Understanding the crack formation of graphite particles in cycled commercial lithium-ion batteries by focused ion beam - scanning electron microscopy

Abstract

The structure degradation of commercial Lithium-ion battery (LIB) graphite anodes with different cycling numbers and charge rates was investigated by focused ion beam (FIB) and scanning electron microscopy (SEM). The cross-section image of graphite anode by FIB milling shows that cracks, resulted in the volume expansion of graphite electrode during long-term cycling, were formed in parallel with the current collector. The crack occurs in the bulk of graphite particles near the lithium insertion surface, which might derive from the stress induced during lithiation and de-lithiation cycles. Subsequently, crack takes place along grain boundaries of the polycrystalline graphite, but only in the direction parallel with the current collector. Furthermore, fast charge graphite electrodes are more prone to form cracks since the tensile strength of graphite is more likely to be surpassed at higher charge rates. Therefore, for LIBs long-term or high charge rate applications, the tensile strength of graphite anode should be taken into account.

Impact of Particle Size Distribution on Performance of Lithium‐Ion Batteries

“…Mechanisms, which may cause capacity loss or improvement are the following: particle cracking, [30,31,48] irreversible lithium plating, [22,31] loss of active material due to macro or micro cracking that leads to contact loss and electrical isolation [1,49,50] and SEI growth [31] . One possible reason for the capacity loss of F3 could be cracking of its coarser particles, which have been similarly suggested on graphite particles by Lin et al [51] . and Bhattacharya et al.…”

“…Mechanisms, which may cause capacity loss or improvement are the following: particle cracking, [30,31,48] irreversible lithium plating, [22,31] loss of active material due to macro or micro cracking that leads to contact loss and electrical isolation [1,49,50] and SEI growth. [31] One possible reason for the capacity loss of F3 could be cracking of its coarser particles, which have been similarly suggested on graphite particles by Lin et al [51] and Bhattacharya et al. [52] Such particle cracking would increase surface area and decrease diffusion length (overpotential) as suggested by Röder et al, [20] but contact loss by mechanical electrode degradation could also result in poor Figure 1.…”

A Review of Degradation Mechanisms and Recent Achievements for Ni‐Rich Cathode‐Based Li‐Ion Batteries

“…Figure 16 a shows that cracks in polycrystalline graphite originate from the stress along the grain boundaries during the Li‐ion intercalation and deintercalation. [ 69 ] Consequently, the propagated cracks result in an irreversible volume expansion of the graphite anode. Another study concluded that the total volume change of graphite unit cells could increase by 13.2% at the complete lithiation state (Figure 16b).…”

A Review on Aging-Aware System Simulation for Plug-In Hybrids

“…Even though the layer protects the anode, a further expansion of the SEI is still possible. Graphite exhibits a volume expansion during cycling, which can crack the SEI layer [42,43]. The SEI can penetrate the electrode and the separator, which can lead to a smaller accessible active surface area [21].…”