The recently reported silicon/graphite(Si/Gr)composite electrode with a layered structure is a promising approach to achieve high capacity and stable cycling of Si-based electrodes in lithium-ion batteries.However,the...The recently reported silicon/graphite(Si/Gr)composite electrode with a layered structure is a promising approach to achieve high capacity and stable cycling of Si-based electrodes in lithium-ion batteries.However,there is still a need to clarify why particular layered structures are effective and why others are ineffective or even detrimental.In this work,an unreported mechanism dominated by the porosity evolution of electrodes is proposed for the degradation behavior of layered Si/Gr electrodes.First,the effect of layering sequence on the overall electrode performance is investigated experimentally,and the results suggest that the cycling performance of the silicon-on-graphite(SG)electrode is much superior to that of the graphite-on-silicon electrode.To explain this phenomenon,a coupled mechanical-electrochemical porous electrode model is developed,in which the porosity is affected by the silicon expansion and the local constraints.The modeling results suggest that the weaker constraint of the silicon layer in the SG electrode leads to a more insignificant decrease in porosity,and consequently,the more stable cycling performance.The findings of this work provide new insights into the structural design of Si-based electrodes.展开更多
Silicon/graphite(Si/Gr)nanocomposites with controlled void spaces and encapsulated by a carbon shell(Si/Gr@void@C)are synthesized by utilizing high-energy ball milling to reduce micron-sized particles to nanoscale,fol...Silicon/graphite(Si/Gr)nanocomposites with controlled void spaces and encapsulated by a carbon shell(Si/Gr@void@C)are synthesized by utilizing high-energy ball milling to reduce micron-sized particles to nanoscale,followed by carbonization of polydopamine(PODA)to form a carbon shell,and finally partial etching of the nanostructured Si core by NaOH solution at elevated temperatures.In particular,the effects of ball milling time and NaOH etching temperature on the electrochemical properties of Si/Gr@void@C are investigated.Increasing the ball milling time results in the improved specific capacity of Si-based anodes.Carbon coating further enhances the specific capacity and capacity retention over charge/discharge cycles.The best cycle stability is achieved after partial etching of the Si core inside Si/Gr@void@C particles at either 70 or 80C,leading to little or no capacity decay over 130 cycles.However,it is found that both carbon coating and NaOH etching processes cause some surface oxidation of the nanostructured Si particles derived from high-energy ball milling.The surface oxidation of the nanostructured Si results in decreases in specific capacity and should be minimized in future studies.The mechanistic understanding developed in this study paves the way to further improve the electrochemical performance of Si/Gr@void@C nanocomposites in future.展开更多
Waste graphitization cathode carbon blocks are a type of hazardous solid waste generated during the aluminum electrolysis process,and their proper disposal is a key step in the resource utilization of discarded graphi...Waste graphitization cathode carbon blocks are a type of hazardous solid waste generated during the aluminum electrolysis process,and their proper disposal is a key step in the resource utilization of discarded graphite.This study utilizes the porous“defect advantage”of a cathode carbon block matrix to prepare silicon-doped and asphalt-coated detoxified and purified waste graphitization cathode carbon blocks for use as high-performance silicon/carbon composite anode materials.The results show that the uniformly silicondoped silicon/carbon composite material features a unique amorphous carbon-encapsulated“locked silicon”structure,which effectively addresses issues such as cathode volume expansion,excessive growth of the solid electrolyte interphase(SEI)film,and poor electrical contact between active materials.Consequently,electrochemical performance is enhanced.After assembly in a half-cell,the PSCC/10%Si@C(purified waste graphitization cathode carbon/10%Si@C)material exhibits optimal electrochemical stability,with an initial charging specific capacity of 514.5 mAh/g at 0.1 C(1 C=170 mA/g)and a capacity retention rate of 95.1%after 100 cycles.At a charge rate of 2.0 C,a specific capacity of 216.9 mAh/g is achieved.This technology provides a new pathway for the economical and high-value utilization of waste cathode carbon blocks and the development of low-cost,high-performance anode materials.展开更多
Graphite,encompassing both natural graphite and synthetic graphite,and graphene,have been extensively utilized and investigated as anode materials and additives in lithium-ion batteries(LIBs).In the pursuit of carbon ...Graphite,encompassing both natural graphite and synthetic graphite,and graphene,have been extensively utilized and investigated as anode materials and additives in lithium-ion batteries(LIBs).In the pursuit of carbon neutrality,LIBs are expected to play a pivotal role in reducing CO_(2)emissions by decreasing reliance on fossil fuels and enabling the integration of renewable energy sources.Owing to their technological maturity and exceptional electrochemical performance,the global production of graphite and graphene for LIBs is projected to continue expanding.Over the past decades,numerous researchers have concentrated on reducing the material and energy input whilst optimising the electrochemical performance of graphite and graphene,through novel synthesis methods and various modifications at the laboratory scale.This review provides a comprehensive examination of the manufacturing methods,environmental impact,research progress,and challenges associated with graphite and graphene in LIBs from an industrial perspective,with a particular focus on the carbon footprint of production processes.Additionally,it considers emerging challenges and future development directions of graphite and graphene,offering significant insights for ongoing and future research in the field of green LIBs.展开更多
Fine-grained nuclear graphite is a key material in high-temperature gas-cooled reactors(HTGRs).During air ingress accidents,core graphite components undergo severe oxidation,threatening structural integrity.Therefore,...Fine-grained nuclear graphite is a key material in high-temperature gas-cooled reactors(HTGRs).During air ingress accidents,core graphite components undergo severe oxidation,threatening structural integrity.Therefore,understanding the oxidation behavior of nuclear graphite is essential for reactor safety.The influence of oxidation involves multiple factors,including temperature,sample size,oxidant,impurities,filler type and size,etc.The size of the filler particles plays a crucial role in this study.Five ultrafine-and superfine-grained nuclear graphite samples(5.9-34.4μm)are manufactured using identical raw materials and manufacturing processes.Isothermal oxidation tests conducted at 650℃-750℃ are used to study the oxidation behavior.Additionally,comprehensive characterization is performed to analyze the crystal structure,surface morphology,and nanoscale to microscale pore structure of the samples.Results indicate that oxidation behavior cannot be predicted solely based on filler grain size.Reactive site concentration,characterized by active surface area,dominates the chemical reaction kinetics,whereas pore tortuosity,quantified by the structural parameterΨ,plays a key role in regulating oxidant diffusion.These findings clarify the dual role of microstructure in oxidation mechanisms and establish a theoretical and experimental basis for the design of high-performance nuclear graphite capable of long-term service in high-temperature gas-cooled reactors.展开更多
The extensive application of lithium-ion batteries in electric vehicles has led to a torrential surge of endof-life batteries.As the dominant anode material,graphite's environmental and resource costs in productio...The extensive application of lithium-ion batteries in electric vehicles has led to a torrential surge of endof-life batteries.As the dominant anode material,graphite's environmental and resource costs in production highlight the necessity of recycling spent graphite(SG).However,SG recycling technologies remain markedly underdeveloped compared to the cathode recovery status,due to perceived lower economic value.This review provides an in-depth analysis of the current SG growth trend and highlights the cost accounting for graphite recycling and the significant importance of advanced recycling technologies.By examining the failure mechanisms of graphite,various recycling and upcycling technologies in both practical application and fundamental research are fully discussed,in terms of the regeneration principle,recycling effect,strengths,and limitations of each method.Furthermore,the multi-purpose applications of recycled graphite beyond LIB anodes are explored to enhance its high-value properties.Finally,the prospects of SG recycling and large-scale application challenges are presented,including economic feasibility,process optimization,and regulatory restrictions.This review provides a comprehensive overview of developments in SG recycling strategies,offering valuable insights for narrowing the gap between fundamental research and practical applications.展开更多
Laser-induced periodic surface structures(LIPSS)have gained increasing attention in the field of micro/nano fabrication,although achieving sub-100-nm period LIPSS with high uniformity remains a significant challenge.I...Laser-induced periodic surface structures(LIPSS)have gained increasing attention in the field of micro/nano fabrication,although achieving sub-100-nm period LIPSS with high uniformity remains a significant challenge.In this work,towards deep-subwavelength LIPSS on highly oriented pyrolytic graphite(HOPG),we demonstrate that ultra-uniform nanogratings of sub-50-nm periods and near-10-nm groove widths can be stably prepared via 800-nm femtosecond laser scanning irradiation with a high-NA objective lens under water immersion.The resulting nanogratings of strong polarization dependence,exhibiting exceptional surface flatness,period stability,and structural integrity,tend to appear at near-damage-threshold fluence regime with an appropriate effective pulse number.It turns out that the water immersion condition can significantly reduce the thermal effects of femtosecond laser ablation on HOPG,and thus via a mild,incubation-like scanning ablation process occurring in the nanogrooves with a continuous or jumping manner,this deep-subwavelength grating can achieve robust elongation growth,ensuring its long-range uniformity as well as minimal deposited debris and structural defects.Interestingly,the different incubation extension mechanisms for the mutually perpendicular and parallel settings between scanning direction and laser polarization bring not only distinct effective-pulse-number windows and somewhat different grating qualities,but also different extension stabilities in nanograting stitching via overlapping scanning lines and thus the optimal scanning strategy of parallel setting for large-area processing.In short,this study presents a convenient laser-processing approach for high precision fabrication of sub-50-nm gratings on HOPG,which would provide new insights into micro/nano-fabrication for optoelectronic metasurfaces and physics of the interaction between ultrafast laser and graphite.展开更多
The impurities and structural cracks within spent graphite(SG)in lithium-ion battery anodes hamper lithium-ion intercalation and extraction after successive charge-discharge operations,thereby yielding poor lithium st...The impurities and structural cracks within spent graphite(SG)in lithium-ion battery anodes hamper lithium-ion intercalation and extraction after successive charge-discharge operations,thereby yielding poor lithium storage behavior.Herein,low-viscosity natural deep eutectic solvent(NDES)composed of citric acid(CA)and betaine hydrochloride was employed to remove the organic impurities in SG via a one-step benign process involving hydrogen bonds and electrostatic interactions at mild conditions of 80℃ for only 30 min.After NDES leaching under optimal conditions(molar ratio of CA to betaine hydrochloride=3:1,80℃,30 min),the as-obtained sample(denoted as BG-3)exhibited an extremely clean surface,moderately enlarged interlayer distance,and more structural defects at the edge of graphite lamellae.These features facilitated lithium-ion intercalation and withdrawal,bestowing BG-3 with remarkable activity in lithium-ion battery(LIB)recycling.For instance,BG-3 delivered a capacity of 438.6 mAh g^(-1) at a current density of 0.1 A g^(-1).Its capacity retention reached 97.9%,accompanied by a Coulombic efficiency of 99.1%,upon completing 100 cycles.A molecular dynamics simulation was employed to illuminate the regeneration mechanism for anode graphite from a theoretical perspective.It revealed that NDES exhibits lower binding energy with all contaminants compared to graphite,which is favorable for NDES to eliminate impurities from graphite surfaces.This study unveils a method of recycling SG from retired LIBs by a short eco-friendly process,providing a competitive blueprint to address the shortage of battery-grade anode graphite and to achieve carbon neutrality.展开更多
To enhance the electrochemical performance of lithium-ion battery anodes with higher silicon content,it is essential to engineer their microstructure for better lithium-ion transport and mitigated volume change as wel...To enhance the electrochemical performance of lithium-ion battery anodes with higher silicon content,it is essential to engineer their microstructure for better lithium-ion transport and mitigated volume change as well.Herein,we suggest an effective approach to control the micropore structure of silicon oxide(SiO_(x))/artificial graphite(AG)composite electrodes using a perforated current collector.The electrode features a unique pore structure,where alternating high-porosity domains and low-porosity domains markedly reduce overall electrode resistance,leading to a 20%improvement in rate capability at a 5C-rate discharge condition.Using microstructure-resolved modeling and simulations,we demonstrate that the patterned micropore structure enhances lithium-ion transport,mitigating the electrolyte concentration gradient of lithium-ion.Additionally,perforating current collector with a chemical etching process increases the number of hydrogen bonding sites and enlarges the interface with the SiO_(x)/AG composite electrode,significantly improving adhesion strength.This,in turn,suppresses mechanical degradation and leads to a 50%higher capacity retention.Thus,regularly arranged micropore structure enabled by the perforated current collector successfully improves both rate capability and cycle life in SiO_(x)/AG composite electrodes,providing valuable insights into electrode engineering.展开更多
Graphite and hexagonal boron nitride(h-BN),despite their structural similarity,exhibit opposing electronic properties,namely,metallic conductivity and wide-bandgap insulation,respectively.In recent years,graphene-h-BN...Graphite and hexagonal boron nitride(h-BN),despite their structural similarity,exhibit opposing electronic properties,namely,metallic conductivity and wide-bandgap insulation,respectively.In recent years,graphene-h-BN heterostructures have attracted significant research interest,with the resulting hybrid B-C-N atomic-layer systems exhibiting distinctive electronic properties.Notably,interface effects play a decisive role in governing the performance of these heterostructures.Nevertheless,owing to the lack of high-quality composites,the interfacial structure in B-C-N materials and the correlation with critical properties such as charge transport and band structure modulation are not fully clear.Here,we report the direct synthesis of a millimeter-sized hexagonal B-C-N composite via a solvent method under high-pressure and high-temperature conditions.Structural characterization reveals that the synthesized B-C-N composite contains isolated graphite and h-BN.Compared with pure h-BN,the B-C-N composite has a narrower bandgap and shows a pronounced photoelectric response in the visible light region.More interestingly,we find a graphite-like B-C compound with a thickness of about 30 nm at the graphite-h-BN interface,which forms Schottky junctions with graphite,thus realizing rectification properties.Our findings provide a method for synthesizing highquality B-C-N composites and offer new insights into the structure of the graphite-h-BN interface.展开更多
All-solid-state batteries(ASSBs)with sulfide-type solid electrolytes(SEs)are gaining significant attention due to their potential for the enhanced safety and energy density.In the slurry-coating process for ASSBs,nitr...All-solid-state batteries(ASSBs)with sulfide-type solid electrolytes(SEs)are gaining significant attention due to their potential for the enhanced safety and energy density.In the slurry-coating process for ASSBs,nitrile rubber(NBR)is primarily used as a binder due to its moderate solubility in non-polar solvents,which exhibites minimal chemical reactivity with sulfide SEs.However,the NBR binder,composed of butadiene and acrylonitrile units with differing polarities,exhibits different chemical compatibility depending on the subtle differences in polarity of solvents.Herein,we systematically demonstrate how the chemical compatibility of solvents with the NBR binder influences the performance of ASSBs.Anisole is found to activate the acrylonitrile units,inducing an elongated polymer chain configuration in the binder solution,which gives an opportunity to strongly interact with the solid components of the electrode and the current collector.Consequently,selecting anisole as a solvent for the NBR binder enables the fabrication of a mechanically robust graphite-silicon anode,allowing ASSBs to operate at a lower stacking pressure of 16 MPa.This approach achieves an initial capacity of 480 mAh g^(-1),significantly higher than the 390 mAh g^(-1)achieved with the NBR/toluene binder that has less chemical compatibility.Furthermore,internal stress variations during battery operation are monitored,revealing that the enhanced mechanical properties,achieved through acrylonitrile activation,effectively mitigate internal stress in the graphite/silicon composite anode.展开更多
To improve the utilization rate and application value of magnesite tailings,magnesia composites were prepared using light-calcined magnesite tailing powder as the raw material,silicon powder,and 95-graphite as additiv...To improve the utilization rate and application value of magnesite tailings,magnesia composites were prepared using light-calcined magnesite tailing powder as the raw material,silicon powder,and 95-graphite as additives,and phenolic resin as the binder by the solid-phase reaction pressureless sintering method.The effects of Si powder and graphite powder additions on the cold modulus of rupture,density,linear change rate,thermal shock resistance,microstructure,and phase composition of the composites were investigated in a carbon embedded atmosphere.The results show that with increasing additions of silicon powder and graphite powder,the forsterite and silicon carbide contents in the materials increase,finally forming an M_(2)S-SiCC multiphase material with M_(2)S as the main crystal phase.The carbon monoxide and silicon monoxide gases produced during the reaction are detrimental to the sintering of the material,resulting in the decrease of the cold modulus of rupture,bulk density,and linear shrinkage,and the increase of the porosity.After thermal shock,the strength retention ratio of the materials increases significantly compared with that of the sample without additives,because both the increased forsterite content and the generation of silicon carbide whiskers in the materials contribute to improving the thermal shock resistance.展开更多
Lithium-ion batteries(LIBs)are an electrochemical energy storage technology that has been widely used for portable electrical devices,electric vehicles,and grid storage,etc.To satisfy the demand for user convenience e...Lithium-ion batteries(LIBs)are an electrochemical energy storage technology that has been widely used for portable electrical devices,electric vehicles,and grid storage,etc.To satisfy the demand for user convenience especially for electric vehicles,the development of a fast-charging technology for LIBs has become a critical focus.In commercial LIBs,the slow kinetics of Li+intercalation into the graphite anode from the electrolyte solution is known as the main restriction for fast-charging.We summarize the recent advances in obtaining fast-charging graphite-based anodes,mainly involving modifications of the electrolyte solution and graphite anode.Specifically,strategies for increasing the ionic conductivity and regulating the Li+solvation/desolvation state in the electrolyte solution,as well as optimizing the fabrication and the intrinsic activity of graphite-based anodes are discussed in detail.This review considers practical ways to obtain fast Li+intercalation kinetics into a graphite anode from the electrolyte as well as analysing progress in the commercialization of fast-charging LIBs.展开更多
Increasing the energy density of conventional lithium-ion batteries(LIBs)is important for satisfying the demands of electric vehicles and advanced electronics.Silicon is considered as one of the most-promising anodes ...Increasing the energy density of conventional lithium-ion batteries(LIBs)is important for satisfying the demands of electric vehicles and advanced electronics.Silicon is considered as one of the most-promising anodes to replace the traditional graphite anode for the realization of high-energy LIBs due to its extremely high theoretical capacity,although its severe volume changes during lithiation/delithiation have led to a big challenge for practical application.In contrast,the co-utilization of Si and graphite has been well recognized as one of the preferred strategies for commercialization in the near future.In this review,we focus on different carbonaceous additives,such as carbon nanotubes,reduced graphene oxide,and pyrolyzed carbon derived from precursors such as pitch,sugars,heteroatom polymers,and so forth,which play an important role in constructing micrometersized hierarchical structures of silicon/graphite/carbon(Si/G/C)composites and tailoring the morphology and surface with good structural stability,good adhesion,high electrical conductivity,high tap density,and good interface chemistry to achieve high capacity and long cycling stability simultaneously.We first discuss the importance and challenge of the co-utilization of Si and graphite.Then,we carefully review and compare the improved effects of various types of carbonaceous materials and their associated structures on the electrochemical performance of Si/G/C composites.We also review the diverse synthesis techniques and treatment methods,which are also significant factors for optimizing Si/G/C composites.Finally,we provide a pertinent evaluation of these forms of carbon according to their suitability for commercialization.We also make far-ranging suggestions with regard to the selection of proper carbonaceous materials and the design of Si/G/C composites for further development.展开更多
Superperiodic feature was observed by scanning tunneling microscopy (STM) on the surface of highly oriented pyrolytic graphite (HOPG) on which silicon was sputtered. The superlattice was analyzed by the moire pattern ...Superperiodic feature was observed by scanning tunneling microscopy (STM) on the surface of highly oriented pyrolytic graphite (HOPG) on which silicon was sputtered. The superlattice was analyzed by the moire pattern hypothesis, and the lattice constant is 7.03 nm. For the superlattice, the observed boundaries between the superlattice and the normal graphite areas were zigzag, which was in good agreement with the result predicted theoretically. In addition, the observed lattice constants varied slightly in the superperiodic feature area. This implies the role of intralayer strain in the formation of the observed superlattice on the graphite surface.展开更多
Nickel-coated graphite particles and two-component silicone-rubber were compounded to form a conductive composite system. The electrical volume resistivity of the composites were examined and compared under constant t...Nickel-coated graphite particles and two-component silicone-rubber were compounded to form a conductive composite system. The electrical volume resistivity of the composites were examined and compared under constant tensile strains, cyclic heating-cooling, electric field and repeated cyclic tensile strains in order to study the mechanism of electrical conductivity behaviors of the conductive composites under stress, temperature and current. The results showed that a peak value of the electrical resistivity appeared previously and then gradually increasing with increasing tensile strain. The electrical resistivity displayed positive temperature coefficient effect during the temperature increasing and decreasing. Applying 5A direct current to the conductive composites lesulted in an increase in the electrical resistance immediately, but no changes were detected under lower currents. Under the repeated cyclic strain, the peak value of the electrical resistivity of each cycle increased with the test cycle. All the electrical resistivity changes were attributed to the conductive networks broken-up and rebuilt in the conductive composites.展开更多
To study the effects of different proportions of aluminum hydroxide and expandable graphite （EG） composites on flame retardation, sealing, mechanical, electrical and other properties of RTV- 1, aluminum hydroxide/ex...To study the effects of different proportions of aluminum hydroxide and expandable graphite （EG） composites on flame retardation, sealing, mechanical, electrical and other properties of RTV- 1, aluminum hydroxide/expandable graphite （ATH/EG） and silicone rubber composites were prepared by the compression molding method. The experimental results show that heat resistance improves with the increase of proportion of EG. Although the resistance coefficient changes, the composite materials still keep good electrical insulating property. Moreover, oxygen index and expansion index rise first then fall. When ATH/EG is 1：1, the oxygen index reaches the highest; the mechanical property of the silicone rubber is not affected under various environments such as acid, alkali, oily, artificial sea water environments, etc.展开更多
Although graphite(G)materials dominate the commercial lithium-ion battery(LIBs)anode market due to their excellent overall performance,their limited rate performance and cycle life hinder applications in highperforman...Although graphite(G)materials dominate the commercial lithium-ion battery(LIBs)anode market due to their excellent overall performance,their limited rate performance and cycle life hinder applications in highperformance fields.To improve the cycling and rate performance of graphite anodes,this study first employed economical and eco-friendly tannic acid(TA)as a carbon coating precursor to coat graphite surfaces viaπ-πstacking interactions.In an oxygen-rich alkaline environment,tannic acid undergoes oxidation polymerization and crosslinks with formaldehyde to form a polymer matrix that coats the graphite surface.After subsequent carbonization,carbon-coated graphite material(G@C)was successfully synthesized.Carbon coatings on graphite effectively lower LIB resistance,enhance lithium-ion diffusion,and prevent exfoliation during cycling,thereby significantly boosting rate performance and prolonging the cycle life of graphite.After 500 cycles at 2C,the specific capacity of G@C was 103.7 mAh g^(-1),with a retention of 89%.However,G exhibited only 68.7 mAh g^(-1) and 85%retention under identical conditions.This carbon-coated graphite modification strategy offers a novel,green,and economical approach for designing and tailoring graphite anode materials for lithium-ion batteries with long cycle life and high rate.展开更多
We adopted the solution impregnation route with aluminum dihydrogen phosphate solution as liquid medium for effective surface modification on graphite substrate.The mass ratio of graphite to Al(H_(2)PO_(4))_(3) change...We adopted the solution impregnation route with aluminum dihydrogen phosphate solution as liquid medium for effective surface modification on graphite substrate.The mass ratio of graphite to Al(H_(2)PO_(4))_(3) changed from 0.5:1 to 4:1,and the impregnation time changed from 1 to 7 h.The typical composite phase change thermal storage materials doped with the as-treated graphite were fabricated using form-stable technique.To investigate the oxidation and anti-oxidation behavior of the impregnated graphite at high temperatures,the samples were put into a muffle furnace for a cyclic heat test.Based on SEM,EDS,DSC techniques,analyses on the impregnated technique suggested an optimized processing conditions of a 3 h impregnation time with the ratio of graphite:Al(H_(2)PO_(4))_(3) as 1:3 for graphite impregnation treatment.Further investigations on high-temperature phase change heat storage materials doped by the treated graphite suggested excellent oxidation resistance and thermal cycling performance.展开更多
SiC reinforced graphite composites were prepared via introducing carbide silicon into the natural graphite flakes（NGF） by hot-pressing process. Their physical and mechanical properties, including density, open poros...SiC reinforced graphite composites were prepared via introducing carbide silicon into the natural graphite flakes（NGF） by hot-pressing process. Their physical and mechanical properties, including density, open porosity, flexural strength, and friction behavior were investigated. The addition of 30vol% Si C increased the bending strength of composites materials to 127 MPa, 2 times higher than 60 MPa of commercial pure graphite block. What was particularly interesting was that the as-obtained graphite composite with 30vol% Si C kept the same low friction coefficient of about 0.1 as pure graphite, and the wear resistance of composites increased.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12072183,12472174,and 12421002).
文摘The recently reported silicon/graphite(Si/Gr)composite electrode with a layered structure is a promising approach to achieve high capacity and stable cycling of Si-based electrodes in lithium-ion batteries.However,there is still a need to clarify why particular layered structures are effective and why others are ineffective or even detrimental.In this work,an unreported mechanism dominated by the porosity evolution of electrodes is proposed for the degradation behavior of layered Si/Gr electrodes.First,the effect of layering sequence on the overall electrode performance is investigated experimentally,and the results suggest that the cycling performance of the silicon-on-graphite(SG)electrode is much superior to that of the graphite-on-silicon electrode.To explain this phenomenon,a coupled mechanical-electrochemical porous electrode model is developed,in which the porosity is affected by the silicon expansion and the local constraints.The modeling results suggest that the weaker constraint of the silicon layer in the SG electrode leads to a more insignificant decrease in porosity,and consequently,the more stable cycling performance.The findings of this work provide new insights into the structural design of Si-based electrodes.
基金MA and LS are grateful to the Rowe Family Endowment Fund,and QH acknowledges Tang Fellowship.The financial support from the U.S.National Science Foundation(NSF)with the award number CMMI-1660572 is acknowledged.Further,the discussion of TEM images with Dr.Satyanarayana Emani is appreciated.The use of the Center for Nanoscale Materials,an Office of Science user facility,was supported by the U.S.Department of Energy,Office of Science,Office of Basic Energy Sciences,under Contract No.DE-AC02-06CH11357.
文摘Silicon/graphite(Si/Gr)nanocomposites with controlled void spaces and encapsulated by a carbon shell(Si/Gr@void@C)are synthesized by utilizing high-energy ball milling to reduce micron-sized particles to nanoscale,followed by carbonization of polydopamine(PODA)to form a carbon shell,and finally partial etching of the nanostructured Si core by NaOH solution at elevated temperatures.In particular,the effects of ball milling time and NaOH etching temperature on the electrochemical properties of Si/Gr@void@C are investigated.Increasing the ball milling time results in the improved specific capacity of Si-based anodes.Carbon coating further enhances the specific capacity and capacity retention over charge/discharge cycles.The best cycle stability is achieved after partial etching of the Si core inside Si/Gr@void@C particles at either 70 or 80C,leading to little or no capacity decay over 130 cycles.However,it is found that both carbon coating and NaOH etching processes cause some surface oxidation of the nanostructured Si particles derived from high-energy ball milling.The surface oxidation of the nanostructured Si results in decreases in specific capacity and should be minimized in future studies.The mechanistic understanding developed in this study paves the way to further improve the electrochemical performance of Si/Gr@void@C nanocomposites in future.
基金supported by the National Natural Science Foundation of China(No.52274346).
文摘Waste graphitization cathode carbon blocks are a type of hazardous solid waste generated during the aluminum electrolysis process,and their proper disposal is a key step in the resource utilization of discarded graphite.This study utilizes the porous“defect advantage”of a cathode carbon block matrix to prepare silicon-doped and asphalt-coated detoxified and purified waste graphitization cathode carbon blocks for use as high-performance silicon/carbon composite anode materials.The results show that the uniformly silicondoped silicon/carbon composite material features a unique amorphous carbon-encapsulated“locked silicon”structure,which effectively addresses issues such as cathode volume expansion,excessive growth of the solid electrolyte interphase(SEI)film,and poor electrical contact between active materials.Consequently,electrochemical performance is enhanced.After assembly in a half-cell,the PSCC/10%Si@C(purified waste graphitization cathode carbon/10%Si@C)material exhibits optimal electrochemical stability,with an initial charging specific capacity of 514.5 mAh/g at 0.1 C(1 C=170 mA/g)and a capacity retention rate of 95.1%after 100 cycles.At a charge rate of 2.0 C,a specific capacity of 216.9 mAh/g is achieved.This technology provides a new pathway for the economical and high-value utilization of waste cathode carbon blocks and the development of low-cost,high-performance anode materials.
基金supported by European Union's Horizon Europe,UK Research and Innovation(UKRI).
文摘Graphite,encompassing both natural graphite and synthetic graphite,and graphene,have been extensively utilized and investigated as anode materials and additives in lithium-ion batteries(LIBs).In the pursuit of carbon neutrality,LIBs are expected to play a pivotal role in reducing CO_(2)emissions by decreasing reliance on fossil fuels and enabling the integration of renewable energy sources.Owing to their technological maturity and exceptional electrochemical performance,the global production of graphite and graphene for LIBs is projected to continue expanding.Over the past decades,numerous researchers have concentrated on reducing the material and energy input whilst optimising the electrochemical performance of graphite and graphene,through novel synthesis methods and various modifications at the laboratory scale.This review provides a comprehensive examination of the manufacturing methods,environmental impact,research progress,and challenges associated with graphite and graphene in LIBs from an industrial perspective,with a particular focus on the carbon footprint of production processes.Additionally,it considers emerging challenges and future development directions of graphite and graphene,offering significant insights for ongoing and future research in the field of green LIBs.
基金supported by the National Key Research and Development Program of China(2024YFA1612900)the National Natural Science Foundation of China(Grant No.52103365 and No.12375270)the Guangdong Innovative and Entrepreneurial Research Team Program,China(Grant No.2021ZT09L227).
文摘Fine-grained nuclear graphite is a key material in high-temperature gas-cooled reactors(HTGRs).During air ingress accidents,core graphite components undergo severe oxidation,threatening structural integrity.Therefore,understanding the oxidation behavior of nuclear graphite is essential for reactor safety.The influence of oxidation involves multiple factors,including temperature,sample size,oxidant,impurities,filler type and size,etc.The size of the filler particles plays a crucial role in this study.Five ultrafine-and superfine-grained nuclear graphite samples(5.9-34.4μm)are manufactured using identical raw materials and manufacturing processes.Isothermal oxidation tests conducted at 650℃-750℃ are used to study the oxidation behavior.Additionally,comprehensive characterization is performed to analyze the crystal structure,surface morphology,and nanoscale to microscale pore structure of the samples.Results indicate that oxidation behavior cannot be predicted solely based on filler grain size.Reactive site concentration,characterized by active surface area,dominates the chemical reaction kinetics,whereas pore tortuosity,quantified by the structural parameterΨ,plays a key role in regulating oxidant diffusion.These findings clarify the dual role of microstructure in oxidation mechanisms and establish a theoretical and experimental basis for the design of high-performance nuclear graphite capable of long-term service in high-temperature gas-cooled reactors.
基金funded by the National Key Research and Development Program of China(grant no.2023YFB3809300)Longzhong Laboratory Research Project(grant no.2024KF-20)+4 种基金the National Science Foundation of China(grant no.52373306)the Key Research and Development Program Project of Hubei Province(grant no.2023BAB140,2024BAA013)the Natural Science Foundation of Hubei Province(grant no.2023AFA053)the Key Research and Development Program of Henan Province(grant no.251111240100)the Postdoctoral Fellowship Program of CPSF(grant no.GZB20230553)。
文摘The extensive application of lithium-ion batteries in electric vehicles has led to a torrential surge of endof-life batteries.As the dominant anode material,graphite's environmental and resource costs in production highlight the necessity of recycling spent graphite(SG).However,SG recycling technologies remain markedly underdeveloped compared to the cathode recovery status,due to perceived lower economic value.This review provides an in-depth analysis of the current SG growth trend and highlights the cost accounting for graphite recycling and the significant importance of advanced recycling technologies.By examining the failure mechanisms of graphite,various recycling and upcycling technologies in both practical application and fundamental research are fully discussed,in terms of the regeneration principle,recycling effect,strengths,and limitations of each method.Furthermore,the multi-purpose applications of recycled graphite beyond LIB anodes are explored to enhance its high-value properties.Finally,the prospects of SG recycling and large-scale application challenges are presented,including economic feasibility,process optimization,and regulatory restrictions.This review provides a comprehensive overview of developments in SG recycling strategies,offering valuable insights for narrowing the gap between fundamental research and practical applications.
基金supported by grants from Natural Science Foundation of Guangdong Province(Grant No.2021A1515012335)National Natural Science Foundation of China(NSFC)(Grant No.11274400)+2 种基金Pearl River S&T Nova Program of Guangzhou(Grant No.201506010059)State Key Laboratory of Optoelectronic Materials and Technologies(Sun Yat-Sen University)(Grant No.OEMT-2024-ZTS-01)State Key Laboratory of High Field Laser Physics(Shanghai Institute of Optics and Fine Mechanics)。
文摘Laser-induced periodic surface structures(LIPSS)have gained increasing attention in the field of micro/nano fabrication,although achieving sub-100-nm period LIPSS with high uniformity remains a significant challenge.In this work,towards deep-subwavelength LIPSS on highly oriented pyrolytic graphite(HOPG),we demonstrate that ultra-uniform nanogratings of sub-50-nm periods and near-10-nm groove widths can be stably prepared via 800-nm femtosecond laser scanning irradiation with a high-NA objective lens under water immersion.The resulting nanogratings of strong polarization dependence,exhibiting exceptional surface flatness,period stability,and structural integrity,tend to appear at near-damage-threshold fluence regime with an appropriate effective pulse number.It turns out that the water immersion condition can significantly reduce the thermal effects of femtosecond laser ablation on HOPG,and thus via a mild,incubation-like scanning ablation process occurring in the nanogrooves with a continuous or jumping manner,this deep-subwavelength grating can achieve robust elongation growth,ensuring its long-range uniformity as well as minimal deposited debris and structural defects.Interestingly,the different incubation extension mechanisms for the mutually perpendicular and parallel settings between scanning direction and laser polarization bring not only distinct effective-pulse-number windows and somewhat different grating qualities,but also different extension stabilities in nanograting stitching via overlapping scanning lines and thus the optimal scanning strategy of parallel setting for large-area processing.In short,this study presents a convenient laser-processing approach for high precision fabrication of sub-50-nm gratings on HOPG,which would provide new insights into micro/nano-fabrication for optoelectronic metasurfaces and physics of the interaction between ultrafast laser and graphite.
基金supported by the National Natural Science Foundation of China(Project Nos.22372051 and 21406044)Australian Research Council/Discovery Early Career Researcher Award(DECRA)funding scheme(DE230100180).
文摘The impurities and structural cracks within spent graphite(SG)in lithium-ion battery anodes hamper lithium-ion intercalation and extraction after successive charge-discharge operations,thereby yielding poor lithium storage behavior.Herein,low-viscosity natural deep eutectic solvent(NDES)composed of citric acid(CA)and betaine hydrochloride was employed to remove the organic impurities in SG via a one-step benign process involving hydrogen bonds and electrostatic interactions at mild conditions of 80℃ for only 30 min.After NDES leaching under optimal conditions(molar ratio of CA to betaine hydrochloride=3:1,80℃,30 min),the as-obtained sample(denoted as BG-3)exhibited an extremely clean surface,moderately enlarged interlayer distance,and more structural defects at the edge of graphite lamellae.These features facilitated lithium-ion intercalation and withdrawal,bestowing BG-3 with remarkable activity in lithium-ion battery(LIB)recycling.For instance,BG-3 delivered a capacity of 438.6 mAh g^(-1) at a current density of 0.1 A g^(-1).Its capacity retention reached 97.9%,accompanied by a Coulombic efficiency of 99.1%,upon completing 100 cycles.A molecular dynamics simulation was employed to illuminate the regeneration mechanism for anode graphite from a theoretical perspective.It revealed that NDES exhibits lower binding energy with all contaminants compared to graphite,which is favorable for NDES to eliminate impurities from graphite surfaces.This study unveils a method of recycling SG from retired LIBs by a short eco-friendly process,providing a competitive blueprint to address the shortage of battery-grade anode graphite and to achieve carbon neutrality.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIT)(No.NRF-2021M3H4A1A02048529)the Ministry of Trade,Industry and Energy(MOTIE)of the Korean government under grant No.RS-2022-00155854support from the DGIST Supercomputing and Big Data Center.
文摘To enhance the electrochemical performance of lithium-ion battery anodes with higher silicon content,it is essential to engineer their microstructure for better lithium-ion transport and mitigated volume change as well.Herein,we suggest an effective approach to control the micropore structure of silicon oxide(SiO_(x))/artificial graphite(AG)composite electrodes using a perforated current collector.The electrode features a unique pore structure,where alternating high-porosity domains and low-porosity domains markedly reduce overall electrode resistance,leading to a 20%improvement in rate capability at a 5C-rate discharge condition.Using microstructure-resolved modeling and simulations,we demonstrate that the patterned micropore structure enhances lithium-ion transport,mitigating the electrolyte concentration gradient of lithium-ion.Additionally,perforating current collector with a chemical etching process increases the number of hydrogen bonding sites and enlarges the interface with the SiO_(x)/AG composite electrode,significantly improving adhesion strength.This,in turn,suppresses mechanical degradation and leads to a 50%higher capacity retention.Thus,regularly arranged micropore structure enabled by the perforated current collector successfully improves both rate capability and cycle life in SiO_(x)/AG composite electrodes,providing valuable insights into electrode engineering.
基金supported by the National Key R&D Program of China(Grant No.2023YFA1406200)the National Science Foundation of China(Grant No.U2032215)+1 种基金Jilin Province Major Science and Technology Program,China(Grant No.20240211002GX)the Science and Technology Development Project of Jilin Province(Grant No.SKL202402004).
文摘Graphite and hexagonal boron nitride(h-BN),despite their structural similarity,exhibit opposing electronic properties,namely,metallic conductivity and wide-bandgap insulation,respectively.In recent years,graphene-h-BN heterostructures have attracted significant research interest,with the resulting hybrid B-C-N atomic-layer systems exhibiting distinctive electronic properties.Notably,interface effects play a decisive role in governing the performance of these heterostructures.Nevertheless,owing to the lack of high-quality composites,the interfacial structure in B-C-N materials and the correlation with critical properties such as charge transport and band structure modulation are not fully clear.Here,we report the direct synthesis of a millimeter-sized hexagonal B-C-N composite via a solvent method under high-pressure and high-temperature conditions.Structural characterization reveals that the synthesized B-C-N composite contains isolated graphite and h-BN.Compared with pure h-BN,the B-C-N composite has a narrower bandgap and shows a pronounced photoelectric response in the visible light region.More interestingly,we find a graphite-like B-C compound with a thickness of about 30 nm at the graphite-h-BN interface,which forms Schottky junctions with graphite,thus realizing rectification properties.Our findings provide a method for synthesizing highquality B-C-N composites and offer new insights into the structure of the graphite-h-BN interface.
基金supported by the Technology Innovation Program(00404166,Development of thin-film coating current collector and aqueous binder to enhance the adhesion and conductivity properties on the silicon-rich anode)funded By the Ministry of Trade,Industry&Energy(MOTIE,Korea),the National Research Council of Science&Technology(NST)grant by the Korea government(MSIT)(No.2710024139)the Institute of Civil Military Technology Cooperation funded by the Defense Acquisition Program Administration and Ministry of Trade,Industry and Energy of Korean government under grant No.22-CM-FC-20。
文摘All-solid-state batteries(ASSBs)with sulfide-type solid electrolytes(SEs)are gaining significant attention due to their potential for the enhanced safety and energy density.In the slurry-coating process for ASSBs,nitrile rubber(NBR)is primarily used as a binder due to its moderate solubility in non-polar solvents,which exhibites minimal chemical reactivity with sulfide SEs.However,the NBR binder,composed of butadiene and acrylonitrile units with differing polarities,exhibits different chemical compatibility depending on the subtle differences in polarity of solvents.Herein,we systematically demonstrate how the chemical compatibility of solvents with the NBR binder influences the performance of ASSBs.Anisole is found to activate the acrylonitrile units,inducing an elongated polymer chain configuration in the binder solution,which gives an opportunity to strongly interact with the solid components of the electrode and the current collector.Consequently,selecting anisole as a solvent for the NBR binder enables the fabrication of a mechanically robust graphite-silicon anode,allowing ASSBs to operate at a lower stacking pressure of 16 MPa.This approach achieves an initial capacity of 480 mAh g^(-1),significantly higher than the 390 mAh g^(-1)achieved with the NBR/toluene binder that has less chemical compatibility.Furthermore,internal stress variations during battery operation are monitored,revealing that the enhanced mechanical properties,achieved through acrylonitrile activation,effectively mitigate internal stress in the graphite/silicon composite anode.
文摘To improve the utilization rate and application value of magnesite tailings,magnesia composites were prepared using light-calcined magnesite tailing powder as the raw material,silicon powder,and 95-graphite as additives,and phenolic resin as the binder by the solid-phase reaction pressureless sintering method.The effects of Si powder and graphite powder additions on the cold modulus of rupture,density,linear change rate,thermal shock resistance,microstructure,and phase composition of the composites were investigated in a carbon embedded atmosphere.The results show that with increasing additions of silicon powder and graphite powder,the forsterite and silicon carbide contents in the materials increase,finally forming an M_(2)S-SiCC multiphase material with M_(2)S as the main crystal phase.The carbon monoxide and silicon monoxide gases produced during the reaction are detrimental to the sintering of the material,resulting in the decrease of the cold modulus of rupture,bulk density,and linear shrinkage,and the increase of the porosity.After thermal shock,the strength retention ratio of the materials increases significantly compared with that of the sample without additives,because both the increased forsterite content and the generation of silicon carbide whiskers in the materials contribute to improving the thermal shock resistance.
文摘Lithium-ion batteries(LIBs)are an electrochemical energy storage technology that has been widely used for portable electrical devices,electric vehicles,and grid storage,etc.To satisfy the demand for user convenience especially for electric vehicles,the development of a fast-charging technology for LIBs has become a critical focus.In commercial LIBs,the slow kinetics of Li+intercalation into the graphite anode from the electrolyte solution is known as the main restriction for fast-charging.We summarize the recent advances in obtaining fast-charging graphite-based anodes,mainly involving modifications of the electrolyte solution and graphite anode.Specifically,strategies for increasing the ionic conductivity and regulating the Li+solvation/desolvation state in the electrolyte solution,as well as optimizing the fabrication and the intrinsic activity of graphite-based anodes are discussed in detail.This review considers practical ways to obtain fast Li+intercalation kinetics into a graphite anode from the electrolyte as well as analysing progress in the commercialization of fast-charging LIBs.
基金Financial support provided by the Australian Research Council(ARC)(grant nos.FT150100109 and LP160101629)is gratefully acknowledged.The authors also acknowledge Dr Tania Silver at the University of Wollongong for editing the English.
文摘Increasing the energy density of conventional lithium-ion batteries(LIBs)is important for satisfying the demands of electric vehicles and advanced electronics.Silicon is considered as one of the most-promising anodes to replace the traditional graphite anode for the realization of high-energy LIBs due to its extremely high theoretical capacity,although its severe volume changes during lithiation/delithiation have led to a big challenge for practical application.In contrast,the co-utilization of Si and graphite has been well recognized as one of the preferred strategies for commercialization in the near future.In this review,we focus on different carbonaceous additives,such as carbon nanotubes,reduced graphene oxide,and pyrolyzed carbon derived from precursors such as pitch,sugars,heteroatom polymers,and so forth,which play an important role in constructing micrometersized hierarchical structures of silicon/graphite/carbon(Si/G/C)composites and tailoring the morphology and surface with good structural stability,good adhesion,high electrical conductivity,high tap density,and good interface chemistry to achieve high capacity and long cycling stability simultaneously.We first discuss the importance and challenge of the co-utilization of Si and graphite.Then,we carefully review and compare the improved effects of various types of carbonaceous materials and their associated structures on the electrochemical performance of Si/G/C composites.We also review the diverse synthesis techniques and treatment methods,which are also significant factors for optimizing Si/G/C composites.Finally,we provide a pertinent evaluation of these forms of carbon according to their suitability for commercialization.We also make far-ranging suggestions with regard to the selection of proper carbonaceous materials and the design of Si/G/C composites for further development.
基金The authors thank the National Natural Science Foundation of China for support by two grants:No.50025204 and No.59895156.
文摘Superperiodic feature was observed by scanning tunneling microscopy (STM) on the surface of highly oriented pyrolytic graphite (HOPG) on which silicon was sputtered. The superlattice was analyzed by the moire pattern hypothesis, and the lattice constant is 7.03 nm. For the superlattice, the observed boundaries between the superlattice and the normal graphite areas were zigzag, which was in good agreement with the result predicted theoretically. In addition, the observed lattice constants varied slightly in the superperiodic feature area. This implies the role of intralayer strain in the formation of the observed superlattice on the graphite surface.
基金Funded by Wuhan Science and Technology Bureau (No.200710321090-18)
文摘Nickel-coated graphite particles and two-component silicone-rubber were compounded to form a conductive composite system. The electrical volume resistivity of the composites were examined and compared under constant tensile strains, cyclic heating-cooling, electric field and repeated cyclic tensile strains in order to study the mechanism of electrical conductivity behaviors of the conductive composites under stress, temperature and current. The results showed that a peak value of the electrical resistivity appeared previously and then gradually increasing with increasing tensile strain. The electrical resistivity displayed positive temperature coefficient effect during the temperature increasing and decreasing. Applying 5A direct current to the conductive composites lesulted in an increase in the electrical resistance immediately, but no changes were detected under lower currents. Under the repeated cyclic strain, the peak value of the electrical resistivity of each cycle increased with the test cycle. All the electrical resistivity changes were attributed to the conductive networks broken-up and rebuilt in the conductive composites.
文摘To study the effects of different proportions of aluminum hydroxide and expandable graphite （EG） composites on flame retardation, sealing, mechanical, electrical and other properties of RTV- 1, aluminum hydroxide/expandable graphite （ATH/EG） and silicone rubber composites were prepared by the compression molding method. The experimental results show that heat resistance improves with the increase of proportion of EG. Although the resistance coefficient changes, the composite materials still keep good electrical insulating property. Moreover, oxygen index and expansion index rise first then fall. When ATH/EG is 1：1, the oxygen index reaches the highest; the mechanical property of the silicone rubber is not affected under various environments such as acid, alkali, oily, artificial sea water environments, etc.
基金supported by the Science and Technology Projects of the State Grid Corporation of China(5500-202323102A-1-1-ZN).
文摘Although graphite(G)materials dominate the commercial lithium-ion battery(LIBs)anode market due to their excellent overall performance,their limited rate performance and cycle life hinder applications in highperformance fields.To improve the cycling and rate performance of graphite anodes,this study first employed economical and eco-friendly tannic acid(TA)as a carbon coating precursor to coat graphite surfaces viaπ-πstacking interactions.In an oxygen-rich alkaline environment,tannic acid undergoes oxidation polymerization and crosslinks with formaldehyde to form a polymer matrix that coats the graphite surface.After subsequent carbonization,carbon-coated graphite material(G@C)was successfully synthesized.Carbon coatings on graphite effectively lower LIB resistance,enhance lithium-ion diffusion,and prevent exfoliation during cycling,thereby significantly boosting rate performance and prolonging the cycle life of graphite.After 500 cycles at 2C,the specific capacity of G@C was 103.7 mAh g^(-1),with a retention of 89%.However,G exhibited only 68.7 mAh g^(-1) and 85%retention under identical conditions.This carbon-coated graphite modification strategy offers a novel,green,and economical approach for designing and tailoring graphite anode materials for lithium-ion batteries with long cycle life and high rate.
基金Funded by Scientific and Technological Innovation Project of Carbon Emission Peak and Carbon Neutrality of Jiangsu Province(No.BE2022028-4)。
文摘We adopted the solution impregnation route with aluminum dihydrogen phosphate solution as liquid medium for effective surface modification on graphite substrate.The mass ratio of graphite to Al(H_(2)PO_(4))_(3) changed from 0.5:1 to 4:1,and the impregnation time changed from 1 to 7 h.The typical composite phase change thermal storage materials doped with the as-treated graphite were fabricated using form-stable technique.To investigate the oxidation and anti-oxidation behavior of the impregnated graphite at high temperatures,the samples were put into a muffle furnace for a cyclic heat test.Based on SEM,EDS,DSC techniques,analyses on the impregnated technique suggested an optimized processing conditions of a 3 h impregnation time with the ratio of graphite:Al(H_(2)PO_(4))_(3) as 1:3 for graphite impregnation treatment.Further investigations on high-temperature phase change heat storage materials doped by the treated graphite suggested excellent oxidation resistance and thermal cycling performance.
基金Funded by the National Natural Science Foundation of China(No.U1134102)
文摘SiC reinforced graphite composites were prepared via introducing carbide silicon into the natural graphite flakes（NGF） by hot-pressing process. Their physical and mechanical properties, including density, open porosity, flexural strength, and friction behavior were investigated. The addition of 30vol% Si C increased the bending strength of composites materials to 127 MPa, 2 times higher than 60 MPa of commercial pure graphite block. What was particularly interesting was that the as-obtained graphite composite with 30vol% Si C kept the same low friction coefficient of about 0.1 as pure graphite, and the wear resistance of composites increased.
