We have recently shown that the storing of a Si/C/CMC electrode in humid atmosphere for a few days before drying and cell assembling has a very positive impact on its cycling performance2. With such a ‘’maturated’’ electrode, an areal capacity higher than 4 mAh cm-2 can be achieved for more than 100 cycles compared to less than 3 cycles for a no matured electrode. The precise mechanism of this maturation process is still unclear
Here, the impact of the maturation step on the mechanical properties of Si/C/CMC electrodes is investigated by means of indentation, peeling and scratch tests. They confirm the higher adhesion and cohesion strengths of the maturated electrode. Its more reversible expansion/contraction behavior upon cycling is also demonstrated from electrochemical dilatometry measurements and in-operando optical microscopy observations (Fig. 1). In addition, focused ion beam scanning electron microscopy (FIB-SEM) tomography shows a better preservation of the pore and Si particle connectivities with cycling for the matured electrode. Lastly, reflectance Fourier transform infrared spectroscopy (ATR-FTIR) complemented by Nuclear Magnetic Resonance (NMR) analyses indicate that the nature and distribution of the Si-CMC bonds are modified by the maturation step. On the basis of these different analyses, a film maturation mechanism is proposed, which opens up new avenues for optimizing the manufacture process of high-performance Si-based electrodes.
1. Z. Karkar, D. Mazouzi, C. Reale Hernandez, D. Guyomard, L. Roué, B. Lestriez. Threshold-like dependence of silicon-based electrode performance on active mass loading and nature of carbon conductive additive. Electrochim. Acta 215 (2016) 276-288.
2. C. Real Hernandez, Z. Karkar, D. Guyomard, B. Lestriez, L. Roué. A film maturation process for improving the cycle life of Si-based anodes for Li-ion batteries. Electrochem. Comm. 61 (2015) 102-105.