Development of Low Fluorinated, Sustainable, and Recyclable Electrolytes Based on γ‐Valerolactone for High‐Performance Sodium‐Ion Batteries

ABSTRACT This study introduces a dual salt novel electrolyte for sodium‐ion batteries (SIBs), consisting of sodium difluoro(oxalato)borate (NaDFOB) and sodium bis(fluorosulfonyl)imide (NaFSI) salts dissolved in the bio‐based γ‐valerolactone (GVL) solvent. Besides its renewable origin, the electrolyte exhibited strong inhibition of anodic dissolution and excellent electrochemical stability (up to 4.3 V vs. Na + /Na). It delivered outstanding cycling stability, with ∼87 % capacity retention after 100 cycles in P2‐Na 2/3 Al 1/9 Fe 1/9 Mn 2/3 Ni 1/9 O 2 (P2‐AFMNO) cathode half cells and ∼80 % retention after 200 cycles in lab‐ scale full cells with hard carbon anodes when cycled within a wide voltage window of 1.5–4.3 V. Post mortem X‐ray photoelectron spectroscopy analysis helped gaining deeper understanding about the decomposition products formed on the interphases. A simple and sustainable water‐based process is employed to successfully recover the GVL solvent. The recovery method enabled recover 85 % of GVL solvent from the recycling process. The feasibility of recycling is further demonstrated by reusing the recovered GVL‐based electrolyte in full cells, which achieved performance comparable to that of the pristine GVL‐based electrolyte and exhibited excellent long‐term stability, retaining approximately 83 % of its capacity after 100 cycles.