Mechanistic Elucidation of Electronically Conductive PEDOT:PSS Tailored Binder for a Potassium‐Ion Battery Graphite Anode: Electrochemical, Mechanical, and Thermal Safety Aspects

Abstract

Potassium‐ion batteries (KIBs) are considered more appropriate for grid‐scale storage than lithium‐ion batteries (LIBs) due to similar operating chemistry, abundant precursors, and compatibility with low‐cost graphite anodes. However, a larger ion reduces rate capabilities and exacerbates capacity fading from volumetric expansion. Herein, conductive polymer, poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), is substituted for standard insulating polyvinylidene fluoride (PVDF). Half‐cells using carbon black (CB) in continuously conductive PEDOT:PSS/CB binder outperforms PVDF/CB by mitigating electrically isolated “dead” graphite, improving 100 cycle capacity retention at C/10 from 63 to 80%. Enhanced electrical contact with PEDOT:PSS/CB also reduces ion impedance and improves rate capabilities. Without CB however, PEDOT:PSS binder performs poorly in electrochemical studies despite promising ex situ electronic conductivity. This discrepancy is mechanistically elucidated through identification of redox activity between PEDOT:PSS and K+ which results in high impedances in the anode operating voltage window. Additionally, the impact of conducting binder on mechanical properties and thermal safety of the anode is investigated. Brittleness and poor wettability of PEDOT:PSS are identified as issues, but greater stability against reactive KC8 reduces overall heat generation. Binder substitution offers a promising means of mitigating issues with current KIB anodes regardless of active material, and the work herein addresses issues towards further improvement.

The Role of Transition Metals on Chemo‐Mechanical Instabilities in Prussian Blue Analogues For K‐Ion Batteries: The Case Study on KNHCF Versus KMHCF

“…Previous studies showed a direct correlation between the evolution of potential‐dependent strain derivatives and nanoscale structural changes in the electrode due to the phase transformations. [ 37–39 ] The evolution of strain derivatives closely mimicked the current evolution in cyclic voltammetry and capacity derivative in the galvanostatic cycle. In both cases, the location of the strain derivatives aligned well with the location of either current peaks or peaks of capacity derivative within 0.03 V margin.…”

“…Li and K intercalation result in almost 1.5% and 17.6% strain generation in graphite composite anodes, respectively. [37,40] Cathode materials are more prone to particle fracture at smaller electrochemical strains due to their brittle nature. [41] For example, strain rates in FePO 4 were ˜0.3% and 2%-SOD (strain rate per unit state-of-discharge) upon Li and Na ion intercalation, respectively.…”

Neuromorphic Carbon for Fast and Durable Potassium Storage

“…[1][2][3][4][5] Due to their low-cost, abundant resources, and low standard reduction potential, potassium-ion batteries (PIBs) have received extensive attention in recent years. [6][7][8][9][10][11] Graphite structure of carbon spheres reduces the stress caused by K + insertion and maintains the integrity of the electrode structure. The NGCs as potassium anode demonstrate exceptional electrochemical performance, functioning at a current density of 100 mA g −1 for > 18 months, cycling > 2400 times, and maintaining a reversible capacity of 225 mAh g −1 .…”

Probing the Formation of Cathode-Electrolyte Interphase on Lithium Iron Phosphate Cathodes via Operando Mechanical Measurements

“…In this study, we develop a nondestructive, operando, and optical method to probe dynamic changes on the composite cathode electrodes by utilizing digital image correlation (DIC) coupled with cryogenic XPS. DIC has been employed to study mechanical deformations in battery electrodes associated with phase transformation and interfacial instabilities. − Here, we utilized the technique to probe the formation of CEI layers on lithium iron phosphate cathodes (LiFePO 4 , LFP). LFP is chosen as a model cathode system due to its well-known two-phase reactions between (olivine phase) LiFePO 4 and (trigonal phase) FePO 4 . − Electrochemical strain evolution is monitored while cycling the cathode in either LiClO 4 , LiTFSI, or LiPF 6 salt-containing electrolyte chemistries.…”