South Star Battery Metals announces positive production of battery grade coated spherical purified graphite.
South Star Battery Metals Corp. (“South Star” or the “Company”) (TSXV: STS) (OTCQB: STSBF), along with its technological partner in the United States (“US Lab”1), announced that South Star has successfully produced uncoated and coated spherical purified graphite (“SPG”) suitable for use as anode active material for lithium-ion batteries (“LiB”).
Richard Pearce, President and CEO of South Star.
We are pleased to continue announcing robust battery testing results.
“The thermal purification process resulted in 99.9993 wt % C without any of the environmental, health and worker safety issues associated with application of hydrofluoric and hydrochloric acids, which are the standard chemicals used in conventional processing of battery grade graphite.”
“Excellent quality uncoated and coated SPG suitable for LiB anodes was produced. Our spherical graphite testing resulted in yields of approximately 74%, which is twice the standard industry yield. The results indicate we would be very cost competitive with a less costly micronization process and exceptional spherical graphite yields.”
“The latest testing highlights the high-quality, high-purity and low-contaminate nature of South Star’s concentrates for value-add and purified graphite products. We will now be constructing battery cells and performing long-term cycle testing and optimizations.”
Purified graphite was successfully micronized using advanced pilot scale mechanical milling system outfitted with two air classification circuits. The latter technology was found to be preferable over micronization in cascading air jet mills.
Specifically, Santa Cruz flake has demonstrated nearly twice higher throughput rate during the mechanical grinding and sizing, as compared to sizing rate in an air-mill of the same nominal size. During sizing step, the size of flakes was reduced to a range of 25 to 30 microns prior to spheroidization. Geometries and shape factors are adjusted based on the battery cell manufacturer’s requirements and the inherent physical characteristics of the graphite.
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Mechanical milling was effective in sizing of its flake and resulted in higher throughput, which translates into lower cost for the same energy input. It should be noted that a reference sample of flake graphite from Madagascar was milled on the same mill concurrently.
Santa Cruz flake material ground at 23% faster than the reference material processed on the same mill to similar particle size distribution.
Once the target sizing geometries have been achieved, uncoated SPG was produced, the micronized graphite was rolled and rounded into elliptical spheres in a specialized mill.
The elliptical shapes are a preferred morphology for higher active loading densities in batteries. They are also preferred due to better rate capacities, safer and generally longer-life LiBs.
The safety aspect of LiBs deserves a standalone comment. Passing criteria for spherical uncoated graphite is defined by the BET (Brunauer, Emmett and Teller) surface area value. The latter has to be less than 10 m2/g for graphite to be considered promising in anode applications.
Many uncoated graphites struggle to deliver such a BET surface area and that requires the application of thick exterior coatings as a way to mitigate this issue. By contrast, Santa Cruz spheroidal flake was determined to have BET values of 6.7 m2/g, which is indicative of the fact that this material will require rather thin surface coatings to make a successful anode for LiBs. Moreover, as much as 47.11 wt % of spheronized Santa Cruz graphite was measured to have tap density in the range from 1.02 to 1.16 g/cm3.
An additional 26.9 wt % of spheroidal particles was harvested with the tap density of 0.9 g/cm3, which is a passing criterion for LiBs. Therefore, a combined total of 74.01 wt% of useable uncoated spheroidal purified graphite was harvested in the process of spheroidization of Santa Cruz natural flake.
In contrast, typical yields of spheroidal product synthesized in the cascade milling circuits by Asian manufacturers of spherical graphite are 35-40 wt % spheres. It is worth noting that higher yield is a prerequisite to the cost leadership position of Santa Cruz natural graphite on the worldwide markets of advanced graphite products.
Finally, uncoated SPG was coated with a nanolayer of soft carbon and heat treated under a blanket of inert gas. The hardened coating provides a layer of protection from exfoliation and general degradation during the normal expansion and contraction cycles associated with charging and discharging.
The coating also reduces ongoing reactions of electrolytes with the graphitic carbon, which results in a reduced battery life. Coated SPG is the basic raw material used to generate battery anodes by casting the coated SPG onto copper foils.
For this round of testing a D50 of 18 microns of purified graphite was produced. Future testing will include optimization of particle size and determining the electrochemical performance of Santa Cruz graphite in the battery cell environment.
The results of the Coated SPG testing indicate excellent physiochemical properties for high-quality LiB anode materials. A summary is presented in Table 1 and Figures 2 and 3, below:
South Star Battery Metals Announces Positive Production of Battery Grade Coated Spherical Purified Graphite, VANCOUVER, BC, June 29, 2021
