Self‐Discharge in Batteries Based on Lignin and Water‐in‐Polymer Salt Electrolyte

Abstract

Lignin, the most abundant biopolymer on earth, has been explored as an electroactive material in battery applications. One essential feature for such lignin‐based batteries to reach successful usage and implementation, e.g., large‐scale stationary grid applications, is to have slow self‐discharge characteristics on top of the essential safety and life‐cycle properties. Water‐in‐polymer salt electrolytes (WIPSEs) have been demonstrated as an attractive route to solve this issue; however, little has been done to understand the fundamentals of actual self‐discharge mechanisms. Herein, the impact of some critical chemical and physical parameters (pH, dissolved oxygen, viscosity, and cutoff potential) on self‐discharge of batteries based on WIPSE and lignin has been investigated. The pH range is crucial as there is an interplay between long‐term stability and high energy density. Indeed, lignin derivatives typically store relatively more charge in acidic media but later promote corrosion affecting device stability. A robust and high‐performing organic battery, incorporating potassium polyacrylate as WIPSE, is demonstrated, which expresses good self‐discharge behavior for a broad range of pH and with little impact on the atmosphere used for manufacturing. It is believed that the investigation will provide critical insights to the research community to promote the advancement of printed large‐scale energy storage devices.

Zinc salt in “Water‐in‐Polymer Salt Electrolyte” for Zinc‐Lignin Batteries: Electroactivity of the Lignin Cathode

“…In CH 3 COOK at pH = 6.2, the L‐C electrode potential reaches 0.08 V in 5 h, while with PAAK the potential drops much slower to reach ≈0.3 V in 5 h. Note that like the self‐discharge curve displays a voltage plateau associated with the faradaic reaction of lignin, a similar profile is found in the self‐discharge in lignin‐based devices. [ 30 ] These results suggest that WIPSE can provide some key advantages over molecular electrolytes, as it displays better performance in terms of cyclic stability and self‐discharge. For this reason, PAAK was chosen as our background electrolyte to introduce the Zn‐salt necessary to a Zn‐lignin battery.…”

Water-in-polymer Salt Electrolyte (WIPSE) for Sustainable Lignin Batteries

“…Aqueous electrolytes, also offer an attractive solution for large-scale batteries because of their low cost, intrinsically nonflammable, often green and environment friendly. 14 Finally, we demonstrated that utilization of WISE can suppress dendritic growth thereby improving the cyclic stability of Zn-lignin battery.…”

“…Therefore, although plotting experimental self-discharge profiles in this manner can be useful for identifying the presence of an ohmic leakage between the electrodes, such profiles are not particularly informative for the design of active materials and chemistries aimed at minimizing self-discharge. 14,60 The diffusion-controlled mechanism of self-discharge, as demonstrated by Conway, is characterized by a linear decrease in potential when plotted against the square root of self-discharge time:…”

“…13 . 14 Additionally, they have also demonstrated the feasibility of organic batteries that operate in an aqueous electrolyte, further showcasing the versatility of lignin as a key component in battery technologies.…”

Mass Transport in “Water-in-Polymer Salt” Electrolytes

“…Large-scale supercapacitors require highly ionically conductive, nonflammable, and nontoxic electrolytes operable at high voltages, which can easily wet the low-cost electrodes such as activated carbons . In commercialized secondary Li-ion batteries, organic electrolytes are typically utilized due to their stability within large working potential windows (3–4 V), thereby producing high specific energy ( E = CV 2 , where C is the specific capacity and V is the cell potential) .…”