Development of Improved Alginate Binder for Silicon Anodes in Lithium-Ion Batteries

Abstract

The need for lithium ion batteries (LIBs) has continuously increased because of the growing markets for large-scale battery application, including electric vehicles (EVs) and energy storage system (ESS). Si-based anodes in LIBs have been suggested as alternatives since Si has exceptionally higher theoretical capacity than conventionally used graphite, low cost, and natural abundance. Recently, the development of binder for Si-based anode in LIBs is important issue for stable battery system because Si suffers from fast capacity fading caused by its large volume change (>300 %) during charging/discharging. Here, we report calcium doped alginate binder which has improved mechanical properties compared to pristine alginate. We focused to demonstrate that alginate binder acquires extreme toughness, resilience and low electrolyte desolvation in the presence of Ca2+ due to the formation of reversible and robust electrostatic crosslinks with Ca2+, so called “Egg-box”, by using tensile tests and swelling experiment. In addition, through a simple spray of Ca-containing solution, we fabricated Ca-alginate cross-linking on the Si-electrode. Using various electrochemical analyses, we confirmed that the electrochemical performance of Si-anode can be significantly enhanced by replacing the pristine alginate with Ca-alginate. Compared with pristine alginate-based electrode, the Ca-alginate electrode exhibited advanced battery performance, such as stable cycle performance (81.6% charge capacity retention after 300 cycles), high reversible capacity (1500 mA h g-1, at 1.0 A g-1), excellent rate capability (1878 mA h g-1, at 0.2 A g-1 and 1175 mA h g-1 at 2.0 A g-1), and high Coulombic efficiency. Besides, the Ca-alginate electrode showed smaller internal resistance and lower electrode expansion than pristine alginate electrode. These results suggest that the simple Ca-spray treatment can be applied to development of commercial Si anode. Moreover, our strategy can be extended to other electrode systems including conversion or alloying based electrode materials.