SiTration, an American clean tech company founded in 2020, develops advanced filtration membrane technology for the efficient and low-cost recovery of critical materials from lithium-ion battery recycling and mining operations. Traditional chemical and thermal separation methods use a lot of energy and resources. This technology aims to replace them with a more sustainable and cost-effective way to recover materials.
Challenges: lithium battery recycling
Why recycle lithium battery
In the heart of our technology-driven world lies a silent yet pressing challenge: the sustainable recycling of lithium-ion batteries. As these batteries power everything from our smartphones to electric vehicles, their omnipresence in daily life underscores a critical need for innovative recycling solutions.
By 2030, 140 million electric vehicles are expected to be on the roads around the world, and 11 million metric tons of Li-ion batteries will have reached the end of their useful lives. At the moment, most used Li-ion batteries end up in landfills, and only about 5% are recycled.
A typical lithium-ion battery has four key components:
- Cathode
Containing different formulations of lithium metal oxides and lithium iron phosphate intercalated on a cathode backing foil/current collector (e.g. aluminum)—for example: LiNiₓMnₘCOₙO₂, LiCoO₂, LiFePO₄, LiMn₂O₄, and LiN₀.₈Co₀.₁₅Al₀.₀₅O₂.
- Anode
Generally containing graphite intercalated on an anode backing foil/current collector (such as copper).
- Electrolyte
Lithium salts such as lithium hexafluorophosphate (LiPF₆), lithium tetrafluoroborate (LiBF₄), and lithium perchlorate (LiClO₄) are dissolved in an organic solvent.
- Separator
Between the cathode and anode: for example, polymer or ceramic based.
So, iron, aluminum, copper, plastics, graphite, cobalt, nickel, manganese, and lithium are all parts of lithium-ion batteries. It is estimated that more than 11 million tons of spent battery packs contain approximately US$65 billion of residual value in metals and other components.
Also, recycling lithium-ion batteries could cut greenhouse gas emissions by about 1.2 billion equivalent tons of CO₂ between 2017 and 2040. This could be done by offsetting or reducing the amount of raw material from primary sources (like mining and refining) and keeping metals (like heavy metals) and other materials from used lithium-ion batteries from going to landfills.
Thus, recovering materials from spent lithium batteries is highly desirable.
How to recycle lithium battery
Pyrometallurgy is a fire process to recover valuable metals from waste lithium ion batteries. The pyrogenic process burns the organic binder in the electrode material by high-temperature incineration at nearly 1,500 ºC and then obtains the metal compound through flotation, precipitation, and other techniques. Today, several large pyrometallurgy facilities recycle Li-ion batteries, recovering cobalt, nickel, and copper but not lithium, aluminum, or any organic compounds.
Hydrometallurgy processing or chemical leaching is a less energy-intensive and less capital-intensive alternative. These processes for extracting and separating cathode metals typically run below 100 ºC and can recover lithium, copper, and other transition metals. Traditional leaching methods have a drawback in that they need caustic reagents like hydrochloric, nitric, and sulfuric acids and hydrogen peroxide. It also requires sodium carbonate (Na₂CO₃) to extract lithium.
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SiTration Technology
SiTration develops innovative silicon membrane technology that enables the separation and extraction of lithium, cobalt, and nickel from “black mass’’ with exceptionally high selectivity and yield. This provides a significant benefit over traditional chemical precipitation, solvent extraction, and thermal crystallization techniques that end up contaminating battery mixtures and requiring high capital and operational costs, thereby limiting extraction.
SiTration’s silicon membrane
SiTration’s silicon membrane has a hierarchical structure composed of macroscopic holes and microscopic rough surface. The membrane is fabricated based on Plasma-enhanced Chemical Vapor Deposition (PECVD) and Metal-Assisted Chemical Etching (MACE). The diagram below depicts the fabrication process of SiTration’s silicon membrane.
- Step 1: PECVD
A layer of polycrystalline or amorphous silicon is deposited on the surface of the silicon wafer via plasma-enhanced chemical vapor deposition (PECVD). A layer of etch protectant (e.g., AllResist) is added on top of the PECVD silicon layer to protect this silicon layer during the MACE process.
- Step 2: Sputtering
After the PECVD silicon layer is coated for protection, the silicon wafer is flipped 180º. The wafer is sputtered with metal nanoparticles, such as silver or gold, on the side of the bulk silicon.
- Step 3: Etching bulk silicon (MACE)
The bulk silicon is etched in chemical etch baths containing water, HF, and hydrogen peroxide at room temperature.
- Step 4: Supptering
The layer of etch protectant is removed. Metal catalyst nanoparticles are sputtered onto the PECVD silicon layer as described in step 2.
- Step 5: Etching (MACE)
The PECVD layer may be etched using the process described in step 3. This forms a microscopic porous PECVD silicon layer.
How SiTration’s silicon membrane works
SiTration’s silicon membrane is highly conductive (below 0.001 ohm/cm). The membrane can be used in electro-filtration and electro-extraction modes to extract target materials, as described below.
- Electro-filtration membrane
This membrane filter has small pores (pore size less than 100 nm) and is designed for recycling lithium ions from a leachate solution of battery black mass.
As depicted in the diagram below, the leachate solution enters the membrane filter from the top and passes through the electric field between the top surface of the conductive membrane filter and the mesh counter electrode.
How SiTration recycles lithium (ref. US20240017215A1).
Mx represents an ion dissolved in an aqueous solution with ionic charge of x. Lithium ions and uncharged components pass through the small pores of the membrane filter as the permeate solution. On the other hand, components with higher charges, such as iron, copper, nickel, and cobalt, are retained in the electric field above the membrane filter.
- Electro-extraction membrane
As depicted in the diagram below, this membrane filter has larger pores and is designed for recycling valuable nickel and cobalt from the leachate solution of battery black mass.