# Improving Cycle Life and Capacity Retention in PVMPO‖Li Dual‐Ion Lithium‐Organic Batteries Using an EC‐Free and FEC Additive Containing Electrolyte

## TL;DR

This paper shows that using an EC-free electrolyte with FEC improves battery performance and longevity in organic lithium batteries.

## Contribution

The study introduces EC-free electrolytes with FEC additives to suppress electrode degradation in PVMPO-based batteries.

## Key findings

- EC-free electrolytes with FEC retain 95 mAh g⁻¹ after 500 cycles, outperforming EC-based systems.
- FEC reduces interfacial resistance and electrode degradation, improving battery stability.
- UV/Vis and SEM analyses confirm reduced electrode damage in FEC-containing systems.

## Abstract

Electrolytes critically influence the electrochemical performance and cycle life of lithium ion batteries (LIBs). This holds especially for organic redox polymer‐based batteries, such as those employing poly(3‐vinyl‐N‐methylphenoxazine) (PVMPO), where solubility limits performance in conventional ethylene carbonate (EC)/ dimethyl carbonate (DMC)‐based electrolytes. Reducing EC content has shown solubility suppression when using ethyl methyl carbonate (EMC) as a co‐solvent, however, capacity fading persists due to PVMPO electrode degradation. To address this degradation, this study explores the use of EC‐free electrolytes, with and without fluoroethylene carbonate (FEC). Electrochemical investigations, UltraViolet/Visible (UV/Vis) spectroscopy, post‐cycling Scanning Electron Microscopy (SEM), Energy Dispersive X‐ray Spectroscopy (EDS) mapping, and X‐ray Photoelectron Spectroscopy (XPS) analyses are employed to evaluate solubility, interfacial properties, and electrode integrity. The EC‐free electrolyte system with FEC retains 95 mAh g‒1, while that without FEC retains 86 mAh g‒1, outperforming the 76 mAh g‒1 observed in EC‐based systems after 500 cycles at 1C. FEC containing electrolyte systems display reduced interfacial resistance, fewer surface cracks, and minimal electrode degradation. These findings demonstrate that EC‐free electrolytes, particularly with FEC, effectively suppress electrode degradation and enhance the cycle life of organic LIBs.

The major bottleneck of PVMPO‐based positive electrodes is electrode degradation during extended cycling with EC‐containing electrolytes. This issue is mitigated by using EC‐free electrolytes with FEC additives, which exhibit reduced interfacial resistance, fewer surface cracks, improved capacity retention, and suppressed electrode degradation, thereby enhancing cycling stability.