Cross-Linked Block Copolymer/Ionic Liquid Self-Assembled Blends for Polymer Gel Electrolytes with High Ionic Conductivity and Mechanical Strength

Abstract

Poly(propylene oxide)–poly(ethylene oxide)–poly(propylene oxide) (PPO–PEO–PPO) block copolymers (BCPs) with cross-linkable end groups were synthesized, blended with an ionic liquid (IL) diluent, and cross-linked to form polymer gel electrolytes. The IL prevented crystallization of PEO at high concentrations, enabling fast ion transport. In addition, the IL was selective for the PEO block, inducing strong microphase separation in what are otherwise disordered or weakly ordered BCP melts. Cross-linking the BCPs in the presence of the IL resulted in the formation of solid, elastic gels with high ionic conductivitiesgreater than 1.0 mS/cm at 25 °C for some compositions. However, it was found that neither the presence or absence of microphase separation nor the BCP composition of the microphase separated gels substantially influenced ionic conductivity. Increasing the cross-link density through the use of phase-selective PEO- and PPO-based cross-linking reagents was also evaluated. It was revealed that confinement of cross-links to the PPO rich domains through the use of PPO-based diacrylates enhanced the mechanical strength of the gels without detriment to the ionic conductivity. Conversely, cross-linking in the PEO-rich domains through the use of PEO-based acrylates significantly reduced conductivity. Isolation of cross-links within a minor nonconducting domain in a microphase separated gel is a viable strategy for mechanical property enhancement without a large sacrifice in conductivity, effectively decoupling ionic conductivity and mechanical strength. This approach yielded solid-like gel electrolytes fabricated from BCPs that can be produced inexpensively, with ionic conductivities of 0.64 mS/cm at 25 °C and a frequency independent storage modulus of approximately 400 kPa.

Development of Electrolytes towards Achieving Safe and High‐Performance Energy‐Storage Devices: A Review

“…[62,261,262] To achieve a good balance between them, the key is to design structures with the ability to absorb a large amount of the liquid component, while maintaining structural integrity. For GEs, achieving high ionic conductivity as well as good mechanical properties is challenging, as the addition of the liquid component will unavoidably deteriorate the mechanical strength of the polymer host through swelling/wetting caused by the liquid.…”

Facile One Pot Polycondensation Method to Synthesize the Crosslinked Polyethylene glycol‐Based Copolymer Electrolytes

“…It can be seen that the copolymer film of GC400‐1000 is more transparent than that of GC400‐2000 as it does not crystallize. The highest ion conductivity at 25 °C is 7.7 × 10 −4 S cm −1 for GC400‐1000 electrolyte, which is higher than that of 1 × 10 −4 S cm −1 required for commercial battery applications . Meanwhile, all the polymer electrolytes in this work have a linear temperature dependence of ion conductivity variation rule which can be represented by Vogel Tamman Fulcher equation (See Figure S6 in the Supporting Information).…”

Deformable and flexible electrospun nanofiber-supported cross-linked gel polymer electrolyte membranes for high safety lithium-ion batteries

“…The crosslinked polymer with EO chains shows a good compatibility with the electrolyte, which is conducive to absorb more liquid electrolytes within the polymer membrane and more electrolytes could be retained. 13 Thus, the electrolyte leakage decreased with the increase in the PPEGMA content.…”