Interpenetrated Gel Polymer Binder for High Performance Silicon Anodes in Lithium-Ion Batteries

Silicon has attracted ever-increasing attention as a high-capacity anode material in Li-ion batteries owing to its extremely high theoretical capacity.¹ However, practical application of silicon anodes is seriously hindered by its fast capacity fading as a result of huge volume changes during the charge/discharge process.^{2, 3} The situation becomes even worse when making it for practical application where high mass loading of active-materials (mg-Si/cm²) on current collectors is necessary for high energy density batteries.^{4, 5}

Polymer binder, one of major components in electrode, is used to bind active materials and conducting particles together onto the current collector. The properties of polymer binders play an important role on the electrochemical performance of the electrodes, especially for the cycle life and irreversible capacity losses.^{6, 7} Poly(vinylidene fluoride) (PVDF) is a conventional binder and widely used in traditional LIBs because of its acceptable adhesion and wide electrochemical window. However, the non-functionalized linear chain structure of the PVDF binder can’t afford sufficient binding to high-capacity anode particles that exhibit huge volume changes.⁶ This requires improved binding characteristics of binders to enable the integrity of the electrodes for long-cycle life. Thus, novel polymer binders with the ability to accommodate this substantial volume changes during lithiation/delithiation of Si anodes are highly desirable.

Here, we report an interpenetrated gel polymer binder for high performance silicon anode through in-situ crosslinking of water soluble poly(acrylic acid) (PAA) and polyvinyl alcohol (PVA) precursors. This gel polymer binder with deformable polymer network and strong adhesion on silicon particles can effectively accommodate the large volume change of silicon anodes upon lithiation/delithiation, leading to an excellent cycling stability and high Coulombic efficiency even at high current densities. Moreover, high areal capacity of ~4.3 mAh/cm² was achieved based on the silicon anode using the gel PAA-PVA polymer binder with a high mass loading. In view of simplicity in using the water soluble gel polymer binder, it is believed that this novel binder has a great potential to be used for high capacity silicon anode in the next generation Li-ion battery, but also for other electrode materials with large volume change during cycling.

Acknowledgements

This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-EE0006447.

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