Hyperaccumulation Route to Ca-Rich Hard Carbon Materials with Cation Self-Incorporation and Interlayer Spacing Optimization for High-Performance Sodium-Ion Batteries

Dual-Functionalized Ca Enables High Sodiation Kinetics for Hard Carbon in Sodium-Ion Batteries

Hard carbons (HCs), while a leading candidate for sodium-ion battery (SIB) anode materials, face challenges in their unfavorable sodiation kinetics since the intricate microstructure of HCs complicates the Na+ diffusion channel. Herein, a Hovenia dulcis-derived HC realizes a markedly enhanced high-rate performance in virtue of dual-functionalized Ca. The interlayer doped Ca2+ effectively enlarges the interlayer spacing, while the in situ-formed CaSe templates induce the formation of hierarchical pore structures and intrinsic defects, significantly providing fast Na+ diffusion channels and abundant active sites and thus enhancing the sodium storage kinetics. Achieved by the synergistic effect of regulation of intrinsic microcrystalline and pore structures, the optimized HC shows remarkable performance enhancements, including a high reversible capacity of 350.3 mA h g-1 after 50 cycles at 50 mA g-1, a high-capacity retention rate of 95.3% after 1000 cycles, and excellent rate performance (108.4 mA h g-1 at 2 A g-1). This work sheds light on valuable insight into the structural adjustment of high-rate HCs, facilitating the widespread utilization of SIBs.

Waste biomass garlic stem-derived porous carbon materials as high-capacity and long-cycling anode for lithium/sodium-ion batteries

Carbon materials are promising anode materials for rechargeable lithium and sodium-ion batteries, due to their low cost, high capacity, and structural designability. In this work, we selected a waste biomass, garlic stem, as the carbon precursor, and we systematically investigated the effect of pyrolysis temperature and time on their battery performance. We find that 800 °C and 2 h are the best pyrolysis conditions, which leads to the optimal carbon material (800C-2H) with a large layer spacing, abundant defect sites, high surface area, and sufficient micro/meso-porous structures. Due to these favorable properties, this carbon anode exhibits an impressive performance for Lithium-ion batteries, with a very high capacity of 480 mAh g-1 and no significant capacity fading after 3000 cycles. Besides, this anode also shows promising performance for Sodium-ion batteries, where a good capacity of 151.9 mAh g-1 and reasonable cycling of 100 cycles are achievable. We also carried out in-situ X-ray diffraction and in-situ Raman spectroscopy experiments to understand the relationship between carbon microstructures and their Li-ion storage.

Bowl-shaped hollow carbon wrapped in graphene grown in situ by chemical vapor deposition as an advanced anode material for sodium-ion batteries

Sodium-ion batteries (SIBs) are expected to be ideal alternatives to lithium-ion batteries (LIBs) in the future due to their abundant and low-cost resource advantages. A key challenge in SIBs is the development of anodes capable of insertion/extraction of sodium ions (Na⁺) with large radii. Here, hollow bowl-shaped porous carbon materials are uniformly modified with vertically grown graphene (denoted as HBC/VGSs) demonstrating a large specific surface area and three-dimensional structure, which are employed as a viable high-performance anode for SIBs. HBC/VGSs anodes are highly effective at storing sodium because of their structural features. As a result, the HBC/VGSs electrodes provide a high reversible capacity of 409 mAh g^-1 after 100 cycles at 0.1 A g^-1, as well as outstanding rate capability (301.6 mAh g^-1 at 5 A g^-1). Moreover, it also shows extraordinary cycling stability (230.3 mAh g^-1 after 2500 cycles at a high current density of 5 A g^-1) that is significantly better than the pristine hollow bowl-shaped porous carbon (HBC). Cyclic Voltammetry (CV) and Galvanostatic Intermittent Titration Technique (GITT) were used to analyze the pseudocapacitance and sodium storage kinetics. It was found that high electrical conductivity and large surface area can improve Na⁺ adsorption and diffusion, enhance the electronic conductivity, and deliver superior capacity and rate. The results, taken as a whole, provide new insight into the creation of long-lasting carbon anodes that deliver optimal performance in SIBs.

From Waste Biomass to Hard Carbon Anodes: Predicting the Relationship between Biomass Processing Parameters and Performance of Hard Carbons in Sodium-Ion Batteries

Sodium-ion batteries (SIBs) serve as the most promising next-generation commercial batteries besides lithium-ion batteries (LIBs). Hard carbon (HC) from renewable biomass resources is the most commonly used anode material in SIBs. In this contribution, we present a review of the latest progress in the conversion of waste biomass to HC materials, and highlight their application in SIBs. Specifically, the following topics are discussed in the review: (1) the mechanism of sodium-ion storage in HC, (2) the HC precursor’s sources, (3) the processing methods and conditions of the HCs production, (4) the impact of the biomass types and carbonization temperature on the carbon structure, and (5) the effect of various carbon structures on electrochemical performance. Data from various publications have been analyzed to uncover the relationship between the processing conditions of biomass and the resulting structure of the final HC product, as well as its electrochemical performance. Our results indicate the existence of an ideal temperature range (around 1200 to 1400 °C) that enhances the formation of graphitic domains in the final HC anode and reduces the formation of open pores from the biomass precursor. This results in HC anodes with high storage capacity (>300 mAh/g) and high initial coulombic efficiency (ICE) (>80%).

Boosting the Initial Coulomb Efficiency of Sisal Fiber-Derived Carbon Anode for Sodium Ion Batteries by Microstructure Controlling

As anode material for sodium ion batteries (SIBs), biomass-derived hard carbon has attracted a great deal of attention from researchers because of its renewable nature and low cost. However, its application is greatly limited due to its low initial Coulomb efficiency (ICE). In this work, we employed a simple two-step method to prepare three different structures of hard carbon materials from sisal fibers and explored the structural effects on the ICE. It was determined that the obtained carbon material, with hollow and tubular structure (TSFC), exhibits the best electrochemical performance, with a high ICE of 76.7%, possessing a large layer spacing, a moderate specific surface area, and a hierarchical porous structure. In order to better understand the sodium storage behavior in this special structural material, exhaustive testing was performed. Combining the experimental and theoretical results, an "adsorption-intercalation" model for the sodium storage mechanism of the TSFC is proposed.

Biomass-Derived Hard Carbon with Interlayer Spacing Optimization toward Ultrastable Na-Ion Storage

Hard carbons as a kind of nongraphitized amorphous carbon have been recognized as potential anode materials for sodium-ion batteries (SIBs) due to its large interlayer spacing. However, the issues in terms of onerous synthetic procedure and elusive working mechanism remains critical bottlenecks for practical implement. Herein, we report a facile production of tubular hard carbon through direct carbonization of platanus flosses (FHC) for the first time. Through optimizing the pyrolysis temperatures, the FHC obtained at 1300 °C possesses a key balance between the interlayer spacing and surface area, which can maintain the substantial active sites as well as reduce the irreversible sodium storage. Accordingly, it can deliver a reversible capacity of 324.6 mAh g^-1 with a high initial Coulombic efficiency of 80%, superb rate property of 107.2 mAh g^-1 at 2 A g^-1, and long operating stability over 1000 cycles. Furthermore, the in situ Raman spectroscopic studies certify that sodium ions are stored in FHC following the "adsorption-insertion" mechanism. Our study could provide a promising route for large-scale development of the biomass-derived carbonaceous anodes for high-performance SIBs.

Coal-Based Semicoke-Derived Carbon Anode Materials with Tunable Microcrystalline Structure for Fast Lithium-Ion Storage

Fast charging capability is highly desired for new generation lithium-ion batteries used in consumer-grade electronic devices and electric vehicles. However, currently used anodes suffer from sluggish ion kinetics due to limited interlayer distance. Herein, the coal-based semicoke was chosen as precursor to prepare cost-effective carbon anodes with high-rate performance through a facile pyrolytic strategy. The evolution of microstructure and its effect on electrochemical performance are entirely studied. The results show that large number of short-ordered defective structures are generated due to the occurrence of turbostatic-like structures when pyrolyzed at 900 °C, which are propitious to large interlayer distance and developed porous structure. High accessible surface area and large interlayer spacing with short-ordered defective domains endow the sample treated at 900 °C under argon (A900) with accelerated ion dynamics and enhanced ion adsorption dominated surface-induced capacitive processes. As a result, A900 delivers high capacity (331.1 mAh g^-1 at 0.1 A g^-1) and long life expectancy (94.8% after 1000 cycles at 1 A g^-1) as well as good rate capability (153.2 mAh g^-1 at 5 A g^-1). This work opens a scalable avenue to fabricating cost-effective, high-rate, and long cycling life carbon anodes.

Ether-based electrolytes for sodium ion batteries

Sodium-ion batteries (SIBs) are considered to be strong candidates for large-scale energy storage with the benefits of cost-effectiveness and sodium abundance. Reliable electrolytes, as ionic conductors that regulate the electrochemical reaction behavior and the nature of the interface and electrode, are indispensable in the development of advanced SIBs with high Coulombic efficiency, stable cycling performance and high rate capability. Conventional carbonate-based electrolytes encounter numerous obstacles for their wide application in SIBs due to the formation of a dissolvable, continuous-thickening solid electrolyte interface (SEI) layer and inferior stability with electrodes. Comparatively, ether-based electrolytes (EBEs) are emerging in the secondary battery field with fascinating properties to improve the performance of batteries, especially SIBs. Their stable solvation structure enables highly reversible solvent-co-intercalation reactions and the formation of a thin and stable SEI. However, although EBEs can provide more stable cycling and rapid sodiation kinetics in electrodes, benefitting from their favorable electrolyte/electrode interactions such as chemical compatibility and good wettability, their special chemistry is still being investigated and puzzling. In this review, we provide a thorough and comprehensive overview on the developmental history, fundamental characteristics, superiorities and mechanisms of EBEs, together with their advances in other battery systems. Notably, the relation among electrolyte science, interfacial chemistry and electrochemical performance is highlighted, which is of great significance for the in-depth understanding of battery chemistry. Finally, future perspectives and potential directions are proposed to navigate the design and optimization of electrolytes and electrolyte/electrode interfaces for advanced batteries.

Enabling Fast Na+ Transfer Kinetics in the Whole-Voltage-Region of Hard-Carbon Anodes for Ultrahigh-Rate Sodium Storage

Efficient electrode materials, that combine high power and high energy, are the crucial requisites of sodium-ion batteries (SIBs), which have unwrapped new possibilities in the areas of grid-scale energy storage. Hard carbons (HCs) are considered as the leading candidate anode materials for SIBs, however, the primary challenge of slow charge-transfer kinetics at the low potential region (<0.1 V) remains unresolved till date, and the underlying structure-performance correlation is under debate. Herein, ultrafast sodium storage in the whole-voltage-region (0.01-2 V), with the Na⁺ diffusion coefficient enhanced by 2 orders of magnitude (≈10^-7 cm² s^-1 ) through rationally deploying the physical parameters of HCs using a ZnO-assisted bulk etching strategy is reported. It is unveiled that the Na⁺ adsorption energy (E_a ) and diffusion barrier (E_b ) are in a positive and negative linear relationship with the carbon p-band center, respectively, and balance of E_a and E_b is critical in enhancing the charge-storage kinetics. The charge-storage mechanism in HCs is evidenced through comprehensive in(ex) situ techniques. The as prepared HCs microspheres deliver a record high rate performance of 107 mAh g^-1 @ 50 A g^-1 and unprecedented electrochemical performance at extremely low temperature (426 mAh g^-1 @ -40 °C).

Realizing Improved Sodium-Ion Storage by Introducing Carbonyl Groups and Closed Micropores into a Biomass-Derived Hard Carbon Anode

Micropores and defects, like oxygen-containing groups, as active sites for sodium-ion storage in hard carbon have attracted considerable attention; nevertheless, most oxygen doping or oxidizing processes inevitably introduce undesired oxygen groups into a carbon framework, leading to deteriorated initial Coulombic efficiency (ICE). Here, precise carbonyl groups and closed micropores are together introduced into biomass-derived hard carbon to enhance the Na-ion storage performance. The hard carbon delivers a large reversible capacity of 354.6 mA h g^-1 at 30 mA g^-1, a high ICE (88.7%), as well as ultra-long cycling stability (277 mA h g^-1 at 0.3 A g^-1 over 1000 cycles; 243 mA h g^-1 at 1 A g^-1 over 5000 cycles). The rate capability and cycling stability of hard carbon in carbonate- and diglyme-based electrolytes are contrasted to demonstrate the superiority of diglyme. Cyclic voltammetry at varied scans and galvanostatic intermittent titration techniques are carried out to clarify the disparity between the two different electrolyte systems. Furthermore, the as-prepared hard carbon is utilized as the anode for sodium-ion full cells exhibiting an energy density of 166.2 W h kg^-1 at 0.2 C and a long-cycle life (47.9% retention over 200 cycles at 1 C).

Boosting Sodium Storage Performance of Hard Carbon Anodes by Pore Architecture Engineering

Hard carbon (HC) displays great potential for high-performance sodium-ion batteries (SIBs) due to its cost-effective, simple fabrication and most likely to be commercialized. However, the complicated microstructures of HC lead to difficulties in deeply understanding the structure-performance correlation. Particularly, evaluation of influence of pore structure on Na storage performances is still causing disputes and rational strategies of designing pore architecture of HC are still necessary. In this work, the skillful and controllable phase-inversion method is applied to construct porous HC with abundantly interconnected and permeable tunnel-like pores, which can promote ionic diffusion and improve electrode-electrolyte interfacial affinity. Structure-performance investigation reveals that porous HC with cross-coupled macropore architecture can boost Na storage performances comprehensively. Compared to pristine HC with negligible pores, well-regulated porous HC anodes show an obvious enhancement on initial Coulombic efficiency (ICE) of 68.3% (only 51.5% for pristine HC), reversible capacity of 332.7 mAh g^-1 at 0.05 A g^-1, rate performance with 67.4% capacity retention at 2 A g^-1 (46.5% for pristine HC), and cycling stability with 95% capacity maintained for 90 cycles (86.4% for pristine HC). Additionally, the ICE can be optimized up to 76% by using sodium carboxymethyl cellulose as a binder. This work provides an important view of optimizing Na storage performances of HC anodes by pore engineering, which can be broadened into other electrode materials.

Elucidating the Mechanism of Fast Na Storage Kinetics in Ether Electrolytes for Hard Carbon Anodes

The sodium storage performance of a hard carbon (HC) anode in ether electrolytes exhibits a higher initial Coulombic efficiency (ICE) and better rate performance compared to conventional ester electrolytes. However, the mechanism behind faster Na storage kinetics for HC in ether electrolytes remains unclear. Herein, a unique solvated Na⁺ and Na⁺ co-intercalation mechanism in ether electrolytes is reported using designed monodispersed HC nanospheres. In addition, a thin solid electrolyte interphase film with a high inorganic proportion formed in an ether electrolyte is visualized by cryo transmission electron microscopy and depth-profiling X-ray photoelectron spectroscopy, which facilitates Na⁺ transportation, and results in a high ICE. Furthermore, the fast solvated Na⁺ diffusion kinetics in ether electrolytes are also revealed via molecular dynamics simulation. Owing to the contribution of the ether electrolytes, an excellent rate performance (214 mAh g^-1 at 10 A g^-1 with an ultrahigh plateau capacity of 120 mAh g^-1 ) and a high ICE (84.93% at 1 A g^-1 ) are observed in a half cell; in a full cell, an attractive specific capacity of 110.3 mAh g^-1 is achieved after 1000 cycles at 1 A g^-1 .

Al-Storage Behaviors of Expanded Graphite as High-Rate and Long-Life Cathode Materials for Rechargeable Aluminum Batteries

The rational design and synthesis of capable cathode materials with low cost that can exhibit good electrochemical performance are key to the development of rechargeable aluminum batteries (RABs). In this article, we have developed low-cost expanded graphite as typical cathode materials for high-performance RABs in pouch cells. Remarkably, the commercial expanded graphite can show high-rate performance, long-term cyclic life, and high energy density (64 Wh kg^-1 based on a whole pouch cell). In particular, it delivers a high capacity of 111 mAh g^-1 at a current density of 2 A g^-1 after 300 cycles and 61.1 mAh g^-1 at a high current density of 50 A g^-1 after 10 000 cycles. The high-rate performance is derived from the rapid kinetic enhancement caused by the chemisorption-involved-intercalation pseudocapacitance effect. Further, a series of facile electrochemical means are used to confirm the intercalation (1.5-2.4 V)-adsorption mechanism (0.5-1.5 V) of expanded graphite. This work can provide significant support for further understanding the Al-storage behaviors of graphite materials in RABs.

PY13FSI-Infiltrated SBA-15 as Nonflammable and High Ion-Conductive Ionogel Electrolytes for Quasi-Solid-State Sodium-Ion Batteries

Exploring electrolytes of high safety is essential to pave the practical route for sodium-ion batteries (SIBs) toward their important applications in large-scale energy storage and power supplies. In this regard, ionogel electrolytes (IEs) have been highlighted owing to their high ionic conductivity, prominent electrochemical and thermal stability, and, more crucially, high interfacial wettability. However, present studies lack an understanding of the interaction of IEs, which determines the ion desolvation and migration. In this article, IEs comprising an SBA-15 host, an ionic liquid, sodium salt, and poly(vinylidene fluoride)-hexafluoro propylene (PVDF-HFP) have been proposed by mechanical ball milling and roller pressing. The component ratio has been optimized based on the balance between ionic conductivity and self-supporting capability of IEs. The optimal IEs showed sufficiently high ionic conductivity (2.48 × 10^-3 S cm^-1 at 30 °C), wide electrochemical window (up to 4.8 V vs Na⁺/Na), and high Na⁺ transference number (0.37). Due to the presence of SBA-15 and an ionic liquid, the IEs exhibited much improved thermal resistance than that of the conventional organic liquid electrolytes (OLEs). Furthermore, Fourier transform infrared (FT-IR) spectroscopy revealed the hydrogen bonding interaction between silanols and the dissolved salts, not only anchoring anions for immobilization but also promoting the dissociation of sodium salts. After being matched with the Na₃V₂(PO₄)₃ (NVP) cathode and metallic Na anode, the SIBs presented a specific discharge capacity of up to 110.7 mA h g^-1 initially at room temperature with 92% capacity retention after 300 cycles. The improved safety and electrochemical performance provided insights into rationally regulating IEs and their interactions with the prospect of strengthening their practical applications in SIBs.