Efficient Surface Passivation of Ti-Based Layered Materials by a Nonfluorine Branched Copolymer for Durable and High-Power Sodium-Ion Batteries.

ABSTRACT

There is a crucial need for low-cost energy storage technology based on abundant sodium ions to realize sustainable development with renewable energy resources. Poly(vinylidene fluoride) (PVDF) is applied as a binder in sodium-ion batteries (SIBs). Nevertheless, PVDF is also known to suffer from a larger irreversible capacity, especially when PVDF is used as the binder of negative electrode materials. In this research, a poly(acrylonitrile)-grafted poly(vinyl alcohol) copolymer (PVA-g-PAN) is tested as a binder with Ti-based layered oxides as potential negative electrode materials for SIBs. The chemical stability tests of PVDF and PVA-g-PAN contacted with metallic sodium have been conducted, which reveals that PVDF experiences a defluorination process, while PVA-g-PAN demonstrates excellent chemical stability. Composite electrodes with PVA-g-PAN demonstrate superior electrochemical performances when compared with the PVDF binder, allowing improvement for initial CE, higher rate capability, and long cyclability over 1500 cycles. Detailed characterization of electrodes via soft X-ray photoelectron spectroscopy and field emission scanning electron microscopy demonstrates that the PVA-g-PAN branched structure allows a more uniform distribution of acetylene black with higher coatability, unlocking enhanced rate performances and efficient passivation of Ti-based oxides without the excessive electrolyte decomposition. These findings open a new way to design practical and durable sodium-ion batteries with a high-power density.