External and Local Short-Circuit Scenarios Applied to Silicon-Graphite/Nickel-Rich Pouch-Type Lithium-Ion Batteries
Authors: Sturm Johannes , Rheinfeld Alexander , Jossen Andreas 
Published: May 2020

The current trend towards increasing the energy density in lithium-ion batteries most noticeable in mobile applications such as the electric vehicle, intensifies research efforts on using suitable, higher capacitive active materials [1], thicker electrode coatings and/or overall bigger sized cells [2]. One essential requirement hereby is, to guarantee or even improve safe operation and lifetime of the battery. Regarding safety incidents [3], short-circuits are often the cause for critical states leading to irreversible damage or total failure (e.g. thermal runaway) of the lithium-ion battery. A better understanding of the short-circuit behavior can help to improve safety systems, to mitigate or even prevent the actual shorting scenario e.g. by applying specified cooling procedures [4]. Applying suitable, experimental test condition makes a simulation of the electrical-thermal, external short-circuit behavior possible on the single-cell level [5]. The related analysis of the cell’s current flux, voltage drop, and heat generation helps, to understand the occurring electrochemical-thermal processes better. Correlation of the experimental findings with the results from electrochemical-thermal simulation studies [6] shows, that the appearing plateau and transition regions of current flux, cell voltage and heat generation are caused by transport limitations in the electrolyte and the active material particles as well as by inhibition of reaction-kinetics. Current work [7] deals with the comparison and correlation of external (i.e. shorting via the current collector tabs) and local (i.e. shorting via nail-penetration in the centre of the active electrode area) short-circuits applied to Graphite/NMC-111 pouch-type lithium-ion cells incorporating moderate electrode loadings (i.e. ≈ 2 mAh cm-2). Considering the trend towards high-energy batteries, this work extends the short-circuit investigations to custom-built, Silicon-graphite/NMC-811 and Silicon-graphite/NCA cells at higher electrode loadings (i.e. > 2.0 mAh cm-2). For the short-circuit measurements, a quasi-isothermal, calorimetric test bench [4] as shown in Figure 1 embeds the single-layered, pouch-type cells between two copper bars in a thermally insulated case. The test bench itself is placed together with the measurement equipment in a custom-built climate chamber at 25°C. The cell under test is either externally shorted via the current collector tabs using a 0V-condition applied by a potentiostat (SP-300, BioLogic Science Instruments), or shorted in the center of the cell using nail-penetration technique with a stainless-steel needle (Ø 1 mm). Three digital multi-meters (DMM, Keysight Technologies), a source measurement unit (SMU, Keysight Technologies), and the potentiostat measure the current flux, cell voltage, and heat rate/cell temperature during an external short-circuit. The same is possible for the local short-circuit except for the current flux, however, the electrical potential in the penetration spot vs. the cell’s negative tab can be measured via electrically conducting the needle. Based on the measurement results, external and local short-circuits are investigated towards similarities and differences appearing in the electrical-thermal behavior. A comparison to common Graphite/NMC-111 cells will discuss the differences to the Silicon-graphite/Nickel-rich cells. Finally, post-mortem analysis presents degradation on a local scale over the electrode width and length (i.e. 3 x 5.45 cm) for the tested cells.
References:
[1] Andre et al., Journal of Material Chemistries A, 3, 6709-6732, 2015.
[2] Blomgren, Journal of The Electrochemical Society, 164 (1), A5019-A5025, 2017.
[3] Abada et al., Journal of Power Sources, 306, 178-192, 2016.
[4] Rheinfeld et al., Journal of The Electrochemical Society, 167, 013511, 2020.
[5] Rheinfeld et al., Journal of The Electrochemical Society, 165 (14), A3427-A3448, 2018.
[6] Rheinfeld et al., Journal of The Electrochemical Society, 166 (2), A151-A177, 2019.
[7] Sturm et al., Manuscript under preparation.
Figure 1: Schematic view of the calorimetric test bench (left, showing the external short-circuit setup) indicating the measurement equipment and the cell under test (middle), which is applied with either a local (i.e. nail-penetration) or an external short-circuit condition. Both scenarios are compared via the measurement signals and post mortem analysis (right) helps to interpret the appearing short-circuit behavior.

Figure 1