Lithium-Ion Battery Degradation: Measuring Rapid Loss of Active Silicon in Silicon–Graphite Composite Electrodes

Abstract

To increase the specific energy of commercial lithium-ion batteries, silicon is often blended into the graphite negative electrode. However, due to large volumetric expansion of silicon upon lithiation, these silicon–graphite (Si–Gr) composites are prone to faster rates of degradation than conventional graphite electrodes. Understanding the effect of this difference is key to controlling degradation and improving cell lifetimes. Here, the effects of state-of-charge and temperature on the aging of a commercial cylindrical cell with a Si–Gr electrode (LG M50T) are investigated. The use of degradation mode analysis enables quantification of separate rates of degradation for silicon and graphite and requires only simple in situ electrochemical data, removing the need for destructive cell teardown analyses. Loss of active silicon is shown to be worse than graphite under all operating conditions, especially at low state-of-charge and high temperature. Cycling the cell over 0–30% state-of-charge at 40 °C resulted in an 80% loss in silicon capacity after 4 kA h of charge throughput (∼400 equiv full cycles) compared to just a 10% loss in graphite capacity. The results indicate that the additional capacity conferred by silicon comes at the expense of reduced lifetime. Conversely, reducing the utilization of silicon by limiting the depth-of-discharge of cells containing Si–Gr will extend their lifetime. The degradation mode analysis methods described here provide valuable insight into the causes of cell aging by separately quantifying capacity loss for the two active materials in the composite electrode. These methods provide a suitable framework for any experimental investigations involving composite electrodes.

Ageing of High Energy Density Automotive Li-ion Batteries: The Effect of Temperature and State-of-Charge

“…These results also show that SiOx electrochemical activity is decreased for the cells that are cycled down to 0% SoC such as R0-50, H0-50, R0-100, and H0-100 (Figure 3 b, c, f, g). This trend is expected as SiOx is known to degrade at cell potentials below 50% SoC [79]. On the contrary, the positive electrode degradation is anticipated at potentials corresponding to ≥50% SoC due to lower stability of the positive electrode upon delithiation [80].…”

“…𝑄 Si = 𝑄 𝑑 − 𝑄 N3 − 𝜃 𝑐 ⋅ 𝑄 Gr The necessary assumption in this estimation is that both the silicon and graphite are fully delithiated following the 0.1C step to 1.5 V. Effectively, this resolves the silicon amount that is kinetically available, which may be somewhat less than the total silicon content determined by other techniques. In spirit, this method of separating the silicon contribution is the same as can be done with fitting the open circuit potential for blended electrodes [79]. However, this manual algebraic calculation provides simplified, quick quantification in concert with the analysis of the differential voltage profiles.…”

Cycle Characterization of SiO-Based Lithium-Ion-Batteries Using Real Load Profiles

“…This expansion leads to the decomposition and reconstruction of the SEI layer, thereby consuming more lithium. 9,48,50,51 At a higher SoC range, the graphite dominates the aging behavior, which can be seen by the similar capacity loss regardless of SiOx content in the cells.…”

Accurate Model Parameter Identification to Boost Precise Aging Prediction of Lithium‐Ion Batteries: A Review

“…[52] Kirkaldy et al observed that the LAM of active Si was greater than that of graphite at low SOC and high temperatures. [62] Zhang et al discovered that the dissolution of transition metals (TMs) was more detrimental to Si than to graphite. [63] The LAM PE is highly dependent on different cathode chemistries.…”