Evaluating Si-Based Materials for Commercially Relevant Li-Ion Batteries

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.

Figure 1 shows the dQ/dV of neat electrodes containing (a) only nano Si and LiPAA binder for which the Li15Si4 peak gradually decreases, and (b) Si-based alloy (V6Neat) and LiPAA binder with a dQ/dV characteristic of amorphous Si.

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.

A review of failure modes for various Si implementations and their impact on full cell cycling will also be presented.