Electrode Side Reactions, Capacity Loss and Mechanical Degradation in Lithium-Ion Batteries

Jiagang Xu,Vincent S Battaglia,Yang-Tse Cheng,Rutooj D Deshpande,Jie Pan

doi:10.1149/2.0291510jes

Abstract

For advancing lithium-ion battery (LIB) technologies, a detailed understanding of battery degradation mechanisms is important. In this article, experimental observations are provided to elucidate the relation between side reactions, mechanical degradation, and capacity loss in LIBs. Graphite/Li(Ni1/3Mn1/3Co1/3)O2 cells of two very different initial anode/cathode capacity ratios (R, both R > 1) are assembled to investigate the electrochemical behavior. The initial charge capacity of the cathode is observed to be affected by the anode loading, indicating that the electrolyte reactions on the anode affect the electrolyte reactions on the cathode. Additionally, the rate of “marching” of the cathode is found to be affected by the anode loading. These findings attest to the “cross-talk” between the two electrodes. During cycling, the cell with the higher R value display a lower columbic efficiency, yet a lower capacity fade rate as compared to the cell with the smaller R. This supports the notion that columbic efficiency is not a perfect predictor of capacity fade. Capacity loss is attributed to the irreversible production of new solid electrolyte interphase (SEI) facilitated by the mechanical degradation of the SEI. The higher capacity fade in the cell with the lower R is explained with the theory of diffusion-induced stresses (DISs).

Highlights

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We propose that the lower capacity loss with increasing anode loading can be explained by two possible stress-related mechanisms: (i) Increased anode loading results in decreasing in current density on the anode surface, which may reduce the electrode particle cracking during cycling. (ii) Increased anode loading decreases anode utilization and reduces the electrode particle expansion and contraction during the respective lithiation and delithiation, reducing the mechanical degradation
Graphite/NMC full cells with two different anode loading levels were tested to establish a better understanding of coulombic efficiency and cell capacity fade rate

Summary

Results and Discussion

Formation cycles.— From Table II we see that, the current densities based on the active NMC weight in cathode (mA/g) are similar for both the cells during formation cycles. = 0.4308 m Ag−1 to the right than the cell with lower anode loading, d dR=1.18 dt This observation can be understood because the larger the loading of the negative electrode, the more area is available for electrolyte reduction, and the greater the marching rate to the right of the discharge endpoint. For the cell with the lower anode loading (R = 1.18), even though the individual rates of marching of the charge and discharge endpoints are slower, the difference between their marching rates is larger, resulting in a greater overall rate of cell capacity fade. The impact of the difference in the rate of marching of the anode (discharge endpoint) and the marching of the cathode (charge end point) is clear: there is a loss of cycleable capacity. We conclude that there are two types of side reaction products: 1. Reaction products: Those which dissolve back into the electrolyte solvents at the operating conditions get oxidized on the cathode and contribute to shuttle reaction

Reaction products

Conclusions

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