Graphite Intercalation Compounds Research Articles

Control of water for high-yield and low-cost sustainable electrochemical synthesis of uniform monolayer graphene oxide

With the rapid development of graphene industry, low-cost sustainable synthesis of monolayer graphene oxide (GO) has become more and more important for many applications such as water desalination, thermal management, energy storage and functional composites. Compared to the conventional chemical oxidation methods, water electrolytic oxidation of graphite-intercalation-compound (GIC) shows significant advantages in environmental-friendliness, safety and efficiency, but suffers from non-uniform oxidation, typically ~50 wt.% yield with ~50% monolayers. Here, we show that water-induced deintercalation of GIC is responsible for the non-uniform oxidation of the water electrolytic oxidation method. Using in-situ experiments, the control principles of water diffusion governing electrochemical oxidation and deintercalation of GIC are revealed. Based on these principles, a liquid membrane electrolysis method was developed to precisely control the water diffusion to achieve a dynamic equilibrium between oxidation and deintercalation, enabling industrial sustainable synthesis of uniform monolayer GO with a high yield (~180 wt.%) and a very low cost (~1/7 of Hummers’ methods). Moreover, this method allows precise control on the structure of GO and the synthesis of GO by using pure water. This work provides new insights into the role of water in electrochemical reaction of graphite and paves the way for the industrial applications of GO.

Study of mechanical properties of Al-based hybrid nanocomposites reinforced with MoS2 nanoflakes and graphite nanoplatelets: an investigation of the synergistic effect

In the present study, Al-based hybrid nanocomposites were developed by powder metallurgy technique using binary hybrid nanofillers consisting of exfoliated MoS2 and GnP as nanofillers. The impact of the MoS2-GnP hybrid nanofiller on the microstructure, mechanical and tribological properties of the Al-based hybrid nanocomposites have been studied. Initially, bulk MoS2 was exfoliated by milling in a high energy planetary ball mill for 30 h and the GnP was synthesized by subjecting the graphite intercalation compound to a thermal shock and subsequently ultrasonicating the thermally exfoliated GnP. The effective exfoliation and structural refinement of both MoS2 and GnP have been confirmed by X-ray diffraction and scanning electron microscopy analysis. Exfoliated MoS2 and GnP were later blended in different ratios of their weight fraction by ultrasonication in an acetone medium. The Al matrix was then reinforced with the various binary hybrid nanofillers consisting of MoS2 and GnP. Wear analysis revealed mechanisms such as abrasion, adhesion, ploughing, delamination, microcracks, deep grooves, and nanofiller pullout in the case of all the nanocomposites. The Al-1 wt.% MoS2(0.3)GnP(0.7) nanocomposite shows superior properties, including the highest relative density (~93.15%), hardness (~476.28 MPa), compressive strength (~337.76 MPa) and outstanding wear resistance among all the Al-MoS2-GnP nanocomposites. Notably, it was observed that straying from the optimal reinforcement loading level can have a detrimental effect on the physical, mechanical, and wear properties of the nanocomposites, resulting in diminished performance and reduced material integrity. The significant improvement in the wear properties of the Al-1 wt.% MoS2(0.3)GnP(0.7) nanocomposite can be attributed to the self-lubricating properties of MoS2 and GnP.

Investigating the Existence of a Cathode Electrolyte Interphase on Graphite in Dual‐Ion Batteries with LiPF6‐Based Aprotic Electrolytes and Unraveling the Origin of Capacity Fade

This study elucidates the presence of a cathode electrolyte interphase (CEI) at graphite positive electrodes (PEs) and assesses its impact on the performance of dual‐ion batteries, being promising candidates for cost‐efficient and sustainable stationary energy storage. Indeed, electrolyte oxidation increases during charge (5 V vs Li|Li+) for decreased C rates, that is longer duration at high state‐of‐charges (SOC) , but effective protection and evidence for CEI formation is missing as no increase in Coulombic efficiencies is observed, even with literature‐known electrolyte additives like vinylene carbonate, fluoroethylene carbonate, or ethylene sulfite in a highly concentrated base electrolyte (4.0 m LiPF6 in dimethyl carbonate) as reference. Via studying charged and pristine PEs by X‐ray photoelectron spectroscopy, PF6−‐graphite intercalation compounds and cointercalated solvent molecules are identified, while indications for CEI are absent within 1000 charge/discharge cycles. Nevertheless, a high capacity retention of ≈94% (referring to 0.1C) is demonstrated. Affirmed by Raman spectroscopy and scanning electron microscopy, the active material remains structurally stable, suggesting capacity fading to be dominated by resistance rise at the PE, likely due to an electronic contact resistance from active material grain boundaries and/or from the interface between electrode particles and the current collector in course of high volume changes; as systematically derived by impedance spectroscopy.

The microwave absorption performance of ZnFe2O4/C composites synthesized by high-temperature mechanochemical technology with graphite intercalation compounds

The microwave absorption performance of ZnFe2O4/C composites synthesized by high-temperature mechanochemical technology with graphite intercalation compounds

Potassium storage behavior and low-temperature performance of typical carbon anodes in potassium-ion hybrid capacitors enabled by Co-intercalation graphite chemistry

Carbon materials are widely explored as anodes for potassium-ion storage, yet the slow K+ desolvation process in electrolyte at low temperatures presents a kinetic limitation that impedes reliable operation in specific conditions. In this work, we systematically investigate the potassium storage behavior of four typical carbon materials—graphite, hard carbon, activated carbon, and graphene—in a 1 M KFSI-Diglyme electrolyte, highlighting a co-intercalation approach that significantly reduces the desolvation energy barrier. The formation of ternary graphite intercalation compounds (t-GICs) through co-intercalation in graphite introduces weak interlayer interactions between the graphite layers and solvated K+, which accelerate K+ diffusion in the anode, thereby enhancing reaction kinetics. This unique mechanism enables the graphite anode to deliver remarkable rate performance (98 mAh g−1 at 0.05 A g−1 and 76 mAh g−1 at 1 A g−1) even at −20 °C. Furthermore, potassium-ion hybrid capacitors (PICs) using the graphite anode achieve impressive cycling stability, with 88 % capacity retention after 2000 cycles at 2 A g−1 and a high power density of 11.1 kW kg−1 (57 Wh kg−1) at −20 °C. These findings provide key insights into the design of robust potassium-ion storage devices capable of sustaining high performance in low-temperature environments.

From Ternary to Quatenary Graphite Intercalation Compound in Na-Ion Batteries

Sodium-ion batteries (SIBs) have emerged alongside the prominence of lithium-ion batteries (LIBs), capturing significant attention. By sharing chemical similarities with LIBs, SIBs have experienced notable growth, not only in research but also in industrial applications throughout 2023, particularly in the development of large-scale battery systems.[1] Graphite, a common anode material in LIBs, has unfavorable thermodynamic properties that limit the formation of binary graphite intercalation compounds (b-GICs). Consequently, this results in a poor specific capacity of approximately 20 mA h g-1 when conventional carbonate-based electrolytes are used in SIBs.[2] However, in 2014, it was confirmed that employing ether-based electrolytes, such as diglyme (2G), could significantly enhance the specific capacity to 110 mA h g-1 through a solvent co-intercalation mechanism. This mechanism involves the intercalation of solvated sodium ions into graphite layers, leading to the formation of ternary graphite intercalation compounds (t-GICs).[3] Despite causing a large expansion of graphite layers to accommodate the solvated ions, co-intercalation shows high reversible cycling behavior and rapid kinetic properties due to the absence of desolvation steps.[4]Previous studies have predominantly focused on the electrochemical solvent co-intercalation in graphite using linear ethers such as mono-, di-, tri-, tetra-, and pentaglyme.[5] Herein, we investigate the potential for reversible electrochemical co-intercalation with alternative solvents, broadening the range of usable electrolytes. Especially, we examine cyclic ethers like tetrahydrofuran (THF) and 1,3-dioxolane (DOL), which show no indication of co-intercalation in graphite.[6] Surprisingly, incorporating diglyme at an additive level facilitates reversible co-intercalate THF and DOL. However, explicit acknowledgment of this phenomenon has been infrequent, and the effect of THF and DOL mixed electrolytes has never been fully explored.When employing mixed electrolytes, i.e., THF/2G and DOL/2G, they show different voltage profiles compared to the pure glyme-based electrolytes, while having equivalent specific capacities of ~90 mA h g-1 and good long-term durability. Operando X-ray diffraction and ex-situ solid-state NMR techniques are extensively utilized to gain comprehensive insights into the co-intercalation reaction of these cyclic ethers, along with Na+-glymes in graphite during the cycling process.The present study demonstrates for the first time the concept of using diglyme as a "gate opener" for the electrochemical synthesis of GICs. Since diglyme serves as a gate opener within the graphite layers, other solvent molecules are capable of co-intercalating, a task they were unable to achieve independently before. According to the changes in voltage profiles and the results of structural characterization, it is indicated that the quaternary graphite intercalation compounds (q-GICs) have formed. The finding of the new role of diglyme as a gate opener will enable the development of various compounds even higher-order GICs. This approach could be applied to design new intercalation electrodes for rechargeable batteries.

New Insights into the Electrochemical Reactions of Fluoride Ions in Carbon-Based Positive Electrodes

The reversible and electrochemical reactions for the formation of graphite intercalation compounds (GICs) are fundamental to their use as electrode reactions in rechargeable batteries. A common practical application is the electrochemical intercalation and de-intercalation of Li+ ions within graphite electrodes of lithium-ion batteries (LIBs). Similarly, dual-graphite batteries (DGBs) employ GIC formation reactions and operate through the intercalation and de-intercalation of both cations and anions at the negative and positive electrodes, respectively, during charging/discharging processes. DGBs are gaining recognition as a viable alternative to LIBs because of their affordability, high operational potentials, reduced resource constraints, and environmental benefits.This study presents the first observation of the electrochemical formation of F-GICs within LiF-containing organic liquid electrolytes. Despite attempts spanning nearly a century, the reversible intercalation of fluoride ions (F−) and their direct detection in electrochemical systems have remained elusive. Fluoride ions, known for their small ionic radius and high electronegativity, are theorized to provide high specific capacity and reaction potential, potentially leading to high energy densities in rechargeable batteries if they can be reversibly intercalated into graphite electrodes. Our findings were substantiated through operando Raman spectroscopy, which revealed changes in the G band peaks (i.e., in-plane mode of sp2 bonded carbon with a planar configuration) in highly oriented pyrolytic graphite (HOPG) during electrochemical oxidation. This indicates the formation of F-GICs. Moreover, the introduction of a LiF-based surface layer on the HOPG electrodes significantly improved the kinetics and reversibility of the electrochemical intercalation and de-intercalation processes of F−.Consequently, based on these results, the present study suggests that the electrochemical formation of F-GICs can occur in organic electrolytes without the need for additional acceptors or additives. Furthermore, this study provides insights into the operando Raman spectra for the electrochemical formation of F-GICs, elucidating the mechanisms of the electrochemical F− reactions in HOPG electrodes. Moreover, enhancing the contact between LiF and the graphite surface can significantly accelerate the rate of F− intercalation, offering a new perspective on the design of graphite positive electrodes for rechargeable batteries. Figure 1

Lithium, Ether, and Graphite: A Retrospective Trilogy of the Anode-Electrolyte Interface

Ethers represent a family of solvents widely applied in various battery chemistries, except in the most successful battery—Li-ion batteries (LIBs). It is believed that ether electrolytes are incompatible with graphite anodes in LIBs due to detrimental solvent co-intercalation and exfoliation. Here, we demonstrate that ether electrolytes at standard salt concentration can enable outstanding reversibility and fast-charge capability of graphite anodes in LIBs. In short, for ether electrolytes, the anion and the solid-electrolyte interphase (SEI) govern the electrochemical behaviors of graphite anodes. Firstly, we point out that exfoliation and co-intercalation are not always the root causes of the documented cell failures using graphite anodes. Matching the reductive stability between solvents and salts is key to resolving the interphase problem. Reductively unstable lithium bis(fluorosulfonyl)imide (LiFSI) is the optimal salt paired with 1,3-dioxolane (DOL), enabling weakened Li-solvent interaction, preferential reduction of the FSI anion, and a homogeneous SEI enriched with inorganic species. Consequently, electrolyte reduction and Li-DOL co-intercalation are inhibited. Secondly, reductively stable LiBF4 paired with dimethoxyethane (DME) realizes improved cyclability of graphite based on a cointercalation mechanism. We conducted a holistic investigation into the nature, function, and formation of the heterogeneous SEI. Specifically, we revealed a self-terminating, heterogeneous interphase based on grainy LiF located on the catalytically active edge plane of natural graphite. Thirdly, we discovered a novel cointercalation mechanism, namely, in-situ synthesis of ternary graphite-intercalation compounds in a new electrolyte. We characterize the progressive cointercalation via operando synchrotron X-ray analyses, supporting reduced volume expansion and high structural integrity of the cointercalated graphite. The resulting t-GIC chemistry delivers unprecedented fast charging (1 minute) and ultralong lifetimes exceeding 10,000 cycles. The full cells based on cointercalated graphite display remarkable cycling stability upon a 15-minute charging and excellent rate capability even at -40°C. In these three case studies combined as a trilogy with strong correlation, we clarify a long-standing confusing issue in the LIBs community—that is, the compatibility between ether electrolytes and graphite anodes. This trilogy summarizes and reflects on past experiences with the anode/electrolyte interface (mostly failures of ether electrolytes when cycling graphite anodes) dating back to the 1970s. Learning from history, we exemplify different intercalation chemistries of graphite based on DOL, DME, and another common ether solvent, paired with 1M lithium salts, all showing approximately 99.9% Coulombic efficiency, high capacity retention, and rapid interphase kinetics. Our findings not only shed light on the enigmatic interphase formed by ether electrolytes but also offer critical insights into future electrolyte design for graphite anodes operated under extreme conditions.

Hierarchical Intercalation of Solvated Tetrafluoroborate Anions into Graphite Electrodes: The Case Studies of Methyl Acetate and γ-Butyrolactone Solutions.

Intercalation of anions unlocks graphite as a positive material in energy storage devices, and the performance could be affected by solvents in solutions. In this context, it is vital to investigate the role of solvents in anion intercalation. Herein, a hierarchical intercalation phenomenon, in which different graphite intercalation compounds are generated in the same solution, is studied in lithium tetrafluoroborate (LiBF4) solutions of carboxylate ester solvents γ-butyrolactone (GBL) and methyl acetate (MA). The evolution modes of the graphite cathode structure during electrochemical intercalation and deintercalation are discussed via in situ X-ray diffraction (XRD) measurements. Based on this, the relationship between GICs and potentials, together with concentrations, is compared in detail. Furthermore, various graphite materials with different surface properties are applied to adjust the anions' solvation status inside graphite sheets.

In situ X-ray diffraction studies on nominal composition of C2Li under high pressure and temperature

Superdense phase between graphite and Li metal, C2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_{2}$$\\end{document}Li, has been significant in the research on both lithium-ion batteries (LIBs) and graphite intercalated compounds (GICs). However, a detailed method for synthesizing C2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_{2}$$\\end{document}Li remains unknown owing to the limited information regarding C2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_{2}$$\\end{document}Li and difficulties in distinguishing C2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_{2}$$\\end{document}Li from C6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_{6}$$\\end{document}Li. Thus, we performed in situ X-ray diffraction measurements on samples with the nominal composition of C2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_{2}$$\\end{document}Li under high pressures and temperatures of up to 10 GPa and 400 ∘C\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\circ }\\hbox {C}$$\\end{document}, respectively. We employed two types of C2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_{2}$$\\end{document}Li samples; one was a mixture of C6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_{6}$$\\end{document} graphite powder and Li metal (C6+3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{6}+3$$\\end{document}Li), and the other was a mixture of C6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_{6}$$\\end{document}Li and Li metal in which the C6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_{6}$$\\end{document}Li was prepared by the electrochemical discharge (reduction) reaction that occurs in LIBs. Considering changes in the d-value based on the 001 diffraction peak from C6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_{6}$$\\end{document}Li or C2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_{2}$$\\end{document}Li, C6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{6}$$\\end{document}Li + 2Li is suitable for synthesizing C2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_{2}$$\\end{document}Li, although the nonaqueous electrolyte used for the electrochemical reaction should be removed to avoid structural transformations to lower-stage compounds such as C12\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_{12}$$\\end{document}Li and C18\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_{18}$$\\end{document}Li during the heating. These findings pave the way toward a method for synthesizing C2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document}Li, which could increase the energy density of LIBs and establish GICs with novel physical and electronic properties.

Self-Standing vanadium oxide pillared carbon microfiber film as an excellent anode for lithium & sodium ion batteries

Insertion of substances (such as atoms/molecules/ions) into the interlayer spaces of graphite to increase its layer separation is found to be extremely useful for sodium-ion batteries (SIBs). Therefore, expanded graphitic systems are the obvious choice as anode material for both lithium/sodium-ion batteries (LIBs/SIBs). Hard carbon-based materials altogether give a decent electrochemical performance, as well as allow structural integrity for long-term use. Herein, we report a facile route to prepare free-standing vanadium oxide doped carbon microfibers (V@CMFs) films. The V@CMFs show ∼ 200 % expansion in the graphitic interlayer distances while accommodating minute deformations in the final compound which is further theoretically verified as the stage-1 type dilute graphite intercalation compound (GICs) with pillar-like structures. Best battery performance was obtained for the 1 % doped (V1@CMFs) sample, with an initial discharge capacity of 1501.8 and 703.4 mAhg−1, reversible capacities of 1253.8 and 288.7 mAhg−1 at 20 mAg−1, and rate capabilities i.e., 362.4 and 108.1 mAhg−1 at 1600 mAg−1, for LIBs and SIBs, respectively. The results revealed that the rate capability and the reversible specific capacity of the 1 % vanadium oxide doped carbon microfibers (V1@CMFs) are significantly superior compared to the pristine and previous reports. Here, the incorporation of just 1 % vanadium oxide acts as a pillar, enhancing the stability and conductivity of the carbon. Thus, the present work highlights the utility of molecularly doped GICs as potential anode materials for LIBs/SIBs.

High-Energy Sodium Ion Batteries Enabled by Switching Sodiophobic Graphite into Sodiophilic and High-Capacity Anodes.

Owing to the crustal abundance of sodium element, sodium ion batteries (SIBs) are considered a promising complementary to lithium-ion battery for stationary energy storage applications. The cointercalation chemistry enables the use of cost-effective graphite as anodes, whereas the low capacity (<130 mAh g-1) and high redox potential (>0.6 V vs. Na/Na+) of graphite significantly limit the energy density of SIBs. Herein, we induce the high-capacity Na metal into sodiophilic ternary graphite intercalation compounds (t-GICs) via co-intercalation and deposition reactions, thereby achieving Na/t-GIC anodes with high capacities and low working voltage (0.18 V). The new anodes exhibit high coulombic efficiencies of above 99.7 % over 550 cycles and a high-rate capacity of 588.4 mAh g-1 at 6 C (10 min per charge). When it is paired with Na3V2(PO4)2F3 (NVPF) cathodes, the SIBs demonstrate a high energy density of 259 Wh kg-1 both electrodes surpassing that of commercial LiFePO4//graphite batteries. The outstanding anode performance is attributed to the tailored sodiophilicity of graphite through manipulating the ether solvents and the in situ generated space among t-GIC flakes to stably accommodate Na metal. Our findings for stable Na plating/striping on sodiophilic graphite materials provide an effective approach for developing advanced SIBs.

High‐Energy Sodium Ion Batteries Enabled by Switching Sodiophobic Graphite into Sodiophilic and High‐Capacity Anodes

AbstractOwing to the crustal abundance of sodium element, sodium ion batteries (SIBs) are considered a promising complementary to lithium‐ion battery for stationary energy storage applications. The cointercalation chemistry enables the use of cost‐effective graphite as anodes, whereas the low capacity (&lt;130 mAh g−1) and high redox potential (&gt;0.6 V vs. Na/Na+) of graphite significantly limit the energy density of SIBs. Herein, we induce the high‐capacity Na metal into sodiophilic ternary graphite intercalation compounds (t‐GICs) via co‐intercalation and deposition reactions, thereby achieving Na/t‐GIC anodes with high capacities and low working voltage (0.18 V). The new anodes exhibit high coulombic efficiencies of above 99.7 % over 550 cycles and a high‐rate capacity of 588.4 mAh g−1 at 6 C (10 min per charge). When it is paired with Na3V2(PO4)2F3 (NVPF) cathodes, the SIBs demonstrate a high energy density of 259 Wh kg−1both electrodes surpassing that of commercial LiFePO4//graphite batteries. The outstanding anode performance is attributed to the tailored sodiophilicity of graphite through manipulating the ether solvents and the in situ generated space among t‐GIC flakes to stably accommodate Na metal. Our findings for stable Na plating/striping on sodiophilic graphite materials provide an effective approach for developing advanced SIBs.

Strategic approaches to observing 39K NMR signals from potassium–graphite intercalation compounds

Abstract Solid-state nuclear magnetic resonance is an invaluable tool for potassium–graphite intercalation compounds, promising anode materials of K-ion batteries, but it has not yet been applied because of several issues. We attempted 39K NMR measurements of potassium–graphite intercalation compounds sealed in glass using an 18.8 T NMR spectrometer with a nuclear magnetic resonance probe adjusted to the samples. The first observed 39K NMR signal of potassium–graphite intercalation compounds showed the possibility of evaluating intralayer density, which cannot be ascertained from Raman measurements.

Quantification of solvent-mediated host-ion interaction in graphite intercalation compounds for extreme-condition Li-ion batteries

Achieving simultaneous fast-charging capabilities and low-temperature adaptability in graphite-based lithium-ion batteries (LIBs) with an acceptable cycle life remains challenging. Herein, an ether-based electrolyte with temperature-adaptive Li+ solvation structure is designed for graphite, and stable Li+/solvent co-intercalation has been achieved at subzero. As revealed by in-situ variable temperature (−20 °C) X-ray diffraction (XRD), the poor compatibility of graphite in ether-based electrolyte at 25 °C is mainly due to the continuous electrolyte decomposition and the in-plane rearrangement below 0.5 V. Former results in a significant irreversible capacity, while latter maintains graphite in a prolonged state of extreme expansion, ultimately leading to its exfoliation and failure. In contrast, low temperature triggers the rearrangement of Li+ solvation structure with stronger Li+/solvent binding energy and shorter Li+–O bond length, which is conducive for reversible Li+/solvent co-intercalation and reducing the time of graphite in an extreme expansion state. In addition, the co-intercalation of solvents minimizes the interaction between Li-ions and host graphite, endowing graphite with fast diffusion kinetics. As expected, the graphite anode delivers about 84% of the capacity at room temperature at −20 °C. Moreover, within 6 min, about 83%, 73%, and 43% of the capacity could be charged at 25, −20, and −40 °C, respectively.

Oscillating Structural Transformations in the Electrochemical Synthesis of Graphene Oxide from Graphite

AbstractElectrochemical synthesis of graphene oxide (GO) is known to occur with potential oscillations, but the structural changes underlying these oscillations have remained unclear. In situ time‐resolved synchrotron radiation X‐ray diffraction demonstrates that the electrochemical synthesis of GO in aqueous H2SO4 can be described as an oscillating reaction. The transformation from graphite to GO proceeds through periodic structural oscillations that correlate with potential cycles. Stage‐1 graphite intercalation compound (GIC) is found only at the peak of the potential cycle, but not at the bottom of the cycle. Stage‐1 GIC is formed in the first half‐cycle from stage‐2 GIC and then transforms into “pristine graphite oxide” (PGO) on the lower side of the potential cycle, after which the cycle restarts with the formation of a new portion of stage‐1 GIC. Water‐washing results in the transformation of PGO into water‐swollen GO with d(001) ~11 Å. These periodic structural changes can be considered a new type of oscillating reaction. The presented results provide broad insights into the oscillating structural changes occurring during the anodic graphite oxidation in aqueous H2SO4 and allow to update of the mechanism of GO electrochemical formation.

Oscillating Structural Transformations in the Electrochemical Synthesis of Graphene Oxide from Graphite.

Electrochemical synthesis of graphene oxide (GO) is known to occur with potential oscillations, but the structural changes underlying these oscillations have remained unclear. In situ time-resolved synchrotron radiation X-ray diffraction demonstrates that the electrochemical synthesis of GO in aqueous H2SO4 can be described as an oscillating reaction. The transformation from graphite to GO proceeds through periodic structural oscillations that correlate with potential cycles. Stage-1 graphite intercalation compound (GIC) is found only at the peak of the potential cycle, but not at the bottom of the cycle. Stage-1 GIC is formed in the first half-cycle from stage-2 GIC and then transforms into "pristine graphite oxide" (PGO) on the lower side of the potential cycle, after which the cycle restarts with the formation of a new portion of stage-1 GIC. Water-washing results in the transformation of PGO into water-swollen GO with d(001) ~11 Å. These periodic structural changes can be considered a new type of oscillating reaction. The presented results provide broad insights into the oscillating structural changes occurring during the anodic graphite oxidation in aqueous H2SO4 and allow to update of the mechanism of GO electrochemical formation.

An eco-friendly approach for graphene nanoplatelets by innovative wet thermal expansion and liquid-phase exfoliation

Cost-effective synthesis of high-structural integrity graphene nanoplatelets (GNPs) remains a grand challenge. This study presents an innovative, environmentally friendly and efficient method for synthesizing high-quality GNPs by integrating wet thermal expansion with liquid-phase exfoliation. The thermal expansion of a wet graphite intercalation compound (GIC) in a semi-closed system improves the expansion effectiveness, minimizes the release of fine dust and improves the hydrophilicity of the resulting product. These improvements significantly enhance the effectiveness and efficiency of the subsequent liquid-phase exfoliation by shearing, which produces GNPs in pure water within 30 min with an overall productivity of 38.24 %. GNPs exhibit desirable properties, e.g. few layers (1–2 nm thick), large lateral dimension (a few microns), high sp2 hybridized carbon content (86 %), rich surface functional groups yet a low oxidation level (C/O ratio = 21.7 and electrical conductivity of ∼ 2055 S cm−1). The simplicity, adjustability and scalability of this method, combined with environmental friendliness, make it suitable for various applications and pave the way for further advancements in sustainable nanotechnology practices.

Deciphering the Impact of Current, Composition, and Potential on the Lithiation Behavior of Si-Rich Silicon-Graphite Anodes.

Adding silicon (Si) to graphite (Gr) anodes is an effective approach for boosting the energy density of lithium-ion batteries, but it also triggers mechanical instability due to Si volume changes upon (de)lithiation reactions. In this work, component-specific (de)lithiation dynamics on Si-rich (30 and 70wt.% Si) SiGr anodes at various charge/discharge C-rates are unveiled and compared to a graphite-only electrode (100Gr) via operando synchrotron X-ray diffraction coupled with differential capacity plots analysis. Results show preferential lithiation of amorphous Si above ≈200mV and competing lithiation of Gr, amorphous Si, and crystalline Si below ≈200mV. Discharge proceeds via sequential delithiation of Gr and amorphous lithium silicide. Si shifts the interconversion potentials of graphite intercalation compounds, lowering the Gr state of charge compared to 100Gr. In the 30%Si electrode, crystalline Si amorphization at potentials <110mV is found to be kinetically hindered at C-rates higher than C/5, which can be key for enhancing the cycling stability of SiGr anodes. The 70%Si electrode exhibits restricted lithium diffusion in Gr, full Si amorphization, and Li15Si4 formation. These findings related to the potential- and current-dependent dynamic changes on SiGr blends are crucial for designing stable high energy density SiGr anodes.

Charge transfer in alkaline-earth metal graphite intercalation compounds

The charge transfer from a metal atom towards the carbon layers in first stage graphite intercalation compounds (GIC) is a fundamental issue to explain under which conditions superconductivity sets in and the electronic properties of such ground state. To study in detail the transfer process and its evolution as a function of the nature of the intercalated metal, and especially taking in consideration the interlayer distance, we performed detailed X-Ray Diffraction and Raman scattering measurements on very high-quality bulk intercalated CaC6, SrC6 and BaC6 samples. We combined both the experimental results with detailed density functional theory calculations to give a coherent picture in which it is possible to follow the evolution of the charge transfer to the carbon layer in full agreement with the experimental data. The full comprehension of such mechanism remains a fundamental issue to explain the variation of the superconducting ground state in first stage GIC.