(128c) A New Three-Dimensional Network Structured Polymeric Binder for Silicon-Based High-Capacity Lithium Ion Anodes.

Silicon materials have several advantages such as high theoretical capacity (~4200 mAh/g), low operation potential (< 0.5 V vs. Li/Li⁺), and abundant resources as anode materials. However, its application has been limited to small amount in anodes because of its huge volume expansion (~300%) during lithiation and de-lithiation. Once the huge volume expansion fails to be accommodated, the delamination between anode components and current collector, pulverization of Si particles, thick SEI layer on Si surface could occur in silicon-based electrodes. The delamination causes serious trouble to electron delivery in electrodes and finally leads to electrical isolation. The pulverization generates dead silicon segments and result in dramatic capacity loss. In addition, thick SEI layer consumes more Li ions and leads to low Li⁺ diffusion.

One way to tackle the aforementioned problems is to design silicon structure and the combination use with graphite. Although significant reports have demonstrated the improvement of silicon structure, the huge volume change of silicon still influences the structural stability of silicon and graphite composite (Si/C) electrodes in practical application. Designing polymeric binder is another valuable method. Polymeric binder combines electrode components (e.g. active materials and conductive materials) and adhere electrode components to current collector. Therefore, the adhesion and structural design of binder effectively alleviates the huge volume change and maintain structural integrity of silicon-based electrodes.

According to our previous research, traditional Poly (vinylidene fluoride) (PVDF) binder could not satisfy the demands in lithium-ion batteries (LIBs) nowadays because of its weak binding force with active materials surface and organic solubility in taxic solvent. Water-based polymeric binders such as poly acrylic acid (PAA), polysaccharides, carboxymethyl cellulose lithium (CMC-Li) and so on have been widely studied in LIBs. However, those leaner polymeric binder lacks of deformation ability and easily result in the structure broken. Branched and multi-dimensional polymeric binder could provide more contacts with silicon surface and distribute stress force to side chains during volume expansion of silicon in lithiation process. In addition, multi-dimensional structure could integrate the functionalities of main chains and side chains. Therefore, it is possible for branched and multi-dimensional binders to offer multiple functionalities such as conductivity, desirable mechanical properties, good electrolyte affinity, etc. In this study, we will present how to achieve branched and multi-dimensional binders using a monomer having numerious adhesive hydroxyl groups. A variety of characterization tools will be used for measuring the electrochemical and binder properties.