Roll-to-roll fabrication of organic nanorod electrodes for sodium ion batteries

Organic electroactive materials derived from biomasses are promising candidates for next generation rechargeable batteries due to the low cost, sustainability and environmental benignity. Since organic materials have very low electronic conductivity, they are normally synthesized into nano-scale and mixed with conductive carbon before electrode fabrication. Herein, we first reported a unique role-to-role fabrication technology by taking advantage of the high solubility of organic materials in water. The synthetic process of nano-size organic materials is merged into the organic electrode fabrication process. 2,5-Dihydroxy-1,4-benzoquinone disodium salt (DHBQDS) is used as a model, and the DHBQDS nanorod electrode is in situ formed by precipitating DHBQDS nanorods from DHBQDS-sodium alginate-carbon black aqueous slurry film on a Cu current collector during electrode drying process. Due to the fast ionic and electronic conductivity of DHBQDS-carbon nanocomposite, the DHBQDS nanorod electrodes deliver a reversible capacity of 167mAhg^-1 at a high current density of 200mAg^-1 after 300 cycles, which is 87% of its initial capacity (capacity decay rate of 0.051% per cycle). To reduce the dissolution of DHBQDS in the electrolyte upon cycling, a thin layer of Al₂O₃ with thickness of 1nm or 2nm is coated on the DHBQDS nanorod electrodes using atomic layer deposition (ALD). The Al₂O₃ coating remarkably suppresses the dissolution of DHBQDS nanorods as evidenced by the increased Coulombic efficiency from 94% to ~100% at a low current density of 50mAg^-1. The reversible capacity of Al₂O₃ coated DHBQDS nanorod electrodes remains at 212mAhg^-1 after 300 cycles with a very low capacity decay rate of 0.049% per cycle. The ALD enhanced organic nanorods exhibit the best reversible capacity and cycle life among the organic electrodes reported for Na-ion batteries.