Influence of cycling profile, depth of discharge and temperature on commercial LFP/C cell ageing: post-mortem material analysis of structure, morphology and chemical composition

Abstract

The paper presents post-mortem analysis of commercial LiFePO4 battery cells, which are aged at 55 °C and − 20 °C using dynamic current profiles and different depth of discharges (DOD). Post-mortem analysis focuses on the structure of the electrodes using atomic force microscopy (AFM) and scanning electron microscopy (SEM) and the chemical composition changes using energy dispersive X-ray spectroscopy (SEM-EDX) and X-ray photoelectron spectroscopy (XPS). The results show that ageing at lower DOD results in higher capacity fading compared to higher DOD cycling. The anode surface aged at 55 °C forms a dense cover on the graphite flakes, while at the anode surface aged at − 20 °C lithium plating and LiF crystals are observed. As expected, Fe dissolution from the cathode and deposition on the anode are observed for the ageing performed at 55 °C, while Fe dissolution and deposition are not observed at − 20 °C. Using atomic force microscopy (AFM), the surface conductivity is examined, which shows only minor degradation for the cathodes aged at − 20 °C. The cathodes aged at 55 °C exhibit micrometer size agglomerates of nanometer particles on the cathode surface. The results indicate that cycling at higher SOC ranges is more detrimental and low temperature cycling mainly affects the anode by the formation of plated Li. Graphic abstract

Lifetime Extension of Lithium-Ion Batteries With Low-Frequency Pulsed Current Charging

“…The disassembly-based post-mortem analysis, the modelbased analysis, and the curve-based analysis are the three methods using to diagnose the aging of Li-ion batteries [34]. The disassembly-based analysis can determine the degradation mechanism by disassembling the aged cell in a special operating environment, and using professional equipment to observe the structure of the electrodes (e.g., atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques) and analyze the chemical composition changes (e.g., energy dispersive X-ray spectroscopy (SEM-EDX) and dV X-ray photoelectron spectroscopy (XPS) techniques) of the aging cells [35]. However, this is a destructive method due to the requirement of disassembling the cell and thus ending the cycling aging test.…”

Recent Health Diagnosis Methods for Lithium-Ion Batteries

“…Simolka et al studied the influence of temperature on the industrial produced LFP/C cell aging, which were cycled under the "worldwide harmonized light vehicles test procedure" (WLTP) ageing profile, named AP 1 . Moreover, the cycling current was doubled using another test profile (AP 2 ) because they wanted to speed up the aging process [64]. Compared with the fresh anode surface, the surface of the anode had some distinct changes, but at the same temperature shows a similar appearance.…”

“…Since AFM has become a functional tool to examine the topography as well as the roughness and the elastic performance by Young's modulus, the anode surfaces were investigated surfaces by using AFM attracted researchers' interests. In Figure 12, images of the height as well as peak force error (PFE) of the anode surface is shown [64]. The fresh anode shows a smooth and flat graphite anode surface in both height and PFE images cathode, and the formation could be attributed to continuous lithiation and delithiation.…”

Lithium-Ion Battery Operation, Degradation, and Aging Mechanism in Electric Vehicles: An Overview

“…In [58], it was predicted that the battery will reach 20% capacity fade un considered aging profile (based on the WLTC driving cycle) after approximately 5 To further accelerate battery aging, Simolka et al selected the last part of the driving cycle (called "extra high"), corresponding to high currents, and named it a [60]. Based on AP1, the authors then doubled the current load in order to creat profile: "AP2".…”

“…On the one hand, discharging cut-off voltage decreases, the surface temperature of the battery in significantly, leading to transition metal dissolution at cathode; on the othe In [58], it was predicted that the battery will reach 20% capacity fade under the considered aging profile (based on the WLTC driving cycle) after approximately 5.8 years. To further accelerate battery aging, Simolka et al selected the last part of the WLTC driving cycle (called "extra high"), corresponding to high currents, and named it as "AP1" [60]. Based on AP1, the authors then doubled the current load in order to create a new profile: "AP2".…”