# Measuring Heat Dissipation and Entropic Potential in Battery Cathodes Made with Conjugated and Conventional Polymer Binders Using Operando Calorimetry

## TL;DR

This study compares heat and entropy in lithium-ion batteries using different polymer binders to improve battery performance.

## Contribution

The study introduces semiconducting polymer binders that reduce heat dissipation in lithium-ion batteries compared to traditional binders.

## Key findings

- Conductive binders produce less Joule heating than PVDF during battery operation.
- Electronic conductivity is more important than ionic conductivity for reducing heat at lower battery rates.
- The entropic signature of polymer doping is clearly observed at potentials below NCA oxidation.

## Abstract

This study explores
the influence of electronic and ionic
conductivities
on the behavior of conjugated polymer binders through the measurement
of entropic potential and heat generation in an operating lithium-ion
battery. Specifically, the traditional poly(vinylidene fluoride) (PVDF)
binder in LiNi0.8Co0.15Al0.05O2 (NCA) cathode electrodes was replaced with semiconducting
polymer binders based on poly(3,4-propylenedioxythiophene). Two conjugated
polymers were explored: one is a homopolymer with all aliphatic side
chains, and the other is a copolymer with both aliphatic and ethylene
oxide side chains. We have shown previously that both polymers have
high electronic conductivity in the potential range of NCA redox,
but the copolymer has a higher ionic conductivity and a slightly lower
electronic conductivity. Entropic potential measurements during battery
cycling revealed consistent trends during delithiation for all of
the binders, indicating that the binders did not modify the expected
NCA solid solution deintercalation process. The entropic signature
of polymer doping to form the conductive state could be clearly observed
at potentials below NCA oxidation, however. Operando isothermal calorimetric measurements showed that the conductive
binders resulted in less Joule heating compared to PVDF and that the
net electrical energy was entirely dissipated as heat. In a comparison
of the two conjugated polymer binders, the heat dissipation was lower
for the homopolymer binder at lower C-rates, suggesting that electronic
conductivity rather than ionic conductivity was the most important
for reducing Joule heating at lower rates, but that ionic conductivity
became more important at higher rates.