Alabama Graphite reports high-performance Si-enhanced coated spherical purified graphite (Si-CSPG) for LIBs
Alabama Graphite Corp. (AGC) reported positive electrochemical results from downstream lithium-ion battery tests recently performed on its silicon-oxide-enhanced coated spherical purified graphite ("Si-CSPG") produced from the AGC’s ultra-high-purity 99.999 wt% C natural flake graphite.
Based on the addition of a 4 wt % silicon oxide (SiOx) to its CSPG, AGC was able to achieve a reversible capacity of 405.03 mAh/g and an irreversible capacity of 439.49 mAh/g. This compared to 347.2 mAh/g reversible capacity and 369.59 mAh/g irreversible capacity for commercial synthetic graphite.
|AGC’S Si-CSPG and standard CSPG vs. commercial synthetic graphite|
|Li-ion Battery Anode Graphite||Reversible Capacity
D50= 25 µm
(Non-Silicon Enhanced CSPG)
D50= 18.3 µm
Anode Graphite (Control)
D50= 15.8 µm
|D (e.g. D50) represents the diameter of powder particles in a given sample, derived by the cumulative volume. The cumulative volume allows the laboratory to determine the D values (represents the diameter of powder particles for the sample)—essentially the range of particles sizes, and an average value.|
Although preliminary and non-optimized, the Si-CSPG test results exceed the maximum theoretical specific capacity for Li-ion anode graphite of 372 mAh/g.
The demonstrated increased electrochemical performance achieved with Si-CSPG was accomplished at a de minimis cost increase compared to AGC’s standard CSPG production costs (US$1,555 per tonne, average cost per tonne of secondary-processed CSPG). A potential bottom-quartile-cost producer, AGC is aware of no other known graphite development company that has published a lower OPEX or initial CAPEX required to produce CSPG.
Without revealing the exact number of cycles achieved in cycling with the Si-CSPG graphite, AGC said it has achieved “impressive” cycling stability to date. Optimization work continues and long-term cycling data will be reported in the coming months.
AGC specifically noted that cycling stability has been achieved with the high loading of active material, in the range of 12 to 13 mg/cm2 and at the calculated calendared electrode density of 1.6 g/cm3. For reference, to AGC’s knowledge, earlier results reported by the industry have never succeeded in achieving stable cycling at the above high loadings of active materials in the electrode. The highest loading of Silicon-enriched graphite-based active materials known to AGC in which a stable cycling has been achieved used anywhere from 1.2 to 5 mg/cm2 loading of electrode active materials in the anode—up to an order of magnitude lower than the loadings used by AGC in the subject test work.
Reduced loadings of active materials in the anode represent an undesirable engineering solution for battery design, AGC said, since it leads to domination of both weight and volume of current collector foils over that of active materials in a cell design.
Consequently, reduced electrode loadings will result in poor specific capacity (as measured in mAh/g) and energy density (as measured in mAh/cm3) on a full cell/battery level. AGC’s anode loadings of active materials are in line with battery industry expectations for CSPG graphite (i.e. above 11 mg/cm2), which makes this result significant from a practical, rather than purely academic point of view, AGC said.
While many academic publications tend to focus on additions of 15 to 50 wt% silicon into the carbon matrix, AGC considers the latter approaches to be unnecessarily high-cost and generally impractical due to inability to match the increased anode capacity with the appropriate cathode.
The source of Si in this project was silicon (scrap) wafer discs, which were ground to the desired particle size and converted into silicon oxide of a preferred, proprietary stoichiometry (SiOx) prior to doping of uncoated spherical purified graphite (SPG) graphite precursor.
Si scrap is sold by the pound for US$15/lb and is a considerably less expensive source of Silicon than vapor-grown nano-silicon, which has a current price of US$500+/kg (or US$1,100+/lb); AGC said that its choice of Si raw material allows for cost efficiencies over any technology that uses vacuum chambers and/or chemical vapor deposition (CVD) or physical vapor deposition (PVD) reactors.
AGC is 100% owner of the only advanced-stage graphite project in the contiguous United States and all requisite downstream secondary processing to manufacture AGC’s Si-CSPG is being conducted in the US. Although AGC’s proprietary, environmentally sustainable process to purify and produce battery-ready graphite is source-agnostic, the secondary process flowsheet has been optimized for Coosa Graphite Project material. AGC cautioned that is not yet in production and that there is no guarantee it will advance to full-scale production. If, following the completion of a feasibility study—which has not yet begun—AGC is able to advance the Coosa Graphite Project into production, the resulting graphite would be sourced from within the contiguous US and AGC might have a potential competitive advantage over other producers of value-added graphite materials sourced from other countries.