Integrating stimuli-responsive materials into energy storage technologies opens a new approach to introduce novel functionalities as well as addressing some of the crucial and unresolved issues. As an example, current flexible lithium-ion batteries (LIBs) still suffer from a fragile or susceptible nature and limited electrochemical performance recovery against severe or repeated mechanical deformations. Thus, integrating a stimuli-responsive material with strong ability to recover from severe and repeated mechanical deformations into the flexible LIBs can be an effective approach to address the shape and performance recovery issue concerning the flexible LIBs [1-3].

Herein, we design and synthesize a solid polymer electrolyte (SPE) based on a shape memory polymer (SMP) to integrate into flexible lithium batteries for smart applications, for example, shape recovery from severe mechanical deformation. SMPs are attractive class of programmable, stimuli-responsive polymer materials demonstrating shape-memory behavior. A SMP has the ability to memorize its original or permanent shape; deform, fix into a temporary or secondary shape; and recover its original form via applying an external stimulus, for example, heat, magnetic or electrical field, light [3]. In fact, when mechanical deformation occurs, batteries typically suffer from reduced power, efficiency, capacity and recovery from the deformation without sacrificing the electrochemical performance would be highly desirable. The shape-memory SPE is made based on a cross-linkable polyethylene oxide (PEO) with controlled crystallinity and the ability to indue shape memory behavior above the melting point. PEO is chosen as a model shape-memory polymer due to its unique properties including low-cost, high dielectric constant and Li⁺-ion solvating ability, high electrochemical and mechanical stability, semi-crystalline nature, and ability to introduce cross-linkable functionalities. In response to a temperature exceeding the melting point of the polymer matrix (~70 ^oC), the engineered shape memory SPE can recover its original shape and size from mechanical deformations, for example, bending and folding. The all-solid-state shape-memory SPEs also show excellent electrochemical performance in Li/Li and Li/LFP cells at ambient temperature. The Li/LFP cell made using the shape memory SPE delivers a specific capacity ~140 mAh g^‒1 with ~92% capacity retention after 100 cycles at 0.2C charge/discharge rate and ~99.85% Coulombic efficiency. Besides excellent electrochemical performance, we demonstrate that a flexible Li based battery made using the shape memory SPE can recover from severe mechanical deformations, for example, bending and folding, upon applying heat. This proof-of-concept study opens up a new approach to design and integrate smart functionalities into energy storage technologies.

Reference

[1] Z. Fang, J. Wang, H. Wu, Q. Li, S. Fan, J. Wang, J. Power Sources 454, 227932 (2020).

[2] M. Koo, K. Park, S. H. Lee, M. Suh, D. Y. Jeon, J. W. Choi, K. Kang, K. J. Lee, Nano Lett. 12, 4810–4816 (2012).

[3] V. Jabbari, V. Yurkiv, M. G. Rasul, M. Cheng, P. Griffin, F. Mashayek, R. Shahbazian-Yassar, Small 2021, 2102666, DOI: 10.1002/smll.202102666.