Selective extraction and upcycling of LiMn2O4 cathode material from first-generation lithium-ion batteries

Browning, Beatrice (2025). Selective extraction and upcycling of LiMn2O4 cathode material from first-generation lithium-ion batteries. University of Birmingham. Ph.D.

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Abstract

The lithium-ion battery scrap pool is set to grow extensively in volume as first-generation electric vehicles reach their end-of-life in upcoming years. There are many key environmental and socioeconomic drivers for the recycling of lithium-ion batteries (Li-ion batteries, or LIBs) and methods to extract and process solid-state electrode materials are an essential part of the recycling process.

Some electrode materials from first-generation cells, such as lithium manganese oxide spinel, or LiMn2O4 (LMO), are no longer extensively used in current-generation vehicle cells. Therefore, in this thesis, experiments investigating the “upcycling” of LMO from lithium-ion battery cathode material are outlined, from quality control-rejected and end-of-life cathodes, in an array of experiments.

In the first results chapter LMO is selectively extracted from quality control-rejected (QCR) and end-of-life (EOL) cathode material followed by interconversion into an array of upcycling products. The experiments outlined highlighted the effectiveness of a selective leaching process for the extraction of LMO from spent cathode material and the success of the interconversion explored. The LMO, Mn oxalate dihydrate, Mn2O3 and Mn3O4 products formed with structures Fd3 ̅m, C12/c1, Pcab and I41/amd respectively, across the pristine and leached QCR and EOL samples in all cases, with minimal contamination that did not jeopardise the material structure, indicating this success.

In the second results chapter, upcycling experiments are conducted with QCR and EOL-derived Mn oxalate to generate MnO─C nanocomposite conversion anodes. In the first section synthetic conditions are investigated to manufacture nanosized MnO suspended in a carbon matrix to ensure that intrinsic issues seen for conversion electrodes, that lead to poor capacity retention, are minimised for optimal electrochemical performance. The conditions chosen for this synthesis involved a mechanochemical route followed by an inert atmosphere heat treatment step, whereby the mechanochemical product was heated to 600 °C and held at this temperature for 4 hours under nitrogen. These conditions gave rise to the desired nanoMnO─C composite for subsequent electrochemical analysis, which was then applied to generated nanosized carbon composite Mn (II) oxide electrodes from lithium-ion battery-derived Mn-based precursors. The electrochemical performance of these leached nanocomposites highlights the upcycling opportunity for redundant LMO leached from QCR and EOL cathodes, with capacities of 777 (±12), and 916 (±37) mAhg-1 reached after 15 cycles, respectively. These capacities exceed the theoretical capacity for MnO, at 755 mAhg-1, significantly in the EOL case, highlighting the potential for upcycled products from leached cathode materials.

In the final chapter Mn oxalate, generated from pristine and leached material in the first chapter, is studied as a conversion anode. Though this anode material has been investigated in the literature, this chapter outlines innovative experiments to develop an electrochemical understanding of Mn oxalate anodes and to determine whether upcycled QCR and EOL Mn oxalate exhibit enhanced electrochemical behaviour when compared to the performance of pristine material. Firstly, electrochemical conditions are tailored to probe the anode material’s fascinating capacity behaviour, by cycling the anode to a 2 V and 3 V voltage maximum. By the 100th cycle, the discharge capacity of the 2 V max cells averaged out at 160 (± 7) mAhg-1 and the 3 V max cells averaged out at 723 (±8) mAhg-1 at 14% and 70% of their first discharge capacity, respectively, indicating the effect of the 3 V maximum voltage on capacity retention. Furthermore, redox activity was much more significant out to 100 cycles for the 3 V max than the 2 V max anode, as exhibited in differential capacity analysis, which indicates that the 3 V max cell undergoes additional redox activity through increased oxidation state of Mn, or even through anionic redox of the oxalate group within the polyanion. In-situ pair distribution function (PDF) analysis gave additional insights into the origin of the interesting electrochemical behaviour, indicating that the conversion product at the end of the first cycle does not resemble Mn oxalate. This structure at the end of charge has been hypothesised to match with a zincblende-structured MnO with space group F4 ̅3m, countering the reports of the reversible conversion reaction outlined extensively in the literature for Mn oxalate, but providing more insights into the electrochemical deviation between the 2 V and 3 V max half-cells. Finally, the electrochemical behaviour of Mn oxalate derived from pristine and leached QCR and EOL LiMn2O4 has been explored to determine the success of upcycling LMO into Mn oxalate conversion anodes. After 100 cycles the capacity recovery of the 3 V max cycled half-cells remained as high as 650 mAhg-1 for the QCR and 475 mAhg-1 for the EOL sample, proving to be highly successful in upcycling the interconverted LiMn2O4 into Mn oxalate material. Though the capacity retention after 100 cycles was lower with an increased degree of contamination from the leached samples, the capacity still outperforms the expected capacity based on the theoretical calculation, at 375 mAhg-1.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):