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

Abstract

Zn‐ion batteries are one of the hot candidates for low‐cost and sustainable secondary batteries. The hydrogen evolution and dendritic growth upon zinc deposition are today's challenges for that technology. One of the new strategies to cope with these issues is to use “water‐in‐salt” electrolyte (WISE), that is, super concentrated aqueous electrolytes, to broaden its electrochemical stability window (ESW), suppressing hydrogen evolution reaction (HER), and perturbing the dendritic growth. Herein, this work proposes to use “water‐in‐polymer salt” electrolyte (WIPSE) concept to mitigate the challenges with Zn ion batteries and bring this technology toward one of the cheapest, greenest, and most sustainable electrodes: Lignin‐carbon (L‐C) electrode. Potassium polyacrylate (PAAK) as WISE bears out as better electrolyte for L‐C electrodes in terms of self‐discharge, cyclic stability, and specific capacity compared to conventional electrolyte based on chemically cousin molecule potassium acetate. Zinc bis(trifluoromethanesulfonyl) imide (Zn(TFSI)2) added into WIPSE shows deposition and dissolution of Zn in Zn//Zn symmetric cell suggesting that Zn2+ are moving into the polyanionic network. Furthermore, the added bis (trifluor omethanesul fonyl) imide (TFSI−) metal salts trigger a ≈40% enhancement of the capacity of L‐C electrode. These results show a new promising direction toward the development of cost‐effective and sustainable Zn‐lignin batteries.

Does Water‐in‐Salt Electrolyte Subdue Issues of Zn Batteries?

“…[ 85 ] An alternative strategy for preparing cost‐effective WISE was proposed by our group by mixing low concentrations of Zn salts with highly concentrated polymer electrolyte to yield a polymer‐based hybrid electrolyte for Zn‐ion batteries. [ 29 ] Therefore, in future, attention should be given on preparing economic and environment‐friendly Zn‐based WISEs. 3)As the solvation shell of Zn 2+ contributes to the performance of ZnBs, future research should consider this aspect of performance. Two published reports contradict each other regarding the solvation sheath of Zn 2+ ions in superconcentrated solution.…”

“…Presumably, in metal‐ion batteries (e.g., Li, Na, and K), the cathodic process of HER occurs before (more positive) the process of metal‐ion reduction or intercalation. [ 29 ] In case the metal redox process such as Zn deposition is proximate to HER, the HER can be reduced to a certain extent by utilizing a basic electrolyte. In principle, the redox potential of the metal remains constant with pH, [ 30 ] whereas the redox potential of the HER varied with the pH, as schematically presented by the Pourbaix diagram [ 31 ] ( Figure a).…”

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

“…The preparation method for electrolytes has been explained in detail in our previous work. , Briefly, diluted polyacrylic acid (purchased from Merch Sigma-Aldric, M w 250 000) solution was neutralized by potassium hydroxide. The obtained solution was dried and mixed with respective water amounts to get different concentrations of WiPSEs.…”

“…One peculiar subclass of WiSEs has been proposed as “water-in-polymer salt” electrolytes (WiPSEs). Earlier studies report on the use of a highly concentrated metal cation polyacrylate (PAA) with either Li + or K + . − In particular, PAALi was fully integrated into a Li-ion battery operating at 2.6 V . However, very little is understood about the transport of ions and water in WiPSEs.…”

Layer-by-layer assembling redox wood electrodes for efficient energy storage

“…The absorption at 1,712 cm -1 in PPy@TrW is assigned to C=O stretching vibration in PPy bulk, indicating non-porous aggregation of PPy on the wood surface [39,40] . The shift from 1,552 to 1,530 cm -1 (C=C stretching) indicates the formation of π-π interactions between CNTs and PPy in the PPy@CNTs@TrW nanocomposite [41] . The peak at 2,978 cm -1 is attributed to the stretching vibration of the -CH 2 -group of the pyrrole ring.…”