Quantifying the Impact of Charge Rate and Number of Cycles on Structural Degeneration of Li-Ion Battery Electrodes

Abstract

A quantitative link between crack evolution in lithium-ion positive electrodes and the degrading performance on cells is not yet well established nor is any single technique capable of doing so widely available. Here, we demonstrate a widely accessible high-throughput approach to quantifying crack evolution within electrodes. The approach applies super-resolution scanning electron microscopy imaging of cross-sectioned NMC532 electrodes, followed by segmentation and quantification of crack features. Crack properties such as crack intensity, crack width and length are quantified as a function of charge rate (1C, 6C, and 9C) and cycle number (25, 225, and 600 cycles). Hundreds of particles are characterized for statistical confidence in the quantitative crack measurements. The data on crack evolution is compared to electrochemical data from full cells and half cells with the NMC532 positive electrodes. We show that while crack evolution strongly correlates with capacity fade in the first 25 cycles, it does not correlate well for the following hundreds of cycles indicating that cracking may not be the dominant cause of capacity fade throughout the cycle-life of cells.

Quantitative Analysis of Origin of Lithium Inventory Loss and Interface Evolution over Extended Fast Charge Aging in Li Ion Batteries

“…We observe that both degradation modes are active but scale with capacity fading with different dependencies. Compared with LLI, the more significant aging mode is cathode particle cracking and structural disordering induced LAM PE , , which has a higher charge acceptance and cathode consumption. LAM PE also exhibits pronounced polynomial relation to capacity fading and a highly dependent reliance on cycling condition.…”

“…Thus, a variety of strategies to mitigate Li plating have been proposed, such as utilizing composite materials, altering the structure of graphite, , optimizing charging protocols, and developing advanced electrolytes . In parallel, the cathode also exhibits significant performance decay under XFC conditions due to surface/interphase issues, , increased cell impedance, loss of active material (LAM), − and mechanical degradation. , …”

“…10 In parallel, the cathode also exhibits significant performance decay under XFC conditions due to surface/interphase issues, 4,11 increased cell impedance, 11 loss of active material (LAM), 12−15 and mechanical degradation. 16,17 Other known sources of performance decline are electrolyte degradation and interface evolution. During normal cell operation, electrolyte degradation participates in the development of the SEI, resulting in the formation of passivating layers at both electrodes.…”