Redwood Materials ($2.8B for lithium battery recycling)

Redwood Materials recycles and refines lithium-ion batteries to create a closed-loop, domestic supply chain. The company was founded by JB Straubel, a former CTO of Tesla, in 2017. Redwood Materials has secured $2.8 billion in total funding for battery recycling and production.

Challenges: lithium battery recycling

Rapid growth of electric vehicles has a substantial effect on the demand for lithium-ion batteries. By 2030, it is anticipated that there will be 140 million electric vehicles on the roads worldwide, while 11 million metric tons of lithium-ion batteries will reach the end of their useful lives. Currently, less than 5% of lithium-ion batteries are recycled, with the majority being disposed of in landfills.

There are two primary methods for recycling lithium-ion batteries: hydrometallurgical and pyrometallurgical processes. In traditional hydrometallurgical processes, batteries are dismantled and shredded. The shredded materials are separated and milled to create a black mass containing valuable cathode elements. Black mass is leached in acidic aqueous solutions, followed by separating individual metal elements from the leach solution.

Due to their similar chemical properties, it is difficult to extract pure metal components from a leach solution using the conventional hydrometallurgical method, which entails time-consuming steps, high operating expenses, and hazardous pretreatment.

In known pyrometallurgical processes, batteries or shredded components undergo reduction smelting at high temperatures. Transition metals such as cobalt, nickel, and manganese are reduced from their oxide, resulting in the formation of a metal alloy phase. The metal alloy is recovered, and its constituent elements are separated and sold.

Lithium and aluminum are converted into their oxides, resulting in the formation of slag. However, the slag is typically disposed of in landfills because its low lithium content (below 10%) relative to aluminum and SiO₂ and the presence of other difficult-to-separate materials (such as calcium) make clean recovery of lithium difficult and uneconomical, resulting in a significant waste of a metal that is becoming increasingly important in industry and consumer electronics.

Redwood Materials Technology

Redwood Materials develops a lithium-ion battery recycling technology that generates high-concentration lithium composites (lithium concentrates) which are further leached to extract lithium compounds that can be returned to the supply chain, particularly battery grade materials.

Generate lithium concentrates

The lithium concentrates are produced using a pyrometallurgical process developed to overcome the deficiencies of traditional methods. This method yields lithium concentrates containing between 13% to 30% Li₂O, as well as SiO₂ and Al₂O₃. Low levels of calcium (such as CaCO₃), which is used as a fluidizer in traditional pyrometallurgical processing, are present in lithium concentrates. The presence of calcium would be problematic in the future processing.

The combination of high lithium content relative to silicon content and low calcium allows for the facile and selective recovery of lithium during the extraction process.

As shown in the figure below, the lithium concentrates production process consists of feeding, metal pour, fluxing, and lithium concentrate pour.

The processes of generating lithium concentrates.

1. Feeding

Lithium batteries, battery scrap, or battery components are fed into a rotating furnace. Oxygen-containing gasses are blown into the furnace to maintain the furnace temperature between 1400 °C and 1500 °C in order to produce a liquid metal phase and a solid lithium concentrate phase.

The pyrometallurgical processes have several advantages over the traditional pyrometallurgical processes:

In conventional pyrometallurgical processing, CaCO₃ is used as a fluidizer, but it is not required in this process.
There is no need for an external heating source, such as fossil fuels or natural gas. Heating can be autothermal, wherein organics (such as plastics, electrolytes, and graphite) in the batteries combust in the presence of oxygen-containing gasses, providing sufficient heating to effect the oxidation/reduction that forms the lithium concentrate and metal alloy phases. However, the traditional pyrometallurgical processes require additional heat input at this stage.
The processes do not require the addition of a flux during battery loading, whereas the traditional pyrometallurgical processes require the addition of flux to help separate metals from the oxides of the slag phase, or to help liquefy or adjust the viscosity of the slag.

2. Metal pour

The process described above generates liquid metal and solid metal oxide phase, i.e. the solid lithium concentrates phase. To separate the liquid metal from the solid lithium concentrates phase, the furnace is tilted. In traditional pyrometallurgical processes, both the liquid metal and slag phases are present.

The production of a solid lithium concentrate phase has a number of benefits, including decreased heating requirements during oxidation/reduction, improved reaction kinetics, and decreased metal loss.

3. Fluxing

After separating the liquid metal phase from the solid lithium concentrate phase, SiO₂ is added to the solid lithium concentrate phase in order to liquefy it for removal from the furnace. Natural gas and oxygen are combusted to heat, produce flux, and fluidize the solid metal oxide, forming a molten lithium concentrate.

4. Lithium concentrates pour

The furnace is once again tilted in order to remove the molten lithium concentrate. Notably, the lithium concentrate contains over 20% Li₂O, which is substantially higher than the known processes for recycling processes for lithium-ion batteries, allowing for the easy and selective recovery of lithium during the extraction process.

Extract lithium from lithium concentrate

The combination of a high lithium content relative to silicon and aluminum content and a low calcium content enables efficient lithium extraction with minimal extraction of aluminum and other inseparable components. The figure below shows the extraction process, which includes size reduction, acid leaching, impurity removal, and lithium extraction.

The processes of extracting lithium from lithium concentrates.

1. Size reduction

Using a crusher and mill, the lithium concentrates are reduced in size. Reducing particle size improves leaching kinetics, thereby reducing processing time.

2. Acid leaching

In an agitated tank, the milled lithium concentrates are then brought into contact with water. The sulfuric acid was dosed so that the pH does not fall below 3 or rise above 4. Throughout the process, the solution is stirred and the reaction temperature is maintained at about 60 °C. After several hours of reaction, the solution is filtered to produce a residual and clarified lithium solution. The residual is washed to recover any remaining lithium.

The residue can be recycled to the beginning of the leaching process as described above. In addition, the clarified lithium solution can be recycled multiple times through the leaching step to increase the amount of Li in solution. This avoids a costly evaporation step.

3. Impurity removal

The clarified lithium solution is then neutralized to a pH of about 7 by adding base, such as NaOH. Filtration of the solids from the neutralized slurry yields a purified lithium-enriched solution.

4. Lithium extraction

Na₂CO₃ is added to the purified lithium-enriched solution to produce solid lithium carbonate, which is then filtered out.

Redwood Materials Products

Redwood Materials focuses on recycling lithium-ion batteries for products such as EVs and consumer electronics, partnering with over a dozen companies including Amazon and Ford, whose EV aspirations could be a boon for Redwood’s business.

Redwood also supplies those recycled raw materials, like copper and lithium, back to its partners that make the batteries, creating what the company calls a “circular supply chain” that’s aimed at reducing the environmental footprint and cost of batteries.

Redwood Materials plans to increase the size of its facilities in Carson City, Nevada, to 550,000 square feet, and to build at another large site in Nevada at the Tahoe-Reno Industrial Center, to manufacture battery materials, including anode copper foil and cathode active materials, at home in the U.S..

Redwood’s next ambition: By 2025, it aims to produce cathode materials for battery cells totaling 100 gigawatt-hours per year, enough to supply over 1 million EVs.

Redwood Materials Funding

Redwood Materials has raised a total of $2.8B in funding over 6 rounds, including a Seed round, a Series B round, a Venture-Series Unknown round, a Series C round, a Corporate round, and a Debt Financing round. Their latest funding was raised on Feb 9, 2023 from a Debt Financing round.