ABSTRACT
Binders play a critical role in stabilizing the cycling performance of silicon (Si) materials by protecting Si particles from pulverization in cycling processes. Poly(acrylic acid) (PAA) and carboxymethyl cellulose (CMC) are the two most studied binders for Si electrodes, of which PAA is an elastic polymer and CMC is a rigid polymer. Starting with the elastic PAA, we study the effect of binder content on the cycling performance of Si electrodes. It is found that regardless of the particle size of Si materials, there is an optimal binder content between 20% and 25% for the cycling stability of the Si electrodes. Compared with the elastic PAA, the rigid CMC binder causes Si electrodes lower capacity and faster capacity fading. AC-impedance analysis reveals that the lower capacity is due to a higher grain boundary resistance (Rgb) of the CMC-coated electrodes, which induces a high charge-transfer resistance (Rct) and consequently high polarization. In the discharging process of Li/Si cells, the high polarization triggers early termination, resulting in underutilization of the Si active material. On the other hand, the fast capacity fading of the CMC-coated electrodes is attributed to the inferior ability of the rigid binder to protect Si particles from pulverization.
ABSTRACT
A homologous series of lithium alkyl mono- and dicarbonate salts was synthesized as model reference compounds for the frequently proposed components constituting the electrolyte/electrode interface in Li-ion batteries. The physicochemical characterization of these reference compounds in the bulk state using thermal analyses and X-ray photoelectron, nuclear magnetic resonance, and Fourier transform infrared spectroscopies establishes a reliable database of comparison for the studies on the surface chemistry of electrodes harvested from Li-ion cells.
