# Bifunctional Electrolyte Additive Enabling Simultaneous Interphase Formation on Both Electrodes in High‐Energy Lithium‐Ion Batteries

## TL;DR

A new electrolyte additive helps form protective layers on both electrodes in lithium-ion batteries, improving performance and lifespan.

## Contribution

A bifunctional additive that forms interphases on both electrodes simultaneously is introduced for the first time.

## Key findings

- The additive forms a SEI on the anode and a CEI on the cathode during battery operation.
- Battery performance improves significantly in NMC811||AG + 20% SiOx cells with the additive.
- Advanced techniques confirm dual interphase formation and electrode stabilization.

## Abstract

The development of next‐generation Lithium‐ion batteries (LIBs) to meet the demands of advancing technology and energy storage requires focus on the formation of effective interphases on both the positive and negative electrodes. Different promising approaches to facilitate effective interphase formation are already known Out of these, the incorporation of film‐forming electrolyte additives is a straight‐forward strategy to achieve this goal. In the presented study, a bifunctional electrolyte additive, (5‐methyl‐2‐oxo‐1,3‐dioxol‐4‐yl)methyl thiophene‐3‐carboxylate composed of two functional motifs, vinylene carbonate (VC) and thiophene, is reported. Upon LIB operation, the additive undergoes in situ splitting, forming a VC‐assisted solid electrolyte interphase (SEI) and a polythiophene‐based cathode electrolyte interphase (CEI) simultaneously. The electrochemical performance of the proposed additive is studied in 250 mAh NMC811||AG + 20% SiO
x
wound pouch cells, and shows considerable improvement in overall battery performance compared to cells with the baseline electrolyte. The additive's dual interphase formation is confirmed through a combination of advanced characterization techniques, including X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and  operando shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS). This study introduces a new design strategy for a multifunctional electrolyte additive, providing a promising pathway to improve overall LIB's performance and lifetime by simultaneous stabilization of both electrodes through facilitated interphase formation.

This article investigates a bifunctional electrolyte additive combining vinylene carbonate and thiophene to enhance high‐voltage lithium‐ion batteries. The additive enables simultaneous interphase formation on both electrodes. Electrochemical tests and advanced techniques such as XPS, operando‐SHINERS, and SEM reveal improved electrode stabilization and overall battery performance with this single‐additive strategy.