Low-temperature aging mechanisms of commercial graphite/LiFePO4 cells cycled with a simulated electric vehicle load profile—A post-mortem study

Abstract

Reduced cycle life is one of the issues hindering the adoption of large lithium-ion battery systems in cold-climate countries. Thus, the aging mechanisms of commercial graphite/LiFePO4 (lithium iron phosphate) cells at low temperatures (room temperature, 0 °C and −18 °C) are investigated here through an extended post-mortem analysis. The cylindrical 2.3 Ah cells were cycled with a simulated battery electric vehicle load profile, and the aged cells were then disassembled inside an argon-filled glove box. A non-cycled cell was also dismantled as a reference. Half-cell testing was utilized to evaluate the degradation of the electrochemical performance of the electrodes, whereas X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, inductively coupled plasma optical emission spectroscopy and Raman spectroscopy were used to characterize the changes in the materials properties. The full-cell performance loss was mostly seen as capacity fade whereas significant changes in the cell impedance were not observed. Depending on the cycling temperature, loss of cyclable lithium due to solid electrolyte interphase growth and/or lithium plating on the graphite electrode were observed, and they are attributed as the main mechanisms responsible for the capacity loss. Furthermore, increased disordering of the graphite electrode was observed for the cell cycled at −18 °C. The graphite disordering was hypothesized to result from diffusion-induced stress and the mechanical stress caused by severe lithium plating. In contrast, the LiFePO4 electrodes showed only minimal signs of degradation regardless of the cycling temperature.

Critical Review on Low‐Temperature Li‐Ion/Metal Batteries

“…[46] Once the overpotential of LIBs oversteps this potential gap, the Li + tends to be reduced on the surface of graphite rather than intercalated into its layers due to the lower nucleation barrier. [19,[47][48][49][50][51] The plated Li could induce a series of parasitic reactions, generating thicker SEI and leading to "dead" lithium, which would severely consume the limited recyclable lithium in cells. More lethal is the formation of Li dendrite and the serious safety risks it brings.…”

Educational Metal–Air Battery

“…Currently, cheap metal–air batteries could be used as low power disposable batteries which can be activated in contact with water; examples of use include electronic pregnancy or virus antibody tests. Rechargeability in aqueous solution (like for alkali metal-ion batteries in organic electrolytes , ) is technically only possible with zinc, but it would need a porous anode and a solid electrolyte to mitigate the formation of dendrites in a liquid electrolyte . The needle-like dendrite growth on zinc may short-circuit the electrodes and uneven deposition reduces battery capacity .…”

Effect of the Charge Process on the Performance of Li-ion Cells during Charge-Discharge Cycling at 0°C

“…[6][7][8][9] Lithium plating is a severe degradation process for Li-ion cells which can reduce their lifetime drastically and compromise the safety of battery systems. [10][11][12][13][14] Lithium plating occurs when the potential of the negative electrode drops below 0 V Li/Li + , which makes the deposition of metallic lithium on the negative electrode thermodynamically possible. 9 This metallic lithium deposited on the anode material surface, can grow dendritically and these dendrites can penetrate the Li-ion cell separator creating internal short circuits which can cause a battery system to go into thermal runaway.…”

“…15,16 It has been identified that the combination of low temperature and high current rates during charging favors the occurrence of lithium plating, since these conditions promote the over polarization of the anode potential. 12,13 Furthermore, it has been stated in the literature that a reliable non-destructive method to detect lithium plating resulting from a previous charging is the appearance of a high voltage plateau at the beginning of the discharge process. 10,12,17 This voltage plateau is a signature of metallic lithium that is being stripped from the anode active material surface.…”