Linear and Nonlinear Aging of Lithium-Ion Cells Investigated by Electrochemical Analysis and In-Situ Neutron Diffraction

Abstract

In this paper, we present an aging study of commercial 18650-type C/LiNi 0.33 Mn 0.33 Co 0.33 O 2 lithium-ion cells. The test procedure comprises varying charging currents, discharging currents and resting times between cycles. The cells show a nonlinear capacity fade after a few hundred equivalent full cycles, if cycled with a standard charging and discharging rate of almost 1C, and different resting times. By increasing the discharging current or decreasing the charging current, the lifetime improves and results in a linear capacity fade. The neutron diffraction experiment reveals a loss of lithium inventory as the dominant aging mechanism for both linearlyand nonlinearly-aged cells. Other aging mechanisms such as the structural degradation of anode or cathode active materials, or the deactivation of active materials, cannot be confirmed. With ongoing aging, we observe an increasing capacity loss in the edge area of the electrodes. Whereas the growth of the solid electrolyte interphase defines the early stage, linear aging, marginal lithium deposition is supposed to cause the later stage, nonlinear aging. Capacity recovery caused by lithium stripping and chemical intercalation is shown to be dependent on the cell's state of health.

Solid–Electrolyte Interphase During Battery Cycling: Theory of Growth Regimes

“…L tun is the reason for this transition. Below this thickness, electrons easily tunnelt hrough the SEI, so that the SEI formation is limited by the Li 0 reactionk inetics.A bove this thickness, diffusion through the SEI becomes dominant, leading to at ransport limitation in agreement with the measurements of Keil et al [67] and the model of Single et al [31] During battery charging (see Figure 8b), the transition betweenr eaction and diffusion limitation is smeared out. We observe in Figure 8b that SEI growth is reactionl imited for at hin SEI and a low OCV.D iffusion limits growth for ah igh OCV and at hick SEI.…”

“…A shift to linear SEI growth was so far observed experimentally by different groups . This transition is typically attributed to mechanical effects, for example, repeated SEI fracture and regrowth .…”

“…Below this thickness, electrons easily tunnel through the SEI, so that the SEI formation is limited by the Li 0 reaction kinetics. Above this thickness, diffusion through the SEI becomes dominant, leading to a transport limitation in agreement with the measurements of Keil et al . and the model of Single et al .…”

“…As hift to linear SEI growth was so far observed experimentally by different groups. [45,51,56,67,68] This transition is typically attributed to mechanical effects, for example, repeated SEI fracture and regrowth. [32,45,69] Our approachs hows ac omplementarye xplanation of linear SEI growth within electrochemistry.…”

Solid-Electrolyte Interphase During Battery Cycling: Theory of Growth Regimes

“…A shift to linear SEI growth was so far observed by different experimental groups [37,43,47,58,59] . This transition is typically attributed to mechanical effects e.g.…”