This is an extract from an interesting article (see below) on why microcrystalline graphite from sugarloaf may in fact be a very good input for battery anodes.
My understanding is that Archer had previously (circa 2015) determined that graphite at Sugarloaf was too high in carbon content for use in battery anodes, however it sounds like recent developments suggest when combined with Silicon it can actually be a very cost effective solution that can potentially also provide a higher energy density.
There are some that are developing Silicon only anode solutions, at early stages of development, and others like Altech (ATC.AX) that are coating graphite with silicon like is being suggested in this article.
Interestingly it also sounds like there are some significant Silica resources that extend from Whyalla/Port Augusta up to near Roxby Downs - search for an article on the SA Energy and Mining Website for an article titled "New Critical Minerals Opportunities". Funnily enough actually feature iTech in the article.
Utilization of impurities and carbon defects in natural microcrystalline graphite to prepare silicon-graphite composite anode for high-performance lithium-ion batteries - Published: 29 July 2021
Bei Liu, Peng Huang, Minqi Liu & Zhiyong Xie - Journal of Materials Science volume
Abstract
Impurities and carbon defects generally hinder practical application of microcrystalline graphite as anode material for lithium-ion batteries. However, the impurities and carbon defects of the natural microcrystalline graphite are found to be the active sites to catalyze silicon deposition during the chemical vapor deposition process. In this work, the impurities and carbon defects of prepared anode material are wrapped by double coatings that are combined by the silicon nanowires and the carbon layer. The composite anode material exhibits a high capacity of 640 mA h g−1 at a current density of 186 mA g−1 after 250 cycles. The results of the density functional theory calculation reveal that the existence of impurities and carbon defects on graphite surface enhances the absorption energy of graphite to silicon during chemical vapor deposition process at 900 °C. By utilizing the impurities and carbon defects, the natural microcrystalline graphite can be employed as a new and low-cost anode material to fabricate the high-performance lithium-ion batteries.
Introduction
At present, natural microcrystalline graphite is mainly used in low value-added products due to its rich reserves and low-cost, such as refractory materials [1], conductive materials [2], wear-resistant lubricating materials [3] and cast-iron additive materials. It is restricted in high value-added fields such as lithium-ion batteries (LIBs) anode materials, mainly because the impurities in graphite, which are the independent mineral inclusions and the impurity ions can replace the carbon atoms or enter the crystal lattice defects of graphite [4], resulting in the difficulty of being purified of the natural microcrystalline graphite. Besides, the abundant carbon defects appeared in the microcrystalline graphite during the processes of mining, crushing and purification have a huge impact on the performance of LIBs [5].There are two main methods for obtaining the pure natural microcrystalline graphite that can be applied in LIBs anode materials. One method is the chemical purification including acid and alkaline disposition [6]. Zhao et al. [7]. using concentrated sulfuric acid (H2SO4) and hydrochloric acid (HCl) in a thermal autoclave to purified nature graphite, followed by carbon coating. The using of general acids can effectively avoid the destructive injury to environment or human that may be brought by the hydrofluoric acid (HF) [8]. And the as-obtained natural graphite anode presented an initial coulombic efficiency of 88.4% with a capacity of 355.8 mA h g−1. As for the alkaline purification, NaOH reacts with SiO2 and Al2O3 in impurities at high temperature to form soluble salts. After filtering and washing, the purity of natural graphite can reach 99.9%. Though the natural graphite after chemical purification has a high purity, almost all countries and regions prohibit the use of chemical purification due to the huge pollution of the by-products [9]. Another method with environmental protection is the physical method [10] that mainly includes the high temperature purification. The impurities are directly volatilized by heating above the boiling point of the impurity phase with no use of any acid. After purification, the purity of natural microcrystalline graphite can reach more than 99.99%. However, the ultra-high energy consumption and high dependence on equipment lead to huge purification costs. The economical and environmentally friendly purification method of natural microcrystalline graphite needs to be addressed.
For the issue of carbon defects in natural microcrystalline graphite, surface coating is a simple and effective method to improve the battery performance [11], [12]. The surface coating method can effectively avoid the direct contact between microcrystalline graphite and the solvent thus can reduce the Li+ consumption during the formation of the solid-electrolyte interphase (SEI) [13]. And the coating layer can prevent the graphite layer from being peeled off caused by the intercalation of solvent molecules [14]. Cheng et al. [15]. fabricated electrically conductive ultrananocrystalline diamond-coated natural graphite-copper composite anode for long life LIBs. Masaki et al. [16]. reported a composite anode of spherical carbon-coated natural graphite which shows excellent battery cycle performance.
Though the natural microcrystalline graphite can be chosen as a decent anode material for LIBs by employing multiple alternative purification methods or coating it with carbon, the manufacturing cost and reversible capacity of the modified natural microcrystalline graphite still have a gap compared with the flake graphite and artificial graphite that have been commercialized. Nano-sized silicon [17] and graphite composite anode materials can simultaneously maintain the high reversible capacity of silicon and the cycling stability of graphite [18]. In Li’s work [19], a mesoporous Si/amorphous carbon/graphite composite was synthesized by high energy ball milling. Si nanoparticles and flake graphite are evolved into microspheres by self-assemble via polycondensation and surface tension of pitch. But the agglomeration of nano-sized Si and the low bonding strength between Si and graphite imply that the composite can be better modified by changing the fabrication method. The chemical vapor deposition (CVD) method is an ideal way to obtain uniform surface coating layer and realize in situ growth of materials on a target substrate [20]. Kim [21] fabricated an amorphous Si nanolayer in edge-plane activated graphite anodes surface using the CVD method employing silane as the Si source. Min Ko et al. [22]. employed silane and obtained a Si-nanolayer-embedded graphite composite for high-energy LIBs.
Herein, we using natural microcrystalline graphite ore as the raw material, after simple multiple flotation and chemical purification (general acids such as HCl, H2SO4 and other non-HF). And silicon nanowire-microcrystalline graphite composite anode was fabricated via CVD methods employing chloromethylsilane as the silicon precursor. During the CVD process, trace impurities that hard to be purified and carbon defects caused during purification processes accelerate the deposition of silicon. The utilization of impurities and carbon defects to catalyze the deposition of silicon, and the silicon can accurately cover the positions of impurities and carbon defects. As a result, the fabricated silicon-microcrystalline graphite composite anode showed an excellent battery performance.
