# Block Copolymer-Enabled Low-Temperature Structural Battery Electrolytes Produced Using Polymerization-Induced Phase Separation

## TL;DR

This paper introduces a new method to create structural battery electrolytes with better conductivity and mechanical strength at low temperatures using block copolymers.

## Contribution

The use of amphiphilic block copolymers in PIPS synthesis to reduce tortuosity and enhance low-temperature performance of structural battery electrolytes.

## Key findings

- Adding 1 wt% of BCP improves ionic conductivity by 78.3% at 25°C and 99% at -30°C.
- The SBE retains 30% and 49% of its capacity at -20°C in different half-cell configurations.
- The method shows good compatibility with lithium iron phosphate and nitroxide radical polymer cells.

## Abstract

Structural battery electrolytes (SBEs) require both high
ionic
conductivity and high mechanical strength and stiffness. However,
SBEs produced using the one-pot polymerization-induced phase separation
(PIPS) synthesis method suffer from high tortuosity which decreases
the effective ionic conductivity. Additionally, conventional liquid
electrolytes demonstrate poor performance in low temperatures and
are unsuitable for applications in cold climates. Here, we report
SBEs generated using PIPS in the presence of an amphiphilic block
copolymer (BCP), which modifies the solid–liquid interface
that forms during polymerization, resulting in lower tortuosity and
improved ionic conductivity. Using a low-temperature liquid electrolyte,
the effect of BCP and resin content on the ionic conductivity and
mechanical properties is examined. Only 1 wt % of BCP additive is
needed to improve the ionic conductivities even at low temperature
(2.34 × 10–3 S/cm at 25 °C and 1.28 ×
10–4 S/cm at −30 °C, which are 78.3%
and 99% higher than a similar SBE with no added BCP). The SBE, tested
in both lithium iron phosphate and nitroxide radical polymer half-cells,
demonstrates good compatibilities with discharge capacities of 145
mAh/g at a C-rate of 0.1 C and 103 mAh/g at a C-rate of 0.2 C, respectively,
at 25 °C. At even lower temperatures of −20 °C, these
cells retained 30 and 49% of their respective capacities.