Sustainability and environmental considerations for LIB anode graphite materials: existing and next-generation

The article is contributed by Shantanu Mitra, Elton Cairns and Vinod Nair

• Issues with synthetic graphite: non-renewable sources, atmospheric pollutants, and particulate matter pollution
• Issues with natural graphite: non-renewable sources, geopolitical concerns, impurities, particulate matter pollution, and inferior battery cycle life
• Alternative supply chain using renewable, low-cost, and low-impurity raw materials such as furan chemicals from biomass waste is highly desirable

The benefits of reduced emissions from electric vehicles (EVs) are well known. As interest in these battery-powered applications continues to grow worldwide, the supply chain of critical materials has become an essential consideration in choosing battery chemistry. Based on predicted EV adoption rates, studies have indicated that the lithium-ion battery (LIB) industry will face a supply shortfall of some raw materials used in constructing LIB cells. In particular, graphite supply for LIB anode applications is expected to fall short of industry demand as early as 2025 [1].

Additionally, given the expanding need for anode graphite, it is estimated that by 2030 another 4–5 million mt/year will be needed [2]. As a result, the industry is concerned about the raw material availability of the graphite supply, the supply chain’s sustainability, and the environmental aspects of the production processes.

There are currently two primary LIB anode materials: synthetic graphite and natural graphite.

While recycled graphite, recovered from spent LIBs, is also a potential source, the recycling industry is still in its infancy. It cannot add meaningful quantities of new supply to the fast-growing demand for more graphite-based anode materials. Moreover, the structural changes to graphite during the cycling and the impurities associated with the recycling processes must be addressed before recycled graphite can be used as a reliable anode material source for cell manufacturing.

Synthetic Graphite

As the name suggests, synthetic graphite is produced from other raw materials. The primary raw material is coke, obtained by carbonizing tar — at 1000oC and higher — from petroleum and coal industry by-products. Following carbonization, these materials are graphitized at temperatures up to 3000oC. At these extremely high temperatures, the carbon atoms realign themselves into hexagonal crystalline structures, forming graphite (with the characteristic d002 X-ray diffraction peak at a 2θ value of 26.4o). Interestingly, most of the global synthetic graphite supply is produced in China.

There are several issues with this approach [3]:

I. The sources for synthetic graphite are not renewable.

II. Some of the impurities in the raw materials, such as sulfur and nitrogen, are released during the carbonization step in the form of atmospheric pollutants (SOx and NOx).

III. The raw materials themselves also release particulate matter pollutants during the carbonization process.

Natural Graphite

Natural graphite — most commonly in the ‘flake’ form — is mined primarily in China (Heilongjiang, Shandong, and Inner Mongolia provinces, amongst others), Brazil, Africa (Tanzania, Madagascar, amongst others), Canada and India.

Mined graphite is converted into anode-grade ‘coated spherical graphite (CSPG) graphite through the following process steps: (Mining) 🡪 (Crushing/Grinding) 🡪 (Flotation) 🡪 (Purification) 🡪 (Micronization) 🡪 (Spheroidization) 🡪 (Coating). More than 90% of the world’s CSPG is made in China.

Production of natural graphite has the following issues:

I. It is not from a renewable source.

II. Graphite mines are not well distributed around the globe, and given the projected demand for LIBs in EVs, graphite has become a strategic material in a geopolitical sense.

III. Mined natural graphite contains impurities that need to be removed to make it “battery-grade,” requiring strong etchants like sodium hydroxide and hydrofluoric acid, which harm human health and the environment.

IV. Natural graphite mining also causes particulate matter pollution due to severe dust emissions.

V. Natural graphite is not as good as synthetic graphite concerning battery cycle life.

While natural graphite is cheaper to produce than synthetic graphite, it still requires significant capital investment.

An alternative: synthetic graphite from a renewable biomass source

Given the size of the market and the shortcomings of the synthetic and natural graphite available today, an alternative supply chain would be highly desirable. The ideal LIB-grade synthetic graphite product should be manufactured from earth-abundant raw materials that are renewable, low-cost, and have low impurity content — using a simple/existing manufacturing process with a good yield.

As it turns out, Furan chemicals present exactly this profile. Furfuryl alcohol (C5H6O2) and Furfural (C5H4O2) are two examples of these products, both containing the 5-atom furan ring (4 C and 1 O):

Furfural can be distilled from the hemicellulose component of biomass (readily available worldwide in agricultural waste, including sugarcane bagasse and corn cobs). Furfuryl alcohol can then be synthesized from furfural by hydrogenation.

The polymerization reactions and structural changes needed to synthesize graphite are shown in Figure 1.

Figure 1. Converting biomass waste extracts into graphite.

These biomass-derived furan-ring compounds have a relatively high percentage of carbon (61.2% in FA and 62.5% in FUR). The polymerization, carbonization, and graphitization processes to convert these furan chemicals into graphite do not involve the loss of substantial amounts of carbon, allowing for high process yields. This feature and the fact that the furan chemicals are derived from agricultural waste and are currently produced in several countries make them strong candidates for an alternate source of synthetic graphite. Additionally, no new manufacturing infrastructure is needed, as the existing synthetic graphite manufacturing processes also apply to biomass-derived precursors to manufacture graphite.

Table 1. Comparison of the materials and processes for all three different types discussed above:

Scanning electron micrographs of the three graphites are shown below.

Figure 2. SEM micrographs of the three types of graphite discussed above.

Furan-derived carbons are being developed by Farad Power, Inc (Sunnyvale, CA) [4] and show materials characteristics and electrochemical measurements similar to synthetic graphite [5], making them excellent candidates for LIB anode applications.

Furthermore, the furan-based synthetic graphite structure can be fine-tuned for NIB anode materials, which typically require a different structure from the graphite used for LIBs. The furan-based raw materials described above can be derived cost-effectively from various natural materials like corn cobs, bagasse, and rice straw, enabling a localized supply chain for LIBs and emerging NIBs.

References

1. Magill, K., & Zimmerman, S. (2022). A Looming Graphite Shortage Could Snarl the EV Battery Supply Chain. Supply Chain Dive. https://www.supplychaindive.com/news/graphite-shortage-ev-electric-vehicles-supply-chain/626870/
2. Holman, J. (2022). FEATURE: Graphite Supply a Concern in Meeting Growing Battery Demand. S&P Global Commodity Insights. https://www.spglobal.com/commodityinsights/en/market-insights/latest-news/energy-transition/021622-feature-graphite-supply-a-concern-in-meeting-growing-battery-demand
3. Dunn, J. B., James, C., Gaines, L., Gallagher, K., Dai, Q., & Kelly, J. C. (2015). Material and Energy Flows in the Production of Cathode and Anode Materials for Lithium Ion Batteries. Argonne National Laboratory. ANL/ESD — 14/10 Rev. https://doi.org/10.2172/1224963.
4. Arnaiz, M., Nair, V., Mitra, S., & Ajuria, J. (2019). Furfuryl Alcohol Derived High-End Carbons for Ultrafast Dual Carbon Lithium Ion Capacitors. Electrochimica Acta, 304, 437–446. https://doi.org/10.1016/j.electacta.2019.02.120
5. Mitra, S., & Nair, V. (2021). Method of making hard-carbon composite material. USPTO 20210091377:A1. US Patent. https://patentimages.storage.googleapis.com/80/c0/ee/63ae859cea0f1b/US20210091377A1.pdf

Vinod Nair (PhD., Electrochemistry) is an accomplished electrochemist with several years of experience in polymer chemistry, material synthesis, sol-gel chemistry, and fabrication of batteries and supercapacitors. He recently spent six years at Calgon Carbon, working on carbons for supercapacitor and battery applications. He is co-founder and CTO at Farad Power, Inc.

Shantanu Mitra (PhD, Materials Science) is a materials scientist by training, with expertise in process development, materials synthesis, and characterization techniques. He has also performed several different roles in his career, including business development, marketing and sales. He is co-founder and CEO of Farad Power, Inc.

Professor Elton Cairns (PhD, Chemical Engineering) is an internationally renowned expert on LIB chemistry. He is currently a Faculty Senior Scientist at Lawrence Berkeley National Labs and Professor of the Graduate School at the Chemical & Biomolecular Engineering Dept. at the University of California, Berkeley. Professor Cairns is a technical advisor to Farad Power, Inc.

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