High Porosity Single-Phase Silicon Negative Electrode Made with Phase-Inversion

Abstract

Herein we present a Si electrode fabrication process that includes a phase-inversion step subsequent to slurry-based electrode casting and discuss its consequences for Si//Ni0.6Co0.2Mn0.2O2 cell performance. The phase inversion consists of extracting 1-methyl-2-pyrrolidinone with water and the concomitant coagulation of the polyacrylonitrile binder. Phase inversion improves capacity retention by 50% during C/5 cycling of Si//Ni0.6Co0.2Mn0.2O2 coin cells between 3.0 and 4.2 V. Phase-inversion Si electrodes have (1) 80% porosity compared to 55% for standard electrodes; and (2) bimodal pore size distribution, consisting of micropores (as in standard electrodes) and macropores with dimensions of 2 to 20 μm. The surface film mass growth rate in phase-inversion electrodes is smaller by 24% than in air-dried Si electrodes. Furthermore, during electrochemical cycling, the overall thickness change rate in phase-inversion electrodes is 5x smaller than in air-dried electrodes. Additionally, the high porosity electrodes display a reduced tendency to deform during electrochemical cycling. The insertion of a phase-inversion step into the electrode fabrication process may thus mitigate the volume expansion of the cell, enabling efficient module and pack design, while also increasing battery durability.