High-value utilization of recovered LiPF6 from retired lithium-ion batteries

Abstract

With the large-scale retirement of new energy vehicles, it is particularly important to recycle and reuse retired lithium-ion batteries (LIBs). However, the current improper handling of spent electrolytes will cause serious environmental problems. Here, we propose a novel, simple and easy-to-implement method to realize the high-value utilization of recovered electrolytes from retired LIBs. Comparing with the initial content of LiPF₆ (1 mol L⁻¹ in a mixed carbonate solvent system, and about 1 g in a 18650 type LIB) in fresh batteries, a maximum leaching efficiency of 29% could be realized during the full-component resource reclamation of retired LIBs, using the selective mixed leaching solvent system of dimethyl carbonate + CHClF₂ (1 : 1, v/v ratio). Then the water and HF impurities are reduced from 80.90 ppm to 4.56 ppm and from 1312.91 ppm to 291.52 ppm by pre-treatment with hexamethyl disilazane (C₆H₁₉NSi₂). Although the purified electrolyte does not meet the standards for re-use in LIBs, it can be used as a synthetic raw material for lithium salt additives. As a typical case, the LiPF₆ salt in a leached electrolyte is recycled into a salt additive of lithium difluorodioxalate phosphate (LiDFBOP) under the preferred reaction conditions (75 °C, 27 h, with a molar ratio of 1 : 3 for LiPF₆ : bis (trimethylsilicon)oxalate), realizing closed-loop recycling. The electrochemical results show that the electrochemical performances of the graphite/Li and LNCA/Li half cells are significantly improved with the addition of the as-prepared LiDFBOP additive. This research gives a large-scale synthesis route to realize high-value utilization of low-quality LiPF₆, and helps establish a full-component resource reclamation process of retired LIBs. It not only improves environmental friendliness, but also realizes the high efficiency utilization of resources.