Graphite Test Work
Important observations in exploratory product development test work conducted to date 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.