore filling from hierarchical porosity in SIBs. JPC-D and JPC-M exhibit more insertion-based capacity than pore-filling processes in PIBs. The presence of inorganic impurities (Ca, Si, Al, and Fe) encapsulated in the carbon structure plays a critical role in developing mesopores. The yield (%) of HC from direct carbonization per kilogram of jute is ∼34%, which makes it cheaper than HC from sugar-based precursors and 1.5 times more affordable than other biomass-derived HC. The jute-based micro-mesoporous HC is a novel, cost-effective, sustainable approach to designing HC for a PRC-based battery-type anode in SIBs and PIBs.

Constructing the continuously-distributed and crystalline-NaF-rich solid electrolyte interface (CC-NaF-SEI) is expected to greatly promote the sodium storage performance of hard carbon (HC) anodes. However, such an impressive concept remains extremely intractable to achieve and lacks an efficiently cost-less strategy. Herein, the application of the commercially available LA133 binder is pioneered to engineer such a CC-NaF-SEI. Through comparative analysis of representative binders with distinct functional groups, reveals the critical role of binder chemistry on SEI regulation. Specifically, the LA133 binder demonstrates a dual-regulation mechanism for CC-NaF-SEI formation. The anion-coordination preferred ─CN bonds induce an anion-enriched interfacial solvation structure, and the ─CONH/─CN groups catalytically cleave P─F bond dissociation in PF6 -, synergistically promoting anion decomposition kinetics to form crystalline NaF. Furthermore, robust hydrogen bonds between multiple polar groups in LA133 and HC surface create the spatially anion-confined microenvironments to guide orderly anion decomposition and facilitate continuous NaF growth into a mechanically integrated SEI. The optimized CC-NaF-SEI endows HC anodes with exceptional sodium storage performance: an ultrahigh initial Coulombic efficiency (95.9%), remarkable reversible capacity (356.6 mAh g-1), and stable cycling under extreme conditions (-20-60°C). This work provides fundamental insights into binder-SEI correlations, establishing a novel paradigm for interfacial optimization in sodium-ion batteries.