Unveiling Residual Charge Effects in the Direct Regeneration of Spent LiFePO ₄

Abstract The emergence of safe crushing technologies for spent lithium‐ion batteries treatment will significantly increase the proportion of incompletely discharged spent LiFePO 4 (IDS‐LFP) in future recycling industry. The IDS‐LFP and fully discharged S‐LFP (FDS‐LFP) with different residual charge show different microstructures and physicochemical properties. However, the current research in direct regeneration mainly focus on FDS‐LFP, the regeneration of IDS‐LFP and the relationship between residual charges and regeneration effect that has received less attention. Therefore, we classify the FDS‐LFP and IDS‐LFP based on their physicochemical properties and investigate the differences in their repair process using three kinds of regeneration methods. Compared to FDS‐LFP, IDS‐LFP exhibits a higher lithium intercalation energy barrier due to vacancies in the bulk. In addition, the proportion of Fe Li anti‐site defects in regenerated IDS‐LFP (IDR‐LFP) (1.3%) is higher than regenerated FDS‐LFP (FDR‐LFP) (0.6%), confirming that IDS‐LFP cannot be completely regenerated. As a result, FDR‐LFP delivers a specific discharge capacity of 137.1 mA h g −1 at 1 C, retaining 81.5% capacity retention after 400 cycles. In sharp contrast, IDR‐LFP only provides a specific discharge capacity of 105.1 mA h g −1 at 1 C. This study provides foundational insights for handing S‐LFP with varying residual charge.