Formulation of Industry-Relevant Silicon Negative Composite Electrodes for Lithium Ion-Cells

Compared with graphite, silicon is a favourable alternative candidate due to a high specific capacity (3572 vs. 372 mAh g) and specific volumetric capacity (2081 vs. 779 mAh cm). However, large capacity fading and low cyclability of Si electrodes is a major issue. Several strategies have been undertaken to overcome these problems. One way is optimising the binder in order to cope at the molecular scale with the expansion and contraction of Si upon alloying and dealloying with Li. Since early works on CMC, several other works proposed alternative binders to CMC, most of them being polysaccharides and/or bearing COOH functional groups. Another way to improve the cycle life is using electrolytes containing a film-forming agent such as VC and/or FEC. Besides, electro-conductive additives also display an important influence for the performance of nano Si-based electrodes with high active mass loadings of about 2.5-3.3mAh per cm2. We found a significant improvement of the electrochemical performance by using reduced graphene oxide (rGO) or exfoliated graphite nanoplatelets instead of carbon black as the conductive additive [1,2]. The influence of electro-conductive additives is not only to play on the electronic conductivity but also on the micromechanics (stress distribution) of the composite films. In a further work, we aimed to design the formulation of these nano Si-based electrodes with high active mass loadings with to wind some cylindrical cells. To reach this goal we looked for: (i) homogeneous and stable slurry-state by adding a dispersant, Poly (acrylic-co-maleic) acid; (ii) suitable mechanical properties for calendaring and battery assembly steps by adding Styrene-co-Butadiene rubber copolymer latex (SB) [3]. However, calendaring is detrimental to long cycle life.