Influence of Vinylene Carbonate on Fe-Dissolution in Lfp/Graphite Pouch Cells Cycled at High Temperatures of 70 °C

Olivine LiFePO4 (LFP) has emerged as a compelling alternative to its counterpart, layered Li[Ni x Mn y Co z ]O 2 (NMC), in commercial lithium-ion cells due to its cost-effectiveness, utilization of abundantly available Fe, and superior safety characteristics. However, LFP/graphite cells exhibit notable degradation in lifetime when subjected to high temperatures compared to NMC. To address this issue, we explore the efficacy of incorporating the electrolyte additive Vinylene Carbonate (VC) to improve the lifetime of LFP/graphite cells at 70 °C. Through μXRF and GCMS analyses conducted at end-of-life (EOL), we observe significant capacity loss in part to Fe-dissolution on the graphite surface at elevated temperatures. This phenomenon triggers SEI rejuvenation and solvent decomposition, resulting in the depletion of lithium inventory. Additionally, we propose a refined SEI-growth model that accounts for the influence of transition metal (Fe) on SEI development of the graphite electrode. Figure 1