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.

Magnetic Force Dilatometry of Silicon-NMC622 Lithium-Ion Coin Cells: The Effects of Binder, Capacity Ratio, and Electrolyte Selection

“…5b). Both electrodes started with initial total porosities of 50%-55%, 80,81 however the binder in the PAN electrodes has been carbonized via pyrolysis. Carbonization of PAN via heat treatment above 500 °C results in a several order of magnitude enhancement in electrical conductivity, but a concomitant ten-fold decrease in elongation due to the transformation from the aliphatic to cyclic polymer backbone.…”

“…We also fabricated silicon electrodes with pyrolyzed polyacrylonitrile (PAN) binder (Goonvean Fibres Ltd) in the same method as the air-dried electrodes described in another previous publication. 81 Briefly, electrode components were mixed in a planetary mixer with N-methyl-2-pyrrolidone to form a slurry, coated onto copper foil by doctor blade, dried at 75 °C overnight, followed by 2 h under vacuum, then heat treated in a tube furnace under high purity nitrogen (275 °C for 1 h then 700 °C for 1 h) before coin cell preparation. The formulation of these electrodes was 84.8/0.4/8.5/6.3 silicon (2 μm)/single-walled carbon nanotubes (SW-CNT, Tuball)/ carbon nano fiber (CNF, Pyrograf)/pyrolyzed polymer, referred to as the "PAN" electrodes.…”

Atomistic Insight into the Role of Porous Structure in Accommodating the Volume Expansion of Silicon Anodes for Lithium-Ion Batteries

“…Several studies have been reported to utilize a variety of porous silicon materials fabricated with various methods as negative electrodes for LIBs. [27][28][29][30][31] For example, Yao et al synthesized silicon hollow nanoparticles using SiO 2 solid spheres as templates for silicon deposition, and the aggregate hollow nanospheres with a uniform pore size of ∼350 nm were formed after etching the templates. 32 They showed that the prepared electrodes exhibited high gravimetric capacity even after 700 cycles (∼1,400 mAh g −1 ).…”