Influence of the Ink Solid Loading on the Properties of Si Based Electrodes for Li-Ion Batteries

Abstract

Silicon is a very promising anode material for Li-ion batteries, compared to commercially available graphite, thanks to its ~ x3 and x10 higher volumetric and specific capacity respectively. However, this capacity comes from the high alloyable lithium content (up to c-Li15Si4), inducing a proportional volume expansion (~ 280%)1, which trigger many electrode failure mechanisms. To cite a few, there is (i) the fragmentation of the electrode coating (and possibly delamination), reducing the electrochemically available active materials, and (ii) the destabilization of the SEI because of the ever changing silicon particles morphology, rousing a perpetual electrolyte degradation accompanied by a rising electrode impedance.In the present work, the influence of the slurry solid loading on silicon electrode properties and performances was studied, as the electrode processing appears promising to circumvent those problematics. Indeed, solid loading has already been linked to improved mechanical, morphological and electronic conductivity properties of electrodes2,3 but these studies focus on positive active materials.Experimentally, the influence of solid loading was investigated on a reference and coordinatively reticulated binder. The reference was a poly(carboxylic acid) binder which was made of dissolved NaCMC in pH ~ 3 buffer solution. To obtain the coordinated binder, zinc(II) was simply added in the reference solution as a coordination agent, before mixing the as-prepared solution with silicon submicrometric particles and graphene nanoplatelets (as conductive additive). In order to increase the solid loading, binder solutions were concentrated and simply added in a lower quantity for the mixing. Afterwards, electrodes were prepared by tape casting the slurry onto copper current collector. Finally, electrodes were punched (active mass loading ~ 1.75 mgsi.cm-² and 3.5mgsi.cm-²), dried and transferred into a glove box (H2O and O2 content < 1 ppm) for Swagelok cell assembly (LP30 + 10 w% FEC is used as an electrolyte).Interestingly, references electrodes were the most sensitive to the increase of solid loading, with much improved electrochemical performances. In order to understand those variations, inks and electrodes were thoroughly characterized by ink rheology, electrode coating conductimetry and MEB/EDX for the morphology/composition analysis, whose results will be presented and discussed.