Designer Polymeric Binders for Silicon-Anode Based Lithium Ion Batteries
Authors: Hamzelui Niloofar , Eshetu Gebrekidan Gebresilassie , Adlfar Vida , Hippler Michael , Figgemeier Egbert 
Published: February 2020

Graphite is known as state-of-the-art anode material in the contemporary commercial lithium-ion batteries (LIBs), and is attributed to its low cost and superior long cycle life. However, its low theoretical specific capacity (372 mAh g-1, based LiC6) limits its usage for the emerging innovative applications such as in the electro mobility (electric vehicles, xEVs), efficient integration of renewable energy sources and deployment of large-scale smart grid/utility storage devices. 1

With extra-high capacity (4200 mAh g-1, based on Li22Si4), suitable operating potential (0.2-0.4 V vs. Li/Li+), high abundance (2nd richest element in the earth crust), low cost, negligible toxicity, superior safety and environment-friendliness, Silicon (Si) is considered as one of the most promising alterative anode material to revolutionize next-generation LIBs. However, despite all these resilient features, intrinsic drawbacks such as low electronic conductivity (~10-3 S cm-1) and Li diffusion coefficient (10-14-10-13 cm2S-1), colossal volume change (200-400% vs. 8-12% for graphite), low initial Coulombic/energy efficiency (ca. 65-85% vs. 90-94% for graphite), unstable solid electrolyte interphase (SEI), electrode swelling and electrolyte drying are among the seemingly challenges hampering its commercialization. 2–4

Among the various strategies, the use of graphite (G)-silicon (Si) composite along with designer polymeric binders represents one of the most enabling approach to overcome the above-mentioned challenges.
Herein, we report on highly robust, new, naturally available, green (aqueous solvent based) and multi-functional polymeric binders for use with an optimized G-Si composite electrodes. Firstly, the composition of G-Si composite was optimized using state-of-the-art binders used in Si-based anode such as carboxymethyl cellulose (CMC) and poly (acrylic acid) (PAA). Following the optimization, highly performing new binders have been developed and investigated. An in-depth investigation of the electrochemical performance (long-term cycling, Coulombic/energy efficiency, and rate capability), surface characterization using X-ray photoelectron spectroscopy (XPS), and thermal reactivity via differential scanning calorimeter (DSC) evidenced the huge potentiality of the new polymeric binders and optimized G-Si composition.

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