Quantitative Analysis of Active Lithium Loss and Degradation Mechanism in Temperature Accelerated Aging Process of Lithium‐Ion Batteries

Abstract Quantifying the aging mechanisms and their evolution patterns during battery aging is crucial for enabling renewable energy. Here, key factors are monitored and quantified affecting the aging processes of LiFePO 4 //graphite battery by a combination of mass spectrometry titration (MST), nuclear magnetic resonance (NMR), cryogenic transmission electron microscopy (cryo‐TEM), and neutron imaging techniques. Electrochemical analysis reveals the loss of active lithium inventory drives battery aging as temperature increases. It is shown that temperature‐induced accelerated decaying rate is 2.01 and 3.45 times at 45 and 65 °C compared with that of rate at 25 °C. Quantitative analysis indicates that irreversible formation of Li x C 6 (x ≤ 1), LiF, ROCO 2 Li, LiH, Li 2 C 2 , and RLi (R = CH 3 , C 2 H 3 , C 2 H 5 , C 3 H 5 ) are the primary components of inactive lithium. The solid eletrolyte interpahse (SEI), excluding Li x C 6 , constitutes over 70% of the total inactive lithium. With increasing cycles, SEI shows a decreasing proportion of LiF and an increasing proportion of ROCO 2 Li. The coupled effects of substantial SEI growth, increased irreversible formation of Li x C 6 , and worsened conductivity result in the rapid aging of batteries tested at high temperatures. In this work, a research toolbox for the quantitative study of aging mechanisms in practical batterysystems has been provided.