Improvement of intermetallics electrochemical behavior by playing with the composite electrode formulation

Abstract

The impact of both various binders and carbon additives on the electrochemical behavior of intermetallics-based (FeSn2, NiSb2, TiSnSb) negative electrodesvs.Li was evaluated and accurately studied for FeSn2. The formulation of the composite electrode allowed enhancement of both the capacity retention as well as the rate capability. CMC/VGCF (carboxymethyl cellulose/vapor grown carbon fiber) used as a binder/conductive additive allows retention of 100% of the specific capacity during 35 cycles at 2C rate (2Li h−1), whereas the fading is dramatic after only a few cycles at a low rate with classical powdered electrodes. Notably, an extra capacity is observed with CMC/VGCF. In the case of FeSn2, it is shown that the improvement of performance achieved with CMC/VGCF results from better efficiency of the conductive additive to form an electronic percolation web around the active material (AM) particles rather than from the buffering of the volume variations of the AM particles, contrary to the case of Si-based electrodes. The improved cycle life is also likely due to the better ability of CMC to cover the particles compared to PVDF (polyvinylidene fluoride), resulting not only in stronger interparticle bonding but also in a better SEI layer. It is suggested that the growing of an insulating SEI layer by the degradation of the liquid electrolyte is an important factor in the fading mechanism of FeSn2 composite electrodes. Finally, the aqueous processing of the FeSn2, NiSb2, and TiSnSb intermetallics-based composite electrodes is feasible.