Hard Carbon Research Articles

B, N Co-Doped Hard Carbon Nano-Sponge Enhancing Half and Full Cell Performance in Na-Ion Batteries.

Hard carbon is a promising anode material for next-generation sodium-ion batteries (NIBs) due to its high specific capacity, low working potential, and excellent structural stability. This research focuses on synthesizing boron- and nitrogen-co-doped hard carbon (BNHC), which shows enhanced sodium storage properties in half and full-cell configurations. The BNHC is prepared using a simple, scalable sol-gel method followed by pyrolysis for carbonization. Its 3D nano-sponge structure provides abundant active sites for sodium storage, while the low surface area and optimal interlayer distance minimize volume expansion during high-rate charge/discharge cycles, ensuring exceptional cycling stability. Compared to undoped hard carbon, BNHC demonstrates significantly improved sodium storage performance. The BNHC electrode achieves a reversible capacity of ≈310 mAh g⁻¹ with ultra-long cycling stability at high current rates and robust rate capability. It delivers ≈115 mAh g⁻¹ at an exceptionally high current density of 10 A g⁻¹. Further, BNHC//NaFePO4 full cell demonstrates excellent cycling stability with ≈206 mAh g⁻¹ at a 150mA g⁻¹ current rate. This study paves the way to commercializing hard carbon as an anode material for sodium-ion batteries.

Closed Pore Architecture and Sodium Cluster Deposit Visualization in Hard Carbon.

Achieving the full potential of hard carbon (HC) for sodium storage requires a deep understanding of its complex porous structure as well as charge storage mechanism. While the contribution of sodium deposition within HC pores to the overall capacity is recognized, detailed visualization and mechanistic understanding of this process remain challenging. This study leverages advanced electron microscopy techniques to probe the intricate pore architecture of HC and directly visualize sodium storage within its pores. By employing an HC material (PHC-1) with rich closed pores as the platform material, electron tomography is utilized to reconstruct the pore architecture of PHC-1, providing quantitative insights into porosity, pore size, and pore structure. Low-dose electron microscopy visualizes metastable sodium clusters filling up within the pores during sodiation. Complementary in-situ and ex-situ characterizations further elucidate the synergistic adsorption-intercalation-filling mechanism of PHC-1. This contribution provides significant insights into the structure-property correlation of HC.

Redefining closed pores in carbons by solvation structures for enhanced sodium storage

Closed pores are widely accepted as the critical structure for hard carbon negative electrodes in sodium-ion batteries. However, the lack of a clear definition and design principle of closed pores leads to the undesirable electrochemical performance of hard carbon negative electrodes. Herein, we reveal how the evolution of pore mouth sizes determines the solvation structure and thereby redefine the closed pores. The precise and uniform control of the pore mouth sizes is achieved by using carbon molecular sieves as a model material. We show when the pore mouth is inaccessible to N2 but accessible to CO2 molecular probes, only a portion of solvent shells is removed before entering the pores and contact ion pairs dominate inside pores. When the pore mouth is inaccessible to CO2 molecular probes, namely smaller than 0.35 nm, solvent shells are mostly sieved and dominated anion aggregates produce a thin and inorganic NaF-rich solid electrolyte interphase inside pores. Closed pores are accordingly redefined, and initial coulombic efficiency, cycling and low-temperature performance are largely improved. Furthermore, we show that intrinsic defects inside the redefined closed pores are effectively shielded from the interfacial passivation and contribute to the increased low-potential plateau capacity.

Recent Advances, Key Strategies, and Challenges in Fast‐Charging Hard Carbon Anodes for Sodium‐Ion Batteries

AbstractSodium‐ion batteries (SIBs) have gradually entered the application market after years of development. To enhance user experience and reduce waiting time, the development of fast‐charging SIBs has become an inevitable trend. However, hard carbon (HC) anode materials currently in use face significant challenges, such as capacity degradation and sodium metal plating during fast‐charging. This paper explores the entire process of Na+ migration from the electrolyte to the bulk phase of the HC and examines the factors influencing Na+ migration at each stage. It then summarizes key strategies for achieving fast‐charging HC for SIBs, with a focus on electrolyte optimization, surface coating, and bulk structural optimization. Finally, the paper highlights the main challenges and future prospects for developing fast‐charging HC anodes, offering valuable insights for advancing fast‐charging SIBs technologies.

Revealing evolution of lithium storage mechanism in hard carbon for designing advanced low temperature li-ion batteries

Revealing evolution of lithium storage mechanism in hard carbon for designing advanced low temperature li-ion batteries

High-energy and long-life O3-type layered cathode material for sodium-ion batteries

O3-type layered oxide for sodium-ion batteries have attracted significant attention owing to their low cost and high energy density. However, their applications are restricted by rapid capacity decay during long-term cycling, with uneven Na+ distribution and microcrack formation being key contributing factors. In this study, a customized reconstruction layer integrating a fast ion conductor NaCaPO4 coating with gradient Ca2+ doping is developed to enhance the surface chemical and mechanical stability of the layered cathodes. The gradient Ca2+ doped interphase facilitates uniform phase transformation within the particles, minimizes lattice mismatch, ensures even Na+ distribution, and mitigates microcrack formation through a pinning effect. Consequently, the optimized sample exhibits improved electrochemical performance and robust reliability under high-voltage conditions and a broad temperature range (−10 to 50 °C). The practical feasibility of a pouch-type full cell paired with a hard carbon anode is demonstrated by a high capacity retention of 82.9% after 300 cycles at 0.5 C. This scalable interface modification strategy provides valuable insights into the development of advanced oxide cathode materials for sodium-ion batteries.

C60 to Modulate the Closed Pore Structures of Hard Carbon for High-Performance Sodium-Ion Batteries.

Hard carbon (HC) has emerged as a highly promising anode material for sodium-ion batteries (SIBs) attributed to its characteristic low-potential charge and discharge plateau. Recent studies have shown that the plateau capacity of HC mainly originates from the filling of the nanoscale closed pores by sodium. However, the precise design of the closed pore structure of HC remains a great challenge. Herein, C60 with a diameter of 0.7 nm is used to promote the formation of closed pores in phenolic resin-based HC. The spherical structure of C60 facilitates the oriented crystallization of graphitic microdomains within phenolic resin-based HC, thereby enhancing the uniformity of the closed pore structure of HC. Furthermore, during high-temperature carbonization, C60 undergoes fragmentation and structural reorganization, which increases the closed pore volume and introduces additional sodium storage sites. As a result, the optimal HC provides an excellent reversible capacity of 361 mA h g-1 at 20 mA g-1 and a high plateau capacity of 268 mA h g-1. This work provides deep insights into the mechanism of forming closed pores on the nanoscale, advancing the development of high-performance SIBs.

Ti-Doped, Mn-Based Polyanionic Compounds of Na4Fe1.2Mn1.8(PO4)2P2O7 for Sodium-Ion Battery Cathode

Na4Fe3(PO4)2P2O7 (NFPP) is recognized as a prospective electrode for sodium-ion batteries (SIBs) because of its structure stability, economic viability and environmental friendliness. Nevertheless, its commercialization is constrained by low operating voltage and limited theoretical capacity, which result in a power density significantly inferior to that of LiFePO4. To address these limitations, in this work, we first designed and synthesized a series of Mn-doped NFPP to enhance its operating voltage, inspired by the successful design of LiFe1-xMnxPO4 cathodes. This approach was implemented to enhance the operating voltage of the material. Subsequently, the optimized Na4Fe1.2Mn1.8(PO4)2P2O7 (1.8Mn-NFMPP) sample was selected for further Ti-doped modification to enhance its cycle durability and rate performance. The final Mn/Ti co-doped Na4Fe1.2Mn1.7Ti0.1(PO4)2P2O7 (0.1Ti-NFMTPP) material exhibited a high operating voltage of ~3.6 V (vs. Na+/Na) in a half cell, with an outstanding reversible capacity of 122.9 mAh g−1 at 0.1 C and remained at 90.6% capacity retention after 100 cycles at 0.5 C. When assembled into a coin-type full cell employing a commercial hard carbon anode, the optimized cathode material exhibited an initial capacity of 101.7 mAh g−1, retaining 86.9% capacity retention over 50 cycles at 0.1 C. These results illustrated that optimal Mn/Ti co-doping is an effective methodology to boost the electrochemical behavior of NFPP materials, achieving mitigation of the Jahn–Teller effect on the Mn3+ and Mn dissolution problem, thereby significantly improving structural stability and cycling performance.

Bark‐Derived Oxygen‐Doped Porous Hard Carbon Anodes for Potassium‐Ion Batteries

Bark‐Derived Oxygen‐Doped Porous Hard Carbon Anodes for Potassium‐Ion Batteries

Bridging Structure and Performance: Decoding Sodium Storage in Hard Carbon Anodes

Bridging Structure and Performance: Decoding Sodium Storage in Hard Carbon Anodes

Carbon material derived from biomass: A study of structural and electrochemical performances for dual-carbon sodium-ion batteries

Abstract Biomass is one of the attractive, renewable, widely available, and cost-effective precursors to obtain carbon. In this work, the carbon-based material derived from coconut shell was produced by carbonization method that is applicable for anode materials especially dual-carbon sodium-ion batteries. The as-synthesized coconut shell was burned to be a charcoal named as HC-A. The charcoal was further proceeded by heating using a furnace with the temperature of 1000°C named as HC-B. Commercial hard carbon named as HC-C was also prepared to compare the quality of samples. The specific capacitance obtained from cyclic voltammetry test of sample HC-A, HC-B, and HC-C with a scan rate of 25 mV/s are 6.73×10-3 F/g, 1.10×10-3 F/g and 4.09×10-3 F/g, respectively. The Na+ ion diffusion coefficient of sample HC-A, HC-B and HC-C obtained from electrochemical impedance spectroscopy test are 5.75 ×10-15cm2s-1, 2.85 ×10-15cm2s-1, and 1.78×10-15cm2s-1. The results display that carbon material from coconut shell and hard carbon commercial have comparable value indicating by the same order of electrochemical quantity. This comprehensive study provides a feasible method and opens new opportunities for biomass carbon, and extends the strategy to design the high-performance anode materials for batteries.

Graphite Cone/Disc Anodes as Alternative to Hard Carbons for Na/K‐Ion Batteries

AbstractAs sodium‐ion batteries compete for dominance in the energy storage market, the problem arises when using traditional graphitic anodes. Graphitic anodes used in Li‐ion batteries do not work well due to the limitation of Na‐ion diffusion and intercalation into graphite lattice. It is demonstrated that graphitic carbon cones and disks, manufactured via the scalable pyrolysis of hydrocarbons, are viable anode candidates for Na‐ion and K‐ion batteries. These distinctive pure graphitic carbon structures, without any heteroatoms present, show excellent Na‐ion intercalation, exhibiting a reversible capacity of ≈230 mAh g−1 at a current rate of 20 mA g−1 and excellent rate performance. The electrode has also been shown to exhibit excellent performance in K‐ion intercalation. Ex situ TEM analysis (at room and cryo temperatures) and solid‐state NMR spectroscopy show intercalated sodium and potassium evidence, revealing the charge storage mechanism. These pure graphitic structures can be a potential anode candidates for the next generation of beyond‐lithium batteries due to their morphologies that allow for reversible intercalation of larger ions without structural modifications.

Rapid Formation Strategy for Enhanced Electrochemical Performance of Hard Carbon Anodes in Sodium-Ion Batteries.

The conventional formation process of sodium-ion batteries (SIBs), which relies on low-current cycling, is one of the most energy-intensive and time-consuming steps in battery production, significantly contributing to overall manufacturing costs. This study systematically evaluates the formation of SIB pouch cells under different protocols and demonstrates that high-rate formation can achieve superior electrochemical performance. Our optimized high-rate formation process reduces formation time by 52.3% compared to the conventional method, presenting a cost-effective and efficient approach to SIB production. Notably, the accelerated formation process promotes the development of a denser, more uniform, and highly stable solid-electrolyte interphase (SEI) on the anode surface, enhancing initial Coulombic efficiency, capacity retention, and long-term cycling stability. These findings provide a promising strategy for improving the scalability and economic viability of SIB technology.

Fe2O3 Nanoparticles on Hard Carbon as Anode of Sodium-Ion Batteries

Hard carbon is a commonly used anode material for sodium-ion batteries (SIBs) due to its high cycling stability. However, its specific capacity is limited due to its intercalation and de-intercalation mechanism. On the contrary, metal oxide has a higher specific capacity due to its conversation mechanism. However, its electric conductivity is low. In this work, a strategy of coating iron oxide (Fe2O[Formula: see text] nanoparticles on the surface of hard carbon is developed to enhance the electrochemical performance of SIB anodes. Composites with different contents of Fe2O3 are synthesized, and their morphology and electrochemical performance are characterized. The results show that the increase of Fe2O3 in composite can obviously increase the capacity of composite. However, the cycling stability is decreased. Composite with 38% Fe2O3 exhibits high reversible specific capacity (413.7[Formula: see text]mAh[Formula: see text]g[Formula: see text] at 100[Formula: see text]mA[Formula: see text]g[Formula: see text], high rate performance (182.1[Formula: see text]mAh[Formula: see text]g[Formula: see text] at 5[Formula: see text]A[Formula: see text]g[Formula: see text], and acceptable cycling stability (333.8[Formula: see text]mAh[Formula: see text]g[Formula: see text] after 100 cycles at 100[Formula: see text]mA[Formula: see text]g[Formula: see text]. GCD curves after different cycles are compared, and the possible reason for capacity decay is suggested.

Probing the Properties of Locally Formed Solid Electrolyte Interphases on Hard Carbon Anodes

AbstractThe solid electrolyte interphase (SEI) formation on hard carbon (HC), as one of the most widely used anode materials in sodium (Na)‐ion batteries, is still not fully understood compared to the SEI formation on anodes used in lithium (Li)‐ion batteries, in terms of passivation properties and stability, which strongly depends on various factors such as experimental parameters and the electrolyte composition. Herein, we report the localized formation of SEI microspots on HC using cyclic voltammetry in combination with scanning electrochemical cell microscopy (SECCM) in non‐aqueous ether‐ and carbonate‐based electrolytes. Using the same instrumental setup for SECCM and for atomic force microscopy (AFM), the locally formed SEI spots could be directly characterized with respect to the morphology, height, passivation and nanomechanical properties in dependence of the experimental deposition parameters such as scan rate and cycling number. In addition, time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) in combination with AFM revealed the chemical composition of the SEI layer by recording spatially resolved 3D mass maps of the SEI spots. This combination of high‐resolution microscopic and spectrometric methods provides new insights into the dynamics of SEI formation as a function of the electrolyte and the experimental parameters.

A “Cool” Route to Battery Electrode Material Recovery

AbstractThe increasing demand for alkali metal‐ion batteries necessitates efficient and sustainable recycling solutions for both end‐of‐life batteries and production scrap. This study introduces a novel, cost‐effective, and scalable electrode delamination technique, termed “ice‐stripping,” which employs sub‐zero freezing to achieve near‐complete (>90%) recovery of electrode coatings. Water is sprayed onto the electrode surface and placed on a sub‐zero surface; the water freezes, forming a strong interfacial bond of the electrode coating to the cold plate. This enables the current collector to be stripped away from the electrode due to the stronger adhesion of the electrode to the plate. Unlike conventional thermal or chemical delamination methods, ice‐stripping minimizes energy consumption, eliminates hazardous chemicals, and preserves the morphology and integrity of reclaimed materials. The technique is successfully applied to scrap and end‐of‐life lithium‐ion and sodium‐ion battery electrodes with various binder systems. Case studies focus on the recovery efficiencies and potential for direct recycling of Prussian white and hard carbon electrodes, graphite from end‐of‐life cells, and cathode and anode manufacturing scrap. Scalability and integration are also discussed. Given its efficiency and sustainability, ice‐stripping represents a transformative step forward in battery recycling technology, reducing environmental impact and promoting material circularity.

Engineering Alkali Lignin Structure Modification: Enhanced Hard Carbon Electrolyte Interface Toward Practical Sodium Ion Batteries.

Hard carbon (HC) exhibits great potential as a promising candidate for sodium-ion batteries owing to its inherent advantages. However, the main challenges in utilizing HC stem from its low initial coulombic efficiency (ICE) and poor rate performance caused by its excessive surface defects. In this study, an effective strategy of employing alkali lignin (AL) is proposed, derived from pulp waste, as a binder for HC to create a uniform and inorganically enriched solid electrolyte interface. AL can modify the surface defects of HC through strong π-π interactions between the aromatic ring of AL and HC, while ingeniously grafting abundant active ─OH and ─COOH groups onto the electrode surface. The strong binder force between AL and electrolyte salts facilitates the formation of an ultra-thin NaF-rich solid electrolyte interface (SEI) layer (10 nm), thereby achieving an exceptional ICE of 91%. Furthermore, owing to its electrochemical activity, AL enables HC anode to exhibit an increasing slope capacity during cycling, compensating for capacity decay at high current densities. Consequently, when assembled into a full battery configuration, excellent rate performance is achieved with a reversible capacity of 282 mAh g-1 even at a current density of 5A g-1.

Designing high-valence sulfur-containing stable and low impedance interface films simultaneously on cathode and anode in the NaNi1/3Fe1/3Mn1/3O2 (NFM)||hard carbon (HC) pouch cells

Designing high-valence sulfur-containing stable and low impedance interface films simultaneously on cathode and anode in the NaNi1/3Fe1/3Mn1/3O2 (NFM)||hard carbon (HC) pouch cells

Revealing the storage mechanism of plateau-dominated S-doped hard carbon as high-performance anode for sodium-ion batteries

Revealing the storage mechanism of plateau-dominated S-doped hard carbon as high-performance anode for sodium-ion batteries

Acidic Potassium Permanganate-Induced Hierarchical Pores in Bamboo-Based Hard Carbon for High-Performance Sodium-Ion Batteries.

Due to its unique structure and high capacity, bamboo-based hard carbon is often regarded as the most promising anode material for sodium-ion batteries. However, low sodium storage ability and poor Na+ transportation limit the development of bamboo-derived hard carbon. In this study, bamboo powder (BP) was pretreated with acidic potassium permanganate, in which the strong oxidizing properties introduced more oxygen-containing functional groups into the carbon skeleton. In addition, the two-step carbonization process facilitated the formation of hierarchical pore structures in the bamboo-based hard carbon (BP-A-P). Electrochemical measurements demonstrated that BP-A-P exhibited superior activity and stability. Under the current multiplication of 0.1 C, a reversible specific capacity of 338 mAh/g was achieved with a high first Coulombic efficiency of 81.7%. The excellent performance in sodium transportation and storage is mainly attributed to the rich micropores and abundant closed pores, which are induced by acidic potassium permanganate. Moreover, BP-A-P exhibits superior stability with a specific capacity maintained at 273 mAh/g after 100 cycles. Thus, acidic potassium permanganate treatment provides a new strategy for achieving complex hierarchical pores in bamboo-based hard carbon for high-performance sodium-ion batteries.