Experimental Analysis of External Short-Circuit Scenarios Applied to Lithium-Ion Cells with Silicon-Dominant Anodes under Different Mechanical Pressures

Lithium-ion cells based on microscale silicon particles as anode material under partial lithiation are economical and offer the potential to enhance energy density while addressing the challenge of reduced cycle stability[1]. However, the safety behavior of this new material needs to be understood. This work presents a comprehensive investigation of the short-circuit (SC) behavior of self-manufactured single-coated, single-layered pouch (SLP) µm-silicon||nickel-rich cells[2] with newly introduced dual reference electrode setup consisting of a lithium reference electrode (LiRE) and a gold wire reference electrode (GWRE)[3]. Six SLP cells are externally shorted at three different compression levels of 5 bar (high pressure – HP), 2 bar (normal pressure – NP), and 0.1 bar (low pressure – LP) using a newly developed, calibrated quasi-isothermal calorimetric short-circuit test bench.

As a result, the same current plateaus and transition zones[4] can be observed for µm-Si||NCA cells for all pressure stages, similar to literature results with graphite||NMC-111[2], silicon-graphite||NCA[4], and silicon-graphite||NMC-811[4] SLP cells. Moreover, a direct dependency of the SC intensity and the heat generation is measured for the differently compressed SLP cells. A higher SC intensity for HP cells, i.e., higher current and higher heat generation, can be ascribed to decreasing impedance values at increased pressure levels. LP cells generate more heat and over-discharge due to prolonged current generation times. The in-built reference electrodes allow for monitoring of the negative terminal voltage, revealing potentials of up to 3.508 V and thus explaining the measured over-discharge in the range of ≈ 25% SoC. This work presents a copper dissolution study showing a potential of 3.475 V vs. Li+/Li as an acceleration point of copper oxidation for the given material combination.
Post-mortem analysis of SLP cells reveals copper deposition on both electrodes and the separator, confirming the over-discharge. The measured negative terminal voltage during the SC was applied as a potential trajectory on Swagelok-type copper T-cells to further investigate and quantify the degree of copper dissolution.

References:
[1]: Jantke et al 2019 J. Electrochem. Soc. 166 A3881
[2]: Rheinfeld et al 2018 J. Electrochem. Soc. 165 A3427
[3]: Solchenbach et al 2016 J. Electrochem. Soc. 163 A2265
[4]: Kriston et al 2017 J. of Power Sources 361 170-181
[5]: Sturm et al 2022 J. Electrochem. Soc. 169 020569