Selective Extraction and Upcycling of LiMn₂O₄ from used First Generation Lithium-Ion Battery Cathodes to Produce Mn-Based Conversion Anodes with Fascinating Electrochemical Properties

A multitude of cathode chemistries have been explored and utilised since the commercialisation of the Li-ion battery (LiB) in the 90s - including transition metal oxide chemistries (such as LiCoO₂, LiFePO₄, and LiMn₂O₄) and mixed transition metal oxide materials (such as NMC, Ni_aMn_bCo_cO_2, and NCA, Ni_aMn_bAl_cO₂). As electric vehicle adoption is rapidly increasing worldwide, the chemistry of Li-ion batteries used are heavily dictated by consumer demand. Customers expect fast-charging batteries with respectable range, factors which are dictated by the intrinsic electrode chemistry. High specific capacity cathodes that are thermally stable are preferable to consumers, as these features give rise to extended vehicle range and charging speeds. Current cathodes which meet these criteria are predominantly Ni-rich mixed TMO materials (such as NMC and NCA) and LiFePO₄.<br/><br/>As LiB technology has advanced over the years, initial cathode chemistries have become outdated with each generation of electric vehicle as companies race to ensure consumer demands are met. LiMn₂O₄ (LMO) is an example of a electrode material that was initially seen in electric vehicle batteries, often in conjunction with a layered Ni-rich phase. As subsequent generation vehicles have been released and their performance and energy densities have been enhanced to meet consumer demand, the LMO material has been phased out as the Ni-rich layered materials with high energy density have been prioritised.<br/><br/>When LiBs reach end-of-life the versatility of LiB cathode scrap pool (between manufacturers and between generations of EVs for the same manufacturer) has proven to be challenging for battery recyclers. Selective extraction of materials is imperative to ensure recycling and upcycling of cathode material is feasible from such an assorted cathode scrap pool. Once selectively extracted, cathode material can be recycled in a closed-loop fashion to regenerate battery grade products. When extracting lesser used and redundant cathode chemistries from preliminary cell structures, it is vital that the maximum value of each product is obtained prior to extraction. Upcycling involves extracting and repurposing material to increase its value, and LMO is a key example of a lesser used material can be upcycled to form a variety of Mn-rich conversion anode materials with interesting properties.<br/><br/>Graphite is the main anode material used in LiBs, however graphite reserves are not infinite, nor are they evenly distributed globally - meaning reliance on other countries is great for this anode material and will only increase as reserves are depleted. There is no question that alternative anode materials are necessary to avoid the likelihood of bottlenecks in graphite supply. Through selective extraction and interconversion of LMO, an array of Mn-rich conversion anodes with fascinating electrochemical properties can be produced. Not only can Mn be extracted from redundant LMO cathode material, but Mn-reserves are cheap, non-toxic and abundant, and it is of great interest to explore these conversion anode materials and their characteristics.<br/><br/>Key electrochemical characteristics that are of great interest within this study include the anode capacities being several times greater than their theoretical capacities, and the increase in capacity that arises during cell cycling. The origin of the phemonena observed have been explored using an array of characterisation techniques, including in-situ Synchotron X-ray diffraction and Pair-distribution function (PDF) analysis, Raman spectroscopy, galvanostatic cycling, cyclic voltammetry, Inductively Coupled Plasma-Optical Emission Spectroscopy and scanning and transmission electron microscopy, to name a few.