Ferroelectric Polymer-Based Composite Layer Coated Zinc Ion Batteries Toward Dendrite-Free Zinc Anodes
Authors: Seol WooJun , Park Hyeonghun , Kim Hyeong-Jin , Jo Ji Young 
Published: July 2022

The lithium ion batteries are dominating rechargeable battery market with advantages of long cycle life, adaptability, and high energy density; however, disadvantages including lithium resource shortage, high processing cost arising from the other battery components (Co-based cathode and electrolyte), and safety concerns due to flammable organic electrolytes and highly reactive lithium species hinder further development to grid-scale batteries.

The zinc ion batteries have been proposed as an alternative for lithium ion batteries owing to suitable electrochemical properties for grid-scale batteries of large specific capacity (820 mAh/g), high volumetric capacity (5854 mAh/cm3), and low redox potential (-0.76 V). Also, zinc’s low cost, environmental abundance, inexpensive mass production, and superior safety due to usage of aqueous electrolyte make zinc ion battery extremely promising for future battery applications.

Prior to the commercialization of zinc ion batteries, a detrimental issue remains with rapid degradation of battery performance mainly due to dendrite formation and additional side reactions during charging and discharging processes. The dendrite growth in association with the reduction of zinc ions during the discharging process causes lifespan shortening related to short circuit arising from separator piercing as well as a decrease of capacity via unceasing of water/electrolyte decomposition accompanied with fast electrolyte depletion. Also, parasitic side reactions between electrode and electrolyte produce hydrogen and zinc sulfate hydroxide while wasting both electrolyte and zinc electrode. These reactions involves electron consumption which severely reduce a Coulombic efficiency and prohibit us from reaching theoretically expected electrochemical performances. Several strategies have been proposed to suppress the dendrite growth and side reactions, such as interfacial electrode modification through an increase of the surface area of zinc anodes, insertion of electrolyte additive, manipulation of crystallographic orientation of electrode.

Here, we propose an additional ferroelectric layer coating onto the zinc electrode for the compression of dendrite growth and the hindrance of the side reaction. Among the ferroelectric materials, we select composites consisting of poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) and barium titanate nanoparticles to take both advantages of P(VDF-TrFE) — cost-effective fabrication, compatibility with battery components, and non-toxicity and of barium titanate — lead-free inorganic ferroelectric materials with high ferroelectricity. The 800 nm-thick P(VDF-TrFE)/barium titanate nanocomposite ferroelectric layer is spin-coated onto a bare zinc electrode and works as an anode for battery operation.

A coated ferroelectric layer serves as a physical barrier to block zinc corrosion and hydrogen reaction. Meanwhile, dendrite suppression achieved by ferroelectric layer resulting from the uniform electric field and additional ionic path can be attributed to longer cycle life. Therefore, we could observe about three times extended cycle life and a decrease of side reaction products (hydrogen, zinc sulfate hydroxide) to the half value or less than bare zinc electrode.