(195c) Synthesis of Novel Intermediate Material for Recovery of Lithium-Ion Batteries

Lithium Ion Batteries (LIBs) are widely used for energy storage in portable devices, electric vehicles, and storage as most countries aim to be environmentally friendly. The use of LIBs is lucrative due to their high specific energy density, high rated voltage, and low self-discharge rate. Primarily LIBs contain cathode-active materials, such as Lithium Cobalt Oxide (LiCoO₂), Lithium Nickel Manganese (LiNi_xMn_yCo_zO₂, x+y+z = 1), a graphite anode, a copper cathode, an aluminum cathode collector, PVDF binder, and the electrolyte. With their increase in consumption, recycling and disposal of LIBs pose a significant challenge for human health and the environment as they contain a high percentage of heavy metals and toxic electrolytes. In recent years, a lot of effort has been made in order to recover different components of the batteries, however, recovery of spent cathode material poses a significant future for the circular economy. The common method to extract the cathode metallic components (such as LiCoO₂, LCO) is pyrometallurgical, hydrometallurgical, mechanical, and mechano-chemical processes. The pyrometallurgical method is energy intensive and low efficient as most of the valuable metal sources are obtained in alloy and lithium is lost in slag. The hydrometallurgical method typically involves the use of inorganic acids and the use of electrochemical processes leading the process to be energy intensive and high material cost. The mechanical and mechano-chemical processes have the benefit of using minimum energy but the downstream processing can be very complex and the use of heavy machinery can make it expensive.

Thus, in the present study, a novel solvothermal method is proposed for the reactive crystallization of an intermediate novel precursor material (PM1), [Li(C₂O₄)]₂[Co₅(OH)₈]. PM1 has a global structure of heterometallic layered double hydroxide with an asymmetric unit that can be represented in Figure 1 (a) and the visual representation can be made from Figure 1(b) which shows the AB layers containing lithium oxalate and cobalt hydroxide that are present in the PM1 structure. Additionally, cobalt can be octahedrally coordinated or tetrahedrally coordinated where systematic depilation takes place.

Lithium cobalt oxide contains a layered structure similar to what has been mentioned in the case of PM1. This enables the recovery of LCO at much lower temperatures T = 300-350ËšC compared to the aforementioned conventional process, making it more energetically favorable. The spent LCO from a battery waste is primarily digested in an organic acid (typically oxalic acid can be used) at elevated temperature (>80ËšC) resulting in Lithium oxalate and cobalt oxalate dihydrate. Later, by adjusting the stoichiometric ratio of cobalt and lithium oxalate to 1:1 in the pH range of 8-10, the PM1 can be synthesized in an aqueous medium at T = 80-100ËšC. Powder X-ray diffraction indicates this new synthetic route is successful in synthesizing LCO with high phase purity at temperatures far below what has been reported previously. However, the presence of excess cobalt in the PM1 lattice leads to the production of an LCO and cobalt oxide (II, III) mixture (CO₃O₄) upon calcination along with CO₂ and H₂O. The separation of CO₃O₄ from the calcined material becomes crucial with a number of novel separation operations developed and characterized to this end. Furthermore, the method has been demonstrated to be extendable to NMC chemistries using an analogous intermediate PM2. In this study, a novel process utilizing these novel intermediates and associated plant designs is developed and compared with industrial processes to demonstrate their economic and industrial feasibility for lithium-ion battery recycling.