Polarisability-dependent separation of lithium iron phosphate (LFP) and graphite in dielectrophoretic filtration

Abstract

Lithium-ion batteries (LIB) are integrated in a wide range of electronic devices that are an integral part of our modern world. Growing number of LIBs that reach their end of life demands development of effective recycling strategies to recover rare and/or expensive battery materials. Dielectrophoresis (DEP) is an electrokinetic particle manipulation technique that allows for selective particle separation based on properties, such as material, size, and shape. Here, we demonstrate separation of lithium iron phosphate (LFP) and graphite using dielectrophoretic filtration. Graphite and LFP are two common LIB anode and cathode materials. We demonstrate both: non-selective separation using pure suspensions of both graphite and uncoated LFP and an isolation of graphite from a mixture of uncoated LFP and graphite. We confirmed that LFP shows negative DEP while graphite shows positive DEP. We determined the conductivity at which material-selective polarisability-based separation becomes possible, thus, proofing the concept of sorting of non-carbon coated lithium iron phosphate (LiFePO4) and graphite. Graphite generally shows high separation efficiency of 70–100 %. Using atomic absorption spectroscopy (AAS), we found a low separation efficiency of LFP between 1 and 15 % from a mixture of graphite and LFP. These results reinforce one possibility of using DEP filtration as a potential method for direct physical recycling of battery material waste.

Keywords

• Lithium-ion batteries
• Filtration
• Separation
• Insulator-based dielectrophoresis
• High-throughput dielectrophoresis