Long-lasting supercapacitor with stable electrode-electrolyte interface enabled by a biopolymer conjugate electrolyte additive

• A biopolymer conjugate additive forms a protective layer for stable supercapacitors. • A simple additive approach ensures stable electrode-electrolyte interface. • Enhanced ion transport efficiency with stable electrode-electrolyte interface. • Demonstrated an impressive 93 % retention for 30,000 cycles at 4.0 mA cm -2 . Supercapacitor is one of most widely researched energy storage system because it stores more charge than capacitor and charges-discharges quicker than batteries. As surface reaction is prominent in the energy storage in supercapacitor, stable interface between electrode and electrolyte is a key to high performance. Although a formation of stable interface was achieved by surface modification of electrode and/or designing of novel materials/composites, they were limited by their complicated processing steps, costs, scalability, and eco-friendliness. In this work, we have firstly introduced a novel electrolyte additive composed of conjugated biopolymer of gum kondagogu/sodium alginate (KS), which is widely available and recyclable. At the KS concentration of 5 mg ml -1 , the capacitance retention improved from 58 % to 93 % for 30,000 cycles at a current density of 4.0 mA cm -2 , which was remarkable given the use of acidic H 2 SO 4 electrolyte and carbon-based electrode. Postmortem analysis revealed the suitable concentration of KS necessary to ensure the interfacial protection as well as alleviation of side reactions by the introduction of KS, which can also be extended and scaled up in an industry scale.