Graphite Products Research Articles

Toward a life cycle inventory for graphite production

AbstractGlobal electrification of mobility and energy storage is driving an unprecedented demand for lithium‐ion batteries (LIBs) for which graphite is one of the major components. Multiple prior studies have attempted to assess the environmental footprint of LIBs by way of life cycle analysis (LCA), and the poor quality of inventory data on the production of graphite (at various purities) has been highlighted consistently. This work reviews the available inventories used in the assessment of natural and synthetic battery‐grade graphite production, and demonstrates that some upstream, downstream, and peripheral processes—including important processes associated with mining, calcination, and other steps—are often omitted, leading to greatly underestimated impacts. It proposes a new rigid framework for comparing different graphite production routes and a corresponding indicative inventory for synthetic graphite production. This inventory is used to estimate the global warming potential and energy demand of synthetic graphite, yielding results of 13.8 kgCO2‐eq/kg and 45.9 MJ/kg, respectively, suggesting that prior literature may have underestimated these results by a factor of two or more. The work concludes by highlighting the need to evaluate a broader suite of applicable impact categories and to fully account for the full suite of by‐and co‐products in future LCAs.

Life cycle assessment of natural graphite production for lithium-ion battery anodes based on industrial primary data

The production of battery materials has been identified as the main contributor to the greenhouse gas (GHG) emissions of lithium-ion batteries for automotive applications. Graphite manufacturing is characterized by energy intense production processes (including extraction), mainly being operated in China with low energy prices and a relatively high GHG emission intensity of electricity generation.Industrial scale primary data related to the production of battery materials lacks transparency and remains scarce in general. In particular, life cycle inventory datasets related to the extraction, refining and coating of graphite as anode material for lithium-ion batteries are incomplete, out of date and hardly representative for today's battery applications. Nevertheless, primary life cycle inventory data of battery materials like graphite, produced on an industrial scale are crucial for a robust evaluation of batteries for electric vehicles, material sourcing and development of robust decarbonization strategies.This paper addresses this issue by first providing a comprehensive overview of the existing graphite datasets and their original sources, and outlining the reasons for wide variations of reported environmental impact results. Furthermore, this paper aims at closing existing data gaps by providing transparent primary data from a Chinese graphite producer from 2019 and assessing the environmental impacts (cradle-to-gate) in form of a life cycle assessment (LCA) for a vertically integrated graphite production. The life cycle inventory covers material, water, energy flows and direct emissions associated with the production of natural graphite anode material for an automotive battery application and associated transport activities along the supply chain. The results of the LCA show that the production of 1000 kg of natural graphite anode material has a global warming potential (GWP) of approximately 9616 kg CO2eq. The subsequent uncertainty analysis in the form of a Monte-Carlo-Analysis with 10000 runs reveals that the 95% confidence interval is in the range between 9297 and 9940 kg CO2eq. This value is more than four times higher than the reported GWP of battery-grade graphite in the ecoinvent database version 3.7.1.

Methodology for a combined uncertainty analysis and data quality rating of existing graphite datasets in context of battery LCAs

Battery raw materials have been identified as one of the main contributors to the overall environmental impact of batteries, however the primary data related to their production remains scarce and is subjected to high uncertainty. In particular, the commercial life cycle inventory datasets related to refining and processing of graphite as an anode material for lithium ion batteries are subjected to in-transparency and are difficult to be traced back. The existing Life Cycle Assessment (LCA) studies on traction batteries make use of these old and partly incomplete graphite datasets without consideration of underlying uncertainties and their effects on the overall environmental impacts. This paper addresses this issue by providing a comprehensive overview of the conventional graphite production processes, a summary of existing graphite datasets, along with their sources and presenting the underlying reasons for the major deviations. Subsequently, the quality of nine different Life Cycle Inventory (LCI) graphite datasets is discussed based on evaluation performed according to EPA data quality guidelines, whereby data gaps are identified and datasets are ranked according to an established data quality rating (DQR) methodology. Furthermore, the paper provides a common base for LCA results of existing graphite production datasets which were remodeled and assessed in Brightway2 (BW2) using background data from a ecoinvent. The results of DQR and LCA reveal major discrepancies in the datasets for the production of battery grade graphite. A Monte Carlo (MC) analysis is also provided to identify uncertainties stemming from technospheric flows, generating result bandwidths. A subsequent case study on state of the art lithium ion battery cell is also presented revealing that the choice of a certain graphite dataset could have a significant impact on the overall LCA results of a battery. The study highlights the need of the graphite datasets to receive more attention in the future.

Effect of pore structure on the thermophysical and frictional properties of high-density graphite

High density graphite is widely used in friction and sealing area. The pore structure inside, which were mainly affected by molding method, has a great effect on its thermophysical properties and friction performance. Herein, isostatic pressing, compression molding and hot molding method were utilized in our work to prepare high density graphite with different pore structure in order to study the relationship between pore structure and the comprehensive property. The results showed that the properties of graphite vary significantly in different directions, which was mainly affected by porosity, pore size distribution, the specific surface area, pore shape and fractal dimension. The influence mechanism of three graphite materials with different pore structures on thermophysical properties was delved, and the correlation between the comprehensive properties of graphite materials and their pore structures was verified. The in-plane comprehensive properties of hot molding graphite were the best, the graphitization degree was the highest (75.4%) and the total porosity was the lowest (15.08%). Especially, according to the pore structure analysis of the graphite, we found a positive correlation between the fractal dimension and the friction and wear properties of the graphite materials. Furthermore, research of pore structure explained the properties of graphite materials and proved the potential application of graphite in friction and sealing fields. • Graphite with different pore structures were prepared by different forming process. • The evolution of pore structure was deduced during the preparation of graphite products. • Pore structure characteristic parameters effect the comprehensive property of graphite. • Hot Molding can improve the orientation and degree of graphitization of the graphite. • Fractal dimension was positively correlated with the friction and wear properties.

RESULTS OF PILOT TESTS OF THE VSEP TECHNOLOGY ON THE EXAMPLE OF PURIFICATION OF CONTAMINATED ACID WASHING WATERS BY NANOFILTRATION

Shown are the results of a series of pilot tests for the purifi cation of waste (contaminated) acidic wash water formed during the production of graphite by the leaching method. The tests were carried out in laboratory and pilot modes (on-site) on the “LP” series machine. Purifi cation was simulated using nanofi ltration membranes using VSEP technology. This technology of vibro- membrane fi ltration makes it possible to purify such waters without preliminary purifi cation and the use of reagents (antiscalant) with a %Recovery more than 90 %. The mechanism for choosing the optimal sheet polymer membrane and the mechanism for determining the best working pressure are shown. Concentration series were carried out to determine the stability of the process and the duration of the fl ushing interval. The test results allow the design of an industrial water purifi cation system.

Effect of graphite microstructure on their physical parameters and wettability properties

To produce castings of titanium, nickel, zinc, copper and many other metal alloys, graphite molds can be used. Using graphite molds has many advantages which are no lubricate or coating layers are needed, high cooling rate, easy of production of complicated shapes. However, for good quality of castings there is needed a good quality of graphite with high mechanical properties and good heat transfer coefficient. Because of no room for manipulating of chemical composite of graphite molds, the most important factor influencing the properties of the molds is their production process. Thus, in the present study mechanical properties of two different type of graphite were investigated. There was graphite produced by different technological processes. One of the processes was a typical graphite production process from the isotropic coke, the second process was an electrolytic method production. Investigations included mechanical tests as well as the structure observations by scanning electron microscope. Chemical analysis was determined by Energy Dispersive X-ray Spectroscopy method additionally, phase analysis using the XRD method was performed. Mechanical properties were obtained by compression tests and three points banding tests at room temperature. It was found that the porosity of a graphite is the key parameter for good its mechanical properties. In addition, it was found that the mechanical anisotropy of graphite is the effect of the production method where the size and distribution of pores play an important role. Ill. 7. Ref. 9.

Development of High Temperature Multi-Layer Laser Flash Artefacts

Delamination of the interlayers of multi-layer systems can cause a degradation in functionality, stability and life span of that system. This is even more pertinent for systems at high temperature. Laser flash analysis (LFA) has long been used for thermophysical properties measurements at high temperatures. Multi-layer reference artefacts, with and without, debonded regions are required for validating the thermal characterisation of such systems using LFA. Although some high-temperature bulk candidate reference materials were developed and studied, e.g. in the European Metrology Research Programme (EMRP) funded Joint Research Project (JRP) ENG08 Metrofission, they were not able to meet the requirements for validating thermal measurements of multi-layer systems using LFA. In the European Metrology Programme for Innovation and Research (EMPIR) funded JRP 17IND11 Hi-TRACE project, the National Physical Laboratory is developing multi-layer reference artefacts, including both fully bonded and partially de-bonded systems for validating thermal characterisation of multi-layer systems at temperatures from room temperature to above 1000 °C using LFA. This paper details the methodology of production, measurement and validation of isotropic graphite and hafnium based multi-layer systems with, and without, partial debonding. Reproducibility, thermal stability and sensitive parameters concerning the thermal response of the artefacts will be discussed, with recommendation on the usage criteria as LFA multi-layer reference artefacts.

Perspective for the use of industrial waste in lubricating compositions to reduce wear in friction pairs

The article presents an analysis of the mechanisms of lubricating action used to reduce the wear of rails and wheels. A review of lubricant compositions that increase the service life of the wheel-rail pair showed that graphite is the main filler used to create rail lubricants. Since the production of synthetic graphite requires high energy costs, this material is relatively expensive. Replacing graphite with cheaper analogs will help reduce the cost of operating rails without losing lubricating properties in friction pairs. Today, there are many lubricant compositions. Many of them require experimental research since they are based only on theoretical knowledge in the field of tribology. In addition, the adhesion properties of a wheel to a rail depend not only on the action of the lubricant but also on weather and climatic conditions. When choosing a rational lubricant, it is worth focusing on a set of factors, and not only on the properties of an individual filler. The data obtained in theoretical analysis cannot always be verified experimentally. The reasons may be economic inexpediency, the complexity of experimental research, or lack of time. The analysis carried out in the course of this work showed that the study of the effect of lubricant components could be optimized using mathematical and digital modeling. The application of these methods will help to select a rational area for research, simulate the behavior of lubricants containing production wastes, and make the mathematical forecast of the operation of friction pairs more accurate.

Possibilities of Graphitization of Unburned Carbon from Coal Fly Ash

The paper presents the characteristics of products annealing at the temperatures of 2400 and 3000 °C of unburned carbon from coal fly ash in terms of its possible use as a starting material in the graphitization process. An amorphous substance (organic substance) with an admixture of some minerals has been found in samples subjected to graphitization. However, the graphite phase is dominant in products subjected to graphitization. Studies have also shown a diverse grain morphology in individual samples. The presence of plate-shaped and tube-shaped grains was found. As the graphitization temperature of the starting material increases (2400 and 3000 °C), the specific surface area in the graphitization products decreases. The total pore volume in the samples after the graphitization process was significantly lower than the pore volume of active carbons produced from other unburned carbon. Average pore diameter is similar to the pore diameter in active carbons. The reflectance value of the matrix for the sample graphitized at 3000 °C is characteristic for graphite. Unburned carbon from Polish fly ash can be used as the starting material for graphitization.

Nitrogen-Doped Carbon Aerogels Derived from Starch Biomass with Improved Electrochemical Properties for Li-Ion Batteries.

Among all advanced anode materials, graphite is regarded as leading and still-unrivaled. However, in the modern world, graphite-based anodes cannot fully satisfy the customers because of its insufficient value of specific capacity. Other limitations are being nonrenewable, restricted natural graphite resources, or harsh conditions required for artificial graphite production. All things considered, many efforts have been made in the investigation of novel carbonaceous materials with desired properties produced from natural, renewable resources via facile, low-cost, and environmentally friendly methods. In this work, we obtained N-doped, starch-based carbon aerogels using melamine and N2 pyrolysis as the source of nitrogen. The materials were characterized by X-ray powder diffraction, elemental analysis, X-ray photoelectron spectroscopy, galvanostatic charge–discharge tests, cyclic voltammetry, and electrochemical impedance spectroscopy. Depending on the doping method and the nitrogen amount, synthesized samples achieved different electrochemical behavior. N-doped, bioderived carbons exhibit far better electrochemical properties in comparison with pristine ones. Materials with the optimal amount of nitrogen (such as MCAGPS-N8.0%—carbon aerogel made from potato starch modified with melamine and CAGPS-N1.2%—carbon aerogel made from potato starch modified by N2 pyrolysis) are also competitive to graphite, especially for high-performance battery applications. N-doping can enhance the efficiency of Li-ion cells mostly by inducing more defects in the carbon matrix, improving the binding ability of Li+ and charge-transfer process.

Study on Purification and Modification Processing Technology of Microcrystalline Graphite

With the continuous development of new energy and new material technology, social industries pay more and more attention to graphite resources, and the related new graphite materials and technologies emerge as the times require in scientific research and practical application. With the continuous development of high-tech graphite industry, the general high-carbon graphite products can not meet the requirements of all walks of life, so it is necessary to further improve the purity of graphite. Therefore, in the research and development process of new graphite materials and technologies, the first step is to realize the purification and processing of graphite raw materials, and then the functional modification processing of graphite can be completed, so that the new graphite materials can meet the application needs of various industries in the society in terms of particle size, morphology or performance. Based on this, the exploration of various purification methods of microcrystalline graphite and the processing technology of functional modification of graphite have practical and theoretical significance.

Modulating carbon growth kinetics enables electrosynthesis of graphite derived from CO2 via a liquid–solid–solid process

Highly graphitic carbon materials have gained considerable interests in practical applications, however, an efficient and cost-effective synthesis strategy using low-grade carbonaceous precursors is still in urgent need. In this work, we successfully synthesize well-crystalline graphite derived from CO2 by molten carbonate electrolysis under a mild operating temperature, where the as-formed carbon atoms follow a “dissolution–precipitation” process on a Ni cathode. Attributed to that Ni cathode can in situ act as a solid solvent for periodically accommodating/dissolving the as-formed carbon atoms, deliberately coordinating carbon formation flux with carbon dissolution flux can lead to the consecutive production of highly crystalline graphite, without contamination of transition metal catalyst. It was found that a low carbon deposition current density and a relatively high operating temperature (650–750 °C) both facilitate the growth of graphite structures, because a moderate current density enables a suitable carbon flux originating from the electro-reduction of the captured CO2 (in the form of CO32− in molten salts), which can more accessibly match the carbon dissolution flux in Ni substrate at an elevated temperature. The thickness of graphite can be easily controlled by electrolysis durations. This work provides a simple strategy to convert CO2 into graphitic carbon products with both promising purity and crystallinity.

GENERALIZED MATHEMATICAL MODEL OF PHYSICAL FIELDS OF TECHNOLOGICAL REDISTRIBUTIONS OF MANUFACTURING ELECTROGRAPHITE PRODUCTS

A generalized mathematical model of the physical fields of the main technological redistributions of electrographite products is developed, which is based on a continuous-discrete approach to the description of nonlinear behavior of solids, liquids and gases, and bulk media. It is shown that the continuous formulation of physical processes in the technology of carbongraphite production is based on the Euler frame of reference and may include the following equations: conservation of mass, momentum and energy, electrical conductivity in the vortex-free approximation of electric potential and transport of chemical components of combustion reactions. The discrete formulation of physical processes in bulk materials used in the technology of production of carbon graphite products is based on the Lagrangian frame of reference and may include the following equations: translational and rotational motion and energy. The application of the generalized mathematical model for construction or refinement of mathematical and numerical models of separate redistributions for performance of the numerical analysis of physical fields and parameters of processes and the equipment on examples of pressing of "green" electrode preparations and theoretical research of effective thermophysical properties of loose carbonaceous materials. On the basis of the developed generalized statement, the complex of separate mathematical models of such redistributions of production of electrographite production as: calcination of carbonaceous materials in electrocalciners, gasification of carbonaceous materials in the equipment of rotary calcination furnaces is also formulated and specified, burning and graphitization of electrographite blanks. Bibl. 40, Fig. 4.

Dynamic material flow analysis of natural graphite in China for 2001-2018

Graphite is considered a critical mineral because of its importance to clean energy transition and global supply concentration. This critical role is evident for electric vehicles that depends on lithium-ion batteries using graphite as anode material. China is the world's largest producer and consumer of natural graphite due to its booming economy and rapid penetration of clean energy driven by carbon neutrality ambition. Given this background, this study conducts a dynamic material flow analysis of natural graphite to reveal the evolution trend of graphite flows in China from 2001 to 2018. Main results include: (1) China's graphite resource experienced extensive utilization to meet demands from domestic consumption (55-83%) and exportation (17-45%); (2) Of the 1643 Gg/yr graphite entering China's anthroposphere, 15% accumulates in in-use stock and 34% enters the waste stage, and secondary graphite only accounts for 0.7-5.7% of the total supply; (3) Releases of graphite (1271 Gg/yr) are mainly divided into tailings, dissipative losses in use, and post-consumer losses; (4) The export-production ratio has increased from 16% in 2001 to 40% in 2018; (5) Graphite demand from electric vehicles is estimated to be 18 times the current level by 2030 (2340 Gg). These results imply that China should not only prepare national policies on managing the overall graphite production activities in response to concerns about domestic resource loss and environmental disruption induced from extractive and processing activities, but also prepare policies encouraging appropriate graphite recycling from safety and economic feasibility perspectives.

Submicrosecond Aggregation during Detonation Synthesis of Nanodiamond.

Detonation nanodiamond (DND) is known to form aggregates that significantly reduce their unique nanoscale properties and require postprocessing to separate. How and when DND aggregates is an important question that has not been answered experimentally and could provide the foundation for approaches to limit aggregation. To answer this question, time-resolved small-angle X-ray scattering was performed during the detonation of high-explosives that are expected to condense particulates in the diamond, graphite, and liquid regions of the carbon phase diagram. DND aggregation into low fractal dimension structures could be observed as early as 0.1 μs, along with a separate scattering population also observed from an explosive that produces primarily graphitic products. A counterexample is the case of a high-explosive that produces nano-onions, where no hierarchical scattering was observed for at least 10 μs behind the detonation front. These results suggest that DND aggregation occurs on time scales comparable to particle formation.

Graphite production in two‐temperature non‐LTE plasmas of C4F7N and C5F10O mixed with CO2, N2, and O2 as eco‐friendly SF6 replacements: A numerical study

AbstractMany recent works have shown that C4F7N and C5F10O have a great potential to replace SF6 as a greenhouse gas. One of the biggest problems for their application is that condensed species (i.e., graphite) may be produced during gas discharges. However, all the previous works are performed under the assumption of local thermodynamic equilibrium (LTE). Therefore, this study investigates the departure of thermodynamic equilibrium and the corresponding effects on the graphite production in the plasmas of C4F7N, C5F10O, and their mixtures with CO2, N2, and O2, based on the two‐temperature (2T) non‐LTE plasma compositions calculated by the Gibbs free energy minimization. The results show that neglecting the nonequilibrium effect can lead to a very inaccurate description of graphite condensation in the above plasmas.

Temperature driven structural transition in the nickel-based catalytic graphitization of coconut coir

Biomass waste is considered as a renewable, low-cost, and environmental friendly carbon source. However, converting a largely disordered carbon materials from biomass wastes into a highly crystalline graphitic carbon nanostructure with low-energy consumption process remains a challenge. Here, we report a simple and low energy process to transform the amorphous carbon structure of coconut coir from Indonesian biomass waste into graphitic nanostructure. A high crystalline graphitic nanostructure has been successfully obtained through two-step process consisting of (1) carbonization process at 500 °C to produce amorphous charcoal, followed by (2) nickel-based catalytic graphitization process at various temperature of 1000 °C to 1300 °C. It is important to note that the temperature process is a main factor in the structural transformation from amorphous to graphitic nanostructures. The structural transformation during catalytic graphitization process was investigated as a function of heat treatment temperature using X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The results show that the carbon structure of coconut coir start to transform from amorphous to ordered graphitic nanostructure at 1200 °C, a temperature lower than that of conventional graphite production, with the highest degree of graphitization (82.16%) and IG/ID ratio of 1.16. Observation using high resolution transmission electron microscopy (HRTEM) reveal the well-defined lattice fringes of graphitic nanostructures with an interplanar distance of 0.3369 nm corresponding to the (0 0 2) crystal plane of pure graphite (0.3354 nm) and less than the disorder carbon (0.3440 nm). In conclusion, this simple process and low energy successfully convert the coconut coir waste into a higher value-added product of graphitic materials as well as reduce the environmental impact of coconut waste.

The impact of burning on the structure and mineral composition of bat guano

Here we addressed the question of whether burning of guano produces a characteristic suite of morphological changes and/or unique mineralogical products. The changes observed in our experimental burning of guano (both fresh and decayed) included colour change (blackening), grain size and morphological change (grain size generally reduced, morphology rendered generally less distinct), alteration of minerals by dehydration (e.g., gypsum to anhydrite, brushite to whitlockite), and production of new minerals or compounds (e.g., augelite, bayerite, giniite, graphite, oldhamite, strontium apatite, tridymite). The key morphological feature we found that may be diagnostic of burning was severe damage to crystals from rapid dehydration (cracks and striations, leading to eventual fragmentation). The key mineralogical feature we found was production of graphite. The high temperature exotic minerals that were produced (giniite, augelite, tridymite, oldhamite) were all found not to be high temperature obligate. Evidence gleaned from the literature suggests that a great number of the minerals associated with high temperatures can also be synthesized in low temperature settings such as weathering or microbial action (exemplified in the extremely complex biology and biochemistry of decaying guano). While the presence of any one of these minerals is not diagnostic of fire, it could be argued that the suite taken as a whole is moderately strong evidence for burning. In future studies, the chemistry of carbon aromaticity may prove to be the best diagnostic test for pyrolysis. A survey of the conditions under which documented spontaneous ignition occurs leads us to conclude that spontaneous ignition of guano inside a cave is an extremely unlikely event, and any suggestion/assertion to this effect should be rigorously supported.

Benzene Ring Knitting Achieved by Ambient-Temperature Dehalogenation via Mechanochemical Ullmann-Type Reductive Coupling.

The current approaches capable of affording conjugated porous networks (CPNs) still rely on solution-based coupling reactions promoted by noble metal complexes or Lewis acids, on-surface polymerization conducted in ultrahigh-vacuum environment at very high temperatures (>200 °C), or mechanochemical Scholl-type reactions limited to electron-rich substrates. To develop simple and scalable approaches capable of making CPNs under neat and ambient conditions, herein, a novel and complementary method to the current oxidative Scholl coupling processes is demonstrated to afford CPNs via direct aromatic ring knitting promoted by mechanochemical Ullmann-type reactions. The key to this strategy lies in the dehalogenation of aromatic halides in the presence of Mg involving the formation of Grignard reagent intermediates. Products (Ph-CPN-1) obtained via direct CC bond formation between 1,2,4,5-tetrabromobenzene (TBB) monomer feature high surface areas together with mesoporous architecture. The versatility of this approach is confirmed by the successful construction of various CPNs via knitting of the corresponding aromatic rings (e.g., pyrene and triphenylene), and even highly crystalline graphite productwas obtained. The CPNs exhibit good electrochemical performance as the anode material in lithium-ion batteries (LIBs). This approach expands the frontiers of CPN synthesis and provides new opportunities to their scalable applications.

Temperature and humidity influence on the strain sensing performance of hybrid carbon nanotubes and graphite cement composites

Cement composites with hybrid conductive fillers carbon nanotubes (CNT) and graphite products (GP), have been tested as strain sensors under varying temperatures (0 °C–60 °C), and moisture conditions (0%–100% saturation degree (SD)). Cement pastes with 1% CNT and 5% GP (purified expanded graphite) presented resistivity values between 50 and 75 Ohm·cm, and their strain sensing response was observed to be independent of the loading conditions. However, the gage factor increased up to four times for higher temperatures, and was influenced by the temperature time history. Gage factors were also increased when drying the material up to a SD of 71% or with entirely dried samples.