Graphite Test Work
Important observations in exploratory product development test work conducted as part of the PEA are summarized follow. Many are directly attributable to the STAX® characteristics.
- High conversion rates to spherical graphite were achieved (75% vs. 30 to 40% for Chinese graphites)
- Direct spheronization was possible as no jet milling of the purified graphite was required prior to the spheronization process
- The entire size distribution of the graphite feed could be used
- Residence time in the spheronizing mill (a high electricity consumer) was half that which has been experienced with conventional Chinese flake graphite and two thirds of the energy input was used
- The product was determined to be electrochemically stable and in the size range applicable to advanced lithium ion battery systems
- A streamlined mineral beneficiation process may be possible, producing graphite concentrate with less equipment and a higher proportion of the result being directed to CSG production
- A record Tap Density value (1.17 g/cm3) was measured with non-milled spheroidal flake (higher density means higher energy storage capabilities)
- Near theoretical performances in electrochemical properties were produced in battery tests with uncoated and coated spheronized STAX® graphite. Figure 8 summarizes the results of tests on coin cell batteries made with uncoated and coated STAX® graphite and presents the best results for each compared to tests with coin cells made with Chinese flake and top grade synthetic graphite.
Notes: 1. Carbons for Electrochemical Energy Storage and Conversion Systems (2010) 2. Lithium-Ion Batteries Science and Technologies (2009)
- The measure of comparison is discharge capacity, a measure of a battery’s energy storage capability once first charged. The best results with STAX® CSG achieved reversible discharge capacity as high as 370.1 Ah/kg - or 0.5% below the theoretical maximum possible. For uncoated CSG, the best result achieved the theoretical maximum of 372 AH/kg. In other tests with uncoated STAX® CSG, the first discharge capacities of most showed a deviation of just 1% from the theoretical maximum and the greatest deviation was 3%. In addition, all the STAX® tests performed demonstrated the ability to achieve the same or similar discharge capacities in repeated subsequent charging/discharging cycles.
- The ability to reach and closely approach theoretical maximum discharge capacity and to consistently maintain high repeated values on cycling demonstrates the high performance potential of STAX® graphite. Coin cell 1220 successfully completed three charge/discharge cycles as seen in Figure 9, the second and third discharge curves show almost complete coincident overlap with the first discharge curve, attesting to repeatability in performance across subsequent charge/discharge cycles.
The Company recognizes that more research and development work is necessary to understand and quantify the significant features of STAX® graphite as well as assess its performance in commercial equipment for establishing purchase specifications. The unique morphologies of STAX® graphite may well turn out to be the major competitive advantage of Graphite One contributing to lower costs and superior performance.
Other Preliminary Test Work
Demonstration work on value-added graphite products using STAX® graphite conducted since the PEA was published is outlined below. The work was performed by Graphite One’s independent industrial partner (“IPP”) at an independent industrial laboratory using graphitic material from the Company’s Graphite Creek Property.
The technical content of this summary was reviewed and approved by Dr. Shane Beattie, the Company’s Chief Technology Officer at the time this information was released and a qualified person as defined by National Instrument 43-101.
Coated Spherical Graphite (CSPG) Test Work
A representative sample of spherical carbon coated graphite (“CSPG”) has been produced and submitted to a leading automotive manufacturer under a Non-Disclosure Agreement (NDA). Initial results are promising, and testing is ongoing.
The IPP’s electrochemical laboratory has assembled half and full battery cells with both carbon-coated and uncoated samples of spheronized STAX® material. The cells were subjected to short- and long- term cycling. Testing performed on these samples determined that STAX® material has high packing densities: > 1.0 g/cm3.
The half cells showed more than 170 stable charge discharge cycles (Figure 10). The reversible capacity on the first cycle was 357.7 mAh/g, and on the 170th cycle, 354.5 mAh/g.
These cycling results suggest a promising future for the use of STAX® graphite as anode active materials in rechargeable lithium-ion battery systems.
Graphite One has adopted an inverted purification flow sheet, where concentrate is purified at the beginning, the opposite of traditional graphite processing flow sheets. As a result, Graphite One plans to redirect all of the material which does not spheronize into other value-added applications. This ensures that nearly all of the concentrate material can be utilized and sold to available high-tech markets.
One of these value-added applications is a conductivity enhancement additive for use in battery cathodes. To this point, the IPP has successfully conducted milling, grinding, and sizing of purified material and converted it into non-spherical ultra-high purity graphite which may qualify for conductivity enhancement grades. The process has generated two relevant products with 99.99+ wt.%C purity level: expanded, delaminated graphite with mean particle size value of 23 microns and purified, milled, natural graphite with mean particle size of 10 microns. Both materials have been tested extensively in alkaline batteries and have also been supplied to a leading alkaline battery company. Initial feedback has been positive and testing is ongoing.
Fire Retardant/Fire Suppressive Graphite Foams
Thermally purified STAX® graphite has been successfully intercalated and turned into an expandable flake product, which was subsequently formulated into fire retardant foam concentrates. This line of test work is being conducted as part of a joint project with the Naval Air Warfare Center Weapons Division of NAVAIR, in Ridgecrest, CA.
The IPP has successfully formulated fire retardant foams capable of extinguishing Class B fires using STAX® purified, expandable graphite. Class B fires are defined as burning oil, gasoline, diesel, and aviation fuel fires (the most difficult to extinguish). Graphite One and the IPP have conducted small scale demonstrations highlighting the increased efficacy of intercalated STAX® graphite in extinguishing oil fires (see Figure 11). Full scale oil fire testing per MIL-F-24385F U.S. Military Test Specifications is anticipated to take place in the third quarter of 2020.
High-Purity Graphite Coatings
The IPP has assessed STAX® material for use in graphite paints and coatings. Ultra-high purity STAX® material has been reduced in size to where the mean particle size is under 2.5 µm and formulated into dispersions. Dispersions were tested in new generation radio frequency and infrared suppressing paints, anti-corrosive coatings, and ultra-high precision metal working applications. The tests are focused on supplying the existing DOD supply chains. Extensive technical data from these tests have been introduced to the Defense Logistics Agency which is responsible for sourcing materials into DOD supply chains. Work on these value-added applications continues as Graphite One’s targeted off-take partners in the specialty industries are receiving prototype demonstration samples and generating technical performance data.
Industrial Synthetic Diamonds as Semiconductor Materials
Purified versions of STAX® material have also been subjected to high pressure - high temperature reactive synthesis and successfully converted into synthetic diamonds using industry-standard technologies. Initially, a 6.5 gigapascal press was used to generate synthetic diamond dust. This is an essential test to preliminarily validate the ability of STAX® material to be converted into synthetic diamonds. Not every graphite precursor can produce diamonds with this method as some lose integrity when under high pressure. However, STAX® purified natural graphite material successfully formed diamond dust under the lower temperature and pressure conditions. The product that came out from this process can be used “as is” for metal working applications, such as pigments for lapping compounds and ultra-hard coatings on drilling, cutting, and grinding equipment and tooling. Diamond dust synthesized from the thermally purified 80 x 100 mesh graphitic material of Graphite Creek origin mostly formed octahedron crystal morphologies. This is the preferred morphology due to being the closest structure to diamond crystals. A typical octahedron crystal formed from STAX® material is shown in Figure 12.
The second phase of this development work subjected STAX® material to higher temperatures and pressures under longer dwell times and resulted in successful synthesis of gemstone-quality diamonds of 3 carats and larger, one of which is shown in Figure 13.
The next step in testing of STAX® material is to dope large synthetic diamonds with appropriate elements to produce next-generation semiconductor materials that would replace silicon wafers in critical applications. For example, where the application temperatures exceed 125° C. Such applications range from rocketry to heat sinks to new generation electronics and harness-free critical mobile component assemblies, such as fast-moving aerial systems and specialty engines. The concept is being reviewed by the engineering community at the Redstone Arsenal, AL and Army Research Laboratory, PA while the IPP is working on delivering prototype samples of new semiconductor devices made from Graphite Creek materials.
Indications of U.S. Government-Listed Critical Minerals and Metals
Lastly, when STAX® material is thermally purified using the high temperature process chosen by Graphite One, the purified graphite flows down the furnace and the impurities sublime into the flu where they are trapped in the gypsum formed in a dual-alkali scrubber. Graphite One’s analysis of the chemical composition of trapped impurities indicates that out of 17 rare earth metals, 16 were present.