Abstract
Cycling Li-ion cells with large capacities requires high currents and hence an expensive measurement setup. Aging the Li-ion cell material in coin cells offers an orders-of-magnitude-lower power requirement to the battery tester. The preparation procedure used in this work allows one to build coin cells in a reproducible manner. The original 40 Ah pouch cells and the corresponding 4.3 mAh coin cells (PAT-Cell) utilizing electrode material from the original cells are cycled with 1C at different temperatures. The results show the same basic aging mechanisms in both cell types: loss of lithium inventory at room temperature but an increasing proportion of loss of active material toward higher temperatures. This is confirmed by similar activation energies in capacity degradation of the 40 Ah cells and the averaged coin cells. However, the capacity of the coin cells decreases faster over time. This is caused by diffusion of moisture into the coin cell housing. Nonetheless, the increasing water contamination over measurement time is not directly linked to the loss of capacity of the coin cells. Thus, the observed aging mechanisms of the 40 Ah cells can be qualitatively transferred to coin cell level.
Highlights
Aging investigations on Li-ion cells are time and cost intensive
The results show the same basic aging mechanisms in both cell types: loss of lithium inventory at room temperature but an increasing proportion of loss of active material toward higher temperatures
If a fully discharged cell (state (1) in Figure 3a) is charged and loss of lithium inventory (LLI) is assumed as degradation mechanism, part of the Li will be lost during charging the cell (2 → 20 ) due to SEI growth
Summary
Aging investigations on Li-ion cells are time and cost intensive. The rate of aging depends on many factors, such as electrode materials; electrolyte composition; cell geometry; and the operational conditions SOC, C-rate, depth of discharge (DOD), and temperature. It is possible to anticipate the reaction rate of water in the electrolyte used in this study (LiPF6 in EC:EMC 30:70 wt.%) This investigation addresses the question of whether the capacity loss ∆SOH, consisting of a calendar. This investigation is used to further prove the transferability of the proposed coin cell aging method to commercial cells
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