Water-in-polyelectrolyte for sustainable Lignin batteries

Cellulose, hemicellulose and lignin are made by the plants in their growth process where 70-80% is dominantly cellulose and hemicellulose, lignin forms 20-30% of the solid weight. Lignin is considered as attractive and electroactive material for energy storage as it can store two electrons per hydroquinone aromatic ring. Redox bio- and synthetic polymers are considered as alternative to conventional inorganic materials because of the versatility of the chemistry to tailor-make their electronic structure, low cost due to the huge abundance of their atomic elements. At present organic electrolytes have wide potential window but are limited by costs, safety and non-ecofriendly issues. Water-based electrolytes are better alternative to organic solvents have much superior ionic conductivities, and are cost effective and non-flammable, however their poor self-discharge behavior impede their practical applications. Potassium polyacrylate (PAAK) polymer electrolytes based on the concept of “water in salt electrolyte” (highly concentrated) shows low leakage current within the electrochemical stability window of water and display low self-discharge decay with the open circuit potential (OCP) drops from 1V (faradic peak) to 0.75V in 100 h. Moreover, the PAAK electrolyte has high ionic conductivity 87 mS/cm and high voltage stability windows (3V). All those features make it a solution for truly safe and high-power energy storage devices. In our battery cell, PAAK was used as electrolyte, lignin-carbon and polyimide-carbon composites as positive and negative electrodes respectively. In a coin cell configuration, the discharge capacity is 19 mAhg-1. Another feature of this is for high power density.