Water‐in‐Polymer Salt Electrolyte for Slow Self‐Discharge in Organic Batteries

Abstract

In electrochemical energy storage devices (ESDs), organic electrolytes are typically used for wide operational potential window, yet they suffer with cost, environmental, flammability issues, and low ionic conductivity when compared with water‐based electrolytes. Hence, for large‐scale applications that require high power and safety, presently there is no true solution. Though water‐based electrolytes have higher ionic conductivities, and are cost‐effective and nonflammable, their high self‐discharge rate with organic/carbon‐based electrodes impedes their commercialization. It is found out that highly concentrated polymer electrolytes on the concept of “water‐in‐salt electrolyte” lead to extremely low leakage current within the electrochemical stability window (ESW) of water, thus solving the issue of self‐discharge in organic/carbon‐based ESDs. Herein, potassium polyacrylate (PAAK) is prepared as “water‐in‐polymer salt electrolyte” (WIPSE) and tested for one of most abundant wood‐based biopolymer lignin and polyimide as positive and negative electrodes, respectively, in both half‐cell and full‐cell. The device shows an open‐circuit voltage drops <0.45 V in 100 h setting a record for organic batteries using aqueous electrolyte. The high ionic conductivity (40–120 mS cm−1) nonflammability of PAAK with high ESW (3.1 V) opens a new direction for truly safe, sustainable, and high power (6.8 kW kg−1) organic ESD manufactured by printing technologies.