Theoretical-molar Fe3+ recovering lithium from spent LiFePO4 batteries: an acid-free, efficient, and selective process
Graphical abstract
Introduction
In recent years, lithium-ion batteries (LIBs), as a high-performance secondary rechargeable green power, have been widely used in various portable electronic devices, electric vehicles and renewable energy storages.(Harper et al., 2019; Li et al., 2018a; Wang et al., 2018a; Yu et al., 2018) Common LIBs include nickel-cobalt-manganese ternary lithium batteries, and lithium iron phosphate batteries (LiFePO4, LFP).(Manthiram et al., 2017; Zheng et al., 2018a; Zeng et al., 2014) With the increase of market demand for LIBs, the consumption of lithium will quickly grow with each passing day.(Shi et al., 2018) However, the limited natural lithium resources such as salt lakes and lithium minerals, are low lithium content and insufficient for the gradually market demand.(Chen et al., 2016) But at the same time, a large number of spent LIBs with abundant valuable elements have been produced in the past few years.(Sonoc et al., 2015) It is common knowledge that the heavy metals and hazardous organic chemicals in these end-of-life LIBs will pose serious threats to the ecological system and human health.(Harper et al., 2019; Al-Thyabat et al., 2013; Georgi-Maschler et al., 2012; Meng et al., 2018; Li et al., 2018b) Hence, recycling spent LIBs has become an important research topic for solving the shortage of lithium resources and the pollution of used batteries. (Wang et al., 2009; Zou et al., 2013; Sencanski et al., 2017; Hu et al., 2017; Heydarian et al., 2018; Sun et al., 2015)
Various kinds of spent LIBs, such as nickel-cobalt-manganese ternary lithium batteries and lithium cobaltate batteries which contain many valuable metals, have been extensively studied.(Gao et al., 2018; Zeng et al., 2015; Zhang et al., 2018; Wang et al., 2018b) However, LiFePO4 batteries do not attract enough attention due to their low valuable metals, even though they are extensively used in electric buses, communication base stations, etc. owing to their superior reversibility, excellent thermal safety, low toxicity, and low-cost.(Li et al., 2018c; Li et al., 2017a; Talebi-Esfandarani et al., 2016) Therefore, how to efficiently and low-cost treat the increasing spent LiFePO4 batteries has become an extremely important study theme.
Generally, there are two ways about recovering spent LFP batteries: direct regeneration process and leaching-resynthesizing process. (Zhang et al., 2019) The principle of direct regeneration process is to require the lithium to be replenished to compensate for the loss during use.(Harper et al., 2019; Song et al., 2017) The advantage of this process is direct and simple, while much obtained regeneration LFP batteries often have poor electrochemical performances because of no rigorously impurity control.(Wang et al., 2018c) Song et al. Song et al. (2019) reported a hydrothermal reaction process to get regenerated LFP with the help of graphene oxide, but yet it was high-cost and difficult for industrialization limited by the complicated synthesis process of graphene oxide. For the second way, various acids are used to leach spent LFP cathode materials, including sulfuric acid (Li et al., 2017b), phosphoric acid(Bian et al., 2015; Yang et al., 2017a), oxalic acid(Li et al., 2018c; Fan et al., 2018), acetic acid(Yang et al., 2018), citric acid(Li et al., 2019), and so on. Li et al.(Li et al., 2017b) revealed a leaching method with stoichiometric H2SO4 and H2O2. However, the inorganic acids frequently do not have sufficient selectivity for impurities such as Al, so it is necessary to separate Al foil before leaching. In general, organic acids could selectively leach lithium, but they are difficult to be applied in practice due to their high-price and difficulty in recycling. Besides, an oxidation (Na2S2O8) leaching (Zhang et al., 2019) was proposed to recovery spent LFP batteries, in which lithium can be efficiently leached out at ambient temperature. Usage-cost owing to the high-price, high-insecurity, and non-recycling of Na2S2O8 impedes its application in the recycling process of spent LFP. Not long ago, Liu et al.(Liu et al. (2019)) proposed a mechanochemically induced substitution by co-grinding LiFePO4 and NaCl, which is simple but must use much excessive materials and needs a long time to activate. Thusly, it is imperative to find a more efficient, low-cost and environmentally friendly way to dispose of spent LFP batteries.
In this paper, two leaching methods using Fe2(SO4)3 to selectively leach Li from the spent LFPs based on a spontaneous substitution reaction were reported, in which Fe3+ was employed to exchange the Li+ and Fe2+ in LFP. It was inspired by the similar olivine-type structure between LiFePO4 and FePO4. When only Fe2(SO4)3 was used, a high Li leaching efficiency was acquired even under a high solid − liquid ratio and a short leaching time. Furthermore, H2O2 was introduced to oxide the generated Fe2+ and thus the new generated Fe3+ could circularly substitute the Fe2+ in LFP, which also obtained a good leaching efficiency of Li. The main advantages for the two routings could be summarized as follow: (1) Li can be efficiently recovered in a short time; (2) Fe2(SO4)3 is theoretical-molar dosage, recyclable, selective and low-cost; (3) no acid is introduced and thus avoid the possible secondary pollution. More importantly, it will provide a new thought relating to recovery of valuable elements in the spent battery materials.
Section snippets
Materials
The spent LFP batteries used in this study were provided by Guizhou Red Star Electronic Material Co., Ltd, Guizhou, China, and were manually dismantled after discharging in a saturated NaCl solution. The plastic cases of the batteries were first removed, then dismantled and separated into cathode electrodes, anode electrodes, organic separators, and plastic shells. The cathode scraps were separated from Al foil by crushing via a pulverizer and mechanical sieving. The obtained powders were used
Effect of different parameters on only Fe2(SO4)3 leaching Li
Fe2(SO4)3 is a cheap and non-toxic chemical material, therefore its application to the recycling of spent LFP batteries will reduce cost and have no pollution. Ferric iron is a Bronsted acid and its aqueous solution is acidic. During the leaching process, Fe3+ in Fe2(SO4)3 are used to substitute Fe2+ from LiFePO4 due to the similar olivine-type structure between LiFePO4 and FePO4. So the theoretical molar ratio of Fe3+ in Fe2(SO4)3 and Fe2+ in the spent LFP batteries is 1:1 (molar ratio Fe2(SO4)
Conclusions
Two innovative methods referring to the non-oxidizing inorganic salt - Fe2(SO4)3 were proposed to recovery lithium from spent LiFePO4 cathode powders. One is only using theoretical Fe2(SO4)3 as the leaching reagent, which has 97.07% of Li leaching efficiency under a high solid − liquid ratio of 500 g/L (molar ratio Fe2(SO4)3 : LiFePO4 = 1:2, at 28 °C for 30 min). The other is using Fe2(SO4)3 with H2O2, which has 96.48 % of Li leaching efficiency under the optimized conditions (molar ratio Fe2
Declaration of Competing Interest
We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled “Theoretical-molar Fe3+ recovering lithium from spent LiFePO4 batteries: an acid-free, efficient, and selective process”.
CRediT authorship contribution statement
Yang Dai: Conceptualization, Data curation, Software, Writing - original draft. Zhaodong Xu: Writing - original draft. Dong Hua: Investigation, Supervision. Hannian Gu: Supervision, Funding acquisition. Ning Wang: Resources, Funding acquisition.
Acknowledgements
The work was financially supported by the National Key Research and Development Program of China (2018YFC1903500), and the Guizhou Science and Technology Major Program (No. [2016]3015). The authors are grateful to Prof. Wan' Group for FTIR determination.
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