Modification of Polysaccharide through Graft Copolymerization as Adhesion Binder for high Capacity Anode of Lithium Ion Battery

Abstract

Silicon demonstrates a next generation anode material for lithium ion battery due to an energy storage capacitor greater than that of commercial graphitic carbon. But, Si based electrode is not still came to nearly commercial market because its high capacity could not remain stable in long-term cycles that result from suffering from repeated volume change of Si during reversible charging and discharging. To further enhance the durability of Si electrode, more researches have been attempted innovative composition and architectures polymer binders to increase storage capacities and improve stability. Polymer binders maintain adhesion between the electrode and current collector, cohesion within the electrode. In addition, the binder serves ensuring the stability of solid electrolyte layer that form on the surface of silicon, and some cases providing electronic and ionic conductivity. To replace the organic solvent binder including polyvinyledene difluoride (PVdF), environmental-friendly water soluble polysaccharide (PS) and other polymers are considered to be a good choice of binders for Si-based anode due to their robust mechanical ability and lower electrolyte-uptake properties while compared with commercial PVDF. However, the mechanical property of PS is still several limited their applications because of its poor mechanical ability. Although, highest brittle PS might be not sustainable condition during slurry preparation with high loading of active material and thus it does not provide structural stability of electrode film. The modification of PS trough graft copolymerization and crosslinking provides tool in the hands of researchers to incorporate targeted properties in backbones for specialized application. That knowledge has already practiced a development new binder system in various batteries, as the result as the branched and single or dual crosslinked designed binder provides to better adhesion modest and structural stability of electrode film compared with pure linear polysaccharides. In our first study, water-treated dual-crosslinked binder systems will be introduced for a high capacity silicon/graphite electrode. And so, maintaining central role play to improve mechanical properties and preserve memory initial state three common PS trough graft copolymerization and dual-crosslinking method. The PS is firstly graft copolymerized with polyacrylamide (PAAm) to product new graft copolymer of PS-graft-PAAm (PS-g-PAAm). In furthermore, PS-g-PAAm is crosslinked with ionic and chemical crosslinker agents to subsequently perform dual-crosslinked PS-g-PAAm network. In addition, both ionic and covalent crosslinkings in the binder maintain their intrinsic good binding properties and additionally enhance lithium ion diffusion. Three types of PS, sodium-alginate (Alg), sodium-carboxymethyl cellulose (CMC), and pectin (Pec), will be employed and compared for their performance as a binder material for high-capacity macroparticles silicon and graphite (Si/C) anodes. A variety of characterization tools will used to examine the electrochemical performance of the electrodes containing the dual-crosslinking binder systems. In summarize, the newly designed saccharide based polymer binder through grafting and dual-crosslinking (PS-g-PAAm and c-PS-g-PAAm) gives better adhesion to active material and current collector, it is still required to enhance the ionic conductivity for high powered electrodes. In another study, our group developed one-step process to prepare sulfonated polysaccharide backbone to provide high ionically conductivity compared to pure polysaccharide. In last chapter, we synthesis sulfonated alginate-graft-polyacrylamide (SAlg-g-PAAm) from pure alginate (Alg) by two in-situ step methods. Herein, sulfonated group propose to increase ionic conductivity and PAAm unite in graft copolymer improves an adhesion ability on poor mechanic ability of Alg. The SAlg-g-PAAm which high ionic conductivity and adhesion polymeric binder is constructed to Si/C anode of LIB, leading to highly stable electrochemical performance compared to natural Alg and non-functionalized graft copolymer.