TEMPO-oxidized Cellulose Nanofibers as Versatile Additives for Highly Stable Silicon Anode in Lithium-ion Batteries

Silicon (Si) has been considered the most promising anode material for next-generation lithium-ion batteries due to its high theoretical capacity and natural abundance. However, the Si anode suffers from massive volume change, which results in challenging cycling performance. Many researches demonstrated that polymeric binder plays an important role to sustain the structural integrity of Si anodes. While most studies about the binder material have been focused on enhancing distinctive properties such as adhesive strength and mechanical property, it has been recently shown that binder distribution can help to improve electrochemical performance. Herein, we introduce TEMPO-oxidized cellulose nanofiber (TOCNF) as a versatile additive for the binder of silicon anode. The one-dimensional morphology of TOCNF efficiently reinforces the mechanical properties of the electrode. The TOCNF additive also contains carboxylic groups with sufficient flexibility to induce intimate interaction with Si via hydrogen bonding. Based on all of these beneficial features of TOCNF, the addition of ∼ 1 wt% of TOCNF of the whole weight of silicon anode slurry significantly improved cycling stability. With pre-mixing, the resulting Si-TOCNF allows efficient water-based binder solution penetration, thus improving uniform binder distribution of electrode. Furthermore, the well-distributed binder protects silicon surface and forms a stable SEI layer. The current study suggests that the TOCNF additive facilitates uniform binder distribution in the electrode with enhanced mechanical properties, leading to improved cycling performance.