Evaluating Si-Based Materials for Li-Ion Batteries in Commercially Relevant Negative Electrodes

Abstract

Methods and criteria for assessing the commercial viability of Si-based materials are discussed and demonstrated with the 3M V6 alloy and 60 nm nano Si powder. These materials are firstly evaluated through the cycling of neat electrodes containing only alloy and binder to characterize the capacity, first cycle efficiency, binder compatibility, and microstructure stability of the material. The alloy displays higher first cycle efficiency, lower fade, and a more stable amorphous microstructure compared to the nano Si, which displays a variable microstructure with a rate dependent presence of crystalline Li₁₅Si₄. The materials are then evaluated in graphite-containing composite electrodes having high areal capacities (> 2 mAh/cm²). In a well designed composite electrode including carbon nanotubes, 3M V6 material was found to cycle with little fade and high coulombic efficiency (∼99.8%) while maintaining a stable dQ/dV. A composite electrode of equivalent volumetric capacity with nano Si powder shows similar capacity retention over 50 cycles but an unacceptably low coulombic efficiency (∼99.2%). High precision coulometry and calorimetry results show surface area as the dominant factor in levels of parasitic reactions with Si based materials.