The energy storage improvement is an important challenge for the future. Silicon is one of the most promising anode material to replace graphite in Li-ion batteries because of its high specific and volumetric capacity 10 times and 3 times higher than graphite (3579 vs. 372 mA.h/g ; 2194 vs. 719 A.h/L). Unfortunately, silicon good performance are associated with a huge particle swelling of +280% during the lithiation against only 10% for graphite. This expansion implies 3 main failure causes including electrode delamination from the current collector.

First, we worked on the electrode optimisation with an industrial approach in terms of active materials, areal capacity (mA.h/cm²) or process for example. We mixed graphite with a commercial silicon oxide named SiOx-C as active material with a mitigated specific capacity of ≈ 1800 mA.h/g but a swelling divided by two (+140%) in order to limit silicon failures effects [1]. We studied the SiOx-C amount impact and the calendering effects on coin-cell cyclability.

After a lot of attempts, the first improvement come from the binder choice (PolyAcrylic Acid) and slurry pH during electrode fabrication [2]. The second upgrade is based on Obrovac study which deals with the graphite type, shape and size [3]. The specific capacity rise by +37% after 50 cycles thanks to these improvements.

The second part of my PhD is the study of the electrode / current collector interface. After the identification of efficient characterisation methods, we want to define the perfect characteristics for a coated current collector in order to limit the electrode delamination from the substrate caused by the silicon swelling.

References

[1]. Reynier, Y.; Vincens, C.; Leys, C.; Amestoy, B.; Mayousse, E.; Chavillon, B.; Blanc, L.; Gutel, E.; Porcher, W.; Hirose, T.; Matsui, C. Practical Implementation of Li Doped SiO in High Energy Density 21700 Cell. J. Power Sources 2020, 450, 227699. https://doi.org/10.1016/j.jpowsour.2020.227699.

[2]. Mazouzi, D.; Lestriez, B.; Roué, L.; Guyomard, D. Silicon Composite Electrode with High Capacity and Long Cycle Life. Electrochem. Solid-State Lett. 2009, 12 (11), A215. https://doi.org/10.1149/1.3212894.

[3]. Du, Z.; Dunlap, R. A.; Obrovac, M. N. High Energy Density Calendered Si Alloy/Graphite Anodes. J. Electrochem. Soc. 2014, 161 (10), A1698–A1705. https://doi.org/10.1149/2.0941410jes.