Piezoelectric gradient electrolytes for environmentally adaptive and stable zinc batteries

Solid polymer electrolyte-based zinc batteries are promising candidates for next-generation electrochemical energy storage due to their cost-effectiveness, enhanced safety and high theoretical energy density. However, their practical deployment is severely hindered by sluggish Zn²⁺ ion mobility, poor interfacial compatibility and uneven electric field distribution. To address the persistent challenges, this work presents a novel asymmetric piezoelectric electrolyte, engineered by the strategic vertical distribution of piezoelectric barium titanate (BTO) nanofillers within a polyvinylidene fluoride (PVDF)-based polymer matrix. This design introduces a built-in gradient electric field across the electrolyte thickness, leveraging the electromechanical properties of BTO to regulate ion transport and interfacial dynamics. On the Zn anode-facing side, the BTO-rich region with a high dielectric constant and enhanced local polarization, promotes zinc salt dissociation and generates a directional electric field that promotes uniform Zn²⁺ flux. This configuration effectively suppresses dendrite formation and mitigates localized charge accumulation. Conversely, the MnO₂ cathode-facing side comprises a softer, polymer-rich phase with lower BTO content, ensuring better interfacial compliance and reduced contact resistance, which is crucial for facilitating efficient ion transport without inducing excessive polarization. As a result, the asymmetric architecture achieves an impressive ionic conductivity of 1.39 mS·cm^-1 and a high Zn²⁺ transference number of 0.69 at room temperature, outperforming conventional SPEs. ZnǀǀZn symmetric cells exhibit outstanding cycle stability, sustaining operation for over 1500 h, while Zn||MnO₂ full batteries demonstrate stable cycling over 1200 cycles. Notably, the battery performs reliably across a wide temperature range from -30 °C to 60 °C, demonstrating strong adaptability to harsh environments. This work provides a scalable and effective strategy for overcoming key limitations in Zn-based batteries by introducing a functionally asymmetric, piezoelectric electrolyte structure. This advancement paves the way for the development of safe, durable, and high-efficiency zinc-ion batteries.