Quantitative elucidation of calendar aging mechanisms is crucial for the development of long-life lithium-ion batteries suitable for large-scale energy storage systems and electric vehicles. In recent years, studies on the calendar aging behavior and mechanisms of lithium-ion batteries under high-temperature storage conditions have generally suggested that elevated temperatures accelerate side reactions, thereby promoting the growth of the solid electrolyte interphase (SEI). However, due to limitations in quantitative characterization techniques, the formation and structural evolution of the SEI at different storage temperatures have not yet been fully clarified.

Recently, the research team of Professors Yong Yang and Zhengliang Gong at Xiamen University employed a combination of mass spectrometry titration (MST), nuclear magnetic resonance (NMR), and gas chromatography–mass spectrometry (GC–MS) to investigate the correlation between calendar aging behavior and temperature in LiFePO4/graphite batteries. This work provides an in-depth analysis of the calendar aging mechanisms of lithium-ion batteries under different storage temperatures. The study, entitled “Calendar Aging of LiFePO4/Graphite Batteries: Quantitative Analysis of Synergistic Effects of SEI Evolution and Electrolyte Decomposition,” was published in the journal ACS Energy Letters.

The results reveal a synergistic degradation mechanism involving SEI evolution and electrolyte decomposition during calendar aging. Loss of lithium inventory (LLI) is identified as the dominant degradation pathway. Elevated storage temperatures significantly accelerate the decomposition of VC, PF6-, and FSI-, leading to excessive SEI growth and deterioration of interfacial kinetics. The coupled effects of electrolyte decomposition, SEI thickening, and kinetic degradation collectively result in rapid capacity fading under high-temperature storage conditions. This study provides important insights into the temperature-dependent evolution of SEI structure and electrolyte decomposition, contributing to a more comprehensive understanding of calendar aging mechanisms in lithium-ion batteries.

Wen Fangmei, a master’s student enrolled in 2022 at our institute; Peng Yufan, a postdoctoral researcher from the College of Chemistry and Chemical Engineering; and Ding Meifang, a master’s student enrolled in 2023, are the co-first authors of this paper. Professors Yong Yang and Zhengliang Gong of Xiamen University, together with Dr. Yimin Wei from CATL, are the co-corresponding authors. This work was supported by the National Key Research and Development Program of China (No. 2021YFB2401800).

Full text link: https://pubs.acs.org/doi/10.1021/acsenergylett.5c02954