Hard Carbon Anode Research Articles

Abnormal Gas Generation during First Discharge Process of Sodium Ion Battery.

In recent years, sodium-ion batteries (SIBs) have attracted a lot of attention and are considered an ideal alternative to lithium-ion batteries (LIBs). The hard carbon (HC) anode in SIBs presents a unique challenge for studying the formation process of the solid electrolyte interphase (SEI) during initial cycling, owing to its distinctive porous structure. This study employs a combination of ultrasonic scanning techniques and differential electrochemical mass spectrometry to conduct an in-depth analysis of the two-dimensional distribution and composition of gases during the formation process. The findings reveal distinct gas evolution behaviors in SIBs compared to LIBs during formation. Notably, significant gas evolution is observed during the discharge phase of the formation cycle in SIBs, with higher discharge rates leading to increased gas evolution rates. This phenomenon is likely attributed to the adsorption of CO2 gas by the abundant pores in HC, followed by desorption during discharge. Furthermore, the study demonstrates that the addition of 5A molecular sieves, which competitively adsorb gases, effectively reduces gas adsorption on the anode during formation, thereby significantly enhancing battery performance. This research elucidates the gas adsorption and desorption behavior at the battery interface, providing new insights into the SEI formation process in SIBs.

Abnormal Gas Generation during First Discharge Process of Sodium Ion Battery

AbstractIn recent years, sodium‐ion batteries (SIBs) have attracted a lot of attention and are considered an ideal alternative to lithium‐ion batteries (LIBs). The hard carbon (HC) anode in SIBs presents a unique challenge for studying the formation process of the solid electrolyte interphase (SEI) during initial cycling, owing to its distinctive porous structure. This study employs a combination of ultrasonic scanning techniques and differential electrochemical mass spectrometry to conduct an in‐depth analysis of the two‐dimensional distribution and composition of gases during the formation process. The findings reveal distinct gas evolution behaviors in SIBs compared to LIBs during formation. Notably, significant gas evolution is observed during the discharge phase of the formation cycle in SIBs, with higher discharge rates leading to increased gas evolution rates. This phenomenon is likely attributed to the adsorption of CO2 gas by the abundant pores in HC, followed by desorption during discharge. Furthermore, the study demonstrates that the addition of 5A molecular sieves, which competitively adsorb gases, effectively reduces gas adsorption on the anode during formation, thereby significantly enhancing battery performance. This research elucidates the gas adsorption and desorption behavior at the battery interface, providing new insights into the SEI formation process in SIBs.

Hard carbon anode materials for hybrid sodium-ion/metal batteries with high energy density

Interest in sodium-ion batteries (SIBs) as a lower-cost alternative to lithium-ion batteries (LIBs) is growing in both scientific and industrial fields. However, uneven premature sodium deposition and dendrite formation during cycling pose a serious safety threat, significantly limiting the application of SIBs. Achieving reversible and dendrite-free sodium metal deposition and dissolution on the anode surface is key to developing anode-less sodium batteries, the next generation of SIBs with energy densities comparable to those of LIBs. In anode-less systems, sodium ions not only intercalate into the anode's structure but also deposit on its surface, thereby multiplying the specific capacity. Here, we evaluate state-of-the-art hard carbon (HC) used in traditional SIBs as a potential anode material for anode-less sodium batteries. We present comprehensive research on sodium-ion/metal storage, depending on the type of carbon anode material, particle size and morphology of hard carbons, and the electrolyte and additives used. Half-cells with microspherical HC and a fluoroethylene carbonate-based electrolyte operated for over 3000 h, yielding an average discharge capacity of 550 mAh g−1, nearly twice that of HC in classic SIBs. Anode-less Na3V2(PO4)3||HC full cells demonstrated up to 25 % higher energy density and working potential compared to traditional full cells.

Reducing defects in hard carbon graphite domain: Employing a fully dynamic bonding with a multi-crosslinked biomass-based binder for enhanced sodium ion storage

Binders are crucial for maintaining the integrity of an electrode and are confronted with the imperative for multifunctionality. Herein, we have developed and synthesized an entirely biomass-based water-soluble binder with outstanding adhesion, conductivity, flowability, and dispersibility for the hard carbon (HC) anode. Specifically, MXene (Ti3C2Tx) reduces the amount of HC graphite domain imperfections, the cross-linked carboxymethyl chitosan (CCS) chain facilitates Na+ movement, and the amphiphilic nature of lignosulfonate (LS) enhances the distribution of active material. As a result, the HC anode achieves an initial coulombic efficiency (ICE) of 88 % and high-capacity retention of 110 % after 100 cycles. This work promotes the progress of green energy in parallel with the promotion of the high-value utilization of biomass.

Spatial confinement strategy modulated by kinetic diameters of gaseous molecules for sodium storage

Constructing closed pore structures is essential for improving the plateau capacity of high-capacity hard carbon (HC) anodes for sodium-ion batteries. However, the absence of a straightforward and efficient strategy for constructing closed pores has hindered the advancement of high-capacity HC anodes. Here, we have developed a spatial confinement strategy for constructing closed pore structures using pyrolytic carbon (PC) as substrate and pyrolysis gas as the carbon source for chemical vapor deposition. The deposition of pyrolysis gas effectively tightens the pore entrance, thereby preventing electrolyte infiltration and transforming the open pores in the PC into highly efficient sites for sodium storage. The obtained optimal anodes demonstrate a remarkable specific capacity of 324.6 mAh g-1. More importantly, we calculate the kinetic diameters of the carbon source molecules from their iso-electron density surfaces and correlate them with the mechanism of closed pore formation, which will effectively guide the fabrication of closed pores for sodium storage.

High temperature induced abundant closed nanopores for hard carbon as high-performance sodium-ion batteries anodes

Hard carbon (HC) stands out as the preeminent anode material for sodium-ion batteries (SIBs) which are deployed in expansive energy storage infrastructures. Herein, the large enough graphene nanosheets interlayer and abundant nanopores with a diameter of ∼2.1 nm induced by adjusting the pyrolysis temperature in the thermosetting phenolic resin-derived hard carbon matrix to augment the performance of the sodium ion storage. The presence of sufficiently large carbon interlayers has been proven to provide active sites for reversible adsorption, enabling effective storage of sodium ions in the high-voltage slope region, while also promoting rapid Na+ transport. Meanwhile, forming abundant closed nanopores with larger sizes helps sodium ion storage in the low-voltage plateau region. In the optimized samples, the formation of sufficient long graphene nanosheets with a perfect crystal lattice, which further shrinks to form enclosed nanopores, effectively reduces defective sites and specific surface area. Additionally, the appropriate content of C-O and C=O functional groups contributes to an exceptional initial Coulombic efficiency (ICE) of up to 93%. Simultaneously, the optimized sample HC-1500 contributes to a remarkable plateau capacity of 294 mAh g-1 during the charging process (high reversible capacity of 403 mAh g-1 at 0.1 C). Moreover, based on the microstructure evolution and Na storage behavior of hard carbon, an “adsorption (27%) – filling (73%)” sodium storage mechanism that the sodium storage as a quasi-metallic sodium state is demonstrated. Consequently, this study will offer valuable insights for the development of hard carbon anodes tailored for high-energy practical SIBs, while also advancing the understanding of sodium storage mechanisms.

A three-in-one strategy of high-entropy, single-crystal, and biphasic approaches to design O3-type layered cathodes for sodium-ion batteries

O3-type layered oxides are promising cathodes for sodium-ion batteries (SIBs). However, severe volume changes, irreversible phase transitions, and sluggish Na+ ion transport kinetics lead to structural collapse and severe capacity loss. Herein, a three-in-one strategy “high entropy, single crystal, and biphase” is proposed to design O3-type layered cathodes for SIBs, which achieves enhanced structural stability and Na+ transport kinetics by the combination effect of multimetal high-entropy, the single crystal, and Li substitution. The as-prepared high-entropy oxide (HEO) cathode, Na(Fe1/6Co1/6Ni1/6Mn1/6Ti1/6)Li1/6O2, exhibits a high reversible capacity of 140.3 mAh g−1, robust cycling stability, exceptional rate capability (86 mAh g−1 at rates of 15C), excellent air-stability, and water-resistance ability. In situ X-ray diffraction reveals that the HEO cathode has highly reversible phase transitions and small volume change (ΔV=3.28 %). Ex situ X-ray absorption spectroscopy reveals that reversible Ni2+/Ni4+, Fe3+/Fe3.6+, and Co3+/Co3.6+ redox couples provide charge compensation for the high-entropy cathode at 2.0∼4.2 V. Notably, the full-cell battery based on the high-entropy cathode and hard carbon anode delivers a specific capacity of 134.3 mAh g−1 and an energy density of 390.8 Wh kg−1. This work provides valuable insights into the design of novel high-performance high-entropy cathodes for SIBs, highlighting a promising avenue for advancing rechargeable battery technology.

Inorganic-Enriched Solid Electrolyte Interphases: A Key to Enhance Sodium-Ion Battery Cycle Stability?

The characteristics of solid electrolyte interphase (SEI) at both the cathode and anode interfaces are crucial for the performance of sodium-ion batteries (SIBs). The research demonstrates the merits of a balanced organic component, specifically the organic sodium alkyl sulfonate (ROSO2Na) featured in this work, in conjunction with the inorganic sodium fluoride (NaF), to enhance the interfacial stability. Using a customized electrolyte, it has optimized the interphase, curbing excess NaF production, and created a thin and uniform NaF/ROSO2Na-rich SEI layer. It offers exceptional protection against interface deterioration, transition metal dissolution, and concurrently ensures a consistent reduction in interfacial impedance. This creative approach results in a substantial improvement in the performance of both the Na0.9Ni0.4Fe0.2Mn0.4O2 cathode and the hard carbon anode. The cathode demonstrates remarkable average Coulombic efficiency exceeding 99.9% and a capacity retention of 81% after 500 cycles. Furthermore, the Ah-level pouch cell has shown outstanding performance with an 87% capacity retention after 400 cycles. Moving beyond the prevailing focus on inorganic-rich SEI, these results highlight the effectiveness of the customized organic-inorganic hybrid SEI formulation in improving SIB technology, offering an adaptable solution that ensures superior interfacial stability.

Steric Hindrance Engineering to Modulate the Closed Pores Formation of Polymer-Derived Hard Carbon for High-Performance Sodium-Ion Batteries.

The closed pores play a critical role in improving the sodium storage capacity of hard carbon (HC) anode, however, their formation mechanism as well as the efficient modulation strategy at molecular level in the polymer-derived HCs is still lacking. In this work, the steric hindrance effect has been proposed to create closed pores in the polymer-derived HCs for the first time through grafting the aromatic rings within and between the main chains in the precursor. The experimental data and theoretical calculation demonstrate that steric-hindrance effect from the aromatic ring side group can increase backbone rigidity and the internal free volumes in the polymer precursor, which can prevent the over graphitization and facilitate the formation of closed pores during the carbonization process. As a result, the as-prepared HC anode exhibits a remarkably enhanced discharge capacity of 340.3 mAh/g at 0.1 C, improved rate performance (210.7 mAh/g at 5 C) as well as boosted cycling stability (86.4 % over 1000 cycles at 2 C). This work provides a new insight into the formation mechanisms of closed pores via steric hindrance engineering, which can shed light on the development of high-performance polymer-derived HC anode for sodium-ion batteries.

Mini-Review on Advanced Characterization Techniques for Insights into the Sodium Storage Mechanism of Hard Carbon Anodes: Recent Advances and Future Perspectives

Mini-Review on Advanced Characterization Techniques for Insights into the Sodium Storage Mechanism of Hard Carbon Anodes: Recent Advances and Future Perspectives

Ameliorating the sodium storage performance of hard carbon anode through rational modulation of binder

Hard carbon anodes have emerged as promising candidates for sodium-ion batteries due to their inherent advantages. Nevertheless, the surface imperfections in these materials often culminate in irreversible electrolyte consumption, fostering the development of a heterogeneous and fragile solid electrolyte interface (SEI), thereby compromising the initial Coulombic efficiency (ICE). Drawing inspiration from the catalytic potential of C=O (carbonyl) bonds in directing preferential salt reduction, we introduce a novel strategy that leverages the modulation of the binder, a long-term overlooked pivotal components in the electrode process. Specifically, Polymethyl methacrylate (PMMA), abundant in C=O groups, is partially substituted for PVDF, ensuring robust adhesion of the electrode material to the current collector while preserving superior mechanical properties. The accurate combination of two binders with delightful compatibility in the state-of-art electrode process, can promote a uniform formation of the SEI on the hard carbon surface enriched in inorganic components, which can ensure long-term interfacial stability and suppresses excessive solvent decomposition and facilitates Na+ transfer at the interface. Consequently, the initial Coulombic efficiency of the hard carbon anode with 70 %PMMA binder achieves 86 %, with prominent cycling stability (88 % capacity retention over 500 cycles) at a high current density of 1.2 A g−1. When paired with high loading cathodes to assemble the pouch cell, it also demonstrates stable operational scenarios.

A Customized Strategy Realizes Stable Cycle of Large‐Capacity and High‐Voltage Layered Cathode for Sodium‐Ion Batteries

High‐voltage P2‐Na0.67Ni0.33Mn0.67O2 layered oxide cathode exhibits significant potential for sodium‐ion batteries, owing to the elevated operating voltage and theoretical energy density beyond lithium iron phosphate, but the large‐volume phase transition is the devil. Currently, this type cathode still suffers from stability–capacity trade‐off dilemma. Herein, a concept of customized strategy via multiple rock‐forming elements trace doping is presented to address the mentioned issue. The customized Mg‐Al‐Ti trace doped cathode maintains a notable capacity of 140.3 mAh g − 1 with an energy density approaching 500 Wh kg − 1, and shows good cycle stability, retaining 89.0% of its capacity after 50 cycles at 0.1C. Additionally, the full cell, paired with a hard carbon anode, achieves an advanced energy density of 303.3 Wh kg−1. The multiple characterizations reveal the failure mechanism of contrast sample involving severe intragranular cracks coupled with layer to rock salt transformation, which reduces active substance and increases charge transfer resistance. The doped sample with increased sliding energy barrier well suppresses this phenomenon. Impressively, the customized strategy can be extended to Mg‐Fe‐Ti system. This research provides a novel concept for the design of high energy sodium‐ion cathode.

Unravelling the anionic stability of an ether-based electrolyte with a hard carbon or metallic sodium anode for high-performance sodium-ion batteries

In hard carbon (HC) anodes, elucidating the relationship between the solid electrolyte interphase formation and the solvated Na+ co-intercalation mechanism is crucial, particularly considering different anionic salts in ether-based electrolytes. Here, we comprehensively explore the impact of different anionic salts on the electrochemical performance of HC/Na half-cell and elucidate the underlying mechanism through experimental studies and theoretical calculations. The surface morphology of the HC anode and its interphasial property are further investigated to evaluate the differences endowed by the presence of various anionic salts in diglyme (2G). The HC/Na half-cells with NaPF6-2G and sodium trifluoromethanesulfonate (NaCF3SO3)-2G display superior electrochemical performance with faster kinetics and lower interfacial resistance than those with NaClO4-2G, sodium bis-(fluorosulfonyl) imide (NaFSI)-2G and sodium bis-(trifluoromethanesulfonyl) imide (NaTFSI)-2G. NaClO4-2G forms a relatively thick interphase layer with high resistance at the electrode/electrolyte interface owing to its insufficient stability. NaFSI-2G and NaTFSI-2G exhibit severe side reactions with Na metal, producing a thick interphase layer on the HC surface with high interfacial resistance from excess electrolyte decomposition, thus deteriorating the electrochemical performance. In summary, the study on the stability of different anionic salts in ether-based electrolyte for the HC anode with the intercalation mechanism provides valuable insights for screening appropriate conductive salts for high-performance sodium-ion batteries, especially when considering Na metal counter/reference electrodes.

Regulation of surface oxygen functional groups in starch-derived hard carbon via pre-oxidation: A strategy for enhanced sodium storage performance

During the process of sodium storage in hard carbon anodes, the significance of surface oxygen functional groups cannot be overlooked. In this work, we utilize starch as raw material to synthesize hard carbon by the process of pre-oxidation and two-step carbonization. XPS analysis reveals that pre-oxidation bolsters the presence of CO bonds, thereby providing more active sites. TEM analysis reveals that hard carbon with pseudo-graphite and graphite-like structure is obtained at relatively high carbonization temperature (1400 °C), and the formation of closed pores results in lower specific surface area. The introduction of appropriate oxygen-containing groups in pre-oxidation process can facilitate the cross-linking of starch chains, promoting the increase of defect sites and the sodium storage performance of hard carbon. A series of samples are prepared at various pre-oxidation temperature. Among them, P200-HC obtained after pre-oxidation at 200 °C and carbonization at 1400 °C exhibits the highest reversible specific capacity of 342.7 mAh g−1 at current density of 0.1 C with an initial Coulombic efficiency of 71.1 %, and capacity retention of 87.3 % at current density of 1 C. The work presents a viable approach for the synthesis of hard carbon derived from starch, thereby expanding the design tactic of sodium-ion batteries with improved performance.

Highly crosslinked resin prepares hard carbon anode for enhanced sodium storage performance and reduced cost

Resins have shown significant potential as a precursor for hard carbons (HCs) in sodium-ion batteries (SIBs) due to their high purity and adjustability. However, the high cost and low Na+ storage capacity limit their industrialization. Herein, the highly crosslinked resin is developed by linear phenolic resin crosslinking with inexpensive hexamethylenetetramine (HMTA) via the C-N and methylene bridges between phenolic rings, which can effectively reduce the resin consumption ratio by over 44% per unit mass and regulate the sodium storage performance of the prepared HC with a high reversible capacity of 323.9 mAh g-1 and an initial coulombic efficiency (ICE) of 90.7% at 15 mA g−1, where a high plateau capacity of 286.8 mAh g-1 is proved to be a coupled storage mechanism of intercalation and pore-filling behavior. Meanwhile, defects associated with hydrogen content, rather than nitrogen defects, are verified to be directly linked to slope capacity. Furthermore, the 18650 cylindrical-type batteries assembled with this HC anode coupled with NaFe1/3Ni1/3Mn1/3O2 cathode achieve a high energy density of about 280.9 Wh kg−1 and excellent capacity retention of 86.4% over 2500 cycles, providing a promising prospect for the practical application of the resin-based HC for SIBs.

Enhancing electric field intensity of interfacial electric double layer to improve properties of solid electrolyte interface for sodium-ion batteries

The electrical double layer (EDL) provides a critical area, where the specific adsorption on the electrode dominates the initial structure and chemical composition of the solid electrolyte interface (SEI) film. Therefore, the SEI can be optimized by adjusting the properties of the EDL. Here, we regulate the properties of EDL to optimize the composition and morphology of the SEI film on the hard carbon anode surface by adding NaF with small molecule structure. The preferential accumulation of NaF additives on the electrode surface enhances the electric field intensity and promotes electrolyte decomposition. That is, the formed SEI film rich in inorganic NaF and B-O components, can significantly improve the storage capacity of sodium ions in the hard carbon anode and accelerate the rapid transport of sodium ions. This strategy enables the cycling capacity to improve by 13.5 %, and maintain a stable capacity retention rate of 86.2 % at the rate of 1C after 500 cycles, thereby extending the lifespan and increasing the capacity of the rechargeable battery. The strategy that utilizing small molecule additives to enhance the electric field intensity of EDL provides a new approach to improve the performances of SEI film and battery performances.

Innovative Tin and hard carbon architecture for enhanced stability in lithium-ion battery anodes

Tin (Sn), with a theoretical capacity of 994 mAh g-1, is a promising anode material for lithium-ion batteries (LIBs). However, fundamental limitations like large volume expansion during charge-discharge cycle and confined electronic conductivity limit its practical utility. Here, we report a new material design and manufacturing method of LIB anodes using Sn and Hard Carbon (HC) architecture, which is produced by Physical Vapor Deposition (PVD). A bilayer HC/Sn anode structure is deposited on a carbon/copper sheet as a function of deposition time, temperature, and substrate heat treatment. The developed anodes are used to make cells with a lithium-ion electrolyte using a specific fabrication process. The morphology, atomic structure, conductivity, and electrochemical performance of the developed HC/Sn anodes are studied with SEM, TEM, XPS, and electrochemical techniques. At a discharge rate of 0.1C, the Snheated + HC anode performs exceptionally well, offering a capacity of 763 mAh g-1. It is noteworthy that it achieves a capacity of 342 mAh g-1 when fast charging at 5C, demonstrating exceptional rate capability. The Snheated + HC anode maintains >97 % Coulombic efficiency of its capacity after 3000 cycles at a rate of 0.1C after 3000 cycles 730.5 mAh g-1 recorded, demonstrating an impressive cycle life. The novel material design approach of the Snheated + HC anode, which has a multi-layered structure and HC acting as a barrier against volumetric expansion and improving electronic conductivity during battery cycling, is perceived as influential in uplifting anode's performance.

An Engineering Porous Spherical Carbon Cathode for High-Energy Sodium-Ion Capacitor.

Sodium-ion hybrid capacitors (SICs) are emerging as promising devices that can balance energy and power output. However, the lack of a high-capacity cathode that can match the anode has limited its further application. In this work, we develop an efficient method to prepare spherical porous carbons (SPCs) with great specific surface area and narrow pore size distribution from coal-based humic acid via spray drying and a subsequent chemical activation process. Thanks to this unique porous structure, the SPC cathode has a superb capacity of 223 F g-1 at 0.05 A g-1, as well as splendid rate performance and cycling stability. SICs constructed by an SPC cathode and hard carbon anode can exhibit a high energy density of 179.8 Wh kg-1 at 155 W kg-1 and achieved 89.4% capacity retention after 10 000 cycles at 0.5 A g-1. This outcome presents a viable approach to attaining high-capacity cathodes for constructing outstanding performance hybrid capacitors.

Manipulating micropore structure of hard carbon as high‐performance anode for Sodium-Ion Batteries

Hard carbon (HC) is the most promising anode material for sodium-ion batteries (SIBs), but its low initial coulombic efficiency (ICE) and specific capacity limit its practical application. Herein, a chemical vapor deposition (CVD) strategy is used to address these challenges via filling the micropores of sucrose-based HC with pyrolysis by-products from acetonitrile, thereby reducing the specific surface area of HC microspheres. This approach mitigates the formation of solid electrolyte interphase (SEI) film leading to an enhancement in ICE. Moreover, the conversion of open micropores into closed pores creates additional storage space for sodium ions, effectively extending the specific capacity within the plateau region. Specifically, the HC prepared with a deposition duration of 1 h demonstrates the most favorable electrochemical performance. The optimal HC anode manifests an enhanced specific capacity of 307.6 mAh g−1 with an ICE of 66.01 % and exhibits excellent cycle stability (84.9 % capacity retention after 200 cycles at 100 mAh g−1). This study provides a feasible approach to optimize hard carbon anode materials for SIBs.

Precisely Tunable Instantaneous Carbon Rearrangement Enables Low-Working-Potential Hard Carbon Toward Sodium-Ion Batteries with Enhanced Energy Density.

As the preferred anode material for sodium-ion batteries, hard carbon (HC) confronts significant obstacles in providing a long and dominant low-voltage plateau to boost the output energy density of full batteries. The critical challenge lies in precisely enhancing the local graphitization degree to minimize Na+ ad-/chemisorption, while effectively controlling the growth of internal closed nanopores to maximize Na+ filling. Unfortunately, traditional high-temperature preparation methods struggle to achieve both objectives simultaneously. Herein, a transient sintering-involved kinetically-controlled synthesis strategy is proposed that enables the creation of metastable HCs with precisely tunable carbon phases and low discharge/charge voltage plateaus. By optimizing the temperature and width of thermal pulses, the high-throughput screened HCs are characterized by short-range ordered graphitic micro-domains that possess accurate crystallite width and height, as well as appropriately-sized closed nanopores. This advancement realizes HC anodes with significantly prolonged low-voltage plateaus below 0.1V, with the best sample exhibiting a high plateau capacity of up to 325mAhg-1. The energy density of the HC||Na3V2(PO4)3 full battery can therefore be increased by 20.7%. Machine learning study explicitly unveils the "carbon phase evolution-electrochemistry" relationship. This work promises disruptive changes to the synthesis, optimization, and commercialization of HC anodes for high-energy-density sodium-ion batteries.