Aging‐Driven Composition and Distribution Changes of Electrolyte and Graphite Anode in 18650‐Type Li‐Ion Batteries

Abstract

A series of low‐temperature studies on LiNi0.80Co0.15Al0.05O2 18650‐type batteries of high‐energy type with different stabilized states of fatigue is carried out using spatially resolved neutron powder diffraction, infrared/thermal imaging, and quasi‐adiabatic calorimetry. In‐plane distribution of lithium in the graphite anode and frozen electrolyte in fully charged state is determined non‐destructively with neutron diffraction and correlated to the introduced state of fatigue. An independent electrolyte characterization is performed via calorimetry studies on variously aged 18650‐type lithium‐ion batteries, where the shape of the thermodynamic signal is evolving with the state of fatigue of the cells. Analyzing the liquid electrolyte extracted/harvested from the studied cells reveals the decomposition of conducting salt to be the main driving factor for fatigue in the electrolyte degradation.

Electrolyte Degradation During Aging Process of Lithium‐Ion Batteries: Mechanisms, Characterization, and Quantitative Analysis

“…[98] Normally, the concentration of the conducting salt LiPF 6 undergoes a significant reduction from its fresh state to an aged state, increasing charge transfer impedance. [6c, 13,100] And the Lithium bis(fluorosulfonyl)imide (LiFSI) emerges as a significant contributor to the SEI formation process in lithium-ion batteries during prolonged cycling processes. [99] This phenomenon can be attributed to the decrease in available lithium ions, which are essential for maintaining the conductivity within the battery.…”

“…The combined effects of these concentration changes may ultimately result in a constant liquidus temperature, indicating the limitations of DTA as it reflects a coupling outcome from concentration changes in each electrolyte component. Petz et al [100] proposed that an inhomogeneous distribution of electrolyte may also lead to peak fusion, affecting the resolution of DTA curves (Figure 12e,f).…”

“…d) DTA analysis of the control electrolyte (1.0 m LiPF 6 in EC: EMC (3:7 wt.%)) before and after formation and formation with 2% VC electrolyte added in control [145]. e) DTS changes of 18650 Li-ion batteries in different aging states [100]. f) DTS changes of electrolytes with different lithium salt concentrations (DMC: EMC: EC ratio remains unchanged) [100].…”

Combination of float charging and occasional discharging to cause serious LIB degradation analyzed by operando neutron diffraction

“…Neutron diffraction is a powerful non-disassembly technique for LIB analysis owing to the ability to detect light atoms like lithium and oxygen, and the highly penetrating nature of neutrons. [23][24][25][26][27] Even though the access to neutron diffraction facilities is limited, highly permeable neutron beam is worth using for non-destructive analysis of commercial LIBs to show the behavior of the electrode materials during operation including reaction inhomogeneity, which is hardly deduced by electrochemistry. In situ neutron diffraction measurement has been applied to the analysis of commercial batteries to identify the degradation factors using the change in the crystal structure inside the aged cell.…”

Lithium-ion Differential Thermal Analysis Studies of the Effects of Long-Term Li-ion Cell Storage on Electrolyte Composition and Implications for Cell State of Health

“…More information as to the experimental methodology can be found in the literature. 10,14,[16][17][18] There is a great deal of information that can be determined from a DTA curve with careful study. Of note in this work is the temperature of the liquidus point.…”