# Waterborne Poly(urethane-urea)s for Lithium-Ion/Lithium-Metal Batteries

## TL;DR

This paper explores water-based polyurethane materials for safer and more sustainable lithium-ion and lithium-metal batteries, focusing on their design and performance trade-offs.

## Contribution

The paper provides a comprehensive review of waterborne poly(urethane-urea)s for battery applications, highlighting design guidelines and performance trade-offs.

## Key findings

- WPU/WPUU materials offer tunable adhesion and mechanics for battery components.
- Trade-offs exist between adhesion and electrolyte uptake, and ionic conductivity and storage modulus.
- Applications include electrode binders, separator coatings, and polymer electrolytes.

## Abstract

Waterborne polyurethane (WPU) and waterborne poly(urethane-urea) (WPUU) dispersions allow safer and more sustainable manufacturing of rechargeable batteries via water-based processing, while offering tunable adhesion and segmented-domain mechanics. Beyond conventional roles as binders and coatings, WPU/WPUU chemistries also support separator/interlayer and polymer-electrolyte designs for lithium-ion and lithium metal systems, where interfacial integrity, stress accommodation, and ion transport must be balanced. Here, we review WPU/WPUU fundamentals (building blocks, dispersion stabilization, morphology, and film formation) and review prior studies through a battery-centric structure–processing–property lens. We point out key performance-limiting trade-offs—adhesion versus electrolyte uptake and ionic conductivity versus storage modulus—and relate them to practical formulation variables, including soft-/hard-segment selection, ionic center/counterion design, molecular weight/topology control, and crosslinking strategies. Applications are reviewed for (i) electrode binders (graphite/Si; cathodes such as LFP and NMC), (ii) separator coatings and functional interlayers, and (iii) gel/solid polymer electrolytes and hybrid composites, with a focus on practical design guidelines for navigating these trade-offs. Future advancements in WPU/WPUU chemistries will depend on developing stable, low-impedance interlayers, enhancing electrochemical behavior, and establishing application-specific design guidelines to optimize performance in lithium metal batteries (LMB).